control-plane | Recommendations
(Note) | +|---------------------------------|--------------------------------| +| B-ISUP | Q.2761, Q.2762, Q.2763, Q.2764 | +| MTP-3 | Q.704 | +| MTP-2 | Q.703 | +| MTP-1 | Q.702 | + +T03.DRW + +NOTE – The B-ISUP is only terminated at the endpoints of the signalling relation. + +FIGURE 8/Q.2010 + +## **Signalling protocol stack if the existing SS No. 7 network interface is used (PA and PQ)** + +# 7 Basic principles of the Asynchronous Transfer Mode (ATM) + +ATM is the transfer mode solution for implementing a B-ISDN. It influences the standardization of digital hierarchies, multiplexing structures, switching and interfaces for broadband signals. + +ATM is used in this Recommendation for addressing a specific packet-oriented transfer mode which uses asynchronous time-division multiplexing techniques. The multiplexed information flow is organized into blocks of fixed size cells. A cell consists of an information field header. The primary role of the header is to identify cells belonging to the same virtual channel within the asynchronous time-division multiplex. Cell sequence integrity on a virtual channel connection is preserved by the ATM layer. + +ATM is a connection-oriented technique. Connection identifiers are assigned to each link of a connection when required and released when no longer needed. In general, signalling and user information are carried on separate ATM layer connections. + +ATM offers a flexible transfer capability common to all services, including connectionless services. Additional functionalities on top of the ATM layer [e.g. in the ATM Adaptation Layer (AAL)] are provided to accommodate various services. The boundary between the ATM layer and the AAL corresponds to the boundary between functions supported by the AAL-specific information. The AAL-specific information is contained in the information field of the ATM cell. + +The information field is transported transparently by the ATM layer. No processing, e.g. error control, is performed on the information field at the ATM layer. + +The header and information field each consists of a fixed integer number of octets. The header size (5 octets) and the information fields (48 octets) remain constant at all reference points, including the User Network Interface (UNI) and the Network Node Interface (NNI), where the ATM technique is applied. Additional details are provided in Recommendations I.150, B-ISDN ATM functional characteristics, and I.361, B-ISDN ATM layer specifications. + +# 8 ATM Adaptation Layer (AAL) functions + +This clause will describe briefly the services that the ATM Adaptation Layer (AAL) must provide to the higher layers in order to support B-ISDN signalling. + +The AAL performs functions required by the control plane and supports the mapping between the ATM layer and the next higher. The functions performed in the AAL depend upon the higher layer requirements for signalling. + +Architecturally, the AAL is a layer between the ATM layer and the next higher layer in the control plane. The B-ISDN protocol reference model is given in Recommendation I.321. + +The signalling AAL is functionally divided into a Common Part (CP) and a Service Specific Part (SSP) as shown in Figure 9. The CP can be used in different SSPs; the SSP is specific to the needs of the service application. The following understanding about the CP and SSP exists at the UNI and NNI respectively. + + + +The diagram illustrates the functional division of the signalling AAL. It shows two main components: SSP-AAL (Service Specific AAL) and CP-AAL (Common Part AAL). The SSP-AAL is connected to 'Service Specific AAL Functions' on its left and 'Peer-to-Peer messages' on its right. The CP-AAL is connected to 'Common Part AAL Functions' on its left and 'Peer-to-Peer messages' on its right. Both components are connected to a central vertical line representing the ATM layer, which is flanked by two oval symbols representing the UNI/NNI interfaces. The text 'T1162150-94/d06' is located at the bottom right of the diagram. + +Functional division of the signalling AAL diagram + +FIGURE 9/Q.2010 +Functional division of the signalling AAL + +## 8.1 Signalling AAL at the UNI + +The protocol stacks showing the AAL functionality at the UNI for point-to-point are illustrated in Figure 6. + +## 8.2 Signalling AAL at the NNI + +The protocol stack showing the AAL functionality at the NNI for point-to-point application in the associated mode and quasi-associated mode is illustrated in Figures 7 and 8. + +# 9 Signalling higher layer functions + +A stage 2 service description is provided in Recommendation Q.71. The higher layer protocols for signalling are, in general, responsible for call and bearer control. As these functions differ somewhat at UNI and at the NNI, different protocols are used. + +## 9.1 UNI + +The call/connection control functions are: + +- call establishment and release1); +- bearer establishment and release, for point-to-point VCCs2) ; +- compatibility checking; +- support of N-ISDN services and signalling interworking between N-ISDN and B-ISDN; +- support of some supplementary services (see Recommendations Q.2951 and Q.2957). + +## 9.2 NNI + +The call/bearer connection control functions are: + +- call establishment and release1); +- bearer connection establishment and release, for point-to-point VCCs2); +- transfer of access transport information; +- support of some supplementary services (see Recommendation Q.2730); +- interworking with N-ISDN services. + +Signalling network functions are according to Recommendation Q.704. For SCS-1 (Release 1), the signalling protocols are based on the Signalling System No. 7 Recommendation. + +--- + +1) For SCS-1 (Release 1), calls and bearer connections are established and released simultaneously. + +2) Other communication configurations will be studied during the 1993-1996 study period. 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+1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:d11594766aaa481bcc8db80a1174fe600c3409d4d344b761a2d01a38b596675f +size 95292 diff --git a/marked/Q/T-REC-Q.2220-200212-I_PDF-E/raw.md b/marked/Q/T-REC-Q.2220-200212-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..e80fcc92a5e1b119f7b2c3176211c1a2c3c14111 --- /dev/null +++ b/marked/Q/T-REC-Q.2220-200212-I_PDF-E/raw.md @@ -0,0 +1,2206 @@ + + + + +The logo of the International Telecommunication Union (ITU) features a globe with a lightning bolt superimposed on it, and the letters 'ITU' in a bold, sans-serif font. + +ITU logo + +INTERNATIONAL TELECOMMUNICATION UNION + +**ITU-T** + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +**Q.2220** + +(12/2002) + +SERIES Q: SWITCHING AND SIGNALLING + +Broadband ISDN – Signalling network protocols + +# --- **Transport-Independent Signalling Connection Control Part (TI-SCCP)** + +ITU-T Recommendation Q.2220 + +--- + +## ITU-T Q-SERIES RECOMMENDATIONS + +## SWITCHING AND SIGNALLING + +| | | +|--------------------------------------------------------------------------------------------------------------|----------------------| +| SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE | Q.1-Q.3 | +| INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING | Q.4-Q.59 | +| FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN | Q.60-Q.99 | +| CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS | Q.100-Q.119 | +| SPECIFICATIONS OF SIGNALLING SYSTEM No. 4 | Q.120-Q.139 | +| SPECIFICATIONS OF SIGNALLING SYSTEM No. 5 | Q.140-Q.199 | +| SPECIFICATIONS OF SIGNALLING SYSTEM No. 6 | Q.250-Q.309 | +| SPECIFICATIONS OF SIGNALLING SYSTEM R1 | Q.310-Q.399 | +| SPECIFICATIONS OF SIGNALLING SYSTEM R2 | Q.400-Q.499 | +| DIGITAL EXCHANGES | Q.500-Q.599 | +| INTERWORKING OF SIGNALLING SYSTEMS | Q.600-Q.699 | +| SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 | Q.700-Q.799 | +| Q3 INTERFACE | Q.800-Q.849 | +| DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 1 | Q.850-Q.999 | +| PUBLIC LAND MOBILE NETWORK | Q.1000-Q.1099 | +| INTERWORKING WITH SATELLITE MOBILE SYSTEMS | Q.1100-Q.1199 | +| INTELLIGENT NETWORK | Q.1200-Q.1699 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2000 | Q.1700-Q.1799 | +| SPECIFICATIONS OF SIGNALLING RELATED TO BEARER INDEPENDENT CALL CONTROL (BICC) | Q.1900-Q.1999 | +| BROADBAND ISDN | Q.2000-Q.2999 | +| General aspects | Q.2000-Q.2099 | +| Signalling ATM adaptation layer (SAAL) | Q.2100-Q.2199 | +| Signalling network protocols | Q.2200-Q.2299 | +| Common aspects of B-ISDN application protocols for access signalling and network signalling and interworking | Q.2600-Q.2699 | +| B-ISDN application protocols for the network signalling | Q.2700-Q.2899 | +| B-ISDN application protocols for access signalling | Q.2900-Q.2999 | + +For further details, please refer to the list of ITU-T Recommendations. + +## **ITU-T Recommendation Q.2220** + +# **Transport-Independent Signalling Connection Control Part (TI-SCCP)** + +## **Summary** + +ITU-T Recs Q.711, Q.712, Q.713, Q.714, Q.715 and Q.716 define the services of the Signalling Connection Control Part (SCCP). The SCCP provides, above the signalling transport network (or networks) connection-oriented, connectionless, routing, and management services. ITU-T Rec. Q.711 defines the services provided; ITU-T Rec. Q.714 describes the procedures performed by the SCCP. These procedures make use of the messages and information elements defined in ITU-T Rec. Q.712, whose formatting and coding aspects are specified in ITU-T Rec. Q.713. ITU-T Rec. Q.715 is a guide for the SCCP and ITU-T Rec. Q.716 defines SCCP performance. + +This Recommendation defines the Transport-Independent Signalling Connection Control Part (TI-SCCP), which consists of a modification to SCCP that allows it to operate on various signalling transport networks. In addition to the MTP3 and MTP3b networks, TI-SCCP can operate on SSCOP and SSCOPMCE based networks as well as on IP-networks by utilizing the transport protocol defined in RFCs 2960 and 3309. + +The independence of the particular signalling transport technology is achieved by basing the TI-SCCP on the Generic Signalling Transport Service (ITU-T Rec. Q.2150.0) and deploying one of the Signalling Transport Converters specified in ITU-T Recs Q.2150.1, Q.2150.2, or Q.2150.3. + +### **Source** + +ITU-T Recommendation Q.2220 was approved on 29 December 2002 by ITU-T Study Group 11 (2001-2004) under the ITU-T Resolution A.8 procedure. + +## FOREWORD + +The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. + +The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. + +In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. + +### NOTE + +In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. + +## INTELLECTUAL PROPERTY RIGHTS + +ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. + +As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. + +© ITU 2004 + +All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. + +## CONTENTS + +###### Page + +| | | | +|-----|---------------------------------------------------------------------------|----| +| 1 | Scope ..... | 1 | +| 2 | References..... | 2 | +| 2.1 | Normative references..... | 2 | +| 2.2 | Informative references..... | 2 | +| 3 | Definitions ..... | 3 | +| 4 | Abbreviations..... | 3 | +| 5 | Signalling network architecture..... | 6 | +| 5.1 | General architecture..... | 6 | +| 5.2 | Interworking of TI-SCCP with SCCP ..... | 7 | +| 6 | Exceptions to ITU-T Rec. Q.711 ..... | 8 | +| 6.1 | General ..... | 8 | +| 6.2 | Scope and field of application ..... | 9 | +| 6.3 | Primitives..... | 9 | +| 6.4 | Removal of the embedded service..... | 10 | +| 6.5 | Reason for return ..... | 10 | +| 6.6 | SCCP management..... | 10 | +| 6.7 | Definition of the lower boundary of the SCCP ..... | 11 | +| 7 | Exceptions to ITU-T Rec. Q.712..... | 12 | +| 7.1 | Signalling connection control part messages ..... | 12 | +| 7.2 | SCCP message parameters ..... | 13 | +| 7.3 | Inclusion of fields in the messages..... | 13 | +| 8 | Exceptions to ITU-T Rec. Q.713 ..... | 13 | +| 8.1 | Introduction ..... | 13 | +| 8.2 | Coding of the general parts..... | 16 | +| 8.3 | SCCP parameters..... | 17 | +| 8.4 | SCCP messages and codes ..... | 17 | +| 8.5 | SCCP management messages and codes..... | 19 | +| 8.6 | Mapping for cause parameter values ..... | 19 | +| 9 | Exceptions to ITU-T Rec. Q.714..... | 19 | +| 9.1 | General ..... | 19 | +| 9.2 | General characteristics of signalling connection control procedures ..... | 20 | +| 9.3 | Addressing and routing..... | 23 | +| 9.4 | Connection-oriented procedures..... | 40 | +| 9.5 | Connectionless procedures ..... | 41 | + +| | Page | | +|---------------|------------------------------------------------------------------------------------------------------------------------|----| +| 9.6 | SCCP management procedures ..... | 43 | +| 9.7 | Annex C – State Transition Diagrams (STD) for the signalling connection control part of Signalling Systems No. 7 ..... | 57 | +| 9.8 | Annex D – State Transition Diagrams (STD) for SCCP management control ..... | 57 | +| 10 | Exceptions to ITU-T Rec. Q.715 ..... | 57 | +| Appendix I – | Aspects of the fully meshed Signalling Transport Network ..... | 57 | +| I.1 | GST supported by the Signalling Transport Converter on MTP and MTP3b ..... | 57 | +| I.2 | GST supported by the Signalling Transport Converter on SSCOP and SSCOPMCE ..... | 57 | +| I.3 | GST supported by the Signalling Transport Converter on SCTP ..... | 57 | +| Appendix II – | Differences between the SCCP and TI-SCCP operating over ITU-T Rec. Q.2150.1 ..... | 58 | + +# Transport-Independent Signalling Connection Control Part (TI-SCCP) + +# 1 Scope + +This Recommendation describes the adaptation of the narrow-band Signalling System No. 7 Signalling Connection Control Part (SCCP) for the capability to deploy the Generic Signalling Transport Service defined in ITU-T Rec. Q.2150.0. + +This Recommendation is written as a set of exceptions to ITU-T Recs Q.711, Q.712, Q.713, Q.714 and Q.715 defining the SCCP. The exceptions to certain clauses of text from the SCCP Recommendations are indicated by using revision marks. (Deleted text is shown using strikeouts, and added text is shown underlined.) + +The protocol defined by this Recommendation is the Signalling Connection Control Part (SCCP) protocol to be used between "Serving Nodes". This protocol is called the "Transport-Independent Signalling Connection Control Part" (TI-SCCP). + +The scope of this Recommendation is shown in Figure 1-1. + + + +The diagram illustrates the scope of the Recommendation. At the top, an **SCCP application** is shown. Below it, a **SAP** (Service Access Point) is indicated, with **Primitives** being exchanged between the application and the **SCCP Signalling Transport Service**. The **SCCP Signalling Transport Service** is connected to the **Transport-Independent Signalling Connection Control Part (TI-SCCP) (this Recommendation)**, which is identified by the reference **Q.2220**. Below the TI-SCCP, three **SAP** points are shown, each with **Primitives** being exchanged. These SAPs connect to the **Generic Signalling Transport Service (Q.2150.0)**. Below the Generic Signalling Transport Service, three examples of transport converters are shown, each with **Primitives** being exchanged. These converters are: + + +- Signalling Transport Converter on MTP3 and MTP3b (Q.2150.1)**, which connects to **Message Transfer Part Level 3 using Q.2140 (MTP3b) (Q.2210)**. +- Signalling Transport Converter on SSCOP and SSCOPMCE (Q.2150.2)**, which connects to **Service Specific Connection Oriented Protocol (SSCOP) (Q.2110)**. +- Signalling Transport Converter on SCTP (Q.2150.3)**, which connects to **Stream Control Protocol (SCTP) Transmission (RFCs 2960 & 3309)**. + + A bracket on the right side of the diagram labels these three bottom protocols as **Examples**. The diagram is identified by the reference **Q.2220\_F01-1** at the bottom right. + +Diagram illustrating the scope of the Recommendation. It shows the hierarchy from SCCP application down to various transport protocols. The top part shows SCCP application connected via SAP to TI-SCCP (this Recommendation) which connects to Generic Signalling Transport Service (Q.2150.0). Below TI-SCCP are three examples of transport converters: MTP3/MTP3b (Q.2150.1), SSCOP/SSCOPMCE (Q.2150.2), and SCTP (Q.2150.3). These connect to Message Transfer Part Level 3 (Q.2210), Service Specific Connection Oriented Protocol (Q.2110), and Stream Control Protocol Transmission (RFCs 2960 & 3309) respectively. A bracket on the right labels the bottom three protocols as 'Examples'. + +Figure 1-1/Q.2220 – Scope of this Recommendation + +# 2 References + +## 2.1 Normative references + +The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. + +- [1] ITU-T Recommendation Q.711 (2001), *Functional description of the signalling connection control part*. +- [2] ITU-T Recommendation Q.712 (1996), *Definition and function of signalling connection control part messages*. +- [3] ITU-T Recommendation Q.713 (2001), *Signalling connection control part formats and codes*. +- [4] ITU-T Recommendation Q.714 (2001), *Signalling connection control part procedures*. +- [5] ITU-T Recommendation Q.715 (2002), *Signalling connection control part user guide*. +- [6] ITU-T Recommendation Q.2150.0 (2001), *Generic signalling transport service*. + +## 2.2 Informative references + +The following ITU-T Recommendations and other documents contain information that may be useful to understanding the usage of this Recommendation. There are no additional provisions of this Recommendation derived from these documents. + +- [B1] ITU-T Recommendation Q.2150.1 (2001), *Signalling transport converter on MTP3 and MTP3b*. +- [B2] ITU-T Recommendation Q.2150.2 (2001), *Signalling transport converter on SSCOP and SSCOPMCE*. +- [B3] ITU-T Recommendation Q.2150.3 (2002), *Signalling transport converter on SCTP*. +- [B4] ITU-T Recommendation Q.2210 (1996), *Message transfer part level 3 functions and messages using the services of ITU-T Recommendation Q.2140*. +- [B5] ITU-T Recommendation Q.2110 (1994), *B-ISDN ATM adaptation layer – Service specific connection oriented protocol (SSCOP)*. +- [B6] ITU-T Recommendation Q.2111 (1999), *B-ISDN ATM adaptation layer – Service specific connection oriented protocol in a multi-link and connectionless environment (SSCOPMCE)*. +- [B7] ITU-T Recommendation Q.701 (1993), *Functional description of the message transfer part (MTP) of Signalling System No. 7*. +- [B8] ITU-T Recommendation Q.704 (1996), *Signalling network functions and messages*. +- [B9] ITU-T Recommendation Q.707 (1988), *Testing and maintenance*. +- [B10] IETF RFC 2960 (2000), *Stream Control Transmission Protocol*. + +# 3 Definitions + +There are no further definitions required other than those contained in the normative references (see 2.1). + +# 4 Abbreviations + +This Recommendation uses the following abbreviations: + +| | | +|------------------|------------------------------------------------------------------| +| AAL | ATM Adaptation Layer | +| AK | Data acknowledgement | +| ATM | Asynchronous Transfer Mode | +| BICC | Bearer Independent Call Control | +| B-ISDN | Broadband-Integrated Services Digital Network | +| B-ISUP | Broadband ISDN User Part (of SS No. 7) | +| CC | Connection Confirm | +| CIC | Call Instance Code | +| CL | Congestion Level | +| CL CL | CL for connectionless services | +| CL CO | CL for connection-oriented services | +| CL mc | Congestion Level "maximum congestion" | +| CL nc | Congestion Level "no congestion" | +| CL st | Congestion Level "step" | +| CR | Connection Request | +| CREF | Connection Refused | +| DPC | Destination Point Code | +| DT1 | Data Form 1 | +| DT2 | Data Form 2 | +| EA | Expedited Data Acknowledgement | +| ED | Expedited Data | +| ERR | Protocol Data Unit Error | +| ES | Encoding Scheme | +| F | Fixed Length | +| GST | Generic Signalling Transport | +| GSTS | Generic Signalling Transport Service | +| GST-SAP | Service Access Point to the Generic Signalling Transport Service | +| GT | Global Title | +| GTAI | Global Title Address Information | +| GTI | Global Title Indicator | +| GTT | Global Title Translation | + +| | | +|-------------------|---------------------------------------------| +| ISDN | Integrated Services Digital Network | +| ISUP | Integrated Services User Part (of SS No. 7) | +| IT | Inactivity Test | +| IWF | Interworking Function | +| L3 | Level 3 | +| LSB | Least Significant Bit | +| LUDT | Long Unitdata | +| LUDTS | Long Unitdata Service | +| M | Mandatory | +| MSB | Most Significant Bit | +| MSG | Message | +| MTP | Message Transfer Part | +| MTP3 | Message Transfer Part level 3 (Narrow-band) | +| MTP3b | Message Transfer Part level 3 (Broadband) | +| MTP-SAP | SAP to access the services provided by MTP | +| NAI | Nature of Address Indicator | +| NI | Network Indicator | +| NNI | Network Node Interface | +| NP | Numbering Plan | +| NPCI | Network Protocol Control Information | +| NPDU | Network Protocol Data Unit | +| NSDU | Network Service Data Unit | +| NSP | Network Service Part | +| O | Optional | +| OPC | Originating Point Code | +| PC | Point Code | +| PDU | Protocol Data Unit | +| RI | Routing Indicator | +| RIL | Restricted Importance Level | +| RL | Restriction Level | +| RLC | Release Complete | +| RL CL | RL for connectionless services | +| RL CO | RL for connection-oriented services | +| RLSD | Released | +| RSC | Reset Confirm | +| RSL | Restriction Sublevel | +| RSL CL | RSL for connectionless services | + +| | | +|-------------------|-----------------------------------------------------| +| RSL CO | RSL for connection-oriented services | +| RSR | Reset Request | +| SAAL | Signalling ATM Adaptation Layer | +| SAP | Service Access Point | +| SCCP | Signalling Connection Control Part | +| SCCP-SAP | SAP to access the SCCP services | +| SCLC | SCCP Connectionless Control | +| SCMG | SCCP Management+ | +| SCOC | SCCP Connection-Oriented Control | +| SCRC | SCCP Routing Control | +| SCTP | Stream Control Transmission Protocol | +| SDU | Service Data Unit | +| SI | Service Indicator | +| SIO | Service Information Octet | +| SLC | Signalling Link Code | +| SLS | Signalling Link Selection | +| SOG | Subsystem-Out-Of-Service-Grant | +| SOR | Subsystem-Out-Of-Service-Request | +| SS | SubSystem | +| SS No. 7 | ITU-T Signalling System No. 7 | +| SSA | Subsystem-Allowed | +| SSC | Subsystem Congested | +| SSCF | Service Specific Coordination Function | +| SSCOP | Service Specific Connection-Oriented Protocol | +| SSCOPMCE | SSCOP in a multi-link or Connectionless Environment | +| SSN | SubSystem Number | +| SSP | Subsystem-Prohibited | +| SSPC | SubSystem-Prohibited Control | +| SST | Subsystem-Status-Test | +| STC | Signalling Transport Converter | +| STP | Signalling Transfer Point | +| TI-SCCP | Transport-Independent SCCP | +| TT | Translation Type | +| UDT | Unitdata | +| UDTS | Unitdata Service | +| UP | User Part (of SS No. 7) | +| V | Variable Length | + +| | | +|-------|---------------------------| +| XUDT | Extended Unitdata | +| XUDTS | Extended Unitdata Service | + +# 5 Signalling network architecture + +## 5.1 General architecture + +The general principle of the architecture of TI-SCCP is shown in Figure 5-1. It depicts a TI-SCCP with ten signalling relations, each accessed via a GST-SAP and a Signalling Transport Converter instance. Three different Signalling Transport Technologies are used with three different types of Signalling Transport Converters. + +NOTE 1 – Currently, three different types of Signalling Transport Converters are defined: + +- Signalling Transport Converter on MTP3 and MTP3b (see ITU-T Rec. Q.2150.1 [B1]); +- Signalling Transport Converter on SSCOP and SSCOPMCE (see ITU-T Rec. Q.2150.2 [B2]); and +- Signalling Transport Converter on SCTP (see ITU-T Rec. Q.2150.3 [B3]). + +A message to be transmitted is passed with a TRANSFER.request primitive (see 6.7) via a particular GST-SAP to a Signalling Transport Converter (STC) instance. The GST-SAP is associated with a particular signalling relation. The STC entity forwards the message to its peer. + +The STC instance of a certain type operates over a specific Signalling Transport Technology and is configured to transport data to a single destination STC. + +Upon receipt of a message, the STC entity at the destination passes the message with a TRANSFER.indication primitive via a particular GST-SAP to the TI-SCCP. This SAP identifies to the TI-SCCP the signalling relation to the TI-SCCP and, thus, identifies also the origin of the message. + + + +The diagram illustrates the architecture of a TI-SCCP. At the top is a large rectangle labeled 'TI-SCCP'. Below it, there are ten vertical lines, each representing a signalling relation. Each line has a 'GST SAP' label and connects to a square box labeled 'STC' followed by its type: 'Type 1', 'Type 2', or 'Type 3'. There are three 'Type 1' STCs, three 'Type 2' STCs, and four 'Type 3' STCs. Below each STC box is another 'Trsp. SAP' label, which connects to a cloud at the bottom. The clouds are labeled 'Signalling Transport Technology A', 'Signalling Transport Technology B', and 'Signalling Transport Technology C'. The connections are as follows: + + +- Three 'Type 1' STCs connect to 'Signalling Transport Technology A'. +- Three 'Type 2' STCs connect to 'Signalling Transport Technology B'. +- Four 'Type 3' STCs connect to 'Signalling Transport Technology C'. + +Diagram of TI-SCCP architecture showing 10 STC instances connected to a central TI-SCCP via GST-SAPs. The STCs are grouped by type (Type 1, Type 2, Type 3) and further grouped by Signalling Transport Technology (A, B, C). Each STC is connected to a specific technology cloud via a Trsp. SAP. + +Q.2220\_F05-1 + +**Figure 5-1/Q.2220 – Selecting a SAP to a Signalling Transport Converter entity to reach a destination independent of the Signalling Transport Technology** + +The status primitives, i.e., START-INFO.indication, IN-SERVICE.indication, OUT-OF-SERVICE.indication, and CONGESTION.indication, are also passed via a specific GST-SAP and, thus, by that indicate which signalling relation indicated its status. + +The signalling transport network from the point of view of a TI-SCCP is a fully meshed network (see Appendix I). + +NOTE 2 – Traditional SCCP networks are fully meshed via the relaying mechanism at the MTP3 layer. + +Figure 5-2 shows an application of this principle by depicting a signalling network that deploys two Signalling Transport Technologies. This signalling network is fully meshed, i.e., 10 signalling relations are used. TI-SCCP "E" is attached to STCs of a single type, i.e., this TI-SCCP can be reached only by utilizing a particular Signalling Transport Technology; the other TI-SCCPs can be reached by either Signalling Transport Technology. + + + +The diagram illustrates a signalling network with five TI-SCCP entities (A, B, C, D, E) at the top. Each TI-SCCP is connected to one or more STC (Signalling Transport Converter) entities below it. TI-SCCP A, B, C, and D are each connected to an STC Type 1 and an STC Type 2. TI-SCCP E is connected only to an STC Type 2. Below the STCs are two large ovals representing 'Signalling Transport Technology A' and 'Signalling Transport Technology B'. Dashed lines show connections from the STCs to these transport technologies. STCs Type 1 and 2 for TI-SCCPs A, B, C, and D have connections to both transport technologies. STC Type 2 for TI-SCCP E has a connection only to Signalling Transport Technology B. A label 'Q.2220\_F05-2' is in the bottom right corner. + +Diagram of a fully meshed signalling network with two transport technologies. + +Figure 5-2/Q.2220 – Selecting a SAP to a Signalling Transport Converter entity to reach a destination independent of the Signalling Transport Technology + +## 5.2 Interworking of TI-SCCP with SCCP + +Figure 5-3 shows the interworking scenario. + + + +The diagram shows two network domains separated by a central 'SCCP IWF' (Interworking Function). On the left, the 'New Technology based Signalling Network' contains five TI-SCCP entities (A, B, C, D, E) in a mesh. TI-SCCP C is connected to the SCCP IWF. On the right, the 'MTP3 or MTP3b Signalling Network' contains five SCCP entities (F, G, H, I, J) in a mesh. SCCP F is connected to the SCCP IWF. Below the main diagram, a detailed view of the interworking point shows a 'GST' (Gateway Signalling Transport) block connected to a 'TI-SCCP' block on the left, and an 'MTP3' block connected to an 'SCCP' block on the right. Both are connected to a central 'IWF' block. A label 'Q.2220\_F05-3' is in the bottom right corner. + +Diagram showing interworking between a New Technology based Signalling Network and an MTP3 or MTP3b Signalling Network. + +Figure 5-3/Q.2220 – Scenario for interworking between TI-SCCP and SCCP + +NOTE – The interworking function ("SCCP IWF") may be collocated with TI-SCCP "C", or SCCP "F", or both. + +### **5.2.1 Messages travelling from an SCCP network towards a TI-SCCP network** + +Messages arriving from an SCCP node get delivered to the SCCP IWF by an MTP-TRANSFER.indication primitive. The parameter quadruple "OPC, DCP, SI, NI" indicates the signalling relation. In addition, an SLS value is indicated. + +At the SCCP IWF the following actions are performed: + +- 1) A UDT message is converted into an XUDT or LUDT message; +NOTE – A UDTS message is never received. +- 2) A sequence control parameter is appended to XUDT, XUDTS, LUDT, and LUDTS messages; +- 3) A regular Global Translation (see 2.4/Q.714 in 9.3/Q.2220) is required as the message enters another signalling network with its own SPC domain; +- 4) The SLS value is put into the sequence control parameter of the XUDT, XUDTS, LUDT, and LUDTS messages (see 3/Q.713 and 4/Q.713 in 8.3/Q.2220 and 8.4/Q.2220); and +- 5) The message is transmitted with the TRANSMIT.request primitive via the appropriate GST-SAP. + +### **5.2.2 Messages travelling from a TI-SCCP network towards an SCCP network** + +A TRANSFER.indication primitive via a GST-SAP delivers messages arriving from a TI-SCCP node to the SCCP IWF. The identity of the GST-SAP indicates the signalling relation. + +At the SCCP IWF the following actions are performed: + +- 1) A regular Global Translation (see 2.4/Q.714 in 9.3) is required as the message enters another signalling network with its own SPC domain; and +- 2) The message is transmitted with the MTP-TRANSMIT.request primitive together with the parameters taken from the result of the Global Translation and the SLS value removed. + +# **6 Exceptions to ITU-T Rec. Q.711** + +The specifications in ITU-T Rec. Q.711 apply with the following exceptions: + +## **6.1 General** + +The SCCP defined in ITU-T Recs Q.711 to Q.716 are based on the MTP3 signalling transport service whereas the Transport-Independent SCCP defined in this Recommendation is based on the Generic Signalling Transport Service (GSTS) defined in ITU-T Rec. Q.2150.0; hence: + +- a) Any reference – in the text of the whole Recommendation – to the service or lower boundary conditions including references to ITU-T Recs Q.701 to Q.707, and/or in ITU-T Rec. Q.2210 shall be replaced with a reference to ITU-T Rec. Q.2150.0. +- b) Any reference to "MTP" is replaced by a reference to "GST", the Generic Signalling Transport. + +NOTE – This includes figures such as Figures 1/Q.711 and 2/Q.711. + +- c) Any reference to "MTP-SAP" is replaced by a reference to "GST-SAP", the Service Access Point to the Generic Signalling Transport Service. + +Further specific exceptions are specified in the following subclauses. + +## 6.2 Scope and field of application + +Replace the 5th paragraph in clause 1/Q.711 with: + +<<<<<<<<----- +The SCCP making use of the services of the ~~GST-MTP~~, as specified in ITU-T Rec. ~~Q.2150.0~~ ~~Q.2210~~, provides the connectionless network service as specified in this Recommendation. A connection-oriented network service can only use the services which are common to ITU-T Recs ~~Q.2150.0-Q.2210~~ and Q.704 for the MTP. In particular, the connection-oriented network service shall use a maximum PDU length that does not exceed 272 octets minus the size of the MTP label. +----->>>>>>>> + +After the last paragraph and Figure 1/Q.711 in clause 1/Q.711 add the following paragraph and Note: + +<<<<<<----- +The Bearer Independent Call Control (BICC) signalling is independent of the underlying transport protocols by utilizing the Generic Signalling Transport Service (GSTS). Functions of the SCCP are however used for the transfer of ISUP Supplementary Services for BICC that are based on the Transaction Capability of Signalling System No. 7. + +NOTE – The Transaction Capability of SS No. 7 itself is based on the services of SCCP. + +## 6.3 Primitives + +Replace Figure 3/Q.711 with the following figure: + + + +<<<<<<----- + +The diagram illustrates the interaction between network layers and their service primitives. At the top is a box labeled 'Upper layers'. Below it is a box labeled 'Transport-Independent Signalling Connection Control Part (TI-SCCP)'. At the bottom is a box labeled 'Generic Signalling Transport'. Between the top and middle boxes is a diamond-shaped interface labeled 'SCCP-SAP' on the left and 'Services of the SCCP' on the right. A double-headed vertical arrow between the top box and this interface is labeled 'N-service primitives'. Between the middle and bottom boxes is another diamond-shaped interface labeled 'GST-SAP' on the left and 'Services of the Generic Signalling Transport' on the right. A double-headed vertical arrow between the middle box and this interface is labeled 'Generic Signalling Transport Services primitives'. + +Diagram showing service primitives between Upper layers, SCCP-SAP, Transport-Independent Signalling Connection Control Part (TI-SCCP), GST-SAP, and Generic Signalling Transport. + +Q.2220\_F06-1(6.3) + +**Figure 6-1/Q.2220 – Service primitives** + +----->>>>>>>> + +## 6.4 Removal of the embedded service + +In 6.1.1.1.1/Q.711, replace the 5th paragraph with the two bullet items and the 6th paragraph with the following: + +<<<<<<<<----- + +For connection establishment there ~~exists an~~ are two alternative boundaries between SCCP and SCCP user with different procedures: + +- the "X.213-like" boundary that is described further in 6.1.1.2, +- the "ISUP-embedded" boundary that is described further in 6.1.1.3. + +The "X.213-like" boundary that requires that establishment procedures are performed by SCCP while in the case of "ISUP-embedded" boundary the ISUP provides the routing of the request for the set-up of a connection section. + +NOTE – The "ISUP-embedded" boundary is not supported. + +----->>>>>>>> + +Remove 6.1.1.3/Q.711 completely, including Tables 7/Q.711, 8/Q.711, and 9/Q.711. + +## 6.5 Reason for return + +Replace the 6th bullet item in the second paragraph of 6.2.2.2.4/Q.711 with: + +<<<<<<<<----- + +- GST out of service MTP failure; + +----->>>>>>>> + +## 6.6 SCCP management + +In Table 14/Q.711, replace the last row with the following: + +<<<<<<<<----- + +| | | | +|-----------|------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +| N-PCSTATE | Indication | Affected signalling point (together with the
Signalling point status
Restricted importance level
Remote SCCP status
Affected SCCP service | +|-----------|------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| + +----->>>>>>>> + +Add the following new subclause: + +<<<<<<<<----- + +### 6.3.2.2.8 Affected SCCP service + +The optional parameter "Affected SCCP service" indicates which of the SCCP services are affected by the restriction of traffic indicated in the "Restricted importance level" parameter. + +"Affected SCCP service" may assume the following values: + +- SCCP connectionless and connection-oriented services; +- SCCP connectionless service; +- SCCP connection-oriented service. + +When this parameter is not provided, it is assumed that both connectionless and connection-oriented services are affected. + +In Table 17/Q.711, add as a new penultimate row (before the Notes) the following: + +| | | +|-----------------------|---| +| Affected SCCP service | O | +|-----------------------|---| + +In Table 17/Q.711, replace the last row (notes) with the following: + +| | | +|-----|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +| c5) | Present if this is the result of
CIC_Control | – | – | +| IN-SERVICE | – | Level | – | – | +| OUT-OF-SERVICE | – | (Note 1) | – | – | +| CONGESTION | – | Level | – | – | +| TRANSFER | Sequence Control
STC User Data
Priority (Note 2) | STC User Data
Priority (Note 2) | – | – | + +– This primitive is not defined. +NOTE 1 – This primitive has no parameters. +NOTE 2 – This parameter is a national option. + +On the establishment of a Signalling Transport Converter entity and the associated Signalling Transport Converter user entity, for example at power up, the initial conditions are the same as if an OUT-OF-SERVICE.indication primitive had been conveyed across the SAP. Also at this time the START-INFO.indication is sent to the TI-SCCP. + +NOTE – The procedures for the primitives IN-SERVICE.indication, OUT-OF-SERVICE.indication, and CONGESTION.indication are specified for traffic limitations (see 2.6/Q.714 in 9.3/Q.2220), for connectionless data transfer (see 4.1/Q.714 in 9.5/Q.2220), and for SCCP management (see clause 5/Q.714 in 9.6/Q.2220). The procedures for the primitives TRANSFER.request and TRANSFER.indication are specified for the data transfer between peer TI-SCCP entities (in 1.5/Q.714 in 9.2/Q.2220). The "STC User Data" parameter in these primitives carry a complete message (message formats are specified in clauses 4 and 5/Q.713 in 8/Q.2220); the "sequence control" parameter conveys the SLS value to allow the lower layers to perform signalling link selection (in 1.5/Q.714 in 9.2/Q.2220). + +# 7 Exceptions to ITU-T Rec. Q.712 + +The specifications in ITU-T Rec. Q.712 apply with the following exceptions: + +## 7.1 Signalling connection control part messages + +*Replace the specification labelled "1.25" with:* + +**1.25 long unitdata (LUDT):** A *Long Unitdata* message is used by the SCCP to send data (along with optional parameters) in a connectionless mode. When the maximum length indication from the Generic Signalling Transport permits, MTP capabilities according to Recommendation Q.2210 are present, it allows sending of NSDU sizes up to 3952 octets without segmentation. + +It is used in Connectionless protocol classes 0 and 1. + +## 7.2 SCCP message parameters + +Replace the specification labelled "2.20" with: + +<<<<<<<<----->>>>>>>> +**2.20 segmentation:** The "segmentation" parameter field is used in the XUDT, XUDTS, LUDT and LUDTS messages to indicate that a SCCP message has been segmented, or, in case of the LUDT(S), that it may undergo segmenting at an ~~MTP/MTP 3b interworking node~~ between the Generic Signalling Transport and an MTP3-based signalling transport. The parameter also contains all the information necessary to allow the correct reassembly of the message. + +Replace the specification labelled "2.22" with: + +<<<<<<<<----->>>>>>>> +**2.22 congestion level:** The "SCCP congestion level" parameter is included in the *Subsystem Congested* message (SSC) to report the severity of the congestion referring to either the whole SCCP node or to the local SCCP. When local SCCP congestion is reported, the "Affected SCCP service" field in the congestion level parameter indicates whether the reported congestion level affects SCCP connectionless, connection-oriented or both services. + +Replace the specification labelled "2.23" with: + +<<<<<<<<----->>>>>>>> +**2.23 long data:** The "long data" parameter is a "data" parameter with a two octet length indicator. It allows sending of up to ~~3968~~ 3952 octets in a single LUDT or LUDTS message when the maximum length indication from the Generic Signalling Transport permits sending of NSDU sizes up to 3968 octets ~~MTP 3b capabilities are present~~. + +## 7.3 Inclusion of fields in the messages + +In Table 1/Q.712, replace note b) at the bottom of the table with: + +<<<<<<<<----->>>>>>>> +b) The segmentation parameter must be included by the originating node, if interworking between the Generic Signalling Transport and an MTP3-based signalling transport ~~MTP/MTP 3b interworking~~ is expected. + +# 8 Exceptions to ITU-T Rec. Q.713 + +The specifications in ITU-T Rec. Q.713 apply with the following exceptions: + +## 8.1 Introduction + +Replace the text in clause 1/Q.713 "General" with: + +<<<<<<<<----->>>>>>>> +This Recommendation specifies the SCCP messages formats and codes for the support of connection-oriented services, connectionless services and the management of SCCP. + +The SCCP messages are passed between SCCP and GSTMTP across the GSTMTP-SAP by means of the STC user data parameter of the MTP-TRANSFER request or indication primitives as appropriate (see Table 6-1/Q.2150.0-1/Q.701). + +~~NOTE The MTP TRANSFER primitive, in addition to the user data parameter, contains four parameters with the contents as follows (see Table 1/Q.701):~~ + +- ~~• the contents of the OPC consisting of information equivalent to 14 bits, to be conveyed in the standard routing label of the MTP;~~ +- ~~• the contents of the DPC consisting of information equivalent to 14 bits, to be conveyed in the standard routing label of the MTP;~~ +- ~~• the contents of the SLS consisting of information equivalent to 4 bits. If the MTP service "in-sequence delivery" of SDUs is a requirement, SCCP shall use the same SLS value for all SDUs with the same sequence control and called address parameters;~~ +- ~~• information equivalent to the contents of the SIO. For SCCP, the encoding for the service indicator is 0011 binary (see Q.704 § 14.2.1)~~ + +A SCCP message consists of the following parts (see Figure 1/Q.713): + +- the message type code; +- the mandatory fixed part; +- the mandatory variable part; +- the optional part, which may contain fixed length and variable length fields. + +The description of the various parts is contained in the following clauses. SCCP management messages and codes are provided in clause 5. + +----->>>>>>>> +*Replace Figure 1/Q.713 with the following figure:* + <<<<<<<<----- + + + +| | | +|-------------------------|----------------| +| Message type code | } SCCP message | +| Mandatory fixed part | | +| Mandatory variable part | | +| Optional part | | + +Q.2220\_F08-1 + +**Figure 8-1/Q.2220 – General layout** + +Replace Figure 2/Q.713 with the following figure: + +<<<<<<<<----- + + + +The diagram illustrates the General SCCP message format. It shows the order of octets (8 to 1) and the structure of the message fields, categorized into Mandatory fixed part, Mandatory variable part, and Optional part. + +| Order of octets | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | | +|-----------------|---------------------------------------|---|---|---|---|---|---|---|-------------------------| +| | Message type code | | | | | | | | | +| | Mandatory fixed length parameter A | | | | | | | | Mandatory fixed part | +| | Mandatory fixed length parameter F | | | | | | | | | +| | Pointer to parameter M | | | | | | | | Mandatory variable part | +| | Pointer to parameter P | | | | | | | | | +| | Pointer to start of optional part | | | | | | | | | +| | Length indicator of parameter M | | | | | | | | | +| | Mandatory variable length parameter M | | | | | | | | | +| | Length indicator of parameter P | | | | | | | | | +| | Mandatory variable length parameter P | | | | | | | | | +| | Parameter name = X | | | | | | | | | +| | Length indicator of parameter X | | | | | | | | Optional part | +| | Optional parameter X | | | | | | | | | +| | Parameter name = Z | | | | | | | | | +| | Length indicator of parameter Z | | | | | | | | | +| | Optional parameter Z | | | | | | | | | +| | End of optional parameters | | | | | | | | | + +Notes: Arrows on the left indicate that 'Pointer to parameter M', 'Pointer to parameter P', and 'Pointer to start of optional part' point to the corresponding length indicators and parameter blocks. Dotted vertical lines separate octets 5 and 6 in several fields. + +Diagram of General SCCP message format showing octet order and field structure. + +Q.2220\_F08-2 + +**Figure 8-2/Q.2220 – General SCCP message format** + +----->>>>>>>> + +*Remove footnote 1 from the 2nd paragraph of 1.4/Q.713 and insert the Note in the mainline text as follows:* + +<<<<<<<<----- + +A pointer is also included to indicate the beginning of the optional part. If the message type indicates that no optional part is allowed, then this pointer will not be present. If the message type indicates that an optional part is possible, but there is no optional part included in this particular message, then a pointer field containing all zeros will be used†. + +NOTE – There are currently messages (RSR and ERR) containing one pointer to the beginning of the optional part although no optional parameters are currently defined for them. + +----->>>>>>>> + +## 8.2 Coding of the general parts + +*Modify Table 2/Q.713 as follows:* + +<<<<<<<<----- + +**Table 2/Q.713 – SCCP parameter name codes** + +| Parameter name | Clauses | Parameter name code
8765 4321 | +|--------------------------------|------------------|-------------------------------------------------------------| +| End of optional parameters | 3.1 | 0000 0000 | +| Importance | 3.19 | 0001 0010 | +| Long data | 3.20 | 0001 0011 | +| Sequence control | 3.21 | 0001 0100 | +| Reserved for International Use | {
{
{
} |
0001 0101
to
1111 0011 | +| Reserved for National Networks | {
{
{
} | 1111 0100
to
1111 1110 | +| Reserved | | 1111 1111 | + +----->>>>>>>> + +*Remove footnote 2 from the first paragraph of 2.3/Q.713 and insert the Note in the mainline text as follows:* + +<<<<<<<<----- + +The pointer value (in binary) gives the number of octets between the most significant octet of the pointer itself (included) and the first octet (not included) of the parameter associated with that pointer2 as shown in the following diagram. + +NOTE – For example, a pointer value of "00000001" indicates that the associated parameter begins in the octet immediately following the most significant octet of the pointer. A pointer value of "00001010" indicates that ten octets of information exist between the most significant octet of the pointer octet (included) and the first octet of the parameter associated with that pointer (not included). A two-octet pointer value of "00000000 00001010" indicates that ten octets of information exist between the most significant octet of the pointer (included) and the first octet of the parameter associated with that pointer (not included). + +## ----->>>>>>>> **8.3 SCCP parameters** + +*Remove footnote 3 from the entry of bit coding "00000010" of 3.14/Q.713 and insert the Note in the mainline text as follows:* + +<<<<<<<----- + +Bits + +8 7 6 5 4 3 2 1 + +• • • + +0 0 0 0 0 0 1 0 point code mismatch3 (see Note) + +• • • + +NOTE – National option (see Table B.2/Q.714). + +----->>>>>>>> + +*Add the following new clause after 3.20/Q.713:* + +<<<<<<<----- + +## **3.21 Sequence control** + +The "sequence control" parameter field is a one-octet field containing the signalling link selection value. + +----->>>>>>>> + +## **8.4 SCCP messages and codes** + +*Replace 4.18/Q.713 and 4.20/Q.713 with the following:* + +<<<<<<<----- + +## **4.18 Extended unitdata (XUDT)** + +The XUDT message contains: + +- four pointers; +- the parameters indicated in Table 19. + + + +## 8.5 SCCP management messages and codes + +Replace Figure 13/Q.713 with the following figure: + + + +<<<<<<<<----- + +| | | | | | | | | +|-------|---|------------------------------|---|-----------------------|---|---|---| +| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | +| Spare | | Affected SCCP service | | SCCP congestion level | | | | + +**Figure 13/Q.713 – SCCP congestion level format** + +----->>>>>>>> + +At the end of 5.2.4/Q.713, add the following paragraph: + +<<<<<<<<----- + +Bits 6-5 indicate which SCCP services are affected by the congestion level, and is coded as follows: + +| Bits | | +|------|------------------------------------------------------| +| 6 | 5 | +| 0 0 | SCCP connectionless and connection-oriented services | +| 0 1 | SCCP connectionless service | +| 1 0 | SCCP connection-oriented service | +| 1 1 | Reserved | + +----->>>>>>>> + +## 8.6 Mapping for cause parameter values + +In Table A.2/Q.713, replace the entry with code "00001010" with the following row: + +<<<<<<<<----- + +| RLSD Message | | N-DISCONNECT primitive | | +|--------------|-----------------------------------------------------|------------------------------------------------------------|------------| +| Code | Release cause | Reason | Originator | +| 00001010 | GST out of service
No SSN
or SSN = 0 | GT
No SSN
or SSN = 0 | No GT
SSN | GT
SSN | +|-------------------|-------------------------------|----------------------------|--------------|-----------------| +| No DPC | (4) | (2) | (4) | (2) | +| DPC = own node | (4) | (2) | (1) | (1), (2) (Note) | +| DPC = remote node | (4) | (3) | (1) | (1), (3) (Note) | + +NOTE – The choice of the appropriate action is outside the scope of this Recommendation. + +#### Action (1) + +- a) If the DPC is not the node itself and the remote DPC, SCCP and SSN are available, then the GSTMTP-TRANSFER.request primitive is invoked unless the compatibility test returns the message to SCLC or unless the message is discarded by the traffic limitation mechanism; +- b) If the DPC is not the node itself and the remote DPC, SCCP and/or SSN are not available, then: + - for connectionless messages, the message return procedure is initiated; + - for CR messages, the connection refusal procedure is initiated. +- c) If the DPC is the node itself, then the procedures in 2.3.1, item 2) above are followed†. +NOTE – The function of routing between local subsystems is implementation dependent. + +#### Action (2) + +- a) If the translation of the global title is successful (see 2.4.4), then: + - if the DPC is the node itself, then the message is passed, based on the message type, to either SCOC or SCLC; + - if the DPC is not the node itself, the compatibility may return the message to SCLC or the message may be discarded by the traffic limitation mechanism. The DPC shall be placed in the "called party address" before ~~then~~ the GSTMTF-TRANSFER.request primitive is invoked ~~unless the compatibility test returns the message to SCLC or unless the message is discarded by the traffic limitation mechanism.~~ +- b) If the translation of the global title is unsuccessful (see 2.4.4), and: + - the message is a connectionless message, then the message return procedure is initiated; + - the message is a CR message, then the connection refusal procedure is initiated. + +#### Action (3) + +The same actions as Action (1) apply, without checking the SSN. + +#### Action (4) + +The "called address" contains insufficient information. If: + +- the message is a connectionless message, then the message return procedure is initiated; +- the message is a CR message, then the connection refusal procedure is initiated. + +## 2.4 *Global title translation* + +### 2.4.1 *General characteristics of the GTT* + +The Global Title Translation (GTT) function shall be invoked within the SCCP routing control (SCRC) under the routing procedures described in 2.3. + +If the GTT function results in a "routing indicator" (see 3.4.1/Q.713) equal to "Route on GT", then the GTT function must provide a global title and the DPC of the SCCP node where that global title will be translated. This process shall be repeated until the GTT function results in a "routing indicator" equal to "Route on SSN", which means that the final destination has been determined. + +The global title addressing capability and the GTT function allow diverse groups of the SCCP addressable entities associated with different applications to establish their own addressing schemes. All the application-specific addressing schemes requiring the GTT shall be specified within the GTT procedural framework stated in this subclause. + +### 2.4.2 *Terminology definitions* + +#### 2.4.2.1 *GT information* + +The GT information is made up of the Global Title Indicator (GTI) and the Global Title (GT). + +##### 1) **Global Title Indicator (GTI)** + +Refer to 3.4.1/Q.713 and 3.4.2.3/Q.713 for the list of global title indicators recognized by the SCCP. The global title indicator is used to determine the content and format of the global title. + +##### 2) **Global Title (GT)** + +The global title consists of the mandatory Global Title Address Information (GTAI) and one or more of the following information elements depending on the GTI: + +###### a) **Encoding Scheme (ES)** + +Refer to 3.4.2.3/Q.713 for the list of encoding schemes recognized by the SCCP. The encoding scheme indicates how the global title address information is encoded. If the encoding scheme is included, then the global title address information shall be decoded accordingly. If the encoding scheme is not included but translation type is included, then the translation rules associated with the translation type should specify the encoding scheme. Refer to d) and 3) for the description of the translation type and translation rules. The meaning of each encoding scheme value is identical for all the GTI values indicating that the encoding scheme is included. + +###### b) **Numbering Plan (NP)** + +Refer to 3.4.2.3.3/Q.713 for the list of numbering plans recognized by the SCCP. The numbering plan indicates how the global title address information is constructed from different parts (e.g. country codes, subscriber number or national significant number) according to the syntax and semantic defined for that particular numbering plan. The semantic of each numbering plan value is identical for all the GTI values indicating that the numbering plan is included. + +###### c) **Nature of Address Indicator (NAI)** + +Refer to 3.4.2.3.1/Q.713 for the list of nature of address indicator values recognized by the SCCP. The nature of address indicator defines the "scope" of the global title address information for a specific numbering plan. The semantic of the nature of address indicator value depends only on the numbering plan. In particular, it does not depend on GTI values. + +###### d) **Translation Type (TT)** + +Refer to 3.4.2.3.2/Q.713 for the list of translation types recognized by the SCCP, and refer to Annex B/Q.713 for the TT values recognized by SCCP when GTI is set to 4. The translation type together with the numbering plan and the nature of address indicator determines a specific translator which defines a specific set of translation rules. + +A particular TT value shall implicitly specify the encoding scheme of the GTAI value if the encoding scheme is not included for a particular GTI. + +A TT value is unique only within the context of a GTI. + +##### 3) **Translation rules** + +A set of rules specifies which type of SCCP addressable entities, associated with some service/application must be unambiguously addressed with the global title address information, and how the global title address information should be interpreted by the GTT function. + +The translation rules should specify which portion of the GTAI is required to unambiguously identify or distinguish one SCCP addressable entity from another pertaining to the applications. However, the rules should not specify which GTAI portion is to be translated to which DPC or DPC + SSN. The determination of the DPC and SSN is implementation-specific and requires local information (see 2.4.3.1) specific to the destination network. The translation rules may specify if the SSN is to be determined from the translation. + +##### 4) Identification of translation rules + +The translation rules shall be uniquely identified by the GTI and its associated TT, NP and NAI values. + +#### 2.4.2.2 Other definitions used in the GTT function + +##### 1) SCCP Entity + +An SCCP Entity is a local GSTMTP-SAP + a ~~DPC~~ + possibly an SSN. + +NOTE – An SCCP Entity with an SSN equal to zero (SSN not known or not used) is different from an SCCP Entity without an SSN value. + +##### 2) SCCP Entity Set + +An SCCP Entity Set is made of one SCCP Entity or is made of two SCCP Entities of the same type (if an SSN is present in one SCCP Entity, then an SSN shall also be present in the other). In the latter case the two SCCP Entities may be considered either as a "primary" SCCP Entity and a "backup" SCCP Entity or may be interpreted as two equal SCCP Entities that can be used for a loadsharing purpose. + +##### 3) DPC + +A DPC is significant only in a given signalling transport MTP-network. Because an SCCP gateway manages several GSTMTP networks, a DPC, as a result of the global title translation, could be accompanied by an identification of the concerned signalling transport MTP-network, i.e., that is the GSTMTP-SAP instance. + +### 2.4.3 Input of the GTT function + +The following types of information can be an input for the GTT function. + +#### 2.4.3.1 Local information (mandatory input) + +The local information contains firstly the routing information and secondly the management information. + +- The routing information is specific to the implementation network and is administratively input to the GTT function. They are static data implementing the "translation rules" required to translate the global title address information for the applications. +- The management information is specific to the state of the network in terms of availability. They are dynamic data reflecting the accessibility of the SCCP nodes (~~accessibility at the MTP and SCCP level~~) and the accessibility of the subsystems handled by the different SCCP nodes. + +#### 2.4.3.2 GT information (mandatory input) + +The GT information is a required input for the GTT function. It contains: + +- the GTI value; +- the TT, NP, NAI and ES values depending on the GTI; +- the GTAI value. + +#### 2.4.3.3 SSN (mandatory input if present) + +Even if SSN equals zero, the SSN is a mandatory input of the GTT function. + +#### 2.4.3.4 Loadsharing information + +If the GTT function is able to handle a loadsharing mechanism, then the value of the Sequence Control parameter SLS may be an input for the GTT function. + +### 2.4.4 Output of the GTT function + +Three types of output are possible for the GTT function: + +- A "successful" output which contains the required parameters to route the message forward in the network or to distribute the message. +- An "unsuccessful" output where no translation exists for the given input (see steps 1, 2 and 4 described in 2.4.5). The failure causes are "no translation for an address of such nature" or "no translation for this specific address". +- An "unsuccessful" output where the translation exists but no available destination can be found (see step 4 described in 2.4.5). The failure causes may be "~~GSTMTP~~ failure", "SCCP failure" or "subsystem failure". + +Refer to 2.6 for the causes used in RLSD, CREF, XUDTS, LUDTS or UDTS messages. + +The two key outputs for the "normal" output of the GTT function are the DPC and the routing indicator. + +If the routing indicator is set to "Route on SSN", then the SSN is a required output of GTT function. The subsystem defined by DPC + SSN is expected to be accessible from SCRC. The DPC may be a local DPC in the case of a GT translation in the destination node. The GT information as an output is optional. + +If the routing indicator is set to "Route on GT", then the GT information is a required output of the GTT function and the DPC provided is expected to be accessible. The GT information is made up of the GTAI and TT, NP, NAI, ES with the corresponding GTI. The SSN is an optional output. + +### 2.4.5 Global title translation function + +When the GTT function is invoked by the SCRC, the GTT function shall perform the following steps: + +- 1) Step 1: the GTI and the three optional parameters TT, NP and NAI should be unambiguously associated to a translator which defines a set of translation rules. If this translator cannot be determined, the GTT function shall be aborted with the cause "no translation for an address of such nature". +- 2) Step 2: the set of translation rules determined by step 1 is used to analyse the GTAI possibly accompanied by the encoding scheme. If no output exists for this GTAI, then the GTT function shall be aborted with the cause "no translation for this specific address". Otherwise the output of this step 2 is at least the Routing Indicator (RI) and an SCCP Entity Set. In addition, if the routing indicator is set to "Route on GT", then a GT information is a mandatory output otherwise the GT information as an output is optional. +- 3) Step 3: if an SSN is available as a GTT function input, then the step 3 consists of using this input SSN as a default value if some SSN are missing in the SCCP Entity Set. It may happen that the value zero appears as an SSN value in the SCCP Entity Set: this is a correct value which overwrites the SSN given as input of the GTT function. +- 4) Step 4: this is where the management information is taken into account and where a loadsharing mechanism can be implemented. + +By definition an SCCP entity is declared accessible when the two following conditions are fulfilled: + +- The DPC concerned is accessible (~~at MTP and SCCP level~~) or the DPC corresponds to the local node. +- If the routing indicator is set on "Route on SSN", then an SSN is present and different from zero and this subsystem is accessible in the node defined by the DPC: + - a) If the SCCP Entity Set contains only one SCCP Entity and this SCCP Entity is inaccessible, then the result of the GTT function is "~~GSTMTP~~ failure", "SCCP failure" + +or "subsystem failure". When the routing indicator is set to "Route on SSN" and if the inaccessibility is due to the absence of SSN in the SCCP Entity or due to an SSN value equal to zero, then the result of the GTT function shall be "no translation for this specific address". + +- b) If the SCCP Entity Set contains only one SCCP Entity and this SCCP Entity is accessible, then: + - If the routing indicator is set to "Route on GT", then the outputs of the GTT function are the RI and the GT information as an output of step 2, the DPC found in the SCCP Entity and possibly the associated SSN as an output of step 3; + - If the routing indicator is set to "Route on SSN", then the outputs of the GTT function are the RI and possibly the GT information as an output of step 2, and the DPC and SSN found in the SCCP Entity as an output of step 3. +- c) If the SCCP Entity Set contains two SCCP Entities and if there is no loadsharing mechanism, then the accessibility of the "primary" SCCP Entity is checked. If this "primary" SCCP Entity is accessible, then this "primary" SCCP Entity is selected as part of the GTT function result. If the "primary" SCCP Entity is inaccessible, then the accessibility of the "backup" SCCP Entity is checked. If this "backup" SCCP Entity is accessible, then this "backup" SCCP Entity is selected as part of the GTT function result. If the "backup" SCCP Entity is inaccessible, then the result of the GTT function is "~~GSTMTP~~ failure", "SCCP failure" or "Subsystem failure" (if the refusal or return causes are different for both SCCP Entities it is an implementation-dependent matter which one is selected). If the inaccessibility is due to the absence of SSN in the two SCCP Entities or due to SSN values equal to zero when the routing indicator is set to "Route on SSN", then the result of the GTT function shall be "no translation for this specific address". +- d) If the SCCP Entity Set contains two SCCP Entities and if there is a loadsharing mechanism implemented, then one of the two SCCP Entities is chosen depending on the loadsharing information and on the accessibility of the SCCP Entities. If one SCCP Entity can be chosen, then this SCCP Entity is selected as part of the GTT function result. If the SCCP Entities are both inaccessible, then the result of the GTT function is "~~GSTMTP~~ failure", "SCCP failure" or "Subsystem failure" (if the refusal or return causes are different for both SCCP Entities it is an implementation-dependent matter which one is selected). If the inaccessibility is due to the absence of SSN in the two SCCP Entities or due to SSN values equal to zero when the routing indicator is set to "Route on SSN", then the result of the GTT function shall be "no translation for this specific address". + +Figure 2 shows the different steps of the global title translation function as well as the parameters used in this global title translation function. + +In Figure 2: + +- an in-bracket parameter means an optional parameter; +- the dashed line with the SLS parameter means that the loadsharing functionality itself is not required in a given implementation. If this functionality is present, then the SLS parameter may be an input parameter. + + + +Figure 2/Q.714 – Steps and parameters of the global title translation function. The diagram illustrates a four-step process for translating a Global Title (GTI) into a Destination Point Code (DPC). Step 1: Input GTI (TT)(NP)(NAI) is processed by a 'Translator selector' to produce a 'Translator Identity'. Step 2: The 'Translator Identity' and 'Routing information' are input to 'Translation rules', which output (TT')(NP')(NAI')(ES')(GTAI') and 'RI'. Step 3: The 'Translation rules' also output an 'SSCP Entity Set' to 'SSN production', which outputs (SSN'). Step 4: The 'SSCP Entity Set' from Step 3 and 'Management information' are input to an 'Availability tester', which outputs (SSN') and 'DPC'. The diagram is divided into four vertical columns labeled Step 1, Step 2, Step 3, and Step 4. Horizontal lines represent data flow between components, and vertical lines separate the steps. A reference code Q.2220\_F02 is in the bottom right corner. + +**Figure 2/Q.714 – Steps and parameters of the global title translation function** + +## 2.5 Compatibility test + +The compatibility test defined in this subclause applies to connectionless procedures only. + +If the network structure is such that incompatibilities requiring segmentation, truncation or message type change are never present, then the compatibility test is not required. + +Based on the available knowledge at the local node, the compatibility test ensures that: + +- 1) the SCRC never attempts to send a message that cannot be understood by the recipient SCCP node; +- 2) the outgoing messages are of the appropriate length to be carried by the underlying GSTMTP. + +The compatibility test in SCRC determines whether: + +- 1) An LUDT message needs to be segmented. +- 2) An LUDTS message needs to be truncated. +- 3) The message type needs to be changed. In some cases, a message may be changed to a type preferred by the recipient node (see 4.1.2). + +If no segmentation, truncation or message type change is required, then the GSTMTP-TRANSFER primitive is invoked unless the message is discarded by the traffic limitation mechanism (see 2.6). Otherwise, the message is passed to SCLC for the necessary changes. + +## 2.6 Traffic limitation mechanism + +The SCCP congestion control procedures may be subject to improvement pending further analysis of the impact of these procedures in different network scenarios and based on the results of operational experience. + +### 2.6.1 General + +The GSTMTP notifies the SCCP of unavailable or congested remote signalling points or remote SCCP unavailability using the appropriate OUT-OF-SERVICEMTP PAUSE indication or CONGESTIONMTP STATUS indication primitive. The SCCP then informs its users. + +Each destination (GSTDPC + MTP-SAP instance) is associated with a Restriction Levels for connectionless (RLCL) and for connection-oriented (RLCO) services, and a RestrictionSubLevels for connectionless (RSLCL) and connection-oriented (RSLCO) which are reported by SCMG (see 5.2.4). + +These levels, together with the importance of the message to be sent, allow the reduction of the traffic towards a congested node by discarding a portion of the concerned traffic. + +### 2.6.2 Importance of a message + +Whenever a message is to be sent, its importance is the minimum of the permitted maximum importance value for the message type (See Table 2), and: + +- at the originating node the importance value (if provided) in the request or response primitive (otherwise the default value from Table 2 applies); +- at a relay node: + - the importance value received in the incoming message contained in the optional parameter "importance" (CR, CC, CREF, RLSD, XUDT, XUDTS, LUDT or LUDTS); or + - a value derived from the national option of the priority parameter in the TRANSFER indication primitive field in the SIO in the MTP field; otherwise + - a default value assigned from Table 2. + +If there is a conflict between the importance parameter and a value derived from the SIO in a received message, then the importance value used is a network choice. + +**Table 2/Q.714 – Default and maximum importance value** + +| Message type | Default importance | Max importance | Message type | Default importance | Max importance | +|--------------|--------------------|----------------|--------------|--------------------|----------------| +| CR | 2 | 4 | RSC | 6 | – | +| CC | 3 | 4 | ERR | 7 | – | +| CREF | 2 | 4 | RLC | 4 | – | +| DT1 | 4 | 6 | RLSD | 6 | 6 | +| DT2 | 4 | 6 | UDT | 4 | 6 | +| AK | 6 | – | UDTS | 3 | – | +| IT | 6 | – | XUDT | 4 | 6 | +| ED | 7 | – | XUDTS | 3 | – | +| EA | 7 | – | LUDT | 4 | 6 | +| RSR | 6 | – | LUDTS | 3 | – | + +The "–" means that the message type is not generated as a result of a primitive from the SCCP user therefore the default importance value always applies. + +NOTE – The values in Table 2 might be revised as operational experiences are gained. How these default and maximum values should be administered is implementation dependent. + +When in a national network the importance information is carried in the priority ~~parameter level in the SIO~~, then it is the task of the gateway between a national network and the international network to provide the mapping between the importance parameter in the SCCP message and the priority ~~parameter in the SIO~~. + +### 2.6.3 *Handling of messages to a congested node* + +When a message has to be sent towards a remote SCCP node, the importance of the message is compared to the restriction level of that remote SCCP node for the service corresponding to the message to be sent (connectionless or connection-oriented): + +- If the importance of the message is greater than RL, then the GSTMTP-TRANSFER primitive is invoked. +- If the importance of the message is lower than RL, then the message is discarded. +- If the importance of a message is equal to RL, then the message shall be discarded proportionately as determined by the RSL value. The portion of traffic reduction is considered to be network-specific. For the international network, the following values are provisionally assigned: + - RSL = 0 $\Rightarrow$ 0% of traffic discarded. + - RSL = 1 $\Rightarrow$ 25% of traffic discarded. + - RSL = 2 $\Rightarrow$ 50% of traffic discarded. + - RSL = 3 $\Rightarrow$ 75% of traffic discarded. + +When a message has to be discarded, then: + +- for connectionless messages, the message return procedure is initiated; +- for CR messages, the connection refusal procedure is initiated; +- for CO messages other than the CR message, no additional actions are taken. If the message was locally originated, the SCCP may inform the user of the discard by issuing an N-INFORM primitive. + +## 2.7 *Calling party address treatment* + +### 2.7.1 *Address indicator* + +The segmenting/reassembly process of connectionless messages requires that an unambiguous calling party address is passed in each segment. The practice of "deleting" the calling party address from an XUDT or LUDT or UDT message by coding its "Address Indicator" bit 1...7 to zero shall not be used for evolving applications, because at some time their messages may grow beyond the limit supported by one (X)UDT message. + +### 2.7.2 *Calling party address in the international network* + +It is the task of the outgoing international gateway2 (or originating international node) to make sure that the calling party address or responding address (i.e. called party address parameter in a CC or CREF message) satisfies the ~~following rules below~~: + +NOTE – An international gateway is an SCCP node having an GST-SAP instance for the international network and at least one GST-SAP instance for a national network. + +- If routing is based on SSN, the DPC, if present, is one as defined in ITU-T Rec. Q.708, the SSN must be present and should be internationally standardized. +- If routing is based on GT, the GTI must be equal to 4, the SSN is either: + - one of the internationally standardized numbers; or + - national SSN value, if no internationally standardized SSN is specified and it is appropriate to use the national value (see Annex B.2/Q.713); or + +- coded as "0" (i.e., "unknown"). +- The Global Title must have international significance. Within a national network, it is a national option to decide on the scope ("significance") of the calling/responding party addresses. However, when the address is only locally or nationally significant, it may be necessary to change the address in relay or gateway nodes by adding a trunk code or country code to the Global Title address information. This is the case whenever the message is routed outside the domain where the address is valid. + +The incoming international gateway (or possibly any other node) may, as part of its optional screening procedures, provide tests to verify the principles specified above. The screening procedures are further specified in 2.7.4. + +### 2.7.3 *Routing indicator* + +When the called party address in an XUDT or LUDT or UDT message has the routing indicator set on "Route on GT", the routing indicator in the calling party address shall also be set to "Route on GT", unless the destination is in the same GSTMTP network and that its GSTMTP routing tables allows the message to be routed back. + +For a CR message, the calling party address may be of the form "Route on SSN" because the subsequent messages will be routed section by section. + +### 2.7.4 *Screening* + +Screening is an optional network-specific function. + +Further screening of the received calling party address may be performed in a node to check, for example, whether a valid translator for NP/TT/NAI is available and/or whether the calling party digits are allowable. + +### 2.7.5 *Inclusion of OPC in the calling party address* + +The rules described in the following subclauses apply. + +#### 2.7.5.1 *LUDT or XUDT or UDT message* + +##### a) *Originating node* + +When the routing indicator of the called party address is set on "Route on GT" and the routing indicator of the calling party address is set on "Route on SSN", the SCCP routing function should include the OPC in the calling party address. In all other cases the inclusion of the OPC in the calling party address is irrelevant. + +##### b) *Relay node* + +When the routing indicator of the calling party address is set on "Route on SSN", and no SPC is present in it, then the OPC shall be derived from the GST-SAP via which the message has been received ~~MTP routing label shall be taken and~~ inserted into the calling party address before sending the message to the next node. When crossing signalling transport network ~~MTP~~-boundaries the value "Route on SSN" is however not allowed (refer to 2.7.2). + +##### c) *Terminating node* + +When the routing indicator of the calling party address is set on "Route on SSN" and an SPC is present in the calling party address, then this SPC identifies the originating SCCP node. + +When the routing indicator of the calling party address is set on "Route on SSN" and no SPC is present in the calling party address, then the OPC derived from the GST-SAP via which the message has been received ~~in the MTP routing label~~ identifies the originating SCCP node. + +#### 2.7.5.2 CR message + +##### a) Originating node + +If the routing indicator of the called party address is set on "Route on GT" and it is known that no coupling will take place in the next relay node, then the SCCP routing function should include a calling party address (also when not given by the local SCCP subsystem), and in the calling party address the OPC is included. + +In this case Routing indicator = Route on SSN + SPC = OPC of the originating node + SSN = SSN of local subsystem + +##### b) Relay node without coupling + +The SCCP routing function shall check the calling party address parameters in the received CR message: + +- When a calling party address parameter is included and an SPC is present, then the calling party address parameter to be sent to the next SCCP node shall be identical to the calling party address parameter of the received CR message. +- When a calling party address parameter is included and the SPC is absent, then the OPC derived from the GST-SAP via which the CR message has been received of the MTP routing label of the received CR message shall be inserted in the calling party address parameter of the CR message to be sent to the next SCCP node. If no SSN is present it may be added with value "unknown". + +In this case Routing indicator is unchanged + SPC = OPC derived from the GST-SAP via which the message has been received of the received MTP routing label + SSN and GT are unchanged + +- When the calling party address parameter is absent, then a calling party address parameter containing the OPC derived from the GST-SAP via which the CR message has been received of the MTP routing label of the received CR message shall be inserted in the CR message to be sent to the next SCCP node. An SSN may be added with value "unknown". + +In this case Routing indicator = "Route on SSN" + SPC = OPC derived from the GST-SAP via which the message has been received of the received MTP routing label + SSN = unknown + no GT + +##### c) Relay node with coupling + +The OPC of the calling party address of the received CR message identifies the originating SCCP node of the incoming connection section. If the calling party address is absent or if no OPC is available in the calling party address, then the OPC derived from the GST-SAP via which the CR message has been received of the MTP routing label of the received CR message is taken for identifying the originating SCCP node of the incoming connection section. + +The SCCP routing function shall check the calling party address parameter in the received CR message: + +- When a calling party address parameter is included and an SPC is present, then the SCCP routing function shall replace the SPC of the received CR message by the OPC of its own node and corresponding to the outgoing signalling transport MTP-network, or shall delete the SPC field from the received calling party address parameter. Deleting the SPC is not advisable, because it means reformatting the message, and it + +may have to be re-included in the next relay node if no coupling is done there. If no SSN is present it may be added with value "unknown". + +In this case Routing indicator is unchanged + SPC = OPC of relay node with coupling + SSN and GT are not changed + +- When a calling party address parameter is included and the SPC is absent, then the calling party address parameter of the CR message to be sent to the next SCCP node may be identical to the calling party address parameter of the CR message received. + +However, if it is known that no coupling will take place in the next relay node, then the SCCP routing function should include an SPC in the calling party address parameter. The SPC is the OPC of its own node and corresponding to the outgoing signalling transport MTP-network. + +- When the calling party address parameter is absent no special actions are necessary. + +However, if it is known that no coupling will take place in the next relay node, the SCCP routing function should include a calling party address parameter containing an SPC. The SPC is the OPC of its own node and corresponding to the outgoing signalling transport MTP-network. + +##### d) *Terminating node* + +The SPC of the calling party address of the received CR message identifies the originating SCCP node of the incoming connection section. If the calling party address is absent or if no SPC is available in the calling party address, then the OPC derived from the GST-SAP via which the CR message has been received ~~of the MTP routing label of the received CR message~~ is taken for identifying the originating SCCP node of the incoming connection section. + +## 2.8 *Routing failures* + +When SCCP routing is unable to transfer a message, one of the causes described in 2.8.1 to 2.8.6 is indicated in the RLSD message (refer to 3.11/Q.713, Release cause), the CREF message (refer to 3.15/Q.713, Refusal cause), the XUDTS, the LUDTS or the UDTS message (refer to 3.12/Q.713, Return cause). + +When an end node is informed of a routing failure, this information is forwarded towards the SCCP user by using the N-DISCONNECT primitive (refer to reason for release in 2.1.1.2.4/Q.711) or the N-NOTICE primitive (refer to reason for return in 2.2.2.2.4/Q.711). Annex A/Q.713 describes the mapping between the causes found in the messages (RLSD, CREF, XUDTS, LUDTS or UDTS) and the reasons found in primitives (N-DISCONNECT, N-NOTICE). + +### 2.8.1 *No translation for an address of such nature* + +The translation was invoked for a combination of translation type, numbering plan and nature of address for which no translation exists in this exchange (refer to 2.4.5, Step 1). + +The following causes apply: + +- Release cause: not applicable. +- Refusal cause: no translation for an address of such nature. +- Return cause: no translation for an address of such nature. + +### 2.8.2 *No translation for this specific address* + +The translation was invoked for a sequence of digits for which no matching (sub)sequence can be found in the translation table, hence translation is inconclusive (refer to 2.4.5, Step 2). The same + +reason applies also when the RI determined by the GTT is set to "Route on SSN" and an SSN is present neither in the SCCP Entity Set, nor as input of the GTT (refer to 2.4.5, Step 4). + +The following causes apply: + +- Release cause: not applicable. +- Refusal cause: destination address unknown. +- Return cause: no translation for this specific address. + +### 2.8.3 **GSTMTP/SCCP/subsystem failure** + +The translation fails because no available route could be found for the concerned destination address (refer to 2.4.5, Step 4). This may be due to failures in: + +- 1) GSTMTP (destination point inaccessible); +- 2) SCCP (SCCP user part unavailable in relay node or end node); +- 3) SCCP subsystem (subsystem prohibited or unavailable); +- 4) a combination of two of the three above reasons when an alternative route exists and both the normal and the backup routes are unavailable. + +The following causes apply: + +- for 1): + - Release cause: GSTMTP failure. + - Refusal cause: destination inaccessible. + - Return cause: GSTMTP failure. +- for 2): + - Release cause: SCCP failure. + - Refusal cause: SCCP failure. + - Return cause: SCCP failure. +- for 3): + - Release cause: subsystem failure. + - Refusal cause: subsystem failure. + - Return cause: subsystem failure. +- for 4): + - Release cause: GSTMTP failure, SCCP failure or subsystem failure. + - Refusal cause: GSTMTP failure, SCCP failure or subsystem failure. + - Return cause: GSTMTP failure, SCCP failure or subsystem failure. + +### 2.8.4 **GSTMTP/SCCP/subsystem congestion** + +Routing failures due to subsystem congestion are for further study. + +When a routing failure due to GSTMTP/SCCP/nodal congestion is detected the following causes apply: + +- In the N-DISCONNECT primitive: QoS not available, transient condition. +- In the N-NOTICE primitive: network congestion. +- In the N-INFORM primitive: network service congestion. +- In the CREF message: QoS unavailable/transient. +- In the XUDTS or LUDTS or UDTS message: network congestion. + +### 2.8.5 Unequipped user + +A local unequipped user is determined by SCRC. + +The following causes apply: + +- Release cause: not relevant. +- Refusal cause: unequipped user. +- Return cause: unequipped user. + +### 2.8.6 Hop counter violation + +The hop counter reaches zero. It is an indication that an excessive routing could be present. + +The following causes apply: + +- Release cause: irrelevant. +- Refusal cause: hop counter violation. +- Return cause: hop counter violation. + +## --- 9.4 Connection-oriented procedures + +*In 3.1.1/Q.714, remove the 3rd paragraph.* + +*In 3.1.4.1/Q.714, remove all material after the first bullet item 4).* + +*In 3.1.4.2/Q.714, replace list item 3) with the following:* + +- +- < > +- 3) The node sending the CC message (identified by ~~the parameter OPC contained in the MTP TRANSFER indication primitive which conveyed the CC message plus the~~ GSTMTP-SAP instance) is associated with the connection section. +- + +*In 3.1.5.1/Q.714, remove all material after the first bullet item 4).* + +*In 3.1.5.1/Q.714, replace list item 2) with the following:* + +- +- < > +- 2) The node sending the CR message (identified by the OPC in the calling party address or by default by ~~the OPC in the MTP label, and~~ the GSTMTP-SAP instance) is associated with the incoming connection section. +- + +*In 3.1.5.2/Q.714, replace list item 3) with the following:* + +- +- < > +- 3) The originating node of the CC message (identified by ~~the OPC in the MTP label plus~~ the GSTMTP-SAP instance) is associated with the outgoing connection section. +- + +*In 3.1.5.2/Q.714, remove all material after the first bullet item 4).* + +*In 3.1.6.1/Q.714, replace list item 2) with the following:* + +<<<<<<<<----- + +- 2) The originating node of the CR message (identified by the OPC in the calling party address or by default by the ~~OPC in the MTP label, and the GST~~MTP-SAP instance) is associated with the incoming connection section. + +>>>>>>>>----- + +*In 3.1.6.1/Q.714, remove all material after the first bullet item 4).* + +*In 3.2.1/Q.714, remove under item 1) the bullet item b).* + +*In 3.2.1.1/Q.714, remove the following text at the end of the paragraph "if the refusal procedure has been initiated by using the refusal indicator in the REQUEST Type 2 interface element, then the refusal cause contains "SCCP user originated" ".* + +*In 3.2.1.2/Q.714, remove the 3rd paragraph.* + +*In 3.2.2/Q.714, remove the bullet item 2).* + +## 9.5 Connectionless procedures + +*In the introduction to clause 4/Q.714, replace list items a) to c) with the following:* + +<<<<<<<<----- + +- a) an environment with only signalling MTP-network(s) supporting a maximum length of 272 octets according to Recommendation Q.704 (pure Q.704); +- b) an environment with only signalling MTP-network(s) supporting a maximum length of 4096 octets (or more) according to Recommendation Q.2210 (pure Q.2210); +- c) an environment where interworking occurs between signalling MTP-networks that support in parts only maximum length of 272 octets and in other parts a maximum length of 4096 octets (or more) according to Recommendations Q.704 and Q.2210. + +>>>>>>>>----- + +*Replace the 2nd paragraph after the list items a) to c) with the following:* + +<<<<<<<<----- + +An implementation shall support the XUDT, XUDTS, LUDT, and LUDTS all-message types, parameters, and parameter values (see ITU-T Rec. Q.713) applicable to the connectionless protocol classes and capabilities of this Recommendation. But the network may allow lesser functionality according to the place of the network(s) in which the implementation is required to operate. + +UDT and UDTS messages are deprecated. In particular, a UDT message shall not be used to transmit user data in protocol class 0 when the destination lies within another signalling network. + +>>>>>>>>----- + +*Remove footnote 5 in the 3rd paragraph after the list items a) to c) and insert the note in the mainline text as follows:* + +<<<<<<<<----- + +The onnectionless procedures allow a user of the SCCP to request transfer of up to 2560-3952 octets5 of user data without first requesting establishment of a signalling connection. + +NOTE – The maximum number of octets depends on the length of the called and calling party addresses, and on whether or not segmentation may occur. + +>>>>>>>>----- + +*Replace the 5th paragraph after the list items a) to c) with the following:* + +<<<<<<<<----- + +Transfer of the user data is accomplished by including the user data in XUDT or LUDT or ~~UDT~~ messages. + +>>>>>>>>----- + +*Replace the last paragraph before 4.1/Q.714 with the following:* + +<<<<<<<<----- + +The SCCP relies on the services of the GST MTP for transfer of SCCP messages. Based on the characteristics of the GST MTP, the protocol class 1 service may be used in such a way that it provides a quality of service that has a lower probability of out-of-sequence messages than that provided by protocol class 0. + +>>>>>>>>----- + +*Replace the 2nd and 3rd paragraphs of 4.1/Q.714 with the following:* + +<<<<<<<<----- + +The user data is then transferred in XUDT or LUDT or ~~UDT~~ message(s), using SCCP and MTP routing functions and the appropriate GST-SAP instance, to the "Called address" indicated in the N-UNITDATA request primitive. If protocol class 1 is used, the sequence control parameter shall be included and contain the SLS value. + +The connectionless data transfer service is also used to transport SCCP management messages, which are transferred in the "data" field of XUDT or LUDT or ~~UDT~~ messages. If protocol class 1 is used, the sequence control parameter shall be included and contain the SLS value. + +>>>>>>>>----- + +*In 4.1/Q.714, replace the note and the two paragraphs after it with the following:* + +<<<<<<<<----- + +NOTE – The SCCP uses the services of the GST MTP and the GST MTP may, under severe network conditions, discard messages (see for example 2.3.5.1/Q.704). Therefore, the user of the SCCP may not always be informed of non-delivery of user data. + +The GST MTP notifies the SCCP of available, unavailable or congested remote signalling points or ~~remote SCCP unavailability~~ using the IN-SERVICE indication, the OUT-OF-SERVICE indication, and the CONGESTION indication. ~~MTP PAUSE indication or MTP STATUS indication~~ primitives. Layer management notifies the SCCP of remote SCCP User Part availability or unavailability. The SCCP then informs its users. + +When an ~~UDT~~ or XUDT or LUDT message is received at the destination node, an N-UNITDATA indication primitive is invoked, after possible reassembly of all segments, except for the SCCP management messages. The SCCP management (SCMG) messages are passed to the SCMG entity instead. + +>>>>>>>>----- + +*In 4.1.1.1.2/Q.714, replace the first two bullet items with the following 3 items:* + +<<<<<<<<----- + +- The SCCP shall place each segment of user data into separate XUDT messages, each with the same Called Party Address ~~and identical MTP routing information (DPC, SLS)~~. +- The Calling Party Address ~~and the OPC~~ in each XUDT message shall be coded identically, in the manner described in 2.1, SCCP Addressing. + +Every XUDT message shall be submitted to the same appropriate GST-SAP instance with the same value in the "Sequence Control" of the TRANSFER.request primitive. + +*In 4.1.1.2.1/Q.714, replace the first paragraph (introduction to bullet items) with the following:* + +Upon receipt of an LUDT or XUDT message with the F-bit set to one and the "remaining segment" field different from zero in the segmentation parameter, the destination SCCP shall initiate a new reassembly process, using the Calling Party Address, the GST-SAP instance through which the LUDT or XUDT was received, ~~MTP routing information~~ and the Segmentation Local Reference to uniquely identify the reassembly process. Initiating a reassembly process involves the following steps: + +*In 4.1.1.2.2/Q.714, replace the first bullet item with the following:* + +- The SCCP shall associate the received XUDT or LUDT message with a particular reassembly process, using the unique combination of the Calling Party Address, the GST-SAP instance through which the LUDT or XUDT was received, ~~MTP routing information,~~ and the Segmentation Local Reference field of the segmentation parameter. If no association is possible, the SCCP shall discard the message. + +**9.6 SCCP management procedures** + +*Replace clause 5/Q.714 with the following:* + +**5 SCCP management procedures** + +**5.1 General** + +The purpose of SCCP management is to provide procedures to maintain network performance by rerouting or throttling traffic in the event of failure in the network. + +Although SCCP management has its own subsystem number, the procedures in this clause do not apply to the SCCP management as an SCCP user. For the cases where the SCCP management's SSN is used to indicate the availability/unavailability of the SCCP, the applicable procedures are explicitly stated as applying to SSN = 1. ~~SSN = "1"~~ is assigned to SCCP management, whereas the remaining SSNs are assigned to SCCP users, except SSN = 0. The status of SSN = 1 is assumed to reflect the status of the entire SCCP at a node. + +SCCP management is organized into two sub-functions: signalling point status management and subsystem status management. Signalling point status management and subsystem status management allow SCCP management to use information concerning the accessibility of remote signalling points and subsystems, respectively, to permit the network to adjust to failure, and recovery. + +SCCP management procedures rely on: + +- 1) out-of-service, in-service, failure, recovery, and congestion information provided in the OUT-OF-SERVICE.indication, IN-SERVICE.indication, and CONGESTION.indication ~~MTP-PAUSE indication, MTP-RESUME indication and MTP-STATUS indication~~ primitives; ~~and~~ + +**ITU-T Rec. Q.2220 (12/2002)** 43 + +- 2) subsystem failure and recovery information, and SCCP (SSN = 1) congestion received in SCCP management messages; and +- 3) indications from layer management about remote SCCP User Part availability or unavailability. + +SCCP management information is currently defined to be transferred using the SCCP connectionless service with no return on error requested. The formats of these messages appear in ~~clause 8ITU-T Recommendation Q.713.~~ + +SCCP management maintains the status of remote SCCP nodes; and the status of remote or local subsystems. It cooperates with the SCCP routing control (including translation function) to stop traffic to inaccessible destinations and to provide rerouting of traffic through alternate routing or through selection of alternate remote subsystems. + +From the perspective of SCCP routing control, the remote SCCP nodes addressed by certain ranges of Global Titles can be operated in several modes; and the SCCP routing control (translation function) are supported by the signalling point status management procedures (see 5.2): + +- 1) *Solitary mode:* The destination subsystem or next translation node is chosen from the one single SCCP node. When that node or its SCCP fails, the SCCP management will notify the SCCP routing control; and the traffic towards the solitary nodes will be discarded or returned if return-option is set. In the case of connection-oriented procedures, the connection section will be refused or released. +- 2) *Replicated service in dominant mode:* The next translation node or destination subsystem can be chosen from two SCCP nodes. Traffic towards a specific subdomain (characterized by ranges of Global Titles) is normally sent to the SCCP of a "primary" node. When the "primary" node is inaccessible, the SCCP management will notify the routing control and this traffic is routed to the SCCP of a "backup" node. As soon as the "primary" node becomes accessible again, the traffic is again routed to it. +- 3) *Replicated service in dynamically loadshared mode:* The next translation node or destination subsystem is chosen from two SCCP nodes. The traffic is dynamically distributed to the next two nodes by the traffic-sending node. The next pair of SCCP nodes receiving the traffic will back-up each other. If one of the nodes becomes inaccessible, the SCCP management will notify the routing control and the traffic will be routed to the other one. As soon as the previously inaccessible node becomes accessible again, the traffic is dynamically distributed to those two nodes again. + +Remote SCCP-subsystems capable of providing the same application service for, as an example, the same subset of service subscribers can be grouped in "subsystem services". Several modes of operation for such a "subsystem service" can be distinguished and are supported by the subsystem status management procedures (see 5.3); when final translation results in "route on SSN". + +- 1) *Solitary subsystems:* When the solitary subsystem fails, the SCCP management will notify the SCCP routing control; and the traffic towards the solitary subsystem will be discarded or returned if the return-option is set. In the case of connection-oriented procedure, the connection section will be refused or released. +- 2) *Replicated subsystems in dominant mode:* the destination subsystem is chosen from two replicated subsystems. The traffic is normally sent to the "primary" subsystem. When the "primary" subsystem is inaccessible, the SCCP management will notify the routing control and this traffic is sent to the "backup" subsystem. As soon as the "primary" subsystem becomes accessible again, the traffic is again routed to it. +- 3) *Replicated subsystem in dynamically loadshared mode:* The destination subsystem is chosen from two replicated subsystems. The traffic is dynamically distributed to the two replicated subsystems. The replicated subsystems receiving the traffic will back up each other. If one of the subsystems becomes inaccessible, the SCCP management will notify the + +routing control and the traffic will be distributed to the other subsystem. As soon as the previously inaccessible subsystem becomes accessible again, the traffic is dynamically sent to those two subsystems again. + +In cases 2) and 3) above, sequences of messages that must go to the same replicated subsystem (e.g., all messages of a TCAP transaction after initial transaction set-up) should use an unambiguous address, so only the initial set-up message (e.g., TCAP:BEGIN) can use the modes 2 and 3. + +SCCP management procedures utilize the concept of a "concerned" subsystem or signalling point. In this context, a "concerned" entity means an entity with an immediate need to be informed of a particular signalling point/subsystem status change, independently of whether SCCP communication is in progress between the "concerned" entity and the affected entity with the status change8. + +NOTE – The definition of "concerned" subsystems or signalling points is network/architecture/application dependent. + +In some situations, the number of concerned subsystem or signalling points for a given subsystem may be zero. In this case, when the subsystem fails, or becomes unavailable, no broadcast of the subsystem prohibited message is performed. Similarly, no broadcast of the subsystem allowed message is performed for that given subsystem when it recovers. + +For nodes/subsystems that are not explicitly notified of status changes, i.e., they are not marked as "concerned", the SSA (subsystem-allowed)/SSP (subsystem-prohibited) messages directed to them is lost or no broadcast will take place after recovering from a ~~GST MTP~~ or SCCP failure, the response method is used. The response method ensures that an SSP (subsystem-prohibited) message is returned for a message to an unavailable subsystem, or an SSA (subsystem-allowed) message is returned as a result of the SST (subsystem-status-test) when the subsystem is available again. + +The signalling point prohibited, signalling point allowed and signalling point congested procedures, specified in 5.2.2, 5.2.3 and 5.2.4 respectively, deal with the accessibility of a signalling point. + +~~The local MTP network availability and unavailability procedures are described in 5.2.5 and 5.2.6, respectively.~~ + +The SCCP reports of SCCP and nodal congestion procedure is specified in 5.2.7 + +The inter- and intra-SCCP Management congestions reporting procedure is specified in 5.2.8. + +The subsystem prohibited and subsystem allowed procedures, detailed in 5.3.2 and 5.3.3 respectively, deal with the accessibility of a subsystem or the SCCP. + +An audit procedure to ensure that necessary subsystem management information is always available is specified in the subsystem status test procedure in 5.3.4. + +A subsystem may request to go out of service, using the coordinated state change control procedure specified in 5.3.5. + +Local subsystems are informed of any related subsystem status by the local broadcast procedure specified in 5.3.6. + +Concerned signalling points are informed of any related subsystem status by the broadcast procedure specified in 5.3.7. + +## **5.2 *Signalling point status management*** + +NOTE – The SCCP congestion control procedures may be subject to improvement pending further analysis of the impact of these procedures in different network scenarios and based on the results of operational experience. + +### 5.2.1 General + +Signalling point status management updates translation and status based on the information of signalling network out-of-service, in-service, failure, recovery, or congestion provided by the OUT-OF-SERVICE indication, IN-SERVICE indication, and CONGESTION indication ~~MTP-PAUSE indication, MTP-RESUME indication, or MTP-STATUS indication~~ primitives. This allows alternative routing to backup signalling points and/or backup subsystems. + +### 5.2.2 Signalling point prohibited + +When SCCP management receives an OUT-OF-SERVICE indication ~~MTP-PAUSE indication~~ primitive relating to a destination that becomes inaccessible, ~~or an MTP-STATUS indication primitive relating to an SCCP that becomes unavailable,~~ SCCP management performs the following actions. + +- 1) Informs the translation function to update the translation tables. +- 2) In the case where the SCCP has received an OUT-OF-SERVICE indication ~~MTP-PAUSE indication~~ primitive, SCCP management marks as "prohibited" the status of the remote signalling point, the remote SCCP and each subsystem at the remote signalling point. + +In the case where the SCCP has received an MTP-STATUS indication from layer management primitive relating to an unavailable SCCP, the SCCP marks the status of the SCCP and each SSN for the relevant destination to "prohibited" ~~and initiates a subsystem status test with SSN=1. If the cause in the MTP-STATUS indication primitive indicates "unequipped user", then no subsystem status test is initiated.~~ + +- ~~3) Discontinues all subsystem status tests (including SSN=1) if an MTP-PAUSE or MTP-STATUS indication primitive is received with a cause of "unequipped SCCP". The SCCP discontinues all subsystem status tests, except for SSN=1, if an MTP-STATUS indication primitive is received with a cause of either "unknown" or "inaccessible".~~ +- 4) Initiates a local broadcast (see 5.3.6.2) of "User-out-of-service" information for each subsystem at that destination. +- 5) Initiates a local broadcast (see 5.3.6.4) of "signalling point inaccessible" information for that destination if an ~~MTP-PAUSE~~ OUT-OF-SERVICE indication primitive is received. +- 6) Initiates a local broadcast of "remote SCCP unavailable", if either an ~~MTP-PAUSE~~ OUT-OF-SERVICE indication primitive or an MTP-STATUS indication from layer management about the SCCP User Part unavailability primitive is received. + +### 5.2.3 Signalling point allowed + +When SCCP management receives an IN-SERVICE indication ~~MTP-RESUME indication~~ primitive relating to a destination that becomes accessible, or when it receives a subsystem allowed message relating to SSN = 1 at a remote destination which had been considered "prohibited", or when timer T(stat info) expires, SCCP management performs the following actions: + +- 1) Sets the congestion state of that signalling point if an IN-SERVICE indication ~~MTP-RESUME indication~~ primitive is received. +- 2) Instructs the translation function to update the translation tables. +- 3) Marks as "allowed" the status of that destination, and the SCCP, if an IN-SERVICE indication ~~MTP-RESUME indication~~ primitive is received. +- 4) Marks as "allowed" the status of the SCCP if a subsystem allowed message is received for SSN = 1, or if timer T(stat info) expires, or if an indication is received from layer management that the peer SCCP User Part is available again. ~~The subsystem status test for SSN=1, if running, is stopped.~~ + +- 5) Marks as "allowed" the status of remote subsystems. As a national network provider option, the subsystem status can be marked as "prohibited" for a list of selected subsystems. For such subsystems, the subsystem status test procedure is initiated9. + +NOTE – This may under certain circumstances be used to solve the problem of message loss when switching back from a backup to a primary node (in case of replicated subsystems in dominant mode), where the status of the subsystem in the primary node is still unknown. + +- 6) Initiates a local broadcast (see 5.3.6.5) of "signalling point accessible" information for that destination if an IN-SERVICE.indication ~~MTP-RESUME indication~~ primitive is received. +- 7) Initiates a local broadcast of "remote SCCP accessible" if either an IN-SERVICE.indication ~~MTP-RESUME indication~~ primitive or a subsystem status allowed message is received for SSN = 1 or if timer T(stat info) expires, or if an indication is received from layer management that the peer SCCP User Part is available again. +- 8) Initiates a local broadcast of "User-in-service" information for a subsystem associated with the IN-SERVICE.indication ~~MTP-RESUME indication~~ primitive. + +### 5.2.4 *Signalling point congested* + +When SCCP management receives a CONGESTION.indication or an IN-SERVICE.indication ~~MTP-STATUS indication~~ primitive relating to signalling network congestion to a signalling point, SCCP management: + +- 1) Determines the severity of the congestion in the remote signalling point and updates that signalling point status to reflect the congestion as follows: +- ~~The GST MTP~~ provides a ~~single congestion level (CL)~~ ~~congestion indication (international method)~~10. + +The severity is reflected by a local internal status variable referred to as "restriction level" $RL_M$ . Each of the $N + 1$ restriction levels except the highest level is further divided into $M$ "restriction sublevels", $RSL_M$ , where: + +$N = 8$ + +$M = 4$ + +The method to compute these levels is as follows: + +CL is divided by N; + +$RL_M$ is set to the quotient of the division above; and + +$RSL_M$ is set to the remainder of the division above. + +NOTE – In the STCs, the value of congestion level "no congestion" ( $CL_{nc}$ ) must be set to "0", the value of congestion level "maximum congestion" ( $CL_{mc}$ ) must be set to " $N imes M$ ", and the value "step" for Congestion Levels ( $CL_{st}$ ) must be set to "1". + +~~The method to compute these levels uses an attack timer $T_a$ and a decay timer $T_d$ .~~ + +~~a) When timer $T_a$ is not running, then:~~ + +~~Timer $T_a$ is started and $T_d$ is (re)started.~~ + +~~if $RL_M$ is equal to N, then no further action is taken.~~ + +~~$RSL_M$ is incremented.~~ + +~~If $RSL_M$ reaches M, then $RSL_M$ is set to zero and $RL_M$ is incremented.~~ + +~~b) When timer $T_a$ is running, the MTP STATUS indication primitive is ignored.~~ + +- 2) Initiates the procedures of 5.2.8. + +When congestion abates, the traffic is gradually resumed. SCCP management: + +- 1) Decreases the restriction level ( $RL_M$ ) in a time controlled manner as follows: + +When timer $T_d$ expires, then $RSL_M$ is decremented and: + +- a) if $RSL_M$ reaches 1 and $RL_M$ is not zero, then $RSL_M$ is reset to $M-1$ and $RL_M$ is decreased by one; +- b) if either $RSL_M$ or $RL_M$ is not zero, then timer $T_d$ is restarted again. + +- 2) Initiates the procedure of 5.2.8. + +When an indication of the end of MTP RESTART is received, the associated $RL_M$ and $RSL_M$ are set to zero. + +The values of $M$ , $N$ , $T_d$ and $T_a$ parameters are administrable and provisional. + +### ***5.2.5 Local MTP network availability*** + +The SCCP will receive an indication of the end of MTP restart from each restarting local MTP SAP instance (there may be one or more MTP SAP instances in a given node). This indication is implementation dependent, see 9.2/Q.704. + +The occurrence of the end of MTP restart for a given local MTP SAP instance means that the local MTP network corresponding to that MTP SAP instance has become available to its local users, including SCCP. When SCCP management receives an indication reporting the end of a MTP Restart, then it: + +- 1) resets the congestion level of the associated signalling points; +- 2) instructs the translation function to update the translation tables, taking into account the accessibility given by the MTP indicating the end of MTP Restart; +- 3) marks as allowed the status of the SCCP and all subsystems for each accessible signalling point; +- 4) initiates a local broadcast (see 5.3.6) of "signalling point accessible" information for the signalling points becoming accessible; +- 5) initiates a local broadcast of "remote SCCP accessible" for the remote SCCPs becoming accessible; and +- 6) initiates a local broadcast of "User in service" (see 5.3.6.3) information for a subsystem associated with the end of the MTP RESTART. + +### ***5.2.6 Local MTP network unavailability*** + +Prior to the end of MTP restart for a given local MTP SAP instance, the local MTP network corresponding to that MTP SAP instance is unavailable to its local users, including SCCP. Any action taken is implementation dependent. + +### ***5.2.7 SCCP reports of SCCP and nodal congestion*** + +This subclause describes procedures related to congestion conditions that are experienced by the SCCP or node and reported by the SCCP. The SCCP notifies the originating/relay nodes sending/relaying traffic towards a congested node of the congestion. A time-controlled procedure is run at the originating/relaying node using two a-status variables, $CL_{sCL}$ and $CL_{CO}$ , which indicates the level of congestion for the connectionless and connection-oriented services at the remote node. + +If the congestion is due to a general congestion state of the node, the application of this procedure should be synchronized with equivalent measures of other affected GSTMTP-Users (e.g., BICCISUP, B-ISUP). Any procedure to synchronize or coordinate these equivalent measures is outside the scope of this Recommendation. + +#### 5.2.7.1 Actions in the congested SCCP node + +When a message arrives at a congested SCCP node, SCCP Routing Control informs SCCP management (see 2.3.1). SCMG shall return an SSC (SCCP/Subsystem-Congested) message (SSC) to the signalling point identified by the OPC in the ~~GST-SAP instance MTP routing label of the MTP-TRANSFER indication primitive and the MTP-SAP from which the message is received.~~ The *SCCP/Subsystem-Congested* message shall indicate the SPC of this congested SCCP node in the "affected PC" parameter, SSN of the SCMG ("1") in the "affected SSN" parameter, and a value in the "congestion level" parameter to indicate the severity of the congestion. Optionally, the affected SCCP service field may indicate whether the connectionless or connection-oriented service is affected or both. Any reaction towards a local originator is implementation dependent. The detection of SCCP or nodal congestion is implementation dependent. + +After reception of the first message by the congested SCCP node, the SSC (SCCP/subsystem-congested) message will be repeated only on the reception of every P-th message regardless of the OPC. + +P is provisionally set to 8. + +#### 5.2.7.2 Action in a relay or originating node + +When a *SCCP/Subsystem-Congested* message is received from the congested SCCP, and the affected signalling point has been marked as "prohibited", no further action is taken. When a *SCCP/Subsystem-Congested* message is received from the congested SCCP, and the affected point code has not been marked as "prohibited", SCCP management shall compare the values of CLsCL and/or CLCO associated with the congested SCCP node with the value in the congestion level parameter indicated in the *SCCP/Subsystem-Congested* message, depending on the affected SCCP service indicated. If the CLsCL and/or CLCO has been marked with a higher congestion level, the value shall remain unchanged, or else the CLsCL and/or CLCO shall be updated with the value of the congestion level parameter of the received *SCCP/Subsystem-Congested*. If the CLsCL has been marked with a higher or same level, the timer for connectionless TconCL shall be restarted. If the CLCO has been marked with a higher or same level, the timer for connection-oriented TconCO shall be restarted. + +If the TconCL timer expires and the CLsCL has not yet reached zero, the CLsCL shall be decremented by one and timer TconCL shall be restarted. If the CLsCL is reduced to zero, the timer TconCL is stopped. + +If the TconCO timer expires and the CLCO has not yet reached zero, the CLCO shall be decremented by one and timer TconCO shall be restarted. If the CLCO is reduced to zero, the timer TconCO is stopped. + +Whenever a remote SCCP is marked as accessible (IN-SERVICE indication, MTP-RESUME, SSA (subsystem-allowed) message, indication from layer management that the peer SCCP is available of the end of MTP-restart received), the congestion levels CLsCL and CLCO stored by SCCP may be changed (network dependent). + +The SCMG shall initiate the procedure of 5.2.8 when the values of CLsCL or CLCO changes. + +The congestion levels CLsCL and CLCO are within the range 0 through 8, with 0 indicating that no congestion is present. + +### 5.2.8 *Inter- and intra-SCMG congestion reports procedure* + +This SCMG procedure uses the values of the following internal status variables: + +- 1) $RL_M$ , restriction level due to receipt of the IN-SERVICE.indication, or CONGESTION.indication primitive MTP-STATUS indication of congestion for each affected SP (see 5.2.4). +- 2) $RSL_M$ , restriction sublevel per $RL_M$ due to receipt of the IN-SERVICE.indication, or CONGESTION.indication primitive MTP-STATUS indication of congestion for each affected SP (see 5.2.4). +- 3) $CL_{SCL}$ and $CL_{CO}$ , SCCP congestion levels due to receipt of the congestion level parameter of an SSC (SCCP/subsystem-congested) message for each affected SP and $SSN = 1$ (see 5.2.7). + +The above values are used as inputs to compute the values of the following variables: + +- a) $RL_{CL}$ and $RL_{CO}$ , SCRC traffic restriction levels for each affected SP. +- b) $RSL_{CL}$ and $RSL_{CO}$ , restriction sublevels per $RL$ for each affected SP. +- c) $RIL$ , restricted importance level parameter reported to SCCP users for each affected SP. As an implementation option, SCCP users subscribed to the connectionless service can be informed of a $RIL$ related to $RL_{CL}$ . The same applies for SCCP connection-oriented users and $RL_{CO}$ . + +If there is any change in $RL_{CL}$ , $RL_{CO}$ , $RSL_{CL}$ or $RSL_{CO}$ , SCRC is informed of the new values ~~of $RL$ and $RSL$~~ . + +If there is any change in restricted importance level, the local broadcast procedure (see 5.3.6.6) is initiated to report the new value of restricted importance level. + +NOTE – The computation is left for further study. + +## 5.3 *Subsystem status management* + +NOTE – The SCCP congestion control procedures may be subject to improvement pending further analysis of the impact of these procedures in different network scenarios and based on the results of operational experience. + +### 5.3.1 *General* + +Subsystem status management updates the subsystem status based on the information of failure, withdrawal, and recovery of subsystems. This allows alternative routing to backup subsystems, if appropriate. Concerned local users are informed of the status changes of other backup subsystems. Subsystem status management procedures are also used to convey the status of the SCCP as a whole. + +### 5.3.2 *Subsystem prohibited* + +A subsystem prohibited message with $SSN = 1$ is not allowed. + +#### 5.3.2.1 *Receipt of messages for a prohibited subsystem (response method)* + +If SCCP routing control receives a message, whether originated locally or not, for a prohibited local system, then SCCP routing control invokes subsystem prohibited control. A *Subsystem-Prohibited* message is sent to the signalling point identified by the OPC in the ~~MTP-TRANSFER indication primitive, and the GSTMTP-SAP~~ instance if the originating subsystem is not local. If the originating subsystem is local, any action taken is implementation dependent. When many indications "message for a prohibited subsystem" are received, the number of SSP (*subsystem-prohibited*) messages sent out per time-interval may be reduced by implementation-dependent mechanisms. + +#### 5.3.2.2 Receipt of Subsystem-Prohibited message or N-STATE request primitive or local user failed + +Under one of the following conditions: + +- a) SCCP management receives an SSP (*Subsystem-Prohibited*) message about a subsystem marked allowed; or +- b) an N-STATE request primitive with "User-out-of-service" information is invoked by a subsystem marked allowed; or +- c) SCCP management detects that a local subsystem has failed, + +then SCCP management does the following: + +- 1) instructs the translation function to update the translation tables; +- 2) marks as "prohibited" the status of that subsystem; +- 3) initiates a local broadcast (see 5.3.6.2) of "User-out-of-service" information for the prohibited subsystem; +- 4) initiates the subsystem status test procedure (see 5.3.4) if the prohibited subsystem is not local; +- 5) initiates a broadcast (see 5.3.7) of SSP (*Subsystem-Prohibited*) messages to concerned signalling points; +- 6) cancels "ignore subsystem status test" and the associated timer if they are in progress and if the newly prohibited subsystem resides at the local node. + +### 5.3.3 Subsystem allowed + +Under one of the following conditions: + +- a) SCCP management receives an SSA (*Subsystem-Allowed*) message about a subsystem other than SSN = 1, marked prohibited; or +- b) an N-STATE request primitive with "User-in-Service" information is invoked by a subsystem marked prohibited, + +then SCCP management does the following: + +- 1) instructs the translation function to update the translation tables; +- 2) marks as "allowed" the status of that subsystem; +- 3) initiates as a local broadcast (see 5.3.6) of "User-in-service" information for the allowed subsystem; +- 4) discontinues the subsystem status test relating to that subsystem if such a test was in progress; +- 5) initiates a broadcast (see 5.3.7) of SSA (*Subsystem-Allowed*) messages to concerned signalling points. + +If the remote SCCP, at which the subsystem reported in the SSA (*Subsystem-Allowed*) message resides, is marked inaccessible, then the message is treated as an implicit indication of SCCP restart, and the procedures in 5.2.3 are executed. + +### 5.3.4 Subsystem status test + +#### 5.3.4.1 General + +The subsystem status test procedure is an audit procedure to verify the status of a SCCP or subsystem marked as prohibited. + +#### 5.3.4.2 Actions at the initiating node + +- a) A subsystem status test is initiated when an SSP (*Subsystem-Prohibited*) message is received (see 5.3.2.2). For a list of selected subsystems, the subsystems status test may also be initiated on receipt of an IN-SERVICE indication MTP\_RESUME indication primitive, a subsystem allowed message with SSN = 1 or the time-out of timer T(stat\_info), or if an indication is received from layer management that the peer SCCP User Part is available again (see also 5.2.3 list item 5). + +A subsystem status test associated with a prohibited subsystem is commenced by starting a timer T(stat\_info) and marking a test in progress. No further actions are taken until the timer expires. + +Upon expiration of the timer, an SST (*Subsystem-Status-Test*) message is sent to SCCP management at the node of the prohibited subsystem and the timer is reset. + +The cycle continues until the test is terminated by another SCCP management function at that node. Termination of the test causes the timer and the "test progress mark" to be cancelled. + +- b) A subsystem status test for SSN = 1 is initiated by layer management as necessary when an MTP-STATUS indication primitive is received with "remote user inaccessibility" or "unknown" information for the SCCP at a remote signalling point. + +~~After sending an SST(SSN = 1), the node should receive either an SSA(SSN = 1) from the restarting node or it should receive an MTP-STATUS indication primitive stating User Part Unavailable. In the case where the SST receiving node has the User Part availability control and its SCCP has not yet recovered, MTP sends a User Part Unavailable (UPU) message to the SST sending node. If neither a SSA(SSN = 1) nor a MTP-STATUS indication primitive (User Part Unavailable) is received by the SST sending SCCP during the duration of the T(stat\_info) timer, then the node should assume that the previously unavailable SCCP has recovered. (This ensures backward compatibility with previous versions of this Recommendation.) If the MTP-STATUS indication primitive stating User Part Unavailable is received before timer T(stat\_info) expires, then an SST(SSN = 1) is sent to the unavailable node when timer T(stat\_info) expires. A subsystem status test associated with an inaccessible SCCP is done in the same way as for the one associated with a prohibited subsystem, the only difference being that it refers to SSN = 1.~~ + +#### 5.3.4.3 Actions at the receiving node + +When SCCP management receives an SST (*Subsystem-Status-Test*) message and there is no "ignore subsystem status test" in progress, it checks the status of the named subsystem. If the subsystem is allowed, then an SSA (*Subsystem-Allowed*) message is sent to the SCCP management at the node conducting the test. If the subsystem is prohibited, no reply is sent. + +In the case where the SST (*Subsystem-Status-Test*) message is testing the status of SCCP management (SSN = 1), if the SCCP at the destination node is functioning, then an SSA (*Subsystem-Allowed*) message with SSN = 1 is sent to SCCP management at the node conducting the test. If the SCCP is not functioning, then the GST MTP cannot deliver the SST (*Subsystem-Status-Test*) message to the SCCP. A UPU message is returned to the SST initiating node by the MTP. + +As soon as its SCCP has recovered, the restarting SCCP should broadcast an SSA (*Subsystem-Allowed*) message for SSN = 1 to all concerned nodes. The restarting SCCP should set the status to "allowed" for the SCCP and all subsystems of remote signalling points that it considers available, based on the GST-SAP instance MTP information at the node. + +### 5.3.5 Coordinated state change + +#### 5.3.5.1 General + +A duplicated subsystem may be withdrawn from service without degrading the performance of the network by using the coordinated state change procedure described below when its backup is not local. The procedure, in the case that the primary and the backup subsystems are co-located, is implementation dependent. + +#### 5.3.5.2 Actions at the requesting node + +When a duplicated subsystem wishes to go out of service, it invokes a N-COORD request primitive. SCCP management at that node sends a SOR (*Subsystem-Out-of-Service-Request*) message to the backup system, sets a timer T(coord.chg) and marks the subsystem as "waiting for grant". + +Arrival of a SOG (*Subsystem-Out-of-Service-Grant*) message at the requesting SCCP management causes the timer T(coord.chg) to be cancelled, the "waiting for grant" state to be cancelled, and a N-COORD confirm primitive to be invoked to the requesting subsystem. SSP (*Subsystem-Prohibited*) messages are broadcast (see 5.3.7) to concerned signalling points. + +In addition, an "ignore subsystem status test" timer is started and the requesting subsystem is marked as "ignore subsystem status test". Subsystem status tests are ignored until the "ignore subsystem status test" timer expires or the marked subsystem invokes a N-STATE request primitive with "User-out-of-service" information. + +If no "waiting for grant" is associated with the subsystem named in the SOG (*Subsystem-Out-of-Service-Grant*) message, then the SOG (*Subsystem-Out-of-Service-Grant*) message is discarded and no further action is taken. + +If the timer associated with the subsystem waiting for the grant expires before a SOG (*Subsystem-Out-of-Service-Grant*) message is received, then the "waiting for grant" is cancelled and the request is implicitly denied. + +#### 5.3.5.3 Actions at the requested node + +When the SCCP management at the node at which the backup subsystem is located receives the SOR (*Subsystem-Out-of-Service-Request*) message, it checks the status of local resources44. If the SCCP has sufficient resources to assume the increased load, then it invokes a N-COORD indication primitive to the backup subsystem. If the SCCP does not have sufficient resources, no further action is taken. + +If the backup system has sufficient resources to allow its duplicate to go out of service, then it informs SCCP management by invoking a N-COORD response primitive. A SOG (*Subsystem-Out-of-Service-Grant*) message is sent to SCCP management at the requesting node. If the backup subsystem does not have sufficient resources, no reply is returned44. + +NOTE – Local resources critical to this particular node are implementation dependent. + +### 5.3.6 Local broadcast + +#### 5.3.6.1 General + +The local broadcast procedure provides a mechanism to inform local allowed concerned subsystems of any related SCCP/subsystem/signalling point status information received. + +#### 5.3.6.2 User-out-of-service + +A local broadcast of "User-out-of-service" information is initiated when: + +- a) an SSP (Subsystem-Prohibited) message is received about a subsystem marked allowed (see 5.3.2.2); +- b) an N-STATE request primitive with "User-out-of-service" information is invoked by a subsystem marked allowed (see 5.3.2.2)42 (see Note); +- c) a local subsystem failure is detected by SCCP management (see 5.3.2.2)42 (see Note); +- d) an ~~OUT-OF-SERVICE.indication MTP-PAUSE indication~~ primitive is received (see 5.2.2); or +- e) an ~~MTP-STATUS indication from layer management that the peer SCCP User Part is unavailable primitive with cause "inaccessible" is received~~ (see 5.2.2). + +NOTE – These cases are applicable when the SCCP is used for routing between local subsystems. This function is implementation dependent. + +SCCP management then informs local allowed concerned SCCP subsystems about the subsystem status by invoking N-STATE indication primitive with "User-out-of-service" information. + +#### 5.3.6.3 User-in-service + +A local broadcast of "subsystem-in-service" information is initiated when: + +- a) an SSA (Subsystem-Allowed) message is received about a subsystem marked prohibited (see 5.3.3); +- b) an N-STATE request primitive where "User-in-service" information is invoked by a subsystem marked prohibited (see 5.3.3); +- c) an ~~IN-SERVICE.indication MTP-RESUME indication~~ primitive is received (see 5.2.3, SCMG action 8)); +- d) an SSA (Subsystem-Allowed) message is received with SSN = 1; about a remote SCCP marked prohibited (see 5.2.3, SCMG action 4)); +- e) timer T(stat info) expires, or; (see 5.2.3, SCMG action 4)); +- f) an indication ~~from layer management that the peer SCCP User Part is available of the end of MTP-Restart is received~~ (see 5.2.5, SCMG action 6)). + +SCCP management then informs local allowed concerned SCCP subsystems, except the newly allowed one in case d) above, about the subsystem status by invoking an N-STATE indication primitive with "User-in-service" information. + +#### 5.3.6.4 Signalling point inaccessible + +A local broadcast of "signalling point inaccessible" or "remote SCCP inaccessible" information is initiated when an OUT-OF-SERVICE indication MTP-PAUSE primitive or an indication from layer management that the peer SCCP User Part is unavailable MTP-STATUS primitive (with "user part unavailable" information for a SCCP) is received. SCCP management then informs local allowed concerned SCCP subsystems about the signalling point status by invoking an N-PCSTATE indication primitive with "signalling point inaccessible" or "remote SCCP inaccessible" information. + +#### 5.3.6.5 Signalling point or remote SCCP accessible + +A local broadcast of "signalling point accessible" or "remote SCCP accessible" information is initiated when an IN-SERVICE indication MTP-RESUME primitive, an SSA (Subsystem-Allowed) message (with SSN = 1) message or an indication of the end of the MTP restart is received or when timer T(stat info) expires or an indication from layer management that the peer SCCP User Part is available. SCCP management then informs local allowed concerned SCCP subsystems about the signalling point status by invoking an N-PCSTATE indication primitive with "signalling point accessible" or "SCCP accessible information". + +#### 5.3.6.6 Restricted importance level reporting + +A local broadcast of "signalling point congested" information is initiated when there is any change in the "restricted importance level" (see 5.2.8). SCCP management then informs local allowed concerned SCCP subsystems about the signalling point status by invoking an N-PCSTATE indication primitive with "restricted importance level" and the new value of the restricted importance level. + +### 5.3.7 Broadcast + +#### 5.3.7.1 General + +The broadcast procedure provides a mechanism that may be used to inform concerned signalling points of any related SCCP/subsystem status change at local or adjacent signalling points. It is a procedure supplementary to that defined in 5.3.2.1. + +The procedure to inform nodes that are not "concerned" of status change is described in 5.3.2.1 and 5.3.4. + +#### 5.3.7.2 Subsystem prohibited + +A broadcast of SSP (Subsystem-Prohibited) messages is initiated when: + +- a) an SSP (Subsystem-Prohibited) message is received about a subsystem presently marked allowed (see 5.3.2.2), and the affected point code identified in the SSP (Subsystem-Prohibited) message is the same as that of the informer signalling point; +- b) an N-STATE request primitive where "User-out-of-service" information is invoked by a subsystem marked allowed (see 5.3.2.2); or +- c) a local subsystem failure is detected by SCCP management (see 5.3.2.2). + +This broadcast permits SCCP management to inform all concerned signalling points, except the informer signalling point, about the subsystem status by SSP (Subsystem-Prohibited) messages. SCCP management does not broadcast if the point code of the prohibited subsystem is different from that of the informer signalling point which originates the SSP (Subsystem-Prohibited) message. + +#### 5.3.7.3 Subsystem allowed + +A broadcast of SSA (Subsystem-Allowed) messages is initiated when: + +- a) an SSA (Subsystem-Allowed) message is received about a subsystem presently marked prohibited and not equal to one (SCMG) (see 5.3.3), and the affected point code identified in the SSA (Subsystem-Allowed) message is the same as that of the informer signalling point; or +- b) an N-STATE request primitive where "User-in-service" information is invoked by a subsystem marked prohibited (see 5.3.3). + +At the end of the SCCP restarting process, the restarting SCCP should broadcast an SSA (Subsystem-Allowed) message for SSN = 1 to all concerned nodes. The restarting SCCP should set the status to "allowed" for the SCCP and all subsystems of the remote signalling points that it considers available based on MTP layer management information at the node. + +Broadcast of SSA (Subsystem-Allowed) messages permits SCCP management to inform all concerned signalling points, except the informer signalling point, about the subsystem status. SCCP management does not broadcast if the point code of the allowed subsystem is different from that of the informer signalling point which originates the SSA (Subsystem-Allowed) message. + +## 5.4 Local SCCP restart + +On a signalling point where SCCP restarts, an indication is given to the SCCP by layer management ~~the MTP~~ about the signalling points, which are accessible during the SCCP restart actions. The response method is used to determine the status of the SCCP and the SCCP subsystems in those signalling points, in the absence of subsystem prohibited messages. + +At the end of the SCCP restart, the status of its own subsystems is not broadcast to concerned signalling points. In this case, the response method is used to inform other nodes attempting to access prohibited subsystems at the restarted signalling points. + +At the completion of SCCP restart, the following actions shall have been taken: + +- 1) SCOC Restart (see 3.8). +- 2) Freezing the Segmentation Local Reference of the segmentation process in SCLC. +- 3) Releasing all the resources, if any used for the reassembly process in SCLC. +- 4) Local broadcast (see 5.3.6.4) of "signalling point accessible" status about the accessible signalling points. +- 5) Local broadcast of "remote SCCP accessible" status about the accessible remote SCCP. +- 6) Reset of the availability statuses related to its local sub-systems as appropriate based on implementation-dependent reporting procedures. +- 7) Updating the translation tables taking into account of the accessibility of remote signalling points reported by the ATP layer management. +- 8) Marking as "allowed" the status of the SCCP and sub-systems at remote signalling points that are reported to be available. +- 9) Computing the traffic restriction parameters $RL_M$ and $RSL_M$ associated with remote signalling points that are reported to be available. +- 10) Broadcast of SSA messages for SSN = 1 for concerned signalling points. The local SCMG shall not broadcast the statuses of its local sub-systems. +- 11) Informing the local allowed concerned sub-systems of the sub-system now available. + +On completion of the above procedures, the SCCP should be considered fully operational. + +## 9.7 Annex C – State Transition Diagrams (STD) for the signalling connection control part of Signalling Systems No. 7 + +Annex C does not apply. + +NOTE – This annex may still be consulted; however, the terminology should be adapted to the Generic Signalling Transport Service being used by this Recommendation. This concerns the names of the primitives being used, the non-visibility of OPC, DPC, etc. In addition, the ISUP embedded procedures are not supported. + +## 9.8 Annex D – State Transition Diagrams (STD) for SCCP management control + +Annex D does not apply. + +NOTE –This annex may still be consulted; however, the terminology should be adapted to the Generic Signalling Transport Service being used by this Recommendation. This concerns the names of the primitives being used, the non-visibility of OPC, DPC, etc. + +# 10 Exceptions to ITU-T Rec. Q.715 + +ITU-T Rec. Q.715 does not apply. + +# Appendix I + +## Aspects of the fully meshed Signalling Transport Network + +## I.1 GST supported by the Signalling Transport Converter on MTP and MTP3b + +#### 1) *MTP3* + +The fully meshed signalling transport network is realized by the relay functionality of the MTP3 layer. The assured data transport is assured by the link-by-link MTP2 connection. + +#### 2) *MTP3b* + +The fully meshed signalling transport network is realized by the relay functionality of the MTP3b layer. The assured data transport is assured by the link-by-link SSCOP connection (MTP3b). + +### I.2 GST supported by the Signalling Transport Converter on SSCOP and SSCOPMCE + +#### 1) *SSCOP* + +The fully meshed signalling transport network is realized by $n \times n$ SSCOP connections. The assured data transport is assured by these end-to-end SSCOP connections. + +These connections use the relay functionality of the underlying ATM transport network. + +#### 2) *SSCOPMCE* + +The fully meshed signalling transport network is realized by $n \times n$ SSCOPMCE connections. The assured data transport is assured by these end-to-end SSCOPMCE connections. + +These connections use the relay functionality of: + +- a) the underlying ATM transport network; +- b) the underlying connectionless network. + +## I.3 GST supported by the Signalling Transport Converter on SCTP + +The fully meshed signalling transport network is realized by $n \times n$ SCTP connections. The assured data transport is assured by these end-to-end SCTP connections. + +These connections use the relay functionality of the underlying connectionless IP network. + +# Appendix II + +## Differences between the SCCP and TI-SCCP operating over ITU-T Rec. Q.2150.1 + +Observing that: + +- a) When transmitting a message, the definitions in TI-SCCP require the TI-SCCP entity to pass a message to be transmitted with a TRANSFER.request primitive (see 6.7) via a particular GST-SAP to a Signalling Transport Converter (STC) instance. The STC for MTP3 or MTP3b is configured with the OPC, DPC, SI, and NI to enable completion of the MTP3 type PDUs. In SCCP, the OPC, DPC, SI, and NI values are selected properly and passed to MTP3 via an MTP-TRANSFER.request primitive. +- b) When receiving a message, the MTP3 selects a Signalling Transport Converter based on the OPC, DPC, SI, and NI values. The STC then passes the message with a TRANSFER.indication primitive via a particular GST-SAP to the TI-SCCP. This SAP identifies to the TI-SCCP the signalling relation to the TI-SCCP and, thus, identifies also the origin of the message. In SCCP, MTP3 passes the message with an MTP-TRANSFER.indication primitive to the SCCP entity. + +In both cases, this amounts to the same operation where the particulars are not visible from outside the system, i.e., the operation of TI-SCCP and SCCP when transferring messages are identical. + +On the management side, PAUSE.indication and RESUME.indication of SCCP are replaced by OUT-OF-SERVICE.indication and IN-SERVICE.indication in TI-SCCP. In TI-SCCP, congestion increase and decrease computations are performed in the STC where in SCCP this calculation takes place in the SCCP. Again, such a difference is not visible from outside the system, i.e., the operation of TI-SCCP and SCCP considering the status indications of the signalling relation are the same. + +Considering the management of neighbouring SCCPs, the only detail needing attention is the User Part Unavailable (UPU) messages that, when received by the STC are discarded, layer management is informed about this. SCCPs receive this message and react by starting a subsystem test (SST). In TI-SCCP, such an SST can be initiated by system management (see 9.6, the exceptions to 5.3.4.2/Recommendation Q.714). Such differences are again not visible from outside the system. + +In conclusion, the operation of SCCP over MTP3 or MTP3b are identical to the operations of TI-SCCP and the Signalling Transport Converter on MTP3 and MTP3b. + +The only difference remaining is the specification that the "sequence control parameter" needs to be included in XUDT and LUDT TI-SCCP messages. + + + +## SERIES OF ITU-T RECOMMENDATIONS + +| | | +|-----------------|--------------------------------------------------------------------------------------------------------------------------------| +| Series A | Organization of the work of ITU-T | +| Series B | Means of expression: definitions, symbols, classification | +| Series C | General telecommunication statistics | +| Series D | General tariff principles | +| Series E | Overall network operation, telephone service, service operation and human factors | +| Series F | Non-telephone telecommunication services | +| Series G | Transmission systems and media, digital systems and networks | +| Series H | Audiovisual and multimedia systems | +| Series I | Integrated services digital network | +| Series J | Cable networks and transmission of television, sound programme and other multimedia signals | +| Series K | Protection against interference | +| Series L | Construction, installation and protection of cables and other elements of outside plant | +| Series M | TMN and network maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits | +| Series N | Maintenance: international sound programme and television transmission circuits | +| Series O | Specifications of measuring equipment | +| Series P | Telephone transmission quality, telephone installations, local line networks | +| Series Q | Switching and signalling | +| Series R | Telegraph transmission | +| Series S | Telegraph services terminal equipment | +| Series T | Terminals for telematic services | +| Series U | Telegraph switching | +| Series 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SUBSCRIBER SIGNALLING +SYSTEM No. 2 (DSS 2) – +ADDITIONAL TRAFFIC PARAMETERS** + +**ITU-T Recommendation Q.2961** + +(Previously "CCITT Recommendation") + +--- + +# FOREWORD + +The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. + +The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). + +ITU-T Recommendation Q.2961 was prepared by ITU-T Study Group 11 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 17th of October 1995. + +--- + +# NOTE + +In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +# CONTENTS + +| | Page | +|---------------------------------------------------------------------------------------------------------------------------------------------------|-------------| +| General information..... | 1 | +| PART 1 – ADDITIONAL SIGNALLING CAPABILITIES TO SUPPORT TRAFFIC PARAMETERS FOR THE TAGGING OPTION AND THE SUSTAINABLE CELL RATE PARAMETER SET .... | 1 | +| 1.1 Scope ..... | 1 | +| 1.2 References..... | 2 | +| 1.3 Definitions ..... | 2 | +| 1.4 Abbreviations..... | 3 | +| 1.5 Description..... | 3 | +| 1.6 Operational requirements..... | 3 | +| 1.7 Primitive and state definitions ..... | 3 | +| 1.8 Coding requirements..... | 3 | +| 1.9 Signalling procedures at the coincident $S_B$ and $T_B$ reference point ..... | 4 | +| 1.10 Signalling procedures at the $T_B$ reference point for interworking with private B-ISDNs ..... | 7 | +| 1.11 Interworking with other networks ..... | 7 | +| 1.12 Interactions with supplementary services ..... | 7 | +| 1.13 Parameter values ..... | 7 | +| 1.14 Dynamic description (SDLs) ..... | 7 | +| Appendix I – Additional definitions..... | 8 | +| I.1 Usage Parameter Control (UPC)..... | 8 | +| I.2 Interpretation of sustainable cell rate and maximum burst size ..... | 8 | +| Appendix II – Generic Cell Rate Algorithm (GCRA)..... | 8 | +| Appendix III – Relation between maximum burst size and intrinsic burst tolerance in conjunction with peak cell rate..... | 10 | +| III.1 Sustainable Cell Rate ..... | 10 | +| Appendix IV – ATM layer traffic handling capabilities and network specific codepoint..... | 12 | +| IV.1 ATM layer traffic handling capabilities..... | 12 | +| IV.2 Network specific codepoint ..... | 12 | + +# **SUMMARY** + +This Recommendation defines the operation of the Digital Subscriber Signalling System No. 2 (DSS 2) for the handling of additional traffic parameters that may be used for basic call and connection control at the $T_B$ or at the coincident $S_B$ and $T_B$ reference point of the user-to-network interface of the Broadband Integrated Services Digital Network (B-ISDN). The additional capabilities defined in this Recommendation enable connection control and resource/bandwidth allocation to support communication between users using a connection oriented variable bit rate network provided bearer capability. + +## **BROADBAND INTEGRATED SERVICES DIGITAL NETWORK (B-ISDN) – DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 2 (DSS 2) – ADDITIONAL TRAFFIC PARAMETERS** + +*(Geneva, 1995)* + +# **General information** + +This Recommendation covers the support of additional traffic parameters for the Broadband Integrated Services Digital Network (B-ISDN) at the $T_B$ reference point or coincident $S_B$ and $T_B$ reference point as defined in Recommendation I.413 [1] by means of the Digital Subscriber Signalling System No. 2 (DSS 2). This Recommendation defines the DSS 2 protocol procedures, formats and functions needed to support the identified ATM traffic related additional capabilities. + +The specifications provided by this Recommendation allow for the signalling of additional traffic parameters beyond the ones already specified by Recommendation Q.2931 [2] for B-ISDN basic call/connection control at the UNI. The additional traffic parameters support a Broadband Connection-Oriented Bearer Service (BCOB) as specified in Recommendation F.811 [3], in particular for services of bearer classes “C” (VBR without timing requirements), and “X”. + +This Recommendation is part of the DSS 2 family of ITU-T Recommendations; it specifies extensions to Recommendation Q.2931, and does not repeat states, information elements, messages and procedures contained therein, but only specifies extensions related to additional traffic parameter indications. + +This Recommendation does not cover procedures for the negotiation and modification/re-negotiation of traffic parameters. + +This is a multipart Recommendation, Part 1 covers only the additional parameters required for the support of the tagging option and the support of Sustainable Cell Rate (SCR) parameter set as specified in Recommendation I.371 [4]. Other parts will be developed to support additional traffic parameters for traffic handling capabilities as they will be defined in the scope of Recommendation I.371 [4]. + +# **PART 1 – ADDITIONAL SIGNALLING CAPABILITIES TO SUPPORT TRAFFIC PARAMETERS FOR THE TAGGING OPTION AND THE SUSTAINABLE CELL RATE PARAMETER SET** + +## **1.1 Scope** + +This Recommendation covers the support of additional traffic parameters for the Broadband Integrated Services Digital Network (B-ISDN) at the $T_B$ reference point or coincident $S_B$ and $T_B$ reference point as defined in Recommendation I.413 [1] by means of the Digital Subscriber Signalling System No. 2 (DSS 2). This Recommendation defines the DSS 2 protocol procedures, formats and functions needed to support the identified ATM traffic related additional capabilities. + +This Recommendation is part of the DSS 2 family of ITU-T Recommendations; it specifies extensions to Recommendation Q.2931, and does not repeat states, information elements, messages and procedures contained therein, but only specifies extensions related to additional traffic parameter indications. + +This part of the Recommendation defines the capabilities to support additional traffic parameters required for the tagging option and the Sustainable Cell Rate parameter set as defined in the Recommendation I.371 [4]. + +This part of the Recommendation does not cover procedures for the negotiation and modification/re-negotiation of traffic parameters. + +## 1.2 References + +The following Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. All references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the references listed below. A list of currently valid ITU-T Recommendations is regularly published. + +- [1] ITU-T Recommendation I.413 (1993), *B-ISDN user-network interface*. +- [2] ITU-T Recommendation Q.2931 (1995), *Broadband Integrated Services Digital Network (B-ISDN) – Digital Subscriber Signalling System No. 2 (DSS 2) – User Network Interface (UNI) layer 3 specification for basic call/connection control*. +- [3] CCITT Recommendation F.811 (1992), *Broadband connection-oriented bearer service*. +- [4] ITU-T Recommendation I.371, *Traffic control and congestion control in B-ISDN*. +- [5] ITU-T Recommendation I.150 (1993), *B-ISDN asynchronous transfer mode functional characteristics*. +- [6] ITU-T Recommendation I.361 (1993), *B-ISDN ATM layer specification*. +- [7] ITU-T Recommendation Q.2951 (1995), *Stage 3 description for number identification supplementary services using B-ISDN Digital Subscriber Signalling System No. 2 (DSS 2) – Basic call*. +- [8] ITU-T Recommendation Q.2957 (1995), *Stage 3 description for additional information transfer supplementary services using B-ISDN Digital Subscriber Signalling System No. 2 (DSS 2) – Basic call*. + +## 1.3 Definitions + +The definitions of Recommendation Annex J/Q.2931 [2] apply. For the purposes of this Recommendation, the following definitions apply in addition: + +**1.3.1 cell loss priority (CLP):** A one-bit indication in the header of each ATM cell. This bit indication may be used by the user to generate traffic flows with two different cell loss ratio objectives, as defined in Recommendation I.150 [5]. + +**1.3.2 traffic contract:** A traffic contract specifies the negotiated traffic and QOS characteristics of an ATM layer connection at the B-ISDN UNI (see Recommendation I.371 [4]). + +**1.3.3 traffic control:** Traffic control at the ATM layer refers to the set of actions taken by the network to avoid congested conditions. A list of traffic control functions is given in Recommendation I.371. + +**1.3.4 traffic parameters:** A traffic parameter is a specification of a particular traffic aspect. It may be quantitative or qualitative. Traffic parameters may for example describe peak cell rate, sustainable cell rate, maximum burst size, etc. + +**1.3.5 tagging:** Tagging means that CLP = 0 cells identified by the UPC function performed on CLP = 0 flow as non-confirming are converted to CLP = 1 cells and merged with the user submitted CLP = 1 traffic flow before the CLP = 0 + 1 traffic flow enters the UPC mechanism (see Recommendation I.371 [4]). + +## 1.4 Abbreviations + +The abbreviations of Annex J/Q.2931 [2] apply. For the purposes of this Recommendation, the following abbreviations apply in addition: + +| | | +|------|------------------------------| +| CAC | Connection Admission Control | +| CDV | Cell Delay Variation | +| CLR | Cell Loss Ratio | +| GCRA | Generic Cell Rate Algorithm | +| IBT | Intrinsic Burst Tolerance | +| MBS | Maximum Burst Size | +| NPC | Network Parameter Control | +| PCR | Peak Cell Rate | +| SCR | Sustainable Cell Rate | +| UPC | Usage Parameter Control | + +## 1.5 Description + +This Part specifies the signalling of additional traffic parameters beyond the ones already specified by Recommendation Q.2931 [2]. In particular, the following additional capabilities are specified: + +- support of traffic parameters for statistical multiplexing using SCR parameter set (sustainable cell rate, maximum burst size); +- use of the “tagging option”. + +## 1.6 Operational requirements + +### 1.6.1 Provision and withdrawal + +The additional traffic indications may be included in signalling messages by the user as specified in this Recommendation without any prior arrangement with the service provider. + +### 1.6.2 Requirements at the originating network side + +The procedures according to 1.9 shall apply. + +### 1.6.3 Requirements at the terminating network side + +The procedures according to 1.9 shall apply. + +## 1.7 Primitive and state definitions + +### 1.7.1 Primitive definitions + +Clause 8/Q.2931 shall apply. + +### 1.7.2 Call states + +See clause 2/Q.2931. No additional call states are defined. + +## 1.8 Coding requirements + +### 1.8.1 Messages + +No additional messages are specified beyond the ones of 3.1/Q.2931. The existing Q.2931 messages that have had their contents modified to support the additional traffic parameters are described below. + +#### 1.8.1.1 SETUP + +Only the maximum length of the ATM traffic descriptor information element included in the SETUP message is changed from 20 to 30 octets to allow inclusion of additional traffic descriptor parameters. + +#### 1.8.1.2 CONNECT + +This message is sent by the called user to the network and by the network to the calling user to indicate call acceptance by the called user. See Table 1 for additions to the structure of this message shown in Table 3-2/Q.2931. + +TABLE 1/Q.2961 + +##### CONNECT message additional content + +| Message type: CONNECT
Significance: global
Direction: both | | | | | +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------|-----------|----------|--------| +| Information element | Reference | Direction | Type | Length | +| ATM traffic descriptor | 8.2.1/Q.2961 | Both | O (Note) | 4-6 | +| NOTE – Included in the user-to-network direction only when the SETUP message contained an ATM traffic descriptor information element with the Tb parameter set to “1”. Included in the network-to-user direction only when the SETUP message contained an ATM traffic descriptor information element with the Tf parameter set to “1”. In this message this information element has only local significance and contains only octets 1, 2, 3, 4, 17 and 17.1. | | | | | + +### 1.8.2 Information elements + +See clause 4/Q.2931. The coding of the ATM traffic descriptor information element is extended and is shown in 1.8.2.1. + +#### 1.8.2.1 ATM traffic descriptor + +The ATM traffic descriptor information element is specified in Recommendation Q.2931 and is extended as shown in Figure 1 and Table 2. The maximum length of this information element is 30 octets. + +## 1.9 Signalling procedures at the coincident SB and TB reference point + +The procedures for basic call/connection control as defined in clause 5/Q.2931 [2] shall apply. Only additional procedures to handle the additional traffic parameters that may be present in the ATM traffic descriptor information element are indicated in the following subclauses. + +### 1.9.1 Procedures for the support of Sustainable Cell Rate parameter set + +The calling party initiates call establishment as specified in 5.1/Q.2931 and 5.2/Q.2931. The rules for selection of traffic parameters for a given direction are specified below: + +- PCR for CLP = (0 + 1) is a mandatory parameter. +- The value of the Sustainable Cell Rate must be less than that for Peak Cell Rate. +- The tagging option may only be used when the traffic descriptor IE includes a parameter on CLP = 0. +- There is a relationship between MBS and Intrinsic Burst Tolerance (IBT) which also depends on the SCR and PCR (see Appendix III). +- The Sustainable Cell Rate and Maximum Burst Size must be provided together for the same CLP indication, for a given direction. +- Forward and backward direction are independent from each other, i.e. the forward direction may use one combination of traffic parameters, while the backward direction uses a different combination of traffic parameters. + +Allowable combinations will depend on the ATM layer traffic handling capabilities. + +| Bits | | | | | | | | Octets | +|--------------------------------------------------|---|---|---|---|---|----|----|-----------------------------| +| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | | +| | | | | | | | | 1 to 8
see Q.2931 (Note) | +| Forward Sustainable Cell Rate Id. (CLP = 0) | | | | | | | | 9* | +| 1 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | | +| Forward | | | | | | | | 9.1* | +| Sustainable Cell Rate | | | | | | | | 9.2* | +| (for CLP = 0) | | | | | | | | 9.3* | +| Backward Sustainable Cell Rate Id. (CLP = 0) | | | | | | | | 10* | +| 1 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | | +| Backward | | | | | | | | 10.1* | +| Sustainable Cell Rate | | | | | | | | 10.2* | +| (for CLP = 0) | | | | | | | | 10.3* | +| Forward Sustainable Cell Rate Id. (CLP = 0 + 1) | | | | | | | | 11* | +| 1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | | +| Forward | | | | | | | | 11.1* | +| Sustainable Cell Rate | | | | | | | | 11.2* | +| (for CLP = 0 + 1) | | | | | | | | 11.3* | +| Backward Sustainable Cell Rate Id. (CLP = 0 + 1) | | | | | | | | 12* | +| 1 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | | +| Backward | | | | | | | | 12.1* | +| Sustainable Cell Rate | | | | | | | | 12.2* | +| (for CLP = 0 + 1) | | | | | | | | 12.3* | +| Forward Maximum Burst Size Id. (CLP = 0) | | | | | | | | 13* | +| 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | | +| Forward | | | | | | | | 13.1* | +| Maximum Burst Size | | | | | | | | 13.2* | +| (for CLP = 0) | | | | | | | | 13.3* | +| Backward Maximum Burst Size Id. (CLP = 0) | | | | | | | | 14* | +| 1 | 0 | 1 | 0 | 0 | 0 | 0 | 1 | | +| Backward | | | | | | | | 14.1* | +| Maximum Burst Size | | | | | | | | 14.2* | +| (for CLP = 0) | | | | | | | | 14.3* | +| Forward Maximum Burst Size Id. (CLP = 0 + 1) | | | | | | | | 15* | +| 1 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | | +| Forward | | | | | | | | 15.1* | +| Maximum Burst Size | | | | | | | | 15.2* | +| (for CLP = 0 + 1) | | | | | | | | 15.3* | +| Backward Maximum Burst Size Id. (CLP = 0 + 1) | | | | | | | | 16* | +| 1 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | | +| Backward | | | | | | | | 16.1* | +| Maximum Burst Size | | | | | | | | 16.2* | +| (for CLP = 0 + 1) | | | | | | | | 16.3* | +| Traffic Management Options Identifier | | | | | | | | 17* | +| 1 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | | +| Spare | | | | | | | | | +| 0 | 0 | 0 | 0 | 0 | 0 | Tb | Tf | 17.1* | + +NOTE – The fields “Forward Peak Cell Rate (for CLP = 0 + 1)” and “Backward Peak Cell Rate (for CLP = 0 + 1)” are mandatory if the ATM traffic descriptor information element is included in the SETUP message. They are optional if the ATM traffic descriptor information element is included in the CONNECT message. + +FIGURE 1/Q.2961 + +#### **ATM traffic descriptor information element** + +TABLE 2/Q.2961 + +#### **ATM traffic descriptor information element** + +- Forward/backward sustainable cell rate (octets i.1-i.3, where i may have the values 9-12): + +A value expressing in pure 3 octet integer representation the number of cells per second, with bit 8 of the first octet being the most significant bit, and bit 1 of the third octet being the least significant bit. + +The “forward” direction is defined as that from the calling user to the called user. + +The “backward” direction is the reverse, i.e. from the called user to the calling user (see Annex J/Q.2931 [2]). + +- Forward/backward maximum burst size (octets i.1-i.3, where i may have the values 13-16): + +The maximum burst size is expressed in cells and is coded as pure 3 octet integer with bit 8 of the first octet being the most significant bit, and bit 1 of the third octet being the least significant bit. + +- Tb (tagging backward) (octet 17.1) + +| Bit | user-to-network (Note 1) | network-to-user (Note 2) | +|-----|--------------------------|--------------------------| +| 2 | | | +| 0 | tagging not allowed | tagging not supported | +| 1 | tagging requested | tagging supported | + +NOTE 1 – At the destination side, if octet 17.1 is omitted, a default of “tagging not allowed” shall apply. At the originating side, the field is spare. + +NOTE 2 – At the destination side, if octet 17.1 is omitted, a default of “tagging not supported” shall apply. At the originating side, the field is spare. + +- Tf (tagging forward) (octet 17.1) + +| Bit | user to network (Note 3) | network to user (Note 4) | +|-----|--------------------------|--------------------------| +| 1 | | | +| 0 | tagging not allowed | tagging not applied | +| 1 | tagging requested | tagging applied | + +NOTE 3 – At the originating side, if octet 17.1 is omitted, a default of “tagging not allowed” shall apply. At the destination side, the field is spare. + +NOTE 4 – At the originating side, if octet 17.1 is omitted, a default of “tagging not applied” shall apply. At the destination side, the field is spare. + +### **1.9.2 Handling of the traffic management options field for the local support of tagging** + +#### **1.9.2.1 Procedures applicable at the originating interface** + +The calling user, by use of the Tf subfield in the ATM traffic descriptor information element, may indicate in the SETUP message that tagging requested or not allowed for the user plane traffic in the forward direction (See Recommendation I.371 [4] for definition of tagging). + +When the network receives a SETUP message with the Tf subfield set to “tagging requested”, and the network accepts the request to apply tagging for the user plane traffic in the forward direction, the network shall upon call acceptance include an ATM traffic descriptor information element in the CONNECT message, set the Tf subfield to “tagging applied”. Otherwise, the network shall not apply tagging and take one of the following actions: + +- 1) include upon call acceptance an ATM traffic descriptor information element in the CONNECT message with Tf subfield “tagging not applied”; +- 2) not include upon call acceptance an ATM traffic descriptor information element in the CONNECT message. + +#### **1.9.2.2 Procedures applicable at the destination interface** + +When the network sends a SETUP message, and the network supports the tagging option for the user plane traffic in the backward direction (see 2.3.1/I.371), the network shall include a Traffic Management Options in this message with the Tb subfield set to “tagging supported”. If the network does not support the tagging option, the network shall take one of the following actions: + +- 1) include a Traffic Management Options field in the ATM traffic descriptor information element in the SETUP message with the Tb subfield set to “tagging not supported”; + +- 2) not include a Traffic Management Options field in the ATM traffic descriptor information element in the SETUP message. + +When the user receives a SETUP message with the Tb subfield set to "tagging supported", and the user wishes to request tagging, the user shall upon call acceptance include an ATM traffic descriptor information element in the CONNECT message with the Tb subfield set to "tagging requested". Otherwise, the user shall take one of the following actions: + +- 1) include an ATM traffic descriptor information element with the Tb subfield set to "tagging not allowed" in the CONNECT message; +- 2) not include ATM traffic descriptor information element in the CONNECT message. + +When the network had indicated to the user that it supports tagging, and it receives a CONNECT message which contains an ATM traffic descriptor information element with Tb subfield set to "tagging requested", the network shall apply tagging for the user plane traffic in the backward direction. Otherwise, it shall not apply tagging. + +### **1.9.3 Handling of specific error conditions** + +When the SETUP message is received with an ATM traffic descriptor information element which contains a combination of traffic parameters that is not allowed (see 1.9.1) the ATM traffic descriptor information element shall be treated as a mandatory information element received with content error (see 5.6.7.2/Q.2931). + +## **1.10 Signalling procedures at the TB reference point for interworking with private B-ISDNs** + +The procedures of 1.9 shall apply. + +## **1.11 Interworking with other networks** + +### **1.11.1 Interaction with entities which do not support the Q.2961 capabilities** + +If an entity which does not support the capabilities described in this Part receives an ATM traffic descriptor information element in a SETUP message with the additional fields defined in 1.8.2, it shall follow the procedures described in 5.6/Q.2931, 5.7/Q.2931 and 5.8/Q.2931 [2]. + +### **1.11.2 Interworking with N-ISDN** + +It is not possible to interwork these capabilities with an N-ISDN entity. + +## **1.12 Interactions with supplementary services** + +The support of the capabilities covered by this Part have no impact on the support of CLIP, CLIR, COLP, COLR, DDI, SUB, UUS and MSN supplementary services as specified in Recommendations Q.2951 [7] and Q.2957 [8]. + +## **1.13 Parameter values** + +Not applicable for this Recommendation. + +## **1.14 Dynamic description (SDLs)** + +Not applicable for this Recommendation. + +# Appendix I + +## Additional definitions + +(This appendix does not form an integral part of this Recommendation) + +It should be noted that Study Group (SG) 13 is producing the definitive work in this area. Therefore the informative text in this appendix will be superseded by I.371 text when available. In the event of conflict, Recommendation I.371 takes precedence over the contents of this appendix. + +## I.1 Usage Parameter Control (UPC) + +Usage parameter control is the set of actions taken by the network to monitor and control traffic in terms of traffic offered and validity of the ATM connection, at the user access. Its main purpose is to protect network resource from malicious as well as unintentional misbehaviour which can affect the QOS of other already established connections by detecting violations of negotiated parameters and taking appropriate actions. + +## I.2 Interpretation of sustainable cell rate and maximum burst size + +SCR and MBS are traffic parameters the calling user may use, if the user can upper bound the realized mean cell rate of the ATM connection to a value below the PCR. If used, the calling user must include both parameters. Note that the PCR for CLP = 0 + 1 traffic is a mandatory parameter of the ATM traffic descriptor information element. + +The SCR is an upper bound on the possible conforming “mean rate” of an ATM connection, where “mean rate” is the number of cells transmitted divided by the “duration of the connection”, where in this case, the “duration of the connection” is the time from the emission of the first cell until the state of the GCRA for the SCR returns to zero after the emission of the last cell of the connection. + +SCR and MBS are defined as parameters of the GCRA (see Appendix II). Enforcement of this parameter set could allow the network operator to allocate sufficient resources for statistical multiplexing using SCR parameter set (sustainable cell rate, maximum burst size), but less than those based on the PCR, and still ensure that the performance objectives (e.g. for cell loss ratio) can be achieved. Further details for the interpretation of the SCR are provided in Appendix III. + +NOTE – The SCR parameter set values (indicated in the ATM traffic descriptor information element) specify the sum of both the user plane information and end-to-end user originated OAM F5 flows. Accordingly no additional OAM traffic descriptor for SCR is needed. + +# Appendix II + +## Generic Cell Rate Algorithm (GCRA) + +(This appendix does not form an integral part of this Recommendation) + +It should be noted that Study Group 13 is producing the definitive work in this area. Therefore the informative text in this appendix will be superseded by I.371 text when available. In the event of conflict, Recommendation I.371 takes precedence over the contents of this appendix. + +The Generic Cell Rate Algorithm (GCRA) is a virtual scheduling algorithm or a continuous-state leaky bucket algorithm as defined by the flowchart in Figure II.1. The GCRA is used to define, in an operational manner, a relationship between a cell rate and an associated tolerance (e.g. between PCR and CDV tolerance, or between SCR and MBS). In addition, for the cell flow of an ATM connection, the GCRA is used to specify the conformance at the UNI to declared values of the above two tolerances. + +For each cell arrival, the GCRA determines whether the cell is conforming with the traffic contract of the connection, and thus the GCRA is used to provide the formal definition of traffic conformance to the traffic contract. Although traffic conformance is defined in terms of the GCRA, the network provider is not obligated to use this algorithm (or this algorithm with the same parameter values) for the Usage Parameter Control (UPC). Rather, the network provider may use any UPC as long as the operation of the UPC does not violate the QOS objectives of a compliant connection. + +The GCRA depends only on two parameters: the increment $I$ and the limit $L$ . These parameters have been denoted by $T$ and $\tau$ respectively in Annex A/I.371, but have been given more generic labels herein since the GCRA will be used in multiple instances. The notation “GCRA( $I$ , $L$ )” means the generic cell rate algorithm with the value of the increment parameter set equal to $I$ and the value of the limit parameter set equal to $L$ . + +The GCRA is formally defined in Figure II.1. Figure II.1 is a generic version of Figure A.1/I.371. The two algorithms in Figure II.1 are equivalent in the sense that for any sequence of cell arrival times, $\{t_a(k), k \geq 1\}$ the two algorithms determine the same cells to be conforming and thus the same cells to be non-conforming. The two algorithms are easily compared if one notices that at each arrival epoch, $t_a(k)$ , and after the algorithms have been executed, $TAT = X + LCT$ , see Figure II.1. An explanation of each algorithm follows. + +The virtual scheduling algorithm updates a Theoretical Arrival Time (TAT), which is the “nominal” arrival time of the cell assuming equally spaced cells when the source is active. If the actual arrival time of a cell is not “too” early relative to the TAT, i.e. if the actual arrival time is after $TAT - L$ , then the cell is conforming, otherwise the cell is non-conforming. + +Tracing the steps of the virtual scheduling algorithm in Figure II.1, at the arrival time of the first cell $t_a(1)$ , the theoretical arrival time TAT is initialized to the current time, $t_a(1)$ . For subsequent cells, if the arrival time of the $k^{\text{th}}$ cell, $t_a(k)$ , is actually after the current value of the TAT then the cell is conforming and TAT is updated to the current time $t_a(k)$ , plus the increment $I$ . If the arrival time of the $k^{\text{th}}$ cell is greater than or equal to $TAT - L$ but less than TAT (i.e. as expressed in Figure II.1, if TAT is less than or equal to $t_a(k) + L$ ), then again the cell is conforming, and the TAT is increased by the increment $I$ . Lastly, if the arrival time of the $k^{\text{th}}$ cell is less than $TAT - L$ (i.e. if TAT is greater than $t_a(k) + L$ ), then the cell is non-conforming and the TAT is unchanged. + +The continuous-state leaky bucket algorithm can be viewed as a finite-capacity bucket whose real-valued content drains out at a continuous rate of 1 unit of content per time-unit and whose content is increased by the increment $I$ for each conforming cell. Equivalently, it can be viewed as the work load in a finite-capacity queue or as a real-valued counter. If at a cell arrival the content of the bucket is less than or equal to the limit value, $L$ , then the cell is conforming, otherwise the cell is non-conforming. The capacity of the bucket (the upper bound on the counter) is $L + I$ . + +Tracing the steps of the continuous-state leaky bucket algorithm in Figure II.1, at the arrival time of the first cell $t_a(1)$ , the content of bucket, $X$ , is set to zero and the last conformance time (LCT) is set to $t_a(1)$ . At the arrival time of the $k^{\text{th}}$ cell, $t_a(k)$ , first the content of the bucket is provisionally updated to the value $X'$ , which equals the content of the bucket, $X$ , after the arrival of the last conforming cell minus the amount the bucket has drained since that arrival, where the content of the bucket is constrained to be non-negative. Second, if $X'$ is less than or equal to the limit value $L$ , then the cell is conforming, and the bucket content $X$ is set to $X'$ plus the increment $I$ for the current cell, and the last conformance time LCT, is set to the current time $t_a(k)$ . If, on the other hand, $X'$ is greater than the limit value $L$ , then the cell is non-conforming and the values of $X$ and LCT are not changed. + + + +``` + +graph TD + Start[Arrival of a cell at time t_a(k) at a given interface, T_B or inter-network interface, on the ATM connection] --> VSA_Start[Virtual scheduling algorithm] + Start --> CS_Start[Continuous-state leaky bucket algorithm] + + subgraph "Virtual scheduling algorithm" + VSA_Start --> VSA_Dec{t_a(k) < TAT - L ?} + VSA_Dec -- Yes --> VSA_Non[Non-conforming cell] + VSA_Dec -- No --> VSA_Conf[TAT = max(t_a(k), TAT) + I +Conforming cell] + VSA_Non --> VSA_Next[next cell] + VSA_Conf --> VSA_Next + VSA_Next --> Start + end + + subgraph "Continuous-state leaky bucket algorithm" + CS_Start --> CS_Calc[X' = X - (t_a(k) - LCT)] + CS_Calc --> CS_Dec{X' > L ?} + CS_Dec -- Yes --> CS_Non[Non-conforming cell] + CS_Dec -- No --> CS_Conf[X = max(0, X') + I +LCT = t_a(k) +Conforming cell] + CS_Non --> CS_Next[next cell] + CS_Conf --> CS_Next + CS_Next --> Start + end + +``` + +Flowcharts for Virtual scheduling algorithm and Continuous-state leaky bucket algorithm. Both start with 'Arrival of a cell at time t\_a(k) at a given interface, T\_B or inter-network interface, on the ATM connection'. The Virtual scheduling algorithm checks if t\_a(k) < TAT - L. If Yes, it's a 'Non-conforming cell'. If No, it's a 'Conforming cell' and TAT = max(t\_a(k), TAT) + I. The Continuous-state leaky bucket algorithm updates X' = X - (t\_a(k) - LCT), then checks if X' > L. If Yes, it's a 'Non-conforming cell'. If No, it's a 'Conforming cell' and X = max(0, X') + I, LCT = t\_a(k). Both algorithms have a 'next cell' loop back to the start. + +Virtual scheduling algorithm + +Continuous-state leaky bucket algorithm + +TAT Theoretical Arrival Time + $t_a(k)$ Time of arrival of a cell + +$X$ Value of the Leaky Bucket counter + $X'$ Auxiliary variable +LCT Last Conformance Time + +$I$ Increment + $L$ Limit + +At the time of arrival $t_a$ of the first cell of connection, $X = 0$ and LCT = $t_a(k)$ + +At the time of arrival $t_a$ of the first cell of the connection, TAT = $t_a(1)$ + +FIGURE II.1/Q.2961 +**Equivalent versions of the generic cell rate algorithm** + +# Appendix III + +## Relation between maximum burst size and intrinsic burst tolerance in conjunction with peak cell rate + +(This appendix does not form an integral part of this Recommendation) + +## III.1 Sustainable Cell Rate + +It should be noted that Study Group 13 is producing the definitive work in this area. Therefore the informative text in this appendix will be superseded by I.371 text when available. In the event of conflict, Recommendation I.371 takes precedence over the contents of this appendix. + +The SCR, denoted as $\Lambda_{SCR}$ , is an upper bound on the possible conforming “mean rate” of an ATM connection, where “mean rate” is the number of cells transmitted divided by the “duration of the connection”; where in this case, the “duration of the connection” is the time from the emission of the first cell until the state of the GCRA for the SCR returns to zero after the emission of the last cell of the connection. Relative to the peak cell rate parameter, $T_{SCR}$ is greater than the peak emission interval $T_{PCR}$ where $T_{SCR}$ is the inverse of $\Lambda_{SCR}$ . + +SCR and MBS are traffic parameters the calling user may use, if the user can upper bound the realized mean cell rate of the ATM connection to a value below the PCR. If used, the calling user must include both parameters. Note that the PCR for CLP = 0 + 1 traffic is a mandatory parameter of the ATM traffic descriptor information element. The value of the SCR must be less than the PCR. For CBR connections, the user would not declare a SCR and would only declare a PCR. + +The SCR and MBS traffic parameters enable the end-user/terminal to describe the future cell flow of an ATM connection in greater detail than just the PCR. If an end-user/terminal is able to specify the future cell flow in greater detail than just the PCR, then the network provider may be able to more efficiently utilize the network resources. This directly benefits the network provider whether public or private, and in the case of public ATM networks, benefits the end-user with possible reduced charges for the connection. + +If the source wants to submit traffic that conforms to the SCR ( $\Lambda_{SCR} = 1/T_{SCR}$ ) and the intrinsic burst tolerance ( $\tau_{IBT}$ ) and the peak cell rate ( $1/T_{PCR}$ ) at the physical layer SAP of the equivalent terminal, then it offers traffic that is conforming to the GCRA( $T_{SCR}$ , $\tau_{IBT}$ ) and the peak emission interval $T_{PCR}$ [i.e. GCRA( $T_{PCR}$ , 0)]. + +The MBS together with the SCR and the GCRA determine the maximum burst size (MBS) that may be transmitted at the peak cell rate and still be in conformance with the GCRA( $T_{SCR}$ , $\tau_{IBT}$ ). The maximum burst size in number of cells is given by: + +$$MBS = \left\lfloor 1 + \frac{\tau_{IBT}}{T_{SCR} - T_{PCR}} \right\rfloor$$ + +where $\lfloor x \rfloor$ stands for the integer part of $x$ . + +In the signalling message, the burst tolerance is conveyed through the MBS which is coded in number of cells. The granularity supported by the signalling message is one cell. The MBS used to derive the value of $\tau_{IBT}$ applies at the physical layer SAP of the equivalent terminal. Note that in order to determine $\tau_{IBT}$ from the MBS, the peak cell rate also needs to be specified. By convention, the peak rate used in the calculation of $\tau_{IBT}$ is the peak cell rate of the CLP = 0 + 1 cell flow. This convention holds whether $\tau_{IBT}$ is associated with the SCR for the CLP = 0, or the CLP = 1, or the CLP = 0 + 1 cell flow of the connection. Also, given the MBS, $T_{PCR}$ , and $T_{SCR}$ , then $\tau_{IBT}$ is not uniquely determined, but can be any value in the half-closed interval: + +$$[(MBS - 1)(T_{SCR} - T_{PCR}), MBS(T_{SCR} - T_{PCR})]$$ + +Hence, in order for all parties to derive a common value for $\tau_{IBT}$ , by convention, the minimum possible value is used. Thus, given the MBS, $T_{PCR}$ , and $T_{SCR}$ , then $\tau_{IBT}$ is set equal to: + +$$\tau_{IBT} = \lceil (MBS - 1)(T_{SCR} - T_{PCR}) \rceil$$ + +Where $\lceil x \rceil$ stands for the first value above $x$ out of a generic list of values for $\tau_{IBT}$ . + +Note that over any closed time interval of length $t$ , the number of cells, $N(t)$ , that can be emitted with spacing no less than $T_{PCR}$ and still be in conformance with GCRA( $T_{SCR}$ , $\tau_{IBT}$ ) is bounded by: + +$$N(t) \leq \min \left( \left\lfloor 1 + \frac{t + \tau_{IBT}}{T_{SCR}} \right\rfloor, \left\lfloor 1 + \frac{t}{T_{PCR}} \right\rfloor \right)$$ + +Observe that if $t$ is greater than or equal to the $MBS \times T_{PCR}$ , then the first term of the above equation applies; otherwise, the second term applies. + +Note that the maximum conforming burst size, defined above, does not imply that bursts of this size with arbitrary spacing between the bursts would be conforming with the GCRA( $T_{SCR}$ , $\tau_{IBT}$ ). Rather, in order for a burst this large to be conforming, the cell stream needs to be idle long enough for the state of the GCRA associated with SCR to become zero (i.e. long enough for the continuous-state leaky bucket to become empty) prior to the burst. + +If a user chooses to specify values for the SCR and MBS traffic parameters and wishes to cell emit conforming bursts at the peak rate, then the appropriate choice of $T_{SCR}$ and $\tau_{IBT}$ depends on the minimum spacing between bursts as well as the burst size. For a cell flow of an ATM connection, if the minimum spacing between bursts at the equivalent terminal is $T_I$ and if the maximum burst size (with inter-cell spacing $T_{PCR}$ ) is $B$ , then the cell flow is conforming with $GCRA(T_{SCR}, \tau_{IBT})$ , if $T_{SCR}$ , $\tau_{IBT}$ are chosen at least large enough to satisfy the following equation: + +$$B = 1 + \left\lfloor \frac{\min(T_I - T_{SCR}, \tau_{IBT})}{T_{SCR} - T_{PCR}} \right\rfloor$$ + +where $\lfloor x \rfloor$ stands for the integer part of $x$ . + +The traffic pattern conforming with the $GCRA(T_{SCR}, \tau_{IBT})$ is in general not unique. Two traffic patterns are equivalent in relationship with the $GCRA(T_{SCR}, \tau_{IBT})$ if they both conform at the physical layer SAP with the $GCRA(T_{SCR}, \tau_{IBT})$ within the equivalent terminal. Therefore, any cell stream that complies with the $GCRA(T_{PCR}, 0)$ and $GCRA(T_{SCR}, \tau_{IBT})$ at the physical layer SAP has a peak cell rate of $R_p = 1/T_{PCR}$ , a mean cell rate which is bounded by $\Lambda_{SCR} = 1/T_{SCR}$ and a burst length which is bounded by $B$ . Note that the bounds $\Lambda_{SCR}$ and $B$ are achievable. For example, a periodic cell stream with period $B * T_{SCR}$ which transmits $B$ cells at the peak rate with inter burst spacing $T_I = B * (T_{SCR} - T_{PCR}) + T_{PCR}$ has peak cell rate $\Lambda$ , sustainable cell rate $\Lambda_{SCR}$ and burst length $B$ , and is compliant with both GCRAs. + +# Appendix IV + +## ATM layer traffic handling capabilities and network specific codepoint + +(This appendix does not form an integral part of this Recommendation) + +## IV.1 ATM layer traffic handling capabilities + +Recommendation I.371 will be providing the specification of new ATM layer traffic handling capabilities. Part 2 of this Recommendation will contain an indication of these capabilities that will be specified in revision 1 of Recommendation I.371. The relationship between these capabilities and the Bearer Classes will be specified and it is not expected that there will be a one-to-one relationship. + +## IV.2 Network specific codepoint + +The subfield identifier coded "10111110" of the ATM traffic descriptor information element is reserved for network specific use. \ No newline at end of file diff --git a/marked/Q/T-REC-Q.2961F-200012-I_PDF-E/2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg b/marked/Q/T-REC-Q.2961F-200012-I_PDF-E/2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..02618e1c9d69bb72ac37b909dab893cd21430aee --- /dev/null +++ b/marked/Q/T-REC-Q.2961F-200012-I_PDF-E/2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:6df3aeb5704678ae54ee7c4613ee4fb55ab0ed7fa77543d0714802f3cb0be873 +size 8357 diff --git a/marked/Q/T-REC-Q.2961F-200012-I_PDF-E/raw.md b/marked/Q/T-REC-Q.2961F-200012-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..a65b21daa36d157e35156e1d5c89e0669dd999c2 --- /dev/null +++ b/marked/Q/T-REC-Q.2961F-200012-I_PDF-E/raw.md @@ -0,0 +1,256 @@ + + + + +ITU logo: A globe with a lightning bolt and the letters ITU. + +INTERNATIONAL TELECOMMUNICATION UNION + +**ITU-T** + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +**Q.2961 F** + +(12/2000) + +SERIES Q: SWITCHING AND SIGNALLING + +Broadband ISDN – B-ISDN application protocols for +access signalling + +--- + +**Digital subscriber signalling system No. 2 +(DSS2) – Additional traffic parameters: +Abstract test suite (ATS) and partial protocol +implementation extra information for testing +(PIXIT) proforma for the network** + +ITU-T Recommendation Q.2961 F + +(Formerly CCITT Recommendation) + +--- + +# ITU-T Q-SERIES RECOMMENDATIONS + +## SWITCHING AND SIGNALLING + +| | | +|--------------------------------------------------------------------------------------------------------------|----------------------| +| SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE | Q.1-Q.3 | +| INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING | Q.4-Q.59 | +| FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN | Q.60-Q.99 | +| CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS | Q.100-Q.119 | +| SPECIFICATIONS OF SIGNALLING SYSTEMS No. 4 AND No. 5 | Q.120-Q.249 | +| SPECIFICATIONS OF SIGNALLING SYSTEM No. 6 | Q.250-Q.309 | +| SPECIFICATIONS OF SIGNALLING SYSTEM R1 | Q.310-Q.399 | +| SPECIFICATIONS OF SIGNALLING SYSTEM R2 | Q.400-Q.499 | +| DIGITAL EXCHANGES | Q.500-Q.599 | +| INTERWORKING OF SIGNALLING SYSTEMS | Q.600-Q.699 | +| SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 | Q.700-Q.849 | +| DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 1 | Q.850-Q.999 | +| PUBLIC LAND MOBILE NETWORK | Q.1000-Q.1099 | +| INTERWORKING WITH SATELLITE MOBILE SYSTEMS | Q.1100-Q.1199 | +| INTELLIGENT NETWORK | Q.1200-Q.1699 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2000 | Q.1700-Q.1799 | +| BROADBAND ISDN | Q.2000-Q.2999 | +| General aspects | Q.2000-Q.2099 | +| Signalling ATM adaptation layer (SAAL) | Q.2100-Q.2199 | +| Signalling network protocols | Q.2200-Q.2299 | +| Common aspects of B-ISDN application protocols for access signalling and network signalling and interworking | Q.2600-Q.2699 | +| B-ISDN application protocols for the network signalling | Q.2700-Q.2899 | +| B-ISDN application protocols for access signalling | Q.2900-Q.2999 | + +For further details, please refer to the list of ITU-T Recommendations. + +## **Digital subscriber signalling system No. 2 (DSS2) – Additional traffic parameters: Abstract test suite (ATS) and partial protocol implementation extra information for testing (PIXIT) proforma for the network** + +## **Summary** + +This Recommendation specifies Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for Testing (PIXIT) proforma for the network at the $T_B$ reference point or coincident $S_B$ and $T_B$ reference point (as defined in ITU-T I.413 [9]) of implementations conforming to the procedures for the handling of additional traffic parameters that may be used for basic call and connection control of the Digital Subscriber Signalling System No. 2 (DSS2) protocol for the Broadband Integrated Services Digital Network (B-ISDN), ITU-T Q.2961 [1], [2], [3], [4], [5] and [6]. + +Other Recommendations of the Q.2961 family specify the Protocol Implementation Conformance Statement (PICS) proforma and Test Suite Structure and Test Purposes (TSS & TP) based on this Recommendation. + +NOTE – This Recommendation related to protocol conformance is published only in English; it is based on an external SDO's standard published in English. + +###### **Source** + +ITU-T Recommendation Q.2961 F was prepared by ITU-T Study Group 11 (2001-2004) and approved under the WTSA Resolution 1 procedure on 6 December 2000. + +## FOREWORD + +The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. + +The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. + +In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. + +## NOTE + +In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +## INTELLECTUAL PROPERTY RIGHTS + +ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. + +As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. + +© ITU 2001 + +All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from ITU. + +## CONTENTS + +| | Page | +|----------------------------------|------| +| 1 Scope ..... | 1 | +| 2 References ..... | 1 | +| 3 Endorsement..... | 2 | +| 4 Coverage ..... | 2 | +| 5 Modifications ..... | 3 | +| 5.1 General modifications..... | 3 | +| 5.2 Technical modifications..... | 3 | +| Appendix I – Bibliography ..... | 3 | + +## **Digital subscriber signalling system No. 2 (DSS2) – Additional traffic parameters: Abstract test suite (ATS) and partial protocol implementation extra information for testing (PIXIT) proforma for the network** + +# 1 Scope + +This Recommendation specifies Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for Testing (PIXIT) proforma for the network at the $T_B$ reference point or coincident $S_B$ and $T_B$ reference point (as defined in ITU-T I.413 [9]) of implementations conforming to the procedures for the handling of additional traffic parameters that may be used for basic call and connection control of the Digital Subscriber Signalling System No. 2 (DSS2) protocol for the Broadband Integrated Services Digital Network (B-ISDN), ITU-T Q.2961 [1], [2], [3], [4], [5] and [6]. + +Other Recommendations of the Q.2961 family specify the Protocol Implementation Conformance Statement (PICS) proforma and Test Suite Structure and Test Purposes (TSS & TP) based on this Recommendation. + +This Recommendation is applicable to equipment, supporting capabilities for the indication of traffic parameters above of the peak cell rate at connection request time, to be attached at either side of a $T_B$ reference point or coincident $S_B$ and $T_B$ reference point when used as an access to the public B-ISDN. + +The ATS realizes test purposes identified in the TSS & TP part of the Recommendation and groups them according to the test suite structure given in the TSS & TP. Test purposes defined in the TSS & TP part but not testable are identified in this Recommendation. + +The supplier of a protocol implementation that is claimed to conform to capabilities defined in a Q.2961-series Recommendation is required to complete a copy of the PICS proforma and the PIXIT proforma provided by the testlab. The PIXIT proforma shall contain the tables identified in the partial PIXIT proforma part of this Recommendation and may contain additional information required by the testlab to be able to appropriately execute the test campaign. + +NOTE – No conformance test service can be provided and therefore no PICS and PIXIT proforma is required to be completed for implementation capabilities not covered by this Recommendation. Regarding capabilities coverage, refer to clause 4. + +## 2 References + +The following Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of currently valid ITU-T Recommendations is regularly published. + +- [1] ITU-T Q.2961.1 (1995), *Digital subscriber signalling system No. 2 – Additional signalling capabilities to support traffic parameters for the tagging option and the sustainable cell rate parameter set.* +- [2] ITU-T Q.2961.2 (1997), *Digital subscriber signalling system No. 2 – Additional traffic parameters: Support of ATM transfer capability in the broadband bearer capability information element.* + +- [3] ITU-T Q.2961.3 (1997), *Digital subscriber signalling system No. 2 – Additional traffic parameters: Signalling capabilities to support traffic parameters for the available bit rate (ABR) ATM transfer capability.* +- [4] ITU-T Q.2961.4 (1997), *Digital subscriber signalling system No. 2 – Additional traffic parameters: Signalling capabilities to support traffic parameters for the ATM block transfer (ABT) ATM transfer capability.* +- [5] ITU-T Q.2961.5 (1999), *Digital subscriber signalling system No. 2 – Additional traffic parameters: Additional traffic parameters for cell delay variation tolerance indication.* +- [6] ITU-T Q.2961.6 (1998), *Digital subscriber signalling system No. 2 – Additional traffic parameters: Additional signalling procedures for the support of the SBR2 and SBR3 ATM transfer capabilities.* +- [7] ITU-T Q.2961 B (2000), *Digital subscriber signalling system No. 2 (DSS2) – Additional traffic parameters: Protocol implementation conformance statement (PICS) proforma.* +- [8] ITU-T Q.2931 (1995), *Digital subscriber signalling system No. 2 – User-network interface (UNI) layer 3 specification for basic call/connection control.* +- [9] ITU-T I.413 (1993), *B-ISDN user-network interface.* +- [10] ETSI EN 301 068-6 V1.1.1 (2000), *Broadband Integrated Services Digital Network (B-ISDN); Digital Subscriber Signalling System No. two (DSS2) protocol; Connection characteristics; ATM transfer capability and traffic parameter indication; Part 6: Abstract Test Suite (ATS) and partial Protocol Implementation eXtra information for testing (PIXIT) proforma specification for the network.* +- [11] ITU-T Q.2931 B (2000), *Broadband integrated services digital network (B-ISDN) – Digital subscriber signalling system No. 2 (DSS2) – User-network interface (UNI) layer 3 specification for basic call/bearer control; Protocol implementation conformance statement (PICS) proforma.* + +## 3 Endorsement + +The text of ETSI EN 301 068-6 [10] was approved by ITU-T as Recommendation Q.2961 F with agreed modifications as given below. + +NOTE – Underlining and/or strike-out is used to highlight new or deleted text where detailed indication of modifications is necessary. + +## 4 Coverage + +This Recommendation covers ITU-T Q.2961.1 [1], Q.2961.2 [2], Q.2961.3 [3], Q.2961.4 [4] and Q.2961.6 [6]. + +NOTE – For testing of Q.2961.6, test groups for checking conformance to Q.2961.1 and Q.2961.2 shall be used with the exception of test groups 02 and 08 ("Traffic management option for support of tagging"). All the signalled parameters (valid and invalid B-BC values, valid and invalid ATM traffic descriptor values, etc.) necessary for testing Q.2961.6 requirements are entered via relevant PIXIT values. + +## 5 Modifications + +### 5.1 General modifications + +Throughout the text of ETSI EN 301 068-6 [10] replace references as shown in the following table: + +| Reference in ETSI EN 301 068-6 | Modified reference | +|--------------------------------|-------------------------------| +| EN 300 443-1 | ITU-T Q.2931 | +| EN 300 443-2 | ITU-T Q.2931 B | +| EN 301 068-1 | Q.2961-series Recommendations | +| EN 301 068-2 | ITU-T Q.2961 B | +| EN 301 068-6 | ITU-T Q.2961 F | +| Standard | Recommendation | + +#### Page 5, Intellectual Property Rights + +Delete the whole clause. + +### Page 5, Foreword + +Delete the whole clause. + +NOTE – It is replaced by the Foreword of this Recommendation. + +#### Page 6, Clause 1 Scope + +Replace the whole clause with the following: + +#### "1 Scope + +See clause 1 Scope of this Recommendation above." + +#### Page 21, History + +Delete the whole clause. + +### 5.2 Technical modifications + +NOTE – Modifications in the TTCN part of this Recommendation are described in terms of changes in the TTCN.GR representation. + +#### 5.2.1 AAL parameters IE + +In the TTCN, Declarations Part, Test Suite Type Definitions, ASN.1 Type Definitions alter definition for the type "AAL\_contents" as below: + +"OCTET STRING(SIZE(1..2047))". + +NOTE – This limitation may be removed in later versions of the TTCN part. + +## APPENDIX I + +## Bibliography + +- [A] ETSI EN 300 443-1 V1.3.5 (1998), *Broadband Integrated Services Digital Network (B-ISDN); Digital Subscriber Signalling System No. two (DSS2) protocol; B-ISDN user-network interface layer 3 specification for basic call/bearer control; Part 1: Protocol specification*. + +- [B] ETSI EN 301 068-1 V1.2.4 (1998) Broadband Integrated Services Digital Network (B-ISDN); Digital Subscriber Signalling System No. two (DSS2) protocol; Connection characteristics; ATM transfer capability and traffic parameter indication; Part 1: Protocol specification. +- [C] ETSI EN 301 068-2 V1.1.3 (2000), *Broadband Integrated Services Digital Network (B-ISDN); Digital Subscriber Signalling System No. two (DSS2) protocol; Connection characteristics; ATM transfer capability and traffic parameter indication; Part 2: Protocol Implementation Conformance Statement (PICS) proforma specification.* +- [D] ETSI EN 301 068-3 V1.1.2 (2000), *Broadband Integrated Services Digital Network (B-ISDN); Digital Subscriber Signalling System No. two (DSS2) protocol; Connection characteristics; ATM transfer capability and traffic parameter indication; Part 3: Test Suite Structure and Test Purposes (TSS&TP) specification for the user.* +- [E] ETSI EN 301 068-4 V1.1.1 (2000), *Broadband Integrated Services Digital Network (B-ISDN); Digital Subscriber Signalling System No. two (DSS2) protocol; Connection characteristics; ATM transfer capability and traffic parameter indication; Part 4: Abstract Test Suite (ATS) and partial Protocol Implementation eXtra Information for testing (PIXIT) proforma specification for the user.* +- [F] ETSI EN 301 068-5 V1.1.2 (2000), *Broadband Integrated Services Digital Network (B-ISDN); Digital Subscriber Signalling System No. two (DSS2) protocol; Connection characteristics; ATM transfer capability and traffic parameter indication; Part 5: Test Suite Structure and Test Purposes (TSS&TP) specification for the network.* +- [G] ETSI ETS 300 406 (1995), *Methods for Testing and Specification (MTS); Protocol and profile conformance testing specifications; Standardization methodology.* + +### SERIES OF ITU-T RECOMMENDATIONS + +| | | +|-----------------|--------------------------------------------------------------------------------------------------------------------------------| +| Series A | Organization of the work of ITU-T | +| Series B | Means of expression: definitions, symbols, classification | +| Series C | General telecommunication statistics | +| Series D | General tariff principles | +| Series E | Overall network operation, telephone service, service operation and human factors | +| Series F | Non-telephone telecommunication services | +| Series G | Transmission systems and media, digital systems and networks | +| Series H | Audiovisual and multimedia systems | +| Series I | Integrated services digital network | +| Series J | Transmission of television, sound programme and other multimedia signals | +| Series K | Protection against interference | +| Series L | Construction, installation and protection of cables and other elements of outside plant | +| Series M | TMN and network maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits | +| Series N | Maintenance: international sound programme and television transmission circuits | +| Series O | Specifications of measuring equipment | +| Series P | Telephone transmission quality, telephone installations, local line networks | +| Series Q | Switching and signalling | +| Series R | Telegraph transmission | +| Series S | Telegraph services terminal equipment | +| Series T | Terminals for telematic services | +| Series U | Telegraph switching | +| Series V | Data communication over the telephone network | +| Series X | Data networks and open system communications | +| Series Y | Global information infrastructure and Internet protocol aspects | +| Series Z | Languages and general software aspects for telecommunication systems | \ No newline at end of file diff --git a/marked/Q/T-REC-Q.2963.3-199805-I_PDF-E/1a827b10290f33d4fec04d0e8ef7a897_img.jpg b/marked/Q/T-REC-Q.2963.3-199805-I_PDF-E/1a827b10290f33d4fec04d0e8ef7a897_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..597b507a9a74e8d98bc7691ede3038e864c18702 --- /dev/null +++ b/marked/Q/T-REC-Q.2963.3-199805-I_PDF-E/1a827b10290f33d4fec04d0e8ef7a897_img.jpg 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Subscriber Signalling System No. 2 – +Connection modification: ATM traffic descriptor +modification with negotiation by the connection +owner** + +ITU-T Recommendation Q.2963.3 + +(Previously CCITT Recommendation) + +--- + +# ITU-T Q-SERIES RECOMMENDATIONS + +## **SWITCHING AND SIGNALLING** + +| | | +|--------------------------------------------------------------------------------------------------------------|----------------------| +| SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE | Q.1–Q.3 | +| INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING | Q.4–Q.59 | +| FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN | Q.60–Q.99 | +| CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS | Q.100–Q.119 | +| SPECIFICATIONS OF SIGNALLING SYSTEMS No. 4 AND No. 5 | Q.120–Q.249 | +| SPECIFICATIONS OF SIGNALLING SYSTEM No. 6 | Q.250–Q.309 | +| SPECIFICATIONS OF SIGNALLING SYSTEM R1 | Q.310–Q.399 | +| SPECIFICATIONS OF SIGNALLING SYSTEM R2 | Q.400–Q.499 | +| DIGITAL EXCHANGES | Q.500–Q.599 | +| INTERWORKING OF SIGNALLING SYSTEMS | Q.600–Q.699 | +| SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 | Q.700–Q.849 | +| DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 1 | Q.850–Q.999 | +| PUBLIC LAND MOBILE NETWORK | Q.1000–Q.1099 | +| INTERWORKING WITH SATELLITE MOBILE SYSTEMS | Q.1100–Q.1199 | +| INTELLIGENT NETWORK | Q.1200–Q.1999 | +| BROADBAND ISDN | Q.2000–Q.2999 | +| General aspects | Q.2000–Q.2099 | +| Signalling ATM adaptation layer (SAAL) | Q.2100–Q.2199 | +| Signalling network protocols | Q.2200–Q.2299 | +| Common aspects of B-ISDN application protocols for access signalling and network signalling and interworking | Q.2600–Q.2699 | +| B-ISDN application protocols for the network signalling | Q.2700–Q.2899 | +| B-ISDN application protocols for access signalling | Q.2900–Q.2999 | + +For further details, please refer to ITU-T List of Recommendations. + +## **ITU-T RECOMMENDATION Q.2963.3** + +## **DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 2 – CONNECTION MODIFICATION: ATM TRAFFIC DESCRIPTOR MODIFICATION WITH NEGOTIATION BY THE CONNECTION OWNER** + +## **Summary** + +The Q.2963 series of Recommendations belongs to the DSS 2 family of ITU-T Recommendations and specifies the procedure of the modification of traffic parameters of a call/connection in the active state. + +Recommendation Q.2963.3 defines the procedure of the ATM Traffic Descriptor modification with negotiation which is equivalent to that specified in Recommendation Q.2962. + +## **Source** + +ITU-T Recommendation Q.2963.3 was prepared by ITU-T Study Group 11 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on the 15th of May 1998. + +## **Keywords** + +MBS, modification, negotiation, PCR, SCR. + +## FOREWORD + +ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. + +The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1. + +In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. + +## NOTE + +In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +## INTELLECTUAL PROPERTY RIGHTS + +The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. + +As of the date of approval of this Recommendation, the ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. + +© ITU 1998 + +All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. + +## CONTENTS + +###### Page + +| | | | +|-------|-------------------------------------------------------------------------------------------------|---| +| 1 | Scope ..... | 1 | +| 2 | References ..... | 1 | +| 3 | Definitions ..... | 2 | +| 4 | Abbreviations ..... | 2 | +| 5 | Description ..... | 2 | +| 5.1 | Modifiable connections ..... | 2 | +| 5.2 | Modification of a point-to-point connection ..... | 3 | +| 5.3 | Negotiation during modification ..... | 3 | +| 6 | Operational requirements ..... | 3 | +| 6.1 | Provision and withdrawal ..... | 3 | +| 6.2 | Requirements on the originating network side ..... | 4 | +| 6.3 | Requirements on the destination network side ..... | 4 | +| 7 | Primitive and state definitions ..... | 4 | +| 7.1 | Primitive definitions ..... | 4 | +| 7.2 | State definitions ..... | 4 | +| 8 | Coding requirements ..... | 4 | +| 8.1 | Messages ..... | 4 | +| 8.1.1 | MODIFY REQUEST ..... | 4 | +| 8.1.2 | MODIFY ACKNOWLEDGEMENT ..... | 5 | +| 8.1.3 | MODIFY REJECT ..... | 5 | +| 8.1.4 | CONNECTION AVAILABLE ..... | 5 | +| 8.2 | Coding of specific message types and specific information element ..... | 5 | +| 8.2.1 | Coding of specific message type ..... | 5 | +| 8.2.2 | Coding of specific information elements ..... | 5 | +| 9 | Signalling procedures at the coincident S B and T B reference point ..... | 6 | +| 9.1 | Modification procedure at the requesting entity ..... | 6 | +| 9.1.1 | Modification request ..... | 6 | +| 9.1.2 | Modification acknowledgment ..... | 6 | +| 9.1.3 | Indication of modification rejection ..... | 6 | +| 9.1.4 | Response to STATUS messages while in the modify request state ..... | 6 | +| 9.1.5 | No response to modification request ..... | 6 | + +| | Page | | +|---------------|---------------------------------------------------------------------------------------------|----| +| 9.2 | Modification procedures at the responding entity ..... | 7 | +| 9.2.1 | Modification indication..... | 7 | +| 9.2.2 | Modification acceptance ..... | 7 | +| 9.2.3 | Modification confirmation ..... | 8 | +| 9.2.4 | Modification rejection..... | 8 | +| 9.3 | Transit entity conveyance of CONNECTION AVAILABLE messages..... | 9 | +| 10 | Procedures at the T B reference point for interworking with private B-ISDNs..... | 9 | +| 11 | Interworking with other networks ..... | 9 | +| 12 | Interworking with supplementary services..... | 9 | +| 13 | Parameter values..... | 9 | +| 14 | Dynamic description SDLs..... | 9 | +| Appendix I – | Example configuration of user and network behaviour during modification procedures ..... | 10 | +| Appendix II – | Guidelines for the use of the instruction indicator ..... | 12 | + +# **DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 2 – CONNECTION MODIFICATION: ATM TRAFFIC DESCRIPTOR MODIFICATION WITH NEGOTIATION BY THE CONNECTION OWNER** + +*(Geneva, 1998)* + +# **1 Scope** + +This Recommendation specifies the signalling protocol for ATM Traffic Descriptor modification with negotiation for the Broadband Integrated Services Digital Network (B-ISDN) at the $T_B$ reference point or coincident $S_B$ and $T_B$ reference point (as defined in Recommendation I.413 [1]) by means of the Digital Subscriber Signalling System No. 2 (DSS 2). This Recommendation extends the ATM Traffic Descriptor modification capability specified in Q.2963.2 to support the traffic parameter negotiation which is equivalent to that specified in Q.2962. + +In addition, this Recommendation specifies the protocol requirements at the $T_B$ reference point where the service is provided to the user via a private B-ISDN. + +The capability described in this Recommendation enables the connection owner to modify the ATM Traffic Descriptor with negotiation for call/connections that have already been established. This Recommendation specifies the procedure of the modification with negotiation of PCR, SCR and MBS using either an Alternative ATM traffic descriptor information element or a Minimum acceptable ATM traffic descriptor information element. + +ATM Traffic Descriptor modification with negotiation is applicable to all connection oriented telecommunication services that are based on single point-to-point calls/connections. The ATM Traffic Descriptor modification with negotiation for point-to-multipoint calls/connections is outside the scope of this Recommendation. + +This Recommendation is applicable to equipment, supporting ATM Traffic Descriptor modification with negotiation, to be attached at either side of a $T_B$ reference point or coincident $S_B$ and $T_B$ reference point when used as an access to the public B-ISDN. + +# **2 References** + +The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision, all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. + +- [1] ITU-T Recommendation I.413 (1993), *B-ISDN user-network interface*. +- [2] ITU-T Recommendation Q.2931 (1995), *Digital Subscriber Signalling System No. 2 – User-Network interface (UNI) Layer 3 specification for basic call/connection control*. +- [3] ITU-T Recommendation Q.2961.1 (1995), *Digital Subscriber Signalling System No. 2 – Additional traffic parameters: Additional signalling capabilities to support traffic parameters for the tagging option and the sustainable cell rate parameter set*. + +- [4] ITU-T Recommendation Q.2962 (1998), *Digital Subscriber Signalling System No. 2 – Connection characteristics negotiation during call/connection establishment phase.* +- [5] ITU-T Recommendation Q.2963.1 (1996), *Digital Subscriber Signalling System No. 2 – Connection modification: Peak cell rate modification by the connection owner.* +- [6] ITU-T Recommendation Q.2963.2 (1997), *Digital Subscriber Signalling System No. 2 – Connection modification: Modification procedures for sustainable cell rate parameters.* + +# 3 Definitions + +For the purpose of this Recommendation, the definitions in clause 3/Q.2963.1 apply. + +# 4 Abbreviations + +This Recommendation uses the following abbreviations: + +| | | +|--------|-----------------------------------------------| +| ATM | Asynchronous Transfer mode | +| B-ISDN | Broadband Integrated Services Digital Network | +| CLP | Cell Loss Priority | +| MBS | Maximum Burst Size | +| PCR | Peak Cell Rate | +| SCR | Sustainable Cell Rate | +| UNI | User-Network Interface | +| VC | Virtual Channel | + +# 5 Description + +The description given in clause 5/Q.2963.2 shall apply with the following addition: + +- 4) The following negotiation capabilities are applicable in the modification procedure: + - negotiation of sets of traffic parameters in the ATM traffic descriptor using an Alternative ATM traffic descriptor; and + - negotiation of individual traffic parameters in the ATM traffic descriptor using a Minimum acceptable ATM traffic descriptor. + +## 5.1 Modifiable connections + +Subclause 5.1/Q.2963.2 shall apply with the replacement of its fourth paragraph with the following sentences. + +During the modification with negotiation of the ATM traffic descriptor, the following rule applies: + +- *Traffic parameters in the backward direction* +When the entity sends a MODIFY REQUEST message that includes a Minimum acceptable ATM traffic descriptor information element, the traffic descriptor for the connection that applies to this entity's reception until completion of the modification procedure is a traffic descriptor for which the parameter values are determined by taking the maximum of the existing value, the value (if any) specified in the ATM traffic descriptor information element, and the value (if any) specified in the Minimum acceptable ATM traffic descriptor information element. When the entity sends a MODIFY REQUEST message that includes + +an Alternative ATM traffic descriptor information element, the traffic descriptor for the connection that applies to this entity's reception until completion of the modification procedure is a traffic descriptor for which the parameter values are determined by taking the maximum of the existing value, the value (if any) specified in the ATM traffic descriptor information element, and the value (if any) specified in the Alternative ATM traffic descriptor information element. + +### - *Traffic parameters in the forward direction* + +When the entity sends a MODIFY REQUEST message that includes a Minimum acceptable ATM traffic descriptor information element, the traffic descriptor for the connection that applies to this entity's transmission until completion of the modification procedure is a traffic descriptor for which the parameter values are determined by taking the minimum of the existing value, the value (if any) specified in the ATM traffic descriptor information element, and the value (if any) specified in the Minimum Acceptable ATM traffic descriptor information element. + +When the entity sends a MODIFY REQUEST message that includes an Alternative ATM traffic descriptor information element, the traffic descriptor for the connection that applies to this entity's transmission until completion of the modification procedure is a traffic descriptor for which the parameter values are determined by taking the minimum of the existing value, the value (if any) specified in the ATM traffic descriptor information element, and the value (if any) specified in the Alternative ATM traffic descriptor information element. + +## 5.2 Modification of a point-to-point connection + +Subclause 5.2/Q.2963.2 shall apply. + +## 5.3 Negotiation during modification + +This Recommendation supports the traffic parameter negotiation in their modification procedure by using an Alternative ATM traffic descriptor or a minimum acceptable ATM traffic descriptor. + +When an Alternative ATM traffic descriptor is used, the parameters of this information element are handled as a single set, whereas a Minimum acceptable ATM traffic descriptor information element allows the specification of a range of values for parameters which are then handled independently for the selection of their respective value. Both the use of Alternative ATM traffic descriptor information element and of the Minimum acceptable ATM traffic descriptor information element allows negotiation of any relevant ATM-related traffic parameters (i.e. peak cell rate, sustainable cell rate and maximum burst size traffic parameters, depending on the ATM transfer capability actually used for the connections). + +# 6 Operational requirements + +The provision of the connection modification capability is a service provider option. + +## 6.1 Provision and withdrawal + +It is a user and a network option to provide the procedures described in this Recommendation. If implemented, the procedures of this Recommendation may be provided as a subscription option to the served user on the origination side. + +## 6.2 Requirements on the originating network side + +See 6.1 above. + +## 6.3 Requirements on the destination network side + +See 6.1 above. + +# 7 Primitive and state definitions + +## 7.1 Primitive definitions + +Clause 8/Q.2931 shall apply. No additional primitives between DSS 2 layer 3 and the Signalling ATM Adaptation Layer are defined for the purpose of this Recommendation. + +## 7.2 State definitions + +Subclause 7.2/Q.2963.1 shall apply. + +# 8 Coding requirements + +## 8.1 Messages + +For the establishment of call/connections, the messages described in Recommendations Q.2931 and Q.2961 remain valid, and do not have to be enhanced. In order to support the modification with negotiation, the following messages are used. + +- MODIFY REQUEST; +- MODIFY ACKNOWLEDGEMENT; +- MODIFY REJECT; +- CONNECTION AVAILABLE. + +### 8.1.1 MODIFY REQUEST + +This message is sent from the modification requesting entity to the modify responding entity to request modification of a single connection. See Table 8-1 for additions to the structure of this message shown in 8.1.1/Q.2963.1 and in 8.1/Q.2963.2. + +**Table 8-1/Q.2963.3 – MODIFY REQUEST message additional content** + +| Message type: MODIFY REQUEST
Significance: Global
Direction: Both | | | | | +|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------|-----------|----------|--------| +| Information element | Reference | Direction | Type | Length | +| Alternative ATM traffic descriptor | 8.2.1/Q.2962 | Both | O (Note) | 4-28 | +| Minimum acceptable ATM traffic descriptor | 8.2.2/Q.2962 | Both | O (Note) | 4-28 | +| NOTE – Either the Alternative ATM traffic descriptor information element or the Minimum acceptable ATM traffic descriptor information element, but not both, shall be included in the MODIFY REQUEST message when traffic parameters are negotiable. | | | | | + +### 8.1.2 MODIFY ACKNOWLEDGEMENT + +This message is sent by the modification responding entity to indicate that the modify request is accepted. See Table 8-2 for additions to the structure of this message shown in 8.1.2/Q.2963.1. + +**Table 8-2/Q.2963.3 – MODIFY ACKNOWLEDGMENT message additional content** + +| Message type: MODIFY ACKNOWLEDGMENT
Significance: Global
Direction: Both | | | | | +|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------|-----------|----------|--------| +| Information element | Reference | Direction | Type | Length | +| ATM traffic descriptor | 4.5.6/Q.2931
8.2.1/Q.2961.1 | Both | O (Note) | 8-30 | +| NOTE – Included to specify the traffic parameter values allocated for the modification if one or more traffic parameters were negotiable in the MODIFY REQUEST message. | | | | | + +### 8.1.3 MODIFY REJECT + +Subclause 8.1.3/Q.2963.1 shall apply. + +### 8.1.4 CONNECTION AVAILABLE + +Subclause 8.1.4/Q.2963.1 shall apply. + +## 8.2 Coding of specific message types and specific information element + +### 8.2.1 Coding of specific message type + +Subclause 8.2.1/Q.2963.1 shall apply. + +### 8.2.2 Coding of specific information elements + +For the establishment of call/connections, the information elements described in Recommendations Q.2931 and Q.2961 remain valid, and do not have to be enhanced. In order to support the modification with negotiation, the following information elements have to be supported. + +#### 8.2.2.1 Broadband report type + +Subclause 8.2.2/Q.2963.1 shall apply. + +#### 8.2.2.2 Alternative ATM traffic descriptor + +Subclause 8.2.1/Q.2962 shall apply with the replacement of the last paragraph with the following paragraph: + +The Alternative ATM traffic descriptor information element can have any combination of traffic parameters that is allowed for the ATM traffic descriptor information element for the specified broadband bearer capability. Within a single MODIFY REQUEST message, the combination of traffic parameters may be different for these two information elements. However, a traffic parameter can be set in the Alternative ATM traffic descriptor information element only if the traffic parameter was assigned to the connection during connection establishment. The alternative bandwidth requirements must be lesser than the parameter values included in the ATM traffic descriptor. + +#### **8.2.2.3 Minimum acceptable ATM traffic descriptor** + +Subclause 8.2.2/Q.2962 shall apply with the replacement of "SETUP" in the last paragraph with "MODIFY REQUEST". + +# **9 Signalling procedures at the coincident SB and TB reference point** + +NOTE – When the OAM traffic descriptor information element is present, the allocation of bandwidth for OAM flow is based on the ATM traffic descriptor agreed (e.g. as received in the MODIFY ACKNOWLEDGE message.) Since the OAM flow allocation is bidirectional (see Note 2 of Table 4-22/Q.2931) the available user cell rate in one direction can be affected by negotiation of bandwidth in the other direction. + +## **9.1 Modification procedure at the requesting entity** + +### **9.1.1 Modification request** + +Subclause 9.1.1/Q.2963.1 and clause 9/Q.2963.2 shall apply with the following addition: + +The requesting entity initiates the modification with negotiation of the connection characteristics by including, in addition to the ATM traffic descriptor information element, either the Minimum acceptable ATM traffic descriptor information element or the Alternative ATM traffic descriptor information element, but not both, in the MODIFY REQUEST message. In the case of the use of the Alternative ATM traffic descriptor information element, the parameters of the information element are handled as a single entity whereas the Minimum acceptable ATM traffic descriptor information element allows the specification of a range of values for parameters which are handled independently. The alternative bandwidth requirements must be less than the parameter values included in the ATM traffic descriptor. If the Minimum acceptable ATM traffic descriptor information element is used, the traffic parameter values indicated shall be less than the corresponding traffic parameter values specified in the ATM traffic descriptor information element. The traffic parameter values specified in the Minimum acceptable ATM traffic descriptor information can be either greater or less than the existing values. + +### **9.1.2 Modification acknowledgment** + +Subclause 9.1.2/Q.2963.1 shall apply with the following addition: + +In case of modification with negotiation, a transit entity and a terminating entity shall allocate the resources which correspond to the ATM traffic descriptor included in the MODIFY ACKNOWLEDGE message. If an ATM traffic descriptor is not included in the MODIFY ACKNOWLEDGMENT message, the ATM traffic descriptor in the MODIFY REQUEST message shall be used for resource allocation. + +### **9.1.3 Indication of modification rejection** + +Subclause 9.1.3/Q.2963.1 shall apply. + +### **9.1.4 Response to STATUS messages while in the modify request state** + +Subclause 9.1.4/Q.2963.1 shall apply. + +### **9.1.5 No response to modification request** + +Subclause 9.1.5/Q.2963.1 shall apply. + +## **9.2 Modification procedures at the responding entity** + +### **9.2.1 Modification indication** + +Subclause 9.2.1/Q.2963.1 and clause 9/Q.2963.2 shall apply with the following addition: + +In case of modification with negotiation, the MODIFY REQUEST message may include the Alternative ATM traffic descriptor or the Minimum acceptable ATM traffic descriptor in addition to the ATM traffic descriptor. + +### **9.2.2 Modification acceptance** + +Subclause 9.2.2/Q.2963.1 and clause 9/Q.2963.2 shall apply with the following addition: + +In case of modification with negotiation, the MODIFY REQUEST message may include the Alternative ATM traffic descriptor or the Minimum acceptable ATM traffic descriptor in addition to the ATM traffic descriptor. + +When the Minimum acceptable ATM traffic descriptor information element is included in the MODIFY REQUEST message and the responding entity is able to provide the traffic parameter values specified in the ATM traffic descriptor information element, the entity shall: + +- if a transit entity: + - progress the modification request with both the ATM traffic descriptor information element and the Minimum acceptable ATM traffic descriptor information element; +- if a terminating entity: + - progress the modification request with the ATM traffic descriptor information element. + +When the Alternative ATM traffic descriptor information element is included in the MODIFY REQUEST message and the responding entity is able to provide the traffic parameter values specified in the ATM traffic descriptor information element and the entity is able to provide the traffic parameter values specified in the Alternative ATM traffic descriptor information element, the entity shall: + +- if a transit entity: + - progress the modification request with both the ATM traffic descriptor information element and the Alternative ATM traffic descriptor information element; +- if a terminating entity: + - progress the modification request with the ATM traffic descriptor information element. + +When the Alternative ATM traffic descriptor information element is included in the MODIFY REQUEST message and the responding entity is able to provide the traffic parameter values specified in the ATM traffic descriptor information element and the entity is not able to provide the traffic parameter values specified in the Alternative ATM traffic descriptor information element, the entity shall progress the modification request with the ATM traffic descriptor information element and without the Alternative ATM traffic descriptor information element. + +#### **9.2.2.1 Minimum acceptable ATM traffic parameter negotiation** + +If the responding entity is not able to provide some of the traffic parameter values indicated in the ATM traffic descriptor information element and the Minimum acceptable ATM traffic descriptor information element is included, the following procedures shall apply: + +If the responding entity is not able to provide some of the traffic parameter values indicated in the ATM traffic descriptor information element but is able to provide at least their corresponding traffic parameter values in the Minimum acceptable ATM traffic descriptor information element, the + +responding entity shall progress the modification request after adjusting the traffic parameter values in the ATM traffic descriptor information element to the values which can be supported. The adjusted parameter values will support at least the corresponding minimum acceptable values. The responding entity shall act as follows: + +- if a transit entity: + - if some of the parameters in the Minimum acceptable ATM traffic descriptor information element are still less than the corresponding parameters in the modified ATM traffic descriptor information element, then the modification shall be progressed with the Minimum acceptable ATM traffic descriptor information element containing all such parameters, in addition to the adjusted ATM traffic descriptor information element. Otherwise, the modification shall progress with the adjusted ATM traffic descriptor information element and without the Minimum acceptable ATM traffic descriptor information element; +- if a terminating entity: + - the modification shall be progressed with the adjusted ATM traffic descriptor information element. + +If the responding entity is not able to provide at least the traffic parameter values indicated in the Minimum acceptable ATM traffic descriptor information element, the responding entity shall reject the modification request. + +#### **9.2.2.2 Alternative traffic parameter negotiation** + +If the responding entity is not able to provide some of the traffic parameter values indicated in the ATM traffic descriptor information element and the Alternative ATM traffic descriptor information element is included, the following procedures shall apply: + +If the responding entity is not able to provide the ATM traffic descriptor indicated in the ATM traffic descriptor information element but is able to provide the ATM traffic descriptor indicated in the Alternative ATM traffic descriptor information element, the responding entity shall progress the modification request by using the contents of the Alternative ATM traffic descriptor information element as the ATM traffic descriptor. + +If the responding entity can provide neither the ATM traffic descriptor indicated in the ATM traffic descriptor information element nor the ATM traffic descriptor indicated in the Alternative ATM traffic descriptor information element, the responding entity shall reject the modification request. + +The MODIFY ACKNOWLEDGE message returned by the terminating entity shall include the ATM traffic descriptor which indicates the finally accepted parameters. The transit entity shall allocate the resources which correspond to this ATM traffic descriptor. If the ATM traffic descriptor is not included in the MODIFY ACKNOWLEDGMENT message, the transit entity shall use the ATM traffic descriptor in the MODIFY REQUEST message for resource allocation. + +### **9.2.3 Modification confirmation** + +Subclause 9.2.3/Q.2963.1 shall apply. + +### **9.2.4 Modification rejection** + +Subclause 9.2.4/Q.2963.1 shall apply with the following addition: + +When both the Minimum acceptable ATM traffic descriptor and the Alternative ATM traffic descriptor information elements are present in a MODIFY REQUEST message, the modification request shall be rejected with cause #73, "unsupported combination of traffic parameters". + +If the parameters of the Alternative ATM traffic descriptor information element or Minimum acceptable ATM traffic descriptor information element are not according to the allowed combinations as specified in 8.2.2.2 and 8.2.2.3 respectively, the network shall handle these information elements as if they were non-mandatory information elements with content error as specified in 5.6.8/Q.2931. + +## **9.3 Transit entity conveyance of CONNECTION AVAILABLE messages** + +Subclause 9.3/Q.2963.1 shall apply. + +# **10 Procedures at the TB reference point for interworking with private B-ISDNs** + +The procedures specified in clause 9/Q.2963.2 shall apply. + +# **11 Interworking with other networks** + +No interworking with other networks has been identified. + +# **12 Interworking with supplementary services** + +Clause 12/Q.2963.2 shall apply. + +# **13 Parameter values** + +The parameter values specified in clause 13/Q.2963.1 shall apply. + +# **14 Dynamic description SDLs** + +The SDLs specified in clause 14/Q.2963.1 shall apply. + +# APPENDIX I + +## Example configuration of user and network behaviour during modification procedures + +These examples show the configuration in which both the initiating and the addressed users are terminating entities. + + + +The diagram illustrates the interaction between an Initiating User, a Network, and an Addressed User during a modification procedure. The sequence of messages is as follows: + +- The Initiating User sends a **MODIFY REQUEST** to the Network. +- The Network forwards the **MODIFY REQUEST** to the Addressed User. +- The Addressed User responds with a **MODIFY ACKNOWLEDGE** to the Network. +- The Network forwards the **MODIFY ACKNOWLEDGE** to the Initiating User. + +Parameter changes are indicated by specific symbols and arrow types: + +- Forward UPC change:** Indicated by a square with a diagonal line from top-left to bottom-right. +- Backward UPC change:** Indicated by a square with a diagonal line from bottom-left to top-right. +- Change of applied forward ATM traffic parameters:** Indicated by a circle with a diagonal line from top-left to bottom-right. +- Change of applied backward ATM traffic parameters:** Indicated by a circle with a diagonal line from bottom-left to top-right. +- Parameter value changes:** + - Increase:** Dashed upward arrow (ATM traffic descriptor IE value) or solid upward arrow (up to finally accepted value). + - Decrease:** Dashed downward arrow (ATM traffic descriptor IE value) or solid downward arrow (down to finally accepted value). +- CAC change:** Indicated by a box containing 'R/A'. +- Network internal actions:** + - Reservation of resources (R):** Shown in a box within the Network entity. + - Allocation of resources (A):** Shown in a box within the Network entity. + +T1199130-98 + +Sequence diagram showing the procedure of modification without request of connection acknowledgement between an Initiating User, a Network, and an Addressed User. The diagram includes message exchanges (MODIFY REQUEST, MODIFY ACKNOWLEDGE) and various parameter change indicators (UPC, ATM traffic parameters, CAC). + +**Figure I.1/Q.2963.3 – Procedure of modification without request of connection acknowledgement** + + + +The diagram illustrates the interaction between an Initiating User, a Network, and an Addressed User for modifying a connection. The sequence of messages is as follows: + +- MODIFY REQUEST:** The Initiating User sends a request to the Network. The Network then forwards this request to the Addressed User. The request includes icons for forward and backward ATM traffic parameter changes, and a box containing 'R' (Reservation of resources). +- MODIFY ACKNOWLEDGE:** The Addressed User responds with an acknowledgement. The Network receives this and forwards it back to the Initiating User. This message includes icons for forward and backward ATM traffic parameter changes, and a box containing 'A' (Allocation of resources). +- CONNECTION AVAILABLE:** Finally, the Network sends a 'CONNECTION AVAILABLE' message to the Addressed User, indicated by a forward ATM traffic parameter change icon. + +**Legend:** + +- Forward UPC change +- Backward UPC change +- Change of applied forward ATM traffic parameters +- Change of applied backward ATM traffic parameters +- Increase of any parameter based on the value specified in the ATM traffic descriptor IE and the value (if any) specified in the Alternative ATM traffic descriptor IE +- Decrease of any parameter based on the value specified in the ATM traffic descriptor IE and the value (if any) specified in the Alternative or Minimum Acceptable ATM traffic descriptor IE +- Increase of any parameter up to the finally accepted value +- Decrease of any parameter down to the finally accepted value +- R/A** CAC change +**R** Reservation of resources +**A** Allocation of resources + +T1199140-98 + +Sequence diagram showing the procedure of modification with request of connection acknowledgement between an Initiating User, Network, and Addressed User. The diagram includes message exchanges for MODIFY REQUEST, MODIFY ACKNOWLEDGE, and CONNECTION AVAILABLE, with various icons indicating parameter changes and resource actions. Forward UPC change icon Backward UPC change icon Change of applied forward ATM traffic parameters icon Change of applied backward ATM traffic parameters icon Upward dashed arrow icon Downward dashed arrow icon Upward solid arrow icon Downward solid arrow icon + +**Figure I.2/Q.2963.3 – Procedure of modification with request of connection acknowledgement** + +# APPENDIX II + +## **Guidelines for the use of the instruction indicator** + +It is suggested that the instruction indicator for the alternative ATM traffic indicator and minimum acceptable ATM traffic descriptor information elements be encoded to indicate "discard, proceed and report status". + +# ITU-T RECOMMENDATIONS SERIES + +| | | +|-----------------|--------------------------------------------------------------------------------------------------------------------------------| +| Series A | Organization of the work of the ITU-T | +| Series B | Means of expression: definitions, symbols, classification | +| Series C | General telecommunication statistics | +| Series D | General tariff principles | +| Series E | Overall network operation, telephone service, service operation and human factors | +| Series F | Non-telephone telecommunication services | +| Series G | Transmission systems and media, digital systems and networks | +| Series H | Audiovisual and multimedia systems | +| Series I | Integrated services digital network | +| Series J | Transmission of television, sound programme and other multimedia signals | +| Series K | Protection against interference | +| Series L | Construction, installation and protection of cables and other elements of outside plant | +| Series M | TMN and network maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits | +| Series N | Maintenance: international sound programme and television transmission circuits | +| Series O | Specifications of measuring equipment | +| Series P | Telephone transmission quality, telephone installations, local line networks | +| Series Q | Switching and signalling | +| Series R | Telegraph transmission | +| Series S | Telegraph services terminal equipment | +| Series T | Terminals for telematic services | +| Series U | Telegraph switching | +| Series V | Data communication over the telephone network | +| Series X | Data networks and open system communications | +| Series Y | Global information infrastructure | +| Series Z | Programming languages | \ No newline at end of file diff --git a/marked/Q/T-REC-Q.2965.1B-200012-I_PDF-E/2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg b/marked/Q/T-REC-Q.2965.1B-200012-I_PDF-E/2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..104a57fbd03964ffd2520508b2be42e03343d20f --- /dev/null +++ b/marked/Q/T-REC-Q.2965.1B-200012-I_PDF-E/2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid 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b/marked/Q/T-REC-Q.3059-202009-I_PDF-E/raw.md @@ -0,0 +1,468 @@ + + +**ITU-T** + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +**Q.3059** + +(09/2020) + +SERIES Q: SWITCHING AND SIGNALLING, AND +ASSOCIATED MEASUREMENTS AND TESTS + +Signalling requirements and protocols for the NGN – +Network signalling and control functional architecture + +# --- **Signalling requirements for service function discovery** + +Recommendation ITU-T Q.3059 + +## ITU-T Q-SERIES RECOMMENDATIONS **SWITCHING AND SIGNALLING, AND ASSOCIATED MEASUREMENTS AND TESTS** + +| | | +|---------------------------------------------------------------------------------------------|----------------------| +| SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE | Q.1–Q.3 | +| INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING | Q.4–Q.59 | +| FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN | Q.60–Q.99 | +| CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS | Q.100–Q.119 | +| SPECIFICATIONS OF SIGNALLING SYSTEMS No. 4, 5, 6, R1 AND R2 | Q.120–Q.499 | +| DIGITAL EXCHANGES | Q.500–Q.599 | +| INTERWORKING OF SIGNALLING SYSTEMS | Q.600–Q.699 | +| SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 | Q.700–Q.799 | +| Q3 INTERFACE | Q.800–Q.849 | +| DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 1 | Q.850–Q.999 | +| PUBLIC LAND MOBILE NETWORK | Q.1000–Q.1099 | +| INTERWORKING WITH SATELLITE MOBILE SYSTEMS | Q.1100–Q.1199 | +| INTELLIGENT NETWORK | Q.1200–Q.1699 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2000 | Q.1700–Q.1799 | +| SPECIFICATIONS OF SIGNALLING RELATED TO BEARER INDEPENDENT CALL CONTROL (BICC) | Q.1900–Q.1999 | +| BROADBAND ISDN | Q.2000–Q.2999 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR THE NGN | Q.3000–Q.3709 | +| General | Q.3000–Q.3029 | +| Network signalling and control functional architecture | Q.3030–Q.3099 | +| Network data organization within the NGN | Q.3100–Q.3129 | +| Bearer control signalling | Q.3130–Q.3179 | +| Signalling and control requirements and protocols to support attachment in NGN environments | Q.3200–Q.3249 | +| Resource control protocols | Q.3300–Q.3369 | +| Service and session control protocols | Q.3400–Q.3499 | +| Service and session control protocols – supplementary services | Q.3600–Q.3616 | +| Service and session control protocols – supplementary services based on SIP-IMS | Q.3617–Q.3639 | +| VoLTE/ViLTE network signalling | Q.3640–Q.3655 | +| NGN applications | Q.3700–Q.3709 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR SDN | Q.3710–Q.3899 | +| TESTING SPECIFICATIONS | Q.3900–Q.4099 | +| PROTOCOLS AND SIGNALLING FOR P2P COMMUNICATIONS | Q.4100–Q.4139 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2020 | Q.5000–Q.5049 | +| COMBATING COUNTERFEITING AND STOLEN ICT DEVICES | Q.5050–Q.5069 | + +*For further details, please refer to the list of ITU-T Recommendations.* + +## Recommendation ITU-T Q.3059 + +# Signalling requirements for service function discovery + +## Summary + +Recommendation ITU-T Q.3059 specifies the signalling requirements for service function discovery based on its functional architecture. The signalling is for the service function path controller to discover and select the service function. + +## History + +| Edition | Recommendation | Approval | Study Group | Unique ID* | +|---------|----------------|------------|-------------|---------------------------------------------------------------------------| +| 1.0 | ITU-T Q.3059 | 2020-09-29 | 11 | 11.1002/1000/14412 | + +## Keywords + +Service function, service function discovery, signalling requirements. + +--- + +\* To access the Recommendation, type the URL
– The IP address of the user equipment used by the subscriber for which profile information is being pushed.
– The addressing domain in which the IP address is significant. | +| Address realm | | | | +| Transport subscriber identifier | User-Name | C | The user that is attached to the network. | +| SCE identity | SCE-Application-Identifier | M | Identifies the SCE originating the request. | +| Requested items | Requested-Information | O | The list of items requested by the SCE. | + +**Table 7-2 – Information query response** + +| Information Element name | Mapping to Diameter AVP | Cat. | Description | +|---------------------------------|-------------------------------------|------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +| Result | Result-Code/
Experimental-Result | M | Result of the request.
Result-Code AVP shall be used for errors defined in the Diameter Base Protocol.
Experimental-Result AVP shall be used for other errors. This is a grouped AVP which contains the 3GPP Vendor ID in the Vendor-Id AVP, and the error code in the Experimental-Result-Code AVP. | +| Transport subscriber identifier | User-Name | O | The user that is attached to the network. | +| Location information | Location-Information | O | Location information (or a pointer to such information) in a form that is suitable for the requesting application. | +| RACE contact point | RACE-Contact-Point | O | The FQDN or IP address of the RACE where resource request shall be sent (i.e., PD-PE address). | +| Access transport network type | Access-Network-Type | O | The type of access network over which IP connectivity is provided to the user equipment. | +| CPE type | CPE-Type | O | The type of user equipment to which the IP address was allocated. | +| IP connectivity status | IP-connectivity-status | O | The status of IP connectivity to/from the user equipment. | +| Physical connection identifier | Physical-Connection-Identifier | O | A local identifier for physical connection of access transport network to which the CPE is attached to (e.g., IP address of PE-FE device, and MAC address or link ID and physical port). | +| Logical connection identifier | Logical-Connection-Identifier | O | A local identifier for logical connection of access transport network to which the CPE is connected (e.g., ATM VPI/VCI, PPP, MPLS label, GTP tunnel and logical port). It can be used to locate the layer 2 connection and pertinent network devices for a particular attached CPE. | + +#### 7.2.1.2 Procedure at the SCE side + +The SCE shall request the information query request by including the following information elements: + +- 1) Either a Globally-Unique-Address AVP or a User-Name AVP will be present. The Globally-Unique-Address AVP shall contain a Frame-IP-Address or Frame-IPv6-Prefix AVP value and an Address-Realm AVP. The Address-Realm AVP shall be obtained from predefined configuration data in SCE. In case of configuration data, all terminal equipments served by a SCE have the same addressing domain. +- 2) The SCE-Application-Identifier AVP shall be present. +- 3) The Requested-Information AVP shall be present if specific information is requested and shall be absent if all available information is requested. + +The requested information AVP may be absent or present, depending on requests. In Annex A, there are some examples of scenarios which show the requested information AVP is used in S-TC1. + +Case 1) shows NACE-SCE bundled authentication scenario in fixed access network. In bundled authentication, the network authentication implies service authentication. After successful NACE authentication, access line information is stored to TUP-PE. This line information is compared with that of SUP-PE in service authentication. In bundled authentication environment, P-CSC-PE shall send information request to TLM-PE to request line information by using IP address as a key of Requested-Information AVP. TLM-PE will fetch line information corresponding to the IP address and send the line information as location information response. + +Case 2) shows NACE-SCE bundled authentication scenario in both fixed and mobile access network. SCE will request authentication data as a Requested-Information AVP. The Requested-Information AVP will be authentication data bound to IP address. Because access point information varies in mobile access network, bundled authentication shall be completed by checking authentication data between TUP-PE and SUP-PE. + +Case 3) shows the case in which SCE requests address of PD-PE for QoS service. SCE needs QoS policy to provide QoS-based service and TLM-PE keeps the contact point of policy server that is PD-PE. P-CSC-PE sends information query to TLM-PE to request the address of PD-PE in Requested-Information AVP. TLM-PE will send back to P-CSC-PE with the address of PD-PE as information response. + +Case 4) shows a scenario of location-based service. When a user is looking for a hospital, location-based service will recommend a closest hospital geographically. To recognize the user's location, the service will make use of the user's authentication data, IP address and line information. + +#### 7.2.1.3 Procedure at the TLM-PE side + + + +``` + +graph TD + Start([NULL]) --> Step1[Check both Globally-Unique-Address AVP & User-Name AVP] + Step1 --> Decision1{Is Globally-Unique-Address AVP present?} + Decision1 -- No --> Decision2{Is User-Name AVP present?} + Decision2 -- No --> Response1[Return an Information Response with Result-Code = DIAMETER_MISSING_AV] + Decision2 -- Yes --> Decision3{Does Subscriber Identity matching User-Name AVP exist?} + Decision3 -- No --> Response2[Return an Information Response with Result-Code = DIAMETER_ERROR_USER_UNKNOWN] + Decision3 -- Yes --> Decision4{The Number of Subscriber Identity matching User-Name AVP > 1} + Decision4 -- No --> Response3[Return an Information Response with Result-Code = DIAMETER_UNABLE_TO_COMPLY] + Decision4 -- Yes --> Decision5{Under temporary overload conditions?} + Decision5 -- Yes --> Response4[Return an Information Response with Experimental-Result-Code = DIAMETER_USER_DATA_NOT_AVAILABLE] + Decision5 -- No --> Decision6{Database error or other error?} + Decision6 -- Yes --> Response5[Return an Information Response with Result-Code = DIAMETER_UNABLE_TO_COMPLY] + Decision6 -- No --> Step2[Check which session data can be returned to SCE from Requested-Information AVP, based on local policy rules and per-subscriber privacy information] + Step2 --> Response6[Return an Information Response with Result-Code = DIAMETER_SUCCESS] + +``` + +Q3221(08)\_F7.1 + +Flowchart of the procedure at the TLM-PE side for a location query. The process starts with NULL, checks for Globally-Unique-Address AVP and User-Name AVP, then evaluates subscriber identity matching and overload conditions to determine the appropriate response code. + +**Figure 7-1 – Procedure side for location query on the TLM-PE side** + +- 1) First, check both Globally-Unique-Address AVP and User-Name AVP. +- 2) If the Globally-Unique-Address AVP is present, go to step 6) to use this information as a key to retrieve the requested session information. Otherwise, go to the next step. +- 3) If the Globally-Unique-Address AVP is absent but the User-Name AVP is present, go to step 5) to use the latter information as a key to retrieve the requested session information. Otherwise, go to the next step. +- 4) Because both the Globally-Unique-Address AVP and the User-Name AVP are absent, return an information query response with Result-Code set to DIAMETER\_MISSING\_AV and stop this procedure. +- 5) If more than one record include the same subscriber identity matching the value of the User-Name AVP and no Globally-Unique-Address AVP is included, return an information query response with Result-Code set to DIAMETER\_UNABLE\_TO\_COMPLY and stop this procedure. Otherwise, go to the next step. +- 6) If no session record is stored for the Globally-Unique-Address AVP or the User-Name AVP, return an information query with the Experimental-Result-Code AVP set to DIAMETER\_ERROR\_USER\_UNKNOWN and stop this procedure. Otherwise, go to the next step. + +- 7) Under temporary overload conditions, the TLM-PE shall stop processing the request and return an information query response with the Experimental-Result-Code set to DIAMETER\_USER\_DATA\_NOT\_AVAILABLE and stop this procedure. The SCE may retry retrieving the required information at a later stage. Otherwise, go to the next step. +- 8) If the TLM-PE cannot fulfil the received request for reasons not stated in the above steps, e.g., due to database error, it shall stop processing the request and set the Result-Code to DIAMETER\_UNABLE\_TO\_COMPLY. +- 9) Check which session data can be returned to the SCE, based on local policy rules and per-subscriber privacy information stored in the TLM-PE. If the session data to be retrieved is currently being updated by another entity, the TLM-PE may delay the response message until the update has been completed and shall include in the response message the updated data requested. The requested operation shall take place and the TLM-PE shall return the Result-Code AVP set to DIAMETER\_SUCCESS and the session data in the information query response and stop this procedure. + +### 7.2.2 Event registration + +#### 7.2.2.1 Overview + +This procedure is used by an SCE to subscribe with the TLM-PE to a particular event. This procedure is mapped to the commands Subscribe-Notifications-Request/Answer defined in the Diameter application specified in Sh interface [ETSI TS 129 329]. Tables 7-3 and 7-4 detail the involved information elements as identified in the NACE and their mapping to Diameter AVPs. + +**Table 7-3 – Event registration request** + +| Information element name | Mapping to Diameter AVP | Cat. | Description | +|---------------------------------|----------------------------|------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +| | Subs-Req-Type | M | Indicates whether the SCE is willing to subscribe or unsubscribe to the notification of the event. | +| Unique IP address | Globally-unique-Address | C | This information element contains:
– The IP address of the user equipment used by the subscriber for which profile information is being pushed.
– The addressing domain in which the IP address is significant. | +| Address realm | | | | +| Transport subscriber identifier | User-Name | C | The user that is attached to the network. | +| Subscription duration | Expiry-Time | O | Duration for which the subscription to the event will be active. | +| Event | Event-Type | M | The type of event to be monitored. | +| SCE identity | SCE-Application-Identifier | M | Identifies the SCE originating the request. | + +**Table 7-4 – Event registration response** + +| Information element name | Mapping to Diameter AVP | Cat. | Description | +|--------------------------|-------------------------------------|------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +| Result | Result-Code/
Experimental-Result | M | Result of the request.
Result-Code AVP shall be used for errors defined in the Diameter Base Protocol.
Experimental-Result AVP shall be used for other errors. This is a grouped AVP which contains the 3GPP Vendor ID in the Vendor-Id AVP, and the error code in the Experimental-Result-Code AVP. | +| | Expiry-Time | O | Acknowledges the absolute time at which the subscription expires. | + +The TLM-PE monitors events related to access sessions. Monitoring of a particular event on a particular session is activated when at least one application function has subscribed to be notified of the occurrence of the event. Subscription to an event may be done implicitly (i.e., through management operations) or explicitly using the event registration/deregistration request. Subscription to an event ceases when one of the following conditions is met: + +- Expiry of the subscription duration. +- Removal of the session record from the TLM-PE. +- Receipt of an explicit request to unsubscribe. + +#### **7.2.2.2 Procedure at the SCE side** + +The SCE shall populate the event registration request as follows: + +- 1) Insert a Subs-Req-Type AVP indicating whether it is willing to subscribe or unsubscribe to the notification of events. +- 2) Insert either a Globally-Unique-Address or a User-Name AVP. The Globally-Unique-Address AVP shall contain a Frame-IP-Address or Frame-IPv6-Prefix AVP value, and an Address-Realm AVP. The Address-Realm AVP shall be included and set either using configuration data (in which case all user equipment served by the SCE is assumed to belong to the same addressing domain) or from the physical or logical interface over which was received a related service request. +- 3) The SCE-Application-Identifier AVP shall be present. +- 4) At least one occurrence of the Event-Type AVP shall be present. +- 5) The Expiry-Time AVP may be present. + +#### **7.2.2.3 Procedure at the TLM-PE side** + +Upon reception of an event registration/deregistration request, the TLM-PE shall, in the following order: + +- 1) Based on the contents of the SCE-Application-Identifier AVP, check whether the SCE is allowed to request monitoring of events. If not, return an event registration response with Result-Code set to DIAMETER\_ERROR\_OPERATION\_NOT\_ALLOWED. +- 2) If the Globally-Unique-Address AVP is present, use this information as a key to identify the session for which event monitoring is being requested. +- 3) If the Globally-Unique-Address AVP is absent but the User-Name AVP is present, use the latter information as a key to the session(s) for which event monitoring is being requested. + +- 4) If both the Globally-Unique-Address AVP and the User-Name AVP are absent, return an event registration/deregistration response with the Result-Code AVP set to DIAMETER\_MISSING\_AVP. +- 5) If no stored session record matches the Globally-Unique-Address AVP or the User-Name AVP and the requested event differs from USER-LOGON, return an event registration response with the Experimental-Result-Code AVP set to DIAMETER\_ERROR\_USER\_UNKNOWN. If the Subs-Req-Type AVP indicates that this is a request to subscribe to the notification of events, the TLM-PE shall check whether the requested event can be reported to the SCE, based on local policy rules and per-subscriber privacy information received from the TAA-PE. If the SCE is not allowed to request monitoring of the event, return an event registration/deregistration response with Result-Code set to DIAMETER\_ERROR\_OPERATION\_NOT\_ALLOWED. If the SCE is allowed to request monitoring of the event, the TLM-PE shall: + - For all session records matching the request, associate the SCE-Application-Identifier with the list of entities that need to be notified when the event identified by the request occurs. The association lasts for the duration indicated by the value of the Expiry-Time AVP as returned to the SCE. If no Expiry-Time AVP is supplied, the TLM-PE should treat it as a request for an unlimited subscription. + - Include in the event registration response an Expiry-Time AVP with the absolute time at which the subscription expires in the case of a successful subscription. This time may be earlier than the requested expiry time. If the TLM-PE includes this AVP, then no notification shall be sent to the SCE after the expiration time. If the TLM-PE does not include this AVP, that indicates an unlimited subscription. + - Set the Result-Code to DIAMETER\_SUCCESS and return an event registration/deregistration response. + +If the Subs-Req-Type AVP indicates that this is a request to unsubscribe to the notification of events, the TLM-PE shall remove the association of the SCE-Identifier with the same list. The Result-Code shall be set to DIAMETER\_SUCCESS if the operation is successful or if the SCE-Identifier was not present in the list. If the Event-Type AVP is absent, the TLM-PE assumes that the SCE is willing to unsubscribe to all events associated with the User-Name or Globally-Unique-Address AVP. + +If a subsequent request is received by the TLM-PE where the Expiry-Time AVP is present but different from what the TLM-PE has previously stored, the TLM-PE should replace the stored expiration time with what was received in the request. + +If the TLM-PE cannot fulfil the received request for reasons not stated in the above steps, e.g., due to database error, it shall stop processing the request and set the Result-Code to DIAMETER\_UNABLE\_TO\_COMPLY. + +### 7.2.3 Notification event + +#### 7.2.3.1 Overview + +This procedure is used by a TLM-PE to notify the SCE of the occurrence of a particular event. This procedure is mapped to the commands Push-Notifications-Request/Answer in the Diameter application specified in Sh interface [ETSI TS 129 329]. Tables 7-5 and 7-6 detail the involved information elements as defined in the NACE and their mapping to Diameter AVPs. + +**Table 7-5 – Notification event request** + +| Information element name | Mapping to Diameter AVP | Cat. | Description | +|---------------------------------|----------------------------|------|----------------------------------------------------------------------------------------------------------------------------------------------------| +| Unique IP address | Globally-unique-Address | C | This information element contains:
– The IP address of the user equipment used by the subscriber for which profile information is being pushed. | +| Address realm | | | – The addressing domain in which the IP address is significant. | +| Transport subscriber identifier | User-Name | C | The user that is attached to the network. | +| SCE identity | SCE-Application-Identifier | M | Identifies the SCE originating the request. | +| Event | Event-Type | M | The type of event to be monitored. | +| | [AVP] | O | AVPs carrying TLM-PE information associated to the reported event. | + +**Table 7-6 – Notification event response** + +| Information element name | Mapping to Diameter AVP | Cat. | Description | +|--------------------------|-------------------------------------|------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +| Result | Result-Code/
Experimental-Result | M | Result of the request.
Result-Code AVP shall be used for errors defined in the Diameter Base Protocol.
Experimental-Result AVP shall be used for other errors. This is a grouped AVP which contains the 3GPP Vendor ID in the Vendor-Id AVP, and the error code in the Experimental-Result-Code AVP. | + +#### **7.2.3.2 Procedure at the TLM-PE side** + +When a monitored event is detected on a particular access session, the TLM-PE issues an event notification request to each of the application functions having registered to this event. + +The event notification request is populated as follows: + +- 1) At least a Globally-Unique-Address or a User-Name AVP shall be included. The Globally-Unique-Address AVP shall contain a Frame-IP-Address or Frame-IPv6-Prefix AVP value, and an Address-Realm AVP. The Address-Realm AVP shall be included and set either using configuration data (in which case all terminal equipment served by the SCE belongs to the same addressing domain) or from the physical or logical interface over which was received a related service request. +- 2) The SCE-Application-Identifier AVP shall be present. +- 3) One or more occurrence of the Event-Type AVP indicating the type of events being notified. + +Based on local policy rules and per-subscriber privacy information previously received from the TAA-PE, the TLM-PE may also include additional information in the event registration/deregistration request. Table 7-7 provides an indication of the AVPs that may be returned for each event. + +**Table 7-7 – Request-Information to AVP mapping** + +| Event | AVP | +|-----------------------------------------|---------------------------------| +| USER-LOGON | IP-Connectivity-Status | +| LOCATION-INFORMATION-CHANGED | Location-Information | +| RACE-CONTACT-POINT-CHANGED | RACE-Contact-Point | +| ACCESS-NETWORK-TYPE-CHANGED | Access-Network-Type | +| CPE-TYPE-CHANGED | CPE-Type | +| LOGICAL-CONNECTION-IDENTIFIER-CHANGED | Logical-Connection-Identifier | +| PHYSICAL-CONNECTION-IDENTIFIER-CHANGED | Physical-Connection-Identifier | +| DEFAULT-CONFIGURATION-CHANGED | Default-Configuration | +| TRANSPORT-RESOURCE-SUBSCRIPTION-CHANGED | Transport-Resource-Subscription | +| IP-ADDRESS-CHANGED | Globally-Unique-Address | +| USER-LOGOFF | IP-Connectivity-Status | + +#### 7.2.3.3 Procedure at the SCE side + +Upon reception of a notification event request, the SCE shall: + +- 1) If neither the globally unique identifier contained in the Globally-Unique-Address AVP nor the subscriber identifier contained in the User-Name AVP are known, return a notification event response with a Result-Code AVP value set to DIAMETER\_ERROR\_USER\_UNKNOWN. +- 2) If the event type contained in the Event-Type AVP is not known, return a notification event response with a Result-Code AVP value set to DIAMETER\_INVALID\_AVP\_VALUE. +- 3) If the event type contained in the Event-Type AVP is known but was not expected, return a notification event response with a Result-Code AVP value set to DIAMETER\_ERROR\_NO\_SUBSCRIPTION\_TO\_DATA. + +If the SCE cannot process the event for reasons not stated in the above steps, return a notification event response with a Result-Code AVP value set to DIAMETER\_UNABLE\_TO\_COMPLY or an Experimental-Result-Code AVP set to DIAMETER\_SYSTEM\_UNAVAILABLE. In the latter case, the TLM-PE is expected to retry after a provisioned time period. After a provisioned number of unsuccessful retries, the TLM-PE is expected to delete the SCE-Identity from the list of application functions registered to the event. + +Otherwise, the event shall be processed and the SCE shall return the Result-Code AVP set to DIAMETER\_SUCCESS in the notification event response. + +# 8 Use of the Diameter base protocol + +With the clarifications listed in the following clauses, the Diameter base protocol defined by [IETF RFC 3588] shall apply. + +## 8.1 Securing Diameter messages + +For secure transport of Diameter messages, IPSec may be used. Guidelines on the use of SCTP with IPSec can be found in [IETF RFC 3554]. + +## 8.2 Accounting functionality + +Accounting functionality (accounting session state machine, related command codes and AVPs) is not used on the S-TC1 interface. + +## 8.3 Use of sessions + +Diameter sessions are implicitly terminated. An implicitly terminated session is one for which the server does not maintain state information. The client does not need to send any re-authorization or session termination requests to the server. + +The Diameter base protocol includes the Auth-Session-State AVP as the mechanism for the implementation of implicitly terminated sessions. + +The client (server) shall include in its requests (responses) the Auth-Session-State AVP set to the value NO\_STATE\_MAINTAINED (1), as described in [IETF RFC 3588]. As a consequence, the server does not maintain any state information about this session and the client does not need to send any session termination request. Neither the Authorization-Lifetime AVP nor the Session-Timeout AVP shall be present in requests or responses. + +## 8.4 Transport protocol + +Diameter messages over the S-TC1 interface shall make use of SCTP [IETF RFC 2960] and shall utilize the new SCTP checksum method specified in [IETF RFC 3309]. + +## 8.5 Routing considerations + +This clause specifies the use of the Diameter routing AVPs Destination-Realm and Destination-Host. + +With regard to the Diameter protocol defined over the S-TC1 interface, the TLM-PE acts as a Diameter server and the SCE acts as the Diameter client. + +If a SCE knows the address/name of the TLM-PE for a certain user, both the Destination-Realm and Destination-Host AVPs shall be present in the request. Otherwise, only the Destination-Realm AVP shall be present and the command shall be routed to a proxy TLM-PE, based on the Diameter routing table in the client. The proxy TLM-PE shall act as a Diameter relay as described in [IETF RFC 3588]. + +Requests initiated by the TLM-PE towards a SCE shall include both Destination-Host and Destination-Realm AVPs. The TLM-PE obtains the Destination-Host AVP to use in requests towards a SCE from configuration data or information received from the TAA-PE/TUP-PE. Consequently, the Destination-Host AVP is declared as mandatory in the ABNF for all requests initiated by the TLM-PE. Destination-Realm AVP is declared as mandatory in the ABNF for all requests. + +To ensure that messages are routed to the correct application at the destination host, the Diameter message header of each message sent shall contain either the S-TC1 application identifier (16777245) or the e2 application identifier (16777231) as agreed during CER/CEA negotiation. (See clause 8.6) + +## 8.6 Advertising application support + +The Capabilities-Exchange-Request and Capabilities-Exchange-Answer commands are specified in the Diameter Base Protocol [IETF RFC 3588]. The Diameter base application identifier (0) shall be used in the Diameter message header of these messages. + +If both the SCE and TLM-PE indicate support of the S-TC1 application, then the S-TC1 application identifier (16777245) shall be used in the Diameter message header of all subsequent messages + +exchanged within this association. Otherwise, the e2 application identifier (16777231) shall be placed in those headers. + +Support of the S-TC1 application within the CER/CEA is indicated by supplying an instance of the Vendor-Specific-Application-Id containing a Vendor-Id AVP set to ITU-T (11502) and an Auth-Application-Id AVP set to S-TC1 (16777245). Support of the e2 application within the CER/CEA is indicated by supplying an instance of the Vendor-Specific-Application-Id containing a Vendor-Id AVP set to ETSI (13019) and an Auth-Application-Id AVP set to e2 (16777231). + +The SCE and TLM-PE shall advertise the support of AVPs specified in 3GPP, ETSI, and ITU-T documents by including the values 10415 (3GPP), 13019 (ETSI), and 11502 (ITU-T) in three different instances of the Supported-Vendor-Id AVP in the CER and CEA commands respectively. + +**Table 8-1 – Vendor identifiers for S-TC1** + +| Vendor | Vendor identifier | +|--------|-------------------| +| 3GPP | 10415 | +| ETSI | 13019 | +| ITU-T | 11502 | + +NOTE – The Vendor-Id AVP included in Capabilities-Exchange-Request and Capabilities-Exchange-Answer commands that are not included in the Vendor-Specific-Application-Id AVPs, as described above, shall indicate the manufacturer of the Diameter node as per [IETF RFC 3588]. + +# 9 Message specification + +## 9.1 Commands + +This Recommendation reuses the Diameter command defined in [ETSI TS 129 329]. Other commands shall be ignored by the SCE and TLM-PE. + +**Table 9-1 – Command code** + +| Command | Abbreviation | Defining reference | Command code | See clause | +|--------------------------------|--------------|--------------------|--------------|------------| +| User-Data-Request | UDR | ETSI TS 129 329 | 306 | 9.1.1 | +| User-Data-Answer | UDA | ETSI TS 129 329 | 306 | 9.1.2 | +| Subscribe-Notification-Request | SNR | ETSI TS 129 329 | 308 | 9.1.3 | +| Subscriber-Notification-Answer | SNA | ETSI TS 129 329 | 308 | 9.1.4 | +| Push-Notification-Request | PNR | ETSI TS 129 329 | 309 | 9.1.5 | +| Push-Notification-Answer | PNA | ETSI TS 129 329 | 309 | 9.1.6 | + +### 9.1.1 User-Data-Request (UDR) command + +The User-Data-Request (UDR) command, indicated by the Command-Code field set to 306 and the "R" bit set in the command flags field, is sent by a Diameter client to a Diameter server in order to request user data. This command is defined in [ETSI TS 129 329] and used with additional AVPs defined in this Recommendation. + +#### Message format + +``` +< User-Data-Request > ::= < Diameter Header: 306, REQ, PXY, 16777245> + < Session-Id > + { Vendor-Specific-Application-Id } + { Auth-Session-State } +``` + +``` + +{ Origin-Host } +{ Origin-Realm } +[ Destination-Host ] +{ Destination-Realm } +[ Globally-Unique-Address ] +[ User-Name ] +[ SCE-Application-Identifier ] +[ Requested-Information ] +*[ AVP ] +*[ Proxy-Info ] +*[ Route-Record ] + +``` + +### 9.1.2 User-Data-Answer (UDA) command + +The User-Data-Answer (UDA) command, indicated by the Command-Code field set to 306 and the "R" bit cleared in the command flags field, is sent by a server in response to the User-Data-Request command. This command is defined in [ETSI TS 129 329] and used with additional AVPs defined in this Recommendation. The Experimental-Result AVP may contain one of the values defined in clause 9.2. + +#### *Message format* + +``` + +< User-Data-Answer > ::= < Diameter Header: 306, PXY, 16777245> + < Session-Id > + { Vendor-Specific-Application-Id } + [ Result-Code ] + [ Experimental-Result ] + { Auth-Session-State } + { Origin-Host } + { Origin-Realm } + [ User-Name ] + [ Physical-Connection-Identifier ] + [ Logical-Connection-Identifier ] + [ Access-Network-Type ] + [ Location-Information ] + [ RACE-Contact-Point ] + [ CPE-Type ] + [ IP-Connectivity-status ] + *[ AVP ] + *[ Failed-AVP ] + *[ Proxy-Info ] + *[ Route-Record ] + +``` + +### 9.1.3 Subscribe-Notification-Request (SNR) command + +The Subscribe-Notification-Request (SNR) command, indicated by the Command-Code field set to 308 and the "R" bit set in the command flags field, is sent by a Diameter client to a Diameter server in order to request notifications of events. This command is defined in [ETSI TS 129 329] and used with additional AVPs defined in this Recommendation. + +#### *Message format* + +``` + +< Subscribe-Notification-Request > ::= < Diameter Header: 308, REQ, PXY, +16777245> + < Session-Id > + { Vendor-Specific-Application-Id } + { Auth-Session-State } + { Origin-Host } + { Origin-Realm } + [ Destination-Host ] + { Destination-Realm } + { Subs-Req-Type } + [ Expiry-Time ] + +``` + +``` + +[ Globally-Unique-Address ] +[ User-Name ] +[ SCE-Application-Identifier ] +*[ Event-Type ] +*[ AVP ] +*[ Proxy-Info ] +*[ Route-Record ] + +``` + +### 9.1.4 Subscribe-Notification-Answer (SNA) command + +The Subscribe-Notification-Answer command, indicated by the Command-Code field set to 308 and the "R" bit cleared in the command flags field, is sent by a server in response to the Subscribe-Notification-Request command. The Result-Code or Experimental-Result AVP may contain one of the values defined in clause 9.2. + +#### *Message format* + +``` + +< Subscribe-Notification-Answer > ::= < Diameter Header: 308, PXY, 16777245> +< Session-Id > +{ Vendor-Specific-Application-Id } +[ Result-Code ] +[ Experimental-Result ] +{ Auth-Session-State } +{ Origin-Host } +{ Origin-Realm } +[ Expiry-Time ] +*[ AVP ] +*[ Failed-AVP ] +*[ Proxy-Info ] +*[ Route-Record ] + +``` + +### 9.1.5 Push-Notification-Request (PNR) command + +The Push-Notification-Request (PNR) command, indicated by the Command-Code field set to 309 and the "R" bit set in the command flags field, is sent by a Diameter server to a Diameter client in order to notify changes in the user data in the server. This command is defined in [ETSI TS 129 329] and used with additional AVPs defined in this Recommendation. + +#### *Message format* + +``` + +< Push-Notification-Request > ::= < Diameter Header: 309, REQ, PXY, 16777245> +< Session-Id > +{ Vendor-Specific-Application-Id } +{ Auth-Session-State } +{ Origin-Host } +{ Origin-Realm } +[ Destination-Host ] +{ Destination-Realm } +*[ Event-Type ] +[ Globally-Unique-Address ] +[ User-Name ] +[ Access-Network-Type ] +[ Location-Information ] +[ RACE-Contact-Point ] +[ CPE-Type ] +[ Logical-connection-identifier ] +[ Physical-connection-identifier ] +[ Access-Network-Type ] +[ Default-Configuration ] +*[ Transport-Resource-Subscription ] +[ IP-Connectivity-Status ] +*[ AVP ] +*[ Proxy-Info ] + +``` + +\*[ Route-Record ] + +### 9.1.6 Push-Notification-Answer (PNA) command + +The Push-Notification-Answer (PNA) command, indicated by the Command-Code field set to 309 and the "R" bit cleared in the command flags field, is sent by a client in response to the Push-Notification-Request command. The Experimental-Result AVP may contain one of the values defined in clause 9.2. + +#### *Message format* + +``` +< Push-Notification-Answer > ::= < Diameter Header: 309, PXY, 16777245> + < Session-Id > + { Vendor-Specific-Application-Id } + [ Result-Code ] + [ Experimental-Result ] + { Auth-Session-State } + { Origin-Host } + { Origin-Realm } + *[ AVP ] + *[ Failed-AVP ] + *[ Proxy-Info ] + *[ Route-Record ] +``` + +## 9.2 Experimental-Result-Code AVP values + +This clause defines specific values of the Experimental-Result-Code AVP used in this Recommendation. Most of these are imported from 3GPP and ETSI specifications, as indicated in the subclauses below. + +### 9.2.1 Experimental-Result-Code AVP values imported from ETSI TS 129 229 + +This subclause defines the specific values of the Experimental-Result-Code AVP imported from [ETSI TS 129 229] (vendor-id is ETSI): + +DIAMETER\_ERROR\_USER\_UNKNOWN (5001) + +The request failed because the IP address or Globally-Unique Address is not found. + +DIAMETER\_USER\_DATA\_NOT\_AVAILABLE (4100) + +The requested data is not available at this time to satisfy the requested operation. + +### 9.2.2 Experimental-Result-Code AVP values imported from ETSI TS 129 329 + +This subclause defines the specific values of the Experimental-Result-Code AVP imported from [ETSI TS 129 329] (vendor-id is ETSI): + +DIAMETER\_ERROR\_NO\_SUBSCRIPTION\_TO\_DATA (5107) + +The SCE received a notification of changes of some information to which it is not subscribed. + +## 9.3 AVPs + +The following tables summarize the AVPs used in this Recommendation, beyond those defined in the Diameter base protocol [IETF RFC 3588]. + +Table 9-2 describes the Diameter AVPs that are used within this Recommendation that have been defined by [ETSI ES 283 035], providing their AVP code values, types, possible flag values and whether or not the AVP may be encrypted. The Vendor-Id header of all AVPs identified in Table 9-2 shall be set to ETSI (13019). These AVPs are described in this Recommendation for information; however, the normative detail for these AVPs is contained in [ETSI TS 283 035]. + +**Table 9-2 – Diameter AVPs imported from ETSI ES 283 035** + +| Attribute name | AVP code | Clause defined | Value type (Note 2) | AVP flag rules (Note 1) | | | | | +|-----------------------|----------|----------------|---------------------|-------------------------|-----|------------|----------|-------------| +| | | | | Must | May | Should not | Must not | May encrypt | +| Location-Information | 350 | 9.3.5 | Grouped | V | M | | | Y | +| RACE-Contact-Point | 351 | 9.3.6 | DiameterIdentity | V | M | | | Y | +| CPE-Type | 352 | 9.3.7 | OctetString | V | M | | | Y | +| Requested-Information | 353 | 9.3.3 | Enumerated | V | | | M | Y | +| Event-Type | 354 | 9.3.11 | Enumerated | V | M | | | Y | + +NOTE 1 – The AVP header bit, denoted as 'M', indicates whether support of the AVP is required. The AVP header bit, denoted as 'V', indicates whether the optional Vendor-ID field is present in the AVP header. For further details, see [IETF RFC 3588]. + +NOTE 2 – The value types are defined in [IETF RFC 3588]. + +Table 9-3 describes the Diameter AVPs defined by the e4 interface protocol [ETSI ES 283 034] and used within this Recommendation. These AVPs are described in this Recommendation for information; however, the normative detail for these AVPs is contained in [ETSI ES 283 034]. The Vendor-Id header of all AVPs defined in Table 9-3 shall be set to ETSI (13019). + +**Table 9-3 – Diameter AVPs imported from ETSI ES 283 034** + +| Attribute name | AVP code | Clause defined | Value type | AVP flag rules | | | | | +|---------------------------------|----------|----------------|-------------|----------------|-----|------------|----------|-------------| +| | | | | Must | May | Should not | Must not | May encrypt | +| Globally-Unique-Address | 300 | 9.3.1 | Grouped | M, V | | | | Y | +| Logical-Connection-Identifier | 302 | 9.3.10 | OctetString | V | M | | | Y | +| Access-Network-Type | 306 | 9.3.4 | Grouped | V | M | | | Y | +| Default-Configuration | 303 | 9.3.14 | Grouped | V | M | | | Y | +| Transport-Resource-Subscription | 304 | 9.3.15 | Grouped | V | M | | | Y | +| IP-Connectivity-Status | 305 | 9.3.8 | Enumerated | V | M | | | Y | +| Physical-Connection-Identifier | 313 | 9.3.9 | UTF8String | V | M | | | Y | + +Table 9-4 describes the Diameter AVPs defined by the Gq interface protocol [ETSI TS 129 209] and used within this Recommendation. These AVPs are described in this Recommendation for information; however, the normative detail for these AVPs is contained in [ETSI TS 129 209]. The Vendor-Id header of all AVPs defined in Table 9-4 shall be set to ETSI (13019). + +**Table 9-4 – Diameter AVPs imported from ETSI TS 129 209** + +| Attribute name | AVP code | Clause defined | Value type | AVP flag rules | | | | | +|----------------------------|----------|----------------|-------------|----------------|-----|------------|----------|-------------| +| | | | | Must | May | Should not | Must not | May encrypt | +| SCE-Application-Identifier | 504 | 9.3.2 | OctetString | M, V | | | | Y | + +Table 9-5 describes the Diameter AVPs defined by the Sh interface protocol [ETSI TS 129 329] and used within this Recommendation. These AVPs are described in this Recommendation for information; however, the normative detail for these AVPs is contained in [ETSI TS 129 329]. The Vendor-Id header of all AVPs defined in Table 9-5 shall be set to ETSI (13019). + +**Table 9-5 – Diameter AVPs imported from ETSI TS 129 329** + +| Attribute name | AVP code | Clause defined | Value type | AVP flag rules | | | | | +|----------------|----------|----------------|------------|----------------|-----|------------|----------|-------------| +| | | | | Must | May | Should not | Must not | May encrypt | +| Expiry-Time | 709 | 9.3.13 | Time | V | | | M | Y | +| Subs-Req-Type | 705 | 9.3.12 | Enumerated | M, V | | | | Y | + +### 9.3.1 Globally-Unique-Address AVP + +The Globally-Unique-IP-Address AVP (AVP code 300 13019) is of type Grouped. + +#### *AVP format* + +``` +Globally-Unique-Address ::= < AVP Header: 300 13019 > + [Framed-IP-Address] + [Framed-IPv6-Prefix] + [Address-Realm] +``` + +### 9.3.2 SCE-Application-Identifier AVP + +The SCE-Application-identifier AVP (AVP code 504 13019) is of type OctetString, and it contains information that identifies the particular service that the SCE service session belongs to. + +### 9.3.3 Requested-Information AVP + +The Requested-Information AVP (AVP code 353 13019) is of type Enumerated. The following values are defined: + +- SUBSCRIBER-ID (0). +- LOCATION-INFORMATION (1). +- RACE-CONTACT-POINT (2). +- ACCESS-NETWORK-TYPE (3). +- CPE-TYPE (4). +- LOGICAL-CONNECTION-IDENTIFIER (5). +- PHYSICAL-CONNECTION-IDENTIFIER (6). +- ACCESS-NETWORK-TYPE (7). +- DEFAULT-CONFIGURATION (8). +- TRANSPORT-RESOURCE-SUBSCRIPTION (9). +- IP-CONNECTIVITY-STATUS (10). + +### 9.3.4 Access-Network-Type AVP + +The Access-Network-Type AVP (AVP code 306 13019) is of type Grouped, and it indicates the type of port on which the user equipment is connected and the type of aggregation network. + +*AVP format* + +``` +Access-Network-Type ::= < AVP Header: 306 13019 > + {NAS-Port-Type} + [Aggregation-Network-Type] +``` + +### 9.3.5 Location-Information AVP + +The Location-Information AVP (AVP code 350 13019) is of type Grouped. + +*AVP format* + +``` +Location-Information ::= < AVP Header: 350 13019 > + [Line-Identifier] + * [AVP] +``` + +### 9.3.6 RACE-Contact-Point AVP + +The RACE-Contact-Point AVP (AVP code 351 13019) is of type DiameterIdentity and identifies the RACE element to which resource reservation requests shall be sent. + +### 9.3.7 CPE-Type AVP + +The CPE-Type AVP (AVP code 352 13019) is of type OctetString and contains a value of the user class DHCP option (77). + +### 9.3.8 IP-Connectivity-Status AVP + +The IP-Connectivity-Status AVP (AVP code 305 13019) is of type Enumerated. + +The following values are defined: + +- IP-CONNECTIVITY-ON (0). +- IP-CONNECTIVITY-LOST (1). + +### 9.3.9 Physical-Connection-Identifier AVP + +The Physical-Connection-Identifier AVP (AVP code 313 13019) is of type UTF8String and identifies the physical access to which the user equipment is connected. It includes a port identifier and the identity of the access node where the port resides. + +### 9.3.10 Logical-Connection-Identifier AVP + +The Logical-connection-identifier AVP (AVP code 302 13019) is of type OctetString. This AVP contains either a Circuit-ID (as defined in IETF RFC 3046) or a technology-independent identifier. + +NOTE – In the xDSL/ATM case, the logical access ID may explicitly contain the identity of the VP and VC carrying the traffic. + +### 9.3.11 Event-Type AVP + +The Event-Type AVP (AVP code 354 13019) is of type Enumerated. The following values are defined: + +- USER-LOGON (0). +- LOCATION-INFORMATION-CHANGED (1) +- RACE-CONTACT-POINT-CHANGED (2) +- ACCESS-NETWORK-TYPE-CHANGED (3) +- CPE-TYPE-CHANGED (4) + +- LOGICAL-CONNECTION-IDENTIFIER-CHANGED (5) +- PHYSICAL-CONNECTION-IDENTIFIER-CHANGED (6) +- IP-ADDRESS-CHANGED (7) +- DEFAULT-CONFIGURATION-CHANGED (8) +- TRANSPORT-RESOURCE-SUBSCRIPTION-CHANGED (9) +- USER-LOGOFF (10) + +The USER-LOGON event is reported when the TLM-PE successfully creates a session record. + +The USER-LOGOFF event is reported when the TLM-PE suppresses a session record. + +All other events are reported when the related part of the session record is modified. + +### 9.3.12 Subs-Req-Type AVP + +The Subs-Req-Type AVP (AVP code 705 13019) is of type Enumerated, and indicates the type of the subscription-to-notifications request. The following values are defined: + +- SUBSCRIBE (0): This value is used by an SCE to subscribe to notifications of changes in data. +- UNSUBSCRIBE (1): This value is used by an SCE to unsubscribe to notifications of changes in data. + +### 9.3.13 Expiry-Time AVP + +The Expiry-Time AVP (AVP code 709 13019) is of type Time. This AVP contains the expiry time of subscriptions to notifications in the TLM-PE. + +### 9.3.14 Default-Configuration AVP + +The Default-Configuration AVP (AVP code 303 13019) is of type Grouped. + +*AVP format* + +``` +Default-Configuration ::= < AVP Header: 303 13019 > + 1* {NAS-Filter-Rule} + [Maximum-Allowed-Bandwidth-UL] + [Maximum-Allowed-Bandwidth-DL] +``` + +### 9.3.15 Transport-Resource-Subscription AVP + +The Transport-Resource-Subscription AVP (AVP code 304 13019) represents Transport-Resource-Subscription element and is of type Grouped. + +*AVP format* + +``` +Transport-Resource-Subscription ::= < AVP Header: 304 13019 > + * [Application-Class-ID] + * [Media-Type] + [Reservation-Priority] + [Maximum-Allowed-Bandwidth-UL] + [Maximum-Allowed-Bandwidth-DL] + [Transport-Class] +``` + +## 9.4 Use of namespaces + +This clause contains the namespaces that have either been created in this Recommendation, or the values assigned to existing namespaces managed by IANA. + +### **9.4.1 AVP codes** + +This Recommendation uses AVP values from the AVP code namespace managed by ETSI for its Diameter vendor-specific applications. See clause 9.3. + +### **9.4.2 Experimental-Result-Code AVP values** + +This Recommendation assigns the Experimental-Result-Code AVP values from the AVP code namespace managed by ETSI for its Diameter vendor-specific applications. See clause 9.2. + +### **9.4.3 Command code values** + +This Recommendation does not assign command code values but uses existing commands defined by the IETF, including those requested by 3GPP. + +### **9.4.4 Application-ID value** + +This Recommendation defines the S-TC1 Diameter application with application ID 16777245. The vendor identifier assigned by IANA to ITU-T (
N Network entity | +|
The UE sends a MCID request in the confirmed state
Ensure that the UE is able to invoke MCID in the confirmed state. The UE sends a Re-INVITE without session modification and no 'mcid' XML element is present. | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +| Preconditions: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +| SIP header values:
Re-INVITE without session modification | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +| Comments: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | +| Test equipment
| INVITE | → User equipment | |
| ← | 100 Trying | |
| ← | 180 Ringing | |
| ← | 200 OK INVITE | |
| ACK | → | |
| ← | Re-INVITE requesting MCID | |
| 200 OK INVITE | ||
| ← | ACK | ← |
| Apply post test routine | ||
The UE sends a MCID request in the early dialogue
Ensure that the UE is able to invoke MCID in the early dialogue. The UE sends a Re-INVITE without session modification and no 'mcid' XML element is present. | | | | | | | +| Preconditions: | | | | | | | +| SIP header values:
Re-INVITE without session modification | | | | | | | +| Comments: | | | | | | | +|
| Test equipment | INVITE → ← 100 Trying ← 180 Ringing ← Re-INVITE requesting MCID 200 OK INVITE → ← ACK ← Apply post test routine | User equipment |
← 100 Trying
← 180 Ringing
← Re-INVITE requesting MCID
200 OK INVITE →
← ACK ←
Apply post test routine | User equipment | +| Test equipment | INVITE →
← 100 Trying
← 180 Ringing
← Re-INVITE requesting MCID
200 OK INVITE →
← ACK ←
Apply post test routine | User equipment | | | | | + +| TSS | TP | MCID reference | Selection expression | | | | +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------|-------------------------------|-----------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------| +| MCID/destination_UE | MCID_U01_003 | Clause 4.5.2.12 of [ITU-T Q.3624 v.1] | PICS 4.5.1/1 AND PICS 4.6.1/2 | | | | +| Test purpose
The UE sends a MCID request using the XML McidRequestIndicator in the confirmed state
Ensure that the UE is able to invoke MCID in the confirmed state. The UE sends a Re-INVITE without session modification. Ensure that the UE is able to send a 'mcid' XML MIME body with the McidRequestIndicator set to 1. | | | | | | | +| Preconditions: | | | | | | | +| SIP header values:
Re-INVITE without session modification
XML mcid
request
McidRequestIndicator = '1' | | | | | | | +| Comments: | | | | | | | +|
| Test equipment | INVITE → ← 100 Trying ← 180 Ringing ← 200 OK INVITE ACK → ← Re-INVITE requesting MCID 200 OK INVITE → ← ACK → Apply post test routine | User equipment |
← 100 Trying
← 180 Ringing
← 200 OK INVITE
ACK →
← Re-INVITE requesting MCID
200 OK INVITE →
← ACK →
Apply post test routine | User equipment | +| Test equipment | INVITE →
← 100 Trying
← 180 Ringing
← 200 OK INVITE
ACK →
← Re-INVITE requesting MCID
200 OK INVITE →
← ACK →
Apply post test routine | User equipment | | | | | + +| | | | | | | | | | | | | | | | | | | | | | | | | | | | | +|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------|-------------------------------------------------------------------|-----------------------------------------------------------------|-----------------------|--|-----------------------|--|--------|---|---|------------|--|---|-------------|--|---|---------------------------|--|--|---------------|---|---|-----|--|--|--------------------------------|--| +| TSS
MCID/destination_UE | TP
MCID_U01_004 | MCID reference
Clause 4.5.2.12 of
[ITU-T Q.3624 v.1] | Selection expression
PICS 4.5.1/1 AND
PICS 4.6.1/2 | | | | | | | | | | | | | | | | | | | | | | | | | +| Test purpose
The UE sends a MCID request using the XML McidRequestIndicator in the early dialogue
Ensure that the UE is able to invoke MCID in the early dialogue. The UE sends a Re-INVITE without session modification.
Ensure that the UE is able to send a 'mcid' XML MIME body with the McidRequestIndicator set to 1. | | | | | | | | | | | | | | | | | | | | | | | | | | | | +| Preconditions:
SIP header values:
Re-INVITE without session modification
XML mcid
request
McidRequestIndicator = '1' | | | | | | | | | | | | | | | | | | | | | | | | | | | | +| Comments:
| Test equipment | User equipment | |
| INVITE | → | |
| ← | 100 Trying | |
| ← | 180 Ringing | |
| ← | Re-INVITE requesting MCID | |
| 200 OK INVITE | → | |
| ← | ACK | |
| Apply post test routine |
– It is recommended that the IaaS CSP provides a virtual machine with clone functions. The cloned VM has identical configuration and CSP/CSC data as the original one. | – 7.4 Interoperability testing of VM clone between the CSC and CSP | +| 18 | 7.1.7 VM backup
– It is recommended that the IaaS CSP provides a virtual machine with backup functions. When the VM becomes faulty or its data is lost, the VM can be restored using its backup stored according to the CSC policy. | – 7.10 Interoperability testing of VM backup between the CSC and CSP | +| 19 | 7.1.8 VM time synchronization
– It is recommended that the IaaS CSP provides time synchronization functions, which allow the CSC to control the VM time. | – 7.5 Interoperability testing of VM time synchronization between the CSC and CSP | +| 20 | 7.1.9 VM reservation
– It is recommended that the IaaS CSP provides processing resources reservation (such as CPU, memory) functions. Resources reservation is used to reserve available resources from IaaS infrastructure before VM is initiated. | – 7.6 Interoperability testing of VM reservation between the CSC and CSP | +| 21 | 7.1.10 VM image
– It is recommended that the IaaS CSP offers the ability for the CSC to provide and use virtual machine images. A VM image consists of infrastructure configuration and CSP data, CSC data or both. | – 7.7 Interoperability testing of VM image between the CSC and CSP | +| 22 | | – It is recommended that the IaaS CSP supports a different machine image format.
– 7.7 Interoperability testing of VM image between the CSC and CSP | +| 23 | | – It is required that the IaaS CSP provides operation handling mechanisms related to image, including, but not limited to, add, import, store, register, deregister, query, update, delete and export.
– 7.7 Interoperability testing of VM image between the CSC and CSP | +| 24 | 7.1.11 VM template
– It is recommended that the IaaS CSP supports the open virtualization format (OVF) template, which is a packaging standard designed to address the portability and deployment of virtual appliances. | – 7.8 Interoperability testing of VM template between the CSC and CSP | +| 25 | | – It is recommended that the IaaS CSP provides operations handling mechanisms related to machine templates, such as upload, update,
– 7.8 Interoperability testing of VM template between the CSC and CSP | + +**Table III.1 – Alignment analysis with functional requirements in [ITU-T Y.3513]** + +| | | Functional requirements in [ITU-T Y.3513] | Test objects in this Recommendation | +|----|---------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------| +| | | disable, enable, query and delete to the CSC. | | +| 26 | 7.2 Storage service functional requirements | – It is recommended that the IaaS CSP provides storage functions, such as block level storage, file level storage and object-based storage, with specific SLAs and charging model to the CSC. The storage functions can be provided to the CSC directly or used by the virtual machine as attached storage. | – 8.6 Interoperability testing of storage life cycle management between the CSC and CSP | +| 27 | | – It is recommended that the IaaS CSP provides the CSC with operations handling mechanisms related to storage, such as create, attach, detach, query and delete a volume of storage at either block level or file-system level, write, read and delete data for a given storage. | – 8.6 Interoperability testing of storage life cycle management between the CSC and CSP | +| 28 | | – It is recommended that the IaaS CSP provides storage utilisation information in response to queries from the CSC. | – 8.7 Interoperability testing of storage utilization status inquiring between the CSC and CSP | +| 29 | 7.2.1 Storage migration | – It is recommended that the IaaS CSP provides storage migration functions. Based on migration policies, data can be migrated between different logical unit numbers (LUNs), different storage devices, local storage to shared storage and vice versa. | – 8.1 Interoperability testing of storage migration between the CSC and CSP | +| 30 | 7.2.2 Storage snapshot | – It is recommended that the IaaS CSP provides storage with snapshot functions. Snapshot can be realized at either block or file-system levels. The data can be restored using the snapshot. | – 8.2 Interoperability testing of storage snapshot between the CSC and CSP | +| 31 | 7.2.3 Storage backup | – It is recommended that the IaaS CSP provides storage with backup functions. Backup can be realized at block level, file level or object-based storage. | – 8.3 Interoperability testing of storage backup between the CSC and CSP | +| 32 | 7.2.4 I/O performance | – It is recommended that the IaaS CSP provides input/output (I/O) limitation for each VM. | – 8.5 Interoperability testing of I/O performance between the CSC and CSP | +| 33 | 7.2.5 Storage resource reservation | – It is recommended that the IaaS CSP provides storage resource (e.g., storage space and LUN) reservation functions. | – 8.4 Interoperability testing of storage resource reservation between the CSC and CSP | + +**Table III.1 – Alignment analysis with functional requirements in [ITU-T Y.3513]** + +| | | Functional requirements in [ITU-T Y.3513] | Test objects in this Recommendation | +|----|---------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------| +| 34 | 7.3 Network service functional requirements | – It is recommended that the IaaS CSP provides network functions, such as IP address, VLAN, virtual switch, load balance, firewall, with specific SLAs or charging model. Network functions are applied to access and interconnect processing and storage resources. | – 9.7 Interoperability testing of load balance between the CSC and CSP
– 9.8 Interoperability testing of firewall between the CSC and CSP | +| 35 | | – It is recommended that the IaaS CSP provides network information in response to queries from the CSC. | – 9.10 Interoperability testing of network information inquiring between the CSC and CSP | +| 36 | 7.3.1 Network policy migration | – It is recommended that the IaaS CSP provides network policy migration along with virtual machine migration. In this case, the network policy of the migrated virtual machine is the same as before the migration. | – 9.1 Interoperability testing of network policy migration between the CSC and CSP | +| 37 | 7.3.2 Network QoS | – It is recommended that the IaaS CSP provides operation handling mechanisms related to the network quality of service (QoS), such as bandwidth limit, bandwidth reservation, traffic shaping, traffic classification, congestion avoidance, at port level, device level and network level. | – 9.2 Interoperability testing of network QoS between the CSC and CSP | +| 38 | 7.3.3 IP Address | – It is recommended that the IaaS CSP provides IP address reservation. | – 9.6 Interoperability testing of IP address reservation between the CSC and CSP | +| 39 | | – It is required that the IaaS CSP allows the CSC to apply, bind, unbind, query, release an IP address to processing resources or storage resources. | – 9.5 Interoperability testing of IP address allocation between the CSC and CSP | +| 40 | | – It is recommended that the IaaS CSP allows the CSC to allocate IP addresses to provisioned processing resources or storage resources with a dynamic or static method. | – 9.5 Interoperability testing of IP address allocation between the CSC and CSP | +| 41 | | – The IaaS CSP can optionally provide network address translation (NAT). | – 9.3 Interoperability testing of network address translation between the CSC and CSP | + +**Table III.1 – Alignment analysis with functional requirements in [ITU-T Y.3513]** + +| | | Functional requirements in [ITU-T Y.3513] | Test objects in this Recommendation | +|----|-----------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +| 42 | 7.3.4 Network isolation | – It is required that the IaaS CSP provides the CSC with isolated tenants' networks. | – 9.4 Interoperability testing of network isolation between the CSC and CSP | +| 43 | | – It is recommended that the IaaS CSP provides the CSC with operations handling mechanisms related to isolated tenants' networks, such as create, query and release. | – 9.4 Interoperability testing of network isolation between the CSC and CSP | +| 44 | 7.3.5 Virtual Networking | – It is recommended that the IaaS CSP manages virtual networking to provide network connectivity amongst various processing and storage resources. | – 9.4 Interoperability testing of network isolation between the CSC and CSP | +| 45 | 7.3.6 Load balance | – It is recommended that the IaaS CSP optimizes infrastructure resources utilization by providing load balance related functions, such as throughput, response time, to avoid overload of any one of the infrastructure resources. | – 9.7 Interoperability testing of load balance between the CSC and CSP | +| 46 | | – The IaaS CSP can optionally provide multipath routing to achieve an optimized traffic management (e.g., to improve network utilization, to guarantee QoS at network congestion or fault). | – 9.9 Interoperability testing of multipath routing between the CSC and CSP | +| 47 | 7.3.7 Firewall | – It is recommended that the IaaS CSP delivers a physical or virtual firewall to the CSC. | – 9.8 Interoperability testing of firewall between the CSC and CSP | +| 48 | 7.3.8 Gateway | – It is recommended that the IaaS CSP provides necessary network interworking functions so that the CSC uses provisioned infrastructure resources as if they are at the CSC's premises. | – 9.4 Interoperability testing of network isolation between the CSC and CSP | +| 49 | 7.3.9 Network configuration | – It is recommended that the IaaS CSP provides the CSC with operations handling mechanisms related to the network configurations according to the objectives of the SLA. | See other network related testing objects:
– 9.5 Interoperability testing of IP address allocation between the CSC and CSP
– 9.2 Interoperability testing of network QoS between the CSC and CSP
– 9.3 Interoperability testing of network address translation between the CSC and CSP | + +## Bibliography + +- [b-ETSI GS NFV-TST 002 V1.1] ETSI GS NFV-TST 002 V1.1 (2016), *Network Functions Virtualisation (NFV); Testing Methodology; Report on NFV Interoperability Testing Methodology.* + + + + + +## SERIES OF ITU-T RECOMMENDATIONS + +| | | +|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------| +| Series A | Organization of the work of ITU-T | +| Series D | Tariff and accounting principles and international telecommunication/ICT economic and policy issues | +| Series E | Overall network operation, telephone service, service operation and human factors | +| Series F | Non-telephone telecommunication services | +| Series G | Transmission systems and media, digital systems and networks | +| Series H | Audiovisual and multimedia systems | +| Series I | Integrated services digital network | +| Series J | Cable networks and transmission of television, sound programme and other multimedia signals | +| Series K | Protection against interference | +| Series L | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant | +| Series M | Telecommunication management, including TMN and network maintenance | +| Series N | Maintenance: international sound programme and television transmission circuits | +| Series O | Specifications of measuring equipment | +| Series P | Telephone transmission quality, telephone installations, local line networks | +| Series Q | Switching and signalling, and associated measurements and tests | +| Series R | Telegraph transmission | +| Series S | Telegraph services terminal equipment | +| Series T | Terminals for telematic services | +| Series U | Telegraph switching | +| Series V | Data communication over the telephone network | +| Series X | Data networks, open system communications and security | +| Series Y | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities | +| Series Z | Languages and general software aspects for telecommunication systems | \ No newline at end of file diff --git a/marked/Q/T-REC-Q.4047-202406-I_PDF-E/0538daaa5583c23e17db3a12f2281a55_img.jpg b/marked/Q/T-REC-Q.4047-202406-I_PDF-E/0538daaa5583c23e17db3a12f2281a55_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..6a574bf4c7fd169a72a97de0395e1970ee6f7092 --- /dev/null +++ b/marked/Q/T-REC-Q.4047-202406-I_PDF-E/0538daaa5583c23e17db3a12f2281a55_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:5d863c71623a2b5a933b672e32a1463a7461603fd81d81e68543e5d90adf3b80 +size 7132 diff --git a/marked/Q/T-REC-Q.4047-202406-I_PDF-E/4801720824e4b5e2361a5564f91cfb70_img.jpg b/marked/Q/T-REC-Q.4047-202406-I_PDF-E/4801720824e4b5e2361a5564f91cfb70_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..8a6adc48e5d36b2489277a0a723bd466d0d3bcae --- /dev/null +++ b/marked/Q/T-REC-Q.4047-202406-I_PDF-E/4801720824e4b5e2361a5564f91cfb70_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:a774f5f4bdc1e7dfdd051015b1f99c2710600cb5fca1587e5e6cbdd66fd2be53 +size 56354 diff --git a/marked/Q/T-REC-Q.4047-202406-I_PDF-E/af7916c89a458fdab6c3f443217388ae_img.jpg b/marked/Q/T-REC-Q.4047-202406-I_PDF-E/af7916c89a458fdab6c3f443217388ae_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..8233b20d5e0d9c3362d00a8918ae81c666475c5e --- /dev/null +++ b/marked/Q/T-REC-Q.4047-202406-I_PDF-E/af7916c89a458fdab6c3f443217388ae_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:5593afc05070c79a574c6aa4bdaf6e364b5436c6aded3e2566996c0c51ace172 +size 57829 diff --git a/marked/Q/T-REC-Q.4047-202406-I_PDF-E/cfef993dcc8fb513de79eb1f93cf26ae_img.jpg b/marked/Q/T-REC-Q.4047-202406-I_PDF-E/cfef993dcc8fb513de79eb1f93cf26ae_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..f73b48f178a94a5b9be0d847d6d799a2adc8fd23 --- /dev/null +++ b/marked/Q/T-REC-Q.4047-202406-I_PDF-E/cfef993dcc8fb513de79eb1f93cf26ae_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:c2fa864f70eec1404a2a388646c70070c3f2503393c96f68302caf758b379511 +size 58493 diff --git a/marked/Q/T-REC-Q.4047-202406-I_PDF-E/d4af765160d04ecef538e5066006dc77_img.jpg b/marked/Q/T-REC-Q.4047-202406-I_PDF-E/d4af765160d04ecef538e5066006dc77_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..bf6f63f3e757ec4c4d6770df55977ecdb0da0ea9 --- /dev/null +++ b/marked/Q/T-REC-Q.4047-202406-I_PDF-E/d4af765160d04ecef538e5066006dc77_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:2c97fd56d52008d51ebb60da79ffc0a13a2cc72da02d208ed00c0f3d92131dce +size 60433 diff --git a/marked/Q/T-REC-Q.4047-202406-I_PDF-E/raw.md b/marked/Q/T-REC-Q.4047-202406-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..9c1bd86bffefcc1f6fcc64f6544da1106b2850d2 --- /dev/null +++ b/marked/Q/T-REC-Q.4047-202406-I_PDF-E/raw.md @@ -0,0 +1,638 @@ + + +# Recommendation**ITU-T Q.4047 (06/2024)** + +SERIES Q: Switching and signalling, and associated measurements and tests + +Testing specifications – Testing specifications for Cloud computing + +--- + +### **Interoperability testing between software-defined networking (SDN) and hypervisor-based computing virtualization** + + + +The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features a blue globe with white lines representing latitude and longitude, and the letters 'ITU' in a bold, blue, sans-serif font superimposed on the globe. + +ITU logo + +## ITU-T Q-SERIES RECOMMENDATIONS + +## Switching and signalling, and associated measurements and tests + +| | | +|--------------------------------------------------------------------------------|----------------------| +| SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE | Q.1-Q.3 | +| INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING | Q.4-Q.59 | +| FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN | Q.60-Q.99 | +| CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS | Q.100-Q.119 | +| SPECIFICATIONS OF SIGNALLING SYSTEMS NO. 4, 5, 6, R1 AND R2 | Q.120-Q.499 | +| DIGITAL EXCHANGES | Q.500-Q.599 | +| INTERWORKING OF SIGNALLING SYSTEMS | Q.600-Q.699 | +| SPECIFICATIONS OF SIGNALLING SYSTEM NO. 7 | Q.700-Q.799 | +| Q3 INTERFACE | Q.800-Q.849 | +| DIGITAL SUBSCRIBER SIGNALLING SYSTEM NO. 1 | Q.850-Q.999 | +| PUBLIC LAND MOBILE NETWORK | Q.1000-Q.1099 | +| INTERWORKING WITH SATELLITE MOBILE SYSTEMS | Q.1100-Q.1199 | +| INTELLIGENT NETWORK | Q.1200-Q.1699 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2000 | Q.1700-Q.1799 | +| SPECIFICATIONS OF SIGNALLING RELATED TO BEARER INDEPENDENT CALL CONTROL (BICC) | Q.1900-Q.1999 | +| BROADBAND ISDN | Q.2000-Q.2999 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR THE NGN | Q.3000-Q.3709 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR SDN | Q.3710-Q.3899 | +| TESTING SPECIFICATIONS | Q.3900-Q.4099 | +| Testing specifications for next generation networks | Q.3900-Q.3999 | +| Testing specifications for SIP-IMS | Q.4000-Q.4039 | +| Testing specifications for Cloud computing | Q.4040-Q.4059 | +| Testing specifications for IMT-2020 and IoT | Q.4060-Q.4099 | +| PROTOCOLS AND SIGNALLING FOR PEER-TO-PEER COMMUNICATIONS | Q.4100-Q.4139 | +| PROTOCOLS AND SIGNALLING FOR COMPUTING POWER NETWORKS | Q.4140-Q.4159 | +| PROTOCOLS AND SIGNALLING FOR QUANTUM KEY DISTRIBUTION NETWORKS | Q.4160-Q.4179 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2020 | Q.5000-Q.5049 | +| COMBATING COUNTERFEITING AND STOLEN ICT DEVICES | Q.5050-Q.5069 | + +For further details, please refer to the list of ITU-T Recommendations. + +# Recommendation ITU-T Q.4047 + +# Interoperability testing between software-defined networking (SDN) and hypervisor-based computing virtualization + +## Summary + +Recommendation ITU-T Q.4047 specifies the interoperability testing between software-defined networking (SDN) and hypervisor-based computing virtualization. This Recommendation introduces the framework for interoperability between SDN and hypervisor-based computing virtualization, which includes the target areas, components and interoperability in different scenarios. The corresponding requirements and the data model framework which should be considered during the interoperability testing between SDN and hypervisor-based computing virtualization are then presented. Test cases of interoperability testing between SDN and hypervisor-based computing virtualization are provided in Appendix I, which describe the involved test procedures. + +## History \* + +| Edition | Recommendation | Approval | Study Group | Unique ID | +|---------|----------------|------------|-------------|--------------------| +| 1.0 | ITU-T Q.4047 | 2024-06-29 | 11 | 11.1002/1000/15958 | + +## Keywords + +Hypervisor-based computing virtualization, interoperability testing, SDN. + +--- + +\* To access the Recommendation, type the URL
hypertext transfer protocol secure ..... | 14 | +| II.1 Key request message ..... | 14 | +| II.2 Key request with identifier message..... | 14 | +| II.3 Response to key request message..... | 15 | +| Bibliography..... | 16 | + + + +###### Recommendation ITU-T Q.4161 + +###### Protocols for Ak interfaces for quantum key distribution networks + +# 1 Scope + +This Recommendation specifies protocols for Ak interfaces for quantum key distribution networks (QKDNs) especially in the following areas: + +- signalling procedures; +- signalling messages and parameters; +- security considerations. + +# 2 References + +The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. + +[ITU-T Q.4160] Recommendation ITU-T Q.4160 (2023), *Quantum key distribution networks – Protocol framework*. + +[ITU-T X.1712] Recommendation ITU-T X.1712 (2021), *Security requirements and measures for QKD networks – Key management*. + +# 3 Definitions + +## 3.1 Terms defined elsewhere + +This Recommendation uses the following terms defined elsewhere: + +**3.1.1 key management** [b-ITU-T Y.3800]: All activities performed on keys during their life cycle starting from their reception from the quantum layer, storage, formatting, relay, synchronization, authentication, to supply to cryptographic application and deletion or preservation depending on the key management policy. + +**3.1.2 key management agent (KMA)** [b-ITU-T Y.3802]: A functional element to manage keys generated by one or multiple quantum key distribution (QKD) modules in a QKD node (trusted node). + +**3.1.3 key manager (KM)** [b-ITU-T Y.3800]: A functional module located in a quantum key distribution (QKD) node to perform key management in the key management layer. + +**3.1.4 key relay** [b-ITU-T Y.3800]: A method to share keys between arbitrary quantum key distribution (QKD) nodes via intermediate QKD node(s). + +**3.1.5 key supply agent (KSA)** [b-ITU-T Y.3802]: A functional element to supply keys to a cryptographic application, being located between a key management agent (KMA) and the cryptographic application. + +NOTE – Application interfaces for cryptographic applications are installed into the key supply agent (KSA). The KSA synchronizes keys, and verifies their integrity via a KSA link before supplying them to the cryptographic application. + +**3.1.6 key supply agent-key (KSA-key)** [b-ITU-T Y.3803]: Key data stored and processed in a key supply agent (KSA), and securely shared between a KSA and a matching KSA. + +**3.1.7 quantum key distribution** [b-ETSI GR QKD 007]: Procedure or method for generating and distributing symmetrical cryptographic keys with information theoretical security based on quantum information theory. + +**3.1.8 quantum key distribution link** [b-ITU-T Y.3800]: A communication link between two quantum key distribution (QKD) modules to operate the QKD. + +NOTE – A QKD link consists of a quantum channel for the transmission of quantum signals, and a classical channel used to exchange information for synchronization and key distillation. + +**3.1.9 quantum key distribution module** [b-ITU-T Y.3800]: A set of hardware and software components that implements cryptographic functions and quantum optical processes, including quantum key distribution (QKD) protocols, synchronization, distillation for key generation, and is contained within a defined cryptographic boundary. + +NOTE – A QKD module is connected to a QKD link, acting as an endpoint module in which a key is generated. These are two types of QKD modules, namely, the transmitters (QKD-Tx) and the receivers (QKD-Rx). + +**3.1.10 quantum key distribution network (QKDN)** [b-ITU-T Y.3800]: A network comprised of two or more quantum key distribution (QKD) nodes connected through QKD links. + +NOTE – A QKDN allows sharing keys between the QKD nodes by key relay when they are not directly connected by a QKD link. + +**3.1.11 quantum key distribution node** [b-ITU-T Y.3800]: A node that contains one or more quantum key distribution (QKD) modules protected against intrusion and attacks by unauthorized parties. + +NOTE – A QKD node can contain a key manager (KM). + +## 3.2 Terms defined in this Recommendation + +None. + +# 4 Abbreviations and acronyms + +This Recommendation uses the following abbreviations and acronyms: + +| | | +|-------|------------------------------------| +| HTTPS | Hypertext Transfer Protocol Secure | +| ID | Identifier | +| KM | Key Manager | +| KMA | Key Management Agent | +| KSA | Key Supply Agent | +| QKD | Quantum Key Distribution | +| QKDN | Quantum Key Distribution Network | +| Rx | Receiver | +| TCP | Transmission Control Protocol | +| TLS | Transport Layer Security | +| Tx | Transmitter | + +# 5 Conventions + +None. + +# 6 Ak interface + +Reference point Ak connects a cryptographic application and a key supply function in a KSA. It is responsible for sending key requests from the cryptographic application to the KSA, performing authentication between the cryptographic application and the KSA, and supplying keys from the KSA to the cryptographic application. + +# 7 Signalling procedure + +The following two modes are specified for key request and key supply at the Ak interface. + +- 1) Key supply upon request mode: Both KMs on the source and destination sides initiate key supplies after receiving key requests from the corresponding cryptographic applications. +- 2) Proactive key supply mode: The KM on the source side initiates key supply upon request, and then instructs the KM on the destination side to supply a key proactively. + +NOTE – The proactive key supply mode can be adopted in scenarios where the cryptographic applications on both sides are restricted to have no direct communication before they have KSA-keys. + +Examples of signalling procedure of key request, key relay, and key supply in QKDN are described in Appendix I of [ITU-T Q.4160]. The protocol suites applied for the signalling are specified in clause 7 of [ITU-T Q.4160]. + +## 7.1 Signalling procedure for key supply upon request mode + +### 7.1.1 Key request on the source side + +When a cryptographic application needs keys for encryption, it sends a key request to the KM, which then supplies keys. If the KM does not have a sufficient number of keys in storage, it initiates key generation or key relay to share the necessary number, and supplies them to the cryptographic applications when their generation or relay is completed. + +Figure 1 shows signalling procedures for key request at the Ak interface on the source side. + + + +``` +sequenceDiagram + participant Cryptographic application + participant KM + Note right of KM: Q.4161(23) + Cryptographic application->>KM: Key request + KM-->>Cryptographic application: Response to key request +``` + +Sequence diagram showing the signalling procedure for a key request at the Ak interface on the source side. A Cryptographic application sends a 'Key request' message to the KM, and the KM responds with a 'Response to key request' message. + +**Figure 1 – Signalling procedures for key request at the Ak interface on the source side** + +### 7.1.2 Key request with identifier on the destination side + +The destination cryptographic application requests a key from the KM to which it is connected. The destination cryptographic application sends a request with the key identifier (ID) that is received from the source cryptographic application in order to specify the key. + +Figure 2 shows signalling procedures for a key request with ID at the Ak interface on the destination side. + + + +``` + +sequenceDiagram + participant CA as Cryptographic application + participant KM as KM + Note right of KM: Q.4161(23) + CA->>KM: Key request with ID + KM-->>CA: Response to key request + +``` + +The diagram illustrates a sequence of messages between a Cryptographic application and a KM. The Cryptographic application sends a 'Key request with ID' to the KM, and the KM responds with a 'Response to key request'. The diagram is labeled 'Q.4161(23)' at the bottom right. + +Sequence diagram showing key request and response between a Cryptographic application and a KM. + +**Figure 2 – Signalling procedures for a key request with identifier at the Ak interface on the destination side** + +## 7.2 Signalling procedure for proactive key supply mode + +### 7.2.1 Session creation on the source side + +When a cryptographic application needs keys for encryption, it first sends a session creation request to the KM on the source side. The source KM then notifies the KM on the destination side to create a session and responds with a session ID to the source cryptographic application when the session is successfully created. Based on the session created, the source cryptographic application can request keys from the source KM. + +Figure 3 shows signalling procedures for a session creation at the Ak interface on the source side. + + + +``` + +sequenceDiagram + participant CA as Cryptographic application + participant KM as KM + Note right of KM: Q.4161(23) + CA->>KM: Session creation request + KM-->>CA: Response to session creation request + +``` + +The diagram illustrates a sequence of messages between a Cryptographic application and a KM. The Cryptographic application sends a 'Session creation request' to the KM, and the KM responds with a 'Response to session creation request'. The diagram is labeled 'Q.4161(23)' at the bottom right. + +Sequence diagram showing session creation request and response between a Cryptographic application and a KM. + +**Figure 3 – Signalling procedures for session creation at the Ak interface on the source side** + +### 7.2.2 Session creation on the destination side + +The destination cryptographic application receives a session creation notification from the KM to which it is connected. The destination KM sends the notification with the session ID that is received from the source KM in order to specify the session. + +Figure 4 shows signalling procedures for session creation at the Ak interface on the destination side. + + + +``` + +sequenceDiagram + participant Cryptographic application + participant KM + Note right of KM: Q.4161(23) + KM->>Cryptographic application: Session creation notification + Cryptographic application-->>KM: Response to session creation notification + +``` + +Sequence diagram for session creation at the destination side. A Cryptographic application sends a 'Session creation notification' to a KM, which responds with a 'Response to session creation notification'. The diagram is labeled Q.4161(23). + +**Figure 4 – Signalling procedures for session creation at the Ak interface on the destination side** + +### 7.2.3 Key request with session identifier on the source side + +With a created session, the KM on the source side supplies KSA-keys on request from the source cryptographic application. + +Figure 5 shows signalling procedure for a key request with a session ID at the Ak interface on the source side. + + + +``` + +sequenceDiagram + participant Cryptographic application + participant KM + Note right of KM: Q.4161(23) + Cryptographic application->>KM: Key request with session ID + KM-->>Cryptographic application: Response to key request with session ID + +``` + +Sequence diagram for key request with session identifier at the source side. A Cryptographic application sends a 'Key request with session ID' to a KM, which responds with a 'Response to key request with session ID'. The diagram is labeled Q.4161(23). + +**Figure 5 – Signalling procedures for key request with session identifier at the Ak interface on the source side** + +### 7.2.4 Proactive key supply on the destination side + +The KM on the destination side proactively supplies KSA-keys to the destination cryptographic application to which it is connected. This scheme is applicable when the key request from the source cryptographic application is received by the source KM, which then instructs the destination KM to supply a key proactively. + +Figure 6 shows signalling procedures for proactive key supply at the Ak interface on the destination side. + + + +``` + +sequenceDiagram + participant Cryptographic application + participant KM + Note right of KM: Q.4161(23) + KM->>Cryptographic application: Proactive key supply + Cryptographic application-->>KM: Response to proactive key supply + +``` + +Sequence diagram for proactive key supply at the destination side. A KM sends a 'Proactive key supply' to a Cryptographic application, which responds with a 'Response to proactive key supply'. The diagram is labeled Q.4161(23). + +**Figure 6 – Signalling procedures for proactive key supply at the Ak interface on the destination side** + +# 8 Signalling messages and parameters + +This clause specifies messages and their parameters for the Ak interface. + +The M/O columns of Tables 1 to 11 relate to signalling of the parameter in columns 1; M indicates mandatory and O indicates optional. + +The messages and parameters specified in this clause are independent of a specific protocol and can have different implementations. The recommended protocol implementations are described in Appendices I and II. + +NOTE – A message parameter described in Tables 1 to 11 is not necessarily mapped to a field in the message payload and might be part of the control parameters of a specific protocol. The data type listed in columns 3 of tables 1 to 11 may vary with specific protocols. + +## 8.1 Messages and parameters for key supply upon request mode + +### 8.1.1 Key request message + +A message is sent from the cryptographic application to the KM on the source side to request keys. + +Table 1 lists the parameters of a key request message. + +**Table 1 – Parameters of key request message** + +| Parameter | Description | Data type | M/O | Remarks | +|----------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------|------------------|-----|---------------------------------------| +| Application source ID | ID of the source cryptographic application (i.e., the application that sends this message) | String | O | | +| Application destination ID | ID of the destination cryptographic application (i.e., the application with which the source cryptographic application requests to communicate) | String | M | | +| Application name | Name of the cryptographic application | String | O | | +| Number of keys | Number of KSA-keys requested | Integer | O | A default value is applied if omitted | +| Size of key | Length of each KSA-key requested | Integer | O | A default value is applied if omitted | +| Extension | Array of extension parameters | Array of objects | O | | + +### 8.1.2 Key request with identifier message + +On receipt of the KSA-key, the source cryptographic application sends the corresponding key ID to the destination cryptographic application. The destination cryptographic application sends a request to the destination KM with the key ID. The destination cryptographic application then receives the key that has been shared between the source and destination KMs. + +Table 2 lists the parameters of a key request with an ID message. + +**Table 2 – Parameters of a key request with identifier message** + +| Parameter | Description | Data type | M/O | Remarks | +|----------------------------|-------------------------------------------------------------------------------------------------|------------------|-----|------------------------------------------------------------------| +| Application source ID | ID of the source cryptographic application | String | M | | +| Application destination ID | ID of the destination cryptographic application (i.e., the application that sends this message) | String | O | | +| Application name | Name of the cryptographic application | String | O | | +| Key IDs | IDs of the KSA-keys requested | Array of objects | M | These IDs are notified from the source cryptographic application | +| Key ID | ID of the KSA-key requested | String | M | | +| Key ID extension | Extensions to key ID | Object | O | | +| Extension | Array of extension parameters | Array of objects | O | | + +### 8.1.3 Response to key request message + +A response to a key request message is sent from the KM to the cryptographic application in response to the key request or the key request with ID from the cryptographic application. The KM supplies the requested KSA-keys to the cryptographic application. There is no difference between the source side and the destination side for the response to the key request. + +Table 3 lists the parameters of a response to a key request message. + +**Table 3 – Parameters of response to key request message** + +| Parameter | Description | Data type | M/O | Remarks | +|---------------|---------------------------------------------|------------------|-----|-------------------------------| +| Keys | Key file consists of key data and metadata. | Array of objects | M | | +| Key | KSA-key data provided for the request | String | M | | +| Key ID | ID of the KSA-key provided | String | M | | +| Key extension | Extensions to key file | Object | O | Hash value, etc. | +| Response | Result of key supply | String | M | Reason for success or failure | +| Extension | Array of extension parameters | Array of objects | O | | + +## 8.2 Messages and parameters for proactive key supply mode + +### 8.2.1 Session creation request message + +A session creation request message is sent from the cryptographic application to the KM on the source side. A session is created to facilitate key supply between the cryptographic applications and the KMs on both sides. + +Table 4 lists the parameters of a session creation request message. + +**Table 4 – Parameters of session creation request message** + +| Parameter | Description | Data type | M/O | Remarks | +|----------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------|------------------|------------|-------------------------------------------------------------------------------------------------------------------------------------| +| Application source ID | ID of the source cryptographic application (i.e., the application that sends this message) | String | M | | +| Application destination ID | ID of the destination cryptographic application (i.e., the application with which the source cryptographic application requests to communicate) | String | M | | +| Application name | Name of the source cryptographic application | String | O | | +| Number of keys | Number of KSA-keys requested | Integer | O | A default value is applied if omitted.
This parameter can be used as the maximum number of KSA-keys requested during one session | +| Extension | Array of extension parameters | Array of objects | O | | + +### 8.2.2 Response to session creation request message + +The response to a session creation request message is sent from the KM to the cryptographic application on the source side. On receipt of a session creation request, the source KM notifies the KM on the destination side to create a session and responds with a session ID to the source cryptographic application when the session is successfully created. + +Table 5 lists the parameters of a response to a session creation request message. + +**Table 5 – Parameters of response to session creation request message** + +| Parameter | Description | Data type | M/O | Remarks | +|------------------|---------------------------------------|------------------|------------|--------------------------------------------------------| +| Session ID | ID of the session created | String | M | | +| Response | Result of the creation of the session | String | M | Success, failure reason, or status table of key supply | +| Source KM ID | ID of the source KM | String | O | | +| Extension | Array of extension parameters | Array of objects | O | | + +### 8.2.3 Session creation notification message + +A session creation notification message is sent from the KM to the cryptographic application on the destination side. The destination KM proactively sends the session ID to the destination cryptographic application and notifies it with the ID of the source cryptographic application requesting to communicate with it. + +Table 6 lists the parameters of a session creation notification message. + +**Table 6 – Parameters of session creation notification message** + +| Parameter | Description | Data type | M/O | Remarks | +|----------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------|------------------|------------|-------------------------------------------------------------------------------------------------------------------------------------| +| Application source ID | ID of the source cryptographic application (i.e., the application that receives this message) | String | M | | +| Application destination ID | ID of the destination cryptographic application (i.e., the application with which the source cryptographic application requests to communicate) | String | M | | +| Application name | Name of the source cryptographic application | String | O | | +| Session ID | ID of the session created | String | M | | +| Number of keys | Number of KSA-keys requested | Integer | O | A default value is applied if omitted.
This parameter can be used as the maximum number of KSA-keys requested during one session | +| Extension | Array of extension parameters | Array of objects | O | | + +### **8.2.4 Response to session creation notification message** + +A response to a session creation notification message is sent from the cryptographic application to the KM in response to the session creation notification on the destination side. The destination cryptographic application notifies the result of the creation of the session to the destination KM. + +Table 7 lists the parameters of a response to a session creation notification message. + +**Table 7 – Parameters of response to session creation notification message** + +| Parameter | Description | Data type | M/O | Remarks | +|------------------|---------------------------------------|------------------|------------|-------------------------------| +| Session ID | ID of the session created | String | M | | +| Response | Result of the creation of the session | String | M | Reason for success or failure | +| Extension | Array of extension parameters | Array of objects | O | | + +### **8.2.5 Key request with session identifier message** + +With a created session, the cryptographic application sends a key request with session ID message to the KM on the source side. The source KM then supplies the requested KSA-keys to the source cryptographic application during the session. + +Table 8 lists the parameters of a key request with a session ID message. + +**Table 8 – Parameters of key request with session identifier message** + +| Parameter | Description | Data type | M/O | Remarks | +|----------------|----------------------------------|------------------|-----|---------------------------------------| +| Session ID | ID of the session created | String | M | | +| Number of keys | Number of KSA-keys requested | Integer | O | A default value is applied if omitted | +| Size of key | Length of each KSA-key requested | Integer | O | A default value is applied if omitted | +| Extension | Array of extension parameters | Array of objects | O | | + +### **8.2.6 Response to key request with session identifier message** + +A response to a key request with a session ID message is sent from the KM to the cryptographic application on the source side. The source KM then supplies the requested KSA-keys to the source cryptographic application during the created session. + +Table 9 lists the parameters of a response to a key request with a session ID message. + +**Table 9 – Parameters of response to key request with session identifier message** + +| Parameter | Description | Data type | M/O | Remarks | +|---------------|--------------------------------------------|------------------|-----|-------------------------------| +| Session ID | ID of the session created | String | M | | +| Keys | Key file consists of key data and metadata | Array of objects | M | | +| Key | KSA-key data provided for the request | String | M | | +| Key ID | ID of the KSA-key provided | String | M | | +| Key extension | Extensions to key file | Object | O | Hash value, etc. | +| Response | Result of key supply | String | M | Reason for success or failure | +| Extension | Array of extension parameters | Array of objects | O | | + +### **8.2.7 Proactive key supply message** + +A proactive key supply message is sent from the KM to the cryptographic application on the destination side. The destination KM proactively supplies the KSA-key to the destination cryptographic application during the created session. + +Table 10 lists the parameters of a proactive key supply message. + +**Table 10 – Parameters of proactive key supply message** + +| Parameter | Description | Data type | M/O | Remarks | +|---------------|--------------------------------------------|------------------|-----|------------------| +| Session ID | ID of the session created | String | M | | +| Keys | Key file consists of key data and metadata | Array of objects | M | | +| Key | KSA-key data supplied | String | M | | +| Key ID | ID of the KSA-key supplied | String | M | | +| Key extension | Extensions to key file | Object | O | Hash value, etc. | +| Extension | Array of extension parameters | Array of objects | O | | + +### 8.2.8 Response to proactive key supply message + +A response to a proactive key supply message is sent from the cryptographic application to the KM in response to proactive key supply on the destination side. The destination cryptographic application notifies the receipt of the KSA-key to the destination KM. + +Table 11 lists the parameters of a response to proactive key supply message. + +**Table 11 – Parameters of response to proactive key supply message** + +| Parameter | Description | Data type | M/O | Remarks | +|------------|--------------------------------------|------------------|-----|-------------------------------| +| Session ID | ID of the session created | String | M | | +| Key ID | ID of the KSA-key received | String | M | | +| Response | Result of the receipt of the KSA-key | String | M | Reason for success or failure | +| Extension | Array of extension parameters | Array of objects | O | | + +# 9 Security considerations + +Key data and associated metadata are transferred through an Ak reference point. Security requirements and measures to protect them are specified in [ITU-T X.1712]. + +# Appendix I + +## Protocol implementation using the transmission control protocol + +(This appendix does not form an integral part of this Recommendation.) + +This appendix describes an implementation using the transmission control protocol (TCP) for messages and parameters that are described in clause 8. + +NOTE 1 – Some parameters are mapped to a part of the control information of the protocol instead of being mapped to a field in the data payload. + +The cryptographic application can connect to the KM using the TCP [b-IETF RFC 9293]. The corresponding message format over the TCP is shown in Figure I.1. + +| Version | MessageID | CommandCode | Length | Payload | +|---------|-----------|-------------|--------|---------| +|---------|-----------|-------------|--------|---------| + +Q.4161(23) + +**Figure I.1 – Message format over the transmission control protocol** + +In Figure I.1: + +Version: the current version of the message format adopted, 2 bytes; + +MessageID: the unique ID of each message, 4 bytes; + +CommandCode: a unique code that denotes different command/response messages transferred at the Ak interface, 2 bytes; + +Length: the length of the message payload, 2 bytes; + +Payload: the message parameters of a specific command/response message, JavaScript object notation data format [b-IETF RFC 8259]. + +NOTE 2 – The transport layer security (TLS) protocol [b-IETF RFC 5246] can be implemented with the TCP for enhanced security. + +On establishment of the connection, mutual authentication between the cryptographic application and the KM is performed. After mutual authentication, a command/response message can be transferred via the Ak interface for key request and key supply. + +NOTE 3 – When applying the TLS protocol, the cryptographic application can verify the validity of a certificate the KM possesses and based on that confirm the ID of the KM it is connecting to. Similarly, the KM can verify the validity of a certificate the cryptographic application possesses and based on that confirm the ID of the connecting cryptographic application. + +Table I.1 lists CommandCode vs. command/response message name. + +**Table I.1 – CommandCode vs. command/response message name** + +| CommandCode | Command/response message name | +|-------------|-------------------------------------------| +| 0x2101 | Key request | +| 0x2102 | Key request with ID | +| 0x1203 | Response to key request | +| 0x2104 | Session creation request | +| 0x1205 | Response to session creation request | +| 0x1206 | Session creation notification | +| 0x2107 | Response to session creation notification | + +**Table I.1 – CommandCode vs. command/response message name** + +| CommandCode | Command/response message name | +|--------------------|-----------------------------------------| +| 0x2108 | Key request with session ID | +| 0x1209 | Response to key request with session ID | +| 0x120A | Proactive key supply | +| 0x210B | Response to proactive key supply | + +The first two digits "12" in a CommandCode indicate that the corresponding message is sent from the KM to the cryptographic application; "21" indicate that the corresponding message is sent from the cryptographic application to the KM. + +# Appendix II + +## Protocol implementation for key supply upon request mode using hypertext transfer protocol secure + +(This appendix does not form an integral part of this Recommendation.) + +The signalling messages and parameters for key supply upon request mode specified in clause 8.1 can be implemented using hypertext transfer protocol secure (HTTPS) according to the protocol and data format of the representational state transfer-based key delivery application programming interface specified in [b-ETSI GS QKD 014]. This appendix describes the mapping of the messages and parameters specified in clause 8.1 to the corresponding data format specified in [b-ETSI GS QKD 014]. + +NOTE – In this implementation, the cryptographic application and the KM correspond to the secure application entity (SAE) and the key management entity defined in [b-ETSI GS QKD 014], respectively. + +## II.1 Key request message + +In this implementation, the key request message specified in clause 8.1.1 corresponds to the HTTPS request of the HTTPS transaction performed as the Get Key method specified in [b-ETSI GS QKD 014]. Table II.1 lists the mapping of the key request message to the Get Key method. + +**Table II.1 – Mapping of key request message to Get Key method** + +| Parameter | M/O | Data type | Implementation in Get Key method | +|----------------------------|-----|------------------|---------------------------------------------------------------------------------------| +| Application source ID | O | String | None | +| Application destination ID | M | String | "{target_SAE_ID}" part of the access URL | +| Application name | O | String | None | +| Number of keys | O | Integer | The "number" item in the key request data format | +| Size of key | O | Integer | The "size" item in the key request data format | +| Extension | O | Array of objects | The "extension_mandatory" or "extension_optional" item in the Key request data format | + +## II.2 Key request with identifier message + +In this implementation, the key request with ID message specified in clause 8.1.2 corresponds to the HTTPS request of the HTTPS transaction performed as the Get Key with ID method specified in [b-ETSI GS QKD 014]. Table II.2 lists the mapping of the key request with ID message to the Get Key with ID method. + +**Table II.2 – Mapping of key request with identifier message to Get Key with ID method** + +| Parameter | M/O | Data type | Implementation in Get Key with ID method | +|----------------------------|-----|------------------|----------------------------------------------| +| Application source ID | M | String | "{initiator_SAE_ID}" part of the access URL | +| Application destination ID | O | String | None | +| Application name | O | String | None | +| Key IDs | M | Array of objects | The "key_IDs" item in the key ID data format | + +**Table II.2 – Mapping of key request with identifier message +to Get Key with ID method** + +| Parameter | M/O | Data type | Implementation in Get Key with ID method | +|------------------|------------|------------------|--------------------------------------------------------| +| Key ID | M | String | The "key_ID" item in the key ID data format | +| Key ID extension | O | Object | The "key_ID_extension" item in the key ID data format | +| Extension | O | Array of objects | The "key_IDs_extension" item in the key ID data format | + +## **II.3 Response to key request message** + +In this implementation, the response to a key request message specified in clause 8.1.3 corresponds to the HTTPS response of the HTTPS transaction performed as the Get Key method or the Get Key with ID method. Table II.3 lists the mapping of the response to a key request message to the Get Key method or the Get Key with ID method. + +**Table II.3 – Mapping of response to key request message +to Get Key/Get Key with ID method** + +| Parameter | M/O | Data type | Implementation in Get Key or
Get Key with ID method | +|------------------|------------|------------------|--------------------------------------------------------------------------------------------| +| Keys | M | Array of objects | The "keys" item in the key container data format | +| Key | M | String | The "key" item in the key container data format | +| Key ID | M | String | The "key_ID" item in the key container data format | +| Key extension | O | Object | The "key_ID_extension" item in the key container data format | +| Response | M | String | The status code of HTTPS transaction performed as Get Key method or Get Key with ID method | +| Extension | O | Array of objects | The "key_container_extension" item in the key container data format | + +# Bibliography + +- [b-ITU-T Y.3800] Recommendation ITU-T Y.3800 (2019), *Overview on networks supporting quantum key distribution*. +- [b-ITU-T Y.3802] Recommendation ITU-T Y.3802 (2020), *Quantum key distribution networks – Functional architecture*. +- [b-ITU-T Y.3803] Recommendation ITU-T Y.3803 (2020), *Quantum key distribution networks – Key management*. +- [b-ETSI GR QKD 007] Group Report ETSI GR QKD 007 V1.1.1 (2018), *Quantum key distribution (QKD); Vocabulary*. +- [b-ETSI GS QKD 014] Group Specification ETSI GS QKD 014 V1.1.1 (2019), *Quantum key distribution (QKD); Protocol and data format of REST-based key delivery API*. +- [b-IETF RFC 5246] IETF RFC 5246 (2008), *The transport layer security (TLS) protocol – Version 1.2*. +- [b-IETF RFC 8259] IETF RFC 8259 (2017), *The JavaScript object notation (JSON) data interchange format*. +- [b-IETF RFC 9293] IETF RFC 9293 (2022), *Transmission control protocol (TCP)*. + + + +## SERIES OF ITU-T RECOMMENDATIONS + +| | | +|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------| +| Series A | Organization of the work of ITU-T | +| Series D | Tariff and accounting principles and international telecommunication/ICT economic and policy issues | +| Series E | Overall network operation, telephone service, service operation and human factors | +| Series F | Non-telephone telecommunication services | +| Series G | Transmission systems and media, digital systems and networks | +| Series H | Audiovisual and multimedia systems | +| Series I | Integrated services digital network | +| Series J | Cable networks and transmission of television, sound programme and other multimedia signals | +| Series K | Protection against interference | +| Series L | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant | +| Series M | Telecommunication management, including TMN and network maintenance | +| Series N | Maintenance: international sound programme and television transmission circuits | +| Series O | Specifications of measuring equipment | +| Series P | Telephone transmission quality, telephone installations, local line networks | +| Series Q | Switching and signalling, and associated measurements and tests | +| Series R | Telegraph transmission | +| Series S | Telegraph services terminal equipment | +| Series T | Terminals for telematic services | +| Series U | Telegraph switching | +| Series V | Data communication over the telephone network | +| Series X | Data networks, open system communications and security | +| Series Y | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities | +| Series Z | Languages and general software aspects for telecommunication systems | \ No newline at end of file diff --git a/marked/Q/T-REC-Q.50-200107-I_PDF-E/0bf9346902e9a3bdabf05ceacc1947f5_img.jpg b/marked/Q/T-REC-Q.50-200107-I_PDF-E/0bf9346902e9a3bdabf05ceacc1947f5_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..af920838b045395fb253b78a4f46659ee66572b6 --- /dev/null +++ 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computing** + +Recommendation ITU-T Q.5003 + +## ITU-T Q-SERIES RECOMMENDATIONS **SWITCHING AND SIGNALLING, AND ASSOCIATED MEASUREMENTS AND TESTS** + +| | | +|--------------------------------------------------------------------------------|----------------------| +| SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE | Q.1–Q.3 | +| INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING | Q.4–Q.59 | +| FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN | Q.60–Q.99 | +| CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS | Q.100–Q.119 | +| SPECIFICATIONS OF SIGNALLING SYSTEMS No. 4, 5, 6, R1 AND R2 | Q.120–Q.499 | +| DIGITAL EXCHANGES | Q.500–Q.599 | +| INTERWORKING OF SIGNALLING SYSTEMS | Q.600–Q.699 | +| SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 | Q.700–Q.799 | +| Q3 INTERFACE | Q.800–Q.849 | +| DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 1 | Q.850–Q.999 | +| PUBLIC LAND MOBILE NETWORK | Q.1000–Q.1099 | +| INTERWORKING WITH SATELLITE MOBILE SYSTEMS | Q.1100–Q.1199 | +| INTELLIGENT NETWORK | Q.1200–Q.1699 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2000 | Q.1700–Q.1799 | +| SPECIFICATIONS OF SIGNALLING RELATED TO BEARER INDEPENDENT CALL CONTROL (BICC) | Q.1900–Q.1999 | +| BROADBAND ISDN | Q.2000–Q.2999 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR THE NGN | Q.3000–Q.3709 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR SDN | Q.3710–Q.3899 | +| TESTING SPECIFICATIONS | Q.3900–Q.4099 | +| PROTOCOLS AND SIGNALLING FOR PEER-TO-PEER COMMUNICATIONS | Q.4100–Q.4139 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2020 | Q.5000–Q.5049 | +| Signalling requirements and architecture of IMT-2020 | Q.5000–Q.5019 | +| Protocols for IMT-2020 | Q.5020–Q.5049 | +| COMBATING COUNTERFEITING AND STOLEN ICT DEVICES | Q.5050–Q.5069 | + +*For further details, please refer to the list of ITU-T Recommendations.* + +## Recommendation ITU-T Q.5003 + +# Signalling requirements and architecture for federated multiaccess edge computing + +## Summary + +Recommendation ITU-T Q.5003 describes signalling requirements and architecture for federated multiaccess edge computing (MEC). This Recommendation specifies signalling requirements, signalling architecture with reference points and security considerations for federated MEC. + +## History + +| Edition | Recommendation | Approval | Study Group | Unique ID* | +|---------|----------------|------------|-------------|---------------------------------------------------------------------------| +| 1.0 | ITU-T Q.5003 | 2022-02-13 | 11 | 11.1002/1000/14925 | + +## Keywords + +Federated MEC, MEC platform, multiaccess edge computing. + +--- + +\* To access the Recommendation, type the URL
provider's coverage..... | 11 | +| I.3 Federation for connecting services deployed on different MEC system..... | 12 | +| Bibliography..... | 13 | + + + +## Recommendation ITU-T Q.5003 + +# Signalling requirements and architecture for federated multiaccess edge computing + +# 1 Scope + +This Recommendation describes the application layer architecture and architectural requirements for the federated multiaccess edge computing (MEC). The scope of this Recommendation covers: + +- Signalling architecture; +- Signalling requirements. + +# 2 References + +The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. + +None. + +# 3 Definitions + +## 3.1 Terms defined elsewhere + +This Recommendation uses the following terms defined elsewhere: + +**3.1.1 multiaccess edge computing** [b-ETSI GS MEC 001]: System which provides an IT service environment and cloud-computing capabilities at the edge of an access network which contains one or more type of access technology, and in close proximity to its users. + +**3.1.2 MEC application** [b-ETSI GS MEC 001]: Application that can be instantiated on an MEC host within the MEC system and can potentially provide or consume MEC services. + +**3.1.3 MEC platform** [b-ETSI GS MEC 001]: Collection of functionality that is required to run MEC applications on a specific MEC host virtualization infrastructure and to enable them to provide and consume MEC services, and that can itself provide a number of MEC services. + +**3.1.4 MEC service** [b-ETSI GS MEC 001]: Service provided via the MEC platform either by the MEC platform itself or by an MEC application. + +**3.1.5 lifecycle management** [b-ETSI GS MEC 001]: Set of functions required to manage the instantiation, maintenance and termination of an MEC application instance. + +## 3.2 Terms defined in this Recommendation + +This Recommendation defines the following term: + +**3.2.1 federated MEC**: A group of multiaccess edge computing systems that belong to several multiaccess edge computing providers, and which jointly provide a unified service across these providers to respond to requests received from application providers by exchanging resources from all of the individual multiaccess edge computing systems. + +# 4 Abbreviations and acronyms + +This Recommendation uses the following abbreviations and acronyms: + +| | | +|------|-----------------------------| +| COTS | Commercial-Off-The-Shelf | +| FE | Functional Entity | +| HW | Hardware | +| IaaS | Infrastructure as a Service | +| IP | Internet Protocol | +| MA | MEC Aggregation | +| MAL | MEC Aggregation Layer | +| MEC | Multiaccess Edge Computing | +| MeML | MEC Management Layer | +| MIL | MEC Infrastructure Layer | +| MNO | Mobile Network Operator | +| MPL | MEC Platform Layer | +| PaaS | Platform as a Service | +| QoE | Quality of Experience | +| SaaS | Software as a Service | +| SDK | Software Development Kit | +| SLA | Service Level Agreement | +| SW | Software | +| UE | User Equipment | +| URL | Uniform Resource Locator | + +# 5 Conventions + +None. + +# 6 Overview + +Multiaccess Edge Computing (MEC) providers have been developing the MEC services and platform separately using different technologies for different vertical domains, which may bring significant drawbacks. They have to deal with specific signalling flows for different interfaces to interwork with different service platforms, which may significantly increase the complexity for the MEC providers. Therefore, there is a strong necessary to specify an architecture with a signalling convergence to provide unified MEC services across different MEC providers, which can be fulfilled by federated MEC. + +Federated MEC is a model which can provide a unified MEC service across MEC providers by exchanging the resources (e.g., cloud-computing resources, network capabilities) of each MEC system and requests from application providers. + +Federated MEC mainly provides the following three functionalities: + +- Authenticating, authorizing each MEC system and sharing its capabilities: This is needed for MEC providers to authenticate and authorize each other and share information related to each MEC system's catalogue with network resources, computing resources, etc. + +- Discovering appropriate MEC systems: When a user moves to another region during MEC service or an application provider requests to interconnect with another application provider, it is supported that each MEC provider discover different MEC systems based on the registered information to maintain the quality that MEC service can originally provide. +- Communicating between MEC systems: After discovering, communicating between MEC systems is supported. Basically, the content type delivered over the communication is not limited, and it can also support the delivery of application packages and application contexts, or the exchange of some media (text, audio or video). + +In this Recommendation, the architectural model and signalling requirements for federated MEC are specified in clause 7; the relevant security considerations in clause 8; and selected use cases for federated MEC are described in Appendix I. + +Note that the concept of MEC federation is also discussed in the other SDOs, e.g., GSMA OPG and ETSI ISG MEC; and there are other relevant specifications [b-GSMA] [b-ETSI GS MEC 035] being developed. + +# 7 Architecture and signalling requirements + +The MEC system is responsible for 1) serving MEC service and application providers' request to host their instances in the network edge; and 2) supporting an end-user to access via user equipment (UE) the MEC services and applications deployed in the MEC infrastructure. + +In order to serve the UE registered or moving to different MEC systems, the MEC service and application providers need to interact with the different MEC systems via different interfaces, contract, policies, Service Level Agreement (SLA), etc. + +In federated MEC, the interactions with MEC service and application providers are aggregated and the different MEC systems federate to deploy the MEC services and applications with no intervention at on-demand locations covered by different MEC providers. + +This clause specifies the architectural model for federated MEC, including signalling requirements for interactions among different functional entities and between different MEC systems. + +## 7.1 Architectural model for federated MEC + +The architectural model for federated MEC consists of four layers, including several functional entities in each layer: + +- MEC aggregation layer (MAL) is responsible for serving the MEC service and application providers' demands towards different MEC systems; +- MEC management layer (MeML) is responsible for the management of MEC services and applications; +- MEC platform layer (MPL) is responsible for provisioning and control of the connectivity to MEC services and applications; +- MEC Infrastructure Layer (MIL) is responsible for the management of the virtualized infrastructure. + +In the architectural model of federated MEC, there are six reference points defined to serve the interactions among the layers and external entities (i.e. MEC services and applications and UE): + +- MS reference point, for interactions between MEC services and applications and MAL; +- MA reference point, for interactions between MAL and MeML; +- MM reference point, for interactions between MAL and MeML; +- MMe reference point, for interactions between MeMLs of different MEC systems; +- MP reference point, for interactions between MPL and MIL; + +- MPe reference point, for interactions between MPLs of different MEC systems; +- MI reference point, for interactions between MIL and UE. + +The architectural model for federated MEC is illustrated in Figure 7-1. + + + +Figure 7-1: Architectural model for federated MEC. The diagram shows a hierarchical structure of layers. At the top is 'MEC services and applications (B2C, B2B and B2B2X services)'. Below it is 'MAL (MEC aggregation layer, federated MEC)' connected via the 'MS reference point'. The MAL connects to two parallel 'MeML (MEC management layer)' blocks via the 'MA reference point'. Each MeML connects to an 'MPL (MEC platform layer)' via the 'MM reference point'. The two MPLs are connected to each other via the 'MMe reference point'. Each MPL connects to a 'MIL (MEC infrastructure layer)' via the 'MP reference point'. The two MILs are connected to each other via the 'MPe reference point'. Each MIL connects to a 'UE' block via the 'MI reference point'. + +**Figure 7-1 – Architectural model for federated MEC** + +### 7.1.1 Functional entities and requirements + +This clause defines functional entities that require for each predefined layer. + +#### 7.1.1.1 MEC aggregation layer + +The MAL is responsible for different service providers' requirements over heterogeneous MEC with the functions described in Figure 7-2 and below. + + + +Figure 7-2: Functional entities for the MEC aggregation layer. The diagram shows a box for 'MAL (MEC aggregation layer)' containing five functional entities in a grid: 'End-to-end orchestration', 'Catalogue', 'Authentication and authorization', 'Runtime', and 'Service repository'. + +**Figure 7-2 – Functional entities for the MEC aggregation layer** + +- The end-to-end orchestration FE supports the lifecycle management of MEC infrastructure resources, platform functions, services and applications over the federation of heterogeneous operator specific MEC platform and management layers. The FE supports necessary functionalities for the services and application providers to deploy and manage their applications, such as to upload, update and delete application images with necessary information. These functionalities are performed with related FEs in MeML and MPL; For the direct interaction between MeMLs and between MPLs of federated MEC systems when, for example, supporting consistent user experience across the MEC provider's coverage or + +connecting services deployed on different MEC system and so on is required, the FE supports the discovery and selection of appropriate MEC system, datacentres and MEC platforms. + +- Catalogue FE manages the collection of operator specific MEC infrastructure resources, platform functions capabilities. +- Runtime FE manages the runtime information of federated MEC. The FE handles, over MeML, services and application providers' requests to subscribe the event notification and run time information related to the network and MEC resources. +- Service repository FE manages and handles the federated MEC services. +- Authentication and Authorization FE manages authentication of the operator specific federated MECs. + +#### 7.1.1.2 MEC management layer + +The MeML provides functionalities which are required for MEC network resource allocating tasks such as allocating cloud and network resources for each required MEC service (that may be in the same or a different MEC provider); see also Figure 7–3. MeML communicates with other MeML in a federated MEC system through an Exchange reference point between them, for example, for the direct delivery of an onboard application package to allow services and application providers of an MEC system to deploy their applications using the MEC resources and services of other federated MEC systems. Discovery and selection of appropriate target MEC systems and necessary information to establish the connection between the MeMLs is provided by end-to-end orchestration FE in the MAL. + + + +The diagram shows the 'MeML (MEC management layer)' as a large rectangle containing six smaller dashed boxes arranged in a 2x3 grid. The top row contains 'Lifecycle management', 'Assurance management', and 'Service management'. The bottom row contains 'SLA management', 'Inventory management', and 'Authentication and authorization'. Below the diagram is the text 'Q.5003(22)'. + +Diagram of the MEC management layer (MeML) functional entities. + +**Figure 7-3 – Functional entities for the MEC management layer** + +- The lifecycle management FE supports the on-boarding, instantiation, configuration, scaling and termination of the MEC application and services over the MEC platform. For federated MEC application and service deployment and management, application images and related information are provided by the end-to-end orchestration FE in the MAL or by the MeML of the peering federated MEC associated with the application provider directly. When UE moves, including in roaming scenarios, to the area where the required MEC service or services are not enabled, the FE supports the relocation of MEC instance(s) over MPL between federated MEC systems as well as in an MEC system. +- The assurance management FE provides a data collection, analytics, and report functionality that supports monitoring and tracking resource usage and application status, and so on. The FE reports runtime MEC information including network information and event notification to the subscribed services and application providers via the runtime FE in MAL. When the services and application provider is associated with another federated MEC system, the FE forwards the information to the MeML of the federated MEC system. +- SLA management supports service-level agreement monitoring risk management tools. + +- Inventory management FE manages MEC infrastructure resources, platform functions, service and application metadata and status, availabilities and so on; The FE supports direct delivery of onboard application packages to the other federated MEC system's lifecycle management FE through a reference point Exchange between MeMLs, allowing services and application providers of an MEC system to deploy their applications using the MEC resources and services of other federated MEC systems. +- The service management FE manages service information such as service profile, request handling, interaction management and so on. +- The authentication and authorization FE manages the authentication of MAL and authentication of itself to MAL, and it authorizes the MAL to interact with the operator specific federated MEC. + +#### 7.1.1.3 MEC platform layer + +The MPL provides functionalities which are required for MEC service processing tasks such as service discovery and service availability via other platforms (that may be in the same or a different MEC provider); see also Figure 7–4. The MPL communicates with other MPLs of federated MEC systems through an exchange reference point between them, as an example, for connecting services deployed on another MEC system platform. The discovery and selection of an appropriate MEC system platform and necessary information to establish the connection between them is provided by the end-to-end orchestration FE in the MAL. + + + +The diagram illustrates the functional entities for the MEC platform layer (MPL). It is a rectangular box containing four smaller dashed boxes arranged in a 2x2 grid. The top-left box is labeled 'Platform', the top-right is 'Connectivity controller', the bottom-left is 'Resource controller', and the bottom-right is 'Topology controller'. Above the grid, the text 'MPL (MEC platform layer)' is centered. Below the diagram, the reference 'Q.5003(22)' is shown. + +Diagram of the MEC platform layer (MPL) showing four functional entities: Platform, Connectivity controller, Resource controller, and Topology controller. + +**Figure 7-4 – Functional entities for the MEC platform layer** + +- The platform functions FE supports operator platform specific functions that may contain operator specific APIs and IaaS/PaaS/SaaS functions. When a service request from the serving local MEC application is not locally available, the FE connects the local MEC application to the services on the appropriate other federated MEC system through an exchange reference point between MPLs. Discovery and selection of the appropriate federated MEC system and platform is performed by the MAL and MeML. +- The connectivity controller FE supports the MEC platform to control an operator's specific connectivity resources. +- The resource controller FE supports the MEC platform to control an operator's specific compute, network and storage resources considering the resource sharing policy between services or MEC service providers, and so on. The FE reports runtime MEC information including network information and event notification to the assurance FE in MeML for the use of subscribed service and application providers. +- The topology controller FE maintains both the physical network and virtual network. + +#### 7.1.1.4 MEC infrastructure layer + +The MIL provides a procedure for allocating and releasing virtualized (compute, storage and networking) resources of the virtualization infrastructure; see also Figure 7–5. + + + +The diagram shows the MIL (MEC infrastructure layer) as a large rectangle containing four dashed boxes arranged in a 2x2 grid. The top-left box is labeled 'Datacentre facility and capability information', the top-right is 'Connectivity resource', the bottom-left is 'Physical infrastructure resource', and the bottom-right is 'Virtual infrastructure resource'. Below the diagram is the text 'Q.5003(22)'. + +Diagram of MIL (MEC infrastructure layer) functional entities + +**Figure 7-5 – Functional entities for the MEC infrastructure layer** + +- Datacentre facility and capability information FE manages various infrastructure information such as racks, shelves, network topology, HVAC capabilities and so on. +- Connectivity resource FE provides connectivity resource between multiaccess networks. +- Physical infrastructure resource FE manages resource information such as a commercial-off-the-shelf (COTS) servers, networks or storage hardware with special-purpose hardware components (e.g., AI inferencing accelerator). +- Virtual infra resource FE supports virtualized computing resources including virtual machine and container, network resources and storage resources that can be pooled and shared between services or dedicated to specific services. For the use of subscribed service and application providers, the FE collects and reports requested runtime MEC information including network information and event notification to the resource controller FE in the MPL. + +#### 7.1.1.5 UE + +UE provides capabilities and an SDK that support specific capabilities and equipment to interact with the MPL; see also Figure 7–6. + + + +The diagram shows the UE as a large rectangle containing two dashed boxes arranged side-by-side. The left box is labeled 'UE capabilities' and the right box is labeled 'MEC SDK'. Below the diagram is the text 'Q.5003(22)'. + +Diagram of UE functional entities + +**Figure 7-6 – Functional entities for UE** + +- The UE capabilities FE provides connectivity with the federated MEC by supporting the provisioning and discovery of MEC services and registration and authentication/authorization of the UE as an MEC client. It also supports retrieving UE-related information (e.g., UE location, application/connection status, measurement data) to the federated MEC for MEC service management such as triggering instantiation/termination of MEC applications or placing the MEC applications based on the UE location. +- MEC SDK FE provides a common software library for client-side MEC applications. + +## 7.2 Signalling requirement for reference point MS + +This clause describes the interface and messages between service providers and MEC aggregators which aims to deliver a service provider's services requirements to aggregators to distribute their services over multioperator MEC (e.g., service description and requirements — HW, SW, network requirement, etc). + +- It is required that reference point MS enable service and application providers to exchange request/response messages with the MAL for the deployment of their services and applications over operator MECs. +- It is recommended that reference point MS allow service and application providers to provide the required information for the optimized orchestration and deployment of their services and applications. The information may include MEC infrastructure requirements, MEC platform requirements, preferred region and data centre to deploy and service availability related requirements, etc. +- It is required that reference point MS enable service and application providers to exchange request/response messages with the MAL for the instantiation, monitoring, updating and deleting their application instances. +- It is required that reference point MS allow service and application providers to access the published catalogues of the operator MECs. The catalogue may include the collection of the operator specific MEC infrastructure resources, MEC platform function capabilities, MEC network capabilities (e.g., capacity, latency), etc. +- It is required that reference point MS allow service and application providers to upload, update and delete application images with necessary information for the instantiations and management of their applications. +- It is recommended that reference point MS allow service and application providers to subscribe to the network information related notification service provided by the operator MECs. The network information may include UE location, radio network information, application instance to UE connection status and traffic throughput, etc. + +## 7.3 Signalling requirement for reference point MA + +This clause describes the interface and messages between the aggregator and each operator's MEC to distribute a service provider's service requirements over heterogeneous MEC (e.g., operator's MEC, Public Cloud, etc.). + +- It is required that reference point MA allow the MAL to exchange request/response messages with the MeML for operator specific federated MEC resource and application information. The information may include collection of resource usage and application performance monitoring data, analytics and application status, etc. +- It is required that reference point MA allow the MAL to exchange request/response messages with the MeML for MEC service lifecycle management such as onboarding, instantiation, configuration, scaling and termination of the MEC application and services over one or more operator specific federated MEC platforms. +- It is required that reference point MA allow the MAL to interact with the MeML to handle service and application providers' MEC service requests. The MEC service request related information may include service profile and quality of service (QoS) requirements, etc. +- It is required that reference point MA enable the MAL and the MeML to authenticate each other. +- It is required that reference point MA allow MeML to authorize MAL to interact with the operator specific federated MEC. +- It is recommended that reference point MA allow MAL to exchange request/response messages with MeML, related to the discovery and selection of other federated MEC system, datacentres and MEC platforms, for the direct interaction between MeMLs and between MPLs of federated MEC systems through Exchange reference points. + +## 7.4 Signalling requirement for reference point MM + +This clause describes the interface and messages between the MeML and the MPL to manage and allocate each operator's cloud and network resources to an onboard service provider's services over each operator's MEC. + +- It is required that reference point MM allow the MeML to exchange request/response messages with the MPL for the enforcement of MEC application and service lifecycle management such as onboarding, instantiation, configuration, scaling and termination of them on the corresponding MEC platform. +- It is required that reference point MM allow the MeML to provide executable application images to the MPL for the instantiation of one or more MEC applications on the selected MEC platform(s). +- It is recommended that reference point MM allow the MPL to report run time MEC information including network information and event notification to the runtime FE in the MAL for the use of subscribed service and application providers. +- It is recommended that reference point MM support the relocation of MEC instances between federated MEC systems as well as in an MEC system when it is required. + +## 7.5 Signalling requirement for reference point MP + +This clause describes the interface and messages between the MPL and the MIL to control and allocate virtualized HW, SW and network related resources. + +- It is required that reference point MP allow the MPL to exchange request/response messages with the MIL to manage the infrastructure resources, such as setup and release of connectivity and physical/virtual infrastructure resources, etc., for the MEC applications and services running on the corresponding MEC platform. +- It is recommended that reference point MP enable the MPL to configure the QoS parameters of the specific MEC application traffic session provided by the connectivity resource in the MIL. +- It is recommended that reference point MP allow the MPL to enforce the routeing and traffic steering rules of MEC application traffic provided by the connectivity resource in the MIL. +- It is recommended that reference point MP allow the MPL to exchange request/response messages with the MIL to collect network related information and event notification. The information and event notification may include radio network performance information, charging and billing related data, network congestion, UE location and connection status, etc. +- It is recommended that reference point MP allow the MPL to exchange request/response messages with the MIL to collect physical/virtual infrastructure resource related information. The information may include infrastructure resource usage statistics, performance monitoring data, and a resource catalogue to be published by the MAL. + +## 7.6 Signalling requirement for reference point MI + +This clause describes the interface and messages between MEC service enabled UE and MEC. To guarantee stable QoS over multioperator MEC, the following factors have to be included: multiaccess capability, local breakout roaming scenario and MEC discovery over UE. + +- It is required that reference point MI enable UE to exchange request/response messages with operator specific federated MEC via the connectivity resource in the MIL to discover, register to and trigger the MEC service(s). The messages may include UE ID, MEC application ID, required UE capabilities, selected application instance access point information (e.g., URL or IP address), etc. + +- It is required that reference point MI enable UE to exchange request/response messages with operator specific federated MEC via the connectivity resource in the MIL to be authenticated and authorized itself. + +## 7.7 Signalling requirement for reference point MMe + +This clause describes the interface and messages between a neighbour operator's MeML to exchange service packet data or other messages (e.g., service requirements, service related data) if there is any necessity to sync up between different service servers based on each service's usage requirements. + +- It is recommended that reference point exchange MMe exchange request/response messages to share and update the information of available regions for the MEC service(s). The information may include region ID, name, geographical location, etc. +- It is recommended that reference point MMe allow the MeML of the local MEC system to deliver the MEC application package(s) and to forward the lifecycle management messages directly to the peering MeML of a remote federated MEC, allowing service and application providers of an MEC system to deploy their applications using the MEC resources and services of other federated MEC systems. The local MeML may provide a MEC application instantiation request, MEC application requirements and service repository data related to the MEC application, etc. to the federated remote MEC. +- It is recommended that reference point MMe allow the MeML of remote peering MeML of the federated MEC to forward the network information and event notification, etc. to the MeML of the local MEC system which delivers the forwarded information to the associated application provider. +- It is recommended that reference point MMe exchange request/response messages, in roaming scenario, etc., to support UE to register to the visited MEC service(s). The messages may include the user profile and authentication information, etc. + +## 7.8 Signalling requirement for reference point MPe + +This clause describes the interface and messages between a neighbour operator's MPL. + +- It is recommended that reference point MPe provide communication between the local MEC application and services on the peering federated MEC system. +- It is recommended that reference point MPe allow the MPL of the visited peer federated MEC to forward the network information (e.g., UE location and connection status), MEC resource usage/performance monitoring data and event notifications to the home MEC MPL, for the use of the MEC service and application provider. + +# 8 Security considerations + +This Recommendation provides signalling architecture and requirements for federated MEC environments. Thus, it is assumed that security considerations in general are based on the security framework from network function virtualization [b-ITU-T X.1046] and [b-ETSI GS NFV-SEC 022] and security requirements and architecture for network slice management and orchestration [b-ITU-T X.1047]. + +# Appendix I + +## Use case of the federated MEC + +(This appendix does not form an integral part of this Recommendation.) + +## I.1 Introduction + +MEC is considered a key successful factor in the 5G era that can provide a low latency user experience and huge data volume. In particular, latency sensitive services such as V2X, remote medical services and VR/AR services which have become popular nowadays are expected to have benefits from being hosted in the distributed cloud close to mobile network users. + +MEC services are typically envisaged as being offered and supplied by mobile network operators. Currently, these MEC systems have been developing separately and become different verticals, which will significantly increase the complexity for application providers in extending the reach of applications. + +To resolve this limitation, MEC providers need to adopt a federation model to interconnect each separated MEC with unified interfaces. The first approach is to make standardized APIs that will make application providers access various MEC systems effectively. In case of a single public cloud vendor, providing consistent QoE (quality of experience) is uncomplicated. However, it can be very useful to define standardized APIs in heterogeneous MEC systems created by multiple operators. Second, a federated MEC can help address poor MEC coverage. As the federated members share their network and resource capabilities and secure interfaces between their systems, the total MEC coverage can be extended and consistent service delivery can be guaranteed. + +## I.2 Federation for easy onboarding of application package + +When an application provider deploys an application package to an MEC system, many discussions on technical procedures and steps are required in addition to business negotiations with the MEC provider. It requires a lot of time and resources for the application provider and it would be a big burden if the application provider decided to interact with several other MEC providers. + +Federated MEC defines and provides standardized APIs to application providers, which can guarantee that technical steps for deployment are same, whether there is interaction with one MEC provider or several MEC providers. + +In addition, once an application package is successfully onboarded in one MEC provider, the MEC provider can directly deliver this package to other federated members with the acceptance of the application provider. It will be very valuable to enrich business opportunities of the application provider. For example, if an application provider with a local business wants to expand its MEC-based services globally, the local MEC provider can deliver an application package to a global MEC provider, which can be deployed globally without the application provider's global on-site technical support. + +## I.3 Federation for supporting consistent user experience across the MEC provider's coverage + +MEC aims to provide compute resources at the nearest place to the customer to improve the data transaction latency of contents or services to end users. As MEC systems are appropriate to provide a low latency and high-volume service within a limited range of areas, it would be difficult for MEC providers to facilitate their MEC systems in every location in a short period of time due to equipment installation costs. + +When users are located in the MEC service enabled area, their MEC service is handled through the operator's MEC node directly. However, when users move to another area where MEC service or systems are not yet enabled (e.g., roaming scenario), they cannot utilize the reliable low latency based services continually even if they hope to receive the same QoS wherever they are. + +In a case of federated MEC, federated MEC providers have already shared related information, such as edge computing resources, network capabilities and the locations of each MEC node, and have interfaces to communicate with each other. When one of the above-mentioned exception scenarios occurs, an MEC provider will be able to find which MEC providers are available and utilize their facilities to provide the same quality of service to users located in that area. + +For example, assuming that MEC provider A covers region I and MEC provider B covers regions I and II, and that they support the same capabilities for a mobile service and federate with each other. Mostly, a user of MEC provider A connects with MEC provider A in region I. However, when the user moves to region II, MEC provider A can interwork with MEC provider B to maintain the services that the user is currently using. + +## **I.4 Federation for connecting services deployed on a different MEC system** + +MEC systems are usually deployed along with mobile network operators, but only the mobile network operator does not have to be an MEC provider. There will be multiple MEC providers over the MEC infrastructure that network operator can physically provide. However, interaction between multiple MEC providers has not yet been considered, especially if MEC providers A and B are deployed on different MNO infrastructures. + +On the other hand, the commercial needs that connect with various services are increasing. For example, a voice recognition service can work as a key feature within other services, such as a navigation service. In that case, the voice recognition service provider is not necessarily the same as the navigation service provider, and each service can cooperate under commercial and technical agreements. When it is decided to deploy each service in an MEC system, a different MEC provider can be selected by each service. In these MEC environments, a service-level agreement will be maintained. + +Once the federation is performed, the federated members will share information about which application providers are deployed and will find the appropriate MEC system that the application provider wants to communicate with, even if each application is deployed on different MEC systems. Additionally, a communication path for an MEC-to-MEC system will be secured. + +# Bibliography + +- [b-ITU-T X.1046] Recommendation ITU-T X.1046 (2020), *Framework of software-defined security in software-defined networks/network functions virtualization networks*. +- [b-ITU-T X.1047] Recommendation ITU-T X.1047 (2021), *Security requirements and architecture for network slice management and orchestration*. +- [b-ETSI GS MEC 001] ETSI GS MEC 001 (2019), *Multi-access edge computing (MEC) terminology*. +- [b-ETSI GS NFV-SEC 022] ETSI GS NFV-SEC 022 (2020), *Network functions virtualisation (NFV) release 2; Security; Access token specification for API access*. +- [b-GSMA] GSM Association (2021), *Operator Platform Telco Edge Requirements*, v1.0. + + + + + +## SERIES OF ITU-T RECOMMENDATIONS + +| | | +|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------| +| Series A | Organization of the work of ITU-T | +| Series D | Tariff and accounting principles and international telecommunication/ICT economic and policy issues | +| Series E | Overall network operation, telephone service, service operation and human factors | +| Series F | Non-telephone telecommunication services | +| Series G | Transmission systems and media, digital systems and networks | +| Series H | Audiovisual and multimedia systems | +| Series I | Integrated services digital network | +| Series J | Cable networks and transmission of television, sound programme and other multimedia signals | +| Series K | Protection against interference | +| Series L | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant | +| Series M | Telecommunication management, including TMN and network maintenance | +| Series N | Maintenance: international sound programme and television transmission circuits | +| Series O | Specifications of measuring equipment | +| Series P | Telephone transmission quality, telephone installations, local line networks | +| Series Q | Switching and signalling, and associated measurements and tests | +| Series R | Telegraph transmission | +| Series S | Telegraph services terminal equipment | +| Series T | Terminals for telematic services | +| Series U | Telegraph switching | +| Series V | Data communication over the telephone network | +| Series X | Data networks, open system communications and security | +| Series Y | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities | +| Series Z | Languages and general software aspects for telecommunication systems | \ No newline at end of file diff --git a/marked/Q/T-REC-Q.5007-202312-I_PDF-E/0538daaa5583c23e17db3a12f2281a55_img.jpg b/marked/Q/T-REC-Q.5007-202312-I_PDF-E/0538daaa5583c23e17db3a12f2281a55_img.jpg new file mode 100644 index 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It features a blue globe with white lines representing latitude and longitude, and the letters 'ITU' in a bold, blue, sans-serif font superimposed on the globe. + +ITU logo + +## ITU-T Q-SERIES RECOMMENDATIONS + +## Switching and signalling, and associated measurements and tests + +| | | +|--------------------------------------------------------------------------------|----------------------| +| SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE | Q.1-Q.3 | +| INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING | Q.4-Q.59 | +| FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN | Q.60-Q.99 | +| CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS | Q.100-Q.119 | +| SPECIFICATIONS OF SIGNALLING SYSTEMS NO. 4, 5, 6, R1 AND R2 | Q.120-Q.499 | +| DIGITAL EXCHANGES | Q.500-Q.599 | +| INTERWORKING OF SIGNALLING SYSTEMS | Q.600-Q.699 | +| SPECIFICATIONS OF SIGNALLING SYSTEM NO. 7 | Q.700-Q.799 | +| Q3 INTERFACE | Q.800-Q.849 | +| DIGITAL SUBSCRIBER SIGNALLING SYSTEM NO. 1 | Q.850-Q.999 | +| PUBLIC LAND MOBILE NETWORK | Q.1000-Q.1099 | +| INTERWORKING WITH SATELLITE MOBILE SYSTEMS | Q.1100-Q.1199 | +| INTELLIGENT NETWORK | Q.1200-Q.1699 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2000 | Q.1700-Q.1799 | +| SPECIFICATIONS OF SIGNALLING RELATED TO BEARER INDEPENDENT CALL CONTROL (BICC) | Q.1900-Q.1999 | +| BROADBAND ISDN | Q.2000-Q.2999 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR THE NGN | Q.3000-Q.3709 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR SDN | Q.3710-Q.3899 | +| TESTING SPECIFICATIONS | Q.3900-Q.4099 | +| PROTOCOLS AND SIGNALLING FOR PEER-TO-PEER COMMUNICATIONS | Q.4100-Q.4139 | +| PROTOCOLS AND SIGNALLING FOR COMPUTING POWER NETWORKS | Q.4140-Q.4159 | +| PROTOCOLS AND SIGNALLING FOR QUANTUM KEY DISTRIBUTION NETWORKS | Q.4160-Q.4179 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2020 | Q.5000-Q.5049 | +| Signalling requirements and architecture of IMT-2020 | Q.5000-Q.5019 | +| Protocols for IMT-2020 | Q.5020-Q.5049 | +| COMBATING COUNTERFEITING AND STOLEN ICT DEVICES | Q.5050-Q.5069 | + +For further details, please refer to the list of ITU-T Recommendations. + +# Recommendation ITU-T Q.5008 + +# Signalling requirements and architecture to support artificial intelligence-based vertical services in future networks including IMT-2020 and beyond + +## Summary + +Recommendation ITU-T Q.5008 provides the signalling requirements and architecture to support artificial intelligence (AI) based vertical services in future networks including IMT-2020 and beyond. These requirements include the signalling information over each of the reference points and service procedures for a high-level AI platform. + +## History \* + +| Edition | Recommendation | Approval | Study Group | Unique ID | +|---------|----------------|------------|-------------|--------------------| +| 1.0 | ITU-T Q.5008 | 2023-12-14 | 11 | 11.1002/1000/15730 | + +## Keywords + +AI, AI platform, MEC, vertical services. + +--- + +\* To access the Recommendation, type the URL
"device-id": STRING,
"data-id": NUMBER,
"data-type": STRING,
"data-value": DATA ELEMENT | + +- The *timestamp* field indicates the time when the value is measured. The time when the value measured by the device reaches the system is mainly utilized. +- The *device-id* field indicates identifiers of the sensor device that measures the value. It is possible to check which sensor the value was measured through the device identifier. That means the location of the value measured can be estimated. +- The *data-id* field indicates identifiers which is identifying each measurement value. +- The *data-type* field indicates what kinds of data, which are defined in clause 7.2. +- The *data-value* field indicates data element, which is defined in clauses 7.2.1 to 7.2.7, corresponding to *data-type*. + +Table 7-9 describes the syntax of the response for *DataCreation*. + +**Table 7-9 – Response message syntax for DataCreation** + +| | | +|---------------------------|-----------------| +| HTTP Response code | rsp_code | +| BODY | None | + +- The *rsp\_code* indicates the result of the request. If successful, this is 200, and it uses an appropriate HTTP response code if it fails. + +### 7.3.2 DataRetrieval + +DataRetrieval is used for retrieving data at the edge networking entity. Table 7-10 describes the syntax of the request message for obtaining entire data resources. + +**Table 7-10 – Request message syntax for DataRetrieval for getting entire data Resources** + +| | | +|--------------------|-------------------------------------------------------------------------------------------------------------------------------------------------| +| HTTP Method | GET | +| HTTP URI | http:// [address of edge networking entity]: [port] / [flowing-water smart aquaculture service] / [version] / [type of event] / r / [data-type] | +| PARAMETERS | "data-type": STRING | + +- The *data-type* field indicates what kinds of data, which are defined in clause 7.2. + +Table 7-11 describes the syntax of the response for *DataRetrieval* for obtaining a specific data resource. + +**Table 7-11 – Request message syntax for DataRetrieval for obtaining a specific data resource** + +| | | +|--------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------| +| HTTP Method | GET | +| HTTP URI | http:// [address of edge networking entity]: [port] / [flowing-water smart aquaculture service] / [version] / [type of event] / r / [data-type] / [device-id] | +| PARAMETERS | "device-id": STRING,
"data-type": STRING | + +- The *device-id* field indicates the identifiers of the sensor device that measures the data value. It is possible to check which sensor the data value was measured through using the device identifier. That means the location of the data value measured can be estimated. +- The *data-type* field indicates the kind of data, which is defined in clause 7.2. + +Table 7-12 describes the syntax of the response for *DataRetrieval*. + +**Table 7-12 – Response message syntax for DataRetrieval** + +| | | +|---------------------------|--------------------------------------------------------------------------------------------------------------------------| +| HTTP Response code | rsp_code | +| BODY | "timestamp": NUMBER,
"device-id": STRING,
"data-id": NUMBER,
"data-type": STRING,
"data-value": DATA ELEMENT | + +- The *rsp\_code* indicates the result of the request. If successful, this is 200, and it uses an appropriate HTTP response code if it fails. +- The *timestamp* field indicates the time when the data value is measured. The time when the data value measured by the device reaches the system is mainly utilized. +- The *device-id* field indicates identifiers of the sensor device that measures data value. It is possible to check which sensor the data value was measured through using the device identifier. That means the location of the data value measured can be estimated. +- The *data-id* field indicates identifiers which is identifying each data value. +- The *data-type* field indicates of the type of data, which is defined in clause 7.2. + +- The *data-value* field indicates data element, which is defined in clauses 7.2.1 to 7.2.7, corresponding to the data-type. + +### 7.3.3 DataUpdate + +DataUpdate is used for updating data at the edge networking entity. Table 7-13 describes the syntax of the request message. + +NOTE – DataUpdate is only supported for configuration data, which is defined in clauses 7.2.1 to 7.2.7. + +**Table 7-13 – Request message syntax for DataUpdate** + +| | | +|--------------------|-----------------------------------------------------------------------------------------------------------------------------------| +| HTTP Method | PUT | +| HTTP URI | http://[address of edge networking entity]:[port]/[flowing-water smart aquaculture service]/[version]/[type of event]/u/[data-id] | +| PARAMETERS | "data-id": NUMBER | +| BODY | "timestamp": NUMBER,
"data-value": DATA ELEMENT | + +- The *data-id* field indicates identifiers which identify each data value. +- The *timestamp* field indicates the time when the data value is measured. The time when the data value measured by the device reaches the system is mainly utilized. +- The *data-value* field indicates data element, which is defined in clauses 7.2.1 to 7.2.7, corresponding to data-type. + +Table 7-14 describes the syntax of the response for *DataUpdate*. + +**Table 7-14 – Response message syntax for DataUpdate** + +| | | +|---------------------------|-----------------| +| HTTP Response code | rsp_code | +| BODY | None | + +- The *rsp\_code* indicates the result of the request. If successful, this is 200, and it uses an appropriate HTTP response code if it fails. + +### 7.3.4 DataDeletion + +DataDeletion is used for deleting data at the edge networking entity. Table 7-15 describes the syntax of the request message. + +**Table 7-15 – Request message syntax for DataDeletion** + +| | | +|--------------------|-----------------------------------------------------------------------------------------------------------------------------------| +| HTTP Method | POST | +| HTTP URI | http://[address of edge networking entity]:[port]/[flowing-water smart aquaculture service]/[version]/[type of event]/d/[data-id] | +| BODY | "data-id": NUMBER | + +– The *data-id* field indicates the identifiers identifying each data value. + +Table 7-16 describes the syntax of the response for *DataDeletion*. + +**Table 7-16 – Response message syntax for DataDeletion** + +| | | +|---------------------------|-----------------| +| HTTP Response code | rsp_code | +| BODY | None | + +– The *rsp\_code* indicates the result of the request. If successful, this is 200, and it uses an appropriate HTTP response code if it fails. + +# Bibliography + +- [b-Fielding] Fielding, R. (2000), *Architectural Styles and the Design of Network-based Software Architectures*, Doctoral Dissertation, University of California, Irvine. + + + + + +## SERIES OF ITU-T RECOMMENDATIONS + +| | | +|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------| +| Series A | Organization of the work of ITU-T | +| Series D | Tariff and accounting principles and international telecommunication/ICT economic and policy issues | +| Series E | Overall network operation, telephone service, service operation and human factors | +| Series F | Non-telephone telecommunication services | +| Series G | Transmission systems and media, digital systems and networks | +| Series H | Audiovisual and multimedia systems | +| Series I | Integrated services digital network | +| Series J | Cable networks and transmission of television, sound programme and other multimedia signals | +| Series K | Protection against interference | +| Series L | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant | +| Series M | Telecommunication management, including TMN and network maintenance | +| Series N | Maintenance: international sound programme and television transmission circuits | +| Series O | Specifications of measuring equipment | +| Series P | Telephone transmission quality, telephone installations, local line networks | +| Series Q | Switching and signalling, and associated measurements and tests | +| Series R | Telegraph transmission | +| Series S | Telegraph services terminal equipment | +| Series T | Terminals for telematic services | +| Series U | Telegraph switching | +| Series V | Data communication over the telephone network | +| Series X | Data networks, open system communications and security | +| Series Y | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities | +| Series Z | Languages and general software aspects for telecommunication systems | \ No newline at end of file diff --git a/marked/Q/T-REC-Q.5037-202601-I_PDF-E/0538daaa5583c23e17db3a12f2281a55_img.jpg b/marked/Q/T-REC-Q.5037-202601-I_PDF-E/0538daaa5583c23e17db3a12f2281a55_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..c1629394c02f697f60ae954ad36bf274fa8082cb --- /dev/null +++ b/marked/Q/T-REC-Q.5037-202601-I_PDF-E/0538daaa5583c23e17db3a12f2281a55_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:3763acd7a0ed56aa30f3f90468c1fb0cb54573eb9045bca3eddf8976b4f0f41d +size 7219 diff --git a/marked/Q/T-REC-Q.5037-202601-I_PDF-E/07b17a620c75522d53916a11e12d1bff_img.jpg b/marked/Q/T-REC-Q.5037-202601-I_PDF-E/07b17a620c75522d53916a11e12d1bff_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..79f2e9de089547d6f36233dff0751510f118c165 --- /dev/null +++ b/marked/Q/T-REC-Q.5037-202601-I_PDF-E/07b17a620c75522d53916a11e12d1bff_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:8df6024331039cd6ca087bb7fb250bf586f56b223aa06b18ab9fe130427febc9 +size 133372 diff --git a/marked/Q/T-REC-Q.5037-202601-I_PDF-E/0e240e8e4783e664047fbdb5fbd0989f_img.jpg b/marked/Q/T-REC-Q.5037-202601-I_PDF-E/0e240e8e4783e664047fbdb5fbd0989f_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..a63014d2c71deb3f0a74aa988e3bda73cff419f2 --- /dev/null +++ b/marked/Q/T-REC-Q.5037-202601-I_PDF-E/0e240e8e4783e664047fbdb5fbd0989f_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:b9fefc0d501d7592cedb51acdb7d99b431ca25deeeb2420a78b589d3d735d76b +size 17028 diff --git a/marked/Q/T-REC-Q.5037-202601-I_PDF-E/bf9297824aec2a021ecbad6f70536914_img.jpg b/marked/Q/T-REC-Q.5037-202601-I_PDF-E/bf9297824aec2a021ecbad6f70536914_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..2b13919b4d6b1966bf2ad5900271c9abef0c8ec8 --- /dev/null +++ b/marked/Q/T-REC-Q.5037-202601-I_PDF-E/bf9297824aec2a021ecbad6f70536914_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:3e726f17c5b06d9bc25be6098938495e2c46d3358e22ab06ec52c9b16b342d37 +size 9369 diff --git a/marked/Q/T-REC-Q.5037-202601-I_PDF-E/raw.md b/marked/Q/T-REC-Q.5037-202601-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..247d8a5e8ef6e8ed64084e670134d37b7b92fbce --- /dev/null +++ b/marked/Q/T-REC-Q.5037-202601-I_PDF-E/raw.md @@ -0,0 +1,464 @@ + + +# Recommendation**ITU-T Q.5037 (01/2026)** + +SERIES Q: Switching and signalling, and associated measurements and tests + +Signalling requirements and protocols for IMT-2020 – +Protocols for IMT-2020 + +--- + +### **Data management interfaces in educational robot systems with intelligent edge computing** + + + +The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features a blue circular emblem with a stylized globe and the letters 'ITU' in white. + +ITU logo + +## ITU-T Q-SERIES RECOMMENDATIONS + +## **Switching and signalling, and associated measurements and tests** + +| | | +|--------------------------------------------------------------------------------|----------------------| +| SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE | Q.1-Q.3 | +| INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING | Q.4-Q.59 | +| FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN | Q.60-Q.99 | +| CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS | Q.100-Q.119 | +| SPECIFICATIONS OF SIGNALLING SYSTEMS NO. 4, 5, 6, R1 AND R2 | Q.120-Q.499 | +| DIGITAL EXCHANGES | Q.500-Q.599 | +| INTERWORKING OF SIGNALLING SYSTEMS | Q.600-Q.699 | +| SPECIFICATIONS OF SIGNALLING SYSTEM NO. 7 | Q.700-Q.799 | +| Q3 INTERFACE | Q.800-Q.849 | +| DIGITAL SUBSCRIBER SIGNALLING SYSTEM NO. 1 | Q.850-Q.999 | +| PUBLIC LAND MOBILE NETWORK | Q.1000-Q.1099 | +| INTERWORKING WITH SATELLITE MOBILE SYSTEMS | Q.1100-Q.1199 | +| INTELLIGENT NETWORK | Q.1200-Q.1699 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2000 | Q.1700-Q.1799 | +| SPECIFICATIONS OF SIGNALLING RELATED TO BEARER INDEPENDENT CALL CONTROL (BICC) | Q.1900-Q.1999 | +| BROADBAND ISDN | Q.2000-Q.2999 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR THE NGN | Q.3000-Q.3709 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR SDN | Q.3710-Q.3899 | +| TESTING SPECIFICATIONS | Q.3900-Q.4099 | +| PROTOCOLS AND SIGNALLING FOR PEER-TO-PEER COMMUNICATIONS | Q.4100-Q.4139 | +| PROTOCOLS AND SIGNALLING FOR COMPUTING POWER NETWORKS | Q.4140-Q.4159 | +| PROTOCOLS AND SIGNALLING FOR QUANTUM KEY DISTRIBUTION NETWORKS | Q.4160-Q.4179 | +| ARTIFICIAL INTELLIGENCE-ENABLED SIGNALLING, TESTING AND MONITORING | Q.4180-Q.4279 | +| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2020 | Q.5000-Q.5049 | +| Signalling requirements and architecture of IMT-2020 | Q.5000-Q.5019 | +| Protocols for IMT-2020 | Q.5020-Q.5049 | +| COMBATING COUNTERFEITING AND STOLEN ICT DEVICES | Q.5050-Q.5069 | + +For further details, please refer to the list of ITU-T Recommendations. + +# Recommendation ITU-T Q.5037 + +# Data management interfaces in educational robot systems with intelligent edge computing + +## Summary + +Recommendation ITU-T Q.5037 defines data management interfaces for an intelligent edge computing-based educational robot system. The data management interface includes data resources and interfaces for data processing. Data resources can be used to decide what data are for. A large amount of data is needed to check the environment and growth status. The interfaces for data processing define a Bluetooth-based application programming interface (API) including data creation, retrieval, update and deletion. + +## History\* + +| Edition | Recommendation | Approval | Study Group | Unique ID | +|---------|----------------|------------|-------------|--------------------| +| 1.0 | ITU-T Q.5037 | 2026-01-13 | 11 | 11.1002/1000/16698 | + +## Keywords + +Data management, edge, education, robot. + +--- + +\* To access the Recommendation, type the URL
Range: 0~4096 | +| Gyroscope sensor Reference | NUMBER(X, Y, Z) | Reference X, Y, Z values of the gyro sensor at factory initialization
X: -1.0~1.0
Y: -1.0~1.0
Z: -1.0~1.0 | + +### 7.2.2 Cube robot dynamic data + +Table 7-2 shows information describing the cube robot dynamic data. + +**Table 7-2 – Cube robot dynamic data** + +| Keyword | Type | Description | +|---------------------|------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------| +| Module Group Number | NUMBER | Group number of the module in the Bluetooth network
Range: 1~76 | +| Module Color Number | NUMBER | Colour code used to distinguish modules
0: Red, 1: Green, 2: Blue,
3: Cyan, 4: Pink, 5: Yellow,
6: Violet, 7: Orange | +| SetScheduledSteps | NUMBER (StepRate, StepAngle, ServoAngle) | Array of angle command schedules for the module
StepRate: -100~100
StepAngle: 0~65535
ServoAngle: -90~90 | + +**Table 7-2 – Cube robot dynamic data** + +| Keyword | Type | Description | +|--------------------|---------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------| +| SetScheduledPoints | NUMBER (StartPoint, EndPoint, Repeat) | Command array for partial playback: start, end, repeat count of schedule steps
StartPoint: 0~65535
EndPoint: 0~65535
Repeat: 0~255 | + +## 7.3 Interfaces for data processing + +This clause describes the application programming interfaces (APIs) for data processing, including creating, retrieving, updating, and deleting data to be used in the reference point Da specified in [ITU-T Q.5001]. The cube robot is a modular robotic system based on Bluetooth Low Energy (BLE) 5.0. Multiple cube robot modules, each sharing an identical hardware architecture, can be interconnected to form various robotic configurations. Each module communicates wirelessly with a central computer in a star network topology. + +This Recommendation provides a technical specification for the cube-based robotic communication structure, data format and network control mechanisms. The system incorporates the concept of edge computing, enabling enhanced distributed control performance within the robot architecture. + +### 7.3.1 Cube robot communication protocol + +#### 7.3.1.1 Basic packet format + +Table 7-3 describes the basic packet format. The basic BLE communication packet structure of the cube robot serves as the foundation for all commands and data transmissions. To ensure clear identification and synchronization, the first 10 bytes of the packet have a fixed length. + +**Table 7-3 – Basic packet format** + +| Field name | Size (Byte) | Data format | Description | +|---------------|-------------|-------------|---------------------------------------------------------------------------------------------------| +| VirtualCubeId | 4 | Hex | BLE address or logical identifier of the cube robot. Automatically assigned upon connection. | +| AssignedId | 2 | Hex | Identifier used when a command contains a specific subtask. | +| OpCode | 1 | Hex | Operation code used to distinguish the type of command. Each function is assigned a unique value. | +| PacketSize | 2 | UInt16 | Total size of the packet, including header and data payload. | +| Property | 1~4 | Hex | Configuration options, including mode, method, step type, etc. | +| Data Payload | Variable | Byte array | Actual data values associated with the command. | +| CRC16 | 2 | Hex | Checksum used to verify the integrity of the packet. | + +#### 7.3.1.2 Cube robot network configuration process + +- After selecting the robot model on the computer, the system enters cube robot connection mode. +- The first cube robot that attempts to connect is designated as the primary cube and is configured to operate in multirole mode. +- At this stage, the primary cube activates its colour light-emitting diode (LED) to red. +- The primary cube connects additional cube robots according to the number required for the selected robot model. +- Each time a secondary cube is connected, the primary cube notifies the computer. The LED colours of the secondary cubes are activated in the order of connection: green, blue, cyan, magenta, yellow. +- Once all required cube robots are connected, the computer sends a signal to the primary cube indicating completion of the robot configuration, along with the command to start sensor data transmission. +- The primary cube sends the start sensor data transmission command to all connected secondary cubes, including itself. +- The primary cube aggregates its own sensor data and the data received from secondary cubes and periodically transmits it to the computer. + +#### 7.3.1.3 Robot operation data transmission and synchronization control + +- Upon entering the robot control interface, the system generates either full or individual operation data and transmits it to the primary cube. +- The primary cube stores its operation data in memory and separates and distributes the relevant data to each corresponding secondary cube. +- After all data is transmitted, time synchronization between the primary cube and secondary cubes is executed to enable coordinated actions. +- Once synchronization is complete, the computer sends a start signal to initiate operations. +- The primary cube and all connected secondary cubes perform the synchronized operations based on the received data. + +### 7.3.2 Detailed description of cube robot commands + +#### 7.3.2.1 Aggregator + +The primary cube serves as the central node in the cube network. This command group, specified in Table 7-4, includes instructions for managing the primary cube's operations based on the BLE multirole framework. It connects to surrounding cubes, assigns virtual identifiers (IDs), configures their sequence representation through LED indicators, and performs system-level tasks such as rebooting. These functions enable the coordination and control of the distributed cube network. + +**Table 7-4 – Aggregator** + +| Command | OpCode | Description | +|----------------------------|--------|---------------------------------------------------------------| +| GetMultiroleVirtualCubeId | AB | Retrieves the virtual cube ID used in multirole configuration | +| GetMultiroleVirtualColor | AC | Retrieves the virtual colour value | +| SetMultiroleVirtualColor | AE | Sets the virtual colour value | +| ClearMultiroleVirtualColor | A0 | Clears the previously set virtual colour | +| RebootMultiroleAggregator | A8 | Reboots the cube robot operating in multirole mode | + +**Table 7-4 – Aggregator** + +| Command | OpCode | Description | +|----------------------|---------------|---------------------------------------------------------------------------------------------------------------| +| SetMultiroleInAction | AD | Configures the cube robot as a primary cube with multirole capability and assigns a group number if specified | + +#### 7.3.2.2 Arduino + +This command group, specified in Table 7-5, is defined to support the control and monitoring of cubes via external development boards such as Arduino and Microbit. When an external board is connected to a cube, this group of commands enables communication over BLE to manage the directly connected cube as well as nearby cubes within range. It facilitates interaction between external controllers and the cube mesh network, enabling real-time coordination and feedback. + +**Table 7-5 – Arduino** + +| Command | OpCode | Description | +|--------------------------------|---------------|-----------------------------------------------------------------------------| +| ArduinoI2C | A2 | Communicates with Arduino using the inter-integrated circuit (I2C) protocol | +| ControlCubino/Arduino/Microbit | A3 | Controls Cubino, Arduino, or Microbit devices via the cube robot interface. | +| ControlLineBot | A4 | Controls a line tracer robot | + +#### 7.3.2.3 Flash and factory + +This command group, specified in Table 7-6, provides functionality for storing user-defined configuration values and system states in the internal flash memory of a cube. It also includes commands related to factory reset procedures. The group ensures that specified settings are retained across device reboots, enabling consistent system behaviour and recoverability in embedded environments. + +**Table 7-6 – Flash and factory** + +| Command | OpCode | Description | +|-----------------------------|---------------|-------------------------------------------------------------| +| FlashDiscoveryGroupId | F9 | Stores the discovery group ID to cube robot flash memory | +| FlashDiscoveryFinishGroupId | FA | Stores the completed discovery group ID | +| FlashExternalPortState | F4 | Saves the state of external ports to flash memory | +| FlashCustomerServicePage | FC | Saves settings related to customer service pages | +| FactoryApplication | FD | Restores factory default or resets to initial configuration | + +#### 7.3.2.4 Query + +This command group, specified in Table 7-7, enables the retrieval of information from all cubes within the BLE-connected network. It is primarily used to read data from external ports, sensors and other hardware interfaces of each cube. Typical applications include system status monitoring, sensor data acquisition and inspection of connection-related metadata. The commands facilitate centralized observation of distributed device states within the network. + +**Table 7-7 – Query** + +| Command | OpCode | Description | +|----------------|---------------|----------------------------------------------------------------------------------------| +| GetProducts | B1 | Retrieves product information and model number of connected cube robots | +| GetPeripherals | BA | Returns the list of external devices (sensors, LEDs, etc.) connected to the cube robot | +| GetSensors | B8 | Retrieves current values of internal sensors such as gyroscope and proximity sensors | + +#### 7.3.2.5 Set + +This command group, specified in Table 7-8, is responsible for controlling hardware components of the cube, including motors, LEDs and buzzers. It also supports the configuration of motion schedules to execute predefined behaviours. Serving as the core interface for robot movement and action control, these commands enable precise and coordinated actuation within the cube system for various robotic applications. + +**Table 7-8 – Set** + +| Command | OpCode | Description | +|-----------------------|---------------|--------------------------------------------------------------------------| +| SetContinuousSteps | CC | Configures continuous motor rotation commands | +| SetSingleSteps | C1 | Executes single-step motor rotation | +| SetAggregateSteps | CD | Controls multiple stepper motors simultaneously | +| SetScheduledSteps | CA | Sets time-based motor rotation schedules | +| SetScheduledPoints | CB | Configures point-based motor control scenarios | +| SetScheduledTimer | C2 | Sets the delay time between scheduled operations | +| SetPauseSteps | C0 | Pauses or resumes stepper motor operations | +| SetSingleServo | E1 | Commands the servo motor to move to a specific angle | +| SetScheduledServo | EA | Configures time-based servo motor movement schedules | +| SetColorLED | CE | Sets the colour of the cube robot LED | +| SetDigitalPort | CF | Sets the state of digital ports to control external circuits | +| SetWs2812bLED | C7 | Controls WS2812B red, green, blue (RGB) LED strips | +| SetPowerState | C9 | Controls the power state or sets the power-saving mode of the cube robot | +| SetInstantTorque | C6 | Applies immediate torque output to motors | +| SetUnpluggedInAction | E2 | Sets behaviour when power is disconnected | +| SetMusicNotesInAction | E8 | Configures melody playback on the cube robot | +| GenerateBuzzerTone | EF | Outputs a simple buzzer tone | + +# Appendix I + +## Use cases of an educational robot system + +(This appendix does not form an integral part of this Recommendation.) + +## I.1 Use case 1: Drawing robot + +This system, which is illustrated in Figure I.1, is designed for constructing and controlling an educational robot capable of drawing. It operates by connecting three cube robots via Bluetooth. Each cube robot is a modular device equipped with motors, sensors and LEDs, and is assigned distinct roles. The first cube robot, connected to the computer via universal serial bus (USB), is designated as the primary cube, indicated by a red LED. The other two cube robots are sequentially connected via Bluetooth and operate as secondary cubes, with green and blue LEDs representing their connection order. + +In this configuration, the two secondary cubes are equipped with motors and wheels and are responsible for vehicle movement. The remaining secondary cube controls the pen mechanism, allowing the robot to lower the pen for drawing and lift it for repositioning, enabling the creation of lines and shapes. + +Once the connection is complete, the primary cube transmits commands to all connected cubes to begin sensor data transmission. Each secondary cube periodically sends sensor data to the primary cube, which in turn forwards the compiled data to the computer. The computer analyses this data and sends corresponding control commands, enabling the robot to operate in real time or follow pre-programmed paths to draw. + +This educational robot system allows students – from elementary to high school levels – to understand fundamental concepts of robotic control and programming through hands-on experience. The Bluetooth-based primary-secondary structure also facilitates learning in areas such as sensor networks and distributed control systems. + + + +A 3D rendering of a drawing robot. It consists of a central cube-shaped robot body with two large, circular, perforated wheels attached to its sides. A vertical pen holder is mounted on top of the cube, holding a pen. The robot is shown from a slightly elevated front-right perspective. + +**Figure I.1 – Use case of a drawing robot** + +## I.2 Use case 2: Arduino-based cube robot + +This system integrates Arduino with cube robots to form an educational robotic platform utilizing BLE communication. Figure I.2 illustrates this use case. Each cube robot has identical hardware and supports BLE multirole functionality, enabling it to act as either as primary or secondary. When an Arduino is connected to a cube robot, it is automatically set as the primary cube. Other cube robots are linked wirelessly via BLE to form a complete robot system, allowing control without the need for a computer – making it highly suitable for classroom use. + +The system follows a specific process: When powered, the Arduino sends a 'Primary Start' command to the connected cube robot via a universal asynchronous receiver transmitter (UART). The cube then operates in multirole mode, functioning as both central and peripheral in BLE terms. The Arduino specifies the number of cube robots to be connected, and the primary cube scans and connects them sequentially. Each connected cube robot receives an assigned ID and a designated LED colour for visual identification. Once all required cube robots are connected, the system is ready for data transmission and control. + +Data flow is bidirectional: In the upstream direction, sensor cubes send data via BLE to the primary cube, which then relays it to the Arduino through UART. In the downstream direction, the Arduino sends control commands to the primary cube, which then distributes them to the appropriate secondary cubes. This continuous interaction enables real-time control and drawing tasks. + +The simplicity of the hardware and the intuitive communication structure enable students to learn key concepts in sensor communication, wireless networking, distributed control and physical robot operation. The system is particularly effective for science, technology, engineering and mathematics (STEM) education, requiring minimal programming skills to set up and control the robot. + + + +A photograph of the Arduino-based cube robot. It is a black, cube-shaped device with a small screen on top and two circular sensors on the front. Wires are visible connecting the top part to the bottom part. + +**Figure I.2 – Use case of the Arduino-based cube robot** + +## **I.3 Use case 3: Convergence system of virtual and physical cube robots** + +This system presents a mixed reality-based robotic platform that integrates virtual and physical cube robots within a metaverse environment. It is suitable for applications in education, experimentation, and simulation. The virtual cube robot, implemented via a digital twin or web-based simulator, interacts seamlessly with the physical cube robot to form a unified interactive system. This convergence structure is especially valuable in environments with limited physical resources or safety constraints, as it allows safe and effective design and testing of robotic behaviours. Additionally, feedback from physical sensor data into the virtual environment creates a closed loop for comparing simulation and real-world performance, enabling iterative optimization. + +A representative use case is the design and execution of a maze-escaping robot. The scenario involves five stages: + +- Robot design using four virtual cube robots within a web simulator – no physical hardware required. +- Testing the sensor-based pathfinding algorithm in the virtual environment. +- Deploying the finalized design and algorithm to physical cube robots. +- Feeding real-world sensor and movement data back into the virtual simulator for analysis. +- Refining the design in the simulator and reapplying it to the physical robot – enabling continuous optimization. + +Data flow in this system is bidirectional. Users design and code in the virtual environment, then deploy to physical cube robots. Conversely, sensor outputs and movement results from physical robots are sent back to the simulator for debugging and refinement. This cyclic data exchange enables real-time validation and adjustment of robotic behaviour. + +This hybrid system offers broad applicability. In education, it enables complete robotic design and programming exercises even without access to hardware. In industrial testing, simulation can precede physical prototyping, reducing time and cost. In special education, learners with cognitive or physical challenges can safely practice control in a virtual setting before transitioning to real hardware. + +In conclusion, the convergence system of virtual and physical cube robots in a metaverse context extends the possibilities of robotic design, education and testing, overcoming the constraints of physical space and resources. + +## **I.4 Use case 4: Blockchain-based copyright verification service for educational robot content** + +Educational robot content presents more complex copyright exemption conditions than ordinary creative works, making it particularly challenging to determine what constitutes permissible use. Although national copyright laws include exceptions for educational purposes – such as reproduction, performance, transmission and quotation – their scope and conditions vary by country and often require nuanced interpretation. Against this background, this clause outlines the concept and design direction for a blockchain-based copyright verification system specifically tailored for educational content. + +This service is a blockchain-based copyright verification system dedicated to educational content. Its primary goals are objective and automated determination of copyright exceptions, utilization of collective intelligence for ambiguous interpretations, and transparent disclosure of all decision-making processes and results. The core design directions are as follows: + +- Chain code-based exception rule encoding: Educational copyright exceptions from different jurisdictions are formalized into rule languages and implemented as smart contracts. This enables the system to automatically assess whether a given content use request qualifies for an exception. By codifying criteria such as the proportion of use, non-profit status and educational purpose, the service ensures objectivity and automation in the decision process. +- Expert voting-based interpretation module: Since automatic determination alone cannot cover all ambiguous cases, uncertain situations are referred to an expert panel. Through a blockchain-based voting mechanism, experts collectively decide whether the use constitutes infringement or permissible use. The voting results are recorded on-chain, ensuring transparency and accountability. +- Blockchain storage of usage history and post-verification: All content usage requests, approvals or denials, actual usage records and activity logs are stored on the blockchain. This not only supports pre-authorization but also enables post-event verification. In cases of copyright disputes, these records can serve as evidence for enforcement by the copyright holder or affected party. + +By incorporating both ex-ante permission and ex-post verification tailored to the unique nature of educational content, this service offers greater applicability in educational contexts than conventional content management systems. Combining blockchain technology with expert governance to address the complex structure of educational copyright exceptions provides a predictable and transparent environment for both educators and copyright owners. Further work is needed to refine the cross-national exception rule models and to design robust expert governance mechanisms. + + + +## SERIES OF ITU-T RECOMMENDATIONS + +| | | +|-----------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------| +| Series A | Organization of the work of ITU-T | +| Series D | Tariff and accounting principles and international telecommunication/ICT economic and policy issues | +| Series E | Overall network operation, telephone service, service operation and human factors | +| Series F | Non-telephone telecommunication services | +| Series G | Transmission systems and media, digital systems and networks | +| Series H | Audiovisual and multimedia systems | +| Series I | Integrated services digital network | +| Series J | Cable networks and transmission of television, sound programme and other multimedia signals | +| Series K | Protection against interference | +| Series L | Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant | +| Series M | Telecommunication management, including TMN and network maintenance | +| Series N | Maintenance: international sound programme and television transmission circuits | +| Series O | Specifications of measuring equipment | +| Series P | Telephone transmission quality, telephone installations, local line networks | +| Series Q | Switching and signalling, and associated measurements and tests | +| Series R | Telegraph transmission | +| Series S | Telegraph services terminal equipment | +| Series T | Terminals for telematic services | +| Series U | Telegraph switching | +| Series V | Data communication over the telephone network | +| Series X | Data networks, open system communications and security | +| Series Y | Global information infrastructure, Internet protocol aspects, next-generation networks, Internet of Things and smart cities | +| Series Z | Languages and general software aspects for telecommunication systems | \ No newline at end of file diff --git a/marked/Q/T-REC-Q.604-199303-I_PDF-E/2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg b/marked/Q/T-REC-Q.604-199303-I_PDF-E/2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..31fc1fc2798375070e87409ba3ca5989b2557849 --- /dev/null +++ b/marked/Q/T-REC-Q.604-199303-I_PDF-E/2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:be8fc7613476751cb71176bd62aa88b879640389ef6af3464b78db8e5cf52118 +size 8279 diff --git a/marked/Q/T-REC-Q.622-198811-I_PDF-E/2763901b7a1fd1b5d704cdc450d12ed0_img.jpg b/marked/Q/T-REC-Q.622-198811-I_PDF-E/2763901b7a1fd1b5d704cdc450d12ed0_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..197df0279e445d90abcfc215e251ebbb52bab25c --- /dev/null +++ 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b/marked/Q/T-REC-Q.622-198811-I_PDF-E/a7d78d22e465dea388b31d0739f9d0cd_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..1b6ea0a1c97a4ed27e276ab860b23f342aef3baf --- /dev/null +++ b/marked/Q/T-REC-Q.622-198811-I_PDF-E/a7d78d22e465dea388b31d0739f9d0cd_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:fc66772f525baacc59886f06a81828701e38359a0980c5b531b25b73f3dd21e1 +size 71339 diff --git a/marked/Q/T-REC-Q.622-198811-I_PDF-E/raw.md b/marked/Q/T-REC-Q.622-198811-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..38c77e4026a9018f86cba472c8f22178c1055955 --- /dev/null +++ b/marked/Q/T-REC-Q.622-198811-I_PDF-E/raw.md @@ -0,0 +1,359 @@ + + + + +The logo of the International Telecommunication Union (ITU) features a globe with a lightning bolt superimposed on it, and the letters 'ITU' in a bold, sans-serif font. + +ITU logo + +INTERNATIONAL TELECOMMUNICATION UNION + +**ITU-T** + +**Q.622** + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +**INTERWORKING OF SIGNALLING SYSTEMS** + +--- + +**LOGIC PROCEDURES FOR OUTGOING +SIGNALLING SYSTEM No. 5** + +**ITU-T Recommendation Q.622** + +(Extract from the *Blue Book*) + +--- + +# NOTES + +- 1 ITU-T Recommendation Q.622 was published in Fascicle VI.6 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below). +- 2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +# LOGIC PROCEDURES FOR OUTGOING SIGNALLING SYSTEM No. 5 + + + +State overview diagram for outgoing Signalling System No. 5. It shows a sequence of states from 00 to 10. State 00 is Idle, 01 is Wait for calling party's category (CPCI), 02 is Wait for country code indicator (CCI), 03 is Wait for ST, 04 is Wait for proceed-to-send, 05 is Wait for time release t3, 06 is Wait for time release t4, 07 is Wait for answer, 08 is Answered, 09 is Clear-back, and 10 is Wait for release-guard. Transitions are shown between consecutive states, with some states (00, 01, 02, 03, 04) having additional transitions to state 10. State 10 has a transition back to state 00. The diagram is labeled CCITT-48600. + +| State number | State description | Sheet reference | Timers running | +|--------------|------------------------------------------|-----------------|----------------| +| 00 | Idle | 1 | | +| 01 | Wait for calling party's category (CPCI) | 1 | | +| 02 | Wait for country code indicator (CCI) | 1 | | +| 03 | Wait for ST | 1 | t 1 | +| 04 | Wait for proceed-to-send | 1 | t 2 | +| 05 | Wait for time release t 3 | 2 | t 3 | +| 06 | Wait for time release t 4 | 2 | t 4 | +| 07 | Wait for answer | 3 | | +| 08 | Answered | 3 | | +| 09 | Clear-back | 3 | | +| 10 | Wait for release-guard | 3 | t 2 | + +FIGURE 1/Q.622 +State overview diagram for outgoing Signalling System No. 5 + +## Supervisory timers for outgoing Signalling System No. 5 + +| | | +|-------------------------------------------|-----------------------------------------| +| t 1 = 4-6 s | Recommendation Q.152, § 3.2.1, b) | +| t 2 = 10-20 s | Recommendation Q.141, § 2.1.3.1, e), i) | +| t 3 = (100 ± 10) + (55 ± 5) ms | Recommendation Q.153, § 3.3.3 | +| t 4 = 2 (55 ± 5) ms | Recommendation Q.153, § 3.3.3 | + +### Procedure not shown + +The following procedure, not directly relevant to interworking, is not shown in the logic procedures: + +P1 = Procedure for non-receipt of release-guard (Recommendation Q.141, § 2.1.3.1, e), i)). + +FIGURE 2/Q.622 + +## Notes to outgoing Signalling System No. 5 + + + +The flowchart illustrates the logic for Outgoing Signalling System No. 5. It starts with a 'Start' terminal leading to a series of process blocks and decision diamonds. Key elements include: + +- Process blocks for sending signals (e.g., KP1, KP2, digits) and waiting for acknowledgments. +- Decision diamonds checking conditions like 'ST signal?', 'Note 1', and 'Note 2'. +- Input/output symbols for receiving and sending signals like 'Acknowledge', 'Proceed to send', and 'Busy flash'. +- Connectors labeled '1' and '2' at the bottom indicating transitions to other parts of the diagram. +- Various paths based on 'Yes' or 'No' outcomes from decision points. + +Flowchart for Outgoing Signalling System No. 5 (FIGURE 1/Q.622 Sheet 1 of 3). + +Note 1 - Fixed or maximum number length reached? + +Note 2 - Has the minimum number of digits been received? + +FIGURE 1/Q.622 (Sheet 1 of 3) +**Outgoing Signalling System No. 5** + +Connector reference + + + +1 + +2 + +3 + +4 + +5 + +6 + +7 + +8 + +9 + +10 + +11 + +12 + +13 + +14 + +15 + +16 + +17 + +18 + +19 + +20 + +21 + +22 + +23 + +24 + +25 + +26 + +27 + +28 + +29 + +30 + +31 + +32 + +33 + +34 + +35 + +36 + +37 + +38 + +39 + +40 + +41 + +42 + +43 + +44 + +45 + +46 + +47 + +48 + +49 + +50 + +51 + +52 + +53 + +54 + +55 + +56 + +57 + +58 + +59 + +60 + +61 + +62 + +63 + +64 + +65 + +66 + +67 + +68 + +69 + +70 + +71 + +72 + +73 + +74 + +75 + +76 + +77 + +78 + +79 + +80 + +81 + +82 + +83 + +84 + +85 + +86 + +87 + +88 + +89 + +90 + +91 + +92 + +93 + +94 + +95 + +96 + +97 + +98 + +99 + +CCITT 40960 + +Flowchart for Outgoing Signalling System No. 5. The process starts with '1' (Connector reference) leading to a decision 'IS IT AN ISDN?' (1). If 'YES', it goes to 'Start' (2) and then to 'ISDN' (3). If 'NO', it goes to 'Start' (4) and then to 'ISDN' (5). From 'Start' (4), it goes to 'Language' (6) and then to 'Language' (7). From 'Start' (2), it goes to 'Start' (8) and then to 'ISDN' (9). From 'Start' (8), it goes to 'Start' (10) and then to 'ISDN' (11). From 'Start' (10), it goes to 'Start' (12) and then to 'ISDN' (13). From 'Start' (12), it goes to 'Start' (14) and then to 'ISDN' (15). From 'Start' (14), it goes to 'Start' (16) and then to 'ISDN' (17). From 'Start' (16), it goes to 'Start' (18) and then to 'ISDN' (19). From 'Start' (18), it goes to 'Start' (20) and then to 'ISDN' (21). From 'Start' (20), it goes to 'Start' (22) and then to 'ISDN' (23). From 'Start' (22), it goes to 'Start' (24) and then to 'ISDN' (25). From 'Start' (24), it goes to 'Start' (26) and then to 'ISDN' (27). From 'Start' (26), it goes to 'Start' (28) and then to 'ISDN' (29). From 'Start' (28), it goes to 'Start' (30) and then to 'ISDN' (31). From 'Start' (30), it goes to 'Start' (32) and then to 'ISDN' (33). From 'Start' (32), it goes to 'Start' (34) and then to 'ISDN' (35). From 'Start' (34), it goes to 'Start' (36) and then to 'ISDN' (37). From 'Start' (36), it goes to 'Start' (38) and then to 'ISDN' (39). From 'Start' (38), it goes to 'Start' (40) and then to 'ISDN' (41). From 'Start' (40), it goes to 'Start' (42) and then to 'ISDN' (43). From 'Start' (42), it goes to 'Start' (44) and then to 'ISDN' (45). From 'Start' (44), it goes to 'Start' (46) and then to 'ISDN' (47). From 'Start' (46), it goes to 'Start' (48) and then to 'ISDN' (49). From 'Start' (48), it goes to 'Start' (50) and then to 'ISDN' (51). From 'Start' (50), it goes to 'Start' (52) and then to 'ISDN' (53). From 'Start' (52), it goes to 'Start' (54) and then to 'ISDN' (55). From 'Start' (54), it goes to 'Start' (56) and then to 'ISDN' (57). From 'Start' (56), it goes to 'Start' (58) and then to 'ISDN' (59). From 'Start' (58), it goes to 'Start' (60) and then to 'ISDN' (61). From 'Start' (60), it goes to 'Start' (62) and then to 'ISDN' (63). From 'Start' (62), it goes to 'Start' (64) and then to 'ISDN' (65). From 'Start' (64), it goes to 'Start' (66) and then to 'ISDN' (67). From 'Start' (66), it goes to 'Start' (68) and then to 'ISDN' (69). From 'Start' (68), it goes to 'Start' (70) and then to 'ISDN' (71). From 'Start' (70), it goes to 'Start' (72) and then to 'ISDN' (73). From 'Start' (72), it goes to 'Start' (74) and then to 'ISDN' (75). From 'Start' (74), it goes to 'Start' (76) and then to 'ISDN' (77). From 'Start' (76), it goes to 'Start' (78) and then to 'ISDN' (79). From 'Start' (78), it goes to 'Start' (80) and then to 'ISDN' (81). From 'Start' (80), it goes to 'Start' (82) and then to 'ISDN' (83). From 'Start' (82), it goes to 'Start' (84) and then to 'ISDN' (85). From 'Start' (84), it goes to 'Start' (86) and then to 'ISDN' (87). From 'Start' (86), it goes to 'Start' (88) and then to 'ISDN' (89). From 'Start' (88), it goes to 'Start' (90) and then to 'ISDN' (91). From 'Start' (90), it goes to 'Start' (92) and then to 'ISDN' (93). From 'Start' (92), it goes to 'Start' (94) and then to 'ISDN' (95). From 'Start' (94), it goes to 'Start' (96) and then to 'ISDN' (97). From 'Start' (96), it goes to 'Start' (98) and then to 'ISDN' (99). + +FIGURE 1/Q.622/Sheet 2 of 3 +Outgoing Signalling System No. 5 + + + +``` + +graph TD + Start((5)) --> WaitAnswer[Wait for answer] + WaitAnswer --> Answer{Answer} + Answer -- Answer --> Ack[Acknowledgement] + Answer -- BTS_A --> BTS_A[BTS A] + Ack --> BTS_B[BTS B] + BTS_A --> BTS_B + BTS_B --> C1((1)) + + C6((6)) --> C10((10)) + C10 --> Pendant([Pendant]) + Pendant --> DataLink{Data link} + DataLink -- BTS_B --> BTS_B2[BTS B] + DataLink -- BTS_C --> BTS_C[BTS C] + BTS_B2 --> C7((7)) + BTS_C --> C7 + + C7((7)) --> Ack2[Acknowledgement] + Ack2 --> Switch[Switch] + Switch --> C8((8)) + + C8((8)) --> LineFwd([Line forward]) + LineFwd --> C11((11)) + C11 --> Pendant2([Pendant]) + Pendant2 --> Switch2[Switch] + Switch2 --> C12((12)) + + C7((7)) --> LineFwd2([Line forward]) + LineFwd2 --> AccessG[Access gateway] + AccessG --> Switch3[Switch] + Switch3 --> C13((13)) + + C6((6)) --> C2((2)) + C2 --> WaitRelGuard[Wait for 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SYSTEM No. 7 (ISUP)** + +**ITU-T Recommendation Q.667** + +(Previously "CCITT Recommendation") + +--- + +## FOREWORD + +The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecommunication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. + +ITU-T Recommendation Q.667 was prepared by the ITU-T Study Group XI (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). + +## --- NOTES + +1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. + +In order not to delay publication of this Recommendation, no change has been made in the text to references containing the acronyms "CCITT, CCIR or IFRB" or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. + +2 In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +## **INTERWORKING OF SIGNALLING SYSTEMS – LOGIC PROCEDURES FOR INTERWORKING OF SIGNALLING SYSTEM No. 7 (TUP) TO SIGNALLING SYSTEM No. 7 (ISUP)** + +(Helsinki, 1993) + + + +``` + + graph LR + 00((00)) --> 01((01)) + 01 --> 02((02)) + 02 --> 03((03)) + 03 --> 04((04)) + 04 --> 05((05)) + 05 --> 06((06)) + 06 --> 07((07)) + 07 --> 00 + 03 --> TopLine[ ] + 04 --> TopLine + 05 --> TopLine + 06 --> TopLine + style TopLine fill:none,stroke:none + +``` + +State overview diagram showing states 00 through 07. States 00 to 06 are in a linear sequence. State 07 is connected from 06 and has a return arrow to 00. There are also return arrows from 03, 04, 05, and 06 to a common line above the states. A label T1141500-92/d01 is present near state 07. + +| State number | State description | Sheet reference | +|---------------------|--------------------------------|------------------------| +| 00 | Idle | 1, 2, 3, 4, 5 | +| 01 | Wait for service provided FITE | 1 | +| 02 | Wait for information FITE | 1 | +| 03 | Wait for continuity FITE | 1 | +| 04 | Wait for address-complete | 1 | +| 05 | Wait for answer | 3 | +| 06 | Answered | 3 | +| 07 | Wait for resume | 4 | + +FIGURE 1/Q.667 + +State overview diagram for interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP) + +FIGURE 2/Q.667 + +(Reserved for future notes) + + + +``` + +graph TD + Idle00([00 Idle]) --> ActTUP[/Activate No. 7
(TUP)/No. 7
(ISUP)/] + ActTUP --> Wait01([01 Wait for
service
provided FITE]) + Wait01 --> FITE30[/FITE 30
service
provided/] + FITE30 --> Wait02([02 Wait for
information
FITES]) + Wait02 --> FITEs913[/FITEs 9-13,
17-19/] + FITEs913 --> Conn1_top((1)) + Conn1_top --> Wait03([03 Wait for
continuity
FITES]) + Wait03 --> Branch{ } + Branch --> FITE25[/FITE 25/] + Branch --> FITE26[/FITE 26/] + Branch --> FITE27[/FITE 27/] + Branch --> FITE1[/FITE 1/] + FITE25 --> SPITE52[SPITE 52] + FITE26 --> SPITE52 + FITE27 --> SPITE52 + FITE1 --> Conn1_bot((1)) + Conn1_bot --> FITE22[/FITE 22/] + FITE22 --> Idle00_end([00 Idle]) + SPITE52 --> ActOut[/Activate
outgoing SS No. 7
(ISUP)/] + ActOut --> FITEA[/FITE A
(Table 1)/] + FITEA --> Conn2((2)) + Conn2 --> Wait04([04 Wait
for address
complete]) + Wait04 --> Conn3((3)) + +``` + +SDL flowchart showing the interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP). The process starts at state '00 Idle', leading to an input 'Activate No. 7 (TUP)/No. 7 (ISUP)', then state '01 Wait for service provided FITE', followed by output 'FITE 30 service provided'. The flow then splits. One path goes to state '02 Wait for information FITES', then input 'FITEs 9-13, 17-19', then state '03 Wait for continuity FITES'. From here, it branches into four parallel inputs: 'FITE 25', 'FITE 26', 'FITE 27', and 'FITE 1'. 'FITE 1' leads to connector '1' and then to output 'FITE 22' and back to '00 Idle'. The other three ('FITE 25', 'FITE 26', 'FITE 27') converge into task 'SPITE 52', followed by input 'Activate outgoing SS No. 7 (ISUP)', then input 'FITE A (Table 1)'. This leads to connector '2' (labeled '2 (x 3)') and then to state '04 Wait for address complete', which ends at connector '3' (labeled '2'). + +FIGURE 3/Q.667 (sheet 1 of 5) +**Interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP)** + + + +The flowchart illustrates the interworking process between Signalling System No. 7 (TUP) and Signalling System No. 7 (ISUP). It starts at the top with a connector labeled '3' with a subscript '1'. The main horizontal line branches into several paths: + +- FITE 22** leads to **FITE Z**, which then leads to a dashed box labeled **(Note)**. From the note, the path leads to **BITE n**, which then leads to an **Idle** state (represented by a double circle with '00'). +- BITE Z** leads to **SPITE 53 (Table 5)**, which then leads to **BITE n**. +- FITE 1** leads to a decision diamond **Country Code FITE?**. + - If **No**, it leads to another decision diamond **SPITE 22?**. + - If **No**, it leads to **Omit Country Code FITE**. + - If **Yes**, it leads to **FITE 1**. + - If **Yes**, it leads to **BITE n**. +- BITE X** leads to **SPITE 53 (Table 2)**, which then leads to **BITE n**. +- BITE 48** leads to **SPITE 53 (Table 4)**, which then leads to **BITE j**. +- BITE 30** leads to **BITE 30**, which then leads to a connector labeled '2' with a subscript '1'. +- FITE 24** leads to **FITE 24**, which then leads to a connector labeled '2' with a subscript '1'. + +Further down the chart, the paths continue: + +- BITE n** (from FITE 1, BITE X, or Country Code FITE? Yes) leads to a connector labeled '4' with a subscript '3'. +- BITE j** (from BITE 48) leads to **BITE k**, which then leads to a connector labeled '5' with a subscript '3'. +- Omit Country Code FITE** (from SPITE 22? No) leads to a connector labeled '2' with a subscript '1'. + +Vertical axis labels on the left are 3, 2, 2, 4, 5, and 2. A text label 'T1125020-90/d03' is present on the right side. + +Flowchart for interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP). + +NOTE – In principle, FITE 22 should result in cause 16. However, in cases where FITE 22 results from a timeout expiry, cause 127 should be sent. + +FIGURE 3/Q.667 (sheet 2 of 5) +**Interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP)** + + + +``` + +graph TD + 4_23((4 +2, 3)) --> 05[05 +Wait for answer] + 05 --> BITE_Z[BITE Z] + 05 --> BITE_Y[BITE Y] + 05 --> FITE_22[FITE 22] + 05 --> FITE_23_1[FITE 23] + BITE_Z --> SPITE_53_6[SPITE 53 +(Table 6)] + SPITE_53_6 --> BITE_n_Z[BITE n] + BITE_n_Z --> 00_Idle_Z[00 +Idle] + BITE_Y --> SPITE_53_3[SPITE 53 +(Table 3)] + SPITE_53_3 --> BITE_n_Y[BITE n] + FITE_22 --> FITE_Z[FITE Z] + FITE_Z -.-> Note["(Note)"] + FITE_Z --> 00_Idle_22[00 +Idle] + FITE_23_1 --> FITE_23_2[FITE 23] + FITE_23_2 --> 4_3((4 +3)) + BITE_n_Y --> 06[06 +Answered] + 5_245((5 +2, 4, 5)) --> 06 + 06 --> 6_4((6 +4)) + +``` + +Flowchart showing the interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP). The process starts at node 4 (2, 3) leading to state 05 'Wait for answer'. From 05, it branches into four paths: BITE Z, BITE Y, FITE 22, and FITE 23. BITE Z leads to SPITE 53 (Table 6) then BITE n then state 00 'Idle'. BITE Y leads to SPITE 53 (Table 3) then BITE n. FITE 22 leads to FITE Z (Note) then state 00 'Idle'. FITE 23 leads to FITE 23 then node 4 (3). From BITE n (Y path), a transition from node 5 (2, 4, 5) leads to state 06 'Answered', which then leads to node 6 (4). Vertical labels 4, 5, 4, 6 are on the left. A note 'T1141510-92/d04' is on the right. + +NOTE – In principle, FITE 22 should result in cause 16. However, in cases where FITE 22 results from a timeout expiry, cause 127 should be sent. + +FIGURE 3/Q.667 (sheet 3 of 5) +**Interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP)** + + + +This flowchart illustrates the interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP) for sheet 4 of 5. It starts at a top junction point labeled with a circle containing '6' and subscript '3'. From this point, four parallel paths descend: + +- Path 1 (BITE Z):** Passes through a BITE Z block, then a SPITE 53 (Table 7) block, then a BITE n block, and finally reaches an 'Idle' state (00). +- Path 2 (FITE 23):** Passes through a FITE 23 block, then another FITE 23 block, and ends at a junction point labeled with a circle containing '5' and subscript '3'. +- Path 3 (FITE 22):** Passes through a FITE 22 block, then a FITE Z block (which has a '(Note)' label next to it), and reaches an 'Idle' state (00). +- Path 4 (BITE 25):** Passes through a BITE 25 block, then another BITE 25 block, then a 'Wait for resume' state (07) which has a junction point labeled with a circle containing '7' and subscript '5' next to it, and finally reaches a junction point labeled with a circle containing '8' and subscript '5'. + +Vertical axis labels on the left are 6, 7, 5, and 8. A document code 'T1125040-90/d05' is in the bottom right. + +Flowchart for interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP) (sheet 4 of 5). + +NOTE – In principle, FITE 22 should result in cause 16. However, in cases where FITE 22 results from a timeout expiry, cause 127 should be sent. + +FIGURE 3/Q.667 (sheet 4 of 5) +**Interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP)** + + + +This flowchart illustrates the interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP) for sheet 5 of 5. It starts at a top junction point labeled with a circle containing '8' and subscript '4'. From this point, four parallel paths descend: + +- Path 1 (FITE 22):** Passes through a FITE 22 block, then a FITE Z block (which has a '(Note)' label next to it), and reaches an 'Idle' state (00). +- Path 2 (FITE 23):** Passes through a FITE 23 block, then another FITE 23 block, and ends at a junction point labeled with a circle containing '7' and subscript '4'. +- Path 3 (BITE 24):** Passes through a BITE 24 block, then a BITE 24 block, and ends at a junction point labeled with a circle containing '5' and subscript '3'. +- Path 4 (BITE Z):** Passes through a BITE Z block and reaches an 'Idle' state (00). + +Vertical axis labels on the left are 8 and 7, 5. A document code 'T1141520-92/d06' is in the bottom right. + +Flowchart for interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP) (sheet 5 of 5). + +NOTE – In principle, FITE 22 should result in cause 16. However, in cases where FITE 22 results from a timeout expiry, cause 127 should be sent. + +FIGURE 3/Q.667 (sheet 5 of 5) +**Interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP)** + +TABLE 1/Q.667 + +### **FITE A construction – Interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP)** + +| Received FITE | CPC | +|---------------|-----| +| 9 | 1 | +| 10 | 2 | +| 11 | 3 | +| 12 | 4 | +| 13 | 5 | +| 17 | 10 | +| 18 | 11 | +| 19 | 12 | +| Pay phone | 15 | + +| Received FITE | SPITE 36 | CCH | +|---------------|----------|-----| +| 25 | Yes | 01 | +| 25 | No | 00 | +| 26 | Yes | 01 | +| 26 | No | 10 | +| 27 | Yes | 01 | +| 27 | No | 10 | + +| SPITE 22 | NAI | +|----------|-----| +| Yes | 100 | +| No | 011 | + +| SPITE 20 | SI | +|----------|----| +| Yes | 01 | +| No | 00 | + +| SPITE 21 | ECI | +|----------|-----| +| Yes | 1 | +| No | 0 | + +| FITE 30
Digital connectivity requested | TMR | +|-------------------------------------------|-----| +| No | 11 | +| Yes | 10 | + +| | | +|-----|---------------------------------| +| CPC | Calling party's category | +| CCH | Continuity check indicator | +| NAI | Nature of address indicator | +| SI | Satellite indicator | +| ECI | Echo control indicator | +| TMR | Transmission medium requirement | + +TABLE 2/Q.667 + +### **BITE X analysis – Interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP)** + +| Received BITE X | | | BITE n to be sent | +|-----------------|----|-----|-------------------| +| CH | ST | CAT | | +| 00 | 00 | 00 | BITE 2 + BITE 27 | +| 00 | 00 | 01 | BITE 2 + BITE 27 | +| 00 | 00 | 10 | BITE 4 | +| 00 | 01 | 00 | BITE 5 | +| 00 | 01 | 01 | BITE 5 | +| 00 | 01 | 10 | BITE 7 | +| 01 | 00 | 00 | BITE 3 | +| 01 | 00 | 01 | BITE 3 | +| 01 | 00 | 10 | BITE 4 | +| 01 | 01 | 00 | BITE 6 | +| 01 | 01 | 01 | BITE 6 | +| 01 | 01 | 10 | BITE 7 | +| 10 | 00 | 00 | BITE 2 + BITE 27 | +| 10 | 00 | 01 | BITE 2 + BITE 27 | +| 10 | 00 | 10 | BITE 4 | +| 10 | 01 | 00 | BITE 5 | +| 10 | 01 | 01 | BITE 5 | +| 10 | 01 | 10 | BITE 7 | + +CH Charge indicator +ST Called party's status indicator +CAT Called party's category indicator + +TABLE 3/Q.667 + +### **BITE Y analysis – Interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP)** + +| Received BITE Y
CH | BITE to be sent | +|-----------------------|-----------------| +| – | BITE 22 | +| 00 | BITE 22 | +| 01 | BITE 23 | +| 10 | BITE 22 | + +NOTE – With this proposal, BITE 22 (answer, charge) may be sent for a call where an address complete no charge message was previously sent. It is assumed that it does result in charging the call. + +TABLE 4/Q.667 + +### **CONNECT analysis – Interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP)** + +| Received CONNECT fields | | | BITE J | BITE K | +|-------------------------|----|-----|------------------|---------| +| CH | ST | CAT | | | +| 00 | 00 | 00 | BITE 2 + BITE 27 | BITE 22 | +| 00 | 00 | 01 | BITE 2 + BITE 27 | BITE 22 | +| 00 | 00 | 10 | BITE 4 | BITE 22 | +| 00 | 01 | 00 | BITE 5 | BITE 22 | +| 00 | 01 | 01 | BITE 5 | BITE 22 | +| 00 | 01 | 10 | BITE 7 | BITE 22 | +| 01 | 00 | 00 | BITE 3 | BITE 23 | +| 01 | 00 | 01 | BITE 3 | BITE 23 | +| 01 | 00 | 10 | BITE 4 | BITE 23 | +| 01 | 01 | 00 | BITE 6 | BITE 23 | +| 01 | 01 | 01 | BITE 6 | BITE 23 | +| 01 | 01 | 10 | BITE 7 | BITE 23 | +| 10 | 00 | 00 | BITE 2 + BITE 27 | BITE 22 | +| 10 | 00 | 01 | BITE 2 + BITE 27 | BITE 22 | +| 10 | 00 | 10 | BITE 4 | BITE 22 | +| 10 | 01 | 00 | BITE 5 | BITE 22 | +| 10 | 01 | 01 | BITE 5 | BITE 22 | +| 10 | 01 | 10 | BITE 7 | BITE 22 | + +NOTE – In this proposal, an answer, no charge BITE is generated when a no charge information is carried through the connect message. + +TABLE 5/Q.667 + +### **Received RELEASE analysis before ACM – Interworking of Signalling System No. 7 (TUP) to Signalling System No. 7 (ISUP)** + +| Received BITE Z
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and the letters ITU. + +INTERNATIONAL TELECOMMUNICATION UNION + +**ITU-T** + +**Q.698** + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +(03/93) + +# **INTERWORKING OF SIGNALLING SYSTEMS** --- + +# **INTERWORKING OF SIGNALLING SYSTEM No. 7 ISUP, TUP AND SIGNALLING SYSTEM No. 6 USING ARROW DIAGRAMS** + +**ITU-T Recommendation Q.698** + +(Previously "CCITT Recommendation") + +--- + +# FOREWORD + +The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecommunication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. + +ITU-T Recommendation Q.698 was prepared by the ITU-T Study Group XI (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). + +--- + +# NOTES + +1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. + +In order not to delay publication of this Recommendation, no change has been made in the text to references containing the acronyms "CCITT, CCIR or IFRB" or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. + +2 In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +# CONTENTS + +| | Page | +|-------------------------------------------------------------------|-------------| +| 1 General ..... | 1 | +| 1.1 Introduction ..... | 1 | +| 1.2 Scope ..... | 1 | +| 1.3 Relationship to other Recommendations ..... | 1 | +| 2 Methodology ..... | 1 | +| 3 Interworking arrow diagrams for successful call set-up ..... | 1 | +| 3.1 Signalling System No. 6 to Signalling System No. 7 ISUP ..... | 1 | +| 3.2 ISUP to Signalling System No. 6 ..... | 2 | +| 3.3 Signalling System No. 7 TUP to ISUP ..... | 2 | +| 3.4 Signalling System No. 7 ISUP to TUP ..... | 3 | +| 4 Interworking arrow diagrams for unsuccessful call set-up ..... | 10 | +| 4.1 Signalling System No. 6 to ISUP ..... | 10 | +| 4.2 ISUP to Signalling System No. 6 ..... | 11 | +| 4.3 Signalling System No. 7 TUP to ISUP ..... | 12 | +| 4.4 Signalling System No. 7 ISUP to TUP ..... | 13 | + + + +# **INTERWORKING OF SIGNALLING SYSTEM No. 7 ISUP, TUP AND SIGNALLING SYSTEM No. 6 USING ARROW DIAGRAMS** + +*(Helsinki, 1993)* + +# **1 General** + +## **1.1 Introduction** + +This Recommendation defines the use of arrow diagrams to provide a comprehensive view of the signalling handshake between ISDN-UP and other common channel signalling systems. The use of primitives as defined in Recommendation Q.699 is also included to gain a further level of understanding in an interworking situation. Detailed signalling interworking information still has to refer to the signalling procedures defined in respective Recommendations. + +## **1.2 Scope** + +This Recommendation provides arrow diagrams for basic calls in which ISDN-UP interworks with other common channel signalling systems. National options are not covered whereas supplementary services are for further study. Typical selective interworking cases are dealt with and references are made to relevant Recommendations. Mapping tables are used to cover interworking situations where there is no one to one correspondence between signals of different common channel signalling systems. + +## **1.3 Relationship to other Recommendations** + +References to other Recommendations are made to clarify the procedures in a number of interworking cases. The following Recommendations are referred to in this Recommendation: Q.118, Q.254-Q.268, Q.699, Q.722-Q.725, Q.762-Q.764. + +# **2 Methodology** + +The interworking model used in this Recommendation is essentially the same as defined in 2.2/Q.699. The use of primitives is also consistent with that interworking model. The symbols used in this Recommendation are described in Table 1. + +# **3 Interworking arrow diagrams for successful call set-up** + +## **3.1 Signalling System No. 6 to Signalling System No. 7 ISUP** + +### **3.1.1 Normal call with calling party disconnect** + +Figure 1 shows normal call set-up. When the calling party sends a CLF, the call is cleared. An REL message (Cause 16) is sent to the succeeding exchange indicating normal clearing. + +### **3.1.2 Normal call with called party disconnect** + +Figure 2 shows normal call set-up. When the called party hangs up, a CLB1 signal is sent to the preceding exchange indicating normal call clearing. + +TABLE 1/Q.698 + +#### **Symbols used** + +| | | +|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------| +|
| Reservation of an incoming/outgoing circuit without through connection |
+| 
| Disconnection of path through the exchange |
+| 
| Through connection of path in both directions |
+| 
| Release of circuit |
+| 
| Indicates I/C and O/G primitives are unconditionally related |
+| 
| Continuity check transceiver |
+| 
| Loop for continuity check |
+| (CI) | Continuity check required in nature of connection indicators |
+| (NI) | Network initiated in suspend/resume indicators |
+
+T114 1660-92/d01
+
+## 3.2 ISUP to Signalling System No. 6
+
+### 3.2.1 Normal call with calling party disconnect
+
+Figure 3 shows normal call set-up. When an REL message (Cause 16) is received from the preceding exchange, a CLF signal is sent to the succeeding exchange to indicate normal call clearing.
+
+### 3.2.2 Normal call with called party disconnect
+
+Figure 4 shows normal call set-up. When the called party hangs up, a CLB1 signal is received from the succeeding exchange. An SUS message is then sent to the preceding exchange to indicate normal call clearing.
+
+## 3.3 Signalling System No. 7 TUP to ISUP
+
+### 3.3.1 Normal call with calling party disconnect
+
+Figure 5 shows normal call set-up. When the calling party sends a CLF, the call is cleared. An REL message (Cause 16) is sent to the succeeding exchange indicating normal clearing.
+
+### 3.3.2 Normal call with called party disconnect
+
+Figure 6 shows normal call set-up. When the called party hangs up, a CLB signal is sent to the preceding exchange indicating normal call clearing.
+
+## 3.4 Signalling System No. 7 ISUP to TUP
+
+### 3.4.1 Normal call with calling party disconnect
+
+Figure 7 shows normal call set-up. When the calling party sends a Release Message (REL), the call is cleared. A CLF message is sent to the succeeding exchange indicating normal clearing.
+
+### 3.4.2 Normal call with called party disconnect
+
+Figure 8 shows normal call set-up. When the called party hangs up, an SUS signal is sent to the preceding exchange indicating normal call clearing.
+
+
+
+The diagram illustrates the signaling sequence for a normal call with calling party disconnect between a Preceding exchange (Outgoing SS No. 6, Incoming SS No. 6), an Interworking exchange (Call control), and a Succeeding exchange (Outgoing ISUP, Incoming ISUP). The sequence is as follows:
+
+- Setup:** The Preceding exchange sends an IAM to the Interworking exchange. The Interworking exchange sends a Setup Ind to the Incoming SS No. 6. The Interworking exchange sends a Setup Req to the Outgoing ISUP. The Outgoing ISUP sends an IAM (CI) to the Succeeding exchange. The Succeeding exchange sends a CCH Tone to the Outgoing ISUP. The Outgoing ISUP sends a COT to the Interworking exchange. The Interworking exchange sends a Cot Ind to the Incoming SS No. 6.
+- Answer:** The Succeeding exchange sends an ADC to the Outgoing ISUP. The Outgoing ISUP sends an ACM to the Interworking exchange. The Interworking exchange sends a Proc Req to the Incoming SS No. 6. The Incoming SS No. 6 sends an ANC to the Preceding exchange. The Interworking exchange sends a Setup Resp to the Incoming SS No. 6.
+- Disconnect:** The Incoming SS No. 6 sends a CLF to the Preceding exchange. The Interworking exchange sends a Rel Ind to the Incoming SS No. 6. The Interworking exchange sends a Rel Req to the Outgoing ISUP. The Outgoing ISUP sends a REL with Cause 16 to the Succeeding exchange. The Succeeding exchange sends a RLC to the Outgoing ISUP. The Outgoing ISUP sends a RLG to the Preceding exchange. The Interworking exchange sends a Rel Resp to the Incoming SS No. 6. The Interworking exchange sends a Rel Conf to the Outgoing ISUP.
+
+NOTE – Cause 16 = Normal clearing.
+
+Sequence diagram showing call flow between Preceding, Interworking, and Succeeding exchanges for a normal call with calling party disconnect.
+
+FIGURE 1/Q.698
+SS No. 6 to ISDN-UP
+Normal call with calling party disconnect
+
+
+
+The diagram illustrates the signaling sequence for a normal call with called party disconnect between an SS No. 6 network and an ISDN-UP network via an Interworking exchange.
+
+- Preceding exchange (Outgoing SS No. 6):**
+ - Sends **IAM** to Incoming SS No. 6.
+ - Receives **CCH Tone** from Interworking exchange.
+ - Sends **COT** to Incoming SS No. 6.
+ - Receives **ADC** from Interworking exchange.
+ - Sends **ANC** to Incoming SS No. 6.
+ - Receives **CLB1** from Interworking exchange.
+ - Sends **CLF** to Incoming SS No. 6.
+ - Receives **RLG** from Interworking exchange.
+- Preceding exchange (Incoming SS No. 6):**
+ - Receives **Setup Ind** from Interworking exchange.
+ - Sends **Cot Ind** to Interworking exchange.
+ - Receives **Proc Req** from Interworking exchange.
+ - Sends **Setup Resp** to Interworking exchange.
+ - Receives **Rel Req** from Interworking exchange.
+ - Sends **Rel Ind** to Interworking exchange.
+ - Receives **Rel Resp** from Interworking exchange (marked with X).
+- Interworking exchange (Call control):**
+ - Sends **Setup Req** to Outgoing ISUP.
+ - Sends **CCH Tone** to Incoming ISUP.
+ - Sends **Cot Req** to Outgoing ISUP.
+ - Receives **Proc Ind** from Outgoing ISUP.
+ - Sends **Setup Conf** to Outgoing ISUP.
+ - Receives **Rel Ind** from Outgoing ISUP.
+ - Sends **Rel Req** to Outgoing ISUP.
+ - Receives **Rel Conf** from Outgoing ISUP.
+ - Internal symbols: T (Timer), R (Relay), X (Switch).
+- Succeeding exchange (Outgoing ISUP):**
+ - Receives **IAM (CI)** from Incoming ISUP.
+ - Receives **CCH Tone** from Incoming ISUP.
+ - Receives **COT** from Incoming ISUP.
+ - Sends **ACM** to Incoming ISUP.
+ - Sends **ANM** to Incoming ISUP.
+ - Sends **SUS (NI)** to Incoming ISUP.
+ - Sends **REL** to Incoming ISUP.
+ - Sends **Cause 16 RLC** to Incoming ISUP.
+- Succeeding exchange (Incoming ISUP):**
+ - Sends **IAM (CI)** to Outgoing ISUP.
+ - Sends **CCH Tone** to Outgoing ISUP.
+ - Sends **COT** to Outgoing ISUP.
+ - Receives **ACM** from Outgoing ISUP.
+ - Receives **ANM** from Outgoing ISUP.
+ - Receives **SUS (NI)** from Outgoing ISUP.
+ - Receives **REL** from Outgoing ISUP.
+ - Receives **Cause 16 RLC** from Outgoing ISUP.
+
+Sequence diagram showing a call flow from a Preceding exchange (SS No. 6) to an Interworking exchange and then to a Succeeding exchange (ISDN-UP). The diagram illustrates the exchange of signaling messages like IAM, Setup Ind, CCH Tone, COT, ADC, ANC, CLB1, CLF, and RLG between the entities. The Interworking exchange contains a 'Call control' block with symbols for timer (T), relay (R), and switch (X).
+
+NOTE – Cause 16 = Normal clearing.
+
+T1141680-92/d03
+
+FIGURE 2/Q.698
+**SS No. 6 to ISDN-UP**
+**Normal call with called party disconnect**
+
+
+
+The diagram illustrates the call flow for a normal call with calling party disconnect from an ISDN-UP network to an SS No. 6 network. The sequence of messages and internal primitives is as follows:
+
+- Outgoing ISUP** sends **IAM (CI)** to **Incoming ISUP**.
+- Incoming ISUP** sends **Setup Ind** (primitive) to **Call control**.
+- Call control** (represented by a circle symbol) sends **Setup Req** (primitive) to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** sends **IAM** to **Incoming SS No. 6**.
+- CCH Tone** is exchanged between **Outgoing ISUP** and **Incoming ISUP**, and between **Outgoing SS No. 6** and **Incoming SS No. 6**. The **Call control** shows a tone connection (T/R symbol).
+- Outgoing ISUP** sends **COT** to **Incoming ISUP**, which sends **Cot Ind** to **Call control**.
+- Call control** sends **Cot Req** to **Outgoing SS No. 6**, which sends **COT** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends **ADC** to **Outgoing SS No. 6**, which sends **Proc Ind** to **Call control**.
+- Call control** sends **Proc Req** to **Incoming ISUP**, which sends **ACM** to **Outgoing ISUP**.
+- Incoming SS No. 6** sends **ANC** to **Outgoing SS No. 6**, which sends **Setup Conf** to **Call control**.
+- Call control** (now showing a quartered circle symbol) sends **Setup Resp** to **Incoming ISUP**, which sends **ANM** to **Outgoing ISUP**.
+- Outgoing ISUP** sends **REL** to **Incoming ISUP**, which sends **Rel Ind** to **Call control**.
+- Call control** (now showing a circle with an X symbol) sends **Rel Req** to **Outgoing SS No. 6**.
+- Incoming ISUP** sends **Cause 16** to **Outgoing ISUP**.
+- Outgoing SS No. 6** sends **CLF** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends **RLG** to **Outgoing SS No. 6**, which sends **Rel Conf** to **Call control**.
+- Incoming ISUP** sends **RLC** to **Outgoing ISUP**, and **Rel Resp** to **Call control**.
+
+T1141690-92/d04
+
+Sequence diagram showing ISDN-UP to SS No. 6 call flow with calling party disconnect. Lifelines: Preceding exchange (Outgoing ISUP), Incoming ISUP, Interworking exchange (Call control), Outgoing SS No. 6, and Succeeding exchange (Incoming SS No. 6).
+
+NOTE – Cause 16 = Normal clearing.
+
+FIGURE 3/Q.698
+**ISDN-UP to SS No. 6**
+**Normal call with calling party disconnect**
+
+
+
+The diagram illustrates the signaling sequence for a normal call with a disconnect at the called party, transitioning from ISDN-UP to SS No. 6. The lifelines are:
+
+
+- Preceding exchange:** Outgoing ISUP and Incoming ISUP.
+- Interworking exchange:** Call control unit containing a timer (T), a relay (R), and a switch symbol.
+- Succeeding exchange:** Outgoing SS No. 6 and Incoming SS No. 6.
+
+ The sequence of messages is as follows:
+
+
+- The Outgoing ISUP sends an **IAM (CI)** to the Incoming ISUP.
+- The Incoming ISUP sends a **Setup Ind** to the Call control.
+- The Call control sends a **Setup Req** to the Outgoing SS No. 6.
+- The Outgoing SS No. 6 sends an **IAM** to the Incoming SS No. 6.
+- Both the Incoming ISUP and Incoming SS No. 6 send a **CCH Tone** to the Call control.
+- The Outgoing ISUP sends a **COT** to the Incoming ISUP.
+- The Incoming ISUP sends a **Cot Ind** to the Call control.
+- The Call control sends a **Cot Req** to the Outgoing SS No. 6.
+- The Outgoing SS No. 6 sends a **COT** to the Incoming SS No. 6.
+- The Outgoing ISUP sends an **ACM** to the Incoming ISUP.
+- The Incoming ISUP sends a **Proc Req** to the Call control.
+- The Call control sends a **Proc Ind** to the Outgoing SS No. 6.
+- The Outgoing SS No. 6 sends an **ADC** to the Incoming SS No. 6.
+- The Outgoing ISUP sends an **ANM** to the Incoming ISUP.
+- The Incoming ISUP sends a **Setup Resp** to the Call control.
+- The Call control sends a **Setup Conf** to the Outgoing SS No. 6.
+- The Outgoing SS No. 6 sends an **ANC** to the Incoming SS No. 6.
+- The Outgoing ISUP sends a **SUS (NI)** to the Incoming ISUP.
+- The Incoming ISUP sends a **Rel Req** to the Call control.
+- The Call control sends a **Rel Ind** to the Outgoing SS No. 6.
+- The Outgoing SS No. 6 sends a **CLB1** to the Incoming SS No. 6.
+- The Outgoing ISUP sends a **REL** to the Incoming ISUP.
+- The Incoming ISUP sends a **Rel** to the Call control.
+- The Call control sends a **Rel Req** to the Outgoing SS No. 6.
+- The Outgoing SS No. 6 sends a **CLF** to the Incoming SS No. 6.
+- The Outgoing ISUP sends a **Cause 16 RLC** to the Incoming ISUP.
+- The Incoming ISUP sends a **Rel** to the Call control.
+- The Call control sends a **Conf** to the Outgoing SS No. 6.
+- The Outgoing SS No. 6 sends a **RLG** to the Incoming SS No. 6.
+- Finally, the Incoming ISUP sends a **Resp** to the Call control, which is marked with an 'X'.
+
+Sequence diagram showing ISDN-UP to SS No. 6 call flow with a disconnect at the called party. Lifelines: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), Succeeding exchange (Outgoing SS No. 6, Incoming SS No. 6). The diagram shows messages like IAM (CI), Setup Ind, Setup Req, CCH Tone, COT, ACM, Proc Req, ANM, Setup Resp, SUS (NI), Rel Req, REL, Cause 16 RLC, and various responses and confirmations between the exchanges and the call control unit.
+
+T1141700-92/d05
+
+NOTE – Cause 16 = Normal clearing by calling party before $T_6$ expires [2.5.1.3 c)/Q.767].
+
+FIGURE 4/Q.698
+**ISDN-UP to SS No. 6**
+**Normal call with called party disconnect**
+
+
+
+The diagram illustrates the signaling sequence for a normal call with calling party disconnect between a Preceding exchange (SS No. 7 TUP) and a Succeeding exchange (SS No. 7 ISUP) via an Interworking exchange with Call control.
+
+**Participants:**
+
+- Preceding exchange:** Outgoing SS No. 7 TUP, Incoming SS No. 7 TUP
+- Interworking exchange:** Call control (containing Transceiver (T/R), Switch, and Multiplexer (X) symbols)
+- Succeeding exchange:** Outgoing SS No. 7 ISUP, Incoming SS No. 7 ISUP
+
+**Sequence of Events:**
+
+- The Outgoing SS No. 7 TUP sends an **IAM (CI)** to the Incoming SS No. 7 TUP.
+- The Incoming SS No. 7 TUP sends a **Setup Ind** to the Call control.
+- The Call control sends a **Setup Req** to the Outgoing SS No. 7 ISUP.
+- The Outgoing SS No. 7 ISUP sends an **IAM (CI)** to the Incoming SS No. 7 ISUP.
+- Wavy lines representing **CCH Tone** are exchanged between the TUP/ISUP and the Call control.
+- The Incoming SS No. 7 TUP sends a **COT** to the Call control.
+- The Call control sends a **Cot Req** to the Outgoing SS No. 7 ISUP.
+- The Outgoing SS No. 7 ISUP sends a **COT** to the Incoming SS No. 7 ISUP.
+- The Incoming SS No. 7 TUP sends an **ACM** to the Call control.
+- The Call control sends a **Proc Req** to the Incoming SS No. 7 TUP.
+- The Incoming SS No. 7 TUP sends a **ANC** to the Call control.
+- The Call control sends a **Setup** to the Outgoing SS No. 7 ISUP.
+- The Outgoing SS No. 7 ISUP sends an **ANM** to the Incoming SS No. 7 ISUP.
+- The Incoming SS No. 7 TUP sends a **CLF** to the Call control.
+- The Call control sends a **Rel** to the Incoming SS No. 7 TUP.
+- The Outgoing SS No. 7 ISUP sends a **REL** to the Incoming SS No. 7 ISUP.
+- The Incoming SS No. 7 TUP sends an **RLG** to the Call control.
+- The Call control sends a **Rel** to the Incoming SS No. 7 TUP.
+- The Outgoing SS No. 7 ISUP sends a **Cause 16** to the Incoming SS No. 7 ISUP.
+- The Incoming SS No. 7 TUP sends a **Resp** to the Call control.
+- The Call control sends a **Conf** to the Outgoing SS No. 7 ISUP.
+- The Incoming SS No. 7 ISUP sends a **RLC** to the Outgoing SS No. 7 ISUP.
+
+Sequence diagram showing a normal call with calling party disconnect between a Preceding exchange (SS No. 7 TUP) and a Succeeding exchange (SS No. 7 ISUP) via an Interworking exchange with Call control. The diagram illustrates the flow of signaling messages like IAM, Setup, CCH Tone, COT, ACM, ANC, CLF, and RLG, as well as internal call control operations.
+
+T1141710-92/d06
+
+NOTE – Cause 16 = Normal clearing.
+
+FIGURE 5/Q.698
+**SS No. 7 TUP to ISUP**
+**Normal call with calling party disconnect**
+
+
+
+```
+
+ sequenceDiagram
+ participant PE as Preceding exchange (Outgoing SS No. 7 TUP)
+ participant IE as Interworking exchange (Call control)
+ participant SE as Succeeding exchange (Incoming SS No. 7 ISUP)
+
+ PE->>IE: IAM (CI)
+ Note over IE: Setup Ind
+ IE->>SE: Setup Req
+ SE->>IE: IAM (CI)
+
+ PE-->>IE: CCH Tone (wavy)
+ Note over IE: T/R Signal
+ IE-->>SE: CCH Tone (wavy)
+
+ PE->>IE: COT
+ Note over IE: Cot Ind
+ IE->>SE: Cot Req
+ SE->>IE: COT
+
+ IE->>PE: ACM
+ Note over IE: Proc Req
+ SE->>IE: ACM
+ Note over IE: Proc Ind
+
+ IE->>PE: ANC
+ Note over IE: Setup Resp
+ SE->>IE: ANM
+ Note over IE: Setup Conf
+
+ IE->>PE: CLB
+ Note over IE: Rel Req
+ SE->>IE: SUS (NI)
+ Note over IE: Rel Ind
+
+ IE->>PE: CLF
+ Note over IE: Rel Ind
+ IE->>SE: REL
+ Note over IE: Rel Req
+
+ PE->>IE: RLG
+ Note over IE: Rel Resp
+ SE->>IE: RLC
+ Note over IE: Rel Conf
+
+```
+
+NOTE – Cause 16 = Normal clearing.
+
+T1141720-92/d07
+
+FIGURE 6/Q.698
+**SS No. 7 TUP to ISUP
+ Normal call with called party disconnect**
+
+8 Recommendation Q.698 (03/93)
+
+
+
+The diagram illustrates the call flow for a normal call with calling party disconnect between an ISUP network and a TUP network. The sequence of messages is as follows:
+
+- Outgoing ISUP** sends **IAM (CI)** to **Incoming ISUP**.
+- Incoming ISUP** sends **Setup Ind** to **Call control**.
+- Call control** sends **Setup Req** to **Outgoing SS No. 7 TUP**.
+- Outgoing SS No. 7 TUP** sends **IAM** to **Incoming SS No. 7 TUP**.
+- CCH Tone** messages are exchanged between the ISUP and TUP networks via the **Call control**.
+- Outgoing ISUP** sends **COT** to **Incoming ISUP**.
+- Incoming ISUP** sends **Cot Ind** to **Call control**.
+- Call control** sends **Cot Req** to **Outgoing SS No. 7 TUP**.
+- Outgoing SS No. 7 TUP** sends **COT** to **Incoming SS No. 7 TUP**.
+- Outgoing ISUP** sends **ACM** to **Incoming ISUP**.
+- Incoming ISUP** sends **Proc Req** to **Call control**.
+- Call control** sends **Proc Ind** to **Outgoing SS No. 7 TUP**.
+- Outgoing SS No. 7 TUP** sends **ANM** to **Incoming SS No. 7 TUP**.
+- Outgoing ISUP** sends **ANM** to **Incoming ISUP**.
+- Incoming ISUP** sends **Setup Resp** to **Call control**.
+- Call control** sends **Setup Conf** to **Outgoing SS No. 7 TUP**.
+- Outgoing ISUP** sends **REL** to **Incoming ISUP**.
+- Incoming ISUP** sends **Rel** to **Call control**.
+- Call control** sends **Rel** to **Outgoing SS No. 7 TUP**.
+- Outgoing SS No. 7 TUP** sends **CLF** to **Incoming SS No. 7 TUP**.
+- Outgoing ISUP** sends **Cause 16** to **Incoming ISUP**.
+- Incoming ISUP** sends **Rel** to **Call control**.
+- Call control** sends **Rel** to **Outgoing SS No. 7 TUP**.
+- Outgoing ISUP** sends **RLC** to **Incoming ISUP**.
+- Incoming ISUP** sends **Resp** to **Call control**.
+- Call control** sends **Conf** to **Outgoing SS No. 7 TUP**.
+- Outgoing SS No. 7 TUP** sends **RLG** to **Incoming SS No. 7 TUP**.
+
+Sequence diagram showing the interworking of Signalling System No. 7 ISUP to No. 7 TUP for a normal call with calling party disconnect. The diagram involves five lifelines: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), and Succeeding exchange (Outgoing SS No. 7 TUP, Incoming SS No. 7 TUP). The sequence of messages includes IAM (CI), Setup Ind, Setup Req, IAM, CCH Tone, Cot Ind, Cot Req, Cot, ACM, Proc Req, Proc Ind, ANM, Setup Resp, Setup Conf, REL, Rel, CLF, Cause 16, Rel, RLC, and RLG. The diagram also includes symbols for timers (T, R) and call state transitions (circles with X).
+
+T1141730-92/d08
+
+NOTE – Cause 16 = Normal clearing.
+
+FIGURE 7/Q.698
+**Interworking of Signalling System No. 7 ISUP to No. 7 TUP**
+**Normal call with calling party disconnect**
+
+
+
+```
+
+sequenceDiagram
+ participant PE as Preceding exchange (Outgoing ISUP)
+ participant IE_IN as Interworking exchange (Incoming ISUP)
+ participant IE_CC as Interworking exchange (Call control)
+ participant IE_OUT as Interworking exchange (Outgoing SS No. 7 TUP)
+ participant SE as Succeeding exchange (Incoming SS No. 7 TUP)
+
+ PE->>IE_IN: IAM (CI)
+ IE_IN-->>IE_CC: Setup Ind
+ IE_CC-->>IE_OUT: Setup Req
+ IE_OUT->>SE: IAM
+
+ Note over PE, SE: CCH Tone (bi-directional wavy lines)
+
+ PE->>IE_IN: COT
+ IE_IN-->>IE_CC: Cot Ind
+ IE_CC-->>IE_OUT: Cot Req
+ IE_OUT->>SE: COT
+
+ SE->>IE_OUT: ACM
+ IE_OUT-->>IE_CC: Proc Ind
+ IE_CC-->>IE_IN: Proc Req
+ IE_IN->>PE: ACM
+
+ SE->>IE_OUT: ANM
+ IE_OUT-->>IE_CC: Setup Conf
+ IE_CC-->>IE_IN: Setup Resp
+ IE_IN->>PE: ANM
+
+ PE->>IE_IN: SUS (NI)
+ IE_IN-->>IE_CC: Rel Req
+ IE_CC-->>IE_OUT: Rel Ind
+ IE_OUT->>SE: CBK
+
+ PE->>IE_IN: REL
+ IE_IN-->>IE_CC: Rel Ind
+ IE_CC-->>IE_OUT: Rel Req
+ IE_OUT->>SE: CLF
+
+ SE->>IE_OUT: RLG
+ IE_OUT-->>IE_CC: Rel Conf
+ IE_CC-->>IE_IN: Rel Resp
+ IE_IN->>PE: Cause 16 RLC
+
+```
+
+Sequence diagram showing the interworking of Signalling System No. 7 ISUP to No. 7 TUP for a normal call with calling party disconnect.
+
+NOTE – Cause 16 = Normal clearing by called party before $T_6$ expires (2.5.1.3. c)/Q.767.
+
+T1141740-92/d09
+
+FIGURE 8/Q.698
+**Interworking of Signalling System No. 7 ISUP to No. 7 TUP**
+**Normal call with calling party disconnect**
+
+# 4 Interworking arrow diagrams for unsuccessful call set-up
+
+## 4.1 Signalling System No. 6 to ISUP
+
+### 4.1.1 Continuity failure on an incoming No. 6 circuit
+
+Figure 9 shows the check-tone not being looped within its timeout period of two seconds. A BLO signal is issued by the preceding exchange. After the reception of a BLA signal, the CLF/RLG sequence is exchanged. On the outgoing side, an REL message (Cause 127) is sent to the succeeding exchange. The RLC message completes the release sequence. A repeat attempt is made on another circuit by the preceding exchange.
+
+### **4.1.2 Continuity failure on an outgoing ISDN-UP circuit**
+
+Figure 10 shows the failure to receive the continuity check-tone from the succeeding exchange within its timeout period of two seconds. A COT (failure) message is sent to the succeeding exchange. A repeat attempt will be made on another circuit and it is assumed that the repeat attempt also fails. In such a case of double failure, a CFL (call failure) signal is sent to the preceding exchange. On the incoming side, a CLF/RLG sequence completes the signalling sequence.
+
+### **4.1.3 Release signal received before address complete**
+
+Figure 11 shows the REL message received from the succeeding exchange. The cause value in the message will determine which CCITT No. 6 signal will be sent to the preceding exchange. The mapping table in the same figure shows this information. An RLC message is sent to the succeeding exchange. On the incoming side, a CLF/RLG sequence completes the signalling sequence.
+
+### **4.1.4 Timeout on address complete message**
+
+Figure 12 shows the failure to receive an ACM signal within its 20-30 second timeout. A REL message (Cause 31) is sent to the succeeding exchange indicating the failure condition. On the incoming side, a CFL (call failure) signal is sent to the preceding exchange. Then, a CLF/RLG sequence completes the signalling sequence.
+
+### **4.1.5 Timeout on answer message**
+
+Figure 13 shows the failure to receive an ANM message within its 1.5-3 minute timeout. After the timeout period, the call is cleared in both directions. A call failure message (CFL) is sent to the preceding exchange and the REL message (Cause 19) is sent to the succeeding exchange. An RLC message is then returned by the succeeding exchange. On the incoming side, RLG signal is returned on receipt of CLF signal.
+
+### **4.1.6 Reset circuit received before ACM**
+
+Figure 14 shows the RSC signal received before the succeeding exchange sends back the ACM message. An RLC message is sent to the succeeding exchange and a repeat attempt is made on another circuit.
+
+### **4.1.7 Reset circuit received after ACM**
+
+Figure 15 shows the RSC message received after the succeeding exchange sends back the ACM message. An RLC message is sent to the succeeding exchange. On the incoming side, a CFL signal is sent to the preceding exchange. Then, a CLF/RLG sequence completes the signalling sequence.
+
+### **4.1.8 Dual seizure (controlling exchange)**
+
+Figure 16 shows the IAM message received from the succeeding exchange in a dual seizure situation. The incoming IAM message is ignored and call set-up continues as if it were a normal call.
+
+### **4.1.9 Dual seizure (non-controlling exchange)**
+
+Figure 17 shows the IAM message received from the succeeding exchange in a dual seizure situation. The incoming IAM message is processed as a normal call. The non-controlling exchange backs off and attempts to set up a call on other circuits of the same or an alternate route.
+
+## **4.2 ISUP to Signalling System No. 6**
+
+### **4.2.1 Continuity failure on an incoming ISUP circuit**
+
+Figure 18 shows the check-tone timing out after its two second timeout period. The preceding exchange issues a COT (failure) message. On the outgoing side, a CLF/RLG sequence completes the signalling sequence.
+
+### **4.2.2 Continuity failure on an outgoing No. 6 circuit**
+
+Figure 19 shows the failure to receive the continuity check-tone from the succeeding exchange within its two second timeout. A BLO signal is sent to the succeeding exchange. When a BLA signal is received, the CLF/RLG sequence is exchanged. A repeat attempt is made on another circuit and it is assumed that the reattempt also fails. In such a case of double continuity failure an REL message (Cause 127) is sent to the preceding exchange. An RLC message completes the signalling sequence.
+
+### **4.2.3 Congestion signal received after address complete**
+
+Figure 20 shows the CGC signal received after ADC signal. On the incoming side an REL message (Cause value 34) is sent to the preceding exchange indicating the congestion condition. An RLC message completes the signalling sequence.
+
+### **4.2.4 Timeout on address complete message**
+
+Figure 21 shows the failure to receive an ADC signal within its 20-30 second timeout. An CLF is sent to the succeeding exchange to clear the call. An RLG is then returned by the succeeding exchange. On the incoming side an REL message (Cause 127) is sent to the preceding exchange to indicate the failure. An RLC message is returned by the preceding exchange to complete the signalling sequence.
+
+### **4.2.5 Timeout on answer message**
+
+Figure 22 shows the failure to receive an ANC message within its 1.5-3 minute timeout. After the timeout period, an REL message (Cause 19) is sent to the preceding exchange and an RLC message is received by the interworking transit to complete the signalling sequence. In parallel, a CLF is sent towards the succeeding exchange.
+
+### **4.2.6 Reset circuit received before ADC**
+
+Figure 23 shows the RSC signal received before the ADC signal is sent back by the succeeding exchange. A CLF signal is sent to the succeeding exchange. After an RLG signal is received, a repeat attempt is made on another circuit.
+
+### **4.2.7 Reset circuit received after ADC**
+
+Figure 24 shows the RSC signal received after the succeeding exchange sends back the ADC signal. A CLF/RLG sequence is exchanged. On the incoming side, an REL message (Cause 31) is sent to the preceding exchange. An RLC message received from the preceding exchange completes the signalling sequence.
+
+### **4.2.8 Dual seizure (controlling exchange)**
+
+Figure 25 shows an IAM signal received from the succeeding exchange in a dual seizure situation. The incoming IAM signal is ignored and call set-up continues as if it were a normal call.
+
+### **4.2.9 Reset circuit (non-controlling exchange)**
+
+Figure 26 shows an IAM signal received from the succeeding exchange in a dual seizure situation. The incoming IAM signal is processed as a normal call. The non-controlling exchange backs off and attempts to set up a call on other circuits of the same or an alternate route.
+
+## **4.3 Signalling System No. 7 TUP to ISUP**
+
+### **4.3.1 Continuity failure on an incoming Signalling System No. 7 TUP circuit**
+
+Figure 27 shows the check-tone not being looped within its timeout period of two seconds. On the outgoing side, an REL message (Cause 31) is sent to the succeeding exchange. The RLC message completes the release sequence. A repeat attempt is made on another circuit by the preceding exchange. On the incoming side, a CCF message is received.
+
+### **4.3.2 Continuity failure on an outgoing ISDN-UP circuit**
+
+Figure 28 shows the failure to receive the continuity check-tone from the succeeding exchange within its timeout period of two seconds. A COT (failure) message is sent to the succeeding exchange. A repeat attempt will be made on another circuit and it is assumed that the repeat attempt also fails. In such a case of double failure, a CFL (call failure) signal is sent to the preceding exchange. On the incoming side, a CLF/RLG sequence completes the signalling sequence.
+
+### **4.3.3 Release signal received before address complete**
+
+Figure 29 shows the REL message received from the succeeding exchange. The cause value in the message will determine which Signalling System No. 7 TUP message will be sent to the preceding exchange. The mapping table in the same figure shows this information. An RLC message is sent to the succeeding exchange. On the incoming side, a CLF/RLG sequence completes the signalling sequence.
+
+### **4.3.4 Timeout on address complete message**
+
+Figure 30 shows the failure to receive an ACM signal within its 20-30 second timeout. An REL message (Cause 31) is sent to the succeeding exchange indicating the failure condition. On the incoming side, a CFL (call failure) signal is sent to the preceding exchange. Then, a CLF/RLG sequence completes the signalling sequence.
+
+### **4.3.5 Timeout on answer message**
+
+Figure 31 shows the failure to receive an ANM message within its 1.5-3 minute timeout. After the timeout period the call is cleared in both directions. A call failure message (CFL) is sent to the preceding exchange and the REL message (Cause 19) is sent to the succeeding exchange. An RLC message is then returned by the succeeding exchange. On the incoming side, RLG signal is returned on receipt of CLF signal.
+
+### **4.3.6 Reset circuit received before ACM**
+
+Figure 32 shows the RSC signal received before the succeeding exchange sends back the ACM message. An RLC message is sent to the succeeding exchange and a repeat attempt is made on another circuit.
+
+### **4.3.7 Reset circuit received after ACM**
+
+Figure 33 shows the RSC message received after the succeeding exchange sends back the ACM message. An RLC message is sent to the succeeding exchange. On the incoming side, a CFL signal is sent to the preceding exchange. Then, a CLF/RLG sequence completes the signalling sequence.
+
+### **4.3.8 Dual seizure (controlling exchange)**
+
+Figure 34 shows the IAM message received from the succeeding exchange in a dual seizure situation. The incoming IAM message is ignored and call set-up continues as if it were a normal call.
+
+### **4.3.9 Dual seizure (non-controlling exchange)**
+
+Figure 35 shows the IAM message received from the succeeding exchange in a dual seizure situation. The incoming IAM message is processed as a normal call. The non-controlling exchange backs off and attempts to set up a call on other circuits of the same or an alternate route.
+
+## **4.4 Signalling System No. 7 ISUP to TUP**
+
+### **4.4.1 Continuity failure on incoming ISUP circuit**
+
+Figure 36 shows the check-tone timing out after its two second timeout period. The preceding exchange issues a COT (failure) message. On the outgoing side, a CLF/RLG sequence completes the signalling sequence.
+
+### **4.4.2 Continuity failure on an outgoing No. 7 TUP circuit**
+
+Figure 37 shows the failure to receive the continuity check-tone from the succeeding exchange within its two second timeout. A CCF signal is sent to the succeeding exchange. A repeat attempt is made on another circuit and it is assumed that the reattempt also fails. In such a case of double continuity failure, an REL message (Cause 127) is sent to the preceding exchange. An RLC message completes the signalling sequence.
+
+### **4.4.3 Congestion signal received after address complete**
+
+Figure 38 shows the CGC signal received after ADC signal. On the incoming side an REL message (Cause value 34) is sent to the preceding exchange indicating the congestion condition. An RLC message completes the signalling sequence.
+
+### **4.4.4 Timeout on address complete message**
+
+Figure 39 shows the failure to receive an ADC signal within its 20-30 second timeout. A CLF is sent to the succeeding exchange to clear the call. An RLG is then returned by the succeeding exchange. On the incoming side an REL message (Cause 127) is sent to the preceding exchange to indicate the failure. An RLC message is returned by the preceding exchange to complete the signalling sequence.
+
+### **4.4.5 Timeout on answer message**
+
+Figure 40 shows the failure to receive an ANC message within its 1.5-3 minute timeout. After the timeout period an REL message (Cause 19) is sent to the preceding exchange and an RLC message is received by the interworking transit to complete the signalling sequence. In parallel, a CLF is sent towards the succeeding exchange.
+
+### **4.4.6 Reset circuit received before ADC**
+
+Figure 41 shows the RSC signal received before the ADC signal is sent back by the succeeding exchange. A CLF signal is sent to the succeeding exchange. After an RLG signal is received, a repeat attempt is made on another circuit.
+
+### **4.4.7 Reset circuit received after ADC**
+
+Figure 42 shows the RSC signal received after the succeeding exchange sends back the ADC signal. A CLF/RLG sequence is exchanged. On the incoming side, an REL message (Cause 31) is sent to the preceding exchange. An RLC message received from the preceding exchange completes the signalling sequence.
+
+### **4.4.8 Dual seizure (controlling exchange)**
+
+Figure 43 shows an IAM signal received from the succeeding exchange in a dual seizure situation. The incoming IAM signal is ignored and call set-up continues as if it were a normal call.
+
+### **4.4.9 Reset circuit (non-controlling exchange)**
+
+Figure 44 shows an IAM signal received from the succeeding exchange in a dual seizure situation. The incoming IAM signal is processed as a normal call. The non-controlling exchange backs off and attempts to set up a call on other circuits of the same or an alternate route.
+
+
+
+The diagram illustrates a call setup and failure scenario across five lifelines: Preceding exchange (Outgoing SS No. 6), Preceding exchange (Incoming SS No. 6), Interworking exchange (Call control), Succeeding exchange (Outgoing ISUP), and Succeeding exchange (Incoming ISUP).
+
+- Outgoing SS No. 6** sends an **IAM** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends a **Setup Ind** to **Call control**.
+- Call control** sends a **Setup Req** to **Outgoing ISUP**.
+- Outgoing ISUP** sends an **IAM (CI)** to **Incoming ISUP**.
+- Both **Incoming SS No. 6** and **Incoming ISUP** send a **CCH Tone** to **Call control**.
+- After a 2-second timer expires, **Call control** detects a **CCH Tone Continuity failure** and sends a **BLO** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends a **Blo Ind** to **Call control**.
+- Call control** sends a **Blo Resp** to **Incoming SS No. 6**.
+- Outgoing ISUP** receives a **REL** from **Incoming ISUP** with **Cause 127**.
+- Outgoing ISUP** sends a **Rel Req** to **Call control**.
+- Call control** sends a **Rel Conf** to **Outgoing ISUP**.
+- Outgoing ISUP** sends an **RLC** to **Incoming ISUP**.
+- Incoming SS No. 6** sends a **BLA** to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** sends a **CLF** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends a **Rel Ind** to **Call control**.
+- Call control** sends a **Rel Resp** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends an **RLG** to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** initiates a **Repeat attempt on another circuit**.
+
+Sequence diagram showing a continuity failure on an I/C No. 6 circuit between an SS No. 6 exchange and an ISDN-UP exchange via an interworking exchange. The diagram shows the flow of messages (IAM, Setup Ind, CCH Tone, BLO, BLA, CLF, RLG, Blo Ind, Blo Resp, Rel Ind, Rel Resp, Setup Req, Rel Req, Rel Conf, IAM (CI), REL, Cause 127, RLC) and the resulting actions like 'Repeat attempt on another circuit'.
+
+T1141750-92/d10
+
+NOTE – Cause 127 = Interworking unspecified.
+
+FIGURE 9/Q.698
+**SS No. 6 to ISDN-UP**
+**Continuity failure on I/C No. 6 circuit**
+
+
+
+The diagram illustrates the interaction between five entities: Preceding exchange (Outgoing SS No. 6), Preceding exchange (Incoming SS No. 6), Interworking exchange (Call control), Succeeding exchange (Outgoing ISUP), and Succeeding exchange (Incoming ISUP). The sequence of messages is as follows:
+
+- IAM**: Outgoing SS No. 6 to Incoming SS No. 6.
+- Setup Ind**: Incoming SS No. 6 to Call control (dashed line).
+- Setup Req**: Call control to Outgoing ISUP (dashed line).
+- IAM (CI)**: Outgoing ISUP to Incoming ISUP.
+- CCH Tone**: Call control to Outgoing SS No. 6 (wavy line).
+- CCH Tone**: Call control to Incoming ISUP (wavy line).
+- Continuity failure after $T_{24}$ (2 sec.) expires**: Indicated at the Interworking exchange.
+- COT**: Outgoing SS No. 6 to Incoming SS No. 6.
+- Cot Ind**: Incoming SS No. 6 to Call control (dashed line).
+- Cot Req**: Call control to Outgoing ISUP (dashed line).
+- COT (failure)**: Outgoing ISUP to Incoming ISUP.
+- CFL**: Outgoing SS No. 6 to Incoming SS No. 6.
+- Cfl Req**: Call control to Incoming SS No. 6 (dashed line).
+- CLF**: Outgoing SS No. 6 to Incoming SS No. 6.
+- Rel Ind**: Call control to Incoming SS No. 6 (dashed line).
+- RLG**: Outgoing SS No. 6 to Incoming SS No. 6.
+- Rel Resp**: Incoming SS No. 6 to Call control (dashed line).
+
+Note in the Succeeding exchange area: COT (failure)
+Repeat attempt on another circuit. If that attempt fails proceed as shown on No. 6 side this diagram [2.9.1 iv/Q.767]
+
+Sequence diagram showing a continuity failure on an outgoing No. 7 circuit between an SS No. 6 exchange and an ISDN-UP exchange via an interworking exchange. The diagram shows the flow of messages like IAM, Setup Ind, CCH Tone, COT, CFL, CLF, and RLG between the entities.
+
+T1141760-92/d11
+
+FIGURE 10/Q.698
+**SS No. 6 to ISDN-UP**
+**Continuity failure on outgoing No. 7 circuit**
+
+
+
+The diagram illustrates the signaling sequence for a call release when the release signal is received before address completion. The entities involved are:
+
+- Preceding exchange:** Outgoing SS No. 6 and Incoming SS No. 6.
+- Interworking exchange:** Call control, which acts as an intermediary. It contains symbols for a timer (T), a relay (R), and a switch (X).
+- Succeeding exchange:** Outgoing ISUP and Incoming ISUP.
+
+Sequence of messages:
+
+- Outgoing SS No. 6** sends **IAM** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends **Setup Ind** to **Call control**.
+- Call control** sends **Setup Req** to **Outgoing ISUP**.
+- Outgoing ISUP** sends **IAM (CI)** to **Incoming ISUP**.
+- CCH Tone** messages are exchanged between **Outgoing SS No. 6** and **Incoming ISUP** via **Call control**.
+- Outgoing SS No. 6** sends **COT** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends **Cot Ind** to **Call control**.
+- Call control** sends **Cot Req** to **Outgoing ISUP**.
+- Outgoing ISUP** sends **COT** to **Incoming ISUP**.
+- Outgoing ISUP** sends **REL (cause)** to **Call control**.
+- Call control** sends **Rel Ind** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends **Rel Req** to **Outgoing SS No. 6** (labeled "see mapping below").
+- Outgoing SS No. 6** sends **CLF** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends **Rel Ind** to **Call control**.
+- Call control** sends **Rel Resp** to **Outgoing ISUP** (marked with an 'X').
+- Outgoing ISUP** sends **RLC** to **Incoming ISUP**.
+- Outgoing SS No. 6** sends **RLG** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends **Rel Resp** to **Call control** (marked with an 'X').
+
+Sequence diagram showing the release signal flow between a Preceding exchange (Outgoing SS No. 6, Incoming SS No. 6), an Interworking exchange (Call control), and a Succeeding exchange (Outgoing ISUP, Incoming ISUP). The diagram illustrates the exchange of IAM, Setup, CCH Tone, COT, REL, CLF, and RLG messages. The Call control block contains symbols for timer (T), relay (R), and switch (X).
+
+T1141770-92/d12
+
+| Cause value in REL message | SS No. 6 signal |
+|----------------------------|-----------------|
+| 1 | UNN |
+| 34 | CGC |
+| 42 | SEC |
+| 17 | SSB |
+| 28 | ADI |
+| 27 | LOS |
+| 4 | SST |
+| Other | CFL |
+
+FIGURE 11/Q.698
+**SS No. 6 to ISDN-UP**
+**Release signal received before address complete**
+
+
+
+```
+
+sequenceDiagram
+ participant PE as Preceding exchange (Outgoing SS No. 6)
+ participant IE_IN as Incoming SS No. 6
+ participant CC as Interworking exchange (Call control)
+ participant IE_OUT as Outgoing ISUP
+ participant SE as Succeeding exchange (Incoming ISUP)
+
+ PE->>IE_IN: IAM
+ IE_IN-->>CC: Setup Ind
+ CC-->>IE_OUT: Setup Req
+ IE_OUT->>SE: IAM (CI)
+ PE-->>SE: CCH Tone (Wavy line)
+ SE-->>PE: CCH Tone (Wavy line)
+ PE->>IE_IN: COT
+ IE_IN-->>CC: Cot Ind
+ CC-->>IE_OUT: Cot Req
+ IE_OUT->>SE: COT
+ Note over CC: ACM Timeout 20-30 sec.
+ CC-->>IE_OUT: Rel Req
+ IE_OUT->>SE: REL
+ SE->>IE_OUT: Cause 31
+ SE->>IE_OUT: RLC
+ IE_OUT-->>CC: Rel Conf
+ CC-->>IE_IN: Cfl Req
+ IE_IN->>PE: CFL
+ Note over PE: (4.8.3/Q.268)
+ PE->>IE_IN: CLF
+ IE_IN-->>CC: Rel Ind
+ CC-->>IE_IN: Rel Resp
+ IE_IN->>PE: RLG
+ Note over SE: (2.10.8.3 & 2.1.4.8/Q.767)
+
+```
+
+The diagram illustrates the interaction between three main entities: Preceding exchange, Interworking exchange, and Succeeding exchange. The sequence of messages is as follows:
+
+- Outgoing SS No. 6** sends an **IAM** (Initial Address Message) to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends a **Setup Ind** (Indication) to **Call control**.
+- Call control** sends a **Setup Req** (Request) to **Outgoing ISUP**.
+- Outgoing ISUP** sends an **IAM (CI)** (Initial Address Message with Calling Information) to **Incoming ISUP**.
+- CCH Tone** is exchanged between the Preceding and Succeeding exchanges (represented by wavy lines).
+- Outgoing SS No. 6** sends a **COT** (Continuity) message to **Incoming SS No. 6**, which triggers a **Cot Ind** to **Call control**, then a **Cot Req** to **Outgoing ISUP**, and finally a **COT** to the **Incoming ISUP**.
+- The **Call control** starts an **ACM Timeout 20-30 sec.** (Address Complete Message Timeout).
+- Upon timeout, **Call control** sends a **Rel Req** to **Outgoing ISUP**, which sends a **REL** (Release) to **Incoming ISUP**.
+- Incoming ISUP** responds with **Cause 31** and **RLC** (Release Complete).
+- Outgoing ISUP** sends a **Conf** (Confirmation) to **Call control**.
+- Call control** sends a **Cfl Req** to **Incoming SS No. 6**, which sends a **CFL** (Call-failure signal) to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** sends a **CLF** (Clear-forward signal) to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends a **Rel Ind** to **Call control**, which responds with **Rel Resp**.
+- Finally, **Incoming SS No. 6** sends an **RLG** (Release-guard signal) to **Outgoing SS No. 6**.
+
+Icons in the **Call control** box indicate state changes and internal logic: a circle for initial state, a box with 'T' and 'R' arrows for transmission/reception paths, a timer icon for the ACM timeout, and an 'X' marking the termination of processes.
+
+Sequence diagram showing a call setup and timeout scenario between a Preceding exchange (SS No. 6) and a Succeeding exchange (ISUP) via an Interworking exchange (Call control).
+
+T1141780-92/d13
+
+NOTE – Cause 31 = Normal unspecified.
+
+FIGURE 12/Q.698
+**SS No. 6 to ISDN-UP**
+**Timeout on address complete message (ACM)**
+
+
+
+The diagram illustrates the signaling sequence between a Preceding exchange (SS No. 6), an Interworking exchange (containing Incoming SS No. 6, Call control, and Outgoing ISUP), and a Succeeding exchange (Incoming ISUP). The sequence is as follows:
+
+```
+
+Preceding Incoming Call Outgoing Succeeding
+Exchange SS No. 6 Control ISUP Exchange
+(SS No. 6) (Interworking) (ISUP)
+ | | | | |
+ |--- IAM --->| | | |
+ | |--Setup Ind-->| | |
+ | | |--Setup Req-->| |
+ | | | |---IAM (CI)-->|
+ | | | | |
+ |<~ CCH Tone ~~~~~~~~~~~~|~~~~~~~~~~~|~ CCH Tone ~>|
+ | | | | |
+ |--- COT --->| | | |
+ | |-- Cot Ind -->| | |
+ | | |-- Cot Req -->| |
+ | | | |--- COT --->|
+ | | | | |
+ |<--- ADC ---| | | |
+ | |<-- Proc Req--| | |
+ | | |<-- Proc Ind--| |
+ | | | |<--- ACM ---|
+ | | | | |
+ |<--- CFL ---| | | |
+ | |<-- Proc Req--| | |
+ | | ANM Timeout | |
+ | | (4.3/Q.118) | |
+ | | | | |
+ |<--- CLF ---| | | |
+ | |<-- Rel Ind --| | |
+ | | |-- Rel Req -->| |
+ | | | |--- REL --->|
+ | | | | (Cause 19)|
+ |<--- RLG ---| | | |
+ | |-- Rel Resp ->| | |
+ | | |<-- Rel Conf--| |
+ | | | |<--- RLC ---|
+
+```
+
+The Call control column includes functional symbols: a circle for initial state, a box with 'T' and 'R' arrows and a sine wave/clock for tone/timing control, a quartered circle representing the start of the ANM timer, and a circle with an 'X' representing the release state after timeout.
+
+Sequence diagram showing SS No. 6 to ISDN-UP interworking with a timeout on the answer message.
+
+T114 1790-92/d14
+
+NOTE – Cause 19 = No answer from user.
+
+FIGURE 13/Q.698
+**SS No. 6 to ISDN-UP**
+**Timeout on answer message**
+
+![Sequence diagram showing the interaction between a Preceding exchange, Interworking exchange, and Succeeding exchange for a call setup and reset procedure. The diagram includes messages like IAM, Setup Ind, CCH Tone, COT, Setup Req, Cot Req, Rel Ind, Rel Resp, RSC, and RLC. It also shows a 'Repeat attempt on another circuit' message with a reference to [2.10.3.1 e/Q.767].](c5452f95f3b28f1bfe29e84fbc2e1267_img.jpg)
+
+The diagram illustrates a call setup and reset sequence between three entities: Preceding exchange, Interworking exchange, and Succeeding exchange.
+
+- Preceding exchange** contains two sub-components: **Outgoing SS No. 6** and **Incoming SS No. 6**.
+- Interworking exchange** contains a **Call control** component with various symbols: a circle, a box with 'T', 'R', and a meter-like symbol, a circle with a cross-hatch, and a circle with an 'X'.
+- Succeeding exchange** contains two sub-components: **Outgoing ISUP** and **Incoming ISUP**.
+
+**Sequence of messages:**
+
+- IAM** (solid line) from Outgoing SS No. 6 to Incoming SS No. 6.
+- Setup Ind** (dashed line) from Incoming SS No. 6 to Call control.
+- CCH Tone** (wavy line) from Call control to Outgoing SS No. 6.
+- COT** (solid line) from Outgoing SS No. 6 to Incoming SS No. 6.
+- Cot Ind** (dashed line) from Incoming SS No. 6 to Call control.
+- Setup Req** (dashed line) from Call control to Outgoing ISUP.
+- IAM (CI)** (solid line) from Outgoing ISUP to Incoming ISUP.
+- CCH Tone** (wavy line) from Outgoing ISUP to Incoming ISUP.
+- COT** (solid line) from Outgoing ISUP to Incoming ISUP.
+- RSC** (solid line) from Incoming ISUP to Outgoing ISUP.
+- Rel Ind** (dashed line) from Outgoing ISUP to Call control.
+- Rel Resp** (dashed line) from Call control to Outgoing ISUP.
+- RLC** (solid line) from Incoming ISUP to Outgoing ISUP.
+- Repeat attempt on another circuit [2.10.3.1 e/Q.767]** (solid line) from Outgoing ISUP to Incoming ISUP.
+
+There are 'X' marks at the bottom of the Call control lifeline, indicating points of failure or error.
+
+Sequence diagram showing the interaction between a Preceding exchange, Interworking exchange, and Succeeding exchange for a call setup and reset procedure. The diagram includes messages like IAM, Setup Ind, CCH Tone, COT, Setup Req, Cot Req, Rel Ind, Rel Resp, RSC, and RLC. It also shows a 'Repeat attempt on another circuit' message with a reference to [2.10.3.1 e/Q.767].
+
+T1141800-92/d15
+
+FIGURE 14/Q.698
+**SS No. 6 to ISDN-UP**
+**Reset circuit received before ACM**
+
+
+
+```
+
+sequenceDiagram
+ participant PE as Preceding exchange (Outgoing SS No. 6)
+ participant ISS6 as Incoming SS No. 6
+ participant CC as Interworking exchange (Call control)
+ participant OISUP as Outgoing ISUP
+ participant SE as Succeeding exchange (Incoming ISUP)
+
+ PE->>ISS6: IAM
+ ISS6-->>CC: Setup Ind
+ CC-->>OISUP: Setup Req
+ OISUP->>SE: IAM (CI)
+ PE-->>CC: CCH Tone
+ CC-->>OISUP: CCH Tone
+ OISUP->>SE: CCH Tone
+ PE->>ISS6: COT
+ ISS6-->>CC: Cot Ind
+ CC-->>OISUP: Cot Req
+ OISUP->>SE: COT
+ PE->>ISS6: ADC
+ ISS6-->>CC: Proc Req
+ SE->>OISUP: ACM
+ OISUP-->>CC: Proc Ind
+ Note over OISUP, SE: [2.10.3.1 a)/Q.767]
+ SE->>OISUP: RSC
+ OISUP-->>CC: Rel Ind
+ CC-->>ISS6: Cfl Req
+ ISS6->>PE: CFL
+ Note over ISS6: (4.8.3/Q.268)
+ CC-->>OISUP: Rel Resp
+ OISUP->>SE: RLC
+ PE->>ISS6: CLF
+ ISS6-->>CC: Rel Ind
+ CC-->>ISS6: Rel Resp
+ ISS6->>PE: RLG
+
+```
+
+The diagram illustrates the signaling sequence for a reset circuit received after ACM. The lifelines are:
+**Preceding exchange (Outgoing SS No. 6)**, **Incoming SS No. 6**, **Interworking exchange (Call control)**, **Outgoing ISUP**, and **Succeeding exchange (Incoming ISUP)**.
+
+Key internal symbols in Call control include a through-connection (T/R) with arrows, a switch symbol (black/white circle), and a release symbol (circle with cross). The sequence ends with a 'Resp' primitive and an 'X' mark indicating circuit release.
+
+Sequence diagram showing SS No. 6 to ISDN-UP interworking for a reset circuit received after ACM. The diagram shows message flows between Preceding exchange, Incoming SS No. 6, Interworking exchange (Call control), Outgoing ISUP, and Succeeding exchange.
+
+T1141810-92/d16
+
+FIGURE 15/Q.698
+**SS No. 6 to ISDN-UP**
+**Reset circuit received after ACM**
+
+
+
+The diagram illustrates the call setup sequence for a 'Dual seizure (controlling exchange)' scenario from SS No. 6 to ISDN-UP. The participants are:
+
+
+- Preceding exchange:** Contains 'Outgoing SS No. 6' and 'Incoming SS No. 6' blocks.
+- Interworking exchange:** Contains a 'Call control' block with symbols for a timer, a transmitter/receiver (T/R), and a switch.
+- Succeeding exchange:** Contains 'Outgoing ISUP' and 'Incoming ISUP' blocks.
+
+ The sequence of messages is as follows:
+
+
+- IAM:** Outgoing SS No. 6 to Incoming SS No. 6.
+- Setup Ind:** Incoming SS No. 6 to Call control (dashed line).
+- Setup Req:** Call control to Outgoing ISUP (dashed line).
+- IAM (CI):** Outgoing ISUP to Incoming ISUP.
+- Ignore I/C IAM (2.10.1.4/Q.767):** Incoming ISUP to Outgoing ISUP.
+- CCH Tone:** Bidirectional exchange between Outgoing SS No. 6 and Call control, and between Outgoing ISUP and Incoming ISUP.
+- COT:** Outgoing SS No. 6 to Incoming SS No. 6.
+- Cot Ind:** Incoming SS No. 6 to Call control (dashed line).
+- Cot Req:** Call control to Outgoing ISUP (dashed line).
+- COT:** Outgoing ISUP to Incoming ISUP.
+- ADC:** Outgoing SS No. 6 to Incoming SS No. 6.
+- Proc Req:** Incoming SS No. 6 to Call control (dashed line).
+- Proc Ind:** Call control to Outgoing ISUP (dashed line).
+- ACM:** Outgoing ISUP to Incoming ISUP.
+- ANC:** Outgoing SS No. 6 to Incoming SS No. 6.
+- Setup Resp:** Incoming SS No. 6 to Call control (dashed line).
+- Setup Conf:** Call control to Outgoing ISUP (dashed line).
+- ANM:** Outgoing ISUP to Incoming ISUP.
+
+Sequence diagram for SS No. 6 to ISDN-UP call setup. It shows interactions between a Preceding exchange (Outgoing and Incoming SS No. 6), an Interworking exchange (Call control), and a Succeeding exchange (Outgoing and Incoming ISUP). The diagram illustrates the flow of messages like IAM, Setup Ind, Setup Req, CCH Tone, COT, ADC, ANC, ACM, and ANM, with a note to 'Ignore I/C IAM (2.10.1.4/Q.767)'.
+
+T1141820-92/d17
+
+FIGURE 16/Q.698
+**SS No. 6 to ISDN-UP**
+**Dual seizure (controlling exchange)**
+
+
+
+The diagram illustrates the call setup process between a Preceding exchange and a Succeeding exchange through an Interworking exchange. The components and their interactions are as follows:
+
+- Preceding exchange:** Contains 'Outgoing SS No. 6' and 'Incoming SS No. 6' blocks.
+ - 'Outgoing SS No. 6' sends an **IAM** (Initial Address Message) to 'Incoming SS No. 6'.
+ - 'Incoming SS No. 6' sends a **Setup Ind** (indication) to the 'Call control' block in the Interworking exchange.
+ - 'Outgoing SS No. 6' sends a **CCH Tone** (wavy line) to the 'Call control' block.
+ - 'Outgoing SS No. 6' sends a **COT** (Call Offered Tone) to 'Incoming SS No. 6'.
+- Interworking exchange:** Contains a 'Call control' block with a circle icon and a 'T/R' (Transceiver) icon.
+ - The 'Call control' block receives a **Setup Req** (request) from the 'Outgoing ISUP' block in the Succeeding exchange.
+ - The 'Call control' block sends a **Setup Ind** (indication) to the 'Outgoing ISUP' block.
+- Succeeding exchange:** Contains 'Outgoing ISUP' and 'Incoming ISUP' blocks.
+ - 'Outgoing ISUP' sends an **IAM (CI)** (Initial Address Message with Calling Information) to the 'Incoming ISUP' block.
+ - 'Outgoing ISUP' sends a **CCH Tone** (wavy line) to the 'Incoming ISUP' block.
+ - 'Outgoing ISUP' receives an **IAM** (Initial Address Message) from the 'Incoming ISUP' block.
+ - Upon receiving the **IAM**, the 'Outgoing ISUP' block executes the following logic:
+ - Process I/C IAM as normal call (2.10.1.4/Q.767)
+ - Non-controlling exchange backs off & repeats attempt on the same or alternate route.
+
+Sequence diagram showing call setup between a Preceding exchange (SS No. 6) and a Succeeding exchange (ISDN-UP) via an Interworking exchange. The diagram illustrates the flow of IAM, COT, CCH Tone, Setup Ind, Setup Req, and the subsequent handling of a dual seizure by the non-controlling exchange.
+
+T1141830-92/d18
+
+FIGURE 17/Q.698
+**SS No. 6 to ISDN-UP**
+**Dual seizure (non-controlling exchange)**
+
+
+
+```
+
+sequenceDiagram
+ participant PE as Preceding exchange (Outgoing ISUP)
+ participant II as Incoming ISUP
+ participant IE as Interworking exchange (Call control)
+ participant OS as Outgoing SS No. 6
+ participant SE as Succeeding exchange (Incoming SS No. 6)
+
+ PE->>II: IAM (CI)
+ II-->>IE: Setup Ind
+ IE-->>OS: Setup Req
+ OS->>SE: IAM
+
+ Note over PE, SE: CCH Tone
+ Note over IE: Continuity failure after T24 (2 sec.) expires
+
+ PE->>II: COT
+ Note over II: (failure)
+ Note over II: (7.3/Q.724)
+
+ IE-->>OS: Rel Req
+ OS->>SE: CLF
+ SE->>OS: RLG
+ IE-->>OS: Rel Conf
+
+```
+
+The diagram illustrates a call setup and failure scenario across five lifelines: Preceding exchange (Outgoing ISUP), Incoming ISUP, Interworking exchange (Call control), Outgoing SS No. 6, and Succeeding exchange (Incoming SS No. 6).
+
+- Call Setup:** The Preceding exchange sends an **IAM (CI)** to the Incoming ISUP. The Incoming ISUP sends a **Setup Ind** (dashed arrow) to the Interworking exchange. The Interworking exchange sends a **Setup Req** (dashed arrow) to the Outgoing SS No. 6. The Outgoing SS No. 6 sends an **IAM** to the Succeeding exchange.
+- Continuity Check:** A **CCH Tone** (represented by wavy lines) is exchanged. On the left, it's between the Preceding exchange and the Interworking exchange. On the right, it's between the Succeeding exchange and the Interworking exchange. Inside the Interworking exchange block, there are symbols for a transmitter (T) and receiver (R) with tone generation and detection icons. A note indicates "Continuity failure after $T_{24}$ (2 sec.) expires".
+- Failure Handling:** The Preceding exchange sends a **COT** to the Incoming ISUP. This is followed by **(failure)** and a reference **(7.3/Q.724)**. An 'X' marks the termination of the call control process. The Interworking exchange sends a **Rel Req** (dashed arrow) to the Outgoing SS No. 6. The Outgoing SS No. 6 sends a **CLF** to the Succeeding exchange. The Succeeding exchange responds with **RLG**. Finally, the Interworking exchange sends a **Rel Conf** (dashed arrow) to the Outgoing SS No. 6.
+
+T1141840-92/d19
+
+Sequence diagram showing a continuity failure on an I/C No. 7 circuit between a Preceding exchange and a Succeeding exchange via an Interworking exchange. The diagram illustrates the flow of ISUP and SS No. 6 messages, including IAM, Setup, CCH Tone, COT, Rel Req, CLF, and RLG. A failure occurs when the CCH Tone is not received by the Interworking exchange after T24 expires. The Interworking exchange then sends a Rel Req to the Outgoing SS No. 6, which responds with CLF and RLG. The Interworking exchange then sends a Rel Conf to the Outgoing SS No. 6. The failure is indicated by (7.3/Q.724).
+
+FIGURE 18/Q.698
+**ISDN-UP to SS No. 6**
+**Continuity failure on I/C No. 7 circuit**
+
+
+
+The diagram illustrates the interaction between five entities: Preceding exchange (Outgoing ISUP), Incoming ISUP, Interworking exchange (Call control), Outgoing SS No. 6, and Succeeding exchange (Incoming SS No. 6).
+
+- Initial Setup:** The Preceding exchange sends an **IAM (CI)** to the Incoming ISUP. The Incoming ISUP sends a **Setup Ind** to the Call control. The Call control sends a **Setup Req** to the Outgoing SS No. 6. The Outgoing SS No. 6 sends an **IAM** to the Succeeding exchange.
+- Continuity Check:** The Call control sends a **CCH Tone** to the Preceding exchange. The Preceding exchange sends a **CCH Tone** to the Incoming ISUP. The Incoming ISUP sends a **Cot Ind** to the Call control. The Call control sends a **CCH Tone** to the Outgoing SS No. 6. The Outgoing SS No. 6 sends a **CCH Tone** to the Succeeding exchange. A note indicates: "Continuity failure after 2 sec. timer expires" at the Outgoing SS No. 6.
+- Error Handling:** The Outgoing SS No. 6 sends a **Blo Req** to the Call control. The Call control sends a **Blo Req** to the Outgoing SS No. 6. The Outgoing SS No. 6 sends a **BLA** to the Call control. The Call control sends a **Rel Req** to the Outgoing SS No. 6. The Outgoing SS No. 6 sends a **RLF** to the Call control. The Call control sends a **Rel Req** to the Incoming ISUP. The Incoming ISUP sends a **REL** to the Preceding exchange. The Preceding exchange sends a **Cause 127** to the Incoming ISUP. The Incoming ISUP sends a **RLC** to the Call control. The Call control sends a **Rel Conf** to the Incoming ISUP. A note indicates: "(4.1.4/Q.261) Repeat attempt on another circuit. If that attempt fails proceed as follows."
+
+Sequence diagram showing a continuity failure on an outgoing No. 6 circuit between an ISDN-UP exchange and an SS No. 6 exchange via an interworking exchange. The diagram shows the flow of messages like IAM, CCH Tone, COT, REL, and RLC, and the resulting error handling when a continuity failure occurs after 2 seconds.
+
+T1141850-92/d20
+
+NOTE – Cause 127 = Interworking unspecified.
+
+FIGURE 19/Q.698
+**ISDN-UP to SS No. 6**
+**Continuity failure on outgoing No. 6 circuit**
+
+
+
+The diagram illustrates the call flow for an ISDN-UP to SS No. 6 connection where a congestion signal is received after address completion. The lifelines are:
+
+
+- Preceding exchange:** Contains 'Outgoing ISUP' and 'Incoming ISUP' components.
+- Interworking exchange:** Contains a 'Call control' component with symbols for timer (T), relay (R), and switches.
+- Succeeding exchange:** Contains 'Outgoing SS No. 6' and 'Incoming SS No. 6' components.
+
+ The sequence of messages is as follows:
+
+
+- The 'Outgoing ISUP' sends an **IAM (CI)** to the 'Incoming ISUP'.
+- The 'Incoming ISUP' sends a **Setup Ind** to the 'Call control'.
+- The 'Call control' sends a **Setup Req** to the 'Outgoing SS No. 6'.
+- The 'Outgoing SS No. 6' sends an **IAM** to the 'Incoming SS No. 6'.
+- Wavy lines representing **CCH Tone** are exchanged between the 'Outgoing ISUP' and 'Incoming ISUP' via the 'Call control'.
+- The 'Outgoing ISUP' sends a **COT** to the 'Incoming ISUP'.
+- The 'Incoming ISUP' sends a **Cot Ind** to the 'Call control'.
+- The 'Call control' sends a **Cot Req** to the 'Outgoing SS No. 6'.
+- The 'Outgoing SS No. 6' sends an **ACM** to the 'Incoming SS No. 6'.
+- The 'Incoming SS No. 6' sends an **ADC** to the 'Outgoing SS No. 6'.
+- The 'Outgoing ISUP' sends a **REL** to the 'Incoming ISUP'.
+- The 'Incoming ISUP' sends a **Proc Req** to the 'Call control'.
+- The 'Call control' sends a **Proc Ind** to the 'Outgoing SS No. 6'.
+- The 'Outgoing SS No. 6' sends a **CGC** to the 'Incoming SS No. 6'.
+- The 'Incoming ISUP' sends a **Rel Req** to the 'Call control'.
+- The 'Call control' sends a **Cgc Ind** to the 'Outgoing SS No. 6'.
+- The 'Outgoing ISUP' sends an **RLC** to the 'Incoming ISUP'.
+- The 'Incoming ISUP' sends a **Rel** to the 'Call control'.
+- The 'Call control' sends a **Rel Req** to the 'Outgoing SS No. 6'.
+- The 'Outgoing SS No. 6' sends a **CLF** to the 'Incoming SS No. 6'.
+- The 'Incoming ISUP' sends a **Conf** to the 'Call control'.
+- The 'Call control' sends a **Rel** to the 'Outgoing SS No. 6'.
+- The 'Outgoing SS No. 6' sends a **RLG** to the 'Incoming SS No. 6'.
+- The 'Call control' sends a **Conf** to the 'Outgoing SS No. 6'.
+- The 'Outgoing SS No. 6' sends a **Cause 34** (No circuits available) to the 'Incoming SS No. 6'.
+
+ The 'Cause 34' message is shown as part of the **REL** message from the 'Outgoing ISUP' to the 'Incoming ISUP', which is then passed through the 'Call control' to the 'Outgoing SS No. 6' and finally to the 'Incoming SS No. 6'.
+
+Sequence diagram showing ISDN-UP to SS No. 6 call flow with congestion signal. Lifelines: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), Succeeding exchange (Outgoing SS No. 6, Incoming SS No. 6). The diagram shows the exchange of messages like IAM, CCH Tone, COT, ACM, REL, RLC, Setup Ind, Cot Ind, Proc Req, Rel Req, Conf, Setup Req, Cot Req, Proc Ind, Cgc Ind, Rel Req, Rel, Conf, ADC, CGC, CLF, RLG. A 'Cause 34' (No circuits available) is indicated in the REL message from the preceding exchange to the succeeding exchange via the interworking exchange.
+
+T1141860-92/d21
+
+NOTE – Cause 34 = No circuits available.
+
+FIGURE 20/Q.698
+**ISDN-UP to SS No. 6**
+**Congestion signal received after address complete**
+
+
+
+The diagram illustrates the interaction between a Preceding exchange and a Succeeding exchange via an Interworking exchange. The Preceding exchange contains Outgoing ISUP and Incoming ISUP lifelines. The Succeeding exchange contains Outgoing SS No. 6 and Incoming SS No. 6 lifelines. The Interworking exchange contains a Call control lifeline with icons for a timer, a transceiver (T/R), and a switch. The sequence of messages is as follows:
+
+
+- IAM (CI)** from Outgoing ISUP to Incoming ISUP.
+- Setup Ind** (dashed) from Incoming ISUP to Call control.
+- Setup Req** (dashed) from Call control to Outgoing SS No. 6.
+- IAM** from Outgoing SS No. 6 to Incoming SS No. 6.
+- CCH Tone** (wavy lines) from Incoming ISUP to Call control, and from Call control to Incoming SS No. 6.
+- COT** from Outgoing ISUP to Incoming ISUP.
+- Cot Ind** (dashed) from Incoming ISUP to Call control.
+- Cot Req** (dashed) from Call control to Outgoing SS No. 6.
+- COT** from Outgoing SS No. 6 to Incoming SS No. 6.
+- REL** from Outgoing ISUP to Incoming ISUP.
+- Rel Req** (dashed) from Incoming ISUP to Call control.
+- Rel Req** (dashed) from Call control to Outgoing SS No. 6.
+- CLF** from Outgoing SS No. 6 to Incoming SS No. 6.
+- RLC** from Outgoing ISUP to Incoming ISUP.
+- Rel Conf** (dashed) from Incoming ISUP to Call control.
+- Rel** from Call control to Outgoing SS No. 6.
+- RLG** from Outgoing SS No. 6 to Incoming SS No. 6.
+- Rel Conf** (dashed) from Outgoing SS No. 6 to Call control.
+- Cause 127** from Outgoing ISUP to Incoming ISUP.
+- ADC Timeout 20-30 sec.** indicated by a crossed-out circle icon in the Call control lifeline.
+- (4.8.1.1 & 4.8.5/Q.268)** text at the bottom right of the Succeeding exchange lifeline.
+
+Sequence diagram showing ISDN-UP to SS No. 6 interworking with an ADC timeout. Lifelines: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), and Succeeding exchange (Outgoing SS No. 6, Incoming SS No. 6). The diagram shows message exchanges for Setup, CCH Tone, COT, REL, and RLC, with a timeout event in the Call control lifeline.
+
+T1141870-92/d22
+
+NOTE – Cause 127 = Interworking unspecified.
+
+FIGURE 21/Q.698
+**ISDN-UP to SS No. 6**
+**Timeout on address complete message (ADC)**
+
+
+
+The diagram illustrates the following sequence of messages and events:
+
+- Preceding exchange** sends **IAM (CI)** to **Incoming ISUP**.
+- Incoming ISUP** sends **Setup Ind** to **Call control** in the **Interworking exchange**.
+- Call control** sends **Setup Req** to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** sends **IAM** to **Incoming SS No. 6**.
+- CCH Tone** is exchanged between the **Preceding exchange** and **Incoming ISUP**, and between the **Outgoing SS No. 6** and **Incoming SS No. 6**.
+- COT** is sent from **Outgoing SS No. 6** to **Incoming SS No. 6**, and from **Incoming ISUP** to **Call control** (**Cot Ind**).
+- ACM** is sent from **Preceding exchange** to **Incoming ISUP**, and from **Incoming SS No. 6** to **Outgoing SS No. 6** (**ADC**).
+- Call control** sends **Proc** to **Incoming ISUP** and **Proc Ind** to **Outgoing SS No. 6**.
+- An **ANC Timeout (4.3/Q.118)** occurs in the **Call control**.
+- Call control** sends **Rel** to **Incoming ISUP** and **Rel** to **Outgoing SS No. 6**.
+- Rel** is sent from **Incoming ISUP** to **Preceding exchange** (**REL**), which includes **Cause 19**.
+- Rel** is sent from **Outgoing SS No. 6** to **Incoming SS No. 6** (**RLF**).
+- RLC** is sent from **Preceding exchange** to **Incoming ISUP**.
+- Call control** sends **Rel Req** to **Incoming ISUP** and **Rel Req** to **Outgoing SS No. 6**.
+- Call control** sends **Conf** to **Incoming ISUP** and **Conf** to **Outgoing SS No. 6**. These messages are marked with an 'X' at the bottom, indicating they are not received or processed.
+
+Sequence diagram showing ISDN call flow between a Preceding exchange and a Succeeding exchange via an Interworking exchange. The diagram illustrates a timeout on the answer message (ANC) from the Succeeding exchange, leading to call release with Cause 19 (No answer from user).
+
+T1141880-92/d23
+
+NOTE – Cause 19 = No answer from user.
+
+FIGURE 22/Q.698
+**ISDN-UP to SS No. 6**
+**Timeout on answer message**
+
+
+
+The diagram illustrates the following sequence of messages:
+
+- Outgoing ISUP** sends **IAM (CI)** to **Incoming ISUP**.
+- Incoming ISUP** sends a dashed **Setup Ind** to **Call control**.
+- Call control** sends a dashed **Setup Req** to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** sends **IAM** to **Incoming SS No. 6**.
+- CCH Tone** messages are exchanged between **Outgoing ISUP** and **Incoming ISUP**, and between **Outgoing SS No. 6** and **Incoming SS No. 6**, with **Call control** in the middle.
+- Outgoing ISUP** sends **COT** to **Incoming ISUP**.
+- Incoming ISUP** sends a dashed **Cot Ind** to **Call control**.
+- Call control** sends a dashed **Cot Req** to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** sends **COT** to **Incoming SS No. 6**.
+- Outgoing SS No. 6** sends **RSC** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends a dashed **Rsc Ind** to **Call control**.
+- Call control** sends a dashed **Rel Req** to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** sends **CLF** to **Incoming SS No. 6**.
+- Call control** sends a dashed **Rel Req** to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** sends **RLG** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends a dashed **Rel Conf** to **Call control**.
+- Call control** receives a message indicated by an 'X'.
+- Outgoing SS No. 6** sends a text message: "Repeat attempt on another circuit (4.8.4/Q.268)".
+
+T1141890-92/d24
+
+Sequence diagram showing ISDN-UP to SS No. 6 call flow with a reset circuit received before ADC. Lifelines: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), Succeeding exchange (Outgoing SS No. 6, Incoming SS No. 6).
+
+FIGURE 23/Q.698
+ ISDN-UP to SS No. 6
+ Reset circuit received before ADC
+
+
+
+The diagram illustrates the signaling sequence for an ISDN-UP to SS No. 6 call. It begins with the Preceding exchange sending an IAM (CI) to the Incoming ISUP, which then sends a Setup Ind to the Interworking exchange's Call control. The Call control responds with a CCH Tone. The Preceding exchange then sends a COT to the Incoming ISUP, which sends a Cot Ind to the Call control. The Call control sends a Cot Req to the Outgoing SS No. 6, which responds with a COT. The Outgoing SS No. 6 then sends an ADC to the Call control, which sends a Proc Ind to the Outgoing SS No. 6. The Outgoing SS No. 6 sends an RSC to the Call control, which sends a Rsc Ind to the Outgoing SS No. 6. The Outgoing SS No. 6 sends a CLF to the Call control, which sends a Rel Req to the Outgoing SS No. 6. The Outgoing SS No. 6 sends a RLG to the Call control, which sends a Rel Conf to the Outgoing SS No. 6. The Call control then sends a Rel Req to the Incoming ISUP, which sends a REL (Cause 31) to the Outgoing ISUP, which sends a RLC to the Incoming ISUP, which sends a Rel Conf to the Call control. The Call control then sends a X mark, indicating a reset circuit.
+
+Sequence diagram showing ISDN-UP to SS No. 6 call flow with a reset circuit. Lifelines: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), Succeeding exchange (Outgoing SS No. 6, Incoming SS No. 6). The diagram shows messages like IAM (CI), Setup Ind, CCH Tone, COT, ACM, REL (Cause 31), RLC, Setup Req, Cot Req, Proc Ind, Rsc Ind, Rel Req, Rel Conf, ADC, RSC, CLF, and RLG. Call control symbols include a circle, a T/R switch, a circle with an X, and a circle with a diagonal line.
+
+T1141900-92/d25
+
+NOTE – Cause 31 = Normal unspecified.
+
+FIGURE 24/Q.698
+**ISDN-UP to SS No. 6**
+**Reset circuit received after ADC**
+
+
+
+The diagram illustrates the call setup process for an ISDN-UP to SS No. 6 connection using dual seizure. The lifelines are:
+
+- Preceding exchange:** Outgoing ISUP and Incoming ISUP.
+- Interworking exchange:** Call control (containing T/R and switching symbols).
+- Succeeding exchange:** Outgoing SS No. 6 and Incoming SS No. 6.
+
+Sequence of messages:
+
+- Outgoing ISUP** sends **IAM (CI)** to **Incoming ISUP**.
+- Incoming ISUP** sends **Setup Ind** to **Call control**.
+- Call control** sends **Setup Req** to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** sends **IAM** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends **IAM** back to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** sends **Setup Req** to **Call control**.
+- Call control** sends **CCH Tone** to **Incoming ISUP**.
+- Incoming ISUP** sends **CCH Tone** to **Outgoing ISUP**.
+- Outgoing ISUP** sends **COT** to **Incoming ISUP**.
+- Incoming ISUP** sends **Cot Ind** to **Call control**.
+- Call control** sends **Cot Req** to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** sends **COT** to **Incoming SS No. 6**.
+- Incoming SS No. 6** sends **ADC** to **Outgoing SS No. 6**.
+- Outgoing SS No. 6** sends **Proc Ind** to **Call control**.
+- Call control** sends **Proc Req** to **Incoming ISUP**.
+- Incoming ISUP** sends **ANM** to **Outgoing ISUP**.
+- Outgoing ISUP** sends **ACM** to **Incoming ISUP**.
+- Call control** sends **Setup Resp** to **Incoming ISUP**.
+- Call control** sends **Setup Conf** to **Outgoing SS No. 6**.
+
+Additional details: The **Call control** lifeline includes a circle symbol at the top, a T/R symbol in the middle, and a switching symbol at the bottom. A note in the **Succeeding exchange** indicates to **Ignore I/C IAM (4.3.5/Q.265)**.
+
+Sequence diagram showing ISDN-UP to SS No. 6 call setup with dual seizure. Lifelines: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), Succeeding exchange (Outgoing SS No. 6, Incoming SS No. 6).
+
+T1141910-92/d26
+
+FIGURE 25/Q.698
+**ISDN-UP to SS No. 6**
+**Dual seizure (controlling exchange)**
+
+
+
+The diagram illustrates the interaction between a Preceding exchange, an Interworking exchange, and a Succeeding exchange during a dual seizure scenario for ISDN-UP to SS No. 6.
+
+- Preceding exchange:** Contains **Outgoing ISUP** and **Incoming ISUP** components.
+ - The **Outgoing ISUP** sends an **IAM (CI)** message to the **Incoming ISUP**.
+ - The **Incoming ISUP** sends a **Setup Ind** message to the **Interworking exchange**.
+ - The **Outgoing ISUP** sends a **CCH Tone** message to the **Incoming ISUP**.
+ - The **Outgoing ISUP** sends a **COT** message to the **Incoming ISUP**.
+- Interworking exchange:** Contains a **Call control** component.
+ - The **Call control** receives the **Setup Ind** message from the **Incoming ISUP**.
+ - The **Call control** sends a **Setup Req** message to the **Outgoing SS No. 6**.
+ - The **Call control** receives a **Setup Ind** message from the **Outgoing SS No. 6**.
+ - The **Call control** sends a **Cot Ind** message to the **Incoming ISUP**.
+- Succeeding exchange:** Contains **Outgoing SS No. 6** and **Incoming SS No. 6** components.
+ - The **Outgoing SS No. 6** receives the **Setup Req** message from the **Call control**.
+ - The **Outgoing SS No. 6** sends an **IAM** message to the **Incoming SS No. 6**.
+ - The **Outgoing SS No. 6** receives an **IAM** message from the **Incoming SS No. 6**.
+ - The **Outgoing SS No. 6** processes the **I/C IAM** as a normal call (4.3.5/Q.26).
+ - The **Outgoing SS No. 6** sends a **CCH Tone** message to the **Incoming SS No. 6**.
+ - The **Outgoing SS No. 6** (Non-controlling exchange) backs off and repeats the attempt on the same or an alternate route.
+
+Sequence diagram showing dual seizure of an ISDN-UP to SS No. 6. The diagram involves five lifelines: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), and Succeeding exchange (Outgoing SS No. 6, Incoming SS No. 6). The sequence shows IAM (CI) and COT messages from the preceding exchange, which are received by the incoming ISUP and then passed to the call control. The call control sends a Setup Req to the outgoing SS No. 6, which receives an IAM. The outgoing SS No. 6 then processes the I/C IAM as a normal call (4.3.5/Q.26) and sends a CCH Tone to the succeeding exchange. The non-controlling exchange (outgoing SS No. 6) backs off and repeats the attempt on the same or an alternate route.
+
+T1141920-92/d27
+
+FIGURE 26/Q.698
+**ISDN-UP to SS No. 6**
+**Dual seizure (non-controlling exchange)**
+
+
+
+```
+
+sequenceDiagram
+ participant PE as Preceding exchange
+Outgoing SS No. 7 TUP
+ participant PI as Preceding exchange
+Incoming SS No. 7 TUP
+ participant IE as Interworking exchange
+Call control
+ participant IO as Interworking exchange
+Outgoing SS No. 7 ISUP
+ participant SE as Succeeding exchange
+Incoming SS No. 7 ISUP
+
+ PE->>PI: IAM (CI)
+ PI-->>IE: Setup Ind
+ Note right of PI: CCH Tone
+Continuity failure after
+2 sec. timer expires
+ PI->>IE: CCF
+ Note right of IE: X
+ IE-->>IO: Setup Req
+ IO->>SE: IAM (CI)
+ SE-->>IE: CCH Tone
+ SE->>IO: REL
+Cause 31
+ IO->>IE: RLC
+ IE-->>IO: Rel Conf
+ Note right of IE: X
+
+```
+
+Sequence diagram showing a continuity failure on an incoming TUP circuit at an interworking exchange. The diagram involves five lifelines: Preceding exchange (Outgoing SS No. 7 TUP), Preceding exchange (Incoming SS No. 7 TUP), Interworking exchange (Call control), Interworking exchange (Outgoing SS No. 7 ISUP), and Succeeding exchange (Incoming SS No. 7 ISUP). The sequence starts with IAM (CI) from the outgoing TUP to the incoming TUP. The incoming TUP sends a Setup Ind to the call control. A CCH Tone is sent from the incoming TUP to the call control, and a continuity failure occurs after a 2-second timer expires. The incoming TUP sends a CCF to the call control. The call control sends a Setup Req to the outgoing ISUP. The outgoing ISUP sends an IAM (CI) to the succeeding exchange. A CCH Tone is sent from the succeeding exchange to the call control. The succeeding exchange sends a REL with Cause 31 to the outgoing ISUP. The outgoing ISUP sends a RLC to the call control. The call control sends a Rel Conf to the outgoing ISUP. There are 'X' marks indicating message exchanges that do not occur or are terminated.
+
+T1141930-92/d28
+
+NOTE – Cause 31 = Normal unspecified.
+
+FIGURE 27/Q.698
+**Signalling System No. 7 TUP to ISUP**
+**Continuity failure on incoming TUP circuit**
+
+
+
+The diagram illustrates the interaction between a Preceding exchange (TUP) and a Succeeding exchange (ISUP) through an Interworking exchange (Call control). The sequence of messages is as follows:
+
+- IAM (CI)**: Sent from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP.
+- Setup Ind**: Sent from Incoming SS No. 7 TUP to Call control.
+- CCH Tone**: Sent from Call control to Outgoing SS No. 7 TUP.
+- COT**: Sent from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP.
+- Cot Ind**: Sent from Incoming SS No. 7 TUP to Call control.
+- CFL**: Sent from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP.
+- Cfl Req**: Sent from Incoming SS No. 7 TUP to Call control.
+- CLF**: Sent from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP.
+- Rel Ind**: Sent from Incoming SS No. 7 TUP to Call control.
+- RLG**: Sent from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP.
+- Rel Resp**: Sent from Call control to Incoming SS No. 7 TUP.
+
+On the ISUP side, the sequence is:
+
+- Setup Req**: Sent from Call control to Outgoing SS No. 7 ISUP.
+- IAM (CI)**: Sent from Outgoing SS No. 7 ISUP to Incoming SS No. 7 ISUP.
+- CCH Tone**: Sent from Incoming SS No. 7 ISUP to Outgoing SS No. 7 ISUP.
+- Continuity failure after $T_{24}$ (<2 sec.) expires**: Indicated on the Incoming SS No. 7 ISUP side.
+- Cot Req**: Sent from Call control to Outgoing SS No. 7 ISUP.
+- COT (failure)**: Sent from Outgoing SS No. 7 ISUP to Incoming SS No. 7 ISUP.
+- Repeat attempt on another circuit. If that attempt fails proceed as shown on TUP side of this diagram [2.9.1 iv/Q.767]**: Indicated on the Incoming SS No. 7 ISUP side.
+
+Sequence diagram showing a continuity failure on an outgoing ISUP circuit between a TUP and an ISUP network via an interworking exchange.
+
+T1141940-92/d29
+
+FIGURE 28/Q.698
+**SS No. 7 TUP to ISUP**
+**Continuity failure on outgoing ISUP circuit**
+
+
+
+The diagram illustrates the signaling sequence for a call release between an SS No. 7 TUP network and an SS No. 7 ISUP network via an Interworking exchange (Call control). The sequence starts with an IAM (CI) from the Preceding exchange (Outgoing SS No. 7 TUP) to the Succeeding exchange (Incoming SS No. 7 ISUP). The Call control receives a Setup Ind and responds with a Setup Req. CCH Tones are exchanged. The Call control receives a COT and responds with a Cot Req. The Preceding exchange receives a Rel Req and sends a CLF. The Call control receives a Rel Ind and responds with a Rel Resp. The Preceding exchange receives a RLG and sends a Rel Resp. The Call control receives a Rel Resp and responds with a Rel Req. The Succeeding exchange receives a REL Cause and sends a RLC. The Call control receives a RLC and responds with a Rel Resp. The sequence ends with a Rel Resp from the Call control to the Preceding exchange.
+
+Sequence diagram showing the interaction between a Preceding exchange (SS No. 7 TUP), an Interworking exchange (Call control), and a Succeeding exchange (SS No. 7 ISUP). The diagram illustrates the release signal flow when received before address complete. The sequence includes IAM (CI), Setup Ind, CCH Tone, COT, Cot Ind, Rel Req, CLF, Rel Ind, RLG, and Rel Resp messages. The Call control block contains symbols for timer (T), relay (R), and switch (X).
+
+T1141950-92/d30
+
+| Cause value in REL message | SS No. 7 TUP signal |
+|----------------------------|---------------------|
+| 42 | SEC |
+| 34 | CGC |
+| 28 | ADI |
+| 1 | UNN |
+| 17 | SSB |
+| 27 | LOS |
+| 4 | SST |
+| 65 | DPN |
+| Other | CFL |
+
+FIGURE 29/Q.698
+**SS No. 7 TUP to ISUP**
+**Release signal received before address complete**
+
+
+
+The diagram illustrates the following sequence of messages and events:
+
+- Preceding exchange (Outgoing SS No. 7 TUP)** sends an **IAM (CI)** message to the **Interworking exchange (Call control)**.
+- The **Call control** sends a **Setup Ind** message to the **Incoming SS No. 7 TUP**.
+- The **Incoming SS No. 7 TUP** sends a **CCH Tone** message to the **Call control**.
+- The **Call control** sends a **Setup Req** message to the **Outgoing SS No. 7 ISUP**.
+- The **Outgoing SS No. 7 ISUP** sends an **IAM (CI)** message to the **Incoming SS No. 7 ISUP**.
+- The **Incoming SS No. 7 ISUP** sends a **CCH Tone** message to the **Call control**.
+- The **Call control** sends a **Cot Ind** message to the **Incoming SS No. 7 TUP**.
+- The **Outgoing SS No. 7 ISUP** sends a **Cot Req** message to the **Call control**.
+- The **Incoming SS No. 7 ISUP** sends a **COT** message to the **Call control**.
+- The **Call control** reaches an **ACM Timeout 20-30 sec.** (indicated by a crossed-out circle icon).
+- The **Call control** sends a **Cfl Req** message to the **Incoming SS No. 7 TUP**.
+- The **Incoming SS No. 7 TUP** sends a **CFL** message (referencing **(6.4.3/Q.724)**) to the **Outgoing SS No. 7 TUP**.
+- The **Call control** sends a **Rel Req** message to the **Outgoing SS No. 7 ISUP**.
+- The **Outgoing SS No. 7 ISUP** sends a **REL** message to the **Incoming SS No. 7 ISUP**.
+- The **Incoming SS No. 7 ISUP** sends a **Cause 31** message to the **Call control**.
+- The **Call control** sends a **Rel Ind** message to the **Incoming SS No. 7 TUP**.
+- The **Incoming SS No. 7 TUP** sends a **CLF** message to the **Outgoing SS No. 7 TUP**.
+- The **Call control** sends a **Rel Req** message to the **Outgoing SS No. 7 ISUP**.
+- The **Outgoing SS No. 7 ISUP** sends a **RLC** message to the **Incoming SS No. 7 ISUP**.
+- The **Call control** sends a **Rel Conf** message to the **Outgoing SS No. 7 ISUP**.
+- The **Incoming SS No. 7 ISUP** sends a **RLG** message (referencing **(2.10.8.3 & 2.1.4.8/Q.767)**) to the **Call control**.
+- The **Call control** sends a **Rel Resp** message to the **Incoming SS No. 7 TUP**.
+
+Sequence diagram showing a call flow between a Preceding exchange (SS No. 7 TUP) and a Succeeding exchange (SS No. 7 ISUP) via an Interworking exchange with Call control. The diagram illustrates a timeout on the address complete message (ACM) and the subsequent release of the call.
+
+T1141960-92/d31
+
+NOTE – Cause 31 = Normal unspecified.
+
+FIGURE 30/Q.698
+**SS No. 7 TUP to ISUP**
+**Timeout on address complete message (ACM)**
+
+
+
+The diagram illustrates a call setup sequence between a Preceding exchange and a Succeeding exchange through an Interworking exchange (Call control).
+
+- Preceding exchange:** Contains two entities: Outgoing SS No. 7 TUP and Incoming SS No. 7 TUP.
+- Interworking exchange:** Contains a Call control entity with symbols for timer (T), relay (R), and a clock. It also indicates an ANM Timeout (4.3/Q.118).
+- Succeeding exchange:** Contains two entities: Outgoing SS No. 7 ISUP and Incoming SS No. 7 ISUP.
+
+**Sequence of messages:**
+
+- The Outgoing SS No. 7 TUP sends an **IAM (CI)** to the Incoming SS No. 7 TUP.
+- The Incoming SS No. 7 TUP sends a **Setup Ind** to the Call control.
+- The Call control sends a **Setup Req** to the Outgoing SS No. 7 ISUP.
+- The Outgoing SS No. 7 ISUP sends an **IAM (CI)** to the Incoming SS No. 7 ISUP.
+- Both exchanges send **CCH Tone** messages to the Call control.
+- The Outgoing SS No. 7 ISUP sends a **COT** to the Incoming SS No. 7 ISUP.
+- The Incoming SS No. 7 ISUP sends a **Cot Req** to the Call control.
+- The Call control sends a **Cot Ind** to the Incoming SS No. 7 TUP.
+- The Outgoing SS No. 7 ISUP sends an **ACM** to the Incoming SS No. 7 ISUP.
+- The Incoming SS No. 7 ISUP sends a **Proc Req** to the Call control.
+- The Call control sends a **Proc Ind** to the Incoming SS No. 7 TUP.
+- The Outgoing SS No. 7 ISUP sends a **REL** to the Incoming SS No. 7 ISUP.
+- The Incoming SS No. 7 ISUP sends a **Cause 19** to the Call control.
+- The Call control sends a **Rel Req** to the Incoming SS No. 7 TUP.
+- The Incoming SS No. 7 TUP sends a **CLF** to the Outgoing SS No. 7 TUP.
+- The Call control sends a **Rel Ind** to the Incoming SS No. 7 TUP.
+- The Incoming SS No. 7 TUP sends a **RLG** to the Outgoing SS No. 7 TUP.
+- The Call control sends a **Rel Resp** to the Incoming SS No. 7 TUP.
+- The Call control sends a **Rel Conf** to the Outgoing SS No. 7 ISUP.
+
+Icons used in the Call control: A circle with 'T' and 'R' (timer/relay), a circle with a clock face (timeout), and a circle with an 'X' (error/abort).
+
+Sequence diagram showing a timeout on an answer message between a Preceding exchange (SS No. 7 TUP) and a Succeeding exchange (SS No. 7 ISUP) via an Interworking exchange (Call control).
+
+T1141970-92/d32
+
+NOTE – Cause 19 = No answer from user.
+
+FIGURE 31/Q.698
+**SS No. 7 TUP to ISUP**
+**Timeout on answer message**
+
+
+
+The diagram illustrates the signaling sequence for a call setup and reset between two different SS No. 7 protocols: TUP (Preceding exchange) and ISUP (Succeeding exchange).
+
+- Preceding exchange (Outgoing SS No. 7 TUP)** sends **IAM (CI)** to the **Incoming SS No. 7 TUP**.
+- The **Incoming SS No. 7 TUP** sends a **Setup Ind** to the **Interworking exchange**.
+- The **Interworking exchange** (Call control) sends a **Setup Req** to the **Outgoing SS No. 7 ISUP**.
+- The **Outgoing SS No. 7 ISUP** sends **IAM (CI)** to the **Incoming SS No. 7 ISUP**.
+- Both exchanges send **CCH Tone** signals.
+- The **Preceding exchange** sends **COT** to the **Incoming SS No. 7 TUP**.
+- The **Incoming SS No. 7 TUP** sends a **Cot Ind** to the **Interworking exchange**.
+- The **Interworking exchange** sends a **Cot Req** to the **Outgoing SS No. 7 ISUP**.
+- The **Outgoing SS No. 7 ISUP** sends **RSC** to the **Incoming SS No. 7 ISUP**.
+- The **Interworking exchange** sends a **Rel Ind** to the **Outgoing SS No. 7 ISUP**.
+- The **Outgoing SS No. 7 ISUP** sends **RLC** to the **Incoming SS No. 7 ISUP**.
+- The **Interworking exchange** sends a **Rel** to the **Outgoing SS No. 7 ISUP**.
+- The **Outgoing SS No. 7 ISUP** sends a **Resp** to the **Interworking exchange**.
+- At the bottom, the text indicates: **Repeat attempt on another circuit [2.10.3.1 e)/Q.767]**.
+
+Sequence diagram showing the interaction between a Preceding exchange (SS No. 7 TUP) and a Succeeding exchange (SS No. 7 ISUP) via an Interworking exchange. The diagram illustrates the flow of signaling messages (IAM, CCH Tone, COT, Setup Ind, Setup Req, Rel Ind, Rel, RSC, RLC) and the handling of a reset circuit before ACM. The Interworking exchange contains a Call control block with symbols for timer (T), relay (R), and switch (X).
+
+T114 1980-92/d33
+
+FIGURE 32/Q.698
+**SS No. 7 TUP to ISUP**
+**Reset circuit received before ACM**
+
+
+
+The diagram illustrates the signaling sequence for a call between a Preceding exchange (SS No. 7 TUP) and a Succeeding exchange (SS No. 7 ISUP) via an Interworking exchange (Call control).
+
+**Sequence of Messages:**
+
+- Outgoing SS No. 7 TUP** sends **IAM (CI)** to **Incoming SS No. 7 TUP**.
+- Incoming SS No. 7 TUP** sends **Setup Ind** to **Call control**.
+- Call control** sends **Setup Req** to **Outgoing SS No. 7 ISUP**.
+- Outgoing SS No. 7 ISUP** sends **IAM (CI)** to **Incoming SS No. 7 ISUP**.
+- CCH Tone** messages are exchanged between the **Outgoing SS No. 7 TUP** and **Incoming SS No. 7 TUP** via the **Call control**.
+- COT** is sent from **Incoming SS No. 7 TUP** to **Call control**, which then sends **Cot Req** to **Outgoing SS No. 7 ISUP**, which in turn sends **COT** to **Incoming SS No. 7 ISUP**.
+- ACM** is sent from **Incoming SS No. 7 TUP** to **Call control**, which sends **Proc Ind** to **Outgoing SS No. 7 ISUP**, which sends **ACM** to **Incoming SS No. 7 ISUP**. A note **[2.10.3.1 a)/Q.767]** is present next to the ACM message.
+- CFL** is sent from **Incoming SS No. 7 TUP** to **Call control**, which sends **Cfl Req** to **Outgoing SS No. 7 ISUP**, which sends **RSC** to **Incoming SS No. 7 ISUP**. A note **(6.3/Q.724)** is present next to the CFL message.
+- RLF** is sent from **Incoming SS No. 7 TUP** to **Call control**, which sends **Rel Ind** to **Outgoing SS No. 7 ISUP**, which sends **RLC** to **Incoming SS No. 7 ISUP**.
+- RLG** is sent from **Incoming SS No. 7 TUP** to **Call control**, which sends **Rel Resp** to **Outgoing SS No. 7 ISUP**. This message is marked with an 'X'.
+
+**Call control internal operations:**
+
+- The **Call control** block contains icons for a timer (T), relay (R), and switch (X).
+- The **Setup Req** message from **Call control** to **Outgoing SS No. 7 ISUP** is associated with the timer (T) icon.
+- The **Cot Req** message from **Call control** to **Outgoing SS No. 7 ISUP** is associated with the relay (R) icon.
+- The **Rel Ind** message from **Call control** to **Outgoing SS No. 7 ISUP** is associated with the switch (X) icon.
+
+Sequence diagram showing the interaction between a Preceding exchange (SS No. 7 TUP), an Interworking exchange (Call control), and a Succeeding exchange (SS No. 7 ISUP). The diagram illustrates the flow of signaling messages for call setup and reset procedures. The Interworking exchange contains icons for timer (T), relay (R), and switch (X) functions.
+
+T1141990-92/d34
+
+FIGURE 33/Q.698
+**SS No. 7 TUP to ISUP**
+**Reset circuit received after ACM**
+
+
+
+The diagram illustrates the signaling sequence for a call setup between a Preceding exchange (SS No. 7 TUP) and a Succeeding exchange (SS No. 7 ISUP) via an Interworking exchange (Call control).
+
+**Sequence of Messages:**
+
+- Outgoing SS No. 7 TUP** sends **IAM (CI)** to **Incoming SS No. 7 TUP**.
+- Incoming SS No. 7 TUP** sends **Setup Ind** to **Call control**.
+- Call control** sends **Setup Req** to **Outgoing SS No. 7 ISUP**.
+- Outgoing SS No. 7 ISUP** sends **IAM (CI)** to **Incoming SS No. 7 ISUP**.
+- Incoming SS No. 7 ISUP** sends **IAM** to **Outgoing SS No. 7 ISUP**.
+- Outgoing SS No. 7 ISUP** sends **Ignore I/C IAM (2.10.1.4/Q.767)** to **Incoming SS No. 7 ISUP**.
+- Call control** sends **CCH Tone** to **Outgoing SS No. 7 ISUP**.
+- Outgoing SS No. 7 ISUP** sends **CCH Tone** to **Incoming SS No. 7 ISUP**.
+- Preceding exchange** sends **COT** to **Incoming SS No. 7 TUP**.
+- Incoming SS No. 7 TUP** sends **Cot Ind** to **Call control**.
+- Call control** sends **Cot Req** to **Outgoing SS No. 7 ISUP**.
+- Outgoing SS No. 7 ISUP** sends **COT** to **Incoming SS No. 7 ISUP**.
+- Preceding exchange** sends **ACM** to **Incoming SS No. 7 TUP**.
+- Incoming SS No. 7 TUP** sends **Proc Req** to **Call control**.
+- Call control** sends **Proc Ind** to **Outgoing SS No. 7 ISUP**.
+- Outgoing SS No. 7 ISUP** sends **ACM** to **Incoming SS No. 7 ISUP**.
+- Preceding exchange** sends **ANC** to **Incoming SS No. 7 TUP**.
+- Incoming SS No. 7 TUP** sends **Setup Resp** to **Call control**.
+- Call control** sends **Rel** to **Outgoing SS No. 7 ISUP**.
+- Outgoing SS No. 7 ISUP** sends **ANM** to **Incoming SS No. 7 ISUP**.
+- Call control** sends **Conf** to **Outgoing SS No. 7 ISUP**.
+
+Sequence diagram showing the interaction between a Preceding exchange (SS No. 7 TUP), an Interworking exchange (Call control), and a Succeeding exchange (SS No. 7 ISUP). The diagram illustrates the flow of signaling messages for a call setup, including IAM (CI), Setup Ind, Setup Req, CCH Tone, COT, Cot Ind, ACM, Proc Req, ANC, Setup Resp, Ignore I/C IAM (2.10.1.4/Q.767), and ANM. The Interworking exchange contains icons for a timer, a relay, and a switch.
+
+T1142000-92/d35
+
+FIGURE 34/Q.698
+**SS No. 7 TUP to ISUP**
+**Dual seizure (controlling exchange)**
+**Reset circuit received after ACM**
+
+
+
+The diagram illustrates the following sequence of events:
+
+- Preceding exchange (Outgoing SS No. 7 TUP)** sends an **IAM** message to the **Interworking exchange**.
+- The **Interworking exchange** (Call control) receives the **IAM** and sends a **Setup Ind** (dashed line) to the **Incoming SS No. 7 TUP**.
+- The **Preceding exchange** sends a **CCH Tone** (wavy line) to the **Interworking exchange**.
+- The **Interworking exchange** receives the **CCH Tone** and sends a **COT** message to the **Incoming SS No. 7 TUP**.
+- The **Interworking exchange** (Call control) sends a **Setup Req** (dashed line) to the **Outgoing SS No. 7 ISUP**.
+- The **Outgoing SS No. 7 ISUP** sends an **IAM (CI)** message to the **Succeeding exchange**.
+- The **Outgoing SS No. 7 ISUP** receives a **CCH Tone** (wavy line) from the **Succeeding exchange**.
+- The **Outgoing SS No. 7 ISUP** sends an **IAM** message to the **Succeeding exchange**.
+- The **Outgoing SS No. 7 ISUP** receives a **Setup Ind** (dashed line) from the **Succeeding exchange**.
+- Inside the **Outgoing SS No. 7 ISUP**, a text box indicates: "Process I/C IAM as normal call (2.10.1.4/Q.767) Non-controlling exchange backs off and repeats attempt on the same or alternate route."
+
+Sequence diagram showing the interaction between a Preceding exchange (SS No. 7 TUP), an Interworking exchange (Call control), and a Succeeding exchange (SS No. 7 ISUP) during a dual seizure scenario. The diagram illustrates the flow of IAM, CCH Tone, and COT messages, and the subsequent setup requests and responses within the Interworking exchange.
+
+T1142010-92d36
+
+FIGURE 35/Q.698
+**SS No. 7 TUP to ISUP**
+**Dual seizure (non-controlling exchange)**
+
+
+
+```
+
+sequenceDiagram
+ participant PE as Preceding exchange
+ participant IE as Interworking exchange
+ participant SE as Succeeding exchange
+
+ Note left of PE: Outgoing ISUP
+ Note left of PE: Incoming ISUP
+ Note right of IE: Call control
+ Note right of SE: Outgoing SS No. 7 TUP
+ Note right of SE: Incoming SS No. 7 TUP
+
+ PE->>PE: IAM (CI)
+ PE->>IE: Setup Ind
+ IE->>SE: Setup Req
+ SE->>SE: IAM
+ SE->>IE: CCH Tone
+ IE->>PE: CCH Tone
+ PE->>PE: COT (failure)
+ PE->>IE: (7.3/Q.724)
+ IE->>SE: Rel Req
+ SE->>SE: CLF
+ SE->>SE: RLG
+ SE->>IE: Rel Conf
+ IE-x PE:
+
+```
+
+Sequence diagram showing the interworking of Signalling System No. 7 ISUP to No. 7 TUP with a continuity failure on the incoming ISUP circuit. The diagram involves five lifelines: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), and Succeeding exchange (Outgoing SS No. 7 TUP, Incoming SS No. 7 TUP). The sequence starts with IAM (CI) from Outgoing ISUP to Incoming ISUP. Incoming ISUP sends Setup Ind to Call control. Call control sends Setup Req to Outgoing SS No. 7 TUP. Outgoing SS No. 7 TUP sends IAM to Incoming SS No. 7 TUP. Incoming SS No. 7 TUP sends CCH Tone to Call control. Call control sends CCH Tone to Incoming ISUP. Incoming ISUP sends COT (failure) to Outgoing ISUP. Outgoing ISUP sends (7.3/Q.724) to Call control. Call control sends Rel Req to Outgoing SS No. 7 TUP. Outgoing SS No. 7 TUP sends CLF to Incoming SS No. 7 TUP. Incoming SS No. 7 TUP sends RLG to Outgoing SS No. 7 TUP. Outgoing SS No. 7 TUP sends Rel Conf to Call control. Call control sends a failure indication (X) to Incoming ISUP.
+
+T1142020-92/d37
+
+FIGURE 36/Q.698
+**Interworking of Signalling System No. 7 ISUP to No. 7 TUP**
+**Continuity failure on incoming ISUP circuit**
+
+
+
+```
+
+sequenceDiagram
+ participant PE as Preceding exchange
+ participant IE as Interworking exchange
+ participant SE as Succeeding exchange
+
+ Note left of PE: Outgoing ISUP
+ Note left of PE: Incoming ISUP
+ Note right of IE: Call control
+ Note right of SE: Outgoing SS No. 7 TUP
+ Note right of SE: Incoming SS No. 7 TUP
+
+ PE->>IE: IAM (CI)
+ IE-->>PE: Setup Ind
+ Note right of IE: [T/R]
+ IE->>SE: Setup Req
+ SE->>SE: IAM
+ Note right of SE: CCH Tone
+ Note right of SE: Continuity failure after 2 sec. timer expires
+ SE->>SE: CCF
+ Note right of SE: Repeat attempt on another circuit
+ IE->>SE: Ccf Req
+ IE->>SE: Ccr Req
+ SE->>SE: CCR
+ Note right of SE: CCH Tone (7.3/Q.724)
+ IE-->>PE: Rel Req
+ PE->>PE: REL
+ Note left of PE: Cause 127
+ PE->>PE: RLC
+ IE-->>PE: Rel Conf
+ Note right of IE: X
+
+```
+
+Sequence diagram showing interworking of Signalling System No. 7 ISUP to No. 7 TUP with a continuity failure on the outgoing TUP circuit. The diagram involves five lifelines: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), and Succeeding exchange (Outgoing SS No. 7 TUP, Incoming SS No. 7 TUP). The sequence shows the call setup, a continuity failure detected by the TUP, and the subsequent error handling messages (CCF, CCR, REL, RLC) sent back to the preceding exchange.
+
+T1142030-92/d38
+
+## NOTES
+
+- 1 Cause 127 = Interworking unspecified.
+- 2 CCR is sent to 1-10 s after failure detection.
+
+FIGURE 37/Q.698
+**Interworking of Signalling System No. 7 ISUP to No. 7 TUP**
+**Continuity failure on outgoing TUP circuit**
+
+
+
+Sequence diagram showing the interworking of Signalling System No. 7 ISUP to No. 7 TUP. The diagram involves four main entities: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), and Succeeding exchange (Outgoing SS No. 7 TUP, Incoming SS No. 7 TUP). The sequence of messages is: 1. Outgoing ISUP sends IAM (CI) to Incoming ISUP. 2. Incoming ISUP sends Setup Ind to Call control. 3. Call control sends Setup Req to Outgoing SS No. 7 TUP. 4. Outgoing SS No. 7 TUP sends IAM to Incoming SS No. 7 TUP. 5. Wavy lines represent CCH Tones between ISUP and TUP via Call control. 6. Outgoing ISUP sends COT to Incoming ISUP. 7. Incoming ISUP sends Cot Ind to Call control. 8. Call control sends Cot Req to Outgoing SS No. 7 TUP. 9. Outgoing SS No. 7 TUP sends COT to Incoming SS No. 7 TUP. 10. Outgoing ISUP sends ACM to Incoming ISUP. 11. Incoming ISUP sends Proc Req to Call control. 12. Call control sends Proc Ind to Outgoing SS No. 7 TUP. 13. Outgoing SS No. 7 TUP sends ADC to Incoming SS No. 7 TUP. 14. Outgoing ISUP sends REL with Cause 34 to Incoming ISUP. 15. Incoming ISUP sends Rel Req to Call control. 16. Call control sends Cgc Ind to Outgoing SS No. 7 TUP. 17. Outgoing SS No. 7 TUP sends CGC to Incoming SS No. 7 TUP. 18. Outgoing ISUP sends RLC to Incoming ISUP. 19. Incoming ISUP sends Rel Conf to Call control (marked with X). 20. Call control sends Rel Req to Outgoing SS No. 7 TUP. 21. Outgoing SS No. 7 TUP sends CLF to Incoming SS No. 7 TUP. 22. Outgoing SS No. 7 TUP sends RLG to Incoming SS No. 7 TUP. 23. Call control sends Rel Conf to Outgoing SS No. 7 TUP (marked with X).
+
+T1142040-92/d39
+
+NOTE – Cause 34 = No circuits available.
+
+FIGURE 38/Q.698
+**Interworking of Signalling System No. 7 ISUP to No. 7 TUP**
+**Congestion signal received after address complete**
+
+
+
+The diagram illustrates the interworking of Signalling System No. 7 ISUP to No. 7 TUP. It shows the following sequence of messages and actions:
+
+- Preceding exchange** (Outgoing ISUP) sends **IAM (CI)** to **Incoming ISUP**.
+- Incoming ISUP** sends **Setup Ind** to the **Interworking exchange** (Call control).
+- The **Call control** unit sends **Setup Req** to the **Outgoing SS No. 7 TUP**.
+- The **Outgoing SS No. 7 TUP** sends **IAM** to the **Incoming SS No. 7 TUP**.
+- Both **CCH Tone** messages are exchanged between the **Outgoing SS No. 7 TUP** and the **Incoming SS No. 7 TUP**.
+- The **Outgoing SS No. 7 TUP** sends **COT** to the **Incoming SS No. 7 TUP**.
+- The **Incoming SS No. 7 TUP** sends **Cot Ind** to the **Call control**.
+- The **Call control** unit sends **Cot Req** to the **Outgoing SS No. 7 TUP**.
+- The **Outgoing SS No. 7 TUP** sends **REL** to the **Incoming SS No. 7 TUP**.
+- The **Incoming SS No. 7 TUP** sends **Cause 31** to the **Outgoing SS No. 7 TUP**.
+- The **Outgoing SS No. 7 TUP** sends **RLC** to the **Incoming SS No. 7 TUP**.
+- The **Call control** unit sends **Rel Req** to the **Outgoing SS No. 7 TUP**.
+- The **Outgoing SS No. 7 TUP** sends **Rel** to the **Incoming SS No. 7 TUP**.
+- The **Call control** unit sends **Rel Conf** to the **Outgoing SS No. 7 TUP**.
+- The **Outgoing SS No. 7 TUP** sends **RLG** to the **Incoming SS No. 7 TUP**.
+- An **ACM Timeout** (20-30 sec.) occurs in the **Call control** unit.
+
+Sequence diagram showing the interworking of Signalling System No. 7 ISUP to No. 7 TUP. The diagram illustrates a call setup and release process between a Preceding exchange (Outgoing ISUP, Incoming ISUP) and a Succeeding exchange (Outgoing SS No. 7 TUP, Incoming SS No. 7 TUP) via an Interworking exchange containing a Call control unit. The process involves IAM (CI), Setup Ind, Setup Req, IAM, CCH Tone, COT, Cot Ind, Cot Req, ACM Timeout (20-30 sec.), REL, Rel Req, Rel, CLF, RLC, Rel Conf, and RLG messages. The Call control unit includes symbols for timer (T), relay (R), and a circle with a cross (X).
+
+T1142050-92/d40
+
+NOTE – Cause 127 = Interworking unspecified.
+
+FIGURE 39/Q.698
+**Interworking of Signalling System No. 7 ISUP to No. 7 TUP**
+**Timeout on address complete message (ACM)**
+
+
+
+The diagram illustrates the interworking of Signalling System No. 7 ISUP to No. 7 TUP. It shows the message exchange between a Preceding exchange (Outgoing ISUP, Incoming ISUP), an Interworking exchange (Call control), and a Succeeding exchange (Outgoing SS No. 7 TUP, Incoming SS No. 7 TUP).
+
+**Sequence of Messages:**
+
+- Outgoing ISUP** sends **IAM (CI)** to **Incoming ISUP**.
+- Incoming ISUP** sends **Setup Ind** to **Call control**.
+- Call control** sends **Setup Req** to **Outgoing SS No. 7 TUP**.
+- Outgoing SS No. 7 TUP** sends **IAM** to **Incoming SS No. 7 TUP**.
+- CCH Tone** messages are exchanged between **Outgoing ISUP** and **Incoming ISUP**, and between **Outgoing SS No. 7 TUP** and **Incoming SS No. 7 TUP**.
+- COT** messages are exchanged between **Outgoing ISUP** and **Incoming ISUP**, and between **Outgoing SS No. 7 TUP** and **Incoming SS No. 7 TUP**.
+- ACM** messages are exchanged between **Outgoing ISUP** and **Incoming ISUP**, and between **Outgoing SS No. 7 TUP** and **Incoming SS No. 7 TUP**.
+- REL** messages are exchanged between **Outgoing ISUP** and **Incoming ISUP**, and between **Outgoing SS No. 7 TUP** and **Incoming SS No. 7 TUP**.
+- Cause 19** is included in the **REL** message from **Outgoing ISUP** to **Incoming ISUP**.
+- RLC** messages are exchanged between **Outgoing ISUP** and **Incoming ISUP**, and between **Outgoing SS No. 7 TUP** and **Incoming SS No. 7 TUP**.
+- Call control** sends **Proc Req** to **Incoming ISUP** and **Proc Ind** to **Outgoing SS No. 7 TUP**.
+- Call control** sends **Rel Req** to **Incoming ISUP** and **Rel Req** to **Outgoing SS No. 7 TUP**.
+- Call control** sends **Rel Conf** to **Incoming ISUP** and **Rel Conf** to **Outgoing SS No. 7 TUP**.
+- Call control** has an **ANC Timeout (4.3/Q.118)** mechanism.
+
+Sequence diagram showing the interworking of Signalling System No. 7 ISUP to No. 7 TUP. The diagram illustrates the message exchange between a Preceding exchange (Outgoing ISUP, Incoming ISUP), an Interworking exchange (Call control), and a Succeeding exchange (Outgoing SS No. 7 TUP, Incoming SS No. 7 TUP). The sequence includes IAM (CI), CCH Tone, COT, ACM, REL, Cause 19, and RLC messages, with a timeout mechanism for the answer message (ANC Timeout (4.3/Q.118)).
+
+T1142060-92/d41
+
+NOTE – Cause 19 = No answer from user.
+
+FIGURE 40/Q.698
+**Interworking of Signalling System No. 7 ISUP to No. 7 TUP**
+**Timeout on answer message**
+
+
+
+Sequence diagram showing the interworking of Signalling System No. 7 ISUP to No. 7 TUP. The diagram involves three main entities: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), and Succeeding exchange (Outgoing SS No. 7 TUP, Incoming SS No. 7 TUP). The sequence of messages is: 1. IAM (CI) from Outgoing ISUP to Incoming ISUP. 2. Setup Ind from Incoming ISUP to Call control. 3. Setup Req from Call control to Outgoing SS No. 7 TUP. 4. IAM from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP. 5. CCH Tone from Outgoing ISUP to Call control. 6. CCH Tone from Call control to Outgoing SS No. 7 TUP. 7. COT from Outgoing ISUP to Incoming ISUP. 8. Cot Ind from Incoming ISUP to Call control. 9. Cot Req from Call control to Outgoing SS No. 7 TUP. 10. COT from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP. 11. Rsc Ind from Outgoing SS No. 7 TUP to Call control. 12. RSC from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP. 13. Rel Req from Call control to Outgoing SS No. 7 TUP. 14. CLF from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP. 15. Rel from Call control to Outgoing SS No. 7 TUP. 16. RLG from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP. 17. Conf from Call control to Outgoing SS No. 7 TUP (marked with an X). 18. 'Repeat attempt on another circuit (1.15.1 f/Q.724)' from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP.
+
+T1142070-92/d42
+
+FIGURE 41/Q.698
+**Interworking of Signalling System No. 7 ISUP to No. 7 TUP**
+**Reset circuit received before ACM**
+
+
+
+Sequence diagram showing the interworking of Signalling System No. 7 ISUP to No. 7 TUP. The diagram involves five lifelines: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), and Succeeding exchange (Outgoing SS No. 7 TUP, Incoming SS No. 7 TUP). The sequence of messages is: 1. IAM (CI) from Outgoing ISUP to Incoming ISUP. 2. Setup Ind from Incoming ISUP to Call control. 3. Setup Req from Call control to Outgoing SS No. 7 TUP. 4. IAM from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP. 5. CCH Tone from Incoming SS No. 7 TUP to Call control. 6. CCH Tone from Call control to Outgoing ISUP. 7. COT from Outgoing ISUP to Incoming ISUP. 8. Cot Ind from Incoming ISUP to Call control. 9. Cot Req from Call control to Outgoing SS No. 7 TUP. 10. COT from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP. 11. ACM from Incoming ISUP to Outgoing ISUP. 12. Proc Req from Call control to Incoming ISUP. 13. Proc Ind from Outgoing SS No. 7 TUP to Call control. 14. ACM from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP. 15. REL from Outgoing ISUP to Incoming ISUP. 16. Rel Req from Call control to Incoming ISUP. 17. Rsc from Incoming SS No. 7 TUP to Outgoing SS No. 7 TUP. 18. RSC from Outgoing SS No. 7 TUP to Incoming SS No. 7 TUP. 19. Cause 31 from Incoming ISUP to Outgoing ISUP. 20. Rel Req from Call control to Incoming ISUP. 21. CLF from Incoming SS No. 7 TUP to Outgoing SS No. 7 TUP. 22. RLC from Incoming ISUP to Outgoing ISUP. 23. Rel Conf from Call control to Incoming ISUP (marked with X). 24. Rel Conf from Outgoing SS No. 7 TUP to Call control (marked with X).
+
+T1142080-92/d43
+
+NOTE – Cause 31 = Normal unspecified.
+
+FIGURE 42/Q.698
+**Interworking of Signalling System No. 7 ISUP to No. 7 TUP**
+**Reset circuit received after ACM**
+
+
+
+The diagram illustrates the signaling sequence for call setup between an ISUP network and a TUP network through an interworking exchange during a dual seizure. The lifelines are:
+
+- Preceding exchange:** Outgoing ISUP and Incoming ISUP.
+- Interworking exchange:** Call control, containing logic symbols for a timer (circle), a transceiver (T/R) with tone/clock icons, and a switch state (crossed circle).
+- Succeeding exchange:** Outgoing SS No. 7 TUP and Incoming SS No. 7 TUP.
+
+The sequence of messages is as follows:
+
+- Outgoing ISUP** sends **IAM (CI)** to **Incoming ISUP**.
+- Incoming ISUP** sends **Setup Ind** to **Call control**.
+- Call control** sends **Setup Req** to **Outgoing SS No. 7 TUP**.
+- Outgoing SS No. 7 TUP** sends **IAM** to **Incoming SS No. 7 TUP**.
+- Simultaneously, **Incoming SS No. 7 TUP** sends an **IAM** to **Outgoing SS No. 7 TUP**. A note indicates: *Ignore I/C IAM (2.5/Q.724)*.
+- CCH Tone** is exchanged between **Outgoing ISUP** and the **Call control** (T/R block), and between **Incoming SS No. 7 TUP** and the **Call control**.
+- Outgoing ISUP** sends **COT** to **Incoming ISUP**, which then sends **Cot Ind** to **Call control**.
+- Call control** sends **Cot Req** to **Outgoing SS No. 7 TUP**, which sends **COT** to **Incoming SS No. 7 TUP**.
+- Incoming SS No. 7 TUP** sends **ACM** to **Outgoing SS No. 7 TUP**, which sends **Proc Ind** to **Call control**.
+- Call control** sends **Proc Req** to **Incoming ISUP**, which sends **ACM** to **Outgoing ISUP**.
+- Incoming SS No. 7 TUP** sends **ANM** to **Outgoing SS No. 7 TUP**, which sends **Setup Conf** to **Call control**.
+- Call control** sends **Setup Resp** to **Incoming ISUP**, which sends **ANM** to **Outgoing ISUP**.
+
+Sequence diagram showing the interworking of Signalling System No. 7 ISUP to No. 7 TUP during a dual seizure where the interworking exchange is controlling. The diagram shows message flows between Preceding exchange, Interworking exchange, and Succeeding exchange.
+
+T1142090-92/d44
+
+FIGURE 43/Q.698
+**Interworking of Signalling System No. 7 ISUP to No. 7 TUP**
+**Dual seizure (controlling exchange)**
+
+
+
+Preceding exchange
+
+Outgoing ISUP
+
+Incoming ISUP
+
+Interworking exchange
+
+Call control
+
+Succeeding exchange
+
+Outgoing SS No. 7 TUP
+
+Incoming SS No. 7 TUP
+
+IAM (CI)
+
+Setup Ind
+
+Setup Req
+
+IAM
+
+Setup Ind
+
+Process I/C IAM as a normal call (2.5/Q.724)
+
+CCH Tone
+
+COT
+
+Cot Ind
+
+Non-controlling exchange backs off and repeats attempt on the same or an alternate route.
+
+Sequence diagram showing the interworking of Signalling System No. 7 ISUP to No. 7 TUP. The diagram involves three main entities: Preceding exchange (Outgoing ISUP, Incoming ISUP), Interworking exchange (Call control), and Succeeding exchange (Outgoing SS No. 7 TUP, Incoming SS No. 7 TUP). The sequence starts with IAM (CI) from Outgoing ISUP to Incoming ISUP, which then sends a Setup Ind to the Call control. The Call control sends a Setup Req to the Outgoing SS No. 7 TUP, which responds with IAM to the Incoming SS No. 7 TUP. The Incoming SS No. 7 TUP sends an IAM back to the Outgoing SS No. 7 TUP, which then sends a Setup Ind to the Call control. The Call control sends a COT to the Incoming ISUP, which sends a Cot Ind to the Outgoing ISUP. Wavy lines represent CCH Tones being exchanged between the Call control and both the Outgoing and Incoming ISUP/TUP units. A note in the Succeeding exchange indicates that the non-controlling exchange backs off and repeats the attempt on the same or an alternate route.
+
+T1142100-92/d45
+
+FIGURE 44/Q.698
+**Interworking of Signalling System No. 7 ISUP to No. 7 TUP**
+**Dual seizure (non-controlling exchange)**
\ No newline at end of file
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+
+
+
+
+The logo of the International Telecommunication Union (ITU) features the letters 'ITU' in a bold, sans-serif font, superimposed on a stylized globe with intersecting lines.
+
+ITU logo
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+**Q.700**
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+(03/93)
+
+**SPECIFICATIONS OF SIGNALLING
+SYSTEM No. 7**
+
+---
+
+**INTRODUCTION TO CCITT
+SIGNALLING SYSTEM No. 7**
+
+**ITU-T Recommendation Q.700**
+
+(Previously "CCITT Recommendation")
+
+---
+
+# FOREWORD
+
+The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecommunication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics.
+
+ITU-T Recommendation Q.700 was revised by the ITU-T Study Group XI (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993).
+
+---
+
+# NOTES
+
+1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.
+
+In order not to delay publication of this Recommendation, no change has been made in the text to references containing the acronyms "CCITT, CCIR or IFRB" or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure.
+
+2 In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+# CONTENTS
+
+*Page*
+
+| | | |
+|-----|------------------------------------------------------------------|----|
+| 1 | General ..... | 1 |
+| 1.1 | Objectives and fields of application..... | 1 |
+| 1.2 | General characteristics ..... | 2 |
+| 1.3 | Components of SS No. 7 ..... | 2 |
+| 1.4 | Description techniques in the Q.7xx-Series Recommendations ..... | 3 |
+| 2 | SS No. 7 signalling network..... | 3 |
+| 2.1 | Basic concepts ..... | 3 |
+| 2.2 | Signalling network components..... | 3 |
+| 2.3 | Signalling point modes ..... | 4 |
+| 2.4 | Signalling routes ..... | 5 |
+| 2.5 | Signalling network structure ..... | 5 |
+| 3 | SS No. 7 functional blocks..... | 6 |
+| 3.1 | Basic functional division ..... | 6 |
+| 3.2 | SS No. 7 architecture ..... | 7 |
+| 4 | OSI layering and SS No. 7 ..... | 9 |
+| 4.1 | OSI Layering ..... | 9 |
+| 4.2 | Relationship between SS No. 7 layering and the OSI model..... | 10 |
+| 4.3 | Primitive Interfaces between SS No. 7 Functions ..... | 10 |
+| 5 | Addressing ..... | 11 |
+| 5.1 | Signalling message structure ..... | 12 |
+| 5.2 | MTP addressing ..... | 12 |
+| 5.3 | SCCP addressing ..... | 15 |
+| 5.4 | User Part addressing ..... | 15 |
+| 5.5 | Labelling ..... | 16 |
+| 6 | Operations administration and maintenance ..... | 16 |
+| 6.1 | Management ..... | 16 |
+| 6.2 | Maintenance and testing ..... | 16 |
+| 6.3 | SS No. 7 measurements ..... | 17 |
+| 7 | Signalling system performance ..... | 17 |
+| 7.1 | Hypothetical Signalling Reference Connection (HSRC)..... | 17 |
+| 7.2 | MTP ..... | 17 |
+| 7.3 | SCCP ..... | 17 |
+| 7.4 | TUP ..... | 18 |
+| 7.5 | ISUP ..... | 18 |
+| 8 | Flow control ..... | 18 |
+| 8.1 | Signalling network flow control ..... | 18 |
+| 8.2 | Signalling node (congestion) flow control..... | 18 |
+| 9 | Compatibility mechanisms and rules in SS No. 7 ..... | 18 |
+| 9.1 | Background..... | 18 |
+| 9.2 | Evolutionary requirements..... | 19 |
+| 9.3 | Forward and backward compatibility ..... | 19 |
+| 9.4 | Compatibility rules for SS No. 7 ..... | 19 |
+| 10 | Glossary..... | 20 |
+
+
+
+# **INTRODUCTION TO CCITT SIGNALLING SYSTEM No. 7**
+
+*(Melbourne 1988; modified at Helsinki 1993)*
+
+# **1 General**
+
+This Recommendation provides an overview of the Signalling System by describing the various functional elements of CCITT Signalling System No. 7 (SS No. 7) and the relationship between these functional elements. This Recommendation provides a general description of functions and capabilities of the Message Transfer Part (MTP), Signalling Connection Control Part (SCCP), Telephone User Part, ISDN User Part (ISUP), Transaction Capabilities (TC), and the Operations, Maintenance and Administration Part (OMAP) which are covered elsewhere in the Q.7xx-Series Recommendations. (This includes Recommendations Q.700 to Q.787.) However, in the case of contradiction between a particular specification and Recommendation Q.700, the particular specification shall apply.
+
+The SS No. 7 ISDN supplementary services are described in the Q.73x-Series Recommendations.
+
+In addition to these functions in the SS No. 7 signalling system, the Q.7xx Series Recommendations describes the SS No. 7 network structure, and also specifies the tests and measurements applicable to SS No. 7.
+
+This Recommendation also contains information about other aspects such as SS No. 7 architecture, flow control and general compatibility rule which are not specified in separate Recommendations, and are applicable to the overall scope of SS No. 7. Recommendation Q.1400 also contains information about architecture and compatibility.
+
+The remainder of this Recommendation describes:
+
+- clause 2: Signalling network concepts components and modes;
+- clause 3: The functional blocks within SS No. 7 and the services provided by them;
+- clause 4: SS No. 7 protocol layering and its relationship to OSI modelling;
+- clause 5: Node, application entity and user part addressing;
+- clause 6: Operations, administration and maintenance aspects of SS No. 7;
+- clause 7: Performance aspects of the functional blocks within SS No. 7;
+- clause 8: Flow control for both the signalling network and within nodes;
+- clause 9: Rules for evolving SS No. 7 protocols while preserving compatibility with earlier versions;
+- clause 10: A cross-reference to a glossary of terms.
+
+## **1.1 Objectives and fields of application**
+
+The overall objective of SS No. 7 is to provide an internationally standardized general purpose common channel signalling (CCS) system:
+
+- optimized for operation in digital telecommunications networks in conjunction with stored program controlled exchanges;
+ - that can meet present and future requirements of information transfer for inter-processor transactions within telecommunications networks for call control, remote control, and management and maintenance signalling;
+- that provides a reliable means for transfer of information in correct sequence and without loss or duplication.
+
+The signalling system meets requirements of call control signalling for telecommunication services such as the telephone, ISDN and circuit switched data transmission services. It can also be used as a reliable transport system for other types of information transfer between exchanges and specialized centres in telecommunications networks (e.g. for
+
+management and maintenance purposes). The system is thus applicable for multipurpose uses in networks that are dedicated for particular services and in multiservices networks. The signalling system is intended to be applicable in international and national networks.
+
+The scope of SS No. 7 encompasses both circuit related and non-circuit related signalling.
+
+Examples of applications supported by SS No. 7 are:
+
+- PSTN;
+- ISDN;
+- Interaction with Network Databases, Service Control Points for service control;
+- Mobiles (Public Land Mobile Network);
+- Operations Administration and Maintenance of Networks.
+
+The signalling system is optimized for operation over 64 kbit/s digital channels. It is also suitable for operation over analogue channels and at lower speeds. The system is suitable for use on point-to-point terrestrial and satellite links. It does not include the special features required for use in point-to-multipoint operation but can, if required, be extended to cover such an application.
+
+### 1.2 General characteristics
+
+Common channel signalling is a signalling method in which a single channel conveys, by means of labelled messages, signalling information relating to, for example, a multiplicity of circuits, or other information such as that used for network management. Common channel signalling can be regarded as a form of data communication that is specialized for various types of signalling and information transfer between processors in telecommunications networks.
+
+The signalling system uses signalling links for transfer of signalling messages between exchanges or other nodes in the telecommunication network served by the system. Arrangements are provided to ensure reliable transfer of signalling information in the presence of transmission disturbances or network failures. These include error detection and correction on each signalling link. The system is normally applied with redundancy of signalling links and it includes functions for automatic diversion of signalling traffic to alternative paths in case of link failures. The capacity and reliability for signalling may thus be dimensioned by provision of a multiplicity of signalling links according to the requirements of each application.
+
+### 1.3 Components of SS No. 7
+
+SS No. 7 consists of a number of components or functions which are defined in the Q.7xx-Series Recommendations.
+
+| SS No. 7 function | Recommendations |
+|-------------------------------------------------------------------|---------------------------|
+| Message Transfer Part (MTP) | Q.701-Q.704, Q.706, Q.707 |
+| Telephone User Part (TUP) (including some supplementary services) | Q.721-Q.725 |
+| Supplementary services | Q.73x Series |
+| Data User Part (DUP) | Q.741 (see Note) |
+| ISDN User Part (ISUP) | Q.761-Q.764, Q.766 |
+| Signalling Connection Control Part (SCCP) | Q.711-Q.714, Q.716 |
+| Transaction Capabilities (TC) | Q.771-Q.775 |
+| Operations Maintenance and Administration Part (OMAP) | Q.750-Q.755 |
+
+NOTE – Functions of the DUP are fully specified in Recommendation X.61.
+
+Other Q.7xx-Series Recommendations which describe other aspects of the signalling system which are not part of the SS No. 7 signalling interfaces are:
+
+| Title | Recommendations |
+|---------------------------------------------------|------------------------|
+| Signalling Network Structure | Q.705 |
+| Numbering of International Signalling Point Codes | Q.708 |
+| Hypothetical signalling reference connection | Q.709 |
+| PABX application | Q.710 |
+| SS No. 7 Test Specification (General) | Q.780 |
+| MTP Level 2 Test Specification | Q.781 |
+| MTP Level 3 Test Specification | Q.782 |
+| TUP Test Specification | Q.783 |
+| ISUP Test Specification | Q.784 |
+| ISUP Supplementary Service Test Specification | Q.785 |
+| SCCP Test Specification | Q.786 |
+| TCAP Test Specification | Q.787 |
+
+Clause 3 describes the relationship between these components.
+
+### **1.4 Description techniques in the Q.7xx-Series Recommendations**
+
+The SS No. 7 Recommendation Series defines the signalling system using prose description which is complemented by SDL diagrams and state transition diagrams. Should any conflict arise between the text and the SDL definition, the textual description is taken as definitive.
+
+Message sequence charts or arrow diagrams are used to illustrate examples of signalling procedures, but are not considered definitive.
+
+Data description are increasingly using ASN.1 method of description.
+
+## **2 SS No. 7 signalling network**
+
+## **2.1 Basic concepts**
+
+A telecommunications network served by common channel signalling is composed of a number of switching and processing nodes interconnected by transmission links. To communicate using SS No. 7, each of these nodes requires to implement the necessary "within node" features of SS No. 7 making that node a signalling point within the SS No. 7 network. In addition, there will be a need to interconnect these signalling points such that SS No. 7 signalling information (data) may be conveyed between them. These data links are the signalling links of SS No. 7 signalling network.
+
+The combination of signalling points and their interconnecting signalling links form the SS No. 7 signalling network.
+
+## **2.2 Signalling network components**
+
+### **2.2.1 Signalling points**
+
+In specific cases there may be a need to partition the common channel signalling functions at such a (physical) node into logically separate entities from a signalling network point of view; i.e. a given (physical) node may be defined as more than one signalling point. One example is an exchange at the boundary between international and national signalling networks.
+
+Any two signalling points, for which the possibility of communication between their corresponding User Part function exists, are said to have a signalling relation.
+
+The corresponding concept for a given User Part is called a user signalling relation.
+
+An example is when two telephone exchanges are directly connected by a bundle of speech circuits. The exchange of telephone signalling relating to these circuits then constitutes a user signalling relation between the Telephone User Part functions in those exchanges in their role as signalling points.
+
+Another example is when administration of customer and routing data in a telephone exchange is remotely controlled from an operation and maintenance centre by means of communication through a common channel signalling system.
+
+Examples of nodes in a signalling network that constitutes signalling points are:
+
+- exchanges (switching centres);
+- service control points;
+- signalling transfer points;
+- operation, administration and maintenance centres.
+
+All signalling points in a SS No. 7 network are identified by a unique code known as a point code (Recommendation Q.704 refers).
+
+### 2.2.2 Signalling links
+
+The common channel signalling system uses signalling links to convey the signalling messages between two signalling points. A number of signalling links that directly interconnect two signalling points which are used as a module constitute a signalling link-set. Although a link set typically includes all parallel signalling links, it is possible to use more than one link set in parallel between two signalling points. A group of links within a link set that have identical characteristics (e.g. the same data link bearer rate) is called a link group.
+
+Two signalling points that are directly interconnected by a signalling link are, from a signalling network structure point of view, referred to as adjacent signalling points. Correspondingly, two signalling points that are not directly interconnected are non-adjacent signalling points.
+
+### 2.2.3 Signalling modes
+
+The term “signalling mode” refers to the association between the path taken by a signalling message and the signalling relation to which the message refers.
+
+In the associated mode of signalling, the messages relating to a particular signalling relation between two adjacent points are conveyed over a link set, directly interconnecting those signalling points.
+
+In the non-associated mode of signalling, the messages relating to a particular signalling relation are conveyed over two or more linksets in tandem passing through one or more signalling points other than those which are the origin and the destination of the messages.
+
+The quasi-associated mode of signalling is a limited case of the non-associated mode where the path taken by the message through the signalling network is pre-determined and, at a given point in time, fixed.
+
+SS No. 7 is specified for use in the associated and quasi-associated modes. The Message Transfer Part does not include features to avoid out-of-sequence arrival of messages or other problems that would typically arise in a fully non-associated mode of signalling with dynamic message routing.
+
+Examples of signalling modes are illustrated in Figure 1.
+
+## 2.3 Signalling point modes
+
+A signalling point at which a message is generated, i.e. the location of the source User Part function, is the originating point of that message.
+
+A signalling point to which a message is destined, i.e. the location of the receiving User Part function, is the destination point of that message.
+
+For a particular signalling relation, the two signalling points thus function as originating and destination points for the messages exchanged in the two directions between them.
+
+
+
+Associated Associated Quasi-associated Quasi-associated
+
+--- Signalling relation
+ — Signalling link set
+
+○ Signalling point with at least user function;
+ whether or not STP-function is present in the context of the graph
+
+□ Signalling point with at least STP-function;
+ whether or not user function is present in the context of the graph
+
+⊞ Signalling point with both user function and STP-function
+
+△ Signalling point;
+ irrelevant whether user function and/or STP-function is present
+
+T1156060-93/d01
+
+Diagram illustrating four signalling modes: Associated (circle-circle), Associated (triangle-triangle), Quasi-associated (circle-circle with a square below one circle), and Quasi-associated (circle-circle with squares below both circles). A legend defines the symbols: dashed line for 'Signalling relation', solid line for 'Signalling link set', circle for 'Signalling point with at least user function', square for 'Signalling point with at least STP-function', circle with square for 'Signalling point with both user function and STP-function', and triangle for 'Signalling point; irrelevant whether user function and/or STP-function is present'. The code T1156060-93/d01 is present.
+
+FIGURE 1/Q.700
+**Example of associated and quasi-associated signalling modes
+ and definition of signalling network graph symbols**
+
+A signalling point at which a message is received on one signalling link and is transferred to another link, i.e. neither the location of the source nor the receiving User Part function, is a Signal Transfer Point (STP).
+
+In the quasi-associated mode, the function of a signalling transfer point is typically located in a few signalling points which may be dedicated to this function, or may combine this function with some other (e.g. switching) function. A signalling point serving as a signalling transfer point functions as an originating and destination point for the messages generated and received by the level 3 function of the MTP also in cases when no user functions are present.
+
+## 2.4 Signalling routes
+
+The pre-determined path, consisting of a succession of signalling points/signalling transfer points and the interconnecting signalling links, that a message takes through the signalling network between the origination point and the destination point is the signalling route for that signalling relation.
+
+All the signalling routes that may be used between an originating point and a destination point by a message traversing the signalling network is the signalling route set for that signalling relation.
+
+## 2.5 Signalling network structure
+
+The signalling system may be used with different types of signalling network structures. The choice between different types of signalling network structures may be influenced by factors such as the structure of the telecommunication network to be served by the signalling system and administrative aspects.
+
+In the case when the provision of the signalling system is planned purely on a per signalling relation basis, the likely result is a signalling network largely based on associated signalling, typically supplemented by a limited degree of quasi-associated signalling for low volume signalling relations. The structure of such a signalling network is mainly determined by the patterns of the signalling relations.
+
+Another approach is to consider the signalling network as a common resource that should be planned according to the total needs for common channel signalling. The high capacity of digital signalling links in combination with the needs for redundancy for reliability then typically leads to a signalling network based on a high degree of quasi-associated signalling with some provision for associated signalling for high volume signalling relations. The latter approach to signalling network planning is more likely to allow exploitation of the potential of common channel signalling to support network features that require communication for purposes other than the switching of connections.
+
+The worldwide signalling network is structured into two functionally independent levels, namely the international and national levels. This structure makes possible a clear division of responsibility for signalling network management and allows numbering plans of signalling points of the international network and the different national networks to be independent of one another.
+
+Further considerations about the structure of the signalling network are given in Recommendation Q.705, and the impact on the message transfer part in Recommendation Q.701.
+
+## **3 SS No. 7 functional blocks**
+
+## **3.1 Basic functional division**
+
+The SS No. 7 comprises the following functional blocks:
+
+- Message Transfer Part (MTP)
+- Telephone User Part (TUP)
+- ISDN User Part (ISUP)
+- Signalling Connection Control Part (SCCP)
+- Transaction Capabilities (TC)
+- Application-Entity (AE) (see Note)
+- Application-Service-Elements (ASEs) (see Note)
+
+NOTE – The glossary shows these as hyphenated terms but the usual convention used in this Recommendation will be unhyphenated.
+
+The fundamental principle of the signalling system structure is the division of functions into a common Message Transfer Part (MTP) on one hand, and separate User Parts for different users on the other. This is illustrated in Figure 2.
+
+The overall function of the Message Transfer Part is to serve as a transport system providing reliable transfer of signalling messages between the locations of communicating user functions.
+
+User functions in SS No. 7 MTP terms are:
+
+- the ISDN User Part (ISUP)
+- the Telephone User Part (TUP)
+- the Signalling Connection Control Part (SCCP)
+- the Data User Part (DUP)
+
+The term “User” in this context refers to any functional entity that utilises the transport capability provided by the Message Transfer Part.
+
+A User Part comprises those functions of, or related to, a particular type of user that are part of the common channel signalling system, typically because those functions need to be specified in a signalling context.
+
+The SCCP also has Users. These are:
+
+- the ISDN User Part (ISUP)
+- Transaction Capabilities (TC)
+- Operations Maintenance and Administration Part (OMAP)
+
+
+
+The diagram illustrates the architecture of SS No. 7, mapping its functional levels to the OSI Reference Model layers. On the left, a column lists the layers: 7, 4-6 (Null), 3, 2, and 1. Above the diagram, a box labeled 'Users of SS No. 7' spans across the top. Below it, the functional blocks are arranged as follows:
+
+
+- Layer 7:** Contains 'TC user' and 'Transaction Capabilities (TC)'.
+- Layers 4-6 (Null):** This section is empty, indicating no specific mapping for these layers.
+- Layer 3:** Contains 'Signalling Connection Control Part (SCCP) (Level 4)'. To its right are two large boxes: 'ISDN User Part (ISDN-UP) (Level 4)' and 'Telephone User Part (TUP) (Level 4)'. An arrow labeled 'Others MTP users' points to the left from the SCCP box.
+- Layers 2 and 1:** These are combined into a single box at the bottom labeled 'MTP (Levels 1-3)'.
+
+ Lines connect the 'TC user' to 'Transaction Capabilities (TC)', which in turn connects to 'SCCP (Level 4)'. The 'SCCP (Level 4)' box connects to both the 'ISDN-UP (Level 4)' and 'TUP (Level 4)' boxes. All three (SCCP, ISDN-UP, and TUP) connect down to the 'MTP (Levels 1-3)' box at the bottom.
+
+Diagram of SS No. 7 Architecture showing layers 1-7 and functional blocks: TC user, Transaction Capabilities (TC), Signalling Connection Control Part (SCCP), ISDN User Part (ISDN-UP), Telephone User Part (TUP), and MTP (Levels 1-3).
+
+T1 156070-93/d02
+
+FIGURE 2/Q.700
+**Architecture of SS No. 7**
+
+## 3.2 SS No. 7 architecture
+
+### 3.2.1 General
+
+From the perspective of an end user, the service provided by a telecommunications network may be regarded as a Network Layer service. However, from a signalling network perspective, the service may be provided at a different layer/level.
+
+Figure 2 shows the Architecture of SS No. 7 and illustrates the functional relationship between the various functional blocks of the SS No. 7 and between the SS No. 7 levels and the OSI Reference Model Layers. This level/layer relationship is described in the following subclauses.
+
+The initial specification of SS No. 7 was based on circuit-related telephony control requirements. To meet these requirements, SS No. 7 was specified in four functional levels, the Message Transfer Part comprising levels 1-3, and the User Parts as level 4.
+
+Figure 3 shows the Functional Levels of SS No. 7. As new requirements have emerged, e.g. for non-circuit related information transfer, SS No. 7 has also evolved to meet these new requirements. There has been a need to align certain elements in SS No. 7 to the OSI 7 Layer Reference Model (see 4.2).
+
+### 3.2.2 Message Transfer Part (MTP) levels 1-3
+
+An overview of the MTP is given in Recommendation Q.701. The MTP is defined in Recommendations Q.701-Q.704, Q.706 and Q.707.
+
+#### 3.2.2.1 Signalling data link functions (level 1)
+
+Level 1 defines the physical, electrical and functional characteristics of a signalling data link and the means to access it. The level 1 function provides a bearer for a signalling link.
+
+The detailed requirements for signalling data links are specified in Recommendation Q.702.
+
+
+
+T1156080-93/d03
+
+Diagram of SS No. 7 functional levels showing four layers: Level 4 (Users Parts: ISDN-UP, SCCP, TUP), Level 3 (Signalling network functions), Level 2 (Signalling link functions), and Level 1 (Signalling data link functions). Brackets on the right group Level 4 as 'Examples of Users Parts' and Levels 1-3 as the 'Message Transfer Part'. A reference code T1156080-93/d03 is at the bottom.
+
+FIGURE 3/Q.700
+SS No. 7 functional levels
+
+#### 3.2.2.2 Signalling link functions (level 2)
+
+Level 2 defines the functions and procedures for and relating to the transfer of signalling messages over one individual signalling data link. The level 2 functions together with a level 1 signalling data link as a bearer, and provides a signalling link for reliable transfer of signalling messages between two points.
+
+The detailed requirements for signalling functions are given in Recommendation Q.703.
+
+#### 3.2.2.3 Signalling network functions (level 3)
+
+Level 3 in principle defines those transport functions and procedures that are common to and independent of the operation of individual signalling links. These functions fall into two major categories:
+
+- a) *Signalling message handling functions* – These transfer the message to the proper signalling link or User Part.
+- b) *Signalling network management functions* – These control the current message routing and configuration of the signalling network facilities and in the case of signalling network failures, control the reconfigurations and other actions to preserve or restore the normal message transfer capability.
+
+The detailed requirements for signalling network functions are given in Recommendation Q.704.
+
+### 3.2.3 Level 4: MTP User functions
+
+Level 4 consists of the different User Parts. Each User Part defines the functions and procedures of the signalling system that are particular to a certain type of user of the system. The following entities are defined as User Parts in SS No. 7.
+
+#### 3.2.3.1 Signalling Connection Control Part (SCCP)
+
+The SCCP is defined in Recommendations Q.711-Q.716. The SCCP provides additional functions to the Message Transfer Part to provide connectionless and connection-oriented network services to transfer circuit-related, and non-circuit-related signalling information.
+
+The SCCP provides the means to
+
+- control logical signalling connections in a SS 7 network;
+- transfer Signalling Data Units across the SS 7 network with or without the use of logical signalling connections.
+
+SCCP provides a routing function which allows signalling messages to be routed to a signalling point based on, for example, dialled digits. This capability involves a translation function which translates the global title (e.g. dialled digits) into a signalling point code and a sub-system number.
+
+SCCP also provides a management function, which controls the availability of the "sub-systems", and broadcasts this information to other nodes in the network which have a need to know the status of the "sub-system". An SCCP sub-system is an SCCP User.
+
+#### **3.2.3.2 Telephone User Part (TUP)**
+
+The SS No. 7 Telephone User Part is defined in Recommendations Q.721-725. The TUP Recommendations define the international telephone call control signalling functions for use over SS No. 7.
+
+#### **3.2.3.3 Data User Part (DUP)**
+
+The Data User Part is referenced in Recommendation Q.741, and the functionality fully defined in Recommendation X.61. It defines the protocol to control interexchange circuits used on data calls, and data call facility registration and cancellation.
+
+#### **3.2.3.4 ISDN User Part (ISUP)**
+
+The ISDN User Part is defined in Recommendations Q.761-Q.764 and Q.766. This Recommendation Series deals with the basic services only.
+
+The ISUP encompasses signalling functions required to provide switched services and user facilities for voice and non-voice applications in the ISDN.
+
+The ISUP is also suited for application in dedicated telephone and circuit-switched data networks and in analogue, and mixed analogue/digital networks.
+
+The ISUP has an interface to the SCCP (which is also a level 4 User Part) to allow the ISUP to use the SCCP for end-to-end signalling.
+
+Supplementary Services handled by the SS No. 7 ISDN application are described in the Q.730-Series Recommendations. These supplementary services embody ISUP signalling messages and procedures. In some cases these services may include an application protocol which uses TC and SCCP.
+
+#### **3.2.3.5 Transaction Capabilities**
+
+Transaction Capabilities are defined in Recommendations Q.771-Q.775.
+
+TC provides the means to establish non-circuit-related communication between two nodes in the signalling network.
+
+#### **3.2.3.6 Applications**
+
+Applications are modelled in layer 7. They are the process which provide the end user of the telephone or ISDN network with the basic and supplementary telecommunication services. They comprise the users of TC.
+
+For details of the architecture of applications, see 3/Q.1400.
+
+## **4 OSI layering and SS No. 7**
+
+## **4.1 OSI Layering**
+
+The purpose of the Reference Model of Open Systems Interconnection for CCITT Applications (see Recommendation X.200) is to provide a well-defined structure for modelling the interconnection and exchange of information between users in a communications system. This approach allows standardized procedures to be defined not only to provide an open systems interconnection between users over a single network, but also to permit interworking between networks to allow communication between users over several networks in tandem.
+
+The approach taken in the OSI reference model is to partition the model used to describe this interconnection and exchange information between users in a communications system into seven layers.
+
+From the point of view of a particular layer, the lower layers provide a “transfer service” with specific features. The way in which a lower layer is realized is immaterial to the next higher layers. Correspondingly, the lower layers are not concerned with the meaning of the information coming from higher layers or the reasons for its transfer.
+
+The characteristics of each layer are described in 3a)/Q.1400 - 3g)/Q.1400.
+
+## 4.2 Relationship between SS No. 7 layering and the OSI model
+
+Evolution of the SS No. 7 architecture since the *Red Book* (1984) increasingly has been based on the Open Systems Interconnection (OSI) reference Model (see 3). OSI considers primarily connection-oriented protocols, that is, protocols that establish a logical connection before transferring data. The Network Service Part (NSP) of SS 7 provides both connectionless and connection oriented protocols.
+
+The OSI layer 1-3 services are provided by the SCCP together with the MTP. The combination of the MTP and the SCCP is called the NSP. Layers 1-3 comprise functions for the transportation of information from one location to another, possibly via a number of communication links in tandem. These functions provide the basis on which a communication network can be built.
+
+There are no protocols currently used in the SS No. 7 architecture that map into layers 4-6. Protocols may be included in these layers in the future if the need for such services arises.
+
+Transaction Capabilities (TC) are defined as a protocol which directly accesses the connectionless SCCP services.
+
+Figure 2 shows the relationship between SCCP and TC, to the OSI 7 Layer Reference Model. Recommendation Q.1400 provides further information about this relationship.
+
+## 4.3 Primitive Interfaces between SS No. 7 Functions
+
+### 4.3.1 General
+
+Interfaces between the functional elements of SS No. 7 are specified using interface primitives. Primitive interface definition does not assume any specific implementation of a service.
+
+### 4.3.2 OSI service primitives
+
+Where the functional element of SS No. 7 is modelled on the OSI 7 layer reference model, e.g. SCCP, TC, service primitives are defined in line with Recommendation X.210.
+
+In line with Recommendation X.210, Figure 4 illustrates the relationship between the terms “service”, “boundary”, “service primitives”, “peer protocol” and “peer entities”. The term “boundary” applies to boundaries between layers, as well as to boundaries between sub-layers.
+
+#### 4.3.2.1 Service primitives
+
+The use of primitives as a modelling tool does not imply any specific implementation of a service in terms of interface primitives.
+
+Four types of service primitive are identified (see Figure 5):
+
+- request: A primitive issued by a service user to invoke a service element.
+- indication: A primitive issued by a service provider to advise that a service element has been invoked by the service user at the peer service access point or by the service provider.
+- response: A primitive issued by the service user to complete at a particular service access point some service element whose invocation has been previously indicated at that service access point.
+- confirmation: A primitive issued by a service provider to complete at a particular service access point some service element previously invoked by a request at that service access point.
+
+Not all four types of service primitives have to be associated with all services.
+
+
+
+The diagram shows two peer entities, each represented by a rectangle labeled 'd'. Above each entity is a horizontal line labeled 'Upper boundary', and below each is a horizontal line labeled 'Lower boundary'. Vertical arrows labeled 'a' (Service) point from the upper boundary to the entity and from the entity to the lower boundary. Vertical arrows labeled 'b' (Service primitive) point from the lower boundary to the entity and from the entity to the upper boundary. A horizontal double-headed arrow labeled 'c' (Peer protocol) connects the two peer entities. The text 'T1156090-93/d04' is located at the bottom right.
+
+Diagram illustrating the types of service primitives between an upper boundary, a lower boundary, and two peer entities (d). Arrows labeled 'a' (Service) and 'b' (Service primitive) point between the boundaries and the entities. Arrows labeled 'c' (Peer protocol) point between the two peer entities.
+
+- a Service
+- b Service primitive
+- c Peer protocol
+- d Peer entities
+
+FIGURE 4/Q.700
+Types of service primitives
+
+
+
+The diagram shows two 'Service user' boxes at the top, each connected to a 'Service provider' box below it. Between the two service providers is a horizontal line. Arrows show the flow of primitives: 'Request' from the left service user to the left service provider; 'Response' from the left service provider to the right service provider; 'Confirmation' from the right service provider to the right service user; and 'Indication' from the right service user to the right service provider. The text 'T1156100-93/d05' is located at the bottom right.
+
+Diagram illustrating service primitives between a service user and a service provider. Arrows labeled 'Request', 'Response', 'Confirmation', and 'Indication' show the flow of primitives between the user and provider.
+
+FIGURE 5/Q.700
+Types of service primitives
+
+## 5 Addressing
+
+Addressing of SS No. 7 messages has to be considered on a number of levels. For example, the message transfer part uses the destination point code to route the message to the appropriate signalling point. The TUP called party address field, or ISUP called party number field, in an Initial Address Message is used to route the call to the appropriate called destination. The capabilities of the various SS No. 7 addressing mechanisms are illustrated by the signalling message structure.
+
+## 5.1 Signalling message structure
+
+A signalling message is an assembly of information, defined at level 3 or 4, pertaining to a call, management transaction, etc., that is transferred as an entity by the message transfer function.
+
+Each message contains service information including a service indicator identifying the source User Part and possibly additional information such as an indication whether the message relates to international or national application of the User Part.
+
+The signalling information of the message includes the actual user information, such as one or more ISDN telephone or data call control signals, management and maintenance information, etc., and information identifying the type and format of the message. It also includes a label that provides information enabling the message to be
+
+- Routed by the level 3 functions through a signalling network to its destination. (This part of the label is known as the Routing label. This is shown in Figure 6.)
+- Directed at the receiving User Part to the particular circuit, call, management or other transaction to which the message is related.
+
+Further details are given in 5.2.
+
+| | | |
+|-----|------------------------|------------------------|
+| SLS | Originating Point Code | Destination Point Code |
+|-----|------------------------|------------------------|
+
+FIGURE 6/Q.700
+
+### SS No. 7 Routing Label
+
+There are four types of label:
+
+- type A for MTP management messages;
+- type B for TUP;
+- type C for ISUP (circuit related) messages;
+- type D for SCCP messages.
+
+These are shown in Figure 7.
+
+The circuit identification code is used as a label for circuit related signalling messages, e.g. TUP or ISUP. The least significant 4 bits of this field (in the TUP) is the Signalling Link Selection (SLS) field, which is used, where appropriate, to perform load sharing (see Recommendation Q.704). In the ISUP, the SLS is a separate field to the circuit identification code.
+
+The SS No. 7 MTP signalling messages at level 2, which carry user information, are called Message Signal Units (MSUs). Figure 8 shows the basic format of the MSU (refer also to Recommendation Q.703) and the breakdown of the MSU. The Signalling Information Field (SIF) is used to carry level 3 or level 4 messages that may be circuit-related (e.g. ISUP, TUP messages) or non-circuit-related (e.g. SCCP). Further details are given on message formats in Recommendations Q.704, Q.713, Q.723, Q.763 and Q.773.
+
+## 5.2 MTP addressing
+
+There is a two part addressing mechanism in the MTP, one part of the mechanism uses the point code which is incorporated in the routing label of every message signal unit, the other part of the mechanism makes use of the service indicator and network indicator within the service information octet.
+
+
+
+MTP management messages: Label type A
+
+| | | | |
+|------------------------|-----|------------------------|------------------------|
+| Management information | SLC | Originating point code | Destination point code |
+|------------------------|-----|------------------------|------------------------|
+
+TUP messages: Label type B
+
+| | | | |
+|------------------------|-----------------|------------------------|------------------------|
+| Signalling information | Circuit ID code | Originating point code | Destination point code |
+| | SLS | | |
+
+ISUP messages: Label type C
+
+| | | | | |
+|------------------------|-----------------|-----|------------------------|------------------------|
+| Signalling information | Circuit ID code | SLS | Originating point code | Destination point code |
+|------------------------|-----------------|-----|------------------------|------------------------|
+
+SCCP messages: Label type D
+
+| | | | |
+|------------------------|-----|------------------------|------------------------|
+| Signalling information | SLS | Originating point code | Destination point code |
+|------------------------|-----|------------------------|------------------------|
+
+Routing label
+
+T1156110-93/d06
+
+A bracket grouping the last three columns of the tables (SLS, Originating point code, and Destination point code) and labeled 'Routing label'.
+
+FIGURE 7/Q.700
+**SS No. 7 message label types**
+
+### 5.2.1 Point codes
+
+Every signalling point (SP) and signalling transfer point (STP), when integrated in an SP, will be allocated its own unique point code. This is used by the MTP routing function to direct outgoing messages towards their destination in the network as indicated by the inclusion of the appropriate point code in the routing label. This point code is known as the destination point code (DPC). The routing label also contains the point code of the SP originating the message signal unit, therefore, the combination of this originating point code (OPC) and DPC will determine the signalling relation (i.e. the network points between which MTP “User” information is exchanged). The DPC is used by the receiving SP/STP discrimination function to determine whether the message is addressed to that SP or requires to be onward routed by means of the signal transfer capability of the STP.
+
+The DPC will always be determined and inserted in the routing label by the level 4 MTP “User”. This will also generally be the same for the OPC but it is possible that since the OPC might be constant it could be inserted by the MTP.
+
+### 5.2.2 Service indicator and network indicator
+
+The 4-bit service indicator (SI) and 2-bit network indicator (NI) are included in the service information octet (SIO) and are used within an SP’s distribution function to determine the “User” the incoming message should be delivered to.
+
+The SI will determine the “User”, e.g. TUP, SCCP, ISUP and the NI will determine which network is concerned, e.g. international or national.
+
+The NI will also in conjunction with the OPC/DPC determine whether a national or international signalling relation/routing is involved.
+
+The NI, together with the standard 14-bit point code, allows for four signalling networks each with up to 16 384 point codes.
+
+
+
+The diagram illustrates the structure of an SS No. 7 signalling message across five layers:
+
+- MTP (Message Transfer Part):** Consists of a sequence of fields: F, CK, SIF, SIO, LI, FIB, FSN, BIB, BSN, and F. An arrow points to the start of the F field, labeled "First bit transmitted".
+- TUP (Telephone User Part):** Contains "TUP Message information elements", "H1 Message type", "H0 Message group", and "Label B".
+- ISUP (ISDN User Part):** Contains "ISUP Message information elements", "Message type", and "Label C".
+- SCCP (Signalling Connection Control Part):** Contains "EOP User message/data", "SCCP Message header", "Message type", and "Label D". A callout box for the "SCCP Message header" indicates it "Includes called and calling party addresses and local references a)".
+- TCAP (Transaction Capabilities Application Part):** Divided into "Component portion" (containing "Component n", "Component 2", and "Component 1") and "Transaction portion".
+
+T1156120-93/d07
+
+Diagram of SS No. 7 signalling message structure showing layers MTP, TUP, ISUP, SCCP, and TCAP with their respective fields and bit sequences.
+
+a) CO only.
+
+BIB Backward indicator bit
+ BSN Backward sequence number
+ CK Check bits
+ F Flag
+ FIB Forward indicator bit
+ FSN Forward sequence number
+ LI Length indicator
+ SF Status field
+ SIF Signalling information field
+ SIO Service information octet
+
+FIGURE 8/Q.700
+**SS No. 7 signalling message structure**
+
+## 5.3 SCCP addressing
+
+Addressing within the SCCP of SS No. 7 makes use of three separate elements:
+
+- DPC;
+- Global Title (GT);
+- Sub-System Number (SSN);
+
+One, two or all of the elements may be present in the Called and Calling Party Address, the main options are:
+
+| | |
+|----------------------------------------------------|---------------------------------------------------------------------------------------------|
+| GTDPC + SSN | When transferring SCCP messages | +| SSN
GT
SSN + GT | When receiving messages from MTP | +| DPC
DPC + (SSN or GT or both)
GT
GT + SSN | When receiving messages from connectionless or connection-oriented control for SCCP routing | + +The form of address used will depend on the service, application and underlying network. + +### 5.3.1 Global Title (GT) + +The Global Title (GT) may comprise of dialled digits or another form of address that will not be recognized in the SS No. 7 network. Therefore, if the associated message requires to be routed over the SS No. 7 network, translation is required. + +Translation of the GT will result in a DPC being produced and possibly also a new SSN and GT. A field is also included in the address indicator to identify the format of the global title. + +### 5.3.2 Destination Point Code (DPC) + +The DPC in an address requires no translation and will merely determine if the message is destined for that SP (incoming message) or requires to be routed over the SS No. 7 signalling network via the MTP. For outgoing messages this DPC should be inserted in the MTP routing label. + +### 5.3.3 Sub-system Number (SSN) + +The SSN will identify a sub-system accessed via the SCCP within a node and may be a User Part, e.g. ISUP, SCCP management or an AE via TC. TC, however, will be invisible to the SCCP. + +When examination of the DPC in an incoming message has determined that the message is for that SP, examination of the SSN will identify the concerned SCCP "User". The presence of an SSN without a DPC will also indicate a message which is addressed to that SP. + +The SSN field has an initial capacity of 255 codes with an extension code for future requirements. + +## 5.4 User Part addressing + +### 5.4.1 Telephone User Part addressing + +The Telephone User Part is capable of handling E.164 (incorporating E.163) addresses in the calling and called party address information elements. + +### 5.4.2 ISDN User Part addressing + +The ISDN User Part address structure is capable of handling E.164 addresses in the calling and called number, and redirecting address information elements. + +### **5.4.3 Signalling connection control part addresses** + +The signalling connection control part is capable of handling E.164 (incorporating E.163), X.121, F.69, E.210, E.211, E.212, E.213 addresses, and the mobile hybrid E.214 address in the calling and called party address information elements. + +The handling of OSI NSAP addresses in SCCP is described in Recommendation Q.711 and 3.2/Q.1400. + +### **5.5 Labelling** + +A variety of methods to label signalling messages is used to allow the signalling system and users of the signalling system to relate a received message to a particular call or transaction. + +For circuit-related messages, (e.g. on a simple telephone call), the TUP (and the ISUP) use the circuit identification code (CIC) to label the message. + +For certain ISUP procedures, call references are used to associate messages with calls. + +SCCP also uses local references on connection-oriented protocols. + +Transaction capabilities use transaction identities and invoke identities to associate transaction messages and components respectively. + +## **6 Operations administration and maintenance** + +## **6.1 Management** + +Management within SS No. 7 is partitioned into two main areas: + +- Signalling network management; +- Signalling system management. + +### **6.1.1 Signalling network management** + +These are functions contained within the MTP and SCCP which, by means of automatic procedures, maintain the required signalling network performance (e.g. changeover of faulty links, forced re-routing, sub-system availability, etc.). + +### **6.1.2 Signalling system management** + +This may be considered as the actions taken by the operator (or by an external automatic mechanism) such as TMN-OS via the Q3 interface to maintain the signalling system performance when problems are identified. + +## **6.2 Maintenance and testing** + +Some of the maintenance, administration and management functions of the signalling system themselves use the signalling system as a data carrying mechanism. + +Testing within SS No. 7 is: + +- initiated automatically as a part of a signalling system management procedures (e.g. signalling route set test in MTP); or +- applied as a result of external activity, e.g. man-machine interface (MMI) or TMN. + +The first form is described in the appropriate Q.7xx Recommendation dealing with MTP or SCCP, etc. The second form includes some MMI or TMN initiated procedures [initiation of MRVT (Recommendation Q.753)], and also pre-in service testing using test cases specified in Recommendations for SS No. 7 tests (Q.78x-Series). + +### **6.2.1 Operations Maintenance and Administration Part (OMAP)** + +Recommendation Q.75x provides procedures and protocols related to operations, maintenance and administration. + +OMAP is situated in the TMN-OS as well as in SS No. 7 SPs of all kinds, OMAP functions include measurement initiation and collection as well as initiation of tests within the SS No. 7 network like MRVT. + +### **6.2.2 Testing** + +Test specifications for SS No. 7 are contained in Q.78x-Series Recommendations and cover MTP level 2, MTP level 3, TUP, ISUP, SCCP and TCAP together with an overview of testing. + +## **6.3 SS No. 7 measurements** + +Recommendation Q.752 specifies the monitoring and measurements appropriate to the MTP, SCCP, ISUP and TCAP. + +## **7 Signalling system performance** + +The performance requirements of SS No. 7 must take account of the performance requirements of the services that are being supported. Each functional component of SS No. 7 has its performance criteria specified in a self-contained Recommendation. An overall performance target is specified in the form of a Hypothetical Signalling Reference Connection (HSRC). + +## **7.1 Hypothetical Signalling Reference Connection (HSRC)** + +The HSRC for SS No. 7 (Recommendation Q.709), identifies components that are used in a signalling relation between signalling end points, signalling points, signalling transfer points, and signalling points with SCCP relay functions, and gives the values for the signalling delays and unavailability parameters. The values used are derived from the figures contained in the individual performance Recommendations for MTP, TUP, SCCP and ISUP. Service performance Recommendations E.721 and I.352 also apply. + +## **7.2 MTP** + +The MTP signalling performance requirements are specified in Recommendation Q.706. This Recommendation includes + +- the parameters for route-set unavailability, MTP malfunction (loss of messages and mis-sequencing), and message transfer times; +- factors affecting performance, for example signalling traffic characteristics (e.g. message sizes, loading potential, security, etc.) and parameters related to transmission characteristics (e.g. bit rates of signalling data links, propagation delays); +- those parameters which have greatest influence on the signalling network queueing delays for example, error control, security arrangements, failures and priorities. + +It should be noted that some functions may affect MTP performance. + +## **7.3 SCCP** + +The SCCP signalling performance requirements are contained in Recommendation Q.716. Parameters identified are signalling connection delays (establishment, unsolicited reset, reset and release signal connection, reset and release failure probability, data message transmit delay, data message delay failure and error probability and SCCP unavailability). + +It should be noted that management functions affect SCCP performance. + +## **7.4 TUP** + +The TUP signalling performance requirements are contained in Recommendation Q.725. Parameters contained in this Recommendation are cross-office performance for TUP supported circuit connection control under normal and abnormal traffic loads. Also specified is the probability of failure of calls due to signalling malfunction. + +## **7.5 ISUP** + +The ISUP signalling performance requirements are contained in Recommendation Q.766. Parameters contained in this Recommendation are cross-office performance for ISUP supported circuit connection control under normal and abnormal traffic loads. Also specified is the probability of failure of an ISDN call due to signalling function. + +## **8 Flow control** + +SS No. 7, in common with other transport mechanisms, needs to limit the input of data when congestion onset is detected. The nature of SS No. 7 will lead to SP/STP overload congestion being spread through the signalling network if no action is taken. This will result in impaired signalling performance and message loss. In addition to signalling network congestion within a node, congestion will also require action to prevent signalling performance from deteriorating. There is thus a need for flow control within the signalling system to maintain the required signalling performance. + +## **8.1 Signalling network flow control** + +This is achieved by incorporating a flow control mechanism in the MTP. On detection of congestion, MTP "Users Parts" are informed by the means of a primitive. The "User Part" should then reduce signalling traffic towards the congested part of the network. If the User is at a remote SP, the information is carried across the network in an appropriate signalling network management message. + +## **8.2 Signalling node (congestion) flow control** + +In addition to network congestion, nodal congestion also requires the remedial action of flow control to prevent the signalling performance from being impaired. Nodal congestion can occur both within the MTP and the MTP "User Part". + +### **8.2.1 MTP nodal flow control** + +If MTP node overload is detected similar action to that used to combat signalling network congestion is required. On detection of that overload, the "User Parts" are informed so that traffic can be reduced. + +### **8.2.2 "User Part" flow control** + +As well as taking action to reduce MTP congestion, mechanisms are also required within each User Part to detect the onset of congestion and to take appropriate action. + +The ISUP and TUP provide signalling procedures which aim to reduce the new calls offered to an exchange which is experiencing processor overload. + +Automatic congestion control provides the means to inform adjacent exchanges of the current workload, and to request that only priority calls are offered to the exchange experiencing overload. + +## **9 Compatibility mechanisms and rules in SS No. 7** + +## **9.1 Background** + +The wide scope of the signalling system requires that the total system include a large diversity of functions and that further functions can be added to cater for extended future applications. As a consequence only a subset of the total system may need to be used in an individual application. + +A major characteristic of the signalling system is that it is specified with a functional structure to ensure flexibility and modularity for diverse applications within one system concept. This allows the system to be realized as a number of functional modules which could ease adaptation of the functional content of an operating SS No. 7 to the requirements of particular applications. + +The CCITT specifications of the signalling system specify functions and their use for international operation of the system. Many of those functions are also required in typical national applications. Furthermore, the system to some extent includes features that are particular to national applications. The CCITT specifications thus form an internationally standardized base for a wide range of national applications of common channel signalling. + +SS No. 7 is a common channel signalling system. However, as a consequence of its modularity and its intended use as a standard base for national applications the system may be applied in many forms. In general, to define the use of the system in a given national application, a selection of the CCITT specified functions must be made and the necessary additional national functions must be specified depending on the nature of the application. + +SS No. 7 is an evolutionary signalling system which has undergone a number of enhancements. To allow ease of evolution it has been necessary to incorporate a number of compatibility mechanisms in various functional elements of SS No. 7, and to apply a number of compatibility rules to protocol enhancement. Detailed specification of the compatibility mechanisms in each functional element of SS No. 7 are given in the appropriate Q.7xx Recommendation. + +Compatibility rules which apply to all functional elements of SS No. 7 are detailed in the following text. + +## **9.2 Evolutionary requirements** + +In application protocols (e.g. ISUP, ASEs), the main evolutionary requirement is the ability to add new subscriber services, and new administration and network services to the protocol. + +In the SCCP and MTP, the evolutionary requirements are different in that initial versions provide basic transport functions which are generally stable. The main enhancements have been in the management aspects of protocols. + +Although the evolutionary requirements are different across the elements of SS No. 7, it is possible to incorporate certain common mechanisms in the various functional elements. + +## **9.3 Forward and backward compatibility** + +Compatibility mechanisms can be considered as being either + +- forward compatibility mechanisms; or +- backward compatibility rules. + +Forward compatibility mechanisms are defined as a scheme to enable a version of a protocol to communicate effectively and interwork with future versions of the protocol. That is, a version of a protocol should not restrict future protocols from providing extra capabilities. + +Backward compatibility rules are defined as a scheme to ensure that future versions of the protocol will be able to send protocol messages to the previous version which will be understood and fully processed by the node supporting the previous version. That is, future versions of a protocol must allow earlier versions to operate with it and not reduce the earlier versions' service level. + +## **9.4 Compatibility rules for SS No. 7** + +Compatibility rules for SS No. 7 protocol evolution are contained in 9/Q.1400. + +Note that the 1992 ISUP Recommendations (Q.76x-Series Recommendations) contain a special compatibility procedure. It uses an instruction indicator, which includes information about the handling of a parameter or message that is not recognized (e.g. discard, pass-on, send Confusion). It is sent with every new message or parameter. For parameters + +containing new values, it is assumed that the instruction indicator for the whole parameter can be used for all values within the parameter. For existing messages, parameters and parameter values, the required action if unrecognized information is received is given in tabular form. + +# 10 Glossary + +A Glossary of terms in SS No. 7 is contained at the back of the Fascicles VI.7, VI.8 and VI.9 of the *Blue Book*. \ No newline at end of file diff --git a/marked/Q/T-REC-Q.721-198811-I_PDF-E/2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg b/marked/Q/T-REC-Q.721-198811-I_PDF-E/2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..64672153e39c851d9e16fdbc702e526c7ba7e8a7 --- /dev/null +++ b/marked/Q/T-REC-Q.721-198811-I_PDF-E/2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:454a9958ffe168868cb7d38a0eb24418dafe31a7a4245c992089b2316ac37d3e +size 7392 diff --git a/marked/Q/T-REC-Q.721-198811-I_PDF-E/raw.md b/marked/Q/T-REC-Q.721-198811-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..10fd0a81be66e358f00bca75bbd7c0c221885146 --- /dev/null +++ b/marked/Q/T-REC-Q.721-198811-I_PDF-E/raw.md @@ -0,0 +1,68 @@ + + + + +The logo of the International Telecommunication Union (ITU) features a globe with a lightning bolt superimposed on it, and the letters 'ITU' in a bold, sans-serif font. + +ITU logo + +INTERNATIONAL TELECOMMUNICATION UNION + +**ITU-T** + +**Q.721** + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +**SPECIFICATIONS OF SIGNALLING SYSTEM No. 7** + +--- + +**FUNCTIONAL DESCRIPTION OF THE +SIGNALLING SYSTEM No. 7 TELEPHONE +USER PART (TUP)** + +**ITU-T Recommendation Q.721** + +(Extract from the *Blue Book*) + +--- + +# NOTES + +1 ITU-T Recommendation Q.721 was published in Fascicle VI.8 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below). + +2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +# **FUNCTIONAL DESCRIPTION OF THE SIGNALLING SYSTEM No. 7 TELEPHONE USER PART (TUP)** + +### **1 General** + +Use of Signalling System No. 7 for telephone call control signalling requires: + +- application of *Telephone User Part* (TUP) functions, in combination with +- application of an appropriate set of *Message Transfer Part* (MTP) functions. + +A general description of the signalling system and the division of functions between the Message Transfer Part and the Telephone User Part are presented in Recommendation Q.700 and the requirements of interaction between those two parts are contained in Recommendation Q.701. + +## **2 Telephone User Part** + +The Telephone User Part specified in these specifications defines the necessary telephone signalling functions for use of Signalling System No. 7 for international telephone call control signalling. It is specified with the aim of providing the same features for telephone signalling as other CCITT telephone signalling systems. + +Signalling System No. 7 can be used to control the switching of all types of international circuits to be used in a worldwide connection, including circuits with speech interpolation and satellite circuits. + +The system meets all requirements defined by the CCITT concerning the service features for worldwide international semiautomatic and automatic telephone traffic. It is designed for the bothway operation of speech circuits. + +When used with homogeneous digital telephone circuits the continuity of these circuits is ensured by the means for transmission quality supervision and failure detection that are inherent in the digital systems providing these circuits. However, the system includes means for link-by-link assurance of continuity check of the speech path when used with analogue telephone circuits and/or digital circuits including certain types of equipment, where fault indications are lost, e.g., circuit multiplication equipment. + +The signalling system is suitable for national telephone applications. Most telephone signalling message types and signals specified for international use are also required in typical national applications. In addition to these, national applications typically require additional signalling message types and signals, the system provides ample spare capacity for such additions. + +The standard label structure specified for telephone signalling messages requires that all exchanges using the signalling system are allocated codes from code plans established for the purpose of unambiguous identification of signalling points. The principles to apply to the international signalling network are specified in Recommendation Q.708. + +## **3 Message Transfer Part** + +The Message Transfer Part of Signalling System No. 7 is specified in Recommendations Q.701 to Q.709. An overview description of the Message Transfer Part is contained in Recommendation Q.701. + +The Message Transfer Part defines a range of functions by which different signalling modes and different signalling network configurations may be realized. 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+(06/97) + +SERIES Q: SWITCHING AND SIGNALLING + +Specifications of Signalling System No. 7 – Transaction +capabilities application part + +--- + +**Guidelines for using transaction capabilities** + +ITU-T Recommendation Q.775 + +(Previously CCITT Recommendation) + +--- + +# ITU-T Q-SERIES RECOMMENDATIONS + +## **SWITCHING AND SIGNALLING** + +| | | +|----------------------------------------------------------|--------------------| +| SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE | Q.1–Q.3 | +| INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING | Q.4–Q.59 | +| FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN | Q.60–Q.99 | +| CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS | Q.100–Q.119 | +| SPECIFICATIONS OF SIGNALLING SYSTEMS No. 4 AND No. 5 | Q.120–Q.249 | +| SPECIFICATIONS OF SIGNALLING SYSTEM No. 6 | Q.250–Q.309 | +| SPECIFICATIONS OF SIGNALLING SYSTEM R1 | Q.310–Q.399 | +| SPECIFICATIONS OF SIGNALLING SYSTEM R2 | Q.400–Q.499 | +| DIGITAL EXCHANGES | Q.500–Q.599 | +| INTERWORKING OF SIGNALLING SYSTEMS | Q.600–Q.699 | +| SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 | Q.700–Q.849 | +| General | Q.700 | +| Message transfer part (MTP) | Q.701–Q.709 | +| Signalling connection control part (SCCP) | Q.711–Q.719 | +| Telephone user part (TUP) | Q.720–Q.729 | +| ISDN supplementary services | Q.730–Q.739 | +| Data user part | Q.740–Q.749 | +| Signalling System No. 7 management | Q.750–Q.759 | +| ISDN user part | Q.760–Q.769 | +| Transaction capabilities application part | Q.770–Q.779 | +| Test specification | Q.780–Q.799 | +| Q3 interface | Q.800–Q.849 | +| DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 1 | Q.850–Q.999 | +| PUBLIC LAND MOBILE NETWORK | Q.1000–Q.1099 | +| INTERWORKING WITH SATELLITE MOBILE SYSTEMS | Q.1100–Q.1199 | +| INTELLIGENT NETWORK | Q.1200–Q.1999 | +| BROADBAND ISDN | Q.2000–Q.2999 | + +For further details, please refer to ITU-T List of Recommendations. + +# **ITU-T RECOMMENDATION Q.775** + +# **GUIDELINES FOR USING TRANSACTION CAPABILITIES** + +## **Summary** + +Revised Recommendation Q.775 provides guidance to TC-Users on defining TC-User ASEs. + +## **Source** + +ITU-T Recommendation Q.775 was revised by ITU-T Study Group 11 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on the 5th of June 1997. + +## FOREWORD + +ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. + +The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1. + +In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. + +## NOTE + +In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +## INTELLECTUAL PROPERTY RIGHTS + +The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. + +As of the date of approval of this Recommendation, the ITU had/had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. + +© ITU 1997 + +All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. + +# CONTENTS + +###### Page + +| | | | +|-------|-------------------------------------------------------------|----| +| 1 | Introduction..... | 1 | +| 1.1 | General..... | 1 | +| 1.2 | Environment..... | 1 | +| 2 | Operations..... | 2 | +| 2.1 | Definition..... | 2 | +| 2.2 | Examples..... | 3 | +| 2.2.1 | Simple operation handlings ..... | 3 | +| 2.2.2 | More complex operation handling..... | 3 | +| 2.3 | Component-related facilities offered to TC-users..... | 5 | +| 2.3.1 | Invocation ..... | 5 | +| 2.3.2 | Cancel (by the TC-user)..... | 6 | +| 2.3.3 | Reject (by the TC-user)..... | 7 | +| 2.3.4 | Remote cancel (by the TC-user)..... | 8 | +| 2.3.5 | Reset of operation timer by the TC-user..... | 10 | +| 2.4 | Component-related abnormal situations ..... | 11 | +| 2.4.1 | Component loss ..... | 11 | +| 2.4.2 | Component duplication..... | 12 | +| 2.4.3 | Component missequencing..... | 14 | +| 2.4.4 | Reject of a component by TC ..... | 15 | +| 2.4.5 | Operation timer expiry..... | 16 | +| 3 | Dialogues ..... | 16 | +| 3.1 | Grouping of components in a message ..... | 16 | +| 3.2 | Dialogue handling facilities ..... | 18 | +| 3.2.1 | Structured dialogue..... | 18 | +| 3.2.2 | Unstructured dialogue..... | 27 | +| 3.3 | Enhanced dialogue control facilities ..... | 27 | +| 3.3.1 | Overview ..... | 27 | +| 3.3.2 | Use of the Application-Context..... | 27 | +| 3.3.3 | Transfer of user data ..... | 28 | +| 3.3.4 | Backward compatibility issues ..... | 29 | +| 4 | Guidance for writing TC-users protocol specifications ..... | 30 | +| 4.1 | Introduction..... | 30 | +| 4.2 | Decomposition of functionality ..... | 30 | +| 4.2.1 | Application process and application entity..... | 30 | +| 4.2.2 | Application service element ..... | 30 | + +| | Page | +|-------------------------------------------------------------------------------------------------------------------|-------------| +| 4.2.3 Communications between peer AEs/ASEs..... | 31 | +| 4.3 How to specify an application context..... | 32 | +| 4.4 How to specify an ASE..... | 33 | +| 4.5 How to specify Operations and Errors..... | 33 | +| 4.5.1 General considerations..... | 33 | +| 4.5.2 Use of the OPERATION MACRO notation ..... | 34 | +| 4.5.3 Use of the ERROR MACRO notation..... | 35 | +| 4.5.4 Use of the (information object) CLASS notation ..... | 36 | +| 4.5.5 The ERROR (information object) CLASS..... | 39 | +| 4.5.6 Examples of Operations and Errors description ..... | 39 | +| 4.5.7 Moving from the MACRO notation to the (information object) CLASS
notation and use of ASN.1 modules ..... | 41 | +| 4.5.8 Allocation and Management of Operation and Error Codes ..... | 43 | +| 4.6 Data types specifications..... | 46 | +| 4.6.1 General..... | 46 | +| 4.6.2 Use of tags ..... | 46 | +| 4.6.3 Instances and types ..... | 47 | +| 4.6.4 Exporting and importing data types..... | 47 | +| 4.7 How to specify abstract syntaxes ..... | 47 | +| 4.8 Encoding rules ..... | 48 | +| 5 Mapping of the generic ROS concepts onto TC services ..... | 49 | +| 5.1 Overview..... | 49 | +| 5.1.1 Notation and concept for the generic ROS model ..... | 49 | +| 5.1.2 Communication model ..... | 50 | +| 5.2 Remote operation service realization..... | 51 | +| 5.2.1 Basic services (stub) ..... | 51 | +| 5.2.2 Bind and unbind operations..... | 52 | +| 5.3 Information transfer ..... | 54 | +| 5.3.1 Association realizations..... | 54 | +| 5.3.2 Transfer realization..... | 54 | +| 5.4 TC-based application context ..... | 54 | +| 5.5 Abstract syntaxes ..... | 55 | +| 5.5.1 Dialogue control ..... | 55 | +| 5.5.2 User-defined syntaxes..... | 56 | +| 5.6 Notation extension ..... | 57 | + +# **GUIDELINES FOR USING TRANSACTION CAPABILITIES** + +*(revised in 1997)* + +# **1 Introduction** + +## **1.1 General** + +The purpose of this Recommendation is to provide guidelines to potential users of Transaction Capabilities (TC-users). The examples given are illustrations only; they indicate how an application may use TCAP, not how TC must be used in all cases. The technical basis of this Recommendation are Recommendations Q.771 to Q.774; in case of misalignment, these should be considered as the primary reference. + +The main purpose of TC is to provide support for interactive applications in a distributed environment. TC is based on the Remote Operations concept defined in Recommendation X.880 (ROS) together with some enhancements and additions specific to the Signalling System No. 7 environment to provide the services needed by TC-users. Interactions between distributed application entities are modelled by Operations. An operation is invoked by an (originating) entity: the other (destination) entity attempts to execute the operation and possibly returns the outcome of this attempt. + +The semantics of an operation (represented by its name and parameters) is not relevant to TC; TC provides facilities which are independent of any particular operation. The TC-user, when defining an application, must: + +- 1) select operations (this involves defining the semantics and syntax of the data exchanged during the operation invocations and its responses); +- 2) select TC facilities to support these operations. Such facilities include the handling of individual operations, and the ability to have a number of related operations attached to an association between TC-users, called a dialogue; +- 3) define the application script (e.g. which of the two peers invokes which operations, the order of message exchange that constitutes the dialogue between the peer TC-users, and their reactions to abnormal situations). + +This Recommendation describes the selection process of defining and using operations. The operations appearing hereafter are fictitious, and are taken for illustration purposes only. Also described are the facilities offered by TC for handling one or a sequence of operations in a dialogue. The definition of specific sequences of operations belongs to the application protocol definition and is beyond the scope of this Recommendation; however, clauses 4 and 5 give a brief indication of what information an application specification should contain. + +TC services are made accessible to TC-users via primitives; these primitives model the interface between TC and its users, but do not constrain any implementation of this interface. + +## **1.2 Environment** + +TC defines the end-to-end protocol between TC-users located in a Signalling System No. 7 network. At present, there is no standard interface defined for the use of TC over any other underlying protocol or network (e.g. X.25) than the SCCP of Signalling System No. 7. + +TC considers users which are real-time sensitive and do not need to exchange large amounts of data. It is considered that for these users, the standard protocols defined for OSI layers 4 to 6 in the + +X-Series of Recommendations would result in excessive overheads and hence are not used. + +As a result, TC cannot support all kinds of applications, and a number of applications will still require more elaborate services such as specified in the X-Series of Recommendations. Beside indicating what TC can do, this Recommendation indicates what it cannot do, in order to help the application designer choose how to support an application. + +# 2 Operations + +## 2.1 Definition + +An operation is invoked by an originating TC-user to request a destination TC-user to perform a given action. + +Each operation belongs to a particular class. This indicates whether either a successful outcome (result), or an unsuccessful outcome (error), or both, or none have to be reported by the destination. + +The class of an operation is not signalled to the remote TC-user at the time the operation is invoked; it is assumed that the applications at both ends have a common understanding of the class of each operation in use. + +As well as the class, the definition of the operation includes a timer value indicating the maximum time in which the operation should be completed and the result reported. + +This timer value is a local matter; it is not conveyed to the remote end through any protocol. It is chosen by the TC-user when defining the operation based on expectations of the round trip time from one TC-user to another and processing delays. + +An operation is defined by: + +- its operation code and the type of any parameters associated with the operation request; +- its class; +- if the class requires report of success, the possible results corresponding to successful executions are defined by a list of parameters; +- if the class requires report of failure, the possible results corresponding to situations where the operation could not be executed completely by the remote TC-user. Each such situation is identified by a specific error cause; the list of these error causes is part of the operation definition. Diagnostic information can be added to the error cause: if present, it is part of the definition; +- the list of possible linked operations, if replies consisting of linked operations are allowed for this operation. Linked operations have to be described separately; +- a timer value indicating the interval by which the operation has to be completed, if any, returned. This timer value can be one of the factors that is used by an implementation to manage the invoke ID associated with the operation invocation. (When the timer associated with an operation invocation has expired, the invoke ID is returned to the pool of invoke IDs after a suitable, implementation-dependent "freezing" period.) + +As a general rule, the choice of the class of an operation should be based on the semantics associated with an operation and operations should not be designed to be carried in any particular message. For instance, if the invoker of the operation does not require any acknowledgement of whether an operation could actually be performed or not, then an operation of Class 4 may be the most appropriate. If an operation invoker does not require explicit acknowledgement that an operation has been performed successfully, but wishes to know if it could not be performed at all, then an operation of Class 2 is suitable. For example, defining an operation such as "Play Announcement" as + +Class 2 or 4 suggests different intentions of the operation invoker even though the actions of the operation performer may be identical. + +## **2.2 Examples** + +### **2.2.1 Simple operation handlings** + +NOTE – The operation invocation should fit into one message, and so should the report of a successful outcome. Reports of success may be segmented using Return Result – Not last and Return Result – Last. + +#### **Class 1 (both success and failure reported)** + +Translate a freephone number into a called subscriber number; return the called number if the translation can be performed, otherwise indicate why it cannot; time allocated: 2 seconds. + +If the response is not returned for an operation invocation after the timer has expired, the TC-user is informed (operation cancel led by TC); it may assume that either the invocation or the response was lost and, depending on the application requirements, take suitable corrective actions (e.g. invoke the operation again, inform local management, etc.). + +#### **Class 2 (only failure reported)** + +Perform a routine test and send a reply only in case something went wrong; time allocated: 1 minute. + +In the case of a Class 2 operation, the TC-user is informed if no result has been received when the timer expires. This is interpreted as a successful outcome, even if the invocation was lost. + +This aspect should be considered when selecting Class 2. + +#### **Class 3 (only success reported)** + +Perform a test: this corresponds to a pessimistic view, where failure is considered as the default option, not requiring any reply. + +Timer expiry is indicated to the TC-user: this should be interpreted by the TC-user as a failure of the operation (but is considered normal by TC, which considers that the operation has terminated). This aspect should be considered when selecting Class 3. + +#### **Class 4 (neither success, nor failure reported)** + +Send a warning, without expecting a reply or acknowledgement of any kind. + +In this case, a result never arises from the invocation of the operation. The TC-user relies upon TC and the network to deliver the invocation. Notification of the timer expiry is a local matter. + +#### **Comparisons with ROSE operation classes (Recommendation X.219)** + +ROSE provides for five classes of operations: Classes 2 to 5, called asynchronous classes, are identical to Classes 1 to 4 of TC. ROSE's Class 1 is a synchronous class; it has no counterpart in TC, where full-duplex exchanges of components are considered. + +However, a TC-user can decide to operate in a synchronous manner (see 3.2.1). + +### **2.2.2 More complex operation handling** + +#### **Operations with segmented results** + +A successful result may be divided into several segments, each of which is indicated to the originator of the operation by one primitive. This facility, using the TC-RESULT-NL primitive, can be used by TC-users to overcome the absence of segmentation in the underlying layers. The last segment is indicated by the TC-RESULT-L primitive. + +The report of an error cannot be segmented. + +When the protocol designer can ensure that segmentation is provided by the underlying layers across the signalling routes on which TC messages are transferred, the use of this segmenting facility is deprecated. + +TC cannot identify a specific segment in the case of a segmented result. + +The TC-user should ensure that each segment can be parsed (i.e. the parameter Parameter of each TC-RESULT-NL/L request primitive should contain enough information to enable the construction of a valid value of the type (or compatible sub-type) associated with the result of the operation. + +Example E1: An operation requests the execution of a test. The result of a correct execution is segmented in three parts P1, P2 and P3 to be returned to the originator. + +A possible primitive sequence for example E1 is given in Table 1. + +**Table 1/Q.775** + +| TC-user A | TC-user B | +|------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------| +| TC-INVOKED req
(Test, Class = 1) | TC-INVOKED ind
(Test)
TC-RESULT-NL req
(P1) | +| TC-RESULT-NL ind
(P1) | TC-RESULT-NL req
(P2) | +| TC-RESULT-NL ind
(P2) | TC-RESULT-L req
(P3) | +| TC-RESULT-L ind
(P3) | | +| Time | | +| NOTE – The timeout value is specified by the originating TC-user at invocation time. A non-final result does not restart it. | | + +#### **Linked operations** + +Another extension to the basic operation scheme is the ability to link an operation invocation to another operation invocation. + +Typically, this facility covers situations where the destination of the original (linked-to) operation requires additional information in order to process this operation: this is the case where menu facilities are used (menu facilities allow a user to make a sequence of choices, each being dependent on the previous ones). + +Example E2: The operation is the execution of a test with several options; before the test is executed, these options are offered for selection to the test originator (TC-user A). Two operations are nested: operation 1 is the test; operation 2 is the option selection. TC-user A first responds to operation 2 before TC-user B can perform the test with the indicated option(s). + +A possible primitive sequence for example E2 is given in Table 2. + +There is no limit to the number of operation invocations which may be linked to a given operation invocation. + +Note that when an operation B is linked to another operation A, they do not have to be nested. The only condition is that the invocation of B should take place before the outcome of A is reported; + +however, operation B does not have to terminate before operation A. + +**Table 2/Q.775** + +| TC-user A | TC-user B | +|----------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------| +| TC-INVOKED req
(Test, Class = 1) | Operation 1 begin
TC-INVOKED ind
(Test)
TC-INVOKED req
(Option-selection, Class = 1) Operation 2 begin | +| TC-INVOKED ind
(Option-selection)
TC-RESULT-L req
(Options) | TC-RESULT-L ind
(Options) Operation 2 end
TC-RESULT-L req
(Test-result) | +| TC-RESULT-L ind
(Test-result) | Operation 1 end | +| Time | | + +## 2.3 Component-related facilities offered to TC-users + +### 2.3.1 Invocation + +So far, operations have been considered from the static point of view. Invocation introduces a dynamic aspect: a specific invocation of an operation has to be differentiated from other possible concurrent invocations of the same or of another operation. + +Each particular activation of an operation is identified by an invoke ID. This invoke ID must be unambiguous. It is selected by the TC-user which originates the operation invocation, and passed to the destination TC-user, which will reflect it in its reply (or each segment of a reply) or in a linked invocation: therefore it correlates the reply to an invocation (or each segment of a reply) or a linked invocation, and the invocation itself. + +The TC-user is free to assign any value to the invoke ID (index, address, . . .) provided that its value can be mapped to an integer which can be encoded in one octet according to the encoding rules specified in Recommendation Q.773. Note that such an integer takes values between -128 and 127. + +The invoke ID associated with an invocation becomes reusable when the last or only segment of a result is received, or when certain abnormal situations are indicated by TC; however, the value should not be reallocated immediately for another operation activation, as immediate reallocation would prevent the correct handling of some situations (see below). + +The period during which an invoke ID is released, but cannot be reallocated, is called the freezing period. This period is implementation-dependent. + +As invoke IDs receive their value dynamically at the time the operation is invoked, their value cannot appear in the specification of the application protocols; rather, a "logical" value, to which a real value is substituted at execution time, should be indicated in order to identify an operation in a single flow. + +Taking invoke IDs into consideration, the sequence of primitives for example E2 above becomes as shown in Table 3: + +**Table 3/Q.775** + +| TC-user A | TC-user B | +|-------------------------------------------------------------------------------|--------------------------------------------------------------------------------------| +| TC-INVOKED req
(1, Test, Class = 1) | TC-INVOKED ind
(1, Test)
TC-INVOKED req
(2, 1, Option-selection, Class = 1) | +| TC-INVOKED ind
(2, 1, Option-selection)
TC-RESULT-L req
(2, Options) | TC-RESULT-L ind
(2, Options)
TC-RESULT-L req
(1, Test-result) | +| TC-RESULT-L ind
(1, Test-result) | | +| Time | | + +where the first parameter of a primitive indicates an invoke ID. When both parameters have to be present, the second one is the linked ID. This is a pure notational convention. + +### **2.3.2 Cancel (by the TC-user)** + +The TC-user requesting invocation of an operation may stop the activity associated with the corresponding invoke ID, for any reason it finds appropriate. However, cancel should in principle be reserved for abnormal situations: the normal method for terminating an operation is to receive a result or to terminate on timer expiry. + +Cancelling has local effect only: it does not prevent the remote TC-user from sending replies to a cancelled operation. When received, these replies will be rejected by TC, as illustrated in the following, which represents a sequence of primitives for the example E1 defined above, where TC-user A cancels the test after receiving the first segment of the result. + +In Table 4, segment P2 is not received by TC-user A: TC detects a reject situation (no active Invoke ID) and therefore does not deliver it to TC-user A, and any attempt by TC-user B to send more segments of the reply is rejected at A's side. + +**Table 4/Q.775** + +| TC-user A | TC-user B | +|----------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------| +| TC-INVOKED req
(1, Test, Class = 1) | TC-INVOKED ind
(1, Test)
TC-RESULT-NL req
(1, P1) | +| TC-RESULT-NL ind
(1, P1)
Cancel decision:
TC-CANCEL req
(1)
TC-REJECT ind
(1, Problem Code)
... | TC-RESULT-NL req
(1, P2)
... | +| Time | | + +### 2.3.3 Reject (by the TC-user) + +The TC-user has the sole responsibility of deciding when to send a reject component or when to return an error (failure to perform an operation) indication. The TC-user may reject a component for any reason it finds appropriate, providing that there is a suitable reject problem code defined in the TC specifications (e.g. mandatory information element missing in an operation, error or reply, unexpected operation, unknown operation, etc.) that it can use for the purpose. + +Similarly, the TC-user decides which error code and diagnostic information (which is specified as part of the TC-user protocol specifications and agreed to by the two peer TC-users for just this purpose) to use when sending an error component. + +The role of the TC-user is illustrated in the following example. + +The TC-user at side A expects, in a given situation, to receive operation Y only as a linked operation. When receiving from side B an Invoke component with an operation code referring to Y but no linked ID, the TC-user at side A may elect to: + +- not perform the operation and return an error with some previously-determined diagnostic parameter specified in the TC-user application specification just for this purpose; +- reject the component as an "unrecognized operation". + +Interpretation of the returned error diagnostic or reject problem code is the responsibility of the TC-user at side B and is not described in the TC Recommendations. + +Reject of an operation invocation, or of a result, affects the whole operation: no more replies will be accepted by TC for this invocation. Reject of a linked operation does not affect the linked-to operation as far as TC is concerned. The TC-user should describe their reactions to such abnormal situations as part of their application script. + +This is illustrated in Table 5 where, in example E2, TC-user A did not expect the option selection process (it may be an optional feature), and rejects the operation with the Problem Code "Unexpected Linked Operation". TC-user B may then decide to execute the test assuming a default option. + +**Table 5/Q.775** + +| TC-user A | TC-user B | +|------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------| +| TC-INVOKED req
(1, Test, Class = 1) | TC-INVOKED ind
(1, Test)
TC-INVOKED req
(2, 1, Option-selection, Class = 1) | +| TC-INVOKED ind
(2, 1, Option-selection)
TC-U-REJECT req
(2, Problem Code) | | +| | TC-U-REJECT ind
(2, Problem Code)
TC-RESULT-L req
(1, Test-result) | +| TC-RESULT-L ind
(1, Test-result) | | +| Time | | + +When an operation invocation is rejected, the TC-user may decide to reinvoke it (e.g. the invoke component was corrupted); this would be a new invocation (new Invoke ID). It may also decide to abort the dialogue. A very simple dialogue (a question and a response) may not define any recovery mechanisms, except when the operation is of critical importance (e.g. a database update). + +### 2.3.4 Remote cancel (by the TC-user) + +TC does not provide any specific service for cancelling the remote execution of an operation in progress. The cancel service provided by the TC-U-CANCEL req primitive has only a local effect (see 2.3.2). + +However, a remote cancel procedure can be defined at the TC-user level, using existing TC services. One solution for the TC-user is to include in one of the ASEs used by the application-context, an operation whose purpose is to cancel existing invocations. + +The following ASN.1 module provides a description of such an operation type. This type (and the associated error type) can be imported in one of the modules used by the TC-user so that it can allocate suitable operation and error codes. Alternatively the TC-user may also design its own operation based on the same principles. + +**TCAP-Tools { ccitt recommendation q 775 modules(2) tools(1) version1(1) }** + +**DEFINITIONS ::=** + +**BEGIN** + +**EXPORTS Cancel, CancelFailed, Cancelled;** + +**IMPORTS OPERATION, ERROR, InvokeIdType** + +**FROM TCAPMessages { ccitt recommendation q 773 modules(2) messages(1) version2(2) };** + +**Cancel ::= OPERATION** + +**ARGUMENT InvokeIdType** + +-- a TC-user may redefine this type to include +-- an empty result so that it becomes a Class 1 operation +**ERRORS { CancelFailed }** +-- timer = 15 s + +**CancelFailed ::= ERROR** +**PARAMETER SET {** + **problem [0] CancelProblem,** + **invokeId [1] InvokeIdType }** + +**CancelProblem ::= ENUMERATED** +{ **unknownInvocation(0),** + **tooLate (1),** + **notCancellable (2) }** + +-- a TC-user may redefine this type to include application-specific problems + +**Cancelled ::= ERROR** +-- an error of this type should be included in the error list of cancellable operations + +**END** + +It is necessary to include a "cancelled" error in the list of errors attached to the cancellable operations. In such a case, the TC-user which receives the cancel request will issue a TC-U-ERROR req primitive to terminate the operation. The receipt of an error component with this error code and the corresponding TC-U-ERROR ind will then terminate the operation at the invoking side. + +The operation to be cancelled is identified by the invokeId which has been allocated to it at invocation time. The invocation of the Cancel operation does not affect the invocation state machine of the operation to be cancelled, because the invokeId carried in the operation argument is not visible to the component sub-layer. + +If the cancellation fails, a user error is reported with three possible diagnostics: + +- unknownInvocation: If the invocation has never happened, or has been forgotten; +- tooLate: If the invocation is still known but the execution is at a stage that does not permit a cancellation; +- notCancellable: The invokeId in the argument of the cancel operation corresponds to an operation which has not been agreed by the TC-users being cancellable by the invoking side. + +When the cancellation is performed with success and no return error with error code indicating "cancelled" is received for the cancelled operation, the timer associated with the cancelled operation will expire, causing a TC-L-CANCEL ind primitive to be issued by TC. + +Alternatively, the TC-user requesting the cancellation may decide to issue a TC-U-CANCEL req immediately after having sent the cancel request so that no further local activities exist for the operation to be cancelled. + +The use of the cancel mechanism makes sense if the Cancel operation is invoked before the expiration of the timer associated with the operation to be cancelled. After this, the invoke Id may not be recognized at the performing side as the operation execution may have completed and the response primitive issued. The ability to cancel the execution of an operation after timer expiry is outside the scope of these guidelines because it would mean that the objective is not to cancel the operation execution but the subsequent actions which may have been triggered at the performing end by the invocation. + +### 2.3.5 Reset of operation timer by the TC-user + +The selection of an appropriate timer value is part of the definition of an operation. The timer supervision is started by TC when the invoke component to which it relates is sent. However, the TC-user has the ability to request TC to reset this timer at any time before it expires. + +The protocol designer selects the timer value according to an estimation of the time required for the completion of the execution of the operation and the transfer of the result. However there are cases where a significant dispersion of the actual execution time is foreseen, making difficult the selection of an appropriate value. + +In order to prevent that the operation timer expires while the request is still in progress, the protocol designer can choose one of the two following approaches: + +- a) select a timer value which is greater than estimated completion time in the worst case; +- b) select a timer value which corresponds to the most likely case and arrange the TC-user in such a way that it uses the TC-RESET-TIMER service when it detects that the completion of the operation will take longer than expected. In that case, appropriate procedures need to be defined in order to ensure that the originating TC-user is informed of this situation (e.g. using linked operations). + +In the following example, the TC-user A invokes several times the "query" operation to retrieve three different pieces of information from a database system which is distributed to two other locations B1 and B2. Since the TC-user A has no knowledge about how the data are distributed over these two locations, it sends all the requests to the TC-user in B1. + +In the first case, the requested information is locally available in B1. In the two other cases, the requested information has to be retrieved from B2. The TC-user B1 notifies the TC-user A that the completion of the request will take more time than expected, invoking a "wait" operation. In the second case, the TC-user A accepts to wait longer than expected and requests TC to reset the operation timer. In the third case, the TC-user A prefers to abandon the operation with a user-specific procedure similar to those described in section 2.3.4. See Table 5 *bis*. + +**Table 5 *bis*/Q.775** + +| TC-user A | TC-user B1 | TC-user B2 | +|-------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------|------------| +| First Query
TC-INVOKE req
(1, query, Timeout = 5 s) | TC-INVOKE ind (1, query)
requested information locally
available
TC-RESULT-L req
(1, query-result) | | +| TC-RESULT-L ind (1, query-result)
Second Query
TC-INVOKE req
(2, query, Timeout = 5 s) | TC-INVOKE ind (2, query)
requested information not locally
available
TC-INVOKE req (3, 2, wait)
TC-INVOKE req (1, query) | | + +**Table 5 bis/Q.775 (concluded)** + +| TC-user A | TC-user B1 | TC-user B2 | +|------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------| +| TC-INVOKE ind (3, 2, wait)
TC-RESET-TIMER req (2) | | TC-INVOKE ind
(1, query)
TC-RESULT-L req
(1, query-result) | +| | TC-RESULT-L ind
(1, query-result)
forward received result to A
TC-RESULT-L req
(2, query-result) | | +| TC-RESULT-L ind (2, query-result)
Third Query
TC-INVOKE req
(3, query, Timeout = 5 s) | TC-INVOKE ind (3, query)
requested information not locally
available
TC-INVOKE req (4, 3, wait)
TC-INVOKE req (2, query) | | +| TC-INVOKE ind (4, 3, wait)
TC-INVOKE req [5, cancel (3)] | | TC-INVOKE ind
(2, query)
TC-RESULT-L req
(2, query-result) | +| | TC-INVOKE ind [5, cancel (3)]
TC-U-ERROR req (3, cancelled)
TC-RESULT-L ind (1, query-
result)
discard received result to A | | +| TC-U-ERROR ind (3, cancelled) | | | + +## 2.4 Component-related abnormal situations + +### 2.4.1 Component loss + +TC assumes a very low probability of message loss in the network; if this probability is too high for an application, it should use the connection-oriented network service approach. If some protocol information needs an upgraded Quality of Service (e.g. charging information), the application should introduce its own mechanisms to obtain higher reliability for this information. + +#### Loss of an operation invocation + +Table 6 illustrates the case, in example E1, where no response to the test is received before the time limit expires. + +**Table 6/Q.775** + +| TC-user A | TC-user B | +|----------------------------------------|------------------| +| TC-INVVOKE req
(1, Test, Class = 1) | | +| Time limit:
TC-L-CANCEL ind
(1) | | +| Time | | + +When a Class 1 operation is lost, the TC-user is informed when the timer associated with the operation expires. When a Class 1 operation with a single result (in a single segment) is lost, TC cannot indicate whether either the operation invocation, or the reply, was lost. If the application needs to discriminate between these two cases, it should do it in the application protocol (e.g. using the time-stamping or acknowledging the operation invocation before replying to it). + +For a Class 2 operation, loss will be considered as a success (whether the invocation, or the failure report, was lost). This, considering the probability of loss, may be acceptable for non-critical operations (e.g. statistical measurements). + +For a Class 3 operation, loss is treated in the same way as operation failure, whether the invocation, or the success report, has been lost. + +For a Class 4 operation, loss will not be visible to TC. + +#### **Loss of a result** + +- Loss of a non-final result is never detected by TC. +- Loss of a final result will eventually be indicated to the TC-user when the time limit is reached, but cannot always be unambiguously interpreted as the loss of a reply; if no non-final result has been received, it may be that the invocation was lost. + +#### **Loss of a linked operation** + +The loss of a linked operation has the same effect as the loss of a non-linked operation. It has no effect on the linked-to operation. + +#### **Loss of a reject component** + +This case should be extremely infrequent, and no application should try to recover from such a situation. If the lost reject concerns an operation invocation, then when the operation times out, the TC-user who invoked the operation will consider that the invocation (or the reply) was lost, and react accordingly; if it concerns a reply, the originator of the reply will not be aware that it was incorrect: it will be up to the originator of the operation to detect the loss. + +### **2.4.2 Component duplication** + +As message duplication is very infrequent in the Signalling System No. 7 network, scripts for No. 7 applications need not define sophisticated scenarios in anticipation of such situations. However, any application in which duplication would be unacceptable should either define its own duplication detection mechanism or use a connection-oriented service. + +#### Duplicate operation invocation + +When an operation invocation is duplicated (by the service provider), the destination TC-user (B) may, or may not, detect the duplication: + +- TC-user B detects the duplication: the duplicate may be rejected using the problem code "duplicated invoke ID". In the case of such a rejection, this can be interpreted by the remote TC-user as rejection of the original invocation; +- TC-user B does not detect the duplication: this may happen when there is a master-slave relationship between A and B, and B executes the operation with no knowledge of the context. + +Assuming the second case in example E1, a possible sequence could be as given in Table 7. + +**Table 7/Q.775** + +| TC-user A | TC-user B | +|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------| +| TC-INVVOKE req
(1, Test, Class = 1) | TC-INVVOKE ind
(1, Test)
TC-INVVOKE ind
(1, Test)
TC-RESULT-NL req
(1, P1)
TC-RESULT-NL req
(1, P1) | +| TC-RESULT-NL ind
(1, P1)
TC-RESULT-NL ind
(1, P1)
A detects an abnormal situation and rejects:
TC-U-REJECT req
(1, Problem Code)
TC detects an abnormal situation and rejects P2:
TC-L-REJECT ind
(1, Problem Code) | Undetected duplication of invocation | +| | TC-RESULT-NL req
(1, P2)
TC-U-REJECT ind
(1, Problem Code) | +| | TC-R-REJECT ind
(1, Problem Code) | +| Time | | + +In this sequence, TC-user B considers two independent test invocations, and responds to each of them. The first result P1 is accepted; TC-user A detects that P1 is received a second time, and rejects it; this terminates the operation, and causes result P2 to be rejected when received (reject by TC). Therefore, both activities at B's side will terminate on receipt of rejects. + +#### Duplicate non-final result + +If a non-final result is duplicated, TC cannot detect it, and will deliver it twice to the TC-user. Detection of this situation is left to the application. + +#### Duplicate final result + +If a final result (RR-L) is duplicated, TC can detect the situation: the second final result is considered as abnormal (the operation has been terminated by the first "final" result), and TC rejects it. + +Table 8 shows a sequence for example E1 where the third segment of the result is duplicated (by the network). + +Comment: Discarding of duplicates in all cases by TC would probably appear to be a helpful feature. However, it should be noted that: + +- 1) it would require another degree of complexity in TC, which contradicts the basic characteristics of TC in the connectionless approach; +- 2) it corresponds to a situation which is extremely infrequent, at least in the No. 7 network. + +To cover these situations when required by an application, it would be better to use a connection-oriented network service approach, since duplication could then be detected and handled at the lower layers. + +Table 8/Q.775 + +| TC-user A | TC-user B | +|------------------------------------------------------------|--------------------------------------| +| TC-INVOKE req
(1, Test, Class = 1) | TC-INVOKE ind
(1, Test) | +| | TC-RESULT-NL req
(1, P1) | +| TC-RESULT-NL ind
(1, P1) | TC-RESULT-NL req
(1, P2) | +| TC-RESULT-NL ind
(1, P2) | TC-RESULT-L req
(1, P3) | +| TC-RESULT-L ind
(1, P3) | | +| TC receives
RR-L (1, P3) | | +| Duplication of P3:
TC-L-REJECT ind
(1, Problem Code) | | +| | TC-R-REJECT ind
(1, Problem Code) | +| Time | | + +### 2.4.3 Component missequencing + +For TC, the order of segmented results is not relevant: if the order is important to the TC-user, appropriate mechanisms should be defined in the application protocol (e.g. by introducing a numbering scheme to identify intermediate replies in a parameter of these replies, or by using a connection-oriented service). + +Due to missequencing, a non-final result may arrive after a final result: when this occurs the non-final result is rejected by TC. This is because the final result causes TC to close the invocation state machine associated with this operation; so when the delayed non-final result is received it cannot be associated with any active invocation state machine. + +The sequence in Table 9 illustrates what happens in example E1 when the last part of the result is received before the second one: both TC-users are informed. + +If a linked operation invocation is received after the final result of the linked-to operation (as a result of a missequencing), the linked operation is rejected. + +TC assumes a very low probability of missequencing; if the supporting network is not satisfactory in this respect, the connection-oriented network service approach should be considered. + +### 2.4.4 Reject of a component by TC + +A general principle when TC receives a component (operation invocation or reply) which is either not formatted correctly, or received out of context (e.g. a reply without a prior operation invocation), is to reject it, which means that: + +- 1) TC forms a Reject component to inform the originator of the faulty component and informs the local TC-user of the Reject component waiting to be sent to the remote end; TC provides whatever information is available on the nature of the component being rejected (if the dialogue has not already been terminated by the remote TC-user). +- 2) In reaction to this, the local TC-user may decide to abort, continue, or end the dialogue. In the last two cases, when the TC-user notifies TC of its decision, the peer TC-user is informed of the reject. + +Table 9/Q.775 + +| TC-user A | TC-user B | +|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------| +| TC-INVOKED req
(1, Test, Class = 1) | TC-INVOKED ind
(1, Test)
TC-RESULT-NL req
(1, P1) | +| TC-RESULT-NL ind
(1, P1)
TC-RESULT-L ind
(1, P3)
RR-NL (1, P2) PDU arrives
Missequenced result:
reject (no active state machine)
TC-L-REJECT ind
(1, Problem Code) | TC-RESULT-NL req
(1, P2)
TC-RESULT-L req
(1, P3) | +| | TC-R-REJECT ind
(1, Problem Code) | +| Time | | + +Possible cases of reject by TC have been encountered in the previous clauses. Whenever the invoke ID is recognized, rejection by TC causes the termination of the operation: a possible recovery by the TC-user is a new invocation of the terminated operation. When the rejected component is not identifiable, the local TC-user is informed of the received malformed component, and a NULL invoke ID value is included in the Reject component waiting to be sent. However, as this Reject component cannot be associated with any known invocation, abort of the dialogue may be the appropriate reaction. + +### 2.4.5 Operation timer expiry + +When TC informs the TC-user of timer expiry (TC-L-CANCEL indication), it indicates that no more information related to the operation invocation (in particular, no reject) can be received. If the peer entity still sends information in relation to this invocation, this information will be discarded when received, provided that the invoke ID of the cancelled operation has not been reallocated. Premature reallocation of invoke ID values is normally avoided by correctly setting timer values and choosing the time an invoke ID is "frozen" after it has been released. In order to compensate for uncertainties in the amount of time required to send information from TC-user to another without accounting for the absolute worst case (which is also in general the most unlikely), an implementation-dependent mechanism avoiding premature reallocation of invoke IDs is required. + +Timer expiry indication corresponds to an abnormal situation only in the case of a Class 1 operation. The TC-user is then aware that either the invocation, or the reply, was lost. If no undesirable side effects arise, another invocation of the same operation can take place after timer expiry. This is illustrated by the sequence in Table 10 for example E1. + +Timer expiry for a Class 2 operation indicates that no failure was received nor will be accepted for this invocation: it is a definite indication of success (for Class 2) if it is assumed that there is no possibility of message loss in the network. A parallel situation applies to Class 3 in case of failure. The indication of timer expiry for a Class 4 operation is a local decision. + +**Table 10/Q.775** + +| TC-user A | TC-user B | +|-----------------------------------------------------------------------------------|-----------------------------| +| TC-INVOKED req
(1, Test, Class = 1) | TC-INVOKED ind
(1, Test) | +| Timer expiry:
TC-L-CANCEL ind
(1)
TC-INVOKED req
(2, Test, Class = 1) | | +| Time | | + +# 3 Dialogues + +Whenever one of the operation handling primitives considered in Clause 2 is issued, a request is passed to TC, but nothing is sent to the remote TC-user until a primitive requesting transmission is issued. These primitives, and their relation with operation handling primitives, are considered now. + +## 3.1 Grouping of components in a message + +The effect of TC-user issuing a component handling primitive (unless this primitive has local effect only), is to build a component to be included in a message. The message is not transmitted until the TC-user requests it. + +Note that a component may also be generated as a consequence of a TC reject procedure: in this case this component is put in the next message for the dialogue unless this dialogue is aborted. + +Provided that the maximum size of a message is not exceeded, several components can be grouped and sent to the remote end as a single message, thereby saving transmission overhead. This is done under control of the TC-user, who explicitly specifies when it wants (all) the component(s) awaiting + +transmission to be sent. The components awaiting transmission are those for which the TC-user has previously issued a component-handling primitive with the same dialogue ID. + +Until such time when the SS No. 7 SCCP layer provides a segmenting and reassemble capability, the TC-user has to ensure that the maximum size of an SS No. 7 message will not be exceeded. + +Example E3, as given in Table 11, shows the beginning of a dialogue with a network service centre where a switch requests instructions (operation 1) and receives a request to connect the call to a given destination address, and a request to send information (e.g. announcement or message to be displayed) to the calling party. Both components are contained in a single message. + +TC-BEGIN and TC-CONTINUE are transmission primitives described in 3.2. + +There may be one transmission primitive for each component (thus there is only one component maximum in each message), or fewer transmission primitives than components which allows the grouping of components within a message. In addition, the information contained in the parameters of the transmission primitives (e.g. addressing information) applies to all the components included in the message. + +At the originating side, the primitive requesting transmission appears after the component handling primitives; this indicates that the transmission of all the preceding components has to take place immediately; it avoids indicating specific components to be transmitted with a given transmission primitive, and allows transmission primitives without any associated component. + +At the destination side, the primitive indicating the reception of transmitted components appears first: it contains control information which is necessary for TC to deliver each of the components (if any) in the message; the last component of the message is indicated to the TC-user by the "Last Component" parameter. The components are delivered to the destination TC-user in the same order as they were passed to TC by the originating TC-user. + +**Table 11/Q.775** + +| TC-user A | TC-user B | +|----------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +| TC-INVOK req
(1, Provide-Instructions, Class = 1)
TC-BEGIN req
(Control parameters) | | +| | TC-BEGIN ind
(Control parameters)
TC-INVOK ind
(1, Provide-Instructions)
TC-INVOK req
(2, 1, Connect-Call)
TC-RESULT-L req
(1, Send-Info)
TC-CONTINUE req
(Control parameters) | +| TC-CONTINUE ind
(Control parameters)
TC-INVOK ind
(2, 1, Connect-Call)
TC-RESULT-L ind
(1, Send-Info) | | +| Time | | + +## 3.2 Dialogue handling facilities + +When two TC-users co-operate in an application, more than one operation invocation is generally required. The resulting flow of components has to be identified so that: + +- 1) components related to the same flow can be identified; +- 2) flows corresponding to several instances of the same application can be identified and allowed to run in parallel. + +Each such flow is called a dialogue by the TC-user and is identified by a corresponding Dialogue ID parameter. The dialogue handling facility provided for this purpose is the structured dialogue. + +When only a single message is required to complete a distributed application, the Unidirectional message of the unstructured dialogue may be used. The originator does not expect a report of the outcome of the operation (i.e. may only invoke Class 4 operations), but may receive a report of a protocol error if one occurs. This report of a protocol error will also be carried in a Unidirectional message. + +### 3.2.1 Structured dialogue + +#### 3.2.1.1 General + +The use of dialogues allows several independent flows of components to coexist between two TC-users. The Dialogue ID parameter is used in both operation handling and transmission (dialogue) handling primitives to determine which component(s) pertain(s) to which dialogue. + +In the following examples, the Dialogue ID parameter is represented (by convention) by the first parameter in these primitives, starting with letter D. Each TC-user has its own reference for a given dialogue. Local references (those used on the interface) are represented here; mapping of these local references onto protocol references (called Transaction IDs) included in messages is done by TC. + +Three primitives have been defined for handling dialogues under normal circumstances; they indicate dialogue begin (TC-BEGIN), continuation (TC-CONTINUE) or end (TC-END). Each of these primitives may be used to request transmission of 0, 1 or several components; these components may contain information relating to one or several operations. + +Table 12 illustrates a possible sequence for example E2, where the test request starts the dialogue, which ends when the test result has been sent. + +**Table 12/Q.775** + +| TC-user A | TC-user B | +|------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------| +| TC-INVOKE req
(D1, 1, Test, Class = 1)
TC-BEGIN req
(D1, Address) | | +| | TC-BEGIN ind
(D2, Address)
TC-INVOKE ind
(D2, 1, Test)
TC-INVOKE req
(D2, 2, 1, Option-selection, Class = 1)
TC-CONTINUE req
(D2) | +| TC-CONTINUE ind
(D1)
TC-INVOKE ind
(D1, 2, 1, Option-selection)
TC-RESULT req
(D1, 2, Options)
TC-CONTINUE req
(D1) | | +| | TC-CONTINUE ind
(D2)
TC-RESULT-L ind
(D2, 2, Options)
TC-RESULT-L req
(D2, 1, Test-result)
TC-END req
(D2) | +| TC-END ind
(D1, normal)
TC-RESULT-L ind
(D1, 1, Test-result) | | +| Time | | +| NOTE – D1 and D2 are local references for the same dialogue and map onto transaction IDs which appear in the messages. | | + +Any grouping of components is allowed in the messages of a dialogue: TC does not check, for instance, that a message terminating a dialogue does not include operation invocations of Class 1. + +Full-duplex exchange of components is assumed: if a TC-user wants to introduce some restrictions, e.g. working in a synchronous mode as defined for ROSE users, it would have to introduce the necessary procedures itself. + +#### 3.2.1.2 Exchange of messages + +Transmission of messages is accomplished with the Quality of Service of the underlying layer services: no flow control or error recovery mechanisms are provided by TC. + +- The first dialogue handling primitive of a dialogue must indicate dialogue begin (TC-BEGIN). Further messages must not be sent from the side originating the dialogue until + +a message is received in the backward direction, indicating dialogue continuation. + +- If a TC-user tries to send a large number of messages in a short amount of time, no flow control mechanism in TC will prevent it. +- SCCP Class 1 in-sequence delivery can be requested as an option, indicated by the Quality of Service parameter. Note that this option may not be available end-to-end when interworking with a network which does not provide it. + +#### 3.2.1.3 Dialogue end + +TC places no restriction on the ability for a TC-user to request dialogue end. It follows that messages may be lost if no precautions are taken in the application on when the dialogue may end. + +In particular, if the application protocol allows both TC-users to issue TC-END primitives at about the same time, and if these primitives trigger transmission of components, it is likely that some (if not all) of these components will not be delivered to their respective destination TC-users. + +It is up to the application to define, if necessary, its own rules concerning the right to end a dialogue: TC will not check them. + +Any message received for a terminated dialogue is discarded if it requests dialogue end, and any message other than an End or an Abort causes the dialogue to be aborted at the remote entity. + +It should be noted that a TC-user cannot reject, by means of a TC-U-REJECT request primitive, any component received in an END message. If it is important for an application to be able to reject any component received or be notified of rejections by the remote end, then all components must be placed in either the initial BEGIN message or subsequent CONTINUE messages. + +The dialogue is terminated by either the pre-arranged method, or by sending an END message containing no components, or REJECT components (if applicable). + +The differences between the three ways of ending a dialogue are as follows. + +##### Prearranged end + +A typical application is the access to a distributed database, where the requesting user (TC-user A) does not know where the information it seeks is located. TC-user A broadcasts a request to each location which might have the information required, and will eventually receive a response from the TC-user which holds this information. Prearranged end avoids messages from the other destinations saying: "I do not have this information". Only the responding destination may continue the dialogue (if so wished); all other destination will, by convention, end the dialogue locally; the originator of the requests will also end the dialogues with the non-responding destinations locally, when it receives the response to its request. Note that the convention is between applications: TC does not check that it is respected, nor is it indicated in the TC protocol. + +Example E4 in Table 13 illustrates this situation, with two destinations B1 and B2; two dialogues (D1, D2) and (D3, D4) are started; B1 happens to own the requested information, and decides to continue the dialogue. + +Prearranged end may also be used when a TC-user wants to send information, and does not expect a reply of any kind afterwards. + +**Table 13/Q.775** + +| TC-user A | TC-user B1 | TC-user B2 | +|----------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------| +| TC-INVOKED req
(D1, 1, Question)
TC-BEGIN req
(D1, Address)
TC-INVOKED req
(D3, 1, Question)
TC-BEGIN req
(D3, Address) | TC-BEGIN ind
(D2, Address)
TC-INVOKED ind
(D2, 1, Question)
TC-RESULT-L req
(D2, 1, Response)
TC-CONTINUE req
(D2)
..... | TC-BEGIN ind
(D4, Address)
TC-INVOKED ind
(D4, 1, Question)
B2 does not have the
information:
TC-END req
(D4, local) | +| TC-CONTINUE ind
(D1)
TC-RESULT-L ind
(D1, 1, Response)
D1 goes on
D3 ends locally
TC-END req
(D3, Local) | | | +| Time | | | + +##### Basic end + +When a TC-user issues the TC-END request primitive, it causes transmission of any pending components to the remote end. TC does not check that all operation invocations have received a response when dialogue end is requested: no notification is given to the TC-user that any pending operation invocations have not received a final result. + +At the receiving end, the dialogue is considered terminated when all the components received within the message indicating the end have been delivered to the TC-user. + +Example: the dialogue ends when the test in example E1, Table 14, receives a response. + +**Table 14/Q.775** + +| TC-user A | TC-user B | +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +|
.....
TC-END ind
(D1)
TC-RESULT-NL ind
(D1, 1, P1)
TC-RESULT-NL ind
(D1, 1, P2)
TC-RESULT-L ind
(D1, 1, P3)
End of dialogue for A
|.....
TC-RESULT-NL req
(D2, 1, P1)
TC-RESULT-NL req
(D2, 1, P2)
TC-RESULT-L req
(D2, 1, P3)
TC-END req
(D2, normal)
End of dialogue for B
| +| Time | | + +##### Abort by the TC-user + +The abort facility allows the TC-user to stop the dialogue at any time. A typical case is when the user abandons the service. The main differences between this and normal ending are: + +- any components for which transmission is pending are not sent to the peer entity; +- peer-to-peer TC-user information can be transmitted at the time the abort is issued, and this is delivered to the remote TC-user. + +The sequence given in Table 15 shows a user abandonment in example E2. + +**Table 15/Q.775** + +| TC-user A | TC-user B | +|------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------| +| TC-INVOKED req(D1, 1, Test, Class = 1)
TC-BEGIN req
(D1, Address) | | +| | TC-BEGIN ind
(D2, Address)
TC-INVOKED ind
(D2, 1, Test)
TC-INVOKED req
(D2, 2, 1, Option-selection, Class = 1)
TC-CONTINUE req
(D2) | +| TC-CONTINUE ind
(D1)
TC-INVOKED ind
(D1, 2, 1, Option-selection)
TC-U-ABORT req
(D1, Cause) | | +| | TC-U-ABORT ind
(D2, Cause) | +| Time | | + +#### 3.2.1.4 Message-related abnormal situations + +These are considered independently from the effects of such events in the Component sub-layer. + +##### Message loss + +TC provides no protection against message loss. Three cases are identified: + +- 1) the message begins a new dialogue: the dialogue will exist at the originating side only, and no message will be allowed in either direction. Eventually, an implementation-dependent mechanism at the originating end ends the dialogue; +- 2) the message continues an existing dialogue: loss is not detected. TC will react (or not) to the loss of included components as indicated in 2.4.1; +- 3) the message ends a dialogue: TC will eventually react (via a timer expiry as described in 2.4.1) if this message contained a response to a Class 1 operation: otherwise an implementation-dependent mechanism ends the dialogue at the destination end. + +##### Message duplication + +Duplication of a BEGIN message causes two transactions to be opened, as indicated below: each of these transactions has its own local ID, and the same destination ID. The TC-user eventually detects that something is wrong, and both dialogues are aborted. + +The sequence given in Table 16 illustrates a duplication of the BEGIN message in Example E2. + +**Table 16/Q.775** + +| TC-user A | TC-user B | +|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +| TC-INVVOKE req
(D1, 1, Test, Class = 1)
TC-BEGIN req
(D1, Address) | | +| | TC-BEGIN ind
(D2, Address)
TC-INVVOKE ind
(D2, 1, Test)
Duplicated BEGIN:
TC-BEGIN ind
(D3, Address)
TC-INVVOKE ind
(D3, 1, Test)
Response to the first Begin
TC-INVVOKE req
(D2, 2, 1, Option-select, Class = 1)
TC-CONTINUE req
(D2)
Response to the second Begin
TC-INVVOKE req
(D3, 2, 1, Option-select, Class = 1)
TC-CONTINUE req
(D3) | +| TC-CONTINUE ind
(D1)
TC-INVVOKE ind
(D1, 2, 1, Option-select)
TC-user considers that this invocation is abnormal, and may reject it, or abort one of the dialogues:
TC-U-ABORT req
(D1, Cause) | | +| | TC-U-ABORT ind
(D3, Cause) | +| Time | | + +At that moment, there is still one dialogue (with local ID D2) at TC-user B's side, but no dialogue at A's side. TC-user B will receive an indication from TC when operation 2 of dialogue D2 times-out with no reply (TC-L-CANCEL ind), and may then decide to abort D2. Note that the situation would be more difficult to detect, had TC-user B not invoked a Class 1 operation. + +Duplication of a CONTINUE message is not detected by TC. + +When an END message is duplicated, the second message is received with an ID which does not correspond to an active dialogue: TC reacts by discarding the duplicate message. + +##### **Missequencing of messages** + +When the missequenced messages involve neither the beginning, nor the end of a dialogue, missequencing is not detected by TC, and may result in component missequencing, to which TC + +would react as indicated in 2.4.3. + +When a message indicating dialogue continuation arrives after a message indicating the end of the same dialogue, it is not delivered, and causes TC to abort the dialogue; the TC-user will probably detect the loss when receiving a premature dialogue end indication. If the application needs to recover from this case, a new dialogue should be started. + +##### Message corruption + +When receiving a corrupted message, TC reacts as indicated in Recommendation Q.774. + +Table 17 shows the sequence of primitives when TC decides to abort the dialogue after receiving a corrupted message in Example E2. + +**Table 17/Q.775** + +| TC-user A | TC-user B | +|-----------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------| +| TC-INVOKED req
(D1, 1, Test, Class = 1)
TC-BEGIN req
(D1, Address) | | +| | TC-BEGIN ind
(D2, Address)
TC-INVOKED ind
(D2, 1, Test)
TC-INVOKED req
(D2, 2, 1, Option-select, Class = 1)
TC-CONTINUE req
(D2) | +| Corrupted message:
TC-P-ABORT ind
(D1, Cause) | TC-P-ABORT ind
(D2, Cause) | +| Time | | + +#### 3.2.1.5 Relations between dialogue and component handling + +The following gives some guidelines on when dialogue end can be requested; if these are not respected, TC will not refuse the request for dialogue end. + +The problems that may result from the collision of messages requesting dialogue end have been considered above. + +Normal end should not be requested when: + +- there are operation invocations pending for the dialogue; +- the application protocol anticipates that replies being transmitted with the termination request could be rejected. + +Many applications might not define recovery scenarios in response to a rejected reply. This legitimizes the transmission of replies or of Class 4 operations in a message indicating dialogue end. The other applications should either use the connection-oriented network service approach, or end the dialogue with a message containing no component, that would be sent only when a reject indication can no longer be received. + +It is recommended that an operation for which a reply is expected not be sent in an END message (i.e. that the TC-user does not issue a TC-END req primitive to trigger the associated component). It + +should be noted that this is not a requirement of the TC protocol nor, except as a sensible guideline, of the TC-user. If a TC-user chooses to send an invoke component for an operation of Class 1, 2 or 3 in an END message, it has no pathological implications for the peer TC protocol machines or the TC-users. It is a local matter on how the performing side discards any components generated as a result of performing the operation when there is no active dialogue. Indeed, the fact that the TC-user invoking the operation has chosen to include it in an END message means that it has decided for this instance to override the operation's inherent semantics and does not care to be told if the operation could be performed or not. + +#### 3.2.1.6 Addressing issues + +The TC-user initiating a dialogue must give the Destination Address and Originating Address to TC. The TC-user providing the Originating Address is responsible for giving this address in such a form that the remote TC can use it, without checking, to reach it. + +TC above connectionless SCCP uses any of the addressing options provided by the SCCP. So any combination of types of address for the destination and Origination addresses is allowed. + +During the establishment of a dialogue the combination of addresses may be optimized by both the B-side TC-user and TC. + +The optional originating address parameter in the first TC-CONTINUE request primitive can be used to change the address which should be used for routing the subsequent messages associated with the dialogue. The actual destination itself should not be changed by this modification. If a new destination is to be reached, the dialogue should be terminated and a new one started to the new destination. + +Example of address changes which do not modify the actual destination are: + +- Initial address was a global title, subsequent address is a PC and SSN for the same destination to allow optimal routing (generally not crossing network boundary). +- A general global title is used to select a database from a set of replicated databases. The responding database returns its own specific Global Title. + +#### 3.2.1.7 Quality of Service + +The dialogue handling request primitives allow the TC-user to request a particular Quality of Service from the network layer. If no specific request is made by the TC-user, default options are selected by SCCP (i.e. no return option, no sequencing). + +If sequence control is requested, the TC-user is also responsible for providing information enabling the network layer to identify a flow of related messages to be delivered in sequence. + +It is recommended that sequence control be requested by TC-users when using the TC-RESULT-NL services. + +When the return option is requested, the TC-user is notified of the non-delivery of the associated message, through the TC-NOTICE ind primitive. + +Although the TC-NOTICE ind is primarily intended to be processed by a management function (e.g. when it indicates that a failure occurred during the translation of a global title), there are cases where the return option may be requested in a TC-BEGIN req or TC-UNI req primitive for determining whether the destination Application Entity (identified by the subsystem number in the destination address) exists at the receiving entity. In such a case, the TC-NOTICE ind might be interpreted in real time. + +In the following example, the TC-user A which resides in a local exchange starts a look-ahead procedure before setting up a call. It requests the return option when issuing the TC-BEGIN req to + +open a dialogue towards the destination local exchange B. The look-ahead procedure is not implemented in node B. Hence, the subsystem number which corresponds to the look-ahead procedure does not exist and the SCCP in node B returns the SCCP message which contained the BEGIN message. The TC-user A is confirmed via the TC-NOTICE ind primitive and starts a basic call (circuit) establishment procedure. + +**Table 18/Q.775** + +| TC-user A | | TC-user B | +|----------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------|----------------------| +| Call processing starts
TC-INVVOKE req
(D1, 1, LookAhead)
TC-BEGIN req (D1, return
option, Dest = B-Address,
Orig = A-Address) | | | +| | UNITDATA (return option,
B-Address, A-Address, BEGIN) | | +| | | SSN-B does not exist | +| | UNITDATA SERVICE
(Return cause, A-Address,
B-Address, BEGIN) | | +| N-NOTICE ind (D1, return cause,
Dest = A-Address, Orig = B-
Address) | | | + +### 3.2.2 Unstructured dialogue + +A Unidirectional message will contain only Class 4 operation invocations or reports of protocol errors in such invocations. Multiple components can be transmitted in a Unidirectional message provided that the maximum message size of a message is not exceeded. + +## 3.3 Enhanced dialogue control facilities + +### 3.3.1 Overview + +As the number of signalling applications using TC grows, it will become necessary to be able to differentiate between them during an instance of communication – particularly when a number of them reside at the same location within a SS No. 7 node. + +The ability to signal at the start of the dialogue which application protocol (among potentially many) is involved in the subsequent exchange of messages is provided by the optional functions and protocol of the Dialogue Portion. The optional Dialogue Portion allows the negotiation of the Application Context and, as a further option within it, the transparent transfer of user data which are not components. The latter might be used to convey, for example, initialization data, versions of user protocols, further refinement of the application context, passwords, etc. + +### 3.3.2 Use of the Application-Context + +The TC-user which begins a dialogue can propose an application-context to its peer by including an application-context-name in the TC-BEGIN req primitive. The application-context refers to the set of ASEs and the associated coordinating rules which may be required during the dialogue. + +If the Application-context-name is acceptable, the responding TC-user can either decide to continue or terminate the dialogue in a normal manner. Except if it requests a prearranged termination, it shall include the same AC-name in the first (or unique) dialogue handling request primitive it uses. + +If the AC-name is not acceptable, the TC-user may elect to: + +- i) Discard the received components and issue a TC-U-ABORT req primitive to indicate that it refuses the dialogue. It shall include an application-context-name in this primitive which is either the one received or an alternative one to be used by the dialogue-initiator to make a new attempt. TC does not provide a standard feature to enable the TC-user to propose more than one alternative AC-name. However, such a procedure can be defined outside the scope of TC using the user-information parameter (see 3.3.3). +- ii) Continue the dialogue but indicate that it makes use of an alternative AC [e.g. one which does not use the ASE(s) it does not support], by including another application-context-name in the first TC-CONTINUE req primitive. The received components may or may not be discarded, depending on prearranged agreement between TC-users. +- iii) Terminate the dialogue in a normal manner but indicate that the response(s) included in the END message are based on an alternative AC [e.g. one which does not use the ASE(s) it does not support], by including another application-context-name in the TC-END req primitive. + +The TC-user may also provide an application-context-name when using the TC-UNI service. In such a case the AC-Name indicates to the peer TC-user how to interpret the received components. + +It is important to note that the application context information conveyed in the dialogue handling APDUs is a name of the type OBJECT IDENTIFIER. Such a name is a reference to a specification (document) where the description of the application context is provided. Such a document can make references to other specifications where, for instance, the abstract syntax of some application protocol is provided. Such specifications can be provided in some formal or semi-formal notation, or plain text. + +The specification of application contexts, their semantics, the assignment of an object identifier value and the dissemination of this information to all parties that wish to communicate is the process of registering an application context. In the case where application contexts are registered as a part of ISDN signalling Recommendations, an example of a typical value might be {ccitt recommendation q xxx ac-name(y)} for the yth application context described in Recommendation q.xxx. + +While in principle, it is possible for the application context description to be very detailed, and to add new application contexts to cover every situation that may occur, it may be easier to maintain such specifications if the number of application contexts are kept within reasonable limits. For example, let us assume that a particular application context name refers to the combined use of ASEs A and B. In certain circumstances, it may be necessary to signal that only a subset of the capabilities of A and/or B will be used for a particular instance of communications. Instead of registering a new application context name to cover this case, the same information can be conveyed in some mutually acceptable syntax in the user information field of the AARQ and AARE APDUs. + +### 3.3.3 Transfer of user data + +TC dialogue handling primitives allow the TC-user to request TC to transfer information not related to component handling facilities (i.e. not based on the Remote Operation paradigm). This information is carried either in the user-information field of dialogue control PDUs or directly in the dialogue portion, once the dialogue is established. + +A typical situation where such facility is required is at dialogue establishment to send some initialization data to the peer (refinement of the application-context, authentication data, + +identification of a destination sub-process within the TC-user, etc.). + +In addition, this facility can be used for application context-negotiation: when the TC-user refuses a dialogue (user-abort in dialogue pending state with abort-reason = application-context-not-supported), it can insert a list of alternative application-context-name in the user data field of the TC-U-ABORT req primitive. These names are then carried as part of the user-data of the dialogue protocol data unit (ABRT). The TC-user which is at the origin of the dialogue establishment request can make a new attempt with one of these contexts. + +In order to use this facility the two TC-users will have to define the syntax and semantics of the information to be conveyed, if any, in each dialogue APDU for every application context. As the ASN.1 type of this user information is EXTERNAL, the syntax of this information can be written using ASN.1 or any other user specific notation. The manner in which this information is encoded can also be user-specific. The EXTERNAL type allows the embedding of a data value from one Abstract Syntax (in this case some user-specific syntax) within another (that of the dialogue APDUs). + +Recommendation X.208 defines the EXTERNAL type as follows: + +``` +EXTERNAL ::= [UNIVERSAL 8] IMPLICIT SEQUENCE { + direct-reference OBJECT IDENTIFIER OPTIONAL, + indirect-reference INTEGER OPTIONAL, + data-value-descriptor ObjectDescriptor OPTIONAL, + encoding CHOICE { + single-ASN1-type [0] ANY, + octet-aligned [1] IMPLICIT OCTET STRING, + arbitrary [2] IMPLICIT BIT STRING } +``` + +Of the three forms of reference to identify the type and encoding of the data value that is contained by the EXTERNAL construction, the TC-user must use the direct-reference. The direct-reference-name will provide the key to identifying both the abstract syntax of the data value and the encoding rules which apply to it. The indirect-reference is used to identify the Presentation Context, the use of which is not supported at present in SS No. 7 signalling. In addition to the direct-reference, the TC-user may also provide an explicit description of the data value in an informal notation through the use of the data-value-descriptor. + +If the external data value is a single ASN.1 type and the Basic Encoding Rules are used to encode this value, any of the choices for the "encoding" field can be used. If the agreed-to encoding of this data value results in an integral number of octets, the encoding choice can use either the "octet-aligned" or "arbitrary" encoding. If the agreed-to encoding of this external data value does not result in an integral number of octets, then the encoding choice of "arbitrary" should be used. + +As the protocol allows a SEQUENCE OF EXTERNAL to be present in the optional user information field of the dialogue control APDUs, the two TC-users are not restricted, when defining an application context, to any particular number in the sequence. (If the segmentation is not provided by the SCCP, TC-users will have to ensure that the Signalling System No. 7 message size restriction is not violated.) + +### 3.3.4 Backward compatibility issues + +The new functions and protocol described in the above subclauses are optional and the specification of their protocol procedures in Recommendations Q.771 through Q.774 are easily distinguishable and can be easily removed from procurement documents, implementation specifications and interface specifications between networks which use these Recommendations as a basis. In such a case, one is left with the TC messages defined in the 1988 Recommendations. No network is obliged to support these new features if it offers no services that require these capabilities. + +A node supporting the 1988 version of TC will not understand the APDUs associated with the Application Context generated by a node conforming to the 1992 Recommendation (or any latter version) and will therefore abort the transaction using the P-ABORT cause "incorrect transaction portion". If the TC-user at a node which supports TC conforming to the 1992 Recommendation (or any latter version) receives an Abort message with the above-mentioned cause in response to a dialogue initiation using Application Context information, it must interpret it, at least in the situations where a network supports a mixture of TC implementations based on the 1992 Recommendation (or any latter version) and the 1988 Recommendations, as the result of communicating with a node that supports only the 1988 TC Recommendations and not as the result of a true syntax error (which is an extremely unlikely event). The TC-user may therefore attempt a retransmission of the message without the additional Application Context information provided, of course, that this information is not crucial to the application. + +It is likely that there will be a period of time during which a network supports both TC implementations conforming to the 1988 Recommendations and to the 1992 Recommendation (or any latter version), as well as applications that will or will not require the support of the Application Context mechanism. Deployment of such capabilities is outside the scope of standards, but it should be kept in mind when deploying services if the inefficiency of transmitting the initial message twice is to be avoided. + +# **4 Guidance for writing TC-users protocol specifications** + +## **4.1 Introduction** + +Recommendation Q.1400 describes how Application Service Elements (ASEs), Application-Contexts (ACs) and Application Entities (AEs) are structured and how an AE is addressed in Signalling System No. 7. This clause illustrates that architecture, considering the functional decomposition of an application, and describes how AEs, ACs, ASEs, operations and errors should be defined. + +## **4.2 Decomposition of functionality** + +### **4.2.1 Application process and application entity** + +A signalling Application Process (AP) communicates through a portion of its software devoted exclusively to communications which is called the Application Entity (AE). An AE, therefore, contains all the functions needed to enable the communications between distributed APs. To summarize subclause 4.1/Q.1400, an AE type is a collection of application-specific communications protocols. The definition of the AE type is a local matter. An AE is the realization of the corresponding AE type at a physical entity. + +### **4.2.2 Application service element** + +On many occasions, it is found that the communications functions for a variety of applications can be grouped into integrated sets of actions such that each such set can be used in more than one AE. Such an integrated set of actions that has the potential of being used in several AEs is called an Application Service Element (ASE). Of course, there are always some application-specific communications functions that can only be used to fulfil the communications needs of the specific application for which it has been defined. + +TC provides a generic means for all signalling applications to communicate using the remote operations paradigm over a connectionless network service. + +A TC-user ASE includes a collection of remote operations that, together with TC, collectively + +provide some overall communications protocol to a signalling application. The ASE definition also specifies which peer TC-user may invoke which operation and in which order. If either TC-user may invoke any of the operations, the ASE is said to be symmetric. The means by which operations are defined and grouped is described in 4.5. + +From the perspective of a TC-user, the mechanism for obtaining the services of a TC-user ASE is the invocation of the latter's operations. Each operation provides a part of the ASE's service in an inherently asymmetric manner as it is invoked by one TC-user and executed by another remote peer. However, the TC-users are not always asymmetric (i.e. one limited to always performing operations and the other to invoking them) but may each be able to invoke or perform the same or different operations. [Indeed the service interface from the TC-user's point of view (which is the subject of further study) may appear quite different from that provided by TC. For example, the invocation of a class 1 operation may be seen by the TC-user as the invocation of a confirmed service while, from the perspective of the TC service interface, it is the consequence of two unconfirmed services, viz. TC-INVOKED and TC-RESULT.] + +Some application contexts may require the use of a specific TC-user ASE involved in the establishment and release of a dialogue. Such an ASE embodies the knowledge of two specific operations (known as bind and unbind operations) which form a connection-package. + +Other applications may also require the use of additional ASEs which are not based on the use of operations. The PDUs of such ASEs are conveyed in the dialogue portion. + +### 4.2.3 Communications between peer AEs/ASEs + +Communications between two AEs at different nodes are possible as long as the two AEs are made aware of their peer's address and support a common Application Context. An application context is the specification of the rules, procedures and behaviour at the external interface between two AEs during an instance of communication between them. The means to specify an application context is defined in 4.3. + +For TC-based applications using the 1988 (*Blue Book*) Recommendations, which rely on the SCCP UNITDATA service, the SCCP SubSystem Number (SSN) provides the role of routing an SS No. 7 message to the AE within a physical entity which supports the precise application protocol being used and also, implicitly, the encoding being used for its messages. That is, the SSN, in addition to being a piece of addressing information, also implicitly defined the application context (roughly, the message set) and the presentation context (the encoding of the messages). + +With the introduction of the protocol for the Dialogue Portion of TC, which contains the application context negotiation mechanism, there is no direct relationship between the AE and the SSN. The application context allows an explicit way of recognizing granularity at the application layer. As (see 6.1.3/Q.1400) one AE may support any number of ASEs, the Application Context identifies the appropriate set of ASEs to be used during the SS No. 7 dialogue. + +These points are illustrated in the figure below. + + + +Four diagrams (Figure A, Figure B, Figure C, Figure D) showing different local implementations of ASE X. Each diagram shows an outer box representing an AE type, accessed by a distinct SSN. Inside each box is a TC (Transport Component) and one or more TC-user ASEs. Figure A: ASE X and ASE Y are grouped with TC, accessed by SSN 1. Figure B: ASE X is grouped with TC, accessed by SSN 2. Figure C: ASE Y is grouped with TC, accessed by SSN 3. Figure D: ASE X and ASE Z are grouped with TC, accessed by SSN 4. A reference number T1180030-96 is shown next to SSN 4. + +Each outer box shows an AE type, which consists of several ASEs, one of which, in the case of interest to us, is always TC. ASEs X, Y and Z represent various TC-user ASEs, such as those for supplementary services. Each AE type is accessed by a distinct SSN. + +Figures A and B show two possible local implementations of ASE X. In one case, shown in Figure A, ASE X has been placed together with ASE Y in an AE type accessed by a particular (possibly locally selected) SSN. In Figure B, ASE X is kept separate. These are two possible implementations for the services provided by ASE X and this choice is not subject to standardization. In Figure D, for instance, some other implementation has chosen to group together ASE X with a completely different ASE, ASE Z, to form an AE type accessed at SSN 4. + +Note that the AE types in the above figures are different to emphasize that AE types are *not* standardized, so that each node does not have to choose the same implementation. Communications to provide the services of ASE X can still take place between two different implementations, one as in Figure A, say, and another as in Figures B or D so long as the SCCP routing data are correctly populated (which is a network management and administration issue) and as long as the operations/parameters/error codes of ASE X are distinct from those of ASEs Y and Z (which is a matter decided at specification time; see 4.5.8 for details). + +The only subject of standardization is the external behaviour of a system. Application contexts define the visible external behaviour between two communicating AEs. Some ACs may be standardized. ASEs are often standardized to permit their reuse in many different application contexts. + +## 4.3 How to specify an application context + +During an instance of communication, the interactions between two AEs as well as the interactions between the ASEs within an AE are governed by the rules of an application-context (AC). + +The definition of an AC should contain, at least: + +- a general description; +- a definition of the complete application protocol between the peer AEs by: + - i) identifying each ASE used by the AC, and indicating which of the peer AEs initiates the service; + - ii) any coordinating rules between these ASEs (e.g. concatenation of the PDUs from different TC-user ASEs, any constraints on the order in which operations from different TC-user ASEs may be invoked, etc.) beside the rules which are an inherent part of the ASE specifications; + - iii) the abstract syntax(es) required by the ASEs; +- any special constraints to ensure that peer AEs with different versions are compatible. + +A name shall be assigned to each application-context. Such a name is a value of type OBJECT IDENTIFIER which is carried (if required) as a value of the application-context-name information element in the dialogue portion. + +Subclause 5.4 specifies an ASN.1 information object class which may be used for defining the static aspect of application contexts based on TC. + +## **4.4 How to specify an ASE** + +A TC-user ASE specification should provide at least: + +- a general description of the purpose of the ASE and its procedures; +- the list of supported operations as well as which side (or both) can invoke which operation; +- any rules on the sequence in which operations may be invoked; +- the detailed description of the procedures; +- how different protocol versions interwork; +- the description of the interactions between the ASE and TC in terms of TC service primitives; +- SDL diagrams. + +The OPERATION-PACKAGE and CONNECT-PACKAGE information object classes defined in Recommendation X.880 may be used for specifying the static aspects of the definition of ASEs which are based on the use of operations. + +## **4.5 How to specify Operations and Errors** + +### **4.5.1 General considerations** + +The set of Operations and Errors which forms a TC user protocol specification can be described using one or several ASN.1 modules. The number of ASN.1 modules to be used is left to the protocol designer and is further discussed in 4.5.5. + +A possible notation for defining Operations and Errors is based on the ASN.1 MACRO facility defined in Recommendation X.208. The OPERATION MACRO and the ERROR MACRO are the data types respectively associated to an Operation and to an Error. However, as the MACRO notation is being phased out from ASN.1, Recommendation X.880 provides an alternative notation using two equivalent information object classes. It also explains how one can migrate from the MACRO notation to the object class notation. + +Each operation (error) belongs to an operation type (error type) which is derived from the OPERATION MACRO (ERROR MACRO) type. + +Each operation type or error type should be given a name (an ASN.1 type reference, which starts with a capital letter). + +Each operation or error should be given a name (an ASN.1 value reference which starts with a lower case letter). + +Recommendation X.219 states that values for a set of operations and errors have to be unique within an abstract syntax. For TC, this currently means that they have to be unique within the scope of a subsystem number, a group of related subsystem numbers or an application-context. + +Type definition can be combined with value allocation or performed in two steps, as illustrated in the following example. + +- Type specification and value assignment are separated: + +``` + +OperationTypeExample1 ::= OPERATION +ARGUMENT ParameterType1 +RESULT ResultType1 +ERRORS { error1, error2 } + +``` + +``` +operationExample1 OperationTypeExample1 ::= localValue 1 +``` + +- Type specification and value assignment are combined: + +``` + +OperationExample1 ::= OPERATION +ARGUMENT ParameterType1 +RESULT ResultType1 +ERRORS { error1, error2 } + ::= localValue 1 + +``` + +Whether it is more appropriate to combine type and by value specifications, as well as the use of global or local value, is further discussed in 4.5.6. + +The notation defined in Recommendation X.880 does not support the two steps' approach. However, the code allocated to an operation or an error can be easily modified using the `recode {}` predefined parameterized operation. In the following example, `operationExample2` is defined as being identical to `operationExample1` (same operation type) but with a different value. + +``` +OperationExample2 ::= recode {operationExample1, 2} +``` + +### 4.5.2 Use of the OPERATION MACRO notation + +#### 4.5.2.1 Use of the type notation + +An Operation type is fully defined as an instance of the OPERATION MACRO type supplemented by an ASN.1 comment indicating the associated timer value. + +The following subclauses provide guidance on the use of the various ASN.1 productions which form the OPERATION MACRO description. + +##### 4.5.2.1.1 Specification of the operation argument + +The following ASN.1 productions indicate how the argument of an operation has to be specified: + +``` + +Parameter ::= ArgKeyword ParameterType | empty +ArgKeyword ::= "PARAMETER" | "ARGUMENT" +ParameterType ::= NamedType | NamedType "OPTIONAL" + +``` + +If information can be provided at Operation invocation, the keyword `PARAMETER` or `ARGUMENT` has to be inserted and followed by the `NamedType` which corresponds to the data structure to be provided, otherwise the keyword shall not be present in the Operation description. + +Both keywords are allowed for backward compatibility purposes with TC-user specifications based on older versions of TC. However, the use of the `"PARAMETER"` keyword is deprecated for defining new applications. + +Although the operation argument is always an optional element of an Invoke component, the specification of the `ParameterType` indicates whether its presence at invocation time is mandatory or optional for the completion of the operation execution. In the latter case, the keyword `"OPTIONAL"` follows the ASN.1 type. + +##### 4.5.2.1.2 Specification of positive outcomes + +The following ASN.1 productions indicate how to specify operations which report success: + +**Result ::= "RESULT" ResultType | empty** +**ResultType ::= ParameterType | empty** + +If information can be returned as a result of a successful Operation execution, the keyword RESULT is to be followed by the NamedType associated with the data structure to be sent. If no information is to be provided but the operation class indicate that the operation report success, the RESULT keyword is to be present in the Operation description but the empty alternative of the Result production is used. If the keyword RESULT is not included in an operation description, this indicates that it does not report success (i.e. Class 2 or 4 operation). + +Although the operation result parameter is always an optional element of a Return Result component, the specification of the ParameterType indicates whether its presence is mandatory or optional from a functional point of view. In the latter case, the keyword "OPTIONAL" follows the ASN.1 type. + +##### 4.5.2.1.3 Associated Errors + +The following ASN.1 productions indicate how to specify operations which report failure: + +**Errors ::= "ERRORS" "{ "ErrorNames" }" | empty** +**ErrorNames ::= ErrorList | empty** +**ErrorList ::= Error | ErrorList "," Error** +**Error ::= value (ERROR) | type** + +If the Operation reports failure, the keyword ERRORS should be included and followed by the list of associated errors, otherwise this keyword should not be present. The errors included in the list can be referenced either using a type reference or a value reference (i.e. an error code). + +##### 4.5.2.1.4 Specification of linked operations + +The following ASN.1 productions indicate how to specify linked operations: + +**LinkedOperations ::= "LINKED" "{ "LinkedOperationNames" }" | empty** +**LinkedOperationNames ::= OperationList | empty** +**OperationList ::= Operation | OperationList "," Operation** +**Operation ::= value (OPERATION) | type** + +If the Operation is the parent operation of a set of linked-operations, the keyword LINKED should be included and followed by the list of child operations. The child operations included in the list can be referenced either using a type reference or a value reference (i.e. an operation code). + +#### 4.5.2.2 Use of the value notation + +The value notation for Operation is either the notation for the value of an element of type INTEGER or the notation for an element of type OBJECT IDENTIFIER. This depends on whether the Operation is allocated a local value or a global value. + +#### 4.5.2.3 Specification of timers + +The timer value associated with an operation type has to be indicated as an ASN.1 comment against the ASN.1 MACRO description of the operation type. + +### 4.5.3 Use of the ERROR MACRO notation + +The type notation for an error is the keyword ERROR optionally followed by the keyword PARAMETER and the ParameterType associated to the information which may be sent as error's parameter. The keyword PARAMETER should not be present if no information is associated with + +the error condition. + +Although the error parameter is always an optional element of a Return Error component, the specification of the ParameterType indicates whether its presence is mandatory or optional from a functional point of view. In the latter case, the keyword "OPTIONAL" follows the ASN.1 type. + +The value notation for an error is either the notation for the value of an element of type INTEGER or the notation for an element of type OBJECT IDENTIFIER. This depends on whether the Operation is allocated a local value or a global value. + +### 4.5.4 Use of the (information object) CLASS notation + +The replacement of the MACRO notation (defined in Recommendation X.209) with the (information object) CLASS notation (defined in Recommendations X.680 to X.683) retains the idea that applications have complex concepts, aspects of which need to be expressed as data structures which are to be conveyed by protocols during communications. Each of these concepts is classified by providing a template, analogous to the MACRO definition, known as an **information object class**. The template for a class shows the attributes of the objects belonging to that class. Recommendations X.680 to X.683 remove the MACRO notation and replace it with the information object CLASS definition. + +#### 4.5.4.1 The OPERATION (information object) CLASS + +Recommendation X.880 defines the OPERATION (information object) CLASS. A slightly modified version is presented in ASN.1 definition below, by removing fields not relevant for TC-based applications. + +The notation defines the template for a class of objects (remote operations) which are assigned the name OPERATION, which consists of ten fields. Each field starts with an ampersand (&), which is an indication that property, and is followed by a field-name beginning with either a lower-case or an upper-case letter. This distinction helps identify the sort of data that may populate the fields when defining an instance of this class. + +Words which are all capitalized are used for standardized keywords such as CLASS and UNIQUE, as well as names to object classes such as OPERATION and ERROR. If a field-name starts with an upper-case letter, it is a placeholder for either an arbitrary ASN.1 type (e.g. &Argument, see ASN.1 below), a set of information objects (e.g. &Errors), or a set of values of some type. If it is a set of information objects, the descriptor of the object class to which they belong follows. If, on the other hand, the field-name starts with a lower-case letter (e.g. &returnResult), it takes the *value* of the ASN.1 type (e.g. BOOLEAN) or an information object class that follows. If a field is marked OPTIONAL, it need not be populated when defining instances of the class. The keyword UNIQUE following a field (e.g. &operationCode) means that the field is a "handle" by which instances of the class in question are identified, and should therefore be unique within any given set or collection of such objects. + +Finally, designers of the ASN.1 notation have permitted a limited amount of user-defined notation through the use of the WITH SYNTAX construct which is appended to the definition of the information object class. It permits a more user-friendly notation for defining instances of a CLASS. In Recommendation X.880, the user-defined syntax for the OPERATION and ERROR CLASSes have deliberately been chosen to strongly resemble the earlier MACRO notation. Subclause 4.5.7 defines the (small) changes that are required to convert an existing operation or error definition from the MACRO definition to one employing the information object CLASS definitions. + +##### **OPERATION ::= CLASS** + +``` + +{ + &ArgumentType OPTIONAL, + &argumentTypeOptional BOOLEAN OPTIONAL, + &ResultType OPTIONAL, + &resultTypeOptional BOOLEAN OPTIONAL, + &returnResult BOOLEAN DEFAULT TRUE, + &Errors ERROR OPTIONAL, + &Linked OPERATION OPTIONAL, + &synchronous BOOLEAN DEFAULT FALSE, + &alwaysReturns BOOLEAN DEFAULT TRUE, + &operationCode Code UNIQUE OPTIONAL +} + +``` + +##### **WITH SYNTAX** + +``` + +{ + [ARGUMENT &ArgumentType [OPTIONAL + &argumentTypeOptional]] + [RESULT &ResultType [OPTIONAL + &resultTypeOptional]] + [RETURN RESULT &returnResult] + [ERRORS &Errors] + [LINKED &Linked] + [SYNCHRONOUS &synchronous] + [ALWAYS RESPONDS &alwaysReturns] + [CODE &operationCode] +} +Code ::= CHOICE +{ + local INTEGER, + global OBJECT IDENTIFIER +} + +``` + +##### **4.5.4.1.1 Specification of the operation argument** + +The field &Argument is an optional type field where an arbitrary ASN.1 type can be placed to define the argument of the remote operation invoked. The application designer provides the type to be used when defining a specific operation. In the user-defined syntax, the type of the accompanying argument follows the keyword ARGUMENT. + +The field &argumentTypeOptional is an optional value field, which takes the value TRUE if a defined argument may optionally be absent from a functional point of view, or FALSE if it must always be present. In the user-defined syntax, the two cases are shown by the keywords OPTIONAL TRUE (respectively OPTIONAL FALSE) succeeding the type definition of the ARGUMENT. + +##### **4.5.4.1.2 Specification of the operation result** + +The field &ResultType is a type field where an arbitrary ASN.1 type can be placed to define the result of performing the remote operation. The application designer provides the type to be used for the result when defining a specific operation. In the user-defined syntax, the type of the accompanying result follows the keyword RESULT. + +The field &resultTypeOptional is an optional value field, which takes the value TRUE if a defined result may optionally be absent from a functional point of view, or FALSE if it must always be present. In the user-defined syntax, the two cases are shown by the keywords OPTIONAL TRUE (respectively OPTIONAL FALSE) succeeding the type definition of the RESULT. + +##### 4.5.4.1.3 Specification of positive outcomes + +The field &returnResult is an optional value field of type BOOLEAN which specifies whether the positive outcome of a remote operation is always reported. In the user-defined syntax, such a field is recognized by the keyword RETURN RESULT. Its absence implies that the operation always returns a result. + +NOTE – This field ensures the explicit recognition of whether an operation returns upon successful completion, even if a result type is not defined for it. + +##### 4.5.4.1.4 Associated errors + +The field &Errors is an optional field where a set of objects (errors) defined by the CLASS ERROR (see 4.5.5) can be placed to define the set of errors which may be returned if the remote operation fails. In the user-defined syntax, the set of errors, if present, are enclosed within braces "{...}" and follow the keyword ERRORS. + +##### 4.5.4.1.5 Specification of linked operations + +The field &Linked is an optional field where a set of objects (operations) defined by the CLASS OPERATION can be placed to define the set of operations which may be linked to the particular operation being defined. In the user-defined syntax, the set of linked operations, if present, are enclosed within braces "{...}" and follow the keyword LINKED. + +##### 4.5.4.1.6 Synchronous nature of the operation + +The field &synchronous is an optional value field which takes the value TRUE if the operation is synchronous (i.e. the invoker must wait for the operation to return before invoking another on the same performer) or FALSE otherwise. In the user-defined notation, the operation code follows the keyword SYNCHRONOUS. + +NOTE – If an operation is synchronous, the field &alwaysReturns (see 4.5.4.1) must be TRUE. + +TC-user operations are asynchronous. This field has been defined to default to FALSE (i.e. asynchronous) if this keyword is absent; so existing and future TC-user applications need not concern themselves about its presence. However, other operations, such as bind and unbind (see 5.2.2.1 and 5.2.2.2) explicitly use this field in their definitions. + +##### 4.5.4.1.7 Operation code + +The field &operationCode is an optional value field which is either an integer (a "locally" unique value) or an OBJECT IDENTIFIER (a globally unique value), and must be chosen to be different from those of any other operations in a given set of operations. In the user-defined notation, the operation code follows the keyword CODE. + +If an operation code value is not defined, it means that this operation cannot be invoked using the Invoke PDU. An example of such an operation is the bind operation (see 5.2.2.1) which is invoked using the bind-invoke PDU defined in 5.2.2.1.2. + +##### 4.5.4.1.8 Classes of operation + +The field &alwaysReturns is a value field of type BOOLEAN which denotes whether the operation always returns or not. In the user-defined syntax, it is denoted by the true or false value accompanying the keyword ALWAYS RETURNS. If absent, it implies that the operation always returns. + +If an operation always returns, it is of Class 1, or 2, or 3. The field &returnResult helps decide if an operation is of Class 1 or 3. The presence or absence of the field &Errors narrows down the previous choice to Class 1 (respectively Class 3). + +##### 4.5.4.1.9 Specification of timers + +There is no notational means to specify timers for operations except as ASN.1 comments. + +### 4.5.5 The ERROR (information object) CLASS + +Recommendation X.880 defines the ERROR (information object) CLASS. A slightly modified version is presented in ASN.1 description below, by removing a field not relevant for TC-based applications. + +``` +ERROR ::= CLASS +{ + &ParameterType OPTIONAL, + ¶meterTypeOptional BOOLEAN OPTIONAL, + &errorCode Code UNIQUE OPTIONAL +} +WITH SYNTAX +{ + [PARAMETER &ParameterType [OPTIONAL ¶meterTypeOptional]] + [CODE &errorCode] +} +``` + +#### 4.5.5.1 Specification of the parameter accompanying an error + +The field &ParameterType is an optional type field where an arbitrary ASN.1 type can be placed to define the parameter accompanying an error report for an operation invocation. The application designer provides the type to be used when defining a specific error. In the user-defined syntax, the type of the accompanying parameter follows the keyword PARAMETER. + +The field ¶meterTypeOptional is an optional value field, which takes the value TRUE if a defined parameter may optionally be absent from a functional point of view, or FALSE if it must always be present. In the user-defined syntax, the two cases are shown by the keywords OPTIONAL TRUE (respectively OPTIONAL FALSE) succeeding the type definition of the PARAMETER. + +#### 4.5.5.2 Error code + +The field &errorCode is a value field which is either an integer (a "locally" unique value) or an OBJECT IDENTIFIER (a globally unique value), and must be chosen to be different from those of any other errors in any given set of errors. In the user-defined notation, the error code follows the keyword CODE. + +If an error code value is not defined, it means that this error cannot be returned using the Return Error PDU. An example of such an error is the error indicating the ability to bind (see 5.2.2.1) which is returned using the bind-error PDU defined in 5.2.2.1.2. + +### 4.5.6 Examples of Operations and Errors description + +This subclause illustrates the part of protocol specification which deals with Operations and associated Errors definitions for a simple TC-user ASE. The purpose of Operations and Errors is briefly described in textual form. Then Operations and Errors, as well as the associated data types, are formally described in one ASN.1 module. + +The following example is based on fictitious freephone like dialogue, between a switching centre and a freephone database. + +#### 4.5.6.1 Operations and Errors purposes + +##### 4.5.6.1.1 Provide routing information + +This operation is invoked by a switching centre to request a remote entity to provide routing + +information in order to establish a call to a subscriber. The routing information provided may be a forwarded-to number and may depend on the calling party number and/or the requested basic service. In the latest case the `getCallingPartyNumber` child operation is invoked. + +##### 4.5.6.1.2 Get calling party number + +This operation is invoked by a network element to request a switching centre to provide the calling party number associated with a call set-up request. + +##### 4.5.6.1.3 Invalid called number + +This error is returned by a network element to indicate that the received called number does not comply with the supported numbering scheme. + +##### 4.5.6.1.4 Subscriber not reachable + +This error is returned by a network element to indicate that there is currently no routing information available corresponding to a called number. + +##### 4.5.6.1.5 Called barred + +This error is returned by a network element to indicate that a call cannot be set up because the calling number conflicts with the barring conditions attached to the called party. + +##### 4.5.6.1.6 Calling party number not available + +This error is returned by a switching centre to indicate that the calling party number cannot be provided. + +##### 4.5.6.1.7 Processing failure + +This error is returned by a network element to indicate a processing failure. + +#### 4.5.6.2 ASN.1 specification + +The following ASN.1 module specifies the operations and associated errors and data types which correspond to the protocol elements described above. In this example type definition of Operations and Errors is combined with value assignment. + +``` +TCAP-Examples { ccitt recommendation q 775 modules(2) examples(2) version1(1) } +DEFINITIONS ::= +BEGIN + +IMPORTS OPERATION, ERROR +FROM TCAPMessages { ccitt recommendation q 773 modules(2) messages(1) version2(2) }; + +provideRoutingInformation OPERATION +ARGUMENT RequestArgument + +RESULT RoutingInformation + +ERRORS { invalidCalledNumber, + subscriberNotReachable, + callBarred, + processingFailure } + +LINKED { getCallingPartyAddress } +-- timer T-pi = 10 s +::= localValue : 1 +``` + +| | | +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------| +|
getCallingPartyAddress
RESULT
ERRORS
-- timer T-gp = 5 s
::= localValue : 2
invalidCalledNumber ERROR ::= localValue : 1
subscriberNotReachable ERROR ::= localValue : 2
calledBarred ERROR ::= localValue : 3
callingPartyAddressNotAvailable ERROR ::= localValue : 4
processingFailure ERROR ::= localValue : 5
-- data types
RequestArgument ::= SEQUENCE {
calledNumber IsdnNumber,
basicService BasicServiceIndicator OPTIONAL
}
RoutingInformation ::= CHOICE {
reroutingNumber [0] IMPLICIT IsdnNumber,
forwardedToNumber [1] IMPLICIT IsdnNumber }
BasicServiceIndicator ::= ENUMERATED {
speech (0),
unrestrictedDigital (1) }
CallingPartyAddress ::= IsdnNumber
IsdnNumber ::= SEQUENCE {
typeOfAddress TypeOfAddress,
digits TelephonyString }
TypeOfAddress ::= ENUMERATED {
national (0),
international (1),
private (2) }
TelephonyString ::= IA5String (FROM ("0" "1" "2" "3" "4" "5" "6" "7" "8" "9" "*" "#")) (SIZE (1..15))
END
|OPERATION
CallingPartyAddress
{ callingPartyAddressNotAvailable,
processingFailure }
| +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------| + +### 4.5.7 Moving from the MACRO notation to the (information object) CLASS notation and use of ASN.1 modules + +All TC-user specifications have hitherto been written using the ASN.1 MACRO notation defined in Recommendation X.208. This subclause shows how the use of these macros can be transformed into the use of the information object CLASS notation. As mentioned in 4.5.4, the user-defined syntax of the OPERATION/ERROR CLASSes have been deliberately chosen in Recommendation X.880 to allow the greatest commonality with the previous construct. From a user's point of view, there are a number of small changes, some of which are a re-positioning of various symbols while others allow for a greater indication within the notation of aspects of an operation which, in the MACRO notation, could only be expressed as comments. + +In this subclause, the *provideRoutingInformation* operation and the *processingFailure* error of 4.5.6.2 are shown in both notations. In each case, on the left-hand side, which shows the macro + +notation, symbols underlined are to be deleted to form the new notation (the right-hand side), while symbols in ***bold italics*** are to be inserted into the old notation to form the new notation. + +| | | | +|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +| provideRoutingInformation OPERATION ::= { ARGUMENT RequestArgument RESULT RoutingInformation ERRORS {invalidCalledNumber / subscriberNotReachable / callBarred / processingFailure } LINKED { getCallingPartyAddress } ::= CODE local : 1 } | $\Rightarrow$ | provideRoutingInformation OPERATION ::= { ARGUMENT RequestArgument RESULT RoutingInformation ERRORS {invalidCalledNumber / subscriberNotReachable / callBarred / processingFailure } LINKED { getCallingPartyAddress } CODE local : 1 } |
+| processingFailure ERROR ::= { ::= CODE local : 5 } | $\Rightarrow$ | processingFailure ERROR ::= { CODE local : 5 } |
+
+#### Use of ASN.1 modules
+
+A module is an ASN.1 construction where a protocol designer collects several types and values definitions.
+
+Theoretically, ASN.1 imposes no constraints upon the number of modules used to define a protocol. All the definitions may be contained in one module or many modules. However, if definitions contained in one module are required in another (e.g. the error used by an operation is defined in another module), then the corresponding definition is made available by EXPORTing it from the module in which it is defined and IMPORTing it into the module in which it is used. This applies to all ASN.1 objects, whether defined by type or value.
+
+This gives the application designer the freedom to structure the modules according to needs, or a self-imposed convention. For example, a single module could contain all the definitions particularly in a single AE, single ASE environment. Alternatively, there could be one module for each ASE definition, each module containing all the operation and errors used exclusively by that ASE. At the other extreme, all the operations and errors could be defined in one "central registry" module and exported for use in the other modules where the ASEs are defined.
+
+It may be necessary to employ a "mixed mode" of ASN.1 notation when defining modules. This arises from the use of the ASN.1:1994 notation defined in Recommendations X.680 to X.683 for some cases where definitions are borrowed from existing ITU-T Recommendations employing the new notation. An example of this is the use of some concepts of ROSE (Recommendation X.880) such as the static definitions of application contexts (see 5.1.1), and the use of X.500 Directory operations for particular Intelligent Network interfaces. It is important to ensure that older modules written in ASN.1:1989 do not have to be rewritten, and can coexist with modules that are written using constructs of ASN.1:1994.
+
+Detailed guidelines for working in this "mixed mode" are provided in Recommendation X.680, but are summarized here:
+
+- A specification may comprise modules in both ASN.1:1989 and ASN.1:1994. However, any given module MUST conform to either the 1989 or the 1994 notation, and comments may be included to indicate which version of the notation is being used in which module.
+
+- Type and value references may be imported into an ASN.1:1994 module from an ASN.1:1989 module so long as:
+ - a) ASN.1:1989 MACRO definitions are NOT imported into a module using ASN.1:1994 notation; and
+ - b) identifiers for SET, SEQUENCE and CHOICE values are present.
+- Type and value references may be imported into an ASN.1:1989 module from an ASN.1:1994 module so long as:
+ - a) new ASN.1:1994 types (CHARACTER STRING, UniversalString, BMPString, EMBEDDED-PDV) are NOT imported.
+
+### 4.5.8 Allocation and Management of Operation and Error Codes
+
+#### 4.5.8.1 General considerations
+
+Subclauses 4.1 to 4.5.4 describe how ACs, ASEs, operations and errors may be specified. Also discussed is how ASEs use operations and errors, and how the ASEs themselves are used in defining the application context between two peer AEs.
+
+ACs and ASEs are convenient modelling and specification tools used to aid in the design of application protocols. At the end, during a dialogue between two TC-users, any TC-based application protocol is made up of the exchange of data values for operations and errors types identified by, respectively, their operation or error codes. The only requirement of Signalling System No. 7 (and ROSE) is that operation and error codes be unique within an Abstract syntax. As there is currently no way to explicitly signal the abstract syntax to which a given operation or error code belongs, the application designer has to ensure that these codes are unique within the scope a subsystem number or of an application-context. In the case where the scope of operation and error codes is an application-context, the protocol designer shall also ensure that the application-context-name is conveyed to the remote end using the protocol of the dialogue portion.
+
+There are many possible schemes regarding the allocation and management of operation and error codes and many factors need to be considered. Two major considerations are AC/ASE structure and the reuse of operations and errors.
+
+#### 4.5.8.2 Import and Export of Operations and Errors
+
+As any other ASN.1 type, Operations and Errors can be exported and imported between ASN.1 modules. This method can be used when there is a need to define an operation whose type corresponds to an existing operation but when the value to be allocated to this new operation is different from the one allocated to the existing one (i.e. for uniqueness purposes). This is illustrated by the following example, where objectIdentifier1 and objectIdentifier2 are fictitious identifiers.
+
+```
+
+ExportingModule { objectIdentifier1 } DEFINITIONS ::=
+BEGIN
+EXPORTS operation1, OperationTypeA, error1, ErrorTypeA;
+
+IMPORTS OPERATION, ERROR FROM TCAPMessages
+{ ccitt recommendation q 773 modules(2) messages(1) version2(2) };
+
+operation1 OPERATION
+ARGUMENT ParameterType1
+RESULT ResultType1
+ERRORS { error1 }
+::= localValue 1
+
+OperationTypeA ::= OPERATION
+
+```
+
+| | |
+|----------|----------------|
+| ARGUMENT | ParameterTypeA |
+| RESULT | ResultTypeA |
+| ERRORS | { ErrorTypeA } |
+
+operation2 OperationTypeA ::= localValue : 2
+
+error1 ERROR
+ PARAMETER DiagnosticType1
+ ::= localValue : 1
+
+ErrorTypeA ::= ERROR
+ PARAMETER DiagnosticTypeA
+
+error2 ErrorTypeA ::= localValue : 2
+
+*-- Note that ParameterType1, ResultType1, ParameterTypeA, ResultTypeA,*
+
+*-- DiagnosticType1 and DiagnosticTypeA have to be defined somewhere if they are not defined*
+
+*-- within this module, they have to be imported from the module where they are defined.*
+
+END
+
+ImportingModule { objectIdentifier2 } DEFINITIONS ::=
+
+BEGIN
+
+IMPORTS OPERATION, ERROR FROM TCAPMessages
+
+{ ccitt recommendation q 773 modules(2) messages(1) version2(2) };
+
+operation1, OperationTypeA, error1, ErrorTypeA
+
+FROM ExportingModule { objectIdentifier1 };
+
+operation2 OPERATION
+
+ARGUMENT ParameterTypeX *-- to be defined somewhere in the module*
+
+::= localValue : 2
+
+error2 ERROR ::= localValue : 2
+
+*-- Value 2 is already in use. Thus value 3 is allocated to the imported objects*
+
+operationA OperationTypeA ::= localValue : 3
+
+errorA ErrorTypeA ::= localValue : 3
+
+END
+
+#### 4.5.8.3 Impact of ASE/AC structure on operation and error code administration
+
+Regarding the AC/ASE structure the options are:
+
+##### 4.5.8.3.1 Monolithic approach – One AC, one ASE
+
+Conceptually, this is the simplest approach. The application protocol is defined by an AC which comprises only one ASE (in addition to TC). All the operations used in that ASE could be defined in one ASN.1 module, which also contains the definition of the ASE's operation package and of the AC. Within the protocol, all operations and errors are identified uniquely by being assigned a unique local (integer) value.
+
+The advantage of this scheme is its simplicity. Its disadvantage is that it does not permit to identify independent building blocks which can evolve separately within the AC definition.
+
+##### 4.5.8.3.2 One AC comprising more than one ASE
+
+In defining an application protocol the designer may choose to structure an AC such that it comprises two or more ASEs. For example, it may be decided to group those elements of protocol concerned with user authentication into one separate ASE (which could be reused in another protocol), and those concerned with the actual data base enquiry into another ASE. This can facilitate modular system design but, when all the constituent ASEs are combined to form the AC, care must be taken
+
+to ensure that different operations/errors contained in different ASEs have not been allocated the same value.
+
+Using the same operation/error in two different ASEs within the same AC does not cause a problem. If the values allocated to this same operation are the same in each case, then within the protocol there will be only one operation/error associated with that value. If different values are allocated, then although it will appear in the protocol that there are two different operations/errors, in the implementation of the application these two different values will cause the same operation/error to be invoked/identified.
+
+However, if within the same AC, an operation defined in one ASE is allocated the same value as a different operation in another ASE, then this will obviously cause a problem. When an ASE is used in only one AC, a simple code allocation scheme can avoid this problem. But when the same ASE is used in several ACs, this can become difficult to administer, and the only "safe" approaches are those described in i) to iii) below.
+
+- i) Two or more ASE protocols share common local operation/error values:
+
+When the ASEs are defined, the values are allocated by the protocol designer(s) so that no clashes can occur. This requires a coordination in the tasks of defining the ASE. This means that the ASEs share the same abstract syntax.
+
+A disadvantage of this scheme is that if one of the ASEs is used in more than one context (i.e. together with different set of ASEs), it is more or less impossible to avoid value clashes for any combination.
+
+- ii) Assign global values (object identifiers) to operations and errors:
+
+Since an object identifier is unique throughout SS No. 7, there is no danger of clashes in values when an ASE is combined with any other one.
+
+One of the disadvantages of this scheme is that when encoded, an object identifier is longer than a simple integer.
+
+- iii) Sharing operations/errors by assigning types when defining operations/errors, instead of values:
+
+This approach assumes that type definition of the operations and errors have been defined independently from value assignment.
+
+When a protocol designer defines an application-context, it collects all the operation and error types used by the required ASEs and allocates suitable values so that no clashes occur.
+
+By doing this, one can consider that the protocol designer defines a new set of ASEs isomorphic to the existing ones which differ only by the values of their operations and errors.
+
+#### **4.5.8.4 Reuse of operation and errors**
+
+Regardless of the number of ASEs included in a protocol, there are situations where it appears suitable to include an existing operation or error when defining a new ASE.
+
+The operation or error can be reused in one of the following manners.
+
+The operation is imported in one of the module defining one of the ASEs. This is only feasible if it is ensured that there is no value clashes.
+
+This can be achieved if:
+
+- i) There is a central registry of operation and errors which uses only values in a reserved range never used by ASE specific operations. This approach imposes a constraint on TC-user ASEs which may not be satisfied in a broader environment (i.e. if Operations or Errors from
+
+DSS 1 or ISO protocols are to be used).
+
+- ii) The operation and errors have been allocated global values. The disadvantage of this approach is that a global value requires more octets to be encoded than a local one and requires official registration within the Object Identifier Tree.
+- iii) The operation or error type is imported in one of the modules defining one of the ASEs, where a suitable value is assigned. This assumes that the exporting protocol uses the two-step approach for the definition of operation and errors or that the required operations and error types are included in a central registry.
+- iv) The operation or error is completely re-defined. Although part of the original definition (e.g. the type of the argument) may be imported.
+
+## 4.6 Data types specifications
+
+### 4.6.1 General
+
+As stated in the previous clause, the type of the information which may accompany an operation invocation, the report of a success or the report of a failure is specified as an ASN.1 data type. This is also valid for the information which may be exchanged as user data of the dialogue portion.
+
+This data type can be a simple built-in type (e.g. integer type, boolean type, null type, octet string type, etc.) or structured one (e.g. sequence type, sequence-of type, choice type, etc). It may also be derived from these types by sub-typing (e.g. size constraint, value range) or tagging.
+
+### 4.6.2 Use of tags
+
+ASN.1 provides a tagging mechanism which allows for defining a type isomorphic to an existing one which thus differs only by virtue of its tag.
+
+As clearly stated in Recommendation X.208 (ASN.1), tags are intended for machine use mainly to ease the decoding process.
+
+Tags are not intended to be used for direct identification of information elements as they are seen from a local application process point of view. How these information elements are locally identified is an implementation matter and depends on the software design and on the language used to manipulate the internal data representation. In this respect, it should be noticed that distinct tags are mainly required in one of the following situations:
+
+- the information elements are members of a (non-ordered) set (i.e. a set type) and therefore their relative position cannot be used to discriminate between two information elements of the same type (thus with the same tag);
+- the information elements are members of an ordered set (i.e. a sequence type) but the presence or absence of optional elements makes it impossible to discriminate between the presence of an optional element and the presence of an immediately following information element of the same type;
+- when two occurrences of the same base type appear in a choice type.
+
+There are four classes of tags. In addition to the Universal class which is used to identify a built-in type, three classes are defined to enable the definition of isomorphic types for decoding purposes:
+
+- The *APPLICATION-WIDE class* – Tags allocated in this class can be used to identify directly the structure of the data type to be decoded. Tags allocated in this class are significant across an application and shall not be used when there is a risk of clash between values. The APPLICATION-WIDE class should be used only if the application is a "closed" domain or if there is a common registry.
+
+- The *CONTEXT-SPECIFIC class* – Tags allocated in this class are only significant in a defined domain. Therefore the decoding process identifies the data structure to be decoded both from the tag value and the context in which it appears. There is a common understanding to consider the context to be restricted to the next higher construction.
+- The *PRIVATE class* which has very similar property to the APPLICATION-WIDE class but is outside the scope of standardization.
+
+It should be noticed that the CONTEXT-SPECIFIC class is the only one (when used correctly) which ensures that there will never be any conflict between values, when data types are imported and exported between modules or protocols.
+
+### 4.6.3 Instances and types
+
+There is a need to clearly differentiate a data type from an instance of a data type (i.e. the actual information elements carried in a message or a sub-structure). For specification and readability purposes, ASN.1 provides a NamedType notation which enables to qualify a specific instance of a data type using an ASN.1 identifier.
+
+It should be noticed that there is no need to define one data type per information element. When two information elements are syntactically equivalent it is obviously more convenient to represent them as two instances of the same data type, or if required for decoding, as instances of two types derived from the same data type by CONTEXT-SPECIFIC tagging and whose definitions will thus appear only within the higher construction definition (i.e. the tagged are only defined in the specific context of the higher construction).
+
+### 4.6.4 Exporting and importing data types
+
+TC based signalling protocols may have to make use of information elements defined in other signalling protocol specifications. Rather than defining a new information element it should be preferred to import the associated type from the specifications where it has been defined first. Data types can be imported formally or informally depending on the way the exporting protocol is specified.
+
+- The exporting protocol is specified using an ASN.1 module which exports the required data types: these data types can be formally imported in one of the modules which define the new protocol.
+- The exporting protocol is not specified using ASN.1 modules: a convenient solution is to define a data type isomorphic to the "octet string" type and to specify informally its internal structure using a reference to the specification where it is defined (i.e. using a comment statements).
+
+## 4.7 How to specify abstract syntaxes
+
+ASE and AC specifications imply that a reference is made to one or several abstract-syntaxes. Each of them represents at an abstract level (i.e. independently of the encoding techniques) sets of data values which may be exchanged during the communication.
+
+There is currently no need for explicitly assigning a name to the abstract-syntax formed by TC messages for a given application because this abstract-syntax is implicitly identified by the subsystem number which addresses the AE. However the structure of the user information conveyed in the dialogue portion shall be defined as part or one or several other(s) abstract-syntax(es).
+
+Thus a protocol designer which wants user-information which are not components to be conveyed by TC shall first define one or several abstract syntax(es) which encompasses all the data types whose values may be conveyed.
+
+It shall also assign a name to each of these abstract-syntaxes. Such a name which is a value of type OBJECT IDENTIFIER will serve as a direct-reference when the actual value will be carried as part of a constructed value of type EXTERNAL, as specified in Recommendation Q.773.
+
+There is currently no formal way to specify an abstract-syntax; however, when this syntax can be described using ASN.1 the simplest manner is to define a choice type built from all the data types which form the abstract syntax.
+
+An abstract syntax can then be informally defined by the following sentence to be included in the protocol specifications:
+
+"The set of data values of type Module-X. Type-A forms an abstract syntax which is identified by the following abstract-syntax-name: APPLICATION-CONTEXT ::= { &associationContract &dialogueMode &termination &componentGrouping &dialogueAndComponentGrouping &AdditionalASEs &AbstractSyntaxes } | CLASS CONTRACT, DialogueMode, Termination OPTIONAL, BOOLEAN DEFAULT TRUE, BOOLEAN DEFAULT TRUE, OBJECT IDENTIFIER OPTIONAL, ABSTRACT-SYNTAX,| +|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------| + +| | | +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| +| &applicationContextName
}
WITH SYNTAX
{
CONTRACT
DIALOGUE MODE
[TERMINATION
[COMPONENT GROUPING ALLOWED
[DIALOGUE WITH COMPONENTS ALLOWED
[ADDITIONAL ASEs
ABSTRACT SYNTAXES
APPLICATION CONTEXT NAME
} | OBJECT IDENTIFIER UNIQUE
&associationContract
&dialogueMode
&termination]
&componentGrouping]
&dialogueAndComponentGrouping]
&AdditionalASEs]
&AbstractSyntaxes
&applicationContextName | +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| + +**DialogueMode ::= ENUMERATED {structured (1), unstructured (2)}** + +**Termination ::= ENUMERATED {basic (1), prearranged (2)}** + +The **&associationContract** field identifies the association contract which is realized by this application context. + +The **&dialogueMode** field indicates whether this application context makes use of the dialogue structured mode facilities or the dialogue unstructured mode facilities. If the association contract definition includes a connection package, the **&dialogueMode** field shall indicate "structured". + +The **&termination** field indicates whether basic or prearranged termination is used to end the dialogue. If this field is absent, the application-context definition does not place any constraint on which end method is used. + +The **&componentGrouping** field indicates whether components might be grouped in a single message. If this field is absent, the application-context definition does not place any restrictions on this issue. + +The **&dialogueAndComponentGrouping** field indicates whether bind and unbind PDUs can be sent in messages which also contain components. If this field is absent, the application-context definition does not place any restrictions on this issue. + +The **&AdditionalASEs** field contains the object identifiers of the ASEs required by the application context (if any) which are not based on the use of Remote Operations. + +The **&AbstractSyntaxes** field contains the abstract syntaxes which are required for the conveyance of information between the objects, including the PDUs for invoking and reporting on the operations in the contract. + +The **&applicationContextName** field contains the value which shall be provided to TC to identify the application context. + +## **5.5 Abstract syntaxes** + +### **5.5.1 Dialogue control** + +The **&AbstractSyntaxes** field of an application-context definition must include the following abstract syntax if the **&dialogueMode** field indicates "structured". + +**dialogue-abstract-syntax ABSTRACT-SYNTAX ::= {DialoguePDU IDENTIFIED BY dialogue-as-id}** + +The **&AbstractSyntaxes** field of an application-context definition must include the following abstract syntax if the **&dialogueMode** field indicates "unstructured". + +**uniDialogue-abstract-syntax ABSTRACT-SYNTAX ::= {UniDialoguePDU IDENTIFIED BY uniDialogue-as-id}** + +### 5.5.2 User-defined syntaxes + +#### 5.5.2.1 General + +The &AbstractSyntaxes field of an application-context definition must include one or more abstract syntaxes to represent the TC messages (including the components) and the bind and unbind PDUs. Such abstract syntaxes must be defined by the application designer. + +TC messages are defined in Recommendation Q.773 while bind and unbind PDUs are defined in Recommendation X.880. + +How many abstract syntaxes are defined to support a particular application context is up to the application designer. However, the following rules shall be followed: + +- a) If the application context realizes an association contract which includes a connection package, the values of the data types: + +**Bind{ac.&associationContract.&connection.&bind}** +**Unbind{ac.&associationContract.&connection.&unbind}** + +shall appear in at least one of these abstract syntaxes. + +- b) For each operation *op* involved in the set of operation packages used by the application context, there shall be at least one of the abstract syntaxes which include the values of the following types: + +**Invoke {TCInvokeIds, OPERATION:op}** +**ReturnResult {OPERATION:op}** + +- c) For each error *err* involved in the set of operation packages used by the application context, there shall be at least one of the abstract syntaxes which include the values of the following types: + +**ReturnError {ERROR:err}** + +- d) At least one of the abstract syntaxes shall include: + +**Reject** + +#### 5.5.2.2 Defining the abstract syntaxes + +Given an operation package, a single abstract syntax which allows the exchange of TC messages carrying invocation and reporting for all of its operations can be defined using the following data type: + +**TCSingleAS {OPERATION-PACKAGE: package} ::= TCMessage { {AllOperations {package}}, {AllOperations {package}} }** + +Or alternatively a pair of abstract syntaxes can be defined based upon the pair of types: + +**TCConsumerAS {OPERATION-PACKAGE: package} ::= TCMessage { {ConsumerPerforms {package}}, {ConsumerPerforms {package}} }** + +**TCSupplierAS {OPERATION-PACKAGE: package} ::= TCMessage { {SupplierPerforms {package}}, {SupplierPerforms {package}} }** + +A single abstract syntax may accommodate a set of packages, provided that the operation and error codes are unique. For example, the following data type can be used as the basis of a single abstract syntax to accommodate all the operation packages involved in an association contract: + +``` + +AllPackagesAS {APPLICATION-CONTEXT:ac} ::= + TCSingleAS + { + combine + { + { + ac.&associationContract.&OperationsOf + | ac.&associationContract.&InitiatorConsumerOf + | ac.&associationContract.&InitiatorSupplierOf + } + {}, + {} + } + } + +``` + +An independent abstract syntax can be defined to represent values of bind and unbind PDUs based on the following type: + +``` + +ConnectionAS {APPLICATION-CONTEXT:ac} ::= CHOICE +{ + bind Bind{ac.&associationContract.&connection.&bind}, + unbind Unbind{ac.&associationContract.&connection.&unbind} +} + +``` + +The object identifier value allocated to this abstract syntax should be included in the &abstract-syntax-name multivalued field of the application-context definition. It is intended to serve as direct reference when values of these PDUs are conveyed in the user-information parameter of Dialogue Control PDUs or directly as value of the Dialogue Portion. + +Additional abstract syntaxes may also be defined to represent values of the PDUs associated with non ROS-based ASEs (see the example in 4.7). + +## 5.6 Notation extension + +The following ASN.1 module contains definitions which enable the designer of a TC-user protocol to specify application contexts and abstract syntaxes as instances of appropriate information object classes. + +``` + +TC-Notation-Extensions {ccitt recommendation q 775 modules(2) notation-extension(4) version1(1)} + +``` + +``` + +DEFINITIONS ::= + +``` + +``` + +BEGIN + +``` + +``` + +IMPORTS + +``` + +``` + +TCMessage{} FROM TCAPMessages {ccitt recommendation q 773 modules(2) messages(1) version3(3)} + +``` + +``` + +Bind{}, Unbind{} FROM Remote-Operations-Generic-ROS-PDUs {joint-iso-ccitt remote-operations(4) generic-ROS-PDUs(6) version1(0)} + +``` + +``` + +AllOperations{}, ConsumerPerforms{}, SupplierPerforms{}, combine{} FROM Remote-Operations-Useful-Definitions {joint-iso-ccitt remote-operations(4) useful-definitions(7) version1(0)} + +``` + +``` + +CONTRACT, OPERATION-PACKAGE FROM Remote-Operations-Information-Objects {joint-iso-ccitt remote-operations(4) informationObjects(5) version1(0)} + +``` + +``` + +UniDialoguePDU, uniDialogue-as-id FROM UnidialoguePDUs +{ccitt recommendation q 773 modules(2) unidialoguePDUs(3) version1(1)} + +``` + +DialoguePDU, dialogue-as-id FROM DialoguePDUs + {ccitt recommendation q 773 modules(2) dialoguePDUs(2) version1(1)} + +APPLICATION-CONTEXT ::= CLASS + { + &associationContract CONTRACT, + &dialogueMode DialogueMode, + &termination Termination OPTIONAL, + &componentGrouping BOOLEAN DEFAULT TRUE, + &dialogueAndComponentGrouping BOOLEAN DEFAULT TRUE, + &AdditionalASEs OBJECT IDENTIFIER OPTIONAL, + &AbstractSyntaxes ABSTRACT-SYNTAX, + &applicationContextName OBJECT IDENTIFIER UNIQUE + } + +WITH SYNTAX + { + CONTRACT &associationContract + DIALOGUE MODE &dialogueMode + [TERMINATION &termination] + [COMPONENT GROUPING ALLOWED &componentGrouping] + [DIALOGUE WITH COMPONENTS ALLOWED &dialogueAndComponentGrouping] + [ADDITIONAL ASEs &AdditionalASEs] + ABSTRACT SYNTAXES &AbstractSyntaxes + APPLICATION CONTEXT NAME &applicationContextName + } + +DialogueMode ::= ENUMERATED {structured (1), unstructured (2)} + +Termination ::= ENUMERATED {basic (1), prearranged (2)} + +dialogue-abstract-syntax ABSTRACT-SYNTAX ::= {DialoguePDU IDENTIFIED BY dialogue-as-id} + +uniDialogue-abstract-syntax ABSTRACT-SYNTAX ::= {UniDialoguePDU IDENTIFIED BY uniDialogue-as-id} + +TCSingleAS {OPERATION-PACKAGE: package} ::= TCMessage { {AllOperations {package}}, {AllOperations {package}} } + +TCConsumerAS {OPERATION-PACKAGE: package} ::= TCMessage { {ConsumerPerforms {package}}, {ConsumerPerforms {package}} } + +TCSupplierAS {OPERATION-PACKAGE: package} ::= TCMessage { {SupplierPerforms {package}}, {SupplierPerforms {package}} } + +AllPackagesAS {APPLICATION-CONTEXT:ac} ::= + TCSingleAS + { + combine + { + { + ac.&associationContract.&OperationsOf + | ac.&associationContract.&InitiatorConsumerOf + | ac.&associationContract.&InitiatorSupplierOf + }, + {}, + {} + } + } + } + +``` +ConnectionAS {APPLICATION-CONTEXT:ac} ::= CHOICE +{ + bind Bind{ac.&associationContract.&connection.&bind}, + unbind Unbind{ac.&associationContract.&connection.&unbind} +} +END +``` + + + +# ITU-T RECOMMENDATIONS SERIES + +- Series A Organization of the work of the ITU-T +- Series B Means of expression: definitions, symbols, classification +- Series C General telecommunication statistics +- Series D General tariff principles +- Series E Overall network operation, telephone service, service operation and human factors +- Series F Non-telephone telecommunication services +- Series G Transmission systems and media, digital systems and networks +- Series H Audiovisual and multimedia systems +- Series I Integrated services digital network +- Series J Transmission of television, sound programme and other multimedia signals +- Series K Protection against interference +- Series L Construction, installation and protection of cables and other elements of outside plant +- Series M TMN and network maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits +- Series N Maintenance: international sound programme and television transmission circuits +- Series O Specifications of measuring equipment +- Series P Telephone transmission quality, telephone installations, local line networks +- Series Q Switching and signalling** +- Series R Telegraph transmission +- Series S Telegraph services terminal equipment +- Series T Terminals for telematic services +- Series U Telegraph switching +- Series V Data communication over the telephone network +- Series X Data networks and open system communication 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b/marked/Q/T-REC-Q.786-199303-I_PDF-E/raw.md @@ -0,0 +1,1170 @@ + + + + +ITU logo: A globe with a lightning bolt and the letters ITU. + +INTERNATIONAL TELECOMMUNICATION UNION + +**ITU-T** + +**Q.786** + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +(03/93) + +**SPECIFICATIONS +OF SIGNALLING SYSTEM No. 7** + +--- + +**SIGNALLING SYSTEM No. 7** + +**SCCP TEST SPECIFICATION** + +**ITU-T Recommendation Q.786** + +(Previously "CCITT Recommendation") + +--- + +# FOREWORD + +The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecommunication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. + +ITU-T Recommendation Q.786 was revised by the ITU-T Study Group XI (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). + +--- + +# NOTES + +1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. + +In order not to delay publication of this Recommendation, no change has been made in the text to references containing the acronyms "CCITT, CCIR or IFRB" or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. + +2 In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +# CONTENTS + +*Page* + +| | | | +|-----|-------------------------------------------|---| +| 1 | Introduction ..... | 1 | +| 2 | Objective of the test specification ..... | 1 | +| 3 | Scope of the test ..... | 1 | +| 4 | General principles of tests ..... | 2 | +| 5 | Test environment..... | 2 | +| 5.1 | SCCP relation ..... | 2 | +| 5.2 | Configuration..... | 2 | +| 6 | Test traffic ..... | 3 | +| 7 | SCCP test list..... | 3 | + + + +# SIGNALLING SYSTEM No. 7 + +# SCCP TEST SPECIFICATION + +(Helsinki, 1993) + +# 1 Introduction + +This Recommendation contains a detailed set of tests for the Signalling System No. 7 Signalling Connection Control Part (SCCP). These tests are intended to validate the protocol specified in Recommendations Q.711-Q.714. This Recommendation conforms to Recommendation Q.780, which describes the basic rules of the test specification. + +# 2 Objective of the test specification + +The objective of the test specification is to provide: + +*Validation* – A level of confidence that a given implementation conforms to the Recommendations Q.711-Q.714 for SS No. 7 SCCP. + +*Compatibility* – A level of confidence that two implementations of SS No. 7 SCCP are able to interwork. + +In order to ensure that this test specification meets this objective, the following criteria are used: + +- 1) The test specification is not intended to provide exhaustive testing of all aspects of the SS No. 7 SCCP. +- 2) All tests should be of a practical nature and implementable using the available technology. +- 3) The test should concentrate on the testing of a normal signalling procedure. Testing of an abnormal signalling procedure will only be identified where this is regarded as particularly useful. +- 4) The test list does not include any tests which are application specific (e.g. IN, mobile application, etc.). If such tests are required, they should be contained in application specific testing documentation. + +# 3 Scope of the test + +The test list is composed to validate routing/addressing and data transfer concerning connectionless SCCP procedures by monitoring and analysing SCCP messages and their contents. SCCP management, segmentation in connectionless SCCP test and connection-oriented procedures are for further study. + +Some tests in this Recommendation require generation of primitives, therefore when performing these tests, appropriate normal system action of the user will have to be chosen which results indicating primitives being generated. + +The testing of primitives is outside the scope of this Recommendation. Both messages and primitives are shown in expected message sequence diagram as indicated below, but primitives are shown for ease of understanding only. + +PRIMITIVE + + + +A double-lined arrow pointing to the right, representing a primitive in a message sequence diagram. + +MESSAGE + + + +A dotted arrow pointing to the right, representing a message in a message sequence diagram. + +An internal routing of SCCP user data is implementation dependent, and therefore all tests related to internal routing may not be possible to execute. In addition, access to various test interfaces may not be available in all implementations. + +# 4 General principles of tests + +The tests are described as “Validation(VAT)” tests or “Validation” and “Compatibility(CPT)” tests. Each test description indicates in the field “type of test” whether the test is a “Validation” test or a “Validation” and “Compatibility” test. + +All questions and checks in the test description should be answered with positive acknowledgement for correct operations. + +Where particular failure conditions are tested with or without the return option set, the test with the return option not set should use the same pre-test conditions and data, with the exception of the return option parameter as the corresponding test with the return option set. + +Some of the described validation tests may not be required to be executed, since the functionality they aim to test is not included in the Implementation Under Test (IUT). In such a case the non-execution of such a test should not be regarded as a non-conformance statement. + +For the test cases which result in returning N-NOTICE indication primitive or UDT message, N-UNIDATA request primitive or UDT message should include the sufficient information to return the N-NOTICE indication primitive or UDT message. + +# 5 Test environment + +## 5.1 SCCP relation + +A signalling relation is required between “SP A” and “SP B” or among “SP A”, “SP B” and “SP C” in order to carry out effective tests. Tested MTPs should be used for compatibility tests. + +## 5.2 Configuration + +Two configurations are required to perform these tests as shown in Figure 1 and Figure 2. + + + +The diagram shows two rectangular boxes representing Service Points (SP). The left box is labeled 'SP' and 'A' inside, with '(Under test)' written below it. The right box is labeled 'SP' and 'B' inside, with 'T1155400-93/d01' written below it. A horizontal arrow points from the right side of the left box to the left side of the right box. Another horizontal arrow points from the left side of the right box to the right side of the left box. The word '(Note)' is written between the two arrows. + +Diagram of SCCP relation between SP A and SP B + +NOTE – The arrows indicate an SCCP relation. + +FIGURE 1/Q.786 +**Test configuration for SCCP – Configuration 1** + + + +The diagram shows three rectangular boxes representing Service Points (SP). The left box is labeled 'SP' and 'C' inside, with '(Note 1)' written below it. The middle box is labeled 'SP' and 'A' inside, with '(Under test)' and '(Note 2)' written below it. The right box is labeled 'SP' and 'B' inside, with 'T1155410-93/d02' and '(Note 1)' written below it. A horizontal arrow points from the right side of the left box to the left side of the middle box. Another horizontal arrow points from the left side of the middle box to the right side of the left box. A third horizontal arrow points from the right side of the middle box to the left side of the right box. A fourth horizontal arrow points from the left side of the right box to the right side of the middle box. + +Diagram of SCCP relation between SP C, SP A, and SP B + +# NOTES + +- 1 The arrows indicate an SCCP relation. +- 2 SP A is used as relay point. + +FIGURE 2/Q.786 +**Test configuration for SCCP – Configuration 2** + +The configurations shown above are functional representations only, e.g. in Configuration 2, SP B and SP C could be the same or could belong to different MTP networks. + +# 6 Test traffic + +The details for test traffic and its format are for further study. + +# 7 SCCP test list + +\* VAT & CPT + +# 1 Connectionless procedure + +## 1.1 SCCP Routing + +### 1.1.1 Messages from SCCP users + +#### 1.1.1.1 Route not on GT + +##### 1.1.1.1.1 Local DPC and SSN included, DPC and SSN available + +###### 1.1.1.1.1.1 GT and SSN included + +###### 1.1.1.1.1.2 GT not included, SSN included + +##### 1.1.1.1.2 Local DPC and SSN included, SSN unavailable – Return option set + +##### 1.1.1.1.3 Local DPC and SSN included, SSN unavailable – Return option not set + +##### \* 1.1.1.1.4 Remote DPC and SSN included, DPC and SSN available + +##### 1.1.1.1.5 Remote DPC and SSN included, DPC and/or SSN unavailable – Return option set + +##### 1.1.1.1.6 Remote DPC and SSN included, DPC and/or SSN unavailable – Return option not set + +#### 1.1.1.2 Route on GT + +##### 1.1.1.2.1 GT translated to local DPC and SSN, and SSN available + +###### 1.1.1.2.1.1 SSN and GT included + +###### 1.1.1.2.1.2 SSN not included , GT included + +##### 1.1.1.2.2 GT translated to local DPC and SSN, and SSN unavailable – Return option set + +##### 1.1.1.2.3 GT translated to local DPC and SSN, and SSN unavailable – Return option not set + +##### 1.1.1.2.4 GT translated to remote DPC and SSN, and DPC and SSN available + +###### 1.1.1.2.4.1 SSN and GT included + +###### \* 1.1.1.2.4.2 SSN not included , GT included + +##### 1.1.1.2.5 GT translated to remote DPC and SSN, and DPC and/or SSN unavailable – Return option set + +##### 1.1.1.2.6 GT translated to remote DPC and SSN, and DPC and/or SSN unavailable – Return option not set + +##### \* 1.1.1.2.7 GT translated to DPC and new or as same GT, and DPC available + +##### 1.1.1.2.8 GT translation failed – Return option set + +##### 1.1.1.2.9 GT translation failed – Return option not set + +### 1.1.2 Messages from MTP + +#### 1.1.2.1 Route on GT + +##### \* 1.1.2.1.1 GT translated to local DPC and SSN, and SSN available + +##### \* 1.1.2.1.2 GT translated to local DPC and SSN, and SSN unavailable – Return option set + +##### \* 1.1.2.1.3 GT translated to local DPC and SSN, and SSN unavailable – Return option not set + +##### \* 1.1.2.1.4 GT translated to remote DPC and SSN, and DPC and SSN available + +##### \* 1.1.2.1.5 GT translated to remote DPC and SSN, and DPC and/or SSN unavailable – Return option set + +- \* 1.1.2.1.6 GT translated to remote DPC and SSN, and DPC and/or SSN unavailable – Return option not set +- \* 1.1.2.1.7 GT translated to DPC and new or as same GT, and DPC available +- \* 1.1.2.1.8 GT translation failed – Return option set +- \* 1.1.2.1.9 GT translation failed – Return option not set +- 1.1.2.2 Route not on GT + - 1.1.2.2.1 Local DPC and SSN, and SSN available + - 1.1.2.2.1.1 GT and SSN included + - \* 1.1.2.2.1.2 GT not included, SSN included + - \* 1.1.2.2.2 Local DPC and SSN unavailable – Return option set + - \* 1.1.2.2.3 Local DPC and SSN unavailable – Return option not set +- 1.2 Data transfer + - 1.2.1 Data transfer with sequential delivery capability + - \* 1.2.1.1 At originating node + - \* 1.2.1.2 At relay node + - 1.2.2 Data transfer with syntax error + - 1.2.3 Message Return + - 1.2.3.1 UDTS deliverable + - 1.2.3.1.1 UDTS deliverable to SCCP user + - 1.2.3.1.2 UDTS deliverable to other SP + - 1.2.3.2 UDTS undeliverable + - 1.2.3.2.1 UDTS undeliverable to SCCP user + - 1.2.4 Segmentation + - Further Study +- 2 SCCP management** + - Further Study +- 3 Connection-oriented procedure** + - Further Study + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | +|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------|----------------|------|------|---------------------------------------------------------|--| +| TEST NUMBER: 1.1.1.1.1.1 | | | | | | | +| REFERENCE: 2.3.2.3) c)/Q.714 | | | | | | | +| TITLE: Message from SCCP users, route not on GT. | | | | | | | +| SUBTITLE: Local DPC and SSN included, DPC and SSN available GT and SSN included. | | | | | | | +| PURPOSE: To verify that the user data can be delivered to the correct SCCP user at SP A when routing not on GT. | | | | | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– DPC of SP A
– SSN
– GT
2. Arrange the SCCP routing control data as follows:
– SSN at SP A available | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B |
| N-UNITDATA req. > N-UNITDATA ind. |
N-UNITDATA req.
>
N-UNITDATA ind.
| | +| SP A | SP B | | | | | | +|
N-UNITDATA req.
>
N-UNITDATA ind.
| | | | | | | +| TEST DESCRIPTION | | | | | | | +| 1. | Arrange SP A to request delivery of user data to an SCCP user at SP A with a DPC and SSN of SP A in the request. | | | | | | +| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | +| 3. | CHECK A: CONFIRM THAT NO MESSAGES WERE SENT BY SP A TO SP B. | | | | | | +| 4. | CHECK B: WAS THE DATA CORRECTLY DELIVERED TO THE SCCP USER AT SP A? | | | | | | + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | +|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------|----------------|------|------|----------------------------------------------|--| +| TEST NUMBER: 1.1.1.1.1.2 | | | | | | | +| REFERENCE: 2.3.2.3) c)/Q.714 | | | | | | | +| TITLE: Messages from SCCP users, route not on GT. | | | | | | | +| SUBTITLE: Local DPC and SSN included, DPC and SSN available GT not included, SSN included. | | | | | | | +| PURPOSE: To verify that the user data can be delivered to the correct SCCP user at SP A when routing not on GT. | | | | | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– DPC of SP A
– SSN
– no GT
2. Arrange the SCCP routing control data as follows:
– SSN at SP A available | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B |
| N-UNITDATA req. > N-UNITDATA ind. < |
>
N-UNITDATA ind.
< | | +| SP A | SP B | | | | | | +| N-UNITDATA req.
>
N-UNITDATA ind.
< | | | | | | | +| TEST DESCRIPTION | | | | | | | +| 1. | Arrange SP A to request delivery of user data to a SCCP user at SP A with a DPC and SSN of SP A in the request. | | | | | | +| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | +| 3. | CHECK A: CONFIRM THAT NO MESSAGES WERE SENT BY SP A TO SP B. | | | | | | +| 4. | CHECK B: WAS THE DATA CORRECTLY DELIVERED TO THE SCCP USER AT SP A? | | | | | | + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | | | +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------|----------------|------|------|----------------------|--|--------------------|--| +| TEST NUMBER: 1.1.1.1.2 | | | | | | | | | +| REFERENCE: 2.3.2 3) b)/Q.714 | | | | | | | | | +| TITLE: Messages from SCCP users, route not on GT. | | | | | | | | | +| SUBTITLE: Local DPC and SSN included, SSN unavailable – Return option set. | | | | | | | | | +| PURPOSE: To verify that data is returned when routing not on GT and return option is set. | | | | | | | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– DPC of SP A
– SSN
2. Arrange return option in N-UNITDATA request to be set
3. Arrange the SCCP routing control data as follows:
– SSN at SP A unavailable | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B |
| N-UNITDATA req. > | |
| N-NOTICE ind. < |
> | | N-NOTICE ind.
< | | +| SP A | SP B | | | | | | | | +| N-UNITDATA req.
> | | | | | | | | | +| N-NOTICE ind.
< | | | | | | | | | +| TEST DESCRIPTION | | | | | | | | | +| 1. | Arrange SP A to request delivery of user data to an SCCP user at SP A with a DPC and SSN of SP A in the request. | | | | | | | | +| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | | | +| 3. | CHECK A: CONFIRM THAT NO MESSAGES WERE SENT BY SP A TO SP B. | | | | | | | | +| 4. | CHECK B: WAS THE SCCP USER ADVISED OF AN APPROPRIATE REASON FOR RETURN? | | | | | | | | + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | +|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------|----------------|------|------|--------------------------|--| +| TEST NUMBER: 1.1.1.1.3 | | | | | | | +| REFERENCE: 2.3.2.3) b)/Q.714 | | | | | | | +| TITLE: Messages from SCCP users, route not on GT. | | | | | | | +| SUBTITLE: Local DPC and SSN included, SSN unavailable – Return option not set. | | | | | | | +| PURPOSE: To verify that data is not returned when routing not on GT and return option is not set. | | | | | | | +| PRE-TEST CONDITIONS:
- 1. Arrange the called address in N-UNITDATA request to contain:
- – DPC of SP A
- – SSN
- 2. Arrange return option in N-UNITDATA request not to be set
- 3. Arrange the SCCP routing control data as follows:
- – SSN at SP A unavailable
| SP A | SP B |
N-UNITDATA req. > |
N-UNITDATA req.
> | | +| SP A | SP B | | | | | | +|
N-UNITDATA req.
> | | | | | | | +| TEST DESCRIPTION | | | | | | | +| 1. | Arrange SP A to request delivery of user data to an SCCP user at SP A with a DPC and SSN of SP A in the request. | | | | | | +| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | +| 3. | CHECK A: CONFIRM THAT NO MESSAGES WERE SENT BY SP A TO SP B. | | | | | | +| 4. | CHECK B: CONFIRM THAT DATA WAS NOT RETURNED TO SCCP USER. | | | | | | + +**SCCP TEST SPECIFICATION** + +| | | | | | | | | | | | | | | | | | +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------|----------------|------------------|--|----|-------------------------------------------------------------------------------------|----|--------------------------------------------------------------------|----|-------------------------------------------------------------------|----|--------------------------------------------------------------------------------------------------------------------|----|-----------------------------------------------------------------------------------------|----|---------------------------------------------| +| TEST NUMBER: 1.1.1.1.4 | | | | | | | | | | | | | | | | | +| REFERENCE: 2.3.2 3) a)/Q.714 | | | | | | | | | | | | | | | | | +| TITLE: Messages from SCCP users, route not on GT. | | | | | | | | | | | | | | | | | +| SUBTITLE: Remote DPC and SSN included, DPC and SSN available. | | | | | | | | | | | | | | | | | +| PURPOSE: To verify that a UDT message can be generated correctly to SP B when routing not on GT. | | | | | | | | | | | | | | | | | +| PRE-TEST CONDITIONS:
- 1. Arrange the called address in N-UNITDATA request to contain:
- – DPC of SP B
- – SSN
- – no GT
- 2. Arrange the SCCP routing control data as follows:
- – DPC at SP B available
- – SSN at SP B available
SP A SP B N-UNITDATA req. > UDT >
| TEST DESCRIPTION | |
| 1. | Arrange SP A to request generating a UDT message to SP B with a remote DPC and SSN. |
| 2. | Record the message sequence and parameters using a signal monitor. |
| 3. | CHECK A: WAS THE UDT MESSAGE CORRECTLY GENERATED BY SP A TO SP B? |
| 4. | CHECK B: WAS THE POINT CODE OF SP B CONTAINED IN THE MTP ROUTING LABEL OF THE UDT MESSAGE AND WAS THE SIO CORRECT? |
| 5. | CHECK C: WERE THE PARAMETER FIELDS SET CORRECTLY AS INDICATED IN THE CHECK TABLE BELOW? |
| 6. | CHECK D: WAS THE MESSAGE SEQUENCE AS ABOVE? |
or
10000000 (Class 0, Return option is set)
or
00000001 (Class 1, Return option is not set)
or
10000001 (Class 1, Return option is set) | +| Called Party Address | | +| 2) Point Code Indicator (Note): | 0 (Signalling point code is not included)
or
1 (Signalling point code is included) | +| 3) SSN Indicator: | 1 (SSN is included) | +| 4) Global Title Indicator: | 0000 (No global title is included) | +| 5) Routing Indicator: | 1 (Routing on DPC) | +| 6) Signalling Point Code (Note): | DPC of SP B (if Point Code Indicator equals to 1) | +| 7) Sub-system Number: | SSN at SP B | +| NOTE – Inclusion of DPC in Called Party Address is implementation dependent for this test. | | + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | | | +|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------|----------------|------|------|----------------------|--|--------------------|--| +| TEST NUMBER: 1.1.1.1.5 | | | | | | | | | +| REFERENCE: 2.3.2.3) b)/Q.714 | | | | | | | | | +| TITLE: Messages from SCCP users, route not on GT. | | | | | | | | | +| SUBTITLE: Remote DPC and SSN included, DPC and/or SSN unavailable – Return option set. | | | | | | | | | +| PURPOSE: To verify that data is returned when routing not on GT and return option is set. | | | | | | | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– DPC of SP B
– SSN
– no GT
2. Arrange return option in N-UNITDATA request to be set
3. Arrange the SCCP routing control data as follows:
– DPC of SP B unavailable and/or
– SSN at SP B unavailable | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B |
| N-UNITDATA req. > | |
| N-NOTICE ind. < |
> | | N-NOTICE ind.
< | | +| SP A | SP B | | | | | | | | +| N-UNITDATA req.
> | | | | | | | | | +| N-NOTICE ind.
< | | | | | | | | | +| TEST DESCRIPTION | | | | | | | | | +| 1. | Arrange SP A to request delivery of user data to SP B with a remote DPC and SSN. | | | | | | | | +| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | | | +| 3. | CHECK A: CONFIRM THAT NO MESSAGES WERE SENT BY SP A TO SP B. | | | | | | | | +| 4. | CHECK B: WAS THE SCCP USER ADVISED OF AN APPROPRIATE REASON FOR RETURN? | | | | | | | | + +# **SCCP TEST SPECIFICATION** + +| | | | +|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------|----------------| +| TEST NUMBER: 1.1.1.1.6 | | | +| REFERENCE: 2.3.2.3) b)/Q.714 | | | +| TITLE: Messages from SCCP users, route not on GT. | | | +| SUBTITLE: Remote DPC and SSN included, DPC and/or SSN unavailable – Return option not set. | | | +| PURPOSE: To verify that data is not returned when routing not on GT and return option is not set. | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– DPC of SP B
– SSN
– no GT
2. Arrange return option in N-UNITDATA request not to be set
3. Arrange the SCCP routing control data as follows:
– DPC of SP B unavailable and/or
– SSN at SP B unavailable | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | +| EXPECTED MESSAGE SEQUENCE:
SP A SP B
N-UNITDATA req.
=====>
| | |
+| TEST DESCRIPTION | | |
+| 1. | Arrange SP A to request delivery of user data to SP B with a remote DPC and SSN. | |
+| 2. | Record the message sequence and parameters using a signal monitor. | |
+| 3. | CHECK A: CONFIRM THAT NO MESSAGES WERE SENT BY SP A. | |
+| 4. | CHECK B: CONFIRM THAT DATA WAS NOT RETURNED TO SCCP USER. | |
+
+# **SCCP TEST SPECIFICATION**
+
+| | | | | | | | | |
+|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------|----------------|------|------|----------------------|--|----------------------|--|
+| TEST NUMBER: 1.1.1.2.1.1 | | | | | | | | |
+| REFERENCE: 2.3.2.4) a) i)/Q.714 | | | | | | | | |
+| TITLE: Messages from SCCP users, route on GT. | | | | | | | | |
+| SUBTITLE: GT translated to local DPC and SSN, and SSN available SSN and GT included. | | | | | | | | |
+| PURPOSE: To verify that the translation based on GT can be performed correctly to a local DPC and SSN and the user data can be delivered to the SCCP user at SP A. | | | | | | | | |
+| PRE-TEST CONDITIONS:=====>
1. Arrange the called address in N-UNITDATA request to contain:
– GT
– no SSN
2. Arrange the SCCP routing control data as follows:
– GT translated to
– DPC of SP A
– new or same SSN
– SSN at SP A available | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B |
| N-UNITDATA req. > | |
| N-UNITDATA ind. < |
> | | N-UNITDATA ind.
< | | +| SP A | SP B | | | | | | | | +| N-UNITDATA req.
> | | | | | | | | | +| N-UNITDATA ind.
< | | | | | | | | | +| TEST DESCRIPTION | | | | | | | | | +| 1. | Arrange SP A to request delivery of user data to a SCCP user at SP A with a GT to be translated at SP A to a DPC and SSN of SP A. | | | | | | | | +| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | | | +| 3. | CHECK A: CONFIRM THAT NO MESSAGES WERE SENT BY SP A TO SP B. | | | | | | | | +| 4. | CHECK B: WAS THE DATA CORRECTLY DELIVERED TO THE SCCP USER AT SP A? | | | | | | | | + +# **SCCP TEST SPECIFICATION** + +| | | | +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------|----------------| +| TEST NUMBER: 1.1.1.2.1.2 | | | +| REFERENCE: 2.3.2.4) a) i)/Q.714 | | | +| TITLE: Messages from SCCP users, route on GT. | | | +| SUBTITLE: GT translated to local DPC and SSN, and SSN available SSN not included, GT included. | | | +| PURPOSE: To verify that the translation based on GT can be performed correctly to a local DPC and SSN and the user data can be delivered to the SCCP user at SP A. | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– GT
– no SSN
2. Arrange the SCCP routing control data as follows:
– GT translated to
– DPC of SP A
– SSN
– SSN at SP A available | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | +| EXPECTED MESSAGE SEQUENCE:
SP A
N-UNITDATA req.
>
N-UNITDATA ind.
<
N-UNITDATA req.
>
N-UNITDATA ind.
<
SP B
- 1. Arrange the called address in N-UNITDATA request to contain:
- – GT
- 2. Arrange return option in N-UNITDATA request to be set
- 2. Arrange the SCCP routing control data as follows:
- – GT translated to
- – DPC of SP A
- – SSN
- – SSN at SP A unavailable
- – GT translated to
| SP A | SP B |
| N-UNITDATA req. > | |
| N-NOTICE ind. < |
> | | N-NOTICE ind.
< | | +| SP A | SP B | | | | | | | | +| N-UNITDATA req.
> | | | | | | | | | +| N-NOTICE ind.
< | | | | | | | | | +| TEST DESCRIPTION | | | | | | | | | +| 1. | Arrange SP A to request delivery of user data to a SCCP user at SP A with a GT to be translated at SP A to a DPC and SSN of SP A. | | | | | | | | +| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | | | +| 3. | CHECK A: CONFIRM THAT NO MESSAGES WERE SENT BY SP A TO SP B. | | | | | | | | +| 4. | CHECK B: WAS THE SCCP USER ADVISED OF AN APPROPRIATE REASON FOR RETURN? | | | | | | | | + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | +|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------|----------------|------|------|---------------------|--| +| TEST NUMBER: 1.1.1.2.3 | | | | | | | +| REFERENCE: 2.3.2.4) a) i)/Q.714 | | | | | | | +| TITLE: Messages from SCCP users, route on GT. | | | | | | | +| SUBTITLE: GT translated to local DPC and SSN, and SSN unavailable – Return option not set. | | | | | | | +| PURPOSE: To verify that data is returned when routing on GT translates at SP A to a local DPC and an unavailable SSN and return option is not set. | | | | | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– GT
2. Arrange return option in N-UNITDATA request not to be set
3. Arrange the SCCP routing control data as follows:
– GT translated to
– DPC of SP A
– SSN
– SSN at SP A unavailable | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B |
| N-UNITDATA req. |
| | +| SP A | SP B | | | | | | +| N-UNITDATA req.
| | | | | | | +| TEST DESCRIPTION | | | | | | | +| 1. | Arrange SP A to request delivery of user data to a SCCP user at SP A with a GT to be translated at SP A to a DPC and SSN of SP A. | | | | | | +| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | +| 3. | CHECK A: CONFIRM THAT NO MESSAGES WERE SENT BY SP A TO SP B. | | | | | | +| 4. | CHECK B: CONFIRM THAT DATA WAS NOT RETURNED TO SCCP USER. | | | | | | + +# **SCCP TEST SPECIFICATION** + +| | | | +|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------|----------------| +| TEST NUMBER: 1.1.1.2.4.1 | | | +| REFERENCE: 2.3.2.4) a) ii)/Q.714 | | | +| TITLE: Messages from SCCP users, route on GT. | | | +| SUBTITLE: GT translated to remote DPC and SSN, and DPC and SSN available SSN and GT included. | | | +| PURPOSE: To verify that the translation based on GT can be performed correctly to remote DPC and SSN, and a SCCP UDT message can be generated correctly to SP B. | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– GT
– SSN
2. Arrange the SCCP routing control data as follows:
– GT translated to
– DPC of SP B
– new or same SSN
– routing on DPC-SSN
– DPC of SP B available
– SSN at SP B available | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | +| EXPECTED MESSAGE SEQUENCE:
SP A SP B
N-UNITDATA req.
=====>
UDT ----->
| | |
+| TEST DESCRIPTION | | |
+| 1. | Arrange SP A to request generating of a UDT message to SP B with a GT to be translated at SP A to a remote DPC and SSN. | |
+| 2. | Record the message sequence and parameters using a signal monitor. | |
+| 3. | CHECK A: WAS THE UDT MESSAGE CORRECTLY GENERATED BY SP A? | |
+| 4. | CHECK B: WAS THE POINT CODE OF SP B CONTAINED IN THE MTP ROUTING LABEL OF THE UDT MESSAGE AND WAS THE SIO CORRECT? | |
+| 5. | CHECK C: WERE THE PARAMETER FIELDS SET CORRECTLY AS INDICATED IN THE CHECK TABLE BELOW? | |
+| 6. | CHECK D: WAS THE MESSAGE SEQUENCE AS ABOVE? | |
+
+| | |
+|------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| TEST NUMBER: 1.1.1.2.4.1 (continued) | |
+| CHECK TABLE (1/1) | |
+| UDT (SP A → SP B) | |
+| 1) Protocol class: | 00000000 (Class 0, Return option is not set)=====>
UDT ----->
or
10000000 (Class 0, Return option is set)
or
00000001 (Class 1, Return option is not set)
or
10000001 (Class 1, Return option is set) | +| Called Party Address | | +| 2) Point Code Indicator (Note): | 0 (Signalling point code is not included)
or
1 (Signalling point code is included) | +| 3) SSN Indicator: | 1 (SSN is included) | +| 4) Global Title Indicator: | Don't care | +| 5) Routing Indicator: | 1 (Routing on DPC) | +| 6) Signalling Point Code (Note): | DPC of SP B (if Point Code Indicator equals to 1) | +| 7) Sub-system Number: | SSN at SP B (result of GT translation) | +| 8) Global Title (Note): | "Appropriate information" | +| NOTE – Inclusion of GT and/or DPC in Called Party Address is implementation dependent for this test. | | + +# **SCCP TEST SPECIFICATION** + +| | | | +|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------|----------------| +| TEST NUMBER: 1.1.1.2.4.2 | | | +| REFERENCE: 2.3.2.4) a) ii)/Q.714 | | | +| TITLE: Messages from SCCP users, route on GT. | | | +| SUBTITLE: GT translated to remote DPC and SSN, and DPC and SSN available SSN not included, GT included. | | | +| PURPOSE: To verify that the translation based on GT can be performed correctly to remote DPC and SSN, and a UDT message can be generated correctly to SP B. | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– GT
– SSN
2. Arrange the SCCP routing control data as follows:
– GT translated to
– DPC of SP B
– SSN
– routing on DPC-SSN
– DPC of SP B available
– SSN at SP B available | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT & CPT | TYPE OF SP: SP | +| EXPECTED MESSAGE SEQUENCE:
SP A SP B
N-UNITDATA req.
=====>
UDT ----->
| | |
+| TEST DESCRIPTION | | |
+| 1. | Arrange SP A to request generating of a UDT message to SP B with a GT to be translated at SP A to a remote DPC and SSN. | |
+| 2. | Record the message sequence and parameters using a signal monitor. | |
+| 3. | CHECK A: WAS THE UDT MESSAGE CORRECTLY GENERATED BY SP A? | |
+| 4. | CHECK B: WAS THE POINT CODE OF SP B CONTAINED IN THE MTP ROUTING LABEL OF THE UDT MESSAGE AND WAS THE SIO CORRECT? | |
+| 5. | CHECK C: WERE THE PARAMETER FIELDS SET CORRECTLY AS INDICATED IN THE CHECK TABLE BELOW? | |
+| 6. | CHECK D: WAS THE MESSAGE SEQUENCE AS ABOVE? | |
+
+TEST NUMBER: 1.1.1.2.4.2 (continued)
+
+## CHECK TABLE (1/1)
+
+### UDT (SP A → SP B)
+
+- | | | |
+|----|-----------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| 1) | Protocol class: | 00000000 (Class 0, Return option is not set)=====>
UDT ----->
or
10000000 (Class 0, Return option is set)
or
00000001 (Class 1, Return option is not set)
or
10000001 (Class 1, Return option is set) | +|----|-----------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| + +### Called Party Address + +- | | | | +|----|-------------------------------|------------------------------------------------------------------------------------------| +| 2) | Point Code Indicator (Note): | 0 (Signalling point code is not included)
or
1 (Signalling point code is included) | +| 3) | SSN Indicator: | 1 (SSN is included) | +| 4) | Global Title Indicator: | Don't care | +| 5) | Routing Indicator: | 1 (Routing on DPC) | +| 6) | Signalling Point Code (Note): | DPC of SP B (if Point Code Indicator equals to 1) | +| 7) | Sub-system Number: | SSN at SP B | +| 8) | Global Title (Note): | "Appropriate information" | + +NOTE – Inclusion of GT and/or DPC in Called Party Address is implementation dependent for this test. + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | | | +|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------|----------------|------|------|----------------------|--|--------------------|--| +| TEST NUMBER: 1.1.1.2.5 | | | | | | | | | +| REFERENCE: 2.3.2.4) a) iii)/Q.714 | | | | | | | | | +| TITLE: Message from SCCP users, route on GT. | | | | | | | | | +| SUBTITLE: GT translated to remote DPC and SSN, and DPC and/or SSN unavailable – Return option set. | | | | | | | | | +| PURPOSE: To verify that data is returned when routing on GT translates at SP A to an unavailable remote DPC and/or SSN and return option is set. | | | | | | | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– GT
2. Arrange return option in N-UNITDATA request to be set
3. Arrange the SCCP routing control data as follows:
– GT translated to
– DPC of SP B
– SSN
– routing on DPC-SSN
– DPC of SP B unavailable and/or
– SSN at SP B unavailable | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B |
| N-UNITDATA req. > | |
| N-NOTICE ind. < |
> | | N-NOTICE ind.
< | | +| SP A | SP B | | | | | | | | +| N-UNITDATA req.
> | | | | | | | | | +| N-NOTICE ind.
< | | | | | | | | | +| TEST DESCRIPTION | | | | | | | | | +| 1. | Arrange SP A to request delivery of user data to SP B with a GT to be translated at SP A to a remote DPC and SSN. | | | | | | | | +| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | | | +| 3. | CHECK A: CONFIRM THAT NO MESSAGES WERE SENT BY SP A TO SP B. | | | | | | | | +| 4. | CHECK B: WAS THE SCCP USER ADVISED OF AN APPROPRIATE REASON FOR RETURN? | | | | | | | | + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | | | | | +|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------|----------------|------|------|--|--|-----------------|--|---|--| +| TEST NUMBER: 1.1.1.2.6 | | | | | | | | | | | +| REFERENCE: 2.3.2.4) a) iii)/Q.714 | | | | | | | | | | | +| TITLE: Message from SCCP users, route on GT. | | | | | | | | | | | +| SUBTITLE: GT translated to remote DPC and SSN, and DPC and/or SSN unavailable – Return option not set. | | | | | | | | | | | +| PURPOSE: To verify that data is not returned when routing on GT translates at SP A to an unavailable remote DPC and/or SSN and return option is not set. | | | | | | | | | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– GT
2. Arrange return option in N-UNITDATA request not to be set
3. Arrange the SCCP routing control data as follows:
– GT translated to
– DPC of SP B
– SSN
– routing on DPC-SSN
– DPC of SP B unavailable and/or
– SSN at SP B unavailable | | | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B |
| N-UNITDATA req. | |
| > | |
1. Arrange the called address in N-UNITDATA request to contain:
– GT
2. Arrange the SCCP routing control data as follows:
– GT translated to
– new or same GT
– DPC of SP B
– routing on GT
– DPC of SP B available | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT & CPT | TYPE OF SP: SP | +| EXPECTED MESSAGE SEQUENCE:
SP A SP B
N-UNITDATA req.
=====>
UDT - - - - ->
| | |
+| TEST DESCRIPTION | | |
+| 1. | Arrange SP A to request generating of a UDT message to SP B with a GT to be translated at SP A to remote DPC and new or same GT. | |
+| 2. | Record the message sequence and parameters using a signal monitor. | |
+| 3. | CHECK A: WAS THE UDT MESSAGE CORRECTLY GENERATED BY SP A? | |
+| 4. | CHECK B: WAS THE POINT CODE OF SP B CONTAINED IN THE MTP ROUTING LABEL OF THE UDT MESSAGE AND WAS THE SIO CORRECT? | |
+| 5. | CHECK C: WERE THE PARAMETER FIELDS SET CORRECTLY AS INDICATED IN THE CHECK TABLE BELOW? | |
+| 6. | CHECK D: WAS THE MESSAGE SEQUENCE AS ABOVE? | |
+
+| | |
+|--------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| TEST NUMBER: 1.1.1.2.7 (continued) | |
+| CHECK TABLE (1/1) | |
+| UDT (SP A → SP B) | |
+| 1) Protocol class: | 00000000 (Class 0, Return option is not set)=====>
UDT - - - - ->
or
10000000 (Class 0, Return option is set)
or
00000001 (Class 1, Return option is not set)
or
10000001 (Class 1, Return option is set) | +| Called Party Address | | +| 2) Point Code Indicator (Note): | 0 (Signalling point code is not included)
or
1 (Signalling point code is included) | +| 3) SSN Indicator: | 0 (SSN is not included)
or
1 (SSN is included) | +| 4) Global Title Indicator: | 0001, 0010, 0011 or 0100 (Global Title included) | +| 5) Routing Indicator: | 0 (Routing on GT) | +| 6) Signalling Point Code (Note): | DPC of SP B (if Point Code Indicator equals to 1) | +| 7) Sub-system Number: | XXXXXXXX (if SSN Indicator equals to 1) | +| 8) Global Title: | a Global Title Data (resulting from GT translation) | +| NOTE – Inclusion of DPC in Called Party Address is implementation dependent for this test. | | + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | | | +|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|------|------|-------------------------|--|-------------------|--| +| TEST NUMBER: 1.1.1.2.8 | | | | | | | | | +| REFERENCE: 2.3.2.4) c)/Q.714 | | | | | | | | | +| TITLE: Message from SCCP users, route on GT. | | | | | | | | | +| SUBTITLE: GT translation failed – Return option set. | | | | | | | | | +| PURPOSE: To verify that data is returned when GT translation failed and return option is set. | | | | | | | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– GT
2. Arrange return option in N-UNITDATA request to be set
3. Arrange the SCCP routing control data as follows:
– GT translated to
– a GT
– DPC of SP B
– routing on GT
– DPC of SP B unavailable | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B |
N-UNITDATA req. | |
| N-NOTICE ind. |
N-UNITDATA req.
| | N-NOTICE ind.
| | +| SP A | SP B | | | | | | | | +|
N-UNITDATA req.
| | | | | | | | | +| N-NOTICE ind.
| | | | | | | | | +| TEST DESCRIPTION | | | | | | | | | +| 1.
2.
3.
4. | Arrange SP A to request delivery of user data with a GT.
Record the message sequence and parameters using a signal monitor.
CHECK A: CONFIRM THAT NO MESSAGES WERE SENT BY SP A TO SP B.
CHECK B: WAS THE SCCP USER ADVISED OF AN APPROPRIATE REASON FOR RETURN? | | | | | | | | + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | +|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------|----------------|------|------|-------------------------|--| +| TEST NUMBER: 1.1.1.2.9 | | | | | | | +| REFERENCE: 2.3.2.4) c)/Q.714 | | | | | | | +| TITLE: Message from SCCP users, route on GT. | | | | | | | +| SUBTITLE: GT translation failed – Return option not set. | | | | | | | +| PURPOSE: To verify that data is not returned when GT translation failed and return option is not set. | | | | | | | +| PRE-TEST CONDITIONS:
1. Arrange the called address in N-UNITDATA request to contain:
– GT
2. Arrange return option in N-UNITDATA request not to be set
3. Arrange the SCCP routing control data as follows:
– GT translated to
– a GT
– DPC of SP B
– routing on GT
– DPC of SP B unavailable | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B |
| N-UNITDATA req. |
N-UNITDATA req.
| | +| SP A | SP B | | | | | | +|
N-UNITDATA req.
| | | | | | | +| TEST DESCRIPTION | | | | | | | +| 1. | Arrange SP A to request delivery of user data with a GT. | | | | | | +| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | +| 3. | CHECK A: CONFIRM THAT NO MESSAGES WERE SENT BY SP A TO SP B. | | | | | | +| 4. | CHECK B: CONFIRM THAT DATA WAS NOT RETURNED TO SCCP USER. | | | | | | + +# **SCCP TEST SPECIFICATION** + +| | | | +|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------|----------------| +| TEST NUMBER: 1.1.2.1.1 | | | +| REFERENCE: 2.3.1.3) a) i)/Q.714 | | | +| TITLE: Messages from MTP, route on GT. | | | +| SUBTITLE: GT translated to local DPC and SSN, and SSN available. | | | +| PURPOSE: To verify that the translation based on GT can be performed correctly to a local DPC and SSN and the user data can be delivered to the SCCP user at SP A. | | | +| PRE-TEST CONDITIONS:
1. Arrange the generation of a UDT message from SP B to SP A with:
– SCCP address information:
– GT
– route on GT
2. Arrange the SCCP routing control data at SP A as follows:
– GT translated to
– DPC of SP A
– new or same SSN
– SSN at SP A available | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT & CPT | TYPE OF SP: SP | +| EXPECTED MESSAGE SEQUENCE:
SP A SP B
<----- UDT
N-UNITDATA ind.
<=====
| | |
+| TEST DESCRIPTION | | |
+| 1. | Arrange SP B to send a UDT message to SP A with a GT to be translated at SP A to a DPC and SSN of SP A. | |
+| 2. | Record the message sequence and parameters using a signal monitor. | |
+| 3. | CHECK A: WAS THE DATA CORRECTLY DELIVERED TO THE SCCP USER AT SP A? | |
+| 4. | CHECK B: WAS THE MESSAGE SEQUENCE AS ABOVE? | |
+
+# **SCCP TEST SPECIFICATION**
+
+| | | | | | | | | | | | | | | |
+|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------|-----------------------------------------------------------|----|---------------|---------------------|----|-----------------------|-----------------------------------------------------------|----|------------------------|-----------------------------------|----|-------|---------------------------------|
+| TEST NUMBER: 1.1.2.1.2 | | | | | | | | | | | | | | |
+| REFERENCE: 2.3.1.3) a) i)/Q.714 | | | | | | | | | | | | | | |
+| TITLE: Messages from MTP, route on GT. | | | | | | | | | | | | | | |
+| SUBTITLE: GT translated to local DPC and SSN, and SSN unavailable – Return option set. | | | | | | | | | | | | | | |
+| PURPOSE: To verify that the data is returned when routing on GT translates to a local DPC and an unavailable SSN, and return option is set. | | | | | | | | | | | | | | |
+| PRE-TEST CONDITIONS:<=====
1. Arrange the generation of a UDT message from SP B to SP A with:
– SCCP address information:
– GT
– route on GT
– Return option set
2. Arrange the SCCP routing control data at SP A as follows:
– GT translated to
– DPC of SP A
– new or same SSN
– SSN at SP A unavailable | | | | | | | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT & CPT | TYPE OF SP: SP | | | | | | | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
SP A SP B
<----- UDT
UDTS ----->
| | | | | | | | | | | | | | |
+| TEST DESCRIPTION | | | | | | | | | | | | | | |
+| 1. | Arrange SP B to send a UDT message to SP A with a GT to be translated at SP A to a DPC and SSN of SP A. | | | | | | | | | | | | | |
+| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | | | | | | | | |
+| 3. | CHECK A: WAS THE UDTS MESSAGE CORRECTLY GENERATED BY SP A? | | | | | | | | | | | | | |
+| 4. | CHECK B: WAS THE POINT CODE OF SP B CONTAINED IN THE MTP ROUTING LABEL OF THE UDTS MESSAGE? | | | | | | | | | | | | | |
+| 5. | CHECK C: WERE THE PARAMETER FIELDS SET CORRECTLY AS INDICATED IN THE CHECK TABLE BELOW? | | | | | | | | | | | | | |
+| 6. | CHECK D: WAS THE MESSAGE SEQUENCE AS ABOVE? | | | | | | | | | | | | | |
+| CHECK TABLE | | | | | | | | | | | | | | |
+| UDTS (SP A → SP B)| 1) | Return cause: | “Appropriate value” |
| 2) | Called party address: | Derived from the calling party address in the UDT message |
| 3) | Calling party address: | “Appropriate information of SP A” |
| 4) | Data: | Same data as in the UDT message |
1. Arrange the generation of a UDT message from SP B to SP A with:
– SCCP address information:
– GT
– route on GT
– Return option not set
2. Arrange the SCCP routing control data at SP A as follows:
– GT translated to
– DPC of SP A
– new or same SSN
– SSN at SP A unavailable | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT & CPT | TYPE OF SP: SP | +| EXPECTED MESSAGE SEQUENCE:
SP A SP B
<----- UDT
| | |
+| TEST DESCRIPTION | | |
+| 1. | Arrange SP B to send a UDT message to SP A with a GT to be translated at SP A to a DPC of SP A and SSN. | |
+| 2. | Record the message sequence and parameters using a signal monitor. | |
+| 3. | CHECK A: CONFIRM THAT NO MESSAGES EXCEPT THOSE FOR MANAGEMENT WERE SENT BY SP A TO SP B. | |
+| 4. | CHECK B: WAS THE MESSAGE SEQUENCE AS ABOVE? | |
+
+# **SCCP TEST SPECIFICATION**
+
+| | | |
+|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------|----------------|
+| TEST NUMBER: 1.1.2.1.4 | | |
+| REFERENCE: 2.3.1 3) a) ii)/Q.714 | | |
+| TITLE: Message from MTP, route on GT. | | |
+| SUBTITLE: GT translated to remote DPC and SSN, and DPC and SSN available. | | |
+| PURPOSE: To verify that the translation based on GT can be performed correctly to a remote DPC and SSN, and a UDT message can be generated correctly to SP C. | | |
+| PRE-TEST CONDITIONS:1. Arrange the generation of a UDT message from SP B to SP A with:
– SCCP address information:
– GT
– route on GT
2. Arrange the SCCP routing control data at SP A as follows:
– GT translated to
– DPC of SP C
– new or same SSN
– route on DPC-SSN
– DPC of SP C available
– SSN at SP C available | | | +| CONFIGURATION: 2 | TYPE OF TEST: VAT & CPT | TYPE OF SP: SP | +| EXPECTED MESSAGE SEQUENCE:
SP B SP A SP C
UDT ----->
| | |
+| TEST DESCRIPTION | | |
+| 1. | Arrange SP B to send a UDT message to SP A with a GT to be translated at SP A to remote DPC and SSN. | |
+| 2. | Record the message sequence and parameters using a signal monitor. | |
+| 3. | CHECK A: WAS THE UDT MESSAGE CORRECTLY GENERATED BY SP A? | |
+| 4. | CHECK B: WAS THE POINT CODE OF SP C CONTAINED IN THE MTP ROUTING LABEL OF THE UDT MESSAGE GENERATED BY SP A AND WAS THE SIO CORRECT? | |
+| 5. | CHECK C: WERE THE PARAMETER FIELDS SET CORRECTLY AS INDICATED IN THE CHECK TABLE BELOW? | |
+| 6. | CHECK D: WAS THE MESSAGE SEQUENCE AS ABOVE? | |
+
+TEST NUMBER: 1.1.2.1.4 (continued)
+
+## CHECK TABLE (1/1)
+
+### UDT (SP A → SP C)
+
+- | | | |
+|----|-----------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| 1) | Protocol class: | 00000000 (Class 0, Return option is not set) UDT ----->
or
10000000 (Class 0, Return option is set)
or
00000001 (Class 1, Return option is not set)
or
10000001 (Class 1, Return option is set) | +|----|-----------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| + +### Called Party Address + +- | | | | +|----|-------------------------------|------------------------------------------------------------------------------------------| +| 2) | Point Code Indicator (Note): | 0 (Signalling point code is not included)
or
1 (Signalling point code is included) | +| 3) | SSN Indicator: | 1 (SSN is included) | +| 4) | Global Title Indicator: | Don’t care | +| 5) | Routing Indicator: | 1 (Routing on DPC) | +| 6) | Signalling Point Code (Note): | DPC of SP C (if Point Code Indicator equals to 1) | +| 7) | Sub-system Number: | SSN at SP C | +| 8) | Global Title (Note): | ‘‘Appropriate information’’ | + +NOTE – Inclusion of GT and/or DPC in Called Party Address is implementation dependent for this test. + + + +**SCCP TEST SPECIFICATION** + +| | | | | | | | | | | | +|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------|----------------|----|------------------------------------------------------------------------------------------------------|----|--------------------------------------------------------------------|----|------------------------------------------------------------------------------------------|----|---------------------------------------------| +| TEST NUMBER: 1.1.2.1.6 | | | | | | | | | | | +| REFERENCE: 2.3.1 3) a) iv)/Q.714 | | | | | | | | | | | +| TITLE: Message from MTP, route on GT. | | | | | | | | | | | +| SUBTITLE: GT translated to remote DPC and SSN, and DPC and/or SSN unavailable – Return option not set. | | | | | | | | | | | +| PURPOSE: To verify that the data is not returned when routing on GT translates to an unavailable remote DPC and/or SSN and return option is not set. | | | | | | | | | | | +| PRE-TEST CONDITIONS:
- 1. Arrange the generation of a UDT message from SP B to SP A with:
- – SCCP address information:
- – GT
- – route on GT
- – return option not set
- – SCCP address information:
- 2. Arrange the SCCP routing control data at SP A as follows:
- – GT translated to
- – DPC of SP C
- – new or same SSN
- – route on DPC-SSN
- – DPC of SP C unavailable and/or SSN at SP C unavailable
- – GT translated to
SP B SP A SP C
UDT >
| | | | | | | | | | |
+| TEST DESCRIPTION | 1. | Arrange SP B to send a UDT message to SP A with a GT to be translated at SP A to remote DPC and SSN. |
| 2. | Record the message sequence and parameters using a signal monitor. |
| 3. | CHECK A: CONFIRM THAT NO MESSAGES EXCEPT THOSE FOR MANAGEMENT WERE SENT BY SP A TO SP B. |
| 4. | CHECK B: WAS THE MESSAGE SEQUENCE AS ABOVE? |
- Arrange the generation of a UDT message from SP B to SP A with:
- SCCP address information:
- GT
- route on GT
- SCCP address information:
- Arrange the SCCP routing control data at SP A as follows:
- GT translated to
- DPC of SP C
- new or same GT
- route on GT
- DPC of SP C available
- GT translated to
SP B
SP A
SP C
UDT
>
UDT
>
| TEST DESCRIPTION | |
| 1. | Arrange SP B to send a UDT message to SP A with a GT to be translated at SP A to remote DPC and new or same GT. |
| 2. | Record the message sequence and parameters using a signal monitor. |
| 3. | CHECK A: WAS THE UDT MESSAGE CORRECTLY GENERATED BY SP A? |
| 4. | CHECK B: WAS THE POINT CODE OF SP C CONTAINED IN THE MTP ROUTING LABEL OF THE UDT MESSAGE GENERATED BY SP A AND WAS THE SIO CORRECT? |
| 5. | CHECK C: WERE THE PARAMETER FIELDS SET CORRECTLY AS INDICATED IN THE CHECK TABLE BELOW? |
| 6. | CHECK D: WAS THE MESSAGE SEQUENCE AS ABOVE? |
or
10000000 (Class 0, Return option is set)
or
00000001 (Class 1, Return option is not set)
or
10000001 (Class 1, Return option is set) | +| Called Party Address | | +| 2) Point Code Indicator (Note): | 0 (Signalling point code is not included)
or
1 (Signalling point code is included) | +| 3) SSN Indicator: | 0 (SSN is not included)
or
1 (SSN is included) | +| 4) Global Title Indicator: | 0001, 0010, 0011 or 0100 (Global Title is included) | +| 5) Routing Indicator: | 0 (Routing on GT) | +| 6) Signalling Point Code (Note): | DPC of SP C (if Point Code Indicator equals to 1) | +| 7) Sub-system Number: | XXXXXXXX (if SSN Indicator equals to 1) | +| 8) Global Title: | a Global Title data (resulting from GT translation)) | +| NOTE – Inclusion of DPC in Called Party Address is implementation dependent for this test. | | + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | | | | | | | | | +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------|-----------------------------------------------------------|----|---------------|---------------------|----|-----------------------|-----------------------------------------------------------|----|------------------------|-----------------------------------|----|-------|---------------------------------| +| TEST NUMBER: 1.1.2.1.8 | | | | | | | | | | | | | | | +| REFERENCE: 2.3.1 3) c)/Q.714 | | | | | | | | | | | | | | | +| TITLE: Message from MTP, route on GT. | | | | | | | | | | | | | | | +| SUBTITLE: GT translation failed – Return option set. | | | | | | | | | | | | | | | +| PURPOSE: To verify that data is returned when GT translation failed and return option is set. | | | | | | | | | | | | | | | +| PRE-TEST CONDITIONS:
1. Arrange the generation of a UDT message from SP B to SP A with:
– SCCP address information:
– GT
– route on GT
– return option set
2. Arrange the SCCP routing control data at SP A as follows:
– GT translation not existing | | | | | | | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT & CPT | TYPE OF SP: SP | | | | | | | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
SP A SP B
< UDT
UDTS >
| | | | | | | | | | | | | | |
+| TEST DESCRIPTION | | | | | | | | | | | | | | |
+| 1. Arrange SP B to send a UDT message to SP A with a GT.2. Record the message sequence and parameters using a signal monitor.
3. CHECK A: WAS THE UDTS MESSAGE CORRECTLY GENERATED BY SP A?
4. CHECK B: WAS THE POINT CODE OF SP B CONTAINED IN THE MTP ROUTING LABEL OF THE UDTS MESSAGE?
5. CHECK C: WERE THE PARAMETER FIELDS SET CORRECTLY AS INDICATED IN THE CHECK TABLE BELOW?
6. CHECK D: WAS THE MESSAGE SEQUENCE AS ABOVE? | | | | | | | | | | | | | | | +| CHECK TABLE | | | | | | | | | | | | | | | +| UDTS (SP A → SP B)
| 1) | Return cause: | “Appropriate value” |
| 2) | Called party address: | Derived from the calling party address in the UDT message |
| 3) | Calling party address: | “Appropriate information of SP A” |
| 4) | Data: | Same data as in the UDT message |
- 1. Arrange the generation of a UDT message from SP B to SP A with:
- – SCCP address information:
- – GT
- – route on GT
- – return option not set
- 2. Arrange the SCCP routing control data at SP A as follows:
- – GT translation not existing
SP A SP B
< UDT
| | | | | | | | | | |
+| TEST DESCRIPTION | 1. | Arrange SP B to send a UDT message to SP A with a GT. |
| 2. | Record the message sequence and parameters using a signal monitor. |
| 3. | CHECK A: CONFIRM THAT NO MESSAGES EXCEPT THOSE FOR MANAGEMENT WERE SENT BY SP A TO SP B. |
| 4. | CHECK B: WAS THE MESSAGE SEQUENCE AS ABOVE? |
1. Arrange the generation of a UDT message from SP B to SP A with:
– SCCP address information:
– SSN
– GT
– route on DPC-SSN
2. Arrange the SCCP routing control data at SP A as follows:
– SSN at SP A available | | | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B |
| < UDT | |
| N-UNITDATA ind. | |
| < |
1. Arrange the generation of a UDT message from SP B to SP A with:
- SCCP address information:
- SSN
- no GT
- route on DPC-SSN
2. Arrange the SCCP routing control data at SP A as follows:
- SSN at SP A available | | | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B |
| <----- UDT | |
| N-UNITDATA ind. | |
| <===== |
1. Arrange the generation of a UDT message from SP B to SP A with:
– SCCP address information:
– SSN
– route on DPC-SSN
– return option set
2. Arrange the SCCP routing control data at SP A as follows:
– SSN at SP A unavailable | | | | | | | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT & CPT | TYPE OF SP: SP | | | | | | | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
SP A SP B
< UDT
UDTS >
| | | | | | | | | | | | | | |
+| TEST DESCRIPTION | | | | | | | | | | | | | | |
+| 1. | Arrange SP B to send a UDT message to SP A with an SSN. | | | | | | | | | | | | | |
+| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | | | | | | | | |
+| 3. | CHECK A: WAS THE UDTS MESSAGE CORRECTLY GENERATED BY SP A? | | | | | | | | | | | | | |
+| 4. | CHECK B: WAS THE POINT CODE OF SP B CONTAINED IN THE MTP ROUTING LABEL OF THE UDTS MESSAGE? | | | | | | | | | | | | | |
+| 5. | CHECK C: WERE THE PARAMETER FIELDS SET CORRECTLY AS INDICATED IN THE CHECK TABLE BELOW? | | | | | | | | | | | | | |
+| 6. | CHECK D: WAS THE MESSAGE SEQUENCE AS ABOVE? | | | | | | | | | | | | | |
+| CHECK TABLE | | | | | | | | | | | | | | |
+| UDTS (SP A → SP B)| 1) | Return cause: | “Appropriate value” |
| 2) | Called party address: | Derived from the calling party address in the UDT message |
| 3) | Calling party address: | “Appropriate information of SP A” |
| 4) | Data: | Same data as in the UDT message |
1. Arrange the generation of a UDT message from SP B to SP A with:
– SCCP address information:
– SSN
– route on DPC-SSN
– return option not set
2. Arrange the SCCP routing control data at SP A as follows:
– SSN at SP A unavailable | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT & CPT | TYPE OF SP: SP | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B | |
| < | UDT |
1. Arrange the generation of a number of N-UNITDATA request with:
– address information identifying SP B:
– sequence control set
2. Arrange the SCCP routing control data as follows:
– SP B available
– SSN at SP B available | | | | | | | | | | | | | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT & CPT | TYPE OF SP: SP | | | | | | | | | | | | | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP A | SP B | |
| N-UNITDATA req. > | > | |
| N-UNITDATA req. > | > | |
| N-UNITDATA req. > | UDT (Class = 1) | > |
| N-UNITDATA req. > | > | |
| N-UNITDATA req. > | > |
> | | > | N-UNITDATA req.
> | | > | N-UNITDATA req.
> | UDT
(Class = 1) | > | N-UNITDATA req.
> | | > | N-UNITDATA req.
> | | > | +| SP A | | SP B | | | | | | | | | | | | | | | | | | | +| N-UNITDATA req.
> | | > | | | | | | | | | | | | | | | | | | | +| N-UNITDATA req.
> | | > | | | | | | | | | | | | | | | | | | | +| N-UNITDATA req.
> | UDT
(Class = 1) | > | | | | | | | | | | | | | | | | | | | +| N-UNITDATA req.
> | | > | | | | | | | | | | | | | | | | | | | +| N-UNITDATA req.
> | | > | | | | | | | | | | | | | | | | | | | +| TEST DESCRIPTION | | | | | | | | | | | | | | | | | | | | | +| 1. | Arrange SP A to send five UDT messages using class 1 protocol. | | | | | | | | | | | | | | | | | | | | +| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | | | | | | | | | | | | | | | +| 3. | CHECK A: WERE THE UDT MESSAGES CORRECTLY GENERATED BY SP A? | | | | | | | | | | | | | | | | | | | | +| 4. | CHECK B: WAS THE POINT CODE OF SP B CONTAINED IN THE MTP ROUTING LABEL OF THE UDT MESSAGES AND WAS THE SIO CORRECT? | | | | | | | | | | | | | | | | | | | | +| 5. | CHECK C: WAS THE MESSAGE SEQUENCE AS ABOVE? | | | | | | | | | | | | | | | | | | | | +| 6. | CHECK D: WERE ALL THE UDT MESSAGES SENT WITH THE SAME SLS CODE CONTAINED IN THE MTP ROUTING LABEL SENT IN THE CORRECT ORDER? | | | | | | | | | | | | | | | | | | | | + +| | | +|------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------| +| TEST NUMBER: 1.2.1.1 ( continued ) | | +| CHECK TABLE (1/1) | | +| UDT (SP A → SP B) | | +| 1) Protocol class: | 00000001 (Class 1, Return option is not set)
or
10000001 (Class 1, Return option is set) | +| Called Party Address | | +| 2) Point Code Indicator (Note): | 0 (Signalling point code is not included)
or
1 (Signalling point code is included) | +| 3) SSN Indicator: | Don't care | +| 4) Global Title Indicator: | Don't care | +| 5) Routing Indicator: | Don't care | +| 6) Signalling Point Code (Note): | DPC of SP C (if Point Code Indicator equals to 1) | +| 7) Sub-system Number: | Don't care | +| 8) Global Title (Note): | "Appropriate information" | +| NOTE – Inclusion of GT and/or DPC in Called Party Address is implementation dependent for this test. | | + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | | | | | | | | | | | | | | | | | +|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------|------|------|------|--|---|---|--|---|---|--------------------|---|--------------------|---|--|--|---|---|--|---|---| +| TEST NUMBER: 1.2.1.2 | | | | | | | | | | | | | | | | | | | | | | | +| REFERENCE: 4/Q.714 | | | | | | | | | | | | | | | | | | | | | | | +| TITLE: Data Transfer. | | | | | | | | | | | | | | | | | | | | | | | +| SUBTITLE: Data Transfer with Sequential Delivery Capability at relay node. | | | | | | | | | | | | | | | | | | | | | | | +| PURPOSE: To verify that SP A uses the same signalling link for all messages using class 1 protocol. | | | | | | | | | | | | | | | | | | | | | | | +| PRE-TEST CONDITIONS:
1. Arrange the generation of a number of SCCP messages with:
– address information (GT) identifying SP C:
– sequence control set
– GT translation necessary in SP A
2. Arrange the SCCP routing control data as follows:
– SP C available
– SSN at SP C available | | | | | | | | | | | | | | | | | | | | | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT & CPT | TYPE OF SP: SP | | | | | | | | | | | | | | | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP B | SP A | SP C | ||
| → | → | |||
| → | → | |||
| UDT (Class = 1) | → | UDT (Class = 1) | → | |
| → | → | |||
| → | → |
(Class = 1) | → | UDT
(Class = 1) | → | | | → | → | | → | → | +| SP B | SP A | SP C | | | | | | | | | | | | | | | | | | | | | +| | → | → | | | | | | | | | | | | | | | | | | | | | +| | → | → | | | | | | | | | | | | | | | | | | | | | +| UDT
(Class = 1) | → | UDT
(Class = 1) | → | | | | | | | | | | | | | | | | | | | | +| | → | → | | | | | | | | | | | | | | | | | | | | | +| | → | → | | | | | | | | | | | | | | | | | | | | | +| TEST DESCRIPTION | | | | | | | | | | | | | | | | | | | | | | | +| 1. | Arrange SP B to send five UDT messages using class 1 protocol, using SP A as relay point. | | | | | | | | | | | | | | | | | | | | | | +| 2. | Record the message sequence and parameters using a signal monitor. | | | | | | | | | | | | | | | | | | | | | | +| 3. | CHECK A: WERE THE UDT MESSAGES CORRECTLY GENERATED BY SP A? | | | | | | | | | | | | | | | | | | | | | | +| 4. | CHECK B: WAS THE POINT CODE OF SP C CONTAINED IN THE MTP ROUTING LABEL OF THE UDT MESSAGES AND WAS THE SIO CORRECT? | | | | | | | | | | | | | | | | | | | | | | +| 5. | CHECK C: WAS THE MESSAGE SEQUENCE AS ABOVE? | | | | | | | | | | | | | | | | | | | | | | +| 6. | CHECK D: WERE ALL THE UDT MESSAGES SENT WITH THE SAME SLS CODE CONTAINED IN THE MTP ROUTING LABEL AND WAS THE ORDER IN WHICH THE MESSAGES WERE SENT THE SAME ORDER IN WHICH THEY WERE RECEIVED? | | | | | | | | | | | | | | | | | | | | | | + +| | | +|------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------| +| TEST NUMBER: 1.2.1.2 ( continued ) | | +| CHECK TABLE (1/1) | | +| UDT (SP A → SP C) | | +| 1) Protocol class: | 00000001 (Class 1, Return option is not set)
or
10000001 (Class 1, Return option is set) | +| Called Party Address | | +| 2) Point Code Indicator (Note): | 0 (Signalling point code is not included)
or
1 (Signalling point code is included) | +| 3) SSN Indicator: | Don't care | +| 4) Global Title Indicator: | Don't care | +| 5) Routing Indicator: | Don't care | +| 6) Signalling Point Code (Note): | DPC of SP C (if Point Code Indicator equals to 1) | +| 7) Sub-system Number: | Don't care | +| 8) Global Title (Note): | "Appropriate information" | +| NOTE – Inclusion of GT and/or DPC in Called Party Address is implementation dependent for this test. | | + +# **SCCP TEST SPECIFICATION** + +| | | | +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------| +| TEST NUMBER: 1.2.2 | | | +| REFERENCE: 4.3/Q.714 | | | +| TITLE: Data Transfer. | | | +| SUBTITLE: Data Transfer with Syntax Error. | | | +| PURPOSE: To verify that a UDT message received with syntax error at SP A is discarded. | | | +| PRE-TEST CONDITIONS:
1. Arrange the generation of a UDT message from SP B to SP A with:
– Syntax error
– return option set | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | +| EXPECTED MESSAGE SEQUENCE:
SP A SP B
<----- UDT
| | |
+| TEST DESCRIPTION | | |
+| 1.2.
3.
4.
5. | Arrange SP B to generate a UDT message with a syntax error.
Record the message sequence and parameters using a signal monitor.
CHECK A: WAS THE UDT MESSAGE DISCARDED AT SP A?
CHECK B: CONFIRM THAT NO MESSAGES WERE SENT BY SP A TO SP B.
CHECK C: WAS THE MESSAGE SEQUENCE AS ABOVE? | | + +# **SCCP TEST SPECIFICATION** + +| | | | +|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------| +| TEST NUMBER: 1.2.3.1.1 | | | +| REFERENCE: 4.2/Q.714 | | | +| TITLE: Data Transfer. | | | +| SUBTITLE: UDTs deliverable to SCCP user. | | | +| PURPOSE: To verify that a UDTs message received at SP A can be delivered correctly to an SCCP user. | | | +| PRE-TEST CONDITIONS:
1. Arrange the generation of a UDTs message from SP B to SP A
2. Arrange the SCCP routing control data as follows:
– SSN at SP A available | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | +| EXPECTED MESSAGE SEQUENCE:
SP A SP B
<----- UDTs
N-NOTICE ind.
<=====
<=====
2.
3.
4.
5. | Arrange SP B to generate a UDTs message to available subsystem at SP A.
Record the message sequence and parameters using a signal monitor.
CHECK A: WAS THE SCCP USER ADVISED OF AN APPROPRIATE REASON FOR RETURN?
CHECK B: CONFIRM THAT NO MESSAGES EXCEPT THOSE FOR MANAGEMENT WERE SENT BY SP A TO SP B.
CHECK C: WAS THE MESSAGE SEQUENCE AS ABOVE? | | + +# **SCCP TEST SPECIFICATION** + +| | | | | | | | | | | | | +|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|------|------|------|--|--|--|---|-------------------|------| +| TEST NUMBER: 1.2.3.1.2 | | | | | | | | | | | | +| REFERENCE: 4.2/Q.714 | | | | | | | | | | | | +| TITLE: Data Transfer. | | | | | | | | | | | | +| SUBTITLE: UDTS deliverable to other SP. | | | | | | | | | | | | +| PURPOSE: To verify that a UDTS message received at SP A can be sent correctly if the SCCP is able to send the message. | | | | | | | | | | | | +| PRE-TEST CONDITIONS:
1. Arrange the generation of a UDTS message from SP B to SP A with:
– SCCP address information:
– GT
– route on GT
2. Arrange the SCCP routing control data at SP A as follows:
– GT translated to DPC of SP C
– destination accessible | | | | | | | | | | | | +| CONFIGURATION: 2 | TYPE OF TEST: VAT | TYPE OF SP: SP | | | | | | | | | | +| EXPECTED MESSAGE SEQUENCE:
| SP C | SP A | SP B |
| < | UDTS < | UDTS |
| | | SP C | SP A | SP B | | | | < | UDTS < | UDTS | +| SP C | SP A | SP B | | | | | | | | | | +| | | | | | | | | | | | | +| < | UDTS < | UDTS | | | | | | | | | | +| TEST DESCRIPTION | | | | | | | | | | | | +|
1.
2.
3.
4.
5.
6.
|Arrange SP B to generate a UDTS message to SP A with a GT to be translated at SP A to remote DPC and SSN.
Record the message sequence and parameters using a signal monitor.
CHECK A: WAS UDTS MESSAGE CORRECTLY GENERATED BY SP A?
CHECK B: WAS THE POINT CODE OF SP C CONTAINED IN THE MTP ROUTING LABEL OF THE UDTS MESSAGE GENERATED BY SP A?
CHECK C: WERE THE PARAMETER FIELDS SET CORRECTLY AS INDICATED IN THE CHECK TABLE BELOW?
CHECK D: WAS THE MESSAGE SEQUENCE AS ABOVE?
| | | | | | | | | | | + +| | | +|------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------| +| TEST NUMBER: 1.2.3.1.2 (continued) | | +| CHECK TABLE (1/1) | | +| UDTS (SP A → SP C) | | +| 1) Return cause: | “Appropriate value” | +| Called Party Address | | +| 2) Point Code Indicator (Note): | 0 (Signalling point code is not included)or
1 (Signalling point code is included) | +| 3) SSN Indicator: | 0 (SSN is not included)
or
1 (SSN is included) | +| 4) Global Title Indicator: | Don't care | +| 5) Routing Indicator: | Don't care | +| 6) Signalling Point Code (Note): | DPC of SP C (if Point Code Indicator equals to 1) | +| 7) Sub-system Number: | XXXXXXXX (if SSN Indicator equals to 1) | +| 8) Global Title (Note): | “Appropriate information” | +| Calling party address | “Appropriate information” | +| Data: | “Appropriate information” | +| NOTE – Inclusion of GT and/or DPC in Called Party Address is implementation dependent for this test. | | + +# **SCCP TEST SPECIFICATION** + +| | | | +|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------|----------------| +| TEST NUMBER: 1.2.3.2.1 | | | +| REFERENCE: 4.2/Q.714 | | | +| TITLE: Data Transfer. | | | +| SUBTITLE: UDTs undeliverable to SCCP user. | | | +| PURPOSE: To verify that a UDTs message to unavailable SCCP user received at SP A is discarded. | | | +| PRE-TEST CONDITIONS:
1. Arrange the generation of a UDTs message from SP B to SP A
2. Arrange the SCCP routing control data as follows:
– SSN at SP A not available | | | +| CONFIGURATION: 1 | TYPE OF TEST: VAT | TYPE OF SP: SP | +| EXPECTED MESSAGE SEQUENCE:
SP ASP B
<----- UDTs
| | |
+| TEST DESCRIPTION | | |
+| 1. | Arrange SP A and SP B to generate a UDTs message to an unavailable sub-system at SP A. | |
+| 2. | Record the message sequence and parameters using a signal monitor. | |
+| 3. | CHECK A: CONFIRM THAT DATA WAS NOT DELIVERED TO SCCP USER. | |
+| 4. | CHECK B: CONFIRM THAT NO MESSAGES EXCEPT THOSE FOR MANAGEMENT WERE SENT BY SP A TO SP B. | |
+| 5. | CHECK C: WAS THE MESSAGE SEQUENCE AS ABOVE? | |
\ No newline at end of file
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+
+
+International Telecommunication Union
+
+**ITU-T**
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+**Q.816.2**
+
+(03/2007)
+
+SERIES Q: SWITCHING AND SIGNALLING
+
+Q3 interface
+
+---
+
+**CORBA-based TMN services: Extensions to
+support service-oriented interfaces**
+
+ITU-T Recommendation Q.816.2
+
+ITU-T
+
+
+
+The logo of the International Telecommunication Union (ITU) features a stylized globe with a red lightning bolt striking across it. To the right of the globe, the text "International Telecommunication Union" is written in a blue, sans-serif font, with "ITU" in a larger, bold font above it.
+
+ITU logo
+
+International
+Telecommunication
+Union
+
+# ITU-T Q-SERIES RECOMMENDATIONS
+
+## **SWITCHING AND SIGNALLING**
+
+| | |
+|--------------------------------------------------------------------------------|--------------------|
+| SIGNALLING IN THE INTERNATIONAL MANUAL SERVICE | Q.1–Q.3 |
+| INTERNATIONAL AUTOMATIC AND SEMI-AUTOMATIC WORKING | Q.4–Q.59 |
+| FUNCTIONS AND INFORMATION FLOWS FOR SERVICES IN THE ISDN | Q.60–Q.99 |
+| CLAUSES APPLICABLE TO ITU-T STANDARD SYSTEMS | Q.100–Q.119 |
+| SPECIFICATIONS OF SIGNALLING SYSTEMS No. 4, 5, 6, R1 AND R2 | Q.120–Q.499 |
+| DIGITAL EXCHANGES | Q.500–Q.599 |
+| INTERWORKING OF SIGNALLING SYSTEMS | Q.600–Q.699 |
+| SPECIFICATIONS OF SIGNALLING SYSTEM No. 7 | Q.700–Q.799 |
+| Q3 INTERFACE | Q.800–Q.849 |
+| DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 1 | Q.850–Q.999 |
+| PUBLIC LAND MOBILE NETWORK | Q.1000–Q.1099 |
+| INTERWORKING WITH SATELLITE MOBILE SYSTEMS | Q.1100–Q.1199 |
+| INTELLIGENT NETWORK | Q.1200–Q.1699 |
+| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR IMT-2000 | Q.1700–Q.1799 |
+| SPECIFICATIONS OF SIGNALLING RELATED TO BEARER INDEPENDENT CALL CONTROL (BICC) | Q.1900–Q.1999 |
+| BROADBAND ISDN | Q.2000–Q.2999 |
+| SIGNALLING REQUIREMENTS AND PROTOCOLS FOR THE NGN | Q.3000–Q.3999 |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+## **ITU-T Recommendation Q.816.2**
+
+# **CORBA-based TMN services: Extensions to support service-oriented interfaces**
+
+# **Summary**
+
+ITU-T Recommendation Q.816.2 defines a set of TMN CORBA services required to support service-oriented interfaces. It specifies how the ORB and common object services should be used in a lightweight fashion for supporting service-oriented interfaces, and defines extensions to the TMN-specific support services defined in ITU-T Recommendations Q.816 and Q.816.1. A CORBA IDL module defining the interfaces to the new TMN-specific support services is provided. The new services and the lightweight use of other CORBA services, along with ITU-T Recommendation X.780.2, compose a framework for CORBA-based service-oriented TMN interfaces with a wide range of applications.
+
+## **Source**
+
+ITU-T Recommendation Q.816.2 was approved on 16 March 2007 by ITU-T Study Group 4 (2005-2008) under the ITU-T Recommendation A.8 procedure.
+
+## **Keywords**
+
+Common object request broker architecture (CORBA), CORBA services, distributed processing, façade, interface definition language (IDL), managed object, managed system, managing system, service orientation, service-oriented façade object, TMN interface.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at EnhancedCurrentAlarmSummaryControl[_F] . |
+| | BestEffort | | |
+| EventReliability | Persistent | O | |
+| | BestEffort | | |
+| Priority | short | | All notifications shall have the default priority 0 to avoid ordering problems. Consumers may use mapping filters to override the default setting as needed. |
+| | LowestPriority | | |
+| | DefaultPriority | R | |
+| | HighestPriority | | |
+| StopTimeSupported | FALSE | O | It is recommended to not use absolute expiry times (on a per-message basis) after which the event can be discarded. |
+| | TRUE | | |
+| StopTime | TimeBase::UtcT | | |
+| Timeout | TimeBase::TimeT | | TimeT is an unsigned long long with unit 100 nanoseconds. The relative expiry time zero would indicate that there is no timeout. However, for alarms and TCAs 30 min is recommended, and for all other notification types 24 h . |
+| | 0 (digit zero) | | |
+| | $18 \cdot 10^9$ (30 min) | O | |
+| | $864 \cdot 10^9$ (24 h) | O | |
+| StartTimeSupported | FALSE | O | It is recommended to not use earliest delivery times (on a per-message basis). |
+| | TRUE | | |
+| StartTime | TimeBase::UtcT | | |
+| MaxEventsPerConsumer | long | | The default setting means that no limits are imposed on the maximum number of events that may be queued for consumers. |
+| | 0 (default) | | |
+
+**Table 1 – Standard QoS properties capabilities**
+
+| QoS property | Potential values | Implementation | Comment, condition(s) |
+|---------------------|--------------------|----------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| OrderPolicy | AnyOrder | | It shall be possible to deliver events in the order of their arrival. In case of fine-grained or coarse-grained interfaces, events may also be buffered in (consumer-defined) priority order and delivered accordingly, in which case events from the same managed object shall have the same priority, and correlated notifications [8] must not be in use. |
+| | FifoOrder | R | |
+| | PriorityOrder | O | |
+| | DeadlineOrder | | |
+| DiscardPolicy | AnyOrder (default) | | It shall be possible to discard events, in case of a buffer overflow, in the order of their arrival. It is recommended to ensure that this cannot happen on a per-channel basis, however, by setting the Admin property RejectNewEvents to TRUE (see NOTIF-8 ). |
+| | FifoOrder | R | |
+| | PriorityOrder | | |
+| | DeadlineOrder | | |
+| | LifoOrder | | |
+| MaximumBatchSize | long | | The default settings mean that event batches are not supported. If the option to support event batches is required (see NOTIF-4 ), these QoS properties must be set as needed (see, for example, [24][25]). |
+| | 1 (default) | O | |
+| PacingInterval | TimeBase::TimeT | | |
+| | 0 (default) | O | |
+| DeliveryReliability | None | | The OS should consider configuring reliable event delivery using event acknowledgement with sequence numbers, if the notification service supports it (see NOTIF-6 ). See also clause 8.7.5.3/ X.780.2 with regard to event identifiers. |
+| | Acknowledgement | O | |
+| RetryInterval | TimeBase::TimeT | O | |
+| Retries | long | O | |
+
+NOTE 10 – This **NOTIF-7** requirement includes **NOTIF-9/Q.816** and **NOTIF-10/Q.816**, as corrected by ITU-T Rec. Q.816/Cor.1. It complies with the 3GPP specification [24] and [25] and the MTNM specification [28].
+
+**(O) NOTIF-8** While support of the `CosNotification::AdminPropertiesAdmin` interface by the notification service is required for the configuration of channel administration policies, its use by operations systems for the standard Admin properties `MaxQueueLength`, `MaxConsumers`, `MaxSuppliers`, and `RejectNewEvents` is optional, the default values of the properties being implementation-defined. It is recommended to set `RejectNewEvents` to TRUE though.
+
+NOTE 11 – This **NOTIF-8** requirement complies with ITU-T Recs Q.816 and Q.816.1, the 3GPP specification [24] and [25], and the MTNM specification [28].
+
+**(O) NOTIF-9** An operations system may support an on-demand pull model for synchronization purposes in addition to the push model (which is triggered by the managed system whenever events originate). It is recommended that the pull mechanisms for event batches and typed events are combined and iterators be used to define highly efficient pull operations per event type with filtering capabilities, which are implemented by the managed system without event channels.
+
+**(R) NOTIF-10** Operations systems in the role of a supplier or a consumer of structured events shall follow the rules shown in Table 2 below for constructing and receiving structured events. Refer to the following standards for further details:
+
+- Sections 2.1.4, 2.2, 3.1.1 and 3.7 of [19] – *in the general case*;
+- **NOTIF-7/Q.816**, the comments of the IDL interface `itut_x780::Notifications` of ITU-T Rec. X.780, and [24], [25] and [26] – *in case of fine-grained and coarse-grained interfaces*;
+- Clause 8.7/X.780.2, the comments of the IDL module `notifications` of ITU-T Rec. X.780.2, and [24], [25], [26] and [28] – *in case of service-oriented interfaces*.
+
+NOTE 12 – Sections 2.2, 3.1.1, 3.7 and Appendix B of [19] contain the *normative* specification of the syntax and semantics of OMG structured events.
+
+**Table 2 – Frameworks mappings of notifications to structured events**
+
+| Field name | Actual field type | Potential field values | Comment |
+|---------------------------------------------------------------------------------------------------|-----------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Fixed event header | | | |
+| event_type | CosNotification::EventType | see Comment | The service-oriented framework extends OMG's and Q.816's understanding of Domains and Event types (Note 1). The values of the type_name field depend on the value of the domain_name field (Note 2). |
+| domain_name | string | "telecommunications" [8] or OS-OS interface class (e.g., IRP document version number string [24], [25] and [26], "tmf_mtnm" [27] and [28]) | |
+| type_name | string | see Comment | |
+| event_name | string | " " | This field does not have a standardized semantics. It could uniquely identify the specific event instance being transmitted, or be used for OS-OS interface class-specific purposes (see, for example, [26]), or be used for vendor-specific purposes. For reasons of interoperability, it is recommended to ignore it. |
+| Variable event header (a list of zero or more name/value pairs, initially with any values) | | | |
+| EventReliability | short | see Table 1 | The OMG defines the standard optional header fields listed here for QoS properties configuration at event level (see section 2.2 of [19]). The recommendations for using these QoS properties given in Table 1 apply likewise. |
+| Priority | short | see Table 1 | |
+| StopTime | TimeBase::UtcT | see Table 1 | |
+| Timeout | TimeBase::TimeT | see Table 1 | |
+| StartTime | TimeBase::UtcT | see Table 1 | |
+| SequenceNumber | long | see NOTIF-6 and section 3.7 of [19] | |
+| ohf_name | any | ohf_value | generic optional header field : indicates further optional fields |
+
+**Table 2 – Frameworks mappings of notifications to structured events**
+
+| Field name | Actual field type | Potential field values | Comment |
+|------------------------------------------------------------------------------------------|-------------------------------------------------------|--------------------------------------------------------|------------------------------------------------------------------------------------------------|
+| Filterable event body (a sequence of name/value pairs, initially with any values) | | | |
+| see Comment | see Comment | see Comment | The potential contents of the filterable event body depends on the event_type (Note 3). |
+| fd_name | any | fd_value | generic filterable data field: indicates further optional fields |
+| Remaining event body (additional event data, initially an Any) | | | |
+| remainder_of_body | any, or an overlay structure, or an MOC (see Comment) | NULL, or an overlay, or a managed object (see Comment) | Actual type and value of this field depend on the value of event_type (Note 4). |
+
+NOTE 1 – The OMG specifies *domain\_name* as an identifier for the vertical industry domain within which the type of event that characterizes a given structured event is defined. ITU-T Recs Q.816 and X.780 adopt the OMG example "telecommunications" for the event types of the fine-grained and coarse-grained framework (see IDL interface *itut\_x780::Notifications* [8]). The service-oriented framework takes into consideration that there need not be a unique CORBA specification (set) for a given vertical industry domain if the domain has a broader scope. For example, in the telecommunications industry there are standard CORBA specifications for fixed networks, namely **TMF MTNM**, and mobile networks, namely **the 3GPP IRPs**. So the semantics of *domain\_name* is extended to include OS-OS interface classes that are specified in CORBA IDL. For example, "tmf\_mtnm" identifies TMF MTNM [27] and [28], and IRP document version number strings, or **IRPVersions** for short, identify 3GPP IRPs [24], [25] and [26].
+
+NOTE 2 – The potential values of *type\_name* are defined in the CORBA specification that is identified by *domain\_name*. In case of "telecommunications", the event type name is the scoped name of the operation defining the event. The interface *Notifications* of X.780 defines 15 such operations, and a constant for each scoped operation name, e.g., `const string attributeValueChangeTypeName = "itut_x780::Notifications::attributeValueChange";`. In case of "tmf\_mtnm", the event type name is one of 13 standard string literals documented in [28] and formally defined in the IDL module *notifications* of ITU-T X.780.2, e.g., `const string NT_OBJECT_CREATION = "NT_OBJECT_CREATION";`. In case of an IRPVersion (e.g., "32.111-3 V6.5"), the document identified by this IRPVersion will specify an interface *NotificationType* that defines standard string literals for the event type names, e.g., `const string NOTIFY_FM_NEW_ALARM = "x1";`.
+
+NOTE 3 – The mandatory and optional NV pairs of the filterable event body depend on *event\_type*. In case of *domain\_name* = "telecommunications", *itut\_x780::Notifications* and **NOTIF-7/Q.816** specify rules for translating each parameter of the event-defining operation into a name/value pair. Optional parameters are either excluded or have a NULL value if not supported. These rules comply with OMG's rules for translating typed events into structured events (2.1.4/[19]). In case of *domain\_name* = "tmf\_mtnm", [28] specifies for each event type all name/value pairs explicitly together with the actual field types. In case of *domain\_name* = endSession() | +| nmsSession | NmsSession_I | eventLossOccurred()
eventLossCleared()
alarmLossOccurred() | +| emsSession | EmsSession_I | getSupportedManagers()
getManager()
getEventChannel() | +| emsSessionFactory | EmsSessionFactory_I | getEmsSession() | + + + +| module | exception, attribute | data type | +|-------------------|----------------------|----------------| +| idlVersion | - | - | +| session | associatedSession | - | +| nmsSession | - | - | +| emsSession | - | managerNames_T | +| emsSessionFactory | - | - | + +\*/ + +// Include list +#include "itut\_x780\_2.idl" +#include "OMGidl/CosNotifyChannelAdmin.idl" + +#pragma prefix "itu.int" + +/\*\* + +## A.1 Module idlVersion + +``` +*/ + +/** + *
This module contains the definition of the Version interface + * of the NML-EML interface.
+ **/ + +module idlVersion +{ + /** + *The interface Version_I allows the NMS to query the current + * version of the IDL interface (IDL version) implemented by the EMS. + * In order to use this CORBA interface, the NMS needs to invoke the + * getVersion() service to figure out which version of the NML-EML interface + * the EMS is providing. getVersion() should be called by any NMS + * before other communications with an EMS. The NMS can determine + * from the response string which IDL version of the EMS is available.
+ * + *For details on how to support multiple versions of the IDL see + * clause 9.1.2.5/Q.816.2 "Server Session Factory interface" and clause + * 10.5.4/X.780.2 "Versioning of CORBA IDL specifications".
+ **/ + interface Version_I + { + /** + *This service returns the version of the IDL interface (IDL version) + * that the corresponding EMS supports.
+ * + *The format of the return string is as follows:
+ * Release.Major[.Minor],
+ * where Release, Major and Minor
+ * are strings that contain only digits.
For example, "2.1" indicates release 2 and major release 1, + * "1.3" indicates release 1 and major release 3, and so on. + * Note that "x.y" has the same meaning as "x.y.0". + * The minor digit is used for bug fixing of the major release + * (e.g., "1.2.1" is a minor release on "1.2").
+ * + * @returns string: The IDL version of the NML-EML interface. + **/ + string getVersion(); + }; // end of interface +}; // end of module + +/** +``` + +### A.2 Module session + +``` +*/ + +/** + *This module contains the definition of the Session interface + * of the NML-EML interface.
+ **/ + +module session +{ + /** + *The Session_I interface provides capabilities to manage a + * client/server connection, which is called a session. Its main + * purpose is to enable either a client or a server to detect the + * loss of communication with the associated party.
+ * +``` + +``` + +*For a single communication session between an NMS and an EMS, there +* are two Session_I objects. One is maintained on the NMS; the other one +* is maintained on the EMS. The Session_I object maintained on the EMS is +* actually an EmsSession_I while the Session_I object maintained on the +* NMS is actually an NmsSession_I (both inherit from Session_I).
+* +*Each Session_I object is responsible to "ping" the other Session_I +* object periodically to detect communication failures. Exactly when this +* is done is up to the implementation.
+* +*When a Session_I object detects a communication failure, or when +* the endSession() operation is called on it, all resources allocated +* with that communication session must be freed and the Session_I object +* must be deleted.
+**/ + +interface Session_I +{ +/** + *This attribute contains a reference to the Session_I object on the + * other side (NMS/EMS) to which the object is associated. It is readonly. + * The attribute can (and should) be checked to make sure the + * NmsSession_I/EmsSession_I association is still valid + * (in particular in case of communication failures).
+ **/ + readonly attribute Session_I associatedSession; + +/** + *Allows for the detection of loss of communication. + * It is implementation-specific to differentiate intermittent + * problems from loss of connection.
+ **/ + void ping(); + +/** + *Allows for a controlled disconnect between associated parties. + * All resources allocated for this session are deleted by the + * operation. Best-effort semantics are expected of invocations of + * this operation (which does not guarantee delivery of the call); + * the default semantics are exactly-once if the operation successfully + * returns or at-most-once if a (standard) exception is returned.
+ **/ + oneway void endSession(); + +}; // end of interface + +}; // end of module + +/** + +A.3 Module nmsSession +*/ + +/** + *This module contains the definition of the NmsSession interface + * of the NML-EML interface.
+ * + *The nmsSession module provides a means for the server to inform the + * NMS in case of notification losses and termination of a loss period.
+ **/ + +module nmsSession +{ + /** + *This interface is instantiated at the NMS. The NMS passes a handle + * to an instance of this interface in the client parameter of the + * getEmsSession() operation of EmsSessionFactory_I.
+ */ + +``` + +``` + +interface NmsSession_I : session::Session_I +{ +/** + *When an EMS fails to push an event, it can notify all connected + * NMSes by invoking this method on every active NmsSession_I. + * This method should also be invoked on any new NmsSession_I set up + * during the event loss period.
+ * + *Once the EMS invokes this method on the NmsSession_Is, it sets + * an internal flag to indicate that it has already informed NMSes of + * event loss. As long as this flag is set, the EMS will not invoke + * this method again. It however may invoke alarmLossOccurred() + * if it discards a non-lifecycle event.
+ * + *When this method is invoked on an NmsSession_I, the NMS comes to + * know that the EMS has failed to push one or more events that may be + * of interest to it. The NMS should consider itself to be potentially + * out-of-sync with the EMS. It should wait until the EMS calls + * eventLossCleared() before resynchronizing with the EMS.
+ * + * @parm globaldefs::Time_T startTime: The time of detection of + * the first notification loss. + * + * @parm string notificationId: The notificationId of the first + * notification lost. + **/ +void eventLossOccurred( + in globaldefs::Time_T startTime, + in string notificationId); + +/** + *The EMS invokes this method to indicate that the event (or + * alarm etc.) loss period is over, and that it is now capable of + * providing all relevant notifications.
+ * + *After invoking this method on the NmsSession_Is, the EMS clears + * the internal flag set by alarmLossOccured() or/and eventLossOccurred(). + * If an event or alarm etc. loss occurs again, alarmLossOccurred() or + * eventLossOccurred() will be called again.
+ * + *How and when the EMS decides to invoke eventLossCleared() is + * an EMS implementation detail.
+ * + * @parm globaldefs::Time_T endTime: The time of the end of + * the event loss period, as determined by the EMS. + **/ +void eventLossCleared( + in globaldefs::Time_T endTime); + +/** + *When an EMS discards an alarm, a TCA, a file transfer status, + * or another non-lifecycle event (with regard to the lifecycle of + * the event source), it can notify all connected NMSes by + * invoking this method on every active NmsSession_I. This service + * should also be invoked on any new NmsSession_I set up during + * the event loss period.
+ * + *Once the EMS invokes this method on the NmsSession_Is, it sets + * an internal flag to indicate that it has already informed NMSes + * of alarm etc. loss. As long as this flag is set, the EMS will not + * invoke this method again. It however may invoke eventLossOccurred() + * if it fails to push a different type of event.
+ * + *When this method is invoked on an NmsSession_I, the NMS comes to + * know that the EMS has discarded one or more alarms, TCAs, file + * transfer statuses, or notifications of other types that may be + * of interest to it. The NMS should consider itself to be potentially + * out-of-sync with the EMS with respect to these notification types. + * It should wait until the EMS calls eventLossCleared() before + * resynchronizing with the EMS on alarms, TCAs, file transfer statuses, + * and the other non-lifecycle notification types.
+ */ + +``` + +``` + +* +* @parm globaldefs::Time_T startTime: The time of the first +* notification discard. +* +* @parm string notificationId: The notificationId of the first +* notification discarded. +**/ +void alarmLossOccurred( + in globaldefs::Time_T startTime, + in string notificationId); + +}; // end of interface + +}; // end of module + +/** + +A.4 Module emsSession +*/ + +/** + *This module contains the definition of the EmsSession interface + * of the NML-EML interface.
+ * + *The emsSession module provides a means for the client to + * interrogate the EMS to determine which manager CORBA interfaces + * (i.e., service-oriented façades) it actually supports. The NMS can + * then retrieve an instance of each of the manager interfaces it + * requires. This capability is achieved using generic IDL so that + * new manager interfaces can be easily added.
+ * + *The module also provides access to the unique OMG event channel + * to be used within the session.
+ **/ + +module emsSession +{ + /** + *Sequence of manager names, i.e., a list of names of service-oriented + * façades, as defined by NML-EML interface specifications that extend + * this framework and preferably derived from the IDL names of the manager + * CORBA interfaces that inherit from common::Common_I.
+ **/ + typedef sequenceA handle to an instance of this interface is gained via the + * emsSessionInterface parameter of the getEmsSession() operation + * of EmsSessionFactory_I.
+ */ + interface EmsSession_I : session::Session_I + { + /** + *This allows an NMS to request the manager CORBA interfaces that + * the EMS implements.
+ * + * @parm managerNames_T supportedManagerList: The list of manager names + * supported by the EMS (see managerNames_T type). + * + * @raises globaldefs::ProcessingFailureException + * EXCPT_INTERNAL_ERROR - Raised in case of non-specific EMS internal + * failure+ * EXCPT_ACCESS_DENIED - Raised in case of security violation
+ **/ + void getSupportedManagers( + out managerNames_T supportedManagerList) + raises(globaldefs::ProcessingFailureException); + } +} + +``` + +``` + +/** + *
This operation allows an NMS to gain access to an instance of + * the specified manager CORBA interface (i.e., service-oriented façade) + * without using the OMG Naming Service.
+ * + * @parm string managerName: The class or type name of the manager + * object that the client wants to access (see getSupportedManagers() + * operation). + * + * @parm common::Common_I managerInterface: A CORBA IOR for the manager + * object. The actual object returned will implement the specified manager + * interface. However it is returned as a Common_I object (see module + * common) so that this operation can be generic. The client should + * narrow the returned object reference to the correct object type. + * + * @raises globaldefs::ProcessingFailureException+ * EXCPT_INTERNAL_ERROR - Raised in case of non-specific EMS internal + * failure
+ * EXCPT_ACCESS_DENIED - Raised in case of security violation
+ *
This operation allows an NMS to gain access to the OMG event + * channel to receive notifications. It returns a reference to a + * NotifyChannel interface instance (which is an EventChannel) as + * defined by the OMG Notification Service. When the EMS supports + * the OMG Telecom Log Service, this operation will return a + * reference to a NotifyLog interface instance (which is a + * NotifyChannel and an EventLog).
+ * + * @parm CosNotifyChannelAdmin::EventChannel eventChannel: + * The event channel (NotifyChannel or NotifyLog) to be used + * by the NMS in this session. + * + * @raises globaldefs::ProcessingFailureException+ * EXCPT_ACCESS_DENIED - Raised in case of security violation
+ *
This module contains the definition of the EmsSessionFactory + * interface of the NML-EML interface.
+ */ + +module emsSessionFactory +{ + /** + *There is a single instance of the EmsSessionFactory_I (per + * supported IDL version). It is the entry point to the server/EMS. + */ + +``` + +``` + + * This instance provides the object reference that the client/NMS + * uses to connect to the server (if the IDL version fits).
+ * + *This CORBA interface implements the Version interface and will + * return the server's IDL version (i.e., the version of the NML-EML + * interface) when getVersion() is called on it.
+ + +interface EmsSessionFactory_I : idlVersion::Version_I +{ + + *This operation allows the client/NMS to obtain the EmsSession_I + * object from which all managers of the server/EMS can be obtained + * (i.e., all service-oriented façade objects actually implemented + * by the server/EMS).
+ * + * @parm string user: The (registered) user or application that is + * trying to access the EMS. The user name can be the empty string + * to indicate that no authentication mechanism is implemented by the + * EMS. The format is defined by the interface specifications + * that extend this framework. + * + * @parm string password: The password/passphrase of the user; it + * can be the empty string. The format and possible encryption are + * defined by the interface specifications that extend this framework. + * + * @parm nmsSession::NmsSession_I client: A handle to the NmsSession_I + * object, instantiated at the NMS, to which the returned EmsSession_I + * object will be associated. + * + * @parm emsSession::EmsSession_I emsSessionInterface: + * A CORBA IOR for the EmsSession_I interface object instantiated + * for the (authenticated) user. + * + * @raises globaldefs::ProcessingFailureException+ * EXCPT_INVALID_INPUT - Raised when client is invalid (see errorReason + * for details provided by the EMS if applicable)
+ * EXCPT_ACCESS_DENIED - Raised in case of security violation + * (e.g., when user or password is invalid) (see errorReason + * for details provided by the EMS if applicable)
+ *
0 V
+12 V
0 V | 0 V
-12 V
0 V
+12 V | -12 V
+12 V
+12 V
-12 V | (Not specified) | To ensure no damage to receiver inputs | +| +10 V
+ 4 V
-10 V
- 4 V | + 4 V
+10 V
- 4 V
-10 V | +6 V
-6 V
-6 V
+6 V | 0
1
1
0 | To guarantee correct operation at $V_i = 6$ V (maintain correct logic state) | +| 300 mV threshold measurement
----- | | | | | +| +0.30 V
0 V | 0 V
+0.30 V | +0.3 V
-0.3 V | 0
1 | } $V_{cm} = 0$ V | +| +7.15 V
+6.85 V | +6.85 V
+7.15 V | +0.3 V
-0.3 V | 0
1 | } $V_{cm} = +7$ V | +| -7.15 V
-6.85 V | -6.85 V
-7.15 V | -0.3 V
+0.3 V | 1
0 | } $V_{cm} = -7$ V | + +FIGURE 7/V.10 + +#### Receiver input sensitivity measurement + +## 6.4 Input balance test + +See Figure 8. + +The balance of the receiver input resistances and internal bias voltages shall be such that the receiver shall remain in the intended binary state under the conditions shown in Figure 8 and described as follows: + +- with $V_i = +720$ millivolts and $V_{cm}$ varied between $-7$ and $+7$ volts; +- with $V_i = -720$ millivolts and $V_{cm}$ varied between $-7$ and $+7$ volts; +- with $V_i = +300$ millivolts and $V_{cm}$ a 1.5 volt peak-to-peak square wave at the highest applicable data signalling rate (this condition is provisional and subject to further study); +- with $V_i = -300$ millivolts and $V_{cm}$ a 1.5 volt peak-to-peak square wave at the highest applicable data signalling rate (this condition is provisional and subject to further study). + +NOTE – The values of $V_i$ are provisional and are the subject of further study. + + + +``` + +graph LR + subgraph Signal_Source + V1[1/2 Vi] + V2[1/2 Vi] + end + R1[500 Ω*] + R2[500 Ω*] + Vcm((Vcm)) + Rec[R] + + V1 --- R1 --- A'[A'] + V2 --- R2 --- B'[B'] + Vcm --- C'[C'] + A' --- Rec + B' --- Rec + C' --- Rec + +``` + +\* Matched. + +T1400110-93/d08 + +Circuit diagram for Receiver input balance test. A differential signal source consists of two series voltage sources, each labeled 1/2 V\_i, connected in series. Each source is in series with a 500 Ω\* resistor. The output terminals are labeled A' and B'. A common-mode voltage source V\_cm is connected between the common ground and terminal C'. A receiver block labeled 'R' is connected between A', B', and C'. The diagram is labeled T1400110-93/d08. + +FIGURE 8/V.10 +**Receiver input balance test** + +# 7 Environmental constraints + +In order to operate an unbalanced interchange circuit at data signalling rates ranging between 0 and 100 kbit/s, the following conditions apply: + +- 1) The total peak differential noise measured between the points A' and B' at the load interchange point (with the generator interchange point connected to a 50-ohm resistor substituted for the generator) shall not exceed the expected amplitude of the received signal minus 0.3 volts (provisional value). +- 2) The worst-case combination of generator-receiver ground potential difference ( $V_g$ , Figure 2) and longitudinally induced peak random noise voltage measured between the receiver points A' or B' and C' with the generator ends of the cable A and C joined together shall not exceed 4 volts. + +# 8 Circuit protection + +Unbalanced generator and load devices complying with this Recommendation shall not be damaged under the following conditions: + +- 1) generator open circuit; +- 2) short-circuit between the conductors of the interconnecting cable; +- 3) short-circuit between the conductors and Point C or C'. + +The above faults 2) and 3) might cause power dissipation in the interchange circuit devices to approach the maximum power dissipation that may be tolerated by a typical integrated circuit (IC) package. The user is therefore cautioned that where multiple generators and receivers are implemented in a single IC package, only one such fault per package might be tolerable at any one time without damage occurring. + +The user is also cautioned that the generator and receiver devices complying with this Recommendation might be damaged by spurious voltages applied between their input or output points and points C and C' (Figure 2). In those applications where the interconnecting cable may be inadvertently connected to other circuits or where it may be exposed to a severe electromagnetic environment, protection should be employed. + +# 9 Category 1 and category 2 receivers + +In order to provide flexibility in the choice of generator (V.10 or V.11), two categories of receiver are defined as follows: + +*Category 1* – Receivers shall have both input terminals A' and B' connected to individual terminals at the load interchange point, independent of all other receivers, as shown in Figure 9, and as applied in Figure A.1. + +*Category 2* – Receivers shall have one terminal connection for each A' input terminal at the load interchange point, and all B' input terminals shall be connected together within the DCE or DTE and shall be brought to one common B' input terminal as shown in Figure 10. + +The specification of the category to be used in any application is part of the appropriate DCE Recommendation, using this type of interface electrical characteristics. + + + +The diagram illustrates the interconnection of signal common return for category 1 receivers. It shows two main sections: DTE (Data Terminal Equipment) on the left and DCE (Data Communications Equipment) on the right. In the DTE section, there are two generators (G) and two receivers (R). The generators have terminals A and C, and the receivers have terminals A', B', and C'. The DCE section also has two receivers (R) with terminals A', B', and C'. The diagram shows signal conductors connecting the A terminals of the DTE generators to the A' terminals of the DCE receivers. A common signal common return is shown, which is connected to the C terminals of the DTE generators and the B' terminals of the DCE receivers. The diagram also shows a signal common return connected to the C' terminals of the DCE receivers. The diagram is labeled with 'Signal conductor', 'Signal common return', 'Circuit 102a', and 'Circuit 102b'. The reference T1400120-93/d09 is at the bottom right. + +Diagram illustrating the interconnection of signal common return for category 1 receivers. The diagram shows two main sections: DTE (Data Terminal Equipment) on the left and DCE (Data Communications Equipment) on the right. In the DTE section, there are two generators (G) and two receivers (R). The generators have terminals A and C, and the receivers have terminals A', B', and C'. The DCE section also has two receivers (R) with terminals A', B', and C'. The diagram shows signal conductors connecting the A terminals of the DTE generators to the A' terminals of the DCE receivers. A common signal common return is shown, which is connected to the C terminals of the DTE generators and the B' terminals of the DCE receivers. The diagram also shows a signal common return connected to the C' terminals of the DCE receivers. The diagram is labeled with 'Signal conductor', 'Signal common return', 'Circuit 102a', and 'Circuit 102b'. The reference T1400120-93/d09 is at the bottom right. + +FIGURE 9/V.10 + +Interconnection of signal common return for category 1 receivers + + + +Diagram showing the interconnection of signal common return for category 2 receivers between DTE and DCE. The diagram is divided into two main sections by vertical dashed lines representing the interface. The left section is labeled 'DTE' and the right 'DCE'. In the DTE section, there are two unbalanced generators (G) at the top and two balanced receivers (R) below them. In the DCE section, there are two balanced receivers (R) at the top and two unbalanced generators (G) below them. Signal conductors connect terminal A of a generator to terminal A' of a receiver. A vertical line on the DTE side connects the C terminals of the generators and the B' terminals of the receivers to a common point grounded in the DTE. This line is labeled 'Signal common return' and 'Circuit 102a' as it crosses to the DCE side. On the DCE side, a similar vertical line connects the B' terminals of the receivers and the C terminals of the generators to a common point grounded in the DCE. This line is labeled 'Signal common return' and 'Circuit 102b' as it crosses to the DTE side. Terminals are labeled A, A', B', C, and C'. A reference number 'T1400130-93/d10' is at the bottom right. + +FIGURE 10/V.10 +**Interconnection of signal common return for category 2 receivers** + +# 10 Signal common return + +The interconnection between the generator and the load interchange points in Figure 2 shall consist of a signal conductor for each circuit and one signal common return for each direction as shown in Figures 9 and 10. Signal common return may be implemented by more than one lead, where required to accomplish interworking, as described in A.2 and as shown in Figure A.1. + +To minimize the effects of ground potential difference $V_g$ and longitudinally-coupled noise on the signal at the load interchange point, the signal common return shall be connected to ground only at the C terminal of the generator interchange point. For example, the B' terminal of all the receivers in DTE which interconnect with unbalanced generators in DCE shall connect to signal common return circuit 102b, which is connected to ground only in DCE. Signal common return circuit 102a is used to interconnect terminal B' of the receivers in DCE with the grounded terminal C of the unbalanced generators in DTE, as in Figures 9 and 10. + +# 11 Detection of generator power-off or circuit failure + +Certain applications require detection of various fault conditions in the interchange circuits, e.g.: + +- 1) generator power-off condition; +- 2) receiver not interconnected with a generator; +- 3) open-circuited interconnecting cable; +- 4) short-circuited interconnecting cable; +- 5) input signal to the load remaining within the transition region ( $\pm 300$ millivolts) for an abnormal period of time. + +When detection of one or more fault conditions is required by specific applications, additional provisions are required in the load and the following items must be determined: + +- a) which interchange circuits require fault detection; +- b) what faults must be detected; +- c) what action must be taken when a fault is detected, e.g. which binary state must the receiver assume? + +The interpretation of a fault condition by a receiver (or load) is application dependent. Each application may use a combination of the following classification: + +*Type 0* – No interpretation. A receiver or load does not have fault detection capability. + +*Type 1* – Data circuits assume a binary 1 state. Control and timing circuits assume an OFF condition. + +*Type 2* – Data circuits assume binary 0 state. Control and timing circuits assume an ON condition. + +*Type 3* – Special interpretation. The receiver or load provides a special indication for interpreting a fault condition. This special indication requires further study. + +The association of the circuit failure detection to particular interchange circuits in accordance with the above types is a matter of the functional and procedural characteristics specification of the interface. + +The interchange circuits monitoring circuit fault conditions in the general telephone network interfaces are indicated in Recommendation V.24. + +The interchange circuits monitoring circuit fault conditions in data network interfaces are indicated in Recommendation X.24 [1]. + +The receiver fault detection type required is specified in the relevant DCE Recommendations. + +# 12 Measurements at the physical interchange point + +The following information provides guidance for measurements when maintenance persons examine the interface for proper operation at the interchange point. + +## 12.1 Listing of essential measurements + +- open-circuit measurements; +- test-termination measurement; +- short-circuit measurement; +- generator output rise time; +- d.c. input sensitivity measurements. + +## **12.2 Listing of optional measurements** + +- the total generator resistance between points A and C shall be equal to or less than 50 ohms; +- power-off measurements; +- receiver input voltage space-space current measurements; +- input balance test; +- check of the required circuit fault detection (clause 11). + +The parameters defined in this Recommendation are not necessarily measurable at the physical interchange point. This is for further study. + +# **Annex A** + +## **Compatibility with other interfaces** + +(This annex forms an integral part of this Recommendation) + +## **A.1 Compatibility of Recommendation V.10 and Recommendation V.11 interchange circuits in the same interface** + +The electrical characteristics of Recommendation V.10 are designed to allow the use of balanced (see Recommendation V.11) and unbalanced circuits within the same interface. For example, the balanced circuits may be used for data and timing whilst the unbalanced circuits may be used for associated control circuit functions. + +## **A.2 Recommendation V.10 interworking with Recommendation V.11** + +The differential receiver specifications of this Recommendation and Recommendation V.11 are electrically identical. It is therefore possible to interconnect an equipment using Recommendation V.10 receivers and generators on one side of the interface with an equipment using Recommendation V.11 generators and receivers on the other side of the interface. Such interconnection would result in interchange circuits according to Recommendation V.11 in one direction and interchange circuits according to this Recommendation in the other direction. Where such interworking is contemplated, the following technical considerations must be taken into account. + +**A.2.1** Interconnecting cable lengths are limited by performance of the circuits working to the Recommendation V.10 side of the interface. + +**A.2.2** The optional cable termination resistance ( $Z_t$ ), if implemented, in the equipment using Recommendation V.11 must be removed. + +**A.2.3** V.10-type receivers shall be of category 1 (see Figure A.1). + +## **A.3 Recommendation V.10 interworking with Recommendation V.28** + +The unbalanced electrical characteristics of this Recommendation have also been designed to permit limited interworking, under certain conditions, with generators and receivers to Recommendation V.28. Where such interworking is contemplated, the following technical limitations must be considered: + +**A.3.1** Separate DTE and DCE signal return paths will not be available at the Recommendation V.28 side of the interface. + + + +Diagram illustrating the interconnection of signal common return by more than one conductor in order to accomplish interoperability of V.10 generators with category 1 receivers. The diagram shows two sections: DTE (Data Terminal Equipment) on the left and DCE (Data Communications Equipment) on the right. The DTE section contains two generators (G) and two receivers (R). The DCE section contains two receivers (R) and two generators (G). The signal conductors are labeled A, B, and C. The signal common return is labeled A', B', and C'. The diagram shows two different wiring configurations: Circuit 102a and Circuit 102b. In Circuit 102a, the signal conductors A, B, and C are connected to the receivers R in the DCE section. In Circuit 102b, the signal conductors A, B, and C are connected to the generators G in the DCE section. The signal common return conductors A', B', and C' are connected to the receivers R in the DTE section. The diagram also shows a ground connection for the signal common return. + +T1400140-93/d11 + +FIGURE A.1/V.10 + +**Interconnection of signal common return by more than one conductor in order to accomplish interoperability of V.10 generators with category 1 receivers** + +- A.3.2** Data signalling-rate limitations according to Recommendation V.28 shall apply. +- A.3.3** Interconnecting cable lengths are limited by the Recommendation V.28 performance restrictions. +- A.3.4** Probability of satisfactory operation will be enhanced by providing the maximum generator voltage possible on the Recommendation V.10 side of the interface within the limitations stipulated in this Recommendation. +- A.3.5** There may be equipment in the field where the V.28 type generators use potentials in excess of 12 volts and up to 25 volts. Where connection to this type of equipment is envisaged, adequate protection for the V.10 receivers is advised. +- A.3.6** Power-off detectors in Recommendation V.28 receivers may not necessarily work with Recommendation V.10 generators. + +# Annex B + +## Considerations for coaxial cable applications – V.10 COAXIAL4) + +(This annex forms an integral part of this Recommendation) + +It is recognized that where coaxial cables are used for interconnecting purposes it may be desirable to include a terminating resistance at the receiver end of the cable. This is considered to be a special case for which special generator characteristics are required. The terminating resistance shall in no case be less than 50 ohms and the reference measurements under 5.2.2 and 5.3 shall be made with a 50-ohm test termination5). Use of this special application will require appropriate agreement with the proper authority. + +The alternative set of electrical characteristics applied in the coaxial cable case is the following. + +#### 5.2.2 *bis* Test termination measurement + +See Figure 4b). + +With a test load ( $R_t$ ) of 50 ohms connected between output points A and C, the magnitude of the output voltage ( $V_t$ ) shall be equal to or greater than 0.5 of the magnitude of $V_0$ . + +#### 5.3.1 *bis* Waveform + +See Figure 5. + +The measurement will be made with a resistor of 50 ohms connected between points A and C. A test signal, with a nominal signal element duration $t_b$ and composed of alternate ones and zeros, shall be applied to the input. The change in amplitude of the output signal during transitions from one binary state to the other shall be monotonic between 0.1 and 0.9 of $V_{ss}$ . + +#### 5.3.2 *bis* Waveshaping + +Waveshaping is not normally required for coaxial cable applications. + +### 10 *bis* Signal common return + +In applications where coaxial cables are used, the screen of the coaxial cable shall be connected to ground only at point C at the generator end as shown in Figure B.1. + +--- + +4) All the electrical characteristics specified in Recommendation V.10 other than those set down in this annex are applicable to the coaxial cable case with a cable case with a cable termination. + +5) For test purposes other than specified in this Recommendation (e.g. signal quality measurement), a transmitter test load of 50 ohms may be used. + + + +The diagram illustrates four different interconnection configurations for a signal conductor (A) and a shield conductor (C) between a Data Terminal Equipment (DTE) and a Data Communications Equipment (DCE) using a coaxial cable. +- The top two configurations show transmission from DTE to DCE. The generator (G) is at the DTE, and the receiver (R) is at the DCE. The signal conductor connects point A to A', and the shield conductor connects point C to B'. A termination impedance $Z_t$ is connected between A' and B'. In the first, the shield is grounded at the DTE. In the second, it is grounded at both ends. +- The bottom two configurations show transmission from DCE to DTE. The generator (G) is at the DCE, and the receiver (R) is at the DTE. The signal conductor connects point A to A', and the shield conductor connects point C to B'. A termination impedance $Z_t$ is connected between A' and B'. In the third, the shield is grounded at the DCE. In the fourth, it is grounded at both ends. + +T1400150-93/d12 + +Four circuit diagrams showing interconnection with coaxial cable between DTE and DCE. Each diagram shows a signal conductor (A) and a shield conductor (C). The DTE side has a generator (G) and the DCE side has a receiver (R). Termination impedance Zt is shown at the DCE end. The diagrams illustrate different grounding and termination configurations for the signal and shield conductors. + +$Z_t$ Optional termination impedance + +FIGURE B.1/V.10 +Interconnection with coaxial cable + +# Appendix I + +## Waveshaping + +(This appendix does not form an integral part of this Recommendation) + +The required waveshaping may be accomplished either by providing a slew-rate control in the generator or by inserting an RC filter at the generator interchange point. A combination of these methods may also be employed. An example of the RC filter method is shown in Figure I.1. Typical values of capacitance $C_w$ , with the value of $R_w$ selected so that $R_w + R_d$ is approximately 50 ohms, are given for typical cable with an interconductor shunt capacitance of approximately 0.05 microfarads per kilometre. + + + +T1400160-93/d13 + +$R_d$ Generator internal resistance + $R_w$ 50 ohms – $R_d$ + +Circuit diagram showing a generator G connected to a receiver R via an interconnecting cable. The generator output has a series resistor Rw and a shunt capacitor Cw connected to ground. The interconnecting cable is represented by dashed lines. The receiver R is connected to a destination D. A label T1400160-93/d13 is in the bottom right corner. + +| $C_w$
(microfarads) | Data signalling rate
range (kbit/s) | +|------------------------|----------------------------------------| +| 1.0 | de 0 - 2.5 | +| 0.47 | de 2.5 - 5 | +| 0.22 | de 5 - 10 | +| 0.1 | de 10 - 25 | +| 0.047 | de 25 - 50 | +| 0.022 | de 50 - 100 | + +FIGURE 1.1/V.10 + +### Example method of waveshaping + +# Appendix II + +## Cable Guidelines + +(This appendix does not form an integral part of this Recommendation) + +No electrical characteristics of the interconnection cable are specified in this Recommendation. However, guidance is given herein concerning operational constraints imposed by cable length and near-end crosstalk. + +The maximum operating distance for the unbalanced interchange circuit is primarily a function of the amount of interference (near-end crosstalk) coupled to adjacent circuits in the equipment interconnection. Additionally the unbalanced circuit is susceptible to exposure to differential noise resulting from any imbalance between the signal conductor and signal common return at the load interchange point. Increasing the physical separation and interconnection cable length between the generator and load interchange points might increase the exposure to common-mode noise and the degree of near-end crosstalk. Accordingly, users are advised to restrict the cable length to a minimum consistent with the generator-load physical separation requirements. + +The curve of cable length versus data signalling rate given in Figure II.1 may be used as a conservative guide. This curve is based upon calculations and empirical data using twisted-pair telephone cable with a shunt capacitance of 0.052 microfarads per kilometre, a 50-ohm source impedance, a 6-volt source signal and maximum near-end crosstalk of 1-volt peak. The rise time ( $t_r$ ) of the source signal at signalling rates below 1000 bit/s is 100 microseconds and above 1000 bit/s is $0.1 t_b$ (see Figure 5). + +The user is cautioned that the curve given in Figure II-1 does not account for common-mode noise or near-end crosstalk levels beyond the limits specified, that may be introduced between the generator and load by exceptionally long cables. On the other hand operation within the signalling-rate and distance bounds of Figure II.1 will usually ensure that the distortion of the signal appearing at the receiver input will be acceptable. Many applications, however, can tolerate greater levels of signal distortion, and correspondingly greater cable lengths can be employed. The generation of near-end crosstalk can be reduced by increasing the amount of waveshaping employed. + +Experience has shown that in most practical cases the operating distance at the lower data signalling rates may be extended to several kilometres. + + + +| Data signalling rate (bit/s) | Cable length (m) | +|------------------------------|------------------| +| 10 2 | 10 3 | +| 10 3 | 10 3 | +| 10 4 | 10 2 | +| 10 5 | 10 1 | + +A log-log graph showing Cable length (m) on the Y-axis versus Data signalling rate (bit/s) on the X-axis. The Y-axis ranges from 10^1 to 10^4, and the X-axis ranges from 10^2 to 10^5. A solid line represents the maximum cable length for a given signalling rate. The line is horizontal at 10^3 m for rates up to 10^3 bit/s, then slopes downward, passing through (10^4, 10^2) and (10^5, 10^1). + +FIGURE II.1/V.10 +Data signalling rate vs cable length for unbalanced +interchange circuit + +## Reference + +- [1] CCITT Recommendation *List of definitions for interchange circuits between data terminal equipment (DTE) and data circuit-terminating equipment (DCE) on public data networks*, Vol. VIII, Rec. X.24. \ No newline at end of file diff --git a/marked/V/T-REC-V.100-198811-I_PDF-E/raw.md b/marked/V/T-REC-V.100-198811-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..3a0b447fb0092e098fcee29289ea29d46ff25e2c --- /dev/null +++ b/marked/V/T-REC-V.100-198811-I_PDF-E/raw.md @@ -0,0 +1,244 @@ + + + + +ITU logo: a globe with the letters ITU and a lightning bolt symbol. + +INTERNATIONAL TELECOMMUNICATION UNION + +# ITU-T + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +## V.100 + +# **DATA COMMUNICATION OVER THE TELEPHONE NETWORK** + +## --- **INTERCONNECTION BETWEEN PUBLIC DATA NETWORKS (PDNs) AND THE PUBLIC SWITCHED TELEPHONE NETWORKS (PSTN)** + +## **ITU-T Recommendation V.100** + +(Extract from the *Blue Book*) + +--- + +## NOTES + +1 ITU-T Recommendation V.100 was published in Fascicle VIII.1 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below). + +2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +## **INTERCONNECTION BETWEEN PUBLIC DATA NETWORKS (PDNs) AND THE PUBLIC SWITCHED TELEPHONE NETWORKS (PSTN)** + +*(Malaga-Torremolinos, 1984)* + +The CCITT, + +*considering that* + +- (a) a data station may have an ingoing or outgoing access to a packet switched public data network (PSPDN) via the national1) PSTN; +- (b) the transmission characteristics of the data station may not be known at the PSPDN access level; +- (c) in this case, the transmission characteristics have to be negotiated between modems before establishing the connection; +- (d) half-duplex modems as well as full duplex modems may be used; + +*proposes* + +that Administrations may optionally introduce the following handshaking procedures including the types of modems to be supported. + +### **1 Procedure description** + +According to the type of modem (see Table 1/V.100), a half-duplex or a duplex procedure is used. + +#### **1.1 Half-duplex procedure** + +See Figure 1/V.100. + +##### **1.1.1 Answer mode modem** + +- a) Following the transmission of the answer sequence in accordance with Recommendation V.25, the modem shall apply an ON condition to circuit 107, and then transmit a segment S1 in accordance with Table 1/V.100 for 294 ms. Interchange circuits 106 and 109 are in the OFF condition during the procedure. +- b) The modem remains silent until it detects S2 (defined in Table 1/V.100) or the synchronizing signals of a V.27 *ter* modem in the fallback mode. +- c) Then the modem conditions itself to the selected mode or disconnects. + +If no response is detected within 2 seconds following the end of the S1 transmission, the modem resumes transmitting S1. + +--- + +1) **International access to a PSPDN via PSTN is not envisaged.** + +TABLE 1/V.100 + +###### **S2 and S1 signals** + +| Categories | Data rate
(bit/s) | Recommendation | Procedure | S2
(calling DCE) | S1
(Answering DCE) | +|----------------------------------------------|----------------------|------------------------------------------------------------------------|-------------------------------------------|----------------------------------------------------|----------------------------------------------------| +| Duplex
asynchronous | 300
1200 | V.21
V.22 | Duplex
Duplex | 980 Hz
1200 Hz | 1650 Hz
1800 + 2250 Hz | +| Duplex
synchronous
(FDM) | 1200
2400 | V.22
V.22 bis | Duplex
Duplex | 1200 Hz
1200 Hz | 1800 + 2250 Hz
1800 + 2250 Hz | +| Duplex
synchronous
(ECT) a) | 2400
4800
9600 | V.26 ter
V.32
V.32 | Half-duplex
Duplex
Duplex | (See V.26 ter )
(See V.32)
(See V.32) | (See V.26 ter )
(See V.32)
(See V.32) | +| Half-duplex
synchronous | 2400
4800
9600 | V.27 ter
(fallback mode)
V.27 ter
(Under study) | Half-duplex
Half-duplex
Half-duplex | None
1400 Hz
1100 Hz | None
2200 Hz
2300 Hz | +| Asymmetric
asynchronous | 75/1200 | V.23 | Duplex | 390 Hz | 1300 Hz | + +a) ECT = echo cancellation technique. + + + +The diagram illustrates the half-duplex procedure timing. It shows three signal lines: 109 (top), 106 (middle), and 107 (bottom). The 'Answering modem' section shows a 2100 Hz tone followed by a 3.4 s interval, then a 75±20 ms connection to the line. The 'Calling modem' section shows a 2100 Hz tone followed by a 3.4 s interval, then a 75±20 ms connection to the line. The S1 and S2 signaling is shown with a 2100 Hz tone and a 75±20 ms connection to the line. The time interval T = 294 ms is marked for the S1 and S2 signaling. The 2100 Hz tone is also shown with a 2.15 s interval. The diagram is labeled 'See Note' and 'CCITT-65360'. + +Timing diagram for the half-duplex procedure showing signaling between Answering and Calling modems and the line. The diagram includes signals 109, 106, and 107. Key events include a 2100 Hz tone, S1 and S2 signaling, and a 75±20 ms connection to the line. Time intervals of 2.15 s, 3.4 s, and T = 294 ms are marked. + +Note – The 2100 Hz tone is transmitted to disable the echo suppressors in case of duplex transmission (see Recommendation V.26 *ter*). For half-duplex transmission, this tone is not mandatory. + +FIGURE 1/V.100 +Half-duplex procedure + +If S2 indicates a capability not available, the modem shall disconnect from the line. + +If S2 indicates a capability available, the modem conditions itself to this mode. + +- d) After the end of reception of S2, in the case of a duplex modem (see V.26 *ter*), in accordance with Recommendation G.164, the modem transmits a $2100 \pm 15$ Hz tone for $500 \pm 50$ ms to disable echo suppressors, then remains silent for $75 \pm 20$ ms. + +*Note* - In the case of half-duplex modems, the transmission of the 2100 Hz tone is not needed. + +##### 1.1.2 Call mode modem + +- a) After connection to line, the modem shall apply an ON condition to circuit 107 (interchange circuits 106 and 109 are in the OFF condition during the procedure). The modem keeps silent during at least 400 ms. + +During this period, it detects S1. + +The calling modem selects a mode of interworking in accordance with S1 or its nominal one. + +- b) Then, it transmits S2 in accordance with Table 1/V.100 or the synchronizing signals of a V.27 *ter* modem in the fallback mode at 2400 bit/s. +- c) Then, it conditions itself to the selected capability. + +#### 1.2 Duplex procedure + +See Figure 2/V.100. + + + +The diagram illustrates the duplex procedure timing. It shows three signal lines at the top: 109, 106, and 107. Lines 109 and 106 are initially low and then transition to high (indicated by dashed lines). Line 107 transitions from low to high at the start of the procedure. Below these, the 'Answering modem' and 'Calling modem' are shown. The answering modem transmits a 2100 Hz tone for 2.15 s, followed by a 3.4 s interval, and then S1. The calling modem receives S1 and then transmits S2. A 'Connection to line' is indicated by an arrow pointing to the line between the modems. The timing for the 2100 Hz tone is 500 ± 50 ms, and the subsequent silence is 75 ± 20 ms. The diagram is labeled CCITT-65370. + +Timing diagram for the Duplex procedure showing signaling between an answering modem and a calling modem. + +FIGURE 2/V.100 +Duplex procedure + +##### 1.2.1 Answer mode modem + +- a) Following the transmission of the answer sequence in accordance with Recommendation V.25, the modem shall apply an ON condition to circuit 107 (interchange circuits 106 and 109 are in the OFF condition during the procedure). +- b) Then, the modem transmits a segment S1 in accordance with Table 1/V.100 at least $40 \pm 10$ ms and until it has detected the end of transmission of S2. + +*Note* - During this period, some exchanges may occur between the two modems according to the Series V Recommendation concerned (see Recommendation V.32). + +If no response is detected within a time period (under study), the modem shall disconnect from line. + +If S2 indicates a capability not available, the modem shall disconnect from the line. + +If S2 indicates a capability available, the modem conditions itself to this mode. + +##### 1.2.2 Call mode modem + +- a) In accordance with Recommendation V.25, after detection of the 2100 Hz tone and a silent period of $75 \pm 20$ ms, the modem shall apply an ON condition to circuit 107 (interchange circuits 106 and 109 are in the OFF condition during the procedure). +- b) The modem detects S1. + +The calling modem selects a mode of interworking in accordance with S1 or its nominal one. + +- c) Then, it transmits S2 in accordance with Table 1/V.100. + +*Note* - If the modem has only one possibility, it may transmit S2 after being connected to line. + +- d) Then, it conditions itself to the selected capability. + +### 2 Combined half and duplex procedure + +This section describes the interworking between a DCE having the capability of handling the two procedures [referred to as two procedures (TP)modem] and DCEs having only one procedure. + +#### 2.1 Interworking with half-duplex procedure + +##### 2.1.1 TP modem in the answering mode + +See Figure 3/V.100. + + + +The diagram illustrates the timing sequence for a TP modem in answering mode. It shows two horizontal timelines. The top timeline is for the 'Answering modem (TP modem)'. It begins with a box labeled 'Line on', followed by a sequence of two boxes labeled 'S1' and 'S1z'. Above the 'S1' box is a bracket labeled 'S1' and the text 'Starts transmitting S1'. The bottom timeline is for the 'Calling modem'. It shows a 'Line on' event followed by a box labeled 'S2'. An arrow points from the end of the 'S2' box on the calling modem timeline to the start of the 'S1z' box on the answering modem timeline. Below the 'S2' box, the text 'Transmits S2' is written. A horizontal arrow labeled 'Time' indicates the direction of the sequence. At the bottom, the text 'TP modem answer mode' is centered. + +Timing diagram for TP modem in answering mode showing the interaction between an answering modem and a calling modem. + +###### 2.1.1.1 Answer TP modem + +- a) After the V.25 sequence, the modem will transmit S1 which is composed of two segments S11 and S12 (as described in Appendix I to Recommendation V.32). + +S11 is a modulated signal transmitted during 294 ms in a 600-3000 Hz bandwidth, S12 is a tone out of the 600-3000 Hz band. + +- b) After the transmission of S12, the modem is waiting for S2. When it detects S2, it stops transmitting S12 and proceeds with the half-duplex procedure. + +###### 2.1.1.2 Calling modem + +The calling modem shall proceed with the half-duplex procedure taking into account that S12 is an out-of-band signal. + +##### 2.1.2 TP modem in the calling mode + +See Figure 4/V.100. + + + +The diagram illustrates the timing for a TP modem in call mode. It shows two horizontal timelines. The top timeline is for the 'Answering modem' and the bottom for the 'Calling modem (TP modem)'. The Answering modem starts with a '2100 Hz' signal, followed by a block labeled 'S1'. The Calling modem starts with an arrow pointing to the line labeled 'Connect to line'. It then receives a signal 'S2'. A dashed arrow points from the end of 'S1' to the start of 'S2'. The reference 'CCITT-65390' is at the bottom right. + +Timing diagram for TP modem call mode showing Answering modem and Calling modem (TP modem) interactions. + +FIGURE 4/V.100 +TP modem callmode + +###### 2.1.2.1 Answering modem + +The answering modem shall proceed with the half-duplex procedure. + +###### 2.1.2.2 Calling TP modem + +The calling TP modem after the V.25 sequence and connection to line remains silent. It detects S1 and shall proceed with the half-duplex procedure. + +#### 2.2 Interworking with duplex procedure + +##### 2.2.1 TP modem in the answering mode + +See Figure 5/V.100. + + + +The diagram illustrates the timing for a TP modem in answer mode. It shows two horizontal timelines. The top timeline is for the 'Answering modem (TP modem)' and the bottom for the 'Calling modem'. The Answering modem starts with a '2100 Hz' signal, followed by blocks labeled 'S11' and 'S12'. The Calling modem starts with an arrow pointing to the line labeled 'Connect to line'. It then receives a signal 'S2'. A solid arrow points from the end of 'S12' to the start of 'S2'. A dashed line extends from the end of 'S2'. A label 'Stops transmitting S2' points to the end of the 'S12' block. The reference 'CCITT-65400' is at the bottom right. + +Timing diagram for TP modem answer mode showing Answering modem (TP modem) and Calling modem interactions. + +FIGURE 5/V.100 +TP modem answer mode + +###### 2.2.1.1 Answering TP modem + +The modem proceeds as in § 2.1.1.1 except that after detection of S2, it shall follow the duplex procedure. + +###### 2.2.1.2 Calling modem + +The calling modem shall proceed with the duplex procedure. + +##### 2.2.2 TP modem in the calling mode + +See Figure 6/V.100. + + + +The diagram illustrates the timing sequence for a TP modem call mode. It features two horizontal timelines. The top timeline, labeled 'Answering modem', shows a '2100 Hz' tone followed by a signal 'S1'. The bottom timeline, labeled 'Calling modem (TP modem)', shows a vertical arrow labeled 'Connect to line' followed by a signal 'S2'. A horizontal double-headed arrow labeled 'Detects S1' spans the time between the 'Connect to line' event and the start of 'S1'. A diagonal arrow points from the 'Detects S1' period to the 'S1' signal on the Answering modem timeline. The reference 'CCITT-V.100' is located at the bottom right of the diagram. + +Timing diagram for TP modem call mode showing the interaction between an Answering modem and a Calling modem (TP modem). + +FIGURE 6/V.100 +TP modem call mode + +###### 2.2.2.1 Answering modem + +The answering modem shall proceed with the duplex procedure. + +###### 2.2.2.2 Calling TP modem + +The calling TP modem after the V.25 sequence and connection to line remains silent. It detects S1 and shall proceed with the duplex procedure. \ No newline at end of file diff --git a/marked/V/T-REC-V.11-199610-I_PDF-E/raw.md b/marked/V/T-REC-V.11-199610-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..5aa6c5e9bf734bb16ad170e1f1b175ea911ff0b9 --- /dev/null +++ b/marked/V/T-REC-V.11-199610-I_PDF-E/raw.md @@ -0,0 +1,596 @@ + + + + +ITU logo: a globe with the letters ITU inside, and a lightning bolt striking the globe. + +INTERNATIONAL TELECOMMUNICATION UNION + +# ITU-T + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +# V.11 + +(10/96) + +SERIES V: DATA COMMUNICATION OVER THE +TELEPHONE NETWORK + +Interfaces and voiceband modems + +--- + +**Electrical characteristics for balanced +double-current interchange circuits operating +at data signalling rates up to 10 Mbit/s** + +ITU-T Recommendation V.11 + +(Previously "CCITT Recommendation") + +--- + +# ITU-T V-SERIES RECOMMENDATIONS DATA COMMUNICATION OVER THE TELEPHONE NETWORK + +- 1 – General +- 2 – Interfaces and voiceband modems** +- 3 – Wideband modems +- 4 – Error control +- 5 – Transmission quality and maintenance +- 6 – Interworking with other networks + +*For further details, please refer to ITU-T List of Recommendations.* + +# FOREWORD + +The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. + +The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). + +ITU-T Recommendation V.11 was revised by ITU-T Study Group 14 (1993-1996) and was approved by the WTSC (Geneva, October 9-18, 1996). + +## --- NOTE + +1. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. +2. The status of annexes and appendices attached to the Series V Recommendations should be interpreted as follows: + - an *annex* to a Recommendation forms an integral part of the Recommendation; + - an *appendix* to a Recommendation does not form part of the Recommendation and only provides some complementary explanation or information specific to that Recommendation. + +© ITU 1997 + +All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. + +# CONTENTS + +| | | Page | +|----|-------------------------------------------------------------------------------------|-------------| +| 1 | Introduction ..... | 1 | +| 2 | Field of application ..... | 1 | +| 3 | Symbolic representation of interchange circuit ..... | 1 | +| 4 | Generator polarities and receiver significant levels ..... | 2 | +| | 4.1 Generator ..... | 2 | +| | 4.2 Receiver ..... | 2 | +| 5 | Generator ..... | 2 | +| | 5.1 Resistance and d.c. offset voltage ..... | 2 | +| | 5.2 Static reference measurements ..... | 3 | +| | 5.3 Dynamic voltage balance and rise time measurements ..... | 5 | +| 6 | Load ..... | 6 | +| | 6.1 Characteristics ..... | 6 | +| | 6.2 Receiver input voltage – Current measurements ..... | 7 | +| | 6.3 D.c. input sensitivity measurements ..... | 7 | +| | 6.4 Input balance test ..... | 8 | +| | 6.5 Terminator ..... | 8 | +| 7 | Environmental constraints ..... | 9 | +| 8 | Circuit protection ..... | 9 | +| 9 | Detection of generator power-off or circuit failure ..... | 9 | +| 10 | Measurements at the physical interchange point ..... | 10 | +| | 10.1 Listing of essential measurements ..... | 10 | +| | 10.2 Listing of optional measurements ..... | 10 | +| | Annex A – Compatibility with other interfaces ..... | 11 | +| | A.1 Compatibility of V.10 and V.11 interchange circuits in the same interface ..... | 11 | +| | A.2 Recommendation V.11 interworking with Recommendation V.10 ..... | 11 | +| | Appendix I – Cable and termination ..... | 11 | +| | I.1 Cable ..... | 11 | +| | I.2 Cable length ..... | 11 | +| | I.3 Cable termination ..... | 13 | +| | Appendix II – Multipoint operation ..... | 13 | +| | Reference ..... | 13 | + +# **ELECTRICAL CHARACTERISTICS FOR BALANCED DOUBLE-CURRENT INTERCHANGE CIRCUITS OPERATING AT DATA SIGNALLING RATES UP TO 10 Mbit/s1)** + +*(Geneva, 1976; amended Geneva, 1980, at Melbourne, 1988, at Helsinki, 1993 and at Geneva, 1996)* + +## **1 Introduction** + +This Recommendation deals with the electrical characteristics of the generator, receiver and interconnecting leads of a differential signalling (balanced) interchange circuit with an optional d.c. offset voltage. + +The balanced generator and load components are designed to cause minimum mutual interference with adjacent balanced or unbalanced interchange circuits (see Recommendation V.10) provided that waveshaping is employed on the unbalanced circuits. + +In the context of this Recommendation, a balanced interchange circuit is defined as consisting of a balanced generator connected by a balanced interconnecting pair to a balanced receiver. For a balanced generator, the algebraic sum of both the outlet potentials, with respect to earth, shall be constant for all signals transmitted; the impedances of the outlets with respect to earth shall be equal. The degree of balance and other essential parameters of the interconnecting pair is a matter for further study. + +Annex A and Appendices I and II are provided to give guidance on a number of application aspects as follows: + +- Annex A – Compatibility with other interfaces. +- Appendix I – Cable and termination. +- Appendix II – Multipoint operation. + +NOTE – Generator and load devices meeting the electrical characteristics of this Recommendation need not operate over the entire data signalling rate range specified. They may be designed to operate over narrower ranges to satisfy requirements more economically, particularly at lower data signalling rates. + +Reference measurements are described which may be used to verify certain of the recommended parameters but it is a matter for individual manufacturers to decide what tests are necessary to ensure compliance with this Recommendation. + +## **2 Field of application** + +The electrical characteristics specified in this Recommendation apply to interchange circuits operating with data signalling rates up to 10 Mbit/s. + +Typical points of application are illustrated in Figure 1. + +Whilst the balanced interchange circuit is primarily intended for use at the higher data signalling rates, its use at the lower rates may be necessary in the following cases: + +- 1) where the interconnecting cable is too long for proper unbalanced circuit operation; +- 2) where extraneous noise sources make unbalanced circuit operation impossible; +- 3) where it is necessary to minimize interference with other signals. + +## **3 Symbolic representation of interchange circuit** + +See Figure 2. + +The equipment at both sides of the interface may implement generators as well as receivers in any combination. Consequently, the symbolic representation of the interchange circuit, Figure 2 below, defines a generator interchange point as well as a load interchange point. + +--- + +1) This Recommendation is also designated as Recommendation X.27 in the X-Series Recommendations. + + + +Diagram showing two typical applications of balanced interchange circuits. The top diagram shows two DTE (Data Terminal Equipment) blocks connected by a balanced interchange circuit, represented by a vertical oval with two horizontal lines passing through it. The bottom diagram shows a DTE block connected to a DCE (Data Communications Equipment) block by a similar balanced interchange circuit. An arrow points from the text 'Circuits to this Recommendation' to the vertical oval in both diagrams. The identifier 'T1400040-93/d01' is located at the bottom right of the diagram. + +FIGURE 1/V.11 + +### Typical applications of balanced interchange circuits + +For data transmission applications, it is commonly accepted that the interface cabling will be provided by the DTE. This introduces the line of demarcation between the DTE plus cable and the DCE. This line is also called the interchange point and physically implemented in the form of a connector. The applications also require interchange circuits in both directions. This leads to an illustration as shown in Figure 3. + +## 4 Generator polarities and receiver significant levels + +### 4.1 Generator + +The signal conditions for the generator are specified in terms of the voltage between output points A and B shown in Figure 2. + +When the signal condition 0 (space) for data circuits or ON for control and timing circuits is transmitted, the output point A is positive with respect to point B. When the signal condition 1 (mark) for data circuits or OFF for control and timing circuits is transmitted, the output point A is negative with respect to point B. + +### 4.2 Receiver + +The receiver differential significant levels are shown in Table 1, where $V_{A'}$ and $V_{B'}$ are respectively the voltages at points A' and B' relative to point C'. + +## 5 Generator2) + +### 5.1 Resistance and d.c. offset voltage + +**5.1.1** The total generator resistance between points A and B shall be less than or equal to 100 ohms and be adequately balanced with respect to point C. The degree of balance required, both static and dynamic, is left for further study). + +2) For test purposes other than specified in this Recommendation (e.g. signal quality measurement), a transmitter test load of 100 ohms may be used. + +#### NOTES + +1 – It is assumed that the value of the dynamic source impedance is in the same range. + +2 – In the event that reflections are experienced on V.11 circuits, either the use of a terminating network at the receiver (in the range of 120 to 126 ohms) or the use of series resistors (approximately 33 ohms) added to the generator output leads, should alleviate this problem. This latter solution has the additional benefit of providing protection from over-voltages but creates a problem with meeting the Test-termination measurement specified in 5.2.2. + + + +Symbolic representation of a balanced interchange circuit diagram. The diagram shows a Generator (G) connected to a Balanced interconnecting cable, which is then connected to a Load (R). The cable has a Cable termination (Zt) at the receiver end. Interchange points are marked: Generator interchange point (A, B) and Load interchange point (A', B'). Zero volt reference interchange points (C, C') are also shown. Voltages are labeled: V\_ab (Generator output voltage between points A and B), V\_ca (Generator voltage between points C and A), V\_cb (Generator voltage between points C and B), Zt (Cable termination impedance), and Vg (Ground potential difference). + +| | | +|-----------------|-------------------------------------------------| +| $V_{ab}$ | Generator output voltage between points A and B | +| $V_{ca}$ | Generator voltage between points C and A | +| $V_{cb}$ | Generator voltage between points C and B | +| $Z_t$ | Cable termination impedance | +| $V_g$ | Ground potential difference | +| A, B and A', B' | Interchange points | +| C, C' | Zero volt reference interchange points | + +#### NOTES + +1 – Two interchange points are shown. The output characteristics of the generator, excluding any interconnecting cable, are defined at the “generator interchange point”. The electrical characteristics to which the receiver must respond are defined at the “load interchange point”. + +2 – Points C and C' may be interconnected and further connected to protective ground if required by national regulations. + +FIGURE 2/V.11 + +#### **Symbolic representation of a balanced interchange circuit** + +**5.1.2** The magnitude of the generator d.c. offset voltage (see 5.2.2) shall not exceed 3 V under all operating conditions. + +### 5.2 Static reference measurements + +The generator characteristics are specified in accordance with measurements illustrated in Figure 4 and described in 5.2.1 to 5.2.4. + +#### 5.2.1 Open-circuit measurement + +See Figure 4 a). + +The open-circuit voltage measurement is made with a 3900-ohm resistor connected between points A and B. In both binary states, the magnitude of the differential voltage ( $V_0$ ) shall not be more than 6.0 volts, nor shall the magnitude of $V_{0a}$ and $V_{0b}$ be more than 6.0 volts. + + + +Figure 3/V.11: Practical representation of the interface. This schematic diagram shows the electrical connection between a Data Terminal Equipment (DTE) and a Data Communications Equipment (DCE) through a cable. The DTE side (left) includes a generator (G) and a receiver (R). The DCE side (right) includes a receiver (R) and a generator (G). A central vertical dashed line represents the 'Line of demarcation'. Points A, B, C, C' are on the DCE side, and A', B', C, C' are on the DTE side. A test load Zt is connected between A and B. Ground connections are shown for 'DTE and Cable' (Note 2) and 'DCE' (Note 2). A connector is shown at the top with points A' and B'. Note 1 indicates that C and C' may be interconnected via the signal ground conductor. The document identifier T1400230-93/d03 is at the bottom right. + +##### NOTES + +- 1 – The zero volt reference interchange point C, C' may be interconnected via the signal ground conductor. +- 2 – Signal ground may be further connected to external protective ground if national regulations require. +- 3 – The type of connector with this electrical characteristic specification depends on the application. ISO specifies, for data transmission over telephone type facilities, a 37-pin connector in ISO 4902 and, for data transmission over data network facilities, a 15-pin connector in ISO 4903. + +FIGURE 3/V.11 + +#### Practical representation of the interface + +TABLE 1/V.11 + +#### Receiver differential significant levels + +| | $V_{A'} - V_{B'} \leq -0.3 \text{ V}$ | $V_{A'} - V_{B'} \geq +0.3 \text{ V}$ | +|-----------------------------|---------------------------------------|---------------------------------------| +| Data circuits | 1 | 0 | +| Control and timing circuits | OFF | ON | + +#### 5.2.2 Test-termination measurement + +See Figure 4 b). + +With a test load of two resistors, each 50 ohms, connected in series between the output points A and B, the differential voltage ( $V_t$ ) shall not be less than 2.0 volts or 50% of the magnitude of $V_0$ , whichever is greater. For the opposite binary state the polarity of $V_t$ shall be reversed ( $-V_t$ ). The difference in the magnitudes of $V_t$ and $-V_t$ shall be less than 0.4 volt. The magnitude of the generator offset voltage $V_{0s}$ measured between the centre of the test load and point C shall not be greater than 3.0 volts. The magnitude of the difference in the values of $V_{0s}$ for one binary state and the opposite binary state shall be less than 0.4 volt. + +NOTE – Under some conditions this measurement does not determine the degree of balance of the internal generator impedances to point C. It is left for further study whether additional measurements are necessary to ensure adequate balance in generator output impedances. + +#### 5.2.3 Short-circuit measurement + +See Figure 4 c). + +With the output points A and B short-circuited to point C, the current flowing through each of the output points A or B in both binary states shall not exceed 150 milliamperes. + +#### 5.2.4 Power-off measurements + +See Figure 4 d). + +Under power-off condition with voltages ranging between +0.25 volt and -0.25 volt applied between each output point and point C, as indicated in Figure 4 d), the magnitude of the output leakage currents ( $I_{xa}$ and $I_{xb}$ ) shall not exceed 100 microamperes. + + + +**a) Open-circuit measurement** + +$$|V_0| \leq 6.0 \text{ V}$$ +$$|V_{0a}| \leq 6.0 \text{ V}$$ +$$|V_{0b}| \leq 6.0 \text{ V}$$ + +**b) Test-termination measurement** + +$$0 |V_t| \geq 2 \text{ V}$$ +$$0.5 V_0 \leq |V_t|$$ +$$\|V_t| - |V_t|\| < 0.4 \text{ V}$$ +$$|V_{0s}| \leq 3.0 \text{ V}$$ +$$|V_{0s}(1) - V_{0s}(0)| < 0.4 \text{ V}$$ + +**c) Short-circuit measurement** + +$$|I_{sa}| < 150 \text{ mA}$$ +$$|I_{sb}| < 150 \text{ mA}$$ + +**d) Power-off measurement** + +$$|I_{xa}| < 100 \text{ } \mu\text{A}$$ +$$|I_{xb}| < 150 \text{ } \mu\text{A}$$ + +\* Matched. + +T1400240-93/d04 + +Figure 4/V.11: Generator-parameter reference measurements. The diagram shows four test setups (a, b, c, d) for a generator G with outputs A, B, and C. Setup (a) is open-circuit measurement with a 3.9 kΩ resistor and voltmeters V0, V0a, and V0b. Setup (b) is test-termination measurement with 50 Ω terminations and voltmeters Vt and V0s. Setup (c) is short-circuit measurement with ammeters Isa and Isb. Setup (d) is power-off measurement with current sources Ixa and Ixb and voltage sources ±0.25 V and ∓0.25 V. A bracket on the left indicates 'Steady-state logic input (1 or 0)'. + +FIGURE 4/V.11 +Generator-parameter reference measurements + +### 5.3 Dynamic voltage balance and rise time measurements + +See Figure 5. + +With the measurement configuration shown in Figure 5, a test signal with a nominal signal element duration $t_b$ and composed of alternate ones and zeros, shall be applied to the input. The change in amplitude of the output signal during transitions from one binary state to the other shall be monotonic between 0.1 and 0.9 $V_{ss}$ within 0.1 of $t_b$ or 20 nanoseconds, whichever is greater. Thereafter the signal voltage shall not vary more than 10% of $V_{ss}$ from the steady state value. + +The resultant voltage due to imbalance ( $V_E$ ) shall not exceed 0.4 V peak-to-peak. + + + +$V_E < 0.4$ V peak-to-peak (provisional) + +$V_{ss}$ Voltage difference between steady-state signal conditions + +a) Matched. + +Circuit diagram for generator dynamic balance and rise-time measurements. A generator G is connected to a load consisting of two 50 ohm resistors in series, with a 50 ohm resistor in parallel to ground. The output voltage V\_E is measured across the parallel resistor. The voltage difference between steady-state signal conditions is V\_ss. The output voltage V\_E is specified to be less than 0.4 V peak-to-peak (provisional). + + + +Timing diagram showing a test signal element with duration t\_b. The signal transitions between steady state '0' and steady state '1' levels, separated by V\_ss. The rise time t\_r+ and fall time t\_r- are indicated. The signal amplitude is specified to be within ±0.1 V\_ss of the steady state levels. The diagram is labeled T1400250-93/d05. + +$t_b$ Nominal duration of the test signal element +for $t_b \geq 200$ ns, $t_r \leq 0.1 t_b$ +for $t_b < 200$ ns, $t_r \leq 20$ ns + +FIGURE 5/V.11 + +#### Generator dynamic balance and rise-time measurements + +## 6 Load + +### 6.1 Characteristics + +The load consists of a receiver (R) and an optional cable termination resistance ( $Z_T$ ) as shown in Figure 2. The electrical characteristics of the receiver are specified in terms of the measurements illustrated in Figures 6, 7 and 8 and described in 6.2, 6.3 and 6.4. A circuit meeting these requirements results in a differential receiver having a high input impedance, a small input threshold transition region between $-0.3$ and $+0.3$ volts differential, and allowance for an internal bias voltage not to exceed 3 volts in magnitude. + +The receiver is electrically identical to that specified for the unbalanced receiver in Recommendation V.10. + +### 6.2 Receiver input voltage – Current measurements + +See Figure 6. + +With the voltage $V_{ia}$ (or $V_{ib}$ ) ranging between $-10$ volts and $+10$ volts, while $V_{ib}$ (or $V_{ia}$ ) is held at $0$ volt, the resultant input current $I_{ia}$ (or $I_{ib}$ ) shall remain within the shaded range shown in Figure 6. These measurements apply with the power supply of the receiver in both the power-on and power-off conditions. + + + +Figure 6/V.11: Receiver input voltage-current measurements. The left diagram shows a circuit with a receiver 'R' having inputs A', B', and C'. A voltage source V\_ia is connected to A' through a current meter I\_ia. A voltage source V\_ib is connected to B' through a current meter I\_ib. The right diagram is a graph of input current (mA) vs. input voltage (V). The x-axis ranges from -10 V to +10 V, with a vertical line at -3 V. The y-axis ranges from -3.25 mA to +3.25 mA. A shaded triangular region represents the allowed current range, bounded by lines passing through (-10, 0), (-3, -3.25), (0, 0), (3, 3.25), and (10, 0). + +FIGURE 6/V.11 +Receiver input voltage-current measurements + +### 6.3 D.c. input sensitivity measurements + +See Figure 7. + + + +Figure 7/V.11: D.c. input sensitivity measurements. The diagram shows a receiver 'R' with inputs A', B', and C'. A voltage source V\_ia is connected to A'. A voltage source V\_ib is connected to B'. A voltage source V\_i is connected between A' and B'. The output of the receiver is labeled 'Output'. The reference code T1400100-93/d07 is at the bottom right. + +| Applied voltages | | Resulting input voltage $V_i$ | Output binary state | Purpose of measurement | | +|--------------------------------|--------------------------------|----------------------------------|---------------------|------------------------------------------------------------------------------|--| +| $V_{ia}$ | $V_{ib}$ | | | | | +| -12 V
0 V
+12 V
0 V | 0 V
-12 V
0 V
+12 V | -12 V
+12 V
+12 V
-12 V | (Not specified) | To ensure no damage to receiver inputs | | +| +10 V
+4 V
-10 V
-4 V | +4 V
+10 V
-4 V
-10 V | +6 V
-6 V
-6 V
+6 V | 0
1
1
0 | To guarantee correct operation at $V_i = 6$ V (maintain correct logic state) | | +| 300 mV threshold measurement | | | | | | +| +0,30 V
0 V | 0 V
+0,30 V | +0,3 V
-0,3 V | 0
1 | $\} V_{cm} = 0$ V
$\} V_{cm} = +7$ V
$\} V_{cm} = -7$ V | | +| +7,15 V
+6,85 V | +6,85 V
+7,15 V | +0,3 V
-0,3 V | 0
1 | | | +| -7,15 V
-6,85 V | -6,85 V
-7,15 V | -0,3 V
+0,3 V | 1
0 | | | +| | | | | | | +| | | | | | | +| | | | | | | + +FIGURE 7/V.11 +Receiver input sensitivity measurement + +Over the entire common mode voltage ( $V_{cm}$ ) range of +7 volts to –7 volts, the receiver shall not require a differential input voltage ( $V_i$ ) of more than 300 millivolts to assume correctly the intended binary state. Reversing the polarity of $V_i$ shall cause the receiver to assume the opposite binary state. + +The maximum voltage (signal plus common mode) present between either receiver input and receiver ground shall not exceed 10 volts nor cause the receiver to malfunction. The receiver shall tolerate a maximum differential voltage of 12 volts applied across its input terminals without being damaged. + +In the presence of the combination of input voltages $V_{ia}$ and $V_{ib}$ specified in Figure 7, the receiver shall maintain the specified output binary state and shall not be damaged. + +NOTE – Designers of equipment should be aware that slow signal transitions with noise present may give rise to instability or oscillatory conditions in the receiving equipment; therefore, appropriate techniques should be implemented to prevent such behaviour. For example, adequate hysteresis may be incorporated in the receiver to prevent such conditions. + +### 6.4 Input balance test + +See Figure 8. + +The balance of the receiver input resistance and internal bias voltages shall be such that the receiver shall remain in the intended binary state under the conditions shown in Figure 8 and described as follows: + +- with $V_i = +720$ millivolts and $V_{cm}$ varied between –7 and +7 volts; +- with $V_i = –720$ millivolts and $V_{cm}$ varied between –7 and +7 volts; +- with $V_i = +300$ millivolts and $V_{cm}$ a 1.5 volt peak-to-peak square wave at the highest applicable data signalling rate (this condition is provisional and subject to further study); +- with $V_i = –300$ millivolts and $V_{cm}$ a 1.5 volt peak-to-peak square wave at the highest applicable data signalling rate (this condition is provisional and subject to further study). + + + +T1400110-93/d08 + +a) Matched. + +Circuit diagram for Receiver input balance test. A differential receiver 'R' has inputs A' and B' and a common mode reference point C'. Input A' is connected to a voltage source labeled '1/2 V\_i' in series with a 500 ohm resistor. Input B' is connected to a voltage source labeled '1/2 V\_i' in series with a 500 ohm resistor. Both sources are referenced to a common mode voltage source V\_cm. The resistors are marked with superscript 'a' indicating they are matched. + +FIGURE 8/V.11 +**Receiver input balance test** + +### 6.5 Terminator + +The use of a cable terminating impedance ( $Z_t$ ) is optional depending upon the specific environment in which the interchange circuit is employed (see Appendix I). In no case shall the total load resistance be less than 100 ohms. + +## 7 Environmental constraints + +In order to operate a balanced interchange circuit at data signalling rates ranging between 0 and 10 Mbit/s, the following conditions apply: + +- 1) For each interchange circuit a balanced interconnecting pair is required. +- 2) Each interchange circuit must be appropriately terminated (see Appendix I). +- 3) The total common-mode voltage at the receiver must be less than 7 volts peak. + +The common mode voltage at the receiver is the worst case combination of: + +- a) generator-receiver ground-potential difference ( $V_g$ , Figure 2); +- b) longitudinally induced random noise voltage measured between the receiver points A' or B' and C' with the generator ends of the cable A, B and C joined together; and +- c) generator d.c. offset voltage, if any. + +Unless the generator is of a type which generates no d.c. offset voltage, the sum of a) and b) above, which is the element of the common mode voltage due to the environment of the interchange circuit, must be less than 4 volts peak. + +## 8 Circuit protection + +Balanced generator and load devices complying with this Recommendation shall not be damaged under the following conditions: + +- 1) generator open circuit; +- 2) short-circuit between the conductors of the interconnecting cable; +- 3) short-circuit between either or both conductors and point C or C'. + +The above faults 2) and 3) might cause power dissipation in the interchange circuit devices to approach the maximum power dissipation that may be tolerable by a typical Integrated Circuit (IC) package. The user is therefore cautioned that where multiple generators and receivers are implemented in a single IC package, only one such fault per package might be tolerable at any one time without damage occurring. + +The user is also cautioned that the generator and receiver devices complying with this Recommendation might be damaged by spurious voltages applied between their input or output points and points C or C' (Figure 2). In those applications where the interconnecting cable may be inadvertently connected to other circuits, or where it may be exposed to a severe electromagnetic environment, protection should be employed. + +## 9 Detection of generator power-off or circuit failure + +Certain applications require detection of various fault conditions in the interchange circuits, e.g.: + +- 1) generator power-off condition; +- 2) receiver not interconnected with a generator; +- 3) open-circuited interconnecting cable; +- 4) short-circuited interconnecting cable; +- 5) input signal to the load remaining within the transition region ( $\pm 300$ millivolts) for an abnormal period of time. + +When detection of one or more fault conditions is required by specific applications, additional provisions are required in the load and the following items must be determined: + +- a) which interchange circuits require fault detection; +- b) what faults must be detected; +- c) what action must be taken when a fault is detected, e.g. which binary state must the receiver assume? + +The interpretation of a fault condition by a receiver (or load) is application dependent. Each application may use a combination of the following classification: + +- *Type 0* – No interpretation. A receiver or load does not have fault detection capability. +- *Type 1* – Data circuits assume a binary 1 state. Control and timing circuits assume an OFF condition. +- *Type 2* – Data circuits assume binary 0 state. Control and timing circuits assume an ON condition. +- *Type 3* – Special interpretation. The receiver or load provides a special indication for interpreting a fault condition. This special indication requires further study. + +The association of the circuit failure detection to particular interchange circuits in accordance with the above types is a matter of the functional and procedural characteristics specification of the interface. + +The interchange circuits monitoring circuit fault conditions in the general telephone network interfaces are indicated in Recommendation V.24. + +The interchange circuits monitoring circuit fault conditions in public data network interfaces are indicated in Recommendation X.24 [1]. + +The receiver fault detection type required is specified in the relevant DCE Recommendations. + +## **10 Measurements at the physical interchange point** + +The following information provides guidance for measurements when maintenance persons examine the interface for proper operation at the interchange point. + +### **10.1 Listing of essential measurements** + +- The magnitude of the generator d.c. offset voltage under all operating conditions. +- Open-circuit measurements. +- Test-termination measurement. +- Short-circuit measurement. +- Dynamic voltage balance and rise time. +- D.c. input sensitivity measurements. + +### **10.2 Listing of optional measurements** + +- The total generator resistance between points A and B shall be equal to or less than 100 ohms and adequately balanced with respect to point C. (It is left for further study as to the degree of balance required both statically and dynamically.) +- Power-off measurements. +- Receiver input voltage-current measurements. +- Input balance test. +- Check of the required circuit fault detection (see clause 9). + +The parameters defined in this Recommendation are not necessarily measurable at the physical interchange point. This is for further study. + +## **Annex A** + +## **Compatibility with other interfaces** + +### **A.1 Compatibility of V.10 and V.11 interchange circuits in the same interface** + +The electrical characteristics of this Recommendation are designed to allow the use of unbalanced (see Recommendation V.10) and balanced circuits within the same interface. For example, the balanced circuits may be used for data and timing whilst the unbalanced circuits may be used for associated control circuit functions. + +### **A.2 Recommendation V.11 interworking with Recommendation V.10** + +The differential receiver specifications of Recommendation V.10 and this Recommendation are electrically identical. It is therefore possible to interconnect an equipment using V.10 receivers and generators on one side of the interface with an equipment using V.11 generators and receivers on the other side of the interface. Such interconnection would result in the interchange circuits according to this Recommendation in one direction and interchange circuits according to Recommendation V.10 in the other direction. Where such interworking is contemplated, the following technical considerations must be taken into account. + +**A.2.1** Interconnecting cable lengths are limited by performance of the circuits working to the V.10 side of the interface. + +**A.2.2** The optional cable termination resistance ( $Z_t$ ), if implemented, in the equipment using this Recommendation must be removed. + +**A.2.3** V.10-type receivers shall be of category 1. + +## **Appendix I** + +## **Cable and termination** + +No electrical characteristics of the interconnecting cable are specified in this Recommendation. Guidance is given herein concerning operational constraints imposed by the length, balance and terminating resistance of the cable. + +### **I.1 Cable** + +Over the length of the cable, the two conductors should have essentially the same values of: + +- 1) capacitance to ground; +- 2) longitudinal resistance and inductance; +- 3) coupling to adjacent cables and circuits. + +### **I.2 Cable length** + +The maximum permissible length of cable separating the generator and the load in a point-to-point application is a function of the data signalling rate. It is further influenced by the tolerable signal distortion and the environmental constraints such as ground potential difference and longitudinal noise. Increasing the distance between generator and load might increase the exposure to ground potential difference. + +As an illustration of the above conditions, the curves of cable length versus data signalling rate in Figure I.1 may be used for guidance. + + + +Curve 1 Terminated interchange circuit +Curve 2 Unterminated interchange circuit + +T1400260-93/d09 + +Figure I.1/V.11: A log-log plot showing Cable length (m) versus Data signalling rate (bit/s) for balanced interchange circuits. The y-axis ranges from 10^1 to 10^4 m, and the x-axis ranges from 10^3 to 10^7 bit/s. Curve 1 (Terminated interchange circuit) is a horizontal line at 10^3 m from 10^3 to 10^5 bit/s, then slopes down to 10^1 m at 10^7 bit/s. Curve 2 (Unterminated interchange circuit) is a horizontal line at 10^3 m from 10^3 to 10^4 bit/s, then slopes down to 10^1 m at 10^6 bit/s. The legend indicates: Curve 1 Terminated interchange circuit, Curve 2 Unterminated interchange circuit. Reference: T1400260-93/d09. + +FIGURE I.1/V.11 + +#### **Data signalling rate versus cable length for balanced interchange circuit** + +These curves are based upon empirical data using twisted pair telephone cable (0.51-mm wire diameter) both unterminated and terminated in a 100-ohm resistive load. The cable length restrictions shown by the curves are based upon the following assumed signal quality requirements at the load: + +- 1) signal rise and fall time equal to, or less than, one-half the duration of the signal element; +- 2) a maximum voltage loss between generator and load of 6 dB. + +At the higher data signalling rates (see Figure I.1), the sloping portion of the curves shows the cable length limitation established by the assumed signal rise and fall time requirements. The cable length has been arbitrarily limited to 1000 metres by the assumed maximum allowable loss of 6 dB. + +These curves assume that the environmental limits specified in this Recommendation have been achieved. At the higher data signalling rates, these conditions are more difficult to attain due to cable imperfections and common-mode noise. Operation within the data signalling rate and distance bounds of Figure I.1 will usually ensure that distortion of the signal appearing at the receiver input will be acceptable. Many applications, however, can tolerate much greater levels of signal distortion and in these cases correspondingly greater cable lengths may be employed. + +Experience has shown that in many practical cases the operating distance at lower signalling rates may extend to several kilometres. + +For synchronous transmission where the data and signal element timing are transmitted in opposite directions, the phase relationship between the two may need to be adjusted to ensure conformity with the relevant requirements of signal quality at the interchange point. + +### **I.3 Cable termination** + +The use of a cable termination resistance ( $Z_t$ ) is optional and dependent on the specific application. At the higher data signalling rates (above 200 kbit/s) or at any data signalling rate where the cable propagation delay is of the order of half the signal element duration, a termination should be used to preserve the signal rise time and minimize reflections. The terminating impedance should match as closely as possible the cable characteristic impedance in the signal spectrum. + +Generally, a resistance in the range of 100 to 150 ohms will be satisfactory, the higher values leading to lower power dissipation. + +At the lower data signalling rates, where distortion and rise-time are not critical, it may be desirable to omit the termination in order to minimize power dissipation in the generator. + +# **Appendix II** + +## **Multipoint operation** + +For further study. A specification for multipoint operation including the version ISO 8482 is under study. + +## **Reference** + +- [1] CCITT Recommendation X.24 (1988), *List of definitions for interchange circuits between Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE) on public data networks.* + +## ITU-T RECOMMENDATIONS SERIES + +- Series A Organization of the work of the ITU-T +- Series B Means of expression +- Series C General telecommunication statistics +- Series D General tariff principles +- Series E Telephone network and ISDN +- Series F Non-telephone telecommunication services +- Series G Transmission systems and media +- Series H Transmission of non-telephone signals +- Series I Integrated services digital network +- Series J Transmission of sound-programme and television signals +- Series K Protection against interference +- Series L Construction, installation and protection of cables and other elements of outside plant +- Series M Maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits +- Series N Maintenance: international sound-programme and television transmission circuits +- Series O Specifications of measuring equipment +- Series P Telephone transmission quality +- Series Q Switching and signalling +- Series R Telegraph transmission +- Series S Telegraph services terminal equipment +- Series T Terminal equipments and protocols for telematic services +- Series U Telegraph switching +- Series V Data communication over the telephone network** +- Series X Data networks and open system communication +- Series Z Programming languages \ No newline at end of file diff --git a/marked/V/T-REC-V.110-200002-I_PDF-E/212c50c4e3d043c989037a01e13c1a98_img.jpg b/marked/V/T-REC-V.110-200002-I_PDF-E/212c50c4e3d043c989037a01e13c1a98_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..da054a441ae0918668bfdfe51ec494b4ef198615 --- /dev/null +++ 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V-SERIES RECOMMENDATIONS **DATA COMMUNICATION OVER THE TELEPHONE NETWORK** + +| | | +|-------------------------------------------------------|--------------------| +| General | V.1–V.9 | +| Interfaces and voiceband modems | V.10–V.34 | +| Wideband modems | V.35–V.39 | +| Error control | V.40–V.49 | +| Transmission quality and maintenance | V.50–V.59 | +| Simultaneous transmission of data and other signals | V.60–V.99 | +| Interworking with other networks | V.100–V.199 | +| Interface layer specifications for data communication | V.200–V.249 | +| Control procedures | V.250–V.299 | +| Modems on digital circuits | V.300–V.399 | + +*For further details, please refer to ITU-T List of Recommendations.* + +## **SUPPORT BY AN ISDN OF DATA TERMINAL EQUIPMENTS WITH V-SERIES TYPE INTERFACES** + +## **Summary** + +This Recommendation defines terminal adaptor (TA) functions for the connection of terminals having interfaces conforming to current V-series Recommendations to the ISDN for both circuit switched and leased circuit services. This includes the following functions: + +- conversion of electrical and mechanical interface characteristics; +- bit rate adaption; +- end-to-end synchronization of entry to and exit from the data transfer phase; +- call establishment and disestablishment based on either manual or automatic calling and/or automatic answering; +- local and end-to-end flow control to support DTEs of differing rates. + +## **Source** + +ITU-T Recommendation V.110 was revised by ITU-T Study Group 16 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on 17 February 2000. + +# FOREWORD + +ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. + +The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1. + +In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. + +## NOTE + +In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +# INTELLECTUAL PROPERTY RIGHTS + +The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. + +As of the date of approval of this Recommendation, the ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. + +© ITU 2000 + +All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. + +# CONTENTS + +| | | Page | +|-------|-------------------------------------------------------------------------------|-------------| +| 1 | Scope..... | 1 | +| 2 | References..... | 2 | +| 3 | Abbreviations..... | 3 | +| 4 | Reference configurations ..... | 4 | +| 4.1 | Terminal adaptor reference model ..... | 4 | +| 4.2 | Connection types..... | 4 | +| 5 | Line signals at S and T reference points ..... | 4 | +| 5.1 | Bit rate adaption of synchronous data signalling rates up to 38.4 kbit/s..... | 4 | +| 5.1.1 | General approach..... | 4 | +| 5.1.2 | Adaption of V-series data signalling rates to the intermediate rates ..... | 5 | +| 5.1.3 | Frame synchronization and additional signalling capacity..... | 11 | +| 5.1.4 | Adaption of intermediate rates to 64 kbit/s ..... | 13 | +| 5.2 | Rate adaption of 48 and 56 kbit/s synchronous user rates to 64 kbit/s ..... | 13 | +| 5.2.1 | Frame synchronization..... | 14 | +| 5.3 | Adaption for asynchronous rates of up to 38 400 bit/s ..... | 15 | +| 5.3.1 | General approach..... | 15 | +| 5.3.2 | Supported asynchronous user rates..... | 15 | +| 5.3.3 | Asynchronous-to-synchronous conversion (RA0)..... | 16 | +| 5.3.4 | Overspeed/underspeed..... | 16 | +| 5.3.5 | Break signal ..... | 16 | +| 5.3.6 | Parity bits ..... | 17 | +| 5.4 | Flow control for use with TAs supporting asynchronous DTEs..... | 17 | +| 5.4.1 | Local flow control: between TA and DTE ..... | 17 | +| 5.4.2 | End-to-end (TA-to-TA) flow control..... | 18 | +| 5.4.3 | Use of channel capacity ..... | 18 | +| 5.4.4 | Requirements of a TA supporting flow control..... | 19 | +| 6 | Interchange circuits..... | 19 | +| 6.1 | Essential and optional interchange circuits..... | 19 | +| 6.2 | Timing arrangement..... | 20 | +| 6.3 | Circuit 106 ..... | 20 | +| 6.4 | Circuit 109 ..... | 20 | +| 6.5 | Electrical/mechanical characteristics of interchange circuits ..... | 20 | +| 6.5.1 | Basic ISDN user/network interface ..... | 20 | +| 6.5.2 | TE2/TA (DTE/DCE) interface ..... | 21 | +| 6.6 | Fault condition on interchange circuits..... | 21 | + +| | Page | +|------------|-------------------------------------------------------| +| 7 | Operating sequence..... 21 | +| 7.1 | TA duplex operation ..... 21 | +| 7.1.1 | Idle (or ready) state ..... 22 | +| 7.1.2 | Connect TA to line state ..... 22 | +| 7.1.3 | Data transfer state ..... 23 | +| 7.1.4 | Disconnect mode ..... 23 | +| 7.1.5 | Loss of frame synchronization..... 24 | +| 7.2 | TA half-duplex operation..... 24 | +| 7.3 | Automatic calling..... 25 | +| 8 | Network-independent clocks ..... 25 | +| 8.1 | Measurement of phase differences..... 25 | +| 8.2 | Positive/negative compensation..... 27 | +| 8.3 | Encoding ..... 27 | +| 9 | In-band parameter exchange state..... 27 | +| 10 | Testing facilities..... 27 | +| Annex A | – Reference configurations ..... 27 | +| A.1 | Introduction..... 27 | +| A.2 | V.110 terminal adaptor reference model..... 27 | +| A.3 | Terminal adaption type ..... 28 | +| A.3.1 | Terminal adaptor – Type A (TA-A) ..... 28 | +| A.3.2 | Terminal adaptor – Type B (TA-B)..... 29 | +| A.4 | Types of end-to-end connection..... 29 | +| Appendix I | – In-band parameter exchange ..... 30 | +| I.1 | Introduction..... 30 | +| I.2 | Definitions ..... 31 | +| I.3 | Overview..... 31 | +| I.4 | Reference configuration..... 32 | +| I.5 | Procedures..... 32 | +| I.5.1 | General..... 32 | +| I.5.2 | Initiating the exchange..... 33 | +| I.5.3 | Parameter exchange..... 34 | +| I.5.4 | Re-synchronization to a new intermediate rate..... 36 | +| I.5.5 | Data transfer..... 37 | +| I.5.6 | Interworking with a TA not supporting IPE ..... 37 | +| I.5.7 | Maintenance..... 37 | +| I.5.8 | Re-entering IPE from the data transfer state..... 38 | + +| | Page | +|---------------------------------------------------------------------------------------------|-------------| +| I.5.9 Error protection and handling..... | 38 | +| I.6 Coding..... | 38 | +| I.6.1 General..... | 38 | +| I.6.2 Rate adaption version identification ..... | 40 | +| I.6.3 Control ..... | 41 | +| I.6.4 Parameters ..... | 41 | +| I.6.5 Status ..... | 44 | +| I.6.6 Maintenance..... | 44 | +| I.7 Timer values ..... | 45 | +| I.7.1 Timer values for parameter exchange..... | 45 | +| I.7.2 Timer values for maintenance ..... | 45 | +| I.8 State transition diagrams..... | 46 | +| I.8.1 General..... | 46 | +| Appendix II – V.25 bis to Q.931 protocol mapping..... | 51 | +| II.1 General..... | 51 | +| II.2 Call origination ..... | 52 | +| II.2.1 Call set-up..... | 52 | +| II.2.2 Call received from remote DTE/TA ..... | 52 | +| II.3 Call clearing (Figures II.2 and II.3)..... | 53 | +| II.3.1 DISCONNECT (from TA) ..... | 53 | +| II.3.2 DISCONNECT (from exchange)..... | 53 | +| II.3.3 DISCONNECT (In-band between TAs)..... | 55 | +| II.3.4 RELEASE COMPLETE..... | 55 | +| II.3.5 Negative response to an incoming call ..... | 55 | +| II.4 Direct call..... | 56 | +| II.4.1 Direct call DTE call set-up and clearing..... | 56 | +| II.4.2 Direct call DCE call set-up and clearing ..... | 56 | +| II.5 Mapping of Q.931 causes to V.25 bis call failure indications and responses..... | 57 | +| II.6 Additional information for handling of exception situations..... | 59 | +| II.6.1 Call collision..... | 59 | +| II.6.2 No channel available..... | 59 | +| II.6.3 Premature call clearing ..... | 59 | + + + +# Recommendation V.110 + +# SUPPORT BY AN ISDN OF DATA TERMINAL EQUIPMENTS WITH V-SERIES TYPE INTERFACES + +*(Malaga-Torremolinos, 1984; amended at Melbourne, 1988; +revised at Geneva in 1992, 1996 and 2000)* + +# 1 Scope + +The ITU-T, + +*considering* + +- a) that the ISDN will offer the universal interfaces to connect subscriber terminals according to the reference configuration described in Recommendation I.411; +- b) that during the evolution of ISDN, however, there will exist for a considerable period data terminal equipments (DTEs) with V-series type interfaces which have to be connected to the ISDN; +- c) that bearer services supported by an ISDN are described in Recommendation I.211; +- d) that the D-channel signalling protocol is described in Recommendations I.430, Q.921 and Q.931, + +*unanimously declares the view* + +- 1 that the scope of this Recommendation shall cover the connection of terminals with interfaces for modems conforming to current V-series Recommendations on the ISDN operating in accordance with circuit switched or leased circuit services; +- 2 that the following circuit switched service capabilities shall be supported: + - data transmission; (and optionally) + - automatic calling and/or automatic answering; +- 3 that the reference configurations of clause 4 shall apply; +- 4 that the support of interworking of terminal equipments (TEs) on an ISDN with DTEs on other types of networks, e.g. public switched telephone network (PSTN), is described in the I.500-series Recommendations; +- 5 that the terminal adaptor (TA) functions necessary to support the connection of DTEs with V-series type interfaces on an ISDN shall include the following: + - conversion of electrical and mechanical interface characteristics; + - bit rate adaption; + - end-to-end synchronization of entry to and exit from the data transfer phase; + - call establishment and disestablishment based on either manual or automatic calling and/or automatic answering; +- 6 that optionally, the following may be included: + - local and end-to-end flow control to support DTEs of differing bit rates. + +# 2 References + +The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. + +- ITU-T Recommendation I.211 (1993), *B-ISDN service aspects*. +- ITU-T Recommendation I.411 (1993), *ISDN user-network interfaces – Reference configurations*. +- ITU-T Recommendation I.430 (1995), *Basic user-network interface – Layer 1 specification*. +- ITU-T Recommendation I.431 (1993), *Primary rate user-network interface – Layer 1 specification*. +- ITU-T Recommendation I.460 (1999), *Multiplexing, rate adaption and support of existing interfaces*. +- ITU-T Recommendation I.463 (1996), *Support by an ISDN of data terminal equipments with V-series type interfaces*. +- ITU-T Recommendation I.515 (1993), *Parameter exchange for ISDN interworking*. +- ITU-T Recommendation I.530 (1993), *Network interworking between an ISDN and a public switched telephone network (PSTN)*. +- ITU-T Recommendation Q.921 (I.441) (1997), *ISDN user-network interface – Data link layer specification*. +- ITU-T Recommendation Q.931 (I.451) (1998), *ISDN user-network interface layer 3 specification for basic call control*. +- ITU-T Recommendation V.10 (X.26) (1993), *Electrical characteristics for unbalanced double-current interchange circuits operating at data signalling rates nominally up to 100 kbit/s*. +- ITU-T Recommendation V.11 (X.27) (1996), *Electrical characteristics for balanced double-current interchange circuits operating at data signalling rates up to 10 Mbit/s*. +- ITU-T Recommendation V.14 (1993), *Transmission of start-stop characters over synchronous bearer channels*. +- ITU-T Recommendation V.24 (1996), *List of definitions for interchange circuits between data terminal equipment (DTE) and data circuit-terminating equipment (DCE)*. +- ITU-T Recommendation V.25 bis (1996), *Synchronous and asynchronous automatic dialling procedures on switched networks*. +- ITU-T Recommendation V.28 (1993), *Electrical characteristics for unbalanced double-current interchange circuits*. +- ITU-T Recommendation V.43 (1998), *Data flow control*. +- ITU-T Recommendation V.54 (1988), *Loop test devices for modems*. +- ITU-T Recommendation X.1 (1996), *International user classes of service in, and categories of access to, public data networks and Integrated Services Digital Networks (ISDNs)*. +- ITU-T Recommendation X.21 (1992), *Interface between Data Terminal Equipment and Data Circuit-terminating Equipment for synchronous operation on public data networks*. + +- ITU-T Recommendation X.30 (I.461) (1993), *Support of X.21, X.21 bis and X.20 bis based Data Terminal Equipments (DTEs) by an Integrated Services Digital Network (ISDN)*. +- ITU-T Recommendation X.150 (1988), *Principles of maintenance testing for public data networks using Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE) test loops*. +- ISO/IEC 2110:1989, *Data communication – 25-pole DTE/DCE interface connector and contact number assignments*. +- ISO/IEC 2593:1993, *Information technology – Telecommunications and information exchange between systems – 34-pole DTE/DCE interface connector mateability dimensions and contact number assignments*. +- ISO 4902:1989, *Information technology – Data communication – 37-pole DTE/DCE interface connector and contact number assignments*. +- ISO/IEC 11569:1993, *Information technology – Telecommunications and information exchange between systems – 26-pole interface connector mateability dimensions and contact number assignments*. + +# 3 Abbreviations + +This Recommendation uses the following abbreviations: + +| | | +|---------|------------------------------------------------| +| CFI | Call Failure Indication | +| CRI | Call Request with Identification | +| CRN | Call Request with Number | +| DC | Device Control | +| DC1 | Device Control one | +| DC3 | Device Control three | +| DCE | Data Circuit-Terminating Equipment | +| DTE | Data Terminal Equipment | +| DTR | Data Terminal Ready | +| IA5 | International Alphabet No. 5 | +| ISDN | Integrated Services Digital Network | +| ISO | International Organization for Standardization | +| IWF | Interworking Function | +| NT | Network Termination | +| PARAM-X | Parameter X (X = 0, 1, 2, 3, 4) | +| ppm | parts per million | +| PSTN | Public Switched Telephone Network | +| RA | Rate Adaption | +| RD | Received Data | +| TA | Terminal Adaptor | +| TA-A | Terminal Adaptor – Type A | +| TA-B | Terminal Adaptor – Type B | + +| | | +|-----|---------------------------| +| TD | Transmitted Data | +| TE | Terminal Equipment | +| TE1 | Terminal Equipment type 1 | +| TE2 | Terminal Equipment type 2 | +| TH | Threshold | +| Tn | Timer n (n = 1, 2, 3) | + +# **4 Reference configurations** + +## **4.1 Terminal adaptor reference model** + +The terminal adaptor functions have been defined in the context of a simple reference model. Annex A describes the reference model in further detail, and defines a basic terminal adaptor TA-A, and an auto-calling/auto-answering terminal adaptor TA-B. + +## **4.2 Connection types** + +The terminal adaptor functions described in this Recommendation take into account interworking between TAs of different types, e.g. V-series TE2 with X.21 TE2, and end-to-end connections of different types. These are described in further detail in Annex A. + +# **5 Line signals at S and T reference points** + +The TA signals at ISDN reference points S or T shall be in conformance with the characteristics of an ISDN's "Basic user/network interface" as described in Recommendations I.430 (layer 1 specification), Q.921 (layer 2 specification) and Q.931 (layer 3 specification). + +## **5.1 Bit rate adaption of synchronous data signalling rates up to 38.4 kbit/s** + +### **5.1.1 General approach** + +The bit rate adaption functions within the TA are shown in Figure 1. The function RA1 converts the user data signalling rate to an appropriate intermediate rate expressed by $2^k \times 8$ kbit/s (where $k = 0, 1, 2$ or $3$ ). RA2 performs the second conversion from the intermediate rates to 64 kbit/s. The data signalling rates of 48 and 56 kbit/s are converted directly into the 64-kbit/s B-channel rate. The intermediate rate of 64 kbit/s is directly mapped into the 64-kbit/s B-channel rate. + + + +The diagram shows the internal structure of a Terminal Adaptor (TA) for bit rate adaption. + +- On the left, a vertical dashed line marks the 'R' reference point with 'V-series' input. + +- Inside the TA box, there are two functional blocks: RA1 and RA2. + +- RA1 is a square block with a diagonal line from bottom-left to top-right. The top-left area is labeled 'V-series' and the bottom-right area is labeled ' $2^k \times 8$ kbit/s'. + +- RA2 is a similar square block with a diagonal line. The top-left area is labeled ' $2^k \times 8$ kbit/s' and the bottom-right area is labeled '64 kbit/s'. + +- A dotted line connects the output of RA1 to the input of RA2. + +- On the right, a vertical dashed line marks the 'S/T' reference point. + +- The diagram is labeled with the reference number 'T1701650-92' at the bottom right. + +Diagram of the two-step bit rate adaption process within a Terminal Adaptor (TA). + +**Figure 1/V.110 – Two-step bit rate adaption** + +### 5.1.2 Adaption of V-series data signalling rates to the intermediate rates + +The intermediate rate used with each of the V-series data signalling rates are shown in Table 1. + +**Table 1/V.110 – First step rate adaption** + +| Data signalling rate (bit/s) | Intermediate rate | | | | +|------------------------------|-------------------|-----------|-----------|-----------| +| | 8 kbit/s | 16 kbit/s | 32 kbit/s | 64 kbit/s | +| 600 | X | | | | +| 1 200 | X | | | | +| 2 400 | X | | | | +| 4 800 | X | | | | +| 7 200 | | X | | | +| 9 600 | | X | | | +| 12 000 | | | X | | +| 14 400 | | | X | | +| 19 200 | | | X | | +| 24 000 | | | | X | +| 28 800 | | | | X | +| 38 400 | | | | X | + +#### 5.1.2.1 Frame structure + +The frame structure is shown in Table 2 and is described in the following paragraphs. + +**Table 2/V.110 – Frame structure** + +| Octet number | Bit number | | | | | | | | +|--------------|------------|-----|-----|-----|-----|-----|-----|----| +| | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | +| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | +| 1 | 1 | D1 | D2 | D3 | D4 | D5 | D6 | S1 | +| 2 | 1 | D7 | D8 | D9 | D10 | D11 | D12 | X | +| 3 | 1 | D13 | D14 | D15 | D16 | D17 | D18 | S3 | +| 4 | 1 | D19 | D20 | D21 | D22 | D23 | D24 | S4 | +| 5 | 1 | E1 | E2 | E3 | E4 | E5 | E6 | E7 | +| 6 | 1 | D25 | D26 | D27 | D28 | D29 | D30 | S6 | +| 7 | 1 | D31 | D32 | D33 | D34 | D35 | D36 | X | +| 8 | 1 | D37 | D38 | D39 | D40 | D41 | D42 | S8 | +| 9 | 1 | D43 | D44 | D45 | D46 | D47 | D48 | S9 | + +As shown in Table 2, the conversion of the V-series rates to the intermediate rates uses an 80-bit frame. The octet zero contains all binary 0, whilst octet 5 consists of a binary 1 followed by seven E bits (see 5.1.2.4). Octets 1-4 and 6-9 contain a binary 1 in bit number 1, a status bit (S- or X-bit) in bit number 8 and six data bits (D-bits) in bit positions 2-7. The order of bit transmission is from left to right and top to bottom. + +#### 5.1.2.2 Frame synchronization + +The 17-bit frame alignment pattern consists of all 8 bits (set to binary 0) of octet zero and bit one (set to binary 1) of the following nine octets (see also 5.1.3). + +#### 5.1.2.3 Status bits (S1, S3, S4, S6, S8, S9 and X) + +The bits S and X may be used to convey channel control information associated with the data bits in the data transfer state, as shown in Table 3. The S-bits are put into two groups SA (= S1, S3, S6, S8) and SB (= S4, S9), permitting the carriage of the condition of two interchange circuits. The X-bit is used to control the condition of circuit 106, and, in addition, signals the state of frame synchronization between TAs (see clause 7). The X-bit can also be used optionally to carry flow control information between TAs supporting asynchronous terminal equipment. This usage is specified in 5.4.2. + +**Table 3/V.110 – General mapping scheme at the TA during the data transfer state** + +| V.24 interchange circuit at DTE/TA interface | Status bit mapping – Direction: TA to ISDN | Status bit mapping – Direction: ISDN to TA | +|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------|--------------------------------------------| +| 105 (Note 3) | Mapped to SB | | +| 106 (Note 1) | | Mapped from X | +| 107 | | Mapped from SA | +| 108 | Mapped to SA | | +| 109 | | Mapped from SB | +| 133 (Note 3) | Mapped to X (Note 2) | | +| NOTE 1 – The condition of circuit 106 may also be affected by the state of any transmit buffer in the TA if end-to-end flow control is supported.
NOTE 2 – The condition of status bit X towards the ISDN may also be affected by the state of any receive buffer in the TA if end-to-end flow control is supported.
NOTE 3 – Circuits 105 and 133 are assigned to the same connector pin on the standardized 25- and 26-pole connectors (ISO/IEC 2110 and ISO/IEC 11569). As circuit 133 is used only in duplex operation and circuit 105 is used only in half-duplex operation, there should be no conflict. The status bit corresponding to the unassigned circuit shall be set to the ON condition during the data transfer state. | | | + +The use of S- and X-bits for synchronization of entry to and exit from the data transfer state is specified in clause 7. + +Table 3 shows the general mapping scheme in the TA between the status bits and the V.24 interchange circuits at the DTE-TA interface during the data transfer state. Which circuits are actually mapped depends on the interoperational case (see A.4) and whether the DTE's mode of operation is duplex (see 7.1) or half duplex (see 7.2). + +The mapping between the status bits and the modem (DCE) control circuits in an interworking function (IWF) is the same as in Table 3 except the directions of the mappings are reversed. For example, circuit 109 is an output from the IWF modem (DCE) and is mapped to status bit SB towards the ISDN. + +For the S- and X-bits, a ZERO corresponds with the ON condition of the respective interchange circuit, a ONE with the OFF condition. + +Control information, conveyed by the S-bits, and user data, conveyed by the D-bits, should not have different transmission delays. The S-bits should therefore transmit control information sampled simultaneously with the D-bits in the positions specified in Table 4 and as presented in Figure 2. + +The X-bit should be presented upon arrival to control circuit 106. Circuit 106 shall respond as defined in 6.3 and, if the X-bit carries flow control information, in 7.2. + +**Table 4/V.110 – Coordination between S-bits and D-bits** + +| S-bit | D-bit | | +|-------|-----------|---------| +| | Octet No. | Bit No. | +| S1 | 2 | 3 (D8) | +| S3 | 3 | 5 (D16) | +| S4 | 4 | 7 (D24) | +| S6 | 7 | 3 (D32) | +| S8 | 8 | 5 (D40) | +| S9 | 9 | 7 (D48) | + + + +The top part of Figure 2 shows the timing relationship between circuits 103, 105, 108, 104, 109, and 107 relative to the 8, 16 or 32 kbit/s bearer on the B-channel. Sampling points for circuits 105 and 108 are marked with asterisks at bit positions 1 and 24 of the B-channel frame. Change points for circuits 107 and 109 are shown at time t0 and t1. + +Timing diagram showing coordination between S-bits and D-bits (Part 1) + + + +The bottom part of Figure 2 continues the timing diagram, showing the next sequence of bits. It illustrates the transition at time t1 and t2, with sampling points and change points aligned with specific bit positions in the B-channel frame (bits 1-48 and 1-2). + +Timing diagram showing coordination between S-bits and D-bits (Part 2) + +\* Indicates the sampling point for circuit 105 and 108 + +Image: Crossed lines symbol + + Indicates the change point for circuits 107 and 109 + +NOTE 1 – In order to maintain conformity with the bit rate adaption of X.1 user classes of service described in Recommendation X.30, the bits S1 and S6, S3 and S8, S4 and S9 are used to convey channel status information associated with the P-, Q- and R-bit groups respectively. + +Refer to 2.1.1.2.3/X.30 for detailed information concerning the mapping of the information on circuit C of the X.21 interface to the S-bits and to the I-bits of the distant interface. + +NOTE 2 – The coordination between S- and D-bits described in Table 4 and in this figure is intended to provide for compatibility with Recommendation X.30. Whether this coordination is strictly necessary in the context of this Recommendation is for further study. + +**Figure 2/V.110 – Coordination between S-bits and D-bits** + +8 Recommendation V.110 (02/2000) + +#### 5.1.2.4 E-bit usage + +The E-bits are used to carry the following information: + +- a) *Rate repetition information:* Bits E1, E2 and E3, in conjunction with the intermediate rate (see Table 2), provide the user data signalling rate (synchronous) identification. The coding of these bits shall be as shown in Table 5. +- b) *Network-independent clock information:* Bits E4, E5 and E6 are used as specified in clause 8 to carry network-independent clock phase information. +- c) *Multiframe information:* Bit E7 is used as indicated in Table 5. + +**Table 5/V.110 – E-bit usage (Note 1)** + +| Intermediate rates kbit/s | | | | E1 | E2 | E3 | E4 | E5 | E6 | E7 | +|---------------------------|-------|--------|--------|----------|----|----------|----|----|----|--------------------| +| 8 | 16 | 32 | 64 | (Note 4) | | (Note 3) | | | | | +| bit/s | bit/s | bit/s | bit/s | | | | | | | | +| 600 | | | | 1 | 0 | 0 | C | C | C | 1 or 0
(Note 2) | +| 1200 | | | | 0 | 1 | 0 | C | C | C | 1 | +| 2400 | | | | 1 | 1 | 0 | C | C | C | 1 | +| | | 12 000 | 24 000 | 0 | 0 | 1 | C | C | C | 1 | +| | 7200 | 14 400 | 28 800 | 1 | 0 | 1 | C | C | C | 1 | +| 4800 | 9600 | 19 200 | 38 400 | 0 | 1 | 1 | C | C | C | 1 | + +NOTE 1 – The data signalling rates of 600, 2400, 4800 and 9600 bit/s are also X.1 user classes of service (see also Recommendation X.30). + +NOTE 2 – In order to maintain compatibility with Recommendation X.30, the 600 bit/s user rate E7 is coded to enable the $4 \times 80$ bit multiframe synchronization. To this end, E7 in the fourth 80-bit frame is set to binary 0 (see 5.1.2.7 and Table 6a). + +NOTE 3 – C indicates the use of E4, E5 and E6 for the transport of network-independent clocking information (see clause 8). These bits shall be set to ONE when unused. + +NOTE 4 – Synchronous rate information is carried by bits E1, E2 and E3 as indicated. Asynchronous rate information must be provided with out-of-band signalling (layer 3 messages in the D-channel) or with in-band parameter exchange as described in Appendix I. + +#### 5.1.2.5 Rate negotiation + +Negotiation of the synchronous rate may be appropriate in interworking situations involving interconnections with modems on the PSTN where the remote modem/DTE has the capability of operating at different rates depending upon the conditions. It may also be appropriate in interconnections for asynchronous transmission specified in 5.3 and accommodate split rate operation. The need for rate negotiation and the method is for further study. + +#### 5.1.2.6 Data bits + +Data are conveyed in D-bits, i.e. up to 48 bits per 80-bit frame. In this Recommendation the octet boundaries of the user's data stream are not defined. + +#### 5.1.2.7 Bit assignment + +The adaption of 600, 1200 and 2400 bit/s rates to the 8 kbit/s intermediate rate are shown in Tables 6a, 6b and 6c, respectively. + +The adaption of 7200, 14 400 and 28 800 bit/s rates to the 16, 32 and 64 kbit/s intermediate rate, respectively, use the data bit assignments shown in Table 6d. + +The adaption of 4800, 9600, 19 200 and 38 400 bit/s rates to the 8, 16, 32 and 64 kbit/s intermediate rate, respectively, use the data bit assignments shown in Table 6e. + +The adaption of 12 000 and 24 000 bit/s user rate to 32 and 64 kbit/s intermediate rate, respectively, use the data bit assignments shown in Table 6f. + +**Table 6a/V.110 – Adaption of 600 bit/s user rate to 8 kbit/s intermediate rates** + +| | | | | | | | | +|---|----|----|----|----|----|----|------------------| +| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | +| 1 | D1 | D1 | D1 | D1 | D1 | D1 | S1 | +| 1 | D1 | D1 | D2 | D2 | D2 | D2 | X | +| 1 | D2 | D2 | D2 | D2 | D3 | D3 | S3 | +| 1 | D3 | D3 | D3 | D3 | D3 | D3 | S4 | +| 1 | 1 | 0 | 0 | E4 | E5 | E6 | E7 a) | +| 1 | D4 | D4 | D4 | D4 | D4 | D4 | S6 | +| 1 | D4 | D4 | D5 | D5 | D5 | D5 | X | +| 1 | D5 | D5 | D5 | D5 | D6 | D6 | S8 | +| 1 | D6 | D6 | D6 | D6 | D6 | D6 | S9 | + +a) See Note 2 to Table 5. + +**Table 6b/V.110 – Adaption of 1200 bit/s user rate to 8 kbit/s intermediate rates** + +| | | | | | | | | +|---|-----|-----|-----|-----|-----|-----|----| +| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | +| 1 | D1 | D1 | D1 | D1 | D2 | D2 | S1 | +| 1 | D2 | D2 | D3 | D3 | D3 | D3 | X | +| 1 | D4 | D4 | D4 | D4 | D5 | D5 | S3 | +| 1 | D5 | D5 | D6 | D6 | D6 | D6 | S4 | +| 1 | 0 | 1 | 0 | E4 | E5 | E6 | E7 | +| 1 | D7 | D7 | D7 | D7 | D8 | D8 | S6 | +| 1 | D8 | D8 | D9 | D9 | D9 | D9 | X | +| 1 | D10 | D10 | D10 | D10 | D11 | D11 | S8 | +| 1 | D11 | D11 | D12 | D12 | D12 | D12 | S9 | + +**Table 6c/V.110 – Adaption of 2400 bit/s user rate to 8 kbit/s intermediate rates** + +| | | | | | | | | +|---|-----|-----|-----|-----|-----|-----|----| +| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | +| 1 | D1 | D1 | D2 | D2 | D3 | D3 | S1 | +| 1 | D4 | D4 | D5 | D5 | D6 | D6 | X | +| 1 | D7 | D7 | D8 | D8 | D9 | D9 | S3 | +| 1 | D10 | D10 | D11 | D11 | D12 | D12 | S4 | +| 1 | 1 | 1 | 0 | E4 | E5 | E6 | E7 | +| 1 | D13 | D13 | D14 | D14 | D15 | D15 | S6 | +| 1 | D16 | D16 | D17 | D17 | D18 | D18 | X | +| 1 | D19 | D19 | D20 | D20 | D21 | D21 | S8 | +| 1 | D22 | D22 | D23 | D23 | D24 | D24 | S9 | + +**Table 6d/V.110 – Adaption of $N^{a)} \times 3600$ bit/s user rate to the intermediate rate** + +| | | | | | | | | +|---|-----|-----|-----|-----|-----|-----|----| +| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | +| 1 | D1 | D2 | D3 | D4 | D5 | D6 | S1 | +| 1 | D7 | D8 | D9 | D10 | F | F | X | +| 1 | D11 | D12 | F | F | D13 | D14 | S3 | +| 1 | F | F | D15 | D16 | D17 | D18 | S4 | +| 1 | 1 | 0 | 1 | E4 | E5 | E6 | E7 | +| 1 | D19 | D20 | D21 | D22 | D23 | D24 | S6 | +| 1 | D25 | D26 | D27 | D28 | F | F | X | +| 1 | D29 | D30 | F | F | D31 | D32 | S8 | +| 1 | F | F | D33 | D34 | D35 | D36 | S9 | + +a) $N = 2, 4$ or $8$ only. + +F Fill bit + +NOTE – This table is not used for asynchronous user rates of $N \times 3600$ bit/s (see 5.3.3). + +**Table 6e/V.110 – Adaption of $N^{a)} \times 4800$ bit/s +user rate to the intermediate rate** + +| | | | | | | | | +|---------------------------|-----|-----|-----|-----|-----|-----|----| +| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | +| 1 | D1 | D2 | D3 | D4 | D5 | D6 | S1 | +| 1 | D7 | D8 | D9 | D10 | D11 | D12 | X | +| 1 | D13 | D14 | D15 | D16 | D17 | D18 | S3 | +| 1 | D19 | D20 | D21 | D22 | D23 | D24 | S4 | +| 1 | 0 | 1 | 1 | E4 | E5 | E6 | E7 | +| 1 | D25 | D26 | D27 | D28 | D29 | D30 | S6 | +| 1 | D31 | D32 | D33 | D34 | D35 | D36 | X | +| 1 | D37 | D38 | D39 | D40 | D41 | D42 | S8 | +| 1 | D43 | D44 | D45 | D46 | D47 | D48 | S9 | +| a) N = 1, 2, 4 or 8 only. | | | | | | | | + +**Table 6f/V.110 – Adaption of $N^{a)} \times 12\,000$ bit/s +user rate to the intermediate rate** + +| | | | | | | | | +|-----------------------------------------------------------------------------------------------------------------------------------------|-----|-----|-----|-----|-----|-----|----| +| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | +| 1 | D1 | D2 | D3 | D4 | D5 | D6 | S1 | +| 1 | D7 | D8 | D9 | D10 | F | F | X | +| 1 | D11 | D12 | F | F | D13 | D14 | S3 | +| 1 | F | F | D15 | F | F | F | S4 | +| 1 | 0 | 0 | 1 | E4 | E5 | E6 | E7 | +| 1 | D16 | D17 | D18 | D19 | D20 | D21 | S6 | +| 1 | D22 | D23 | D24 | D25 | F | F | X | +| 1 | D26 | D27 | F | F | D28 | D29 | S8 | +| 1 | F | F | D30 | F | F | F | S9 | +| a) N = 1 or 2 only.
F Fill bit
NOTE – This table is not used for asynchronous user rates of $N \times 12\,000$ bit/s (see 5.3.3). | | | | | | | | + +### 5.1.3 Frame synchronization and additional signalling capacity + +#### 5.1.3.1 Search for frame synchronization + +The following 17-bit alignment pattern is used to achieve frame synchronization: + +``` + +00000000 1YYYYYYY 1YYYYYYY 1YYYYYYY 1YYYYYYY +1YYYYYYY 1YYYYYYY 1YYYYYYY 1YYYYYYY 1YYYYYYY + +``` + +The bits marked 'Y' are not part of the frame alignment pattern. They carry the user data (D bits) and S and X status bits as shown in Table 2. To ensure a reliable synchronization, it is recommended that at least two 17-bit alignment patterns in consecutive frames be detected. + +Once frame synchronization is achieved, it is recommended that a persistence check be made of the status bits $S = X = \text{OFF}$ condition of 7.1.2 prior to proceeding to transparent data transfer with the status bits $S = X = \text{ON}$ condition, as shown in Figure 3 and described in clause 7. + + + +The diagram illustrates the synchronization of entry to and exit from the data transfer phase between two TE2 entities (TE2 CALLING and TE2 CALLED) via a B-channel. The sequence is as follows: + +- Initial State:** B-channel connection established. Both TA entities are in a state where 108.1/2 = ON, 105 = ON, 107 = OFF, 106 = OFF, and 109 = OFF. +- Entry to data phase:** + - Both TA entities initiate a "Frame search". + - During the search, the status of 107 changes to ON, which stops the search process ("Stopped by 107 ON"). + - Once the search is stopped, the status of 105 changes to ON/OFF. +- Data phase:** + - The data transfer phase begins with the status of 108.1/2 changing to OFF. + - The status of 105 remains OFF. + - The status of 107 remains ON, 106 remains 105, and 109 remains ON. +- Exit from data phase:** + - The data transfer phase ends with the status of 108.1/2 changing to OFF. + - The status of 105 remains OFF. + - The status of 107 changes back to OFF, 106 changes back to 105, and 109 changes back to OFF. +- Final State:** B-channel disconnection. Both TA entities return to the initial state where 108.1/2 = ON, 105 = ON, 107 = OFF, 106 = OFF, and 109 = OFF. + +**Legend:** + +- B-channel connection of TA +- ⊗ B-channel disconnection of TA +- × Bidirectional switch-through TE2 +- > < Bidirectional disconnection of TE2 +- △ TA disconnecting procedure according to 7.1.4 started + +Sequence diagram showing TA synchronization of entry to and exit from data transfer phase between two TE2 entities via a B-channel. The diagram is divided into three main sections: Entry to data phase, Data phase, and Exit from data phase. It details the states of various signals (108.1/2, 105, 107, 106, 109) and the status of the B-channel connection and TA disconnection procedure. + +T1701430-92 + +**Figure 3/V.110 – TA synchronization of entry to and exit from data transfer phase** + +#### 5.1.3.2 Frame synchronization monitoring and recovery + +Monitoring of the frame synchronization shall be a continuous process using the same procedures as for initial detection. + +Loss of frame synchronization shall not be assumed unless at least three consecutive frames, each with at least one framing bit error, are detected. + +Following loss of frame synchronization, the TA shall enter a recovery state as discussed in 7.1.5. If recovery is not successful, further maintenance procedures may be used. + +### 5.1.4 Adaption of intermediate rates to 64 kbit/s + +Since rate adaption of a single intermediate rate (e.g. 8, 16, or 32 kbit/s) to the 64 kbit/s B-channel rate and the possible multiplexing of several intermediate rate streams1 to the 64 kbit/s B-channel rate must be compatible to enable interworking, a common approach is needed for the second step rate adaption and, possibly, for intermediate rate multiplexing. This second step rate adaption method is described in Recommendation I.460. + +## 5.2 Rate adaption of 48 and 56 kbit/s synchronous user rates to 64 kbit/s + +The 48 and 56 kbit/s user data signalling rates are adapted to the 64 kbit/s B-channel rate in one step as indicated in Tables 7a, 7b or 7c respectively. + +**Table 7a/V.110 – Adaption of 48 kbit/s user rate to 64 kbit/s** + +| Octet number | Bit number | | | | | | | | +|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------|-----|-----|-----|-----|-----|-----|----| +| | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | +| 1 | 1 | D1 | D2 | D3 | D4 | D5 | D6 | S1 | +| 2 | 0 | D7 | D8 | D9 | D10 | D11 | D12 | X | +| 3 | 1 | D13 | D14 | D15 | D16 | D17 | D18 | S3 | +| 4 | 1 | D19 | D20 | D21 | D22 | D23 | D24 | S4 | +| NOTE 1 – 48 kbit/s is also a X.1 user class of service (see also 2.2.1/X.30). | | | | | | | | | +| NOTE 2 – Refer to 5.1.2.3 for the use of status bits and bit X; however for international operation over restricted 64-kbit/s bearer capabilities, bit X must be set to binary 1. | | | | | | | | | + +1 Multiplexing of several intermediate rate streams is for further study. + +**Table 7b/V.110 – Adaption of 56 kbit/s user rate to 64 kbit/s** + +| Octet number | Bit number | | | | | | | | +|--------------|------------|-----|-----|-----|-----|-----|-----|---| +| | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | +| 1 | D1 | D2 | D3 | D4 | D5 | D6 | D7 | 1 | +| 2 | D8 | D9 | D10 | D11 | D12 | D13 | D14 | 1 | +| 3 | D15 | D16 | D17 | D18 | D19 | D20 | D21 | 1 | +| 4 | D22 | D23 | D24 | D25 | D26 | D27 | D28 | 1 | +| 5 | D29 | D30 | D31 | D32 | D33 | D34 | D35 | 1 | +| 6 | D36 | D37 | D38 | D39 | D40 | D41 | D42 | 1 | +| 7 | D43 | D44 | D45 | D46 | D47 | D48 | D49 | 1 | +| 8 | D50 | D51 | D52 | D53 | D54 | D55 | D56 | 1 | + +**Table 7c/V.110 – Alternative frame structure for the adaption of 56 kbit/s user rate to 64 kbit/s** + +| Octet number | Bit number | | | | | | | | +|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------|-----|-----|-----|-----|-----|-----|----| +| | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | +| 1 | D1 | D2 | D3 | D4 | D5 | D6 | D7 | 0 | +| 2 | D8 | D9 | D10 | D11 | D12 | D13 | D14 | X | +| 3 | D15 | D16 | D17 | D18 | D19 | D20 | D21 | S3 | +| 4 | D22 | D23 | D24 | D25 | D26 | D27 | D28 | S4 | +| 5 | D29 | D30 | D31 | D32 | D33 | D34 | D35 | 1 | +| 6 | D36 | D37 | D38 | D39 | D40 | D41 | D42 | 1 | +| 7 | D43 | D44 | D45 | D46 | D47 | D48 | D49 | 1 | +| 8 | D50 | D51 | D52 | D53 | D54 | D55 | D56 | 1 | +| NOTE 1 – Refer to 5.1.2.3 for the use of status bits and bit X. | | | | | | | | | +| NOTE 2 – This table is a permitted option to provide for signalling to enter and to leave the data phase. However, the recommended approach shall be as in Table 7b and the responsibility shall be on the user of this table to ensure that interworking can be achieved. | | | | | | | | | + +### 5.2.1 Frame synchronization + +At the user data signalling rate of 48 kbit/s, the frame alignment pattern consists of 1011 in bit 1 of consecutive octets of one frame. To ensure reliable synchronization, it is suggested that at least five 4-bit alignment patterns in consecutive frames be detected. + +At the user data signalling rate of 56 kbit/s with the alternative frame structure according to Table 7c, the frame alignment pattern consists of 0YYY1111 in bit 8 of consecutive octets of one frame. Bits marked with Y may be either "0" or "1". To ensure a reliable synchronization, it is suggested that at least four 5-bit (01111) alignment patterns in the 8-bit sequence of 0YYY1111 in consecutive octets be detected. + +Frame synchronization monitoring and recovery is described in 5.1.3.2. + +## 5.3 Adaption for asynchronous rates of up to 38 400 bit/s + +### 5.3.1 General approach + +The bit rate adaption functions within the TA are shown in Figure 4. A three-step method is employed with the functional blocks RA0, RA1, and RA2. The RA0 function is an asynchronous-to-synchronous conversion step, for support of the rates specified in Table 8, using the same technique as defined in Recommendation V.14. It produces a synchronous bit stream defined by $2^n \times 600$ bit/s (where $n = 0$ to 6). The functions RA1 and RA2 are the same as specified in 5.1. Function RA1 adapts the user rate to the next higher rate expressed by $2^k \times 8$ kbit/s (where $k = 0, 1, 2$ or 3). RA2 performs the second conversion to 64 kbit/s. + + + +Figure 4/V.110 – Three-step rate adaption bit. The diagram shows a three-step process for rate adaptation. Step 1 (RA0) is 'Stop bit manipulation', converting an asynchronous rate R to a synchronous rate of 2^n x 600 bit/s. Step 2 (RA1) is a rate adaptation block that takes the synchronous rate and outputs a rate of 2^k x 8 bit/s. Step 3 (RA2) is another rate adaptation block that takes the rate from Step 2 and outputs a final rate of 64 bit/s. The input is R and the output is S/T. The diagram is labeled T1701670-92. + +Figure 4/V.110 – Three-step rate adaption bit + +### 5.3.2 Supported asynchronous user rates + +The asynchronous user rates to be supported, mandatory and optional, are specified in Table 8. + +Table 8/V.110 – Asynchronous user rates + +| Data rate
(bit/s) | Rate tolerance
(%) | Number of
data units | Number of
stop elements | RA0/RA1 rate
(bit/s) | RA1 rate
(kbit/s) | +|----------------------|-----------------------|-------------------------|----------------------------|-------------------------|----------------------| +| 50 | ±2.5 | 5 | 1.5 | 600 | 8 | +| 75 | ±2.5 | 5, 7 or 8 | 1, 1.5 or 2 | 600 | 8 | +| 110 | ±2.5 | 7 or 8 | 1 or 2 | 600 | 8 | +| 150 | ±2.5 | 7 or 8 | 1 or 2 | 600 | 8 | +| 200 | ±2.5 | 7 or 8 | 1 or 2 | 600 | 8 | +| 300* | ±2.5 | 7 or 8 | 1 or 2 | 600 | 8 | +| 600* | +1 – 2.5 | 7 or 8 | 1 or 2 | 600 | 8 | +| 1 200* | +1 – 2.5 | 7 or 8 | 1 or 2 | 1 200 | 8 | +| 2 400* | +1 – 2.5 | 7 or 8 | 1 or 2 | 2 400 | 8 | +| 3 600 | +1 – 2.5 | 7 or 8 | 1 or 2 | 4 800 | 8 | +| 4 800* | +1 – 2.5 | 7 or 8 | 1 or 2 | 4 800 | 8 | +| 7 200 | +1 – 2.5 | 7 or 8 | 1 or 2 | 9 600 | 16 | +| 9 600* | +1 – 2.5 | 7 or 8 | 1 or 2 | 9 600 | 16 | +| 12 000 | +1 – 2.5 | 7 or 8 | 1 or 2 | 19 200 | 32 | +| 14 400 | +1 – 2.5 | 7 or 8 | 1 or 2 | 19 200 | 32 | +| 19 200 | +1 – 2.5 | 7 or 8 | 1 or 2 | 19 200 | 32 | + +**Table 8/V.110 – Asynchronous user rates (*concluded*)** + +| Data rate
(bit/s) | Rate tolerance
(%) | Number of
data units | Number of
stop elements | RA0/RA1 rate
(bit/s) | RA1 rate
(kbit/s) | +|------------------------------------------------------------------------|-----------------------|-------------------------|----------------------------|-------------------------|----------------------| +| 24 000 | +1 – 2.5 | 7 or 8 | 1 or 2 | 38 400 | 64 | +| 28 800 | +1 – 2.5 | 7 or 8 | 1 or 2 | 38 400 | 64 | +| 38 400 | +1 – 2.5 | 7 or 8 | 1 or 2 | 38 400 | 64 | +| NOTE 1 – * indicates rate whose support is mandatory for universal TA. | | | | | | +| NOTE 2 – Number of data bits includes possible parity bits. | | | | | | + +### 5.3.3 Asynchronous-to-synchronous conversion (RA0) + +The RA0 function is only used with asynchronous V-series interfaces. Incoming asynchronous data is padded by the addition of stop elements to fit the nearest channel rate defined by $2^n \times 600$ bit/s. Thus, a 7200 bit/s user data signalling rate shall be adapted to a synchronous 9600 bit/s stream and a 110 bit/s user data signalling rate shall be adapted to synchronous 600 bit/s stream. The resultant synchronous stream is fed to RA1. Padding with stop elements is inhibited during the transmission of the break signal as described in 5.3.5. + +### 5.3.4 Overspeed/underspeed + +A terminal adaptor shall insert additional stop elements when its associated terminal is transmitting with a lower than nominal character rate. If the terminal is transmitting characters with an overspeed of up to 1% (or 2.5% in the case of nominal speeds lower than 600 bit/s), the asynchronous-to-synchronous converter may delete stop elements as often as is necessary to a maximum of one every eight characters at 1% overspeed. The converter on the receiving side shall detect deleted stop elements and re-insert them in the received data stream (circuit 104). + +The nominal length of the start elements and data units shall be the same for all characters. The length of the stop element may be reduced as much as 12.5% by the receiving converter for nominal speeds exceeding 300 bit/s to allow for overspeed in the transmitting terminal. For nominal speeds less than or equal to 300 bit/s, a 25% reduction in stop element is allowed. + +### 5.3.5 Break signal + +The terminal adaptor shall detect and transmit the break signal as follows: + +If the converter detects M to $2M + 3$ bits, all of start polarity, where M is the number of bits per character in the selected format including start and stop elements, the converter shall transmit $2M + 3$ bits of start polarity. + +If the converter detects more than $2M + 3$ bits, all of start polarity, the converter shall transmit all these bits as start polarity. + +For the cases where the asynchronous rate is lower than the synchronous rate for the converter, the following rules shall apply: + +- the converter shall transmit start polarity (to RA1) for a time period equal to $2M + 3$ bits at the asynchronous rate if the converter has detected M to $2M + 3$ bits of start polarity; +- the converter shall transmit (to RA1) start polarity for a time period as long as the received break condition if the converter has detected more than $2M + 3$ bits of start polarity; +- the $2M + 3$ or more bits of start polarity received from the transmitting side shall be output to the receiving DTE; + +- the DTE must transmit on circuit 103 at least 2M bits of stop polarity after the start polarity break signal before sending further data characters. The converter shall then regain character synchronism from the following stop to start transition. + +### **5.3.6 Parity bits** + +Possible parity bits included in the user data are considered as data bits by the RA0 function. + +## **5.4 Flow control for use with TAs supporting asynchronous DTEs** + +A flow control option, for use with TAs supporting asynchronous DTEs, is described in this subclause. Flow control allows the connection of asynchronous DTEs operating at different user data rates by reducing the character output of the faster to that of the slower. Support of flow control will require the use of the end-to-end (TA-to-TA) protocol defined in 5.4.2 and an incoming line (from network) buffer in addition to a selected local protocol (see 5.4.1). Depending upon the local flow control protocol employed, there will also be a requirement for character buffering from the DTE interface. The size of this buffer is not defined in this Recommendation because it is dependent upon implementation. Criteria for buffer dimensioning may be found in Recommendation V.43. + +Local flow control of the DTE interface is required where the DTE operates at a rate higher than the synchronous rate established between TAs. End-to-end flow control is required where the synchronous rate established between TAs is consistent with the operating rate of one DTE (or interworking unit) and higher than the synchronous rate consistent with the operating rate of the other DTE (or interworking unit). Both local and end-to-end flow control could be required in some applications. + +### **5.4.1 Local flow control: between TA and DTE** + +Connection may be made between TAs connected to asynchronous DTEs operating at two different character rates. It is the responsibility of the TA connected to the faster DTE to execute a local flow control protocol to reduce the character rate to that of the slower DTE. This operation will require some buffer storage in the TA. A TA may support several different local flow control protocols, although only one will be selected at any one time. There are a number of such protocols in use, some of which are detailed in the following subclauses. DTE-DCE flow control mechanisms are described in detail in Recommendation V.43. + +#### **5.4.1.1 133/106 operation** + +This is a bidirectional (DCE and DTE control each other) out-of-band flow control mechanism, utilizing two of the interchange circuits specified in Recommendation V.24. A DCE not-ready condition is indicated by turning circuit 106 OFF and cleared by turning circuit 106 (ready for sending) ON. A DTE not-ready condition is indicated by an ON-to-OFF transition and cleared by an OFF-to-ON transition of circuit 133 (ready for receiving). + +#### **5.4.1.2 105/106 operation** + +This is a unidirectional (DCE controls DTE) out-of-band flow control mechanism, utilizing two of the interchange circuits specified in Recommendation V.24. If a DTE requires to transmit a character, it turns ON circuit 105 (request to send). The DTE can only begin transmission when it receives in return circuit 106 ON (ready for sending). If, during transmission of a block of characters circuit 106 goes OFF, the DTE shall cease transmission (after completing the transmission of any character of which transmission has started) until circuit 106 turns ON again. + +NOTE – The apparent conflict between this and 7.1.2.4 (Note 1) and 7.1.3.1 a) is for further study. + +#### **5.4.1.3 XON/XOFF operation** + +This is an in-band flow control mechanism using two characters of the International Alphabet No. 5 (IA5) set for XON and XOFF operation. It may be used either unidirectionally (DCE controls DTE) or bidirectionally (DCE and DTE control each other). If a DTE (or DCE) receives an XOFF character, it shall cease transmission. When it receives an XON character, it may resume transmission. The characters typically used for XON and XOFF are device control one (DC1) and device control three (DC3) (bit combinations 1/1 and 1/3 in Recommendation T.50) respectively, although alternative bit combinations can be used. + +#### **5.4.1.4 Other methods** + +Alternative and non-standard methods of asynchronous flow control are in use, and these may be mapped onto the TA flow control protocol. + +### **5.4.2 End-to-end (TA-to-TA) flow control** + +Matching (by reduction) of the transmitted character rate of the DTE to the rate of the TA is not sufficient in all cases to guarantee correct operation, and end-to-end flow control may be required. + +The X-bit is used to carry flow control information. A TA will buffer incoming characters. When the number of buffered characters exceeds a threshold TH1, depending upon implementation, the TA will set the X-bit of its outgoing frames to OFF. + +Upon receipt of a frame containing an X-bit set to OFF, a TA will execute its selected local flow control procedure indicating that the attached DTE must stop sending characters, and cease the transmission of data after completion of the character in progress by setting the data bits in the outgoing frames to ONE. + +When the buffer contents of a TA which has initiated an end-to-end flow control drops below threshold TH2, the TA will reset the outgoing X-bit to ON. + +When the far-end TA receives a frame with the X-bit set to ON, it will recommence data transmission, and, by use of the local flow control procedure, indicate to the attached DTE that it may continue. + +NOTE – There may be a delay between initiation of the end-to-end flow control protocol and termination of the incoming character stream. The characters arriving during this time must be buffered, and the total buffer size will depend upon the character rate, round-trip delay and the buffer threshold. + +### **5.4.3 Use of channel capacity** + +Upon accepting a call from a TA supporting flow control and operating at a different user rate and/or intermediate rate, the called TA will adopt the identical intermediate rate and bit repetition factor. This will override the parameters normally selected. In such cases, the TA connected to the faster DTE will execute a local flow control procedure to reduce the character rate to that of the slower DTE. + +Thus, if a faster DTE calls a slower DTE, the faster intermediate channel rate and bit repetition factor will be adopted by the TAs on both ends. To reduce the character rate received by the slower DTE, its TA will exercise end-to-end flow control and cause the TA on the calling side to utilize local flow control. + +If a slower DTE calls a faster DTE, the slower intermediate channel rate and bit repetition factor will be adopted by the TAs on both ends. To reduce the character rate transmitted by the faster DTE, its TA will exercise local flow control. + +If the called TA does not implement the intermediate rate and bit repetition factor used by the calling TA, the call shall be rejected. + +### 5.4.4 Requirements of a TA supporting flow control + +The following are general requirements for a TA supporting flow control: + +- i) A TA supporting flow control shall be capable of operating with an intermediate rate and bit repetition factor that is independent of the asynchronous speed used at its DTE interface. +- ii) A TA supporting flow control shall, if possible, adapt to the intermediate rate and bit repetition factor required for an incoming call. User rate information will be obtained from signalling. +- iii) A TA supporting flow control shall be capable of executing a local flow control protocol to reduce the character rate to that of the far-end DTE. +- iv) A TA supporting flow control will support the use of end-to-end (TA-to-TA) flow control using the X-bit, and will contain a character buffer. + +# 6 Interchange circuits + +## 6.1 Essential and optional interchange circuits + +The essential and optional interchange circuits are listed in Table 9. + +**Table 9/V.110** + +| Interchange circuit (Note 1) | | | +|------------------------------|------------------------------------------------|-------| +| Number | Description | Notes | +| 102 | Signal ground or common return | | +| 102a | DTE common return | 2 | +| 102b | DCE common return | 2 | +| 103 | Transmitted data | | +| 104 | Received data | | +| 105 | Request for sending | 3, 8 | +| 106 | Ready for sending | | +| 107 | Data set ready | | +| 108/1 | Connect data set to line | 4 | +| 108/2 | Data terminal ready | 4 | +| 109 | Data channel received line signal detector | | +| 113 | Transmitter signal element timing (DTE source) | 5 | +| 114 | Transmitter signal element timing (DCE source) | | +| 115 | Receiver signal element timing (DCE source) | | +| 125 | Calling indicator | 6 | +| 133 | Ready for receiving | 7, 8 | +| 140 | Loopback/maintenance test | 9 | +| 141 | Local loopback | 9 | +| 142 | Test indicator | 9 | + +**Table 9/V.110 (concluded)** + +NOTE 1 – All essential circuits and any others which are provided shall comply with the functional and operational requirements of Recommendation V.24. All interchange circuits provided shall be properly terminated in the data terminal equipment and in the data circuit-terminating equipment in accordance with the appropriate Recommendation for electrical characteristics (see 6.5). + +NOTE 2 – Interchange circuits 102a and 102b are required where the electrical characteristics defined in Recommendation V.10 are used at data signalling rates above 20 kbit/s. + +NOTE 3 – Not required for DTEs designed to operate with DCEs in the continuous carrier (duplex) mode and where in addition the DTE is not intended to exhibit out-of-band flow control (see 5.4). + +NOTE 4 – This circuit shall be capable of operating as circuit 108/1 or 108/2, depending on its use (by the associated DTE). + +NOTE 5 – The use of circuit 113 is for further study since its application is restricted by the synchronous nature of ISDN. + +NOTE 6 – This circuit is used with the automatic answering terminal adaptor function. + +NOTE 7 – Required for duplex DTEs that use bidirectional out-of-band (133/106) flow control. + +NOTE 8 – Circuits 105 and 133 are assigned to the same connector pin on the standardized 25- and 26-pole connectors (ISO/IEC 2110 and ISO/IEC 11569). As circuit 133 is used only in duplex operation and circuit 105 is used only in half duplex operations, there should be no conflict. + +NOTE 9 – The use for loopback testing is for further study. + +## **6.2 Timing arrangement** + +The TA shall derive ISDN timing from the received bit stream of the ISDN's basic user/network interface (see clauses 5/I.430 and 8/I.430). This network timing shall be used by the TA to provide the DTE with transmitter signal element timing on circuit 114 and receiver signal element timing on circuit 115. + +## **6.3 Circuit 106** + +After the start-up and retrain synchronization sequences, the ON state of circuit 106 shall be delayed relative to the ON state of circuit 105 (where implemented) by an interval of at least $N$ bits (a value of $N$ equal to 24 has been proposed, but the value is for further study). ON to OFF state transitions of circuit 106 shall follow ON to OFF state transitions of circuit 105 (when implemented) by less than 2 ms. Where circuit 105 is not implemented, the initial circuit 106 transition to the ON state shall be delayed by an interval greater than or equal to $N$ bits relative to the corresponding transition in the state of circuit 109. Subsequent transitions in the state of circuit 106 should occur solely in accordance with the operating sequences defined in clause 7, or when used for the optional flow control defined in 5.4. + +## **6.4 Circuit 109** + +OFF to ON and ON to OFF transitions of circuit 109 should occur solely in accordance with the operating sequence defined in clause 7. + +## **6.5 Electrical/mechanical characteristics of interchange circuits** + +### **6.5.1 Basic ISDN user/network interface** + +The electrical and mechanical characteristics of the basic ISDN user/network interface are described in clauses 8/I.430 and 10/I.430. + +### **6.5.2 TE2/TA (DTE/DCE) interface** + +#### **6.5.2.1 Rates less than or equal to 19.2 kbit/s** + +Use of electrical characteristics conforming to Recommendations V.28 is recommended together with the connector and pin assignment plans specified by ISO/IEC 2110 and ISO/IEC 11569. + +#### **6.5.2.2 Rates greater than 19.2 kbit/s** + +Use of electrical characteristics conforming to Recommendations V.10 and/or V.11 is recommended together with the use of the connector and pin assignment plan specified by ISO 4902. + +- i) Concerning circuits 103, 104, 113, 114 and 115, both the generators and the receivers shall be in accordance with Recommendation V.11. +- ii) In the case of circuits 105, 106, 107 and 109, generators shall comply with Recommendation V.10 or alternatively Recommendation V.11. The receivers shall comply with Recommendation V.10, category 1, or Recommendation V.11 without termination. +- iii) In the case of all other circuits, Recommendation V.10 applies, with receivers configured as specified by Recommendation V.10 for category 2. + +NOTE – Equipment may be encountered that uses the interface defined in Appendix II of former Recommendation V.35 (withdrawn) together with the connector and pin assignment plan specified by ISO/IEC 2593. + +## **6.6 Fault condition on interchange circuits** + +See clause 7/V.28 for association of the receiver failure detection types. + +**6.6.1** The DTE should interpret a fault condition on circuit 107 as an OFF condition using failure detection type 1. + +**6.6.2** The data circuit-terminating equipment (DCE) shall interpret a fault condition on circuits 105 and 108 as an OFF condition using failure detection type 1. + +**6.6.3** All other circuits not referred to above may use failure detection types 0 or 1. + +# **7 Operating sequence** + +Four interoperational cases for a V.110 TA are described in A.4. This clause describes the operating sequence for a V-series TE2 (DTE) communicating with another V-series TE2 via V.110 TAs connected through the ISDN. This clause also applies to the V-series TE2 side of the other three interoperational cases. + +The operating sequence is specified such that a pair of TAs connected via the ISDN shall exhibit behaviour (as observed at the DTE-DCE interfaces) that is equivalent to that exhibited by a pair of V-series modems interconnected via the PSTN. + +For a TA communicating with an interworking function, the behaviour observed at the TA's DTE-DCE interface is equivalent to that exhibited by a V-series modem. The detailed operating sequence is for further study. + +## **7.1 TA duplex operation** + +When using the TA to provide data transmission service within ISDN, the call is established over a 64-kbit/s connection using the procedures applicable to the particular network and/or terminal configuration. + +The internal arrangement of the TA functional parts and the DTE (with a V-series type interface) is not within the scope of this Recommendation. It is assumed that means are provided to control the entry to and the exit from the data transfer mode. For example, it is assumed that the means are provided to control circuits 108/1 (Connect data set to line) or 108/2 (Data terminal ready) internally, that is within the station at the customer premises. However, for the purpose of this Recommendation circuit 108/2, as defined in Recommendation V.24, is assumed. In this subclause, the SA and SB groups of status bits are treated as a single sequence of S-bits. + +NOTE – The operating sequence of a duplex V.110 TA has been specifically designed such that a V-series TE2 connected to the ISDN via a V.110 TA can interoperate with an X.21 TE2 connected via an X.30 TA. + +The operating sequence described in this clause is illustrated in Figure 3. + +### **7.1.1 Idle (or ready) state** + +**7.1.1.1** During the idle (or ready) state the TA (DCE) will be receiving the following from the DTE: + +- Circuit 103 = Continuous binary 1. +- Circuit 105 = See Note. +- Circuit 108/1 = OFF; circuit 108/2 = ON. + +NOTE – In many duplex DTEs circuit 105 is either permanently in the ON condition or it is not present. If not present, the function must be set in an ON condition in the TA. See 7.1.2.4 for the case where a duplex DTE can operate circuit 105. + +**7.1.1.2** During the idle (or ready) state the TA will transmit continuous binary 1s into the B- and D-channels (i.e. all bits of Table 2 = binary 1). + +**7.1.1.3** During the idle (or ready) state the TA (DCE) will transmit the following toward the DTE: + +- Circuit 104 = Continuous binary 1. +- Circuit 107 = OFF. +- Circuit 106 = OFF. +- Circuit 109 = OFF. + +### **7.1.2 Connect TA to line state** + +**7.1.2.1** When the TA is to be switched to the data mode, circuit 108 must be ON. Switching to the data mode causes the TA to transmit the following towards the ISDN (refer to Table 2): + +- a) frame synchronization pattern as described in 5.1.3.1 and 5.2.1; +- b) data bits = binary 1; +- c) status bits S = OFF and X = OFF (ON = binary 0, OFF = binary 1). + +NOTE 1 – At this time, circuit 103 is not connected to the data channel (e.g. the binary 1 condition of the data bits is generated within the TA). + +NOTE 2 – In the following description only the inter-operation between TE2/TA (DTE/DCE) interface and the intermediate rate frames (see Tables 6a to 6f) and the 64 kbit/s frame of Tables 7a and 7c are discussed. The second step of rate adaption encoding and decoding and the multiplexing and demultiplexing of the ISDN basic user/network interface are discussed in Recommendations I.460 and I.430, respectively. + +**7.1.2.2** At this time (i.e. switching to data mode) the receiver in the TA will begin to search for the frame synchronization pattern in the received bit stream (see 5.1.3.1 and 5.2.1) and start timer T1. A suggested value is 10 s (see I.7.1). + +**7.1.2.3** When the receiver recognizes the frame synchronization pattern, it causes the S- and X-bits in the transmitted frames to be turned ON (provided that circuit 108 is ON). + +**7.1.2.4** When the receiver recognizes that the status of bits S and X are in the ON condition, it will perform the following functions: + +- a) Turn ON circuit 107 toward the DTE and stop timer T1. + +NOTE 1 – A duplex DTE that implements and is able to operate circuit 105 may be expected to turn this circuit ON at any time. However, if not previously turned ON, it must be turned ON in response to the ON condition on circuit 107. + +- b) Then, circuit 103 may be connected to the data bits in the frame; however, the DTE must maintain a binary 1 condition on circuit 103 until circuit 106 is turned ON in the next portion of the sequence. +- c) Turn ON circuit 109 and connect the data bits to circuit 104. +NOTE 2 – Binary 1 is being received on circuit 104 at this time. +- d) After an interval of *N* bits (see 6.3), it will turn ON circuit 106. +- e) Circuit 106 transitioning from OFF to ON will cause the transmitted data to transition from binary 1 to the data mode. + +If circuit 107 has not been turned ON, after expiring of timer T1 the TA shall be disconnected according to the procedures specified in 7.1.4. + +### **7.1.3 Data transfer state** + +**7.1.3.1** While in the data transfer state, the following circuit conditions exist: + +- a) circuits 105 (when implemented), 107, 108/1 or 108/2 and 109 are in the ON condition; +- b) data is being transmitted on circuit 103 and received on circuit 104; +- c) circuits 133 (when implemented) and 106 are in the ON condition unless local out-of-band flow control is being used, in which case, either or both circuits may be in the ON or the OFF condition. + +**7.1.3.2** While in the data transfer state, the following status bit conditions exist: + +- a) status bits S in both directions are in the ON condition; +- b) status bits X in both directions are in the ON condition unless end-to-end flow control is being used, in which case status bit X in either or both directions may be in the ON or the OFF condition. + +**7.1.3.3** While in the data transfer state, for the interoperational cases not involving an interworking function (IWF): + +- a) the S status bits shall not be mapped to/from the interchange circuits according to Table 3; +- b) the X status bits shall not be mapped according to Table 3 unless end-to-end flow control is implemented. + +NOTE – Certain equipment designed prior to the publication of this version of V.110 may map one or both of the S status bits to/from the interchange circuits according to Table 3. + +The use of the S and X status bits in the data transfer state to carry status information to/from the modem in an IWF is for further study. + +### **7.1.4 Disconnect mode** + +**7.1.4.1** At the completion of the data transfer phase, the local DTE will indicate a disconnect request by turning OFF circuit 108. This will cause the following to occur: + +- a) the status bits S in the frame toward ISDN will turn OFF, status bits X are kept ON; +- b) circuit 106 will be turned OFF; +- c) the data bits in the frame will be set to binary 0. + +To guard against the failure of the remote TA to respond to the disconnect request, the local TA may start a timer T2 (suggested value 5 s) which is stopped by the reception or transmission of any D-channel clearing message (DISCONNECT, RELEASE, RELEASE COMPLETE). If the timer expires, the local TA should clear the call via the ISDN D-channel signalling protocol. + +**7.1.4.2** If circuit 108 is still ON at the remote TA, this TA will recognize the transition of the status bits S from ON to OFF and the data bits from data to binary 0 as a disconnect request and it will turn OFF circuits 107 and 109. This DTE should respond by turning OFF circuit 108 and transferring to disconnected mode. The disconnection will be signalled by the TA via the ISDN D-channel signalling protocol. At this time, the DTE/DCE interface should be placed in the idle (or ready) state. + +**7.1.4.3** The TA at the station that originated the disconnect request will recognize reception of S = OFF or the loss of framing signals as a disconnect acknowledgement and turn OFF circuits 107 and 109 and transfer to disconnected mode. The disconnection will be signalled by the TA via the ISDN D-channel signalling protocol. At this time, the DTE/DCE interface should be placed in the idle (or ready) state. + +### **7.1.5 Loss of frame synchronization** + +In the event of loss of frame synchronization, the (local) TA should attempt to resynchronize as follows: + +- a) Place circuit 104 in binary 1 condition (passes from the data mode). +- b) Turn OFF status bit X in the transmitted frame. +- c) The remote TA upon recognition of status bit X OFF will turn OFF circuit 106 which will cause the remote DTE to place circuit 103 in a binary 1 condition. +- d) The local TA should attempt to resynchronize on the incoming signal. +- e) If after an interval of three seconds the local TA cannot attain synchronization, it should send a disconnect request by turning OFF all of the status bits for several (at least three) frames with data bits set to binary 0 and then disconnect by turning OFF circuit 107 and transferring to the disconnected mode as discussed in 7.1.4.2. + +NOTE 1 – The values of three seconds and three frames are provisional and should be confirmed or amended after further study. + +- f) If resynchronization is achieved, the local TA should turn ON status bit X toward the distant station. +- g) If resynchronization is achieved, the TA (which has turned OFF circuit 106) should, after an interval of *N* bits (see 6.3), turn ON circuit 106. This will cause circuit 103 to change from binary 1 to the data mode. + +NOTE 2 – During a resynchronization attempt, circuits 107 and 109 should remain ON. + +## **7.2 TA half-duplex operation** + +The data call establishment for the interworking of half-duplex DTEs equipped with V-series type interfaces is the same as discussed in 7.1. The only difference between half-duplex operation is in the control of the circuits 105, 106, and 109, as follows. + +NOTE – This is a unique application; therefore, TA arranged for half-duplex operation will not be able to interwork with either a V-series or an X-series duplex DTE (TE2). + +**7.2.1** In a TA arranged to accommodate half-duplex DTEs, circuit 109 will be under the control of the status bits SB in the incoming frame, as follows: + +- a) If at the local interface circuit 109 is OFF and circuit 104 is in the binary 1 state, the DTE may "request to send" by turning ON circuit 105. + +- b) The TA will then turn ON status bits SB in the transmitted frame which will at the remote interface turn ON circuit 109 and connect circuit 104 to the data bit stream of the incoming frame. +- c) After an $N$ bit interval (see 6.3) the local TA will turn ON circuit 106, which will allow the local DTE to transmit data on circuit 103. +- d) Upon completion of the transmission, the local DTE will turn OFF circuit 105. This will in turn: + - turn OFF circuit 106 at the local interface, and circuit 103 will revert to the binary 1 state; + - turn OFF status bits SB which will in turn at the remote TA turn OFF circuit 109 and place circuit 104 in a binary 1 condition. +- e) At this time the remote DTE is able to reverse the sequence by turning ON circuit 105. + +## 7.3 Automatic calling + +The mapping of V.25 *bis* automatic calling and automatic answering procedures to the ISDN D-channel signalling protocols is described in Appendix II. + +# 8 Network-independent clocks + +In cases where synchronous data signals at user rates up to and including 19.2 kbit/s are received from outside the ISDN (e.g. through an interworking unit from a DTE/modem on the PSTN), the data may not be synchronized to the ISDN. Such a situation would exist where the signals are received through an interworking unit from voiceband data modems on the analogue PSTN, where the transmit data from the remote modem is synchronized to the modem clock (normal case for such applications). The frequency tolerance of such modems is 100 ppm. The following method shall be used to enable transfer of those data signals and the corresponding bit timing information via the 80-bit frame to the receiving TA. + +## 8.1 Measurement of phase differences + +The phase difference between the following two frequencies will be measured: + +- i) $R1 = 0.6 \times$ the nominal intermediate rate (except where Fill bits are used; see Note), synchronized with the ISDN; +- ii) $R2 = 0.6 \times$ the nominal intermediate rate (except where Fill bits are used; see Note), derived from and synchronized with the bit timing received from the remote synchronous source, e.g. modem. + +NOTE – Clocks R1 and R2 are nominally either 4800, 9600 or 19 200 Hz at 8 kbit/s, 16 kbit/s and 32 kbit/s intermediate rate, respectively. + +Where Fill bits are used, in the cases of 7200 and 14 400 bit/s R1 and R2 will have the same nominal rate as the user bit rate. + +Compensation will affect one, one-half, one-quarter or one-eighth of a user data bit, dependent upon the bit repetition factor. + +A state diagram for the transmitting TA showing the phase of R2 relative to R1 appears in Figure 5. Table 10 shows the related bit coding. + + + +``` + +graph TD + 0["0%"] + P20["+20%"] + P40["+40%"] + M20["-20%"] + M40["-40%"] + + 0 <--> P20 + P20 <--> P40 + 0 <--> M20 + M20 <--> M40 + P40 -- "+" --> M40 + M40 -- "-" --> P40 + + subgraph FastClock [Fast clock R2 > R1] + FC_Arrow(( )) --> 0 + end + + subgraph SlowClock [Slow clock R2 < R1] + SC_Arrow(( )) --> 0 + end + +``` + +Detailed description: A circular state diagram with five states: 0% at the top, +20% and +40% on the left, -20% and -40% on the right. Double-headed arrows connect adjacent states (0 to +20, +20 to +40, 0 to -20, -20 to -40). A large curved arrow on the left labeled 'Fast clock (R2 > R1)' points downwards. A similar arrow on the right labeled 'Slow clock (R2 < R1)' points downwards. At the bottom, two curved arrows labeled 'Compensation' connect the +40% and -40% sides; the inner arrow is labeled '+' and the outer arrow is labeled '-'. Reference code T1701680-92 is in the lower right. + +Figure 5/V.110 – Network-independent clocking state diagram + +NOTE 1 – Phase measurements are given relative to R1 by the formula: Phase = phase (R2) – phase (R1). + +NOTE 2 – Receipt of a bit combination requiring an illegal move of more than one state will cause a legal move of one state in the appropriate direction. + +NOTE 3 – The initial state of both the receiving and transmitting sides of the TA will be 0%. + +**Figure 5/V.110 – Network-independent clocking state diagram** + +Comparison of R1 and R2 will give a phase difference relative to R1 which will be encoded as shown in Table 10. The resultant 3-bit code will be transmitted in bit positions E4, E5 and E6, and used for clock control at the receiving TA. + +**Table 10/V.110 – Coding of E-bits for network-independent clocking** + +| Displacement (in % of nominal R1 clock period at $n \times 4800$ bit/s, $n = 1, 2$ or $4$ ) | Coding in the 80-bit frame | | | +|---------------------------------------------------------------------------------------------|----------------------------|----|----| +| | E4 | E5 | E6 | +| Nominally 0 | 1 | 1 | 1 | +| +20 | 0 | 0 | 0 | +| +40 | 0 | 0 | 1 | +| -40 | 0 | 1 | 0 | +| -20 | 0 | 1 | 1 | +| Compensation control | | | | +| Positive compensation of a one | 1 | 0 | 1 | +| Positive compensation of a zero | 1 | 0 | 0 | +| Negative compensation | 1 | 1 | 0 | + +To avoid continuous jitter between neighbouring displacement positions, hysteresis shall be applied, as follows: + +The displacement code shall be changed only when the measured phase difference between R1 and R2 is 15% (of the R1 clock period) more or less than the difference indicated by the existing displacement code. + +*Example* – Bit combination 000 indicates a phase difference of nominally 20%. This bit combination will be changed into 001 when the measured phase difference is 35% or more, and into 111 when the measured phase difference is 5% or less. + +## **8.2 Positive/negative compensation** + +On transition from the +40% state to the –40% state, an extra user D-bit has to be transmitted in the 80-bit frame, using bit E6 (positive compensation). At the receiving TA, this extra bit will be inserted between D24 and D25 as shown in Table 2, immediately following the E-bits. + +On transition from the –40% state to the +40% state, a bit combination is transmitted in the 80-bit frame (E4, E5 and E6 = 1, 1, 0, respectively), indicating to the receiving TA that bit D25 of the 80-bit frame, being set to ONE, does not contain user data and should be removed (negative compensation). + +## **8.3 Encoding** + +The encoding of the measured phase difference for clock control and the positive/negative compensation control overrides and replaces the clock control coding. + +# **9 In-band parameter exchange state** + +The capabilities provided and operation in an optional in-band parameter exchange state are described in Appendix I. + +# **10 Testing facilities** + +The provision of maintenance test loops is for further study, taking in consideration Recommendations X.150 and V.54. + +# **ANNEX A** + +## **Reference configurations** + +## **A.1 Introduction** + +Figures A.1 and A.2 show the two basic reference models used in the development of this Recommendation, and provide valuable examples of the way in which the terminal adaptor may be used. These are provided simply as an aid to the interpretation of this Recommendation and should not be seen as restrictive in any way. + +## **A.2 V.110 terminal adaptor reference model** + +Figure A.1 shows the basic reference model for a V.110 terminal adaptor. + + + +Figure A.1/V.110 – Terminal adaptor reference model diagram. The diagram shows a block diagram of a terminal adaptor. On the left, a box labeled 'TE2' is connected to a vertical dashed line labeled 'R'. This line connects to a large box labeled '(1)'. Box (1) is connected to two parallel boxes labeled '(2)' and '(3)'. These two boxes are connected to a large box labeled '(4)'. Box (4) is connected to a vertical dashed line labeled 'S/T', which is then connected to a box labeled 'NT'. The reference number 'T1701690-92' is located at the bottom right of the diagram. + +NT Network Termination + +TE2 Data terminal equipment (DTE) with an interface complying to Recommendation V.24 + +(1) R interface functions (according to Recommendations V.24, V.28, etc.) + +(2) Specific TA functions (e.g. data rate adaption) + +(3) Control access signalling function (e.g. signalling in accordance with Recommendations Q.921 and Q.931, auto calling in accordance with Recommendation V.25 *bis*) + +(4) S/T interface layer 1 functions (according to Recommendation I.430) + +**Figure A.1/V.110 – Terminal adaptor reference model** + +The elements (1), (2), (3) and (4) shown in Figure A.1 represent the functionality required of a terminal adaptor. The elements are not intended to correspond to separate physical units. However, a terminal adaptor need not necessarily constitute a single physical unit. The functions of these elements are: + +- 1) Provision of layer 1, in accordance with Recommendations V.24 and V.28 or other applicable Recommendations and ISO/IEC 2110 or other applicable standards, of the interface at reference point R. +- 2) Specific TA functions, including the adaption of the TE2 data (rate and format) for transmission over an ISDN B-channel and provision of R-interface lead control information. This Recommendation covers primarily these functions. +- 3) Network control signalling functions, including the mapping of call control signals (in accordance with Recommendation V.25 *bis* or other applicable standard) at the R-interface into signals (according to Recommendation Q.931) for transmission on the D-channel across the S/T interface. +- 4) Provision of layer 1, in accordance with Recommendation I.430 of the interface at reference points S or T. + +## **A.3 Terminal adaption type** + +### **A.3.1 Terminal adaptor – Type A (TA-A)** + +The TA-A provides manual call control functions and the functions necessary for data transfer. The following data transfer functions are included: + +- a) Conversion of electrical, mechanical, functional and procedural characteristics of the V-series type interface(s) to those required by an ISDN at reference points S and/or T, as discussed in 6.5; +- b) Bit rate adaption of the V-series data signalling rates to the 64-kbit/s B-channel rate as described in 5.1, 5.2 and 5.3; +- c) End-to-end synchronization of entry to and exit from the data transfer phase, as described in clause 7. + +Terminal adaptor TA-A may be implemented using a physically separate TE1 for providing the network control signalling function, unit (3) in Figure A.1, or the function may be part of an integrated implementation. The function provides for data connection establishment when using the circuit-mode 64-kbit/s unrestricted bearer service. The function includes provisions for speech and data connection establishment when using for speech, both circuit-mode 64-kbit/s bearer service usable for 3.1-kHz audio information transfer, and, for data, the circuit-mode 64-kbit/s unrestricted bearer service concurrently on two B-channels. + +### **A.3.2 Terminal adaptor – Type B (TA-B)** + +The TA-B includes, in addition to those functions provided by a TA-A, the mapping functions necessary to convert the automatic calling and/or automatic answering procedures of Recommendation V.25 *bis* to the ISDN D-channel signalling protocol. This additional functionality is in functional unit (3) in Figure A.1. Terminal adaptor type B is to be used with the 64-kbit/s unrestricted bearer service. + +The need for provisions covering functional unit (3) in Figure A.1 for the implementation of a type B-terminal adaptor is for further study. + +NOTE – Reference to the use of the term "unrestricted bearer". During an interim period, some networks may only support restricted 64-kbit/s signal digital information transfer capability, i.e. information transfer capability solely restricted by the requirement that the all-zero octet is not allowed. Such networks may offer bearer services with restricted transport capabilities. + +## **A.4 Types of end-to-end connection** + +The terminal adaptor functions described in this Recommendation take into account the end-to-end connection types shown in Figure A.2. The figure shows the interoperational cases considered in this Recommendation, as follows: + +- V-series TE2 with V-series TE2; +- V-series TE2 with X.21 TE2; +- V-series TE2 with TE1; +- V-series TE2 with V-series DTE on the PSTN through an interworking function (IWF). + +NOTE – The adaption of terminals by the connection of modem-equipped TE2s to the analogue side of a CODEC to provide for the use of 3.1-kHz bearer capabilities is not addressed in this Recommendation. + +Interworking with PSTNs may be provided on the basis of a trunk interconnection using interworking functions (IWFs) (see Note 1 of Figure A.2). The reference connections illustrated in Figure A.2 do not envisage a direct connection between an ISDN in one country and a public switched telephone network (PSTN) in another country via a network-provided interworking function in the first country. However, access to non-ISDN countries could be through the normal PSTN international connections. + + + +Figure A.2/V.100 – Network reference connections. The diagram shows three connection paths from a central 'ISDN' block. Path 1: TE2 (Terminal Equipment 2) connected to TA-V (Terminal Adaptor V-series) via an R (Reference) interface, which then connects to the ISDN via an S/T (Signalling/Terminal) interface. Path 2: TE2 connected to TA-X (Terminal Adaptor X.21 or X.21 bis) via an R interface, which then connects to the ISDN via an S/T interface. Path 3: TE1 (Terminal Equipment 1) connected to the ISDN via an S/T interface. From the ISDN, three paths emerge: 1. 'International transit' leading to 'To ISDN in another country'. 2. A path through TA-V to another TE2, with an S/T interface between ISDN and TA-V, and an R interface between TA-V and TE2. 3. A path through an IWF (Interworking Function) to 'To national PSTN (Note 2)'. The IWF is labeled '(Note 1)'. The reference T1701700-92 is at the bottom right. + +IWF Interworking function + +TA-V Terminal adaptor function – (DTEs with V-series interfaces) + +TA-X Terminal adaptor function – (DTEs with X.21 or X.21 *bis* interfaces). See Recommendation X.30. + +NOTE 1 – The location of this interworking function is discussed in Recommendation I.510 and general requirements are given in Recommendations I.515 and I.530. The need for a Recommendation covering detailed requirements for such an IWF is for further study. + +NOTE 2 – For access to national non-ISDN terminals or international access to PSTNs of non-ISDN countries. + +**Figure A.2/V.100 – Network reference connections** + +# APPENDIX I + +## In-band parameter exchange + +## I.1 Introduction + +During the evolution of ISDN there will exist for a considerable period: + +- DTEs with V-series type interfaces which are to be connected to an ISDN by terminal adaptors; and +- requirements for interoperation between DTEs/TAs connected to ISDNs, that are interconnected with facilities which do not provide for the full ISDN out-of-band signalling capability necessary to support parameter exchange between terminal adaptors. + +Considering that Recommendation I.530 defines interworking between an ISDN and a PSTN in general, that Recommendation I.515 describes the parameter exchange for interworking between ISDNs and existing networks, the specific procedure to be used for in-band parameter exchange (IPE) within the context of terminal adaptors following this Recommendation is as described in this appendix. This procedure is consistent with Recommendations I.530 and I.515. + +It enhances the capability of V.110 TA in order to support: + +- the transfer of the end-to-end information required for the compatibility checking of data calls; +- an exchange of terminal adaptor parameter information; and +- an exchange of information related to maintenance operations. + +## I.2 Definitions + +For the IPE, which is described in this appendix, the following definitions apply. These definitions are ordered logically to minimize forward referencing. + +**I.2.1 TA:** A terminal adaptor. + +**I.2.2 calling TA:** The TA requesting the connection to be established. + +**I.2.3 called TA:** The TA accepting the connection. + +**I.2.4 originating TA:** The TA which is responsible for initiating the next exchange of parameter information. Initially, the calling TA takes on the role of the originating TA. + +**I.2.5 answering TA:** The TA which is not responsible for initiating the next exchange of parameter information. Initially, the called TA takes on the role of the answering TA. + +**I.2.6 parameter information:** Terminal adaption protocol information, TA parameters, and (optionally) maintenance information. + +**I.2.7 parameter block:** The complete set of parameter information structured into message groups which are transferred by each TA towards the other during each parameter exchange. + +**I.2.8 message group:** The arrangement of octets based on a repeated sequence of command octets followed by a series of three LOW-HIGH data octet pairs. Each message group transfers one octet of the parameter information. + +**I.2.9 sequence of command octets:** The repeated transmission of at least 32 command octets transmitted without interval for 64-kbit/s unrestricted and restricted channels. In the case of asynchronous IPE the sequence may be interrupted, within the limits of the procedures. + +**I.2.10 series of LOW-HIGH data octet pairs:** The transmission of six octets grouped into three pairs of LOW-HIGH data octets, the LOW data octet being transmitted in each pair before the HIGH data octet. The six octets are transmitted without interval for 64-kbit/s unrestricted and restricted channels. In the case of asynchronous IPE, the transmission of the six octets may be interrupted, within the limits of the procedures. + +**I.2.11 verification:** Establishment of the validity of a piece of data according to the specified error handling procedures. + +## I.3 Overview + +The in-band parameter exchange (IPE) described in this appendix is based on the transfer of parameter information within the user data stream of an established connection. Specific IPE rates have been selected to cover the application of IPE to connections based on 64-kbit/s unrestricted channels, 64-kbit/s restricted channels and intermediate rate channels. For IPE at rates other than 64 kbit/s, rate adaption according to this Recommendation is applied to the user data stream containing the parameter information. + +In the case of IPE within intermediate rate channels, it is first necessary to achieve frame synchronization according to this Recommendation before the exchange can commence. The parameter information is transferred in a parameter block during one or more exchanges between the two TAs. The block structure is based on message groups, containing a sequence of command octets which identify the information carried in the message group, and a series of general purpose LOW-HIGH data octet pairs which carry the information. The command octets are always transmitted in a repeated sequence of at least 32 octets to allow persistency error handling techniques to be employed. The LOW-HIGH data octet pairs are always transmitted in a series of three to enable majority voting error recovery techniques to be used. + +After the first exchange of parameters, the called TA determines whether the parameter exchange has been successful. If it is, both TAs proceed to the data transfer state directly unless the agreed data transfer rate first requires re-synchronization to a new intermediate rate according to this Recommendation. After the first exchange, and each subsequent exchange, the responsibility for determining the success of the exchange is transferred, to allow the negotiation of parameters to progress evenly. Status information is also transferred during the IPE to enable both TAs to monitor the progression of the exchange. If at any time either TA concludes that a successful exchange of parameters cannot be achieved, the TA should clear the connection. + +Interworking with TAs not supporting IPE is specified. + +## I.4 Reference configuration + +Figure I.1 gives an example of a scenario for an IPE procedure. It illustrates the connection of ISDNs using the connectivity of existing networks. As the evolution towards an ubiquitous international ISDN capability proceeds, the connection of ISDN islands will often use existing network capabilities. Two alternatives are indicated in Figure I.1. Either arrangement indicated may exist though the use of "digital connectivity" based on the existing integrated digital network (IDN) has many advantages including the avoidance of the need for layer 1 interworking functions. The IDN, however, does not have the ISDN signalling capability and this leads to the need for an IPE procedure. The IPE capability is required to enable communicating TAs to exchange parameters as well as to perform other operations such as maintenance functions. Even where the ISDN signalling capability is available, the IPE capability may be used to provide enhanced parameter exchange. + + + +The diagram illustrates two ISDN networks connected via two different paths. The top path uses 'Digital connectivity (IDN)' with dashed boxes labeled 'IWF' (Interworking Function) at each end. The bottom path uses 'PSTN' (Public Switched Telephone Network) with solid boxes labeled 'IWF' at each end. Each ISDN network is connected to a TA (Terminal Adapter) and a TE1 (Terminal Equipment 1) via S/T interfaces. The TA is also connected to a TE2 via an R (Ring) interface. The PSTN path includes a DCE (Data Circuit-terminating Equipment) and a DTE (Data Terminal Equipment) connected via R interfaces. + +T1701710-92 + +Figure I.1/V.110 – Reference configuration diagram showing two ISDN networks connected via Digital connectivity (IDN) and PSTN, with various interworking functions (IWF) and terminal equipment (TE1, TE2, TA, DCE, DTE). + +**Figure I.1/V.110 – Reference configuration** + +## I.5 Procedures + +### I.5.1 General + +Subclause I.5 describes the procedures which permit a TA to exchange parameter and maintenance information in-band by using messages within the user data stream. + +Once the call has been established, the IPE is initiated at one of four user data rates as per Table I.1. It is recommended that, where possible, the IPE is performed using the unrestricted/restricted 64 kbit/s rate. If the TA is not capable of starting at this rate, then the appropriate default + +intermediate rate is used. Default intermediate-rate channels are selected according to this Recommendation for single stream operation described in Recommendation I.460. Subrate multiplexing cannot be supported until the IPE is complete. + +The final rate of data transfer is not restricted by the choice of IPE user rate. (See Table I.1.) It is therefore possible for an IPE at 4.8 kbit/s async, for example, to agree on the use of 64 kbit/s unrestricted during the data transfer state. For IPE at rates other than 64 kbit/s, rate adaption according to this Recommendation is applied to the user data stream containing the IPE information. In order to prevent unintended disconnection when rate adaption according to this Recommendation is used, it is necessary to avoid the condition S = OFF, X = ON and all the data bits set to ZERO. This is achieved by the use of asynchronous characters with one stop bit and the permanent setting of bit 8 in all octets to ONE. + +**Table I.1/V.110 – Selection of IPE user rate** + +| IPE intermediate rate | IPE data rate | +|--------------------------------------|----------------------| +| Unrestricted/restricted (64 kbit/s) | 56 kbit/s | +| 32 kbit/s intermediate-rate channel | 19.2 kbit/s async | +| 16 kbits/s intermediate-rate channel | 9.6 kbit/s async | +| 8 kbits/s intermediate-rate channel | 4.8 kbit/s async | + +Subclause I.5.2 describes how IPE is initiated, with the procedures for IPE itself described in I.5.3. If the parameter exchange results in the selection of a data rate based on a different intermediate rate to that used for IPE, re-synchronization is required. The procedures for re-synchronization and data transfer are given in I.5.4 and I.5.5 respectively. In I.5.6, the procedures for interworking with a TA not supporting IPE are given. In I.5.7 the procedures associated with maintenance are described. Subclause I.5.8 defines re-entry to IPE from the data transfer state, and I.5.9 provides the procedures for error protection and handling. Message codings are given in I.6, timer values in I.7 and state transition diagrams in I.8. + +### **I.5.2 Initiating the exchange** + +An IPE TA requires a local memory flag (the re-entry flag) to control the re-entry into IPE from the data transfer state. + +During the inactive state, the TA shall transmit continuous ONES into the B-channel (see I.8). Once a connection has been established, both TAs will initiate the parameter exchange at the selected user rate and set the re-entry flag to ZERO. Before beginning the parameter exchange, both TAs start timer T2 and may send repeated IDLE status octets (see I.6.5). + +In the case where the TAs operate on a different IPE user rate, the following procedure shall be applied: + +- during the first half of period T2, the called TA only tries to adapt to the IPE rate of the calling TA before transmitting its initial exchange of information; +- during the second half of period T2, the calling TA only tries to adapt to the called TA, and retransmits the initial exchange of information at the called TA user rate. + +If timer T2 expires before a complete parameter block has been received, both TAs shall begin data transfer using their default parameters. + +In the case of user rates of 4.8, 9.6 or 19.2 kbit/s, the TA first completes the frame synchronization procedure described in this Recommendation, with the changes detailed below: + +- a) The transmitter sends frames towards its peer with status information S = OFF and X = OFF and enters the awaiting synchronization-parameter exchange state (state 6). +- b) When the TA recognizes the frame synchronization pattern in the awaiting synchronization-parameter exchange state (state 6), it verifies the status information received and then enters the appropriate state, in a coordinated manner, as follows: + - Data transfer (state 4), upon receipt of S = ON and X = ON (see I.5.6); + - IPE default exchange (state 5), upon receipt of S = OFF and X = OFF; + - Parameter exchange (state 7), upon receipt of S = OFF and X = ON (see I.5.3). +- c) When the TA is in the IPE default exchange state (state 5), it shall transmit frames with status information S = OFF and X = ON and verify the status information received and then enter the appropriate state, in a coordinated manner, as follows: + - Data transfer (state 4), upon receipt of S = ON and X = ON (see I.5.6); + - Parameter exchange (state 7), upon receipt of S = OFF and X = ON (see I.5.3). + +In the case of user rates of 56 or 64 kbit/s, there is no frame synchronization requirement. + +### **I.5.3 Parameter exchange** + +#### **I.5.3.1 Octet alignment** + +In the case of user rates of 4.8, 9.6 or 19.2 kbit/s, each octet of the parameter exchange message is carried as a single start-stop character (see I.6.1). In the case of user rates of 56 or 64 kbit/s, network-provided octet alignment shall be used. + +#### **I.5.3.2 Transfer of parameters** + +The correct interpretation of this subclause requires careful adherence to the definitions made in I.2, particularly for the meaning of a "sequence of command octets" (I.2.9) and a "series of LOW-HIGH data octet pairs" (I.2.10). Further detailed information is given in I.5.9 and I.6. + +After the connection has been established, the calling TA takes on the role of the originating TA and the called TA the role of the answering TA. + +The originating TA begins by starting timer T1 and transmitting a sequence of XSTART command octets (see I.6.3). After verifying the receipt of the XSTART command octets, the answering TA starts Timer T1 and begins parameter transfer as described below. Once the originating TA has verified the receipt of the RA VERSION command octet (at the start of the parameter transfer) from the answering TA, the originating TA also begins parameter transfer in the same manner. Figure I.2 portrays the normal sequence of events during the parameter exchange. + + + +The diagram illustrates the initial sequence of events during a parameter exchange between a **Calling TA (Originating TA)** and a **Called TA (Answering TA)**. + +**Calling TA (Originating TA) Sequence:** + +- XSTART**: Initiates the call. +- RA VERSION (1)**: First RA version message. +- RA VERSION ( $\geq 32$ )**: Subsequent RA version messages, each containing: + - (Pair 1)**: LOW, HIGH + - (Pair 2)**: LOW, HIGH + - (Pair 3)**: LOW, HIGH + - PARAM-X(1)**: First parameter X. +- PARAM-X ( $\geq 32$ )**: Subsequent parameter X messages, each containing: + - (Pair 1)**: LOW, HIGH + - (Pair 2)**: LOW, HIGH + - (Pair 3)**: LOW, HIGH + - FILL**: Fill data. +- FILL**: Final fill data. +- etc.**: Indicates further events. + +**Called TA (Answering TA) Sequence:** + +- IDLE**: Initial state. +- IDLE (X START)**: Response to XSTART. +- RA VERSION (1)**: First RA version message received. +- RA VERSION ( $\geq 32$ )**: Subsequent RA version messages received, each containing: + - (Pair 1)**: LOW, HIGH + - (Pair 2)**: LOW, HIGH + - (Pair 3)**: LOW, HIGH + - PARAM-X(1)**: First parameter X received. +- PARAM-X ( $\geq 32$ )**: Subsequent parameter X messages received, each containing: + - (Pair 1)**: LOW, HIGH + - (Pair 2)**: LOW, HIGH + - (Pair 3)**: LOW, HIGH + - FILL**: Fill data received. +- FILL**: Final fill data received. +- etc.**: Indicates further events. + +**Repetition:** The sequence of RA VERSION and PARAM-X messages is repeated for each parameter, as indicated by the "Repeat for each parameter" label on the right side of the diagram. + +Sequence diagram showing the initial sequence of events during a parameter exchange between a Calling TA (Originating TA) and a Called TA (Answering TA). The diagram illustrates the flow of XSTART, RA VERSION, and PARAM-X messages, including their components like LOW, HIGH, and FILL, and the repetition of these for multiple parameters. + +T1701720-92 + +Figure I.2/V.110 – Initial sequence of events during a parameter exchange + +The parameter transfer commences with the transmission of a sequence of RA VERSION command octets followed by a series of LOW-HIGH data octet pairs containing the rate adaption identifier (see I.6.2). Directly following the transmission of the rate adaption identifier, the transfer continues with the parameters themselves in five groups: PARAM-0 to PARAM-4 (see I.6.4), transmitted in ascending order. Each group begins with the transmission of a sequence of the appropriate PARAM command octet followed by a series of LOW-HIGH data octet pairs which carry the parameters. At the completion of the parameter information transfer, both TAs send repeated FILL status octets until the next stage of the parameter exchange. Transmission of the complete parameter block shall be made within the period T2. + +After receiving and processing the rate adaption and parameter information, the answering TA determines whether the parameters exchanged in both directions are compatible, or whether it can adapt to the parameters of the originating TA. In either case, the exchange has been successful and the procedures described in I.5.3.3 are followed. If the parameters were not compatible and the answering TA decides to continue, it now takes on the role of the originating TA and recommences the parameter exchange with the transmission of a sequence of XSTART command octets. The parameter transfer procedures therefore continue as described above, but with the roles of originating and answering carried out by the opposing TAs. In the first exchange, the called TA should attempt to adapt to the parameters of the calling TA. When continuing the exchange, the new originating TA should attempt, as far as possible, to move the values of its next transmitted parameters towards the values of those previously received. If either TA determines that there is no point in continuing the parameter exchange, the procedures described in I.5.3.4 are followed. + +Parameter information continues to be exchanged in this manner, with alternate reversal of the roles of originating and answering TA until the outcome is successful, unsuccessful, or timer T1 expires. + +In order that the service offered is not degraded from that provided without IPE, a TA should connect using its default parameters upon expiry of timer T1. This does not prohibit either TA initiating disconnection at any time. + +#### **I.5.3.3 Successful exchange** + +A parameter exchange is considered successful when the last set of TA parameters transferred in both directions are compatible, or when the answering TA can adapt to the parameters of the originating TA. The answering TA shall notify the originating TA of a successful exchange before proceeding; this notification is provided by the transmission of a sequence of READY status octets. Both TAs shall set the re-entry flag to ONE. In any case, both TAs will proceed into the data transfer state (see I.5.5.1) unless re-synchronization to a new intermediate rate is required (see I.5.4). + +#### **I.5.3.4 Unsuccessful exchange** + +If at any time during the exchange either TA concludes that a successful exchange of parameters cannot be achieved or that the rate adaption protocols are not compatible, the TA should clear the connection. + +### **I.5.4 Re-synchronization to a new intermediate rate** + +If the outcome of the IPE is the selection of a user data rate requiring a new intermediate rate, re-synchronization will be necessary, and the TA enters the awaiting re-synchronization state (state 8). Whilst in this state the transmitter of the TA will send frames with S = OFF and X = OFF towards the peer TA in the new intermediate rate channel agreed. The default intermediate-rate channel positions correspond to those recommended for single stream operation in Recommendation I.460. + +At the same time, the receiver of the TA will commence searching for the frame synchronization pattern in the selected sub-rate channel. When the TA recognizes the frame synchronization pattern, it shall verify the status information received and enter the appropriate state, in a coordinated manner, as follows: + +- Data transfer (state 4), upon receipt of S = ON and X = ON (see I.5.6); +- No exchange (state 9), upon receipt of S = OFF and X = OFF. + +When the TA is in the no exchange state (state 9), it shall transmit frames with status information S = ON and X = ON and enter the data transfer state (state 4) upon receipt of S = ON and X = ON. + +### **I.5.5 Data transfer** + +#### **I.5.5.1 Transition into the data transfer state** + +Entry into the data transfer state should be carried out in a coordinated manner, as described by this Recommendation by both TAs after sufficient time has been given to enable the processing of the parameter information. + +#### **I.5.5.2 The data transfer state** + +The procedures on entering the data transfer state (state 4) and the values of S and X status information in the case of data rates less than 56 kbit/s are described in this Recommendation. + +### **I.5.6 Interworking with a TA not supporting IPE** + +A TA may choose to bypass IPE; for example, when it is used in a pre-configured arrangement, or when the parameter exchange can be effected by out-of-band signalling. In this situation a TA supporting IPE may receive S = ON and X = ON verified status information, causing the TA to directly enter the data transfer state. See I.8. + +A TA not supporting IPE can receive frames containing the status information S = OFF and X = ON from its peer. In this situation the non-IPE TA may either continue to transmit the status information S = OFF and X = OFF, or change to the data transfer state and transmit the status information S = ON and X = ON. Both cases will lead to entry into the data transfer state without IPE. See I.8. + +In the case of IPE at 64 kbit/s unrestricted or restricted, or in the case of a TA continuing to transmit the status information S = OFF and X = OFF, timer T2 ensures that service is not degraded from that provided without IPE. See I.8. + +### **I.5.7 Maintenance** + +A TA maintenance (MNT) call is made by indicating in PARAM-0 that the calling TA requires MNT support and by directly following the parameter transfer with a MAINTENANCE message group identifying the function required (see I.6.6). A TA which supports MNT shall indicate in PARAM-0 that MNT support is available. When an MNT function is requested by a calling TA, the called TA capable of supporting MNT shall acknowledge the request by initiating a subsequent parameter exchange including at the end the identical MAINTENANCE message group, before continuing directly to invoke the required MNT function. + +A successful MNT call with no timer required is terminated by either TA clearing the call. A successful MNT call with timer required returns the called TA to the inactive state upon expiry of timer T3, or to the Null state upon disconnection. + +A TA which does not support MNT shall indicate in PARAM-0 of the initial exchange that no MNT support is provided, and should clear the connection after the initial parameter exchange when an MNT call is received. + +### **I.5.8 Re-entering IPE from the data transfer state** + +Test loopbacks in this Recommendation refer to the I.600 series. The major application of this facility is to provide a mechanism to allow a remote loopback to be established for maintenance purposes without disconnecting the equipment in the established path. This mechanism may also be used generally to re-enter IPE. + +This mechanism is not applicable to unrestricted 64-kbit/s or restricted 64-kbit/s connection types, or when the rate during data transfer is 64 kbit/s, 56 kbit/s or 48 kbit/s. + +If re-entry to IPE is required and the re-entry flag has the value ONE, then the initiating TA enters the awaiting re-entry to IPE state (state 10) and transmits S = OFF, X = ON and D = IDLE. Re-entry to IPE in order to set a test loop 4 shall only be initiated by a calling TA. + +Receipt of S = OFF, X = ON and D = IDLE shall cause a TA in state 4 to re-enter the parameter exchange state (state 7) at the IPE user rate defined in I.5.1 which is of the same intermediate rate as that used for data transfer. + +Receipt of S = OFF, X = ON and D = IDLE shall cause the initiating TA to re-enter the parameter exchange state (state 7) at the IPE user rate defined in I.5.1 which is of the same intermediate rate as that used for data transfer. + +### **I.5.9 Error protection and handling** + +Error protection and handling are required to overcome the possibility of data corruption. In addition, error recovery procedures are required, for example in the case of loss of frame synchronization. + +To protect against data corruption, IPE commands shall be sent in a repeated sequence of at least 32 octets. Verification of the correct receipt of a command octet can then be carried out based on persistence checking techniques. Once a verified command octet has been received, it can be identified by the codings given in I.6. Any command octet not recognized shall be ignored. To protect against data corruption, LOW-HIGH data message pairs shall be sent in groups of three pairs. This enables majority voting techniques to be employed by the receiving TA. + +Upon the detection of irrecoverable data corruption during the parameter exchange, loss of frame synchronization or other situations requiring the exchange to be restarted, the TA shall complete the current message flow and initiate error recovery by transmitting a sequence of XSTART command octets and assuming the role of the originating TA. Upon receipt of a sequence of XSTART commands octets, a TA will recommence the parameter exchange as described in I.5.3.2. In this case of a collision of XSTART octets, the original originating and answering roles are assumed by the TAs. + +## **I.6 Coding** + +### **I.6.1 General** + +Information transfer during IPE is based on a group of messages. These messages are used to carry out a variety of tasks. The messages associated with rate adaption identification are described in I.6.2, whilst those associated with the actual parameter transfer are given in I.6.4. The messages associated with the control of the IPE are described in I.6.3, and I.6.5 covers those used to indicate status. Finally, I.6.6 covers the coding of the maintenance message. + +The messages are all based on octets structured as shown in Figure I.4. + +In the case of a user rate of 64 kbit/s, the octets are transmitted to line in bit sequence from bit 1 to bit 8. Network-provided octet alignment shall be used. + +In the case of a user rate of 56 kbit/s, the data is transmitted to line in bit sequence from bit 1 to bit 7 followed by an 8th bit set to ONE – according to this Recommendation, rate adaption (in total this is the equivalent data stream to 64 kbit/s). Network-provided octet alignment shall be used. + +In the case of user rates of 4.8, 9.6 or 19.2 kbit/s, the octets are packaged as single start-stop characters, using the following format: + +- 1 start bit; +- 8 data bits (in order of transmission shown in Figure I.3); +- No parity; and +- 1 stop bit. + + + +The diagram shows a horizontal line representing a transmission sequence. It starts with a box labeled 'Start', followed by a series of eight boxes labeled 'b1', 'b2', 'b3', 'b4', 'b5', 'b6', 'b7', and 'b8'. The sequence ends with a box labeled 'Stop'. + +Diagram of asynchronous character format showing a sequence of bits from b1 to b8 between a Start and Stop bit. + +**Figure I.3/V.110 – Asynchronous character format** + + + +The diagram shows a horizontal line with two arrows above it. The top arrow is labeled '4.8, 9.6, 19.2' and '64 kbit/s'. The bottom arrow is labeled '56 kbit/s'. Below the arrows is a table with 8 columns labeled '1' through '8'. The word 'Bit' is to the left of the table. + +| | | | | | | | | | +|-----|---|---|---|---|---|---|---|---| +| Bit | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | +|-----|---|---|---|---|---|---|---|---| + +Diagram showing bit rates and bit positions for asynchronous character format. + +bit 8: Set to ONE (and ignored on receipt) + +NOTE – Equivalent data stream to that for 64 kbit/s is created with 56 kbit/s when rate adaption according to this Recommendation is used. + +bit 7: Set to ZERO for IPE data + +Set to ONE for IPE signal + +*For IPE data* + +bit 6: Set to ONE + +(Set to ZERO: message reserved for private use and ignored if not implemented) + +bit 5: Set to ZERO when carrying data bits d0-d3 + +Set to ONE when carrying data bits d4-d7 + +bits 1-4: Carrying data bits (d0-d3) or (d4-d7) + +*For IPE signal* + +bit 6: Set to ONE + +(Set to ZERO: message reserved for private use and ignored if not implemented) + +bit 5: Set to ZERO for command messages + +Set to ONE for status messages + +bits 1-4: The signal code + +**Figure I.4/V.110 – Octet structure of the IPE coding** + +Figure I.5 provides a complete set of octet codings for use in IPE. + +| | | Message | ← 4.8, 9.6, 19.2 and 64 kbit/s → | | | | | | | | | +|-------------|---------|-------------|----------------------------------|----|----|----|----|----|----|----|--| +| | | | ← 56 kbit/s → | | | | | | | | | +| | | | b1 | b2 | b3 | b4 | b5 | b6 | b7 | b8 | | +| IPE signals | Command | PARAM-0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | | +| | | PARAM-1 | 0 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | | +| | | PARAM-2 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 1 | | +| | | PARAM-3 | 0 | 0 | 1 | 1 | 0 | 1 | 1 | 1 | | +| | | PARAM-4 | 0 | 1 | 0 | 0 | 0 | 1 | 1 | 1 | | +| | | RA VERSION | 0 | 1 | 0 | 1 | 0 | 1 | 1 | 1 | | +| | | XSTART | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | | +| | | MAINTENANCE | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | | +| | Status | | | | | | | | | | | +| | | | | | | | | | | | | +| | | READY | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | | +| | | IDLE | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | | +| | | FILL | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | | +| | | INACTIVE | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | | +| | | | | | | | | | | | | +| IPE data | | | | | | | | | | | | +| | | LOW | d0 | d1 | d2 | d3 | 0 | 1 | 0 | 1 | | +| | | HIGH | d4 | d5 | d6 | d7 | 1 | 1 | 0 | 1 | | + +NOTE – All spare codings are reserved (unless indicated for private use). Any octet received and verified which is not recognized shall be ignored. + +**Figure I.5/V.110 – IPE octet codings** + +### I.6.2 Rate adaption version identification + +Transfer of the rate adaption identifier is achieved by a message group based on three octets and transferred according to the procedures described in I.5.3.2 and I.5.9. The message consists of a sequence of RA VERSION command octets followed by a series of LOW-HIGH data octet pairs, the LOW data octet being transmitted in the pair before the HIGH data octet. Figure I.6 shows the message codings for rate adaption identification. + +| | b1 | b2 | b3 | b4 | b5 | b6 | b7 | b8 | +|-------------------------------------------|----|----|----|----|-----|----|----|----| +| RA VERSION | 0 | 1 | 0 | 1 | 0 | 1 | 1 | 1 | +| LOW | d0 | d1 | d2 | d3 | 0 | 1 | 0 | 1 | +| HIGH | d4 | d5 | d6 | d7 | 1 | 1 | 0 | 1 | +| Rate adaption version identifier encoding | | | | | | | | | +| HIGH | | | | | LOW | | | | +| d7 | d6 | d5 | d4 | | d3 | d2 | d1 | d0 | +| I3 | I2 | I1 | I0 | | x | x | x | x | +| I3 | I2 | I1 | I0 | | | | | | +| 0 | 0 | 0 | 1 | | | | | | + +I3-I0: Identifier V.110 + +x Reserved (if not used, set to ZERO and ignored on receipt) + +NOTE – All other codings are reserved. + +**Figure I.6/V.110 – Rate adaption version Identifier** + +### I.6.3 Control + +Before each transfer of TA parameter information can begin, a sequence of XSTART command octets is transmitted by the originating TA towards the answering TA as described in I.5.3.2 and I.5.9. Figure I.7 shows the coding for the XSTART command octet. + +| | b1 | b2 | b3 | b4 | b5 | b6 | b7 | b8 | +|--------|----|----|----|----|----|----|----|----| +| XSTART | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | + +**Figure I.7/V.110 – XSTART coding** + +### I.6.4 Parameters + +Transfer of the TA parameters is achieved in a series of five message groups each based on three octets and transferred according to the procedures described in I.5.3.2 and I.5.9. Each message group consists of a sequence of PARAM-X command octets (PARAM-0 to PARAM-4) followed by a series of LOW-HIGH data octet pairs, the LOW data octet being transmitted in the pair before the HIGH data octet. Figure I.8 shows the command octet codings and Figures I.9 to I.13 show the data octet codings for parameter transfer. + +| | b1 | b2 | b3 | b4 | b5 | b6 | b7 | b8 | +|---------|----|----|----|----|----|----|----|----| +| PARAM-X | 0 | x2 | x1 | x0 | 0 | 1 | 1 | 1 | +| | | x2 | x1 | x0 | | | | | +| PARAM-0 | | 0 | 0 | 0 | | | | | +| PARAM-1 | | 0 | 0 | 1 | | | | | +| PARAM-2 | | 0 | 1 | 0 | | | | | +| PARAM-3 | | 0 | 1 | 1 | | | | | +| PARAM-4 | | 1 | 0 | 0 | | | | | +| LOW | d0 | d1 | d2 | d3 | 0 | 1 | 0 | 1 | +| HIGH | d4 | d5 | d6 | d7 | 1 | 1 | 0 | 1 | + +**Figure I.8/V.110 – Format of parameter message group** + +| | | HIGH | | | | LOW | | | | +|----|--------------------------------------------------------------------------------------------------------------------------------------------|------|----|--------|--------|-----|----|----|--------| +| | | d7 | d6 | d5 | d4 | d3 | d2 | d1 | d0 | +| | | Sp | Sp | Ms | Mr | x | x | x | Ex | +| Sp | (Spare): Set to ZERO on transmission, ignored on reception | | | | | | | | | +| Ms | (Maintenance supported):
Maintenance not supported
Maintenance supported | | | 0
1 | | | | | | +| Mr | (Maintenance required):
Maintenance not required
Maintenance required | | | | 0
1 | | | | | +| Ex | (Extension):
If TA does not require octet alignment according to Rec. X.30
If TA does require octet alignment according to Rec. X.30 | | | | | | | | 0
1 | +| x | Reserved
(if not used, set to ZERO and ignored on receipt) | | | | | | | | | + +**Figure I.9/V.110 – Parameter 0 encoding** + +| | | HIGH | | | | LOW | | | | +|------------|---------------------------------------------------------------|------|----|----|----|-----|----|----|----| +| | | d7 | d6 | d5 | d4 | d3 | d2 | d1 | d0 | +| P2-P0 | Parity | P2 | P1 | P0 | Mo | x | x | x | Ch | +| | Odd | 0 | 0 | 0 | | | | | | +| | Even | 0 | 1 | 0 | | | | | | +| | None | 0 | 1 | 1 | | | | | | +| | Forced to ZERO | 1 | 0 | 0 | | | | | | +| | Forced to ONE | 1 | 0 | 1 | | | | | | +| Mo (Mode) | Asynchronous | | | | | 0 | | | | +| | Synchronous | | | | | 1 | | | | +| Ch (Check) | DTE Parity check made when required | | | | | | | | 0 | +| | No DTE parity check made when required | | | | | | | | 1 | +| x | Reserved
(if not used, set to ZERO and ignored on receipt) | | | | | | | | | + +**Figure I.10/V.110 – Parameter 1 encoding** + +| | | HIGH | | | | LOW | | | | +|------------------------------------------|---------------------------------------------------------------|------|----|----|----|-----|----|----|----| +| | | d7 | d6 | d5 | d4 | d3 | d2 | d1 | d0 | +| S1-S0 | Stop bits | S1 | S0 | C1 | C0 | x | x | x | Cx | +| | Not used | 0 | 0 | | | | | | | +| | 1 | 0 | 1 | | | | | | | +| | 1.5 | 1 | 0 | | | | | | | +| | 2 | 1 | 1 | | | | | | | +| | | | | | | | | | | +| C1-C0 | Character length | | | C1 | C0 | | | | | +| | Not used | | | 0 | 0 | | | | | +| | 5 | | | 0 | 1 | | | | | +| | 7 | | | 1 | 0 | | | | | +| | 8 | | | 1 | 1 | | | | | +| NOTE – Character length includes parity. | | | | | | | | | | +| Cx | (Character length extension): | | | | | | | | | +| | Standard C1-C0 codings used | | | | | | | | 0 | +| | 9-bits character length used | | | | | | | | 1 | +| x | Reserved
(if not used, set to ZERO and ignored on receipt) | | | | | | | | | + +**Figure I.11/V.110 – Parameter 2 coding** + +| | | HIGH | | | | LOW | | | | +|--------|---------------------------------------------------|------|----|----|----|-----|----|----|----| +| | | d7 | d6 | d5 | d4 | d3 | d2 | d1 | d0 | +| | | Sp | R6 | R5 | R4 | R3 | R2 | R1 | R0 | +| Sp(d7) | Set to ZERO on transmission, ignored on reception | | | | | | | | | +| R6-R0 | Rates | R6 | R5 | R4 | R3 | R2 | R1 | R0 | | +| | Reserved | 0 | 0 | 0 | 0 | 0 | 0 | 0 | | +| | 600 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | | +| | 1200 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | | +| | 2400 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | | +| | 3600 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | | +| | 4800 | 0 | 0 | 0 | 0 | 1 | 0 | 1 | | +| | 7200 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | | +| | Reserved | 0 | 0 | 0 | 0 | 1 | 1 | 1 | | +| | 9600 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | | +| | 14 400 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | | +| | Reserved | 0 | 0 | 0 | 1 | 0 | 1 | 0 | | +| | 19 200 | 0 | 0 | 0 | 1 | 0 | 1 | 1 | | +| | Reserved | 0 | 0 | 0 | 1 | 1 | 0 | 0 | | +| | Reserved | 0 | 0 | 0 | 1 | 1 | 0 | 1 | | +| | 48 000 | 0 | 0 | 0 | 1 | 1 | 1 | 0 | | +| | 56 000 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | | +| | Reserved | 0 | 0 | 1 | 0 | 0 | 0 | 0 | | +| | 50 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | | +| | 75 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | | +| | 110 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | | +| | 150 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | | +| | 200 | 0 | 0 | 1 | 0 | 1 | 0 | 1 | | +| | 300 | 0 | 0 | 1 | 0 | 1 | 1 | 0 | | +| | 12 000 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | | +| | Reserved | 0 | 0 | 1 | 1 | 0 | 0 | 0 | | +| | | | | | to | | | | | +| | Reserved | 1 | 1 | 1 | 1 | 1 | 1 | 0 | | +| | 64 000 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | | + +**Figure I.12/V.110 – Parameter 3 encoding** + +| | | HIGH | | | | LOW | | | | +|------|----------------------------------------------------------------------------------------------|------|--------|----------|----------|-----|----|----|--------| +| | | d7 | d6 | d5 | d4 | d3 | d2 | d1 | d0 | +| | | Sp | Fc | TNI
C | RNI
C | x | x | x | Mm | +| NIC | Network Independent Clock (see clause 5) | | | | | | | | | +| Sp | (Spare):
Set to ZERO on transmission, ignored on reception | | | | | | | | | +| Fc | (Flow control):
No end-to-end flow control supported
End-to-end flow control supported | | 0
1 | | | | | | | +| TNIC | If TA need not use NIC
If TA needs to use NIC | | | 0
1 | | | | | | +| RNIC | If TA cannot accept NIC
If TA can accept NIC | | | | 0
1 | | | | | +| Mm | (Modem):
TA not connected to a modem
TA connected to a modem | | | | | | | | 0
1 | +| x | Reserved
(if not used, set to ZERO and ignored on receipt) | | | | | | | | | + +**Figure I.13/V.110 – Parameter 4 encoding** + +### I.6.5 Status + +To inform the peer TA that a parameter exchange has been successful, a sequence of READY status octets shall be transmitted towards the peer according to the procedures in I.5. Figure I.14 shows the coding for the READY status octet. + +To inform the peer TA that it is in an idle condition prior to parameter exchange, a sequence of IDLE status octets are transmitted towards the peer according to the procedures in I.5. Figure I.15 shows the message coding for the IDLE status octet. + +The FILL status octet is used as a fill between parameter transfers, according to the procedures in I.5. Figure I.16 shows the coding for the FILL status octet. + +To inform the peer TA that the channel is currently inactive, a sequence of INACTIVE status octets are transmitted towards the peer according to the procedures in I.5. Figure I.17 shows the coding for the INACTIVE status octet. + +| | b1 | b2 | b3 | b4 | b5 | b6 | b7 | b8 | +|-------|----|----|----|----|----|----|----|----| +| READY | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | + +**Figure I.14/V.110 – READY octet coding** + +| | b1 | b2 | b3 | b4 | b5 | b6 | b7 | b8 | +|------|----|----|----|----|----|----|----|----| +| IDLE | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | + +**Figure I.15/V.110 – IDLE octet coding** + +| | b1 | b2 | b3 | b4 | b5 | b6 | b7 | b8 | +|------|----|----|----|----|----|----|----|----| +| FILL | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 1 | + +**Figure I.16/V.110 – FILL octet coding** + +| | b1 | b2 | b3 | b4 | b5 | b6 | b7 | b8 | +|----------|----|----|----|----|----|----|----|----| +| INACTIVE | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | + +**Figure I.17/V.110 – INACTIVE octet coding** + +### I.6.6 Maintenance + +This message group based on three octets is used to carry information in association with maintenance operations. The message group consists of a sequence of MAINTENANCE command octets followed by a series of LOW-HIGH data octet pairs, the LOW data octet being transmitted in the pair before the HIGH data octet. Figure I.18 shows the message codings. + +| | | | | | | | | | | +|----------------------|---------------------------------------------------|----|----|----|-----|----|----|----|----| +| | | b1 | b2 | b3 | b4 | b5 | b6 | b7 | b8 | +| MAINTENANCE | | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 1 | +| LOW | | d0 | d1 | d2 | d3 | 0 | 1 | 0 | 1 | +| HIGH | | d4 | d5 | d6 | d7 | 1 | 1 | 0 | 1 | +| Maintenance encoding | | | | | | | | | | +| HIGH | | | | | LOW | | | | | +| | | d7 | d6 | d5 | d4 | d3 | d2 | d1 | d0 | +| | | Sp | Rt | L1 | L0 | x | x | x | R1 | +| Sp(d7) | Set to ZERO on transmission, ignored on reception | | | | | | | | | +| Rt | (Request for timer T3 – see I.5.7): | | | | | | | | | +| | No timer required | | 0 | | | | | | | +| | Timer required | | 1 | | | | | | | +| L1-L0 | (Loop required): | | | | L1 | L0 | | | | +| | No loopback | | | | 0 | 0 | | | | +| | Test loop 4 | | | | 0 | 1 | | | | +| | (I.600-series Recommendations) | | | | | | | | | +| | Reserved | | | | 1 | 0 | | | | +| | Reserved | | | | 1 | 1 | | | | +| R1 | (d0 test loop 5): | | | | | | | | R1 | +| | (I.600-series Recommendations) | | | | | | | | 0 | +| | Test loop 5 not required | | | | | | | | 0 | +| | Test loop 5 required | | | | | | | | 1 | +| x | Reserved | | | | | | | | | +| | (if not used, set to ZERO and ignored on receipt) | | | | | | | | | + +NOTE 1 – Test loop 5 is applied as near to the interface at the R reference point as practicable, and is outside the scope of this Recommendation. + +NOTE 2 – Loop definitions 4 and 5 are defined in the I.600-series Recommendations. + +NOTE 3 – Definitions are for the direction calling TA- to -called TA. In the reverse direction, they represent confirmation of the maintenance function. + +**Figure I.18/V.110 – Coding of MAINTENANCE message group** + +## I.7 Timer values + +### I.7.1 Timer values for parameter exchange + +Timer T1 shall be at least 8 s but less than timer T1 in 7.1.2.2. + +Timer T2 shall be 3 s. + +### I.7.2 Timer values for maintenance + +Timer T3 shall be 60 s. + +## **I.8 State transition diagrams** + +### **I.8.1 General** + +In this subclause, state transition diagrams are provided to show the states of a terminal adaptor in the following situations: + +- terminal adaptor not supporting the exchange of parameter information (Figure I.19); +- terminal adaptor interworking with a terminal adaptor not supporting the exchange of parameter information (Figure I.20); +- terminal adaptor capable of supporting the exchange of parameter information (Figure I.21); +- terminal adaptor capable of supporting a maintenance test loop 4 (Figure I.22). + +Following is a summary of the basic states involved: + +| | | +|----------|-----------------------------------------------| +| State 0 | Null | +| State 1 | Inactive | +| State 2 | Awaiting synchronization – Data transfer | +| State 3 | Default exchange | +| State 4 | Data transfer | +| State 5 | IPE default exchange | +| State 6 | Awaiting synchronization – Parameter exchange | +| State 7 | Parameter exchange | +| State 8 | Awaiting re-synchronization | +| State 9 | No exchange | +| State 10 | Awaiting re-entry to IPE | +| State 11 | Maintenance loop 4 loopback | + + + +``` + +stateDiagram-v2 + state "0. Null" as Null { + Undefined + } + state "1. Inactive" as Inactive { + ONEs (inactive) + } + state "2. Awaiting sync transfer" as Awaiting { + S = OFF X = OFF + d = ONEs + } + state "3. Default exchange" as Default { + S = ON X = ON + d = ONEs + } + state "4. Data transfer" as Data { + S = ON X = ON + d = DATA + } + + Null --> Inactive : Connect + Inactive --> Awaiting : Initiate data transfer + Awaiting --> Awaiting : Frame sync timer expires + Awaiting --> Default : Rx S = ON, X = ON + Awaiting --> Data : Rx S = OFF, X = OFF + Default --> Data : Rx S = ON, X = ON + Data --> Awaiting : Rx S = ON, X = ON + +``` + +The diagram illustrates the state transitions for a TA not supporting IPE. It consists of four states represented by rounded rectangles with a horizontal line separating the state name from the internal variables. + +- 0. Null**: Internal variable is *Undefined*. A **Connect** event transitions to state 1. +- 1. Inactive**: Internal variable is *ONEs (inactive)*. An **Initiate data transfer** event transitions to state 2. +- 2. Awaiting sync transfer**: Internal variables are *S = OFF*, *X = OFF*, and *d = ONEs*. + - A **Frame sync timer expires** event loops back to this state. + - An **Rx S = ON, X = ON** event transitions to state 3. + - An **Rx S = OFF, X = OFF** event transitions to state 4. +- 3. Default exchange**: Internal variables are *S = ON*, *X = ON*, and *d = ONEs*. An **Rx S = ON, X = ON** event transitions to state 4. +- 4. Data transfer**: Internal variables are *S = ON*, *X = ON*, and *d = DATA*. An **Rx S = ON, X = ON** event loops back to state 2. + +State diagram for TA not supporting IPE. The diagram shows four states: 0. Null, 1. Inactive, 2. Awaiting sync transfer, and 4. Data transfer. Transitions are triggered by events like 'Connect', 'Initiate data transfer', 'Frame sync timer expires', and 'Rx S = ON/X = ON'. + +T1701890-92 + +NOTE – Release sequences not shown. + +**Figure I.19/V.110 – State diagram: TA not supporting IPE** + + + +``` + +stateDiagram-v2 + state "0. Null\nUndefined" as State0 + state "1. Inactive\nONEs (inactive)" as State1 + state "2. Awaiting\nsync transfer\nS = OFF, X = OFF\nd = ONEs" as State2 + state "3. Default\nexchange\nS = ON, X = ON\nd = ONEs" as State3 + state "4. Data transfer\nS = ON, X = ON\nd = DATA" as State4 + state "5. IPE default\nexchange\nS = OFF, X = ON\nd = IDLE" as State5 + state "6. Awaiting\nsync exchange\nS = OFF, X = OFF\nd = IDLE" as State6 + + State0 --> State1 : Connect + State1 --> State2 : Initiate data transfer + State1 --> State6 : Initiate parameter exchange\nSet re-enter flag = 0 + State2 --> State3 : Rx S = ON\nX = ON + State2 --> State0 : Frame sync\ntimer expires + State3 --> State4 : Rx S = ON\nX = ON + State4 --> State2 : Rx S = OFF\nX = ON\n(optional) + State4 --> State0 : Frame sync\ntimer expires + State6 --> State2 : Rx S = OFF\nX = OFF + State6 --> State5 : Rx S = OFF\nX = OFF + State6 --> State4 : Rx S = ON\nX = ON + State6 --> State0 : Frame sync\ntimer expires + State5 --> State4 : T2 or\nRx S = ON\nX = ON + State3 --> State2 : Rx S = OFF\nX = OFF + +``` + +NOTE – Release sequences not shown. + +State diagram showing transitions between states 0 to 6 for a TA not supporting IPE. Transitions are triggered by events like 'Connect', 'Initiate data transfer', 'Frame sync timer expires', and signal conditions for Rx S and X. + +**Figure I.20/V.110 – State diagram: Interworking with a TA not supporting IPE** + + + +``` + + graph TD + S0[0. Null] -- Undefined --> S1[1. Inactive] + S1 -- Connect --> S1 + S1 -- Initiate data transfer --> S2[2. Awaiting sync transfer] + S2 -- Frame sync timer expires --> S0 + S2 -- Rx S=ON, X=ON --> S3[3. Default exchange] + S2 -- Rx S=OFF, X=OFF --> S5[5. IPE default exchange] + S3 -- Rx S=OFF, X=ON optional --> S2 + S3 -- Rx S=ON, X=ON --> S4[4. Data transfer] + S1 -- Initiate parameter exchange, Set re-enter flag = 0 --> S6[6. Awaiting sync exchange] + S6 -- Frame sync timer expires --> S0 + S6 -- Rx S=OFF, X=OFF --> S5 + S6 -- Rx S=ON, X=ON --> S7[7. Parameter exchange] + S6 -- Rx S=OFF, X=ON --> S7 + S5 -- Rx S=OFF, X=ON --> S7 + S7 -- Xstart --> S7 + S7 -- T2 or Rx S=ON, X=ON --> S4 + S7 -- New intermediate rate --> S8[8. Await resync] + S8 -- Frame sync timer expires --> S0 + S8 -- Rx S=OFF, X=OFF --> S9[9. No exchange] + S9 -- Rx S=ON, X=ON, Set re-enter flag = 1 --> S4 + S4 -- 58K/64K or no change, Set re-enter flag = 1 --> S4 + S4 -- Rx S=ON, X=ON, Set re-enter flag = 1 --> S4 + S4 -- T1 --> S7 + S4 -- If re-entry flag = 1 and re-entry required --> S10[10. Await re-enter IPE] + S10 -- Rx S=OFF, X=ON, d=IDLE --> S7 + +``` + +Detailed description of states: +**0. Null**: Undefined state. +**1. Inactive**: ONEs (inactive). +**2. Awaiting sync transfer**: S = OFF, X = OFF, d = ONEs. +**3. Default exchange**: S = ON, X = ON, d = ONEs. +**4. Data transfer**: S = ON, X = ON, d = DATA. +**5. IPE default exchange**: S = OFF, X = ON, d = IDLE. +**6. Awaiting sync exchange**: S = OFF, X = OFF, d = IDLE. +**7. Parameter exchange**: S = OFF, X = ON (IPE message). +**8. Await resync**: S = OFF, X = OFF, d = ONEs. +**9. No exchange**: S = ON, X = ON, d = ONEs. +**10. Await re-enter IPE**: S = OFF, X = ON, d = IDLE. + +State diagram for TA supporting IPE showing transitions between states 0 to 10 based on signal conditions and timers. + +NOTE – Release sequences not shown. + +**Figure I.21/V.110 – State diagram: TA supporting IPE** + +**Recommendation V.110 (02/2000)** 49 + + + +``` + +stateDiagram-v2 + [*] --> 0 + 0: 0. Null\nUndefined + 1: 1. Inactive\nONEs (inactive) + 2: 2. Awaiting sync transfer\nS = OFF, X = OFF\nd = ONEs + 3: 3. Default exchange\nS = ON, X = ON\nd = ONEs + 4: 4. Data transfer\nS = ON, X = ON\nd = DATA + 5: 5. IPE default exchange\nS = OFF, X = ON\nd = IDLE + 6: 6. Awaiting sync exchange\nS = OFF, X = OFF\nd = IDLE + 7: 7. Parameter exchange\nS = OFF, X = ON\n(IPE message) + 8: 8. Await resync\nS = OFF, X = OFF\nd = ONEs + 9: 9. No exchange\nS = ON, X = ON\nd = ONEs + 10: 10. Await re-enter IPE\nS = OFF, X = ON\nd = IDLE + 11: 11. Maintenance loop 4\nUndefined + + 0 --> 1: Connect + 1 --> 0: Disconnect + 1 --> 2: Initiate data transfer + 2 --> 0: Frame sync timer expires + 2 --> 3: Rx S = ON, X = ON + 2 --> 4: Rx S = OFF, X = OFF + 3 --> 4: Rx S = ON, X = ON + 4 --> 2: Rx S = OFF, X = ON (optional) + 1 --> 6: Initiate parameter exchange\nSet re-enter flag = 0 + 6 --> 0: Frame sync timer expires + 6 --> 5: Rx S = OFF, X = OFF + 6 --> 7: Rx S = OFF, X = ON + 6 --> 11: Rx S = ON, X = ON + 5 --> 7: Rx S = OFF, X = ON + 7 --> 7: Xstart + 7 --> 4: 58K/64K or no change.\nSet re-enter flag = 1 + 7 --> 8: New intermediate rate + 8 --> 0: Frame sync timer expires + 8 --> 9: Rx S = OFF, X = OFF + 8 --> 4: Rx S = ON, X = ON\nSet re-enter flag = 1 + 9 --> 4: Rx S = ON, X = ON\nSet re-enter flag = 1 + 4 --> 10: If re-entry flag = 1 and re-entry required + 10 --> 7: Rx S = OFF, X = ON\nd = IDLE + 10 --> 4: Rx S = OFF, X = ON\nd = IDLE + 11 --> 1: T3 + 11 --> 7: Loop 4 request + 7 --> 11: T1 + 4 --> 7: T2 or Rx S = ON, X = ON + +``` + +State diagram for Maintenance loop 4 showing transitions between 12 states based on signal conditions and timers. + +T1701920-92 + +**Figure I.22/V.110 – State diagram: Maintenance loop 4** + +50 + +**Recommendation V.110 (02/2000)** + +# APPENDIX II + +## V.25 bis to Q.931 protocol mapping + +## II.1 General + +The D-channel signalling capabilities of the ISDN customer-access are as defined in Recommendation Q.931. The mapping of the V.25 *bis* interface signalling procedures to the Q.931 protocol at the S/T reference point are described below. + +The logical representation of this mapping function is shown in Figure II.1. + + + +Terminal adaptor (TA) + +Mapping + +V.25 *bis* DCE functions S-interface signalling functions + +Mapping + +Logical interface + +T1701370-91 + +Figure II.1/V.110 – Terminal adapter V.25 bis mapping. The diagram shows a box labeled 'Terminal adaptor (TA)' containing two columns: 'V.25 bis DCE functions' on the left and 'S-interface signalling functions' on the right. Two horizontal arrows labeled 'Mapping' connect the columns, one pointing right at the top and one pointing left at the bottom. To the left of the box is a vertical line with 'R' above it and '===|=== ' below it. To the right is a vertical line with 'S, T' above it and '===|===== ' below it. Below the box is the text 'Logical interface'. In the bottom right corner is the text 'T1701370-91'. + +**Figure II.1/V.110 – Terminal adapter V.25 *bis* mapping** + +The D-channel signalling capabilities provided to V.25 *bis* based terminals shall comprise the signalling messages as defined in Recommendation Q.931. + +The following description and figures depict examples of V.25 *bis* mapping to the ISDN call control procedures. It is recognized that other possibilities and user options exist. But this subclause is intended to provide general guidelines for a satisfactory means of V.25 *bis* support. Only the normal call establishment and clearing procedures are shown. The following subclauses are titled with the terms of signalling messages at the S-interface. + +*Recall of the circuit list involved in the V.25 bis call set-up* + +- Ready for sending (106). +- Data set ready (107). +- Data terminal ready (108/2). +- Transmit data (103). +- Receive data (104). +- Calling indicator (125). + +This appendix deals with call establishment and clearing. Any specific use of V.24 interchange circuits herein described only applies during these phases. The management of interchange circuits during the data transmission phase is not part of this appendix. + +The state of other interchange circuits is not part of this appendix. However, to ensure maximum compatibility with existing equipment, the other interchange circuits provided should retain their normal function as defined in Recommendation V.24 during the automatic call procedure. + +Particularly to ensure correct operation of the DTE, the condition of circuit 109 should follow the condition of circuit 106. + +The DTE may choose to hold circuit 105 ON during the automatic calling procedure, but the TA is not required to recognize this condition. + +## **II.2 Call origination** + +### **II.2.1 Call set-up** + +#### **II.2.1.1 From TA** + +In the DTE ready state (see Recommendation V.25 *bis*), the present circuit 108/2 ON and 103 = '1'. The TA presents 106 = OFF, 107 = OFF, 125 = OFF and 104 = '1' (state 2 of the V.25 *bis* state diagram). + +In response to detecting circuit 108/2 ON, the TA presents 106 ON which is equivalent to a Proceed to Select indication (X-Series Recommendations), and the DTE enters the DTE-DCE dialogue by presenting Call Request Command call request with identification (CRI) or call request with number (CRN). In response to 108/2 ON, the TA will have initiated the interface at the S/T reference point layer 1 activation as in Recommendation I.430. + +The layer 2 at the interface at the S/T reference point shall be established on request of layer 3 when the set-up message is to be sent, according to Recommendation Q.931. + +When the end of the valid command is received at the R-interface, the TA transmits a set-up message via the D-channel requesting the unrestricted 64-kbit/s bearer capability, for a transfer in circuit mode. + +The user may also specify the layer 1 terminal adaption in the low layer compatibility information element of the call SETUP message. (See Annex L/Q.931 entitled *Low layer information coding principles*.) + +The called party address information element shall be encoded *en bloc* with the complete address of the called party as received from the V.25 *bis* interface. + +#### **II.2.1.2 SETUP acknowledge/call proceeding (from exchange)** + +The network reaction on the SETUP message received from the TA can be either: + +- Sending of a CALL PROCEEDING +When the call proceeding message is received on the D-channel of the interface at the S/T reference point, the B-channel will be allocated and the TA connects to the B-channel. +- Sending a SETUP Acknowledge +When the SETUP Acknowledge message to the TA is received on the D-channel at the interface at the S/T reference point, the B-channel will be allocated to the TA. + +#### **II.2.1.3 CONNECT (from exchange)** + +When a CONNECT is received on the D-channel at the interface at the S/T reference point, the TA transmits any DCE response to the calling DTE and enters state 5 Answer Tone Detected by turning 106 OFF. + +The TA proceeds to the Connect to Line state as described in 7.1.2 completing the V.25 *bis* control phase with circuit 107 ON. + +### **II.2.2 Call received from remote DTE/TA** + +#### **II.2.2.1 Call SETUP (from exchange)** + +The TA should accept a SETUP message regardless of the V.25 *bis* interface state 1 or state 2. When a SETUP message is received on the D-channel at the S interface, the TA shall follow the procedures for determining compatibility checking (data signalling rate) found in Recommendation Q.931. If the TA determines that it can respond to the incoming call, it follows the procedures of Recommendation Q.931. + +The TA indicates an incoming call via the V.25 *bis* interface by setting 125 = ON, 104 = '1' and 107 = OFF; thereby entering state 8 Incoming Call. + +If the DTE does not present 108/2 = ON within a timer time T', the TA rejects the call with a CALL REJECT indicating no answer from DTE. + +#### **II.2.2.2 CONNECT (from TA)** + +When state 9 Incoming Call Recognized is presented by the DTE turning circuit 108/2 ON (note that this may be immediate if the DTE presents 108/2 permanent ON) to accept the incoming call, the TA transmits a CONNECT message via the D-channel of the interface at the S/T reference point. + +#### **II.2.2.3 CONNECT Acknowledge (from exchange)** + +When a CONNECT Acknowledge message is received on the D-channel at the interface at the S/T reference point, the TA, selected by this message, signals Line Seized (state 13) by presenting circuit 125 = OFF to the DTE after presenting positive responses if any. + +The TA proceeds to the Connect to Line state as described in 7.1.2 completing the V.25 *bis* call control phase with circuit 107 = ON. + +## **II.3 Call clearing (Figures II.2 and II.3)** + +### **II.3.1 DISCONNECT (from TA)** + +A clearing by the DTE (state 7) 103 = '1' 108/2 = OFF is transmitted by the TA via the B-channel to the remote DTE. + +The TA at the clearing DTE on recognizing state 7 at the V.25 *bis* interface, disconnects the circuits 103, 104 and 108/2 from the B-channel. The TA causes the status and data bits on the B-channel to correspond to circuit 108/2 OFF and 103 = '1' and awaits for Clearing Acknowledge from remote DTE (108/2 = OFF, 103 = '1') for a timer time of 10 s. The TA then transmits DCE Clear Confirmation by turning OFF 107 to the clearing DTE (no corresponding state of the V.25 *bis* interface). It also transmits a DISCONNECT message via the D-channel at the interface at the S/T reference point. + +After reception of the RELEASE message on the D-channel, the TA sends RELEASE COMPLETE to the exchange, and the DTE enters DTE Ready or DTE Not Ready states. + +### **II.3.2 DISCONNECT (from exchange)** + +In the case of the clearing by the network, the local exchange transmits the DISCONNECT message via the D-channel to the TA to be cleared. After reception of the DISCONNECT message in the TA, the TA transmits a RELEASE message on the D-channel to the exchange. + +If the V.25 *bis* interface is in the call establishment phase and has not yet reached state 5, 6 or 12, and if the DISCONNECT contains the reason for clearing, the TA moves to DTE-DCE dialogue state 3 and transmits the corresponding Call Failure Indication to the DTE prior to Call Clearing. + +Otherwise the TA transmits the DCE clear indication (107 = OFF, 103 = '1'), via the V.25 *bis* interface to the DTE, which sends back to the TA the DTE Clear Confirmation which is identical to Clearing by DTE 108/2 = OFF, 104 = '1' as described in 4.3.3/V.24, (no V.25 *bis* interface states). If the DTE does not present 108/2 = OFF within a timer "T", the TA sends DISCONNECT to the D-channel at the expiration of the timer. + + + +Sequence diagram for DTE call establishment and clearing. The diagram shows the interaction between DTE and TA. DTE sends 'DTE ready' to TA. TA sends 'Call request' to DTE. DTE sends 'DTE-DCE dialogue' to TA. TA sends 'Call establishment' to DTE. DTE sends 'Answer tone detected' to TA. TA sends 'Call connected' to DTE. DTE sends 'Call failure indication' to TA. TA sends 'Ready for data alineation' to DTE. DTE sends 'Data transfer' to TA. TA sends 'Clearing by DTE' to DTE. DTE sends 'DCE clear confirmation' to TA. TA sends 'DCE ready' to DTE. DTE sends 'DTE ready or DTE not ready' to TA. TA sends 'RELEASE COMPLETE' to DTE. The diagram also shows 'SETUP' from TA to (D), 'CALL PROCEEDING' from (D) to TA, 'CONNECT' from TA to (D), 'End-to-end synchronization' from (D) to TA, 'DTR = OFF, TD = 1' from TA to (D), 'Clear acknowledge' from (D) to TA, 'DISCONNECT' from TA to (D), and 'RELEASE' from (D) to TA. + +T1701380-91 + +DTR Data Terminal Ready +TD Transmitted Data + +**Figure II.2/V.110 – Recommendation V.25 *bis* – Example of DTE call establishment and call clearing** + + + +Sequence diagram for DCT call establishment and clearing. The diagram shows the interaction between TA and DTE. TA sends 'DTE ready/Not ready' to DTE. DTE sends 'Incoming call' to TA. TA sends 'Incoming call recognized' to DTE. DTE sends 'Incoming call accepted' to TA. TA sends 'Line seized' to DTE. DTE sends 'Ready for data' to TA. TA sends 'Data transfer' to DTE. DTE sends 'Clearing by remote DTE' to TA. TA sends 'Clearing by DTE' to DTE. DTE sends 'DCE ready' to TA. TA sends 'DTE ready/Not ready' to DTE. The diagram also shows 'SETUP' from (D) to TA, 'CONNECT' from TA to (D), 'CONNECT ACKNOWLEDGE' from (D) to TA, 'End-to-end synchronization' from (B) to TA, 'DTR = OFF, RD = 1' from TA to (B), 'DISCONNECT' from TA to (D), 'RELEASE' from (D) to TA, and 'RELEASE COMPLETE' from TA to (D). + +T1701390-91 + +RD Received Data + +**Figure II.3/V.110 – Recommendation V.25 *bis* – Example of DCT call establishment and call clearing** + +### II.3.3 DISCONNECT (In-band between TAs) + +When the DTE initiates the Clearing by DTE, this status is transmitted in slot within the B-channel and received as DCE clear indication equivalent to a PSTN disconnect in the DTE 107 = OFF. + +The TA recognizes the clear request received in-band via the B-channel at the interface at the S/T reference point, separates the 103 108/2 leads from the B-channel and transmits to the DTE the DCE Clear Indication, 104 = OFF, 107 = OFF. + +After the DTE to be cleared has received DTE Clear Confirmation, (108/2 = OFF, 104 = '1') from the clearing DTE, it transmits a DISCONNECT message via the D-channel, and clears the B-channel. + +After reception of a release message on the D-channel, the TA releases the call reference, sends a RELEASE COMPLETE message to the exchange, and the V.25 *bis* interface enters the state DTE Not Ready or DTE Ready depending on the state of 108/2. + +### II.3.4 RELEASE COMPLETE + +When the RELEASE COMPLETE is received via the D-channel at the interface at the S/T reference point of the TA of the cleared DTE, the V.25 *bis* interface enters DTE Ready or DTE Not Ready depending on the state of circuit 108/2. + +### II.3.5 Negative response to an incoming call + +RELEASE COMPLETE message, including the appropriate case code, is sent by a TA supporting a terminal which is compatible with information contained in the SETUP message, to indicate that the call cannot be accepted at this time for the following reason: busy condition of the called terminal (see Figure II.4). + + + +The diagram illustrates the sequence of events for a negative response to an incoming call. It features six vertical lifelines: DTE A, TA, ET a, ET b, TA, and DTE B. The process is divided into two main phases: 'Call set-up' and 'Call clearing'. + +- Call set-up:** DTE A sends a 'Call request' to the first TA. The first TA sends 'Set-up Call proceeding' to ET a. ET a sends a dashed 'SETUP' message to ET b. ET b sends a dashed 'Release complete (cause)' message to the second TA. +- Call clearing:** The second TA sends 'DISCONNECT (cause)' to ET a. ET a sends 'RELEASE RELEASE COMPLETE' to the first TA. The first TA sends a 'Call failure indication' to DTE A. + +Sequence diagram showing the negative response to an incoming call between DTE A, TA, ET a, ET b, and DTE B. + +T1701400-91 + +**Figure II.4/V.110 – Negative response to an incoming call** + +## II.4 Direct call + +### II.4.1 Direct call DTE call set-up and clearing + +The process is best described in Figure II.5. + + + +``` + +sequenceDiagram + participant DTE + participant TA + participant D as (D) + participant B as (B) + + DTE->>TA: Ready (108/1 = OFF) + DTE->>TA: Call request (108/1 = ON) + TA->>D: SETUP + D->>TA: CALL PROCEED + TA->>D: CONNECT + TA->>B: End-to-end synchronization + B->>DTE: Ready for data (107 = ON) + DTE->>TA: Data transfer + DTE->>TA: Clearing by DTE (108/1 = OFF) + TA->>B: DTR = OFF, TD = 1 + B->>D: DISCONNECT + D->>TA: RELEASE + TA->>B: RELEASE COMPLETE + B->>DTE: DCE ready (107 = OFF) + +``` + +The diagram illustrates the sequence of events for a direct DTE call. It involves three main entities: DTE (Data Terminal Equipment), TA (Terminal Adapter), and two external components labeled (D) and (B). The process begins with DTE sending a 'Ready (108/1 = OFF)' signal to TA, followed by a 'Call request (108/1 = ON)'. TA then sends 'SETUP' to (D), which responds with 'CALL PROCEED'. TA sends 'CONNECT' to (D). TA then sends 'End-to-end synchronization' to (B), which responds with 'Ready for data (107 = ON)' to DTE. DTE sends 'Data transfer' to TA. DTE then sends 'Clearing by DTE (108/1 = OFF)' to TA. TA sends 'DTR = OFF, TD = 1' to (B), which responds with 'DISCONNECT' to (D). (D) sends 'RELEASE' to TA, which then sends 'RELEASE COMPLETE' to (B). Finally, (B) sends 'DCE ready (107 = OFF)' to DTE. + +Sequence diagram for Direct DTE call establishment and clearing (Figure II.5/V.110). + +T1701410-91 + +**Figure II.5/V.110 – Recommendation V.25 bis – Direct DTE call establishment and call clearing** + +### II.4.2 Direct call DCE call set-up and clearing + +The process is best described in Figure II.6. + + + +``` + +sequenceDiagram + participant TA + participant DTE + participant D as (D) + participant B as (B) + + D->>TA: SETUP + TA->>DTE: Incoming call (107 = OFF, 125 = ON) + DTE->>TA: Incoming call accepted (108/1 = ON) + TA->>D: CONNECT + D->>TA: CONNECT ACKNOWLEDGE + TA->>B: End-to-end synchronization + B->>DTE: Ready for data (107 = ON, 125 = OFF) + DTE->>TA: Data transfer + TA->>B: Clearing by DCE + B->>D: DTR = OFF, RD = 1 + D->>TA: DISCONNECT + TA->>D: RELEASE + D->>TA: RELEASE COMPLETE + TA->>DTE: DTE clear confirmation + DTE->>TA: DTE ready (108/1 = OFF) + +``` + +The diagram illustrates the sequence of events for a direct DCE call. It involves three main entities: TA (Terminal Adapter), DTE (Data Terminal Equipment), and two external components labeled (D) and (B). The process begins with (D) sending 'SETUP' to TA. TA sends 'Incoming call (107 = OFF, 125 = ON)' to DTE, which responds with 'Incoming call accepted (108/1 = ON)'. TA sends 'CONNECT' to (D), which responds with 'CONNECT ACKNOWLEDGE'. TA sends 'End-to-end synchronization' to (B), which responds with 'Ready for data (107 = ON, 125 = OFF)' to DTE. DTE sends 'Data transfer' to TA. TA sends 'Clearing by DCE' to (B). (B) sends 'DTR = OFF, RD = 1' to (D). (D) sends 'DISCONNECT' to TA, which then sends 'RELEASE' to (D). (D) sends 'RELEASE COMPLETE' to TA. TA sends 'DTE clear confirmation' to DTE, which then sends 'DTE ready (108/1 = OFF)' to TA. + +Sequence diagram for Direct DCE call establishment and clearing (Figure II.6/V.110). + +T1701420-91 + +**Figure II.6/V.110 – Recommendation V.25 bis – Direct DCE call establishment and call clearing** + +## II.5 Mapping of Q.931 causes to V.25 *bis* call failure indications and responses + +In several cases, it will be necessary to map causes from Recommendations Q.931 to V.25 *bis* indications. The TA shall use Table II.1 to map the causes from Q.931 messages to V.25 *bis* Call Failure Indication or Call Progress Signals. The cause codes are provided by the ISDN to the TA. + +Handling of the Call Failure Indication (CFI) by the DTE may be a national matter. CFI (AB) is to be taken by the DTE as no use for the DTE to call again, some changes need to be done within the DTE before the call can be successful; CFI (ET) is to be taken by the DTE as a transient condition, the DTE may retry the call without changes; CFI (NT) indicates a serious failure of the call and the DTE should wait before retrying the call. CFI (INV) is reserved for local invalid commands and is not a mapping of an ISDN cause code. + +Not all Q.931 causes will be reported to the R interface. The general principles kept in Table II.1 are to distinguish between normal events (in a call) causes 0 to 31, resource unavailable causes 32 to 47, service not available causes 48 to 63, service not implemented causes 64 to 79, invalid message causes 80 to 95, protocol error causes 96 to 111, interworking causes 112 to 127. + +**Table II.1/V.110** + +| Item | Q.931 cause | ISDN code | V.25 bis call response | V.25 bis code | +|------|------------------------------------------------------------|-----------|-------------------------------|----------------------| +| 1 | Unassigned or unallocated number | 1 | Not obtainable | AB | +| 2 | No route to specified transit network | 2 | Not obtainable | NT | +| 3 | No route to destination | 3 | Not obtainable | AB | +| 4 | Channel unacceptable | 6 | Not obtainable | ET | +| 5 | Call awarded and being delivered in an established channel | 7 | | AB | +| 6 | Normal call clearing | 16 | Not applicable | None | +| 7 | User busy | 17 | Number busy | ET | +| 8 | No user responding | 18 | No connection | NT | +| 9 | No answer from user (user alerted) | 19 | No connection | NT | +| 10 | Call rejected | 21 | No connection | NT | +| 11 | Number changed | 22 | Changed number | AB | +| 12 | Non-selected user clearing | 26 | No connection | AB | +| 13 | Destination out of order | 27 | No connection | NT | +| 14 | Invalid number format (address incomplete) | 28 | Selection signals error | AB | +| 15 | Facility rejected | 29 | | AB | +| 16 | Respond to status ENQUIRY | 30 | | AB | +| 17 | Normal, unspecified | 31 | | AB | +| 18 | No circuit/channel available | 34 | No connection | ET | +| 19 | Network out of order | 38 | No connection | NT | +| 20 | Temporary failure | 41 | Out of order | NT | +| 21 | Switching equipment congestion | 42 | Network congestion | NT | +| 22 | Access information discarded | 43 | No connection | NT | + +**Table II.1/V.110 (continued)** + +| Item | Q.931 cause | ISDN code | V.25 bis call response | V.25 bis code | +|-------------|----------------------------------------------------------------------------------------|------------------|-------------------------------|----------------------| +| 23 | Requested circuit/channel not available | 44 | No connection | ET | +| 24 | Resource unavailable, unspecified | 47 | Network congestion | NT | +| 25 | Quality of service unavailable | 49 | | AB | +| 26 | Requested facility not subscribed | 50 | | AB | +| 27 | Bearer capability not authorized | 57 | Incompatible user class | AB | +| 28 | Bearer capability not presently available | 58 | Network congestion | ET | +| 29 | Service or option not available, unspecified | 63 | No connection | AB | +| 30 | Bearer capability not implemented | 65 | Invalid facility request | AB | +| 31 | Channel type not implemented | 66 | Invalid facility request | AB | +| 32 | Requested facility not implemented | 69 | Invalid facility request | AB | +| 33 | Only restricted digital information bearer capability is available | 70 | Invalid facility request | AB | +| 34 | Service or option not implemented, unspecified | 79 | Invalid facility request | AB | +| 35 | Invalid call reference value | 81 | | NT | +| 36 | Identified channel does not exist | 82 | No report | | +| 37 | A suspended call exists, but this call identity does not | 83 | No report | | +| 38 | Call identity in use | 84 | No report | | +| 39 | No call suspended | 85 | No report | | +| 40 | Call having the requested call identity has been cleared | 86 | No report | | +| 41 | Incompatible destination | 88 | | AB | +| 42 | Invalid transit network selection | 91 | No report | | +| 43 | Invalid message, unspecified | 95 | No report | | +| 44 | Mandatory information element is missing | 96 | No report | | +| 45 | Message type non-existent or not implemented | 97 | Protocol error, no report | | +| 46 | Message not compatible with call state or message type non-existent or not implemented | 98 | Protocol error, no report | | +| 47 | Information element/parameter non-existent or not implemented | 99 | Protocol error, no report | | +| 48 | Invalid information element contents | 100 | Protocol error, no report | | + +**Table II.1/V.110 (concluded)** + +| Item | Q.931 cause | ISDN code | V.25 bis call response | V.25 bis code | +|----------------------------------------------------------------------------------------------------------------------|----------------------------------------|-----------|---------------------------|---------------| +| 49 | Message not compatible with call state | 101 | Protocol error, no report | | +| 50 | Recuperation on timer expiry | 102 | No report | | +| 51 | Protocol error, unspecified | 111 | Protocol error, no report | | +| 52 | Interworking, unspecified | 127 | Not applicable | | +| NOTE – New call failure indication to report ISDN related situations at the V.25 bis interface is for further study. | | | | | + +## **II.6 Additional information for handling of exception situations** + +When the call is cleared prematurely or a call failure occurs, the rules of Recommendations Q.931 and of V.25 bis apply. The following procedures are derived for the mutual mapping between the R and the S reference points. + +### **II.6.1 Call collision** + +Incoming call from the exchange has priority on outgoing call to the exchange (for V.25 bis DTE which is normally attached to PSTN). + +#### **II.6.1.1 Call collision at the V.25 bis interface** + +The TA shall accept an incoming SETUP message. When at the V.25 bis interface a call collision is detected (TA presents incoming call indication, V.25 bis DTE presents call request), the TA will delay the outgoing call to monitor for incoming calls and will accept the incoming call and not process the outgoing call. + +#### **II.6.1.2 Call collision at the interface at the S/T reference point** + +The procedures defined in Recommendation Q.931 will apply. + +### **II.6.2 No channel available** + +If no channel including no B-channel at the interface at the S/T reference point is available for connection establishment, an outgoing SETUP message is answered from the exchange by a RELEASE COMPLETE message with the cause 34 = no channel available. This is mapped at the V.25 bis interface in the call failure indication ET (Engaged Tone). + +### **II.6.3 Premature call clearing** + +##### **II.6.3.1 No answer to outgoing SETUP** + +If an outgoing SETUP is not answered by the exchange, the DTE will after a time out which is fixed by the national Administrations' T2 timer, initiate the clearing by DTE by dropping 108/2 = OFF. The TA on its S reference point, will send a RELEASE COMPLETE message (cause code 31: normal, unspecified). The V.25 bis interface will go back to DTE Ready or DTE Not Ready. + +On the other hand, if a TA is provided with the optional timer T303 (see Recommendation Q.931) it may start the clearing procedure at the interface at the S/T reference point interface as above by transmitting RELEASE COMPLETE (cause code 102: recovery on timer expiry). At the V.25 bis interface, the TA sends the call failure indication No Tone. + + + + + +# ITU-T RECOMMENDATIONS SERIES + +| | | +|-----------------|--------------------------------------------------------------------------------------------------------------------------------| +| Series A | Organization of the work of the ITU-T | +| Series B | Means of expression: definitions, symbols, classification | +| Series C | General telecommunication statistics | +| Series D | General tariff principles | +| Series E | Overall network operation, telephone service, service operation and human factors | +| Series F | Non-telephone telecommunication services | +| Series G | Transmission systems and media, digital systems and networks | +| Series H | Audiovisual and multimedia systems | +| Series I | Integrated services digital network | +| Series J | Transmission of television, sound programme and other multimedia signals | +| Series K | Protection against interference | +| Series L | Construction, installation and protection of cables and other elements of outside plant | +| Series M | TMN and network maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits | +| Series N | Maintenance: international sound programme and television transmission circuits | +| Series O | Specifications of measuring equipment | +| Series P | Telephone transmission quality, telephone installations, local line networks | +| Series Q | Switching and signalling | +| Series R | Telegraph transmission | +| Series S | Telegraph services terminal equipment | +| Series T | Terminals for telematic services | +| Series U | Telegraph switching | +| Series V | Data communication over the telephone network | +| Series X | Data networks and open system communications | +| Series Y | Global information infrastructure and Internet protocol aspects | +| Series Z | Languages and general software aspects for telecommunication systems | + +\*18325\* + +Printed in 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TELECOMMUNICATION UNION + +# ITU-T + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +## V.12 + +(08/95) + +# **DATA COMMUNICATION OVER THE TELEPHONE NETWORK** --- + +# **ELECTRICAL CHARACTERISTICS FOR BALANCED DOUBLE-CURRENT INTERCHANGE CIRCUITS FOR INTERFACES WITH DATA SIGNALLING RATES UP TO 52 Mbit/s** + +## **ITU-T Recommendation V.12** + +(Previously "CCITT Recommendation") + +--- + +# FOREWORD + +The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. + +The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). + +ITU-T Recommendation V.12 was prepared by ITU-T Study Group 14 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 29th of August 1995. + +# --- NOTES + +1. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. +2. The status of annexes and appendices attached to the Series V Recommendations should be interpreted as follows: + - an *annexes* to a Recommendation forms an integral part of the Recommendation; + - an *appendix* to a Recommendation does not form part of the Recommendation and only provides some complementary explanation or information specific to that Recommendation. + +# CONTENTS + +| | Page | +|-----------------------------------------------------------|-------------| +| 1 Scope..... | 1 | +| 2 References..... | 2 | +| 3 Definitions..... | 2 | +| 4 Electrical characteristics..... | 2 | +| 4.1 Generator characteristics..... | 3 | +| 4.1.1 Open circuit measurement..... | 3 | +| 4.1.2 Test termination measurements..... | 3 | +| 4.1.3 Short-circuit measurement ..... | 4 | +| 4.1.4 Output signal waveform..... | 4 | +| 4.2 Load characteristics ..... | 5 | +| 4.2.1 Input current-voltage measurements ..... | 5 | +| 4.2.2 Input sensitivity measurements ..... | 6 | +| 4.2.3 Cable termination..... | 7 | +| 4.2.4 Fail-safe operation ..... | 7 | +| 4.3 Interconnecting cable electrical characteristics..... | 8 | +| 5 Circuit protection ..... | 8 | +| Appendix I – Guidelines for application ..... | 8 | +| I.1 Example on an interconnecting cable ..... | 8 | +| I.1.1 Length ..... | 8 | +| I.1.2 Cable physical characteristics ..... | 9 | +| I.1.3 Cable termination..... | 9 | +| I.2 Examples of generators and receivers ..... | 9 | +| I.2.1 ECL – Emitter coupled logic technology ..... | 9 | +| I.2.2 Fail-safe biasing of receivers ..... | 9 | + +# **SUMMARY** + +This Recommendation specifies the electrical characteristics of a balanced digital interchange circuit, that may be employed when specified for the interchange of serial binary signals between Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE) or in any point-to-point interconnection of serial binary signals between data equipments. The balanced digital interchange circuit will normally be utilized on data and timing, or control circuits where the data signalling rate is up to a maximum limit of 52 Mbit/s. + +# **ELECTRICAL CHARACTERISTICS FOR BALANCED DOUBLE-CURRENT INTERCHANGE CIRCUITS FOR INTERFACES WITH DATA SIGNALLING RATES UP TO 52 Mbit/s** + +*(Geneva, 1995)* + +# **1 Scope** + +This Recommendation specifies the electrical characteristics of a balanced digital interchange circuit, normally implemented in integrated circuit technology, that may be employed when specified for the interchange of serial binary signals between Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE) or in any point-to-point interconnection of serial binary signals between data equipments. + +The interchange circuit includes a generator connected by a balanced interconnecting cable to a load consisting of a receiver and a termination. The electrical characteristics of the circuit are specified in terms of required voltage, and current values obtained from direct measurements of the generator and receiver components at the interchange points. The logic function of the generator and the receiver is not defined by this Recommendation, as it is application dependent. Minimum electrical requirements for the interconnecting cable are furnished. + +The provisions of this Recommendation may be applied to the circuits employed at the interchange between equipments where information being conveyed is in the form of binary signals. + +Typical points of applicability for this Recommendation are depicted in Figure 1. + + + +T1401070-94/d01 + +DTE Data Terminal Equipment +DCE Data Circuit-Terminating Equipment + +Interface Generator +Interface Receiver +Balanced Interface Circuit + +Diagram showing the application of a balanced digital interchange circuit between DTE and DCE equipment. The DTE side contains an Interface Generator and an Interface Receiver. The DCE side contains an Interface Receiver and an Interface Generator. Two balanced interface circuits connect the generator of one side to the receiver of the other side. A legend below defines the symbols: DTE (Data Terminal Equipment), DCE (Data Circuit-Terminating Equipment), Interface Generator (arrow pointing right), Interface Receiver (arrow pointing left), and Balanced Interface Circuit (two parallel lines). The reference T1401070-94/d01 is noted at the bottom right of the diagram. + +FIGURE 1/V.12 +**Applications of balanced digital interchange circuit** + +The balanced digital interchange circuit will normally be utilized on data and timing, or control circuits where the data signalling rate is up to a maximum limit of 52 Mbit/s. + +# 2 References + +The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other referenced Standards are subject to revision, all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent editions of the Recommendations and other references listed below. A list of currently valid ITU-T Recommendations is regularly published. + +- ITU-T Recommendation V.11 (1993), *Electrical characteristics for balanced double-current interchange circuits operating at data signalling rates up to 10 Mbit/s.* + +# 3 Definitions + +For the purposes of this Recommendation, the following definition applies: + +**3.1 star (\*):** It represents the opposite input condition for a parameter. For example, the symbol Q represents the receiver output state for one input condition, while Q\* represents the output state for the opposite input state. + +# 4 Electrical characteristics + +The balanced digital interchange circuit is shown in Figure 2. The circuit consists of three parts: the generator (G), the balanced interconnecting cable, and the load. The load is composed of a receiver (R) and a cable termination/fail-safe network. The electrical characteristics of the generator and the receiver are specified in terms of direct electrical measurements while the interconnecting cable is described in terms of its electrical characteristics. + + + +T1401080-94/d02 + +Circuit diagram of a balanced digital interchange circuit. The diagram is divided into three sections: Generator, Balanced interface cable, and Load. The Generator section contains a triangle symbol 'G' with two output lines, A and B, each with a pull-down resistor 'Rgp = 332 Ω' connected to 'Vee'. The Balanced interface cable section shows two parallel lines connecting points A, B to A', B'. The Load section contains a triangle symbol 'R' with two input lines, A' and B', each with a pull-up resistor 'Rrp = 1.5 k Ω' connected to 'Vee'. A termination resistor 'Rt = 110 Ω' is connected between A' and B'. A common potential difference 'Vcpd' is indicated between the common points C and C'. + +| | | | | +|------|-------------------------------------------------------|--------|----------------------------| +| G | Generator | A, B | Generator Interface Points | +| Rgp | Generator Pull Down Resistor | A', B' | Receiver Interface Points | +| R | Receiver | C | Generator Circuit Common | +| Rt | Termination Resistor | C' | Receiver Circuit Common | +| Rrp | Receiver Bias Resistor (Optional, Receiver Dependent) | | | +| Vcpd | Common Potential Difference | | | +| Vee | Negative Voltage Power Supply | | | + +NOTE – All resistors $\pm 2\%$ . + +FIGURE 2/V.12 +Balanced digital interchange circuit + +## 4.1 Generator characteristics + +The generator electrical characteristics are specified in accordance with the measurements illustrated in Figures 3 to 6 and described in 4.1.1 through 4.1.4. The generator circuit meeting these requirements results in a low impedance balanced source that will produce a differential voltage applied to the interconnecting cable in the range of 590 mV to 1500 mV. + +The signalling sense of the voltages appearing across the interconnecting cable are defined as follows: + +- a) The A terminal of the generator shall be negative with respect to the B terminal for a binary 0 (SPACE or OFF) state. +- b) The A terminal of the generator shall be positive with respect to the B terminal for a binary 1 (MARK or ON) state. + +NOTE – The sense of data binary 0 (SPACE) and data binary 1 (MARK) are inverted from that specified in Recommendation V.11. The logic function of the generator and the receiver is beyond the scope of this Recommendation, and therefore is not defined. + +#### 4.1.1 Open circuit measurement (Figure 3) + +For either binary state, the magnitude of the differential voltage ( $V_{oc}$ or $V_{oc}^*$ ) measured between the two generator output terminals shall not exceed 1.5 V. + + + +Steady state logic input (1 or 0) + +332 $\Omega$ + +332 $\Omega$ + +Vee + +Vee + +A + +B + +$V_{oc}$ + +Open circuit measurement + +$|V_{oc}| < 1.5 \text{ V}, \quad |V_{oc}^*| < 1.5 \text{ V}$ + +T1401090-94/d03 + +Measured Parameter + +Circuit diagram for open circuit measurement of the generator. A logic generator 'G' has two outputs, A and B. Each output is connected to a 332 Ω resistor, which is then connected to a Vee terminal. A voltmeter measures the differential voltage Voc between terminals A and B. The diagram includes the text 'Open circuit measurement' and the inequalities |Voc| < 1.5 V and |Voc\*| < 1.5 V. A legend shows a circle with an arrow pointing to the text 'Measured Parameter'. The reference T1401090-94/d03 is also present. + +FIGURE 3/V.12 +Open circuit measurement + +#### 4.1.2 Test termination measurements (Figure 4) + +With a test load of the resistors shown in Figure 4, the magnitude of the differential output voltage ( $V_t$ ), shall be 590 mV or greater. For the opposite binary state, the polarity of $V_t$ shall be reversed ( $V_t^*$ ). The magnitude of the difference between $V_t$ and $V_t^*$ shall be less than 100 mV. The value of the generator offset voltage ( $V_{os}$ ), measured between the centre point of the test load and the generator circuit common shall be in the range of $-1.6 \text{ V}$ to 0 for either binary state. The magnitude of the difference of $V_{os}$ for one binary state and $V_{os}^*$ for the opposite binary state shall be 100 mV or less. + + + +Steady state logic input (0 or 1) + +332 $\Omega$ + +332 $\Omega$ + +Vee + +Vee + +A + +B + +54.9 $\Omega$ + +54.9 $\Omega$ + +Vt + +Vos + +T1401100-94/d04 + +*Test termination measurements* + $|V_t| > 590 \text{ mV}, |V_t^*| > 590 \text{ mV}$ + $||V_t| - |V_t^*|| < 100 \text{ mV}$ + $0 \text{ V} > V_{os} > -1.6 \text{ V}, 0 \text{ V} > V_{os}^* > -1.6 \text{ V}$ + $|V_{os} - V_{os}^*| < 100 \text{ mV}$ + +Measured Parameter + +Circuit diagram for Figure 4/V.12: Test termination measurements. A generator G with steady state logic input (0 or 1) is connected to two 332 Ω resistors leading to terminals A and B. Both A and B are connected to Vee through switches. A load consisting of two 54.9 Ω resistors in series is connected between A and B. A voltmeter Vt measures the voltage across this load. Another voltmeter Vos measures the common-mode voltage at the center tap of the load relative to ground. A legend shows a circle with an arrow labeled 'Measured Parameter'. + +FIGURE 4/V.12 +**Test termination measurements** + +#### 4.1.3 Short-circuit measurement (Figure 5) + +With the generator output terminals short-circuited, the magnitude of the current ( $I_{os}$ ) between the output terminals shall not exceed 50 mA for either state. + + + +Steady state logic input (0 or 1) + +332 $\Omega$ + +332 $\Omega$ + +Vee + +Vee + +A + +B + +Ios + +T1401110-94/d05 + +*Short-circuit measurement* + $|I_{os}| < 50 \text{ mA}, |I_{os}^*| < 50 \text{ mA}$ + +Measured Parameter + +Circuit diagram for Figure 5/V.12: Short-circuit measurement. Similar to Figure 4, but the load is replaced by a short circuit between terminals A and B. An ammeter Ios measures the current flowing through the short circuit. The legend for 'Measured Parameter' is repeated. + +FIGURE 5/V.12 +**Short-circuit measurement** + +#### 4.1.4 Output signal waveform (Figure 6) + +During transitions of the generator output between alternating binary states (one-zero-one-zero, etc.), the differential voltage measured across the 110 $\Omega$ test load connected between the generator output terminals shall be such that the voltage monotonically changes between 0.2 and 0.8 of $V_{ss}$ within 0.5 ns to 2.3 ns. After achieving a steady state value, the signal voltage shall not vary more than 10% of $V_{ss}$ from that value, until the next binary transition occurs, and at no time shall the instantaneous magnitude of $V_t$ or $V_t^*$ exceed 1500 mV nor be less than 590 mV. $V_{ss}$ is defined as the voltage difference between the two steady state values of the generator output. + + + +Figure 6/V.12: Output signal waveform. The diagram shows a differential signal waveform with a 0 V Differential baseline. The signal transitions between levels of 1.1 Vss, 0.9 Vss, 0.8 Vss, and 0.2 Vss. Key timing parameters are labeled: tb (nominal time duration of the unit interval), tr (rise time), and tf (fall time). + +$t_b$ The nominal time duration of the unit interval at the applicable data signalling rate + $0.5 \text{ ns} < t_r \text{ or } t_f < 2.3 \text{ ns}$ + $V_{ss}$ Difference in the steady state voltages + $V_{ss} = |V_t - V_t^*|$ + + + +Circuit diagram of the output signal waveform measurement setup. A driver (G) is connected to terminals A and B. Each terminal is connected to Vee through a 332 Ω resistor. A 110 Ω load is connected between A and B, where the differential voltage Vt is measured. The diagram is labeled T1401120-94/D06. + +FIGURE 6/V.12 +**Output signal waveform** + +### 4.2 Load characteristics + +The load is composed of a receiver (R) and a termination/fail-safe network as shown in Figure 2. The electrical characteristics of a receiver without termination or fail-safe provision are specified in terms of measurements illustrated in Figures 7 to 9 and described in 4.2.1 and 4.2.2. A circuit meeting these requirements results in a differential receiver having a high input impedance, and a small input threshold between $\pm 150 \text{ mV}$ . + +#### 4.2.1 Input current-voltage measurements (Figure 7) + +With the voltage on one leg, $V_{ia}$ (or $V_{ib}$ ), ranging from $-0.5 \text{ V}$ to $-2.0 \text{ V}$ , while the voltage on the other leg, $V_{ib}$ (or $V_{ia}$ ), is held at $-1.32 \text{ V}$ , the resultant input current $I_{ia}$ (or $I_{ib}$ ) shall be no greater than $350 \mu\text{A}$ . These measurements apply with the receiver's power supplies in both power-on and power-off conditions (as defined by the integrated circuit manufacturer). Note that these measurements are made with any termination resistor or fail-safe provision disconnected. + + + +``` + +graph LR + S1(( )) -- Via --> A'[A'] + S2(( )) -- Vib --> B'[B'] + A' --> R[R] + B' --> R + C'[C'] --> R + R --- G[Ground] + Iia(( )) -.-> A' + Iib(( )) -.-> B' + +``` + +T1401130-94/d07 + +Circuit diagram for receiver input current-voltage measurements. A receiver block 'R' has inputs A', B', and C'. A common input line is connected to A' and B'. Two voltage sources, Via and Vib, are connected in series to this common line. Currents Iia and Iib are indicated flowing into the inputs. The receiver is grounded at C'. + +FIGURE 7/V.12 +**Receiver input current-voltage measurements** + +#### 4.2.2 Input sensitivity measurements (Figure 8) + +Over an entire input voltage range of $-0.5\text{ V}$ to $-2.0\text{ V}$ (referenced to receiver circuit common), the receiver shall not require a differential input voltage of more than $150\text{ mV}$ to correctly assume the intended binary state. Reversing the polarity of $V_i$ shall cause the receiver to assume the opposite binary state. The receiver is required to maintain correct operation for differential input voltages ranging between $150\text{ mV}$ and $1.5\text{ V}$ in magnitude. Note that these measurements are made with any termination resistor or fail-safe provision disconnected. + + + +Vcm $-0.575\text{ V to } -1.925\text{ V}$ + +Vi (V) measured from B' to A' + +T1401140-94/d08 + +Figure 8/V.12: Input sensitivity measurements. The left part shows a circuit diagram where a receiver 'R' has inputs A', B', and C'. A common mode voltage Vcm is applied to all inputs. A differential input voltage Vi is applied between A' and B'. The right part is a graph of Vi (V) measured from B' to A' versus time. The graph shows a trapezoidal pulse with a peak-to-peak value of 1.5 V. The transition region is marked between +150 mV and -150 mV. The maximum operational range is indicated as the total voltage swing from +1.5 V to -1.5 V. + +FIGURE 8/V.12 +**Input sensitivity measurements** + +Figure 9 illustrates the minimum and maximum operating voltages of the receiver. Note that the logic function of the receiver is not defined by this Recommendation. + + + +T1401150-94/d09 + +Circuit diagram of a receiver input stage. A balanced differential input is shown with terminals A', B', and C'. A voltage source Vvia is connected between A' and B'. A voltage source Vib is connected between B' and C'. The differential voltage Vid is measured between A' and B'. The receiver is represented by a triangle labeled 'R' with its non-inverting input connected to A' and its inverting input connected to B'. The output of the receiver is connected to C'. A ground symbol is shown at the bottom right. A legend below the diagram shows a circle with an arrow pointing to it labeled 'Measured Parameter' and a circle with an arrow pointing away from it labeled 'Applied Voltage'. + +NOTE $V_{cm} = (V_{ia} + V_{ib})/2$ , $V_{id} = V_{ia} - V_{ib}$ . + +| Applied voltages | | Resulting input voltage | Resulting common mode voltage | +|------------------|---------|-------------------------|-------------------------------| +| Via | Vib | Vid | Vcm | +| -0.50 V | -0.65 V | +0.150 V | -0.575 V | +| -0.65 V | -0.50 V | -0.150 V | -0.575 V | +| -0.50 V | -2.00 V | +1.50 V | -1.25 V | +| -2.00 V | -0.50 V | -1.50 V | -1.25 V | +| -1.85 V | -2.00 V | +0.150 V | -1.925 V | +| -2.00 V | -1.85 V | -0.150 V | -1.925 V | + +FIGURE 9/V.12 + +##### Receiver input sensitivity table + +#### 4.2.3 Cable termination + +For all applications, the use of a cable termination is required. The recommended value is $110 \Omega \pm 2\%$ . The termination resistor is connected across the cable at the load end of the cable, as close to the receiver input poles as possible. + +#### 4.2.4 Fail-safe operation + +Other Recommendations and specifications using these electrical characteristics of the balanced digital interchange circuit may require that specific interchange circuits be made fail-safe to certain fault conditions. Such fault conditions may include one or more of the following: + +- 1) open-circuited interconnecting cable; +- 2) generator in power-off condition. + +When detection of one or more of the above fault conditions is required by specific applications, additional provisions are required in the load, and the following items must be determined and specified. + +- 1) Which interchange circuits require fault detection? +- 2) What faults must be detected? +- 3) What action must be taken when a fault is detected? + +The method of detection of fault conditions is application-dependent and is therefore not further specified. (See 1.2.2.) + +## 4.3 Interconnecting cable electrical characteristics + +The cable shall consist of twisted pair conductors and have an overall shield. The two wires of each pair shall be connected to the same signal, one to the A/A' and the other to the B/B' signal poles. + +| | | +|-------------------------------------------------------|----------------------------| +| Maximum single conductor DC Resistance (DCR) at 20 °C | 3.5 $\Omega$ | +| Differential Impedance at 50 MHz | 110 $\Omega \pm 11 \Omega$ | +| Maximum Signal Attenuation at 50 MHz | 4.5 dB | +| Mutual Capacitance within pair at 1 kHz | 47.6 $\pm$ 6.5 pF/m | +| Propagation Delay maximum: | 79 ns | +| Skew (pair-to-pair) | 2.0 ns | + +See Appendix I.1.2 for further guidance on an example of an interconnecting cable. + +## 5 Circuit protection + +Balanced digital interchange generator and receiver devices, under either the power-on or power-off condition, complying to this Recommendation shall not be damaged under the following conditions: + +- a) generator open circuit; +- b) short-circuit across the balanced interconnecting cable; +- c) short-circuit to circuit common. + +# Appendix I + +## Guidelines for application + +## I.1 Example on an interconnecting cable + +The following subclause provides further information to 4.3 and provides additional guidance concerning operational constraints imposed by the cable parameters of length and termination. + +### I.1.1 Length + +The nominal length of cable separating the generator and the load is 15 metres. + +#### I.1.2 Cable physical characteristics + +The following physical characteristics apply to the cable: + +| | | +|--------------------------|---------------------------------------------------------------------------------------------------------------------------------------------| +| Conductor: | 0.08 mm 2 , 7 strands of 0.13 mm, tinned annealed copper, nominal diameter 0.38 mm. | +| Insulation: | Polyethylene or polypropylene; 0.24 mm nominal wall thickness; 0.86 mm $\pm$ 0.025 mm outside diameter. | +| Foil Shield: | 0.051 mm nominal aluminium/polyester laminated tape spiral wrapped around the cable core. | +| Braid Shield: | Braided 0.13 mm, tinned plated copper in accordance with 80% minimum coverage, in electrical contact with the aluminium of the foil shield. | +| Outside Diameter: | $\leq$ 10.6 mm. | + +#### I.1.3 Cable termination + +The characteristic impedance of twisted pair cable is a function of frequency, wire size and type as well as the kind of insulating materials employed. For example, the characteristic impedance of average 0.08 mm2, copper conductor, plastic insulated twisted pair cable, to a 50 MHz sine wave will be approximately 110 $\Omega$ . + +## I.2 Examples of generators and receivers + +#### I.2.1 ECL – Emitter coupled logic technology + +Emitter Coupled Logic (ECL) families such as 10K, 10H, and 100K have been developed that meet the requirements of this Recommendation by a number of integrated circuit manufacturers. The 100K family is compensated for both Power Supply Voltage and Operating Temperature variations; offering constant thresholds and output levels over both ranges. Some other families are only Power Supply Voltage compensated. The 100K family also accepts a wide range of power supply voltages (Vee) from –4.2 V to –5.7 V. + +#### I.2.2 Fail-safe biasing of receivers (Figure I.1) + +In the event that the interchange cable is not present, the receiver must default to a known state. The method of fail-safe biasing is application and component specific, therefore is beyond the scope of this Recommendation. + +External resistors can be used to bias the receiver's input into a known state ( $\geq$ 150 mV differential) for the case of the disconnected cable. For example, a 1.5 k $\Omega$ pull-up and pull-down resistor will bias the receiver to 177 mV, defaulting the receiver to an OFF state. + + + +The diagram illustrates a fail-safe biasing circuit for a differential receiver 'R'. The receiver has two inputs, A' and B'. Input A' is connected to a 1.5 k $\Omega$ resistor that pulls the signal up to the negative supply voltage Vee. A 110 $\Omega$ termination resistor is connected between inputs A' and B'. Input B' is connected to a 1.5 k $\Omega$ resistor that pulls the signal down to ground. The diagram is labeled T1401160-94/d10. + +Circuit diagram for receiver fail-safe biasing. It shows a differential receiver 'R' with two inputs, A' and B'. Input A' is connected to a 1.5 kΩ resistor pulling up to Vee. A 110 Ω resistor is connected between inputs A' and B'. Input B' is connected to a 1.5 kΩ resistor pulling down to ground. The diagram is labeled T1401160-94/d10. + +FIGURE I.1/V.12 + +**Receiver fail-safe biasing** + +It should be noted that it is not necessary to use external resistors on all families of receivers. Some receiver integrated circuits have this feature internal to the integrated circuit. \ No newline at end of file diff --git a/marked/V/T-REC-V.13-199303-I_PDF-E/raw.md b/marked/V/T-REC-V.13-199303-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..0fbd16a860c7edea924ee5d016558768ac7f0a47 --- /dev/null +++ b/marked/V/T-REC-V.13-199303-I_PDF-E/raw.md @@ -0,0 +1,90 @@ + + + + +ITU logo: a globe with the letters ITU inside, crossed by a lightning bolt. + +INTERNATIONAL TELECOMMUNICATION UNION + +# ITU-T + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +## V.13 + +(03/93) + +### DATA COMMUNICATION OVER THE TELEPHONE NETWORK + +--- + +### SIMULATED CARRIER CONTROL + +### ITU-T Recommendation V.13 + +(Previously "CCITT Recommendation") + +--- + +# FOREWORD + +The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecommunication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. + +ITU-T Recommendation V.13 was revised by the ITU-T Study Group XVII (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). + +## --- NOTES + +1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. + +In order not to delay publication of this Recommendation, no change has been made in the text to references containing the acronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. + +2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +# SIMULATED CARRIER CONTROL + +(Melbourne, 1988; revised Helsinki, 1993) + +The CCITT + +*considering* + +- (a) that there is a wide variety of duplex data systems available; +- (b) that some data terminal equipment (DTE) operate 2-way alternate over these systems. + +*recommends* + +that the following procedure be employed for simulated circuit 105 to circuit 109 operation, when specifically called for in a CCITT Recommendation. + +## 1 Scope + +This Recommendation applies wherever a requirement for control of a remote circuit 109 by a local circuit 105 exists, and where switching OFF and ON of a modem carrier is impossible or impractical. Examples of such environments are: + +- sub-channels of modems containing multiplex facilities; +- modems with long equalizer/echo canceller training sequences; +- high efficiency multiplexers containing no control channels; +- PCM channels used for 64 bit/s data transmission. + +## 2 Location of the simulation function + +Within this Recommendation the function is described as though it were located between the DTE and the remaining part of the data circuit-terminating equipment (DCE). Location with respect to the loop device as defined in Recommendation V.54 is for further study. + +## 3 Operation + +When circuit 105 is OFF the DCE will transmit a pattern of bits (idle pattern) produced by scrambling a binary 1 with the polynomial $1 + x^{-3} + x^{-7}$ , in lieu of data bits for that port. No particular starting state is specified for the scrambler. When circuit 105 turns ON, the DCE will immediately transmit a pattern of 8 bits (ON pattern) produced by scrambling a binary 0 with the polynomial $1 + x^{-3} + x^{-7}$ , after which data bits are sent (Note 1). Circuit 106 may be turned ON within 8 bit intervals after circuit 105 turns ON, and the first bit appearing on circuit 103 after circuit 106 turns ON should be sent as the first data bit (see Note 2). When circuit 106 is turned ON before transmission of the ON pattern has been completed, data bits appearing on circuit 103 are stored in a data buffer for subsequent transmission. + +At the remote DCE circuit 109 is turned OFF whenever a sufficient number of successive bits in the above idle pattern is detected (see Note 3). Circuit 109 is turned ON after detecting a pattern of 8 bits produced by scrambling a binary 0 with the polynomial $1 + x^{-3} + x^{-7}$ (Note 4). Circuit 104 (received data) is held at binary 1 when circuit 109 is OFF (see also Notes 5, 6, 7). + +## NOTES + +- 1 The starting state of the scrambler used for scrambling a binary 0 with the polynomial $1 + x^{-3} + x^{-7}$ should be the same as the ending scrambler state after scrambling binary 1. +- 2 Additional circuit 106 turn ON delays may be provided as manufacturer's options. +- 3 The number of successive bits of the idle pattern required to be detected to turn circuit 109 OFF is recommended to be 48-64. Before circuit 109 turns OFF, the idle pattern may appear on circuit 104. +- 4 It is recommended that circuit 109 be turned ON only if the ON pattern is preceded by a sufficient number of consecutive scrambled ones. The protection against failure to recognize the ON pattern when transmission errors occur is subject to further study. The length of the ON pattern required to be detected to turn circuit 109 ON is provisionally fixed to 8. +- 5 Following an ON to OFF transition of circuit 105, circuit 105 should be ignored for at least 128 bit intervals so that at least 128 bits produced by scrambling a binary 1 are sent to the remote modem. +- 6 When circuit 105 is OFF, precaution should be taken that the output of the scrambler is not continuous 1, but rather is a 127 bit pseudo-random sequence. +- 7 Circuit 109 may be erroneously turned ON at the time of receiving the idle pattern, or circuit 109 may remain OFF at the time of receiving the ON pattern, when transmission errors occur. It may also turn OFF due to simulation by user data. +- 8 In order to prevent circuit 109 from incorrectly staying in the OFF condition, due to a failure to detect the ON pattern, it is recommended that circuit 109 should be placed in the ON condition, following a reasonable period of time during which the OFF pattern has not been detected. \ No newline at end of file diff --git a/marked/V/T-REC-V.130-199508-I_PDF-E/raw.md b/marked/V/T-REC-V.130-199508-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..09eb7cde323087cb21ed297794b988d34bfcf7ed --- /dev/null +++ b/marked/V/T-REC-V.130-199508-I_PDF-E/raw.md @@ -0,0 +1,714 @@ + + + + +ITU logo: a globe with the letters ITU and a lightning bolt symbol. + +INTERNATIONAL TELECOMMUNICATION UNION + +# ITU-T + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +## V.130 + +(08/95) + +**DATA COMMUNICATION OVER +THE TELEPHONE NETWORK** + +--- + +**ISDN TERMINAL ADAPTOR FRAMEWORK** + +**ITU-T Recommendation V.130** + +(Previously "CCITT Recommendation") + +--- + +# FOREWORD + +The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. + +The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). + +ITU-T Recommendation V.130 was prepared by ITU-T Study Group 14 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 29th of August 1995. + +--- + +# NOTES + +1. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. +2. The status of annexes and appendices attached to the Series V Recommendations should be interpreted as follows: + - an *annex* to a Recommendation forms an integral part of the Recommendation; + - an *appendix* to a Recommendation does not form part of the Recommendation and only provides some complementary explanation or information specific to that Recommendation. + +# CONTENTS + +| | | Page | +|----|----------------------------------------------------------------------|-------------| +| 1 | Scope and introduction..... | 1 | +| | 1.1 Scope ..... | 1 | +| | 1.2 Introduction ..... | 1 | +| 2 | References ..... | 1 | +| 3 | Definitions..... | 3 | +| 4 | Abbreviations ..... | 3 | +| 5 | Reference models ..... | 3 | +| | 5.1 Functional reference model ..... | 4 | +| | 5.2 Protocol reference model ..... | 6 | +| | 5.3 Interworking model ..... | 8 | +| | 5.4 Call mapping model..... | 9 | +| 6 | Connection establishment (Call control)..... | 9 | +| | 6.1 Auto-calling procedures..... | 9 | +| | 6.2 Multi-Use bearer service applications ..... | 10 | +| 7 | Rate adaptation protocol and parameter negotiation ..... | 11 | +| | 7.1 Out-of-band (Q.931) procedures ..... | 12 | +| | 7.2 In-band negotiation procedures ..... | 12 | +| 8 | TE2 – TA interface considerations..... | 13 | +| | 8.1 Physical interfaces ..... | 13 | +| | 8.2 Flow control and buffering ..... | 13 | +| | 8.3 Embedded interfaces..... | 13 | +| 9 | Multi-protocol terminal adaptor ..... | 14 | +| 10 | Adaptation to 3.1 kHz audio bearer (GSTN interworking)..... | 15 | +| | 10.1 Introduction ..... | 15 | +| | 10.2 Terminal adaptor with codec ..... | 15 | +| | 10.3 Combined modem and terminal adaptor..... | 16 | +| 11 | Management..... | 17 | +| | Appendix I – Protocol model for a V.110 TA (asynchronous mode) ..... | 17 | + +# **SUMMARY** + +This Recommendation provides information on the functions of a terminal adaptor from both the conceptual and practical points of view. The expression “Terminal Adaptor” is commonly used to refer to a stand-alone item of equipment (or alternatively a printed circuit card plugged into a terminal) that allows a non-ISDN terminal to be connected to an ISDN user-network interface. Formally though, Terminal Adaptor (TA) is the name of one of the (conceptual) Functional Groups defined in Recommendation I.411. The TA Functional Group contains functions that allow a TE2 (non-ISDN) terminal to use the services provided by an ISDN. The popular understanding of the term TA is thus well aligned with the theoretical definition. This Recommendation coordinates information from other Recommendations, expands on topics only briefly discussed elsewhere, describes the relationship between Terminal Adaptors and Modems, and provides tutorial material, and guidance on future enhancements and applications. + +# ISDN TERMINAL ADAPTOR FRAMEWORK + +(Geneva, 1995) + +# 1 Scope and introduction + +## 1.1 Scope + +The purpose of this ISDN Terminal Adaptor Framework Recommendation is to: + +- a) coordinate information from other Recommendations; +- b) expand on topics only briefly discussed elsewhere; +- c) describe the relationship between Terminal Adaptors and Modems; +- d) provide tutorial material; +- e) provide guidance on future enhancements and applications. + +## 1.2 Introduction + +Formally, the expression “Terminal Adaptor” (TA) refers to one of the (conceptual) Functional Groups defined in Recommendation I.411. The TA is described in 3.4.4/I.411 and contains functions that allow a TE2 (non-ISDN) terminal to use the services provided by an ISDN. + +However, the expression “Terminal Adaptor” is also used to refer to a stand-alone item of equipment (or alternatively a printed circuit card plugged into a terminal) that allows a non-ISDN terminal to be connected to an ISDN user-network interface. + +Also, there already exist a number of Recommendations which describe terminal adaptors and terminal adaptation protocols that allow terminals conforming to V- or X-Series Recommendations to be connected to the ISDN. Certain material in these Recommendations is of more general application and is referred to in this Recommendation. + +This Recommendation examines in detail the functions of a terminal adaptor from both the conceptual and practical points of view. + +Clause 10 describes a particular type of TA which is a combination of TA and modem functions. It allows a V-Series DTE to be connected to the ISDN and use the 3.1 kHz audio bearer service to communicate with another V-Series DTE attached via a modem to the GSTN. This means that no network-provided interworking function (modem pool) is required, only the digital-to-analogue conversion and signalling facilities that are already provided for telephony. + +# 2 References + +The following Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. + +- CCITT Recommendation G.711 (1988), *Pulse code modulation (PCM) of voice frequencies*. +- ITU-T Recommendation H.244 (1995), *Synchronized aggregation of ISDN B-channels*. +- ITU-T Recommendation I.231.9 (1993), *Circuit mode 64 kbit/s and 8 kHz structured multi-use bearer service category*. +- ITU-T Recommendation I.320 (1993), *ISDN protocol reference model*. +- ITU-T Recommendation I.333 (1993), *Terminal selection in ISDN*. + +- ITU-T Recommendation I.411 (1993), *ISDN user-network interfaces – Reference configurations.* +- ITU-T Recommendation I.430 (1993), *Basic user-network interface – Layer 1 specification.* +- ITU-T Recommendation I.431 (1993), *Primary rate user-network interface – Layer 1 specification.* +- ITU-T Recommendation I.501 (1993), *Service interworking.* +- ITU-T Recommendation I.515 (1993), *Parameter exchange for ISDN interworking.* +- ITU-T Recommendation I.530 (1993) *Network interworking between an ISDN and a Public Switched Telephone Network (PSTN).* +- ITU-T Recommendation Q.931 (1993), *Digital Subscriber Signalling System No. 1 (DSS 1) – ISDN user-network interface layer 3 specification for basic call control.* +- ITU-T Recommendations T.200-Series1), *Programming communication interface for terminal equipment connected to ISDN.* +- ITU-T Recommendation V.8 (1994), *Procedures for starting sessions of data transmission over the general switched telephone network.* +- ITU-T Recommendation V.10 (1993), *Electrical characteristics for unbalanced double-current interchange circuits operating at data signalling rates nominally up to 100 kbit/s.* +- ITU-T Recommendation V.11 (1993), *Electrical characteristics for balanced double-current interchange circuits operating at data signalling rates up to 10 Mbit/s.* +- ITU-T Recommendation V.14 (1993), *Transmission of start-stop characters over synchronous bearer channels.* +- ITU-T Recommendation V.24 (1993) *List of definitions for interchange circuits between Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE).* +- CCITT Recommendation V.25 bis (1988), *Automatic calling and/or answering equipment on the General Switched Telephone Network (GSTN) using the 100-series interchange circuits.* +- ITU-T Recommendation V.25 ter (1995), *Serial asynchronous automatic dialling and control.* +- ITU-T Recommendation V.28 (1993), *Electrical characteristics for unbalanced double-current interchange circuits.* +- ITU-T Recommendation V.12 (1995), *Electrical characteristics for balanced double-current interchange circuits for interfaces with data signalling rates up to 52 Mbit/s.* +- CCITT Recommendation V.42 bis (1988) *Data compression procedures for Data Circuit-Terminating Equipment (DCE) using error correcting procedures.* +- ITU-T Recommendation V.58 (1994), *Management information model for V-Series DCEs.* +- CCITT Recommendation V.110 (I.463) (1992), *Support of data terminal equipment with V-Series type interfaces by an integrated services digital network.* +- CCITT Recommendation V.120 (I.465) (1992), *Support by an ISDN of data terminal equipment with V-Series type interfaces with provision for statistical multiplexing.* +- CCITT Recommendation X.24 (1988), *List of definitions for interchange circuits between Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE) on public data networks.* +- ITU-T Recommendation X.25 (1993), *Interface between Data Terminal Equipment (DTE) and Data Circuit-Terminating Equipment (DCE) for terminals operating in the packet mode and connected to public data networks by dedicated circuit.* + +--- + +1) Presently at the stage of draft. + +- ITU-T Recommendation X.30 (I.461) (1993), *Support of X.21, X.21 bis and X.20 bis based data terminal equipments DTEs by an Integrated Services Digital Network (ISDN)*. +- ITU-T Recommendation X.31 (I.462) (1993), *Support of packet mode terminal equipment by an ISDN*. +- ISO/IEC 2110:1989, *Information technology – Data communication – 25-pole DTE/DCE interface connector and contact number assignments*. +- ISO/IEC 13871, *Information technology – Telecommunications and information exchange between systems – Private telecommunications networks – Digital channel aggregation*. + +# 3 Definitions + +For the purposes of this Recommendation, the following definition applies: + +**3.1 **modem:**** The term modem is used to refer to a functional block (sometimes called a digital modem) whose overall functionality is equivalent to that of a modem connected to a codec. A modem has no internal analogue components and only digital interfaces. + +# 4 Abbreviations + +For the purposes of this Recommendation, the following abbreviations are used: + +| | | +|--------|---------------------------------------------------------------| +| BC | Bearer Capability | +| CLI | Calling Line Identification | +| DTE | Data Terminal Equipment | +| HLC | High Layer Compatibility | +| IPE | In-band Parameter Exchange | +| IWF | Interworking Function | +| LLC | Low Layer Compatibility | +| MIB | Management Information Base | +| MSN | Multiple Subscriber Number | +| MTA | Multi-protocol Terminal Adaptor | +| NT | Network Termination | +| PID | Protocol Identification | +| SUB | Sub-addressing | +| TA | Terminal Adaptor | +| TE1 | ISDN data terminal | +| TE2 | DTE with a non-ISDN interface | +| UDI-TA | Unrestricted Digital Information with Tones and Announcements | + +# 5 Reference models + +According to clause 3/I.411, the Terminal Adaptor (TA) functional group lies between the R and S reference points and contains functions that allow a TE2 (non-ISDN) terminal to use the services provided by an ISDN. + +Clause 4/I.411 describes various physical configurations involving the TA functional group and the simplest one has interfaces at both the R and S reference points. However, other arrangements are possible and actual items of equipment containing the TA functional group may also contain other functional groups, resulting in the interface on the network side not being at the S reference point. + +In general though, for simplicity, the configuration with interfaces at the R and S reference points is used throughout this Recommendation. Also, for clarity, the expression "interface at the R (or S) reference point" is abbreviated to "R (or S) interface". + +Alternative arrangements on the network side are discussed in the subclause describing the network interface functions (5.1.4). + +## 5.1 Functional reference model + +The Functional Reference Model in Figure 1 is derived from Figure A.1/V.110. Figure 1 shows the main functional blocks that make up a terminal adaptor. These functions are described below. + + + +Figure 1: Terminal adaptor functional reference model. The diagram shows a block diagram of a terminal adaptor. On the left, a box labeled 'TE2' is connected to a vertical dashed line labeled 'R'. This line connects to block (1). Block (1) is connected to blocks (2) and (3). Block (2) is connected to block (4). Block (3) is connected to block (4). Block (4) is connected to a vertical dashed line labeled 'S', which is then connected to an empty box. Below blocks (1) and (4) is a large box labeled (6). Two arrows point from box (6) up to blocks (1) and (4), with the text 'Connections to other functional blocks' above the arrows. Below box (6) is a dashed line labeled (7), with a vertical line connecting them. The text '(Note)' is below (7). The identifier 'T1400940-94/d01' is to the right of box (6). + +- NT Network termination +- TE2 Data terminal equipment (DTE) with a non-ISDN interface +- (1) Terminal interface functions +- (2) User (U) plane functions +- (3) Control (C) plane functions +- (4) Network interface functions +- (5) Synchronization between User and Control functions +- (6) Management and maintenance control +- (7) Local control and management interface + +NOTE – This interface is optional. It is needed if the TA cannot be adequately controlled from the R interface. + +FIGURE 1/V.130 + +### Terminal adaptor functional reference model + +### 5.1.1 Terminal interface functions + +This block provides physical layer functions at the R interface according to applicable Recommendations or International or National Standards. (These are listed in 8.1.) Alternatively this interface may be internal to a piece of equipment and therefore not subject to standardization. + +### 5.1.2 User (U) plane functions + +The main U plane function is the adaptation of the user's information signalling rate and format at the R interface to that of the ISDN B- or other channel(s) being used at the S interface. + +Additional U plane functions include: + +- end-to-end mapping of the states of R interface control signals; +- in-band notification/checking/negotiation of adaptation protocol (for multi-protocol TAs); +- in-band notification/checking/negotiation of adaptation protocol parameters; +- handling error conditions detected at the R interface; +- recovery of timing information (network independent clock); +- end-to-end flow control between TAs (methods are described in both Recommendations V.110 and V.120); +- multiplexing of several user connections into one ISDN call; +- aggregation of several ISDN calls to provide one user connection. Protocols for this purpose are described in Recommendation H.244 and the complementary International Standard, ISO/IEC 13871; +- detection and optional correction of errors that occur between the TAs; +- compression of the user information stream to increase the effective throughput; +- encryption of the user information stream for security purposes; +- modem function (see 10.3). + +NOTE – Recommendations may not yet exist to provide all the functions described above. + +### **5.1.3 Control (C) plane functions** + +The main C plane function is the mapping function needed to convert between the automatic calling and/or answering procedures used at the R interface and the ISDN D-channel signalling protocol. For R interfaces with little or no automatic calling and/or answering capability, the deficiency must be made up by a local management function. + +Additional C plane functions include: + +- out-of-band notification/checking/negotiation of adaptation protocol (for multi-protocol TAs); +- out-of-band notification/checking/negotiation of adaptation protocol parameters; +- security checking of incoming calls using the Calling Line Identification (CLI) supplementary service; +- identification of a particular TA on a shared ISDN access using, for example, the Multiple Subscriber Number (MSN) or Sub-addressing (SUB) supplementary services. The terminal selection process is discussed in detail in Recommendation I.333. + +### **5.1.4 Network interface functions** + +This block provides physical layer functions at the interface on the ISDN side. For the S interface, T interface or coincident S and T interface, these functions are specified in Recommendation I.430 or I.431. Alternatively this interface may be internal to a piece of equipment and therefore not subject to standardization, for example, the functions of TA and NT2 may be combined. Also, for connection to some ISDNs, provision of the NT1 function is the responsibility of the subscriber, not the network-provider. In this case the NT1 and TA functions may be combined into one piece of equipment, which is commonly called a “Terminal Adaptor”. + +### **5.1.5 Synchronization between User and Control plane functions** + +This block synchronizes signalling (in the C plane) with user information flow (in the U plane). An example is: + +- starting the rate adaptation protocol when the call has been connected. + +### 5.1.6 Management and maintenance control + +This block provides overall control of the TA and may in addition provide maintenance functions. Examples are: + +- storage of ISDN numbers for Calling Line Identification (CLI) checking of incoming calls; +- control of maintenance loops. + +### 5.1.7 Local control and management interface + +This optional interface is required if the TA cannot be adequately controlled from the R interface. An example is: + +- a keypad to provide manual call control; +- indicator lights or an alphanumeric display to show the status of the TA. + +## 5.2 Protocol reference model + +A terminal adaptor performs protocol conversion in both the control and user planes. The concept of planes is discussed in 2.2/I.320. + +### 5.2.1 Control plane + +The TA performs conversion in the control plane between the signalling procedures at the R and S interfaces. This requires a pair of protocol stacks linked by a signalling conversion function (Figure 2A). At the S interface all three protocol layers must be present (ISDN D-channel signalling protocol). The structure of the R-signalling layer varies from one R interface to another and will depend on the nature of the protocol at the R interface. The signalling conversion function provides a mapping between the primitive operations of the two signalling protocols. Examples of primitive operations are the commands to setup and clear a call. Auto-calling procedures are described in 6.1. + +For some R interfaces, it may not be possible to perform certain management functions via the R interface. This deficiency must be made up by a local management function. It may involve manual intervention, either at the time the operation takes place (e.g. to place a call) or at some time in advance (e.g. to store a called party number). + +Example of R-signalling layers: + +- For an X.25 interface it is X.25 layer 2 and the call control part of layer 3. +- For a V-Series interface one possibility is V.25 *bis*. + +The ISDN D-channel signalling protocol may also be used to carry out the additional functions described in 5.1.3. The ability to perform these functions depends on the availability of certain features in the ISDN to which the TA is attached. + +### 5.2.2 User plane + +The TA serves as a relay for user information between the R and S interfaces. This requires a pair of protocol stacks linked by a relay function (Figure 2B). At the S interface the adaptation protocol is used to allow the user's information to be carried in a B, D, H or other channel using an appropriate ISDN bearer service. If required, a higher bit-rate channel may be formed by aggregating two or more of these channels. + +The choice of adaptation protocol is determined by the combination of channel type and bearer service used over that channel. For example, V.110 is designed for use over the 64 kbit/s unrestricted (or restricted) circuit mode bearer service, carried in a B channel. V.120 is more flexible in its usage and can operate using an unrestricted (or restricted) circuit mode bearer service carried in a B or H channel or, alternatively, a frame mode bearer service carried in a B, H or D channel. + +The adaptation protocol may, in addition, support the functions described in 5.1.2. + +A particular TA implementation is not limited to the use of a single adaptation protocol. Choice of protocol can be by configuration or by negotiation on a call by call basis. Clause 9 describes such a Multi-protocol Terminal Adaptor (MTA). + + + +| | | +|------------------------|------------------------------------| +| Signalling conversion | | +| R-signalling
(Note) | Rec. Q.931 | +| | Rec. Q.921 | +| R-physical | Rec. I.430 or I.431
(D-channel) | + +R +S + +T1400950-94/d02 + +Diagram of the Control (C) plane protocol reference model for a terminal adaptor. It shows a stack of three layers: 'Signalling conversion' at the top, 'R-signalling (Note)' in the middle, and 'R-physical' at the bottom. The 'R-signalling' layer is further divided into two sub-layers: 'Rec. Q.931' and 'Rec. Q.921'. The 'R-physical' layer is associated with 'Rec. I.430 or I.431 (D-channel)'. The stack is connected to an 'R' interface on the left and an 'S' interface on the right. A reference 'T1400950-94/d02' is noted near the S interface. + +NOTE – The structure of the R-signalling layer varies from one R interface to another. + +FIGURE 2A/V.130 + +#### **Terminal adaptor protocol reference model – Control (C) plane** + + + +| | | +|-----------------------|----------------------------------------------------| +| Relay | | +| R-layer 2
(Note 1) | Adaptation
layer
(Note 2) | +| R-physical | I.430 or I.431
(B-or other channel)
(Note 3) | + +R +S + +T1400960-94/d03 + +Diagram of the User (U) plane protocol reference model for a relay. It shows a stack of three layers: 'Relay' at the top, 'R-layer 2 (Note 1)' in the middle, and 'R-physical' at the bottom. The 'R-layer 2' layer is associated with 'Adaptation layer (Note 2)'. The 'R-physical' layer is associated with 'I.430 or I.431 (B-or other channel) (Note 3)'. The stack is connected to an 'R' interface on the left and an 'S' interface on the right. A reference 'T1400960-94/d03' is noted near the S interface. + +##### NOTES + +- 1 Layer 2 at the R interface may be null. +- 2 The structure of the Adaptation layer varies from one type of TA to another. +- 3 Any channel provided for user information may be used at the S interface. + +FIGURE 2B/V.130 + +#### **Terminal adaptor protocol reference model – User (U) plane** + +## 5.3 Interworking model + +The Interworking Model in Figure 3 shows possible interworking scenarios for a terminal adaptor. It is a simplified version of the diagram in Figure 1/I.515. The general requirements for successful interworking are: + +### 5.3.1 TE2 + TA to TE2 + TA (scenario a) + +The two TE2 + TA combinations must have a minimum common functionality for communication to be successful, for example both TAs must support the same rate adaptation protocol operating at the same bit rate. + +### 5.3.2 TE2 + TA to TE1 (scenario b) + +The TE1 must contain functionality such that it is compatible with the TE2 + TA. Thus, a TE1 which is ended to be able to interwork with an adapted TE2 will need to contain some of the functions described within this Recommendation. These functions are in addition to those required for communication between directly connected terminals (TE1 to TE1). + +### 5.3.3 TE2 + TA to non-ISDN network via IWF (scenario c) + +The requirements for the TA in this scenario depend very much on the type of non-ISDN network concerned and the functionality of the IWF. In many cases the IWF will need to contain some of the functions described in this Recommendation, for example, it may need to terminate the rate adaptation protocol used over the ISDN. It may also need a further adaptation function to the non-ISDN network. In the case of the GSTN this would be a modem. Alternatively, as described in clause 10, the modem function could be placed in the TA and the 3.1 kHz audio bearer service be used to interwork with the GSTN. + +### 5.3.4 TE1 to non-ISDN network via IWF (scenario d) + +In this scenario the TE1 must have equivalent functionality to the TE2 + TA in scenario (c). It will therefore need to contain some of the functions described in this Recommendation. + + + +The diagram illustrates the interworking model. It shows two rows of components. The top row consists of a box labeled 'TE1' connected by a solid line labeled 'S' to a central oval labeled 'ISDN (Note 2)'. This oval is connected by a solid line to a box labeled 'IWF', which is then connected by a solid line to a box labeled 'Non-ISDN network (Note 1)'. The bottom row consists of a box labeled 'TE2' connected by a solid line labeled 'R' to a box labeled 'TA', which is connected by a solid line labeled 'S' to the central 'ISDN (Note 2)' oval. The oval is connected by a solid line labeled 'S' to another box labeled 'TA', which is connected by a solid line labeled 'R' to a box labeled 'TE2'. Inside the 'ISDN (Note 2)' oval, four dashed lines represent interworking scenarios: 'a' connects the bottom-left 'TA' to the bottom-right 'TA'; 'b' connects the bottom-left 'TA' to the top-left 'TE1'; 'c' connects the bottom-right 'TA' to the top-left 'TE1'; and 'd' connects the top-left 'TE1' to the top-right 'IWF'. The reference 'T1400970-94/d04' is located at the bottom right of the diagram. + +Diagram of the Interworking Model showing TE1, TE2, TA, IWF, and ISDN/Non-ISDN networks with interworking scenarios a, b, c, and d. + +TE1 ISDN data terminal +TE2 Data terminal equipment (DTE) with a non-ISDN interface +TA Terminal Adaptor +IWF Interworking Function + +Interworking scenarios: +a TE2 + TA to TE2 + TA +b TE2 + TA to TE1 +c TE2 + TA to non-ISDN network +d TE1 to non-ISDN network + +#### NOTES + +- 1 Examples of non-ISDN networks are Circuit and Packet Switched Public Data Networks and the GSTN. +- 2 For the purposes of this figure, NT1 and NT2 functions are considered to be within the ISDN. + +FIGURE 3/V.130 +Interworking model + +## 5.4 Call mapping model + +Because a TA can provide multiplexing or channel aggregation there is not always a one-to-one mapping between calls as seen by the TE2(s) and calls over the ISDN. + +In the diagrams below, each rectangle represents a call. Those above the dotted line (which represents the time dimension) are as seen at the TE2 side of the TA and those below the line, the ISDN side. + +In Figure 4 three cases are shown where the durations of the calls on both sides of the TA are the same. The first is for a simple TA where there is a 1:1 mapping between the calls at the TE2 and ISDN sides. An example is the V.110 TA described in Appendix I. + +The second is for a TA which multiplexes several (in this case three) TE2 calls into one ISDN call. An example would be a TA using the statistical multiplexing feature of Recommendation V.120. + +The third case is for a TA using channel aggregation to synthesize a 128 kbit/s channel out of two ISDN 64 kbit/s circuit mode calls. + + + +The diagram illustrates three call mapping scenarios between TE2 (R) and ISDN (S) over time. Each scenario is represented by a horizontal timeline with rectangles indicating call durations. + +- 1 : 1 mapping:** A single rectangle on the TE2 (R) side is connected by a horizontal arrow to a single rectangle on the ISDN (S) side, indicating a direct one-to-one mapping. +- Multiplexing:** Three rectangles on the TE2 (R) side are connected by a horizontal arrow to a single, longer rectangle on the ISDN (S) side, indicating that multiple TE2 calls are multiplexed into a single ISDN call. +- Channel aggregation:** Two rectangles on the ISDN (S) side are connected by a horizontal arrow to a single, longer rectangle on the TE2 (R) side, indicating that two ISDN calls are aggregated into a single TE2 call. The ISDN side rectangles are labeled with the reference T1401300-95/d05. + +Diagram illustrating call mapping for three different types of TA: 1:1 mapping, Multiplexing, and Channel aggregation. + +FIGURE 4/V.130 +Call mapping for three different types of TA + +Figure 5 illustrates a more complex situation. It shows a possible sequence of TE2 and ISDN calls for an X.25 DTE connected to an X.31 TA. When the first X.25 call request appears from the TE2 (on the left) an ISDN call is set up. As time proceeds (moving to the right) the first X.25 call is disconnected, but other calls have been set up and so the ISDN call remains in progress. Only when the last X.25 call has been disconnected can the ISDN call be cleared. The continuation of the ISDN call for a short time beyond the end of the last X.25 call is a timeout period to reduce the risk of clearing an ISDN call, only to find that another needs to be set up almost immediately. The duration of this timeout period is determined by performance and cost factors. + +# 6 Connection establishment (Call control) + +## 6.1 Auto-calling procedures + +In order to maximize the ease of use of a TA it is desirable that an existing TE2 (DTE) should be able to use an auto-calling procedure in the same way that it would when connected to a modem or a dedicated public data network (PSPDN or CSPDN). + + + +Figure 5/V.130: Call mapping for an X.31 TA. The diagram shows a timeline with two main entities: TE2 (R) (X.25 DTE) and ISDN (S). TE2 (R) has three rectangular blocks representing calls, with the first block being the longest. ISDN (S) has a single, long rectangular block representing a call that spans the duration of the first TE2 (R) call. A horizontal arrow labeled 'Time' points to the right. The reference T1401310-95/d06 is at the bottom right. + +FIGURE 5/V.130 +Call mapping for an X.31 TA + +Mappings between auto-calling procedures at the R interface and the signalling protocol at the S interface are already described in the following Recommendations: + +- Recommendation X.30 (I.461): for X.21 based DTEs; +- Recommendation X.31 (I.462): for X.25 based DTEs; +- Recommendation V.110 (I.463): for DTEs supporting V.25 *bis* procedures (Appendix II/V.110). + +The V.25 *bis* procedures described in Appendix II/V.110 could be applied to other types of terminal adaptors for V-Series DTEs. Examples are TAs containing a modem function or using V.120 rate adaptation. + +Recommendation V.25 *ter* contains a description of alternative auto-calling procedures for asynchronous V-Series DTEs. The mapping of these on to the Q.931 signalling protocol is for further study. As well as containing call control commands, Recommendation V.25 *ter* also has commands for configuration and status monitoring. A proposal has been made to use a Management Information Base (MIB) to provide the mapping between V.25 *ter* and Q.931 primitive operations. An example of such a MIB (for V-Series DCEs) is to be found in Recommendation V.58. + +## 6.2 Multi-Use bearer service applications + +The Multi-Use bearer service is defined in Recommendation I.231.9. It provides a Bearer Capability (BC) of 64 kbit/s Unrestricted Digital Information with Tones and Announcements (UDI-TA). As a network option it can provide automatic fallback to the 3.1 kHz audio or speech BC to allow interworking with ISDN 3.1 kHz audio or speech terminals or terminals on the GSTN. + +A multi-protocol terminal adaptor (MTA – as described in clause 9) containing an adaptation function conforming to either Recommendation V.110 or V.120 and a MODEC function (see Appendix I) could use the Multi-Use bearer service with the fallback option to simplify the selection of its operating mode. + +The operation of terminals which use the “bearer capability selection option” of the Multi-Use bearer service is described in 3.3/I.501 and is summarized below. + +### 6.2.1 Outgoing calls + +For an outgoing call the MTA’s SETUP message contains UDI-TA (Unrestricted Digital Information with Tones and Announcements) as the preferred BC with 3.1 kHz as the fallback. Subsequent operation depends on any BC contained in the CONNECT message received from the ISDN: + +#### 6.2.1.1 BC = UDI-TA + +The TA operates in the 64 kbit/s unrestricted mode. Optionally, in-band procedures may then be used by the MTA to select a rate adaptation scheme, for example, V.110 or V.120. + +#### 6.2.1.2 BC = 3.1 kHz audio or no BC specified (possibly with GSTN interworking indicated) + +The TA operates in the 3.1 kHz audio mode. Optionally, the MODEM can then commence (in-band) modem identification procedures. + +### 6.2.2 Incoming calls + +For an incoming call the MTA's response depends on the BC(s) contained in the SETUP message: + +#### 6.2.2.1 BC = both UDI-TA and 3.1 kHz + +Providing the TA is otherwise compatible (e.g. the rate adaptation specified in the LLC information element is acceptable) then it responds with a CONNECT message containing the UDI-TA BC and operates in 64 kbit/s unrestricted mode. Otherwise it responds with the 3.1 kHz BC and operates in the 3.1 kHz audio (modem) mode. This allows 3.1 kHz (modem) interworking with other terminal adaptors which support the Multi-Use bearer service but use incompatible rate adaptation protocols in 64 kbit/s unrestricted mode. + +#### 6.2.2.2 BC = UDI-TA or 64 kbit/s unrestricted digital + +The TA responds with a CONNECT message containing the BC copied from the SETUP message and operates in the 64 kbit/s unrestricted mode. + +#### 6.2.2.3 BC = 3.1 kHz only (possibly with GSTN interworking indicated) + +The TA responds with a CONNECT message containing the BC copied from the SETUP message and operates in the 3.1 kHz audio (modem) mode. + +# 7 Rate adaptation protocol and parameter negotiation + +For many applications, both calling and called terminals can be preconfigured and no negotiation is required. Recommendation I.515 identifies a number of circumstances in which parameter exchange might be required. One of these is the selection of the rate adaptation protocol to be used. Further negotiation may then be required to select the values of parameters for a particular protocol. There are two possible ways of negotiating protocols and parameters. Out-of-band procedures using D channel signalling (Recommendation Q.931) can be used before and possibly after call establishment. In-band procedures can be used only once the call has been established. Figure 6 shows a taxonomy of the negotiation processes that can be used. + + + +``` +graph TD + Root[ ] --- Predefined[Predefined +(no negotiation required)] + Root --- Negotiation[Negotiation required] + Negotiation --- After[After call +establishment] + Negotiation --- Before[Before call +establishment +(out-band only)] + After --- InBand[In-band] + After --- OutBand[Out-band] + InBand --- ID[Identification protocol] + InBand --- SelfID[Self-identification] +``` + +T1401320-95/d07 + +A hierarchical tree diagram showing the taxonomy of negotiation processes. The root splits into 'Predefined (no negotiation required)' and 'Negotiation required'. 'Negotiation required' splits into 'After call establishment' and 'Before call establishment (out-band only)'. 'After call establishment' splits into 'In-band' and 'Out-band'. 'In-band' further splits into 'Identification protocol' and 'Self-identification'. The identifier 'T1401320-95/d07' is located at the bottom right of the diagram area. + +FIGURE 6/V.130 +Ataxonomy of negotiation processes + + + +# 8 TE2 – TA interface considerations + +The interface at the R reference point between the TA and the TE2 functional blocks may be a physical interface or may be embedded within a piece of equipment. + +## 8.1 Physical interfaces + +Recommendations X.30, X.31, V.110 and V.120 describe TAs for terminals with interfaces conforming to V- and X-Series Recommendations at rates up to 56 kbit/s. However, the use in TAs of techniques such as data compression and channel aggregation will result in a need for interfaces at significantly higher bit rates. + +Applicable Recommendations and International Standards are: + +- Interchange circuits – Recommendation V.24, Recommendation X.24; +- Electrical characteristics – Recommendation V.10, Recommendation V.11, Recommendation V.12, Recommendation V.28; +- Interface connectors and pin assignments – ISO/IEC 2110. + +## 8.2 Flow control and buffering + +No flow control or buffering is needed for the simple situation in which two TE2s are connected using V.110 TAs and the bit rates of both TE2s are the same as that of the V.110 protocol. The same is true when Recommendation V.120 is used in a similar situation without error correction. + +In more complex circumstances the effective rate across the ISDN will not be the same as the bit rate of one or other of the TE2s. Possible circumstances are: + +- the TE2s (using V.110 or V.120 TAs) have different interface bit rates; +- Recommendation V.120 is being used with error correction and retransmissions are reducing the effective throughput; +- Recommendation V.120 is being used with a data compression protocol, e.g. V.42 *bis*, which is resulting in a variable effective throughput; +- Recommendation V.120 is being used with statistical multiplexing of a number of data streams. + +In such cases it is necessary to decouple the terminal from the ISDN by providing buffering and flow control. In the data compression and statistical multiplexing cases, it is desirable to operate the TE2 interface at a rate comparable to the maximum possible rate over the ISDN (subject to the terminal being able to accept this) and to use flow control to reduce the rate as necessary. End-to-end flow control between the TAs is a U-plane function (5.1.2). In addition, local flow control will be needed at the TE2-TA interface. Techniques for local flow control during asynchronous operation are described in 2.4.1/V.110. + +## 8.3 Embedded interfaces + +A common form of construction for an ISDN interface for some terminals is that of a plug-in printed circuit card. Depending on the nature of the interface between this card and the rest of the terminal the complete unit may form either a TE1 or a TE2 + TA. In particular, in some cases the interface behaves like the DTE interface of a modem although it does not necessarily have the same physical characteristics. In this case the card can reasonably be described as a TA. In other cases the card functions are much more closely integrated into the terminal and it is not reasonable to separate them, the whole terminal being described as a TE1. + +The T.200-Series Recommendations describe a “Programme communication interface for terminal equipment connected to ISDN”. This is a software interface between application software and the ISDN interface software and hardware. It is through this interface that the application transfers data and management information. This includes information required to control any terminal adaptation functions that are present. + +# 9 Multi-protocol terminal adaptor + +A Multi-Protocol Terminal Adaptor (MTA) supports more than one adaptation protocol in the user plane. The actual protocol used is chosen on a per call basis. Figure 7 shows such a TA which supports three different adaptation functions (shown as U plane functions 1, 2 and 3). These could be, for example, rate adaptation conforming to Recommendations V.110 and V.120 using the 64 kbit/s unrestricted BC, and a modem function (clause 10) using the 3.1 kHz audio BC. + +The selection of the appropriate U plane function could be made by the user or automatically during or immediately after call set-up. The following is a possible automatic procedure. + +If the type of network (ISDN or GSTN) to which the called terminal is attached is known, then the MTA can originate a call specifying the appropriate bearer service and, optionally, for the ISDN only, LLC and/or HLC information. + +If the type of network is unknown then the following procedure can be adopted: + +- 1) Originate the call with a 64 kbit/s bearer specified and, optionally, LLC and/or HLC information. If the destination is on the ISDN and the call succeeds then an in-band protocol (e.g. Appendix I/I.515) can be used to select a rate adaptation protocol. Otherwise proceed to step 2. +- 2) If the call cannot be completed because the called terminal was incompatible (i.e. on the GSTN or a 3.1 kHz terminal on the ISDN) then the call is reoriginated with a 3.1 kHz bearer specified. When the call has been connected then modem facility negotiation can proceed using, for example, the procedure specified in Recommendation V.8. + +The need to have to make a second call attempt in some cases is undesirable as it increases both the effective call set-up time and the signalling load on the network. + +A better approach (if the network supports it) is for the originating terminal to use the Multi-Use bearer service with the 3.1 kHz audio interworking option. This allows a single call set-up to be used (see 6.2). + + + +The diagram illustrates the architecture of a Multi-protocol terminal adaptor (MTA). On the left, a 'V-Series DTE' box is connected to an 'R' interface, represented by a vertical dashed line. This interface leads into a large block labeled 'R interface function'. To the right of this block is a vertical stack of four functional blocks: 'U Plane function 1', 'U Plane function 2', 'U Plane function 3', and 'Call control function'. These are connected to an 'S interface function' block, which is further connected to an 'S' interface, also represented by a vertical dashed line. Below the main functional blocks is a 'Management and maintenance control' block. Two upward-pointing arrows connect this block to the 'R interface function' and 'S interface function' blocks, with the label 'Connections to other functional blocks' above the arrows. A dashed line extends downwards from the 'Management and maintenance control' block, labeled 'Local control and management interface (optional)'. The reference 'T1401330-95/d08' is located at the bottom right of the diagram. + +Block diagram of a Multi-protocol terminal adaptor (MTA) showing its internal components and interfaces. + +FIGURE 7/V.130 +Multi-protocol terminal adaptor + +# 10 Adaptation to 3.1 kHz audio bearer (GSTN interworking) + +## 10.1 Introduction + +Recommendation I.530 identifies two alternative ways of providing data communications between ISDN and GSTN subscribers. + +- i) The DTE (TE2) of the ISDN subscriber is connected to a TA which rate adapts the information flow to 64 kbit/s according to, for example, Recommendation I.463 (V.110). At a suitable interworking point within the network, the original information flow is extracted and converted to an "analogue" form by a modem for transfer over the GSTN to the remote terminal (i.e. the usage of modem pools). This mechanism is described in Recommendation I.515. +- ii) The DTE (TE2) of the ISDN subscriber is connected to a modem which in turn is connected to a TA incorporating a codec. Interworking between the ISDN and GSTN is handled as for telephony. This second case, "Terminal Adaptor with CODEC", is shown in Figure 8. + + + +``` +graph LR; DTE[V-series DTE] -.->|"(Note 1)"| Modem[V-Series modem]; Modem -.->|"(Note 2) R"| TA[Terminal Adaptor with CODEC]; TA -.->|S| GSTN[ ]; +``` + +Diagram showing the connection between a V-series DTE, a V-Series modem, and a Terminal Adaptor with CODEC. The V-series DTE is connected to the V-Series modem via a dashed line labeled (Note 1). The V-Series modem is connected to the Terminal Adaptor with CODEC via a dashed line labeled R (Note 2). The Terminal Adaptor with CODEC is connected to the GSTN via a dashed line labeled S. The diagram is labeled T1401340-95/d09. + +###### NOTES + +- 1 This is the normal interface between a V-Series DTE and a Modem. +- 2 This R interface is the same as an interface between a modem and the GSTN. It is the subject of national standardization. + +FIGURE 8/V.130 + +### V-Series DTE connect to the ISDN via Modem and a TA with a CODEC + +## 10.2 Terminal adaptor with codec + +The "Terminal Adaptor with codec" can be described by reference to Figure 1 (Functional Reference Model). It has an R interface which is the same as that presented to a Modem by the GSTN. The "R interface functions" block (1) emulates the line card at a local exchange, performing such functions as power feeding, ringing current generation, hook switch and DTMF or pulse dialling detection and 2-4 wire conversion (hybrid). This interface is subject to national standardization. + +The "User plane functions" block (2) consists of a codec which conforms to Recommendation G.711. A-law or $\mu$ -law coding is chosen to suit national requirements. In addition this functional block is required to generate dial-tone in response to the off-hook condition being detected at the R interface. + +The "Control plane functions" block converts between the signalling at the R and S interfaces. This TA uses the 3.1 kHz audio bearer service. + +## 10.3 Combined modem and terminal adaptor + +A modem and a terminal adaptor can be combined into a single piece of equipment (Figure 9). This causes the R reference point to move to the interface with the DTE. The analogue interface between the modem function and the TA with codec function becomes internal and therefore not subject to standardization. It is then possible to remove from the TA and the modem the analogue line interface components that were associated with their being physically separate items of equipment. + +Figure 10 shows how the process of integrating a modem into a terminal adaptor can be taken a stage further by defining a new functional block, a modec (sometimes called a digital modem), which has no internal analogue functions and only digital interfaces. Interface (a) is the DTE's bit or character stream. Interface (b) is an octet stream which is the same as the PCM coding (according to Recommendation G.711) of the voiceband signal at the analogue (GSTN) interface of an equivalent modem. This TA uses the 3.1 kHz audio bearer service. + + + +``` + +graph LR + DTE[V-Series DTE] -- R --- CMTA[Combined modem and Terminal Adaptor] + subgraph CMTA + MF[V-Series modem function] -- "(Note)" --- TAF[TA function with CODEC] + end + TAF --- S + +``` + +Figure 9: V-Series DTE connected to the ISDN via a combined Modem and TA. The diagram shows a V-Series DTE block on the left connected via a line to a large box labeled 'Combined modem and Terminal Adaptor'. Inside this box are two smaller blocks: 'V-Series modem function' and 'TA function with CODEC'. A dashed vertical line labeled 'R' marks the interface between the DTE and the combined unit. Another dashed vertical line labeled '(Note)' marks the internal interface between the modem function and the TA function. A third dashed vertical line labeled 'S' marks the interface on the right side of the combined unit. The reference T1401350-95/d10 is at the bottom right. + +NOTE – This is an internal analogue interface and is not subject to standardization. + +FIGURE 9/V.130 + +### V-Series DTE connected to the ISDN via a combined Modem and TA + + + +``` + +graph TD + DTE[V-Series DTE] -- R --- RIF[R interface function] + RIF -- a --- MODEC[MODEC (Note)] + RIF --- CCF[Call control function] + MODEC -- b --- STIF[S/T interface function] + CCF --- STIF + STIF --- S + MMC[Management and Maintenance Control] --> RIF + MMC --> MODEC + MMC --> STIF + LCMI[Local control and management interface (optional)] -.- MMC + +``` + +Figure 10: Functional model of a TA incorporating a MODEC. The diagram shows a V-Series DTE block on the left connected to an 'R interface function' block. This block is connected to a 'MODEC (Note)' block via interface 'a' and to a 'Call control function' block. The MODEC block and Call control function block are both connected to an 'S/T interface function' block on the right, with the MODEC connection labeled 'b'. Below these is a 'Management and Maintenance Control' block with arrows pointing up to the R interface, MODEC, and S/T interface blocks. A dashed line labeled 'Local control and management interface (optional)' connects to the Management block. Dashed vertical lines labeled 'R' and 'S' mark the external interfaces. The reference T1401360-95/d11 is at the bottom right. + +NOTE – A modec eliminates the analogue functions of a modem and a codec. + +FIGURE 10/V.130 + +### Functional model of a TA incorporating a MODEC + +# 11 Management + +For further study. + +# Appendix I + +## Protocol model for a V.110 TA (asynchronous mode) + +This appendix contains an example showing how the Protocol Reference Model (see 5.2) can be used. Figures I.1 and I.2, respectively, show the protocol models for the C and U planes of a TA intended to connect an asynchronous (start-stop) terminal to an ISDN Basic Access. It uses V.110 rate adaptation and V.25 *bis* or V.25 *ter* auto-calling. + + + +| Signalling conversion | | +|--------------------------------------------|--------------------| +| Rec. V.25 bis
or v.25 ter | Rec. Q.931 | +| Start-stop
character
format | Rec. Q.921 | +| Rec. V.24,
Rec. V.28 | I.430
D-channel | + +R + +S T1401030-94/d12 + +Figure I.1/V.130: V.110 Terminal adaptor protocol model – Control (C) plane. The diagram shows a protocol stack for the Control plane. At the top is a box labeled 'Signalling conversion'. Below it are two columns of boxes. The left column contains 'Rec. V.25 bis or v.25 ter', 'Start-stop character format', and 'Rec. V.24, Rec. V.28'. The right column contains 'Rec. Q.931', 'Rec. Q.921', and 'I.430 D-channel'. The stack is connected to a horizontal line representing the interface. On the left side of the line is a dashed vertical line labeled 'R'. On the right side is a dashed vertical line labeled 'S' with the reference 'T1401030-94/d12' below it. + +FIGURE I.1/V.130 + +### V.110 Terminal adaptor protocol model – Control (C) plane + + + +| Relay | | +|-----------------------------------|---------------------| +| | V.110 RA0
(V.14) | +| | V.110 RA1 | +| Start-stop
character
format | V.110 RA2 | +| Rec. V.24,
Rec. V.28 | I.430
B-channel | + +R + +S T1401370-95/d13 + +Figure I.2/V.130: V.110 Terminal adaptor protocol model – User (U) plane. The diagram shows a protocol stack for the User plane. At the top is a box labeled 'Relay'. Below it are two columns of boxes. The left column contains 'Start-stop character format' and 'Rec. V.24, Rec. V.28'. The right column contains 'V.110 RA0 (V.14)', 'V.110 RA1', 'V.110 RA2', and 'I.430 B-channel'. The stack is connected to a horizontal line representing the interface. On the left side of the line is a dashed vertical line labeled 'R'. On the right side is a dashed vertical line labeled 'S' with the reference 'T1401370-95/d13' below it. + +FIGURE I.2/V.130 + +## V.110 Terminal adaptor protocol model – User (U) plane + +In the control plane (Figure I.1), on the terminal side, signalling is performed using the V.25 *bis* or V.25 *ter* protocol which is carried by an asynchronous (start-stop) character stream over a physical interface with V.24 signal definitions and V.28 electrical characteristics. The signalling conversion function maps between the V.25 *bis* or V.25 *ter* commands and responses and the Q.931 messages on the network side. + +In the user plane (Figure I.2), on the terminal side, the user's information is carried in the start-stop character format. This character stream is then subjected to the three stages of rate adaptation in the V.110 protocol stack. The RA0 function uses the method described in Recommendation V.14 to generate a synchronous bit stream. This is then subjected to first and second stage rate adaptation by the RA1 and RA2 functions to produce a 64 kbit/s stream that is carried over the ISDN B-channel. The process is reversed for the information stream received from the network. \ No newline at end of file diff --git a/marked/V/T-REC-V.14-199303-I_PDF-E/raw.md b/marked/V/T-REC-V.14-199303-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..1f69261e3c412930f43030cd58c2a7bb0e21ca8a --- /dev/null +++ b/marked/V/T-REC-V.14-199303-I_PDF-E/raw.md @@ -0,0 +1,202 @@ + + + + +ITU logo: a globe with the letters ITU and a lightning bolt symbol. + +INTERNATIONAL TELECOMMUNICATION UNION + +# ITU-T + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +## V.14 + +(03/93) + +**DATA COMMUNICATION OVER +THE TELEPHONE NETWORK** + +--- + +**TRANSMISSION OF START-STOP +CHARACTERS OVER SYNCHRONOUS +BEARER CHANNELS** + +**ITU-T Recommendation V.14** + +(Previously "CCITT Recommendation") + +--- + +# FOREWORD + +The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecommunication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. + +ITU-T Recommendation V.14 was revised by the ITU-T Study Group XVII (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). + +# --- NOTES + +1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Telecommunication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. + +In order not to delay publication of this Recommendation, no change has been made in the text to references containing the acronyms “CCITT, CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. + +2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +# CONTENTS + +| | | Page | +|---|----------------------------------------------------------------------------------------------------------------------|-------------| +| 1 | Scope..... | 1 | +| | 1.3 Operation of DTE-DCE interface after failure to establish error-correcting (Recommendation V.42) operation ..... | 1 | +| 2 | Data signalling rates ..... | 1 | +| 3 | Signalling rate ranges of the start-stop characters at the converter input ..... | 1 | +| 4 | Start-stop character format ..... | 1 | +| 5 | Margin of the converter input..... | 2 | +| 6 | Selection of synchronous or asynchronous modes of operation ..... | 2 | +| 7 | Async-to-sync conversion method ..... | 2 | +| | 7.1 Transmitter..... | 2 | +| | 7.2 Receiver ..... | 2 | +| | 7.3 Break signal ..... | 3 | +| | 7.4 Tandem operation ..... | 3 | +| | 7.5 Testing facilities..... | 3 | +| | Annex A – Inclusion of an async-to-sync converter into a synchronous DCE ..... | 4 | + + + +# TRANSMISSION OF START-STOP CHARACTERS OVER SYNCHRONOUS BEARER CHANNELS + +*(Melbourne, 1988; revised Helsinki, 1993)* + +# **1 Scope** + +**1.1** This Recommendation describes a method of conveying start-stop characters over synchronous bearer channels using an async-to-sync converter in the data signalling rate range of up to 19 200 bit/s. Start-stop characters at signalling rates below or equal to 300 bit/s can be conveyed over synchronous bearer channels by oversampling at a signalling rate of at least 1200 bit/s. + +NOTE – The conversion method provided here replaces the conversion method applied earlier to Recommendations V.22, V.22 *bis*, V.26 *ter* and V.32. + +**1.2** This converter may be an intermediate device inserted into the data lines of both circuit 103 in the transmitter and circuit 104 in the receiver inside a synchronous DCE (see Figure A.1), or a stand-alone unit in certain applications. + +## **1.3 Operation of DTE-DCE interface after failure to establish error-correcting (Recommendation V.42) operation** + +DCEs may be designed to employ primarily the asynchronous-to-synchronous conversion associated with the error-correcting function specified in Recommendation V.42. Such DCEs are normally also capable of interworking, in a fallback mode, with DCEs employing the asynchronous-to-synchronous conversion in conformance with this Recommendation, but retaining the buffering of data and the flow control across the DTE-DCE interface. Further details may be found in 7.9/V.42. + +# **2 Data signalling rates** + +The conversion method shall be limited to signalling rates of up to 19 200 bit/s preferring the standard signalling rates of Recommendation V.5. + +The nominal signalling rates for both the start-stop characters and the synchronous DCE shall be the same. The tolerance of the signalling rate of the synchronous transmission shall be $\pm 0.01\%$ . + +# **3 Signalling rate ranges of the start-stop characters at the converter input** + +The conversion method is capable of tolerating the signalling rates of the DTE in two ranges: + +- a) basic range: +1% to –2.5%; +- b) extended range: +2.3% to –2.5%. + +The use of the basic signalling rate range is preferred since it results in lower distortion. The choice of range shall be made at the time of installation, and shall be the same for both transmitter and receiver. It is not intended to be under customer control. + +# **4 Start-stop character format** + +It shall be possible to condition the converter to accept the following formats; viz: + +- a) a one-unit start element, followed by seven data units, and a stop element of the unit in length (9-bit characters); +- b) a one-unit start element, followed by eight data units, and a stop element of one unit in length (10-bit characters); + +- c) a one-unit start element, followed by nine data units, and a stop element of one unit in length (11-bit characters); + +the converter may also accept characters consisting of: + +- d) a one-unit start element, followed by six data units, and a stop element of one unit in length (8-bit characters). + +Note that character formats c) and d) do not conform to International Alphabet No. 5. + +The character format selected shall be the same for both transmitter and receiver. The characters shall be in accordance with Recommendation V.4 regardless of whether they conform to International Alphabet No. 5. It shall be possible to transmit characters continuously or with any additional continuous stop element of arbitrary length between characters. + +NOTE – In each of the four formats, data units can be replaced by additional stop units. For example, format c) will allow 11-bit characters consisting of a one-unit start element, followed by eight data units and a stop element of two units to be handled. + +### 5 Margin of the converter input + +The effective net margin of the converter for transmitting of start-stop characters applied to the input of the converter shall be at least 40%. This figure is a subject for further study. + +### 6 Selection of synchronous or asynchronous modes of operation + +Selection for synchronous or asynchronous modes of operation shall be provided by switch (or similar means) enabling the user to perform normal transmission and testing in each mode of operation, respectively. + +In synchronous mode of operation the converter is totally bypassed in both directions. + +### 7 Async-to-sync conversion method + +The general method to handle the speed differences between the intracharacter signalling rate of the start-stop characters and the data signalling rate of the synchronous bearer channel will be the insertion/deletion of stop elements at the transmitter and reinsertion of deleted stop elements at the receiver. Means are provided to transfer continuous start polarity (break signals) as well. + +#### 7.1 Transmitter + +In the transmit direction the start-stop characters shall be adapted to the signalling rate of the synchronous bearer channel by: + +- deleting stop elements in case of overspeed of the start-stop characters; +- insertion of additional stop elements in case of underspeed of the start-stop characters. + +##### 7.1.1 Basic signalling rate range + +No more than one stop element shall be deleted for any eight consecutive characters. + +##### 7.1.2 Extended signalling rate range + +No more than one stop element shall be deleted for any four consecutive characters. + +#### 7.2 Receiver + +The intracharacter signalling rate provided by the converter shall be in the range of the nominal data rate to the limit of the specified overspeed tolerance, i.e. +1% in the basic and +2.3% in the extended data signalling range. The length of the stop element shall not be reduced by more than 12.5% for the basic signalling rate range (or 25% for the optional extended signalling rate range) to allow for overspeed in the transmitting terminal. The nominal length of the start and data elements for all characters shall be the same. + +2 Recommendation V.14 (03/93) + +NOTE – Equipments exists in the field which delete stop elements more frequently than specified in 7.1.1 and 7.1.2. However, in these equipments there will always be at least one additional inserted stop element between deleted stop elements. + +## **7.3 Break signal** + +### **7.3.1 Transmitter** + +If the converter detects $M$ to $2M + 3$ bits all of “start” polarity, where $M$ is the number of bits per character in the selected format, the converter shall transmit $2M + 3$ bits of “stop” polarity. If the converter detects more than $2M + 3$ bits all of “start” polarity the converter shall transmit all these bits as “start” polarity. + +NOTE – The converter must receive at least $2M$ bits of “stop” polarity after the “start” polarity break signal in order to ensure that it regains the character synchronism. + +### **7.3.2 Receiver** + +The $2M + 3$ or more bits of “start” polarity received from the transmitting modem shall be transferred to the output of the converter, and the character synchronism shall be regained from the following “stop” to “start” transition. + +NOTE – In some earlier implementations an uninitiated NUL character may precede the break signal at the output of the converter when no measures have been taken to prevent this. + +## **7.4 Tandem operation** + +Tandem operation between two ends comprising async-to-sync conversions can be established only by using cascaded synchronous bearer channels. + +## **7.5 Testing facilities** + +All the tests recommended in the relevant Recommendations can be performed in asynchronous operation as well, where this converter is used, with the exception of self test end-to-end. + +# Annex A + +## Inclusion of an async-to-sync converter into a synchronous DCE + +(This annex forms an integral part of this Recommendation) + + + +Block diagram of an async-to-sync converter within a synchronous DCE. A DTE (Data Terminal Equipment) is connected to a DCE (Data Communications Equipment) box. The DTE sends data 103 to the DCE and receives data 104 from the DCE. Inside the DCE box, there is an 'Async-to-sync converter' block. A switch labeled 'SY' (Synchronous mode) is connected to the converter. The converter has four data paths: 'TD' (Transmitted data) going to 'Sync, Signal converter, etc.', 'TDC' (Transmitter signal element timing) going to the converter, 'RDC' (Receiver signal element timing) going to the converter, and 'RD' (Received data) going to the converter. The DCE box is labeled 'T1400180-93/d01'. + +| | | +|-----|---------------------------------------------------------------------------------------------------------------------------------------------| +| 103 | Transmitted data; data input to the DCE | +| TD | Transmitted data; the synchronous output of the converter following the async-to-sync conversion of start-stop characters to be transmitted | +| TDC | Transmitter signal element timing; internal timing information for the generation of synchronous transmitted data | +| RDC | Receiver signal element timing; internal timing information associated with synchronous received data | +| RD | Received data; the input of the converter for the restoration of start-stop characters | +| 104 | Received data; data output from the DCE | +| SY | Synchronous mode; selection of the required mode of operation (asynchronous or synchronous) | + +FIGURE A.1/V.14 + +NOTE – Other interchange circuits which are provided are not involved in the operation of the async-to-sync converter but must comply with the requirements of the relevant DCE Recommendations including the conditions of the timing circuits (i.e. 113, 114 and 115) during both the asynchronous modes of operation. \ No newline at end of file diff --git a/marked/V/T-REC-V.140-200501-I_PDF-E/raw.md b/marked/V/T-REC-V.140-200501-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..1f5f72d12fd6f65978a559e2f5a9085c23e1a82d --- /dev/null +++ b/marked/V/T-REC-V.140-200501-I_PDF-E/raw.md @@ -0,0 +1,1318 @@ + + +I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n + +# ITU-T + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +## V.140 + +(01/2005) + +SERIES V: DATA COMMUNICATION OVER THE +TELEPHONE NETWORK + +Interworking with other networks + +--- + +**Procedures for establishing communication +between two multiprotocol audiovisual +terminals using digital channels at a multiple of +64 or 56 kbit/s** + +ITU-T Recommendation V.140 + +# ITU-T V-SERIES RECOMMENDATIONS DATA COMMUNICATION OVER THE TELEPHONE NETWORK + +| | | +|-------------------------------------------------------|--------------------| +| General | V.1–V.9 | +| Interfaces and voiceband modems | V.10–V.34 | +| Wideband modems | V.35–V.39 | +| Error control | V.40–V.49 | +| Transmission quality and maintenance | V.50–V.59 | +| Simultaneous transmission of data and other signals | V.60–V.99 | +| Interworking with other networks | V.100–V.199 | +| Interface layer specifications for data communication | V.200–V.249 | +| Control procedures | V.250–V.299 | +| Modems on digital circuits | V.300–V.399 | + +*For further details, please refer to the list of ITU-T Recommendations.* + +# ITU-T Recommendation V.140 + +# Procedures for establishing communication between two multiprotocol audiovisual terminals using digital channels at a multiple of 64 or 56 kbit/s + +## Summary + +This Recommendation describes a standardized method for automatic mode negotiation, detection of bit alignment, and confirmation of subchannel connectivity for multimedia terminals on digital networks. This new protocol provides backward compatibility with existing standards and creates an extensible mechanism to negotiate future protocols. + +The two primary benefits from implementing this Recommendation are: + +- 1) improved reliability in completing calls and successfully establishing multimedia communications, since peculiar network characteristics (such as "restricted" networks) that interfere with call establishment and protocol negotiations are automatically handled by V.140 procedures; and +- 2) for terminals that support multiple communication modes, an automatic means of selecting modes. + +Principal features of this Recommendation include the ability to find bit alignment, detect remote network type, and perform in-band testing of channel characteristics; a flexible and extensible capability exchange and mode selection facility is also built-in. + +V.140 procedures apply to every channel of a multi-channel call and begin following establishment of the end-to-end digital connection, and before any multimedia or other communication protocols are initiated. The procedures are divided into three phases: + +- Phase 1 – Send/search for V.140 signature (note that V.8/V.8 *bis*, voice, and H.221 FAS, or any subset of these may be simultaneously transmitted). If such signature is detected, proceed to: +- Phase 2 – Characterize the digital connection (64 vs 56 kbit/s, detect octet/septet alignment), and diagnose any odd characteristics of the network, (i.e., it could be restricted, that is, it transfers only 7 of 8 bits to the far-end). Once this is complete, +- Phase 3 – Exchange mode capabilities (similar to V.8 *bis*) and select desired operation mode. Modes can include voice communications, multimedia communications, and channel aggregation protocols, but capabilities are kept simple, given that the purpose of this Recommendation is only to select a particular protocol, not to determine all of the parameters related to that protocol (which can typically be determined using the protocol itself). + +The Phase 1 procedures have been designed to allow simultaneously signalling of other protocols, such as H.320, to minimize the amount of time lost in beginning communications if a terminal that implements V.140 finds itself communicating with a terminal that does not. + +Following Phase 3, a terminal can immediately begin procedures associated with the selected operation mode. + +This revised version incorporates corrections to errors noted between the original approval in February 1998 until November 2004. In particular, the bit order illustrated in Figure 11 has been corrected to match the body text, and in Annex A incomplete ASN.1 syntax has been restored and references to multilink operation according to Annex F/H.324 have been added. + +###### Source + +ITU-T Recommendation V.140 was approved on 8 January 2005 by ITU-T Study Group 16 (2005-2008) under the ITU-T Recommendation A.8 procedure. + +## FOREWORD + +The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. + +The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. + +In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. + +### NOTE + +In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. + +## INTELLECTUAL PROPERTY RIGHTS + +ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. + +As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. + +© ITU 2005 + +All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. + +## CONTENTS + +| | Page | +|--------------------------------------------------------------------------------|-------------| +| 1 Introduction and scope..... | 1 | +| 2 References..... | 1 | +| 3 Definitions ..... | 2 | +| 4 Abbreviations..... | 3 | +| 5 Conventions ..... | 3 | +| 6 Overview ..... | 4 | +| 6.1 Phase 1 – V.140 signature transmission and acquisition..... | 4 | +| 6.2 Phase 2 – Channel characterization..... | 4 | +| 6.3 Phase 3 – Capability exchange and mode selection ..... | 5 | +| 6.4 Using V.140 to switch among multimedia operation modes ..... | 5 | +| 6.5 Interoperability with terminals that do not support V.140 ..... | 5 | +| 6.6 Interworking with PSDSNs ..... | 6 | +| 7 Network types..... | 6 | +| 8 Signals ..... | 7 | +| 8.1 Data stream model..... | 7 | +| 8.2 Phase 1 – V.140 signature block and compatible protocol field ..... | 8 | +| 8.3 Phase 2 – Alignment probing ..... | 12 | +| 8.4 Phase 3 signals..... | 15 | +| 8.5 Phase 3 HDLC framing ..... | 17 | +| 9 Procedures ..... | 19 | +| 9.1 Channel establishment..... | 19 | +| 9.2 Phase 1 – Signature transmission and acquisition..... | 20 | +| 9.3 Phase 2 – Determination of network characteristics and bit alignment ..... | 22 | +| 9.4 Phase 3 – Role arbitration, capability exchange, and mode selection..... | 26 | +| 9.5 Entering selected mode..... | 28 | +| 10 Resuming V.140 from a selected mode..... | 28 | +| Annex A – ASN.1 definition of Phase 3 PDU values..... | 29 | + + + +# ITU-T Recommendation V.140 + +## **Procedures for establishing communication between two multiprotocol audiovisual terminals using digital channels at a multiple of 64 or 56 kbit/s** + +# **1 Introduction and scope** + +This Recommendation defines automatic mode negotiation and selection for multiprotocol audiovisual terminals connected to digital networks such as the ISDN. The procedures in this Recommendation are intended to avoid interference with those of pre-existing Recommendations. + +The procedures in this Recommendation automatically determine network connectivity and bit alignment between terminals. Also, they enable prompt and accurate negotiation of a common mode of operation when one or both terminals support multiple protocols for audiovisual communication. For example, a terminal might support H.320, H.324 over voiceband modem, and H.323 over ISDN; in this case, the procedures in this Recommendation would be used to negotiate a common protocol, e.g., H.323. Once a mode is selected, further negotiations as recommended for that mode may use information derived from V.140 negotiations, if applicable. + +V.140 procedures can also be used to provide an optional initial voice telephony mode before proceeding to multimedia telephony, and to switch from one multimedia telephony mode to another, or back into voice telephony mode. + +The means by which digital channels are established between terminals are outside the scope of this Recommendation (see ITU-T Rec. H.200/AV.420). Information regarding the nature of the endpoint terminals available from D-channel signalling may be useful in further accelerating V.140 negotiations; use of such information is for further study. + +The procedures of this Recommendation concern only the flow of signals along the fixed digital paths used for the transport of audiovisual content during the call, at integer multiples of 64 kbit/s (or 56 kbit/s in certain networks). + +# **2 References** + +The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. + +- ITU-T Recommendation G.711 (1988), *Pulse code modulation (PCM) of voice frequencies*. +- ITU-T Recommendation H.221 (2004), *Frame structure for a 64 to 1920 kbit/s channel in audiovisual teleservices*. +- ITU-T Recommendation H.242 (2004), *System for establishing communication between audiovisual terminals using digital channels up to 2 Mbit/s*. +- ITU-T Recommendation H.320 (2004), *Narrow-band visual telephone systems and terminal equipment*. +- ITU-T Recommendation H.324 (2002), *Terminal for low bit-rate multimedia communication*. + +- ITU-T Recommendation V.8 (2000), *Procedures for starting sessions of data transmission over the public switched telephone network*. +- ITU-T Recommendation V.8 bis (2000), *Procedures for the identification and selection of common modes of operation between data circuit-terminating equipments (DCEs) and between data terminal equipments (DTEs) over the general switched telephone network and on leased point-to-point telephone-type circuits*. +- ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002, *Information technology – Abstract Syntax Notation One (ASN.1): Specification of basic notation*. +- ITU-T Recommendation X.691 (2002) | ISO/IEC 8825-2:2002, *Information technology – ASN.1 encoding rules: Specification of Packed Encoding Rules (PER)*. +- ISO/IEC 3309:1993, *Information technology – Telecommunications and information exchange between systems – High-level data link control (HDLC) procedures – Frame structure*. +- ISO/IEC 13871:1995, *Information technology – Telecommunications and information exchange between systems – Private telecommunications networks – Digital channel aggregation*. + +# 3 Definitions + +This Recommendation defines the following terms: + +- 3.1 56C interface:** A 56 kbit/s network interface which transfers all bits to the far-end. +- 3.2 64C interface:** A 64 kbit/s network interface which transfers all bits to the network. +- 3.3 64R interface:** A 64 kbit/s network interface which transfers 7 of each 8 bits to the far-end, for a net throughput of 56 kbit/s. +- 3.4 acquire:** To detect a signal a sufficient number of times to meet the specified acquisition criteria. +- 3.5 aligned channel:** A channel for which network byte timing is available to the terminal. Ordinarily, an aligned channel is needed to transport unframed G.711 voice telephony. Network interfaces which do not pass network byte timing, such as V.35 interfaces, cause the terminal to operate as if connected to a non-aligned channel. +- 3.6 byte:** A septet for networks with either a 56C or 64R interface. Also, an octet for networks with a 64C interface. +- 3.7 detect:** To receive a given signal a single time. +- 3.8 octet:** A group of 8 bits. For Phases 1 and 2, if on an aligned channel, each new octet begins at the time specified by network timing. +- 3.9 protocol data unit (PDU):** An HDLC frame carrying a Phase 3 message. +- 3.10 public switched data service network (PSDSN):** A 56 kbit/s public switched data service network, for example the "Switched-56" network in the United States as specified by TIA/EIA-596. Such a network may be sensitive to emulation of escape codes by data entering the network via a 64C interface. +- 3.11 restricted channel:** A channel carried on a network whose B-channels are effectively restricted to 56 kbit/s, or whose channels at $H_0$ or higher are restricted by ones-density considerations. This can be because the terminal is on a 56C interface or a 64R interface or because of the nature of the network. + +**3.12 round-trip:** Given two terminals, A and B, connected via an ISDN, a round-trip is the transmission via the ISDN of a message from terminal A to terminal B and then from terminal B to terminal A; it is generally assumed that the time required to process and otherwise manipulate the message is negligible compared to the time required for transmission and propagation. + +**3.13 reflected signature pattern (RSP):** A bit pattern transmitted during Phase 2 that is computed from the bit pattern in a particular subchannel as received from a remote terminal. RSP is transmitted in the same subchannel in which it is received to signal the alignment of subchannels received at the terminal. + +**3.14 septet:** A group of 7 bits. If on an aligned channel, each new septet begins at the time specified by network timing. + +**3.15 signature pattern (SP):** A bit pattern transmitted within an individual subchannel to signal the presence of V.140 support and to permit determination of subchannel alignment and continuity. + +**3.16 subchannel:** The bits in a particular bit position of a sequence of bytes. Bits within a byte are numbered 1, 2, 3, 4, ... in order of decreasing significance. The number of the subchannel is the same as the number of the bit position. For example, the sequence of bits in bit position 4 in successive bytes form the bitstream corresponding to subchannel 4. + +**3.17 terminal:** Any of several types of endpoint devices connected to a digital network, including digital terminal equipment and Multipoint Control Units (MCUs). + +# 4 Abbreviations + +This Recommendation uses the following abbreviations: + +| | | +|-------|----------------------------------------------| +| BC | Bearer Capability | +| CPF | Compatible Protocol Field | +| FCS | Frame Check Sequence | +| GSTN | General Switched Telephone Network | +| HLC | High-Level Capability | +| ISDN | Integrated Services Digital Network | +| PCM | Pulse Code Modulation (per ITU-T Rec. G.711) | +| PDU | Protocol Data Unit | +| PSDSN | Public Switched Data Service Network | +| RSP | Reflected Signature Pattern | +| SP | Signature Pattern | +| UDI | Unrestricted Digital Information | + +# 5 Conventions + +The word "shall" is used in this Recommendation to specify a mandatory requirement. + +The word "should" is used in this Recommendation to specify a suggested, but not required, course of action. + +The word "may" is used in this Recommendation to specify an optional course of action, without expressing a preference. + +References in this Recommendation to specific ASN.1 message structures are presented in **this typeface**. + +# 6 Overview + +The procedures involve three phases: + +- Phase 1 – Send/search for V.140 signature (note that V.8/V.8 *bis*, voice, and H.221 FAS, or any subset of these may be simultaneously transmitted). If signature is detected, proceed to: +- Phase 2 – Characterize digital connection (64 vs 56 kbit/s, detect octet/septet alignment). +- Phase 3 – Exchange mode capabilities (similar to V.8 *bis*) and select desired operation mode. + +Once Phase 3 is complete, the selected mode (H.320, H.324, voice, etc.) is entered and normal call startup proceeds. + +Each phase should take little more than one round-trip time to complete, so the complete V.140 procedure should finish in little over 3½ round-trip times. Under typical circumstances (an intracontinental call via a 64 kbit/s clear interface), less than 1 second will be added to call startup. + +If no "signature" is detected, this indicates that the far-end does not support V.140. The terminal then falls back to any other non-V.140 protocol supported, such as H.320 (if H.221 FAS is detected) or V.8/V.8 *bis* GSTN modes (if V.8/V.8 *bis* is detected), or voice telephony. + +These procedures are designed so that terminals can transition from one phase of V.140 to the next at different times without ill effects: the timing of such transitions does not need to be precisely synchronized between terminals. + +## 6.1 Phase 1 – V.140 signature transmission and acquisition + +Phase 1 begins with the establishment of the end-to-end digital connection. + +A repeating 80-bit pattern containing the V.140 signature is transmitted. The purpose of the signature is to indicate to the far-end that this terminal implements V.140, and is capable of proceeding to the later phases. + +The signature has special characteristics. It is transmitted in the low-order bits of each byte to minimize the disruption of G.711 audio and permit simultaneous 48 kbit/s G.711 audio operation. + +These characteristics make it possible for the V.140 terminal to signal its signature while also sending GSTN modem tones and H.320 signals for compatibility with existing GSTN and H.320 ISDN terminals (see 6.5), as well as carrying normal speech telephony without startup delay. + +If the V.140 signature is detected in received data, this indicates that the far-end also supports V.140. The terminal then mutes received audio and enters Phase 2. + +If, after a time-out, the V.140 signature has not been found, the terminal may proceed to any other non-V.140 protocol it supports. If it was also searching for other protocols while looking for the V.140 signature, it may have already detected the far-end's ability to use these modes, and so has not lost any time starting these protocols. + +Otherwise, the terminal can continue the call as a voice telephone call, or can initiate another non-V.140 protocol. + +## 6.2 Phase 2 – Channel characterization + +There are a variety of national digital network types and interfaces in use. These include 64 and 56 kbit/s networks, and networks and interfaces which do or do not provide octet (or septet) timing. Even between two terminals with 64 kbit/s ISDN connections with network octet timing, it is possible on some national networks to have an intervening 56 kbit/s link. The nature of the end-to-end digital link, including rate and bit alignment, must be confirmed before the link can be used for multimedia communication. + +Upon entering Phase 2, each terminal probes the channel to determine the relative octet (if 64 kbit/s) or septet (if 56 kbit/s) alignment between the terminals. This is accomplished using Signature Patterns (SP) that are transmitted independently in each of the eight bit positions on the line. + +The bit position in which each SP appears at the receiver tells the receiver about relative alignment between transmitter and receiver. After the SP is detected, each receiver reflects its received SP back to the transmitter. Each terminal can then determine bit alignment and any network restriction for each direction of transmission. + +Once this procedure is complete, the terminals proceed to Phase 3. + +## **6.3 Phase 3 – Capability exchange and mode selection** + +In Phase 3, the two terminals exchange mode capabilities and select a mode. + +Using the entire 64 (or 56) kbit/s bandwidth, each terminal sends an HDLC-framed message containing a simple list of its capabilities (detailed capability exchange is left to the procedures of the selected mode). One terminal, normally the calling terminal, then selects a single mode from the list. + +The terminal which would ordinarily choose the mode can instead send a **youChoose** message to the far-end, requiring that the other end decide. This can be useful for situations where the calling terminal does not know the intended purpose of the call. + +Once Phase 3 is complete, the terminals go directly to the selected mode. + +## **6.4 Using V.140 to switch among multimedia operation modes** + +These procedures may be used to switch from one multimedia telephony mode to another, or back into voice telephony mode, by re-starting the Phase 3 procedures after termination of a previous mode. + +Also, Phase 1 V.140 procedures may be used in a "late-start" mode, after a period of G.711 voice telephony. + +## **6.5 Interoperability with terminals that do not support V.140** + +In order to support interoperability with existing terminals that do not support V.140, the Phase 1 V.140 signature has been designed to accommodate simultaneous signalling of other compatible protocols. The procedures given below specify how to use the facilities in V.140 to promote interoperability with particular protocols. + +A terminal that is attached to an aligned channel and supports G.711 audio: + +- shall transmit G.711 audio truncated to 6 bits during Phase 1 (see 8.2.1). + +A terminal that supports V.140 and H.320: + +- should transmit signals for H.320 operation as defined in ITU-T Rec. H.221 during Phase 1 of V.140 (see 8.2.1 and 8.2.2); +- should not respond to any signals defined by H.320 (i.e., should not complete Sequence A) until it fails to detect the V.140 Phase 1 signature from the far-end terminal. + +A terminal that supports GSTN modem operation (e.g., as defined in ITU-T Rec. V.34): + +- should transmit signals for GSTN modem operation as defined by V.8 or V.8 *bis* during Phase 1 of V.140 (see 8.2.2); +- should not respond to any signals defined by V.8 or V.8 *bis* until it fails to detect the V.140 Phase 1 signature from the far-end terminal. + +A terminal that supports ISO/IEC 13871: + +- should search for received signals as defined by ISO/IEC 13871 during Phase 1 of V.140 in order to determine if the far-end terminal supports ISO/IEC 13871 but does not support V.140; +- should not respond to any such signals until it fails to detect the V.140 Phase 1 signature from the far-end terminal. + +## 6.6 Interworking with PSDSNs + +Experience indicates that when a call is made from a 64 kbit/s ISDN to some Public Switched Data Service Networks (PSDSN), the low-order bit of each ISDN octet is transported without modification from the ISDN to the PSDSN. This bit is often used by PSDSN devices, such as Channel Service Units (CSUs), for in-band signalling of supervisory messages from the network to the CSU. Under some circumstances, bit values of zero in this position activate features of the CSU leading to loopback of the data stream, call termination, or entry of the CSU into a test mode. In the United States, the code values used for supervisory functions are standardized in TIA/EIA-596. + +The procedures given in this Recommendation have been designed to avoid emulation of PSDSN supervisory messages. In certain cases, particular octet values are either mandated or forbidden for this reason. + +# 7 Network types + +This Recommendation addresses terminals connected to the following types of digital network interfaces: + +- 64 kbit/s clear interfaces (64C) and restricted interfaces (64R) – variants of the same interface; +- 56 kbit/s clear interfaces (56C); +- $H_0$ interfaces ( $H_0$ ); +- $H_{11}$ interfaces ( $H_{11}$ ); +- $H_{12}$ interfaces ( $H_{12}$ ). + +A terminal cannot determine if a 64 kbit/s interface is 64C or 64R without using these procedures, since the clear or restricted characteristic is a result of a particular network route and may change from one call to the next. In effect, 64R and 64C are variants of the same interface. + +The terminal can be connected to only one of the five network types listed at any particular time. The terminal will know which of the five digital network interfaces it is using. + +In every case, the terminal implementing these procedures shall have direct access to and control of the network interface. For example, it is acceptable to use a digital terminal adapter as an interface to the network, but not a channel aggregation device based upon the protocol defined by ISO/IEC 13871 that does not also implement the procedures of this Recommendation. + +NOTE – The terminal may use these procedures to negotiate the subsequent use of ISO/IEC 13871 and other channel aggregation protocols, but the procedures of this Recommendation must be executed first of all. + +Each network type may or may not have byte-timing alignment from the network. + +The procedures of this Recommendation shall be used on each digital channel of every call, including digital voice-only calls, as said channel becomes available for use. + +64C interfaces transfer all bits to the far-end, at a rate of 64 kbit/s. + +64R interfaces locally interface at 64 kbit/s, but transfer 7 of each 8 bits to the far-end, for a net throughput of 56 kbit/s. One bit in each 8 is not transferred by the network. 64R interfaces are not specifically addressed in the procedures of Phase 1 because a terminal may not be aware whether it is connected to a 64C or 64R interface; however, the procedures of Phase 2 shall be used by terminals to identify which bit of the 8 is not being transferred to the far-end. Once terminals know which bit position in each octet is not being transferred, terminals shall ensure that valid data is never placed in said bit position, i.e., that bit shall be skipped. + +Terminals on 64R interfaces shall follow the procedures for 64C terminals, except that if a terminal has a priori information that it is on a 64R interface, and if it has network byte timing alignment, it shall fill subchannel 8 with binary ONES at all times, and otherwise follow the procedures for 56C interfaces. + +56C interfaces transfer all bits to the far-end, at a rate of 56 kbit/s. + +An $H_0$ , $H_{11}$ or $H_{12}$ channel may be regarded as consisting of a number of 64 kbit/s Time-Slots (TS), as defined and numbered in ITU-T Rec. H.221. The lowest-numbered of these TS shall be used by terminals to transmit the various signals described in this Recommendation; however, any terminal attempting to receive such signals shall search for them in any and all TS. The results of the procedures described in this Recommendation apply to all TS. + +The procedures to be followed for connections that consist of multiple 64 kbit/s B-channels interworking with an $H_0$ , $H_{11}$ or $H_{12}$ channel or multiple $H_0$ channels interworking with an $H_{11}$ or $H_{12}$ channel are for further study. + +# 8 Signals + +## 8.1 Data stream model + +All signals for Phases 1 and 2 are defined using a byte-oriented model of the data stream (as is used in ITU-T Rec. H.221). In the case of 64C interfaces, the data stream is modelled as a series of octets, whereas in the case of 56C interfaces, the data stream is modelled as a series of septets. + +Figure 1 illustrates subchannels within the byte-oriented data stream carrying example 8-bit values "1, 2, 3, 4, 5". 56C interfaces send only subchannels 1 through 7; this is illustrated through shading of subchannel 8 in Figure 1 and subsequent figures. All references in this Recommendation to transmission of information in subchannel 8 apply only to 64C interfaces. + +For each byte, subchannel 1 holds the most significant bit of G.711 audio samples in ISDN telephony, and is the first bit transmitted by the network. Subchannel 8 holds the least significant bit of G.711 audio samples, and is the last bit transmitted by the network. + +For signals carried within a single subchannel, bits are sent starting with the most significant bit of the signal; signals are shown in vertical columns (each column representing a subchannel) with the most significant bit at the top of the column. + +| Byte number | (MSB)
Subchannel 1 | Subchannel 2 | Subchannel 3 | Subchannel 4 | Subchannel 5 | Subchannel 6 | Subchannel 7 | (LSB)
Subchannel 8 | +|-------------|-----------------------|--------------|--------------|--------------|--------------|--------------|--------------|-----------------------| +| n | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | +| n + 1 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | +| n + 2 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | +| n + 3 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | +| etc. | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 1 | + +Figure 1/V.140 – Illustration of data stream model + +## 8.2 Phase 1 – V.140 signature block and compatible protocol field + +An 80-byte Phase 1 signal is repeatedly transmitted during Phase 1. There are two forms of the Phase 1 signal: one that shall be transmitted by terminals attached to aligned channels and another that shall be transmitted by terminals attached to non-aligned channels. The differences between the two forms of the Phase 1 signal are irrelevant to terminals that receive said signal. + +### 8.2.1 Terminals attached to aligned channels + +Terminals attached to aligned channels have some flexibility in determining certain characteristics of the signal to be transmitted during Phase 1. Within the Phase 1 signal, subchannels 1-6 shall carry PCM audio according to G.711, truncated to 6 bits, unless the terminal does not support G.711 audio. Any valid audio signal may be transmitted, including speech or GSTN modem signalling such as V.8 or V.8 *bis*. + +If the terminal does not support G.711 audio, subchannels 1-6 shall carry all binary ONES. + +Subchannel 7 shall carry a "signature block" consisting of 80 bits. Bits 1 through 16 shall contain a "Compatible Protocol Field" (CPF), which carries either all binary ONES or a compatible protocol. The CPF is followed by the 8 bit "Signature Pattern" (SP) field defined for that subchannel, i.e., SP-G (see 8.2.3), which is followed by a fill pattern of 8 bits set to binary ONE. SP is repeated four times in the subchannel, as is the fill pattern. The 16-bit CPF, combined with four repetitions each of the SP and the fill pattern complete the 80 bit signature block. V.140 signature blocks shall be transmitted in subchannel 7 only. + +Subchannel 8 shall also carry a block of 80 bits. Like subchannel 7, bits 1 through 16 shall contain a CPF. However, the remaining bits shall carry all binary ONES. + +NOTE – The CPF is primarily intended to carry H.221 FAS and BAS signalling. However, the provision of a CPF in both subchannels 7 and 8 does not imply that H.221 FAS and BAS (or some other compatible protocol) should be sent in both subchannels simultaneously. The CPF merely provides a reserved portion of the Phase 1 signal for the use of other protocols. Use of CPF by a compatible protocol should comply with the Recommendation for that protocol. Any portion of any CPF which is not used to transmit a compatible protocol should carry all binary ONES. + +In order to avoid emulation of PSDSN supervisory messages, terminals that transmit octets and are attached to aligned channels shall check each of the first 16 octets of the 80-octet Phase 1 signal to determine if that octet has one of the values listed in the column of Table 1 labelled "Forbidden" Value. If so, that octet shall not be transmitted; instead, it shall be replaced by the corresponding value in the column of Table 1 labelled "Safe" Replacement. All remaining octets of the 80-octet Phase 1 signal have the low-order bit set to binary ONE by definition and therefore cannot take on any of the "Forbidden" values. + +**Table 1/V.140 – Translation of byte values for "safe" transmission of audio** + +| "Forbidden" value | "Safe" replacement | +|-------------------|--------------------| +| 2A | 28 | +| 2E | 30 | +| AA | A8 | +| AC | A8 | +| AE | B0 | + +Subchannel 8 also carries a repeated 80-bit pattern which shall be aligned with the 80-bit pattern in subchannel 7. Bits 1 through 16 carry a CPF, like subchannel 7, but the remaining bits carry all binary ONES. + +The V.140 signature block is always 80 bits in length, regardless of the subchannel in which it is signalled. + +While transmitting the Phase 1 signal, terminals on aligned channels should concurrently transmit compatible protocols, such as H.221 framing, G.711 audio, and modem modulations within G.711 audio. Subchannels 7 and 8 are used because they occupy the least significant bit positions of G.711 audio, and so will be minimally disruptive of audio signals. + + + +The diagram illustrates the V.140 Phase 1 signal structure, organized by bit number (subchannel) from MSB (1) to LSB (8). The structure is divided into three main sections: + +- Bits 1-6: G.711 "safe" audio**: Occupies the top row of the first six subchannels. +- Bits 1-6: G.711 audio**: Occupies the bottom seven rows of the first six subchannels. +- Compatible protocol field**: Occupies the top row of subchannels 7 and 8 (shaded). +- SP-G and All 1s**: Subchannels 7 and 8 contain alternating SP-G and All 1s fields in the bottom seven rows. + +Annotations on the right side indicate the total size and repetition patterns: + +- 16 septets/octetes**: Points to the top row (Compatible protocol field). +- 4 repetitions of SP-x/ fill pattern**: Points to the bottom seven rows of subchannels 7 and 8. +- 64 septets/octetes total**: Points to the entire bottom seven rows of subchannels 7 and 8. + +A vertical arrow on the left indicates the total length of **80 septets or octets** for the first six subchannels. + +V.140\_F02 + +Diagram of the V.140 Phase 1 signal structure showing bit positions 1-8 across subchannels, with fields for G.711 audio, compatible protocol fields, and SP-G/All 1s patterns. + +**Figure 2/V.140 – Phase 1 signal for terminals attached to aligned channels +(shaded bit position not present on 56C interfaces)** + +### 8.2.2 Terminals attached to non-aligned channels + +Terminals attached to non-aligned channels transmit a somewhat different Phase 1 signal from the one just described; these terminals shall not transmit G.711 audio at all. + +If the terminal transmits octets, the first 16 it transmits shall be chosen from those in Table 2. This selection of values accommodates all possible choices for the CPF, which is carried in bits 1 through 16 of subchannels 7 and 8. If the terminals transmits septets, bits 1 through 16 in subchannels 1 through 6 shall be set to binary ONE. + +**Table 2/V.140 – Safe values for transmission during +the first 16 bytes of the Phase 1 signal** + +| | +|----| +| F8 | +| FD | +| FE | +| FF | + +After the first 16 octets, the following pattern of 16 octets is repeated 4 times (hexadecimal codes are given): + +DD FF EE DD EE DD FF 00 FF FF FF FF FF FF FF FF + +This pattern contains the SP fields assigned to subchannels 7 and 8 (SP-G and SP-H) embedded within it (see 8.2.3). Terminals sending septets should simply drop the least significant bit of each hexadecimal code. + +The V.140 signature block is always 80 bits in length, regardless of the subchannel in which it is signalled. + +While transmitting the Phase 1 signal, terminals should concurrently transmit compatible protocols such as H.221 framing by transmitting the codes in Table 2 during the first 16 bytes of the Phase 1 signal to set appropriate values in the CPF. + + + +| MSB | | Bit number (subchannel) | | | | LSB | | +|------------------------------------------------------------------------|---|-------------------------|---|---|---|---------------------------|---------------------------| +| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | +| Safe values | | | | | | Compatible protocol field | Compatible protocol field | +| Special sequence (hex) incl. SP-G and SP-H:
DD FF EE DD EE DD FF 00 | | | | | | SP-G | SP-H | +| All 1s | | | | | | | | +| Special sequence (hex) incl. SP-G and SP-H:
DD FF EE DD EE DD FF 00 | | | | | | SP-G | SP-H | +| All 1s | | | | | | | | +| Special sequence (hex) incl. SP-G and SP-H:
DD FF EE DD EE DD FF 00 | | | | | | SP-G | SP-H | +| All 1s | | | | | | | | +| Special sequence (hex) incl. SP-G and SP-H:
DD FF EE DD EE DD FF 00 | | | | | | SP-G | SP-H | +| All 1s | | | | | | | | + +80 septets or octets + +16 septets/octets + +4 repetitions of SP-x/ fill pattern + +64 septets/octets total + +V.140\_F03 + +Diagram of Phase 1 signal structure for terminals attached to non-aligned channels. The diagram shows a sequence of 80 septets/octets (8 bytes) organized into 10 rows. Each row contains a 'Safe values' field (bits 1-6), a 'Compatible protocol field' (bits 7-8), and a 'Compatible protocol field' (bits 1-2). The 'Safe values' field is divided into two parts: 'Special sequence (hex) incl. SP-G and SP-H: DD FF EE DD EE DD FF 00' (bits 1-4) and 'All 1s' (bits 5-6). The 'Compatible protocol field' is divided into two parts: 'SP-G' (bits 1-2) and 'SP-H' (bits 3-4). The 'Compatible protocol field' is shaded. Annotations indicate that the shaded bit position is not present on 56C interfaces, and that the total length is 80 septets/octets, with 4 repetitions of SP-x/ fill pattern and 64 septets/octets total. + +**Figure 3/V.140 – Phase 1 signal for terminals attached to non-aligned channels +(shaded bit position not present on 56C interfaces)** + +### 8.2.3 Signature Pattern (SP) field + +The "SP" field is 8 bits in length and contains a unique pattern which depends upon the subchannel in which it is being transmitted. + +SP is transmitted within individual subchannels to signal the presence of V.140 support and to permit determination of subchannel alignment and end-to-end connectivity. + +The 8 SP values are uniquely distinguishable from each other so that if subchannel alignment is lost in the network, the receiver can determine the transmitter's subchannel alignment by finding particular SP values in received subchannels. + +The SP values are given in Table 3, and their transmission in the data stream is illustrated in Figure 4. + +**Table 3/V.140 – Signature pattern values** + +| Subchannel number | Signature pattern name | Signature pattern value | +|-------------------|------------------------|-------------------------| +| 1 | SP-A | 10101100 | +| 2 | SP-B | 01011010 | +| 3 | SP-C | 10110110 | +| 4 | SP-D | 01101100 | +| 5 | SP-E | 11011010 | +| 6 | SP-F | 10110100 | +| 7 | SP-G | 01101010 | +| 8 | SP-H | 11010110 | + +| Byte number | Subchannel 1 | Subchannel 2 | Subchannel 3 | Subchannel 4 | Subchannel 5 | Subchannel 6 | Subchannel 7 | Subchannel 8 | +|-------------|--------------|--------------|--------------|--------------|--------------|--------------|--------------|--------------| +| 1 | 1 | 0 | 1 | 0 | 1 | 1 | 0 | 1 | +| 2 | 0 | 1 | 0 | 1 | 1 | 0 | 1 | 1 | +| 3 | 1 | 0 | 1 | 1 | 0 | 1 | 1 | 0 | +| 4 | 0 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | +| 5 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | +| 6 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | +| 7 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | 1 | +| 8 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | + +**Figure 4/V.140 – Transmission of SP values in data stream** + +Only SP-G and SP-H are used in Phase 1. All eight SP values are used in Phase 2. + +## 8.3 Phase 2 – Alignment probing + +During Phase 2, terminals alternately transmit two fields, Field A and Field B. No other signals shall be transmitted during this phase; audio and any compatible protocol shall be turned off. Each field is 8 bytes in length, and each field is composed only of contiguous bytes. The terminal shall commence transmission of the Phase 2 signal immediately after it completes its final transmission of the Phase 1 signal (see Figure 5). + + + +MSB Bit number (subchannel) LSB + +1 2 3 4 5 6 7 8 + +Phase 1 signal + +Phase 2 signal + +V.140\_F05 + +Diagram illustrating the transition from Phase 1 to Phase 2 across 8 subchannels. The diagram shows two phases separated by a horizontal line. Phase 1 (top) has subchannels 1-5 as solid lines and 6-8 as dashed lines. Phase 2 (bottom) has subchannels 1-5 as dashed lines and 6-8 as solid lines. The labels 'Phase 1 signal' and 'Phase 2 signal' are centered in their respective sections. The top is labeled 'MSB' and 'Bit number (subchannel)' with bit numbers 1-8. The bottom is labeled 'LSB'. Wavy lines on the left and right indicate continuation. + +**Figure 5/V.140 – Transition from Phase 1 to Phase 2** + +Variation of the contents of Fields A and B during the subphases 2a, 2b, and 2c allow these fields to be used both as probing signals for a particular subphase and as acknowledgment of the far-end's most recent signal. + +Terminals on 56C interfaces shall transmit only subchannels 1 through 7 of Field A and Field B as presented in this clause. + +Phase 2 consists of three subphases: 2a, 2b, and 2c. + +### **8.3.1 Phase 2a – Initial values** + +In Phase 2a, Field A contains SP, as defined above, in all subchannels. + +NOTE – The values of SP are defined such that the last bit of the SP for every subchannel is set to binary ZERO. This feature can be used confirm where each SP begins in a subchannel. + +Field B contains all binary ONES in all subchannels. + +Figure 6 illustrates the Phase 2a signal, with Field A above the heavy line, and Field B below it. + +| Byte number | (MSB)
1 | 2 | 3 | 4 | 5 | 6 | 7 | (LSB)
8 | +|-------------|-------------|-------------|-------------|-------------|-------------|-------------|-------------|-------------| +| 1 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 2 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 3 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 4 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 5 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 6 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 7 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 8 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 9 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 10 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 11 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 12 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 13 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 14 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 15 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 16 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | + +**Figure 6/V.140 – Phase 2a signal** + +### 8.3.2 Phase 2b – After SP acquisition + +A transmitter switches to Phase 2b after it has acquired SP from the received Field A; the procedure for doing so is described in 9.3.1.2. + +In Phase 2b, Field A contains SP, as defined above, in all subchannels (unchanged from Phase 2a). + +Field B contains "Reflected Signature Pattern" (RSP) as defined by the procedures for computing RSP in 9.3.2.1. + +The actual value of RSP in Field B depends on the relative alignment of byte timing between the two terminals and the treatment of subchannels in the network between them. + +The Phase 2b signal is illustrated in Figure 7. + +| Byte number | (MSB)
1 | 2 | 3 | 4 | 5 | 6 | 7 | (LSB)
8 | +|-------------|-------------------------------------------|-------------|-------------|-------------|-------------|-------------|-------------|-------------| +| 1 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 2 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 3 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 4 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 5 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 6 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 7 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 8 | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| 9 | RSP as calculated from received SP | | | | | | | | +| 10 | RSP as calculated from received SP | | | | | | | | +| 11 | RSP as calculated from received SP | | | | | | | | +| 12 | RSP as calculated from received SP | | | | | | | | +| 13 | RSP as calculated from received SP | | | | | | | | +| 14 | RSP as calculated from received SP | | | | | | | | +| 15 | RSP as calculated from received SP | | | | | | | | +| 16 | RSP as calculated from received SP | | | | | | | | + +**Figure 7/V.140 – Phase 2b signal** + +### 8.3.3 Phase 2c – After RSP acquisition + +A transmitter switches to Phase 2c after it has acquired RSP from the received Field B. + +In Phase 2c, Field A contains all binary ONES (as a signal that RSP has been acquired). + +Field B contains "Reflected Signature Pattern" (RSP) as defined by the procedures for computing RSP in 9.3.2.1 (unchanged from Phase 2b). + +The Phase 2c signal is illustrated in Figure 8. + +| Byte number | (MSB)
1 | 2 | 3 | 4 | 5 | 6 | 7 | (LSB)
8 | +|-------------|-------------------------------------------|---|---|---|---|---|---|------------| +| 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 2 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 3 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 4 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 5 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 6 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 7 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 8 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| 9 | RSP as calculated from received SP | | | | | | | | +| 10 | RSP as calculated from received SP | | | | | | | | +| 11 | RSP as calculated from received SP | | | | | | | | +| 12 | RSP as calculated from received SP | | | | | | | | +| 13 | RSP as calculated from received SP | | | | | | | | +| 14 | RSP as calculated from received SP | | | | | | | | +| 15 | RSP as calculated from received SP | | | | | | | | +| 16 | RSP as calculated from received SP | | | | | | | | + +Figure 8/V.140 – Phase 2c signal + +## 8.4 Phase 3 signals + +Phase 3 signals are used to establish authority for mode selection, to exchange capabilities, to select a common operation mode from among the expressed capabilities, and to provide indications for abnormal termination of V.140. + +Phase 3 signals consist of HDLC-framed PDUs defined using ASN.1 syntax according to ITU-T Rec. X.680 and coded according to the packed encoding rules of ITU-T Rec. X.691. These PDUs are sent using the entire bit rate available on the channel. The actual PDUs are defined in Annex A. This clause describes the HDLC framing and semantics for each PDU. + +Phase 3 signals use a bit-oriented model of the channel. All bits of Phase 3 messages shall be transmitted bit-sequentially without regard to the interface type, and without regard to network byte timing alignment, with the following exception: if any bit positions within each byte of the channel are not being transferred to the far-end by the network (as determined by the Phase 2 procedures), the terminal shall insert a binary ONE at those bit positions so that they are skipped. The receiver of Phase 3 signals should perform the converse of the operations performed by the transmitter (see 9.3.4). + +During Phase 3, the following PDUs may be transmitted: + +- **roleAndCapability**; +- **youChoose**; +- **modeSelect**; +- **modeSelectAcknowledge**; +- **terminate**; +- **nonStandard**. + +The **nonStandard** PDU may be used to extend this set as needed. Although the meaning of non-standard messages is defined by individual organizations, equipment built by any manufacturer may signal any non-standard message, as long as the meaning of the message is known. + +Non-standard capabilities and modes may be issued using the **NonStandardParameter** structure. + +### 8.4.1 **roleAndCapability PDU** + +The **roleAndCapability** PDU transmitted by a terminal shall contain a declaration of the role taken by that terminal in establishing the network connection; a random value used for role arbitration when both terminals have taken the same role in establishing the network connection (e.g., for leased line connections); and a list of the capabilities for multimedia and other communication protocols available on that terminal. + +The **role** field of the **roleAndCapability** PDU takes one of three values: **answer**, **originate**, or **unknown**. The terminal shall assign the value of **originate** to the **role** field of any **roleAndCapability** PDU it transmits if the call was initiated at that terminal and the value of **answer** if the call was initiated at the other terminal. If the terminal lacks sufficient information to determine which end actually initiated the call, it shall assign the value of **unknown** to the **role** field. The value transmitted by the terminal in the **role** field shall be fixed for the duration of a network connection. The **arbitrationField** contains a 32-bit random number chosen using a random number generator with a uniform probability distribution. If a call consists of more than one digital channel, then the same **role** field and **arbitrationField** (random number) shall be selected and used in the Phase 3 procedures for all channels of that call. + +The **capabilitySet** field of the **roleAndCapability** PDU contains a sequence of one or more **Capability** structures, each expressing the terminal's ability to work in a particular multimedia or other communication protocol. The transmitter shall include the complete list of modes in which it is currently able to operate. The list of possible modes is defined in Annex A, and may be extended in the future. Capabilities shall be listed in order of preference, from most-preferred to least-preferred. + +NOTE – The terminal transmitting a **modeSelect** PDU is not required to take account of the order of preference of capabilities received from the far-end terminal, although it should do so. + +Some individual capabilities include additional sub-capability information. These indicate that the terminal is capable of using the stated sub-modes within the capability indicated. The far-end terminal may use this information to influence its choice of modes. + +### 8.4.2 **modeSelect PDU** + +The **modeSelect** PDU shall contain a single mode which has been selected from the far-end's **capabilitySet** as the mode of operation to follow completion of V.140 negotiation. The **modeSelect** PDU is structured differently than the **Capability** structure of the **roleAndCapability** PDU, since some individual modes include additional information. This information shall be used by the far-end terminal to set up the appropriate sub-mode as requested. + +### 8.4.3 youChoose PDU + +The **youChoose** PDU may be transmitted in place of the **modeSelect** PDU by a terminal which would otherwise choose the selected mode. It indicates that that terminal has deferred selection to the other terminal. + +### 8.4.4 modeSelectAcknowledge PDU + +The **modeSelectAcknowledge** PDU indicates reception and acceptance of a **modeSelect** PDU. + +### 8.4.5 terminate PDU + +The **terminate** PDU indicates abnormal termination of V.140 negotiations. The **terminate** PDU includes a cause field and optional fields with values as required for a particular cause field. + +## 8.5 Phase 3 HDLC framing + +Messages shall use the frame structure shown in Figure 9. + +NOTE – HDLC framing used in V.140 is similar to that in ITU-T Rec. V.8 *bis*. + + + +| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | | +|--------------------|---|---|---|---|---|---|---|---------| +| Flag | | | | | | | | Octet 1 | +| Flag | | | | | | | | 2 | +| 0 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | | +| 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0 | | +| 0 | 1 | 1 | 0 | 0 | 0 | 0 | 1 | | +| 0 | 1 | 1 | 0 | 0 | 1 | 0 | 0 | | +| Information field | | | | | | | | | +| FCS (first octet) | | | | | | | | N – 2 | +| FCS (second octet) | | | | | | | | N – 1 | +| Flag | | | | | | | | N | + +Figure 9/V.140 – Phase 3 message structure + +### 8.5.1 Format convention + +The basic format convention used for messages is illustrated in Figure 10. Bits are grouped into octets. The bits of each octet are shown horizontally and are numbered from 1 to 8. Octets are displayed vertically and are numbered from 1 to N. + +The octets are transmitted in ascending numerical order. Within an octet, bit 1 is the first bit to be transmitted. + +For the two-octet Frame Check Sequence (FCS) field, bit 1 of the first octet is the MSB and bit 8 of the second octet is the LSB (Figure 11). + + + +| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | | +|---|---|---|---|---|---|---|---|---------| +| | | | | | | | | Octet 1 | +| | | | | | | | | 2 | +| | | | | | | | | ... | +| | | | | | | | | N | + +Figure 10/V.140 – Format convention + +| 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | | +|----------------|---|---|---|---|---|---|-----------------|--------------------| +| 2 8 | | | | | | | 2 15 | 1st octet of field | +| 2 0 | | | | | | | 2 7 | 2nd octet of field | + +**Figure 11/V.140 – FCS mapping convention** + +### 8.5.2 Flag sequence + +Messages shall start and end with the standard HDLC flag octet (01111110) as defined in ISO/IEC 3309. Two flags shall be sent to begin each message (the use of two increases error resilience). One flag shall follow the FCS of each message. As a result, there shall be three flags between consecutive messages. + +### 8.5.3 Distinguishing sequence + +Following the sequence of two flag octets at the beginning of the message and preceding the information field, there shall be a four-octet sequence with the hexadecimal values 73 62 61 64. This sequence serves to distinguish this PDU format from others that use a similar HDLC framing structure. + +### 8.5.4 Information field + +The contents of the information field shall consist of an integral number of octets containing a single PDU structured in accordance with Annex A. PDUs shall be encoded from the ASN.1 by applying the packed encoding rules specified in ITU-T Rec. X.691 using the basic aligned variant. The bit string that results from the ASN.1 encoding shall be placed in the octet string in the information field in the order such that for each octet, the leading bit is placed in bit 1 and the trailing bit is placed in bit 8. + +### 8.5.5 Frame check sequence field + +The FCS field is 16 bits (2 octets) in length. As defined in ISO/IEC 3309, it shall be the one's complement of the sum (modulo 2) of: + +- the remainder of $x^k (x^{15} + x^{14} + x^{13} + x^{12} + x^{11} + x^{10} + x^9 + x^8 + x^7 + x^6 + x^5 + x^4 + x^3 + x^2 + x + 1)$ divided (modulo 2) by the generator polynomial $x^{16} + x^{12} + x^5 + 1$ , where *k* is the number of bits in the frame existing between, but not including, the last bit of the final opening flag and the first bit of the FCS, excluding bits (binary **ZEROs**) inserted for transparency; and +- the remainder of the division (modulo 2) by the generator polynomial $x^{16} + x^{12} + x^5 + 1$ , of the product of $x^{16}$ by the content of the frame existing between, but not including, the last bit of the final opening flag and the first bit of the FCS, excluding bits inserted for transparency. + +As a typical implementation at the transmitter, the initial content of the register of the device computing the remainder of the division is preset to all binary **ONES** and is then modified by division by the generator polynomial (as described above) on the information field. The one's complement of the resulting remainder is transmitted as the 16-bit FCS. + +As a typical implementation at the receiver, the initial content of the register of the device computing the remainder of the division is preset to all binary **ONES**. The final remainder, after multiplication by $x^{16}$ and then division (modulo 2) by the generator polynomial $x^{16} + x^{12} + x^5 + 1$ of the serial incoming protected bits and the FCS, will be 0001110100001111 ( $x^{15}$ through $x^0$ , respectively) in the absence of transmission errors. + +### 8.5.6 Transparency + +The transmitting terminal shall examine the contents of the information and FCS fields (everything between the opening and closing flags) and insert a binary **ZERO** after every sequence of five contiguous binary **ONES** to ensure that the flag octet is not simulated within the frame. The receiving + +terminal shall examine the contents of the frame between the opening and closing flags and discard any binary ZERO which directly follows five contiguous binary ONES. + +# 9 Procedures + +The general sequence of signal exchanges required for completion of the procedures in this Recommendation is shown in Figure 12. + + + +Figure 12/V.140 – 'Ladder' diagram of the sequence of signals and phases of V.140. The diagram shows a vertical timeline with a central vertical line. To the left of the line are 'Signals transmitted' and to the right are 'Signals received'. The sequence is as follows: 1. Phase 1: H.247 signature is transmitted. 2. Phase 2a: SP-G or SP-H is received. 3. Phase 2b: Field A = SP is transmitted, and Field B = RSP is received. 4. Phase 2c: Field A = 1 s and Field B = RSP are transmitted. 5. Phase 3: Field A = 1 s or HDLC Flags are received, and V.140\_F12 is transmitted. + +**Figure 12/V.140 – "Ladder" diagram of the sequence of signals and phases of V.140** + +All signals shall be transmitted repeatedly until acknowledged. Whenever one signal is changed to another, for example when moving from one phase or sub-phase to the next, the change shall only take place at an allowed boundary as defined for the signal prior to the change. The allowed boundaries are as follows: + +- Phase 1: the completion of the 80 byte Phase 1 signal. +- Phase 2: the completion of Field B. +- Phase 3: the completion of an HDLC frame. + +## 9.1 Channel establishment + +The end-to-end digital connection shall be established according to the procedures appropriate for the network in use, according to national standards. + +### 9.1.1 Interactions with ISDN D-channel signalling + +Terminals originating calls on the ISDN shall signal the ISDN Bearer Capabilities (BC) and High Level Capabilities (HLC) according to either the row marked "Attempt 1" or the row marked "Attempt 2" in Table 5. If the call is rejected by the network and the indicated Cause, as defined in ITU-T Rec. Q.850, is one of those listed in Table 4, the originating terminal shall automatically re-try the call attempt using different values of BC and HLC according to Table 5. Since this procedure incorporates a call re-try mechanism, terminals shall not use the bearer capability selection option. + +NOTE – The bearer capability selection option allows a calling terminal to encode two bearer capabilities in a setup message, such that the alternative bearer capability is automatically invoked in case the preferred bearer capability is unavailable or if interworking (e.g., to the PSTN) is encountered (see ITU-T Rec. Q.931). + +Originating terminals shall continue call attempts according to Table 5 until the BC value is no longer compatible with any desired mode of operation, or until reaching the end of the table. + +Terminals initiating a call on the ISDN should eliminate protocols from the Phase 3 capability set that are not appropriate given the BC and HLC signalled for the call. Similarly, answering terminals should disable all locally supported protocols inappropriate for the received values of BC and HLC, and should remove those protocols from the Phase 3 capability set. + +**Table 4/V.140 – List of causes that may indicate an incompatible BC +(see ITU-T Rec. Q.931)** + +| Cause No.
(from ITU-T Rec. Q.850) | Cause name
(from ITU-T Rec. Q.850) | +|----------------------------------------------|-----------------------------------------------| +| 18 | No user responding | +| 57 | Bearer capability not authorized | +| 58 | Bearer capability not presently available | +| 63 | Service or option not available, unspecified | +| 65 | Bearer service not implemented | +| 88 | Incompatible destination | + +**Table 5/V.140 – BC and HLC values for ISDN calls** + +| | BC (Information transfer capability) | HLC value | +|-----------|-----------------------------------------------------------|---------------------------------| +| Attempt 1 | Unrestricted digital information with tones/announcements | None, or per national standards | +| Attempt 2 | Unrestricted Digital Information (UDI) | None, or per national standards | +| Attempt 3 | UDI, rate adapted to 56 kbit/s | None, or per national standards | +| Attempt 4 | 3.1 kHz audio | None, or per national standards | +| Attempt 5 | Speech | None, or per national standards | + +## 9.2 Phase 1 – Signature transmission and acquisition + +If the procedures of V.140 are in use, an optional period of G.711 voice telephony may begin when the called party answers. In this mode, users have the opportunity to speak with one another before proceeding to multimedia telephony. During this period, the terminal shall continuously search for a Phase 1 signature from the far-end terminal. + +If the terminal is conditioned to go directly into digital communication mode, this optional period shall be bypassed, and the terminal shall proceed directly to Phase 1 immediately upon end-to-end network connection of the digital channel. If the terminal is conditioned for initial G.711 voice telephony mode, the terminal shall proceed to Phase 1 when either of the following conditions is met: + +- the user manually causes the terminal to initiate transmission of the Phase 1 signature; or +- the terminal detects a Phase 1 signature from the far-end terminal. + +### 9.2.1 Transmitter procedure + +In Phase 1, terminals shall repeatedly transmit the appropriate Phase 1 signal. The Phase 1 signal to be transmitted by a terminal attached to an aligned channel is described in 8.2.1. A somewhat different Phase 1 signal is to be transmitted by a terminal attached to a non-aligned channel, and is described in 8.2.2. + +In either case, the CPF field shall carry a compatible protocol or bits set to binary ONE. Such compatible protocol signals may be sent in order that far-end terminals of these types which do not support these procedures may initiate their negotiation. + +### 9.2.2 Receiver procedure + +The receiver shall search all received subchannels in the received Phase 1 signal, i.e., subchannels 1 to 8, for SP-G and SP-H. Presence of either of these signals indicates that the far-end supports V.140. + +The terminal may carry out any procedures (i.e., related to another protocol) during Phase 1 of V.140 that do not interfere with any phase of V.140. For example, while searching for SP, the receiver may search for signals conforming to any other protocols supported locally. However, the terminal shall proceed with another protocol only: + +- 1) if and when it is established that the far-end does not support V.140, as defined in 9.2.2.1; or +- 2) after selection of that protocol by the Phase 3 procedure. + +In addition, if the receiver is on an aligned channel, bits 1-6 of each byte may be decoded as audio according to ITU-T Rec. G.711 and delivered to the user while executing this procedure, so that voice telephony is established immediately upon connection of the circuit, if the far-end terminal supports voice telephony. + +If the receiver decodes G.711 audio, it shall automatically determine the proper G.711 law of the incoming audio, for example by using the procedures of Appendix I/G.725. Note that the G.711 law is allowed to be different in each direction. + +Terminals attached to non-aligned channels need not search for G.711 audio or modem tones (as defined in V.8 and V.8 *bis*, since such terminals cannot decode or otherwise use audio signals without a framing pattern (e.g., provided by ITU-T Rec. H.221). + +#### 9.2.2.1 Signature pattern (SP) acquisition criteria and time-out + +To acquire an SP (either SP-G or SP-H), the terminal shall attempt to detect, within any single subchannel, all four occurrences of that SP properly positioned within 3 contiguously received 80-bit Phase 1 signals. If the attempt is successful, the terminal shall enter Phase 2a. + +Since SP is included in the Phase 2a signal, the signature can still be acquired from a far-end terminal which has already entered Phase 2a. + +If SP acquisition does not occur within 2 to 8 seconds of connection of the digital channel, the receiver shall interpret this as an indication that the far-end terminal does not support V.140, and shall terminate V.140 procedures. The local terminal may then optionally disconnect the channel, or may optionally proceed with any other protocol supported by the terminal, such as voice telephony, H.320, HDLC-based protocols, or GSTN modem signalling such as V.8 or V.8 *bis*. + +NOTE 1 – There is a small probability ( $\sim 2^{-128}$ ) that a completely random signal could emulate the signature within the Phase 1 signal. This probability may be slightly higher if the signal is not completely random, i.e., if it is made up of G.711 audio or V.8/V.8 *bis* modem signals. + +NOTE 2 – Terminals that allow periods approaching the upper limit of the above range (i.e., 8 seconds) to elapse before terminating V.140 procedures can encounter interoperability problems when interworking with terminals that do not implement V.140 procedures because other protocols such as H.320 and ISO/IEC 13871 may time out. + +## 9.3 Phase 2 – Determination of network characteristics and bit alignment + +Upon entry to Phase 2, the terminal shall disconnect the output of the audio decoder from any sound output devices and cease transmitting audio and all other protocols. + +Phase 2 signals shall begin with Field A immediately following the final Phase 1 signal. Field A and Field B shall be transmitted alternately throughout Phase 2. + +Terminals on 56C interfaces shall transmit only bits 1 through 7 of Field A and Field B. + +### 9.3.1 Phase 2a – Transmitting and acquiring SP in each subchannel + +#### 9.3.1.1 Transmitter procedure + +The transmitter shall repeatedly transmit the Phase 2a signal. + +This signal serves to acknowledge the acquisition of the far-end's Phase 1 signal and to transmit a unique SP in each subchannel, with SP-A in subchannel 1, SP-B in subchannel 2, SP-C in subchannel 3, SP-D in subchannel 4, SP-E in subchannel 5, SP-F in subchannel 6, and continuing to transmit SP-G and SP-H in subchannels 7 and 8, respectively, in case the far-end has not yet proceeded to Phase 2a. + +#### 9.3.1.2 Receiver procedure + +In Phase 2a, the receiver shall search all received subchannels for any of the eight values of SP and the "all binary ONES" pattern. Since the subchannel alignment between the transmitter and receiver may be different, transmitted SP patterns may appear in different subchannel positions at the receiver. + +Moreover, if the receiver detects the "all binary ONES" pattern in one subchannel and correct values of SP in at least four other subchannels, it is possible that one of the bytes in the 8-byte sequence that comprises the transmitted SP patterns has been corrupted by network equipment: every bit in that byte will be a binary ONE (see Figure 13 for an example). The terminal shall determine if this is the case by checking, as follows, the subchannels that contain neither SP nor all binary ONES: + +- if these subchannels contain a pattern similar to SP except for a single replacement of binary ZERO with binary ONE; and +- if the replacement occurs in the same bit position for all such subchannels, + +then the terminal shall consider all eight values of SP to have been detected correctly if and only if all subsequently received SPs are corrupted in the same fashion. + +| Byte number | Subchannel 1 | Subchannel 2 | Subchannel 3 | Subchannel 4 | Subchannel 5 | Subchannel 6 | Subchannel 7 | Subchannel 8 | +|-------------|--------------|--------------|--------------|--------------|--------------|--------------|--------------|--------------| +| x | 1 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | +| x + 1 | 0 | 1 | 0 | 1 | 1 | 0 | 1 | 1 | +| x + 2 | 1 | 0 | 1 | 1 | 0 | 1 | 1 | 0 | +| x + 3 | 0 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | +| x + 4 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | +| x + 5 | 1 | 0 | 1 | 1 | 0 | 1 | 1 | 1 | +| x + 6 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | +| x + 7 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | + +**Figure 13/V.140 – Example of corruption of SP values by network equipment: +Subchannel 7 is all ONES and byte (x + 6) is corrupted, also all ONES** + +For each subchannel, SP shall be considered to have been acquired when it is detected in four consecutive Field A positions. + +For each subchannel, the all-binary-ONEs pattern shall be considered to have been acquired when it is detected in four consecutive Field A positions. + +If SP is not acquired in at least 7 subchannels within two seconds of entry into Phase 2a, the V.140 procedures shall terminate. + +The receiver shall stop searching for additional SP or all-binary-ONEs patterns in subchannels when any one of the following conditions is satisfied: + +- SPs have been acquired in all subchannels; or +- after 20 Field A positions beyond the point at which the seventh SP pattern was acquired, given that the eighth SP has been replaced by a pattern of all binary ONEs. + +Subchannels on which SP was not acquired shall be considered to be unusable in the direction toward the local terminal. The terminal shall then determine the subchannel numbering of the transmitting terminal and determine which subchannel, if any, is not transmitted or not passed through the network by examining Field A. It shall then proceed to Phase 2b. + +NOTE 1 – The difference between the number of a subchannel and the number of the SP (SP-A = 1, SP-B = 2, etc.) acquired in that subchannel indicates the number of bit positions that the bytes transmitted by the far-end terminal are rotated, i.e., if SP-E is received in subchannel 1, the transmitted signal is rotated 4 bit positions to the left. + +NOTE 2 – If a terminal acquires a pattern of all binary ONEs in any subchannel, that subchannel is not being transmitted by or passed through the network from the far-end terminal. + +### **9.3.2 Phase 2b – Reflected SP and alignment recovery** + +#### **9.3.2.1 Transmitter procedure** + +The transmitter shall repeatedly transmit the Phase 2b signal. + +This signal serves to acknowledge the acquisition of SP and to transmit a "Reflected Signature Pattern" (RSP) in each subchannel in Field B, while continuing to transmit SP in all subchannels in Field A, in case the far-end has not yet proceeded to Phase 2b. + +The value of the RSP for each subchannel is computed from the received Field A on the same subchannel. + +RSP shall be computed for each subchannel as follows: + +- 1) If SP was acquired on the received subchannel $n$ (where $n$ takes the values 1 to 8), subchannel $n$ of transmitted Field B shall contain the one's complement of the first 7 bits of the SP (the correct SP as defined in Table 3 shall be sent even if a corrupted version was received) followed by a binary ZERO. +- 2) Otherwise, the first 7 bits of that subchannel of transmitted Field B shall be set to binary ONE, and the eighth bit of that subchannel shall be set to binary ZERO. + +NOTE – The RSP is one's complemented so that the receiver can unambiguously distinguish Field A from Field B, even in case of loss of synchronization. + +#### **9.3.2.2 Receiver procedure** + +In Phase 2b, the receiver shall search all received subchannels in Field B for any of the eight possible values of RSP and the "all binary ONEs" pattern. Since the subchannel alignment between the transmitter and receiver may be different, transmitted RSP patterns may appear in different subchannel positions at the receiver. + +Moreover, if the receiver detects the "all binary ONEs" pattern in one subchannel and correct values of RSP in at least four other subchannels, it is possible that one of the bytes in the 8-byte sequence + +that comprises the transmitted RSP patterns has been corrupted by network equipment – every bit in that byte will be a binary ONE (see 9.3.1.2 for an example of this phenomenon at work in Phase 2a). The terminal shall determine if this is the case by checking, as follows, the subchannels that contain neither RSP nor all binary ONES: + +- if these subchannels contain a pattern similar to RSP except for a single replacement of binary ZERO with binary ONE; and +- if the replacement occurs in the same bit position for all such subchannels, + +then the terminal shall consider all eight values of RSP to have been detected correctly if, and only if, all subsequently received RSPs are corrupted in the same fashion. + +RSP shall be considered to have been acquired when it is detected in 4 consecutive Field B positions. If RSP is not acquired in at least 6 subchannels within 2 seconds of entry into Phase 2b, the V.140 procedures shall terminate. + +NOTE – Even if network misalignment and restriction is different in each direction of transmission, the receiver of the Phase 2b signal will detect, at most, two Field B subchannels without RSP. One of these will have been anticipated based on the result of Phase 2a, and the other will indicate which subchannel is restricted in the network direction toward the far-end. + +The receiver shall stop searching for additional RSP patterns in subchannels when any one of the following conditions is satisfied: + +- RSPs have been acquired in all subchannels; or +- after 20 Field B positions beyond the point at which the sixth RSP pattern was acquired, given that the remaining RSPs have been replaced either by a pattern of all binary ONES or by a pattern of 7 binary ONES followed by a binary ZERO. + +The terminal shall then determine subchannel alignment and presence as received at the far-end terminal by examining Field B. It shall then proceed to Phase 2c. + +### 9.3.3 Determination of network characteristics and bit-alignment from received SP/RSP + +The primary goal of the procedures of Phase 2a and 2b is to determine whether a 64 kbit/s interface is restricted (i.e., 64R rather than 64C), because terminals that ascertain that their interface is 64R must then compensate for those subchannels that do not carry data. See 9.3.4 for details. + +If all of the received subchannels in Phase 2a contain valid SP, the interface is 64C or 56C, and no special procedures are required. + +NOTE 1 – In some cases, when the "all-binary-ONES pattern" is referred to below, a pattern of 7 binary ONES and one binary ZERO may be assumed to be synonymous with the all-binary-ONES pattern. If a terminal acquires a pattern of 7 binary ONES, and one binary ZERO in any subchannel in Field B, a subchannel is not being transmitted by or passed through the network from the local terminal. This pattern was received at the far-end terminal as all binary ONES and but was sent back as specified in 9.3.2.1 (7 binary ONES and one binary ZERO). + +However, if any of the received subchannels in Phase 2a contain the all-binary-ONES pattern rather than the expected SP, the interface is 64R. The received subchannel that contains the all-binary-ONES pattern does not carry any useful data and shall be ignored (see 9.3.4). + +Moreover, if during Phase 2b there are one or two subchannels that contain the all-binary-ONES pattern rather than the expected RSP, a subchannel is not being transmitted by the near-end terminal. To determine which subchannel is not being transmitted, the terminal shall identify the RSP(s) missing from the Phase 2b signal. Each missing RSP can be associated with a subchannel by assuming that RSPs are transmitted in subchannels in the order RSP-A through RSP-H, i.e., if subchannel $x$ contains RSP-A, subchannel $(x + 1) \bmod 8$ will contain RSP-B, subchannel $(x + 2) \bmod 8$ will contain RSP-C, and so forth up to RSP-H. Once this association is done, one or more of these RSP(s) will be missing (i.e., replaced by the all-binary-ONES pattern) and is, therefore, not being received from the far-end terminal. Hence, one of the corresponding SPs is not being + +transmitted to the far-end by the network (although the near-end terminal is attempting to transmit it). + +NOTE 2 – If the result of Phase 2a indicates that only 7 subchannels are active, and Phase 2b results in 7 RSP patterns and one pattern of all binary ONES, this also indicates that a subchannel is not being transmitted by or passed through the network from the local terminal; it can be assumed that two directions of restriction overlap, since networks are always restricted in both directions. + +In order to determine which RSP and hence which SP is not being transmitted, the terminal shall identify the subchannel that DOES NOT contain all binary ONES in Phase 2a but DOES contain all binary ONES in Phase 2b. The RSP corresponding to this subchannel is missing, and the SP corresponding to this RSP was not transmitted by the network. See Figure 14 for an example. + +NOTE 3 – In the example shown in Figure 14, the results of Phases 2a and 2b for a particular terminal are shown. In this case, the terminal received all-binary-ONES in subchannel 4 during Phase 2a, rather than SP-H, which was expected. Also, during Phase 2b, the terminal received all-binary-ONES in subchannels 4 and 7; it was expecting RSP-B and RSP-E, respectively, in those subchannels. Since the all-binary-ONES pattern was received in subchannel 4 during both Phase 2a or Phase 2b, it can be inferred that this subchannel 4 does not contain valid received data. However, subchannel 7 DID contain valid data during Phase 2a, but NOT during Phase 2b. Therefore, RSP-E was never received because it was never sent by the far-end; the far-end did not send it because it did not receive SP-E, and therefore subchannel 5 is not being transmitted to the far-end by the network and should not be used. + +| | Subchannel
1 | Subchannel
2 | Subchannel
3 | Subchannel
4 | Subchannel
5 | Subchannel
6 | Subchannel
7 | Subchannel
8 | +|--------------------------------------------|-----------------|-----------------|-----------------|--------------------------------------|-----------------|-----------------|------------------------------------------------------------|-----------------| +| SP sent | SP-A | SP-B | SP-C | SP-D | SP-E | SP-F | SP-G | SP-H | +| SP received
(Phase 2a) | SP-E | SP-F | SP-G | All ONES | SP-A | SP-B | SP-C | SP-D | +| RSP received
(Phase 2b) | RSP-G | RSP-H | RSP-A | All ONES | RSP-C | RSP-D | All ONES | RSP-F | +| RSP NOT
received | | | | RSP-B | | | RSP-E | | +| Channel not
transmitted
from far-end | | | | No data
received
here | | | | | +| SP not
transmitted
from near-end | | | | | | | SP-E
not received,
but data is
received | | + +(No data is received on subchannel 4 during Phases 2a and 2b, +therefore, it is not being transferred from the far-end. +Data IS received on subchannel 7, but RSP-E should have been.) + +**Figure 14/V.140 – Example of determination of network characteristics +from Phase 2a and Phase 2b** + +Relative misalignment of subchannels between terminals can also be determined using the information accumulated during Phases 2a and 2b, if necessary (most protocols do not require any compensation for such misalignment, but a few do, e.g., unframed G.711 audio). + +### 9.3.4 Phase 2c – Concluding Phase 2 and proceeding to Phase 3 + +At the conclusion of Phase 2, each terminal has knowledge of the relative alignment of subchannels between the terminals, as well as knowledge, if any, of the subchannels which are not transmitted to and from the remote terminal. Each terminal shall use such knowledge as follows: + +- When transmitting bytes during Phase 2c, the terminal shall leave out bits as necessary to avoid sending data in a subchannel that is not being transmitted or passed through the + +network to the far-end terminal. The terminal shall follow this procedure, when appropriate, for other protocols (typically, protocols that include a framing signal), EXCEPT: + +- during Phase 3, when the terminal shall insert fill bits as necessary to avoid sending data in a subchannel that is not being transmitted (or passed through the network) to the far-end terminal. Also, the terminal shall follow this procedure when appropriate for other protocols (typically, protocols based upon HDLC). +- When receiving bytes, the terminal shall skip bits to eliminate data received in a subchannel that is not being received (or passed through the network) from the far-end terminal. +- If the terminal is to support protocols that require proper alignment (e.g., unframed G.711 audio) of subchannels between transmitter and receiver, the transmitter shall compensate as necessary for any relative misalignment of the subchannels between it and the far-end terminal so that the far-end terminal will receive data properly aligned on octet boundaries. + +The terminal shall follow the above procedures for the duration of the network connection, i.e., during Phases 2c and 3 and in any protocols or procedures used subsequently. + +#### 9.3.4.1 Transmitter procedure + +The transmitter shall repeatedly transmit the Phase 2c signal. + +This signal serves to acknowledge the acquisition of RSP, while continuing to transmit RSP in all subchannels, in case the far-end has not yet proceeded to Phase 2c. + +#### 9.3.4.2 Receiver procedure + +In Phase 2c, the receiver shall search for: + +- Field A of the Phase 2c signal; and +- two or more contiguous HDLC flags (01111110) coded according to the Phase 3 signalling. + +This signal shall be considered to have been acquired when either four consecutive Phase 2c Field A signals are detected or when two sets of two contiguous HDLC flags are detected. If this signal is not acquired within two seconds of entry into Phase 2c, the V.140 procedures shall terminate, and the terminal shall disconnect the channel or proceed as otherwise pre-conditioned. + +NOTE – The HDLC flags will be detected if the far-end terminal enters Phase 3 before the near-end terminal does. + +Upon acquiring this signal, the terminal shall proceed to Phase 3. + +## 9.4 Phase 3 – Role arbitration, capability exchange, and mode selection + +In Phase 3, the two terminals exchange capabilities, select a protocol mode, and initiate operation in the selected mode. + +Throughout Phase 3, the most recently transmitted message PDUs shall be repeated continuously, one message in each HDLC frame, until a different message PDU is transmitted or V.140 procedures terminate. + +### 9.4.1 roleAndCapability transmission + +Upon entering Phase 3, the terminal shall transmit the **roleAndCapability** PDU. + +Upon receiving a **roleAndCapability** PDU, the terminal shall assign a numerical value to the **role** parameter in said PDU according to Table 6 and also to the **role** parameter value that it transmitted. If these numerical values differ, the terminal shall be the "Initiator" if it has the higher number or the "Responder" if it has the lower number. + +**Table 6/V.140 – Initiator/Responder determination table** + +| Role | Value | +|------------------|-------| +| originate | 3 | +| unknown | 2 | +| answer | 1 | + +If the two values from Table 6 are equal, each terminal's **arbitrationField** value shall be substituted for its **role** value. The terminal with the higher value shall be considered the Initiator, and the other terminal shall be considered the Responder. + +If the two values from Table 6 are equal, and the **arbitrationField** values are equal, the terminal shall transmit the **terminate** PDU with the **cause** value set to **roleCollision**. + +### 9.4.2 Initiator procedure + +The Initiator shall transmit either: + +- 1) the **modeSelect** PDU to choose the selected mode; or +- 2) the **youChoose** PDU to defer selection to the other terminal; or +- 3) the **terminate** PDU with the **cause** field set to **noSuitableModes**. This should occur only if the far-end's capability set did not include any protocol modes useful to the calling user. + +When transmitting the **modeSelect** PDU, the Initiator should take account of the order of preferences of capabilities indicated in the **roleAndCapability** PDU it had previously received from the Responder. + +If the Initiator sent **modeSelect**, it shall wait for receipt of the **modeSelectAcknowledge** PDU, and upon receiving it, shall terminate V.140 procedures and begin the selected protocol mode. + +If the Initiator sent **youChoose**, it shall wait for receipt of the **modeSelect** PDU, and upon receiving it, shall transmit the **modeSelectAcknowledge** PDU 20 times, then terminate V.140 procedures and begin the selected protocol mode. + +The Initiator shall not transmit the **youChoose** PDU unless it has identified one or more useful common modes; i.e., the **roleAndCapability** PDU it had previously received from the Responder must contain useful modes that are the same as those signalled by the Initiator using the **roleAndCapability** PDU. + +### 9.4.3 Responder procedure + +The Responder shall wait for receipt of either a **modeSelect** PDU, a **youChoose** PDU, or a **terminate** PDU. + +If the Responder receives **modeSelect**, it shall transmit the **modeSelectAcknowledge** PDU 20 times, then terminate V.140 procedures and begin the selected protocol mode. + +If the Responder receives **youChoose**, it shall transmit the **modeSelect** PDU, then wait for receipt of the **modeSelectAcknowledge** PDU, and upon receiving it, shall terminate V.140 procedures and begin the selected protocol mode. When transmitting the **modeSelect** PDU, the Responder should take account of the order of preferences of capabilities indicated in the **roleAndCapability** PDU it had previously received from the Initiator. + +The Responder shall never transmit **youChoose**. + +### 9.4.4 General Phase 3 procedures + +The procedures in this clause apply to all of Phase 3, for both Initiator and Responder, in addition to the procedures above. + +Any terminal which has sent the **modeSelect** PDU shall wait for the **modeSelectAcknowledge** PDU to arrive. While waiting, such a terminal shall also search for signals appropriate to the protocol mode selected. Any such terminal shall repeatedly send the **modeSelect** PDU until either: + +- signals appropriate to the selected protocol mode are detected; or +- the **modeSelectAcknowledge** PDU is received with a correct FCS field. + +If either of these two events occurs, the terminal shall immediately cease transmitting Phase 3 PDUs and shall begin transmission of signals and execution of procedures appropriate to the selected protocol mode for negotiation, exchange of capabilities, etc. as defined for that protocol. + +Unrecognized **nonStandard** messages and capabilities shall be ignored. + +#### 9.4.4.1 Time-out and abnormal termination + +If the terminal waits longer than two seconds for a responding PDU, the terminal shall transmit the **terminate** PDU with the **cause** field set to **timerExpiration**. + +Any terminal receiving a PDU, other than those specified as appropriate in these procedures, shall transmit the **terminate** PDU with the **cause** field set to **protocolViolation**. + +Any terminal receiving a **modeSelect** PDU containing a mode which was not listed in its transmitted **capabilitySet** shall transmit the **terminate** PDU with the **cause** field set to **modeNotAvailable**. + +Any terminal transmitting the **terminate** PDU for any reason shall transmit it 20 times, then terminate V.140 procedures. The terminal may optionally disconnect the channel at that point. + +If the terminal receives the **terminate** PDU with a correct FCS field, it shall immediately terminate V.140 procedures. The terminal may optionally disconnect the channel at that point. + +## 9.5 Entering selected mode + +Terminals shall enter the selected protocol mode by stopping all transmission of data related to V.140 and starting procedures appropriate to the selected mode. Terminals shall not transmit useful data bits in subchannels which were identified in Phase 2 as not being passed by the network, and shall skip or otherwise ignore bits in similar received subchannels (see 9.3.4). + +Terminals entering G.711 audio, or any mode making use of G.711 audio (such as GSTN modem modulations over G.711 audio) as the selected mode shall continuously examine subchannels 7 and 8 for resumption of Phase 1 signalling by the far-end. + +# 10 Resuming V.140 from a selected mode + +The procedures of V.140 can be used to select another operation mode after termination of a previously selected mode. + +Terminals shall return to V.140 from selected modes by one of the following procedures: + +- Terminals returning to V.140 from G.711 audio shall follow the procedures of V.140 starting with Phase 1. +- Terminals returning to V.140 from any other mode shall terminate transmissions by any protocols other than V.140 and provide a clear channel for V.140 procedures. The terminal shall then follow the procedures of Phase 3. + +In either case, the terminal initiating return to V.140 shall be considered the Originator for the Phase 3 **roleAndCapability** message, and the responding terminal shall be considered the Answerer. + +This feature may be used to provide an optional initial phase at the beginning of a multimedia call in which users have the opportunity to speak in voice telephony mode before proceeding to multimedia telephony. This feature may also be used to switch from one multimedia telephony mode to another, or back into voice telephony mode. + +# Annex A + +## ASN.1 definition of Phase 3 PDU values + +This annex specifies the syntax of PDUs using the notation defined in ASN.1 according to ITU-T Rec. X.680 | ISO/IEC 8824-1. + +``` +HDISPATCH DEFINITIONS AUTOMATIC TAGS ::= +BEGIN + +-- Export all symbols + +-- ===== +-- Top level PDUs +-- ===== + +HDispatchPDU ::= CHOICE { + nonStandard NonStandardMessage, + roleAndCapability RoleAndCapabilityMessage, + modeSelect Mode, + youChoose NULL, + modeSelectAcknowledge NULL, + terminate TerminateMessage, + ... +} + +RoleAndCapabilityMessage ::= SEQUENCE { + role + CHOICE {originate NULL, + unknown NULL, + answer NULL, + ...}, + arbitrationField INTEGER(0..4294967295), -- 32 bit random # + capabilitySet SEQUENCE SIZE (1..65535) OF Capability, + ... +} + +Capability ::= CHOICE { + nonStandard NonStandardParameter, + isdn + CHOICE {isdnCapability IsdnCapability, + multilinkAdditionalConnection NULL, + -- Express this cap alone to force-- + -- association of this channel with + -- an existing call + is13871 + SEQUENCE -- "BONDING" protocol-- {withIsdnCapability + IsdnCapability, + ...}, + h244 + SEQUENCE -- channel aggregation protocol-- {withIsdnCapability + IsdnCapability, + ...}, + ...}, + ... +} + +IsdnCapability ::= CHOICE { + g711aLaw SEQUENCE {...}, + g711uLaw SEQUENCE {...}, + h320 SEQUENCE {...}, +} +``` + +``` + +h324AnnexD SEQUENCE {...}, +h324Multilink SEQUENCE {...}, +group4Fax SEQUENCE {...}, +t120 SEQUENCE {...}, +t140 SEQUENCE {...}, -- text chatting protocol +v110 SEQUENCE {...}, +v120 SEQUENCE {...}, +rfc1661 SEQUENCE {withH323 BOOLEAN, + ...}, +... +} + +Mode ::= CHOICE { + nonStandard NonStandardParameter, + plainIsdnMode IsdnMode, + h244 IsdnMode, + is13871 IsdnMode, -- BONDING protocol + multilinkAdditionalConnection + SEQUENCE {callAssociationNumber INTEGER(0..4294967295), + ...}, + ... +} + +IsdnMode ::= CHOICE { + nonStandard NonStandardParameter, + g711aLaw SEQUENCE {...}, + g711uLaw SEQUENCE {...}, + h320 SEQUENCE {...}, + h324AnnexD SEQUENCE {...}, + h324Multilink SEQUENCE {...}, + group4Fax SEQUENCE {...}, + t120 SEQUENCE {...}, + rfc1661 SEQUENCE {...}, + ... +} + +TerminateMessage ::= SEQUENCE { + cause + CHOICE {nonStandard NonStandardParameter, + timerExpiration NULL, + roleCollision NULL, + noSuitableModes NULL, + invalidModeSelected NULL, + protocolViolation NULL, + modeNotAvailable NULL, + ...}, + ... +} + +-- ===== +-- Non standard Message definitions +-- ===== + +NonStandardMessage ::= SEQUENCE {nonStandardData NonStandardParameter, + ... +} + +NonStandardParameter ::= SEQUENCE { + nonStandardIdentifier NonStandardIdentifier, + data OCTET STRING +} + +``` + +``` + +NonStandardIdentifier ::= CHOICE { + object OBJECT IDENTIFIER, + h221NonStandard + SEQUENCE {t35CountryCode INTEGER(0..255), -- country, per T.35-- + t35Extension INTEGER(0..255), -- assigned nationally-- + manufacturerCode INTEGER(0..65535)} +} -- assigned nationally + +END + +``` + +The use of ITU-T Recs G.722 and G.725 within these procedures is for further study. + +The following refers to fields and structures used within the **roleAndCapability** PDU: + +- **g711aLaw**, **g711uLaw**, **h320**, **h324AnnexD**, **h324Multilink**, **group4Fax**, **t120**, **t140**, **v110**, or **v120** assigned to an **IsdnCapability** field shall indicate that the terminal can support operation according to ITU-T Recs G.711 (A-law encoding), G.711 ( $\mu$ -law encoding), H.320, Annex D/H.324, T.6, T.120, T.140, V.110, or V.120, respectively. +- **rfc1661** assigned to the **IsdnCapability** structure shall indicate that the terminal can support operation according to RFC 1661 (also known as Internet Standard 51), as adopted by the Internet Engineering Task Force (IETF). If the **withH323** sub-field is set true, the terminal can support operation according to ITU-T Rec. H.323 overlying the protocol defined in RFC 1661. +- **is13871** assigned to the **isdn** structure which is within the **Capability** structure shall indicate that the terminal can support channel aggregation according to the procedures of ISO/IEC 13871 (also known as BONDING), and the accompanying **withIsdnCapability** field shall indicate a communications protocol which can be run in conjunction with ISO/IEC 13871. +- **h244** assigned to the **isdn** structure within the **Capability** structure shall indicate that the terminal can support channel aggregation using the procedures of ITU-T Rec. H.244, and the accompanying **withIsdnCapability** field shall indicate a protocol which can be run in conjunction with said procedures. + +The following refers to fields and structures used within the **modeSelect** PDU: + +- **g711aLaw**, **g711uLaw**, **h320**, **h324AnnexD**, **h324Multilink**, **group4Fax**, **t120**, **t140**, **v110**, or **v120** assigned to the **plainIsdnMode** field (an **IsdnMode** structure) shall indicate that the terminal has selected operation according to ITU-T Recs G.711 (a-law encoding), G.711 ( $\mu$ -law encoding), H.320, Annex D/H.324, Annex F/H.324, T.6, T.120, T.140, V.110, or V.120, respectively. +- **rfc1661** assigned to the **plainIsdnMode** field (an **IsdnMode** structure) shall indicate that the terminal has selected operation according to RFC 1661 (Internet Standard 51), the Point-to-Point protocol, as adopted by the Internet Engineering Task Force (IETF). +- **is13871** (an **IsdnMode** structure) assigned to the **Mode** structure shall indicate that the terminal has chosen to use the ISO/IEC 13871 channel aggregation protocol, and the value selected for the **is13871** field shall indicate which communications protocol shall be used in conjunction with ISO/IEC 13871. +- **h244** (an **IsdnMode** structure) assigned to the **Mode** structure shall indicate that the terminal has chosen to use the H.244 channel aggregation protocol, and the value selected for the **h244** field shall indicate which communications protocol shall be used in conjunction with ITU-T Rec. H.244. + + + + + +## SERIES OF ITU-T RECOMMENDATIONS + +| | | +|-----------------|---------------------------------------------------------------------------------------------| +| Series A | Organization of the work of ITU-T | +| Series D | General tariff principles | +| Series E | Overall network operation, telephone service, service operation and human factors | +| Series F | Non-telephone telecommunication services | +| Series G | Transmission systems and media, digital systems and networks | +| Series H | Audiovisual and multimedia systems | +| Series I | Integrated services digital network | +| Series J | Cable networks and transmission of television, sound programme and other multimedia signals | +| Series K | Protection against interference | +| Series L | Construction, installation and protection of cables and other elements of outside plant | +| Series M | Telecommunication management, including TMN and network maintenance | +| Series N | Maintenance: international sound programme and television transmission circuits | +| Series O | Specifications of measuring equipment | +| Series P | Telephone transmission quality, telephone installations, local line networks | +| Series Q | Switching and signalling | +| Series R | Telegraph transmission | +| Series S | Telegraph services terminal equipment | +| Series T | Terminals for telematic services | +| Series U | Telegraph switching | +| Series V | Data communication over the telephone network | +| Series X | Data networks, open system communications and security | +| Series Y | Global information infrastructure, Internet protocol aspects and next-generation networks | +| Series Z | Languages and general software aspects for telecommunication systems | \ No newline at end of file diff --git a/marked/V/T-REC-V.15-198811-I_PDF-E/raw.md b/marked/V/T-REC-V.15-198811-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..5aefaa603b7be5bbd0c6802e644219263b770594 --- /dev/null +++ b/marked/V/T-REC-V.15-198811-I_PDF-E/raw.md @@ -0,0 +1,85 @@ + + + + +ITU logo: a globe with the letters ITU and a lightning bolt symbol. + +INTERNATIONAL TELECOMMUNICATION UNION + +# ITU-T + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +## V.15 + +# DATA COMMUNICATION OVER THE TELEPHONE NETWORK --- + +## USE OF ACOUSTIC COUPLING FOR DATA TRANSMISSION + +### ITU-T Recommendation V.15 + +(Extract from the *Blue Book*) + +--- + +## NOTES + +1 ITU-T Recommendation V.15 was published in Fascicle VIII.1 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below). + +2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +## **USE OF ACOUSTIC COUPLING FOR DATA TRANSMISSION** + +*(Geneva, 1972; amended at Malaga-Torremolinos, 1984)* + +*Note* - Acoustic coupling is a technique used to couple the output of a modem to an analogue telecommunication facility using acoustic energy/power between the device and a telephone instrument. As such, it provides for minimum complexity of attachment as well as excellent galvanic isolation. However, the technique does limit the data signalling rates used and does limit the functionality which can be provided by the associated modem. Since this arrangement will generally be used to communicate with a permanently installed V Series modem at a remote station, the characteristics of the modem will, accordingly, comply with requirements defined elsewhere in these Series V Recommendations, e.g., V.21 or V.23. As far as functionality permits, interfaces with the associated DTE will be as defined in those Recommendations. Because of operator intervention required in manipulating the telephone handset, automatic calling and automatic answering are not normally considered part of the functionality of an acoustically coupled modem. However, an acoustically coupled modem can call a remote station which has automatic answering capability and can observe the protocol defined in Recommendation V.25, § 6, "Manual data station calling automatic answering data station" as modified herein. + +The CCITT, + +*considering* + +that there is a wide variety of telephone instruments in existence and that the acoustic path involved in the use of any coupling device cannot be accurately prescribed for all cases, and hence it will be difficult to ensure satisfactory transmission in all situations, + +*recommends* + +**1** that acoustic coupling of data transmission equipment via telephone instruments to the telephone transmission network should not be used for permanent installations. + +It is, however, recognized that there may be a need for a means to provide temporary connection of portable data transmission equipment to the network in circumstances where it may not be possible to obtain convenient access to the subscriber's line terminals. + +The use of acoustic coupling for temporary communications is subject to the agreement of the Administration in charge of the telephone network to which the equipment will be connected. + +If an Administration decides to permit acoustic coupling for temporary data transmission stations, the acoustic coupling equipment conforms to the following: + +- 1) The maximum power output of the subscriber's equipment to the line shall not exceed 1 mW at any frequency. + +The mean permitted telephone line signal power shall not exceed -13 dBm0. + +- 2) If $p$ is the signal power in the frequency band 0-4 kHz, the signal power outside this band shall not exceed the following values when integrated over any period of approximately 3 seconds: + +$p$ - 20 dB in the band 4 to 8 kHz, + +$p$ - 40 dB in the band 8 to 12 kHz, + +$p$ - 60 dB in each 4-kHz band above 12 kHz. + +- 3) The frequencies emitted by the transducer shall be such as not to interfere with national and international telephone signalling systems and pilot signals involved in the telephone connection envisaged. +- 4) Adequate protection shall be provided in the transducer to avoid causing any dangerous electric potential and currents to the telephone system. +- 5) It shall not be possible to cause acoustic shock to telephone users under any normal condition or when the acoustic coupler develops any single fault. +- 6) The mechanical arrangements of the transducer shall not cause mechanical damage to the telephone instrument. +- 7) In addition to the contents of this Recommendation, the regulations of the national Administration must also be complied with. + +**2** that acoustically coupled equipment be compatible with "hard-wired counterparts" at the remote location to the extent that: + +- 1) The characteristics of the equivalent V Series (V.21, V.23, etc.) modem line signals are complied with (otherwise communication will be impossible). +- 2) An equivalent V.24 interface is provided to the DTE, with the following exceptions: + - circuit 108 is power ON indicator only, and cannot be used to control the connection of the modem to the line; + - circuit 125 is inoperative; only manual answering can be accomplished. +- 3) Acoustically coupled modem equipment designed to operate with remote modems: + - which have automatic answering capability, and + - which are specifically dedicated and are adapted (by means of optionally extended answer tone duration) to working with acoustically coupled calling stations + +shall operate in the mode prescribed in Recommendation V.25, § 6 where placement of the telephone instrument handset on the acoustic coupler by the operator is tantamount to depressing a data button, as specified in § 6. + +These modems shall also comply with the response time requirements of circuits 106 and 109 as specified in the appropriate modem Recommendation. \ No newline at end of file diff --git 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sha256:ecc78b0b2babfe69a7403cfbc96321645dfacab54881cfb1cd0ce602758d5126 +size 78824 diff --git a/marked/V/T-REC-V.151-200605-I_PDF-E/ff0299b306c850173d9aac7783bf1780_img.jpg b/marked/V/T-REC-V.151-200605-I_PDF-E/ff0299b306c850173d9aac7783bf1780_img.jpg new file mode 100644 index 0000000000000000000000000000000000000000..4a0615ae9136c6019d3f9b14182e376382e8e64a --- /dev/null +++ b/marked/V/T-REC-V.151-200605-I_PDF-E/ff0299b306c850173d9aac7783bf1780_img.jpg @@ -0,0 +1,3 @@ +version https://git-lfs.github.com/spec/v1 +oid sha256:532e565d4a28310741a17e869e79f6cfbfaf27c7a063c4434d7a57635d76c86f +size 145986 diff --git a/marked/V/T-REC-V.151-200605-I_PDF-E/raw.md b/marked/V/T-REC-V.151-200605-I_PDF-E/raw.md new file mode 100644 index 0000000000000000000000000000000000000000..95362ac7cfa4e0321f727a29f1eef562182b1ae3 --- /dev/null +++ b/marked/V/T-REC-V.151-200605-I_PDF-E/raw.md @@ -0,0 +1,3229 @@ + + +I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n + +**ITU-T** + +TELECOMMUNICATION +STANDARDIZATION SECTOR +OF ITU + +**V.151** + +(05/2006) + +SERIES V: DATA COMMUNICATION OVER THE +TELEPHONE NETWORK + +Interworking with other networks + +--- + +**Procedures for the end-to-end connection of +analogue PSTN text telephones over an +IP network utilizing text relay** + +ITU-T Recommendation V.151 + + + +The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features a blue globe with a red lightning bolt striking it. To the right of the globe, the text 'ITU' is written in a large, bold, blue font, and below it, the words 'International Telecommunication Union' are written in a smaller, blue font. + +ITU logo: a globe with a red lightning bolt and the text 'ITU International Telecommunication Union' + +# ITU-T V-SERIES RECOMMENDATIONS DATA COMMUNICATION OVER THE TELEPHONE NETWORK + +| | | +|-------------------------------------------------------|--------------------| +| General | V.1–V.9 | +| Interfaces and voiceband modems | V.10–V.34 | +| Wideband modems | V.35–V.39 | +| Error control | V.40–V.49 | +| Transmission quality and maintenance | V.50–V.59 | +| Simultaneous transmission of data and other signals | V.60–V.99 | +| Interworking with other networks | V.100–V.199 | +| Interface layer specifications for data communication | V.200–V.249 | +| Control procedures | V.250–V.299 | +| Modems on digital circuits | V.300–V.399 | + +*For further details, please refer to the list of ITU-T Recommendations.* + +# **ITU-T Recommendation V.151** + +## **Procedures for the end-to-end connection of analogue PSTN text telephones over an IP network utilizing text relay** + +## **Summary** + +This Recommendation defines the inter-operation of two PSTN to IP Network gateways that facilitate the end-to-end connection of analogue text telephone terminals over an IP network utilizing text relay. + +Amendment 1 introduces Annex E, which defines the RTP payload format for the transport of text as T.140 character data over IP networks, removing the need to make a reference to an historic RFC published by the IETF. It also includes minor editorial changes throughout the document to make references to the newly introduced Annex, removing references to the RFC. + +## **Source** + +ITU-T Recommendation V.151 was approved on 29 May 2006 by ITU-T Study Group 16 (2005-2008) under the ITU-T Recommendation A.8 procedure. + +This release includes new Annex E introduced by V.151 (2006) Amendment 1, approved on 29 August 2007 by ITU-T Study Group 16 (2005-2008) under the ITU-T Recommendation A.8 procedure + +## **Keywords** + +PSTN textphone, text over IP, text relay, text telephony, ToIP. + +## FOREWORD + +The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. + +The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. + +The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. + +In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. + +## NOTE + +In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. + +Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. + +## INTELLECTUAL PROPERTY RIGHTS + +ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. + +As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. + +© ITU 2008 + +All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. + +## CONTENTS + +| | Page | +|-----------------------------------------------------------------|-------------| +| 1 Scope ..... | 1 | +| 2 References..... | 1 | +| 3 Definitions ..... | 2 | +| 4 Abbreviations..... | 3 | +| 5 Introduction ..... | 4 | +| 5.1 Overview of Text over IP ..... | 4 | +| 5.2 ToIP system architecture ..... | 4 | +| 5.3 Compliance requirements..... | 5 | +| 5.4 Relationship with other V.15x Recommendations..... | 5 | +| 6 Text telephone-over-IP functions ..... | 6 | +| 7 Connection and network scenarios ..... | 6 | +| 7.1 Service and performance requirements for ToIP..... | 7 | +| 7.2 Audio and text functionality ..... | 7 | +| 8 Transport methods ..... | 8 | +| 8.1 Audio mode ..... | 8 | +| 8.2 VBD mode..... | 8 | +| 8.3 Text relay mode..... | 9 | +| 8.4 Switching between transport modes..... | 10 | +| 9 ToIP operational modes ..... | 11 | +| 10 Text Relay PHY layer operation..... | 12 | +| 11 IP transport for text relay ..... | 12 | +| 11.1 Single and dual port operation of text relay ..... | 13 | +| 11.2 Text relay throughput ..... | 13 | +| 12 Support of DTMF in ToIP ..... | 13 | +| 13 Transition out of text relay ..... | 13 | +| 14 T.140 encoding of text relay ..... | 14 | +| 14.1 Character set support ..... | 14 | +| 14.2 TIA-825A and T.50 encoding requirements ..... | 14 | +| 15 Gateway-to-gateway protocol definitions and procedures ..... | 14 | +| 15.1 Gateway capability and call set-up messages..... | 14 | +| 15.2 Gateway call discrimination messages..... | 16 | +| 16 Start-up mode of operation ..... | 16 | +| 16.1 Inter-relationship with V.150.1 ..... | 16 | +| 16.2 Inter-relation with V.152 ..... | 16 | +| 17 Voiceband data modem interworking requirements..... | 17 | +| 18 Facsimile interworking requirements ..... | 17 | + +| | Page | +|-----------------------------------------------------------------------------------------------------------|-------------| +| 19 Call set-up procedures ..... | 17 | +| 20 Call discrimination procedures ..... | 17 | +| 20.1 V.8 bis processing ..... | 17 | +| 20.2 V.8 CI/XCI processing ..... | 17 | +| 20.3 Call discrimination overview ..... | 18 | +| 20.4 Call discrimination SDL diagrams ..... | 18 | +| 20.5 Visual flow control ..... | 32 | +| Annex A – Procedures for the optional support of SPRT protocol ..... | 33 | +| A.1 Overview ..... | 33 | +| A.2 SDP negotiation ..... | 33 | +| A.3 H.245 negotiation ..... | 34 | +| Annex B – Definition of capabilities for use within H.245-based systems ..... | 35 | +| Annex C – SDP description of sessions supporting V.151 ..... | 39 | +| Annex D – Interworking IP text devices with V.151 gateways ..... | 41 | +| D.1 Introduction ..... | 41 | +| D.2 Exchanging capabilities and opening media streams ..... | 41 | +| D.3 State transition and text handling ..... | 42 | +| Annex E – Payload format and signaling syntax for real-time text transported within an audio stream ..... | 44 | +| E.1 Overview ..... | 44 | +| E.2 Payload format ..... | 44 | +| E.3 Use of redundancy ..... | 45 | +| Appendix I – Background to PSTN text telephony ..... | 47 | +| Appendix II – ToIP call discrimination call flows ..... | 48 | +| II.1 Scope ..... | 48 | +| II.2 Scenarios for call discrimination flows ..... | 48 | +| II.3 Scenarios with SSE protocol being used ..... | 49 | +| II.4 Scenarios with payload type switching being used ..... | 72 | +| Appendix III – The use of [IETF RFC 2198] in [ITU-T V.151] ..... | 83 | +| Appendix IV – Text buffering and transmission ..... | 84 | +| Appendix V – Probing sequence ..... | 85 | +| Bibliography ..... | 86 | + +# ITU-T Recommendation V.151 + +## Procedures for the end-to-end connection of analogue PSTN text telephones over an IP network utilizing text relay + +# 1 Scope + +This Recommendation defines the interoperation of two PSTN to IP Network gateways that facilitate the end-to-end connection of analogue text telephone terminals over an IP network. + +## 2 References + +The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. + +- [ITU-T F.700] ITU-T Recommendation F.700 (2000), *Framework Recommendation for multimedia services*. +- [ITU-T F.703] ITU-T Recommendation F.703 (2000), *Multimedia conversational services*. +- [ITU-T G.177] ITU-T Recommendation G.177 (1999), *Transmission planning for voiceband services over hybrid Internet/PSTN connections*. +- [ITU-T G.711] ITU-T Recommendation G.711 (1998), *Pulse code modulation (PCM) of voice frequencies*. +- [ITU-T H.245] ITU-T Recommendation H.245 (2006), *Control protocol for multimedia communication*. +- [ITU-T H.248.1] ITU-T Recommendation H.248.1 (2005), *Gateway control protocol: Version 3*. +- [ITU-T H.323 Ann.P] ITU-T Recommendation H.323 (2003), *Packet-based multimedia communications systems, Annex P: Transfer of modem signals over H.323*. +- [ITU-T V.8] ITU-T Recommendation V.8 (2000), *Procedures for starting sessions of data transmission over the public switched telephone network*. +- [ITU-T V.8 bis] ITU-T Recommendation V.8 bis (2000), *Procedures for the identification and selection of common modes of operation between data circuit-terminating equipments (DCEs) and between data terminal equipments (DTEs) over the general switched telephone network and on leased point-to-point telephone-type circuits*. +- [ITU-T V.18] ITU-T Recommendation V.18 (2000), *Operational and interworking requirements for DCEs operating in the text telephone mode*. +- [ITU-T V.21] ITU-T Recommendation V.21 (1988), *300 bits per second duplex modem standardized for use in the general switched telephone network*. +- [ITU-T V.150.0] ITU-T Recommendation V.150.0 (2003), *Modem-over-IP networks: Foundation*. + +| | | +|-----------------|--------------------------------------------------------------------------------------------------------------------------------| +| [ITU-T V.150.1] | ITU-T Recommendation V.150.1 (2003), Modem-over-IP networks: Procedures for the end-to-end connection of V-series DCEs. | +| [ITU-T V.152] | ITU-T Recommendation V.152 (2005), Procedures for supporting voice-band data over IP networks. | +| [IETF RFC 2198] | IETF RFC 2198 (1997), RTP Payload for Redundant Audio Data. | +| [IETF RFC 2327] | IETF RFC 2327 (1998), SDP: Session Description Protocol. | +| [IETF RFC 2733] | IETF RFC 2733 (1999), An RTP Payload Format for Generic Forward Error Correction. | +| [IETF RFC 2833] | IETF RFC 2833 (2000), RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals. | +| [IETF RFC 3407] | IETF RFC 3407 (2002), Session Description Protocol (SDP) Simple Capability Declaration. | + +## 3 Definitions + +This Recommendation defines the following terms: + +**3.1 Baudot:** A five-bit code formerly used in Teletype machines including those text telephones that operate per TIA-825-A standard. The use of the term "Baudot" in this Recommendation is expanded to also include the modulation used by text telephones complying with TIA-825-A. + +**3.2 constant carrier PTP:** A PSTN Textphone (PTP) modulation that uses a carrier signal whose transmission is maintained in-between text spurts. Examples of constant carrier PTP modulations schemes include PTPs that utilize V.21 and V.23 modulations. Constant carrier modulations are also referred to as full duplex (FDX) modulations in this Recommendation. + +**3.3 gateway:** A gateway converts media provided in one type of network to the format required in another type of network. For example, a gateway could terminate bearer channels from a switched circuit network (e.g., DS0s) and media streams from a packet network (e.g., RTP streams in an IP network). + +**3.4 IP text device:** Native IP device that supports text communications and provides text communications interoperability with V.151-compliant gateways. Examples include IP-based IVR systems, voicemail systems, and IP phones. + +**3.5 non-constant carrier PTP:** A PTP modulation that uses a carrier that is only transmitted during a text spurt (and possibly for a period before the text spurt as a preamble). An example of non-constant carrier PTP modulations schemes is that used by EDT-based PTP devices. Non-constant carrier modulations are also referred to as half-duplex (HDX) modulations in this Recommendation. + +**3.6 PSTN textphone:** Term used in this Recommendation to represent all classes of text telephones, including TDD devices. + +**3.7 protocol conversion:** The interworking of dissimilar PTP terminals performed by the ToIP gateways. + +**3.8 telecommunications terminal for the deaf:** A term used in the USA for equipment that provides text telephony. It is synonymous to text telephone. + +**3.9 text over IP:** The dependable transport of analogue PSTN text telephones signals over IP networks using the methods and procedures as defined in this Recommendation. + +**3.10 text spurt:** A sequence of one or more characters transmitted in a text telephony signal without loss of carrier. + +**3.11 text telephone mode:** The operational mode when two devices are interconnected to provide text telephone communications. + +**3.12 text telephone:** A device incorporating text telephony functions. + +**3.13 text telephony:** A telecommunications capability that supports real-time text conversation on communication networks. + +**3.14 voice-band data:** The transport of modem signals over a voice channel of a packet network with the encoding appropriate for modem signals. + +## **3.15 Conventions** + +This Recommendation includes mandatory requirements, recommendations and options; these are designated by the words "shall," "should," and "may" respectively. + +A State Signalling Event (SSE) message is indicated using SSE:
), where is one of the defined media states and is the applicable reason code.
+
+## **4 Abbreviations**
+
+This Recommendation uses the following abbreviations:
+
+| | |
+|--------|----------------------------------------------|
+| ANS | V.25 Answer Tone |
+| ASNam | V.8 Answer Tone |
+| ASN.1 | Abstract Syntax Notation One |
+| CI | V.8 Call Indicator |
+| DS0 | Digital Signal level 0 |
+| DCE | Data Circuit-terminating Equipment (Modem) |
+| DTE | Data Terminal Equipment |
+| FEC | Forward Error Correction |
+| FDX | Full Duplex |
+| FoIP | Fax over Internet Protocol |
+| G1 | On-Ramp Gateway |
+| G2 | Off-Ramp Gateway |
+| HDX | Half Duplex |
+| I1 | Originating end-point IP Text telephone |
+| I2 | Answering end-point IP Text telephone |
+| IP | Internet Protocol |
+| IP-TLP | IP Transport Layer Protocol |
+| ITD | IP Text Device |
+| IVR | Interactive Voice Response |
+| MoIP | Modem over Internet Protocol |
+| PCM | Pulse Code Modulation |
+| PHY | Physical transport layer of modem connection |
+| PSTN | Public Switched Telephone Network |
+
+| | |
+|------|------------------------------------------------------------|
+| PTP | PSTN Textphone |
+| QoS | Quality of Service |
+| RIC | Reason Identifier Code |
+| RTP | Real Time Protocol |
+| SPRT | Simple Packet Relay Transport (Annex B of [ITU-T V.150.1]) |
+| SSE | State Signalling Events |
+| SSRC | Synchronization Source |
+| T1 | Originating end-point analogue PSTN Text Telephone |
+| T2 | Answering end-point analogue PSTN Text Telephone |
+| TDD | Telecommunications Devices for the Deaf |
+| TDM | Time division multiplex(ing) |
+| ToIP | Text Telephony over IP |
+| UDP | User Datagram Protocol |
+| VBD | Voice Band Data Mode |
+| VoIP | Voice over Internet Protocol |
+| XCI | Signal used in V.18 |
+
+## **5 Introduction**
+
+## **5.1 Overview of Text over IP**
+
+Text Telephony over IP (ToIP) is the dependable transport of analogue modulated signals generated by PSTN text telephone over an IP Network. The types of such text telephones and the characteristics of their line signals are described in [ITU-T V.18]. There are three basic models that can be considered for support of this application. These models are dependent upon the transmission characteristics and Quality of Service of the IP network in which the text telephone conversation is being established. The models can be summarized as:
+
+- a) Support of text telephony over VoIP connections (i.e., utilizing audio mode transport). This model is outside the scope of this Recommendation.
+- b) Support of text telephony utilizing Voice Band Data (VBD) transport as defined in [ITU-T V.152].
+- c) Support of text telephony utilizing Text Relay transport with VBD fallback according to this Recommendation.
+
+This Recommendation includes support for PSTN Textphone (PTP) devices that utilize modulations covered in [ITU-T V.18], including its Annexes A through G. Gateways compliant to this Recommendation are required to support full re-modulation/demodulation of one or more of these PTP modulations in order to transport the data using text relay. The remaining modulations shall be supported using VBD transport. The text relay procedures described in this Recommendation cover the entire set of PTP modulations and can be scaled down for specific implementations that support a subset of the modulations described in [ITU-T V.18].
+
+## **5.2 ToIP system architecture**
+
+Architecturally, this Recommendation primarily considers the support of a PSTN to IP to PSTN structure otherwise called a hybrid Internet/PSTN connection as defined in [ITU-T G.177]. Figure 5-1 illustrates a typical Text Telephony over IP application.
+
+
+
+Diagram illustrating typical VoIP applications. A central cloud labeled 'IP network' is connected to two gateways. The left gateway connects to a 'Central Office' (server rack) and a 'PSTN textphone'. The right gateway connects to a 'Central office' (server rack) and a 'PSTN textphone'. Both gateways also connect to 'IP textphone' devices. Arrows labeled 'PSTN' indicate connections between the gateways and the PSTN textphones. The diagram is labeled 'V.151(06)\_F5-1'.
+
+**Figure 5-1 – Typical ToIP applications**
+
+The possible connection combinations are:
+
+- a) PSTN Text Telephone to PSTN Text Telephone;
+- b) PSTN Text Telephone to IP Text Telephone.
+
+This Recommendation deals with PSTN Text Telephone to PSTN Text Telephone operation. PSTN Text Telephone to IP Text Devices that support the protocol defined in Annex E is described in Annex D.
+
+## 5.3 Compliance requirements
+
+This Recommendation does not require behaviour that is inconsistent with other Recommendations, or with national regulatory requirements, and shall be interpreted accordingly. Neither does it preclude the use of proprietary or non-standard text telephones; however, it does caution that if such devices are used, then care should be taken so as not to harm the functionality and procedures defined herein.
+
+In order to be compliant with this Recommendation, an implementation must provide functionality that is defined as mandatory.
+
+## 5.4 Relationship with other V.15x Recommendations
+
+The V.15x series of Recommendations (currently including [ITU-T V.150.1] and [ITU-T V.152]) define the support of data modems (using VBD or relay) and facsimile modems (using VBD) over IP networks. Modem over IP (MoIP) support is either through modem-relay mode or voiceband data mode. Since PTP endpoints utilize data modems at the physical layer, there may be interaction between the procedures defined by the various V.15x-series Recommendations for the case when the gateway has implemented and successfully negotiated the support with the remote gateway. For each V.15x Recommendation, there is a requirement that the support for it be successfully negotiated with the remote gateway during the signalling phase of the call for the procedures defined in the Recommendation to be used by the gateway.
+
+Gateways compliant with this Recommendation may also concurrently implement data MoIP support via [ITU-T V.150.1] and/or VBD support via [ITU-T V.152].
+
+# 6 Text telephone-over-IP functions
+
+Figure 6-1 provides a conceptual reference model for a ToIP gateway. The model shows two stacks conjoined by the ToIP application. The left-hand stack is that of a typical text telephone which has a signal converter (modulation). The right-hand stack represents the IP networking functions of a ToIP Gateway. The ToIP application as indicated in Figure 6-1 is defined by the normative contents of this Recommendation.
+
+
+
+Figure 6-1: ToIP gateway reference model. This block diagram shows the interaction between a text telephone and a ToIP gateway. At the top is a 'ToIP application' block. Below it, on the left, is a 'Signal converter' block connected to a 'Telephony interface'. On the right is a stack of IP networking functions: 'Codecs (audio and VBD)', 'RFC 2833', 'SSE protocol (opt.)', 'T.140 encode', 'Annex E', 'IP-TLP (SPRT opt.)', 'RTP', and 'UDP/IP'. The 'ToIP application' has bidirectional arrows connecting to each of these IP networking blocks. The 'Signal converter' has a bidirectional arrow to the 'ToIP application'. The 'UDP/IP' block has a bidirectional arrow to the 'IP network' at the bottom. A reference 'V.151(06)\_F6-1' is noted at the bottom right.
+
+**Figure 6-1 – ToIP gateway reference model**
+
+# 7 Connection and network scenarios
+
+Figure 7-1 below provides a reference diagram which matches that of Figure 5-1. It adds the concepts that a Text Telephone may be connected via a PSTN telephone or an IP telephone as well through acoustic couplers.
+
+
+
+Figure 7-1: Reference diagram for a Text-over-IP network architecture. This diagram illustrates various connection scenarios. A central oval represents 'One or more IP network(s)'. Four 'IP endpoint (IP phone)' icons are connected to this network. 'Interconnect #1' connects a 'PSTN-based text telephone' to a 'PSTN phone', which then connects to an 'IP endpoint (IP media gateway)'. 'Interconnect #2' connects another 'PSTN phone' to an 'IP endpoint (IP media gateway)'. 'Interconnect #3' connects a 'PSTN-based text telephone (TTY/TDD)' to an 'IP endpoint (IP phone)' via 'Acoustic coupling'. 'Interconnect #4' connects a 'PSTN-based text telephone' to an 'IP endpoint (IP media gateway)'. A 'Native IP text telephone' is also shown as an 'IP endpoint' within the IP network. A reference 'V.151(06)\_F7-1' is noted at the bottom right.
+
+**Figure 7-1 – Reference diagram for a Text-over-IP network architecture**
+
+Interconnect #1 is an acoustic coupling between a PTP device to an analogue PSTN phone. Interconnect #2 is the connection between the PSTN phone that is acoustically coupled to the PTP device. The IP gateway connected at the interconnect #2 point shall support the transmission of text signals from the end PTP device using this Recommendation.
+
+Interconnect #3 is an acoustic coupling of a PTP device to an IP endpoint (e.g., an IP phone). The support of the transport of the PTP signals over IP in this interconnect is described in Annex D.
+
+Interconnect #4 is the direct interconnection of a PTP device to a gateway via the PSTN or other time division multiplexing (TDM) network (e.g., an enterprise TDM network). The IP gateway connect at the interconnect #4 point shall support the transmission of text signals from the end PTP device using this Recommendation.
+
+## **7.1 Service and performance requirements for ToIP**
+
+#### **7.1.1 Applicability of [ITU-T F.703] to ToIP**
+
+[ITU-T F.703] describes the end-user performance requirements for PTP devices operating in the PSTN. Gateways compliant to this Recommendation, when inserted between two end PTP devices, should be designed to maintain the user experience as defined in [ITU-T F.703].
+
+#### **7.1.2 Gateway performance**
+
+In order to maintain the end-user performance to that specified in [ITU-T F.703], gateways should consider the appropriate design and use of:
+
+- modulator/demodulators;
+- jitter buffer operation and jitter buffer sizes;
+- fault-tolerant schemes to compensate for IP network impairments when appropriate. Fault-tolerant schemes that should be used include [IETF RFC 2198] redundancy, [IETF RFC 2733] FEC, or SPRT;
+- minimizing delay through gateway while maintaining performance related to character loss.
+
+The performance of ToIP can be dependent upon the performance of the IP network connecting the two gateways. Gateways compliant to this Recommendation should utilize supplementary fault-tolerance schemes in order to meet the performance requirements given the network conditions that they are operating under. In environments with network QoS that does not achieve the end-to-end performance requirements, there is a need to supplement text telephone connections with fault-tolerance schemes such as [IETF RFC 2198] redundancy, [IETF RFC 2733] FEC, or SPRT.
+
+#### **7.1.3 Support of simultaneous voice and text**
+
+[ITU-T V.18] describes the application of [ITU-T V.61] for the simultaneous transmission of voice and text. The support of this mode of operation is for further study.
+
+#### **7.1.4 Interoperability of various text telephone types**
+
+PTP devices can use one of a number of modulations and character encodings as described in [ITU-T V.18]. This Recommendation makes allowances for the interconnection of PTP devices that utilize different modulations and/or character encodings through the use of text relay. As described further in clause 20, if the gateways support the modulation of their local PTP devices, the connection may result in use of Text Relay mode achieving protocol conversion scenario. If the connection results in use of VBD mode for PTP signal transport, the PTP devices must have a common capability or else the connection will not be established between the PTP devices.
+
+### **7.2 Audio and text functionality**
+
+Many PTP schemes on the PSTN support alternating between voice and text during the call. For the hearing impaired, a common use scenario of PTP is for the hearing-impaired user to speak to the
+
+remote user but receive responses using text telephony. Another common use scenario of PTP for persons with a speech disability is to use text telephony to transmit while receiving voice responses. Other scenarios include interactive voice response (IVR) systems where network voice announcements may be preceded by a short burst of text, with the voice announcement followed by a longer burst of text telephony. For all PTP types, alternation between text and voice is bidirectional; i.e., there will never be text in one direction while speech is being sent in the other direction. Systems that are constant carrier-based will drop carrier during portions of the call that speech is being sent. Systems that are not based on constant carrier for text will alternate between text spurts and speech spurts during the call.
+
+This Recommendation provides support for alternating between voice and text spurts as long as both end-point PTPs are operating in a mode that supports voice and text.
+
+#### **7.2.1 Interactive voice response system support**
+
+In interactive voice response (IVR) applications that support text telephony, the IVR system will generate voice and text announcements to the end user. The end user may generate DTMF signals in response to these voice and/or text announcements. Gateways that are compliant to [ITU-T V.151] shall support IVR applications which include text signalling as described in this clause.
+
+For support of IVR, a gateway shall enable its DTMF receiver processing concurrently with the ToIP support. If a DTMF digit is received while the gateway is regenerating a text message, the gateway shall signal this DTMF digit to the remote gateway using the pre-negotiated method for DTMF signalling across the IP network (e.g., voice encoded or [IETF RFC 2833]) while continuing to play out all the remaining text of the message out the PSTN link.
+
+Since DTMF ToIP is supported using normal DTMF signalling methods across the IP network, the gateway shall be able to support DTMF text-based IVR applications without any additional procedures.
+
+## **8 Transport methods**
+
+This clause provides an overview of the transport modes with which a ToIP gateway could be operating. Gateways that are compliant to this Recommendation shall support ToIP utilizing either text relay or VBD mode.
+
+## **8.1 Audio mode**
+
+In this mode, the channel processes speech signals. This mode may include the use of compression algorithms and other processing functions that are not suitable for the transport of text telephony signals. This mode of operation may be considered suitable for the purposes of transporting text telephony signals if the speech processing is benign to those signals. Depending upon the QoS of the network, the use of fault-tolerant mechanisms such as FEC and redundancy may be appropriate.
+
+Gateways operating per this Recommendation shall not use Audio mode for the transport of text telephony signals.
+
+## **8.2 VBD mode**
+
+Voice Band Data mode (VBD) of operation is defined in [ITU-T V.152]. VBD mode is suitable for the transport of text telephony signals. Depending upon the QoS of the network the use of fault-tolerant mechanisms such as FEC and redundancy may be appropriate.
+
+Since VBD mode is also suitable for the transport of non-text signals (e.g., speech), gateways may choose to stay in VBD mode for the duration of the call after the transition to ToIP, including possibly periods of speech interspersed with the text telephony signals. Gateways negotiate the capability to leave VBD mode during call set-up procedures as defined in clause 15.1.2. If the
+
+negotiation of this operation fails, gateways shall not transition out of VBD mode when PTP signals are no longer present (see clause 8.4.4).
+
+A V.151-compliant gateway may use VBD mode for the transport of PTP signals for the following conditions:
+
+- 1) The PTP signal modulation detected is one that is not supported for text relay by both gateways.
+- 2) Probing sequence timeouts as specified in clause 20.
+
+Since VBD mode provides a transport of the PTP signals without the demodulation of these signals, interworking of dissimilar PTP types (i.e., protocol conversion) is not supported when using VBD mode.
+
+## **8.3 Text relay mode**
+
+Text relay mode of operation is characterized by the termination of the text telephone physical layer function at the gateway and the transport of the text characters between gateways.
+
+Text relay gateways demodulate the text telephony signals and present the user data to the gateway's ToIP application. The format of this data can be variable. This user data is then encoded as defined by [ITU-T T.140]. Once the characters are encoded, they may be relayed over the IP network using a suitable transport protocol (i.e., an IP Transport Layer Protocol, IP-TLP). The default IP-TLP for this Recommendation is defined in Annex E. Depending upon the QoS of the network the use of fault-tolerant mechanisms (redundancy and/or FEC) may be appropriate. The optional use of SPRT as defined in [ITU-T V.150.1] as the IP-TLP is also supported by this Recommendation.
+
+#### **8.3.1 Supported modes in text relay**
+
+FDX text telephony modes are those modes that have a constant carrier present. For V.18 modes, FDX modes supported by this Recommendation include:
+
+- a) ITU V.18 text telephony utilizing V.21 modulation.
+- b) Bell 103 based text telephony modems.
+- c) ITU V.23 Videotex terminals ("Minitel").
+- d) ITU V.21 encoded per ITU T.50.
+
+HDX-based text telephony modes do not have a carrier present while not transmitting text. For V.18 modes, HDX modes supported by this Recommendation include:
+
+- EDT (European Deaf Telephone) utilizing V.21 frequencies at 110 bit/s;
+- 5-bit FSK Baudot terminals at 45.45 bit/s or at 50 bit/s.
+
+Gateways shall support one or more of the modes specified above using text relay. The modes supported by the gateway shall be advertised in the call signalling protocols as described in their appropriate annexes. If the gateway only supports a single mode for text relay, this mode should be a mode that is commonly used in the region in which the gateway is deployed.
+
+DTMF is used for text telephony in some PTP devices in addition to other purposes for DTMF (e.g., address signalling, control of voice mail). DTMF is not supported as a text relay method by gateways following this Recommendation. DTMF is supported by using normal DTMF transport over IP schemes as described in clause 12. DTMF support using text relay and interoperability of DTMF PTP devices with PTP devices that are currently supported using text relay is for further study.
+
+### **8.4 Switching between transport modes**
+
+This clause describes the requirements for switching between the transport modes described above.
+
+For alternating text and voice, text shall be given priority. The gateway shall use text mode as long as there is text to be transmitted and played out.
+
+When the gateway is in connection with an HDX text telephone, voice can be conveyed between bursts of text without further consideration.
+
+When the gateway is in connection with an FDX-based text telephone, detection of a drop in carrier from the text telephone shall cause the gateway to also drop the carrier and go to voice mode. Detection of carrier again, or text arriving from the IP side shall cause the gateway to start sending carrier again and entering text mode. Reception of a command between the gateways for changing mode to voice may cause the gateway to change mode to voice.
+
+#### **8.4.1 Payload type indication method**
+
+The default method for switching between transport modes is using RTP payload types to indicate a transition from one mode to another.
+
+For SPRT, the payload type field in the SPRT header can be used for indication of a media switch to SPRT.
+
+A gateway can initiate a switch to a new transport mode (initiator gateway) by generating packets encoded in the new transport mode and using the payload type indicating the transport mode being switched to. The initiator gateway will then discard incoming packets that arrive that do not use the new payload type encoding. These packets may be received until the remote gateway receives the new payload type encoding and switches to the new transport mode. The remote gateway (responder gateway), upon receiving packets with the new payload type, will immediately transition to the new transport mode and generate packets (if required) using the new encoding and proper payload type.
+
+#### **8.4.2 SSE method**
+
+State signalling event (SSE) protocol may optionally be used to control transitions between transport methods. Use of SSE protocol for transport mode transitions is determined at call set-up through the gateways indicating the capability of SSEs. If both gateways indicate the SSE capability, SSEs shall be used to control the transition of transport methods. If either gateway does not indicate SSE capability, the default method of payload type indication shall be used.
+
+The optional SSE protocol is given in Annex C of [ITU-T V.150.1]. For the purposes of ToIP, the accepted media states used are audio, voice band data (VBD), text relay probing and text relay.
+
+When the SSE protocol is being used, the optional Reason Identifier Code (RIC) field in the SSE payload shall be sent and filled in with the appropriate code.
+
+#### **8.4.3 Transitioning to ToIP transport**
+
+This clause provides the requirements at the gateway when transitioning to a non-audio transport mode that will be used to carry the text telephony signal over the IP network.
+
+The ToIP gateway should minimize as much as possible the leakage (audio encoding) of the PTP signals into the IP network. If more than 50% of a bit of a character is leaked into the IP network, an extraneous character may be generated to the remote PTP device.
+
+To minimize the possibility of an erroneous character due to signal leakage in audio mode, the regenerating gateway should wait one character time from the onset of the possible leakage to regenerate the character. Silence may be generated when the gateway introduces this delay.
+
+The first character received on the PSTN interface of the gateway shall be transmitted only once to the IP network, i.e., it shall not be lost nor erroneously repeated by the gateway.
+
+#### **8.4.4 Transitioning from ToIP transport**
+
+Upon detection of loss of carrier or other signal event indicating that the local PTP device is no longer in the connected state, the gateways shall initiate a transition out of text relay mode and into audio mode. For payload type switching protocol, the gateways shall encode incoming signals using the RTP audio encoding. For the SSE protocol, the gateway shall initiate a switch to Audio mode by generating an SSE(AUDIO) to the remote gateway.
+
+When a gateway detects that the remote gateway has initiated a switch out of text relay mode and into audio mode, it shall drop carrier with its local PTP device (if carrier is still being generated by the gateway) and transition to audio mode transport.
+
+#### **8.4.5 Modulation support scenarios for text relay**
+
+To be compliant with this Recommendation, a gateway shall support full physical layer modulation/demodulation for at least one of the modes used by PTP devices as described in clause 8.3.1. The gateway shall also support the detection of signals used for all the PTP modulations listed in clause 8.3.1. This detection capability is used by the call discrimination procedures for the initiation of transitioning to VBD mode so that VBD can be used between the PTP devices even if the modulation is not fully supported by the gateway.
+
+The transition to text relay not only depends on the modulation being supported by the local gateway and PTP device, but also on the modulation supported by the remote gateway and the modulation used by the remote PTP device; in other words, even though the local gateway and the local PTP support the same modulation, text relay might not be the mode that is used. VBD could be the mode decided on instead. The call discrimination procedures defined in clause 20 use the knowledge of the modulations supported by both gateways and the signals observed from the PTP devices in determining whether text relay can be used. The overall goal of the call discrimination procedures is to ensure connectivity of the PTP devices with the use of text relay as the secondary goal.
+
+In the case where the PTP devices do not support a common modulation, the call discrimination procedures may still result in the use of text relay mode if the gateways do support their local PTP modulations. This scenario is what is referred to as protocol conversion throughout this Recommendation.
+
+Since the optional SSE protocol includes the mandatory indication of the signals that are being detected which caused the SSE to be generated, call discrimination procedures that use SSE will have additional flexibility resulting in more cases of using text relay in protocol conversion scenarios.
+
+## **9 ToIP operational modes**
+
+PTP signals shall either be carried using VBD mode or Text Relay mode. The call discrimination procedures defined in clause 20 define how the gateways shall transition from audio mode to either VBD or text relay mode when PTP signals are present. In the case where text relay mode is used, there still might be a stage where VBD is used during the call discrimination phase.
+
+The call discrimination procedures will guarantee that PTP devices will communicate if they are able to communicate over a PSTN connection, either through the preferred mode of text relay or using the fallback VBD mode. Additionally, the call discrimination procedures may result in the use of text relay mode to allow for connectivity of PTP devices that would not normally connect in a PSTN connection through the use of protocol conversion.
+
+## **10 Text Relay PHY layer operation**
+
+This clause describes the functionality and expected behaviour of the Text Relay PHY. The PHY in this context is defined as the physical layer of the PSTN text telephone to gateway connection and does not include the IP physical layer.
+
+The goal of ToIP is to ensure connectivity of analogue PSTN text telephony terminals on IP networks. This Recommendation does not require nor preclude the use of non-standard mechanisms. The ToIP procedures take into account that there are two independent PSTN connections to be established in order to provide a single end-to-end connection of the end-point text telephony terminals. The establishment of the text telephone physical layer consists of two stages. The first stage involves call discrimination including the detection and discrimination of the text telephony signals on the PSTN interface of the gateway. The second stage involves the establishment of the physical layer connection between the gateway and the text telephony terminal. The procedures that define this process are described in clause 20.
+
+The overall connection physical layer may be selectively transported in either VBD or text relay. The call discrimination and mode selection procedures define the rules for this choice.
+
+Text relay supports the ability for each gateway to connect with text telephones using different modulation modes. This allows for the possible interoperability of dissimilar text telephony devices across the IP network, although there are some limitations to this mode of interoperation. It is also possible to match the modulations on each PSTN link if necessary.
+
+To aid the call discrimination process, gateways exchange their preference for call discrimination and their supported modulation capability set. This exchange happens during call set-up using signalling mechanisms.
+
+The call discrimination procedures include mechanisms that attempt to match the modulation used on each PSTN call leg. This is not guaranteed, though, so differing modulations and differing signalling rates may result. In the case that the signalling rates differ on each PSTN call leg in text relay mode, buffer management and flow control may be required; Appendix IV provides relevant information on text buffering and transmission.
+
+# **11 IP transport for text relay**
+
+This Recommendation assumes that the IP protocol conforms to the following standards: [IETF RFC 791], [IETF RFC 950], [IETF RFC 919] and [IETF RFC 920]. This Recommendation does not impact any IP network topology, IP packet distribution and routing protocols, which are independent of this Recommendation.
+
+The default IP Transport Layer Protocol for this Recommendation shall be the protocol defined in Annex E. Optionally, the simple packet transport protocol (SPRT) as defined in Annex B of [ITU-T V.150.1] may be used if mutually negotiated. The use of other IP transport protocols is for further study.
+
+Since Annex E specifies transport of T.140-encoded data on RTP, it inherits the same reliability characteristics of any RTP media stream. Improved transport reliability may be achieved by utilizing [IETF RFC 2198] (Redundancy) and or [IETF RFC 2733] (Forward Error Correction). The use of these is optional but encouraged. Appendix III provides guidance for the use of [IETF RFC 2198] and [IETF RFC 2733].
+
+If using RTP for text relay transport, audio/t140c media type shall be supported by the gateway. Use of text/t140 media type for interoperability with non-V.151 devices that also use text/t140 is for further study.
+
+[IETF RFC 2198] (RTP redundancy) shall be implemented by gateways compliant to this Recommendation. [IETF RFC 2733] (RTP FEC) and SPRT may also be implemented by the gateway. Use of one or more of these mechanisms during a ToIP session is required if network conditions are such that acceptable performance cannot be achieved without them. Appendix III provides guidance on the use of [IETF RFC 2198].
+
+## **11.1 Single and dual port operation of text relay**
+
+Text relay packets shall be transmitted in the IP network on the same UDP port used for non text-relay packet (e.g., voice). Transmission of text relay packets on a separate UDP port is for further study.
+
+## **11.2 Text relay throughput**
+
+Gateways compliant to this Recommendation shall support PTPs operating at their full character speed.
+
+Characters received by the gateway from the PTP shall be transmitted to the IP network character by character. Characters should be sent into the IP network by the receiving gateway without delay. In the case that flow control is required (e.g., to honour the IP network character per second (CPS) value provided by the remote gateway through external signalling), some buffering of the character data before transmission into the IP or PSTN network may be required.
+
+Appendix IV provides information on how a gateway should handle buffering for the case when different signalling rates are used on the different PSTN call legs.
+
+## **12 Support of DTMF in ToIP**
+
+PTP devices that utilize DTMF tones to transmit characters as per Annex B of [ITU-T V.18] are supported by this Recommendation. DTMF tones should be carried in the IP network using [IETF RFC 2833], but may be supported using *UserInputIndication* H.245 messages for systems based on [ITU-T H.245]. Since DTMF PTP is only supported through the transmission of DTMF digits through the IP network without the discrimination of PTP DTMF digits from DTMF digits used for other purposes during the call (e.g., voice mail control, IVR), both end PTP devices must operate in DTMF mode for the end-to-end PTP connection to work.
+
+# **13 Transition out of text relay**
+
+A gateway receiving PTP signals shall initiate a switch to audio mode from text relay mode upon detection of loss of carrier. A gateway may implement a silence guard time between detection of loss of carrier and the initiation of a switch to audio mode to avoid multiple mode transitions in the case of two closely-timed text spurts. This silence guard time is recommended to be between 700 and 1000 ms. If non-carrier signals are detected in this guard time, the gateway should immediately initiate a switch to audio mode.
+
+For payload type switching, the gateway transitions to audio by encoding signals using the audio encoding and audio payload type.
+
+For the SSE protocol, the gateway will generate an SSE(AUDIO) to the remote gateway to initiate the switch to audio mode (see clause 20).
+
+The remote gateway, upon detecting the switch to audio mode initiated by the local gateway, shall stop generating carrier and transition to audio encoding, generating acknowledgement SSE(AUDIO) if SSE protocol is being used.
+
+## **14 T.140 encoding of text relay**
+
+Annex E requires the encoding of all text data using [ITU-T T.140]. For consistency and ensuring compatibility, all transport of text, whether it uses RTP, SPRT or some other IP-TLP, shall use [ITU-T T.140].
+
+### **14.1 Character set support**
+
+Gateways compliant with this Recommendation shall support 7-bit T.50 characters and 5-bit characters in Annex A of [ITU-T V.18] if the associated PTP mode is supported by the gateway for text relay. If the character set is supported, the gateway shall have the capability of mapping the T.50 or V.18 Annex A character set to T.140 upon demodulation of the PTP signal. The gateway shall also support the mapping of T.140 to T.50 or V.18 Annex A when remodulating the signal to the local PTP device. The mapping of the 5-bit character codes to 7-bit T.50 characters is described in Annex A of [ITU-T V.18].
+
+For PTP modes that utilizes a character set other than T.50 or V.18 Annex A, issues may arise between mapping of certain national characters to a character set other than the PTP's character set. This may lead to the inability to map characters correctly for the case when using protocol conversion between two different national PTP modes. Mapping between national character sets is not addressed in [ITU-T V.18]. Support of character sets other than T.50 and 5-bit characters in Annex A of [ITU-T V.18] and for mapping between national character sets is for further study.
+
+### **14.2 TIA-825A and T.50 encoding requirements**
+
+These requirements are required for gateways that support TIA-825A and T.50 Text telephones.
+
+For the case where a gateway is receiving text data from a peer gateway which in turn is connected to a TIA-825A or T.50 Text telephone and if for some reason that gateway detects the loss of a character in the packet network (e.g., due to congestion or packet loss) then it shall use the apostrophe character to replace the missed character if no other mechanisms for determining the lost character value are used. Also, if the T.140 lost character (0xFFFF hexadecimal) is received, then it too shall be translated to an apostrophe when playing out the character to a TIA-825A or T.50 receiver.
+
+Note that [ITU-T T.140] specifies that the 'new line' character is encoded as 0x2028 hexadecimal. If received by a gateway from a peer gateway and it is to be encoded to TIA-825A or T.50, the character shall be encoded as the two characters 'CR' 'LF' (Carriage Return and Line Feed).
+
+## **15 Gateway-to-gateway protocol definitions and procedures**
+
+### **15.1 Gateway capability and call set-up messages**
+
+This clause defines the functionality of the messages that are exchanged between gateways during the call set-up phase. These definitions are used by the following protocols: Annex G of [ITU-T H.323], [ITU-T H.245] and SIP/SDP. The values shown in this set of messages represent what should be functionally indicated by the signalling protocol.
+
+#### 15.1.1 Text telephone modulation support
+
+A list of the modulations supported in text relay mode by the gateway is shown in Table 15-1. Gateways compliant to this Recommendation shall advertise the support for at least one of these modulations.
+
+**Table 15-1 – PTP modulations**
+
+| Modulation | Description |
+|------------|-------------------------------------------------------------------------------------------|
+| V18 | V.18 "native mode" V.21 modulation |
+| BELL103 | Bell 103 based PTP modems (Annex D of [ITU-T V.18]) |
+| V23 | Videotext terminals ("Minitel"; see Annex E of [ITU-T V.18]) |
+| V21 | V.21 encoded per [ITU-T T.50] (Annex F of [ITU-T V.18]) |
+| EDT | European Deaf Telephone utilizing V.21 frequencies at 110 bit/s (Annex C of [ITU-T V.18]) |
+| TIA825 | Baudot terminals at 45.45 bit/s or at 50 bit/s (Annex A of [ITU-T V.18]) |
+
+#### 15.1.2 Remain in VBD preference
+
+This capability indicates the preference of the gateway to switch out of VBD mode when text signals are no longer present when using VBD for text transport. Both gateways must indicate this preference for it to be used in the call. Table 15-2 shows the valid values for VBD mode preference.
+
+**Table 15-2 – VBD mode preference**
+
+| VBD mode preference | Description |
+|---------------------|--------------------------------------------------------------------|
+| False (default) | Stay in VBD mode for the duration of the call. |
+| True | Switch back to AUDIO mode when text signals are no longer present. |
+
+#### 15.1.3 Characters per second (CPS)
+
+This optional parameter is an indication of the maximum number of characters per second that may be received in a session. If this parameter is not received by a gateway during the signalling of the call, a value of 30 shall be used. Gateways shall utilize this parameter to implement flow control with their local PTP device so as not to exceed transmission of characters into the IP network at a rate higher than indicated.
+
+#### 15.1.4 VBD parameters
+
+The specification of the VBD parameters is found in [ITU-T V.152].
+
+#### 15.1.5 SSE parameters
+
+If the optional SSE protocol is to be used, parameters are signalled as per clause E.1.3 of [ITU-T V.150.1] for SDP and clause F.6 of [ITU-T V.150.1] for H.245. To use the SSE protocol instead of the default payload type switching protocol for mode control, both gateways must signal the support for all of the SSE event encodings defined in Table 15-3.
+
+**Table 15-3 – Required SSE event encodings**
+
+| Event encoding
(Decimal) | Indicated media state |
+|-------------------------------------|------------------------------|
+| 1 | Initial Audio |
+| 2 | Voice Band Data (VBD) |
+| 5 | Text Relay |
+| 6 | Text Relay Probing |
+
+#### 15.1.6 SPRT parameters
+
+If the optional IP-TLP SPRT is to be used, then the following parameters are required to be indicated:
+
+Maximum payload size of SPRT channels 0 to 2, and maximum window size for SPRT channels 1 and 2. SPRT channel 3 shall not be used, so no configuration of it is required.
+
+## 15.2 Gateway call discrimination messages
+
+#### 15.2.1 SSE reason identifier codes
+
+Reason Identifier Codes to be used with the optional SSE protocol are defined in Table 12 of [ITU-T V.150.1]. The appropriate SSE RIC shall be sent with the SSE messages when the SSE protocol has been successfully negotiated between the gateways.
+
+# 16 Start-up mode of operation
+
+ToIP gateways will need to co-exist with other "over-IP" mechanisms. (For example Voice over IP, Facsimile over IP, and Modem over IP.) The entry into Text over IP mode corresponding to the beginning of the call discrimination procedures defined in clause 20 happens when certain signals are detected while the gateway is operating in Voice over IP mode. Text over IP mode may also be entered from the Modem over IP (V.150.1) call discrimination procedures as described in clause 16.1.
+
+### 16.1 Inter-relationship with V.150.1
+
+If V.150.1 support is implemented and successfully negotiated by the gateway (in addition to V.151 support), text relay mode as described in this Recommendation shall be entered into using the SSE protocol procedures as described in clause 18 of [ITU-T V.150.1] for supported PTP types that utilize answer tones. For supported PTP types that do not use answer tones, the procedures defined in this Recommendation shall be used.
+
+## 16.2 Inter-relation with V.152
+
+If V.152 support is implemented and successfully negotiated by the gateway (in addition to V.151 support) and V.150.1 support is not successfully negotiated or implemented by the gateway, the procedures described in this Recommendation shall take precedence over those defined in [ITU-T V.152] for signal stimuli that represents V.151 text relay mode supported PTP types. For
+
+non-PTP signal stimuli that would initiate use of VBD operation, procedures defined in [ITU-T V.152] shall be used.
+
+# **17 Voiceband data modem interworking requirements**
+
+Certain PTP modes are indistinguishable from voiceband data applications. Examples of this include PTP modes that utilize V.21 and V.23 modulations. Call discrimination procedures defined in clause 20 have been designed so that if both end devices are voiceband data modems that use such modulations, the connection will result in use of text relay between the two end modems if V.151 text relay using these modulations is supported by both gateways. If either gateway does not support the modulation for text relay, the connection will result in VBD mode between the two gateways.
+
+In the case that the connection results in text relay, the modem data will be encoded utilizing T.140 encoding. Data integrity between the end modems will be ensured as long as the data modems are using 8-bit character sizes (including parity). For other character sizes, the data will be corrupted due to the assumption that the data is encoded using T.140.
+
+So as not to corrupt the data in the case that text relay mode is used for voiceband data modems, the CPS (character per second) value advertised by the gateway in the call signalling parameters should be greater than or equal to the highest signalling rate for all modulations supported by the gateway.
+
+## **18 Facsimile interworking requirements**
+
+Facsimile uses similar signals to those used by certain PTP devices, including V.8 start-up sequence and answer tone. If ToIP is supported for modulations that use signals also used for facsimile, the procedures defined in this Recommendation may be exited and facsimile processing procedures entered (e.g., relay or VBD) upon detection of the signal being generated by a facsimile instead of a PTP. Examples of these detection events include recognition of the CM call function as indicating facsimile, or the existence of a V.21 flag sequence.
+
+## **19 Call set-up procedures**
+
+The call set-up procedures are defined in Annexes B and C of this Recommendation and in Annex G of [ITU-T H.323].
+
+## **20 Call discrimination procedures**
+
+The following clause defines the procedures to be used by a ToIP gateway during the call discrimination phase of the connection. The call discrimination phase starts when text telephony signals are first present on the PSTN interface of either gateway. The call discrimination phase ends when end-to-end connectivity using V.151 is established between the two terminal PTP devices.
+
+### **20.1 V.8 *bis* processing**
+
+In all operating modes (e.g., audio, VBD), ToIP gateways shall monitor and detect V.8 *bis* dual tone on the PSTN link and prevent further V.8 *bis* signals from being transmitted into the IP network, thereby disabling V.8 *bis* protocol between the PTP devices. The support of V.8 *bis* by the PTP devices is for further study.
+
+### **20.2 V.8 CI/XCI processing**
+
+V.8 CI/XCI signals can be carried in audio mode or, optionally, cause initiation of a transition to VBD mode. If CI/XCI is carried in voice mode, there is a probability that the CI/XCI will not successfully be detected by the remote PTP. This misdetection is due to the possible corruption of the signal by the voice codec and other signal processing distortions implicit in voice mode.
+
+[ITU-T V.8] does not treat CI/XCI as reliable signals (i.e., V.8 allows for the loss or non-transmission of CI/XCI in the protocol definition), so carriage of these signals using voice mode is acceptable. If CI/XCI is not detected properly by the remote PTP device, there can be up to an additional 3 seconds of delay for the ANSam tone generation relative to the case where CI/XCI is detected.
+
+## 20.3 Call discrimination overview
+
+Gateways compliant to this Recommendation shall transport PTP signals that they are capable of detecting and discriminating using either text relay transport or VBD transport. Text relay is the preferred mode of transport for the support PTP signals with VBD the fallback mode of transport. The fallback to VBD may occur because the end-to-end establishment of a PTP connection was not possible due to the lack of support of the local PTP modulation type at one or both of the gateways, or the inability to negotiate to text relay mode based on the procedures defined in this clause.
+
+Appendix II provides flow diagrams of example call discrimination scenarios that are useful in understanding the call discrimination procedures described in this clause. These call flows are examples only. The text and SDL diagrams provided in this clause provide the normative description of the call discrimination for ToIP.
+
+Depending on the type of modulation supported by the PTPs and the gateways, this Recommendation supports several call discrimination procedures.
+
+A gateway that supports a subset of the V.18 PTP modulations may scale down the procedures defined in this clause. The scaled-down procedures will fully support text relay for the modulations supported by the gateway, with VBD support for those modulations not supported by the gateway.
+
+## 20.4 Call discrimination SDL diagrams
+
+This clause provides the SDL processing description for the procedures defined by the call discrimination call flows as described in Appendix II.
+
+The SDL diagrams define the procedures at the gateway for call discrimination processing. These SDL diagrams are derived from the call discrimination call flows given in Appendix II. The symbols used in the SDL diagrams are defined in Figure 20-1 below.
+
+
+
+Figure 20-1 – SDL diagram definition. This diagram defines the symbols used in SDL diagrams. It includes: a 'Start' symbol (a rounded rectangle with a semi-circular end on the left), a 'procedure call' symbol (a rectangle with double vertical lines on the left and right sides), a 'received IP message' symbol (a rectangle with a pointed right side), a 'sent IP message' symbol (a rectangle with a pointed left side), a 'state' symbol (a rounded rectangle), a 'received signal processing primitive' symbol (a rectangle with a pointed right side and double vertical lines on the left), a 'sent signal processing primitive' symbol (a rectangle with a pointed left side and double vertical lines on the right), and a 'decision' symbol (a diamond shape). The text 'V.151(06)\_F20-1' is located at the bottom right of the diagram.
+
+**Figure 20-1 – SDL diagram definition**
+
+#### 20.4.1 Detection of PTP signals
+
+Table 20-1 describes the signals that shall be detected by the gateway for the purpose of transitioning to either VBD or text relay mode per the SDLs.
+
+**Table 20-1 – Signal detection criteria**
+
+| Signal detected | Detected TTY mode | SSE RIC |
+|----------------------------------------------|--------------------------------------------|-----------------------------------------------|
+| 390-Hz tone for 1 second | V.23 Annex E of [ITU-T V.18] call mode | V.23 Low channel |
+| 1300-Hz tone for 1 second | V.23 Annex E of [ITU-T V.18] answer mode | V.23 High channel |
+| 980-Hz tone for 1 second | V.21 Annex F of [ITU-T V.18] call mode | V.21 Ch1 |
+| 1650-Hz tone for 1 second | V.21 Annex F of [ITU-T V.18] answer mode | V.21 Ch2 |
+| V.21 low-band modulated character, 110 bit/s | EDT Annex C of [ITU-T V.18] | V.21 Ch1 |
+| 1270-Hz tone for 1 second | Bell 103 Annex D of [ITU-T V.18] call mode | Bell 103 modem |
+| 1400-Hz mark, 1800-Hz space FSK signals | Baudot Annex A of [ITU-T V.18] | TIA-825A (50 bit/s)
TIA-825A (45.45 bit/s) |
+
+A PTP conforming to Annex C of [ITU-T V.18] can send a 980-Hz tone for 1 second after the last character transmitted in a burst of characters. Since, in this case, the 980-Hz tone follows a valid character sequence that indicates Annex C of [ITU-T V.18], the gateway should not use this signal to incorrectly designate the PTP as an Annex F of [ITU-T V.18] PTP.
+
+The Bell 103 high-band mark tone (2225 Hz) is treated the same as ANS in the call discrimination procedures, not as a PTP mark tone. This is because a Bell 212 data modem connection will start out with a 2225-Hz tone as well, but a 1270-Hz tone will never be received, so the connection should stay in VBD.
+
+The 1300-Hz V.23 mark should not be confused with a calling tone using the same frequency (duration of 0.5-0.7 s on). Implementations shall take care not to initiate transitions to VBD/text relay based on a calling tone.
+
+Further details on the requirements for the detection of PTP characters for the purpose of mode transitions are given in clause 8.4.3.
+
+#### 20.4.2 SDL state variables
+
+The SDLs make use of the *tty\_mode* state variable to track the PTP modulation type detected by the gateway. This state variable is local to each gateway and is initialized to "unknown" at the start of the procedures.
+
+#### 20.4.3 Payload type switching SDL diagrams
+
+The following SDL diagrams define the procedures at the gateway for call discrimination processing when using payload type switching. These SDL diagrams are derived from the call discrimination call flows given in Appendix II. The symbols used in the SDL diagrams are defined in Figure 20-1.
+
+NOTE 1 – In the following diagrams (Figure 20-2) for payload type switching SDLs, the paths are only used when both gateways have indicated support for native V.18 text relay.
+
+
+
+```
+
+graph TD
+ Start([Start]) --> Process[tty_mode=unknown
+PT=audio]
+ Process --> audio([audio])
+
+```
+
+V.151(06)\_F05
+
+SDL flowchart for payload type switching (sheet 1 of 6). It starts with a 'Start' terminal, followed by a process block 'tty\_mode=unknown PT=audio', and ends with an 'audio' state terminal. The label V.151(06)\_F05 is at the bottom right.
+
+**Figure 20-2 – SDL for payload type switching (sheet 1 of 6)**
+
+
+
+```
+
+graph TD
+ audio_in([audio]) --> Junction(( ))
+ Junction --> CI_XCI[/CI/XCI/]
+ Junction --> PT_VBD_in[/PT=VBD/]
+ Junction --> ANSam[/ANSam/]
+ Junction --> ANS[/ANS/]
+
+ CI_XCI --> VBD_preferred{VBD
+preferred}
+ VBD_preferred -- yes --> PT_VBD_proc1[PT=VBD]
+ PT_VBD_proc1 --> VBD1([VBD])
+ VBD_preferred -- no --> audio_out([audio])
+
+ PT_VBD_in --> PT_VBD_proc2[PT=VBD]
+ PT_VBD_proc2 --> VBD2([VBD])
+
+ ANSam --> tty_mode_V18[tty_mode=V.18
+PT=VBD]
+ tty_mode_V18 --> VBD3([VBD])
+
+ ANS --> tty_mode_FDX[tty_mode=FDX
+PT=VBD]
+ tty_mode_FDX --> VBD4([VBD])
+
+```
+
+V.151(06)\_F06
+
+SDL flowchart for payload type switching (sheet 2 of 6). It branches from an 'audio' state terminal into four parallel input paths. Path 1: CI/XCI input leads to a decision 'VBD preferred'. If 'yes', PT=VBD process block leads to VBD state; if 'no', audio state. Path 2: PT=VBD input leads to PT=VBD process block, then VBD state. Path 3: ANSam input leads to tty\_mode=V.18 PT=VBD process block, then VBD state. Path 4: ANS input leads to tty\_mode=FDX PT=VBD process block, then VBD state. The label V.151(06)\_F06 is at the bottom right.
+
+**Figure 20-2 – SDL for payload type switching (sheet 2 of 6)**
+
+
+
+```
+
+graph TD
+ Input1[HDX character
+(clause 20.4.3.1)] --> D1{G1 & G2
+support modulation}
+ Input2[FDX answering
+carrier detect
+(clause 20.4.3.2)] --> B1[tty_mode=FDX
+PT=VBD]
+ Input3[PT=TR] --> B2[connect with
+local PTP
+(clause 20.4.3.3)]
+ Input4[2225 Hz] --> B3[tty_mode=FDX
+PT=VBD]
+
+ D1 -- no --> B4[PT=VBD]
+ D1 -- yes --> B5[PT=TR]
+ B4 --> O1([VBD])
+ B5 --> B6[PT=TR(CHAR)]
+ B6 --> O2([TR])
+ B1 --> O3([VBD])
+ B2 --> B7[tty_mode=X
+PT=TR]
+ B7 --> O4([TR])
+ B3 --> O5([VBD])
+
+```
+
+V.151(06)\_F07
+
+SDL flowchart for payload type switching (sheet 3 of 6). The flowchart starts with four parallel inputs: 'HDX character (clause 20.4.3.1)', 'FDX answering carrier detect (clause 20.4.3.2)', 'PT=TR', and '2225 Hz'. Each input leads to a specific processing block. The 'HDX character' block leads to a decision 'G1 & G2 support modulation'. If 'no', it sets 'PT=VBD' and outputs 'VBD'. If 'yes', it sets 'PT=TR' and outputs 'PT=TR(CHAR)' then 'TR'. The 'FDX answering carrier detect' block sets 'tty\_mode=FDX' and 'PT=VBD', outputting 'VBD'. The 'PT=TR' block connects with local PTP (clause 20.4.3.3), sets 'tty\_mode=X' and 'PT=TR', outputting 'TR'. The '2225 Hz' block sets 'tty\_mode=FDX' and 'PT=VBD', outputting 'VBD'.
+
+Figure 20-2 – SDL for payload type switching (sheet 3 of 6)
+
+![SDL flowchart for payload type switching (sheet 4 of 6). The flowchart starts with a 'VBD' oval, which branches into four paths, each labeled with '[§ 20.4.3 Note 1]'. The first path leads to 'CM (w/ call function = text)', then a decision 'G1 & G2 support V.18 native'. If 'no', it outputs 'VBD'; if 'yes', it sets 'tty_mode=V.18' and outputs 'VBD'. The second path leads to 'end of JM (w/ call function = text)', then a decision 'G1 & G2 support V.18 native'. If 'no', it outputs 'VBD'; if 'yes', it sets 'tty_mode=V.18' and 'PT=TR', outputting 'TR'. The third path leads to 'end of CJ', then a decision 'tty+mode=V.18'. If 'no', it outputs 'VBD'; if 'yes', it sets 'tty_mode=V.18' and 'PT=TR', outputting 'TR'. The fourth path leads to 'PT=TR', then 'connect (clause 20.4.3.4)', then 'tty_mode=X' and 'PT=TR', outputting 'TR'.](a149b400127a3e3e50b3c98d27c5935c_img.jpg)
+
+```
+
+graph TD
+ Start([VBD]) -- "[§ 20.4.3 Note 1]" --> B1[CM (w/ call
+function =
+text)]
+ Start -- "[§ 20.4.3 Note 1]" --> B2[end of JM (w/
+call function =
+text)]
+ Start -- "[§ 20.4.3 Note 1]" --> B3[end of CJ]
+ Start -- "[§ 20.4.3 Note 1]" --> B4[PT=TR]
+
+ B1 --> D1{G1 & G2
+support
+V.18 native}
+ D1 -- no --> O1([VBD])
+ D1 -- yes --> B5[tty_mode=V.18]
+ B5 --> O2([VBD])
+
+ B2 --> D2{G1 & G2
+support
+V.18 native}
+ D2 -- no --> O3([VBD])
+ D2 -- yes --> B6[tty_mode=V.18
+PT=TR]
+ B6 --> O4([TR])
+
+ B3 --> D3{tty+mode=V.18}
+ D3 -- no --> O5([VBD])
+ D3 -- yes --> B7[tty_mode=V.18
+PT=TR]
+ B7 --> O6([TR])
+
+ B4 --> B8[connect
+(clause 20.4.3.4)]
+ B8 --> B9[tty_mode=X
+PT=TR]
+ B9 --> O7([TR])
+
+```
+
+V.151(06)\_F08CM
+
+SDL flowchart for payload type switching (sheet 4 of 6). The flowchart starts with a 'VBD' oval, which branches into four paths, each labeled with '[§ 20.4.3 Note 1]'. The first path leads to 'CM (w/ call function = text)', then a decision 'G1 & G2 support V.18 native'. If 'no', it outputs 'VBD'; if 'yes', it sets 'tty\_mode=V.18' and outputs 'VBD'. The second path leads to 'end of JM (w/ call function = text)', then a decision 'G1 & G2 support V.18 native'. If 'no', it outputs 'VBD'; if 'yes', it sets 'tty\_mode=V.18' and 'PT=TR', outputting 'TR'. The third path leads to 'end of CJ', then a decision 'tty+mode=V.18'. If 'no', it outputs 'VBD'; if 'yes', it sets 'tty\_mode=V.18' and 'PT=TR', outputting 'TR'. The fourth path leads to 'PT=TR', then 'connect (clause 20.4.3.4)', then 'tty\_mode=X' and 'PT=TR', outputting 'TR'.
+
+Figure 20-2 – SDL for payload type switching (sheet 4 of 6)
+
+
+
+```
+
+graph TD
+ Start(( )) --> A[/modem X
+detected
+(clause
+20.4.3.5)/]
+ A --> B{tty_mode
+=V.18}
+ B -- yes --> C([VBD])
+ B -- no --> D{tty_mode
+=FDX}
+ D -- yes --> C
+ D -- no --> E{G1 & G2
+support X}
+ E -- yes --> F[connect with
+PTP using X
+(clause 20.4.3.6)]
+ E -- no --> C
+ F --> G[PT=TR]
+ G --> H[/PT=TR/]
+ H --> I([TR])
+ J[Send character
+in Text Relay
+packet if available
+(e.g. for HDX modems),
+otherwise send NULL] -.- H
+
+```
+
+V.151(06)\_F09
+
+SDL flowchart for payload type switching (sheet 5 of 6). The flow starts with an input 'modem X detected (clause 20.4.3.5)'. It proceeds to a decision 'tty\_mode = V.18'. If 'yes', it transitions to state 'VBD'. If 'no', it proceeds to another decision 'tty\_mode = FDX'. If 'yes', it transitions to state 'VBD'. If 'no', it proceeds to a third decision 'G1 & G2 support X'. If 'no', it transitions to state 'VBD'. If 'yes', it performs the task 'connect with PTP using X (clause 20.4.3.6)', then sets 'PT=TR'. It then sends an output 'PT=TR' while simultaneously executing the comment 'Send character in Text Relay packet if available (e.g. for HDX modems), otherwise send NULL'. Finally, it enters state 'TR'.
+
+**Figure 20-2 – SDL for payload type switching (sheet 5 of 6)**
+
+
+
+```
+
+graph TD
+ TR([TR]) --> CL[/carrier loss/]
+ CL --> PT[PT=audio]
+ PT --> audio([audio])
+
+```
+
+V.151(06)\_F10
+
+Figure 20-2: SDL for payload type switching. The diagram shows a vertical flow: an oval labeled 'TR' points to a chevron-shaped box labeled 'carrier loss', which points to a rectangular box labeled 'PT=audio', which finally points to an oval labeled 'audio'. The text 'V.151(06)\_F10' is located to the right of the 'audio' oval.
+
+**Figure 20-2 – SDL for payload type switching (sheet 6 of 6)**
+
+##### **20.4.3.1 HDX character**
+
+This event corresponds to the detection of an HDX PTP signal as per clause 20.4.1.
+
+##### **20.4.3.2 FDX answering carrier detect**
+
+This event corresponds to the detection of a carrier generated by an FDX PTP device as described in clause 20.4.1.
+
+##### **20.4.3.3 Connect with local PTP**
+
+This procedure box is entered when a TR payload type is received while the connection is in audio mode. This is the case when an HDX modulation has been detected by the remote gateway and both gateways support this HDX modulation. The gateway entering this procedure box shall attempt to connect with its local PTP device using an HDX modulation.
+
+##### **20.4.3.4 Connect**
+
+In this procedure box, the gateway shall attempt to connect with its local PTP device using modulations that it supports. The gateway should be able to connect to its local PTP device since the remote gateway would not have sent the TR payload unless the PTP modulation that it detected was also supported for text relay by the local gateway. It is assumed for this case that the PTP devices are compatible.
+
+The gateway shall perform the automode probing as defined in Figure 2b of [ITU-T V.18] and its corresponding text. The gateway shall not generate the ANSam signal at the beginning of these procedures, i.e., it shall skip over the generate ANSam block in Figure 2b of [ITU-T V.18] and go straight to the probing flows. The gateway shall only probe for modulations that it supports for text relay.
+
+In order to allow for data modem connections over text relay, the gateway shall probe for supported FDX modulations before probing for supported HDX modulations.
+
+##### **20.4.3.5 Modem X detected**
+
+This event corresponds to the detection of a PTP modulation as per clause 20.4.1.
+
+##### **20.4.3.6 Connect with PTP using X**
+
+The gateway shall connect with its local PTP device using the modulation detected and transition the channel to text relay mode through the generation of TR encoded RTP packets to the remote gateway.
+
+#### 20.4.4 SDL for SSE protocol
+
+The following SDL diagrams define the procedures at the gateway for call discrimination processing when using SSE protocol switching. These SDL diagrams are derived from the call discrimination call flows given in Appendix II. The symbols used in the SDL diagrams are defined in Figure 20-1.
+
+NOTE 1 – In the following diagrams (Figure 20-3) for SSE SDLs, the paths are only used when both gateways have indicated support for native V.18 text relay.
+
+
+
+```
+graph TD; Start([Start]) --> Process[tty_mode=unknown]; Process --> Data([a, a]);
+```
+
+V.151(06)\_F11
+
+Figure 20-3 (sheet 1 of 10) is a simple SDL diagram. It starts with a 'Start' terminal, followed by a process block 'tty\_mode=unknown', and ends with a data object 'a, a'. The label 'V.151(06)\_F11' is at the bottom right.
+
+Figure 20-3 – SDL for SSE protocol (sheet 1 of 10)
+
+
+
+```
+graph TD; Start([a,a]) --> Branch(( )); Branch --> Event1[/Start of CI/XCI/]; Event1 --> Decision1{VBD Preferred?}; Decision1 -- Yes --> Process1[/SSE(VBD:CI/XCI)/]; Decision1 -- No --> Data1([a, a]); Process1 --> Data2([v, a]); Branch --> Event2[/SSE(TP:X)/]; Event2 --> Process2[/start auto-mode/probing
+(clause 20.4.4.1)/]; Process2 --> Event3[/SSE(TP, p\')/]; Event3 --> Data3([tp, tp]); Branch --> Event4[/end of CI/XCI/]; Event4 --> Process3[/tty_type=V.18/]; Process3 --> Process4[/squellch TDM line/]; Process4 --> Event5[/SSE(TP, CI/XCI)/]; Event5 --> Data4([tp, a]); Branch --> Event6[/SSE(VBD:X)/]; Event6 --> Decision2{ }; Note[X=tty modulation
+not supported using
+text-relay by other
+gateway OR FDX
+and not supported by
+this gateway] -.-> Decision2; Decision2 -- yes --> Process5[/turn off
+detectors/]; Decision2 -- no --> Event7[/SSE(VBD:p\')/]; Process5 --> Event7; Event7 --> Data5([v, v]);
+```
+
+V.151(06)\_F12
+
+Figure 20-3 (sheet 2 of 10) is a complex SDL diagram starting from state 'a,a'. It branches into four main paths. Path 1: 'Start of CI/XCI' event leads to a decision 'VBD Preferred?'. If 'Yes', it goes to 'SSE(VBD:CI/XCI)' and then 'v, a'. If 'No', it goes to 'a, a'. Path 2: 'SSE(TP:X)' event leads to 'start auto-mode/probing (clause 20.4.4.1)', then 'SSE(TP, p\')', and then 'tp, tp'. Path 3: 'end of CI/XCI' event leads to 'tty\_type=V.18', then 'squellch TDM line', then 'SSE(TP, CI/XCI)', and then 'tp, a'. Path 4: 'SSE(VBD:X)' event leads to a decision diamond. A note points to this diamond: 'X=tty modulation not supported using text-relay by other gateway OR FDX and not supported by this gateway'. If 'yes', it goes to 'turn off detectors' and then 'SSE(VBD:p\')', leading to 'v, v'. If 'no', it goes directly to 'SSE(VBD:p\')' and then 'v, v'. The label 'V.151(06)\_F12' is at the bottom right.
+
+Figure 20-3 – SDL for SSE protocol state (a,a) Part 1 (sheet 2 of 10)
+
+
+
+```
+
+graph TD
+ TopLine[ ] --- L1[ ]
+ TopLine --- L2[ ]
+ TopLine --- L3[ ]
+ TopLine --- L4[ ]
+
+ L1 --> E1[/2225 Hz/]
+ E1 --> P1[tty_type= Bell103]
+ P1 --> S1{{SSE (VBD:2225)}}
+ S1 --> O1([v, a])
+
+ L2 --> E2[/ANSam/]
+ E2 --> P2[tty_type=V.18]
+ P2 --> S2{{SSE (VBD:ANSam)}}
+ S2 --> O2([v, a])
+
+ L3 --> E3[/ANS detect/]
+ E3 --> S3{{SSE (VBD:ANS)}}
+ S3 --> O3([v, a])
+
+ L4 --> E4[/carrier detected X
+(clause 20.4.4.2)/]
+ E4 --> P4[turn off detectors]
+ P4 --> D1{text relay support for X?}
+ D1 -- no --> S4{{SSE (VBD:X)}}
+ S4 --> O4([v,a])
+ D1 -- yes --> D2{(X=FDX) && !(remote gateway support)}
+ D2 -- yes --> S5{{SSE(VBD:X)}}
+ S5 --> O5([v, a])
+ D2 -- no --> P5[tty_mode=X]
+ P5 --> S6{{SSE(TP,X)}}
+ S6 --> O6([tp, a])
+
+```
+
+V.151(06)\_F13
+
+SDL flowchart for SSE protocol state (a,a) Part 2. The diagram shows four parallel event paths from a common top line. Path 1: '2225 Hz' event leads to 'tty\_type= Bell103' process, then 'SSE (VBD:2225)' process, and finally 'v, a' output. Path 2: 'ANSam' event leads to 'tty\_type=V.18' process, then 'SSE (VBD:ANSam)' process, and finally 'v, a' output. Path 3: 'ANS detect' event leads to 'SSE (VBD:ANS)' process, and finally 'v, a' output. Path 4: 'carrier detected X (clause 20.4.4.2)' event leads to 'turn off detectors' process, then a decision 'text relay support for X?'. If 'no', it leads to 'SSE (VBD:X)' process and 'v,a' output. If 'yes', it leads to another decision '(X=FDX) && !(remote gateway support)'. If 'yes' to this second decision, it leads to 'SSE(VBD:X)' process and 'v, a' output. If 'no', it leads to 'tty\_mode=X' process, then 'SSE(TP,X)' process, and finally 'tp, a' output. The identifier 'V.151(06)\_F13' is located at the bottom right of the diagram area.
+
+Figure 20-3 – SDL for SSE protocol state (a,a) Part 2 (sheet 3 of 10)
+
+
+
+```
+
+graph TD
+ Start([v,v]) --> SSE_TR_X[SSE(TR, X)]
+ Start --> SSE_TR_CJ[SSE(TR, CJ)]
+ Start --> End_CI_XCI[/end CI/XCI/]
+
+ Note1[§ 20.4.4 Note 1] --> SSE_TR_CJ
+
+ SSE_TR_X --> D1{tty_type= Bell103?}
+ D1 -- yes --> SSE_TR_Bell103{{SSE(TR: Bell103)}}
+ SSE_TR_Bell103 --> Act1[Connect to Bell103]
+ Act1 --> End1([tr, tp])
+
+ D1 -- no --> D2{tty_type= V.18?}
+ D2 -- yes --> SSE_TR_Y{{SSE(TR, Y)
+(Y is the modulation used locally, Y=X if available)}}
+ SSE_TR_Y --> Act2[connect to V.18 modem with Y
+(clause 20.4.4.4)]
+ Act2 --> End2([tr, tp])
+
+ D2 -- no --> D3{X=CI/XCI}
+ D3 -- yes --> SSE_TP_P1{{SSE(tp, p')}}
+ SSE_TP_P1 --> End3([tp, tp])
+
+ D3 -- no --> Act3[start automodem originating
+(clause 20.4.4.5)]
+ Act3 --> SSE_TP_P1
+
+ SSE_TR_CJ --> D4{tty_type= v.18}
+ D4 -- yes --> Act4[connect V.18(V.21)]
+ Act4 --> SSE_TR_P1{{SSE(TR, p')}}
+ SSE_TR_P1 --> End4([tr, tr])
+
+ D4 -- no --> SSE_A{{SSE(A)}}
+ SSE_A --> End5([a, i])
+
+ End_CI_XCI --> Act5[tty_type=V.18]
+ Act5 --> SSE_TP_CI_XCI{{SSE(tp, CI/XCI)}}
+ SSE_TP_CI_XCI --> Act6[squelch transmitter]
+ Act6 --> End6([tp, v])
+
+ Note2[Can only receive SSE(TR) in VBD mode for case of V.8 through VBD because of failure to detect CI/XCI]
+ Note2 -.-> End4
+
+```
+
+V.151(06)\_F14\_CM
+
+SDL flowchart for SSE protocol state (v,v) Part 1. The flowchart starts with state 'v,v' and branches into three main paths: SSE(TR, X), SSE(TR, CJ), and end CI/XCI. Each path contains various state transitions, decision diamonds, and actions based on 'tty\_type' and other conditions. A note at the top right points to the SSE(TR, CJ) path. A dashed box at the bottom right contains a note about VBD mode.
+
+Figure 20-3 – SDL for SSE protocol state (v,v) Part 1 (sheet 4 of 10)
+
+
+
+```
+
+graph TD
+ TopLine[ ]
+ TopLine -- "[§ 20.4.4 Note 1]" --> JM[JM
+(text mode)]
+ TopLine -- "[§ 20.4.4 Note 1]" --> CM[CM
+(text mode)]
+ TopLine -- "[§ 20.4.4 Note 1]" --> endCJ[end of CJ]
+ TopLine -- "[§ 20.4.4 Note 1]" --> CD[Carrier detect X
+(clause 20.4.4.2)]
+
+ JM --> G1G2_1{G1 & G2
+support
+V.18 native?}
+ G1G2_1 -- yes --> ttyV18_1[tty_type=V.18]
+ ttyV18_1 --> vv1_1((v,v))
+ G1G2_1 -- no --> vv1_1
+
+ CM --> G1G2_2{G1 & G2
+support
+V.18 native?}
+ G1G2_2 -- yes --> ttyV18_2[tty_type=V.18]
+ ttyV18_2 --> vv1_2((v,v))
+ G1G2_2 -- no --> vv1_2
+
+ endCJ --> ttyV18_3{tty_type=
+V.18?}
+ ttyV18_3 -- yes --> SSE_TR_CJ[SSE(TR:CJ)]
+ SSE_TR_CJ --> connectV18[connect
+V.18(V.21)]
+ connectV18 --> trv1((tr,v))
+ ttyV18_3 -- no --> vv1_3((v,v))
+
+ CD --> ttyV18_4{tty_type=
+V.18?}
+ ttyV18_4 -- no --> turnOff[turn off
+detectors]
+ turnOff --> XFDX{X==FDX
+&&
+!(remote gateway
+support)}
+ XFDX -- yes --> vv1_4((v,v))
+ XFDX -- no --> ttyX[tty_type=X]
+ ttyX --> SSE_TP_X[SSE(TP,X)]
+ SSE_TP_X --> tpv1((tp,v))
+ ttyV18_4 -- yes --> AllowEnd[Allow end-to-end probing
+when V.18 answers
+non-V.18]
+ AllowEnd -.-> vv1_5((v,v))
+ AllowEnd -.-> V151F15[V.151(06)_F15]
+
+```
+
+SDL flowchart for SSE protocol state (v,v) Part 2. The flowchart starts with four parallel paths from a common top line. Path 1: JM (text mode) -> G1 & G2 support V.18 native? -> yes -> tty\_type=V.18 -> v,v; no -> v,v. Path 2: CM (text mode) -> G1 & G2 support V.18 native? -> yes -> tty\_type=V.18 -> v,v; no -> v,v. Path 3: end of CJ -> tty\_type=V.18? -> yes -> SSE(TR:CJ) -> connect V.18(V.21) -> tr,v; no -> v,v. Path 4: Carrier detect X (clause 20.4.4.2) -> tty\_type=V.18? -> no -> turn off detectors -> (X==FDX) && !(remote gateway support) -> yes -> v,v; no -> tty\_type=X -> SSE(TP,X) -> tp,v; yes -> Allow end-to-end probing when V.18 answers non-V.18 -> v,v. A dashed box around the 'Allow end-to-end probing...' note is labeled V.151(06)\_F15.
+
+Figure 20-3 – SDL for SSE protocol state (v,v) Part 2 (sheet 5 of 10)
+
+
+
+```
+
+graph TD
+ Start([tp, tp]) --> ANSam[/ANSam/]
+ Start --> SSETRX[/SSE(TR:X)/]
+ Start --> AutoMode[/Auto-mode/
+probing time-out/]
+
+ ANSam --> SSETRANSam{{SSE(TR:ANSam)}}
+ SSETRANSam --> StartConnectPTP[start connect
+with answering
+V.18 PTP
+(clause 20.4.4.6)]
+ StartConnectPTP --> EndTrTp1([tr, tp])
+
+ SSETRX --> TTYType{tty_type =
+unknown}
+ TTYType -- yes --> SSEA{{SSE(A)}}
+ SSEA --> EndAi([a, i])
+ TTYType -- no --> StartConnectPTP2[start connect
+with PTP
+(clause 20.4.4.3)]
+ StartConnectPTP2 --> SSETRp'{{SSE(TR, p')}}
+ SSETRp' --> EndTrTp2([tr, tp])
+
+ AutoMode --> SSEVBDTimeout{{SSE(VBD:Timeout)}}
+ SSEVBDTimeout --> TurnOffDetectors[turn off detectors]
+ TurnOffDetectors --> EndVtp([v, tp])
+
+ Note[Error if we get here
+without knowing the
+TTY type] -.-> TTYType
+
+```
+
+V.151(06)\_F16
+
+SDL flowchart for SSE protocol state (tp, tp) Part 1. The flowchart starts with state 'tp, tp' and branches into three paths: ANSam, SSE(TR:X), and Auto-mode/probing time-out. The ANSam path leads to SSE(TR:ANSam) and then to 'start connect with answering V.18 PTP (clause 20.4.4.6)', resulting in state 'tr, tp'. The SSE(TR:X) path leads to a decision 'tty\_type = unknown'. If 'yes', it leads to SSE(A) and then state 'a, i'. If 'no', it leads to 'start connect with PTP (clause 20.4.4.3)', then SSE(TR, p'), and finally state 'tr, tp'. The Auto-mode/probing time-out path leads to SSE(VBD:Timeout) and then 'turn off detectors', resulting in state 'v, tp'. A dashed line connects the ANSam path to the 'tty\_type = unknown' decision with the note 'Error if we get here without knowing the TTY type'. The diagram is labeled V.151(06)\_F16.
+
+**Figure 20-3 – SDL for SSE protocol state (tp,tp) Part 1 (sheet 6 of 10)**
+
+
+
+```
+
+graph TD
+ Start(( )) --> Carrier[carrier detected X
+(clause 20.4.4.2)]
+ Start --> SSE_VBD_X[SSE(VBD:X)]
+
+ Carrier --> TextRelay{text relay support for X?}
+ TextRelay -- yes --> FDX{X=FDX &&! remote gateway support}
+ TextRelay -- no --> SSE_VBD_X
+
+ FDX -- yes --> SSE_TR_X[SSE(TR,X)]
+ FDX -- no --> SSE_VBD_X
+
+ SSE_TR_X --> Connect[connect using modulation X]
+ Connect --> End_TR(tp, tp)
+
+ SSE_VBD_X --> TurnOff1[turn off detectors]
+ TurnOff1 --> End_V(tp, tp)
+
+ SSE_VBD_X --> SSE_VBD_p[SSE(VBD:p')]
+ SSE_VBD_p --> TurnOff2[turn off detectors]
+ TurnOff2 --> End_V2(v, v)
+ End_V2 --- V151(V.151(06)_F17)
+
+```
+
+SDL flowchart for SSE protocol state (tp, tp) Part 2. The flowchart shows two main paths. The left path starts with 'carrier detected X (clause 20.4.4.2)', leading to a decision 'text relay support for X?'. If 'yes', it checks '(X=FDX) &&! (remote gateway support)'. If 'yes', it sends 'SSE(TR,X)', then 'connect using modulation X', and ends at 'tr, tp'. If 'no', it sends 'SSE(VBD:X)', then 'turn off detectors', and ends at 'v, tp'. If 'no' to the first decision, it sends 'SSE(VBD:X)', then 'turn off detectors', and ends at 'v, tp'. The right path starts with 'SSE(VBD:X)', then 'SSE(VBD:p\')', then 'turn off detectors', and ends at 'v, v' with label 'V.151(06)\_F17'.
+
+Figure 20-3 – SDL for SSE protocol state (tp, tp) Part 2 (sheet 7 of 10)
+
+
+
+```
+
+graph TD
+ Start(tp, v) --> StartTimer[start timer]
+ StartTimer --> SSE_TR_X[SSE(TR, X)]
+ StartTimer --> SSE_TP_p[SSE(TP, p')]
+ StartTimer --> TimerExpired[Timer expired]
+
+ SSE_TR_X --> TTYUnknown{tty_type=unknown}
+ TTYUnknown -- yes --> SSE_A_1[SSE(A)]
+ SSE_A_1 --> ai_1(a, i)
+ TTYUnknown -- no --> StartConnect[start connect with PTP
+(clause 20.4.4.3)]
+ StartConnect --> SSE_TR_p[SSE(TR, p')]
+ SSE_TR_p --> tr_tr(tr, tr)
+
+ SSE_TP_p --> tp_tp(tp, tp)
+ TimerExpired --> SSE_A_2[SSE(A)]
+ SSE_A_2 --> ai_2(a, i)
+
+```
+
+Error if we get here without knowing the TTY type
+
+V.151(06)\_F18
+
+SDL diagram for SSE protocol (sheet 8 of 10). The diagram shows a sequence of events and actions. It starts with an event 'tp, v' leading to an action 'start timer'. From 'start timer', three parallel paths emerge: 1) An event 'SSE(TR, X)' leads to a decision 'tty\_type=unknown'. If 'yes', it leads to an action 'SSE(A)' and then 'a, i'. If 'no', it leads to an action 'start connect with PTP (clause 20.4.4.3)', followed by an event 'SSE(TR, p\')' and then 'tr, tr'. A dashed box points to the 'yes' path with the text 'Error if we get here without knowing the TTY type'. 2) An event 'SSE(TP, p\')' leads to 'tp, tp'. 3) An event 'Timer expired' leads to an action 'SSE(A)' and then 'a, i'. The diagram is labeled V.151(06)\_F18.
+
+Figure 20-3 – SDL for SSE protocol (sheet 8 of 10)
+
+
+
+```
+
+graph TD
+ Start(*y, *x) --> StartTimer[start timer]
+ StartTimer --> TimerExpired[Timer expired]
+ StartTimer --> SSE_y_p[SSE(*y, p')]
+
+ TimerExpired --> SSE_A[SSE(A)]
+ SSE_A --> ai(a, i)
+ SSE_y_p --> yy(*y, *y)
+
+```
+
+$(y, x) = \{(v, a), (tp, a), (tr, tp), (tr, v), (v, tp), (a, tr)\}$
+
+V.151(06)\_F19
+
+SDL diagram for SSE protocol (sheet 9 of 10). The diagram shows a sequence of events and actions. It starts with an event '\*y, \*x' leading to an action 'start timer'. From 'start timer', two parallel paths emerge: 1) An event 'Timer expired' leads to an action 'SSE(A)' and then 'a, i'. 2) An event 'SSE(\*y, p\')' leads to '\*y, \*y'. The diagram is labeled V.151(06)\_F19.
+
+Figure 20-3 – SDL for SSE protocol (sheet 9 of 10)
+
+
+
+```
+
+sequenceDiagram
+ Start([tr, tr]) --> CarrierLoss[carrier loss]
+ CarrierLoss --> SSEA[SSE(A)]
+ SSEA --> End([a, tr])
+
+```
+
+V.151(06)\_F20
+
+Sequence diagram for the SSE protocol. It starts with an oval containing 'tr, tr', followed by a rectangle labeled 'carrier loss', then a rectangle labeled 'SSE(A)', and ends with an oval labeled 'a, tr'. The diagram is labeled V.151(06)\_F20.
+
+**Figure 20-3 – SDL for SSE protocol (sheet 10 of 10)**
+
+##### 20.4.4.1 Auto-mode/probing
+
+In this procedure box, the gateway starts the auto-mode/probing processing described in this clause. The purpose of the auto-mode/probing process is to determine what modulation its local PTP device supports. This procedure starts when the gateway receives an SSE(TP) from the remote gateway. If the RIC in the SSE(TP) indicates CI/XCI was detected, the gateway shall perform the "automodding originating" procedure as defined in clause 5.1 of [ITU-T V.18] with the modification of only looking for modulations that it supports for text relay.
+
+If the RIC in the SSE(TP) indicates a signal detected other than CI/XCI, the gateway shall perform automode probing as defined in Figure 2b of [ITU-T V.18] and its corresponding text. The gateway shall not generate the ANSam signal at the beginning of these procedures, i.e., it shall skip over the generate ANSam block in Figure 2b of [ITU-T V.18] and go straight to the probing flows. The gateway shall only probe for modulations that it supports for text relay.
+
+The gateway shall continue the auto-mode/probing procedures until one of the following events occur:
+
+- A PTP modulation that is supported for text relay is detected.
+- A PTP modulation that is not supported for text relay is detected.
+- Auto-mode/probing time-out occurs.
+
+Auto-mode/probing time-out occurs when the gateway has proceeded through at least two cycles of probing as defined in [ITU-T V.18] for the modulations that it supports for text relay without detection of a response from the local PTP device.
+
+In the scenario where an HDX PTP is originating the call and that PTP generates characters before the answering PTP generates any signal, the gateway connected to the answering PTP would begin the probing sequence as described in this clause. Since the PTP device that the gateway is probing is the answering PTP, there is likelihood that the probing would fail in the case the answering PTP is HDX. The fall back to VBD would not result in a successful connection because the two PTP devices are of different types; i.e., the originating is HDX and the answering is FDX. If the answering PTP is FDX, the probing should still be successful and the PTP modems connect using text relay.
+
+If a gateway supports a subset of the modulations described in [ITU-T V.18] for text relay, the gateway only probes for those modulations it supports. If the gateway supports the modulation indicated by the SSE(TP) RIC, the gateway shall start probing with this modulation if the modulation is an FDX type, else the gateway should start probing with this modulation (i.e., for HDX type).
+
+##### **20.4.4.2 Carrier detect X**
+
+In this event box, the gateway has detected a signal that indicates the presence of a local PTP device. Clause 20.4.1 describes the signals that shall be detected for determining the presence of a local PTP device.
+
+##### **20.4.4.3 Start connect with PTP**
+
+In this procedure box, the gateway shall start the connect sequence with its local PTP.
+
+If the gateway's *tty\_mode* state variable is V.18, the gateway shall use the modulation indicated by the RIC of the received SSE(TR) to connect with the PTP if that modulation is supported by the gateway. If the gateway does not support the modulation indicated by the RIC in the received SSE(TR), the gateway shall use a supported modulation that is closest to the signalling rate of the modulation indicated in the RIC.
+
+If the gateway's *tty\_mode* state variable is not V.18, the gateway shall use the modulation indicated by *tty\_mode* to connect with the local PTP device.
+
+##### **20.4.4.4 Connect to V.18 modem with Y**
+
+A gateway will enter this procedure box only if it is connected with a V.18-compliant PTP device.
+
+The gateway shall use the modulation indicated by the RIC of the received SSE(TR) to connect with the V.18 PTP if that modulation is supported by the gateway. If the gateway does not support the modulation indicated by the RIC in the received SSE(TR), the gateway shall use a supported modulation that is closest to the signalling rate of the modulation indicated in the RIC.
+
+#### **20.4.4.5 Start "automodding originating"**
+
+The gateway shall perform the "automodding originating" procedure as defined in 5.1 of [ITU-T V.18]. The gateway shall continue the "automodding originating" processing until one of the following events occurs:
+
+- A PTP modulation that is supported for text relay is detected.
+- A PTP modulation that is not supported for text relay is detected.
+- Auto-mode/probing time-out occurs.
+
+Auto-mode/probing time-out occurs when the gateway has proceeded through at least two cycles of probing as defined in [ITU-T V.18] for the modulations that it supports for text relay without the detection of a response from the local PTP device.
+
+##### **20.4.4.6 Start connect with answering V.18 PTP**
+
+When this procedure box is entered, both PTP devices are V.18-compliant. A gateway that enters this procedure box is connected to the answering V.18 PTP device. The gateway shall use V.21 as defined in V.18 if this modulation is supported. If V.21 as defined in [ITU-T V.18] is not supported, the gateway should use a supported modulation that is closest to the V.21 signalling rate.
+
+## **20.5 Visual flow control**
+
+During normal call discrimination procedure there may be situations where the local PTP device is connected for a time to the local gateway without an end-to-end connection established between the endpoint PTP devices. An example would be a local PTP connected to its local gateway while the remote gateway is performing a probing sequence with its local PTP device in order to establish a connection with it. In these situations, the gateway could optionally provide a message to its local PTP device indicating to the user to wait before sending text. The gateway could then follow up with a message indicating to the user that it is clear to send once the remote gateway establishes a connection with its PTP device. The messages to be used are beyond the scope of this Recommendation.
+
+## Annex A
+
+## Procedures for the optional support of SPRT protocol
+
+(This annex forms an integral part of this Recommendation)
+
+### A.1 Overview
+
+To use SPRT protocol, the SSE protocol must be negotiated in addition to SPRT being negotiated. If the SSE protocol is not negotiated, RTP shall be used for transmitting T.140 encoded data.
+
+Parameters for SPRT are defined in Annex B of [ITU-T V.150.1]. Transport channel 3 shall not be used for transporting T.140 encoded data.
+
+SPRT defines several formats for carrying data. If SPRT is used then the default format for transporting T.140 encoded data shall be I\_OCTET\_INFO as described in clause 15.4.11.1 of [ITU-T V.150.1].
+
+### A.2 SDP negotiation
+
+The SPRT capability is advertised in SDP as a latent capability following the syntax specified in [IETF RFC 3407]. The media type is "audio" and the transport name assigned "udpsprt". The media format is "v150tr". The following example illustrates the advertisement of an RTP media stream that uses G.711 for audio and SPRT for the transport of real-time text:
+
+```
+m=audio 49230 RTP/AVP 0
+a=sgn:0
+a=cdsc:1 audio udpsprt 100
+a=cpar:a=sprtmap:100 v150tr/8000
+```
+
+In the above example, the payload type associated with SPRT is 100.
+
+The optional parameters associated with the SPRT transport protocols are declared via the SDP attribute "sprtparm" and vendor-specific parameters are declared via the SDP attribute "vndpar" as illustrated in the syntax below:
+
+```
+a=cpar:a=sprtparm:
+
+a=cpar:a=vndpar:
+[]
+```
+
+Refer to Annex E of [ITU-T V.150.1] for a full description of the above parameters.
+
+### A.3 H.245 negotiation
+
+The SPRT capability is advertised in [ITU-T H.245] as a generic audio capability. The capability is specified as follows:
+
+**Table A.1 – Capability identifier for V.150.1**
+
+| | |
+|-----------------------------|----------------------------------------------------------------------------------------------------------------------------------------|
+| Capability name | SPRT Text Relay Capability |
+| Capability class | Audio capability |
+| Capability identifier type | Standard |
+| Capability identifier value | {itu-t (0) recommendation (0) v (22) 151 toip (0) } |
+| maxBitRate | The maxBitRate field shall not be included and shall be ignored if received. |
+| Collapsing | This field shall not be included and shall be ignored if received. |
+| nonCollapsing | This field shall not be included and shall be ignored if received. |
+| nonCollapsingRaw | This field shall be present and shall contain a value encoded using the ALIGNED variant of BASIC-PER for the ASN.1 type defined below. |
+| Transport | This field shall not be included and shall be ignored if received. |
+
+The ASN.1 syntax associated with SPRT is:
+
+```
+V151SPRT-CAPABILITY DEFINITIONS AUTOMATIC TAGS ::= BEGIN
+
+IMPORTS
+ NonStandardParameter FROM MULTIMEDIA-SYSTEM-CONTROL;
+
+V150MoIPCapability ::= SEQUENCE
+{
+ nonStandard SEQUENCE OF NonStandardParameter OPTIONAL,
+ sprtParameters SEQUENCE
+ {
+ maxPayloadSizeChannel0 INTEGER(140..256) OPTIONAL, -- Default 140
+ maxPayloadSizeChannel1 INTEGER(132..256) OPTIONAL, -- Default 132
+ maxWindowSizeChannel1 INTEGER(32..96) OPTIONAL, -- Default 32
+ maxPayloadSizeChannel2 INTEGER(132..256) OPTIONAL, -- Default 132
+ maxWindowSizeChannel2 INTEGER(8..32) OPTIONAL, -- Default 8,
+ maxPayloadSizeChannel3 INTEGER(140..256) OPTIONAL, -- Default 140
+ ...
+ } OPTIONAL,
+ ...
+}
+END
+```
+
+Equipment manufacturers may use the **nonStandard** field to signal any non-standard information that is specific to their ToIP implementations as it relates to SPRT. The first octet of the data field within the non-standard parameter shall be the vendor-specific "vendor-tag", as specified in clause 8 of [ITU-T V.150.0]. A value of 0 in the first octet means that the parameters is not bound to the specified vendor ID (i.e., it is not bound to the value of **nonStandard.object** or **nonStandard.h221NonStandard** values). This "vendor-tag" may be used in other related messages, such as SSE messages.
+
+Refer to Table B.2 of [ITU-T V.150.1] for description and default values for the **sprtParameters**.
+
+## Annex B
+
+## Definition of capabilities for use within H.245-based systems
+
+(This annex forms an integral part of this Recommendation)
+
+This annex defines the capabilities that need to be exchanged between H.245-based systems for the transmission of analogue PSTN text telephony signals over packet-based networks.
+
+The payload format used for the transmission of text characters is described in Annex E.
+
+H.323 systems have a means of advertising the ability to transport text over RTP using the "t140" capability defined in [ITU-T H.245]. However, this capability does not provide a means to advertise supported modulations, such as Baudot. Annex G of [ITU-T H.323] also does not define those modulations, but it does have a means to allow another specification, such as [b-TIA-1001] or [ITU-T V.151], to do that.
+
+Gateways compliant to this Recommendation must be able to support the transmission of text interleaved with audio. The respective capability definition for H.245-based systems is in Table B.1, as taken from Annex G of [ITU-T H.323].
+
+**Table B.1 – H.245 capability definition for text transport (T140Audio)**
+
+| | |
+|------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Capability name: | T140Audio |
+| Capability class: | Audio Capability |
+| Capability identifier type: | Standard. |
+| Capability identifier value: | itu-t (0) recommendation (0) h (8) 323 annex(1) g (7) audio(0) |
+| maxBitRate | The maxBitRate field shall be included and indicate the maximum bits per second. When using the Flow Control Command or other signals in relation to this capability, any maxBitRate field shall be interpreted to be in units of bits/s, as opposed to the typical 100 bits/s used in H.245. This is due to the low bit rate nature of real-time text communication, including the low bit rates used by many PSTN textphone protocols. |
+| nonCollapsing | This field shall not be included and shall be ignored if received. |
+| nonCollapsingRaw | This field shall not be included and shall be ignored if received. |
+| Transport | This field shall not be included. |
+
+Devices may also advertise, either in the terminal capability set, the Open Logical Channel, or both, the capability to receive a specified number of characters per second. Devices may advertise the maximum characters per second via the below optional parameter.
+
+**Table B.2 – Characters per second parameter**
+
+| | |
+|-----------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Parameter name: | cps |
+| Parameter description: | This is a collapsing capability.
Indicates the maximum number of characters per second that may be received on a session. When carried inside an Open Logical Channel (OLC), it indicates the maximum transmission rate that the other endpoint may use if it opens a corresponding text session. |
+| Parameter identifier value: | standard: 0 |
+| Parameter status: | Optional |
+| Parameter type: | unsignedMin |
+| Supersedes: | – |
+
+The Textphone Modulations parameter is an optional parameter that indicates the set of supported modulations for text relay. Absence of this parameter may be interpreted to mean that all modulations are supported or that the device is a native IP device.
+
+**Table B.3 – Textphone Modulations Parameter**
+
+| Parameter name: | Textphone Modulations | | | | | | | | | | | | | | | | |
+|-----------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----|---------|---|--------|---|-----|---|---------|---|-----|---|-----|---|-----|-----|----------|
+| Parameter description: | This is a non-collapsing capability.
Indicates the gateway's supported textphone modulations. | | | | | | | | | | | | | | | | |
+| Parameter identifier value: | standard: 100 | | | | | | | | | | | | | | | | |
+| Parameter status: | Optional | | | | | | | | | | | | | | | | |
+| Parameter type: | booleanArray, populated as follows (bit 0 = lsb)
Bit Meaning 0 TIA825 1 EDT 2 BELL103 3 V23 4 V18 5 V21 6-7 Reserved
| Bit | Meaning | 0 | TIA825 | 1 | EDT | 2 | BELL103 | 3 | V23 | 4 | V18 | 5 | V21 | 6-7 | Reserved |
+| Bit | Meaning | | | | | | | | | | | | | | | | |
+| 0 | TIA825 | | | | | | | | | | | | | | | | |
+| 1 | EDT | | | | | | | | | | | | | | | | |
+| 2 | BELL103 | | | | | | | | | | | | | | | | |
+| 3 | V23 | | | | | | | | | | | | | | | | |
+| 4 | V18 | | | | | | | | | | | | | | | | |
+| 5 | V21 | | | | | | | | | | | | | | | | |
+| 6-7 | Reserved | | | | | | | | | | | | | | | | |
+| Supersedes: | – | | | | | | | | | | | | | | | | |
+
+Devices may advertise their preference for switching out of VBD mode between text spurts when VBD mode is used for text.
+
+**Table B.4 – Remain In VBD Not Preferred Parameter**
+
+| | |
+|-----------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| Parameter name: | RemainInVBDNotPreferred |
+| Parameter description: | This is a collapsing capability.
Indicates that the gateway would prefer to switch out of VBD mode between text spurts. Both gateways must indicate this preference for the gateway to switch out of VBD mode after a text spurt, else the gateway shall remain in VBD mode for the duration of the call. |
+| Parameter identifier value: | standard: 101 |
+| Parameter status: | Optional |
+| Parameter type: | Logical |
+| Supersedes: | – |
+
+These capabilities are advertised as part of the Terminal Capability Set message exchanged between two devices. These capabilities are also used in Open Logical Channel (OLC) messages in Fast Connect and normal H.245 logical channel signalling.
+
+Below is an example of an OLC message that has G.729 audio, text, and redundancy protecting the text packets, and RFC 2833 for DTMF transport.
+
+```
+{
+ forwardLogicalChannelNumber 1,
+ forwardLogicalChannelParameters {
+ dataType : multiplePayloadStream {
+ element {
+ dataType : audioData : g729 2
+ },
+ element {
+ dataType : redundancyEncoding {
+ primary {
+ dataType : audioData : genericAudioCapability {
+ capabilityIdentifier : standard {
+ itu-t (0) recommendation (0) h (8)
+ 323 annex(1) g (7) audio(0)
+ },
+ nonCollapsing {
+ {
+ parameterIdentifier : standard : 100,
+ parameterValue : booleanArray : 00000011b
+ },
+ {
+ parameterIdentifier : standard : 101,
+ parameterValue : logical : NULL
+ },
+ },
+ },
+ payloadType 97 -- The PT for the redundant encoding
+ },
+ secondary {
+ {
+ dataType : audioData : genericAudioCapability {
+ capabilityIdentifier : standard {
+ itu-t (0) recommendation (0) h (8)
+ 323 annex(1) g (7) audio(0)
+ },
+ nonCollapsing {
+ {
+ parameterIdentifier : standard : 100,
+ parameterValue : booleanArray : 00000001b
+ },
+ {
+ parameterIdentifier : standard : 101,
+ parameterValue : logical : NULL
+ },
+ },
+ payloadType 97 -- The PT for the redundant encoding
+ }
+ }
+ }
+ }
+ }
+ }
+ }
+}
+```
+
+```
+
+ }
+ },
+ payloadType 101 -- The PT for the RFC 2198 packet
+},
+element {
+ dataType : audioData : audioTelephonyEvent {
+ audioTelephoneEvent : "0-15"
+ },
+ payloadType 102
+}
+},
+multiplexParameters : h2250LogicalChannelParameters {
+ sessionID 1
+}
+}
+
+```
+
+Note that the gateway only indicated support for [b-ANSI/TIA-825] (Baudot) and EDT PSTN PTP devices in the above example. The assumption is that the gateway will either use VBD (not shown in this example) for other PSTN PTP types, or will transition to text relay in order to provide interworking between dissimilar PSTN PTP types.
+
+## Annex C
+
+## SDP description of sessions supporting V.151
+
+(This annex forms an integral part of this Recommendation)
+
+This annex defines the syntax that needs to be exchanged between SDP-based systems for the transmission of analogue PSTN Text Telephony signals over packet-based networks. The payload format used for the transmission of text characters is described in Annex E.
+
+The text relay capability and associated procedures are represented in SDP using the MIME type "audio/t140c". A very simple example of the use of the audio/t140c within SDP is:
+
+```
+m=audio 7200 RTP/AVP 18 100
+a=rtpmap:98 t140c/8000
+```
+
+This specifies the use of G.729 as payload type 18 along with audio/t140 as payload type 100. Note that the clock rate specified is 8000 Hz. The clock rate value should have the same value as for any audio codec packets interleaved in the same RTP stream.
+
+In some cases, it is necessary to limit the rate at which characters are transmitted. For example, when a PSTN gateway is interworking between an IP device and a PSTN textphone, it may be necessary to limit the character rate from the IP device in order to avoid throwing away characters in case of buffer overflow at the PSTN gateway.
+
+To control the character transmission rate, the MIME parameter "cps" in the "fmt" attribute is defined. It is used in SDP with the following syntax:
+
+```
+a=fmt: cps=
+```
+
+The field is populated with the payload type that is used for text. The field contains an integer representing the maximum number of characters that may be received per second. The value shall be used as a mean value over any 10-second interval.
+
+Devices in receipt of this parameter shall adhere to the request by transmitting characters at a rate at or below the specified value. In absence of this parameter, devices shall not transmit more than 30 characters per second.
+
+The 'gpmid' (general purpose media descriptor) syntax attribute is used for signaling the set of supported textphone modulations. The general format for this attribute line is:
+
+```
+a=gpmid:
+```
+
+The value of shall be set to the value of the RTP payload type for text. The shall be a comma-separated list of modulations following the following syntax:
+
+```
+modulations = "tpmods=" modulation *(", " modulation)
+modulation = "tia825" | "edt" | "bell1103" | "v23" |
+"v18" | "v21"
+```
+
+Absence of the textphone modulations attribute may be interpreted to mean all modulations are supported or that the device is a native IP device. A gateway compliant to this Recommendation shall send the textphone modulations attribute.
+
+The VBD mode preference attribute is used to indicate the preference a gateway has for switching out of VBD mode and into AUDIO mode between text spurts when VBD is used for transmission
+
+of text. Both gateways must indicate the preference to switch out of VBD mode after a text spurt else the gateway shall remain in VBD mode for the duration of the call. The value of shall be set to the value of the RTP payload type for text. The shall indicate the gateway's preference. A 'remain-in-vbd=yes' indicates preference to stay in VBD mode, while 'remain-in-vbd=no' indicates preference to switch between VBD and AUDIO modes between text spurts. This attribute is optional. If it is not sent, the gateway is indicating that its preference is to not switch out of VBD mode after text spurt.
+
+Redundancy of audio media as defined in [IETF RFC 2198] may be used to provide better reliability in networks where packet loss exists. The example below shows how SDP may be used to signal an offer to send G.729 audio interleaved with text protected with two levels of redundancy:
+
+```
+m=audio 7200 RTP/AVP 18 98 100
+a=rtpmap:98 t140c/8000
+a=fmtp:98 cps=20
+a=gpmid:98 tpmids=baudot,edt
+a=gpmid:98 remain-in-vbd=no
+a=rtpmap:100 red/8000
+a=fmtp:100 98/98/98
+```
+
+Note that the gateway only indicated support for Baudot PSTN and EDT PTP devices in the above example. The assumption is that the gateway will either use VBD (not shown in this example) for other PSTN PTP types or will use relay in order to provide interworking between dissimilar PSTN PTP types.
+
+## Annex D
+
+## Interworking IP text devices with V.151 gateways
+
+(This annex forms an integral part of this Recommendation)
+
+### D.1 Introduction
+
+Some non-gateway IP devices in the network that do not have means of modulating or demodulating PSTN textphone signals, such as IVR systems, voicemail systems, IP phones, or other devices, may support the transmission of real-time text over IP networks and, ideally, interwork with V.151-compliant gateways in order to provide a means through which users of PSTN textphone devices can communicate with those IP devices. This class of devices is referred to herein as an "IP text device" (ITD). This annex defines the procedures that may be used in order to allow for such interworking between V.151 gateways and ITDs.
+
+### D.2 Exchanging capabilities and opening media streams
+
+When establishing a call, an ITD shall advertise support for ToIP in accordance with Annex B or Annex C, with one notable important exception: the ITD shall not include a list of supported modulations. Absence of the list of modulations shall be used as an indicator to the V.151 gateway that the remote side is an ITD.
+
+Further, ITD devices shall not utilize SSEs in order to control state transition to ToIP. Rather, once a media flow is established to transport T.140 characters, either the gateway or the ITD may transmit text immediately and without further negotiation. Payload type switching is used to transition between audio and text relay modes.
+
+In general, ITDs transmit text characters when communicating with other ITDs using [b-IETF RFC 4103], which specifies the establishment of a separate RTP stream specifically for transmitting text characters. However, since PSTN gateway devices interleave audio and text data, ITDs need to support both [b-IETF RFC 4103] to interwork with other ITDs and V.151 for communicating with PSTN gateways. As such, ITDs shall indicate support for both transport methods when exchanging capability information.
+
+Further, when H.323-based ITDs utilize the Fast Connect procedures to offer media streams, those systems should offer proposals for both [b-IETF RFC 4103] and V.151 (refer to Annexes C and G of [ITU-T H.323]). Those proposals would be separate proposals within the fastStart SEQUENCE transmitted to the receiver. As an abbreviated example, an H.323 device might send the following three forward logical channel proposals in fastStart (the proposed media format(s) within a single OLC are shown within braces):
+
+{ G.711, V.151 }, { G.711, RFC 4103 }
+
+If the called device is an ITD, it may accept the G.711 proposal to establish an audio stream and the RFC 4103 for text. The fastStart response would contain:
+
+{ G.711 }, { RFC 4103 }
+
+If the called device is a gateway, it would accept the proposal for G.711 and V.151/Annex E data interleaved within the same media stream. The fastStart response would contain:
+
+{ G.711, V.151 }
+
+The foregoing does not preclude the use of H.245 logical channel signalling to open compatible media streams and merely serves as an illustration.
+
+Similar logic follows for SDP-based systems. Consider the following abbreviated example SDP that might be found in an offer sent by an ITD:
+
+```
+m=audio 7200 RTP/AVP 0 98
+a=rtpmap:98 t140c/8000
+a=fmtp:98 cps=20
+m=text 7202 RTP/AVP 99
+a=rtpmap:99 t140/1000
+a=fmtp:99 cps=20
+```
+
+If the answering device is another ITD, it would accept the RFC 4103 stream and remove the V.151 (t140c) proposal, as shown in this response:
+
+```
+m=audio 7200 RTP/AVP 0
+m=text 7202 RTP/AVP 99
+a=rtpmap:99 t140/1000
+a=fmtp:99 cps=20
+```
+
+If the answering device is a gateway, it would accept the V.151 stream and indicate that does not wish to utilize RFC 4103 by setting the port to zero (0), as illustrated below:
+
+```
+m=audio 7200 RTP/AVP 0 98
+a=rtpmap:98 t140c/8000
+a=fmtp:98 cps=20
+m=text 0 RTP/AVP 99
+```
+
+Note that while the use of RFC 2198 redundancy or other fault tolerance scheme is not shown in these abbreviated examples, appropriate mechanisms should be employed to protect the transmission of the text stream in accordance with this Recommendation.
+
+### **D.3 State transition and text handling**
+
+The following description assumes that a V.151-compliant gateway is in communication with an ITD and media flows have been established to transport text over IP in accordance with Annex E.
+
+When the gateway compliant to this annex detects a PSTN textphone that it supports using text relay, it shall autonomously connect to the textphone. After connection, the gateway shall decode the characters received and transmit those to the ITD, giving proper respect to the maximum character-per-second (CPS) parameter advertised by the ITD. Determining the type of PSTN textphone device in use is the responsibility of the gateway and the ITD need not concern itself with what kind of PSTN textphone device is connected to the gateway.
+
+Likewise, when the ITD sends characters to the gateway using TR payload type, the gateway shall perform a probing, as necessary, to determine the type of PSTN device connected, if any. While probing, the gateway shall buffer any characters received and transmit those when probing completes and the gateway is connected to the text phone. The size of the character buffer is a matter of implementation, but should support the reception and buffering of characters for at least 60 seconds at the specified maximum character-per-second (CPS) value signalled to the ITD.
+
+If the gateway does not support the modulation used by the PSTN textphone device, the gateway may transmit the received textphone signals via VBD or the audio stream, depending on the capabilities of the ITD. Further, the gateway may simply discard characters received from the ITD or transmit them to the PSTN textphone device using a pre-provisioned modulation.
+
+
+
+```
+
+sequenceDiagram
+ participant T1
+ participant G1
+ participant ITD
+
+ T1->>G1: PTP response probing
+ T1->>G1: CHAR
+ G1->>T1: Auto-mode probing
+ G1->>ITD: CHAR
+ ITD->>G1: PT = Annex E
+
+```
+
+Legend: Text relayed signals
+
+V.151(06)\_FD.1
+
+Sequence diagram showing text relay call flow between T1, G1, and ITD. T1 sends PTP response probing and CHAR to G1. G1 sends Auto-mode probing to T1 and CHAR to ITD. ITD sends PT = Annex E to G1. A legend indicates yellow boxes are text relayed signals.
+
+NOTE – Automode probing as defined in Figure 2b of [ITU-T V.18]. The character(s) sent in the Annex E payload by ITD should be used in the auto-mode probing sequence. Further characters received from ITD shall be buffered by G1 until connection is established with T1. Upon connection with T1, G1 shall transmit all buffered characters.
+
+**Figure D.1 – Example text relay call flow for ITD/gateway text relay interoperability**
+
+## Annex E
+
+## Payload format and signaling syntax for real-time text transported within an audio stream
+
+(This annex forms an integral part of this Recommendation)
+
+### E.1 Overview
+
+This annex defines the payload format specification for transporting real-time text over IP networks within an audio stream. The payload format for these packets utilizes ITU-T Rec. T.140 for the character encoding. Characters are transmitting through an audio stream, either switched with voice packets or in parallel to voice packets.
+
+### E.2 Payload format
+
+When transporting real-time text within an audio steam, text packets are differentiated from audio packets, SSE messages, DTMF signals, or other packets by the payload type value negotiated during session establishment or when the session is later modified. Text packets shall be assigned a payload type value that allows the endpoint to unambiguously recognize text packets from other packets transmitted within the audio stream.
+
+The real-time text packets shall utilize T.140 for character encoding, transported using the real-time transport protocol (RTP), and shall be encoded as shown in Figure E.1.
+
+
+
+| | | | |
+|------------------------------------------|---------------------|---------------------|------|
+| 0 | 1 | 2 | 3 |
+| 0 1 2 3 4 5 6 7 8 9 | 0 1 2 3 4 5 6 7 8 9 | 0 1 2 3 4 5 6 7 8 9 | 0 1 |
+| v=2 | P | X | CC=0 |
+| M | PT | | |
+| Sequence Number | | | |
+| Timestamp | | | |
+| Synchronization Source (SSRC) Identifier | | | |
+| T.140 Block Counter | | | |
+| T.140-Encoded Data Block | | | |
+
+Figure E.1: Payload format diagram showing the structure of an RTP packet for real-time text. The diagram is a horizontal bar divided into fields with bit indices 0 to 31 above. The fields are: v=2 (bits 0-1), P (bit 2), X (bit 3), CC=0 (bits 4-7), M (bit 8), PT (bits 9-15), Sequence Number (bits 16-31). Below the bar, the fields are grouped: Timestamp (bits 16-31), Synchronization Source (SSRC) Identifier (bits 16-31), T.140 Block Counter (bits 16-23), and T.140-Encoded Data Block (bits 24-31).
+
+Figure E.1 – Payload format
+
+The definition of the first 3 octets is found in Section 5.1 of IETF RFC 3550. Implementations shall adhere to the following usage of these fields:
+
+This M-bit shall be set to '1' for the initial packet transmitted for any given SSRC value presented on the wire and shall be set to '1' following a period of 'silence' where no RTP packets are transmitted. In all other cases where packets are transmitted successively, this bit shall be set to '0'. A period of 'silence' is defined to be more than 300 ms without transmitting a packet.
+
+The payload type (PT) field shall contain a dynamic payload type value negotiated by the two endpoints.
+
+The sequence number and timestamp fields shall increase in accordance with IETF RFC 3550.
+
+The SSRC used for text should be the same SSRC value as used for other audio, allowing for synchronized interleaving of audio and text. This means that the clock rate used for audio transmission should be the same rate as used for text packets.
+
+There may be cases, however, where it is desired to transmit audio and text within the same stream in parallel and having overlapping timestamps. For example, if a user speaks while typing at the same time using devices that enable simultaneous voice and text, both audio and text may be presented to the network. In such cases, a separate SSRC may be used in order to separate the voice
+
+source from the text source and allow for overlapping timestamps and different sequence number spaces. Such usage of multiple payloads with an RTP stream is discussed in IETF RFC 3550.
+
+The actual payload of the RTP packet is comprised of a T.140 block counter and a chunk of T.140-encoded data. Those two components of the payload are described in the following clauses.
+
+#### **E.2.1 T.140 block counter**
+
+The T.140 block counter is similar in purpose to the sequence number and is necessary since text packets and audio packets may share the same sequence number space. Without this counter, it would not otherwise be possible to detect lost text packets.
+
+The T.140 block counter shall be initialized to zero for the first text packet transmitted and, once passing the value 0xFFFF, shall be reset to zero.
+
+Devices that receive a text packet containing a T.140 block counter that has incremented higher than expected shall assume that the difference between the recently received counter value and the expected counter value indicates the number of lost text packets. Note, however, that there may be multiple characters within a text packet, so this does not serve to indicate the number of lost characters.
+
+#### **E.2.2 T.140-Encoded Data Block**
+
+The T.140-encoded data block ("T.140 block") contains text information as described in ITU-T Rec. T.140. The contents of this field shall be UTF-8 encoded and shall include no extra framing.
+
+It should be noted that, in most cases, this field is comprised of one or more text characters. However, it is permissible to have zero characters for the purpose of enabling transmission of redundant data packets as discussed in clause E.3. It should also be noted that, while most elements within this field constitute single characters, some elements are multiple-character sequences. Any composite character sequence (CSS) elements should be placed in a single RTP packet.
+
+### **E.3 Use of redundancy**
+
+Use of redundancy, such as the redundancy mechanism described in [IETF RFC 2198], provides a high degree of resiliency in the face of packet loss. When transmitting a constant stream of packets, [IETF RFC 2198] is quite clear on the contents of the data packets, including the primary and redundant parts of the RFC 2198 packet.
+
+However, in cases where there is "silence" for a period of time, [IETF RFC 2198] is not explicitly clear about how a device should deliver redundant data. More specifically, [IETF RFC 2198] requires that all packets contain a primary encoding, though during a period of "silence" there would not be information available to transmit as primary data. For this reason, when transmitting text as redundant information and without any new text to transmit, devices shall transmit RTP packets that contain no "primary" data: both the "T.140 block counter" and "T.140 block" shall be absent from the RTP payload. This absent primary T.140 data is referred to as an "empty T.140 block".
+
+Figure C.2 shows what an RFC 2198 redundancy packet might look like when the primary encoding is absent (i.e., there is an empty T.140 block) and a single redundant encoding of a previously transmitted T.140 block ("R") is present. It is important to note that the sequence number for the RFC 2198 packet continues to increase, as specified in [IETF RFC 2198] and IETF RFC 3550, so that it is possible for the system and network to accurately measure overall packet loss. However, character loss is detected through missing T.140 block counters, not gaps in the RTP packet sequence numbers. In this way, if a packet is lost, then the character may be recovered through these redundant transmissions without any apparent loss observed by the user.
+
+A device should not re-transmit an empty T.140 block as a redundant encoding, as doing so merely consumes bandwidth unnecessarily and does not improve the robustness of the system.
+
+| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
+|------------------------------------------|------------|---|---|------|---|---|---|---|-----------------------------|---|---|---|---|---|----------------------------|---|---|---|---|---|------------------|---|---|---|---|---|---|---|---|---|---|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|--|
+| 0 | | | | | | | | | | 1 | | | | | | | | | | 2 | | | | | | | | | | 3 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
+| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0 | 1 | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
+| v=2 | | P | X | CC=0 | | | | M | "RED" PT | | | | | | Sequence Number of Primary | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
+| Timestamp of Primary Encoding | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
+| Synchronization Source (SSRC) Identifier | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
+| 1 | "t140c" PT | | | | | | | | Timestamp offset of "R" | | | | | | | | | | | | "R" Block Length | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
+| 0 | "t140c" PT | | | | | | | | T.140 Block Counter for "R" | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
+| T.140 Block "R" | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
+
+**Figure E.2 – RFC 2198 redundancy packet with empty T.140 block**
+
+## Appendix I
+
+## Background to PSTN text telephony
+
+(This appendix does not form an integral part of this Recommendation)
+
+Text telephone systems were implemented mainly for distant conversation with deaf, hard-of-hearing, speech-impaired and deaf-blind users. The text telephone systems offer a real-time, character-by-character, conversation in text, optionally combinable with voice. The text telephone service is described generally in [ITU-T F.700] and [ITU-T F.703] and user needs are described in [b-ETSI ETR 333], *Human Factors, Text Telephony; Basic user requirements and recommendations*.
+
+With the PSTN, there are seven different, openly specified signalling methods used in text telephony. These signalling methods are country-specific. The signalling methods are TIA-825A (Baudot), DTMF, EDT, V.21, Bell103, Minitel and V.18. Each uses a different modulation and character encoding in the transmission of text. The methods are described in the annexes of [ITU-T V.18].
+
+[ITU-T V.18] is an auto-mode mechanism that attempts to enable communication with all the legacy mode of operation at the physical layer level. If both end-point text telephones are V.18, they encode their data using the character set, defined in ITU-T Rec. T.140. [ITU-T V.21] is the common or native modulation for V.18, while ITU-T Rec. V.61 is specified for use of simultaneous voice and text.
+
+There also exist several proprietary flavours of the existing standardized modulations, which are not part of [ITU-T V.18].
+
+## Appendix II
+
+## ToIP call discrimination call flows
+
+(This appendix does not form an integral part of this Recommendation)
+
+### II.1 Scope
+
+This appendix contains a set of example call flow diagrams for this Recommendation. It does not represent a complete set. *If there is any conflict between these diagrams and the SDL contained in the main body of the Recommendation, the SDL will govern.*
+
+The following diagrams illustrate ToIP call flows. In the diagrams:
+
+- the white vertical rectangles under the ToIP endpoints (G1 and G2) give the state of the respective endpoint;
+- the shaded vertical rectangles under the text telephony terminals (T1 and T2) and the ToIP endpoints (G1 and G2) give the signals that are being transmitted by the respective Terminal or endpoint;
+- while in audio and VBD mode, the ToIP endpoints are continually transmitting and receiving audio CODEC packets as defined elsewhere in this Recommendation. For clarity, these packets are only explicitly shown when special circumstances surround them.
+
+### II.2 Scenarios for call discrimination flows
+
+Table II.1 lists all possible scenarios of PTP devices and gateway types. Each of these scenarios is considered in the following clauses.
+
+**Table II.1 – Possible PSTN text phone connection scenarios**
+
+| T1 Type
(calling) | T2 Type
(called) | T1 $\cap$
G1 $\neq$ 0 | T2 $\cap$
G2 $\neq$ 0 | Connect
mode |
+|----------------------|---------------------|--------------------------|--------------------------|---------------------------------------------------------------|
+| V.18 | V.18 | Y | Y | TR |
+| V.18 | V.18 | N | Y | SSEs:
TR
Else:
VBD |
+| V.18 | V.18 | Y | N | SSEs:
TR
Else:
VBD |
+| V.18 | V.18 | N | N | Same as scenario 3 |
+| FDX | V.18 | Y | Y | TR unless T1 is Bell 103 and G2 does not support Bell 103 |
+| FDX | V.18 | N | Y | VBD |
+| FDX | V.18 | Y | N | Same as scenario 5 |
+| FDX | V.18 | N | N | VBD |
+| V.18 | FDX | Y | Y | TR unless no SSEs and G1 and G2 do not both support T2's mode |
+| V.18 | FDX | N | Y | Same as scenario 9 |
+
+**Table II.1 – Possible PSTN text phone connection scenarios**
+
+| T1 Type
(calling) | T2 Type
(called) | T1
G1 0 | T2
G2 0 | Connect
mode |
+|------------------------------|-----------------------------|--------------------------------------------------------|--------------------------------------------------------|--------------------------------------------------|
+| V.18 | FDX | Y | N | VBD |
+| V.18 | FDX | N | N | VBD |
+| FDX | FDX | Y | Y | TR
VBD if G1 does not support T2 and T1 = T2. |
+| FDX | FDX | N | Y | VBD
No connect if T1 != T2 |
+| FDX | FDX | Y | N | Same as scenario 14 |
+| FDX | FDX | N | N | Same as scenario 14 |
+| HDX | V.18 | Y | Y | TR |
+| HDX | V.18 | N | Y | VBD |
+| HDX | V.18 | Y | N | VBD |
+| HDX | V.18 | N | N | VBD |
+| V.18 | HDX | Y | Y | TR |
+| V.18 | HDX | N | Y | VBD |
+| V.18 | HDX | Y | N | VBD |
+| V.18 | HDX | N | N | VBD |
+| HDX | HDX | Y | Y | TR |
+| HDX | HDX | N | Y | VBD
No connect if T1 != T2 |
+| HDX | HDX | Y | N | Same as scenario 26 |
+| HDX | HDX | N | N | Same as scenario 26 |
+| FDX | HDX | Y | Y | TR |
+| FDX | HDX | N | Y | No connect |
+| FDX | HDX | Y | N | No connect |
+| FDX | HDX | N | N | No connect |
+| HDX | FDX | Y | Y | TR |
+| HDX | FDX | N | Y | No connect |
+| HDX | FDX | Y | N | No connect |
+| HDX | FDX | N | N | No connect |
+
+### **II.3 Scenarios with SSE protocol being used**
+
+#### **II.3.1 Scenario #1**
+
+T1 = V.18 PTP
+
+T2 = V.18 PTP
+
+G1 = supports V.18 native mode
+
+G2 = supports V.18 native mode
+
+
+
+NOTE 1 – VBD may optionally be used for CI/XCI signal. If VBD is used, there is an SSE(VBD:CI/XCI) handshake here.
+
+NOTE 2 – CI/XCI may be detected by T2. If not detected, there will be up to 3 seconds of additional delay before ANSsam is generated.
+
+Figure II.1 – Scenario #1 call flow diagram (SSE) (sheet 1 of 2). The diagram illustrates the signaling sequence between four entities: T1, G1, G2, and T2. T1 (CI/XCI) sends a signal to G1 (CI/XCI). G1 sends PT = AUDIO/PT = VBD to G2 (CI/XCI). G1 also sends SSE(TP:CI/XCI) to G2. G2 sends SSE(TP:p') to G1. G1 sends SSE(TR:ANSam) to G2. G2 sends SSE(TR:p') to G1. G1 sends PT = TR(CHAR) to G2. G2 sends PT = TR(CHAR) to G1. T2 (ANSam) sends ANSsam to G2. G2 sends V.21(L) MARK to T2. T2 sends CHAR to G2. G2 sends V.21(H) MARK to T2. T2 sends V.21(L) MARK to G2. T2 sends V.21(H) to G2. A legend indicates that yellow boxes represent Text relayed signals and hatched boxes represent VBD signals. Note 1: PT = AUDIO/PT = VBD. Note 2: CI/XCI.
+
+**Figure II.1 – Scenario #1 call flow diagram (SSE) (sheet 1 of 2)**
+
+##### Description
+
+Since T1 is the V.18 calling PTP, it will generate a CI/XCI sequence. Since G1 is a V.151-compliant gateway that supports SSE protocol, it will detect CI/XCI indicating to G1 that it is connected to a V.18 PTP terminal. Upon detection of CI/XCI, G1 may continue to transmit the CI/XCI sequence using audio mode to G2, or it may optionally initiate a transition to VBD mode by sending an SSE(VBD:CI/XCI) to G2. The diagram does not show the optional VBD SSE negotiation at this point. After CI/XCI sequence is completely transmitted to G2 (either through audio or VBD encoding), G1 shall send an SSE(TP:CI/XCI) to G2 and terminate regeneration of signals to T1. G1 shall stay in the mode of silence generation to T1 until it exits the TP state via an SSE from G2.
+
+Upon reception of the SSE(TP:CI/XCI) from G1, G2 will enter an answering auto-mode probing state. The answering auto-mode probing state would consist of G2 listening for PTP signals from T2. Since T2 is a V.18 PTP answering terminal, it will generate ANSsam signal either immediately after the CI/XCI sequence if it is detector, or within 3 seconds if the CI/XCI is not detected. Upon detection of the ANSsam signal from T2 by G2, G2 will send an SSE(TR:V.18) indicating that it has detected ANSsam signal from T2 and that T2 is a V.18 modem and that G1 should start its text relay connect sequence. G2 will then start the V.8 connect sequence with T2 (since G2 supports native V.18).
+
+Upon reception of the SSE(TR:V.18) from G2, G1 will start a V.8 connect sequence with T1 and successfully connect with it. At this time, G1 and G2 are free to transmit receive characters via RTP. Any characters that are received by the gateway from the remote gateway before the gateway has completed the start-up (or probing) sequence with its local PTP will be buffered and sent after establishing connection with the local PTP.
+
+
+
+NOTE – As per V.8 specification, the silence period between CJ/JM signal and the generation of V.21 carrier must be $75 \pm 5$ ms.
+
+Figure II.2 – Scenario #1 call flow diagram (SSE) (sheet 2 of 2). This diagram illustrates the signaling sequence between two gateways (G1 and G2) and two terminals (T1 and T2) during a call setup. G1 and G2 are represented by vertical bars with various signal blocks. T1 and T2 are represented by vertical bars with various signal blocks. The diagram shows the flow of signals: T1 sends CM and CJ to G1; G1 sends ANSam and JM to T1. G2 sends ANSam and JM to T2. G1 sends V.21(L) MARK and CHAR to T1. G2 sends V.21(L) MARK and CHAR to T2. The diagram also shows the flow of signals between G1 and G2: G1 sends SSE(VBD:ANSam) and SSE(VBD:p') to G2; G2 sends SSE(TR:CJ) and SSE(TR:p') to G1. G1 sends PT = VBD to G2. G2 sends PT = TR(CHAR) to G1. G1 sends PT = TR(CHAR) to G2. The diagram includes a legend: Yellow boxes represent Text relayed signals, and Blue hatched boxes represent VBD signals. A note indicates that the silence period between CJ/JM signal and the generation of V.21 carrier must be 75 ± 5 ms.
+
+**Figure II.2 – Scenario #1 call flow diagram (SSE) (sheet 2 of 2)**
+
+##### Description
+
+This call flow takes into consideration the case where CI/XCI is not detected by G1, possibly because the ANSam tone was generated first due to the manner in which the call was established. G2, upon detecting the ANSam, will initiate a transition to VBD mode. While in VBD mode, both gateways will monitor the V.8 signals at their PCM interfaces, G1 seeing the CM signal indicating a PTP device and G2 seeing the JM signal indicating a PTP device. At the end of CJ reception, G1 will initiate a transition to text relay mode through the generation of an SSE(TR) to G2. The transition from VBD to text relay mode needs to be handled so that the V.21 carrier generated by the gateways meets the $75 \pm 5$ ms as required by [ITU-T V.8].
+
+For the case where the end of CI/XCI corresponds to the beginning of ANSam such that there is a cross-over of TP and VBD SSEs in the IP network, per the SSE protocol definition the gateways will end up in VBD mode. As this diagram demonstrates, in this case the gateway will eventually go to text relay mode at the end of V.8.
+
+#### II.3.2 Scenario #2
+
+T1 = V.18 PTP
+
+T2 = V.18 PTP
+
+G1 = supports FDX modulation (V.23 in this example)
+
+G2 = support V.18 native mode
+
+
+
+NOTE 1 – VBD may optionally be used for CI/XCI signal. If VBD is used, there is an SSE(VBD:CI/XCI) handshake here.
+
+NOTE 2 – CI/XCI may be detected by T2. If not detected, there will be up to 3 seconds of additional delay before ANSAm is generated.
+
+Figure II.3 – Scenario #2 call flow diagram (SSE). The diagram shows the interaction between four entities: T1, G1, G2, and T2. T1 sends CI/XCI to G1. G1 sends PT = AUDIO/PT = VBD to G2. G1 sends SSE(TP:CI/XCI) to G2. G2 sends CI/XCI to T2. T2 sends ANSAm to G2. G2 sends SSE(TR:ANSAm) to G1. G1 sends SSE(TR:p') to G2. G2 sends SSE(TR:p') to G1. G2 sends PT = TR(Char) to G1. G1 sends PT = TR(Char) to T1. T1 sends 390 Hz carrier to G1. G1 sends 2100 Hz ANS to G2. G2 sends CM to G1. G2 sends CJ to G1. G2 sends V.21(L) MARK to G1. G1 sends CHAR to G2. G2 sends CHAR to T2. T2 sends V.21(H) to G2. G2 sends V.21(L) MARK to G2. G2 sends V.21(H) to G2. The diagram also includes a legend for Text relayed signals (yellow) and VBD signals (blue hatched).
+
+**Figure II.3 – Scenario #2 call flow diagram (SSE)**
+
+##### Description
+
+Since T1 is the V.18 calling PTP, it will generate a CI/XCI sequence. Since G1 is a V.151-compliant gateway that supports SSE protocol, it will detect CI/XCI indicating to G1 that it is connected to a V.18 PTP terminal. Upon detection of CI/XCI, G1 may continue to transmit the CI/XCI sequence using audio mode to G2, or it may optionally initiate a transition to VBD mode by sending an SSE(VBD:CI/XCI) to G2. The diagram does not show the optional VBD SSE negotiation at this point. After CI/XCI sequence is completely transmitted to G2 (either through audio or VBD encoding), G1 shall send an SSE(TP:CI/XCI) to G2 and terminate regeneration of signals to T1. G1 shall stay in the mode of silence generation to T1 until it receives an SSE response from G2.
+
+Upon reception of the SSE(TP:CI/XCI) from G1, G2 will enter an answering auto-mode probing state. Since T2 is a V.18 PTP answering terminal, it will generate ANSAm signal either immediately after the CI/XCI sequence if it is detector, or within 3 seconds if the CI/XCI is not detected. Upon detection of the ANSAm signal from T2 by G2, G2 will send an SSE(TR:V.18) indicating that it has detected ANSAm signal from T2 and that T2 is a V.18 modem and that G1 should start its text relay connect sequence. G2 will then start the V.8 connect sequence with T2 (since G2 supports native V.18).
+
+Upon reception of the SSE(TR:V.18) from G2, G1 will start a connect sequence with T1. Since it knows that T1 is a V.18 PTP terminal, G1 will successfully be able to connect with it using the FDX modulation scheme that G1 supports. G1 starts the answering sequence for its supported modulation. At this time, G1 and G2 are free to transmit receive characters via RTP. Any characters that are received by the gateway from the remote gateway before the gateway has completed the start-up (or probing) sequence with its local PTP will be buffered and sent after establishing connection with the local PTP.
+
+#### II.3.3 Scenario #3
+
+T1 = V.18 PTP
+
+T2 = V.18 PTP
+
+G1 = support V.18 native mode
+
+G2 = supports FDX mode (V.21 in this example)
+
+
+
+NOTE 1 – VBD may optionally be used for CI/XCI signal. If VBD is used, there is an SSE(VBD:CI/XCI) handshake here.
+
+NOTE 2 – CI/XCI may be detected by T2. If not detected, there will be up to 3 seconds of additional delay before ANSAm is generated.
+
+Figure II.4 – Scenario #3 call flow diagram (SSE). The diagram shows the sequence of events between four entities: T1, G1, G2, and T2. T1 (V.18 PTP) sends CI/XCI to G1. G1 then sends PT = AUDIO/PT = VBD to G2. G1 also sends SSE(TP:CI/XCI) to G2. G2 sends CI/XCI to T2. T2 sends ANSAm to G2. G2 sends SSE(TR:ANSAm) to G1. G1 sends SSE(TR:p') to G2. G2 sends V.21(L) MARK to G1. G1 sends PT = TR(CHAR) to G2. G2 sends CHAR to G1. G1 sends V.21(L) MARK to G2. G2 sends V.21(H) MARK to T2. T2 sends CHAR to G2. G2 sends V.21(L) MARK to G2. A legend indicates that yellow boxes represent text relayed signals and blue hatched boxes represent VBD signals. Notes 1 and 2 provide additional context on VBD usage and CI/XCI detection.
+
+**Figure II.4 – Scenario #3 call flow diagram (SSE)**
+
+##### Description
+
+Since T1 is the V.18 calling PTP, it will generate a CI/XCI sequence. Since G1 is a V.151-compliant gateway that supports SSE protocol, it will detect CI/XCI indicating to G1 that it is connected to a V.18 PTP terminal. Upon detection of CI/XCI, G1 may continue to transmit the CI/XCI sequence using audio mode to G2, or it may optionally initiate a transition to VBD mode by sending an SSE(VBD:CI/XCI) to G2. The diagram does not show the optional VBD SSE negotiation at this point. After CI/XCI sequence is completely transmitted to G2 (either through audio or VBD encoding), G1 shall send an SSE(TP:CI/XCI) to G2 and terminate regeneration of signals to T1. G1 shall stay in the mode of silence generation to T1 until it receives an SSE indicating a new mode from G2.
+
+Upon reception of the SSE(TP:CI/XCI) from G1, G2 will enter an answering auto-mode probing state. Since T2 is a V.18 PTP answering terminal, it will generate ANSAm signal either immediately after the CI/XCI sequence if it is detector, or within 3 seconds if the CI/XCI is not detected. Upon detection of the ANSAm signal from T2 by G2, G2 will send an SSE(TR:V.18) indicating that it has detected ANSAm signal from T2 and that T2 is a V.18 modem and that G1 should start its text relay connect sequence. G2 will then continue with its answering auto-mode probing procedures, waiting for V.21 mark to be generated by T2 to respond with V.21 mark.
+
+Upon reception of the SSE(TR:V.18) from G2, G1 will reply with an SSE(TR:p') completing the switch to text relay mode and it will start a V.18 answering modem sequence to connect with T1. Any characters that are received by the gateway from the remote gateway before the gateway has completed the start-up (or probing) sequence with its local PTP will be buffered and sent after establishing connection with the local PTP.
+
+#### II.3.4 Scenario #4
+
+T1 = V.18 PTP
+
+T2 = V.18 PTP
+
+G1 = supports FDX modulation (V.23 in this example)
+
+G2 = support HDX modulation (Baudot in this example)
+
+
+
+NOTE 1 – VBD may optionally be used for CI/XCI signal. If VBD is used, there is an SSE(VBD:CI/XCI) handshake here.
+
+NOTE 2 – CI/XCI may be detected by T2. If not detected, there will be up to 3 seconds of additional delay before ANSAm is generated.
+
+V.151(06)\_FII.5
+
+Figure II.5 – Scenario #4 call flow diagram (SSE). The diagram illustrates the signaling sequence between four entities: T1 (V.18 PTP), G1 (V.151-compliant gateway), G2 (gateway), and T2 (V.18 PTP). T1 sends a CI/XCI signal to G1. G1 then sends PT = AUDIO/PT = VBD to G2. G1 also sends SSE(TP:CI/XCI) to G2. G2 sends SSE(TR:ANSam) to G1 and SSE(TR:p') to T2. T2 sends ANSAm to G2. G2 sends PT = TR(CHAR) to G1. G1 sends PT = TR(CHAR) to T1. G2 sends Baudot to T2. T2 sends Baudot to G2. The diagram also shows a 2100 Hz ANS signal from G1 to T1, a 1300 Hz carrier signal from G1 to T1, and a 390 Hz carrier signal from T1 to G1. A legend indicates that yellow boxes represent text relayed signals and blue hatched boxes represent VBD signals. Notes 1 and 2 provide additional context on VBD usage and CI/XCI detection.
+
+**Figure II.5 – Scenario #4 call flow diagram (SSE)**
+
+##### Description
+
+Since T1 is the V.18 calling PTP, it will generate a CI/XCI sequence. Since G1 is a V.151-compliant gateway that supports SSE protocol, it will detect CI/XCI indicating to G1 that it is connected to a V.18 PTP terminal. Upon detection of CI/XCI, G1 may continue to transmit the CI/XCI sequence using audio mode to G2, or it may optionally initiate a transition to VBD mode by sending an SSE(VBD:CI/XCI) to G2. The diagram does not show the optional VBD SSE negotiation at this point. After CI/XCI sequence is completely transmitted to G2 (either through audio or VBD encoding), G1 shall send an SSE(TP:CI/XCI) to G2 and terminate regeneration of signals to T1. G1 shall stay in the mode of silence generation to T1 until it receives an SSE response from G2 indicating a new mode (either VBD or text relay).
+
+Upon reception of the SSE(TP:CI/XCI) from G1, G2 will enter an answering auto-mode probing state. Since T2 is a V.18 PTP answering terminal, it will generate ANSAm signal either immediately
+
+after the CI/XCI sequence if it is detected, or within 3 seconds if the CI/XCI is not detected. Upon detection of the ANSam signal from T2 by G2, G2 will send an SSE(TR:V.18) indicating that it has detected ANSam signal from T2 and that T2 is a V.18 modem and that G1 should start its text relay auto-mode probing sequence. Since G2 does not support native V.18 mode, it will not respond to the ANSam generated by T2, but will wait until it detects a PTP modulation that it supports (Baudot in this example). After detecting the Baudot probing signal from T2, G2 will immediately respond with Baudot, triggering T2 to go into Baudot mode. The Baudot probing character that was detected by G2 is sent to G1 using text relay mode.
+
+Upon reception of the SSE(TR:V.18) from G2, G1 will start a connect sequence with T1. Since it knows that T1 is a V.18 PTP terminal, G1 will successfully be able to connect with it using the FDX modulation scheme that G1 supports. At this time, G1 and G2 are free to transmit receive characters via RTP. Any characters that are received by the gateway before the gateway has completed the start-up (or probing) sequence with its local PTP will be buffered and sent after establishing connection with the local PTP.
+
+#### II.3.5 Scenario #5
+
+T1 = FDX modulation PTP (Bell 103 in this example)
+
+T2 = V.18 PTP
+
+G1 = supports FDX modulation (Bell 103 in this example)
+
+G2 = supports FDX modulation (Bell 103 in this example)
+
+
+
+NOTE 1 – Allow end-to-end V.18 probing until T1 responds. G2 does not respond to any probing sequences that it supports during this probing.
+
+NOTE 2 – SSE(TR) is only sent by G1 at this point if G2 supports T1's modulation; otherwise, stay in VBD mode.
+
+V.151(06)\_FII.6
+
+Figure II.6 – Scenario #5 call flow diagram (SSE). The diagram shows the interaction between four entities: T1, G1, G2, and T2. T1 and T2 are terminals, while G1 and G2 are gateways. The diagram illustrates the sequence of signals and data flow. T2 sends ANSam and V.18 probing signals to G2. G2 sends SSE(VBD:ANSam) and SSE(VBD:p') to G1. G1 sends PT = VBD to T1. T1 sends 2225 Hz MARK and 1270 Hz MARK signals to G1. G1 sends 2225 Hz MARK and CHAR signals to G2. G2 sends SSE(TR:CHAR) and PT = TR(CHAR) to T2. T2 sends 2225 Hz MARK and CHAR signals to G2. The diagram also includes a legend for Text relayed signals (yellow) and VBD signals (blue).
+
+Figure II.6 – Scenario #5 call flow diagram (SSE)
+
+##### Description
+
+Since T2 is a V.18 answering PTP, it will generate ANSam after 3 seconds (because CI/XCI was not received). Since G2 is a V.151-compliant gateway that supports SSE protocol, it will detect ANSam and initiate a switch to VBD mode. T2 is allowed to probe T1 using VBD mode. G2 does not respond to any of the T2 probing sequences, even those that represent modulations that G2 supports since it has not been established that an end-to-end text relay connection can be successfully made between all gateways and PTP devices. Upon detection by G1 of a PTP FDX modulation probing response from T1 that it supports, G1 will send an SSE(TP:X) to G2 (X is the modulation that was detected, Bell 103 in this example) only if G2 also supports this modulation. If G2 does not support this modulation, the gateways stay in VBD mode and the PTP devices connect using VBD for the entire session. In the case where T1 and T2 are not PTP, but data modems, requiring that both PSTN legs of the call be of the same modulation type will result in successful connection for data modems as well as PTP devices using proper character treatments.
+
+#### II.3.6 Scenario #6
+
+- T1 = FDX modulation PTP (V.21 in this example)
+- T2 = V.18 PTP
+- G1 = does not support modulation used by T1
+- G2 = don't care
+
+
+
+The diagram shows a sequence of events between four entities: T1, G1, G2, and T2.
+1. T2 sends ANSam. G2 detects it and sends SSE(VBD:ANSam) to G1. G1 responds with SSE(VBD:p').
+2. G1 sends ANSam to T1.
+3. T2 begins V.18 probing. This is passed through G2 and G1 to T1.
+4. T1 responds with V.21(H) MARK and CHAR.
+5. G1 receives this and passes it as V.21(L) MARK and CHAR to G2 via PT = VBD.
+6. G2 passes V.21(H) MARK and CHAR to T2.
+7. T2 responds with V.21(L) MARK and CHAR, which is passed back through G2 and G1 to T1 as V.21(H) MARK and CHAR.
+
+**Legend:**
+ Text relayed signals
+ VBD signals
+
+NOTE – Allow end-to-end V.18 probing until T1 responds. G2 does not respond to any probing sequences that it supports during this probing.
+
+Figure II.7 – Scenario #6 call flow diagram (SSE).
+
+**Figure II.7 – Scenario #6 call flow diagram (SSE)**
+
+##### **Description**
+
+Since T2 is a V.18 answering PTP, it will generate ANSam after 3 seconds (because CI/XCI was not received). Since G2 is a V.151-compliant gateway that supports SSE protocol, it will detect ANSam and initiate a switch to VBD mode. T2 is allowed to probe T1 using VBD mode. G2 does not respond to any of the T2 probing sequences, even those that represent modulations that G2 supports since it has not been established that a end-to-end text relay connection can be successfully made between all gateways and PTP devices. Since the modulation that is responded to by T1 is not supported by G1, G1 does not initiate a switch to text relay mode and the connection remains in VBD mode for the entire call.
+
+#### **II.3.7 Scenario #7**
+
+T1 = FDX modulation PTP (Bell 103 in this example)
+
+T2 = V.18 PTP
+
+G1 = supports FDX modulation (Bell 103 in this example)
+
+G2 = supports FDX modulation (Bell 103 in this example) (Does not support native V.18)
+
+##### **Description**
+
+This scenario plays out identical to scenario #5. The only difference between these scenarios is that G2 does not support native V.18 mode, but the call flow is identical.
+
+#### **II.3.8 Scenario #8**
+
+T1 = FDX modulation PTP (V.21 in this example)
+
+T2 = V.18 PTP
+
+G1 = does not support modulation used by T1
+
+G2 = does not support native V.18 mode
+
+##### **Description**
+
+This scenario plays out identical to scenario #6. The only difference between these scenarios is that G2 does not support native V.18 mode, but the call flow is identical.
+
+#### **II.3.9 Scenarios #9 and #10**
+
+T1 = V.18 PTP
+
+T2 = FDX modulation PTP (V.21 in this example)
+
+G1 = supports any modulation
+
+G2 = supports modulation of T2 (V.21 in this example)
+
+
+
+NOTE 1 – VBD may optionally be used for CI/XCI signal. If VBD is used, there is an SSE(VBD:CI/XCI) handshake here.
+
+NOTE 2 – CI/XCI may be detected by T2.
+
+NOTE 3 – ANS tone is optional.
+
+NOTE 4 – Start originate, mode answer probing upon reception of SSE(TR) with same modulation as supported by T2 if available at G1.
+
+NOTE 5 – G1 buffers characters received from G2 until it has completed connection with T1.
+
+V.151(06)\_FIL.8
+
+Figure II.8 – Scenarios #9 and #10 call flow diagram (SSE). The diagram shows a sequence of events between four entities: T1, G1, G2, and T2. T1 sends CI/XCI to G1. G1 sends PT = AUDIO/PT = VBD to G2. G1 sends SSE(TP:CI/XCI) to G2. G2 sends SSE(TR:p') to G1. G2 sends ANS to T2. G2 sends V.21(H) MARK to T2. G2 sends CHAR to T2. G2 sends V.21(L) MARK to T2. G1 sends PT = TR (CHAR) to G2. G1 sends PT = TR(CHAR) to G2. G1 sends V.21(L) MARK to G2. A legend indicates that yellow boxes represent text relayed signals and blue boxes represent VBD signals. Notes 1 through 5 provide additional context for the diagram.
+
+**Figure II.8 – Scenarios #9 and #10 call flow diagram (SSE)**
+
+##### Description
+
+Since T1 is the V.18 calling PTP, it will generate a CI/XCI sequence. Since G1 is a V.151-compliant gateway that supports SSE protocol, it will detect CI/XCI indicating to G1 that it is connected to a V.18 PTP terminal. Upon detection of CI/XCI, G1 may continue to transmit the CI/XCI sequence using audio mode to G2, or it may optionally initiate a transition to VBD mode by sending an SSE(VBD:CI/XCI) to G2. The diagram does not show the optional VBD SSE negotiation at this point. After CI/XCI sequence is completely transmitted to G2 (either through audio or VBD encoding), G1 shall send an SSE(TP:CI/XCI) to G2 and terminate regeneration of signals to T1. G1 shall stay in the mode of silence generation to T1 until it receives an SSE response from G2 indicating a new mode (either VBD or text relay).
+
+Upon reception of the SSE(TP:CI/XCI) from G1, G2 will enter an answering auto-mode probing state. Since T2 is a V.21 PTP answering terminal, it can either generate ANS or go straight to V.21 MARK generation (ANS signal is optional). Upon detection of the V.21 MARK from T2 by G2, G2 will send an SSE(TR:V.18) indicating that it has detected a valid PTP signal from T2 and that G1 should start its text relay auto-mode probing sequence. G2 will then connect with T2 and start to transmit receive characters using text relay mode.
+
+Upon reception of the SSE(TR:V.18) from G2, G1 will start a connect sequence with T1. Since it knows that T1 is a V.18 PTP terminal, G1 will successfully be able to connect with it using the first modulation scheme used in the probing sequence. G1 should use the modulation scheme being used by T2 and G2 if it is supported by G1 (i.e., attempt to match modulations at both call legs). Any characters that are received by the gateway from the remote gateway before the gateway has completed the start-up (or probing) sequence with its local PTP will be buffered and sent after establishing connection with the local PTP.
+
+**II.3.10 Scenarios #11 and #12**
+
+T1 = V.18 PTP
+
+T2 = FDX modulation PTP (V.21 in this example)
+
+G1 = supports any modulation
+
+G2 = does not support modulation of T2
+
+
+
+```
+
+ sequenceDiagram
+ participant T1
+ participant G1
+ participant G2
+ participant T2
+
+ Note over T1, T2: Note 1: PT = AUDIO/PT = VBD
+ T1->>G1: CI/XCI
+ G1-->>G2: SSE(TP:CI/XCI)
+ Note right of G2: Note 2
+ G2->>T2: CI/XCI
+ G2-->>G1: SSE(TP:p')
+ Note over G2: Note 3
+ T2->>G2: ANS
+ Note over G2: Note 4
+ G2-->>G1: SSE(VBD:TO)
+ G1-->>G2: SSE(VBD:p')
+ T2->>G2: V.21(H) MARK
+ G1->>T1: V.21(H) MARK
+ T1->>G1: V.21(L) MARK
+ G1->>G2: PT = VBD
+ G2->>T2: V.21(L) MARK
+ T2->>G2: CHAR
+ G1->>T1: CHAR
+ T1->>G1: CHAR
+ G1->>G2: PT = VBD
+ G2->>T2: CHAR
+ T2->>G2: V.21(H) MARK
+ G1->>T1: V.21(L) MARK
+ G2->>T2: V.21(L) MARK
+
+```
+
+V.151(06)\_FII.9
+
+Figure II.9 – Scenarios #11 and #12 call flow diagram (SSE)
+
+- Text relayed signals
+- VBD signals
+- NOTE 1 – VBD may optionally be used for CI/XCI signal. If VBD is used, there is an SSE(VBD:CI/XCI) handshake here.
+- NOTE 2 – CI/XCI may be detected by T2.
+- NOTE 3 – ANS tone is optional.
+- NOTE 4 – G2 times out looking for valid PTP signal that it supports.
+
+**Figure II.9 – Scenarios #11 and #12 call flow diagram (SSE)**
+
+**Description**
+
+Since T1 is the V.18 calling PTP, it will generate a CI/XCI sequence. Since G1 is a V.151-compliant gateway that supports SSE protocol, it will detect CI/XCI indicating to G1 that it is connected to a V.18 PTP terminal. Upon detection of CI/XCI, G1 may continue to transmit the CI/XCI sequence using audio mode to G2, or it may optionally initiate a transition to VBD mode by sending an SSE(VBD:CI/XCI) to G2. The diagram does not show the optional VBD SSE negotiation at this point. After CI/XCI sequence is completely transmitted to G2 (either through audio or VBD encoding), G1 shall send an SSE(TP:CI/XCI) to G2 and terminate regeneration of signals to T1. G1 shall stay in the mode of silence generation to T1 until it receives an SSE response from G2 indicating a new mode (either VBD or text relay).
+
+Upon reception of the SSE(TP:CI/XCI) from G1, G2 enters into an answering auto-mode probing state, searching for a signal that it detects as a valid PTP signal. Since G2 does not support the modulation supported by T2, it will detect a non-text relay support signal in the answering auto-mode probing state and generate an SSE(VBD:TO) to G1. This will transition the call to VBD mode and the connection with stay in this mode for the remainder of the PTP session.
+
+**ITU-T Rec. V.151 (05/2006)** 59
+
+#### II.3.11 Scenarios #13 and #14
+
+T1 = FDX modulation PTP (V.21 in this example)
+
+T2 = FDX modulation PTP (same as T1)
+
+G1 = supports modulation of T1
+
+G2 = supports modulation of T2
+
+
+
+NOTE 1 – Generation of ANS signal by T2 is optional.
+ NOTE 2 – If ANS was not generated by T2, G2 shall initiate transition to VBD upon V.21 mark detection.
+ NOTE 3 – G1 responds with SSE(TR) only if it detects T1 to be same modulation as T2. If not, G1 responds with SSE(VBD).
+ NOTE 4 – Only send SSE(TR) if G1 supports modulation of T2; otherwise, stay in VBD mode.
+
+Figure II.10 – Scenarios #13 and #14 call flow diagram (SSE). The diagram shows the sequence of events between T1, G1, G2, and T2. T2 initiates the call with ANS, followed by V.21(H) MARK and CHAR. G2 receives these and sends SSE(VBD:ANS) and SSE(VBD:p') to G1. G1 then sends SSE(TP:V.21 ch1) and SSE(TP:p') to G2. G2 sends SSE(TR:V.21 ch2) and SSE(TR:p') to G1. G1 then sends PT = TR to G2. G2 sends PT = TR to T2. The diagram also shows V.21(L) MARK and CHAR signals between T1 and G1. A legend indicates that yellow boxes represent text relayed signals and blue hatched boxes represent VBD signals. Notes 1-4 provide additional context on the optional generation of ANS, the transition to VBD mode, and the conditions for sending SSE(TR).
+
+**Figure II.10 – Scenarios #13 and #14 call flow diagram (SSE)**
+
+##### Description
+
+T2 being the answering PTP device will initiate the generation of a FDX signal, optionally preceded by the ANS signal. Since G2 is a V.151-compliant gateway that supports SSE protocol, upon detection of the ANS tone, G2 will initiate a switch to VBD mode. When G2 detects the carrier for a FDX modulation that it supports for text, it shall generate a SSE(TP) if G1 has also indicated support for this modulation. If G1 does not support the modulation used by T2, the connection will remain in VBD for the duration of the call.
+
+Upon reception of the SSE(TP), G1 shall enter an originate mode auto-probing sequence, starting with the modulation indicated in the SSE(TP) from G2. Since T1 is the same modulation as T2, G1 will connect with T1 using this modulation. Upon detection of the response signal from T1, G1 will generate an SSE(TR) to G2 indicating that the connection has transitioned to text relay mode.
+
+Upon reception of the SSE(TR) from G1, G2 will start the connect sequence with T2.
+
+In this scenario, T1 and T2 modulations must be the same for the PTP connection to be established. There is no support for protocol conversion in this scenario. Ensuring that T1 and T2 modulations
+
+are the same allows non-PTP data modems that use the same physical layer modulation to also be supported using relay.
+
+T1 = FDX modulation PTP (Bell 103 in this example)
+ T2 = FDX modulation PTP (same as T1)
+ G1 = supports modulation of T1
+ G2 = supports modulation of T2
+
+
+
+Detailed description of Figure II.10-1: A sequence diagram with four vertical lifelines labeled T1, G1, G2, and T2 from left to right.
+ - T2 sends a 2225 Hz tone to G2.
+ - G2 sends SSE(VBD:Tone 2225 Hz) and SSE(VBD:p') to G1.
+ - G1 sends SSE(TP:Bell103 chan 1) and SSE(TR:Bell 103 chan 2) to G2.
+ - G2 responds with SSE(TR:V.21 ch2) to G1.
+ - Data exchange follows: G1 sends PT=TR to G2, and G2 sends PT=TR to G1.
+ - Signal states are shown in boxes: T1 has 'CHAN 1 MARK' and 'CHAR'; G1 has 'CHAN 2 MARK' and 'CHAR'; G2 has 'CHAN 1 MARK' and 'CHAR'; T2 has '2225 Hz', 'CHAN 2 MARK', and 'CHAR'.
+ - Legend: Yellow shaded boxes represent 'Text relayed signals'; Blue hatched boxes represent 'VBD signals'.
+ - A note at the bottom states: 'NOTE – Only send SSE(TR) if G2 supports modulation of T2; otherwise, stay in VBD mode.'
+
+*V.151(06)\_FII.10(bis)*
+
+Figure II.10-1 – Scenarios #13 and #14 (Bell 103) call flow diagram (SSE)
+
+**Figure II.10-1 – Scenarios #13 and #14 (Bell 103) call flow diagram (SSE)**
+
+**Description**
+
+Bell 103 is a special case of the FDX to FDX scenario since, unlike other FDX modems such as V.21, the originating modem is first to generate carrier upon detection of the 2225-Hz answer tone.
+
+T2 being the answering Bell 103 PTP device will initiate the generation of 2225-Hz answer tone. Since G2 is a V.151-compliant gateway that supports SSE protocol, upon detection of the 2225-Hz tone, G2 will initiate a switch to VBD mode. When G1 detects MARK for a Bell 103 originating modem that it supports for text, it shall generate an SSE(TP) if G2 has also indicated support for this modulation. If G2 does not support the modulation used by T2, the connection will remain in VBD for the duration of the call.
+
+Upon reception of the SSE(TP), G2 shall respond with an SSE(TR) to transition the connection into text relay mode and start a connection with T2.
+
+Upon reception of the SSE(TR) from G2, G1 will start the connect sequence with T1.
+
+**ITU-T Rec. V.151 (05/2006)** 61
+
+In this scenario, T1 and T2 modulations must be the same for the PTP connection to be established. There is no support for protocol conversion in this scenario. Ensuring that T1 and T2 modulations are the same allows non-PTP data modems that use the same physical layer modulation to also be supported using relay.
+
+#### II.3.12 Scenarios #15 and #16
+
+T1 = FDX modulation PTP (V.21 in this example)
+
+T2 = FDX modulation PTP (same as T1)
+
+G1 = don't care
+
+G2 = does not support modulation of T2
+
+
+
+NOTE 1 – Generation of ANS signal by T2 is optional.
+
+NOTE 2 – If ANS was not generated by T2, G2 shall initiate transition to VBD upon V.21 mark detection.
+
+V.151(06)\_FII.11
+
+Figure II.11 – Scenarios #15 and #16 call flow diagram (SSE). The diagram shows the interaction between T1, G1, G2, and T2. T1 and T2 are PTP devices using V.21 modulation. G1 is a gateway that doesn't care, and G2 is a gateway that doesn't support T2's modulation. The flow starts with T2 sending an ANS signal to G2. G2 then sends SSE(VBD:ANS) to G1 and SSE(VBD:p') to T1. G1 then sends V.21(H) MARK to T1. T1 then sends V.21(L) MARK and CHAR to G1. G1 then sends PT = VBD to G2. G2 then sends V.21(L) MARK and CHAR to T2. T2 then sends V.21(H) MARK to G2. A legend indicates that yellow boxes represent text relayed signals and blue hatched boxes represent VBD signals. Notes 1 and 2 provide additional context on the ANS signal generation and the transition to VBD mode.
+
+**Figure II.11 – Scenarios #15 and #16 call flow diagram (SSE)**
+
+##### Description
+
+T2 being the answering PTP device will initiate the generation of an FDX signal, optionally preceded by the ANS signal. Since G2 is a V.151-compliant gateway that supports SSE protocol, upon detection of the FDX signal or the ANS tone, G2 will initiate a switch to VBD mode. Since G2 does not support the FDX modulation being used by T2, it will not initiate a transition to text relay mode through generation of SSE(TR). Upon detection of the modulation signal, if the channel is not already in VBD mode, G2 will initiate a transition to VBD mode. When T1 detects the carrier from T1 (since it may support the T1/T2 modulation), it will not initiate a transition to text relay since G2 had indicated that it does not support this modulation.
+
+In this scenario, T1 and T2 modulations must be the same for the PTP connection to be established. There is no support for protocol conversion in this scenario.
+
+#### II.3.13 Scenarios #17 and #19
+
+T1 = HDX modulation PTP (Baudot in this example)
+
+T2 = V.18 PTP
+
+G1 = supports T1's modulation
+
+G2 = don't care
+
+
+
+The diagram illustrates a call flow between four entities: T1, G1, G2, and T2.
+1. T2 sends an ANSam signal.
+2. G2 detects ANSam and sends SSE(VBD:ANSam) to G1 and SSE(VBD:p') to T1 (indicated by red dashed arrows).
+3. G1 and T2 enter ANSam state (blue hatched boxes).
+4. T2 initiates V.18 probing, which passes through G2 and G1 to T1.
+5. T1 responds with a Baudot character.
+6. G1 detects Baudot and sends PT = VBD to G2.
+7. G1 sends SSE(TP:Baudot) to G2 and SSE(TR:Baudot) to G2.
+8. G2 sends SSE(TR:p') to T1.
+9. G2 sends PT = TR (CHAR) to G1.
+10. Text relayed signals (yellow boxes) are exchanged: G1 sends Baudot to T1, and G2 sends Baudot to T2.
+Legend: Yellow boxes = Text relayed signals; Blue hatched boxes = VBD signals.
+
+NOTE 1 – Allow end-to-end V.18 probing until T1 responds. G2 does not respond to any probing sequences that it supports during this probing.
+
+NOTE 2 – SSE(TP) is only sent by G1 at this point if G2 is not V.18 native only; otherwise, stay in VBD mode.
+
+NOTE 3 – G2 starts auto-mode probing after receiving SSE(TR) from G1. Probing should start with T1 modulation if supported by G2.
+
+V.151(06)\_FII.12
+
+Figure II.12 – Scenarios #17 and #19 call flow diagram (SSE)
+
+**Figure II.12 – Scenarios #17 and #19 call flow diagram (SSE)**
+
+##### Description
+
+T2 will generate a V.8 ANSam signal at the start of the call. Upon detection of the ANSam, G2 will initiate a transition to VBD mode through generation of a SSE(VBD:ANSam). The V.18 probing is allowed to be performed end-to-end through the VBD channel. G2 will not respond to any probing signals even in cases where it supports the modulation in the probing signals.
+
+Upon detection of a PTP modulation signal supported by G1 (a Baudot character in this example), G1 shall immediately send an SSE(TP) to G2. In cases where G2 only support V.18 native mode, G1 shall not generate the SSE(TR) and the connection shall remain in VBD mode for the duration of the call.
+
+Upon reception of the SSE(TR) from G1, G2 shall start its originating auto-mode probing state, waiting for T2 to generate an appropriate signal to respond to. If G2 supports T1's modulation, it shall use that modulation.
+
+For the case of EDT, discrimination between data modems and PTP devices is determined by the half-duplexity of the signal. For data modems, the signal will be full duplex (i.e., there will be energy in both directions). For PTP, this will be half duplex. If EDT was being used by T1, G1 will
+
+only initiate a switch to text relay mode if it did not see energy in the opposite direction when it detected the EDT character.
+
+#### II.3.14 Scenarios #18 and #20
+
+T1 = HDX modulation PTP (Baudot in this example)
+
+T2 = V.18 PTP
+
+G1 = does not support T1's modulation
+
+G2 = don't care
+
+
+
+Legend:
+
+- Text relayed signals (Yellow box)
+- VBD signals (Blue hatched box)
+
+NOTE – Allow end-to-end V.18 probing until T1 responds. G2 does not respond to any probing sequences that it supports during this probing.
+
+V.151(06)\_FII.13
+
+Figure II.13 – Scenarios #18 and #20 call flow diagram (SSE). The diagram shows a sequence of events between four entities: T1, G1, G2, and T2. T2 initiates the call with an ANSam signal, followed by V.18 probing, and then Baudot. G2 responds to T2's Baudot with PT = VBD. G2 also sends SSE(VBD:ANSam) to G1 and SSE(VBD:p') to T1. G1 responds to T1's Baudot with PT = VBD. T1 then sends Baudot to G1. A note indicates that G2 does not respond to any probing sequences it supports during this probing. A legend at the bottom left identifies yellow boxes as 'Text relayed signals' and blue hatched boxes as 'VBD signals'. The diagram is labeled V.151(06)\_FII.13 at the bottom right.
+
+**Figure II.13 – Scenarios #18 and #20 call flow diagram (SSE)**
+
+##### Description
+
+T2 will generate a V.8 ANSam signal at the start of the call. Upon detection of the ANSam, G2 will initiate a transition to VBD mode through generation of a SSE(VBD:ANSam). The V.18 probing is allowed to be performed end to end through the VBD channel. G2 will not respond to any probing signals even in cases where it supports the modulation in the probing signals.
+
+Since G1 does not support the modulation used by T1, it will not detect a valid PTP signal and no transition to text relay mode will be initiated. T1 will connect with T2 using VBD mode for the duration of the call.
+
+#### II.3.15 Scenarios #21 and #22
+
+T1 = V.18 PTP
+
+T2 = HDX modulation PTP (Baudot in this example)
+
+G1 = supports any modulation
+
+G2 = supports modulation of T2
+
+
+
+NOTE 1 – VBD may optionally be used for CI/XCI signal. If VBD is used, there is an SSE(VBD:CI/XCI) handshake here.
+
+NOTE 2 – CI/XCI may be detected by T2.
+
+NOTE 3 – G1 will use modulation of T2 if it is available; otherwise, use first modulation on normal probing sequence.
+
+Figure II.14 – Scenarios #21 and #22 call flow diagram (SSE). The diagram shows a sequence of messages between four entities: T1, G1, G2, and T2. T1 sends a CI/XCI signal to G1. G1 then sends PT = AUDIO/PT = VBD to G2. G2 sends CI/XCI to T2. G1 sends SSE(TP:CI/XCI) to G2. G2 sends SSE(TP:p') to G1. G1 sends SSE(TR:Baudot) to G2. G2 sends SSE(TR:p') to G1. G1 sends PT = TR to G2. G2 sends PT = TR to G1. G1 sends Baudot to T1. G2 sends Baudot to T2. Notes: Note 1 points to the PT = AUDIO/PT = VBD message. Note 2 points to the CI/XCI signal from G2 to T2. Note 3 points to the Baudot signal from G1 to T1. Legend: Yellow box = Text relayed signals, Blue box = VBD signals.
+
+**Figure II.14 – Scenarios #21 and #22 call flow diagram (SSE)**
+
+##### Description
+
+Since T1 is the V.18 calling PTP, it will generate a CI/XCI sequence. Since G1 is a V.151-compliant gateway that supports SSE protocol, it will detect CI/XCI indicating to G1 that it is connected to a V.18 PTP terminal. Upon detection of CI/XCI, G1 may continue to transmit the CI/XCI sequence using audio mode to G2, or it may optionally initiate a transition to VBD mode by sending an SSE(VBD:CI/XCI) to G2. The diagram does not show the optional VBD SSE negotiation at this point. After CI/XCI sequence is completely transmitted to G2 (either through audio or VBD encoding), G1 shall send an SSE(TP:CI/XCI) to G2 and terminate regeneration of signals to T1. G1 shall stay in the mode of silence generation to T1 until it receives an SSE response from G2 indicating a new mode (either VBD or text relay).
+
+Upon reception of the SSE(TR:CI/XCI) from G1, G2 will enter an answering auto-mode probing state, searching for a signal that it detects as a valid PTP signal. Once a valid PTP signal is detected by G2, G2 will send an SSE(TR) to G1. After the SSE(TR:p') response is received from G1, G2 will start to transmit received characters using text relay.
+
+Upon receiving a SSE(TR) from G2, G1 will start a connect sequence with T1 (which it knows is a V.18 PTP device). G1 shall use the modulation being used by T2 if it is supported, or else will use the first modulation in the normal auto-mode probing sequence. G1 shall buffer the character received from G2 until it has established connection with T1.
+
+#### II.3.16 Scenarios #23 and #24
+
+T1 = V.18 PTP
+
+T2 = HDX modulation PTP (Baudot in this example)
+
+G1 = supports any modulation
+
+G2 = does not support modulation of T2
+
+
+
+NOTE 1 – VBD may optionally be used for CI/XCI signal. If VBD is used, there is an SSE(VBD:CI/XCI) handshake here.
+
+NOTE 2 – CI/XCI may be detected by T2.
+
+NOTE 3 – Since G2 is a V.151-compliant gateway, it is required to detect all varieties of V.18 modulations for the purposes of initiating transition to VBD mode.
+
+V.151(06)\_FII.15
+
+Figure II.15 – Scenario #23 and #24 call flow diagram (SSE). The diagram shows a sequence of events between four entities: T1, G1, G2, and T2. T1 sends a CI/XCI signal to G1. G1 then sends PT = AUDIO/PT = VBD to G2. G2 sends CI/XCI to T2. T2 sends Baudot to G2. G2 sends PT = VBD to G1. G1 sends PT = VBD to T1. G1 also sends SSE(TP:CI/XCI) to G2 and SSE(TP:p') to G2. G2 sends SSE(VBD:Baudot) to G1 and SSE(VBD:p') to G1. A legend indicates that yellow boxes represent text relayed signals and blue hatched boxes represent VBD signals. Notes 1, 2, and 3 provide additional context.
+
+**Figure II.15 – Scenario #23 and #24 call flow diagram (SSE)**
+
+##### Description
+
+Since T1 is the V.18 calling PTP, it will generate a CI/XCI sequence. Since G1 is a V.151-compliant gateway that supports SSE protocol, it will detect CI/XCI indicating to G1 that it is connected to a V.18 PTP terminal. Upon detection of CI/XCI, G1 may continue to transmit the CI/XCI sequence using audio mode to G2, or it may optionally initiate a transition to VBD mode by sending an SSE(VBD:CI/XCI) to G2. The diagram does not show the optional VBD SSE negotiation at this point. After CI/XCI sequence is completely transmitted to G2 (either through audio or VBD encoding), G1 shall send an SSE(TP:CI/XCI) to G2 and terminate regeneration of signals to T1. G1 shall stay in the mode of silence generation to T1 until it receives an SSE response from G2 indicating a new mode (either VBD or text relay).
+
+Upon reception of the SSE(TP:CI/XCI) from G1, G2 will enter an answering auto-mode probing state, searching for a signal that it detects as a valid PTP signal. When G2 detects a signal that is not a PTP modulation that it supports for modem relay, G2 will transmit to G1 an SSE(VBD). G1 will respond with an SSE(VBD:p') completing the transition to VBD mode. The connection will stay in VBD mode for the duration of the session.
+
+#### II.3.17 Scenario #25
+
+T1 = HDX protocol (Baudot in this example)
+
+T2 = HDX protocol (Baudot in this example)
+
+G1 = supports T1's modulation
+
+G2 = supports T2's modulation
+
+
+
+NOTE 1 – Probing sequence start with Baudot modulation if available (since SSE indicated Baudot being used by T2).
+
+NOTE 2 – Received characters are buffered by G2 until mode transition to TR is complete.
+
+NOTE 3 – Received characters are buffered by G1 until mode transition to TR is complete.
+
+NOTE 4 – Since Baudot is half duplex, G1 shall wait for loss of carrier from T1 before transmitting received characters from G2.
+
+V.151(06)\_FII.16
+
+Figure II.16 – Scenario #25 call flow diagram (SSE). The diagram shows the interaction between four entities: T1, G1, G2, and T2. T1 and T2 are terminals, while G1 and G2 are gateways. The sequence of events is as follows: 1. T2 sends 'Baudot Char's' to G2. 2. G2 sends 'SSE(TP:Baudot)' to G1 (Note 1). 3. G1 sends 'Baudot probing' to T1. 4. T1 sends 'Baudot Char's' to G1. 5. G1 sends 'SSE(TR:Baudot)' to G2 (Note 3). 6. G2 buffers the characters and sends 'SSE(TR:p\')' to G1 (Note 2). 7. G1 sends 'Baudot Char's' to T1. 8. G1 sends 'PT = TR(CHAR)' to G2. 9. G2 sends 'Baudot Char's' to T2. 10. T2 sends 'Baudot Char's' to G2. 11. G2 sends 'PT = TR(CHAR)' to G1 (Note 4). 12. G1 sends 'Baudot Char's' to T1. The diagram uses yellow boxes for text relayed signals and blue hatched boxes for VBD signals. A legend at the bottom left defines these symbols. Notes 1-4 provide additional context for the sequence.
+
+**Figure II.16 – Scenario #25 call flow diagram (SSE)**
+
+##### Description
+
+T2, being the called PTP terminal, will, according to PTP etiquette, initiate the first text transmission. Since G2 supports the HDX modulation used by T2, it will detect the modulation per V.151 requirements and send an SSE(TP:Baudot) to G1 indicating this G2 shall not respond to T1 until transition to text relay mode is complete and it receives characters from G1. G2 may send the received characters to G1 after receiving the SSE(TP:p\') from G1. These characters may be used by G1 when generating probing sequences.
+
+Upon reception of the SSE(TP:Baudot) from G2, G1 shall enter originating auto-mode probing state. If G1 supports Baudot, it shall start the probing sequence with Baudot. Upon receiving a valid response from T1, G1 shall send an SSE(TR:Baudot) response back to G2. G2 will then immediately respond with an SSE(TR:p\') completing the transition to text relay mode.
+
+Once in text relay mode, G1 and G2 will send their received characters via RTP. Note that since Baudot (and all other NCC modulations) are half duplex, the gateways might have to buffer characters received from the IP network until their local terminals have stopped transmitting.
+
+**II.3.18 Scenario #26**
+
+T1 = HDX protocol (Baudot in this example)
+ T2 = HDX protocol (Baudot in this example)
+ G1 = does not support T1's modulation
+ G2 = supports T2's modulation
+
+
+
+```
+
+ sequenceDiagram
+ participant T1
+ participant G1
+ participant G2
+ participant T2
+ Note over G2, T2: Note 1
+ T2->>G2: Baudot Char's
+ G2-->>G1: SSE(TP:Baudot)
+ rect rgb(255, 255, 0)
+ Note right of G1: Auto-mode probing
+ end
+ G1-->>G2: SSE(TP:p')
+ Note over G1, G2: Note 2
+ G1-->>G2: SSE(VBD:TO)
+ G2-->>G1: SSE(VBD:p')
+ T2->>G1: PT = VBD
+ rect rgb(173, 216, 230)
+ Note right of G1: Baudot Char's
+ end
+ G1->>T1: Baudot Char's
+ T1->>G2: PT = VBD
+ rect rgb(173, 216, 230)
+ Note right of G2: Baudot Char's
+ end
+ G2->>T2: Baudot Char's
+
+```
+
+- Text relayed signals
+- VBD signals
+
+NOTE 1 – Received characters are buffered by G2 until mode transition to TR is complete. These characters will be discarded in this case since the channel does not complete transition to text relay.
+ NOTE 2 – G1 times out during auto-mode probing.
+
+**Figure II.17 – Scenario #26 call flow diagram (SSE)**
+
+Figure II.17 – Scenario #26 call flow diagram (SSE)
+
+**Description**
+
+T2, being the called PTP terminal, will, according to PTP etiquette, initiate the first text transmission. Since G2 supports the HDX modulation used by T2, it will detect the modulation per V.151 requirements and send an SSE(TP:Baudot) to G1 indicating a request to transition to text relay mode. G2 shall buffer all received characters until a transition to text relay mode is complete. G2 shall not respond to T1 until transition to text relay mode is complete and it receives characters from G1.
+
+Upon reception of the SSE(TP:Baudot) from G2, G1 shall enter originating auto-mode probing state. Since G1 does not support the T1 modulation in this scenario, G1 will eventually time out and send a SSE(VBD) to G2, transitioning the session to VBD mode. G2 will discard the buffered characters and complete the transition to VBD mode by responding to G1 with an SSE(VBD:p'). The channel shall remain in VBD mode for the duration of the session.
+
+68 ITU-T Rec. V.151 (05/2006)
+
+#### II.3.19 Scenario #27
+
+T1 = HDX protocol (Baudot in this example)
+
+T2 = HDX protocol (Baudot in this example)
+
+G1 = supports T1's modulation
+
+G2 = does not support T2's modulation
+
+
+
+Legend:
+
+- Text relayed signals (Yellow box)
+- VBD signals (Blue hatched box)
+
+NOTE – V.151-compliant gateways are required to detect PTP modulations for purposes of initiating transition to VBD mode.
+
+Figure II.18 – Scenario #27 call flow diagram (SSE). The diagram shows a sequence of events between four entities: T1, G1, G2, and T2. T1 sends 'Baudot Char's' to G1. G1 sends 'Baudot probing' to T1. G2 sends 'SSE(VBD:Baudot)' to G1 and 'SSE(VBD:p\')' to G1. G1 sends 'PT = VBD' to G2. G2 sends 'Baudot Char's' to T2. A 'Note' box points to the 'SSE(VBD:Baudot)' and 'SSE(VBD:p\')' messages. A legend indicates that yellow boxes represent 'Text relayed signals' and blue hatched boxes represent 'VBD signals'. The diagram is labeled 'V.151(06)\_FII.18'.
+
+**Figure II.18 – Scenario #27 call flow diagram (SSE)**
+
+##### Description
+
+T2, being the called PTP terminal, will, according to PTP etiquette, initiate the first text transmission. G2 will detect the Baudot signal and initiate a transition to VBD mode since it is not a modulation that it supports for text relay. The session will remain in VBD mode.
+
+If the connection did not follow PTP etiquette, and T1 transmitted first, G1 would initiate a transition to text relay mode through transmission of an SSE(TR) to G2. G2 would time out (or detect unsupported PTP signal) and respond with SSE(VBD) as per scenario #26.
+
+#### II.3.20 Scenario #28
+
+T1 = HDX protocol (Baudot in this example)
+
+T2 = HDX protocol (Baudot in this example)
+
+G1 = does not support T1's modulation
+
+G2 = does not support T2's modulation
+
+**Description**
+
+In this scenario, neither gateway supports the modulation used by their local PTP devices. Since the gateways are V.151-compliant, they will detect a PTP signal that is not supported via text relay and will initiate a transition to VBD mode. The gateway receiving the SSE(VBD) will respond with SSE(VBD) and the transition to VBD will be completed. The gateways will stay in VBD mode for the duration of the call.
+
+**II.3.21 Scenario #29**
+
+T1 = FDX PTP device (V.21 in this example)
+
+T2 = HDX PTP device (Baudot in this example)
+
+G1 = supports T1's modulation
+
+G2 = supports T2's modulation
+
+
+
+The diagram illustrates a call flow between T1, G1, G2, and T2.
+ Sequence of events:
+ 1. T2 sends 'Baudot Char's' to G2.
+ 2. G2 sends SSE(TP:Baudot) to G1. Note 2 indicates received characters are buffered by G2 until mode transition to TR is complete.
+ 3. G1 starts 'Probing' towards T1. Note 1 indicates probing sequence starts with Baudot modulation if available.
+ 4. G1 sends SSE(TP:p') to G2.
+ 5. T1 responds to G1 with V.21 (low) signals.
+ 6. G1 transitions to V.21 (high) and sends SSE(TR:V.21 ch1) to G2.
+ 7. G1 also sends SSE(TR:p') to G2.
+ 8. G2 sends PT = TR(CHAR) to G1.
+ 9. G1 sends CHAR to T1 and PT = TR(CHAR) to G2.
+ 10. G2 sends 'Baudot Char's' to T2.
+
+Figure II.19 – Scenario #29 call flow diagram (SSE)
+
+ Text relayed signals
+
+▒▒▒ VBD signals
+
+NOTE 1 – Probing sequence start with Baudot modulation if available (since SSE indicated Baudot being used by T2).
+
+NOTE 2 – Received characters are buffered by G2 until mode transition to TR is complete.
+
+**Figure II.19 – Scenario #29 call flow diagram (SSE)**
+
+**Description**
+
+As per PTP etiquette, T2 will initially transmit a character which will be detected by G2 as a valid PTP modulation supported for text relay. G2 will then generate an SSE(TP) to G1. G2 may send characters received to G1 so that G1 could use these in its probing signals.
+
+Upon reception of the SSE(TP) from G2, G1 will start an originating auto-mode probing sequence with T1. G1 should start the auto-mode probing sequence with T2's modulation if it is supported. Since G1 supports the FDX modulation in this scenario, it will eventually connect with T1, at which time it shall send an SSE(TR) to G2 indicating it has successfully connected with a PTP device in text relay mode.
+
+70 ITU-T Rec. V.151 (05/2006)
+
+When G2 receives the SSE(TR) from G1, it will respond with SSE(TR:p') completing the transition to text relay mode and send any buffer characters to G1.
+
+#### II.3.22 Scenarios #30 to #32
+
+In these scenarios, either or both of the gateways does not support the modulation of its local PTP device. Both PTP devices are not V.18 PTP devices, and one is FDX based while the other is HDX based. No successful connection will be achieved, although the channel may be transitioned to VBD mode since the gateway should detect either of the PTP signals.
+
+#### II.3.23 Scenario #33
+
+T1 = HDX PTP device (Baudot in this example)
+
+T2 = FDX PTP device (V.21 in this example)
+
+G1 = supports T1's modulation
+
+G2 = supports T2's modulation
+
+
+
+The diagram illustrates a sequence of signals between four entities: T1, G1, G2, and T2.
+- T2 starts by sending an ANS signal to G2.
+- G2 sends SSE(VBD:ANS) to G1 and SSE(VBD:p') back to G1.
+- G1 sends ANS to T1.
+- T2 then sends V.21 High signals.
+- G2 sends SSE(TP:V.21 ch2) and SSE(TP:p') to G1.
+- G1 performs Probing and then Baudot modulation with T1.
+- T1 sends Baudot characters.
+- G1 sends SSE(TR:Baudot) to G2.
+- G2 responds with SSE(TR:p').
+- G1 sends PT = TR to G2.
+- G2 sends V.21 Low and CHAR to T2.
+- G1 sends Baudot to T1.
+- Notes 1, 2, and 3 are referenced at specific points in the sequence.
+
+- Text relayed signals
+- VBD signals
+
+NOTE 1 – Probing sequence starts with V.21 modulation if available (since SSE indicated V.21 being used by T2).
+
+NOTE 2 – Send SSE(TR:V.21) if G1 supports T2 and reason codes are used; otherwise, stay in VBD mode.
+
+NOTE 3 – Characters are buffered by G2 until transition to text relay mode complete.
+
+Figure II.20 – Scenario #33 call flow diagram (SSE).
+
+V.151(06)\_FII.20
+
+**Figure II.20 – Scenario #33 call flow diagram (SSE)**
+
+##### Description
+
+Since T2 is an FDX answering PTP, it will initiate the call by either sending the optional ANS signal or carrier. Upon detection of the ANS signal, G2 will transition to VBD mode by sending an SSE(VBD). Upon detection of a PTP character, G2 will send an SSE(TP) to G1 to not respond to T2 (until it gets an SSE(TR) from T1).
+
+Upon receiving the SSE(TR) from G2, G1 will start an auto-mode probing sequence, starting with the modulation used by T2 if available. If G1 receives a response from T1 that indicates that T1 is a HDX PTP device that uses a modulation that is supported by G1, G1 will respond with a SSE(TR)
+
+indicating this to G2. If G1 gets a response from T1 for an FDX modulation that is not the same as that being used by T2, G1 will send an SSE(VBD) as per scenarios #13 and #14.
+
+When G2 receives the SSE(TR) response from G1, it will respond with SSE(TR:p') completing the transition to text relay mode. G2 will then start the connect sequence with T2.
+
+**II.3.24 Scenarios #34 to #36**
+
+In these scenarios, either or both of the gateways does not support the modulation of its local PTP device. Both PTP devices are not V.18 PTP devices, and one is FDX based while the other is HDX based. No successful connection will be achieved, although the channel may be transitioned to VBD mode since the gateway should detect either of the PTP signals.
+
+**II.4 Scenarios with payload type switching being used**
+**II.4.1 Scenario #1**
+
+T1 = V.18 PTP
+T2 = V.18 PTP
+G1 = supports V.18 native mode
+G2 = supports V.18 native mode
+
+
+
+Detailed description of Figure II.21: A call flow diagram showing the interaction between T1, G1, G2, and T2. The vertical axis represents time. Signals are exchanged between these entities. T1 sends CI/XCI to G1. G1 sends PT = AUDIO/PT = VBD to G2. G2 sends CI/XCI to T2. T2 responds with ANSam to G2. G2 sends PT = AUDIO/PT = VBD to G1. G1 sends ANSam to T1. T1 sends CM to G1. G1 sends PT = AUDIO/PT = VBD to G2. G2 sends CM to T2. T2 sends JM to G2. G2 sends PT = AUDIO/PT = VBD to G1. G1 sends JM to T1. T1 sends CJ to G1. G1 sends PT = AUDIO/PT = VBD to G2. G2 sends CJ to T2. Then, V.21 signals are exchanged: T1 sends V.21(L) MARK and CHAR to G1. G1 sends PT = TR(CHAR) to G2. G2 sends V.21(H) CHAR and V.21(H) to T2. T2 sends V.21(H) CHAR and V.21(H) to G2. G2 sends PT = TR(CHAR) to G1. G1 sends V.21(H) MARK and CHAR to T1. Note 1 indicates VBD may optionally be used for CI/XCI signal. Note 2 indicates CI/XCI may be detected by T2; if not, there is up to 3 seconds delay before ANSam is generated. Legend: Yellow boxes represent Text relayed signals, hatched boxes represent VBD signals.
+
+| T1 | G1 | Network (G1 to G2) | G2 | T2 |
+|----------------|--------------|-----------------------|--------------|-------------------|
+| CI/XCI → | (Note 1) | PT = AUDIO/PT = VBD → | | → CI/XCI (Note 2) |
+| | | ← PT = AUDIO/PT = VBD | ← CI/XCI | |
+| ← ANSam | ANSam (VBD) | | | ANSam → |
+| | | PT = AUDIO/PT = VBD ← | | |
+| CM → | | PT = AUDIO/PT = VBD → | | |
+| | | PT = AUDIO/PT = VBD ← | CM (VBD) | → CM |
+| CJ → | JM (VBD) | PT = AUDIO/PT = VBD → | | JM ← |
+| | | | CJ (VBD) | → CJ |
+| V.21(L) MARK → | V.21(H) MARK | PT = TR(CHAR) → | | V.21(H) CHAR ← |
+| CHAR → | CHAR | | V.21(L) MARK | V.21(H) ← |
+| V.21(L) MARK → | V.21(H) MARK | PT = TR(CHAR) ← | CHAR | V.21(H) → |
+
+Figure II.21 – Scenario #1 call flow diagram (Payload type)
+
+ Text relayed signals
+ VBD signals
+ NOTE 1 – VBD may optionally be used for CI/XCI signal.
+ NOTE 2 – CI/XCI may be detected by T2. If not detected, there will be up to 3 seconds of additional delay before ANSam is generated.
+
+**Figure II.21 – Scenario #1 call flow diagram (Payload type)**
+**Description**
+
+Since T1 is the V.18 calling PTP, it will generate a CI/XCI sequence. G1 may optionally detect CI/XCI and transmit it in VBD mode. Upon detection of ANSam by G2, if G1 has not already switched to VBD encoding based on CI/XCI detection, G2 will start VBD encoding. The V.8 handshake is allowed to proceed using VBD mode. G1 and G2 monitor the local CM or
+
+72
+
+ITU-T Rec. V.151 (05/2006)
+
+CJ sequences to determine that the endpoint devices are PTP devices. After completion of V.8 sequence between the two PTP devices using VBD mode, the gateways shall (within the 75-ms requirement) transition to text relay mode, locally generating the appropriate V.21 carrier and transmitting received characters via text relay encoding.
+
+#### II.4.2 Scenarios #2, #3 and #4
+
+In these scenarios, both of the PTP devices are V.18 devices. As in scenario #1, the connection will enter VBD mode either through detection of the CI/XCI or through detection of ANSam. Since one or both of the gateways in these scenarios does not support V.18 native mode, the connection shall stay in VBD mode. The gateways shall monitor the CM/JM sequence, detecting the V.18 PTP devices but maintaining a VBD connection.
+
+#### II.4.3 Scenario #5
+
+T1 = FDX modulation PTP (Bell 103 in this example)
+
+T2 = V.18 PTP
+
+G1 = supports FDX modulation (Bell 103 in this example)
+
+G2 = supports FDX modulation (Bell 103 in this example)
+
+
+
+Legend:
+
+- Text relayed signals (Yellow)
+- VBD signals (Hatched)
+
+NOTE – Allow end-to-end V.18 probing until T1 responds. G2 does not respond to any probing sequences that it supports during this probing.
+
+V.151(06)\_FII.22
+
+Figure II.22 – Scenario #5 call flow diagram (Payload type). This sequence diagram shows the interaction between four entities: T1, G1, G2, and T2. T1 and G1 are on the left, G2 and T2 are on the right. T1 and G1 have vertical timelines. T1's timeline shows a '1270 Hz SPACE' block followed by a 'CHAR' block. G1's timeline shows a hatched 'ANSam' block, a hatched 'V.18 Probing' block, and a yellow '2225 Hz MARK' block. G2's timeline shows a hatched 'ANSam' block, a hatched 'V.18 Probing' block, and a yellow '1270 Hz SPACE' block followed by a 'CHAR' block. T2's timeline shows a hatched 'ANSam' block, a hatched 'V.18 Probing' block, and a yellow '2225 Hz MARK' block followed by a 'CHAR' block. Red arrows indicate signal types: 'PT = VBD' from G2 to G1, 'PT = TR(NULL)' from G1 to G2, 'PT = TR(CHAR)' from G1 to G2, and 'PT = TR(CHAR)' from G2 to G1. A 'Note' box points to the 'V.18 Probing' blocks. A legend at the bottom left shows a yellow box for 'Text relayed signals' and a hatched box for 'VBD signals'. The text 'V.151(06)\_FII.22' is at the bottom right.
+
+**Figure II.22 – Scenario #5 call flow diagram (Payload type)**
+
+##### Description
+
+Since T2 is a V.18 answering PTP, it will generate ANSam after 3 seconds (because CI/XCI was not received). Since G2 is a V.151-compliant gateway, it will detect ANSam and initiate a switch to VBD mode. T2 is allowed to probe T1 using VBD mode. G2 does not respond to any of the T2 probing sequences, even those that represent modulations that G2 supports since it has not been established that an end-to-end text relay connection can be successfully made between all gateways and PTP devices. Upon detection by G1 of a PTP FDX modulation probing response from T1 that it
+
+supports, G1 will initiate a switch to text relay. In the case where T1 and T2 are not PTP, but data modems, we should require that both PSTN legs of the call be of the same modulation type so as to result in successful connection for data modems as well as PTP devices using proper character treatments. There are no mechanisms in payload type switching for ensuring this.
+
+#### II.4.4 Scenario #6
+
+T1 = FDX modulation PTP (V.21 in this example)
+
+T2 = V.18 PTP
+
+G1 = does not support modulation used by T1
+
+G2 = don't care
+
+
+
+Legend:
+
+- Text relayed signals (Yellow box)
+- VBD signals (Blue hatched box)
+
+NOTE – Allow end-to-end V.18 probing until T1 responds. G2 does not respond to any probing sequences that it supports during this probing.
+
+Figure II.23 – Scenario #6 call flow diagram (Payload type). The diagram shows a call flow between four entities: T1, G1, G2, and T2. T1 and G1 are on the left, G2 and T2 are on the right. T1 sends V.21(H) MARK and CHAR signals. G1 sends ANSam and V.18 probing signals. G2 sends PT = VBD signals. T2 sends ANSam, V.18 probing, V.21(L) MARK, CHAR, and V.21(L) MARK signals. A legend indicates that yellow boxes represent text relayed signals and blue hatched boxes represent VBD signals. A note indicates that G2 does not respond to any probing sequences that it supports during this probing.
+
+Figure II.23 – Scenario #6 call flow diagram (Payload type)
+
+##### Description
+
+Since T2 is a V.18 answering PTP, it will generate ANSam after 3 seconds (because CI/XCI was not received). Since G2 is a V.151-compliant gateway, it will detect ANSam and initiate a switch to VBD mode. T2 is allowed to probe T1 using VBD mode. G2 does not respond to any of the T2 probing sequences, even those that represent modulations that G2 supports since it has not been established that an end-to-end text relay connection can be successfully made between all gateways and PTP devices. Since the modulation that is responded to by T1 is not supported by G1, G1 does not initiate a switch to text relay mode and the connection remains in VBD mode for the entire call.
+
+#### **II.4.5 Scenario #7**
+
+T1 = FDX modulation PTP (Bell 103 in this example)
+
+T2 = V.18 PTP
+
+G1 = supports FDX modulation (Bell 103 in this example)
+
+G2 = supports FDX modulation (Bell 103 in this example) (Does not support native V.18)
+
+##### **Description**
+
+This scenario plays out identical to scenario #5. The only difference between these scenarios is that G2 does not support native V.18 mode, but the call flow is identical.
+
+#### **II.4.6 Scenario #8**
+
+T1 = FDX modulation PTP (V.21 in this example)
+
+T2 = V.18 PTP
+
+G1 = does not support modulation used by T1
+
+G2 = does not support native V.18 mode
+
+##### **Description**
+
+This scenario plays out identical to scenario #5. The only difference between these scenarios is that G2 does not support native V.18 mode, but the call flow is identical.
+
+#### **II.4.7 Scenarios #9 and #10**
+
+T1 = V.18 PTP
+
+T2 = FDX modulation PTP (V.21 in this example)
+
+G1 = supports any modulation
+
+G2 = supports modulation of T2 (V.21 in this example)
+
+
+
+NOTE 1 – VBD may optionally be used for CI/XCI signal. If VBD is used, there is an SSE(VBD:CI/XCI) handshake here.
+
+NOTE 2 – CI/XCI may be detected by T2.
+
+NOTE 3 – ANS tone is optional.
+
+NOTE 4 – Transition to text relay mode only if both G1 and G2 support the modulation used by T1 and T2.
+
+Figure II.24 – Scenarios #9 and #10 call flow diagram (Payload type). This sequence diagram shows the interaction between four entities: T1, G1, G2, and T2. T1 sends CI/XCI to G1. G1 sends PT=AUDIO/PT=VBD to G2 (Note 1). G2 sends CI/XCI to T2 (Note 2). G2 sends PT=VBD to G1 (Note 3). G1 sends PT=VBD to G2. G1 sends PT=TR(NULL) to G2 (Note 4). G1 sends PT=TR(CHAR) to G2. G2 sends PT=TR(CHAR) to G1. G1 sends PT=TR(CHAR) to G2. The diagram also shows V.21(H) MARK, V.21(L) MARK, and CHAR signals. A legend indicates that yellow boxes represent text relayed signals and blue hatched boxes represent VBD signals. The diagram is labeled V.151(06)\_FII.24.
+
+**Figure II.24 – Scenarios #9 and #10 call flow diagram (Payload type)**
+
+##### Description
+
+Since T1 is the V.18 calling PTP, it will generate a CI/XCI sequence. G1 may optionally detect CI/XCI and transmit it in VBD mode. Upon detection of ANS by G2, if G1 has not already switched to VBD encoding based on CI/XCI detection, G2 will start VBD encoding. Text relay mode is entered by G1 detecting a valid PTP modulation from T1 in response to signals generated by T2. G1 only switches to text relay encoding if both G1 and G2 support the modulation that is being used by T1 and T2. There is no protocol conversion supported in this scenario, since it is not known at the time of switchover to text relay if the terminal devices are PTP or data modem devices. By guaranteeing that both PSTN call legs are the same modulation, data modems can transparently be supported.
+
+In the case where ANS was not generated, G2 will detect the carrier signal from T2 and initiate switch to VBD mode. Note that for V.21, initial FDX answering signals are distinct from signals used by EDT modems. This is important because the call flow from non-FDX answer devices is quite different.
+
+#### II.4.8 Scenarios #11 and #12
+
+In these scenarios, G2 does not support the modulation used by T1. As in scenarios #9 and #10, the connection will enter VBD mode either through the detection of CI/XCI by G1 or ANS by G2. Since G2 does not support the modulation used by T2, G1 will not transition the connection to text relay encoding even if it detects the PTP modulation used. The connection will stay in VBD mode.
+
+#### II.4.9 Scenarios #13 and #14
+
+T1 = FDX modulation PTP (V.21 in this example)
+
+T2 = FDX modulation PTP (same as T1)
+
+G1 = supports modulation of T1
+
+G2 = supports modulation of T2
+
+
+
+NOTE 1 – Generation of ANS signal by T2 is optional.
+
+NOTE 2 – If ANS was not generated by T2, G2 shall initiate transition to VBD upon V.21 mark detection.
+
+NOTE 3 – Only use text relay encoding if G2 supports modulation of T1; otherwise, stay in VBD mode.
+
+Figure II.25 – Scenarios #13 and #14 call flow diagram (Payload type). The diagram shows the interaction between four entities: T1, G1, G2, and T2. T1 and T2 are terminals, while G1 and G2 are gateways. The diagram illustrates the flow of signals and the state transitions between VBD (Voice Band Data) and TR (Text Relay) modes. T2 initiates the call with an ANS signal. G2 detects this and transitions to VBD mode. G2 then sends a PT=VBD signal to G1. G1 sends a V.21(L) MARK signal to T1. T1 sends a V.21(H) MARK signal to G1. G1 then sends a PT=VBD signal to G2. G2 sends a PT=TR(NULL) signal to G1. G1 sends a V.21(L) MARK signal to T1. T1 sends a CHAR signal to G1. G1 then sends a PT=TR signal to G2. G2 sends a V.21(L) MARK signal to T2. T2 sends a CHAR signal to G2. The diagram also shows a V.21(H) MARK signal from T1 to G1. A legend indicates that yellow boxes represent text relayed signals and blue hatched boxes represent VBD signals. Notes 1, 2, and 3 provide additional context on the generation of ANS signals and the use of text relay encoding.
+
+**Figure II.25 – Scenarios #13 and #14 call flow diagram (Payload type)**
+
+##### Description
+
+T2 being the answering PTP device will initiate the generation of a FDX signal, optionally preceded by the ANS signal. Since G2 is a V.151-compliant gateway, upon detection of the ANS tone, G2 will initiate a switch to VBD mode. When G2 detects the carrier for a FDX modulation that it supports for text, it shall initiate a transition to text relay mode through the generation of a packet containing the NULL character encoded using TR payload type if G1 has also indicated support for this modulation. If G1 does not support the modulation used by T2, the connection will remain in VBD for the duration of the call.
+
+Upon reception of TR payload type from G2, G1 shall enter an originate mode auto-probing sequence. Since T1 is the same modulation as T2, G1 will connect with T1 using this modulation. Upon detection of the response signal from T1, G1 will encode the received characters using text relay payload type.
+
+T1 = FDX modulation PTP (Bell 103 in this example)
+ T2 = FDX modulation PTP (same as T1)
+ G1 = supports modulation of T1
+ G2 = supports modulation of T2
+
+
+
+```
+
+sequenceDiagram
+ participant T1
+ participant G1
+ participant G2
+ participant T2
+
+ Note over T2: 2225 Hz
+ T2->>G2: 2225 Hz
+ G2->>G1: PT = VBD
+ Note over G1: 2225 Hz (VBD signal)
+ G1->>T1: 2225 Hz
+
+ Note over T1: CHAN 1 MARK
+ T1->>G1: CHAN 1 MARK
+ Note over G1: (Text relayed signal)
+ G1->>G2: PT = TR(NULL)
+ Note over G2: CHAN 1 MARK
+ G2->>T2: CHAN 1 MARK
+
+ Note over T1: CHAR
+ T1->>G1: CHAR
+ G1->>G2: PT = VBD
+ G2->>G1: PT = TR
+ Note over G1: CHAN 2 MARK
+ G1->>T1: CHAN 2 MARK
+
+ Note over T2: CHAN 2 MARK
+ T2->>G2: CHAN 2 MARK
+ Note over G2: CHAR
+ G2->>G1: PT = TR
+ Note over G1: CHAR
+ G1->>T1: CHAR
+
+ Note over T2: CHAR
+ T2->>G2: CHAR
+ Note over G2: CHAN 1 MARK
+ G2->>T1: CHAN 1 MARK
+
+ Note over T2: CHAN 2 MARK
+ T2->>G2: CHAN 2 MARK
+
+```
+
+NOTE – Only use text relay encoding if G2 supports modulation of T1; otherwise, stay in VBD mode.
+
+Figure II.25-1 – Scenarios #13 and #14 (Bell 103) call flow diagram (Payload type) Legend: Yellow box for Text relayed signals, Blue hatched box for VBD signals.
+
+**Figure II.25-1 – Scenarios #13 and #14 (Bell 103) call flow diagram (Payload type)**
+
+### Description
+
+Bell 103 is a special case of the FDX to FDX scenario since, unlike other FDX modems such as V.21, the originating modem is first to generate carrier upon detection of the 2225-Hz answer tone.
+
+T2 being the answering Bell 103 PTP device will initiate the generation of 2225-Hz answer tone. Since G2 is a V.151-compliant gateway, upon detection of the 2225-Hz tone, G2 will initiate a switch to VBD mode. When G1 detects MARK for a Bell 103 originating modem that it supports for text, it shall initiate a transition to text relay mode through the generation of a packet containing the NULL character encoded using TR payload type if G2 has also indicated support for this modulation. If G2 does not support the modulation used by T2, the connection will remain in VBD mode for the duration of the call.
+
+Upon reception of the TR payload type, G2 will start connect sequence with T2.
+
+In this scenario, T1 and T2 modulations must be the same for the PTP connection to be established. There is no support for protocol conversion in this scenario. Ensuring that T1 and T2 modulations are the same allows non-PTP data modems that use the same physical layer modulation to also be supported using relay.
+
+#### II.4.10 Scenarios #15 and #16
+
+In these scenarios, G2 does not support the modulation used by T2. As in scenario #13, the connection will enter VBD mode by the detection of ANS or constant carrier by either gateway.
+
+78 ITU-T Rec. V.151 (05/2006)
+
+T1 will not initiate a transition to text relay encoding since G2 does not support the detected modulation.
+
+#### II.4.11 Scenarios #17, #18, #19 and #20
+
+These scenarios are identical to the call flow described in the SSE case, with the exception of using payload type switching instead of SSE protocol.
+
+#### II.4.12 Scenarios #21 and #22
+
+T1 = V.18 PTP
+
+T2 = HDX modulation PTP (Baudot in this example)
+
+G1 = supports any modulation
+
+G2 = supports modulation of T2
+
+
+
+NOTE 1 – VBD may optionally be used for CI/XCI signal. If VBD is used, there is an SSE(VBD:CI/XCI) handshake here.
+
+NOTE 2 – CI/XCI may be detected by T2.
+
+NOTE 3 – Only use text relay encoding if G1 supports the modulation being used by T2.
+
+V.151(06)\_FII.26
+
+Figure II.26 – Scenarios #21 and #22 call flow diagram (Payload type). The diagram shows a sequence of events between four entities: T1, G1, G2, and T2. T1 sends CI/XCI signals to G1. G1 sends PT = AUDIO/PT = VBD to G2 (Note 1). G2 sends CI/XCI to T2 (Note 2). T2 sends Baudot to G2. G2 sends PT = TR to G1 (Note 3). G1 sends Baudot to T1. T1 sends Baudot to G1. G1 sends PT = TR to G2. G2 sends Baudot to T2. A legend indicates that yellow boxes represent text relayed signals and blue hatched boxes represent VBD signals. Notes 1, 2, and 3 provide additional context for the signals.
+
+**Figure II.26 – Scenarios #21 and #22 call flow diagram (Payload type)**
+
+##### Description
+
+In this scenario, G1 may switch to VBD encoding on the detection of CI/XCI. When the signal from T2 is detected by G2, G2 will start text relay encoding only if G1 also supports this modulation. In scenario #21, this will result in text relay being used for the session.
+
+#### II.4.13 Scenarios #23 and #24
+
+T1 = V.18 PTP
+
+T2 = HDX modulation PTP (Baudot in this example)
+
+G1 = don't care
+
+G2 = does not support modulation of T2
+
+
+
+NOTE 1 – VBD may optionally be used for CI/XCI signal. If VBD is used, there is an SSE(VBD:CI/XCI) handshake here.
+
+NOTE 2 – CI/XCI may be detected by T2.
+
+NOTE 3 – G2 is required to be able to detect modulation for the purpose of transitioning to VBD encoding.
+
+V.151(06)\_FII.27
+
+Figure II.27 – Scenarios #23 and #24 call flow diagram (Payload type). The diagram shows a sequence of messages between T1, G1, G2, and T2. T1 sends CI/XCI to G1. G1 sends PT = AUDIO/PT = VBD to G2. G2 sends CI/XCI to T2. T2 sends Baudot to G2. G2 sends PT = VBD to G1. G1 sends Baudot to T1. T1 sends Baudot to G1. G1 sends PT = VBD to G2. G2 sends Baudot to T2. A legend indicates that yellow boxes represent text relayed signals and blue hatched boxes represent VBD signals. Notes 1, 2, and 3 provide additional context.
+
+**Figure II.27 – Scenarios #23 and #24 call flow diagram (Payload type)**
+
+##### Description
+
+In this scenario, G1 may switch to VBD encoding on the detection of CI/XCI. If G1 did not switch to VBD on CI/XCI, G2 will initiate a switch to VBD encoding upon detection of a PTP signal that it does not support in text relay mode. The session will stay in VBD mode. Note G1 will not initiate a transition to text relay mode upon detection of the PTP signal from T1 since it knows that G2 does not support this modulation.
+
+#### II.4.14 Scenarios #25 and #26
+
+The call flow for these scenarios is the same as scenarios #21 and #22. The difference in the scenarios is that T1 is a V.18 modem, but this does not affect the operation of the gateways. If T1 and T2 are not the same modulation, the connection will fail since there is no support for conversion in these scenarios.
+
+#### II.4.15 Scenario #27
+
+The connection stays in VBD for this scenario. Since G2 does not support text relay for the HDX modulation used by T2, it will transition to VBD mode upon detection of the signal. G1 does support the modulation used by T1, but it will not transition to text relay mode since G2 does not support this modulation. If G1 detects the first signal, it will instead transition to VBD mode. If T1 and T2 use different HDX modulations, the connection will fail since there is no support for conversion in this scenario.
+
+#### II.4.16 Scenario #28
+
+Neither gateway supports text relay for the modulations used by T1 and T2. The gateways will transition to VBD encoding upon detection of the signal from their local PTP devices and the connection will remain in VBD mode.
+
+### II.4.17 Scenario #29
+
+T1 = FDX PTP device (V.21 in this example)
+ T2 = HDX PTP device (Baudot in this example)
+ G1 = supports T1's modulation
+ G2 = supports T2's modulation
+
+
+
+```
+
+ sequenceDiagram
+ participant T1
+ participant G1
+ participant G2
+ participant T2
+ Note over G1: Probing
+ G2->>G1: PT = TR(CHAR) (Red arrow)
+ T2->>G2: Baudot Char's
+ Note right of G2: Note
+ T1->>G1: V.21 (low)
+ G1->>T1: V.21 (high)
+ G2->>G1: PT = TR(CHAR) (Red arrow)
+ G1->>T1: CHAR
+ G1->>G2: PT = TR(CHAR) (Red arrow)
+ Note over G2: Baudot Char's
+ G2->>T2: (Signal arrow)
+
+```
+
+Legend:
+ [Yellow Box] Text relayed signals
+ [Hatched Box] VBD signals
+ NOTE – Text relay is only used if T2 is included in the modulations supported by G1. Use VBD if T2 is not included in G1's modulations.
+
+**Figure II.28 – Scenario #29 call flow diagram (Payload type)**
+
+Figure II.28 – Scenario #29 call flow diagram (Payload type)
+
+#### Description
+
+Strange restriction since not using SSEs: If T1 is supported by G1, T1 is not T2, and G1 does not support T2, then this will not connect (since G2 will try to go to VBD). It will work if SSEs are used. Restriction since we are leaning towards T1=T2 and want to go to VBD for that mode (no signalling mechanisms available to put us back into VBD).
+
+Upon detection of the non-constant carrier signal from T2, G2 will start text relay encoding if G1 supports this modulation, otherwise G2 will initiate switch to VBD. Upon receiving text relay encoded packet, G1 will start its auto-mode probing sequence with T1.
+
+### II.4.18 Scenario #30
+
+T1 = FDX PTP device (V.21 in this example)
+ T2 = HDX PTP device (Baudot in this example)
+ G1 = does not support T1's modulation
+ G2 = supports T2's modulation
+
+**ITU-T Rec. V.151 (05/2006)** 81
+
+##### **Description**
+
+In this scenario, G1 does not have a modulation that is used by T1. G2, after detecting the PTP modulation from T2 that it supports and that G1 supports, will start sending text relay packets to G1. G1 will start its auto-mode probing sequence, but will eventually time out since there is no common modulation between T1 and G1. The connection will fail as it would if there was no IP network involved since T1 and T2 are not compatible devices.
+
+#### **II.4.19 Scenarios #31 and 32**
+
+In these scenarios, either or both of the gateways does not support the modulation of its local PTP device. Both PTP devices are not V.18 PTP devices, and one is FDX based while the other is HDX based. No successful connection will be achieved, although the channel may be transitioned to VBD mode since the gateway should detect either of the PTP signals.
+
+#### **II.4.20 Scenarios #33 and #36**
+
+##### **Description**
+
+Will not connect. G2 will go into VBD mode on ANS, but never get to a character. If G1 does send a character (originator initiates text), then G1 will send PT=TR, then G2 will do FDX handshake. Implies that G2 is monitoring incoming signals, even though it has not yet sent PT=TR.
+
+# **Appendix III**
+
+## **The use of [IETF RFC 2198] in [ITU-T V.151]**
+
+(This appendix does not form an integral part of this Recommendation)
+
+Redundancy is implemented using [IETF RFC 2198]. Annex E provides further clarification of how RFC 2198 redundancy can be used for the ToIP application. If using redundancy to improve performance over lossy networks, gateways should implement redundancy as described in these RFCs. The exception is that the buffer time for sending packets with redundant block and no primary blocks at the end of a text spurt should be 300 ms.
+
+# **Appendix IV**
+
+## **Text buffering and transmission**
+
+(This appendix does not form an integral part of this Recommendation)
+
+When using the procedures in this Recommendation, text transmission may be negotiated with different speeds for different endpoints. There may also be cases when one leg of the call has successfully negotiated and connected and starts to handle text, while the other has not completed text negotiation.
+
+Both these situations require a buffer for text to be maintained in the gateways. There is no flow control available for PSTN text telephony, so human habits will be the limiting factor for the gateway buffer.
+
+The transport methods have an out-of-band signalling parameter for character rate that can control where the buffer needs to be located.
+
+A general rule is that a user will not create continuous output for more than one minute before expecting a response or making a pause. However, if input is by means of voice-to-text technologies at the maximum character rate of 30 characters per second, that means there is an input of 1800 characters. If the output is to the slowest possible text telephone, the US Baudot method, performing 6 characters per second, the buffer will build up $1800 - 360 = 1440$ characters.
+
+This calculation leads to a general indication that a gateway buffer of 2 kbytes should be sufficient.
+
+Once connected through a gateway, characters shall be transmitted between terminals involved in the call using negotiated protocols and buffering strategies.
+
+# Appendix V
+
+## Probing sequence
+
+(This appendix does not form an integral part of this Recommendation)
+
+Appendix I of [ITU-T V.18] provides useful information on the ordering of automode probing sequences. These orderings are based upon the transmitting PTP supporting all of the V.18 modulations and with the *a priori* knowledge that the PTP is trying to call another PTP. These assumptions are not necessarily the case for media gateways. Once being given some indication that the gateway is to establish a connection for the purposes of connecting two PTPs, a gateway has to discover whether the endpoint on its PSTN connection is a PTP by the generation of probing sequences. It is the response to these probes that assist in the discrimination. A gateway does not have the geographical advantage either, since a gateway may be physically located in a different country or area than the PTP to which it is connected. Consequently, depending upon circumstances, it is possible that either one or two complete automode probing cycles may occur before being able to discriminate a PTP type. The amount of time to perform this discovery if a full V.18 implementation is used may take longer than one minute. This is not desirable from a user satisfaction perspective, and could lead to larger instances of call failure for the IP network than that of the legacy PSTN. If connect times at the remote gateway/PTP connection take a significant amount of time, the calling side user may start typing instead of waiting for the answering user to start typing, possibly causing the calling PTP device to start carrier before receiving any answering signals.
+
+An alternative approach that can be utilized by gateways is to use an adaptive automode probing sequence ordering. This approach can be used by gateways to order their automode probing sequences based upon what modulations they support and what information they are provided by a peer gateway. This information could be provided by the optional use of SSEs.
+
+For typical usage scenarios, the majority of PTP connections will be between like PTP devices. That is expected because the call will be established between two endpoints that have already been connected on previous occasions or the number of the PTP being called is a known PTP endpoint. Examples of known PTP endpoints include government services, relay services, and published numbers. This type of information can be used to determine the best ordering of the automode sequence.
+
+There are a variety of methods and criteria that can be used when defining and using the automode probing sequences. These guidelines recommend that such criteria be determined by typical usage and application of PTP than an inflexible fixed sequence order.
+
+# Bibliography
+
+- [b-ANSI/TIA-825] ANSI/TIA-825-A-2003, *A Frequency Shift Keyed Modem for Use on the Public Switched Telephone Network.*
+- [b-ETSI ETR 333] ETSI ETR 333 (1998-05), *Human Factors (HF); Text Telephony; Basic user requirements and recommendations.*
+- [b-IETF RFC 791] IETF RFC 791 (1981), *Internet Protocol.*
+- [b-IETF RFC 919] IETF RFC 919 (1984), *Broadcasting Internet Datagrams.*
+- [b-IETF RFC 920] IETF RFC 920 (1984), *Domain Requirements.*
+- [b-IETF RFC 950] IETF RFC 950 (1985), *Internet Standard Subnetting Procedure.*
+- [b-IETF RFC 4103] IETF RFC 4103 (2005), *RTP Payload for Text Conversation.*
+- [b-TIA 1001] TIA 1001 (2004), *Transport of TIA-825-A Signals over IP Networks.*
+
+
+
+# SERIES OF ITU-T RECOMMENDATIONS
+
+| | |
+|-----------------|---------------------------------------------------------------------------------------------|
+| Series A | Organization of the work of ITU-T |
+| Series D | General tariff principles |
+| Series E | Overall network operation, telephone service, service operation and human factors |
+| Series F | Non-telephone telecommunication services |
+| Series G | Transmission systems and media, digital systems and networks |
+| Series H | Audiovisual and multimedia systems |
+| Series I | Integrated services digital network |
+| Series J | Cable networks and transmission of television, sound programme and other multimedia signals |
+| Series K | Protection against interference |
+| Series L | Construction, installation and protection of cables and other elements of outside plant |
+| Series M | Telecommunication management, including TMN and network maintenance |
+| Series N | Maintenance: international sound programme and television transmission circuits |
+| Series O | Specifications of measuring equipment |
+| Series P | Telephone transmission quality, telephone installations, local line networks |
+| Series Q | Switching and signalling |
+| Series R | Telegraph transmission |
+| Series S | Telegraph services terminal equipment |
+| Series T | Terminals for telematic services |
+| Series U | Telegraph switching |
+| Series V | Data communication over the telephone network |
+| Series X | Data networks, open system communications and security |
+| Series Y | Global information infrastructure, Internet protocol aspects and next-generation networks |
+| Series Z | Languages and general software aspects for telecommunication systems |
\ No newline at end of file
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@@ -0,0 +1,1436 @@
+
+
+I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n
+
+# ITU-T
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+## V.152
+
+(09/2010)
+
+SERIES V: DATA COMMUNICATION OVER THE
+TELEPHONE NETWORK
+
+Interworking with other networks
+
+# --- **Procedures for supporting voice-band data over IP networks**
+
+Recommendation ITU-T V.152
+
+
+
+The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features a blue globe with two red lightning bolts striking it. To the right of the globe, the text "ITU" is written in a large, bold, blue font, and below it, the words "International Telecommunication Union" are written in a smaller, blue font.
+
+ITU logo: a globe with red lightning bolts and the text 'ITU International Telecommunication Union'
+
+## ITU-T V-SERIES RECOMMENDATIONS **DATA COMMUNICATION OVER THE TELEPHONE NETWORK**
+
+| | |
+|-------------------------------------------------------|--------------------|
+| General | V.1–V.9 |
+| Interfaces and voiceband modems | V.10–V.34 |
+| Wideband modems | V.35–V.39 |
+| Error control | V.40–V.49 |
+| Transmission quality and maintenance | V.50–V.59 |
+| Simultaneous transmission of data and other signals | V.60–V.99 |
+| Interworking with other networks | V.100–V.199 |
+| Interface layer specifications for data communication | V.200–V.249 |
+| Control procedures | V.250–V.299 |
+| Modems on digital circuits | V.300–V.399 |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+# Recommendation ITU-T V.152
+
+# Procedures for supporting voice-band data over IP networks
+
+## Summary
+
+Voice-band data traffic has traditionally been transported by circuit switched systems and equipment. With the advent of the networks optimized for the transport of Internet Protocol (IP), and as a result of its considerable growth and pervasive nature, more and more voice-band data traffic is expected to be carried over IP networks.
+
+Given that voice and voice-band data services remain a significant part of telecommunications, there is a need to ensure a high quality of service for voice and voice-band data carried in part, or wholly, via IP. Recommendation ITU-T V.152 defines procedures for equipment that interconnect GSTN networks with IP networks to provide satisfactory, transparent delivery of modulated voice-band data (VBD) as encoded audio content over IP (data modems, facsimile terminals and text telephones).
+
+Annex B defines a method that uses data signal detection and silence insertion in voiceband data that adds a means of providing bandwidth savings during transmission.
+
+Annex C addresses a problem discovered during the implementation of ITU-T V.152 gateways with the transmission of facsimile terminals. While this issue has been resolved by an amendment to Recommendation ITU-T T.30, due to the extremely large numbers of terminals deployed in the field and the low probability that they would be corrected retroactively, it was considered pre-emptive to include a solution in an ITU-T V.152 media gateway.
+
+This Recommendation is complementary to the modem relay and voice-band data Recommendations (Recommendations ITU-T V.150.0 and V.150.1).
+
+This revision includes the updating of references, general editing improvements for clarity and many additional examples of call control. It also integrates changes introduced by Corrigendum 1 (2005) for clarification to clauses 7.1 and 7.1.1; by Corrigendum 2 (2006) for clarifications on the use and control of echo cancellers and the application of IETF RFC 2833 with VBD; and by Amendment 1 (2009) for new Annexes B and C.
+
+## History
+
+| Edition | Recommendation | Approval | Study Group |
+|---------|-----------------------------|------------|-------------|
+| 1.0 | ITU-T V.152 | 2005-01-08 | 16 |
+| 1.1 | ITU-T V.152 (2005) Cor. 1 | 2005-09-13 | 16 |
+| 1.2 | ITU-T V.152 (2005) Cor. 2 | 2006-05-29 | 16 |
+| 1.3 | ITU-T V.152 (2005) Amend. 1 | 2009-03-16 | 16 |
+| 2.0 | ITU-T V.152 | 2010-09-13 | 16 |
+
+## Keywords
+
+Echo canceller, facsimile over IP, gateway, Internet gateway, Internet Protocol, IP gateway, media gateway, media gateway controller, modem over IP, quality of service, speech coding, TDM, TDM-IP gateway, text over IP, textphone over IP, text telephone, VBD, voice-band data, voice gateway, voice over IP, VoIP.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure, e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at
+```
+
+In the context of VBD declaration, the must be an RTP/AVP payload type. The is a semicolon-separated list of "parameter=value" pairs. For RTP/AVP formats, these pairs address parameters that are not part of their standard MIME definition. For sessions supporting this Recommendation, the parameter of interest is the Boolean 'vbd' that may have the value of 'yes' or 'no'. When set to 'yes', the attribute indicates that the implementation supports VBD mode as described in this Recommendation.
+
+Omission of the "gpmid" attribute with a "vbd=yes" attribute/value pair for any codec in the SDP session description shall be construed as non-support of VBD mode operation as defined in this Recommendation.
+
+Setting vbd=no is an explicit indication that the payload type will not be used for vbd.
+
+Note that this is not the same as omitting the gpmid attribute with vbd.
+
+The payload type marked for voice-band data (VBD) treatment should be a dynamic payload type. It is possible that a codec, such as PCMU, be declared with both static and dynamic payload types, with only one of the two marked for voice-band data use (see example 1 below). If a codec, such a PCMU or PCMA, is declared with only a static payload type, and is also marked for voice-band data use, then this codec must not be used for carrying voice (see example 2 below).
+
+#### **7.1.0.2 Packetization time (a=maxptime:)**
+
+In addition to negotiating support of ITU-T V.152 and the corresponding RTP payload type, an ITU-T V.152 implementation should include the 'maxptime' attribute (maximum multiple ptime) to indicate the supported packetization period for all codec payload types.
+
+```
+a=maxptime:
+```
+
+This attribute is a media-level attribute. The maxptime attribute defines a list of maximum packetization time values, expressed in milliseconds, the endpoint is capable of using (sending and receiving) for this connection. There shall be precisely one entry in the list for each entry provided in the "m=" line. Each entry is separated by a space. Entry number j in this list defines the maximum packetization time for entry number j in the "m=" line. The first entry in the list shall be a
+
+decimal number whereas subsequent entries in the list shall be either a decimal number or a hyphen. For those media formats where a single maximum packetization rate does not apply (e.g., non-voice codecs such as telephone-event or comfort noise), a hyphen ("-") shall be included at the corresponding location in the list of packetization periods.
+
+When receiving an SDP session description, the maxmptime attribute conveys the list of maximum packetization periods that the remote endpoint is capable of using for this connection; one for each media format in the "m=" line. For media formats whose packetization period is specified as a hyphen ("-"), the VBD gateway shall use one of the maximum packetization periods that was actually specified in the list.
+
+The "a=ptime" attribute, defined in [IETF RFC 4566], shall be ignored if the SDP session description contains the "maxmptime" attribute.
+
+If the "maxmptime" attribute is absent, then the value of the "ptime" attribute, if present, shall be taken as indicating the packetization period for all codecs present in the "m=" line.
+
+If neither the 'ptime' nor 'maxmptime' attribute are present in the SDP session description, then an ITU-T V.152 implementation shall assume the default packetization period defined in [IETF RFC 3550] (which is 20 ms for ITU-T G.711 and ITU-T G.726-32k). An ITU-T V.152 implementation shall not transmit ITU-T V.152 packets with a packetization time greater than the one offered by the remote end.
+
+#### 7.1.0.3 Examples
+
+Several application scenario examples are provided below.
+
+##### 7.1.0.3.1 Example 1 – Multiple audio and multiple VBD codec types
+
+Below is an SDP-related example that indicates support of ITU-T V.152 as per this Recommendation. For clarity purposes, the example only shows the media descriptions of the SDP session description.
+
+Table 1 provides the encoding of example 1 using Legacy SDP Offer/Answer syntax.
+
+Figure 1 illustrates the four possible media configurations, offered in this example.
+
+Table 2 provides the encoding of example 1 in Revised SDP Offer/Answer syntax.
+
+Table 1 – Example SDP encoding – "Example 1" offer in Legacy SDP Offer/Answer syntax
+
+| SDP encoding (shortened SDP description) | Comments |
+|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| m=audio 3456 RTP/AVP 18 0 13 96 98 99
a=maxmptime:10 10 - - 20 20
a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15, 34, 35
a=rtpmap:98 PCMU/8000
a=gpmd:98 vbd=yes
a=rtpmap:99 G726-32/8000
a=gpmd:99 vbd=yes | In the example, static payload type '0' and dynamic payload type '98' each represent the encoding format 'PCMU'. The payload type '0' is not associated with VBD. The payload types '98' (PCMU) and '99' (32 kbit/s ADPCM) are, however, associated with VBD. Concerning the maximum packetization times for each payload type: Voice packets use 10 ms, VBD packets use 20 ms, and a dash is assigned to payload types 13 (silence indication packets) and 96 (IETF RFC 4733) packets) indicating that a maximum ptime is not applicable or necessary. |
+
+
+
+Diagram showing potential media configurations for VoIP and VBD codecs. The top section, 'Audio mode (VoIP)', contains 'G.729 without silence suppression' and 'G.711 μ-law with silence suppression', with a '10 ms maximum packetization time' note. The bottom section, 'Voiceband data mode (V.152 VBDolP)', contains 'G.711 μ-Law' and 'G.726-32', with a '20 ms maximum packetization time' note. A 'Session Configurations' box with a dashed line connects the two sections. Four numbered lines (1-4) show combinations: 1 (G.729 to G.711), 2 (G.729 to G.726-32), 3 (G.711 to G.726-32), and 4 (G.711 to G.729).
+
+**Figure 1 – Potential media configurations offered in example 1**
+
+**Table 2 – Example SDP encoding – "Example 1" offer in Revised SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| ; SESSION CONFIGURATIONS a=sescap:1 1,3 ; VoIP = G729, VBDoIP = V.152 (PCMU) a=sescap:2 1,4 ; VoIP = G729, VBDoIP = V.152 (G726) a=sescap:3 2,3 ; VoIP = PCMU, VBDoIP = V.152 (PCMU) a=sescap:4 2,4 ; VoIP = PCMU, VBDoIP = V.152 (G726) ; ACTUAL CONFIGURATION (due to backward compatibility) m=audio 3456 RTP/AVP 18 0 13 96 98 99 a=maxmptime:10 10 - - 20 20 a=rtpmap:96 telephone-event/8000 a=fmtp:96 0-15, 34, 35 a=rtpmap:98 PCMU/8000 a=gpmid:98 vbd=yes a=rtpmap:99 G726-32/8000 a=gpmid:99 vbd=yes ; ; POTENTIAL CONFIGURATIONS a=tcap:1 RTP/AVP ; transport for VoIP & VBDoIP a=acap:1 ptime:10 ; for Audio mode a=acap:2 ptime:20 ; for VBD mode a=mcap:1 G729/8000 ; audio codec 1 a=mcap:2,5 PCMU/8000 ; audio codec 2 & VBD codec 1 a=mcap:3 CN/8000 ; comfort noise for audio c. 2 a=mcap:4 telephone-event/8000 ; NTE codec a=mcap:6 G726-32/8000 ; VBD codec 2
| Offered (4) session configurations:
- • Preference 1: Audio (ITU-T G.729), VBD (ITU-T V.152 PCMU) & NTE ([IETF RFC 4733])
- • Preference 2: Audio (ITU-T G.729), VBD (ITU-T V.152 G.726-32) & NTE ([IETF RFC 4733])
- • Preference 3: Audio (PCMU including silence suppression), VBD (ITU-T V.152 PCMU) & NTE ([IETF RFC 4733])
- • Preference 4: Audio (PCMU including silence suppression), VBD (ITU-T V.152 G.726-32) & NTE ([IETF RFC 4733])
NOTE – The "a=-ms" operator is used to remove all legacy attribute lines on session and media description level.
The two audio and two VBD settings are defined as individual potential configurations, in order to assign individual packetization times. This approach allows to avoid usage of "a=maxmptime:" parameter. The concept of session configurations is applied for the four audio/VBD combinations.
|
+
+**Table 2 – Example SDP encoding – "Example 1" offer in Revised SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------|
+| a=mfcap:4 0-15,32-35 ; value range DTMF &
VBD stimuli
a=mscap:5 gpmd vbd=yes ; for V.152 PCMU
a=mscap:6 gpmd vbd=yes ; for V.152 G726-32
a=pcfg:1 t=1 a=-ms:1 m=1,4 pt=1:18,4:96
a=pcfg:2 t=1 a=-ms:1 m=2,3,4
pt=2:0,3:13,4:96
a=pcfg:3 t=1 a=-ms:2 m=5 pt=5:98
a=pcfg:4 t=1 a=-ms:2 m=6 pt=6:99 | |
+
+The following main advantages may be noted concerning Revised versus Legacy SDP Offer/Answer:
+
+- the ITU-T V.152 introduced SDP attribute "*a=maxptime*:" may be replaced by IETF SDP elements;
+- there is an explicit indicated, preferred order with regard to the offered media configurations (this is missing in Legacy SDP Offer/Answer: it is unclear, e.g., whether configuration 2 is preferred over configuration 3 or vice versa); and
+- the answerer in Legacy SDP Offer/Answer could select both audio codecs and/or both VBD codecs (which may require subsequent Offer/Answer cycles).
+
+##### 7.1.0.3.2 Example 2 – Single audio codec, two VBD codec options
+
+Table 3 provides the encoding of example 2 in Legacy SDP Offer/Answer syntax.
+
+Figure 2 illustrate the two possible media configurations, offered in this example.
+
+**Table 3 – Example SDP encoding – "Example 2" offer in Legacy SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|-----------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| m=audio 3456 RTP/AVP 0 18 98
a=gpmd:0 vbd=yes
a=rtpmap:98 G726-32/8000
a=gpmd:98 vbd=yes
a=ptime:20 | In this example, the static payload type '0' (PCMU) is marked for VBD treatment, along with the dynamic payload type '98' (mapped to 32 kbit/s ADPCM). Thus, payload type '0' must not be used for carrying voice. It also indicates that the VBD gateway can receive voice and VBD packets with a size of 20 ms. |
+
+
+
+The diagram shows two main sections: 'Audio codec' and 'Voiceband data mode (V.152 VBDolP)'. The 'Audio codec' section contains a box for 'G.729 without silence suppression' with a '20 ms packetization time' label. The 'Voiceband data mode' section contains two boxes: 'G.711 μ-law' and 'G.726-32', both with a '20 ms packetization time' label. A dashed box labeled 'Potential Configurations:' is connected to the 'G.729 without silence suppression' box by a line labeled '1' and to the 'G.726-32' box by a line labeled '2'. The 'G.711 μ-law' box is also connected to the 'G.729 without silence suppression' box by a line labeled '1'.
+
+Diagram illustrating potential media configurations for audio and voiceband data modes.
+
+**Figure 2 – Potential media configurations offered in example 2**
+
+NOTE – The use of static payload types for VBD is strongly discouraged because there is a danger that a non-ITU-T V.152 system would see a proposal with, say, [ITU-T G.711] VBD and [ITU-T G.729]. However, not understanding the VBD attributes, it may consider ITU-T G.711 as a valid audio codec. However, network operators may prefer that [ITU-T G.711] not be utilized, except in the case where VBD is necessary, and that all voice shall be [ITU-T G.729]. To illustrate this point, consider this offer:
+
+```
+m=audio 15400 RTP/AVP 0 18
+a=gpmd:0 vbd=yes
+```
+
+and consider this answer:
+
+```
+m=audio 15400 RTP/AVP 0 18
+```
+
+The systems would then, most likely, communicate using [ITU-T G.711], rather than the intended [ITU-T G.729], for voice. This is a possible issue and inherent to Legacy SDP Offer/Answer protocol. This problem may be avoided by explicit potential configuration in Revised SDP Offer/Answer, see Table 4.
+
+**Table 4 – Example SDP encoding – "Example 2" offer in Revised SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| ; ACTUAL CONFIGURATION (due to backward compatibility) m=audio 3456 RTP/AVP 0 18 98 a=gpmd:0 vbd=yes a=rtpmap:98 G726-32/8000 a=gpmd:98 vbd=yes a=ptime:20 ; ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP & VBDoIP a=acap:1 ptime:20 ; common packetization time a=mcap:1 G729/8000 ; audio codec a=mcap:2 PCMU/8000 ; VBD codec 1 a=mcap:3 G726-32/8000 ; VBD codec 2 a=mscap:2 gpmd vbd=yes ; for V.152 PCMU a=mscap:3 gpmd vbd=yes ; for V.152 G726-32 a=pcfg:1 t=1 a=-ms:1 m=1,2 pt=1:18,2:0 a=pcfg:2 t=1 a=-ms:1 m=1,3 pt=1:18,3:98
| Offered (2) potential configurations:
- • Preference 1:
Audio (ITU-T G.729), VBD (ITU-T V.152 PCMU) - • Preference 2:
Audio (ITU-T G.729), VBD (ITU-T V.152 G.726-32)
If answerer supports Revised SDP Offer/Answer protocol, then either potential configuration 1 or 2 is selected, but not both.
|
+
+### 7.1.1 Mechanism for indicating support of ITU-T V.152 using ITU-T H.248/Megaco
+
+Under ITU-T H.248, the media gateway controller (MGC) uses local and remote descriptors to reserve and commit MG resources for media decoding and encoding for the given stream(s) and termination to which they apply. The MG includes these descriptors in its response to indicate what it is actually prepared to support. When text encoding the protocol, the descriptors consist of SDP session descriptions that describe the call capabilities.
+
+Support of ITU-T V.152 shall only be applied on ephemeral terminations via the local and/or remote descriptors.
+
+For an MG to reserve and commit resources for more than one call capability alternative, the MGC must set the ReserveGroup and ReserveValue properties of the LocalControlDescriptor to 'True'.
+
+Thus, if a list of payload types is offered in a local and/or remote descriptor, such as the following example 3 of an Add ephemeral termination command illustrates (the same applies if the command was a Modify or Move), the media gateway will select from the list only those payloads for which it can reserve and commit resources and shall send a reply to the MGC containing the alternatives for the local and/or remote descriptor that it selected, as described in [ITU-T H.248.1]:
+
+**Table 5 – Example ITU-T H.248 encoding (example 3a)**
+
+| ITU-T H.248 text encoding | Comments |
+|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| 1) MGC request (MGC to MG): MEGACO/3 [123.123.123.4]:55555 Transaction = 11 { Context = \$ { Add = \$ { Media { Stream = 1 { LocalControl { | The MGC requests support for four media configurations:
- • two audio configurations ('G.729' and 'PCMU' codec types); and
- • two VBDoIP configurations (VBD codec types 'PCMU' and 'G.726-32').
|
+
+**Table 5 – Example ITU-T H.248 encoding (example 3a)**
+
+| ITU-T H.248 text encoding | Comments |
+|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------|
+| Mode = RecOnly, ReserveGroup = ON, ReserveValue = ON }, Local { v=0 c=IN IP4 \$ m=audio \$ RTP/AVP 18 0 98 99 a=rtpmap:98 PCMU/8000 a=gpmid:98 vbd=yes a=rtpmap:99 G726-32/8000 a=gpmid:99 vbd=yes }; IP termination for audio and VBD } } } } } | |
+| 2) MG reply (MG to MGC response): MEGACO/3 [123.123.123.4]:55555 Transaction = 11 { Context = 34444 { Add = Te/1 { Media { Stream = 1 { LocalControl { Mode = RecOnly, ReserveGroup = ON, ReserveValue = ON }, Local { v=0 c=IN IP4 11.09.19.65 m=audio 1970 RTP/AVP 18 0 98 99 a=rtpmap:98 PCMU/8000 a=gpmid:98 vbd=yes a=rtpmap:99 G726-32/8000 a=gpmid:99 vbd=yes }; IP termination for audio and VBD } } } } } | |
+
+Alternatively, an MGC may leave it up to the MG whether it wants to indicate that it supports VBD, as per this Recommendation, and to select its dynamic payload type for VBD mode of operation by including CHOOSE (i.e., \$) in the payload type list field as example 3b illustrates:
+
+**Table 6 – Example ITU-T H.248 encoding (example 3b)**
+
+| H.248 text encoding | Comments |
+|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| 1) MGC request (MGC to MG): MEGACO/3 [123.123.123.4]:55555 Transaction = 11 { Context = \$ { Add = \$ { Media { Stream = 1 { LocalControl { Mode = RecOnly, ReserveGroup = ON, ReserveValue = ON }, Local { v=0 c=IN IP4 \$ m=audio \$ RTP/AVP 18 0 \$ ; Wildcard ; in format list }; IP termination for audio and VBD } } } } } | The MGC applies the wildcard CHOOSE ('\$') in the media description:
- the wildcard is in the format list (see also clause 6.11 of [ITU-T H.248.39]);
- such an underspecification implies "a priori knowledge" at the MG side, in order to choose an "appropriate" media format;
- e.g., it is expected that the MG selects a VBDolP format, but not anything else (like, e.g., another audio codec type);
- such kind of behaviour is either under the responsibility of the network management or could be defined in an ITU-T H.248 profile specification.
|
+| 2) MG reply (MG to MGC response): MEGACO/3 [123.123.123.4]:55555 Transaction = 11 { Context = 34444 { Add = Te/1 { Media { Stream = 1 { LocalControl { Mode = RecOnly, ReserveGroup = ON, ReserveValue = ON }, Local { v=0 c=IN IP4 11.09.19.65 m=audio 1970 RTP/AVP 18 0 98 99 a=rtpmap:98 PCMU/8000 a=gpmid:98 vbd=yes a=rtpmap:99 G726-32/8000 a=gpmid:99 vbd=yes ; The MGC should ; supply sufficient information ; for unambiguous resource ; selections by the MG, ; see clause 7.1.8 of ; [ITU-T Rec. H.248.1] Version 3 }; IP termination for audio and VBD } } } } } | The MG selects two VBDolP configurations (besides the two audio configurations 'G.729' and 'PCMU'):
- the selection of multiple media configurations is due to ReserveValue 'True';
- the MGC knows now by this response that the MG supports the two requested audio formats and furthermore two VBDolP configurations with VBD codecs 'PCMU' and 'G.726-32';
- it is expected that there will be a further MGC/MG request/response cycle in order to enable (at least) just a single VBDolP configuration (because multiple VBD configurations (but also multiple audio configurations) are typically meaningless from service perspective);
- thus, the MGC would use ReserveValue 'False' in the subsequent request.
|
+
+**Table 6 – Example ITU-T H.248 encoding (example 3b)**
+
+| H.248 text encoding | Comments |
+|------------------------|----------|
+| } } } } }
| |
+
+Once an MG has acknowledged a set of call capability alternatives, the MG is requested to reserve resources so that it can decode or encode the media stream according to any of the alternatives. Thus, in the above example 3a, if the MG supports [ITU-T G.729] and [ITU-T G.711] for audio and [ITU-T G.711] for VBD, (as per this Recommendation), then, in accordance with [ITU-T H.248.1], the MG must reserve resources such that it can decode one RTP stream in any of the formats in its response at any time during the call, i.e., ITU-T G.711 audio format, ITU-T G.729 audio format or ITU-T G.711 VBD format.
+
+If a specific relay mechanism (e.g., ITU-T T.38, ITU-T V.150.1, etc.) is indicated as the preferred mechanism above that of VBD, then, for the applicable devices, the relay mechanisms shall be used instead of VBD. For example, if a remote descriptor indicates ITU-T T.38 as preferred over VBD, then an MG shall use ITU-T T.38 for all G3FE equipment instead of VBD.
+
+This is a request for multiple media groups. There must be an order of preference. The preference may be either the "descending order rule" of ITU-T H.248 in case of a complete parameter specification by the MGC concerning the preferred media names, or a corresponding rule shall be provisioned in both ITU-T H.248 MG peers in case of "parameter under specification" (in ITU-T H.248 descriptors) by MGC.
+
+If an MG cannot guarantee that it can commit and reserve the resources for VBD for the call being set up, then, in accordance with [ITU-T H.248.1], it shall not include the 'gpmd' attribute (that indicates support of ITU-T V.152) in its response SDP session description.
+
+Note that this mechanism does not preclude an ITU-T H.248 MG implementation from sending to the MGC observedEvents indicating signals detected, as described in [ITU-T H.248.2] (e.g., call type discrimination package).
+
+#### **7.1.2 Mechanism for indicating support of ITU-T V.152 using SIP**
+
+A gateway answering an SDP session description offer that shows the capability to perform the relay model described in [IETF RFC 3264] shall be used to earmark one or more RTP payload types for VBD operation as defined in this Recommendation.
+
+Just as a SIP-compliant terminal would indicate support of more than one audio codec payload or support of other payload types (e.g., [IETF RFC 4733] for DTMF relay) within a media stream, a SIP-compliant implementation shall indicate support of [ITU-T V.152] by including the payload types as described in clause 7.1.
+
+If multiple media descriptions are being offered and if the implementations cannot support simultaneous reception and transmission of the various media types, then the 'group', 'mid' and 'FID' attributes described in [IETF RFC 3388] shall be used to indicate alternative support of each of the offered media types (as illustrated below in example 5).
+
+Once a gateway has indicated support of [ITU-T V.152] in addition to other mechanisms within an SDP session description (such as, but not limited to, audio, facsimile relay via ITU-T T.38 DTMF relay as per [IETF RFC 4733], etc.), the gateway shall be capable of switching between any of the supported, and mutually negotiated, RTP payload types, at any time during a call.
+
+#### 7.1.2.1 Mechanism for indicating preference of VoIP relay mechanisms above VBD
+
+SIP currently does not have a mechanism for indicating in a clear manner that a gateway would like to use a specific relay mechanism (e.g., ITU-T T.38, ITU-T V.150.1, text relay) instead of VBD. Hence, this clause defines the syntax and use of an attribute that indicates a preference list of modem and facsimile transport methods in an ITU-T V.152 implementation that supports any of the following alternative transport methods:
+
+- facsimile relay of IP via [ITU-T T.38];
+- modem relay over IP via [ITU-T V.150.1];
+- text relay.
+
+##### 7.1.2.1.1 SDP attribute for transport method indication (a=pmft:)
+
+The 'pmft' attribute and its formatting in the SDP session description is described by the following ABNF syntax:
+
+```
+pmft-attribute = "a=pmft:" *(SPACE modem-fax-transport)
+modem-fax-transport = 1* ("V1501" / "T38" / "V151")
+```
+
+This attribute allows an ITU-T V.152 implementation to indicate whether it prefers any of the listed relay transport mechanism above the VBD mode. Omission of this attribute in an SDP session description means that VBD mode is the preferred transport mechanism of voice-band data.
+
+When included in an SDP session description, this attribute shall always be placed at the session level.
+
+For example, an ITU-T V.152 implementation that also supports [ITU-T V.150.1] for modems and [ITU-T T.38] for facsimile, and prefers to use these relay mechanisms whenever possible instead of VBD, shall include, at the session level of the SDP session description, the following 'pmft' attribute:
+
+```
+a=pmft: T38 V1501
+```
+
+An ITU-T V.152 implementation that receives the above 'pmft' attribute, and is able to support both the relay mechanisms specified in this example, shall include the same 'pmft' attribute in its response. Thus, when the call is set up, all G3FE shall be transported via [ITU-T T.38]; voice-band modems that are supported by [ITU-T V.150.1] shall be transported via [ITU-T V.150.1] and all other modems (e.g., text telephones) shall be transported by [ITU-T V.152].
+
+A gateway answering an SDP session description offer that includes the 'pmft' attribute, if indicating preference of the supported relay mechanism over VBD, shall include in the response SDP session description the 'pmft' attribute with the relay mechanism specified. If a relay mechanism is not supported, then that relay mechanism shall be removed from the list of the pmft attribute.
+
+Once a specific relay mechanism (e.g., ITU-T T.38, ITU-T V.150.1, etc.) is indicated as the preferred mechanism above that of VBD, such relay mechanisms shall be used instead of VBD.
+
+A gateway answering an SDP session description offer that shows the capability to perform relay mechanisms but does not include the 'pmft' attribute may include in the response SDP session description the 'pmft' attribute with the relay mechanisms specified to show a preference to use these.
+
+##### 7.1.2.1.2 Examples – Preferences VBDolP (ITU-T V.152) versus FoIP (ITU-T T.38)
+
+For example: if the initial SDP session description offer from a gateway that only supports [ITU-T V.152] and [ITU-T T.38] does not include the 'pmft' attribute because it prefers to use VBD above ITU-T T.38, then it would include an SDP session description such as the one described in Table 7 for in Legacy SDP Offer/Answer syntax.
+
+**Table 7 – Example SDP encoding – O/A cycle in Legacy SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| 1) OFFER: v=0 o=Offerer 0 0 IN IPV4 <IPAddressA> s=- t=0 0 p=+1 965 1109-1965 c=IN IP4 <IPAddressA> a=group:FID 1 2 m=audio <udpPort x> RTP/AVP 18 0 13 96 a=mid:1 a=ptime:10 a=rtpmap:96 PCMU/8000 a=gpmid: 96 vbd=yes m=image <udpPort y> udptl t38 a=mid:2 a=T38version:0 a=T38FaxRateManagement:transferredTCF a=T38FaxUdpEC:t38UDPRedundancy
| [IETF RFC 3388] is required in Legacy SDP Offer/Answer in order to indicate two media configurations in parallel: 1) audio VoIP or ITU-T V.152 VBDolP, and 2) ITU-T T.38 FoIP.
The example offer provides two audio codecs for VoIP.
|
+| 2) ANSWER: v=0 o=Answerer 0 0 IN IPV4 <IPAddressB> s=- t=0 0 p=+1 965 0203-1970 c=IN IP4 <IPAddressB> a=group:FID 1 2 a=pmft: T38 m=audio <udpPort x> RTP/AVP 18 0 13 96 a=mid:1 a=ptime:10 a=rtpmap:96 PCMU/8000 a=gpmid: 96 vbd=yes m=image <udpPort y> udptl t38 a=mid:2 a=T38version:0 a=T38FaxRateManagement:transferredTCF a=T38FaxUdpEC:t38UDPRedundancy
| However, the answerer gateway (that may not be in as reliable a network) may always prefer ITU-T T.38 over VBD for facsimile transmission. Thus, it would include in its response, e.g., such an answer.
|
+
+Figure 3 illustrates the four possible media configurations, offered in this example, and positively acknowledged by the answerer.
+
+
+
+The diagram illustrates four potential session configurations (1, 2, 3, 4) connecting audio codecs to voiceband data modes and fax relay modes. The top section, labeled 'Audio codecs', contains two boxes: 'G.729 without silence suppression' and 'G.711 μ-law with silence suppression'. The bottom section, labeled 'Voiceband data mode (V.152 VBDolP)', contains two boxes: 'G.711 μ-Law' (labeled 'VBD codec') and 'T.38-UDPTL/UDP' (labeled 'Fax relay codec'). A dashed box labeled 'Session Configurations:' points to the connections. Configuration 1 connects G.729 to G.711 μ-Law. Configuration 2 connects G.711 μ-law to T.38-UDPTL/UDP. Configuration 3 connects G.729 to T.38-UDPTL/UDP. Configuration 4 connects G.711 μ-law to G.711 μ-Law.
+
+Diagram showing four potential session configurations (1, 2, 3, 4) connecting audio codecs (G.729, G.711) to voiceband data modes (V.152, T.38) and fax relay modes.
+
+**Figure 3 – Potential session configurations offered in this example**
+
+The offerer gateway, on receipt of such an answer, shall transport G3FE data using ITU-T T.38, i.e., potential configuration 3 or 4) and all other modems, or non-G3FE must be transported via ITU-T V.152 (i.e., potential configuration 1 or 2). There are still two audio options (due to two audio codecs). Such a situation is unfortunate (because it is not required for VoIP applications) and may be resolved by a subsequent negotiation cycle. Alternatively, a single cycle negotiation, using Revised SDP Offer/Answer, may be applied (Table 8).
+
+**Table 8 – Example SDP encoding: O/A cycle in Revised SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| 1) OFFER: ; SESSION CONFIGURATIONs a=sescap:1 1 ; VoIP = G.729, VBDolP = V.152 (G.711) a=sescap:2 2 ; VoIP = G.711, VBDolP = V.152 (G.711) a=sescap:3 3,5 ; VoIP = G.729, FoIP = T.38 UDPTL/UDP a=sescap:4 4,5 ; VoIP = G.711, FoIP = T.38 UDPTL/UDP ; LATENT CONFIGURATION for T.38 a=tcap:2 udptl ; T.38 FoUDPTL/UDP transport variant a=mcap:5 t38 ; T.38 FoIP codec (subtype = 't38') a=acap:11 T38FaxVersion:0 a=acap:12 T38FaxRateManagement:transferredTCF a=acap:13 T38FaxUdpEC:t38UDPRedundancy a=acap:14 (... additional T.38 attributes may be included) a=lcfg:5 mt=image t=2 m=5 a=11,12,13,14,...
| [IETF RFC 3388] is not required! Potential parallel media configurations (for ITU-T T.38 if G3FE stimuli are detected) are specified via the concept of session configurations in Revised SDP Offer/Answer. The ITU-T T.38 media configuration relates to a latent configuration because call may start with speech phase first:
Offered (2) potential session configurations: see Figure 3.
|
+
+**Table 8 – Example SDP encoding: O/A cycle in Revised SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| ; ACTUAL CONFIGURATION (due to backward compatibility) ... omitted, see Table 7 ... ; ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP and VBD oIP a=acap:1ptime:10 a=mcap:1 G729/8000 ; audio codec 1 a=mcap:2,4 PCMU/8000 ; audio codec 2 and VBD codec a=mcap:3 CN/8000 ; comfort noise for audio c. 2 a=mscap:4 gpm d vbd=yes ; for V.152 PCMU a=pcfg:1 t=1 a=-ms:1 m=1,4 pt=1:18,4:96 a=pcfg:2 t=1 a=-ms:1 m=2,3,4 pt=1:0,3:13,4:96 a=pcfg:3 t=1 a=-ms:1 m=1 pt=1:18 a=pcfg:4 t=1 a=-ms:1 m=2,3 pt=1:0,3:13
| |
+| 2) ANSWER: ...
| Answerer would, e.g., just acknowledge session configuration 1 (for ITU-T V.152, non-G3FE modem) and 3 (for ITU-T T.38 G3FE emulation) if [ITU-T G.729] is supported (and thus the selected audio codec).
|
+
+The following main advantages may be noted concerning Revised versus Legacy SDP Offer/Answer:
+
+- the ITU-T V.152 introduced SDP attribute "*a=pmft:*" may be replaced by IETF SDP syntax ("order principle within session and potential configurations in Revised SDP Offer/Answer");
+- [IETF RFC 3388] is not required because parallel media configurations are specified via the concept of session configurations in Revised SDP Offer/Answer; and
+- single cycle negotiation (because Answerer would already select 1-out-of-2 audio codecs).
+
+#### 7.1.3 Examples of indicating support for ITU-T V.152 using the session description protocol
+
+This clause shall provide a few examples of SDP session descriptions sent by implementations that support ITU-T V.152 in addition to other Recommendations (such as, but not limited to, voice, [ITU-T T.38], ToIP, and [ITU-T V.150.1]).
+
+#### 7.1.3.1 Example 4 – Two audio codecs and one VBD codec (overlapping with audio)
+
+An implementation that supports ITU-T V.152 (using the dynamic payload type 96 and ITU-T G.711 $\mu$ -law as the VBD codec) and the voice codecs ITU-T G.711 $\mu$ -law, silence suppression and ITU-T G.729, shall transmit the following SDP session description, only those lines that are relevant to this Recommendation are highlighted in bold, see Table 9.
+
+Figure 4 illustrates the two possible media configurations, offered in this example.
+
+**Table 9 – Example SDP encoding – "Example 4" offer in Legacy SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------|
+| 1) OFFER: v=0 o=- 0 0 IN IPV4 <IPAddressA> s=- t=0 0 p=+1 c=IN IP4 <IPAddressA> m=audio <udpPort A> RTP/AVP 18 0 13 96 a=ptime:10 a=rtpmap:96 PCMU/8000 a=gpmid: 96 vbd=yes
| |
+
+
+
+The diagram illustrates potential media configurations. It is divided into two main sections: 'Audio mode (VoIP)' and 'Voiceband data mode (V.152 VBDolP)'. The 'Audio mode (VoIP)' section contains two 'Audio codecs': 'G.729 without silence suppression (Tp = 10 ms)' and 'G.711 μ-law with silence suppression (Tp = 10 ms)'. The 'Voiceband data mode (V.152 VBDolP)' section contains one 'VBD codec': 'G.711 μ-Law (Tp = 10 ms)'. A dashed box labeled 'Potential Configurations:' points to two possible connections: '1' connects the 'G.729' codec to the 'G.711 μ-Law' VBD codec, and '2' connects the 'G.711 μ-law' codec to the 'G.711 μ-Law' VBD codec.
+
+Diagram illustrating potential media configurations for audio codecs and VBD codec.
+
+**Figure 4 – Potential media configurations offered in this example**
+
+An ITU-T V.152 implementation that receives an SDP session description, as in the above example, shall interpret it as the remote gateway's capability to support ITU-T V.152 and that the payload type that shall be used for VBD packets is 96.
+
+The Legacy SDP Offer is unclear whether one or two audio codecs may be selected, e.g., the answerer may agree to both audio codecs ("which is for the emulation of PSTN modem calls not required"). This ambiguity may be avoided by the concept of potential configurations in Revised SDP Offer/Answer (see Table 10).
+
+**Table 10 – Example SDP encoding – "Example 4" offer in Revised SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| ; ACTUAL CONFIGURATION (due to backward compatibility) m=audio <udpPort A> RTP/AVP 18 0 13 96 a=ptime:10 a=rtpmap:96 PCMU/8000 a=gpmd: 96 vbd=yes ; ; POTENTIAL CONFIGURATIONS a=tcap:1 RTP/AVP ; transport for VoIP and VBDoIP a=acap:1 ptime:10 ; common packetization time a=mcap:1 G729/8000 ; audio codec 1 a=mcap:2,4 PCMU/8000 ; audio codec 2 and VBD codec 1 a=mcap:3 CN/8000 ; comfort noise for audio c. 2 a=mscap:4 gpmd vbd=yes ; for V.152 PCMU a=pcfg:1 t=1 a=--ms:1 m=1,4 pt=1:18,4:96 a=pcfg:2 t=1 a=--ms:1 m=2,3,4 pt=1:0,3:13,4:96
| Offered (2) potential configurations:
- • Preference 1: Audio (ITU-T G.729), VBD (ITU-T V.152 PCMU)
- • Preference 2: Audio (PCMU incl. silence suppression), VBD (ITU-T V.152 PCMU)
|
+
+#### 7.1.3.2 Example 5 – ITU-T V.152 to non-ITU-T V.152 (OCL with ITU-T V.152 and [ITU-T T.38], ACL without ITU-T V.152)
+
+A call is set up between gateway A that supports, the Supported Configuration (Codec) List $SCL_{A}$ , ITU-T V.152 with PCMU as VBD codec, ITU-T T.38 UDPTL/UDP, and voice codecs ITU-T G.729 and PCMU with [IETF RFC 3389] silence suppression and voice codec ITU-T G.729 and PCMU, and a Gateway B that supports ( $SCL_{B}$ ) ITU-T T.38 UDPTL/UDP, silence suppression and voice codecs ITU-T G.729 and PCMU inclusive silence suppression, but does not support ITU-T V.152.
+
+NOTE – Voice codec ITU-T G.729 is used here without silence suppression. This would require support of ITU-T G.729B and the correspondent SDP indication via attribute line "*a=fmtp:18 annexb=yes*".
+
+The SDP transmitted by gateway A, the Offered Configuration (Codec) List $OCL_{A}$ (= $SCL_{A}$ ), will be of the form described in the "Offer" in Table 11.
+
+Gateway B, which does not support VBD shall respond with an SDP, the Answered Configuration (Codec) List $ACL_{B}$ (= $SCL_{B}$ ), that omits all reference to ITU-T V.152 (see Answer in Table 11).
+
+**Table 11 – Example SDP encoding – O/A cycle in Legacy SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------|
+| 1) OFFER: v=0 o=GatewayA 0 0 IN IPV4 <IPAddressA> s=- t=0 0 p=+1 c=IN IP4 <IPAddressA> a=group:FID 1 2 m=audio <udpPort x> RTP/AVP 18 0 13 96 a=mid:1 a=ptime:10 a=rtpmap:96 PCMU/8000 a=gpmd: 96 vbd=yes m=image <udpPort y> udptl t38 a=mid:2 a=T38version:0 a=T38FaxRateManagement:transferredTCF a=T38FaxUdpEC:t38UDPRedundancy (.....additional T.38 attributes may follow.....)
| |
+| 2) ANSWER: v=0 o=GatewayB 0 0 IN IPV4 <IPAddressB> s=- t=0 0 p=+1 c=IN IP4 <IPAddressB> a=group:FID 1 2 m=audio <udpPort w> RTP/AVP 18 0 13 a=mid:1 a=ptime:10 m=image <udpPort z> udptl t38 a=mid:2 a=T38version:0 a=T38FaxRateManagement:transferredTCF a=T38FaxUdpEC:t38UDPRedundancy (.....additional T.38 attributes may follow.....)
| |
+
+On receipt of the above SDP, gateway A shall understand that gateway B does not perform ITU-T V.152. Thus, gateway A shall not transition into a VBD mode. The agreed Negotiated Configuration (Codec) List NCL is thus equal to $ACL_B (= SCL_B)$ . The NCL contains both audio codecs, which might be a problem, at least an unfortunate and not desired situation for PSTN modem call types.
+
+Such an (single cycle O/A) NCL may be avoided by the usage of Revised SDP Offer/Answer (see Table 12), which allows to specify an OCL as Preferred Configuration (Codec) List PCLA. Figure 5 illustrates the four possible session configurations offered in this example. The Answerer is only supporting session configurations 3 and 4 (due to SCLB), and shall just acknowledge session configuration 3 due to its preference by the Offerer.
+
+
+
+The diagram illustrates four potential session configurations (1, 2, 3, 4) connecting audio codecs to VBD or fax relay codecs. The top section, 'Audio mode (VoIP)', contains two audio codecs: 'G.729 without silence suppression' and 'G.711 μ-law with silence suppression'. The bottom section, 'Voiceband data mode (V.152 VBDolP)', contains a 'VBD codec' labeled 'G.711 μ-Law'. The bottom right section, 'Fax relay mode (T.38 FoIP)', contains a 'Fax relay codec' labeled 'T.38-UDPTL/UDP'. The connections are: 1 (G.729 to G.711 μ-Law), 2 (G.711 μ-law to T.38-UDPTL/UDP), 3 (G.729 to T.38-UDPTL/UDP), and 4 (G.711 μ-law to G.711 μ-Law). A dashed box labeled 'Session Configurations:' points to the connections.
+
+Figure 5: Potential session configurations offered in this example. The diagram shows four session configurations (1, 2, 3, 4) connecting audio codecs to VBD or fax relay codecs. Audio mode (VoIP) includes G.729 without silence suppression and G.711 μ-law with silence suppression. Voiceband data mode (V.152 VBDolP) includes G.711 μ-Law. Fax relay mode (T.38 FoIP) includes T.38-UDPTL/UDP. Connections: 1 (G.729 to G.711 μ-Law), 2 (G.711 μ-law to T.38-UDPTL/UDP), 3 (G.729 to T.38-UDPTL/UDP), 4 (G.711 μ-law to G.711 μ-Law).
+
+Figure 5 – Potential session configurations offered in this example
+
+Table 12 – Example SDP encoding – O/A cycle in Revised SDP Offer/Answer syntax
+
+| SDP encoding (shortened SDP description) | Comments |
+|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| 1) OFFER: ; SESSION CONFIGURATIONS a=sescap:1 1 ; VoIP = G.729, VBDolP = V.152 (G.711) a=sescap:2 2 ; VoIP = G.711, VBDolP = V.152 (G.711) a=sescap:3 3,5 ; VoIP = G.729, FoIP = T.38 UDPTL/UDP a=sescap:4 4,5 ; VoIP = G.711, FoIP = T.38 UDPTL/UDP ; LATENT CONFIGURATION for T.38 a=tcap:2 udptl ; T.38 FoUDPTL/UDP transport variant a=mcap:5 t38 ; T.38 FoIP codec (subtype = 't38') a=acap:11 T38FaxVersion:0 a=acap:12 T38FaxRateManagement:transferredTCF a=acap:13 T38FaxUdpEC:t38UDPRedundancy a=acap:14 (... additional T.38 attributes may be included) a=lcfg:5 mt=image t=2 m=5 a=11,12,13,14,... ; ACTUAL CONFIGURATION (due to backward compatibility) ... omitted ... ;
| Offered (4) potential configurations (as session configurations due to 'voice' and 'facsimile'):
- • Preference 1: Audio (ITU-T G.729), VBD (ITU-T V.152 PCMU)
- • Preference 2: Audio (PCMU with silence suppression), VBD (ITU-T V.152 PCMU)
- • Preference 3: Audio (ITU-T G.729) and fax relay (ITU-T T.38 FoUDPTL/UDP)
- • Preference 4: Audio (PCMU) and fax relay (ITU-T T.38 FoUDPTL/UDP)
|
+
+**Table 12 – Example SDP encoding – O/A cycle in Revised SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------|
+| ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP and VBD oIP a=acap:1ptime:10 a=mcap:1 G729/8000 ; audio codec 1 a=mcap:2,4 PCMU/8000 ; audio codec 2 and VBD codec a=mcap:3 CN/8000 ; comfort noise for audio c. 2 a=mscap:4 gpm d vbd=yes ; for V.152 PCMU a=pcfg:1 t=1 a=-ms:1 m=1,4 pt=1:18,4:96 a=pcfg:2 t=1 a=-ms:1 m=2,3,4 pt=1:0,3:13,4:96 a=pcfg:3 t=1 a=-ms:1 m=1 pt=1:18 a=pcfg:4 t=1 a=-ms:1 m=2,3 pt=1:0,3:13
| |
+| 2) ANSWER: ... a=sescap:3
| The Answerer selects the 3rd session configuration.
|
+
+#### 7.1.3.3 Example 6 – ITU-T V.152 to non-ITU-T V.152 (OCL with ITU-T V.152 and ITU-T V.150.1, ACL without ITU-T V.152)
+
+Gateway A supports voice codecs ITU-T G.729, ITU-T V.152 and ITU-T V.150.1. Gateway B also supports ITU-T V.150.1 and voice codec ITU-T G.729 but does not support ITU-T V.152.
+
+NOTE – This example 6 shows the minimum number of lines needed to construct an SDP-compliant session descriptor that includes all attributes that are mandatory for the representation of SPRT modem relay and ITU-T V.152.
+
+In this example, ports 49230 and 49232 (see Offer in Table 13) are used for the RTP/AVP and SPRT media streams, respectively. Within the RTP/AVP media stream, the static payload types of 0 (PCMU) and 8 (PCMA) are marked for VBD treatment via the 'gpm d' attribute, and thus cannot be used for voice.
+
+Also note, in accordance with SIP, the SDP in Table 13 implies simultaneous support of audio 'rtp/avp' and audio 'udpsprt'. To indicate that only one media type can be supported at a time, the 'group' attribute with the FID semantics, together with the 'mid' attribute, should be used as specified in [IETF RFC 3388] (see example 5, clause 7.1.3.2).
+
+Gateway B does not support ITU-T V.150.1 (implementations which also must support VBD). Gateway B shall respond with an SDP as follows (see Answer in Table 13).
+
+**Table 13 – Example SDP encoding – O/A cycle in Legacy SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------|
+| 1) OFFER: SDP from Gateway A: v=0 o=Gateway A 25678 753849 IN IP4 128.96.41.1 s= c=IN IP4 128.96.41.1 t=0 0 m=audio 49230 RTP/AVP 0 8 18 97 98 a=gpmd:0 vbd=yes a=gpmd:8 vbd=yes a=rtpmap:97 telephone-event/8000 a=fmtp:97 0-15,32,33,34,35,66,70 a=rtpmap:98 v150fw/8000 m=audio 49232 udpsprt 100 a=sprtmap:100 v150mr/8000 a=fmtp:100 mr=0; mg=1;DSCselect=3;mrmodes=1,2;jmdelay=no;versn =1.1
| |
+| 2) ANSWER: v=0 o=GatewayB 25678 753849 IN IP4 128.96.41.1 s= c=IN IP4 128.96.41.1 t=0 0 m=audio 49230 RTP/AVP 0 8 18 97 98 a=gpmd:0 vbd=yes a=gpmd:8 vbd=yes a=rtpmap:97 telephone-event/8000 a=fmtp:97 0-15,32,33,34,35,66,70 a=rtpmap:98 v150fw/8000 m=audio 49232 udpsprt 100 a=sprtmap:100 v150mr/8000 a=fmtp:100 mr=0; mg=1;DSCselect=3;mrmodes=1,2;jmdelay=no;versn =1.1
| |
+
+Because both gateways have negotiated support of SSE, they shall use SSEs to indicate transition between voice and VBD.
+
+Figure 6 illustrates the three possible session configurations, offered in this example. The Answerer is not supporting session configuration 3 (due to lack of support of [ITU-T V.150.1]), and is acknowledging session configuration 1 (due to support of PCMU as VBD codec), see Table 14.
+
+
+
+Diagram showing potential session configurations for audio mode (VoIP). The top box is 'Audio mode (VoIP)' containing 'G.729 without silence suppression'. Three lines labeled 1, 2, and 3 connect this box to three boxes below. Line 1 connects to 'G.711 μ-law' (part of 'Voiceband data mode (V.152 VBDolP)'). Line 2 connects to 'G.711 A-law' (also part of 'Voiceband data mode (V.152 VBDolP)'). Line 3 connects to 'V.150.1 SPRT' (part of 'Modem relay mode (V.150.1 MoIP)'). A dashed box labeled 'Session Configurations:' encloses the three lines. A dashed box labeled 'VBD codecs' encloses the two G.711 boxes. A dashed box labeled 'Modem relay codec' encloses the V.150.1 SPRT box.
+
+**Figure 6 – Potential session configurations offered in this example**
+
+**Table 14 – Example SDP encoding – O/A cycle in Revised SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| 1) OFFER: ; SESSION CONFIGURATIONs a=sescap:1 1 ; VoIP = G.729, VBDoIP = V.152 (PCMU) a=sescap:2 2 ; VoIP = G.729, VBDoIP = V.152 (PCMA) a=sescap:3 3,4 ; VoIP = G.729, MoIP = V.150.1 SPRT ; LATENT CONFIGURATION for V.150.1 a=tcap:2 udpsprt ; V.150.1 SPRT/UDP transport variant a=mcap:6 v150mr/8000 ; V.150.1 MoIP codec a=mfcap:6 mr=0; mg=1; CDSCselect=3; mrmodes=1,2; jmdelay=no; versn=1.1 a=lcfg:4 mt=audio t=2 m=6 pt=6:100 ; ACTUAL CONFIGURATION (due to backward compatibility) ... omitted ... ; ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP, ; VBDoIP, SSEoIP & NTEoIP a=acap:1 ptime:10 a=mcap:1 G729/8000 ; audio codec a=mcap:2 PCMU/8000 ; VBD codec 1 a=mcap:3 PCMA/8000 ; VBD codec 2 a=mcap:4 telephone-event/8000 ; NTE codec a=mcap:5 v150fw/8000 ; SSE protocol
| Offered (4) potential configurations (as session configurations due to 'voice' and 'facsimile'):
- • Preference 1: Audio (ITU-T G.729), VBD (ITU-T V.152 PCMU)
- • Preference 2: Audio (ITU-T G.729), VBD (ITU-T V.152 PCMA)
- • Preference 3: Audio (ITU-T G.729) and modem relay (ITU-T V.150.1 using SPRT (simple packet relay transport over UDP))
Some MoIP configuration details:
- – ITU-T V.8-compatible modem relay (mr = 0);
- – media gateway of type "No Trans-compression" (mg = 1);
- – Call discrimination mode selection "Mixed" (CDSCselect = 3);
- – supported modulation types "1" (ITU-T V.34 duplex), "2" (ITU-T V.34 Half-duplex) (mrmodes = 1, 2);
- – JM delay procedure "No" (jmdelay=no);
- – state signalling event (SSE) protocol supports "Yes" (see v150fw declaration for SSE-over-RTP packets with PT = 98);
- – SSE event types: "1" (initial audio), "3" (modem relay), "4" (text relay), "5" (fax relay);
|
+
+**Table 14 – Example SDP encoding – O/A cycle in Revised SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------|
+| a=mscap:2,3 gpmd vbd=yes ; for V.152 PCMU & PCMA
a=mfcap:4 0-15,32-35,66,70 ; value range of NTE
a=mfcap:5 1,3-5 ; SSE event types
a=mfcap:5 expack=yes ; SSE reliability
a=pcfg:1 t=1 a=-ms:1 m=1,2,4
pt=1:18,2:96,4:97
a=pcfg:2 t=1 a=-ms:1 m=1,3,4
pt=1:18,3:99,4:97
a=pcfg:3 t=1 a=-ms:1 m=1,4,5
pt=1:18,4:97,5:98 | – SSE assured transport (using 'Explicit Acknowledgement' method). |
+| 2) ANSWER:
...
a=sescap:1 | The Answerer selects the 1st session configuration. |
+
+#### 7.1.4 Optional ITU-T V.152 capabilities
+
+This clause describes the SDP representation of information that may be optionally declared at session establishment time. The absence of their declaration shall be construed by an ITU-T V.152 implementation as an indication that the remote ITU-T V.152 implementation does not support them.
+
+#### 7.1.4.1 Declaration of redundancy and forward error correction
+
+The declaration, in SDP, of [IETF RFC 2198] redundancy and [IETF RFC 5109] FEC, shall conform to the rules in the applicable IETF source documents. When supporting text telephones, on networks where the error character service requirements as specified in clause A.3 of [b-ITU-T F.700] is exceeded due to packet loss, then this Recommendation strongly encourages the appropriate use of [IETF RFC 2198] redundancy and [IETF RFC 5109] FEC for the IP network to which it is attached. However, on some networks, the application of redundancy/FEC may contribute to the character error rate and should not be used.
+
+##### 7.1.4.1.1 Example 7 – Packet redundancy for ITU-T V.152 with PCMU as VBD codec
+
+Although the [IETF RFC 2198] rules are not repeated here, declaring [IETF RFC 2198] support with a redundancy level of three for a VBD codec is illustrated with an example (see Tables 15 and 16).
+
+Figure 7 illustrates the offered media configuration in example 7.
+
+**Table 15 – Example SDP encoding – "Example 7" offer in Legacy SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|---------------------------------------------------------------------------------------------------------------|----------|
+| 1) OFFER:
m=audio 3456 RTP/AVP 0 15 102
a=gpmd:0 vbd=yes
a=rtpmap:102 red/8000
a=fmtp:102 0/0/0/0 | |
+
+
+
+Diagram showing a potential media configuration. It consists of two main dashed boxes. The top box is labeled 'Audio codec' and contains 'Audio mode (VoIP)' and a rounded rectangle labeled 'G.728'. The bottom box is labeled 'VBD codec' and contains 'Voiceband data mode (V.152 VBDolP)' and a rounded rectangle labeled 'G.711 μ-law with Packet Redundancy'. A vertical line connects the bottom of the 'G.728' box to the top of the 'G.711 μ-law...' box, with a '1' on the line. A dashed oval labeled 'Potential Configuration:' points to this connection line.
+
+**Figure 7 – Potential media configuration offered in this example**
+
+**Table 16 – Example SDP encoding – "Example 7" offer in Revised SDP Offer/Answer syntax**
+
+| SDP encoding (shortened SDP description) | Comments |
+|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| ; ACTUAL CONFIGURATION (due to backward compatibility) m=audio 3456 RTP/AVP 0 15 102 a=gpmd:0 vbd=yes a=rtpmap:102 red/8000 a=fmtp:102 0/0/0/0 ; ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP & VBDolP a=mcap:1 G728/8000 ; audio codec a=mcap:2 PCMU/8000 ; VBD codec a=mcap:3 RED/8000 ; RTP RFC 2198 redundancy a=mfcap:3 %2%/ %2%/ %2%/ %2% ; RFC 2198 redundancy format a=mscap:2 gpmd vbd=yes ; for V.152 PCMU a=pcfg:1 t=1 a=-ms m=2,1,3 pt=2:0,1:15,3:102
| Offered potential configuration:
- • Preference 1: Audio (ITU-T G.728), VBD (ITU-T V.152 PCMU with packet redundancy)
|
+
+##### 7.1.4.1.2 Example 8 – Forward error correction for ITU-T V.152 with PCMU as VBD codec
+
+Examples of the declaration of FEC support are found in [IETF RFC 5109]. This includes the use of a separate FEC stream and the combination of the FEC stream with the primary stream via IETF RFC 2198 encapsulation. In the case when FEC is a separate stream, [IETF RFC 5109] uses an 'fmtp' line to associate this stream with an IP address and port. When FEC packets are sent to the same IP address and port (albeit a different SSRC) as the media packets they qualify, there is no need for the 'fmtp' line to associate the 'parityfec' payload type with an IP address and port. Thus, in the following SDP segment (see Table 17), the last line is superfluous and may be omitted. Likewise, the absence of an 'fmtp' line associating an IP address and port with a FEC payload type will be construed to mean that the FEC packets are to be sent to the same IP address and port as the media packets they qualify.
+
+Table 17 – Example SDP encoding – "Example 8" offer in Legacy SDP Offer/Answer syntax
+
+| SDP encoding (shortened SDP description) | Comments |
+|--------------------------------------------------------------------------------------------------------------------------------------------------------------|----------|
+| 1) OFFER: c=IN IP4 224.2.17.12 t=0 0 m=audio 49170 RTP/AVP 0 15 78 a=gpmd:0 vbd=yes a=rtpmap:78 parityfec/8000 a=fmtp:78 49170 IN IP4 224.2.17.12
| |
+
+Figure 8 illustrates the offered media configuration in example 8.
+
+
+
+The diagram illustrates the potential media configuration offered in this example. It consists of two main dashed-line boxes. The top box is labeled "Audio mode (VoIP)" and contains a rounded rectangle labeled "Audio codec" containing "G.728". The bottom box is labeled "Voiceband data mode (V.152 VBDoIP)" and contains a rounded rectangle labeled "VBD codec" containing "G.711 μ-law with Forward Error Correction". A vertical dashed line labeled "Potential Configuration:" connects the two boxes, with a small oval and the number "1" indicating a specific configuration path.
+
+Diagram of potential media configuration showing Audio mode (VoIP) with G.728 codec and Voiceband data mode (V.152 VBDoIP) with G.711 μ-law with Forward Error Correction codec.
+
+Figure 8 – Potential media configuration offered in this example
+
+Table 18 – Example SDP encoding – "Example 8" offer in Revised SDP Offer/Answer syntax
+
+| SDP encoding (shortened SDP description) | Comments |
+|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| ; ACTUAL CONFIGURATION (due to backward compatibility) c=IN IP4 224.2.17.12 t=0 0 m=audio 49170 RTP/AVP 0 15 78 a=gpmd:0 vbd=yes a=rtpmap:78 parityfec/8000 a=fmtp:78 49170 IN IP4 224.2.17.12 ; ; POTENTIAL CONFIGURATIONs a=tcap:1 RTP/AVP ; transport for VoIP & VBDoIP a=mcap:1 G728/8000 ; audio codec a=mcap:2 PCMU/8000 ; VBD codec a=mcap:3 parityfec/8000 ; RTP RFC 5109 FEC a=mcap:2 gpmd vbd=yes ; for V.152 PCMU a=pcfg:1 t=1 a=-ms m=2,1,3 pt=2:0,1:15,3:78
| Offered potential configuration:
- • Preference 1: Audio (ITU-T G.728), VBD (ITU-T V.152 PCMU forward error correction)
|
+
+#### 7.1.4.2 Optional vendor-specific parameters
+
+The 'vndpar' (vendor parameters) attribute may be used to declare vendor codes for coordinating enhanced operation over and above those indicated in this Recommendation. It shall be possible to safely ignore vendor-specific parameters and still maintain interoperability with equipment conforming to this Recommendation. Hence, proprietary enhancements cannot be a substitute for the basic features required for compliance with this Recommendation.
+
+The format of the 'vndpar' attribute line is as follows:
+
+```
+a=vndpar:
+[]
+```
+
+The , a decimal, indicates the format of the following field. The following values are defined:
+
+| Integer representation | Vendor ID format |
+|------------------------|--------------------------------|
+| 1 | [ITU-T T.35] |
+| 2 | IANA Private enterprise number |
+
+The may be represented in hex or in decimal format. If represented in hex, it has a '0x' prefix. Generally, if the vendor ID format is ITU-T T.35, the hexadecimal format is preferred. If it is the IANA private enterprise number (), the decimal format is preferred.
+
+When the vendor ID format is ITU-T T.35, the vendor ID consists of a country code followed by a vendor code. The country code consists of four octets and the vendor ID consists of two octets. If the representation of the vendor ID is hexadecimal, leading zeros in the country code may be omitted, while leading zeros in the vendor code may not be omitted.
+
+When the is the vendor's private enterprise number, leading zeros may be omitted.
+
+The is a decimal integer between 0-255. If used, values in the range 1-255 are uniquely mapped, via the 'vndpar' attribute, to the combination of the vendor specified in the and the proprietary capabilities indicated by . This mapping, which exists for the duration of a session, does not persist across sessions. Further, each side may choose this integer independently of the other end. Due to the compactness of this index, a gateway or endpoint may use it in a number of places. A value of 0 is a null value. When present, it is equivalent to omitting the . A null value of the is not associated with any vendor ID.
+
+It shall be possible for an endpoint or gateway to declare multiple (1-255) 'vndpar' attribute lines in an SDP session description. Each of these lines may indicate a different vendor. In addition, multiple 'vndpar' lines may indicate the same vendor. When multiple 'vndpar' lines are declared in an SDP session descriptor, each value of must either be unique within all 'vndpar' lines in the session descriptor or null (0). If non-null, the may serve as a dynamically assigned feature identifier for the vendor.
+
+Inclusion of the parameter is optional. When included, this is a vendor-defined octet string consisting of one or more octets. Since it consists of an integer number of octets, it is represented by an even number of hex characters. No '0x' prefix is needed. No size limitation is specified since SDP parsers can ignore another vendor's string without checking its length. A vendor is permitted to add additional structure to the field such that features are identified by their position in this field. A vendor may also elect to add explicit
+
+feature identification within the `` field. When present, these supplement the ``.
+
+Note that the vendor is not precluded from using the `` field to communicate parameters that are not related to ITU-T V.152.
+
+## 7.2 Use of VBD in ITU-T H.323 systems
+
+ITU-T H.323 systems support ITU-T V.152 through the use of the `vBDCapability` capability defined in [ITU-T H.245]. This capability, which is a type of `AudioCapability`, is used during capability exchange and in the open logical channel (OLC) signalling to indicate support for VBD channels and to signal the opening of those channels. Since VBD media flows are generally switched within a single RTP session with normal voice audio and other audio-related media (e.g., [IETF RFC 4733]), OLC proposals and terminal capability set messages generally utilize the multiple payload stream (MPS) constructs in [ITU-T H.245].
+
+### 7.2.1 Fast connect procedures
+
+ITU-T H.323 systems may offer one or more logical channel proposals in the SETUP message transmitted to the called party. The ITU-T H.323 device orders those logical channel proposals in order of preference. This allows an endpoint to indicate its preferred mode of operation and allows the called device to understand what is preferred, but to also accept any alternative modes offered by the calling device.
+
+If the calling device prefers to use VBD for the transport of all voice-band data, including facsimile, text, and modem signalling, the first proposal in the OLC would consist of a non-VBD audio codec and a VBD codec. If the calling endpoint also supports ITU-T T.38 relay over RTP, for example, it might offer as a second proposal a non-VBD audio codec, a VBD codec, and ITU-T T.38. In this way, the called device knows that the calling device prefers to use VBD for all voice-band data, but is also willing to do ITU-T T.38 relay over RTP in the case that the called device has this preference. As with normal Fast Connect procedures, the called device is free to accept any of the alternative proposals or refuse all of them and utilize normal ITU-T H.245 signalling to open logical channels.
+
+Generally, ITU-T H.323 devices would also signal as additional OLC proposals, ones that contain different audio codecs in combination with VBD codecs. Further, devices would also signal alternatives that offered only a non-VBD codec as the choice for media, in the case that the called device does not support this Recommendation. The choice of OLC proposals, the order of proposals, and the selection is a matter of implementation.
+
+ITU-T H.323 devices compliant with this Recommendation may also utilize Extended Fast Connect, which allows devices to renegotiate media streams and to make counter-proposals to those OLCs offered by the remote endpoint. Refer to [b-ITU-T H.460.6] for the procedures related to Extended Fast Connect.
+
+By no means does this Recommendation override the rules defined in [ITU-T H.323] related to Fast Connect procedures or the rules defined in [b-ITU-T H.460.6] for Extended Fast Connect.
+
+### 7.2.2 Exchanging VBD capabilities
+
+Devices specify support for VBD by including capabilities of the type `vBDCapability` in the ITU-T H.245 `TerminalCapabilitySet` message. As with other types of media, these capabilities may be grouped into capability descriptors to signal sets of simultaneous capabilities. Further, since VBD is generally one type of audio that is switched within the same RTP session as other media, `vBDCapability` capabilities are generally only defined as part of a multiple payload stream. However, since a device may wish to open a VBD stream that does nothing more than transmit media as VBD, capabilities may be defined and used outside of an MPS.
+
+### 7.2.3 ITU-T H.245 logical channel signalling procedures
+
+Once ITU-T H.323 devices have exchanged capabilities, they may open logical channels by transmitting open logical channel messages. The procedures for logical channel signalling are defined in [ITU-T H.323] and no additional procedures are defined in this Recommendation.
+
+Since ITU-T H.323 devices operate asynchronously, it is possible that one device may transmit an OLC message offering one set of capabilities, while the peer device transmits an OLC with an incompatible set of capabilities. For example, one device may propose an OLC that suggests the use of {G.729, VBD/G.711, T.38} while the peer device sends an OLC which suggests the use of {G.723.1, VBD/G.726}. Of course, both messages should be independently legal based on the exchanged capabilities. While [ITU-T H.323] permits devices to use different audio codecs in each direction, it may not be preferred. In this case, the fact that one side proposes to use T.38 over RTP and the other side does not is a problem. In all such cases, [ITU-T H.323] specifies that the master shall resolve such conflicts by rejecting the OLC with a reason of **masterSlaveConflict** or other appropriate reason. Devices should not fail as a result, but should converge to a common mode.
+
+Devices should utilize the request mode message in [ITU-T H.245] in order to suggest a compatible mode of operation. Either the master or the slave device may transmit a request mode message. Note, however, that the request may be rejected. Ultimately, the slave device may have no choice, except to use the preferred mode of the master. Even so, the master should honour requests from the slave device when possible.
+
+As an example to illustrate the opening of a media channel in accordance with this Recommendation, consider an OLC that has an ITU-T G.729 voice stream, an ITU-T G.711 A-law VBD stream that is protected with redundancy encoding, an [IETF RFC 4733] stream, and an ITU-T T.38 over RTP stream. The **OpenLogicalChannel** would essentially have a composition similar to what is shown here:
+
+```
+{
+ forwardLogicalChannelNumber 1,
+ forwardLogicalChannelParameters {
+ dataType : multiplePayloadStream {
+ element {
+ dataType : audioData : g729 2
+ },
+ element {
+ dataType : redundancyEncoding {
+ primary {
+ dataType : audioData : vbd : g711Alaw64k 160
+ },
+ secondary {
+ {
+ dataType : audioData : vbd
+ }
+ : g711Alaw64k 160,
+ }
+ },
+ payloadType 101 -- The PT for the RFC 2198 packet
+ },
+ element {
+ dataType : audioData : audioTelephonyEvent {
+ audioTelephoneEvent : "0-15,32,33"
+ },
+ payloadType 102
+ },
+ element {
+ dataType : audioData : genericDataCapability {
+ capabilityIdentifier : standard {
+ itu-t(0) recommendation(0) t(20) 38
+ }
+ }
+ }
+ }
+ }
+}
+```
+
+```
+
+ h245-audio-capability(0)
+ },
+ nonCollapsing {
+ {
+ parameterIdentifier : standard : 0,
+ parameterValue : booleanArray : 0
+ },
+ {
+ parameterIdentifier : standard : 1,
+ parameterValue : unsignedMin : 0
+ },
+ {
+ parameterIdentifier : standard : 2,
+ parameterValue : genericParameter
+ {
+ {
+ parameterIdentifier : standard : 1,
+ parameterValue : logical
+ }
+ }
+ },
+ {
+ parameterIdentifier : standard : 3,
+ parameterValue : unsigned32Max : 200
+ },
+ {
+ parameterIdentifier : standard : 4,
+ parameterValue : unsigned32Max : 72
+ },
+ },
+},
+payloadType 103
+}
+},
+}
+},
+multiplexParameters : h2250LogicalChannelParameters {
+ sessionID 1
+}
+}
+
+```
+
+## 7.3 Mid-call negotiation using session description protocol
+
+There might be the need for mid-call ITU-T V.152 negotiations, if ITU-T V.152 was not negotiated during the call establishment phase and if VBD stimuli were detected in a "mid-call phase".
+
+### 7.3.1 Possible use cases
+
+Example use cases:
+
+- 1) A call is started with negotiated audio VoIP only (neither ITU-T V.152 VBDoIP nor any packet relay mechanism like ITU-T T.38 FoIP was indicated and negotiated);
+- 2) There might be mid-call VBD stimuli detected.
+NOTE – The VBD stimuli detection logic in VoIP gateways may be always enabled, independent of the call-individual negotiation;
+- 3) Any mid-call VBD stimuli detection shall trigger a capability renegotiation (e.g., via SIP re-INVITE);
+- 4) Preferred media configuration may be ITU-T T.38 FoIP (thus, SDP Offer in SIP re-INVITE only contains ITU-T T.38 and no other alternative);
+
+- 5) However, if ITU-T T.38 fails, then ITU-T V.152 VBD over IP may be negotiated in a subsequent SDP Offer/Answer cycle.
+
+### **7.3.2 SIP/SDP mid-call negotiations**
+
+The possibility of the above-mentioned mid-call scenarios should be superseded by the application of Revised SDP Offer/Answer during the call establishment phase. See the advantages listed in clause 7.3.2.2.
+
+#### **7.3.2.1 SIP/SDP mid-call negotiations using Legacy SDP Offer/Answer**
+
+Step 4 in clause 7.3.1 implies at least one negotiation cycle.
+
+Step 5 in clause 7.3.1 implies at least one further negotiation cycle.
+
+#### **7.3.2.2 SIP/SDP mid-call negotiations using Revised SDP Offer/Answer**
+
+The problem of possible mid-call negotiations may be simply addressed by Revised SDP Offer/Answer, because:
+
+- supported media and transport capabilities (here: ITU-T T.38, ITU-T V.152) may be already checked out during the call establishment phase;
+- preferences and alternatives may be indicated and agreed already during the call establishment phase (here: ITU-T T.38 would fail, ITU-T V.152 would be selected for VBD);
+- concept of latent configuration allows to identify a possible, later (i.e., "mid-call") media configuration (here: start with audio, but later VBD stimuli detection will lead to an operational mode change).
+
+Consequently, a possible mid-call change shall be already clarified during the call establishment phase when both gateway entities support Revised SDP Offer/Answer. This obsoletes any SIP signalling (see steps 3 to 5 in clause 7.3.1) due to the autonomous state transitioning capability of ITU-T V.152 gateways.
+
+# **8 The use of IETF RFC 4733 modem/facsimile/text telephone events**
+
+IETF RFC 4733 telephone-events ANS (32), /ANS (33), ANSam (34) and /ANSam (35) can optionally be used as an alternative method for the transport of these signals in audio or VBD packets. If these events are declared by a media gateway, the remote media gateway may use [IETF RFC 4733] to transmit these signals. If both media gateways indicate the support of IETF RFC 4733 telephone-events ANS (32), /ANS (33), ANSam (34) and /ANSam (35), the gateway generating the events shall use [IETF RFC 4733] to transmit these signals. In either case, when [IETF RFC 4733] is used for transporting these signals, the gateways shall suppress the transport of these signals in audio or VBD packets. The amount of in-band signal leakage into the IP network using audio encoding for ANS, ANSam, /ANS, and /ANSam signals shall be less than 50 ms.
+
+IETF RFC 4733 telephone-events ANS (32), /ANS (33), ANSam (34) and /ANSam (35) could be used by the media gateways for the tone disabling ([ITU-T G.168]) of the echo canceller function if provided and enabled in the media gateway and shall be used for the generation of the appropriate signal on the TDM interface. If either end does not indicate this support, then the media gateways shall detect the 2100 Hz tone with phase reversals signal for echo canceller tone disabling on their incoming VBD packet stream.
+
+# 9 VBD stimuli
+
+This clause lists the stimuli that should be detected, per type of application, by a VBD gateway to initiate a transition to the VBD mode of operation, as described in clause 10.
+
+The list of stimuli below is not exhaustive and there may be other tones that can be used to initiate a transition to VBD for the listed applications:
+
+- *For facsimile applications:*
+ - CED as per [ITU-T T.30];
+ - ANSam as per [ITU-T V.8];
+ - Preamble as per clause 5.3.1 of [ITU-T T.30];
+ - CNG as per [ITU-T T.30].
+- *For modem applications:*
+ - ANS as per [ITU-T V.8];
+ - ANSam as per [ITU-T V.8];
+ - 2225 Hz answer tone as per Appendix VI of [ITU-T V.150.1];
+ - Unscrambled binary ones signal as per [b-ITU-T V.22];
+ - CI signals that precede ANSam, as per [ITU-T V.8];
+ - Initiating Segment 1 dual tones (1375 Hz and 2002 Hz) as per [b-ITU-T V.8bis].
+- *For text telephony applications:*
+ - ANS as per [ITU-T V.8];
+ - ANSam as per [ITU-T V.8];
+ - Text telephone signals as defined by clause 5.1.1 of [ITU-T V.18];
+ - DTMF signals only if [IETF RFC 4733] telephone-events are not supported;
+ - CI signals that precede ANSam, as per [ITU-T V.8];
+ - Calling tone (CT) signals that precede ANS, as per [b-ITU-T V.25];
+ - Initiating Segment 1 dual tones (1375 Hz and 2002 Hz) as per [b-ITU-T V.8bis].
+
+In addition to the above list, if any other unrecognized tonal non-voice signal is detected, this may be used to transition into VBD mode.
+
+VBD gateways should keep signal leakage to a minimum to prevent erroneous behaviour of end terminals.
+
+# 10 Procedures for transitioning between audio mode and VBD mode
+
+This clause describes the transitioning mechanism for an implementation that only supports VBD as per this Recommendation and voice, but does not support any relay mechanisms such as ITU-T T.38 or ITU-T V.150.1, nor VBD as per [ITU-T V.150.1].
+
+The mechanism described in this clause shall be the default mandatory mechanism used by ITU-T V.152-compliant gateways if no other mechanisms have been successfully negotiated between the gateways, otherwise the mutually negotiated mechanism (such as those described in clause 11) shall be used in preference to this method.
+
+## 10.1 Procedures for state transitioning
+
+### 10.1.1 Audio-to-VBD transition
+
+The transition from audio mode to VBD mode is performed when the VBD detectors classify an input signal as VBD.
+
+Detection of the stimuli described in clause 9 shall be carried out at least in the direction from the GSTN to the IP network; however, detection in the direction from the IP network to the GSTN network is not precluded. The bidirectional VBD stimuli detection capability of a VBD gateway improves the probability of correct and timely gateway local state transition, which offers a more robust VBD service and state transition.
+
+On detection of any of the stimuli described in clause 9, if the corresponding IETF RFC 4733 telephone-event has not been mutually negotiated, a ITU-T V.152 implementation must transmit them as in-band VBD packets.
+
+If the ITU-T V.8 CI and the ITU-T V.8*bis* signals are transmitted in-band rather than as IETF RFC 4733 events, a shift to VBD must not lose any part of the signals. The choice of using in-band indication or IETF RFC 4733 for indicating these signals is dependent upon capability declaration, whether a VBD channel is available, and the preference of the transmitter.
+
+When in the VBD media state, a media gateway may use [IETF RFC 4733] in lieu of voice-band transmission to communicate to the remote gateway any of the voice-band data stimuli indicated in clause 9.
+
+The use of [IETF RFC 4733] in this case is contingent on the capabilities declared by the remote gateway.
+
+When in the VBD media state, the unscrambled binary ones signal is communicated in-band. There is no [IETF RFC 4733] support for this signal.
+
+When in the VBD media state, the text telephone signals are communicated in-band. The media gateway shall not lose any characters at the onset of in-band VBD transmission.
+
+The gateway shall suppress a voice-band data stimulus from the bearer path if it intends to convey the stimulus as an IETF RFC 4733 telephone event. This shall be done immediately on detection of the stimulus. A media gateway knows, prior to the detection of a voice-band data stimulus, whether it will transmit the stimulus in-band or via an IETF RFC 4733 telephone event. This knowledge is based on the remote gateway's capabilities (whether it can receive an IETF RFC 4733 encoding of that stimulus) and the local gateway's own choice (since it may use in-band transmission regardless of the remote gateway's capability declaration).
+
+Once VBD has been mutually negotiated by the two gateways, using the procedures described in clause 7, a gateway that complies with this Recommendation shall be able to receive and appropriately decode, from the IP network, RTP packets with any of the supported negotiated payload types for a particular call. Hence, an ITU-T V.152 implementation shall transition from voice to VBD on receipt of an RTP packet that has the negotiated VBD payload type.
+
+Additionally, gateways may optimize operation by doing one of the following:
+
+- Loading both the audio and VBD codecs to streamline quick, on-the-fly transitions between talkspurts and textspurts.
+- Staying in the VBD mode across talkspurts and textspurts.
+
+Thus, on detection, in the direction from the GSTN to IP network of the appropriate VBD signals, a VBD gateway shall transition to VBD and transmit as soon as possible RTP packets with the corresponding negotiated VBD payload type. Reception of an RTP packet that has the pre-negotiated VBD payload type at the remote end shall cause a VBD gateway to transition to VBD mode, but only if, prior to receiving the VBD RTP packet, it received RTP packets that correspond to the state it was previously in (e.g., voice packets). The reason for the latter rule is explained below:
+
+Consider two VBD gateways, termed A and B, connected via an IP network and each having a GSTN network on their other sides. There will be a period during a call when both VBD gateways are in VBD mode. Gateway A transitions into audio mode due to detection of voice signals in the direction from the GSTN to the IP network, which will cause it to transition into voice and transmit voice RTP packets. While the first transmitted voice RTP packet is traversing the IP network, the remote end (gateway B) is still transmitting VBD RTP packets, because it has not detected anything on its GSTN side, nor has it yet received the voice RTP packets. To avoid gateway A from transitioning erroneously back into VBD mode, it must not transition back to VBD until it has first received (the pre-negotiated) voice RTP packets, which it should expect to receive due to it (i.e., gateway A) transitioning into voice.
+
+NOTE – An implementation shall be able to handle out-of-order RTP packets (e.g., a voice packet followed by a VBD packet that was actually sent before the voice packet).
+
+### **10.1.2 VBD-to-audio transition**
+
+Transition from VBD to voice may be carried out by detection:
+
+- In the direction from the GSTN to IP network of any of the following stimuli:
+ - end of modem or facsimile signals;
+ - voice signals;
+ - detection in both directions, GSTN to IP and IP to GSTN, of silence. With the following caveats:
+ - For text telephones, the appropriate detection of silence must be considered because text telephone conversations may have long periods of silence.
+ - For the case of facsimile calls, the silence period should be greater than the T2 timer defined in [ITU-T T.30].
+ - MGC signalling or other out-of-band signalling methods.
+- In the direction from IP to GSTN network due to receipt of RTP packets that have non-VBD payload types, only after the first VBD RTP packet has been received. This will avoid the situation of an incorrect transition into audio mode when it has transitioned to VBD mode on detection of VBD signals on its TDM side and is still receiving voice RTP packets (because the remote end has not yet transitioned, based on reception of the VBD RTP packets).
+
+## 10.2 State machine – Overview
+
+The above described transition criteria are also summarized in Figure 9.
+
+
+
+```
+graph LR;
+ AUDIO((AUDIO mode)) -- "Detection VBD signals" --> VBD((VBD mode));
+ VBD -- "VBD RTP packet and previous RTP packets were voice RTP packets" --> AUDIO;
+ AUDIO -- "Bidirectional silence" --> VBD;
+ VBD -- "TDM voice or TDM end-of-modem signal" --> AUDIO;
+ AUDIO -- "Voice RTP packets and previous RTP packets were VBD RTP packets" --> VBD;
+ VBD -- "MGC signalling or other out-of-band signalling" --> AUDIO;
+```
+
+Figure 9 – Voice-VBD transitioning state diagram. A state machine diagram with two states: AUDIO mode and VBD mode. Transitions are as follows: AUDIO to VBD: 'Detection VBD signals'; VBD to AUDIO: 'VBD RTP packet and previous RTP packets were voice RTP packets'; AUDIO to VBD: 'Bidirectional silence'; VBD to AUDIO: 'TDM voice or TDM end-of-modem signal'; AUDIO to VBD: 'Voice RTP packets and previous RTP packets were VBD RTP packets'; VBD to AUDIO: 'MGC signalling or other out-of-band signalling'. Reference: V.152(10)\_F9.
+
+Figure 9 – Voice-VBD transitioning state diagram
+
+## 10.3 Enforced state transition by call/session control
+
+The call/session control may enforce state transitioning based on detected VBD stimuli in the bearer-path, which are reported to the call control, or the media capability negotiation during call establishment or modification, or other policies (like, e.g., preferred media formats of a service provider). This capability is indicated by the arrow "*MGC signalling or ...*" in Figure 9.
+
+Procedures for such transitioning behaviour would be dependent on the specific applied signalling protocols (e.g., ITU-T H.323, SIP, ITU-T H.248, etc.), which are therefore beyond the scope of this Recommendation.
+
+# 11 Optional procedures for indicating to a remote end transition into VBD using state signalling events
+
+This clause describes the procedures that an ITU-T V.152 implementation must use when using the state signalling event protocol as defined in Annexes C, E and F of [ITU-T V.150.1].
+
+Note that the use of SSE is optional for ITU-T V.152 implementation and subject to negotiation with the remote gateway. When one or both of the two gateways does not support SSE operation, then transitions to and from the VBD mode shall be governed by the procedures defined in clause 10.
+
+## 11.1 Declaration of SSEs
+
+The SSE capability shall be signalled as defined in clause F.6 of [ITU-T V.150.1]. The minimum set of state signalling events that shall be supported for VBD operation are events 0 through 3 which are basic to the SSE protocol. The null SSE event (0) shall never be sent and should be ignored if received.
+
+## 11.2 Transition to the VBD mode for ITU-T V.150.1 gateways
+
+When both gateways support [ITU-T V.150.1], then transitions to and from the VBD mode is governed by ITU-T V.150.1 procedures. These transitions are synchronized via the SSE protocol.
+
+## 11.3 Transition to the VBD mode for non- ITU-T V.150 cases
+
+When one or both of the two gateways does not support ITU-T V.150.1 operation, then transitions to and from the VBD mode shall be governed by the procedures in this clause. An attempt shall be made to make these procedures isomorphic to ITU-T V.150.1 procedures so that media gateways do not incur the burden of supporting and testing multiple VBD switching mechanisms.
+
+An ITU-T V.152-compliant media gateway that has successfully negotiated support of SSE media gateway shall respond to a voice-band data stimulus by immediately transitioning the connection to the VBD media state and issuing an SSE indicating this state (see clause C.5.2 of [ITU-T V.150.1]). As with all other media state transitions, this is contingent on resource availability. On making this transition locally, the stimulus-detecting media gateway may start sending VBD packets immediately.
+
+On receiving an SSE indicating the VBD media state (SSE:VBD), a media gateway shall immediately transition the connection to the VBD media state if it has the resources to do so. Before making this transition, it may ignore any in-band VBD packets it receives (see clause 20.4 of [ITU-T V.150.1]).
+
+The transition to a VBD media state in response to detecting a voice-band data stimulus (such as an answer tone variant) is illustrated in Figure 10. In this example, the on-ramp (call-originating) gateway G1 and the off-ramp (call-terminating) gateway G2 support VBD operation.
+
+On detecting a voice-band data stimulus, gateway G2 determines whether it has the resources to transition the session to the VBD media state. If it does, then it immediately makes the transition and sends SSE:VBD (event code 2) to gateway G1. While in the VBD media state, it uses an RTP payload type marked for VBD treatment.
+
+On receiving SSE:VBD, gateway G1 determines whether it has the resources to transition the session to the VBD media state. If it does, then it immediately makes the transition and sends an SSE:VBD back to gateway G2, confirming that its media state has changed to VBD. If it does not, then it sends an SSE:audio (event code 1) on receiving a SSE:VBD from G2.
+
+
+
+```
+sequenceDiagram
+ participant G1 as On-ramp gateway (G1)
+ participant G2 as Off-ramp gateway (G2)
+ Note over G1: G1 in initial audio mode
+ Note over G2: G2 in initial audio mode
+ Note over G2: VBD stimulus detected
+ Note over G2: Transition to VBD mode
+ G2->>G1: SSE: VBD
+ Note over G1: Transition to VBD mode
+ G1->>G2: SSE: VBD
+```
+
+The diagram shows the interaction between two gateways, G1 (On-ramp) and G2 (Off-ramp). G1 starts in 'initial audio mode'. G2 starts in 'initial audio mode', detects a 'VBD stimulus', and transitions to 'VBD mode'. G2 then sends an 'SSE: VBD' message to G1. Upon receiving this message, G1 transitions to 'VBD mode' and sends an 'SSE: VBD' message back to G2. The diagram is labeled V.152(10)\_F10.
+
+Sequence diagram illustrating the initiation of VBD operation in response to VBD stimulus detection between On-ramp gateway (G1) and Off-ramp gateway (G2).
+
+**Figure 10 – Initiation of VBD operation in response to VBD stimulus detection**
+
+When sending SSE:VBD, gateways G1 and G2 may use suitable reason information codes (RICs) defined in [ITU-T V.150.1]. An example is the RIC indicating an answer tone. A null code, which conveys no information, may also be used. The SSE:VBD from G1 may indicate a p' state transition as the reason information code. Since p' is defined as a gateway's view of the other gateway's protocol state, this indicates that this SSE from G1 is a response to a received SSE.
+
+Distinctions based on RIC codes (ITU-T V.8 versus non- ITU-T V.8, text vs. non-text) may be used to optimize play-out buffer settings and FEC levels for different applications of VBD. Additionally, when the RIC indicates text, gateways may optimize operation by doing one of the following:
+
+- Loading both the audio and VBD codecs to streamline quick, on-the-fly transitions between talkspurts and textspurts.
+- Staying in the VBD mode across talkspurts and textspurts.
+
+## **11.4 Transition from the VBD media mode**
+
+On detecting a termination of data transmission, media gateways shall locally transition the connection to the audio mode and issue an SSE:audio (Initial audio SSE, event code 1) to the remote gateway. If it receives an SSE:audio, it shall change the media state to initial audio and respond back with an SSE:audio.
+
+The criteria for determining the termination of data transmission are application-specific and are not defined here. Examples of such criteria are the detection of voice or of pre-determined intervals of silence. A transition to the modem, fax or text media states is not a termination of data transmission.
+
+By declaring support of the SSE protocol, gateways implicitly declare support for events 1-3 which are basic to the protocol. In order to be used, support for other SSEs such as SSE:FR (Facsimile relay SSE, event code 4) and SSE:TR (Text relay SSE, event code 5) shall be explicitly declared.
+
+Transitions from the VBD media state to the MR (modem relay), FR (facsimile relay) and TR (text relay) states are permitted. These media state transitions are contingent on:
+
+- 1) Declaration of the applicable capabilities at call establishment.
+- 2) Availability of resources at the time of the state transition.
+
+In the modem relay case, these are synchronized using SSE:MR (Modem relay SSE, event code 3) per [ITU-T V.150.1].
+
+SSE:TR (Text relay SSE, event code 5) is recommended to synchronize media shifts from VBD to the text relay mode, and vice versa. For example, when ITU-T V.21 signals are followed by Annex A of [ITU-T V.18] signals in end-to-end ITU-T V.18 automodring, there may be a shift to VBD based on the ANS preceding [ITU-T V.21], and possibly another shift to TR if the gateway does not support VBD for Annex A of [ITU-T V.18].
+
+For autonomous media shifts from VBD to facsimile relay, two cases arise from [ITU-T T.38]:
+
+- 1) For gateways that comply with [ITU-T V.150.1] and Annex F of [ITU-T T.38], SSE:FR is used. Both single-port and multi-port operation is supported.
+- 2) For all other gateways, port activity monitoring is used. Note that single-port operation for audio RTP and ITU-T T.38 udptl packets is not supported; however, single-port operation may be used if audio RTP and the optional ITU-T T.38 RTP procedure are being used.
+
+Since facsimile switchovers are tolerant in terms of signal timing, external signalling can be used in lieu of the autonomous VBD-to-FR media shifts described in the last paragraph. Examples of external signalling are SIP re-invites, ITU-T H.245 RequestMode/CLC/OLC and ITU-T H.248.1 context modification. End-to-end timing issues that often jeopardize the use of external signalling with modem traffic do not exist for facsimile traffic.
+
+For a session that is in the VBD media state, a gateway may reject SSE:MR, SSE:FR or SSE:TR with an SSE:VBD or SSE:audio. If used, SSE:audio causes a transitioning of the session to an audio mode.
+
+The SSE reason identifier codes for VBD mode are defined in Table 12 of [ITU-T V.150.1].
+
+
+
+Sequence diagram for ITU-T V.18 text telephone using VBD. The diagram shows four lifelines: T1, G1, G2, and T2. T1 and T2 are endpoints (A), while G1 and G2 are gateways (A, T, V). T1 sends 'V8-CM = V.18' to G1. G1 sends 'SSE:TR(RC = 37)' to G2. G2 sends 'SSE:VBD(RC = 37)' to G1. G1 sends 'SSE:VBD(ack)' to G2. T2 sends 'ANSam' to G2. A long 'VBD' arrow spans from T1 to T2. Reference: V.152(10)\_F11
+
+**Figure 11 – ITU-T V.18 text telephone using VBD**
+
+
+
+Sequence diagram for ITU-T V.34 modem using VBD. The diagram shows four lifelines: M1, G1, G2, and M2. M1 and M2 are endpoints (A), while G1 and G2 are gateways (A, T, V). M1 sends 'ANSam' to G1. G1 sends 'SSE:TR(RC = 22)' to G2. G2 sends 'SSE:VBD(RC = 22)' to G1. G1 sends 'SSE:VBD(ack)' to G2. M2 sends 'ANSam' to G2. A long 'VBD' arrow spans from M1 to M2. Reference: V.152(10)\_F12
+
+**Figure 12 – ITU-T V.34 modem using VBD**
+
+
+
+Sequence diagram for Group 3 facsimile (without CNG/CED tones) using VBD. The diagram shows four lifelines: F1, G1, G2, and F2. F1 and F2 are endpoints (A), while G1 and G2 are gateways (A, T, V). F1 sends 'V.21(H) Flags' to G1. G1 sends 'SSE:TR(RC = 13)' to G2. G2 sends 'SSE:VBD(RC = 13)' to G1. G1 sends 'SSE:VBD(ack)' to G2. F2 sends 'V.21 (H) Flags' to G2. A long 'VBD' arrow spans from F1 to F2. Reference: V.152(10)\_F13
+
+**Figure 13 – Group 3 facsimile (without CNG/CED tones) using VBD**
+
+## **11.5 Security – Optional**
+
+When the VBD mode is used to transport data payloads, it lends itself easily to secure, encrypted operation based on SRTP (Secure RTP). Support of security features is not required by ITU-T V.152 compliant implementations and is negotiated at call establishment.
+
+Based on declarations at the time of session establishment, it is possible to encrypt some RTP payload types (e.g., voice, VBD and IETF RFC 4733 events), while passing other RTP payload types (e.g., SSEs) unencrypted. Such selective encryption will allow fast response times to SSEs, without compromising the security of media sourced by the end-user. When one end proposes encrypted operation for a set of payload formats, and the other end does not support encryption, the preferred outcome is a rejection of the proposal and termination of the connection attempt. At this point, either the on-ramp or off-ramp media gateway or media gateway controller can counter-propose a non-encrypted connection through the call signalling protocol(s) in use.
+
+# **Annex A**
+
+## **Vendor-defined messages**
+
+(This annex forms an integral part of this Recommendation.)
+
+Vendor-specific messages may be supported within ITU-T V.152, subject to negotiation with the remote end. In general, an ITU-T V.152 implementation may support up to 255 vendor identifiers (vendor-ID) for a given call. Each vendor-ID may be unique or specific and tied to either a single or multiple sets of attributes. A unique vendor-Tag may also be assigned to each set of attributes associated with a vendor-ID to allow simpler use within ITU-T V.152.
+
+Usually the vendor-ID is provided during the external signalling used during the call set-up (i.e., ITU-T H.245, ITU-T H.248 or SDP, etc.). The format used in signalling schemes may be compliant to either [ITU-T T.35] or the IANA private enterprise number. The choice is up to the vendor.
+
+When the vendor-ID format is ITU-T T.35, the vendor-ID consists of a country code followed by a vendor code. The country code consists of four octets and the vendor-ID consists of two octets. If the representation of the vendor-ID is hexadecimal, leading zeros in the country code may be omitted, while leading zeros in the vendor code may not be omitted.
+
+When the vendor-ID is the vendor's IANA private enterprise number, leading zeros may be omitted.
+
+The vendor-Tag is a decimal integer with a value between 0 and 255. If used, values in the range of 1 to 255 are uniquely mapped to the combination of vendor-ID and vendor-specific information. The choice of this integer made by a gateway is independent of the choice made by its peer gateway. Due to the compactness of this index, a gateway or endpoint may use it in a number of places to simplify the messaging. A value of zero for the vendor-Tag is a null value. When present, it is equivalent to omitting the vendor-Tag. A null value of the vendor-Tag is not associated with any vendor-ID. If non-null, the vendor-Tag may serve as a dynamically assigned vendor-specific identifier.
+
+The vendor-specific information is an octet string consisting of one or more octets as defined by the vendor. Since it consists of an integer number of octets, it is represented by an even number of hex characters. No "0x" prefix is needed. Limitation on size is context specific. Details where size is limited will be indicated appropriately.
+
+# Annex B
+
+## Use of data signal detection and silence insertion in voiceband data
+
+(This annex forms an integral part of this Recommendation.)
+
+### B.1 Introduction
+
+Data signal detector (DSD) and silence insertion in VBD mode is a technique that reduces the transmission bandwidth over IP networks by inserting silence indicator descriptors during the silence periods of a voiceband data modem connection. This is especially efficient for half-duplex data transmissions. This annex provides guidance on DSD and silence insertion for gateways compliant to this Recommendation.
+
+## B.2 Guideline for the use of DSD
+
+When in the VBD state, a data signal detector monitors and analyses the voiceband analogue input signals. The data signal detector categorizes the analysed signal to be either a correct voiceband modem signal or silence. The means of determining this signal categorization is implementation specific and this Recommendation does not describe any particular method in detail. However, an example is: once in the VBD state, a gateway may monitor the signal energy level (this is the same signal as used for driving ITU-T V.24 Circuit 109) and use that for determining the presence of silence. In this instance, echo levels must be accounted for in the analysis process.
+
+Most modem procedures include a short silence between different training and data mode phases. These vary from $70 \pm 5$ ms for [ITU-T T.30] to $75 \pm 5$ ms for high speed duplex data modems. In these instances, it is important to maintain the fidelity of these short silence periods. A DSD detector shall use a silence validation time greater than 80 ms.
+
+Upon the qualified detection of silence, the gateway transmits a silence insertion description (SID) frame to inform the peer gateway of the beginning of the silence period. The SID frame format shall be that specified for use with the selected VBD codec. For example if ITU-T G.711 is the codec being used, then the SID format shall comply with Appendix II of [ITU-T G.711].
+
+In the SID frame, the level field is set to zero and the N1~Nm fields are set to zero. Only an initial SID frame needs to be transmitted per silence period.
+
+The receiving gateway upon receiving a SID frame or packet shall play out the SID frame zero level data as silence. The level of the transmitted analogue silence shall be less than -55 dBm. The receiving gateway shall continue to play out silence until it receives a valid VBD data packet.
+
+To ensure that the signal can be detected at the receiver side, the maximum response time for a DSD detector to detect the silence to data transition should be less than 1.5 ms. The transmitting gateway shall detect the presence of a voiceband signal and transmit a valid VBD packet without delay.
+
+## B.3 Negotiation of the DSD capability with SDP
+
+Gateways shall mutually negotiate the capability of DSD. Clause 7.1 explains the detailed procedure for negotiation using SDP. The DSD negotiation shall comply with the procedures described in clause 7.1, and use two a-line attributes to indicate support of DSD capability.
+
+If VBD MGW supports DSD capability, the SDP attribute should indicate:
+
+```
+m=audio 3456 RTP/AVP 0 18 98 99
+a=rtpmap:98 PCMA/8000
+a=gpmd:98 vbd=yes
+a=rtpmap:99 CN/8000
+a=gpmd:99 dsd=yes
+```
+
+"a=gpmid:99 dsd=yes" indicates that the device supports the DSD capability; "a=rtpmap:99 CN/8000" shows that the device sends SID frame with payload type 99. If mutually negotiated, both gateways can use the DSD procedures described in this annex.
+
+If a VBD MGW does not support DSD capability, the SDP attribute should indicate:
+
+```
+m=audio 3456 RTP/AVP 0 18 98 99
+a=rtpmap:98 PCMA/8000
+a=gpmid:98 vbd=yes
+a=rtpmap:99 CN/8000
+a=gpmid:99 dsd=no
+```
+
+"a=gpmid:99 dsd=no" indicates that the device does not support or does not want to use DSD.
+
+To maintain compatibility with gateways using a previous version of this Recommendation that would not support DSD capability, the absence of the gpmid attribute for DSD is interpreted to be the same as "dsd=no" capability.
+
+### B.4 Negotiation of the DSD capability with [ITU-T H.245]
+
+Clause 7.2 explains the use of VBD in ITU-T H.323 systems. ITU-T H.323 systems support ITU-T V.152 through the use of the **VBDCapability** capability defined in [ITU-T H.245]. This capability, which is a type of **AudioCapability**, is used during capability exchange and in the open logical channel (OLC) signalling to indicate support for VBD channels and to signal the opening of those channels. An extension to the **VBDCapability** is needed to indicate the DSD capability.
+
+```
+VBDCapability ::=SEQUENCE
+{
+ type AudioCapability, -- shall not be "vbd"
+ dsd BOOLEAN
+ ...
+}
+```
+
+If VBD MGW supports DSD capability, the dsd attribute should indicate "TRUE". If a VBD MGW does not support the DSD capability, the dsd attribute should indicate "FALSE". The absence of the dsd attribute for DSD is interpreted as no support for the DSD capability.
+
+# Annex C
+
+## Use of ITU-T V.21 preamble for echo canceller control in an ITU-T V.152 gateway
+
+(This annex forms an integral part of this Recommendation.)
+
+For the scenario where an ITU-T V.34 facsimile terminal is being called by a standard G3 facsimile terminal, the procedures defined in [ITU-T T.30] stipulate that the connection proceeds as a standard G3 facsimile. Also, [ITU-T T.30] recommends that the ITU-T V.34 facsimile terminal should transmit an ITU-T V.8 answer tone with phase reversals, thereby tone disabling any gateway echo cancellers in the connection. In this situation, the gateway echo cancellers will be left in the disabled state when proceeding into ITU-T T.30 standard G3 modes. This has a direct impact upon the performance of standard G3 facsimile terminals as described in [ITU-T G.168] and [b-ITU-T G.161], which require that echo cancellers be in their initial cancelling state in order to provide the best conditions for a facsimile transmission.
+
+[ITU-T T.30] (2006) was updated to correct this situation and defines how the ITU-T T.30 procedures will allow for the re-enabling of echo cancellers to their initial cancelling state. However, this particular scenario remains an issue to be considered as there are many millions of facsimile terminals that do not support the 2006 version of [ITU-T T.30].
+
+This annex describes a method that may be used to rectify this condition in gateways compliant to this Recommendation. This method consists in using the detected presence of the V.21High Channel HDLC encoded FLAG preamble as defined in [ITU-T T.30] to initiate a transition from the tone disabled state back to the initial cancelling state. Once the echo canceller has returned to its initial state, the standard G3 facsimile procedure will operate as intended. (See Figure C.1.)
+
+
+
+The diagram illustrates the sequence of events and echo canceller (EC) status transitions during a fax call setup between a standard G3 sending terminal and a V.34 receiving terminal, passing through two gateways (A and B).
+
+**Entities:**
+
+- Sending facsimile (standard G3)**
+- EC status in gateway A**
+- EC status in gateway B**
+- Receiving facsimile (V.34)**
+
+**Sequence of Events and States:**
+
+- Initial State:** Both Gateway A and Gateway B are in the *Initial cancelling state*.
+- Voice mode:** CNG signal is sent from Sending facsimile to Receiving facsimile.
+- Signal:** /ANSam is sent from Receiving facsimile to Sending facsimile.
+- Transition:** G.168 EC may enter tone disabled state.
+- Disabled State:** Both Gateway A and Gateway B enter the *Tone disabled state*.
+- Signal:** V.21 preamble\DIS is sent from Receiving facsimile to Sending facsimile.
+- Detection & Recovery:**
+ - Gateway A: Detects V.21 Preamble and returns to EC initial cancelling state.
+ - Gateway B: May detect packet side V.21 preamble and return EC to initial cancelling state.
+- Final State:** Both gateways return to *Initial cancelling state*.
+- Signal:** V.21 preamble\DIS is sent from Sending facsimile to Receiving facsimile.
+
+V.152(10)\_FC.1
+
+Sequence diagram showing the fax procedure and echo canceller status after enabling by ITU-T V.21 preamble. The diagram involves four entities: Sending facsimile (standard G3), EC status in gateway A, EC status in gateway B, and Receiving facsimile (V.34).
+
+**Figure C.1 – Fax procedure and echo canceller status after enabling by ITU-T V.21 preamble**
+
+### **Gateway to echo canceller signalling**
+
+This procedure is only valid for media gateways compliant to this Recommendation. Note that in this application, echo cancellers may be embedded within the media gateway or be external to it. The signalling of the gateway to the echo canceller can be via proprietary means if it is an embedded type in the gateway, or by some standardized means if connected to an external echo canceller. The means definition of external echo canceller control is for further study.
+
+# Bibliography
+
+- [b-ITU-T F.700] Recommendation ITU-T F.700 (2000), *Framework Recommendation for multimedia services*.
+- [b-ITU-T G.161] Recommendation ITU-T G.161 (2004), *Interaction aspects of signal processing network equipment*.
+- [b-ITU-T H.460.6] Recommendation ITU-T H.460.6 (2002), *Extended Fast Connect feature*.
+- [b-ITU-T J.171] Recommendation ITU-T J.171 (2002), *IP-Cablecom Trunking Gateway Control Protocol (TGCP)*.
+- [b-ITU-T V.8bis] Recommendation ITU-T V.8bis (2000), *Procedures for the identification and selection of common modes of operation between data circuit-terminating equipments (DCEs) and between data terminal equipments (DTEs) over the public switched telephone network and on leased point-to-point telephone-type circuits*.
+- [b-ITU-T V.22] Recommendation ITU-T V.22 (1988), *1200 bits per second duplex modem standardized for use in the general switched telephone network and on point-to-point 2-wire leased telephone-type circuits*.
+- [b-ITU-T V.24] Recommendation ITU-T V.24 (2000), *List of definitions for interchange circuits between data terminal equipment (DTE) and data circuit-terminating equipment (DCE)*.
+- [b-ITU-T V.25] Recommendation ITU-T V.25 (1996), *Automatic answering equipment and general procedures for automatic calling equipment on the general switched telephone network including procedures for disabling of echo control devices for both manually and automatically established calls*.
+- [b-ITU-T V.150.0] Recommendation ITU-T V.150.0 (2003), *Modem-over-IP networks: Foundation*.
+- [b-IETF RFC 2234] IETF RFC 2234 (1997), *Augmented BNF for Syntax Specifications: ABNF*.
+- [b-IETF RFC 3711] IETF RFC 3711 (2004), *The Secure Real-time Transport Protocol (SRTP)*.
+- [b-IETF RFC 5939] IETF RFC 5939 (2010), *SDP Capability Negotiation*.
+- [b-IETF Draft MediaCapNeg] draft-ietf-mmusic-sdp-media-capabilities, *SDP media capabilities Negotiation*.
+
+
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+| | |
+|-----------------|---------------------------------------------------------------------------------------------|
+| Series A | Organization of the work of ITU-T |
+| Series D | General tariff principles |
+| Series E | Overall network operation, telephone service, service operation and human factors |
+| Series F | Non-telephone telecommunication services |
+| Series G | Transmission systems and media, digital systems and networks |
+| Series H | Audiovisual and multimedia systems |
+| Series I | Integrated services digital network |
+| Series J | Cable networks and transmission of television, sound programme and other multimedia signals |
+| Series K | Protection against interference |
+| Series L | Construction, installation and protection of cables and other elements of outside plant |
+| Series M | Telecommunication management, including TMN and network maintenance |
+| Series N | Maintenance: international sound programme and television transmission circuits |
+| Series O | Specifications of measuring equipment |
+| Series P | Terminals and subjective and objective assessment methods |
+| Series Q | Switching and signalling |
+| Series R | Telegraph transmission |
+| Series S | Telegraph services terminal equipment |
+| Series T | Terminals for telematic services |
+| Series U | Telegraph switching |
+| Series V | Data communication over the telephone network |
+| Series X | Data networks, open system communications and security |
+| Series Y | Global information infrastructure, Internet protocol aspects and next-generation networks |
+| Series Z | Languages and general software aspects for telecommunication systems |
\ No newline at end of file
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+
+
+I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n
+
+# ITU-T
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+# V.153
+
+(12/2009)
+
+SERIES V: DATA COMMUNICATION OVER THE
+TELEPHONE NETWORK
+
+Interworking with other networks
+
+---
+
+**Interworking between ITU-T T.38 and
+ITU-T V.152 using IP peering for real-time
+facsimile services**
+
+Recommendation ITU-T V.153
+
+
+
+The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features a blue globe with a red lightning bolt striking it, and the text "ITU" in blue, with "International Telecommunication Union" in smaller blue text below it.
+
+ITU logo
+
+# ITU-T V-SERIES RECOMMENDATIONS **DATA COMMUNICATION OVER THE TELEPHONE NETWORK**
+
+| | |
+|-------------------------------------------------------|--------------------|
+| General | V.1–V.9 |
+| Interfaces and voiceband modems | V.10–V.34 |
+| Wideband modems | V.35–V.39 |
+| Error control | V.40–V.49 |
+| Transmission quality and maintenance | V.50–V.59 |
+| Simultaneous transmission of data and other signals | V.60–V.99 |
+| Interworking with other networks | V.100–V.199 |
+| Interface layer specifications for data communication | V.200–V.249 |
+| Control procedures | V.250–V.299 |
+| Modems on digital circuits | V.300–V.399 |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+# **Recommendation ITU-T V.153**
+
+# **Interworking between ITU-T T.38 and ITU-T V.152 using IP peering for real-time facsimile services**
+
+## **Summary**
+
+Recommendation ITU-T V.153 defines service interworking between two IP domains, whereby one IP domain is using voiceband data over IP (VBDoIP) transport according to Recommendation ITU-T V.152 and the other IP domain is using facsimile relay over IP (FoIP) transport according to Recommendation ITU-T T.38. Two modes of operation are specified for the T.38-to-V.152 interworking function: native versus emulated interworking.
+
+The T.38-to-V.152 interworking technology is subject of the user plane and typically located in IP-to-IP gateway equipment, like border routers or border gateways.
+
+## **History**
+
+| Edition | Recommendation | Approval | Study Group |
+|---------|----------------|------------|-------------|
+| 1.0 | ITU-T V.153 | 2009-12-14 | 16 |
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at 1) Request (MGC to MG): MEGACO/2 [11.9.19.65] ... Add = ip/2/\$/\$ { ; IP "V.152" Termination Media { Stream = 1 { ; there is just one Stream per Term. LocalControl{ ipdc/realn = "providerX.com" ; IP network indication (here "V.152 domain") Mode=SendReceive, ReservedGroup = OFF, ReservedValue = OFF ; because just single ; audio codec }, Local{ v=0 c=IN IP4 \$ m=audio \$ RTP/AVP 8 101 111 a=maxptime:20 - 30 a=rtpmap:101 telephone-event/8000 ; RFC 4733/4 a=rtpmap:111 PCMA/8000 ; ITU-T V.152 a=gpmid:111 vbd=yes }, Remote{ ; Remote descriptor might also be sent in ; a later Modify request v=0 c=IN IP4 19.70.3.2 m=audio 54530 RTP/AVP 8 101 111 a=maxptime:20 - 30 a=rtpmap:101 telephone-event/8000 ; RFC 4733/4 a=rtpmap:111 PCMA/8000 ; ITU-T V.152 a=gpmid:111 vbd=yes } }, Events = 1234 {ctyp/dtone} ; MGC requests H.248.2 ; ctyp/dtone event ; notification }, Add = ip/8/\$/\$ { ; IP "T.38" Termination Media { Stream = 1 { ; there is just one Stream per Term. LocalControl{ ipdc/realn = "providerY.com" ; IP network indication (here "T.38 domain") Mode=SendReceive, ReservedGroup = OFF, ; one media group ReservedValue = OFF ; just one audio codec, might ; also be ON in case two or ; audio codecs are requested ; in 'audio' media descr. }, Local{ v=0 ; Single Media Group "audio flow" c=IN IP4 \$ ... m=audio \$ RTP/AVP 8 127 a=rtpmap:127 telephone-event/8000 a=ptime:20 }, Remote{ v=0 ; Single Media Group "audio flow" c=IN IP4 12.9.19.65 ... m=audio 100 RTP/AVP 8 127 a=rtpmap:127 telephone-event/8000 a=ptime:20 } }, }, } | IP "V.152" termination:
In this example, the MGC requests (from the local MG) a PCMA audio codec with telephone-events and a PCMA VBD codec. The Reserve property values are false due to single group and single "media format" for Stream 1 (NOTE – RFC 4733/4734 and V.152 are supplementary media formats with regard to the audio format, see clause 7.1.7.1.3 of [ITU-T H.248.1]).
Local Descriptor:
The MGC selects RTP PT equal to 111 for the VBD codec due to MGC provisioning. Ditto for RFC 4733/4734 codec. The maxptime attribute is used in this example due to different packetization times in each state.
Remote Descriptor:
The MGC generates the RD (and LD) based on the SDP O/A process, which corresponds to the offered audio and VBD codec from the remote PSTN gateway. The MGC is aware that the remote gateway is ITU-T V.152 compliant (due to ITU-T V.152 SDP in the received SIP offer).
Events descriptor:
The MGC subscribes for the ITU-T H.248.2 ctyp/dtone event on the "V.152" IP termination (Note) to be notified in case (fax) modem specific events are detected.
IP "T.38" termination:
The Reserved Group property value is Off as the MG requests to reserve resources only for the PCMA audio codec. ITU-T T.38 specific resources will be reserved and allocated later on during the actual MGC controlled transitioning (see stream modification by Step 3 – Table II.3).
|
+
+**Table II.1 – Example ITU-T H.248 stream descriptors – Creation of a V.152-to-T.38 context – ITU-T T.38 MGC controlled transitioning method – Step 1**
+
+| ITU-T H.248 encoding (shortened command) | Comment |
+|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------|
+| 2) Reply (MG to MGC): MEGACO/2 [11.9.19.70] ... Add = ip/2/2/1 { ; IP "V.152" Termination Media { Stream = 1 { ; there is just one Stream per Term. Local{ v=0 c=IN IP4 19.70.27.4 m=audio 40008 RTP/AVP 8 101 111 a=maxptime:20 - 30 a=rtpmap:101 telephone-event/8000 ; RFC 4733/4 a=rtpmap:111 PCMA/8000 ; ITU-T V.152 a=gpmd:111 vbd=yes }, Remote{ ; Remote descriptor might also be sent in ; a later Modify request v=0 c=IN IP4 19.70.3.2 m=audio 54530 RTP/AVP 8 101 111 a=maxptime:20 - 30 a=rtpmap:101 telephone-event/8000 ; RFC 4733/4 a=rtpmap:111 PCMA/8000 ; ITU-T V.152 a=gpmd:111 vbd=yes } }, }, Add = ip/8/3/2 { ; IP "T.38" Termination Media { Stream = 1 { ; there is just one Stream per Term. Local{ v=0 ; Single Media Group "audio flow" c=IN IP4 12.9.4.6 ... m=audio 40120 RTP/AVP 8 127 a=rtpmap:127 telephone-event/8000 a=ptime:20 }, Remote{ v=0 ; Single Media Group "audio flow" c=IN IP4 12.9.19.65 ... m=audio 100 RTP/AVP 8 127 a=rtpmap:127 telephone-event/8000 a=ptime:20 } }, }, } | The two ADD reply commands do successfully acknowledge the requested media capabilities and stream configurations.
|
+| NOTE – It may be noted that the ITU-T H.248.2 event is associated to the ITU-T V.152 side termination and not the ITU-T T.38 side termination since after the autonomous transition to the ITU-T V.152 this termination may reliably detect corresponding fax modem related events – even in case compressing audio codecs had been requested in the initial Add.request.
| |
+
+**Step 2 (Table II.2):** request/reply cycle, initiated now by the MG due to detected events. This event notification will be the trigger for the MGC for starting step 3.
+
+**Table II.2 – Example ITU-T H.248 stream descriptors – V.152-to-T.38 context –
+ITU-T T.38 MGC controlled transitioning method – Step 2**
+
+| ITU-T H.248 encoding (shortened command) | Comment |
+|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| 3) Notification Request (MG to MGC): MEGACO/2 [11.9.19.70] ... Notify = ip/2/2/1 { ; IP "V.152" Termination ObservedEvents = 1234 {20081203T12101025 : ctyp/dtone{dtt=V21flag}} } | The "V.152" side IP termination may additionally report further observed events, e.g., regarding CNG or CED tone detection before reporting detection of ITU-T V.21 flags. Corresponding notification requests are not shown here. These events may be received and observed either in-band (possibly after the autonomous transition to VBD) or out-of-band via RFC 4733/4734 NTE events. |
+| 4) Notification Reply (MGC to MG): MEGACO/2 [11.9.19.65] ... Notify = ip/2/2/1
| |
+
+**Step 3 (Table II.3):** request/reply cycle for modifying the two stream endpoints. The first MODIFY.request command is necessary for disabling the event detection logic, associated on the ITU-T V.152 side. The second MODIFY.request command creates and configures the local ITU-T T.38 endpoint.
+
+It may be noted that the ITU-T T.38 packet flow as well as the previously established ITU-T G.711 audio flow share both the same ITU-T H.248 stream (which is identified by the value '1'). Actually, there are three transport flows carried by that stream: PCMA/RTP media flow, RTCP control flow and ITU-T T.38 UDPTL flow. The three flow components are discriminated by three separate IP transport addresses. The RFC 4733/4734 packet traffic relates to a sub-flow component, sharing the same transport address with RTP audio, but uses a different payload type codepoint (values '127' and '8' respectively).
+
+**Table II.3 – Example ITU-T H.248 stream descriptors – V.152-to-T.38 context –
+ITU-T T.38 MGC controlled transitioning method – Step 3**
+
+| ITU-T H.248 encoding (shortened command) | Comment |
+|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| 5) Modification Request (MGC to MG): MEGACO/2 [11.9.19.65] ... Modify = ip/2/2/1 { ; IP "V.152" Termination Events }, Modify = ip/8/3/2 { ; IP "T.38" Termination Media { TerminationState { ipfax/faxstate = Negotiating ; initial fax state }, Stream = 1 { ; there is just one Stream per Term. LocalControl{ ipdc/realm = "providerY.com" ; IP network indication (here "T.38 domain") Mode=SendReceive, ReservedGroup = OFF , ; one media group ReservedValue = OFF ; just one media format t38 }, Local{ v=0 ; Media Group "packet relay flow for fax" c=IN IP4 \$ m=image \$ udptl t38 a=T38FaxVersion:1 a=T38FaxRateManagement:transferredTCF a=T38FaxUdpEC:t38UDPFEC a=T38FaxMaxBufferSize:2000 a=T38MaxDatagram:512 a=T38MaxBitRate:14400 | IP "V.152" termination:
MGC clears ctyp/dtone event subscription.
IP "T.38" termination:
MGC modifies the IP termination with a T.38 specific session/media description. The MGC generates the RD based on the SDP O/A process. Note that the RD may also be sent by the MGC in an additional subsequent modification request (depending on when the remote address and media information is available).
MGC sets the faxstate property to the initial value 'Negotiating' and subscribes for the 'faxconnchange' event to ensure notification in case the end-of-fax event is observed.
The applied T.38 transfer mode is based on UDPTL/UDP/IPv4 transport in this example.
|
+
+**Table II.3 – Example ITU-T H.248 stream descriptors – V.152-to-T.38 context –
+ITU-T T.38 MGC controlled transitioning method – Step 3**
+
+| ITU-T H.248 encoding (shortened command) | Comment |
+|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------|
+| (... additional T.38 attributes may be included) }, Remote{ v=0 ; Media Group "packet relay flow for fax" c=IN IP4 12.9.19.65 .. m=image 102 udpt1 t38 a=T38FaxVersion:1 a=T38FaxRateManagement:transferredTCF a=T38FaxUdpEC:t38UDPFEC a=T38FaxMaxBufferSize:2000 a=T38MaxDatagram:512 a=T38MaxBitRate:14400 (... additional T.38 attributes may be included) } }, Events = 1235 { ipfax/faxconnchange ; registration for end-of-fax ; event } } | |
+| 6) Modification Reply (MG to MGC): MEGACO/2 [11.9.19.70] ... Modify = ip/8/3/2 { ; IP "T.38" Termination Media { Stream = 1 { ; there is just one Stream per Term. Local{ v=0 ; Media Group "packet relay flow for fax" c=IN IP4 12.9.4.6 m=image 58130 udpt1 t38 a=T38FaxVersion:1 a=T38FaxRateManagement:transferredTCF a=T38FaxUdpEC:t38UDPFEC a=T38FaxMaxBufferSize:2000 a=T38MaxDatagram:512 a=T38MaxBitRate:14400 (... additional T.38 attributes may be included) }, Remote{ v=0 ; Media Group "packet relay flow for fax" c=IN IP4 12.9.19.65 .. m=image 102 udpt1 t38 a=T38FaxVersion:1 a=T38FaxRateManagement:transferredTCF a=T38FaxUdpEC:t38UDPFEC a=T38FaxMaxBufferSize:2000 a=T38MaxDatagram:512 a=T38MaxBitRate:14400 (... additional T.38 attributes may be included) } } }}} | Again, a positive acknowledgement by the MG
|
+
+**Step 4 (Table II.4):** request/reply cycle, initiated now by the MG due to a detected event concerning successful end of fax transmission. This event notification will be the trigger for the MGC for starting step 5 in order to switch back to audio.
+
+**Table II.4 – Example ITU-T H.248 stream descriptors – V.152-to-T.38 context –
+ITU-T T.38 MGC controlled transitioning method – Step 4**
+
+| ITU-T H.248 encoding (shortened command) | Comment |
+|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------|
+| 7) Notification Request (MG to MGC): MEGACO/2 [11.9.19.70] ... Notify = ip/8/3/2 { ObservedEvents = 1235 { ipfax/faxconnchange{faxconnchnge=EOF} } } | "T.38" IP termination reports detection of end-of-fax event. |
+| 8) Notification Reply (MGC to MG): MEGACO/2 [11.9.19.65] ... Notify = ip/8/3/2
| |
+
+**Step 5 (Table II.5):** request/reply cycle for restoring the audio information again on the ITU-T T.38 side.
+
+**Table II.5 – Example ITU-T H.248 stream descriptors – V.152-to-T.38 context –
+ITU-T T.38 MGC controlled transitioning method – Step 5**
+
+| ITU-T H.248 encoding (shortened command) | Comment |
+|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| 9) Modification Request (MGC to MG): MEGACO/2 [11.9.19.65] ... Modify = ip/2/2/1 { ; IP "V.152" Termination Events = 1234 {ctyp/dtone} ; MGC requests H.248.2 ; ctyp/dtone event ; notification }, Modify = ip/8/3/2 { ; IP "T.38" Termination Media { Stream = 1 { ; there is just one Stream per Term. LocalControl{ ipdc/realm = "providerY.com" ; IP network indication (here "T.38 domain") Mode=SendReceive, ReservedGroup = OFF, ; one media group ReservedValue = OFF ; just one audio codec, might ; also be ON in case two or ; audio codecs are requested ; in 'audio' media descr. }, Local{ v=0 ; Single Media Group "audio flow" c=IN IP4 12.9.4.6 ... m=audio 40120 RTP/AVP 8 127 a=rtpmap:127 telephone-event/8000 a=ptime:20 }, Remote{ v=0 ; Single Media Group "audio flow" c=IN IP4 12.9.19.65 ... m=audio 100 RTP/AVP 8 127 a=rtpmap:127 telephone-event/8000 a=ptime:20 } } } } | IP "V.152" termination:
The MGC subscribes for the ITU-T H.248.2 ctyp/dtone event on the "V.152" IP termination to be notified in case (fax) modem specific events are detected.
IP "T.38" termination:
MGC restores the audio codec based LD and RD. There is no need to modify the faxstate property as the MG sets this implicitly whenever the fax state changes.
|
+
+**Table II.5 – Example ITU-T H.248 stream descriptors – V.152-to-T.38 context –
+ITU-T T.38 MGC controlled transitioning method – Step 5**
+
+| ITU-T H.248 encoding (shortened command) | Comment |
+|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------|
+| 10) Modify Reply (MG to MGC): MEGACO/2 [11.9.19.70] ... Modify = ip/2/2/1, Modify = ip/8/3/2 { ; IP "T.38" Termination Media { Stream = 1 { ; there is just one Stream per Term. Local{ v=0 ; Single Media Group "audio flow" c=IN IP4 12.9.4.6 ... m=audio 40120 RTP/AVP 8 127 a=rtpmap:127 telephone-event/8000 a=ptime:20 }, Remote{ v=0 ; Single Media Group "audio flow" c=IN IP4 12.9.19.65 ... m=audio 100 RTP/AVP 8 127 a=rtpmap:127 telephone-event/8000 a=ptime:20 } } } } | |
+
+The two selected media formats for audio are identical at both terminations; there is thus not any audio transcoding enforced (when in audio state).
+
+It may be noted that the major portion of ITU-T H.248 signalling traffic is related to the ITU-T T.38 side, whereas the ITU-T V.152 termination is fairly simple and straightforward from a gateway control perspective.
+
+##### **II.4.2.2 V.152-to-T.38 context and ITU-T T.38 autonomous transitioning method**
+
+[ITU-T T.38] also defines an MG autonomous transition method for ITU-T H.248 controlled ITU-T T.38 bearer endpoints.
+
+# Bibliography
+
+- [b-ITU-T T.4] Recommendation ITU-T T.4 (2003), *Standardization of Group 3 facsimile terminals for document transmission*.
+- [b-ITU-T T.6] Recommendation ITU-T T.6 (1988), *Facsimile coding schemes and coding control functions for Group 4 facsimile apparatus*.
+- [b-ITU-T V.150.0] Recommendation ITU-T V.150.0 (2003), *Modem-over-IP networks: Foundation*.
+- [b-ITU-T V.150.1] Recommendation ITU-T V.150.1 (2003), *Modem-over-IP networks: Procedures for the end-to-end connection of V-series DCEs*.
+- [b-ITU-T V.151] Recommendation ITU-T V.151 (2006), *Procedures for the end-to-end connection of analogue PSTN text telephones over an IP network utilizing text relay*.
+- [b-3GPP 29.332] 3GPP TS 29.332 (2009), *Media Gateway Control Function (MGCF) – IM Media Gateway (IM-MGW); Mn interface*.
+- [b-ETSI ES 283 002] ETSI ES 283 002 (2005), *Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN); PSTN/ISDN Emulation Subsystem (PES); NGN Release 1 H.248 Profile for controlling Access and Residential Gateways*.
+- [b-ETSI TS 182 012] ETSI TS 182 012 (2008), *Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN); IMS-based PSTN/ISDN Emulation Sub-system (PES); Functional architecture/IMS-based PES architecture; Ver. 2.1.4*.
+- [b-IETF RFC 3264] IETF RFC 3264 (2002), *An Offer/Answer Model with the Session Description Protocol (SDP)*.
+
+
+
+
+
+## SERIES OF ITU-T RECOMMENDATIONS
+
+| | |
+|-----------------|---------------------------------------------------------------------------------------------|
+| Series A | Organization of the work of ITU-T |
+| Series D | General tariff principles |
+| Series E | Overall network operation, telephone service, service operation and human factors |
+| Series F | Non-telephone telecommunication services |
+| Series G | Transmission systems and media, digital systems and networks |
+| Series H | Audiovisual and multimedia systems |
+| Series I | Integrated services digital network |
+| Series J | Cable networks and transmission of television, sound programme and other multimedia signals |
+| Series K | Protection against interference |
+| Series L | Construction, installation and protection of cables and other elements of outside plant |
+| Series M | Telecommunication management, including TMN and network maintenance |
+| Series N | Maintenance: international sound programme and television transmission circuits |
+| Series O | Specifications of measuring equipment |
+| Series P | Terminals and subjective and objective assessment methods |
+| Series Q | Switching and signalling |
+| Series R | Telegraph transmission |
+| Series S | Telegraph services terminal equipment |
+| Series T | Terminals for telematic services |
+| Series U | Telegraph switching |
+| Series V | Data communication over the telephone network |
+| Series X | Data networks, open system communications and security |
+| Series Y | Global information infrastructure, Internet protocol aspects and next-generation networks |
+| Series Z | Languages and general software aspects for telecommunication systems |
\ No newline at end of file
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+
+
+
+
+ITU logo: a globe with the letters ITU inside.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+# CCITT
+
+# V.17
+
+THE INTERNATIONAL
+TELEGRAPH AND TELEPHONE
+CONSULTATIVE COMMITTEE
+
+**DATA COMMUNICATION
+OVER THE TELEPHONE NETWORK**
+
+---
+
+**A 2-WIRE MODEM FOR FACSIMILE
+APPLICATIONS WITH RATES UP
+TO 14 400 bit/s**
+
+**Recommendation V.17**
+
+---
+
+
+
+CCITT logo: a stylized globe with the letters CCITT inside.
+
+Geneva, 1991
+
+# FOREWORD
+
+The CCITT (the International Telegraph and Telephone Consultative Committee) is a permanent organ of the International Telecommunication Union (ITU). CCITT is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The Plenary Assembly of CCITT which meets every four years, establishes the topics for study and approves Recommendations prepared by its Study Groups. The approval of Recommendations by the members of CCITT between Plenary Assemblies is covered by the procedure laid down in CCITT Resolution No. 2 (Melbourne, 1988).
+
+Recommendation V.17 was prepared by Study Group XVII and was approved under the Resolution No. 2 procedure on the 22 of February 1991.
+
+## --- CCITT NOTE
+
+In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication Administration and a recognized private operating agency.
+
+© ITU 1991
+
+All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.
+
+## Recommendation V.17
+
+# A 2-WIRE MODEM FOR FACSIMILE APPLICATIONS WITH RATES UP TO 14 400 bit/s
+
+## 1 Introduction
+
+This Recommendation defines the modulation methods and operating sequences for a modem intended only for use in high speed facsimile applications.
+
+Appropriate T-Series Recommendations should be consulted regarding operating procedures and other features employed in facsimile transmission applications, as these differ from those recommended for high speed modems for general applications.
+
+The modem has the following principal characteristics:
+
+- a) Provision for half duplex operation at data signalling rates of:
+ - 14 400 bit/s synchronous,
+ - 12 000 bit/s synchronous,
+ - 9600 bit/s synchronous,
+ - 7200 bit/s synchronous;
+- b) Quadrature amplitude modulation with synchronous line transmission at 2400 symbols per second.
+- c) Inclusion of data scramblers, adaptive equalizers and eight-state trellis coding.
+- d) Two sequences for training and synchronization: long train and resync.
+
+## 2 Line signals
+
+### 2.1 *Carrier frequency*
+
+The channel carrier frequency is $1800 \pm 1$ Hz. The receiver must be able to operate with received frequency offsets of up to $\pm 7$ Hz.
+
+### 2.2 *Modulation*
+
+The modulation rate shall be $2400 \pm 0.01\%$ symbols per second.
+
+### 2.3 *Signal element codings*
+
+#### 2.3.1 *Signal element codings for 14 400 bit/s*
+
+The scrambled data stream to be transmitted is divided into groups of six consecutive data bits, which are ordered according to their time of occurrence. As shown in Figure 1/V.17, the first two bits in each group, $Q1_n$ and $Q2_n$ (where n designates the sequence number of the group) are first differentially encoded into $Y1_n$ and $Y2_n$ according to Table 1/V.17.
+
+
+
+See Table 1/V.17
+
+See Figures 2/V.17 to 5/V.17
+
+| a | b | S1 | S2 |
+|---|---|----|----|
+| 0 | 0 | 0 | 0 |
+| 0 | 1 | 1 | 0 |
+| 1 | 0 | 1 | 0 |
+| 1 | 1 | 0 | 1 |
+
+Block diagram of Trellis coding at 14 400, 12 000, 9600 and 7200 signalling rates. The diagram shows a Differential encoder and a Convolutional encoder. The Differential encoder takes inputs Q1n and Q2n and produces outputs Y1n and Y2n. The Convolutional encoder takes inputs Y1n and Y2n and produces outputs Y0n and Y1n. A Signal element mapping block takes inputs Q3n, Q4n, Q5n, and Q6n and produces outputs Y1n and Y2n. A table below the diagram shows the mapping from inputs a and b to outputs S1 and S2.
+
+T1701600-92/d01
+
+FIGURE 1/V.17
+
+Trellis coding at 14 400, 12 000, 9600 and 7200 signalling rates
+
+TABLE 1/V.17
+
+Differential coding for use with trellis coding
+
+| Input | | Previous outputs | | Outputs | |
+|-----------------|-----------------|-------------------|-------------------|-----------------|-----------------|
+| Q1 n | Q2 n | Y1 n-1 | Y2 n-1 | Y1 n | Y2 n |
+| 0 | 0 | 0 | 0 | 0 | 0 |
+| 0 | 0 | 0 | 1 | 0 | 1 |
+| 0 | 0 | 1 | 0 | 1 | 0 |
+| 0 | 0 | 1 | 1 | 1 | 1 |
+| 0 | 1 | 0 | 0 | 0 | 1 |
+| 0 | 1 | 0 | 1 | 0 | 0 |
+| 0 | 1 | 1 | 0 | 1 | 1 |
+| 0 | 1 | 1 | 1 | 1 | 0 |
+| 1 | 0 | 0 | 0 | 1 | 0 |
+| 1 | 0 | 0 | 1 | 1 | 1 |
+| 1 | 0 | 1 | 0 | 0 | 1 |
+| 1 | 0 | 1 | 1 | 0 | 0 |
+| 1 | 1 | 0 | 0 | 1 | 1 |
+| 1 | 1 | 0 | 1 | 1 | 0 |
+| 1 | 1 | 1 | 0 | 0 | 0 |
+| 1 | 1 | 1 | 1 | 0 | 1 |
+
+The two differentially encoded bits Y1n and Y2n are used as inputs to a systematic convolutional encoder which generates a redundant bit Y0n. This redundant bit and the six information-carrying bits Y1n, Y2n, Q3n, Q4n, Q5n and Q6n are then mapped into the coordinates of the signal element to be transmitted according to the signal space diagram shown in Figure 2/V.17.
+
+
+
+Figure 2/V.17: A 128-point signal structure diagram for trellis-coded 14 400 bit/s data signalling. The diagram shows 128 signal points arranged in a cross-like grid pattern. The horizontal axis represents the in-phase component, labeled with angles 180° on the left and 0° on the right, and a scale from -8 to 8. The vertical axis represents the quadrature component, labeled with 90° at the top and 270° at the bottom, also with a scale from -8 to 8. Each point is marked with a dot and a 7-bit binary label (Q6n Q5n Q4n Q3n Y2n Y1n Y0n). Four specific points are highlighted with circles and letters: 'A' at (-6, -2) labeled 1111010, 'B' at (2, -6) labeled 0010010, 'C' at (6, 2) labeled 1100010, and 'D' at (-2, 6) labeled 1001010. The diagram includes a technical identifier T1701610-92/d02.
+
+*Note* – The binary numbers denote Q6n, Q5n, Q4n, Q3n, Y2n, Y1n, Y0n. A, B, C and D refer to synchronizing signal elements.
+
+FIGURE 2/V.17
+
+**A 128-point signal structure used with the trellis-coded 14 400 bit/s data signalling rate**
+
+#### 2.3.2 Signal element codings for 12 000 bit/s
+
+The scrambled data stream to be transmitted is divided into groups of five consecutive data bits, which are ordered according to their time of occurrence. As shown in Figure 1/V.17, the first two bits in each group, $Q1_n$ and $Q2_n$ (where $n$ designates the sequence number of the group) are first differentially encoded into $Y1_n$ and $Y2_n$ according to Table 1/V.17.
+
+The two differentially encoded bits $Y1_n$ and $Y2_n$ are used as inputs to a systematic convolutional encoder which generates a redundant bit $Y0_n$ . This redundant bit and the five information-carrying bits $Y1_n$ , $Y2_n$ , $Q3_n$ , $Q4_n$ and $Q5_n$ are then mapped into the coordinates of the signal element to be transmitted according to the signal space diagram shown in Figure 3/V.17.
+
+
+
+Detailed point data (X, Y, Label):
+(-7, 7): 010100; (-5, 7): 010001; (-3, 7): 111110; (-1, 7): 000111 (D); (1, 7): 011100; (3, 7): 011001; (5, 7): 110110; (7, 7): 010111;
+(-7, 5): 110101; (-5, 5): 110000; (-3, 5): 111011; (-1, 5): 000010; (1, 5): 100101; (3, 5): 100000; (5, 5): 110011; (7, 5): 010010;
+(-7, 3): 011110; (-5, 3): 100111; (-3, 3): 001100; (-1, 3): 001001; (1, 3): 101110; (3, 3): 001111; (5, 3): 111100; (7, 3): 111001 (C);
+(-7, 1): 011011; (-5, 1): 100010; (-3, 1): 101101; (-1, 1): 101000; (1, 1): 101011; (3, 1): 001010; (5, 1): 000101; (7, 1): 000000;
+(-7, -1): 000100 (A); (-5, -1): 000001; (-3, -1): 001110; (-1, -1): 101111; (1, -1): 101100; (3, -1): 101001; (5, -1): 100110; (7, -1): 011111;
+(-7, -3): 111101; (-5, -3): 111000; (-3, -3): 001011; (-1, -3): 101010; (1, -3): 001101; (3, -3): 001000; (5, -3): 100011; (7, -3): 011010;
+(-7, -5): 010110; (-5, -5): 110111; (-3, -5): 100100; (-1, -5): 100001; (1, -5): 000110; (3, -5): 111111; (5, -5): 110100; (7, -5): 110001;
+(-7, -7): 010011; (-5, -7): 110010; (-3, -7): 011101; (-1, -7): 011000; (1, -7): 000011 (B); (3, -7): 111010; (5, -7): 010101; (7, -7): 010000.
+
+Figure 3/V.17: A 64-point signal structure diagram for 12,000 bit/s trellis coding. The diagram shows a constellation on a 2D plane with axes labeled in degrees (0°, 90°, 180°, 270°) and numerical coordinates from -7 to +7. Points are labeled with 6-bit binary strings representing Q5n, Q4n, Q3n, Y2n, Y1n, Y0n. Four specific points are circled and labeled A, B, C, and D for synchronization.
+
+T1701620-92/d03
+
+Note – The binary numbers denote $Q5_n$ , $Q4_n$ , $Q3_n$ , $Y2_n$ , $Y1_n$ , $Y0_n$ . A, B, C and D refer to synchronizing signal elements.
+
+FIGURE 3/V.17
+
+**A 64-point signal structure used with the trellis-coded 12 000 bit/s
+data signalling rate**
+
+#### 2.3.3 Signal element codings for 9600 bit/s
+
+The scrambled data stream to be transmitted is divided into groups of four consecutive data bits, which are ordered according to their time of occurrence. As shown in Figure 1/V.17, the first two bits in each group, $Q1_n$ and $Q2_n$ (where $n$ designates the sequence number of the group) are first differentially encoded into $Y1_n$ and $Y2_n$ according to Table 1/V.17.
+
+The two differentially encoded bits $Y1_n$ and $Y2_n$ are used as inputs to a systematic convolutional encoder which generates a redundant bit $Y0_n$ . This redundant bit and the four information-carrying bits $Y1_n$ , $Y2_n$ , $Q3_n$ and $Q4_n$ are then mapped into the coordinates of the signal element to be transmitted, according to the signal space diagram shown in Figure 4/V.17.
+
+
+
+The diagram is a 32-point signal space diagram. The horizontal axis represents the real part and the vertical axis represents the imaginary part. The axes are labeled with angles: 90° at the top, 180° on the left, 0° on the right, and 270° at the bottom. The axes also have numerical labels: -8, -4, 4, 8 on the horizontal axis and 8, 4, -4, -8 on the vertical axis. The 32 points are arranged in a grid-like pattern. Four points are circled and labeled A, B, C, and D. Point A is at (-4, -4), Point B is at (4, -4), Point C is at (4, 4), and Point D is at (-4, 8). The points are labeled with 5-bit binary numbers. The diagram is identified as T1701630-92/d04.
+
+Figure 4/V.17: A 32-point signal structure for trellis-coded 9600 bit/s data signalling rate. The diagram shows a 32-point signal space diagram in a 2D plane with axes from -8 to 8. The points are labeled with 5-bit binary numbers (Q4n, Q3n, Y2n, Y1n, Y0n). Four points are circled and labeled A, B, C, and D, representing synchronizing signal elements. The axes are labeled with angles 90°, 180°, 0°, and 270°. The diagram is identified as T1701630-92/d04.
+
+Note – The binary numbers denote $Q4_n$ , $Q3_n$ , $Y2_n$ , $Y1_n$ , $Y0_n$ . A, B, C and D refer to synchronizing signal elements.
+
+FIGURE 4/V.17
+
+**A 32-point signal structure for trellis-coded 9600 bit/s data signalling rate**
+
+#### 2.3.4 Signal element codings for 7200 bit/s
+
+The scrambled data stream to be transmitted is divided into groups of three consecutive data bits, which are ordered according to their time of occurrence. As shown in Figure 1/V.17, the first two bits in each group, $Q1_n$ and $Q2_n$ (where $n$ designates the sequence number of the group) are first differentially encoded into $Y1_n$ and $Y2_n$ according to Table 1/V.17.
+
+The two differentially encoded bits $Y1_n$ and $Y2_n$ are used as inputs to a systematic convolutional encoder which generates a redundant bit $Y0_n$ . This redundant bit and the three information-carrying bits $Y1_n$ , $Y2_n$ and $Q3_n$ are then mapped into the coordinates of the signal element to be transmitted according to the signal space diagram shown in Figure 5/V.17.
+
+
+
+Figure 5/V.17: A 16-point signal structure for trellis-coded 7200 bit/s data signalling rate. The diagram shows a 4x4 grid of points in a signal space defined by angles 0°, 90°, 180°, and 270° on the horizontal axis and values -6, -2, 2, 6 on the vertical axis. Each point is labeled with a 4-bit binary number (Q3n, Y2n, Y1n, Y0n). Four points are circled and labeled A, B, C, and D, representing synchronizing signal elements. Point A is at (-6, -2) with label 0110. Point B is at (2, -6) with label 0101. Point C is at (6, 2) with label 0010. Point D is at (-2, 6) with label 0001. The text 'T1701640-92/d05' is located at the bottom right of the diagram.
+
+Note – The binary numbers denote $Q3_n$ , $Y2_n$ , $Y1_n$ , $Y0_n$ . A, B, C and D refer to synchronizing signal elements.
+
+FIGURE 5/V.17
+A 16-point signal structure for trellis-coded 7200 bit/s data signalling rate
+
+### 2.4 Transmitted spectra
+
+With continuous binary ONES applied to the input of the scrambler, the transmitted energy density at 600 Hz and 3000 Hz should be attenuated by $4.5 \pm 2.5$ dB with respect to the maximum energy density between 600 Hz and 3000 Hz.
+
+## 3 Interchange circuits
+
+### 3.1 List of interchange circuits
+
+References in the Recommendation to V.24 interchange circuit numbers are intended to refer to the functional equivalent of such circuits and are not intended to imply the physical implementation of such circuits. For example, references to circuit 103 should be understood to refer to the functional equivalent of circuit 103 (see Table 2/V.17).
+
+TABLE 2/V.17
+
+### **Interchange circuits**
+
+| Number | Description |
+|----------|------------------------------------------------|
+| 102 | Signal ground or common return |
+| 103 | Transmitted data |
+| 104 | Received data |
+| 105 | Request to send |
+| 106 | Ready for sending |
+| 107 | Data set ready |
+| 108/1 or | Connect data set to line (Note) |
+| 108/2 | Data terminal ready (Note) |
+| 109 | Data channel received line signal detector |
+| 114 | Transmitter signal element timing (DCE source) |
+| 115 | Receiver signal element timing (DCE source) |
+| 125 | Calling indicator |
+
+*Note* – This circuit shall be capable of operating as circuit 108/1 or circuit 108/2.
+
+### 3.2 *Transmit data*
+
+The modem shall accept data from the facsimile control function on circuit 103; the data on circuit 103 shall be under the control of circuit 114.
+
+### 3.3 *Receive data*
+
+The modem shall pass data to the facsimile control function on circuit 104; data on circuit 104 shall be under the control of circuit 115.
+
+### 3.4 *Timing arrangements*
+
+Clocks shall be included in the modem to provide the facsimile control function with transmitter element timing on circuit 114 and receiver signal element timing on circuit 115.
+
+### 3.5 *Data rate control*
+
+This shall be provided by a connection between the modem and the facsimile control function; the nature of this connection is beyond the scope of this Recommendation.
+
+### 3.6 *Circuits 106 and 109 response times*
+
+After the training and synchronizing sequences defined in § 5, circuit 106 shall follow OFF to ON or ON to OFF transitions of circuit 105 within 3.5 ms. The OFF to ON transition of circuit 109 is part of the training sequence specified in § 5. Circuit 109 shall turn OFF 30 to 50 ms after the level of the received signal appearing at the line terminal of the modem falls below the relevant threshold defined in § 3.7. Following a dropout, after the initial handshake, circuit 109 shall turn ON 40 to 205 ms after the level of the received signal appearing at the line terminal of the modem exceeds the relevant threshold defined in § 3.7.
+
+### 3.7 *Circuit 109 threshold*
+
+- > –43 dBm ON.
+- > –48 dBm OFF.
+
+The condition of circuit 109 between the ON and OFF levels is not specified except that the signal detector shall exhibit a hysteresis action, such that the level at which the OFF to ON transition occurs shall be at least 2 dB greater than that for the ON to OFF transition.
+
+Circuit 109 thresholds are specified at the input to the modem when receiving scrambled binary ONEs.
+
+Administrations are permitted to change these thresholds where transmission conditions are known.
+
+*Note* – Circuit 109 ON to OFF response time should be suitably chosen within the specified limits to ensure that all valid data bits have appeared on circuit 104.
+
+### 3.8 *Clamping*
+
+The DCE shall hold, where implemented, circuit 104 in the binary ONE condition and circuit 109 in the OFF condition when circuit 105 is in the ON condition and, where required to protect circuit 104 from false signals, for a period of $150 \pm 25$ ms following the ON to OFF transition on circuit 105. The use of this additional delay is optional, based on system considerations.
+
+## 4 **Scrambler and descrambler**
+
+The modem shall use a self-synchronizing scrambler/descrambler with the generator polynomial:
+
+$$1 + x^{-18} + x^{-23}$$
+
+At the transmitter, the scrambler shall effectively divide the message data sequence by the generating polynomial. The coefficients of the quotient of this division, taken in descending order, form the data sequence which shall appear at the output of the scrambler. At the receiver, the received data sequence shall be multiplied by the scrambler generating polynomial to recover the message sequence.
+
+## 5 **Operating sequences**
+
+### 5.1 *Training and synchronizing sequences*
+
+Two separate sequences of training and synchronizing signals are defined in Table 3/V.17.
+
+The long train sequence is for initial establishment of a connection or for retraining when needed.
+
+The resync. sequence is for resynchronization after a successful long train.
+
+TABLE 3/V.17
+
+**Training and synchronizing signals**
+
+| | Segment 1 | Segment 2 | Segment 3 | Segment 4 | | |
+|------------|-------------------|---------------------------|---------------|----------------|-----------------------|-----------------------|
+| | ABAB alternations | Equalizer training signal | Bridge signal | Scrambled ONEs | Total symbol interval | Approximate time (ms) |
+| Long train | 256 | 2976 | 64 | 48 | 3344 | 1393 |
+| Resync. | 256 | 38 | 64 | 48 | 342 | 142 |
+
+#### 5.1.1 Segment 1: ABAB alternations
+
+This segment consists of alternations between states A and B as shown in Figures 2/V.17 to 5/V.17.
+
+#### 5.1.2 Segment 2: equalizer training signal
+
+This segment consists of the sequential transmission of four signal elements A, B, C, and D as shown in Figures 2/V.17 to 5/V.17.
+
+The equalizer conditioning pattern is a pseudo-random sequence at 4800 bit/s generated by the $1 + x^{-18} + x^{-23}$ data scrambler. During segment 2, any differential quadrant encoding is disabled and the scrambled dibits are encoded as shown in Table 4/V.17.
+
+With a binary ONE applied to the input, the initial scrambler state shall be selected to produce the following scrambler output pattern and corresponding signal elements:
+
+TABLE 4/V.17
+
+Encoding for four phase training signal
+
+| | | | | | | | | | | | | | | | |
+|----|----|----|----|----|----|----|----|----|----|----|----|----|----|----|----|
+| 00 | 01 | 00 | 01 | 00 | 01 | 00 | 01 | 00 | 01 | 00 | 01 | 10 | 01 | 10 | 01 |
+| C | D | C | D | C | D | C | D | C | D | C | D | B | D | B | D |
+
+Segment 2
+
+| Dibit | Signal state |
+|-------|--------------|
+| 00 | C |
+| 01 | D |
+| 11 | A |
+| 10 | B |
+
+#### 5.1.3 Segment 3: bridge signal
+
+This segment, which is used only during an initial long train, consists of a 16-bit binary sequence transmitted eight times. The sequence as defined in Table 5/V.17 is scrambled, and transmitted at 4800 bit/s using the signal elements A, B, C, and D as defined in Figures 2/V.17 to 5/V.17.
+
+TABLE 5/V.17
+
+##### **Segment 3: Bit designations**
+
+| | | | | | | | | | | | | | | | |
+|---|---|---|---|---|---|---|---|---|---|----|----|----|----|----|----|
+| B | B | B | B | B | B | B | B | B | B | B | B | B | B | B | B |
+| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
+| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 1 |
+
+*Note 1* – The B0 bit is the first bit in the data stream as it enters the scrambler.
+
+*Note 2* – Any use of bits 4-6, 8-10, 12-14 would be for further study. Some existing equipment may set one or more of these bits to binary ONE; such bits shall be ignored.
+
+The dibits are differentially encoded as defined in Table 6/V.17.
+
+The differential encoder shall be initialized using the final symbol of the previous segment. The first two bits and subsequent dibits of each 16-bit sequence shall be encoded as one signal state.
+
+TABLE 6/V.17
+
+##### **Segment 3: Dibit encoding**
+
+| Dibit | Phase change | Previous output/output |
+|-------|--------------|------------------------|
+| 00 | + 90 degrees | A/B, B/C, C/D, D/A |
+| 01 | 0 degrees | A/A, B/B, C/C, D/D |
+| 10 | 180 degrees | A/C, B/D, C/A, D/B |
+| 11 | – 90 degrees | A/D, B/A, C/B, D/C |
+
+#### 5.1.4 Segment 4
+
+Scrambled binary ONES shall be sent at the channel data bit rate.
+
+For the long train sequence, the differential encoder shall be initialized using the first symbol of segment 3.
+
+For the short train sequence, the differential encoder shall be initialized using the last symbol of segment 2.
+
+The convolutional encoder initial state shall be initialized to zero.
+
+The scrambler shall be clocked at the bit rate and the scrambler output sequence encoded as defined in § 4. The initial scrambler state is that state produced by the last symbol interval of the previous segment.
+
+The duration of segment 4 is 48 symbol intervals. At the end of segment 4, circuit 106 is turned ON and data are applied to the input of the data scrambler.
+
+Circuit 109 shall be turned ON during the reception of segment 4.
+
+### 5.2 *Turn OFF sequence*
+
+After an ON to OFF transition of circuit 105, the line signals emitted after remaining data or the end of the training check signal during retrain procedure have been transmitted are shown in Table 7/V.17.
+
+TABLE 7/V.17
+**Turn OFF sequence**
+
+| Segment A | Segment B | Total of segments | Approximate time |
+|---------------------------|-----------------------|-------------------|------------------|
+| Continuous scrambled ONEs | No transmitted energy | | |
+| 32 SI | 48 SI | 80 SI | 33 ms |
+
+SI denotes Symbol intervals
+
+*Note* – If an OFF to ON transition of circuit 105 occurs during the turn OFF sequence, it will not be taken into account until the end of the turn OFF sequence.
+
+### 5.3 *Talker echo protection (TEP) signal*
+
+A TEP signal may, optionally, be transmitted prior to the transmission of training and synchronization sequences. The TEP signal shall consist of an unmodulated carrier for a duration of 185 to 200 ms followed by a silent period of 20 to 25 ms.
+
+When used, the TEP signal shall be considered as part of the training sequences.
+
+Alternative methods for achieving the intended benefits of a TEP signal are for further study.
\ No newline at end of file
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+
+
+
+
+The logo of the International Telecommunication Union (ITU) is located in the top left corner. It features a stylized globe with the letters 'ITU' superimposed on it. A lightning bolt is depicted striking the globe from the top left.
+
+ITU logo: a globe with the letters ITU and a lightning bolt.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+**V.2**
+
+# **DATA COMMUNICATION OVER THE TELEPHONE NETWORK**
+
+## --- **POWER LEVELS FOR DATA TRANSMISSION OVER TELEPHONE LINES**
+
+## **ITU-T Recommendation V.2**
+
+(Extract from the *Blue Book*)
+
+---
+
+## NOTES
+
+1 ITU-T Recommendation V.2 was published in Fascicle VIII.1 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+
+2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## POWER LEVELS FOR DATA TRANSMISSION OVER TELEPHONE LINES
+
+*(New Delhi, 1960; amended at Geneva, 1964 and 1980)*
+
+The objectives in specifying data signal levels are as follows:
+
+- a) To ensure satisfactory transmission and to permit coordination with devices such as signalling receivers or echo suppressors, the data signal levels on international circuits should be controlled as closely as possible,
+- b) To ensure correct performance of multichannel carrier systems from the point of view of loading and noise, the mean power of data circuits should not differ much from the conventional value of channel loading (-15 dBm0 for each direction of transmission: see Note below). This conventional value makes allowance for a reasonable proportion P (dependent on the transmission systems and probably less than 50%; the value will have to be specified in subsequent studies) of the channels in a multichannel system being used for nonspeech applications at fixed power levels at about -13 dBm0 for each direction of transmission.
+
+If the proportion of nonspeech applications (including data) does not exceed the above value P, the mean power of -13 dBm0 for each direction of transmission would be allowable for data transmission also.
+
+However, assuming that the proportion of nonspeech circuits is appreciably higher than P (due to the development of data transmission) on international carrier systems, a reduction of this power by 2 dB might be reasonable (these values require further study).
+
+*Note* - The distribution of long-term mean power among the channels in a multichannel carrier telephone system (conventional mean value of -15 dBm0), probably has a standard deviation in the neighbourhood of 4 dB (see [2]).
+
+- c) It is probable that Administrations will wish to fix specific values for the signal power level of data modulators either at the subscriber's line terminals or at the local exchanges. The relation between these values and the power levels on international circuits depends on the particular national transmission plan; in any case, a wide range of losses among the possible connections between the subscriber and the input to international circuits must be expected.
+- d) Considerations a) to c) suggest that specification of the maximum data signal level only is not the most useful form. One alternative proposal would be to specify the nominal power at the input to the international circuit. The nominal power would be the statistically estimated mean power obtained from measurement on many data transmission circuits.
+
+For these reasons, the CCITT
+
+*unanimously declares the following view:*
+
+### **1 Data transmission over leased telephone circuits (private wires) set up on carrier systems**
+
+1.1 The maximum power output of the subscriber's equipment into the line shall not exceed 1 mW at any frequency.
+
+1.2 For systems transmitting tones continuously, e.g., frequency-modulation systems, the maximum power level at the zero relative level point shall be -13 dBm0. When transmission of data is discontinued for any appreciable time, the power level should preferably be reduced to -20 dBm0 or lower.
+
+---
+
+1) Recommendation V.2 corresponds to Recommendation H.15 [1].
+
+1.3 For systems not transmitting tones continuously, e.g., amplitude-modulation systems, the signal characteristics should meet all of the following requirements:
+
+- i) The maximum value of the 1-minute mean power shall not exceed -13 dBm0.
+- ii) Provisionally, the maximum value of the instantaneous power shall not exceed a level corresponding to that of a 0 dBm0 sine wave signal. This limit should be confirmed or amended after further study.
+- iii) Provisionally, the maximum signal power determined for a 10-Hz bandwidth centred at any frequency shall not exceed -10 dBm0. This limit should be confirmed or amended after further study.
+
+*Note 1* - It is estimated that the proportion of international circuits which are carrying data transmissions is approximately 20%. If the proportion should reach a high level (approximately 50% or even less in the case of high-usage systems), the limits now proposed would need to be reconsidered.
+
+*Note 2* - Supplement No. 16 [3] of the Yellow Book, Volume III, gives information on the out-of-band power of signals applied to leased telephone-type circuits.
+
+### **2 Data transmission over the switched telephone system**
+
+2.1 The maximum power output of the subscriber's equipment into the line shall not exceed 1 mW at any frequency.
+
+2.2 For systems transmitting tones continuously, such as frequency- or phase-modulation systems, the power level of the subscriber's equipment should be fixed at the time of installation to allow for loss between his equipment and the point of entry to an international circuit, so that the corresponding nominal level of the signal at the international circuit input shall not exceed -13 dBm0.
+
+2.3 For systems not transmitting tones continuously, e.g. amplitude-modulation systems, the signal characteristics should meet all of the following requirements (see also Note 1 to § 1.3):
+
+- i) The maximum value of the 1-minute mean power shall not exceed -13 dBm0.
+- ii) Provisionally, the maximum value of the instantaneous power shall not exceed a level corresponding to that of a 0 dBm0 sine wave signal. This limit should be confirmed or amended after further study.
+- iii) Provisionally, the maximum signal power determined for a 10 Hz bandwidth centred at any frequency shall not exceed -10 dBm0. This limit should be confirmed or amended after further study.
+
+*Note 1* - In practice, it is no easy matter to assess the loss between a subscriber's equipment and the international circuit, so that § 2 of the present Recommendation should be taken as providing general planning guidance.
+
+*Note 2* - In switched connections, the loss between subscribers' telephones may be high: 30 to 40 dB. The level of the signals received will then be very low, and these signals may suffer disturbance from the dialling pulses sent over other circuits.
+
+If there is likely to be a heavy demand for international connections for data transmission over the switched network, some Administrations might want to provide special 4-wire subscriber lines. If so, the levels to be used might be those proposed for leased circuits.
+
+## **References**
+
+- [1] CCITT Recommendation *Power levels for data transmission over telephone lines*, Vol. III, Rec. H.51.
+- [2] *Measurement of the load of telephone circuits*, Green Book, Vol. III-2, Supplement No. 5, ITU, Geneva, 1973.
+- [3] *Out-of-band characteristics of signals applied to leased telephone-type circuits*, Vol. III, Supplement No. 16.
\ No newline at end of file
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+
+
+
+
+ITU logo: a globe with the letters ITU and a lightning bolt symbol.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+# ITU-T
+
+# V.21
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+# DATA COMMUNICATION OVER THE TELEPHONE NETWORK ---
+
+## 300 BITS PER SECOND DUPLEX MODEM STANDARDIZED FOR USE IN THE GENERAL SWITCHED TELEPHONE NETWORK
+
+### ITU-T Recommendation V.21
+
+(Extract from the *Blue Book*)
+
+---
+
+### NOTES
+
+1 ITU-T Recommendation V.21 was published in Fascicle VIII.1 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+
+2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+© ITU 1988, 1993
+
+All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.
+
+### Recommendation V.21
+
+## 300 BITS PER SECOND DUPLEX MODEM STANDARDIZED FOR USE IN THE GENERAL SWITCHED TELEPHONE NETWORK1)
+
+*(Geneva, 1964; amended at Mar del Plata, 1968,
+and at Geneva, 1972, 1976 and 1980,
+and at Malaga-Torremolinos, 1984)*
+
+*Note* - The modem, designed for use on connections set up by switching in the general telephone network, can obviously be used on leased lines.
+
+A system of data transmission at a low data signalling rate, such that data could be transmitted over a telephone circuit operated alternatively for telephone calls and data transmissions, using simple input/output equipment and easy operating procedures, would be economical.
+
+The data signalling rate must be such as to allow the use of current types of data sources and sinks, especially electromechanical devices.
+
+The system for data transmission will be duplex, either for simultaneous two-way data transmission or for the transmission of signals sent in the backward direction for error-control purposes. The transmission must be such that use can be made of normal telephone circuits, and this applies both to the bandwidth available and to the restrictions imposed by signalling in the telephone networks.
+
+The two correspondents are brought into contact by a telephone call, and the circuit is put into the data-transmission position:
+
+- a) manually by agreement between the operators, or
+- b) automatically.
+
+For these reasons, the CCITT
+
+*unanimously declares the following view*
+
+**1** Data transmission may take place at low data signalling rates on telephone calls set up on switched telephone circuits (or on leased telephone circuits).
+
+**2** The communication circuit for data transmission is a duplex circuit whereby data transmission in both directions simultaneously is possible at 300 bit/s or less.
+
+The modulation is a binary modulation obtained by frequency shift, resulting in a modulation rate being equal to the data signalling rate.
+
+*Note* - Attention is drawn to the fact that there may be in operation some old-type V.21 modems for which the maximum data signalling rate is 200 bit/s.
+
+**3** For channel No. 1, the nominal mean frequency is 1080 Hz.
+
+For channel No. 2, it is 1750 Hz.
+
+The frequency deviation is $\pm 100$ Hz. In each channel, the higher characteristic frequency ( $F_A$ ) corresponds to a binary 0.
+
+---
+
+1) See Note under § 2 of this Recommendation.
+
+The characteristic frequencies2) as measured at the modulator output must not differ by more than $\pm 6$ Hz from the nominal figures.
+
+A maximum drift frequency of $\pm 6$ Hz is assumed for the line. Hence the demodulation equipment must tolerate drifts of $\pm 12$ Hz between the frequencies received and their nominal values.
+
+**4** Data may be transmitted by synchronous or asynchronous procedures. With synchronous operation, the modem will not have to provide the signals which would be necessary to maintain synchronism when transmission is not proceeding.
+
+**5** When echo control device disabling is required, it is recommended that the procedures specified in Recommendation V.25 be followed.
+
+**6** The maximum power output of the modem into the line shall not exceed 1 mW.
+
+The power level of the modem should be adjusted to make allowance for loss between this equipment and the point of entry to an international circuit, so that the corresponding nominal level of the signal at the international circuit input shall not exceed - 13 dBm0 (see Recommendation V.2, § 2).
+
+**7** a) When both channels are used for simultaneous both-way data transmission, channel No. 1 is used for transmission of the caller's data (i.e. the person making the telephone call) towards the called station, while channel No. 2 is used for transmission in the other direction.
+
+b) When one channel is used for data transmission and the other is used for transmission of check signals, service signals, etc., only, it is channel No. 1 which is used for transmission from the calling to the called station regardless of the direction in which the data are transmitted.
+
+c) The procedure for the assignment of the channels described under a) and b) above applies in the case of the general service of data transmission, making it possible to transmit data or check signal, service signal, etc., bilaterally between any two subscribers. In special cases which do not come under this rule, the procedure of assignment of the channels is determined by the prior agreement between the correspondents, bearing in mind the requirement proper to each service.
+
+## **8 Interchange circuits**
+
+**8.1** *List of interchange circuits essential for the modems when used on the general switched telephone network or non switched leased telephone circuits (see Table 1 /V.21)*
+
+The configurations of interchange circuits are those essential for the particular switched network or leased circuit requirement indicated. Where one or more of such requirements are provided in a modem, then all of the appropriate interchange circuit facilities should be provided.
+
+---
+
+2)The nominal characteristic frequencies;
+
+channel No. 1 ( $F_A = 1180$ Hz and $F_Z = 980$ Hz);
+
+channel No. 2 ( $F_A = 1850$ Hz and $F_Z = 1650$ Hz).
+
+TABLE 1/V.21
+
+| Interchange circuit | | General switched telephone network including terminals equipped for manual calling, manual answering, automatic calling, automatic answering
(Note 1) | Non-switched leased telephone circuits
(Note 1) | |
+|---------------------|--------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------|------------|
+| Number | Designation | | Point-to-point | Multipoint |
+| 102 | Signal ground or common return | X | X | X |
+| 103 | Transmitted data | X | X | X |
+| 104 | Received data | X | X | X |
+| 105 | Request to send | - | X (Note 2) | X |
+| 106 | Ready for sending | X | X | X |
+| 107 | Data set ready | X | X | X |
+| 108/1 | Connect data set to line | X (Note 3) | X | X |
+| 108/2 | Data terminal ready | X (Note 3) | X (Note 4) | - |
+| 109 | Data channel received line signal detector | X | X | X |
+| 125 | Calling indicator | X | - | - |
+| 126 | Select transmit frequency | - | - | X |
+
+*Note 1* - All essential interchange circuits and any others which are provided shall comply with the functional and operational requirements of Recommendation V.24. All interchange circuits indicated by X shall be properly terminated in the data terminal equipment and in the data circuit-terminating equipment in accordance with the appropriate Recommendation for electrical characteristics (see § 9).
+
+*Note 2* - Circuit 105 is not required when alternate voice/data service is used on non-switched leased point-to-point circuits.
+
+*Note 3* - The circuit shall be capable of operation as circuit 108/1 - *connect data set to line* or circuit 108/2 - *data terminal ready* depending on its use.
+
+*Note 4* - In the leased point-to-point case, where alternate voice/data service is to be provided, circuit 108/2 may be used optionally.
+
+### 8.2 Response times of circuits 106 and 109
+
+#### 8.2.1 Definitions
+
+8.2.1.1 Circuit 109 response times are the times that elapse between the connection or removal of a tone to or from the modem receive line terminals and the appearance of the corresponding ON or OFF condition on circuit 109.
+
+The test tone should have a frequency corresponding to the characteristic frequency of binary 1 and be derived from a source with an impedance equal to the nominal input impedance of the modem under test.
+
+The level of the test tone should fall into the level range between 1 dB above the actual threshold, of the received line signal detector and the maximum admissible level of the received signal. At all levels within this range the measured response times shall be within the specified limits.
+
+8.2.1.2 Circuit 106 response times are the times from the connection of an ON or OFF condition on:
+
+- circuit 105 (where it is provided) to the appearance of the corresponding OFF or ON condition on circuit 106;
+- circuit 109 (where circuit 105 is not provided) to the appearance of the corresponding ON or OFF condition on circuit 106.
+
+#### 8.2.2 Response times
+
+TABLE 2/V.21
+
+| | | |
+|--------------------|-----------------------|--------------------------|
+| Circuit 106 | | |
+| OFF to ON | 20-50 ms (see Note 1) | 400-1000 ms (see Note 2) |
+| ON to OFF | | ≤ 2ms |
+| Circuit 109 | | |
+| OFF to ON | ≤ 20 ms (see Note 1) | 300-700 ms (see Note 2) |
+| ON to OFF | | 20-80 ms |
+
+*Note 1* - These times are used on leased point-to-point networks without alternate voice data facilities and on leased multipoint facilities.
+
+*Note 2* - These times are used in the general switched network service and on leased point-to-point circuits with alternate voice data.
+
+### 8.3 Threshold of data channel received line signal detector
+
+Level of received line signal at received line signal terminals of modem for all types of connection, i.e. general switched telephone network or non-switched leased telephone circuit:
+
+| | | |
+|--------------|---------|-----------------|
+| greater than | -43 dBm | circuit 109 ON |
+| less than | -48 dBm | circuit 109 OFF |
+
+The condition of circuit 109 for levels between -43 dBm and -48 dBm is not specified except that the signal detector shall exhibit a hysteresis action such that the level at which the OFF to ON transition occurs shall be at least 2 dB greater than for the ON to OFF transition.
+
+Where transmission conditions are known on switched or leased circuits, Administrations should be permitted at the time of modem installation to change these response levels of the received line signal detector to less sensitive values (e.g. -33 dBm and -38 dBm respectively).
+
+### 8.4 Fault condition of interchange circuits
+
+See Recommendation V.28, § 7 for association of the receiver failure detection types).
+
+- 8.4.1 The DTE should interpret a fault condition on circuit 107 as an OFF condition using failure detection type 1.
+- 8.4.2 The DCE should interpret a fault condition on circuits 105 and 108 as an OFF condition using failure detection type 1.
+- 8.4.3 All other circuits not referred to above may use failure detection type 0 or 1.
+
+## 9 Electrical characteristics of interchange circuits
+
+Use of electrical characteristics conforming to Recommendation V.28 is recommended together with the connector and pin assignment plan specified by ISO 2110.
+
+*Note* - Manufacturers may wish to note that the long-term objective is to replace electrical characteristics specified in Recommendation V.28, and that Study Group XVII has agreed that the work shall proceed to develop a more efficient, all-balanced, interface for the V-Series application which minimises the number of interchange circuits.
+
+**10** The following information is provided to assist equipment manufacturers:
+
+- a) The nominal range of attenuations in subscriber-to-subscriber connections is from 5 to 30 dB at the reference frequency (800 or 1000 Hz), assuming up to 35 dB attenuation at the frequency 1750 Hz.
+- b) The data modem should have no adjustment for send level or receive sensitivity under the control of the operator.
+
+## **Reference**
+
+- [1] CCITT Recommendation *Echo suppressors*, Vol. III, Rec. G.164.
\ No newline at end of file
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+
+
+
+
+ITU logo: a globe with the letters ITU and a lightning bolt symbol.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+# ITU-T
+
+## V.22
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+# DATA COMMUNICATION OVER THE TELEPHONE NETWORK ---
+
+**1200 BITS PER SECOND DUPLEX MODEM
+STANDARDIZED FOR USE IN THE GENERAL
+SWITCHED TELEPHONE NETWORK AND
+ON POINT-TO-POINT 2-WIRE LEASED
+TELEPHONE-TYPE CIRCUITS**
+
+**ITU-T Recommendation V.22**
+
+(Extract from the *Blue Book*)
+
+---
+
+## NOTES
+
+1 ITU-T Recommendation V.22 was published in Fascicle VIII.1 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+
+2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+© ITU 1988, 1993
+
+All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.
+
+## Recommendation V.22
+
+## 1200 BITS PER SECOND DUPLEX MODEM STANDARDIZED FOR USE IN THE GENERAL SWITCHED TELEPHONE NETWORK AND ON POINT-TO-POINT 2-WIRE RELEASED TELEPHONE-TYPE CIRCUITS
+
+(Geneva, 1980; amended at Malaga-Torremolinos, 1984; and at Melbourne, 1988)
+
+## 1 Introduction
+
+1.1 This modem is intended for use on connections on General Switched Telephone Networks (GSTNs), and on point-to-point circuits when suitably conditioned.
+
+The principal characteristics of this modem are as follows:
+
+- a) duplex operation on 2-wire GSTN and point-to-point leased circuits,
+- b) channel separation by frequency division,
+- c) differential phase shift modulation for each channel with synchronous line transmission at 600 bauds (nominal),
+- d) inclusion of a scrambler,
+- e) inclusion of test facilities.
+
+1.2 Recognizing the wide range of application, this Recommendation provides for three alternative configurations. The choice of alternative is a matter for the Administration concerned. The facilities given by the alternatives are:
+
+### *Alternative A*
+
+1200 bit/s synchronous
+
+600 bit/s synchronous (optional)
+
+### *Alternative B*
+
+| | | |
+|----------------------------------|---|---------------------|
+| 1200 bit/s synchronous | } | as in Alternative A |
+| 600 bit/s synchronous (optional) | | |
+
+1200 bit/s start-stop
+
+600 bit/s start-stop (optional)
+
+### *Alternative C*
+
+| | | |
+|----------------------------------|---|---------------------|
+| 1200 bit/s synchronous | } | as in Alternative B |
+| 600 bit/s synchronous (optional) | | |
+| 1200 bit/s start-stop | | |
+| 600 bit/s start-stop (optional) | | |
+
+An asynchronous mode having capability of handling 1200 bit/s start-stop and asynchronous data at up to 300 bit/s.
+
+The selection of the asynchronous mode is made during the handshaking sequence (see § 6). This gives compatibility between Alternative B and Alternative C.
+
+*Note* - The possibility of transmitting low speed anisochronous data in Alternatives A and B is left for further study.
+
+## 2 Line signals
+
+### 2.1 Carrier and guard tone frequencies
+
+The carrier frequencies shall be $1200 \pm 0.5$ Hz for the low channel and $2400 \pm 1$ Hz for the high channel. A guard tone of $1800 \text{ Hz} \pm 20$ Hz, to be transmitted only when the modem is transmitting in the high channel, may be disabled as a national option. An alternative guard tone of $550 \pm 20$ Hz may be incorporated as a national option. The question of international calls between countries requiring different guard tones is left for further study.
+
+### 2.2 Data and guard tone line signal levels
+
+The 1800-Hz guard tone shall be at a level of $6 \pm 1$ dB below the level of the data power in the high channel. The level of the optional 550 Hz tone is for further study. The total power transmitted to line shall be in accordance with Recommendation V.2 and shall be the same for transmission in either channel. Because of the 1800-Hz guard tone, the power level of data signals in the high channel will be approximately 1 dB lower than data signals in the low channel.
+
+### 2.3 Fixed compromise equalizer
+
+Fixed compromise equalization shall be incorporated in the modem. Such equalization shall be equally shared between transmitter and receiver. The characteristics of the equalizer shall be the responsibility of each Administration to recommend nationally. The possibility of producing compromise characteristics for international implementation is for further study.
+
+### 2.4 Spectrum and group-delay characteristic
+
+After making allowance for the nominal specified compromise equalizer characteristic, the transmitted line signal shall have a frequency spectrum equivalent to the square root of a raised cosine shaping with a 75% roll-off and within the limits of Figure 1/V.22. Similarly, the group delay of the transmitter output shall be within $\pm 150$ microseconds over the frequency range 900 Hz-1500 Hz (low channel) and 2100 Hz-2700 Hz (high channel). These figures are provisional.
+
+
+
+| Carrier frequency (Hz) | Relative amplitude (dB) - Solid line | Relative amplitude (dB) - Dashed line |
+|------------------------|--------------------------------------|---------------------------------------|
+| -600 | -20 | - |
+| -550 | - | -20 |
+| -450 | -5 | -5 |
+| -300 | -2 | -2 |
+| -200 | -1 | -1 |
+| -125 | -0.5 | -0.5 |
+| 0 | 0 | 0 |
+| 125 | -0.5 | -0.5 |
+| 200 | -1 | -1 |
+| 300 | -2 | -2 |
+| 450 | -5 | -5 |
+| 550 | - | -20 |
+| 600 | -20 | - |
+
+Figure 1/V.22: Amplitude limits for transmitted line signal (unequalized). The graph shows relative amplitude in dB versus carrier frequency in Hz. The y-axis ranges from -25 to 0.75 dB, and the x-axis ranges from -600 to 600 Hz. Two curves define the limits: a solid line and a dashed line. The solid line starts at -20 dB at -600 Hz, rises to -5 dB at -400 Hz, peaks at 0 dB at 0 Hz, and falls to -20 dB at 600 Hz. The dashed line starts at -20 dB at -550 Hz, rises to -5 dB at -450 Hz, peaks at 0 dB at 0 Hz, and falls to -20 dB at 550 Hz. The area between the two curves is shaded with diagonal lines. The text 'CCITT - 20321' is at the bottom right.
+
+FIGURE 1/V.22
+
+Amplitude limits for transmitted line signal (unequalized)
+
+### 2.5 Modulation
+
+#### 2.5.1 Data signalling rates
+
+Alternatives A and B: The data signalling rate transmitted to line shall be 1200 bit/s or 600 bit/s $\pm 0.01\%$ with a modulation rate of 600 baud $\pm 0.01\%$ .
+
+Alternative C: In Modes i), ii), iii) and iv) (§ 4) the data signalling rates are as in Alternatives A and B. In Mode v), the data signalling rate transmitted to line shall be 1205.1 bit/s with a modulation rate of $602.5 \pm 0.5$ baud. Optionally in Mode v), the line rate shall be $1223 \pm 2$ bit/s with a modulation rate of $611.5 \pm 1$ baud.
+
+#### 2.5.2 Encoding of data bits
+
+##### 2.5.2.1 1200 bits per second
+
+The data stream to be transmitted shall be divided into groups of 2 consecutive bits (dibits). Each dibit shall be encoded as a phase change relative to the phase of the preceding signal element (see Table 1/V.22). At the receiver, the dibits shall be decoded and the bits reassembled in correct order. The left-hand digit of the dibit is the one occurring first in the data stream as it enters the modulator portion of the modem after the scrambler.
+
+TABLE 1/V.22
+
+| Dibit values
(1200 bit/s) | Bit values
(600 bit/s) | Phase change
(Modes i, ii, iii, iv) | Phase change
(Mode v) |
+|------------------------------|---------------------------|----------------------------------------|--------------------------|
+| 00 | 0 | + 90° | + 270° |
+| 01 | - | 0° | + 180° |
+| 11 | 1 | + 270° | + 90° |
+| 10 | - | + 180° | 0° |
+
+*Note* - The phase change is the actual on-line phase shift in the transition region from the centre of one signalling element to the centre of the following signalling element.
+
+##### 2.5.2.2 600 bits per second
+
+Each bit shall be encoded as a phase change relative to the phase of the preceding signal element (see Table 1/V.22).
+
+### 2.6 Received signal frequency tolerance
+
+Noting that the frequency tolerance of the transmitter carriers is $\pm 1$ Hz or less, and assuming a maximum shift of $\pm 6$ Hz in the connection, the receiver shall be able to accept errors of at least $\pm 7$ Hz in the received frequencies.
+
+## 3 Interchange circuits
+
+### 3.1 Table of interchange circuits (Note 1 of Table 2/V.22)
+
+Essential and optional interchange circuits are listed in Table 2/V.22.
+
+TABLE 2/V.22
+
+#### **Interchange circuits (Note 1)**
+
+| Interchange circuit | | Notes |
+|---------------------|------------------------------------------------|--------|
+| No. | Description | |
+| 102 | Signal ground or common return | Note 2 |
+| 103 | Transmitted data | |
+| 104 | Received data | |
+| 105 | Request to send | |
+| 106 | Ready for sending | |
+| 107 | Data set ready | |
+| 108/1 | Connect data set to line | Note 3 |
+| 108/2 | Data terminal ready | Note 3 |
+| 109 | Data channel received line signal detector | Note 4 |
+| 111 | Data signalling rate selector (DTE source) | |
+| 113 | Transmitter signal element timing (DTE source) | |
+| 114 | Transmitter signal element timing (DCE source) | |
+| 115 | Receiver signal element timing (DCE source) | Note 6 |
+| 125 | Calling indicator | Note 6 |
+| 140 | Loopback/maintenance test | Note 7 |
+| 141 | Local loopback | |
+| 142 | Test indicator | |
+
+*Note 1* - All essential interchange circuits and any others which are provided shall comply with the functional and operational requirements of Recommendation V.24. All interchange circuits provided shall be properly terminated in the data terminal equipment and in the data circuit-terminating equipment in accordance with the appropriate Recommendation for electrical characteristics (see § 3.5).
+
+*Note 2* - Some automatic calling equipments are designed to emit a calling tone to line by turning ON circuit 105 to the calling modem. The general switched telephone network (GSTN) constant carrier handshake is such that no calling tone will be emitted by the V.22 modem when used with these equipments.
+
+*Note 3* - This circuit shall be capable of operation as circuit 108/1 or 108/2 depending on its use.
+
+*Note 4* - This circuit is optional if only the 1200 bit/s speed [modes i) and ii) as defined in §§ 4.1, 4.2 and 4.3] is provided in the modem. If the 600 bit/s speed [modes iii) and iv)] is also provided, this circuit is essential.
+
+*Note 5* - When the modem is not operating in a synchronous mode any signals on this circuit shall be disregarded. Many DTEs operating in an asynchronous mode do not have a generator connected to this circuit.
+
+*Note 6* - When the modem is not operating in a synchronous mode, this circuit shall be clamped to the OFF condition. Many DTEs operating in an asynchronous mode do not terminate this circuit.
+
+*Note 7* - This circuit is for use with the general switched telephone network only.
+
+### 3.2 *Circuits 106 and 109 response times (see Table 3/V.22)*
+
+Circuit 106 response times are from the application of an ON or OFF condition on circuit 105. See also § 6 for operating sequences.
+
+TABLE 3/V.22
+
+| | Constant carrier | Controlled carrier |
+|--------------------|------------------|--------------------|
+| Circuit 106 | | |
+| OFF to ON | $\leq 2$ ms | 210 to 275 ms |
+| ON to OFF | $\leq 2$ ms | $\leq 2$ ms |
+| Circuit 109 | | |
+| OFF to ON | 105 to 205 ms | 105 to 205 ms |
+| ON to OFF | 10 to 24 ms | 10 to 24 ms |
+
+### 3.3 *Circuit 109 thresholds*
+
+High channel threshold:
+
+| | | |
+|--------------|---------|-----------------|
+| greater than | -43 dBm | circuit 109 ON |
+| less than | -48 dBm | circuit 109 OFF |
+
+Low channel threshold:
+
+| | | |
+|--------------|---------|-----------------|
+| greater than | -43 dBm | circuit 109 ON |
+| less than | -48 dBm | circuit 109 OFF |
+
+The condition of circuit 109 between the ON and OFF levels is not specified, except that the signal detector shall exhibit a hysteresis action such that the level at which the OFF to ON transition occurs shall be at least 2 dB greater than for the ON to OFF transition.
+
+Circuit 109 thresholds are specified at the input to the modem excluding the effects of the compromise equalizer.
+
+Circuit 109 shall not respond to the 1800-Hz or 550-Hz guard tones, or the 2100-Hz (nominal) answer tone during the handshake sequence.
+
+Administrations are permitted to change these thresholds where transmission conditions are known.
+
+### 3.4 *Circuit 111 and data rate control*
+
+Data rate selection may be by switch (or similar means) or by circuit 111 or a combination of both.
+
+The ON condition on circuit 111, where provided, shall select 1200 bit/s operation and the OFF condition shall select 600 bit/s operation.
+
+### 3.5 *Electrical characteristics of interchange circuits*
+
+Use of electrical characteristics conforming to Recommendation V.28 is recommended together with the connector and pin assignment plan specified by ISO 2110.
+
+*Note* - Manufacturers may wish to note that the long-term objective is to replace electrical characteristics specified in Recommendation V.28, and that Study Group XVII has agreed that the work shall proceed to develop a more efficient, all-balanced, interface for the V-Series application which minimizes the number of interchange circuits.
+
+### 3.6 *Fault condition of interchange circuits*
+
+(See Recommendations V.28, § 7 for association of the receiver failure detection types.)
+
+- 3.6.1 The DTE should interpret a fault condition on circuit 107 as an OFF condition using failure detection type 1.
+- 3.6.2 The DCE should interpret a fault condition on circuits 105 and 108 as an OFF condition using failure detection type 1.
+- 3.6.3 All other circuits not referred to above may use failure detection type 0 or 1.
+
+## 4 **Modes of operation over the DTE/DCE interface**
+
+### 4.1 *Alternative A*
+
+The modem can be configured for the following modes of operation:
+
+Mode i) 1200 bit/s $\pm$ 0.01% synchronous
+
+Mode iii) 600 bit/s $\pm$ 0.01% synchronous (optional).
+
+In these modes of operation, the modem shall accept synchronous data from the DTE on circuit 103 under control of circuit 113 or circuit 114. The data shall then be scrambled in accordance with § 5 and then passed to the modulator for encoding in accordance with § 2.5.2.
+
+In addition to standard V.24 transmitter timing arrangements, the modem shall provide capabilities to derive transmit signal element timing from receiver signal element timing.
+
+### 4.2 *Alternative B*
+
+The modem can be configured for the following modes of operation:
+
+Mode i) 1200 bit/s $\pm$ 0.01% synchronous
+
+Mode ii) 1200 bit/s start-stop 8, 9, 10 or 11 bits per character
+
+| | |
+|------------------------------------------------------------------|------------|
+| (Mode iii) 600 bit/s $\pm$ 0.01% synchronous optional | } optional |
+| (Mode iv) 600 bit/s start-stop 8, 9, 10 or 11 bits per character | |
+
+The synchronous modes are as given in Alternative A.
+
+In the start-stop modes, the modem shall accept a data stream of start-stop characters from the DTE at a nominal rate of 1200 or 600 bits per second. The start-stop data to be transmitted shall be converted, in conformity with Recommendation V.14, to a synchronous data stream suitable for transmission in accordance with § 4.1
+
+Demodulated data shall be decoded in accordance with § 2.5.2, then descrambled in accordance with § 5 and then passed to the converter in conformity with Recommendation V.14 for regaining the data stream of start-stop characters.
+
+The intracharacter signalling rate provided to the DTE over circuit 104 shall be in the ranges given in Table 4/V.22 when operating in the basic or in the extended signalling rate ranges, respectively.
+
+TABLE 4/V.22
+
+#### **Intracharacter signalling rate range**
+
+| Data rate | Signalling rate range | |
+|------------|-----------------------|--------------------|
+| | Basic | Extended |
+| 600 bit/s | 600 to 606 bit/s | 600 to 614 bit/s |
+| 1200 bit/s | 1200 to 1212 bit/s | 1200 to 1227 bit/s |
+
+### 4.3 *Alternative C*
+
+The modem can be configured for the following modes of operation.
+
+Mode i) 1200 bit/s ± 0.01% synchronous
+
+Mode ii) 1200 bit/s start-stop 8, 9, 10 or 11 bits per character
+
+| | | |
+|-----------------------------------------------------------------------------------------------------------------------|---|----------|
+| (Mode iii) 600 bit/s ± 0.01% synchronous optional
(Mode iv) 600 bit/s start-stop 8, 9, 10 or 11 bits per character | } | optional |
+|-----------------------------------------------------------------------------------------------------------------------|---|----------|
+
+Mode v) An asynchronous mode having capability of handling 1200 bit/s start-stop and anisochronous data at up to 300 bit/s.
+
+Modes i) to iv) are as given in Alternative B.
+
+#### 4.3.1 *Basic modes*
+
+In Alternative C, the modem shall incorporate Modes i), ii), iii) and iv) given in Alternative B, plus Mode v), in which the modem transmitter sends data at a rate always greater than the input data rate, and thus disables the receiver buffer. The GSTN handshaking sequence allows automatic selection of Modes ii) or v). Modes i), iii) and iv) must be selected at installation. On leased circuits there is no automatic mode selection. The line encoding for specific dibit values is described in Table 1/V.22.
+
+#### 4.3.2 *Transmitter*
+
+In Mode v), the modem shall accept a data stream of start-stop characters from the DTE at a nominal rate of a 0 to 300 bit/s or 1200 bit/s automatically. The transmitter buffer that converts incoming data to a synchronous data stream at 1205 bit/s or 1223 bit/s shall:
+
+- a) start its asynchronous bit counter on either data transition,
+- b) always transmit the last bit received over circuit 103 after the bit counter has elapsed,
+- c) sample incoming data during the bit count at 1205 Hz or 1223 Hz depending upon line rate.
+
+This will assure that incoming data at 0 to 300 bit/s shall pass through the buffer with a maximum introduced distortion of 25% at 300 bit/s (and 12.5% at 150 bit/s), and that break signals pass through the buffer unchanged.
+
+The length and structure of incoming characters shall be the same as given in Alternative B. Within Mode v) at 1200 bit/s asynchronous, two adjacent character formats, e.g. 9- and 10-bit character, can be handled automatically. As in Alternative B, the modem shall derive its line signal clock from internal clock circuits, or alternatively, from receiver signal element timing, as an installation option.
+
+#### 4.3.3 Basic signalling rate range
+
+In Mode v), the intracharacter signalling rate provided by the DTE on circuit 103 must be:
+
+1205 bit/s line rate 0 to 301 bit/s and 1170 to 1204 bit/s
+
+1223 bit/s line rate 0 to 305 bit/s and 1190 to 1221 bit/s
+
+Selection of line rate is made in the transmitter by installer option and automatically detected in the receiver.
+
+## 5 Scrambler and descrambler
+
+### 5.1 Scrambler
+
+A self synchronizing scrambler having the generating polynomial $1 \oplus x^{-14} \oplus x^{-17}$ shall be included in the modem transmitter. The message data sequence applied to the scrambler shall be effectively divided by the generating polynomial. The coefficients of the quotients of this division, taken in descending order, form the data sequence which shall appear at the output of the scrambler. The scrambler output data sequence
+
+$$D_s = D_i \oplus D_s \cdot x^{-14} \oplus D_s \cdot x^{-17}$$
+
+where
+
+$D_s$ is the data sequence at the output of the scrambler
+
+$D_i$ is the data sequence applied to the scrambler
+
+$\oplus$ denotes modulo 2 addition
+
+$\cdot$ denotes binary multiplication
+
+Figure 2/V.22 shows a suitable implementation.
+
+To prevent occasional inadvertent instigation of remote loop 2 caused by scrambler lockup, circuitry shall be included to detect a sequence of 64 consecutive ones at the scrambler output ( $D_s$ ) and, if detected, invert the next input to the scrambler, $D_i$ . This circuitry will not operate during handshaking or during the instigation of remote loop 2.
+
+
+
+$D_s = D_i \oplus D_s \cdot x^{-14} \oplus D_s \cdot x^{-17}$ CCITT-28332
+
+Logic diagram of a scrambler implementation. The diagram shows a feedback loop where the output D\_s is fed back through two delay elements (x^-14 and x^-17) and added to the input D\_i to produce the output D\_s. A detector monitors the output D\_s for a sequence of 64 consecutive ones, and if detected, it inverts the input D\_i. The diagram includes a 'Detector' block, a 'See Note 2' block, and a 'Detector' block. The output D\_s is fed back through two delay elements (x^-14 and x^-17) and added to the input D\_i to produce the output D\_s. The diagram is labeled with the equation D\_s = D\_i \oplus D\_s \cdot x^{-14} \oplus D\_s \cdot x^{-17} and the reference CCITT-28332.
+
+*Note 1* Marks (binary 1) and spaces (binary 0) at the V.24 interface correspond to ones and zeros, respectively, in this logic diagram.
+
+*Note 2* Circuitry shall be included to detect a sequence of 64 consecutive binary ones at the scrambler output ( $D_s$ ) and, if detected, invert the next input to the scrambler ( $D_i$ ).
+
+FIGURE 2/V.22
+
+Scrambler
+
+5.2 *Descrambler*
+
+A self synchronizing descrambler having the polynomial $1 \oplus x^{-14} \oplus x^{-17}$ shall be provided in the modem receiver. The message data sequence produced after demodulation shall be effectively multiplied by the generating polynomial $1 \oplus x^{-14} \oplus x^{-17}$ to form the descrambled message. The coefficients of the recovered message sequence taken in descending order form the output data sequence $D_o$ , which is given by
+
+$$D_o = D_s (1 \oplus x^{-14} \oplus x^{-17})$$
+
+Figure 3/V.22 shows a suitable implementation.
+
+
+
+The diagram shows a self-synchronizing descrambler implementation. Input data $D_s$ enters a series of shift register stages labeled $x^{-1}$ . There are 17 stages in total. Taps are taken after the 14th stage ( $D_s \cdot x^{-14}$ ) and the 17th stage ( $D_s \cdot x^{-17}$ ). These two taps are combined in an XOR gate (circle with a plus). The result of this XOR operation is then XORed with the original input $D_s$ to produce the output data $D_o$ . A 'Detector' block monitors the input $D_s$ , and its output goes to a 'See Note 2' block which can influence the final output. The equation $D_o = D_i = D_s (1 \oplus x^{-14} \oplus x^{-17})$ is shown below the diagram. The reference CCITT-28342 is in the bottom right.
+
+Figure 3/V.22 Descrambler block diagram
+
+*Note 1* - Marks (binary 1) and spaces (binary 0) at the V.24 interface correspond to ones and zeros, respectively, in this logic diagram.
+
+*Note 2* - Circuitry may be included to detect a sequence of 64 consecutive ones at the input to the descrambler ( $D_s$ ) and, if detected, invert the next output from the descrambler, ( $D_o$ ). This detector should not begin operating until the handshaking sequence is complete. If this circuitry is included, detection of the initiation signal described in § 7.1.1 (unscrambled binary ones) should be performed at the point $D_o$ .
+
+FIGURE 3/V.22
+
+**Descrambler**
+
+**6 Operating sequences**
+
+6.1 *Channel and operating mode selection*
+
+On the general switched telephone network, the modem at the calling data station shall transmit in the low channel and receive in the high channel (call mode). The modem at the answering data station shall receive in the low channel and transmit in the high channel (answer mode).
+
+Where calls are established on the GSTN by operators, bilateral agreement between users on channel allocation will be necessary. On point-to-point leased circuits, channel allocation will be by bilateral agreement between Administrations or users. In these cases the method of selection of call or answer mode is a national matter.
+
+On point-to-point leased circuits, selection of Modes i) to v) will be by bilateral agreement between Administrations or users. The method of selection is a national matter.
+
+6.2 *V.25 automatic answering sequence*
+
+The V.25 automatic answering sequence shall be transmitted from the answer mode modem on international GSTN connections. The transmission of the sequence may be omitted on point-to-point leased circuits or on national connections on the GSTN, where permitted by the Administration.
+
+**Fascicle VIII.1 - V.22** **9**
+
+### 6.3 Operating sequences for Alternatives A and B
+
+#### 6.3.1 GSTN - constant carrier
+
+The means of achieving initial synchronism between the call mode modem and the answer mode modem on international GSTN connections is shown in Figure 4/V.22. The alternative handshake without V.25 automatic answering is shown in Figure 5/V.22.
+
+
+
+**Call mode modem**
+
+Transmitted line signal
+
+Silence > 400 ms
+
+Connect to line
+
+Wait $456 \pm 10$ ms
+
+Scrambled binary 1
+
+Data
+
+Detect unscrambled binary 1 in $155 \pm 50$ ms
+
+107
+
+Detect scrambled binary 1 in $270 \pm 40$ ms
+
+Wait $765 \pm 10$ ms
+
+109
+
+106a)
+
+104
+
+Clamped to binary 1
+
+Binary 1
+
+Data
+
+**Answer mode modem**
+
+Transmitted line signal
+
+Silence $2150 \pm 350$ ms
+
+2100 Hz
+
+3300 $\pm$ 700 ms
+
+Unscrambled binary 1 and 1800 Hz
+
+75 $\pm$ 20 ms
+
+107
+
+Detect scrambled binary 1 or binary 0 in $270 \pm 40$ ms
+
+Wait $765 \pm 10$ ms
+
+106a)
+
+109
+
+Note – Binary 0 comes from Alternative C
+
+104 clamped to binary 1
+
+Binary 1
+
+Data
+
+a) Assumes circuit 105 has been turned on.
+
+CCITT-34630
+
+The diagram illustrates the handshake sequence between a Call mode modem and an Answer mode modem. The Call mode modem starts with a silence period of more than 400 ms before connecting to the line. It then waits for 456 ± 10 ms before sending scrambled binary 1. The Answer mode modem receives this signal and detects unscrambled binary 1 within 155 ± 50 ms. It then sends scrambled binary 1, which the Call mode modem detects within 270 ± 40 ms. Both sides then wait for 765 ± 10 ms before sending data. The diagram also shows the timing for the 2100 Hz and 3300 Hz signals and the 1800 Hz signal. The sequence is labeled with circuit numbers 104, 106a), 107, 109, and 110.
+
+Timing diagram for GSTN handshake sequence showing Call mode and Answer mode modem signals and actions.
+
+FIGURE 4/V.22
+
+Handshake sequence for Alternatives A and B (with V.25 auto-answering)
+
+
+
+**Call mode modem**
+
+Transmitted line signal
+
+Connect to line
+
+Wait $456 \pm 10$ ms
+
+Detect unscrambled binary 1 in $155 \pm 50$ ms
+
+Scrambled binary 1
+
+Detect scrambled binary 1 in $270 \pm 40$ ms
+
+Wait $765 \pm 10$ ms
+
+107
+
+109
+
+106a)
+
+104
+
+Clamped to binary 1
+
+Binary 1
+
+Data
+
+**Answer mode modem**
+
+Transmitted line signal
+
+Unscrambled binary 1 and 1800 Hz
+
+Scrambled binary 1 and 1800 Hz
+
+Data and 1800 Hz
+
+Connect to line
+
+Detect scrambled binary 1 or binary 0 in $270 \pm 40$ ms
+
+Wait $765 \pm 10$ ms
+
+107
+
+106a)
+
+109
+
+Note – Binary 0 comes from Alternative C
+
+104 clamped to binary 1
+
+Binary 1
+
+Data
+
+a) Assumes circuit 105 has been turned on.
+
+CCITT-34840
+
+Timing diagram for V.22 Handshake sequence for Alternatives A and B. The diagram shows two scenarios: Call mode modem and Answer mode modem. It details the sequence of signals (Transmitted line signal, Connect to line), detection times for binary 1 (unscrambled and scrambled), and the resulting states of various circuits (104, 106, 107, 109).
+
+FIGURE 5/V.22
+
+#### Handshake sequence for Alternatives A and B (without V.25 auto-answer sequence)
+
+##### 6.3.1.1 Call mode modem
+
+Once the call mode modem has connected to line, it shall be conditioned to receive signals in the high channel and shall apply an ON condition to circuit 107 in accordance with Recommendation V.25. The modem shall remain silent until unscrambled binary 1 is detected for $155 \pm 50$ ms, and after waiting for $456 \pm 10$ ms shall transmit scrambled binary 1 in the low channel. Upon detecting scrambled binary 1 in the high channel in $270 \pm 40$ ms, the modem shall turn circuit 109 ON, then wait a further $765 \pm 10$ ms. Circuit 106 shall then respond to the condition of circuit 105 according to Table 3/V.22 constant carrier mode. When circuit 106 is OFF, circuit 103 shall be clamped to the binary 1 condition.
+
+*Note* - Manufacturers may wish to note that in certain countries, for national purposes, modems are in service which emit an answering tone of 2225 Hz instead of unscrambled binary 1.
+
+##### 6.3.1.2 *Answer mode modem*
+
+Once the answer mode modem has connected to line and immediately following the V.25 answer sequence, the modem shall be conditioned to receive signals in the low channel. It shall then apply an ON condition to circuit 107 and transmit unscrambled binary 1. Upon detecting scrambled binary 1 or 0 in the low channel in $270 \pm 40$ ms, the modem shall transmit scrambled binary 1 in the high channel, and after waiting for $765 \pm 10$ ms, apply an ON condition to circuit 109. Circuit 106 shall then respond to the condition of circuit 105 according to Table 3/V.22, constant carrier mode. When circuit 106 is OFF, circuit 103 shall be clamped to the binary 1 condition.
+
+Where both modems are manually connected to line this sequence will apply irrespective of whether the call or answer mode modem is connected to line first.
+
+After completion of the handshake sequence, any inadvertent loss and reappearance of the received line signal should not cause another handshake sequence to be generated. Circuit 109 should respond with the response times given in Table 3/V.22.
+
+#### 6.3.2 *GSTN and point-to-point leased circuits - controlled carrier*
+
+Once an ON condition has been applied to circuit 105 by the DTE, the modem shall transmit a synchronizing signal corresponding to binary 1 applied to circuit 103. The ON condition shall be applied to circuit 106, 210 to 275 ms after starting to transmit the synchronizing signal. The receiving modem shall establish timing and descrambler synchronization and then turn circuit 109 ON in 105 to 205 ms.
+
+Each direction of transmission shall be independently controlled.
+
+*Note* - Controlled carrier operation on GSTN is optional. For circuits with echo suppressors, controlled carrier working is not recommended.
+
+### 6.4 *Operating sequence for Alternative C*
+
+Refer to Figure 6/V.22.
+
+#### 6.4.1 *GSTN - constant carrier*
+
+##### 6.4.1.1 *Call mode modem*
+
+If configured for Modes i), iii), or iv), the handshake sequence proceeds as for Alternative B. If configured for Mode v), the handshaking sequence shall automatically select Mode ii) or v). This sequence shall be as follows:
+
+Once the call mode modem has connected to line, it shall be conditioned to receive signals in the high channel and shall apply an ON condition to circuit 107 in accordance with Recommendation V.25. The modem shall remain silent until unscrambled binary 1 [Mode ii)] is detected for $155 \pm 50$ ms and after waiting for $456 \pm 10$ ms shall transmit scrambled binary 0 [Mode ii)] in the low channel. Upon detecting scrambled binary 1 [Mode ii)] in the high channel within $270 \pm 40$ ms, the modem shall turn circuit 109 ON, enter Mode ii), then wait a further $765 \pm 10$ ms. Upon detecting scrambled binary 1 [Mode v)] in the high channel in $270 \pm 40$ ms, the modem shall turn ON circuit 109, enter Mode v), then wait a further $765 \pm 10$ ms. Circuit 106 shall then respond to the condition of circuit 105 according to Table 3/V.22 constant carrier mode. When circuit 106 is OFF, circuit 103 shall be clamped to the binary 1 condition.
+
+See also the note in § 6.3.1.1.
+
+##### 6.4.1.2 *Answer mode modem, Mode v)*
+
+Once the answer mode modem has connected to line and immediately following the V.25 answer sequence, the modem shall be conditioned to receive signals in the low channel. It shall then apply an ON condition to circuit 107 and transmit unscrambled binary 1 [Mode ii)].
+
+If scrambled binary 0 [Mode ii)] is detected in the low channel for $270 \pm 40$ ms, the modem shall enter Mode v), transmit scrambled binary 1 [Mode v)] in the high channel and after waiting for $765 \pm 10$ ms apply an ON condition to circuit 109.
+
+If scrambled binary 1 [Mode ii)] is detected in the low channel for $270 \pm 40$ ms, the modem shall enter Mode ii), transmit scrambled binary 1 [Mode ii)] in the high channel and after waiting for $765 \pm 10$ ms apply an ON condition to circuit 109.
+
+Circuit 106 shall respond to the condition of circuit 105 according to Table 3/V.22 constant carrier mode. When circuit 106 is OFF circuit 103 shall be clamped to the binary 1 condition.
+
+#### 6.4.2 *GSTN and point-to-point leased circuits*
+
+Controlled carrier operation as in § 6.3.2.
+
+##### **Call mode modem**
+
+![Timing diagram for Call mode modem handshake sequence. It shows the interaction between a Transmitted line signal and a Connect to line signal. The sequence includes detecting unscrambled binary 1 [mode ii] in 155 ± 50 ms, waiting 456 ± 10 ms, detecting scrambled binary 0 [mode ii], and then detecting scrambled binary 1 [mode ii] from Alternative B modem in 270 ± 40 ms. This leads to Scrambled binary 1 [mode ii] and Data [mode ii]. A wait of 765 ± 10 ms follows, then detecting scrambled binary 1 [mode v] from Alternative C modem in 270 ± 40 ms, leading to Scrambled binary 1 [mode v] and Data [mode v]. Signal levels 107, 109, and 106a are indicated. A note '104 Clamped to binary 1' is present.](bd0b93e7a46ede276d0a3b79ac487bd9_img.jpg)
+
+**Call mode modem**
+
+Transmitted line signal
+
+Connect to line
+
+Wait $456 \pm 10$ ms
+
+Detect unscrambled binary 1 [mode ii] in $155 \pm 50$ ms
+
+Scrambled binary 0 [mode ii]
+
+Detect scrambled binary 1 [mode ii] from Alternative B modem
+
+In $270 \pm 40$ ms enter mode ii)
+
+Scrambled binary 1 [mode ii]
+
+Data [mode ii]
+
+Wait $765 \pm 10$ ms
+
+Detect scrambled binary 1 [mode v] from Alternative C modem
+
+In $270 \pm 40$ ms enter mode v)
+
+Scrambled binary 1 [mode v]
+
+Data [mode v]
+
+107
+
+109
+
+106a)
+
+104 Clamped to binary 1
+
+Binary 1
+
+Data
+
+Timing diagram for Call mode modem handshake sequence. It shows the interaction between a Transmitted line signal and a Connect to line signal. The sequence includes detecting unscrambled binary 1 [mode ii] in 155 ± 50 ms, waiting 456 ± 10 ms, detecting scrambled binary 0 [mode ii], and then detecting scrambled binary 1 [mode ii] from Alternative B modem in 270 ± 40 ms. This leads to Scrambled binary 1 [mode ii] and Data [mode ii]. A wait of 765 ± 10 ms follows, then detecting scrambled binary 1 [mode v] from Alternative C modem in 270 ± 40 ms, leading to Scrambled binary 1 [mode v] and Data [mode v]. Signal levels 107, 109, and 106a are indicated. A note '104 Clamped to binary 1' is present.
+
+##### **Answer mode modem**
+
+![Timing diagram for Answer mode modem handshake sequence. It shows the interaction between a Transmitted line signal and a Connect to line signal. The sequence includes detecting scrambled binary 1 [mode ii] from Alternative B modem, then detecting scrambled binary 1 [mode ii] and 1800 Hz in 270 ± 40 ms, leading to Scrambled binary 1 [mode ii] and Data [mode ii] and 1800 Hz. A wait of 765 ± 10 ms follows, then detecting scrambled binary 0 [mode ii] from Alternative C modem, leading to Scrambled binary 1 [mode v] and 1800 Hz and Data [mode v] and 1800 Hz. Signal levels 107, 109, and 106a are indicated. A note '104 Clamped to binary 1' is present.](7efae06af3af43ffe5d4b956a679cf54_img.jpg)
+
+**Answer mode modem**
+
+Transmitted line signal
+
+Connect to line
+
+Detect scrambled binary 1 [mode ii] from Alternative B modem
+
+In $270 \pm 40$ ms enter mode ii)
+
+Scrambled binary 1 [mode ii] and 1800 Hz
+
+Data [mode ii] and 1800 Hz
+
+Wait $765 \pm 10$ ms
+
+Detect scrambled binary 0 [mode ii] from Alternative C modem
+
+In $270 \pm 40$ ms enter mode v)
+
+Scrambled binary 1 [mode v] and 1800 Hz
+
+Data [mode v] and 1800 Hz
+
+107
+
+109
+
+106a)
+
+104 Clamped to binary 1
+
+Binary 1
+
+Data
+
+Timing diagram for Answer mode modem handshake sequence. It shows the interaction between a Transmitted line signal and a Connect to line signal. The sequence includes detecting scrambled binary 1 [mode ii] from Alternative B modem, then detecting scrambled binary 1 [mode ii] and 1800 Hz in 270 ± 40 ms, leading to Scrambled binary 1 [mode ii] and Data [mode ii] and 1800 Hz. A wait of 765 ± 10 ms follows, then detecting scrambled binary 0 [mode ii] from Alternative C modem, leading to Scrambled binary 1 [mode v] and 1800 Hz and Data [mode v] and 1800 Hz. Signal levels 107, 109, and 106a are indicated. A note '104 Clamped to binary 1' is present.
+
+a) Assumes circuit 105 has been turned on.
+
+CCITT - 34.651
+
+FIGURE 6/V.22
+
+Handshake sequence for Alternative C (without V.25 auto-answer sequence)
+
+## **7 Testing facilities**
+
+### **7.1 Test loops**
+
+Test loops 2 (local and remote) and 3 as defined in Recommendation V.54 shall be provided. Interface operation shall be as defined in Recommendation V.54. Instigation and termination sequences are not compatible with Recommendation V.54.
+
+#### **7.1.1 Instigation of remote loop 2**
+
+Signals controlling the application of remote loop 2 may only be transmitted after the synchronizing andshake has been completed.
+
+As in Recommendation V.54, the modems are referred to as modem A and modem B.
+
+When modem A is instructed to instigate a remote loop 2, the modem shall transmit an initiation signal of unscrambled binary 1.
+
+Modem B shall detect 154-231 ms of the initiation signal, and then transmit to modem A scrambled alternate binary ones and zeros (reversals) at 1200 bit/s (or 600 bit/s).
+
+Modem A shall detect 231-308 ms of scrambled reversals, cease transmission of the initiation signal, and then transmit scrambled binary 1 at 1200 bit/s (or 600 bit/s).
+
+Modem B shall detect the loss of initiation signal and activate loop 2 within modem B.
+
+Modem A, upon receiving 231-308 ms of scrambled binary 1 shall indicate to the DTE that it may begin sending test messages.
+
+#### **7.1.2 Termination of remote loop 2**
+
+When modem A is instructed to terminate a remote loop 2, the line signal shall be suppressed for a period of $77 \pm 10$ ms, after which transmission shall be restored.
+
+Modem B detects the loss of line signal in $17 \pm 7$ ms and detects the reappearance of the signal within $155 \pm 50$ ms, after which it returns to normal operation.
+
+### **7.2 Self tests**
+
+#### **7.2.1 Self test end-to-end**
+
+Upon activation of the self-test switch an internally generated data pattern of alternate binary ones and zeros (reversals) at the selected bit rate shall be applied to the scrambler. An error detector, capable of identifying errors in a stream of reversals shall be connected to the output of the descrambler. The presence of errors shall be indicated by a visual indicator. All generating interchange circuits except 114 (if used), 115 and 142 shall be clamped to the binary 1 or OFF condition. If circuit 113 is used, the DCE shall disregard this interchange circuit and use its internal clock.
+
+#### **7.2.2 Self test with loop 3**
+
+Loop 3 shall be applied to the modem as defined in Recommendation V.54. The self-test switch shall be activated and DCE operation shall be as in § 7.2.1.
+
+#### **7.2.3 Self test with remote loop 2**
+
+The modem shall be conditioned to instigate a loop 2 at the remote modem as specified in § 7.1. The self-test switch shall be activated and DCE operation shall be as in § 7.2.1.
+
+It shall be possible to perform the above tests (§§ 7.2.1, 7.2.2 and 7.2.3) with or without the DTE connected to the modem. These tests employ an internally generated data pattern that is controlled by a switch on the DCE.
+
+7.2.4 During any self-test mode, interchange circuits 103, 105 and 108 will be ignored. Note that self tests do not test asynchronous-to-synchronous converter circuits in either the transmitter or receiver.
+
+*Note* - Inclusion of remote loop signalling according to Recommendation V.54 is for further study.
\ No newline at end of file
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+
+
+
+ITU logo: a globe with the letters ITU and a lightning bolt symbol.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+***V.22 bis***
+
+# **DATA COMMUNICATION OVER THE TELEPHONE NETWORK** ---
+
+**2400 BITS PER SECOND DUPLEX MODEM
+USING THE FREQUENCY DIVISION
+TECHNIQUE STANDARDIZED FOR USE ON
+THE GENERAL SWITCHED TELEPHONE
+NETWORK AND ON POINT-TO-POINT
+2-WIRE LEASED TELEPHONE-TYPE
+CIRCUITS**
+
+**ITU-T Recommendation V.22 *bis***
+
+(Extract from the *Blue Book*)
+
+---
+
+## NOTES
+
+1 ITU-T Recommendation V.22 *bis* was published in Fascicle VIII.1 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+
+2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## **2400 BITS PER SECOND DUPLEX MODEM USING THE FREQUENCY DIVISION TECHNIQUE STANDARDIZED FOR USE ON THE GENERAL SWITCHED TELEPHONE NETWORK AND ON POINT-TO-POINT 2-WIRE LEASED TELEPHONE-TYPE CIRCUITS**
+
+*(Malaga-Torremolinos, 1984; and at Melbourne, 1988)*
+
+The CCITT,
+
+*considering*
+
+(a) that there is a demand for data transmission at 2400 bit/s in the duplex mode over the General Switched Telephone Network (GSTN) and on point-to-point 2-wire leased telephone-type circuits;
+
+(b) that there is a demand to have the fall-back mode compatibility with modems in accordance with Recommendation V.22;
+
+(c) that in this case the frequency division technique shall be used,
+
+*(unanimously) declares*
+
+that the characteristics of the modems for this service shall provisionally be as follows:
+
+## **1 Introduction**
+
+These modems are intended for use on connections on the GSTN and on point-to-point 2-wire leased telephone-type circuits (see Note). The principal characteristics of these modems are as follows:
+
+- a) duplex mode of operation on the GSTN and point-to-point leased circuits,
+- b) channel separation by frequency division,
+- c) quadrature amplitude modulation for each channel with synchronous line transmission at 600 baud (nominal),
+- d) inclusion of a scrambler,
+- e) inclusion of an adaptive equalizer and a compromise equalizer,
+- f) inclusion of test facilities,
+- g) data signalling rates of:
+ - 2400 bit/s synchronous,
+ - 2400 bit/s start-stop,
+ - 1200 bit/s synchronous,
+ - 1200 bit/s start-stop,
+- h) it is compatible with a V.22 modem operating in Modes i) or ii) at the 1200 bit/s signalling rate and includes automatic bit rate recognition.
+
+*Note* - In certain countries the use of such modems over the GSTN may not be allowed.
+
+## 2 Line signals
+
+### 2.1 Carrier and guard tone frequencies
+
+The carrier frequencies shall be $1200 \pm 0.5$ Hz for the low channel and $2400 \pm 1$ Hz for the high channel. A guard tone of $1800 \pm 20$ Hz, to be transmitted only when the modem is transmitting in the high channel, may be disabled as a national option. An alternative guard tone of $550 \pm 20$ Hz, to be transmitted only when the modem is transmitting in the high channel, may be incorporated as a national option.
+
+### 2.2 Data and guard tone line signal levels
+
+The 1800 Hz or 550 Hz guard tones shall be levels $6 \pm 1$ dB or $3 \pm 1$ dB, respectively, below the level of the data signal power in the high channel. Because of the 1800 Hz guard tone, the power level of data signals in the high channel will be approximately 1 dB lower than that of data signals in the low channel.
+
+### 2.3 Fixed compromise equalizer
+
+Fixed compromise equalization shall be incorporated in the modem transmitter.
+
+### 2.4 Spectrum and group delay characteristics
+
+The transmitted line signals, excluding the characteristics of the fixed compromise equalizer, shall have a frequency amplitude spectrum equivalent to the square root of a raised cosine shaping with 75% roll-off and within the limits shown in Figure 1/V.22 bis. Similarly, the group delay of the transmitter output shall be within the range of $\pm 150$ microseconds over the frequency ranges 900-1500 Hz (low channel) and 2100-2700 Hz (high channel). These figures are provisional.
+
+
+
+Figure 1/V.22 bis: Amplitude limits for transmitted line signal (unequalized). The graph shows Amplitude in dB on the y-axis (ranging from -25 to 0.75) versus Carrier frequency in Hz on the x-axis (ranging from -600 to 600). Two curves represent the upper and lower limits of the signal spectrum, showing a raised cosine shape with 75% roll-off. The upper curve starts at -20 dB at -600 Hz, rises to -4 dB at -300 Hz, peaks at 0 dB at 0 Hz, and falls back to -20 dB at 600 Hz. The lower curve starts at -20 dB at -550 Hz, rises to -9 dB at -450 Hz, peaks at -4 dB at 0 Hz, and falls back to -20 dB at 550 Hz. The area between the curves is shaded with diagonal lines. The x-axis has labels for -600, -550, -475, -450, -300, -200, -125, 125, 200, 300, 400, 450, 475, 550, and 600 Hz. The y-axis has labels for -25, -20, -15, -10, -9, -5, -4, -2, -0.75, 0, and 0.75 dB. The text 'CCITT - 28321' is at the bottom right of the graph area.
+
+FIGURE 1/V.22 bis
+
+**Amplitude limits for transmitted line signal (unequalized)**
+
+### 2.5 Modulation
+
+#### 2.5.1 Data signalling rates
+
+The data rate transmitted to line shall be 2400 bit/s or 1200 bit/s $\pm 0.01\%$ with a modulation rate of 600 baud $\pm 0.01\%$ .
+
+#### 2.5.2 Encoding of data bits
+
+##### 2.5.2.1 2400 bits per second
+
+The data stream to be transmitted shall be divided into groups of 4 consecutive bits (quadbits). The first two bits of a quadbit shall be encoded as a phase quadrant change relative to the quadrant occupied by the preceding signal element. (See Figure 2/V.22 *bis* and Table 1/V.22 *bis*.)
+
+The last two bits of each quadbit define one of 4 signalling elements associated with the new quadrant (see Figure 2/V.22 *bis*). The left hand bits in Table 1/V.22 *bis* and Figure 2/V.22 *bis* are the first of each pair in the data stream as it enters the modulator portion of the modem after the scrambler.
+
+TABLE 1/V.22 *bis*
+
+##### Line encoding
+
+| First two bits in quabit (2400 bit/s)
or dibit values (1200 bit/s) | Phase
quadrant change | |
+|-----------------------------------------------------------------------|------------------------------|------|
+| 00 | 1→ 2
2→ 3
3→ 4
4→ 1 | 90° |
+| 01 | 1→ 1
2→ 2
3→ 3
4→ 4 | 0° |
+| 11 | 1→ 4
2→ 1
3→ 2
4→ 3 | 270° |
+| 10 | 1→ 3
2→ 4
3→ 1
4→ 2 | 180° |
+
+
+
+The diagram shows a signal constellation for CCITT V.22 bis. It is a 5x5 grid of points centered at the origin. The horizontal axis has labels -3, -1, 1, 3. The vertical axis has labels 3, 1, -1, -3. The quadrants are labeled: Phase Quadrant 2 (top-left), Phase Quadrant 1 (top-right), Phase Quadrant 3 (bottom-left), and Phase Quadrant 4 (bottom-right). Bit pairs are assigned to the points: 11, 01, 10, 11 in the top row; 10, 00, 00, 01 in the second row; 01, 00, 00, 10 in the third row; and 11, 10, 01, 11 in the bottom row. The origin (0,0) is labeled 00. The reference CCITT-46140 is noted at the bottom right.
+
+Signal constellation diagram for CCITT V.22 bis, showing four phase quadrants with bit pairs and coordinates.
+
+FIGURE 2/V.22 *bis*
+Signal constellation
+
+##### 2.5.2.2 1200 bits per second
+
+The data stream to be transmitted shall be divided into groups of 2 consecutive bits (dibits). The dibits shall be encoded as a phase quadrant change relative to the quadrant occupied by the preceding signal element (see Table 1/V.22 *bis*). The signalling elements corresponding to 01 in the signal constellation (Figure 2/V.22 *bis*) shall be transmitted irrespective of the quadrant concerned. This ensure compatibility with Recommendation V.22.
+
+### 2.6 Received signal frequency tolerance
+
+The receiver shall be able to operate with received frequency offsets of up to $\pm 7$ Hz.
+
+## 3 Interchange circuits
+
+### 3.1 Essential and optional interchange circuits
+
+These are listed in Table 2/V.22 *bis*.
+
+### 3.2 Circuits 106 and 109 response times
+
+After the handshaking sequences, circuit 106 will follow OFF to ON or ON to OFF transitions of circuit 105 within 3.5 ms. The OFF to ON transition of circuit 109 is part of the handshake sequence specified in § 6. Circuit 109 shall turn OFF 40 to 65 ms after the level of the received signal appearing at the line terminal of the modem falls below the relevant threshold defined in § 3.3. In the fall-back mode, the response time may be reduced to a value in the 10 to 24 ms range specified in Recommendation V.22. Following a dropout, after the initial handshake, circuit 109 shall turn ON 40 to 205 ms after the level of the received signal appearing at the line terminal of the modem exceeds the relevant threshold defined in § 3.3.
+
+### 3.3 *Circuit 109 threshold*
+
+High channel threshold:
+
+- greater than -43 dBm circuit 109 ON
+- less than -48 dBm circuit 109 OFF
+
+Low channel threshold:
+
+- greater than -43 dBm circuit 109 ON
+- less than -48 dBm circuit 109 OFF
+
+The condition of circuit 109 between the ON and OFF levels is not specified except that the signal detector shall exhibit a hysteresis action, such that the level at which the OFF to ON transition occurs shall be at least 2 dB greater than that for the ON to OFF transition.
+
+Circuit 109 thresholds are specified at the input to the modem when receiving scrambled binary 1.
+
+Administrations are permitted to change these thresholds where transmission conditions are known.
+
+Circuit 109 shall not respond to the 1800 Hz or the 550 Hz guard tones, or the 2100 Hz (nominal) answer tone during the handshake sequence.
+
+### 3.4 *Circuit 111 and data rate control*
+
+Data rate selection may be by switch (or similar means) or by circuit 111 or a combination of both.
+
+The ON condition on circuit 111, where provided, shall select 2400 bit/s operation and the OFF condition shall select 1200 bit/s operation.
+
+TABLE 2/V.22 *bis*
+
+#### **Interchange circuit (Note 1)**
+
+| Interchange circuit | | Notes |
+|---------------------|------------------------------------------------|--------|
+| No. | Description | |
+| 102 | Signal ground or common return | Note 2 |
+| 103 | Transmitted data | |
+| 104 | Received data | |
+| 105 | Request to send | |
+| 106 | Ready for sending | |
+| 107 | Data set ready | Note 3 |
+| 108/1 | Connect data set to line | |
+| 108/2 | Data terminal ready | Note 3 |
+| 109 | Data channel received line signal detector | Note 4 |
+| 111 | Data signalling rate selector (DTE source) | |
+| 112 | Data signalling rate selector (DCE source) | Note 5 |
+| 113 | Transmitter signal element timing (DTE source) | |
+| 114 | Transmitter signal element timing (DCE source) | |
+| 115 | Receiver signal element timing (DCE source) | Note 6 |
+| 125 | Calling indicator | Note 6 |
+| 140 | Loopback/maintenance test | Note 7 |
+| 141 | Local loopback | |
+| 142 | Test indicator | |
+
+*Note 1* - All essential interchange circuits and any others which are provided must comply with the functional and operational requirements of Recommendation V.24. All interchange circuits provided must be properly terminated in the data terminal equipment in accordance with the appropriate Recommendation for electrical characteristics (see § 3.5).
+
+*Note 2* - Some automatic calling equipments are designed to emit a calling tone to line by turning ON circuit 105 to the calling modem. The general switched telephone network (GSTN) constant carrier handshake is such that no calling tone will be emitted by the V.22 *bis* modem when used with these equipments.
+
+*Note 3* - This circuit shall be capable of operation as circuit 108/1 or 108/2 depending on its use.
+
+*Note 4* - This circuit is optional.
+
+*Note 5* - When the modem is not operating in a synchronous mode at the interface, any signals on this circuit shall be disregarded. Many DTEs operating in an asynchronous mode do not have a generator connected to this circuit.
+
+*Note 6* - When the modem is not operating in a synchronous mode at the interface, this circuit shall be clamped to the OFF condition. Many DTEs operating in an asynchronous mode do not terminate this circuit.
+
+*Note 7* - This circuit is for use with the general switched telephone network only.
+
+### 3.5 *Electrical characteristics of interchange circuits*
+
+3.5.1 Use of electrical characteristics conforming to Recommendation V.28 is recommended together with the connector and pin assignment plan specified by ISO 2110.
+
+*Note* - Manufacturers may wish to note that the long-term objective is to replace electrical characteristics specified in Recommendation V.28, and that Study Group XVII has agreed that the work shall proceed to develop a more efficient, all-balanced, interface for the V-Series application which minimizes the number of interchange circuits.
+
+### 3.6 *Fault condition of interchange circuits*
+
+See Recommendation V.28, § 7 for association of the receiver failure detection types.)
+
+3.6.1 The DTE should interpret a fault condition on circuit 107 as an OFF condition using failure detection type 1.
+
+3.6.2 The DCE should interpret a fault condition on circuits 105 and 108 as an OFF condition using failure detection type 1.
+
+3.6.3 All other circuits not referred to above may use failure detection types 0 or 1.
+
+## 4 **Modes of operation**
+
+The modem can be configured for the following modes of operation:
+
+Mode 1 2400 bit/s $\pm$ 0.01% synchronous
+
+Mode 2 2400 bit/s start-stop 8, 9, 10 or 11 bits per character
+
+Mode 3 1200 bit/s $\pm$ 0.01% synchronous
+
+Mode 4 1200 bit/s start-stop 8, 9, 10 or 11 bits per character.
+
+### 4.1 *Transmitter*
+
+4.1.1 In the synchronous modes of operation, the modem shall accept synchronous data from the DTE on circuit 103 under control of circuit 113 or circuit 114. The data shall then be scrambled in accordance with § 5 and then passed to the modulator for encoding in accordance with § 2.5.
+
+4.1.2 In the start-stop modes, the modem shall accept a data stream of start-stop characters from the DTE at a nominal rate of 2400 or 1200 bits per second. The start-stop data to be transmitted shall be converted in conformity with Recommendation V.14 to a synchronous data stream suitable for transmission in accordance with § 4.1.1
+
+### 4.2 *Receiver*
+
+Demodulated data shall be decoded in accordance with § 2.5.2, then descrambled in accordance with § 5.2 and then passed to the converter in conformity with Recommendation V.14 for regaining the data stream of start-stop characters.
+
+The intracharacter signalling rate provided to the DTE over circuit 104 shall be in the ranges given in Table 3/V.22 *bis* when operating in the basic or in the extended signalling rate ranges, respectively.
+
+TABLE 3/V.22 *bis*
+
+#### **Intracharacter signalling rate range**
+
+| Data rate | Signalling rate range | |
+|--------------------------|------------------------------------------|------------------------------------------|
+| | Basic | Extended |
+| 2400 bit/s
1200 bit/s | 2400 to 2424 bit/s
1200 to 1212 bit/s | 2400 to 2455 bit/s
1200 to 1227 bit/s |
+
+## **5 Scrambler and descrambler**
+
+### **5.1 Scrambler**
+
+A self synchronizing scrambler having the generating polynomial $1 \oplus x^{-14} \oplus x^{-17}$ shall be included in the modem transmitter. The message data sequence applied to the scrambler shall be effectively divided by the generating polynomial. The coefficients of the quotients of this division, taken in descending order, form the data sequence which shall appear at the output of the scrambler. The scrambler output data sequence shall thus be:
+
+$$D_s = D_i \oplus D_s \cdot x^{-14} \oplus D_s \cdot x^{-17}$$
+
+where
+
+$D_s$ is the data sequence at the output of the scrambler
+
+$D_i$ is the data sequence applied to the scrambler
+
+$\oplus$ denotes module 2 addition
+
+$\cdot$ denotes binary multiplication.
+
+Figure 3/V.22 *bis* shows a suitable implementation.
+
+To prevent occasional inadvertent instigation of remote loop 2 caused by scrambler lockup, circuitry shall be included to detect a sequence of 64 consecutive ones at the scrambler output ( $D_s$ ) and, if detected, invert the next input to the scrambler ( $D_i$ ) and reset the counter of 64 consecutive ones. This circuitry shall operate whenever the scrambler is operational. No scrambler initialization is required during the handshake or retrain sequence.
+
+
+
+$D_s = D_i \oplus D_s \cdot x^{-14} \oplus D_s \cdot x^{-17}$
+
+CCITT-28332
+
+Block diagram of a scrambler implementation. The input data sequence D\_i is fed into a feedback loop. A 'Detector' block monitors the output D\_s for a sequence of 64 consecutive ones. If detected, it triggers an 'In-verter' block to invert the next input D\_i. The output D\_s is also fed back through two delay blocks, x^-14 and x^-17, and combined with the input D\_i using modulo 2 addition (represented by circles with a plus sign). The equation D\_s = D\_i \oplus D\_s \cdot x^{-14} \oplus D\_s \cdot x^{-17} is shown below the diagram. The reference CCITT-28332 is noted in the bottom right.
+
+*Note* — Marks (binary 1) and spaces (binary 0) at the V. 24 interface correspond to ones and zeros, respectively, in this logic diagram.
+
+FIGURE 3/V.22 *bis*
+
+#### **Scrambler**
+
+### 5.2 Descrambler
+
+A self synchronizing descrambler having the polynomial $1 \oplus x^{-14} \oplus x^{-17}$ Shall be provided in the modem receiver. The message data sequence produced after demodulation shall be effectively multiplied by the generating polynomial $1 \oplus x^{-14} \oplus x^{-17}$ to form the descrambled message. The coefficients of the recovered message sequence taken in descending order form the output data sequence $D_o$ which is given by
+
+$$D_o = D_s (1 \oplus x^{-14} \oplus x^{-17})$$
+
+where the notation is as defined in § 5.1.
+
+Circuitry may be included to detect a sequence of 64 consecutive ones at the input to the descrambler ( $D_s$ ) and, if detected, invert the next output from the descrambler ( $D_o$ ). This detector shall operate whenever the descrambler is operational.
+
+Figure 4/V.22 *bis* shows a suitable implementation.
+
+
+
+$D_o = D_s (1 \oplus x^{-14} \oplus x^{-17})$ CCITT-28342
+
+Block diagram of a descrambler implementation. The input D\_s is split into two paths. One path goes through a series of delay blocks (x^-1) to produce D\_s \* x^-14 and D\_s \* x^-17. The other path goes through a 'Detector' block, which then feeds into an 'In-verter' block. The output of the 'In-verter' is D\_o. The output of the descrambler is also D\_o. The equation D\_o = D\_s (1 \oplus x^{-14} \oplus x^{-17}) is shown below the diagram. The reference CCITT-28342 is also present.
+
+*Note* — Marks (binary 1) and spaces (binary 0) at the V. 24 interface correspond to ones and zeros, respectively, in this logic diagram.
+
+FIGURE 4/V.22 *bis*
+
+#### Descrambler
+
+## 6 Operating sequences
+
+### 6.1 Channel allocation and signalling rate selection
+
+#### 6.1.1 GSTN
+
+On the general switched telephone network, the modem at the calling data station shall transmit in the low channel and receive in the high channel (call mode). The modem at the answering data station shall receive in the low channel and transmit in the high channel (answer mode).
+
+In some situations however, such as when calls are established on the GSTN by operators, bilateral agreement on channel allocations will be necessary.
+
+Signalling rate selection at the call mode modem shall be either manual or by means of a logical condition applied on circuit 111 (if this circuit is provided). The handshake sequence, as defined in § 6.3.1, allows each modem to automatically condition itself to operate at the correct signalling rate.
+
+#### 6.1.2 Point-to-point leased circuits
+
+Channel allocation and signalling rate selection on point-to-point leased circuits will, in general, be by bilateral agreement between users.
+
+### 6.2 V.25 automatic answering sequence
+
+The V.25 automatic answering sequence shall be transmitted from the answer mode modem on international GSTN connections. The transmission of the sequence may be omitted in national connections on point-to-point leased circuits or on the GSTN, where permitted by the Administrations.
+
+### 6.3 *Handshake sequence*
+
+#### 6.3.1 *GSTN*
+
+The means of achieving synchronism between the calling modem and the answering modem on international GSTN connections is shown in Figures 5/V.22 *bis*, 6/V.22 *bis* and 7/V.22 *bis*. Both calling and answering modems shall be manually conditioned to operate either in the synchronous modes (Modes 1 and 3), or in the start-stop modes (Modes 2 and 4). If both calling and answering modems are V.22 *bis* modems, the handshake will normally condition both modems to operate at 2400 bit/s. If however one or both of the modems has been set to operate at 1200 bit/s, either manually or via circuit 111, then the handshake will condition both modems to operate at 1200 bit/s. If either the calling or answering modem is a V.22 modem operating in V.22 Modes i) or ii) the handshake will condition both the V.22 *bis* and V.22 modem to operate at 1200 bit/s. The signalling rate is communicated to the DTE by a logical condition on circuit 112. The handshake sequence is independent of which modem, calling or answering, is connected to line first.
+
+##### 6.3.1.1 *Interworking at 2400 bit/s*
+
+###### 6.3.1.1.1 *Calling modem*
+
+- a) On connection to line the calling modem shall be conditioned to receive signals in the high channel at 1200 bit/s and transmit signals in the low channel at 1200 bit/s in accordance with § 2.5.2.2. It shall apply an ON condition to circuit 107 in accordance with Recommendation V.25. The modem shall initially remain silent.
+- b) After $155 \pm 10$ ms of unscrambled binary 1 has been detected, the modem shall remain silent for a further $456 \pm 10$ ms then transmit an unscrambled repetitive double dibit pattern of 00 and 11 at 1200 bit/s for $100 \pm 3$ ms. Following this signal the modem shall transmit scrambled binary 1 at 1200 bit/s.
+- c) If the modem detects scrambled binary 1 in the high channel at 1200 bit/s for $270 \pm 40$ ms, the handshake shall continue in accordance with §§ 6.3.1.2.1 c) and d). However, if unscrambled repetitive double dibit 00 and 11 at 1200 bit/s is detected in the high channel, then at the end of receipt of this signal the modem shall apply an ON condition to circuit 112.
+- d) $600 \pm 10$ ms after circuit 112 has been turned ON the modem shall begin transmitting scrambled binary 1 at 2400 bit/s, and $450 \pm 10$ ms after circuit 112 has been turned ON the receiver may begin making 16-way decisions.
+- e) Following transmission of scrambled binary 1 at 2400 bit/s for $200 \pm 10$ ms, circuit 106 shall be conditioned to respond to circuit 105 and the modem shall be ready to transmit data at 2400 bit/s.
+- f) When 32 consecutive bits of scrambled binary 1 at 2400 bit/s have been detected in the high channel the modem shall be ready to receive data at 2400 bit/s and shall apply an ON condition to circuit 109.
+
+###### 6.3.1.1.2 *Answering modem*
+
+- a) On connection to line the answering modem shall be conditioned to transmit signals in the high channel at 1200 bit/s in accordance with § 2.5.2.2 and receive signals in the low channel at 1200 bit/s. Following transmission of the answer sequence in accordance with Recommendation V.25, the modem shall apply an ON condition to circuit 107 and then transmit unscrambled binary 1 at 1200 bit/s.
+- b) If the modem detects scrambled binary 1 or 0 in the low channel at 1200 bit/s for $270 \pm 40$ ms, the handshake shall continue in accordance with §§ 6.3.1.2.2 b) and c). However, if unscrambled repetitive double dibit 00 and 11 at 1200 bit/s is detected in the low channel, at the end of receipt of this signal the modem shall apply an ON condition to circuit 112 and then transmit an unscrambled repetitive double dibit pattern of 00 and 11 at 1200 bit/s for $100 \pm 3$ ms. Following these signals the modem shall transmit scrambled binary 1 at 1200 bit/s.
+- c) $600 \pm 10$ ms after circuit 112 has been turned ON the modem shall begin transmitting scrambled binary 1 at 2400 bit/s, and $450 \pm 10$ ms after circuit 112 has been turned ON the receiver may begin making 16-way decisions.
+- d) Following transmission of scrambled binary 1 at 2400 bit/s for $200 \pm 10$ ms, circuit 106 shall be conditioned to respond to circuit 105 and the modem shall be ready to transmit data at 2400 bit/s.
+- e) When 32 consecutive bits of scrambled binary 1 at 2400 bit/s have been detected in the low channel the modem shall be ready to receive data at 2400 bit/s and shall apply an ON condition to circuit 109.
+
+
+
+**Calling modem**
+
+Connect to line
+
+S1
+
+Scrambled binary 1 at 1200 bit/s
+
+Scrambled binary 1 at 2400 bit/s
+
+Data
+
+$456\text{ ms } \pm 10\text{ ms}$
+
+$100 \pm 3\text{ ms}$
+
+$600\text{ ms } \pm 10\text{ ms}$
+
+$200\text{ ms } \pm 10\text{ ms}$
+
+Detect unscrambled binary 1 in $155 \pm 10\text{ ms}$
+
+107
+
+112
+
+$450 \pm 10\text{ ms}$
+
+Begin 16-way decisions in receiver
+
+Detect end of S1 signal in upper channel
+
+104 clamped to binary 1
+
+109
+
+104 unclamped (binary 1)
+
+Detect 32 consecutive bits of binary 1 at 2400 bit/s
+
+106
+
+**Answering modem**
+
+Connect to line
+
+2100 Hz for $3300 \pm 700\text{ ms}$
+
+Unscrambled binary 1 at 1200 bit/s
+
+S1
+
+Scrambled binary 1 at 1200 bit/s
+
+Scrambled binary 1 at 2400 bit/s
+
+Data
+
+Silence $2150 \pm 350\text{ ms}$
+
+$75\text{ ms } \pm 20\text{ ms}$
+
+$100 \pm 3\text{ms}$
+
+$600\text{ ms } \pm 10\text{ ms}$
+
+$200\text{ ms } \pm 10\text{ ms}$
+
+Detect 32 consecutive bits of binary 1 at 2400 bit/s
+
+106
+
+107
+
+112
+
+$450 \pm 10\text{ ms}$
+
+Begin 16-way decisions in receiver
+
+Detect end of S1 signal in lower channel
+
+104 clamped to binary 1
+
+109
+
+104 unclamped (binary)
+
+Data
+
+CCITT-01200
+
+**V.22 bis signal:**
+S1 = Unscrambled double dibit 00 and 11 at 1200 bit/s for $100 \pm 3\text{ ms}$ .
+
+Timing diagram for V.22 bis signal handshake sequence at 2400 bit/s with V.25 automatic answering. The diagram shows the interaction between a Calling modem and an Answering modem. The Calling modem sends S1, Scrambled binary 1 at 1200 bit/s, Scrambled binary 1 at 2400 bit/s, and Data. The Answering modem receives these and responds with Unscrambled binary 1 at 1200 bit/s, S1, Scrambled binary 1 at 1200 bit/s, Scrambled binary 1 at 2400 bit/s, and Data. Key timing points include: 456 ms ± 10 ms for detecting unscrambled binary 1, 600 ms ± 10 ms for detecting end of S1 signal, and 200 ms ± 10 ms for detecting 32 consecutive bits of binary 1 at 2400 bit/s. Signal levels 106, 107, 109, and 112 are indicated.
+
+FIGURE 5/V.22 bis
+
+###### Handshake sequence at 2400 bit/s (with V.25 automatic answering)
+
+
+
+**V.22 calling modem**
+
+Connect to line
+
+Scrambled binary 1 at 1200 bit/s
+
+Data
+
+$456\text{ ms } \pm 10\text{ ms}$
+
+$765\text{ ms } \pm 10\text{ ms}$
+
+Detect unscrambled binary 1 in $155 \pm 10\text{ ms}$
+
+107
+
+Detect scrambled binary 1 in $270 \pm 40\text{ ms}$
+
+109
+
+106
+
+104 clamped to binary 1
+
+104 unclamped (binary 1)
+
+Data
+
+**V.22 bis answering modem**
+
+Connect to line
+
+2100 Hz for $3300 \pm 700\text{ ms}$
+
+Unscrambled binary 1 at 1200 bit/s
+
+Scrambled binary 1 at 1200 bit/s
+
+Data
+
+Silence $2150 \pm 350\text{ ms}$
+
+$75\text{ ms } \pm 20\text{ ms}$
+
+$765\text{ ms } \pm 10\text{ ms}$
+
+Detect scrambled binary 1 or binary 0 in $270 \pm 10\text{ ms}$
+
+107
+
+112
+
+106
+
+109
+
+104 clamped to binary 1
+
+104 unclamped (binary 1)
+
+Data
+
+CCITT - 65330
+
+Timing diagram for V.22 calling modem handshake sequence at 1200 bit/s with V.25 automatic answering. The diagram shows the interaction between a V.22 calling modem and a V.22 bis answering modem. The V.22 calling modem sends Scrambled binary 1 at 1200 bit/s and Data. The V.22 bis answering modem receives these and responds with Unscrambled binary 1 at 1200 bit/s, Scrambled binary 1 at 1200 bit/s, and Data. Key timing points include: 456 ms ± 10 ms for detecting unscrambled binary 1, 765 ms ± 10 ms for detecting scrambled binary 1 or binary 0, and 75 ms ± 20 ms for detecting scrambled binary 1 or binary 0. Signal levels 106, 107, 109, and 112 are indicated.
+
+FIGURE 6/V.22 bis
+
+###### Handshake sequence at 1200 bit/s with V.22 calling modem (with V.25 automatic answering)
+
+
+
+**V.22 bis calling modem**
+
+**V.22 answering modem**
+
+**V.22 bis signal:**
+ S1 = Unscrambled double dibit 00 and 11 at 1200 bit/s for 100 ± 3 ms.
+
+CCITT - 65341
+
+Timing diagram for V.22 bis calling modem handshake sequence. The diagram shows the sequence of events between a calling modem and an answering modem. The calling modem starts with a 'Connect to line' signal, followed by a period of silence (2150 ± 350 ms). It then transmits 'S1' (Unscrambled double dibit 00 and 11 at 1200 bit/s for 100 ± 3 ms). The answering modem detects 'S1' and transmits '2100 Hz for 3300 ± 700ms'. The calling modem then transmits 'Scrambled binary 1 at 1200 bit/s' for 765 ms ± 10 ms. The answering modem detects this and transmits 'Data'. The calling modem then transmits 'Data'.
+
+FIGURE 7/V.22 bis
+
+###### Handshake sequence at 1200 bit/s with V.22 answering modem (with V.25 automatic answering)
+
+##### 6.3.1.2 Interworking at 1200 bit/s
+
+The following handshake is identical to the Recommendation V.22 alternative A and B handshake.
+
+###### 6.3.1.2.1 Calling modem
+
+- On connection to line the calling modem shall be conditioned to receive signals in the high channel at 1200 bit/s and transmit signals in the low channel at 1200 bit/s in accordance with § 2.5.2.2. It shall apply an ON condition to circuit 107 in accordance with Recommendation V.25. The modem shall initially remain silent.
+- After 155 ± 10 ms of unscrambled binary 1 has been detected, the modem shall remain silent for a further 456 ± 10 ms then transmit scrambled binary 1 at 1200 bit/s (a preceding V.22 bis signal, as shown in Figure 7/V.22 bis, would not affect the operation of a V.22 answer modem).
+- On detection of scrambled binary 1 in the high channel at 1200 bit/s for 270 ± 40 ms the modem shall be ready to receive data at 1200 bit/s and shall apply an ON condition to circuit 109 and an OFF condition to circuit 112.
+- 765 ± 10 ms after circuit 109 has been turned ON, circuit 106 shall be conditioned to respond to circuit 105 and the modem shall be ready to transmit data at 1200 bit/s.
+
+###### 6.3.1.2.2 *Answering modem*
+
+- a) On connection to line the answering modem shall be conditioned to transmit signals in the high channel at 1200 bit/s in accordance with § 2.5.2.2 and receive signals in the low channel at 1200 bit/s.
+
+Following transmission of the answer sequence in accordance with V.25 the modem shall apply an ON condition to circuit 107 and then transmit unscrambled binary 1 at 1200 bit/s.
+
+- b) On detection of scrambled binary 1 or 0 in the low channel at 1200 bit/s for $270 \pm 40$ ms the modem shall apply an OFF condition to circuit 112 and shall then transmit scrambled binary 1 at 1200 bit/s.
+- c) After scrambled binary 1 has been transmitted at 1200 bit/s for $765 \pm 10$ ms the modem shall be ready to transmit and receive data at 1200 bit/s, shall condition circuit 106 to respond to circuit 105 and shall apply an ON condition to circuit 109.
+
+*Note* - Manufacturers may wish to note that in certain countries, for national purposes, modems are in service which emit an answering tone of 2225 Hz instead of unscrambled binary 1.
+
+#### 6.3.2 *Point-to-point leased circuits*
+
+##### 6.3.2.1 *Interworking at 2400 bit/s*
+
+Operation on leased circuits shall be continuous carrier in both directions. On initial power on and after line signal interruptions, operation shall be according to § 6.5.
+
+### 6.4 *Retrain sequence (2400 bit/s operation)*
+
+A retrain may be initiated during data transmission between two V.22 *bis* modems if either modem incorporates a means of detecting loss of equalization.
+
+Transmission of a retrain sequence shall be initiated either by detection of loss of equalization or by detection of unscrambled repetitive double dibit 00 and 11 at 1200 bit/s from the distant modem.
+
+The following sequence of events shall take place during the retrain:
+
+- a) Following detection of loss of equalization or the end of detection of unscrambled repetitive double dibit 00 and 11 at 1200 bit/s from the distant modem, the OFF condition shall be applied to circuit 106 and circuit 104 may be clamped to binary 1. The modem shall transmit an unscrambled repetitive double dibit pattern of 00 and 11 at 1200 bit/s for $100 \pm 3$ ms. Following this signal the modem shall transmit scrambled binary 1 at 1200 bit/s.
+- b) $600 \pm 10$ ms after the end of detection of unscrambled repetitive double dibit 00 and 11 at 1200 bit/s from the distant modem, the modem shall begin transmitting scrambled binary 1 at 2400 bit/s and $450 \pm 10$ ms after the end of this detection the receiver may begin making 16-way decisions.
+- c) Following transmission of scrambled binary 1 at 2400 bit/s for $200 \pm 10$ ms, circuit 106 shall be conditioned to respond to circuit 105 and the modem shall be ready to transmit data at 2400 bit/s.
+- d) When 32 consecutive bits of scrambled binary 1 at 2400 bit/s have been detected from the remote modem, the modem shall be ready to receive data at 2400 bit/s and shall remove the clamp from circuit 104.
+
+A retrain between two modems is shown in Figure 8/V.22 *bis*. Clocks presented on circuits 114 and 115 shall remain at 2400 bit/s during the entire retrain sequence.
+
+If a modem has transmitted a retrain signal and has not received unscrambled repetitive double dibit 00 and 11 at 1200 bit/s immediately prior, or during, or within a time interval equal to the maximum expected two-way propagation delay, the modem shall return to the beginning of the retrain signal as defined above and repeat the procedure until unscrambled repetitive double dibit 00 and 11 is received from the remote modem. A time interval of 1.2 seconds is recommended for the maximum expected two-way propagation delay.
+
+If the modem fails to synchronize on the received retrain sequence, the modem shall transmit another retrain signal.
+
+During this retraining, circuits 109 and 107 shall remain ON.
+
+
+
+Modem 1
+
+| Data | S1 | Scrambled binary 1 at 1200 bit/s | Scrambled binary 1 at 2400 bit/s | Data |
+|-----------------|-------------------------|--------------------------------------|------------------------------------------------------|--------------------------|
+| | $100 \pm 3 \text{ ms}$ | $600 \text{ ms} \pm 10 \text{ ms}$ | $200 \text{ ms} \pm 10 \text{ ms}$ | |
+| | 106 | Detect end of S1 signal in channel 2 | | 106 |
+| | | $450 \text{ ms} \pm 10 \text{ ms}$ | | |
+| | | Begin 16-way decisions in receiver | | |
+| Unreliable data | 104 clamped to binary 1 | | 104 clamped to binary 1 | 104 unclamped (binary 1) |
+| | | | Detect 32 consecutive bits of binary 1 at 2400 bit/s | Data |
+
+Modem 2
+
+| Data | S1 | Scrambled binary 1 at 1200 bit/s | Scrambled binary 1 at 2400 bit/s | Data |
+|-----------------|--------------------------------------|------------------------------------|------------------------------------------------------|------|
+| | $100 \pm 3 \text{ ms}$ | $600 \pm 10 \text{ ms}$ | $200 \text{ ms} \pm 10 \text{ ms}$ | |
+| | 106 | | Detect 32 consecutive bits of binary 1 at 2400 bit/s | 106 |
+| | | $450 \text{ ms} \pm 10 \text{ ms}$ | | |
+| | | Begin 16-way decisions in receiver | | |
+| Unreliable data | 104 clamped to binary 1 | 104 clamped to binary 1 | 104 unclamped (binary 1) | Data |
+| | Detect end of S1 signal in channel 1 | | | |
+
+CCITT-81330
+
+V.22 bis signal:
+
+S1 = Unscrambled double dibit 00 and 11 at 1200 bit/s for $100 \pm 3 \text{ ms}$ .
+
+FIGURE 8/V.22 bis
+
+#### A retrain at 2400 bit/s
+
+### 6.5 Operation after loss of line signal
+
+When the modem detects loss of received line signal (as specified in §§ 3.2 and 3.3) it shall turn OFF circuit 109 and shall clamp circuit 104 to binary 1. If received line signal is then detected (as specified in §§ 3.2 and 3.3) the modem shall turn ON circuit 109 but shall leave circuit 104 clamped to binary 1. If during the next 100 ms the modem detects a retrain sequence it shall proceed according to § 6.4 above. If the modem has not detected a retrain sequence by the end of the same 100 ms it shall remove the clamp from circuit 104. If at any time after turning ON circuit 109 following a drop out the modem detects loss of equalization, it shall proceed according to § 6.4 above.
+
+### 6.6 Optional rate signalling
+
+A modem may optionally instigate a rate change in response to a change in circuit 111 or manually, by a switch (or other means). The request may be made to change the operating rate from 1200 bit/s to 2400 bit/s or from 2400 bit/s to 1200 bit/s without disconnection from the GSTN (Note 1).
+
+#### 6.6.1 *Instigation of a rate change*
+
+- a) Upon initiation of a rate change, manually or by a change in the condition of circuit 111, the modem shall apply an OFF condition to circuit 106, clamp circuit 104 to binary ones and shall transmit unscrambled repetitive double dibit 00 and 11 at 1200 bit/s for $100 \pm 3$ ms. During this procedure, circuits 109 and 107 shall remain on.
+- b) Following this, the modem shall transmit scrambled R1 as defined in Table 3/V.22 *bis* at a rate of 1200 bit/s.
+- c) $450 \pm 10$ ms after detection of unscrambled repetitive double dibit 00 and 11 at 1200 bit/s from the distant modem, the receiver shall examine the descrambled repetitive dibits R2 from the distant modem to determine the operating rate for subsequent transmission as defined in Table 3/V.22 *bis*; at this time, the receiver may begin making decisions at the rate indicated by R2 which may differ from R1.
+- d) $600 \pm 10$ ms after detection of unscrambled repetitive double dibit 00 and 11 at 1200 bit/s from the distant modem, the transmission shall begin transmission of scrambled binary ones at a rate indicated by the dibit R2 from the distant modem. Following transmission of $200 \pm 10$ ms of scrambled binary ones, the modem shall condition circuit 106 to respond to circuit 105 and the modem shall be ready to transmit data.
+- e) When 32 consecutive bits of scrambled binary one at the rate indicated by dibit R2 from the distant modem have been detected, the modem shall set circuit 112 to indicate the operating rate and unclamp circuit 104.
+- f) If a modem has transmitted a rate change sequence and has not received unscrambled repetitive double dibit 00 and 11 at 1200 bit/s immediately prior, or during, or within a time interval equal to the maximum expected two-way propagation delay, the modem may return to the beginning of the rate change sequence as defined above and repeat the procedure until unscrambled repetitive double dibit 00 and 11 is received from the remote modem. A time interval of 1.2 seconds is recommended for the maximum expected two-way propagation delay.
+
+#### 6.6.2 *Response to a rate change*
+
+- a) When the modem detects unscrambled repetitive double dibit 00 and 11 at 1200 bit/s from the distant modem, the modem shall turn circuit 106 OFF and clamp circuit 104 to binary one. During this procedure, circuit 109 and 107 shall remain on.
+- b) When the end of unscrambled repetitive double dibit 00 and 11 at 1200 bit/s from the distant modem is detected, the modem shall condition its receiver for operation at 1200 bit/s and examine the descrambled repetitive dibit R1 (Note 2).
+- c) After having detected 32 consecutive rate dibits R1, at 1200 bit/s, the modem shall transmit unscrambled repetitive double dibit 00 and 11 at 1200 bit/s for $100 \pm 3$ ms followed by transmission of scrambled repetitive dibit R2 defining the operating rate (Note 3).
+- d) $450 \pm 10$ ms after the detection of 32 consecutive rate dibits R1 at 1200 bit/s from the distant modem, the modem may condition its receiver to begin operation at the data rate indicated by R2.
+- e) $600 \pm 10$ ms after the detection of 32 consecutive rate dibits R1 at 1200 bit/s, the modem shall begin transmission of scrambled binary ones at the data rate indicated by R2. After $200 \pm 10$ ms of scrambled binary ones, the modem shall condition circuit 106 to respond to circuit 105 and the modem shall be ready to transmit data.
+- f) When 32 consecutive bits of scrambled binary one, at the rate indicated by the dibit R2 have been detected from the distant modem, the modem shall set circuit 112 to indicate the operating rate and unclamp circuit 104.
+
+*Note 1* - This mode of operation, where implemented, should be provided on both GSTN circuits and leased circuits.
+
+*Note 2* - In the event where the initiating modem is requesting a retrain, the responding modem may delay transmission of the S1 sequence (which should be transmitted immediately following the detection of the end of receipt of the S1 sequence per § 6.4) by more than 32 dibit duration after receipt of the end of the S1 sequence from the initiating modem.
+
+*Note 3* - It is the intent that for a rate change to occur, dibit R2 be set equal to dibit R1. Modems not supporting this option may return a dibit R2 that differs from R1.
+
+TABLE 4/V.22 bis
+
+| Operating rate | Dibit R1 and R2 |
+|----------------|-----------------|
+| 2400
1200 | 11
01 or 10 |
+
+
+
+**Initiating modem**
+
+| | | | | |
+|------|----|----------------------------------|-------------------------------|-----------------|
+| Data | S1 | Scrambled dibit R1 at 1200 bit/s | Scrambled binary 1 at R2 rate | Data at R2 Rate |
+|------|----|----------------------------------|-------------------------------|-----------------|
+
+100 ± 3 ms
+
+450 ± 10 ms
+
+200 ± 10 ms
+
+106
+
+104 clamped to binary 1
+
+104 data
+
+104 clamped to binary 1
+
+104 unclamped (binary 1)
+
+Data
+
+Detect 32 consecutive bits of binary 1 at R2 rate and assert CT 112 to reflect R2 rate
+
+600 ± 10 ms
+
+100 ± 3 ms
+
+Detect end of S1 signal in channel 2
+
+**Responding modem**
+
+| | | | | |
+|------|----|----------------------------------|-------------------------------|------|
+| Data | S1 | Scrambled dibit R2 at 1200 bit/s | Scrambled binary 1 at R2 rate | Data |
+|------|----|----------------------------------|-------------------------------|------|
+
+600 ± 10 ms
+
+200 ± 10 ms
+
+450 ± 10 ms
+
+Detect 32 consecutive bits of binary 1 at R2 rate and assert CT 112 to reflect R2 rate
+
+Detect end of S1 signal in channel 1
+
+Begin receiver decisions based on R2 rate
+
+106
+
+104 clamped to binary 1
+
+104 data
+
+104 clamped to binary 1
+
+104 unclamped (binary 1)
+
+Data
+
+106
+
+Detect 32 consecutive bits of binary 1 at R2 rate and assert CT 112 to reflect R2 rate
+
+Timing diagram for the optional rate change sequence in V.22 bis. The diagram shows the interaction between an Initiating modem and a Responding modem. The Initiating modem sends Data, S1, Scrambled dibit R1 at 1200 bit/s, Scrambled binary 1 at R2 rate, and Data at R2 Rate. The Responding modem sends Data, S1, Scrambled dibit R2 at 1200 bit/s, Scrambled binary 1 at R2 rate, and Data. Key events include: Date change initiated, Detect 32 consecutive bits of binary 1 at R2 rate and assert CT 112 to reflect R2 rate, Detect end of S1 signal in channel 2, Detect end of S1 signal in channel 1, and Begin receiver decisions based on R2 rate. Time intervals are specified as 100 ± 3 ms, 450 ± 10 ms, 600 ± 10 ms, and 200 ± 10 ms. Data fields are 106, 104 clamped to binary 1, 104 unclamped (binary 1), and 104 data.
+
+FIGURE 9/V.22 bis
+
+#### Optional rate change sequence
+
+## 7 Testing facilities
+
+### 7.1 Test loops
+
+Test loops 2 (local and remote) and 3 as defined in Recommendation V.54 shall be provided. Interface operation shall be as defined in Recommendation V.54. Instigation and termination sequences are not compatible with Recommendation V.54.
+
+#### 7.1.1 *Instigation of remote loop 2*
+
+Signals controlling the application of remote loop 2 may only be transmitted after the synchronizing handshake has been completed.
+
+As in Recommendation V.54, the modems are referred to as Modem A and Modem B.
+
+When Modem A is instructed to instigate a remote loop 2, the modem shall transmit an initiation signal of unscrambled binary 1 at 2400 bit/s (or 1200 bit/s).
+
+Modem B shall detect 154-231 ms of the initiation signal, and then transmit to Modem A scrambled alternating binary ones and zeros (reversals) at 2400 bit/s (or 1200 bit/s).
+
+Modem A shall detect 231-308 ms of scrambled reversals, cease transmission of the initiation signal, and then transmit scrambled binary 1 at 2400 bit/s (or 1200 bit/s).
+
+Modem B shall detect the loss of initiation signal and achieve loop 2 within Modem B.
+
+Modem A, upon receiving 231-308 ms of scrambled binary 1 shall indicate to the DTE that it may begin sending test messages.
+
+#### 7.1.2 *Termination of remote loop 2*
+
+When Modem A is instructed to terminate a remote loop 2 the line signal shall be suppressed for a period of $77 \pm 10$ ms, after which transmission shall be restored.
+
+Modem B detects the loss of line signal in 40 to 65 ms and detects the re-appearance of the signal within $155 \pm 50$ ms, after which the modem B returns to normal operation.
+
+### 7.2 *Self tests*
+
+#### 7.2.1 *Self test end-to-end*
+
+Upon activation of the self test switch, an internally generated data pattern of alternative binary ones and zeros (reversals) at the selected bit rate shall be applied to the scrambler. An error detector, capable of identifying errors in a stream of reversals, shall be connected to the output of the descrambler. The presence of errors shall be indicated by a visual indicator. All generating interchange circuits except 114 (if used), 115, 125 and 142 shall be clamped to the binary 1 or OFF condition. If circuit 113 is used, the DCE shall disregard this interchange circuit and use its internal clock.
+
+#### 7.2.2 *Self test with loop 3*
+
+Loop 3 shall be applied to the modem as defined in Recommendation V.54. The self-test switch shall be activated and DCE operation shall be as in § 7.2.1.
+
+#### 7.2.3 *Self test with remote loop 2*
+
+The modem shall be conditioned to instigate a loop 2 at the remote modem as specified in § 7.1. The self-test switch shall be activated and DCE operation shall be as in § 7.2.1.
+
+It shall be possible to perform the above tests (in §§ 7.2.1, 7.2.2 and 7.2.3) with or without the DTE connected to the modem. These tests employ an internally generated data pattern that is controlled by a switch on the DCE.
+
+7.2.4 During any self-test mode, interchange circuits 103, 105 and 108 will be ignored. Note that self tests do not test asynchronous-to-synchronous converter circuits in either the transmitter or receiver.
+
+*Note* - Inclusion of remote loop signalling according to Recommendation V.54 is for further study.
\ No newline at end of file
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+
+
+
+
+ITU logo: a globe with the letters ITU and a lightning bolt symbol.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+# ITU-T
+
+## V.23
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+# DATA COMMUNICATION OVER THE TELEPHONE NETWORK ---
+
+## 600/1200-BAUD MODEM STANDARDIZED FOR USE IN THE GENERAL SWITCHED TELEPHONE NETWORK
+
+## ITU-T Recommendation V.23
+
+(Extract from the *Blue Book*)
+
+---
+
+### NOTES
+
+1 ITU-T Recommendation V.23 was published in Fascicle VIII.1 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+
+2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+### Recommendation V.23
+
+## 600/1200-BAUD MODEM STANDARDIZED FOR USE IN THE GENERAL SWITCHED TELEPHONE NETWORK
+
+*(Geneva, 1964; amended at Mar del Plata, 1968, Geneva, 1972, 1976 and 1980,
+Malaga-Torremolinos, 1984 and at Melbourne, 1988)*
+
+*Note* - The modem, designed for use on connections set up by switching in the general telephone network, can obviously be used on leased lines.
+
+**1** The principal characteristics recommended for a modem to transmit data at medium speed in the general switched telephone network are as follows:
+
+- use of modulation rates up to 600/1200 bauds on the communication channel (see Recommendation V.5);
+- frequency modulation with synchronous or asynchronous mode of operation;
+- inclusion of a backward channel at modulation rates up to 75 bauds for error control, use of this channel being optional.
+
+### **2 Modulation rates and characteristic frequencies for the forward data-transmission channel**
+
+| | $F_0$ | $F_Z$
(symbol 1,
mark) | $F_A$
symbol 0,
space) |
+|--------------------------|---------|------------------------------|------------------------------|
+| Mode 1: up to 600 bauds | 1500 Hz | 1300 Hz | 1700 Hz |
+| Mode 2: up to 1200 bauds | 1700 Hz | 1300 Hz | 2100 Hz |
+
+It is understood that the modem would be used in mode 1 when the presence of long loaded cables and/or the presence on some connections of signalling receivers operating close to 2000 Hz would prevent satisfactory transmission in mode 2. The modem could be used in mode 2 on suitable connections.
+
+### **3 Tolerances on the characteristic frequencies for the forward channel**
+
+It should be possible with all rates of modulation to permit a tolerance, at the transmitter, of $\pm 10$ Hz on both the $F_A$ and $F_Z$ frequencies. This tolerance should be considered as a limit.
+
+Acceptance of these tolerances would give a tolerance of $\pm 10$ Hz for the mean-frequency $F_0 = (F_A + F_Z)/2$ .
+
+The tolerance on the frequency difference $F_A - F_Z$ with regard to the nominal value would be $\pm 20$ Hz.
+
+A maximum frequency drift of $\pm 6$ Hz has been assumed in the connection between the modems which might consist of several carrier circuits connected in tandem. This would make the tolerances on the mark and space frequencies at the receiving modem $\pm 16$ Hz.
+
+### 4 Modulation rate and characteristic frequencies for the backward channel
+
+The modulation rate and characteristic frequencies for the backward channel are as follows:
+
+| | $F_Z$ | $F_A$ |
+|--------------------------------|---------------------|----------------------|
+| | (symbol 1,
mark) | (symbol 0,
space) |
+| Modulation rate up to 75 bauds | 390 Hz | 450 Hz |
+
+In the absence of any signal on the backward channel interface, the condition Z signal is to be transmitted.
+
+### 5 Tolerances on the characteristic frequencies of the backward channel
+
+As the backward channel is a VF telegraph-type channel, the frequency tolerances should be as recommended in Recommendation R.35 [1] for frequency-shift voice-frequency telegraphy.
+
+The $\pm 6$ -Hz frequency drift in the connection between the modems postulated in § 3 above would produce additional distortion in the backward channel. This should be taken into account in the design.
+
+### 6 Division of power between the forward and backward channels
+
+Considering the following table which shows the levels of power for total power remaining equal to 1 mW:
+
+| Forward channel level
(dBm) | Backward channel level
(dBm) |
+|---------------------------------------|----------------------------------------|
+| 0 | - $\infty$ |
+| - 1 | - 7 |
+| - 2 | - 4 |
+| - 3 | - 3 |
+
+equal division of power between the forward and backward channels could be recommended provisionally.
+
+### 7 The following information is provided to assist equipment manufacturers:
+
+- The nominal range of attenuations in subscriber-to-subscriber connections is from 5 to 30 dB at the reference frequency (800 or 1000 Hz), assuming up to 35-dB attenuation at the recommended mean frequency ( $F_0$ ) of the forward channel.
+- A convenient range of sensitivity at the mean frequency $F_0$ for data receivers has been found to be - 40 to 0 dBm for the forward channel at the subscribers' terminals.
+- The data modem should have no adjustment for send level or receive sensitivity under the control of the operator.
+
+### 8 Interchange circuits
+
+The configurations of interchange circuits are those essential for the particular switched network or leased circuit requirement as indicated in Tables 1/V.23 and 2/V.23. Where one or more of such requirements are provided in a modem, then all the appropriate interchange circuits should be provided.
+
+8.1 *List of interchange circuits essential for the modems when used on the general switched telephone network, including terminals equipped for manual calling or answering or automatic calling or answering (see Table 1/V.23).*
+
+8.2 *List of interchange circuits essential for the modems when used on non-switched leased telephone circuits (see Table 2/V.23)*
+
+8.3 *Response times of circuits 106 and 109, 121 and 122*
+
+8.3.1 *Definitions*
+
+8.3.1.1 Circuits 109 and 122 response times are the times that elapse between the connection or removal of a tone to or from the modem receive line terminals and the appearance of the corresponding ON or OFF condition on circuits 109 and 122.
+
+The test tone should have a frequency corresponding to the characteristic frequency of binary 1 and be derived from a source with an impedance equal to the nominal input impedance of the modem.
+
+The level of the test tone should fall within the level range between 3 dB above the actual threshold of the received line signal detector and the maximum admissible level of the received signal. At all levels within this range the measured response times shall be within the specified limits.
+
+TABLE 1/V.23
+
+| Interchange circuit | | Forward (data) channel
one-way system
(Note 1) | | | | Forward (data) channel
either way system
(Note 1) | |
+|-----------------------------------------|-------------------------------------------------|------------------------------------------------------|----------------|-----------------------|----------------|---------------------------------------------------------|-----------------------------|
+| No. | Designation | Without backward channel | | With backward channel | | Without
backward
channel | With
backward
channel |
+| | | Transmit
end | Receive
end | Transmit
end | Receive
end | | |
+| 102 | Signal ground or common return | X | X | X | X | X | X |
+| 103 | Transmitted data | X | - | X | - | X | X |
+| 104 | Received data | - | X | - | X | X | X |
+| 105 | Request to send | - | - | - | - | X | X |
+| 106 | Ready for sending | X | - | X | - | X | X |
+| 107 | Data set ready | X | X | X | X | X | X |
+| 108/1
or
108/2
(Note 2)
109 | Connect data set to line
Data terminal ready | X | X | X | X | X | X |
+| | Data channel received line signal detector | - | X | - | X | X | X |
+| 111 | Data signalling rate selector (DTE) | X | X | X | X | X | X |
+| 114
(Note 3) | Transmitter signal element timing (DCE) | X | - | X | - | X | X |
+| 115
(Note 3) | Receiver signal element timing (DCE) | - | X | - | X | X | X |
+| 118 | Transmitted backward channel data | - | - | - | X | - | X |
+| 119 | Receiver backward channel data | - | - | X | - | - | X |
+| 120 | Transmit backward channel line signal | - | - | - | - | - | X |
+| 121
(Note 4) | Backward channel ready | - | - | - | X | - | X |
+| 122
(Note 4) | Backward channel received line signal detector | - | - | X | - | - | X |
+| 125 | Calling indicator | X | X | X | X | X | X |
+
+*Note 1* - All essential interchange circuits and any others which are provided shall comply with the functional and operational requirements of Recommendation V.24. All interchange circuits indicated by X shall be properly terminated in the data terminal equipment and in the data circuit-terminating equipment in accordance with the appropriate Recommendation for electrical characteristics (see § 9).
+
+*Note 2* - This circuit shall be capable of operation as circuit 108/1 - *Connect data set to line* or circuit 108/2 - *Data terminal ready* depending on its use.
+
+*Note 3* - These circuits are required when the optional clock is implemented in the modem.
+
+*Note 4* - These circuits are not required if the modem is operating in an asymmetrical duplex mode.
+
+TABLE 2/V.23
+
+| Interchange circuit | | Forward (data) channel
one-way system
(Note 1) | | | | Forward data
channel either
way or both ways
simultaneously system
(Note 1) | |
+|---------------------|------------------------------------------------|------------------------------------------------------|----------------|-----------------------|----------------|-----------------------------------------------------------------------------------------|-----------------------------|
+| No. | Designation | Without backward channel | | With backward channel | | Without
backward
channel | With
backward
channel |
+| | | Transmit
end | Receive
end | Transmit
end | Receive
end | | |
+| 102 | Signal ground or common return | X | X | X | X | X | X |
+| 103 | Transmitted data | X | - | X | - | X | X |
+| 104 | Received data | - | X | - | X | X | X |
+| 105 | Request to send | X | - | X | - | X | X |
+| 106 | Ready for sending | X | - | X | - | X | X |
+| 107 | Data set ready | X | X | X | X | X | X |
+| 108/1 | Connect data set to line | X | X | X | X | X | X |
+| 109 | Data channel received line signal detector | - | X | - | X | X | X |
+| 111 | Data signalling rate selector (DTE) | X | X | X | X | X | X |
+| 114
(Note 2) | Transmitter signal element timing (DCE) | X | - | X | - | X | X |
+| 115
(Note 2) | Receiver signal element timing (DCE) | - | X | - | X | X | X |
+| 118 | Transmitted backward channel data | - | - | - | X | - | X |
+| 119 | Received backward channel data | - | - | X | - | - | X |
+| 120 | Transmit backward channel line signal | - | - | - | X | - | X |
+| 121 | Backward channel ready | - | - | - | X | - | X |
+| 122 | Backward channel received line signal detector | - | - | X | - | - | X |
+
+*Note 1* - All essential interchange circuits and any others which are provided shall comply with the functional and operational requirements of Recommendation V.24. All interchange circuits indicated by X shall be properly terminated in the data terminal equipment and in the data circuit terminating equipment in accordance with the appropriate Recommendation for electrical characteristics (see § 9).
+
+*Note 2* - These circuits are required when the optional clock is implemented in the modem.
+
+8.3.1.2 Circuit 106 response times are from the connection of an ON or OFF condition on:
+
+- circuit 105 (where it is provided) to the appearance of the corresponding ON or OFF condition on circuit 106;
+- circuit 122 (where circuit 105 is not provided) to the appearance of the corresponding ON or OFF condition on circuit 106 in a configuration having a single data channel together with a single backward channel only;
+- circuit 107 (where circuits 105 and 122 are not provided) to the appearance of the corresponding ON or OFF condition on circuit 106;
+
+8.3.1.3 Circuit 121 response times are from the connection of an ON or OFF condition on:
+
+- circuit 120 (where it is provided) to the appearance of the corresponding ON or OFF condition on circuit 121;
+- circuit 109 (where circuit 120 is not provided) to the appearance of the corresponding ON or OFF condition on circuit 121.
+
+#### 8.3.2 Response times
+
+TABLE 3/V.23
+
+| | | | |
+|-------------|-----------|--------------------------------|--------------------------------------------------------------------------|
+| Circuit 106 | OFF to ON | 750 ms to 1400 ms (see Note 1) | a) 20 ms to 40 ms
(see Note 2)
b) 200 ms to 275 ms
(see Note 2) |
+| | ON to OFF | $\leq 2$ ms | |
+| Circuit 109 | OFF to ON | 300 ms to 700 ms (see Note 1) | 10 ms to 20 ms (see Note 1) |
+| | ON to OFF | 5 ms to 15 ms | |
+| Circuit 121 | OFF to ON | 80 ms to 160 ms | |
+| | ON to OFF | $\leq 2$ ms | |
+| Circuit 122 | OFF to ON | $< 80$ ms | |
+| | ON to OFF | 15 ms to 80 ms | |
+
+*Note 1* - For automatic calling and answering, the longer response times of circuits 106 and 109 are to be used during call establishment only.
+
+*Note 2* - The choice of response times depends upon the system application:
+
+- a) no protection given against line echoes;
+- b) protection given against line echoes.
+
+*Note 3* - The above parameters are provisional and are the subject of further study.
+
+#### 8.4 Threshold of data channel and backward channel received line signal detectors
+
+Level of received line signal at receive line terminals of modem for all types of connections, i.e. general switched telephone network or non-switched leased telephone circuits:
+
+| | |
+|-----------------------|----------------------|
+| greater than - 43 dBm | circuits 109/122 ON |
+| less than - 48 dBm | circuits 109/122 OFF |
+
+The condition of circuits 109 and 122 for levels between -43 dBm and -48 dBm is not specified except that the signal detectors shall exhibit a hysteresis action such that the level at which the OFF to ON transition occurs is at least 2 dB greater than that for the ON to OFF transition.
+
+Where transmission conditions are known on switched or leased circuits, Administrations should be permitted at the time of modem installation to change these response levels of the received line signal detectors to less sensitive values (e.g. -33 dBm and -38 dBm respectively).
+
+#### 8.5 *Clamping in half-duplex mode*
+
+The DCE, when operating in half-duplex mode on a 2-wire line, shall hold, where implemented:
+
+- i) circuit 104 in the binary 1 condition and circuit 109 in the OFF condition when circuit 105 is in the ON condition and, where required to protect circuit 104 from false signals, for a period of $150 \pm 25$ milliseconds following the ON to OFF transition on circuit 105. The use of this additional delay is optional, based on system considerations;
+- ii) circuit 119 in the binary 1 condition and circuit 122 in the OFF condition when circuit 120 is in the ON condition and, where required to protect circuit 119 from false signals, for a time interval following the ON to OFF transition on circuit 120. The specific duration of this time interval is left for further study. The additional delay is optional, based on system considerations.
+
+#### 8.6 *Fault condition of interchange circuits*
+
+(See Recommendation V.28, § 7 for association of the receiver failure detection types).
+
+8.6.1 The DTE should interpret a fault condition on circuit 107 as an OFF condition using failure detection type 1.
+
+8.6.2 The DCE should interpret a fault condition on circuits 105 and 108 as an OFF condition using failure detection type 1.
+
+8.6.3 All other circuits not referred to above may use failure detection types 0 or 1.
+
+### 9 **Electrical characteristics of interchange circuits**
+
+Use of electrical characteristics conforming to Recommendation V.28 is recommended together with the connector pin assignment plan specified by ISO 2110.
+
+*Note* - Manufacturers may wish to note that the long-term objective is to replace electrical characteristics specified in Recommendation V.28, and that Study Group XVII has agreed that the work shall proceed to develop a more efficient, all balanced, interface for the V-Series application which minimizes the number of interchange circuits.
+
+### 10 **Equipment for the disablement of echo suppressors**
+
+When echo control device disabling is required, it is recommended that the procedures specified in Recommendation V.25 be followed.
+
+### 11 **Inclusion of a clock in the modem**
+
+A clock is not an essential item in the standardized modem. However, the modem may conveniently include a clock when used primarily for synchronous transmission.
+
+If such a clock is included in the modem, a synchronizing pattern consisting of alternate binary 0 and binary 1 at clock rate should be transmitted for the whole interval between the OFF to ON transitions of interchange circuits 105 and 106. Users should note that part of this synchronizing pattern may appear at the distant receiver on circuit 104 after the OFF to ON transition of circuit 109. The data terminal equipment should make provision to differentiate between these false signals and true data.
+
+### **Reference**
+
+- [1] CCITT Recommendation *Standardization of FMVFT systems for a modulation rate of 50 bauds*, Vol. VII, Rec. R.35.
\ No newline at end of file
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+
+
+
+
+ITU logo: a globe with the letters ITU and a lightning bolt symbol.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+# ITU-T
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+## V.230
+
+**DATA COMMUNICATION
+OVER THE TELEPHONE NETWORK**
+
+---
+
+**GENERAL DATA COMMUNICATIONS
+INTERFACE LAYER 1 SPECIFICATION**
+
+**ITU-T Recommendation V.230**
+
+(Extract from the *Blue Book*)
+
+---
+
+# NOTES
+
+1 ITU-T Recommendation V.230 was published in Fascicle VIII.1 of the *Blue Book*. This file is an extract from the *Blue Book*. While the presentation and layout of the text might be slightly different from the *Blue Book* version, the contents of the file are identical to the *Blue Book* version and copyright conditions remain unchanged (see below).
+
+2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+# GENERAL DATA COMMUNICATIONS INTERFACE LAYER 1 SPECIFICATION
+
+(Melbourne, 1988)
+
+## 1 General
+
+This Recommendation defines the layer 1 characteristics of a General Data Communications Interface (GDCI) between Data Circuit-Terminating Equipment (DCE) and/or Data Terminal Equipment (DTE). Applications include DTE-DCE interfaces, DCE-DCE interfaces, and possible DTE-DTE interfaces (see Figure 1/V.230). The interface specification is based on the ISDN basic user-network interface defined in Recommendation I.430. The differences between the GDCI and the ISDN basic user-network interface provide for the different wiring configurations expected for these interfaces, and they provide a means by which equipment conforming to V.230 can identify whether it has been connected to an interface operating according to V.230 or to an interface operating according to I.430. The characteristics of the GDCI have been chosen so that it is possible to design terminals which are compatible with both I.430 and V.230, and so that inadvertent connection of I.430 equipment to a V.230 passive bus or of GDCI equipment to an I.430 passive bus will not result in passive bus malfunction.
+
+*Note* - DTE-DTE interfaces are not defined by CCITT.
+
+
+
+Diagram illustrating GDCI applications. It shows three main configurations: 1. A DTE connected to a DCE, which is then connected to a V.230 interface. 2. A DCE connected to a DCE, which is then connected to a V.230 interface. 3. A DTE connected to a DCE, which is then connected to a V.230 interface. Below these, there is a section labeled 'Up to 8 units' showing a DTE (or DCE) connected to a V.230 interface. To the right, there is an 'Analogue interface' section showing a V.230 interface connected to an analogue interface. The diagram is labeled 'T1700300-88'.
+
+FIGURE 1/V.230
+
+### GDCI applications
+
+## 2 Service characteristics
+
+### 2.1 Services required from the physical medium
+
+Layer 1 of this interface requires a balanced metallic transmission medium, for each direction of transmission, capable of supporting 192 kbit/s.
+
+### 2.2 Services provided to layer 2
+
+Layer 1 provides the following services to layer 2 and the management entity.
+
+#### 2.2.1 *Transmission capability*
+
+Layer 1 provides the transmission capability, by means of appropriately encoded bit streams, for the BV and DV channels and the related timing and synchronization functions.
+
+*Note* - The BV and DV channels correspond to the B and D channels, respectively, as defined in the I-Series Recommendations. Use of the BV and DV channels is defined in Recommendations V.yy and V.zz (V.yy and V.zz: still under study).
+
+#### 2.2.2 *Activation/deactivation*
+
+Layer 1 provides the signalling capability and the necessary procedures to enable equipment to be deactivated when required and reactivated when required. The activation and deactivation procedures are defined in § 6.2.
+
+#### 2.2.3 *D-channel access*
+
+Layer 1 provides the signalling capability and the necessary procedures to enable equipment to gain access to the common resource of the DV channel in an orderly fashion while meeting the performance requirements of the DV-channel signalling system. These DV-channel access control procedures are defined in § 6.1
+
+#### 2.2.4 *Maintenance*
+
+Layer 1 provides the signalling capability, procedures and necessary functions at layer 1 to enable the maintenance functions to be performed.
+
+#### 2.2.5 *Status indication*
+
+Layer 1 provides an indication to the higher layers of the status of layer 1.
+
+### 2.3 *Primitives between layer 1 and other entities*
+
+Primitives represent, in an abstract way, the logical exchange of information and control between layer 1 and other entities. They neither specify nor constrain the implementation of entities or interfaces.
+
+The primitives to be passed across the layer 1/2 boundary or to the management entity and parameter values associated with these primitives are defined and summarized in Table 1/V.230. For a description of the syntax and use of the primitives, refer to Recommendation X.211 and relevant detailed description in § 6.
+
+TABLE 1/V.230
+
+#### **Primitives associated with layer 1**
+
+| Generic name | Specific name | | Parameter | | Message unit contents |
+|------------------|---------------|------------|--------------------|--------------|---------------------------------------------------------------------------------------------|
+| | Request | Indication | Priority indicator | Message unit | |
+| L1 < - - > L2 | | | | | |
+| PH-DATA | X
(Note 1) | X | X
(Note 2) | X | Layer 2 peer-to-peer message |
+| PH-ACTIVATE | X | X | - | - | |
+| PH-DEACTIVATE | X | X | - | - | |
+| M < - - > L1 | | | | | |
+| MPH-ERROR | - | X* | - | X | *Type of error or recovery from a previously reported error |
+| MPH-ACTIVATE | X | X | - | - | |
+| MPH-DEACTIVATE | X | X | - | - | |
+| MPH- INFORMATION | - | X | - | X | Connected
Attached V-DCE
Attached V-DTE
Attached NT
Attached TE
Disconnected |
+
+*Note 1* - PH-Data Request implies underlying negotiation between layer 1 and layer 2 for the acceptance of the data.
+
+*Note 2* - Priority indication applies only to the request type.
+
+## 3 Modes of operation
+
+Both point-to-point and point-to-multipoint modes of operation, as described below, are intended to be accommodated by the layer 1 characteristics of the GDCL. In this Recommendation, the modes of operation apply only to the layer 1 procedural characteristics of the interface and do not imply any constraints on modes of operation at higher layers.
+
+### 3.1 Point-to-point operation
+
+Point-to-point operation at layer 1 implies that only one source (transmitter) and one sink (receiver) are active at any one time in each direction of transmission at an S or T reference point. (Such operation is independent of the number of interfaces which may be provided on a particular wiring configuration - see § 4.)
+
+### 3.2 Point-to-multipoint operation
+
+Point-to-multipoint operation at layer 1 allows more than one equipment (source and sink pair) to be simultaneously active at a GDCL. (The multipoint mode of operation may be accommodated, as discussed in § 4, with point-to-point or point-
+
+to-multipoint wiring configurations.)
+
+## 4 Types of wiring configuration
+
+The electrical characteristics of the GDCI are determined on the basis of certain assumptions about the various wiring configurations which may exist in the user premises. These assumptions are identified in two major configuration descriptions, §§ 4.1 and 4.2, together with additional material contained in Annex A to this Recommendation. Figure 2/V.230 shows a general reference configuration for wiring in the user premises.
+
+
+
+Figure 2/V.230: Reference configuration for wiring in the user premises location. The diagram shows a horizontal line representing a cable. On the left, a box labeled 'DTEd' is connected to the line at interface point I\_A0. A terminating resistor 'TR' is connected to the line at this point. Further along the line, there are several interface points labeled I\_A1, I\_An, and I\_B. At I\_A1, a box labeled 'DTE1' is connected. At I\_An, a box labeled 'DTEn' is connected. At I\_B, a box labeled 'DCE' is connected. A terminating resistor 'TR' is also connected to the line at I\_B. A double-headed arrow labeled 'd\_s' indicates the distance between the two terminating resistors. A double-headed arrow labeled 'd\_n' indicates the distance between I\_A1 and I\_An. A double-headed arrow labeled 'd\_s' indicates the distance between I\_An and I\_B. The text 'T1700460-89' is located at the bottom right of the diagram.
+
+| | |
+|----|-------------------------------------------------------------------------------------|
+| TR | Terminating resistor |
+| I | Electrical interface |
+| B | Location of I B when the terminating resistor (TR) is include in the DCE |
+
+FIGURE 2/V.230
+
+### Reference configuration for wiring in the user premises location
+
+### 4.1 Point-to-point configuration
+
+A point-to-point wiring configuration implies that only one source (transmitter) and one sink (receiver) are interconnected on an interchange circuit.
+
+### 4.2 Point-to-multipoint configuration
+
+A point-to-multipoint wiring configuration allows more than one source to be connected to the same sink or more than one sink to be connected to the same source on an interchange circuit. Such distribution systems are characterized by the fact that they contain no active logic elements performing functions (other than possibly amplification or regeneration of the signal).
+
+The equipment connected to interface point IB must operate in the "master timing mode" discussed in § 6.6. This equipment is normally a V-DCE. The equipment connected to interface points IA0 through IAn must operate in the "slave timing mode". These are normally V-DTEs, although a V-DCE may be connected to this point to achieve a DCE-to-DCE connection on the GDCI. Use of a V-DTE as the master timing mode equipment is for further study.
+
+### 4.3 Wiring polarity integrity
+
+For a point-to-point wiring configuration, the two wires of the interchange circuit pair may be reversed. However, for a point-to-multipoint wiring configuration, the wiring polarity integrity of the interchange circuit (slave-to-master direction) must be maintained between slave mode equipment.
+
+In addition, the wires of the optional pairs, which may be provided for powering, may not be reversed in either configuration.
+
+### 4.4 Location of the interfaces
+
+The wiring in the user premises is considered to be one continuous cable run with jacks for the equipment attached directly to the cable or using stubs less than 1 meter in length. The jacks are located at interface points IA and IB (see Figure 2/V.230). One interface point, IA, is adjacent to the master mode equipment. The other interface point, IB, is adjacent to the master mode equipment. However, in some applications, the equipment may be connected to the wiring without the use of a jack or with a jack which accommodates multiple interfaces. The required electrical characteristics (described in § 8) for IA and IB are different in some aspects.
+
+### 4.5 *Wiring associated with the equipment*
+
+The wiring connecting the V-DCE or V-DTE to associated jacks or to other equipment affects the interface electrical characteristics. Equipment that is not permanently connected to the interface wiring may be equipped with one of the following means of connection to the interface point:
+
+- a hard wired connecting cord (of not more than 10 m in the case of a V-DTE and not more than 3 m in the case of a V-DCE) equipped with a suitable plug, or
+- a jack with a connecting cord (of not more than 10 m in the case of a V-DTE and not more than 3 m in the case of a V-DCE) equipped with a suitable plug at each end, or
+- two jacks with suitable connecting cords or cables which may be used to form a "daisy-chain" connection from one equipment unit to the next, provided that the connecting cords and cables meet the distance limitations set in Annex A. In this case, the electrical interface exists inside the equipment, where the two jacks are wired together with each pin on one jack connected to the like-numbered pin on the other jack and to the internal circuitry of the equipment.
+
+The requirements of V.230 apply to the interface point ( $I_A$ or $I_B$ ), and the cord forms part of the associated equipment. Note that the equipment may attach directly to the interface wiring without a detachable cord.
+
+Although an equipment may be provided with a cord of less than 5 m in length, it shall meet the requirements of this Recommendation with a cord having a minimum length of 5 m. As specified above, the equipment cord may be detachable. Such a cord may be provided as part of the equipment, or the equipment may be designed to conform to the electrical characteristics specified in § 8 with a "standard ISDN basic access TE cord" conforming to the requirements specified in § 8.9 of Recommendation I.430, and having the maximum permitted capacitance.
+
+The use of an extension cord, of up to 25 m in length, with an equipment in point-to-point operation, is permitted. (The total attenuation of the wiring and of the cord in this case should not exceed 6 dB.)
+
+## 5 **Functional characteristics**
+
+The following paragraphs show the functions for the interface.
+
+### 5.1 *Interface functions*
+
+#### 5.1.1 *BV channel*
+
+This function provides, for each direction of transmission, two independent 64 kbit/s channels for use as BV channels.
+
+#### 5.1.2 *Bit timing*
+
+This function provides bit (signal element) timing at 192 kbit/s to enable the equipment to recover information from the aggregate bit stream.
+
+#### 5.1.3 *Octet timing*
+
+This function provides 8 kHz timing for the equipment.
+
+#### 5.1.4 *Frame alignment*
+
+This function provides information to enable equipment to recover the time division multiplexed channels.
+
+#### 5.1.5 *DV channel*
+
+This function provides, for each direction of transmission, one DV channel at a bit rate of 16 kbit/s.
+
+#### 5.1.6 *DV channel access procedure*
+
+This function is specified to enable slave mode equipment to gain access to the common resource of the DV channel in an orderly controlled fashion. The functions necessary for these procedures include an echoed DV channel at a bit rate of 16 kbit/s in the direction master to slave equipment. For the definition of the procedures relating to DV channel access, see § 6.1.
+
+#### 5.1.7 *Power feeding*
+
+This function provides for the capability to transfer power across the interface. The direction of power transfer depends on the application. In a typical application, it may be desirable to provide for power transfer from the V-DCE towards V-DTEs in order to, for example, power an adaptor for a unit which does not conform to V.230. (In some applications, unidirectional power feeding or no power feeding at all, across the interface, may apply.) Other Recommendations concerning power feeding capability are contained in § 9.
+
+#### 5.1.8 *Activation and deactivation*
+
+Activation is necessary to initialize an equipment when power is applied, or when it is connected to the GDCL. Deactivation and activation may also be used to control entry to and exit from a low power consumption mode. The procedures and precise conditions under which these actions take place are specified in § 6.2. For many applications, it will be appropriate for the equipment to remain in the active state at all times after initial activation.
+
+### 5.2 *Interchange circuits*
+
+Two interchange circuits, one for each direction of transmission, shall be used to transfer digital signals across the interface. All of the functions described in § 5.1, except for power feeding, shall be carried by means of a digitally multiplexed signal structured as defined in § 5.4.
+
+### 5.3 *Connected/disconnected indication*
+
+The criterion used by equipment to determine whether it is connected or disconnected at the interface is reception of valid incoming frames.
+
+The layer 1 entity within the equipment shall inform the management entity of the connection status using the MPH-INFORMATION INDICATION primitive. The method for determining the message unit contents is discussed in § 6.2.
+
+### 5.4 *Frame structure*
+
+In both directions of transmission, the bits shall be grouped into frames of 48 bits each. The frame structure shall be identical for all configurations (point-to-point and point-to-multipoint).
+
+#### 5.4.1 *Bit rate*
+
+The nominal transmitted bit rate at the interfaces shall be 192 kbit/s in both directions of transmission.
+
+#### 5.4.2 Binary organization of the frame
+
+The frame structures are different for each direction of transmission. Both structures are illustrated diagrammatically in Figure 3/V.230.
+
+
+
+Figure 3/V.230: Frame structure at the GDCI. The diagram shows two bit streams: 'MASTER TO SLAVE' and 'SLAVE TO MASTER'. The 'MASTER TO SLAVE' stream starts with D, L, F, L, followed by a 2-bit offset, then B1, B1, B1, B1, B1, B1, B1, E, D, A, FA, N, B2, B2, B2, B2, B2, B2, B2, E, D, M, B1, B1, B1, B1, B1, B1, B1, E, D, S, B2, B2, B2, B2, B2, B2, B2, E, D, L, F, L. The 'SLAVE TO MASTER' stream starts with D, L, F, L, followed by a 2-bit offset, then B1, B1, B1, B1, B1, B1, B1, L, D, L, FA, L, B2, B2, B2, B2, B2, B2, B2, L, D, L, B1, B1, B1, B1, B1, B1, B1, L, D, L, B2, B2, B2, B2, B2, B2, B2, L, D, L, F, L. A legend defines the bits: F (framing bit), L (DC balancing bit), D (DV-channel bit), E (DV-echo-channel bit), FA (Auxiliary framing bit), N (bit set to a binary value N = FA), B1 (bit within BV channel 1), B2 (bit within BV channel 2), A (bit used for activation), S (S-channel multiframe bit), and M (multiframe bit).
+
+Note 1 - Dots demarcate those parts of the frame that are independently DC-balanced.
+
+Note 2 - The FA bit in the direction slave to master is used as a Q bit in every fifth frame if the Q channel capability is applied (see § 6.3.3).
+
+Note 3 - The nominal 2-bit offset is as seen from the slave mode equipment (IA in Figure 1/V.230). The corresponding offset at the master mode equipment may be greater due to delay in the interface cable and varies by configuration.
+
+FIGURE 3/V.230
+
+##### Frame structure at the GDCI
+
+##### 5.4.2.1 Slave to master
+
+Each frame consists of the following groups of bits; each individual group is DC-balanced by its last bit (L bit):
+
+| Bit position | Group |
+|--------------|----------------------------------------------------|
+| 1 and 2 | framing signal with balance bit |
+| 3-11 | BV1 channel (first octet) with balance bit |
+| 12 and 13 | DV-channel bit with balance bit |
+| 14 and 15 | FA auxiliary framing bit or Q bit with balance bit |
+| 16-24 | BV2 channel (first octet) with balance bit |
+| 25 and 26 | DV-channel bit with balance bit |
+| 27-35 | BV1 channel (second octet) with balance bit |
+
+| | |
+|-----------|---------------------------------------------|
+| 36 and 37 | DV-channel bit with balance bit |
+| 38-46 | BV2 channel (second octet) with balance bit |
+| 47 and 48 | DV channel bit with balance bit |
+
+##### 5.4.2.2 *Master to slave*
+
+Frames transmitted by the master contain an echo channel (E bits) used to retransmit the DV bits received from the slaves. The DV-echo channel is used for DV-channel access control. The last bit of the frame (L bit) is used for balancing each complete frame.
+
+The bits are grouped as follows:
+
+| Bit position | Group |
+|---------------------|--------------------------------------|
+| 1 and 2 | framing signal with balance bit |
+| 3-10 | BV1 channel (first octet) |
+| 11 | E, DV-echo-channel bit |
+| 12 | DV-channel bit |
+| 13 | bit A used for activation |
+| 14 | F A auxiliary framing bit |
+| 15 | N bit (coded as defined in § 6.3) |
+| 16-23 | BV2 channel (first octet) |
+| 24 | E, DV-echo-channel bit |
+| 25 | DV-channel bit |
+| 26 | M, multiframing bit |
+| 27-34 | BV1 channel (second octet) |
+| 35 | E, DV-echo-channel bit |
+| 36 | DV-channel bit |
+| 37 | S, layer 1 multiframe channel bit |
+| 38-45 | BV2 channel (second octet) |
+| 46 | E, DV-echo-channel bit |
+| 47 | DV-channel bit |
+| 48 | frame balance bit |
+
+##### 5.4.2.3 *Relative bit positions*
+
+At the slave mode equipment, timing in the direction to the master mode equipment shall be derived from the frames received from the master mode equipment.
+
+The first bit of each frame transmitted from a slave equipment towards the master equipment shall be delayed, nominally, by two bit periods with respect to the first bit of the frame received from the master equipment. Figure 3/V.230 illustrates the relative bit positions for both transmitted and received frames.
+
+### 5.5 Line code
+
+For both directions of transmission, pseudo-ternary coding is used with 100% pulse width as shown in Figure 4/V.230. Coding is performed in such a way that a binary ONE is represented by no line signal; whereas, a binary ZERO is represented by a positive or negative pulse. The first binary ZERO following the framing balance bit is of the same polarity as the framing balance bit. Subsequent binary ZEROs must alternate in polarity. A balance bit is a binary ZERO if the number of binary ZEROs following the previous balance bit is odd. A balance bit is a binary ONE if the number of binary ZEROs following the previous balance bit is even.
+
+
+
+Figure 4/V.230: Pseudo-ternary code example of application. The diagram shows the mapping of binary values to a line signal. Binary values: 0 1 0 0 1 1 0 0 0 1 1. Line signal: A horizontal line representing the signal level. For binary 0, there is a positive pulse. For binary 1, there is no signal (the line remains at the baseline). For binary 0, there is a negative pulse. For binary 0, there is a positive pulse. For binary 1, there is no signal. For binary 1, there is no signal. For binary 0, there is a negative pulse. For binary 0, there is a positive pulse. For binary 0, there is a negative pulse. For binary 1, there is no signal. For binary 1, there is no signal. The signal alternates polarity for binary zeros. A time axis 't' with an arrow is shown at the bottom right. Below the diagram is the text 'CCITT - 62 730'.
+
+FIGURE 4/V.230
+
+#### Pseudo-ternary code - example of application
+
+### 5.6 Timing considerations
+
+Equipment may employ one of two timing sources, if available, for transmission of frames across the interface:
+
+- timing derived from an internal source or from an external source conveyed to the equipment by other means (e.g. timing derived from the receive line timing by a V-DCE). This is referred to as "master timing mode". Exactly one equipment on a GDCI bus must operate in this mode.
+- timing derived from the receive side of the interface ("loopback timing"). This is referred to as "slave timing mode".
+
+## 6 Interface procedures
+
+### 6.1 DV-channel access procedure
+
+The following procedure allows for a number of slave mode equipments connected in a multipoint configuration to gain access to the DV channel in an orderly fashion. The procedure always ensures that, even in cases where two or more equipments attempt to access the DV channel simultaneously, one, but only one, of the equipments will be successful in completing transmission of its information. This procedure relies upon the use of layer 2 frames delimited by flags consisting of the binary pattern "01111110" and the use of zero bit insertion to prevent flag imitation (see Recommendation I.441).
+
+The procedure also permits equipment to operate in a point-to-point manner.
+
+#### 6.1.1 Interframe (layer 2) time fill
+
+When a slave mode equipment has no layer 2 frames to transmit, it shall send binary ONES on the DV channel, i.e., the interframe time fill in the slave-to-master direction shall be all binary ONES.
+
+When a master timing mode equipment has no layer 2 frames to transmit, it shall send binary ONES or HDLC flags on the DV channel, i.e., the interframe time fill in the master-to-slave direction shall be either all binary ONES or repetitions of the octet "01111110". When the interframe time fill is HDLC flags, the flag which defines the end of a frame may define the start of the next frame.
+
+#### 6.1.2 D-echo channel
+
+The master timing mode equipment, on receipt of a DV-channel bit, shall reflect the binary value, in the next available DV-echo-channel bit position towards the slave mode equipment.
+
+#### 6.1.3 *DV-channel monitoring*
+
+Slave mode equipment, while in the active condition, shall monitor the DV-echo channel, counting the number of consecutive binary ONES. If a ZERO bit is detected, the equipment shall restart counting the number of consecutive ONE bits. The current value of the count is called C.
+
+*Note* - C need not be incremented after the value eleven has been reached.
+
+#### 6.1.4 *Priority mechanism*
+
+Layer 2 frames are transmitted using one of two priority classes. Priority class 1 frames are given priority over priority class 2 frames. Furthermore, to ensure that within each priority class all competing equipments are given a fair access to the DV channel, once an equipment has successfully completed the transmission of a frame, it is given a lower level of priority within that class. The equipment is given back its normal level within a priority class when all equipments have had an opportunity to transmit information at the normal level within that priority class.
+
+The priority class of a particular layer 2 frame may be a characteristic of the equipment which is preset at manufacture or at installation, or it may be passed down from layer 2 as a parameter of the PH-DATA REQUEST primitive. A dual mode (GDCI/ISDN) terminal may thus use the PH-DATA REQUEST primitive to establish the proper priorities for its operation.
+
+The priority mechanism is based on the requirement that slave mode equipment may start layer 2 frame transmission only when C (see § 6.1.3) is equal to, or exceeds, the value $X_1$ for priority class 1 or is equal to, or exceeds, the value $X_2$ for priority class 2. The value of $X_1$ shall be eight for the normal level and nine for the lower level of priority. The value of $X_2$ shall be ten for the normal level and eleven for the lower level of priority.
+
+In a priority class, the value of the normal level of priority is changed into the value of the lower level of priority (i.e., higher value) when the equipment has successfully transmitted a layer 2 frame of that priority class.
+
+The value of the lower level of priority is changed back to the value of the normal level of priority when C (see § 6.1.3) equals the value of the lower level of priority (i.e., higher value).
+
+#### 6.1.5 *Collision detection*
+
+While transmitting information in the DV channel, slave mode equipment shall monitor the received DV-echo channel and compare the last transmitted bit with the next available DV-echo bit. If the transmitted bit is the same as the received echo, the equipment shall continue its transmission. If, however, the received echo is different from the transmitted bit, the equipment shall cease transmission immediately and return to the DV-channel monitoring state.
+
+#### 6.1.6 *Priority system*
+
+Annex B describes an example of how the priority system may be implemented.
+
+### 6.2 *Activation/deactivation*
+
+#### 6.2.1 *Definitions*
+
+##### 6.2.1.1 *Slave mode equipment states (normally DTE)*
+
+6.2.1.1.1 State F1 (inactive): In this inactive state, the equipment is not transmitting. This state is entered upon loss of power.
+
+6.2.1.1.2 State F2 (sensing): This state is entered after the equipment has been powered on, but has not determined the type of signal (if any) being received.
+
+6.2.1.1.3 State F3 (deactivated): This is the deactivated state of the physical protocol. Neither the master nor the slave equipment is transmitting.
+
+6.2.1.1.4 State F4 (awaiting signal): When the equipment is requested to initiate activation by means of an ACTIVATE REQUEST primitive, it transmits a signal (INFO 1) and waits for a response.
+
+6.2.1.1.5 State F5 (identifying input): At the first receipt of any signal from the master mode equipment, the slave mode equipment ceases to transmit INFO 1 and awaits identification of signal INFO 2 or INFO 4.
+
+6.2.1.1.6 State F6 (synchronized): When the equipment receives an activation signal (INFO 2) from the master, it responds with a signal (INFO 3) and waits for normal frames (INFO 4).
+
+6.2.1.1.7 State F7 (identifying interface): This is a transition state during entry to normal activation. When this state is entered, a timer (T4) is started, and the appropriate (DTE or DCE) identification character is transmitted on the multiframe Q channel. This state continues until either a V-series identification character is received on the multiframe S channel or T4 times out.
+
+6.2.1.1.8 State F8 (lost framing): This is the condition where the equipment has lost frame synchronization and is awaiting re-synchronization by receipt of INFO 2 or INFO 4 or deactivation by receipt of INFO 0.
+
+6.2.1.1.9 State F9 (activated): This is the normal active state with the protocol activated in both directions. Both the master and slave mode equipments are transmitting normal frames.
+
+##### 6.2.1.2 *Master mode equipment states (normally DCE)*
+
+6.2.1.2.1 State G1 (deactive): In this deactivated state, the equipment is not transmitting.
+
+6.2.1.2.2 State G2 (pending activation): In this partially active state, the master mode equipment sends INFO 2 while waiting for INFO 3. This state will be entered after receiving an ACTIVATE REQUEST primitive, or on the receipt of INFO 0 or lost framing while in state G3 or G5. Then the choice to eventually deactivate is up to higher layers within the equipment.
+
+6.2.1.2.3 State G3 (identifying interface): This is a transition state during entry to normal activation. When this state is entered, a timer (T4) is started, and the appropriate (DTE or DCE) identification character is transmitted on the multiframe S channel. This state continues until either a V-series identification (DTE or DCE) is received on the multiframe Q channel or T4 times out.
+
+6.2.1.2.4 State G4 (pending deactivation): When the equipment wishes to deactivate, it may wait for a timer to expire before returning to the deactivated state.
+
+6.2.1.2.5 State G5 (active): This is the normal active state where the master and slave mode equipment are transmitting INFO 4 and INFO 3 respectively. A deactivation may be initiated by a DEACTIVATE REQUEST primitive, or the equipment may remain in the active state all the time, under non-fault conditions.
+
+##### 6.2.1.3 *Activate primitives*
+
+The following primitives should be used between layers 1 and 2 and between layer 1 and the management entity in the activation procedures. For use in state diagrams, etc., abbreviations of the primitive names are also given.
+
+PH-ACTIVATE REQUEST (PH-AR)
+
+PH-ACTIVATE INDICATION (PH-AI)
+
+MPH-ACTIVATE REQUEST (MPH-AR)
+
+MPH-ACTIVATE INDICATION (MPH-AI)
+
+##### 6.2.1.4 *Deactivate primitives*
+
+The following primitives should be used between layers 1 and 2 and between layer 1 and the management entity in the deactivation procedures. For use in state diagrams, etc., abbreviations of the primitive names are also given.
+
+MPH-DEACTIVATE REQUEST (MPH-DR)
+
+MPH-DEACTIVATE INDICATION (MPH-DI)
+
+PH-DEACTIVATE REQUEST (PH-DR)
+
+PH-DEACTIVATE INDICATION (PH-DI)
+
+##### 6.2.1.5 Management primitives
+
+The following primitives should be used between layer 1 and the management entity. For use in state diagrams, etc., abbreviations of the primitive names are also given.
+
+MPH-ERROR INDICATION (MPH-EI)
+Message unit contains type of error or recovery from a previously reported error.
+
+MPH-INFORMATION INDICATION (MPH-II)
+Message unit contains information regarding the physical layer conditions. The provisionally defined parameters are: connected, disconnected, attached DTE, attached DCE, attached TE, and attached NT.
+
+Note - Implementation of primitives in equipment is not for recommendation.
+
+#### 6.2.2 Signals
+
+The identifications of specific signals across the GDCI are given in Table 2/V.230. Also included is the coding for these signals.
+
+TABLE 2/V.230
+
+Definition of INFO signals (Note 1)
+
+| Signals from MASTER TO SLAVE | | Signals from SLAVE TO MASTER | |
+|------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------|
+| INFO 0 | No signal | INFO 0 | No signal |
+| | | INFO 1
(Note 2) | A continuous signal with the following pattern: Positive ZERO, negative ZERO, six ONEs |
+| | | 
| |
+| | | Nominal bit rate = 192 kbit/s | |
+| INFO 2
(Note 3) | Frame with all bits of BV, DV and DV-echo channels set to binary ZERO. Bit A set to binary ZERO. N and L bits set according to the normal coding rules. | INFO 3 | Synchronized frames with operational data on BV and DV channels. |
+| INFO 4 | Frames with operational data on BV, DV and DV-echo channels. Bit A set to binary ONE. | | |
+
+Note 1 - For configurations where the wiring polarity may be reversed (see § 4.3) signals may be received with the polarity of the binary ZEROs inverted. All receivers should be designed to tolerate wiring polarity reversals.
+
+Note 2 - Slave mode equipment which does not need the capability to initiate activation of a deactivated V.230 interface need not have the capability to send INFO 1. In all other respects, this equipment shall be in accordance with § 6.2. It should be noted that in the point-to-multipoint configuration more than one slave mode equipment transmitting simultaneously will produce a bit pattern, as received by the master mode equipment, different from that described above, e.g., two or more overlapping (asynchronous) instances of INFO 1.
+
+Note 3 - During the transmission of INFO 2 or INFO 4, the F bits and the M/bits from the master mode equipment provide the Q-bit pattern designation as described in § 6.3.3.
+
+#### 6.2.3 *Activation/deactivation procedure for slave mode equipment*
+
+##### 6.2.3.1 *General procedures*
+
+All slave mode equipment conforms to the following procedures (these statements are an aid to understanding; the complete procedures are specified in § 6.2.3.2):
+
+- a) Equipment, when first connected, when power is applied, or upon the loss of frame alignment (see § 6.3.1.1) shall transmit INFO 0. However, an equipment that is disconnected but powered could be transmitting INFO 1 when connected.
+- b) Equipment transmits INFO 3 when frame alignment is established (see § 6.3.1.2). However, the satisfactory transmission of operational data cannot be assured prior to the receipt of INFO 4.
+- c) Equipment shall, when power is removed, initiate the transmission of INFO 0 before frame alignment is lost.
+
+##### 6.2.3.2 *Specification of the procedure*
+
+The procedure for equipment to follow during activation/deactivation is shown in the form of a finite state matrix Table 3/V.230. The use of the primitives at the layer 1/2 boundary and at the layer 1 /management entity boundary are also included. Those primitives serve to identify the connection status, and to identify whether other equipment connected to the passive bus is operating according to V.230 or I.430.
+
+TABLE 3/V.230
+
+###### **Activation/deactivation layer 1 finite state matrix for GDCI slave (DTE)**
+
+| Event | State name | Inactive | Seizing | Deactivated | Awaiting signal | Identifying input | Synchronized | Identifying interface | Lost framing | Activated |
+|------------------------------|--------------|----------|------------------|------------------|---------------------------------------|---------------------------------------|---------------------------------------|---------------------------------------|---------------------------------------|---------------------------------------|
+| | State number | F1 | F2 | F3 | F4 | F5 | F6 | F7 | F8 | F9 |
+| | INFO sent | INFO 0 | INFO 0 | INFO 0 | INFO 1 | INFO 0 | INFO 3 | INFO 3 | INFO 0 | INFO 3 |
+| Loss of power | | / | F1 | MPH-II(d);
F1 | MPH-II(d),
MPH-DI,
PH-DI;
F1 | MPH-II(d),
MPH-DI,
PH-DI;
F1 | MPH-II(d),
MPH-DI,
PH-DI;
F1 | MPH-II(d),
MPH-DI,
PH-DI;
F1 | MPH-II(d),
MPH-DI,
PH-DI;
F1 | MPH-II(d),
MPH-DI,
PH-DI;
F1 |
+| App. of power | | F2 | / | / | / | / | / | / | / | / |
+| MPH-Act. Req. or PH-Act. Req | | / | | ST.T3
F4 | | | - | | - | |
+| Expiry T3 | | / | / | - | MPH-DI,
PH-DI;
F3 | MPH-DI,
PH-DI;
F3 | MPH-DI
PH-DI;
F3 | - | - | - |
+| Rec. INFO 0 | | / | MPH-II(c);
F3 | - | - | - | MPH-DI,
PH-DI;
F3 | MPH-DI,
PH-DI;
F3 | MPH-DI,
PH-DI,
MPH-EI2
F3 | MPH-DI,
PH-DI;
F3 |
+| Rec. any signal (Note 1) | | / | - | - | F6 | - | / | / | - | / |
+| Rec. INFO 2 | | / | MPH-II(c);
F6 | F6 | / | F6 | - | MPH-EI1;
F6 | MPH-EI2
F6 | MPH-EI1;
F6 |
+
+TABLE 3/V.230 (cont.)
+
+| Event | State name | Inactive | Seizing | Deactivated | Awaiting signal | Identifying input | Synchronized | Identifying interface | Lost framing | Activated |
+|----------------------|--------------|----------|------------------------------------|---------------------------|-----------------|---------------------------|----------------------------------------|-----------------------------------------------|----------------------------------------|-----------------|
+| | State number | F1 | F2 | F3 | F4 | F5 | F6 | F7 | F8 | F9 |
+| | INFO sent | INFO 0 | INFO 0 | INFO 0 | INFO 1 | INFO 0 | INFO 3 | INFO 3 | INFO 0 | INFO 3 |
+| Rec. INFO 4 (Note 2) | | / | MPH-II(c),
MF-Q,
ST.T4
F7 | Send MF-Q
ST.T4;
F7 | / | Send MF-Q
ST.T4;
F7 | MPH-E12,
Send MF-Q,
ST.T4;
F7 | - | MPH-E12,
Send MF-Q,
ST.T4;
F7 | - |
+| Rec. MF-S (DTE) | | / | / | / | / | / | / | PH-AI,
MPH-AI,
MPH-II
(a-DTE);
F9 | / | Send MF-Q;
- |
+| Rec. MF-S(DCE) | | / | / | / | / | / | / | PH-AI,
MPH-AI,
MPH-II
(a-DCE);
F9 | / | Send MF-Q;
- |
+| Expiry T4 | | - | - | - | - | - | - | PH-AI,
MPH-AI,
MPH-II
(a-NT);
F9 | - | - |
+| Lost framing | | / | / | / | / | / | MPH-EI1;
F8 | MPH-EI1;
F8 | - | MPH-EI1;
F8 |
+
+| | |
+|---------------|------------------------------------------------------------------------|
+| – | No change, no action |
+| | Impossible by the definition of the layer 1 service |
+| / | Impossible situation |
+| a, b; Fn | Issue primitives or take actions "a" and "b" and then go to state "Fn" |
+| PH-AI | Primitive PH - ACTIVATE INDICATION |
+| PH-DI | Primitive PH - DEACTIVATE INFORMATION |
+| MPH-AI | Primitive MPH - ACTIVATE INDICATION |
+| MPH-DI | Primitive MPH - DEACTIVATE INDICATION |
+| MPH-EI1 | Primitive MPH - ERROR INDICATION REPORTING ERROR |
+| MPH-EI2 | Primitive MPH - ERROR INDICATION REPORTING RECOVERY |
+| MPH-II(c) | Primitive MPH - INFORMATION INDICATION (connected) |
+| MPH-II(d) | Primitive MPH - INFORMATION INDICATION (disconnected) |
+| MPH-II(a-DCE) | Primitive MPH - INFORMATION INDICATION (attached, V-series DCE) |
+| MPH-II(a-DTE) | Primitive MPH - INFORMATION INDICATION (attached, V-series DTE) |
+| MPH-II(a-NT) | Primitive MPH - INFORMATION INDICATION (attached, I-series NT) |
+| MF-Q | Multiframe V-series equipment ID on Q-channel (either DTE or DCE ID) |
+| MF-S | Multiframe V-series equipment ID on Q-channel |
+| ST.T3 | Start timer T3 |
+| ST.T4 | Start timer T4 |
+
+Primitives are signals in a conceptual queue and will be cleared on recognition, while the INFO signals are continuous signals which are available all the time. The multiframe signals must be sent for a fixed number of multiframe periods, provisionally 6 periods.
+
+*Note 1* - This event reflects the case where a signal is received and the equipment has not (yet) determined whether it is INFO 2 or INFO 4.
+
+*Note 2* - Timer 4 (T4) is a supervisory timer which provides for the master timing mode equipment(s) to recognize the multiframe identification signal and reply. If no reply is received before T4 times out, connection to an I-series NT is assumed. The value of T4 is provisionally 500 ms.
+
+#### 6.2.4 Activation/deactivation for master mode equipment
+
+##### 6.2.4.1 Activating/deactivating equipment
+
+The procedure is shown in the form of a finite state matrix Table 4/V.230. The primitives at the layer 1/2 boundary and layer 1/management entity boundary are also shown. Those primitives serve to identify the connection status, and to identify whether other equipment connected to the passive bus is operating according to V.230 or I.430.
+
+##### 6.2.4.2 Non-activating/non-deactivating equipment
+
+The behaviour of such equipment is the same as that of an activating/deactivating equipment never receiving DEACTIVATE REQUEST primitive. States G1 (deactive), G4 (pending deactivation) and timers 1 and 2 may not exist for such equipment.
+
+#### 6.2.5 Timer values
+
+Timers are defined in the finite state matrix tables for both the master and slave mode GDCI equipment. The following values are defined for timers:
+
+- Timer 1 in master mode equipment: values from 2 s (for GDCI only application) to 30 s (for dual mode GDCI or ISDN application) are acceptable.
+- Timer 2 in master mode equipment: values from 25 to 100 ms are acceptable. The value may be zero if the equipment does not provide for deactivation.
+- Timer 3 in slave mode equipment: value must be selected longer than the worst case time to activate the equipment. The value should be at least one second longer than the value of T1 in the master equipment connected to the GDCI.
+- Timer 4: This is the time allowed for other equipment in the GDCI to recognize a V-series equipment ID on the multiframe (S or Q) channel and to respond. This should normally take less than 30 ms, so the value of T4 is provisionally set to 50 ms.
+
+#### 6.2.6 Activation and deactivation times
+
+Slave mode equipment in the deactivated state (F3) shall, upon receipt of INFO 2, establish frame synchronization and begin transmission of INFO 3 within 100 ms. It shall recognize receipt of INFO 4 within two frames (in the absence of errors).
+
+Slave mode equipment in the "waiting for signal" state (F4) shall, upon the receipt of INFO 2, cease the transmission of INFO 1 and initiate the transmission of INFO 0 within 5 ms and then respond to INFO 2, within 100 ms, as above. (Note that in Table 3/V.230, the transition from F4 to F5 is indicated as the result of the receipt of "any signal" which is in recognition of the fact that the equipment may not know that the signal being received is INFO 2 until after it has recognized the presence of a signal.)
+
+Master mode equipment use of the "deactivated" and "pending activation" states remains a topic for future study. If these states and transitions are implemented, the timing recommendations of I.430 § 6.2.6.2 should be followed.
+
+#### 6.2.7 Multiframe identification codes
+
+Two characters must be selected from the unassigned values on the multiframe Q channel to identify a V-series DTE and a V-series DCE operating in the slave timing mode. Similarly, one character must be selected from the unassigned values on the multiframe S channel (SC1) to identify a V-series DCE operating in the master timing mode.
+
+Since there are only 16 characters available on each of these multiframe channels, the selection must be done carefully. The following character codes have provisionally been selected for the purpose of identifying V-series equipment using a GDCI:
+
+| Value (S 11 S 12 S 13 S 14 or Q 1 Q 2 Q 3 Q 4 ) | Meaning |
+|-----------------------------------------------------------------------------------------------------------------------------------------|--------------------|
+| 1101 on Q channel | V-DTE, slave mode |
+| 1100 on Q channel | V-DCE, slave mode |
+| 0110 on S channel | V-DCE, master mode |
+
+*Note* - These codes are unassigned in the current US Draft Specification.
+
+TABLE 4/V.230
+
+##### **Activation/deactivation layer 1 finite state matrix for CDCI master (DCE)**
+
+| State name
State number
Event
INFO sent | Deactive | Pending activation | Identifying interface | Pending deactivation | Active |
+|------------------------------------------------------|-----------------|-------------------------------------------------------|-------------------------------------------|----------------------|---------------------------|
+| | G1 | G2 | G3 | G4 | G5 |
+| | INFO 0 | INFO 2 | INFO 4 | INFO 0 | INFO 4 |
+| MPH -Act. Req. or PH-Act. Req. | Start T1;
G2 | | | Start T1;
G2 | |
+| MPH-Deact. Req. or PH-Deact. Req. | | Start T2;
PH-DI;
G4 | Start T2;
PH-DI;
G4 | | Start T2;
PH-DI;
G4 |
+| Expiry T1 (Note 1) | - | Start T2;
PH-DI;
G4 | / | - | / |
+| Expiry T2 (Note 2) | - | - | - | G1 | - |
+| Rec. INFO 0 | - | - | MPH-DI,
MPH-EI;
G2 | G1 | MPH-DI,
MPH-EI;
G2 |
+| Rec. INFO 1 | Start T1;
G2 | - | / | - | / |
+| Rec. INFO 3 | / | Stop T1,
Start T4,
Send MF-S;
G3
(Note 3) | - | - | - |
+| Rec. MF-Q (DTE) | / | / | PH-AI,
MPH-AI,
MPH-II(a-DTE);
G5 | - | Send MF-S;
- |
+| Rec. MF-Q (DCE) | / | / | PH-AI,
MPH-AI,
MPH-II(a-DTE);
G5 | - | Send MF-S;
- |
+| Expiry T4 | - | - | PH-AI,
MPH-AI,
MPH-II(a-TE);
G5 | - | - |
+| Lost framing | / | / | MPH-DI
MPH-EI
G2 | - | MPH-DI,
MPH-EI;
G2 |
+
+| | |
+|----------|--------------------------------------------------------------------|
+| — | No change, no action |
+| | Impossible by the definition of the layer 1 service |
+| / | Impossible situation |
+| a, b; Gn | Issue primitives or take actions "a" and "b" then go to state "Gn" |
+| PH-AI | Primitive PH - ACTIVATE INDICATION |
+| PH-DI | Primitive PH - DEACTIVATE INDICATION |
+| MPH-AI | Primitive MPH - ACTIVATE INDICATION |
+
+| | |
+|---------------|------------------------------------------------------------------------------------|
+| MPH-DI | Primitive MPH - DEACTIVATE INDICATION |
+| MPH-EI | Primitive MPH - ERROR INDICATION REPORTING ERROR |
+| MPH-II(a-DCE) | Primitive MPH - INFORMATION INDICATION (attached, V-series DCE) |
+| MPH-II(a-DTE) | Primitive MPH - INFORMATION INDICATION (attached, V-series DTE) |
+| MPH-II(a-TE) | Primitive MPH - INFORMATION INDICATION (attached, I-series TE) |
+| MF-S | Multiframe V-series equipment ID on S-channel (currently only a DCE ID is defined) |
+| MF-Q | Multiframe V-series equipment ID on Q-channel (DCE or DTE) |
+
+Primitives are signals in a conceptual queue and will be cleared on recognition, while the INFO signals are continuous signals which are available all the time. The multiframe signals must be sent for a fixed number of multiframe periods, provisionally 6 periods.
+
+*Note 1* - Timer 1 (T1) is a supervisory timer which has to take into account the overall time to activate.
+
+*Note 2* - Timer 2 (T2) prevents unintentional reactivation. Its value is normally between 25 ms and 100 ms. This implies that a slave timing mode equipment must recognize INFO 0 and react on it within 25 ms. If the master timing mode equipment is able to unambiguously recognize INFO 1, or if the master timing mode equipment does not use the MPH-DEACTIVATE REQUEST primitive, then the value of T2 may be 0.
+
+*Note 3* - Timer 4 (T4) is a supervisory timer which provides time for the slave timing mode equipment(s) to recognize the multiframe identification signal and reply. If no reply is received before T4 times out, connection to an I-series TE is assumed. The value of T4 is provisionally 50 ms.
+
+### 6.3 *Frame alignment procedures*
+
+The first bit of each frame is the framing bit, $f$ ; it is a binary ZERO.
+
+The frame alignment procedure makes use of the fact that the framing bit is represented by a pulse having the same polarity as the preceding pulse (line code violation). This allows rapid reframing.
+
+According to the coding rule, both the framing bit and the first binary ZERO bit following the framing balance bit (in the same frame) produce a line code violation. To guarantee secure framing, the auxiliary framing bit pair $F_A$ and N in the direction master-to-slave or the auxiliary framing bit $F_A$ with the associated balancing bit L in the direction slave-to-master are introduced. This ensures that there is a line code violation at 14 bits or less from the framing bit F, due to $F_A$ or N being a binary ZERO bit (master-to-slave) or to $F_A$ being a binary ZERO bit (slave-to-master) if the $F_A$ bit position is not used as a Q bit. The framing procedures do not depend on the polarity of the framing bit F, and thus are not sensitive to wiring polarity.
+
+The coding rule for the auxiliary framing bit pair $F_A$ and N, in the direction master-to-slave, is such that N is the binary opposite of $F_A$ ( $N = \overline{F_A}$ ). The $F_A$ and L bits in the direction slave-to-master are always coded such that the binary values of $F_A$ and L are equal.
+
+#### 6.3.1 *Frame alignment procedure in the direction master-to-slave to slave timing mode equipment*
+
+Frame alignment, on initial activation of the slave mode equipment, shall comply with the procedures defined in § 6.2.
+
+##### 6.3.1.1 *Loss of frame alignment*
+
+Loss of frame alignment may be assumed when a time period equivalent to two 48-bit frames has elapsed without having detected valid pairs of line code violations obeying the $\leq 14$ bit criterion as described above. The slave timing mode equipment shall cease transmission immediately.
+
+##### 6.3.1.2 *Frame alignments*
+
+Frame alignment may be assumed to occur when three consecutive pairs of line code violations obeying the $\leq 14$ bit criterion have been detected.
+
+#### 6.3.2 *Frame alignment in the direction slave-to-master timing mode equipment*
+
+The criterion of a line code violation at 13 bits or less from the framing bit (F) shall apply except if the Q channel (see § 6.3.3) is provided, in which case the 13-bit criterion applies in four out of five frames.
+
+##### 6.3.2.1 *Loss of frame alignment*
+
+The master mode equipment may assume loss of frame alignment if a time equivalent to at least two 48-bit frames has elapsed since detecting consecutive violations according to the 13-bit criterion, if all $F_A$ bits have been set to binary ZERO. Otherwise, a time period equivalent to at least three 48-bit frames shall be allowed before assuming loss of frame alignment. On detection of loss of frame alignment, the master equipment shall continue transmitting towards the slave equipment.
+
+##### 6.3.2.2 *Frame alignment*
+
+The master timing mode equipment may assume that frame alignment has been regained when three consecutive pairs of line code violations obeying the 13-bit criterion has been detected.
+
+#### 6.3.3 *Multi-framing*
+
+A multi-frame described in the following paragraphs is intended to provide extra layer 1 capacity in the slave-to-master direction through the use of an extra channel between the slave and master equipment (Q channel).
+
+The use of the Q bits shall be the same in point-to-point as in point-to-multipoint configurations. Future standardization for the use of Q bits is for further study. (There is no inherent collision detection mechanism provided, and any collision detection mechanism that is required for any application of the Q bits will be outside the scope of this Recommendation.)
+
+##### 6.3.3.1 *General mechanism*
+
+- a) Q bit identification: The Q bits (slave mode to master mode equipment) are defined to be the bits in the $F_A$ bit position of every fifth frame. The Q bit positions in the slave-to-master direction are identified by binary inversions of the $F_A/N$ bit pair ( $F_A$ = binary ONE, $N$ = binary ZERO) in the master-to-slave direction. The provision for identification of the Q-bit positions in the master-to-slave direction permits all slave mode equipment to synchronize transmission in Q-bit positions, thereby avoiding interference of $F_A$ bits from one equipment with the Q bits of a second equipment in passive bus configurations.
+- b) Multi-frame identification: A multi-frame, which provides for structuring the Q bits in groups of four (Q1-Q4), is established by setting the M bit, in position 26 of the master-to-slave frame, to binary ONE in every twentieth frame. This structure provides for 4-bit characters in a single channel, slave-to-master.
+
+##### 6.3.3.2 *Q-bit position identification algorithm*
+
+The Q-bit position identification algorithm is illustrated in Table 5/V.230. Two examples of how such an identification algorithm can be realized are as follows. The slave mode equipment Q-bit identification algorithm may be simply the transmission of a Q-bit in each frame in which a binary ONE is received in the $F_A$ -bit position of the master-to-slave frame (i.e., echoing of the received $F_A$ bits). Alternatively, to minimize the Q-bit transmission errors that could result from errors in the $F_A$ bits of master-to-slave frames, a slave mode equipment may synchronize a frame counter to the Q-bit rate and transmit Q bits in every fifth frame, i.e., in frames in which $F_A$ should be present. Q bits would be transmitted only after counter synchronization to the binary ONES in the $F_A$ bit positions of the master-to-slave frames is achieved (and only if such bits are received). When the counter is not synchronized (not achieved or lost), a slave mode equipment which uses such an algorithm shall transmit binary ZEROS in Q-bit positions. The algorithm used by a slave mode equipment to determine when synchronization is defined to be achieved or the algorithm used to determine when it is defined to be lost is not described in this Recommendation.
+
+No special Q-bit identification is required in the master mode equipment because the maximum round trip delay of the master-to-slave-to-master is a small fraction of a frame, and therefore, Q-bit identification is inherent in the master timing mode equipment.
+
+TABLE 5/V.230
+
+###### **Q-bit position identification and multiframe structure**
+
+| Frame number | MASTER TO SLAVE
F A bit position | SLAVE TO MASTER
F A bit position
(1, 2) | MASTER TO SLAVE
M bit |
+|--------------|------------------------------------------------|----------------------------------------------------------|--------------------------|
+| 1 | ONE | Q1 | ONE |
+| 2 | ZERO | ZERO | ZERO |
+| 3 | ZERO | ZERO | ZERO |
+| 4 | ZERO | ZERO | ZERO |
+| 5 | ZERO | ZERO | ZERO |
+| 6 | ONE | Q2 | ZERO |
+| 7 | ZERO | ZERO | ZERO |
+| 8 | ZERO | ZERO | ZERO |
+| 9 | ZERO | ZERO | ZERO |
+| 10 | ZERO | ZERO | ZERO |
+| 11 | ONE | Q3 | ZERO |
+| 12 | ZERO | ZERO | ZERO |
+| 13 | ZERO | ZERO | ZERO |
+| 14 | ZERO | ZERO | ZERO |
+| 15 | ZERO | ZERO | ZERO |
+| 16 | ONE | Q4 | ZERO |
+| 17 | ZERO | ZERO | ZERO |
+| 18 | ZERO | ZERO | ZERO |
+| 19 | ZERO | ZERO | ZERO |
+| 20 | ZERO | ZERO | ZERO |
+| 1 | ONE | Q1 | ONE |
+| 2 | ZERO | ZERO | ZERO |
+| etc. | | | |
+
+*Note 1* - If the Q bits are not used by a slave mode equipment, the Q bits shall be set to binary ONE.
+
+*Note 2* - Where multiframe identification is not provided with a binary ONE in an appropriate M bit, but where Q-bit positions are identified, Q bits 1 through 4 are not distinguished.
+
+##### 6.3.3.3 *Slave timing mode equipment multiframe identification*
+
+The first frame of the multiframe is identified by the M bit equal to a binary ONE. Slave mode equipment shall use the M bit equal to a binary ONE to identify the start of the multiframe.
+
+The algorithm used by a slave mode equipment to determine when synchronization or loss of synchronization of the multiframe is achieved is not described in this Recommendation.
+
+#### 6.3.4 S channel structuring algorithm
+
+The algorithm for structuring the S bits (master-to-slave frame bit position 37) into an S channel uses the same combination of the $F_A$ bit inversions and the M bit that is used to structure the Q channel as described in § 6.3.3. The S channel structure, shown in Table 6/V.230, provides for five subchannels, SC1 through SC5. Each subchannel SCn is comprised of the bits SCn1 through SCn4 which provides for the transfer of one 4-bit character per multiframe (5 ms). This Recommendation discusses the use of subchannel SC1 only. Subchannels SC2 through SC5 are reserved for future use, and shall be coded with all binary ZEROs. The coding and use of the 4-bit character of SC1 are discussed in § 6.2.7.
+
+TABLE 6/V.230
+
+**S-channel structure**
+
+| Frame number | $F_A$ bit | M bit | S bit |
+|--------------|-----------|-------|-------|
+| 1 | ONE | Q1 | SC11 |
+| 2 | ZERO | ZERO | SC21 |
+| 3 | ZERO | ZERO | SC31 |
+| 4 | ZERO | ZERO | SC41 |
+| 5 | ZERO | ZERO | SC51 |
+| 6 | ONE | ZERO | SC12 |
+| 7 | ZERO | ZERO | SC22 |
+| 8 | ZERO | ZERO | SC32 |
+| 9 | ZERO | ZERO | SC42 |
+| 10 | ZERO | ZERO | SC52 |
+| 11 | ONE | ZERO | SC13 |
+| 12 | ZERO | ZERO | SC23 |
+| 13 | ZERO | ZERO | SC33 |
+| 14 | ZERO | ZERO | SC43 |
+| 15 | ZERO | ZERO | SC53 |
+| 16 | ONE | ZERO | SC14 |
+| 17 | ZERO | ZERO | SC24 |
+| 18 | ZERO | ZERO | SC34 |
+| 19 | ZERO | ZERO | SC44 |
+| 20 | ZERO | ZERO | SC54 |
+| 1 | ONE | ONE | SC11 |
+| 2 | ZERO | ZERO | SC21 |
+| etc. | | | |
+
+*Note* - Subchannels SC2 through SC5 are reserved for future standardization and are set to all binary ZEROs.
+
+### 6.4 Idle channel code on the BV channels
+
+A slave mode equipment shall send binary ONES in any BV channel which is not assigned to it.
+
+## 7 Layer 1 maintenance
+
+Test loopbacks, similar to those defined in Recommendation I.430, are for further study.
+
+## 8 Electrical characteristics
+
+### 8.1 Bit rate
+
+#### 8.1.1 Nominal rate
+
+The nominal bit rate is 192 kbit/s.
+
+#### 8.1.2 Tolerance
+
+The tolerance (free running mode) is $\pm 100$ ppm.
+
+### 8.2 Jitter and bit-phase relationship between slave mode equipment input and output
+
+#### 8.2.1 Test configurations
+
+The jitter and phase deviation measurements are carried out with four different waveforms at the slave mode equipment input, in accordance with the following configurations:
+
+- i) point-to-point configuration with 6 dB attenuation measured between the two terminating resistors at 96 kHz (high capacitance cable),
+- ii) short passive bus with 8 units (including the unit under test) clustered at the far end from the signal source (high capacitance cable),
+- iii) a) and b) short passive bus with the unit under test adjacent to the signal source and the other seven units clustered at the far-end from the signal source (high and low capacitance cable);
+- iv) ideal test signal condition, with one source connected directly to the receiver of the unit under test (i.e., without artificial line).
+
+Examples of waveforms that correspond to the configurations i), ii), iiia) and iiib) are given in Figures 5/V.230 to 8/V.230. Test configurations which can generate these signals are given in Annex C.
+
+
+
+FIGURE 5/V.230: Waveform for test configuration i) - point-to-point (6 dB). The graph shows normalized amplitude on the y-axis from -1.0 to 1.0 and time in clock periods on the x-axis from 0.10 to 2.10. The plot shows multiple overlapping signal traces forming an eye diagram pattern, with transitions occurring between -0.5 and 0.5 normalized amplitude levels. A small label 'T1808970-89' is in the bottom right corner.
+
+FIGURE 5/V.230
+
+**Waveform for test configuration i) - point-to-point (6 dB)
+( $C = 120$ nF/km)**
+
+
+
+Figure 6/V.230: A line graph showing normalized amplitude versus time in clock periods. The y-axis ranges from -1.40 to 1.40 with major grid lines every 0.20 units. The x-axis ranges from 0.10 to 2.10 with major grid lines every 0.20 units. The graph displays multiple signal traces that show a step-like transition from approximately -1.00 to +1.00 around 0.25 clock periods, followed by a return to -1.00 around 1.10 clock periods. The traces exhibit some overshoot and ringing. The identifier 'CCITT-83511' is located in the bottom right corner of the plot area.
+
+FIGURE 6/V.230
+
+**Waveform for test configuration ii) - short passive bus with 8 clustered slave mode equipments at the far end ( $C = 120 \text{ nF/km}$ )**
+
+
+
+Figure 7/V.230: A line graph showing normalized amplitude versus time in clock periods. The y-axis ranges from -1.40 to 1.40 with major grid lines every 0.20 units. The x-axis ranges from 0.10 to 2.10 with major grid lines every 0.20 units. The graph displays multiple signal traces that show a step-like transition from approximately -1.00 to +1.00 around 0.25 clock periods, followed by a return to -1.00 around 1.10 clock periods. The traces exhibit some overshoot and ringing. The identifier 'CCITT-83521' is located in the bottom right corner of the plot area.
+
+FIGURE 7/V.230
+
+**Waveform for test configuration iii a) - short passive bus with 1 slave mode equipment near to the matter mode equipment and 7 slave mode equipments at the far end ( $C = 120 \text{ nF/km}$ )**
+
+
+
+Figure 8/V.230: Waveform for test configuration iii b) - short passive but with 1 slave mode equipment near to the master mode equipment and 7 slave mode equipments at the far end (C = 30 nF/km). The graph plots Amplitude (normalized) on the y-axis from -1.40 to 1.40 against Time (clock periods) on the x-axis from 0.10 to 2.10. The waveform shows multiple overlapping signal paths with transitions at approximately 0.30, 1.00, and 1.30 clock periods.
+
+FIGURE 8/V.230
+
+**Waveform for test configuration iii b) - short passive but
+with 1 slave mode equipment near to the waster mode equipment and
+7 slave mode equipments at the far end ( $C = 30 \text{ nF/km}$ )**
+
+#### 8.2.2 *Timing extraction jitter*
+
+Timing extraction jitter, as observed at the slave mode equipment output, shall be within $-7\%$ to $+7\%$ of a bit period, when the jitter is measured using a high pass filter with a cut-off frequency (3 dB point) of $30 \text{ Hz}$ under the test conditions described in § 8.2.1. The limitation applies with an output data sequence having binary ZEROs in both BV channels and with input data sequences described in a) to c) following. The limitation applies to the phase of all zero-volt crossings of all adjacent binary ZEROs in the output data sequence.
+
+- a) A sequence consisting of continuous frames with all binary ONES in DV, DV-echo and both BV channels.
+- b) A sequence, repeated continuously for at least 10 seconds, consisting of:
+ - 40 frames with continuous octets of "10101010" (the first bit to be transmitted is binary ONE) in both BV channels and continuous binary ONES in DV and DV-echo channels followed by:
+ - 40 frames with continuos binary ZEROs in DV, DV-echo and both BV channels.
+- c) A sequence consisting of a pseudo-random pattern with a length of $2^{19} - 1$ in DV, DV-echo and both BV channels. (This pattern may be generated with a shift register with 19 stages with the outputs of the first, the second, the fifth and the nineteenth stages added together (modulo 2) and fed back to the input.)
+
+#### 8.2.3 *Total phase deviation, input to output*
+
+The total phase deviation (including effects of timing extraction in the slave mode equipment), between the transitions of signal elements at the output of the slave mode equipment and the transitions of signal elements associated with the signal applied to the input, should not exceed the range of $-7\%$ to $+15\%$ of a bit period. This limitation applies to the output signal transitions of each frame with the phase reference defined as the average phase of the crossing of zero volts which occurs between the framing pulse and its associated balance pulse at the start of the frame and the corresponding crossings at the start of the three preceding frames of the input signal. For the purposes of demonstrating compliance of an equipment, it is sufficient to use (as the input signal phase reference) only the crossing of zero volts between the framing pulse and its associated balance pulse of the individual frame. This latter method, requiring a simpler test set, may create additional jitter at frequencies higher than about $1 \text{ kHz}$ and is therefore more restrictive. The limitation applies to the phase of the zero-volt crossings of all adjacent binary ZEROs in the output data sequence, which shall be as defined in § 8.2.2. The limitation applies under all test conditions described in § 8.2.1, with the additional input signal conditions specified in a) to d) following, and with superimposed jitter as specified in Figure 9/V.230 over the range of frequencies from $5 \text{ Hz}$ to $2 \text{ kHz}$ . The limitation applies for input bit rates of $192 \text{ kbit/s} \pm 100 \text{ ppm}$ .
+
+- a) A sequence consisting of continuous frames with all binary ONEs in the DV, DV-echo and both BV channels.
+- b) A sequence consisting of continuous frames with the octet "10101010" (the first bit to be transmitted is binary ONE) in both BV channels and binary ONEs in DV and DV-echo channels.
+- c) A sequence of continuous frames with binary ZEROs in DV, DV-echo and both BV channels.
+- d) A sequence of continuous frames with a pseudo-random pattern, as described in § 8.2.2 c), in DV, and both BV channels.
+
+
+
+| Frequency (Hz) | Peak-to-peak jitter |
+|----------------|---------------------|
+| 5 | 0.5 |
+| 50 | 0.05 |
+| 2000 | 0.05 |
+
+Figure 9/V.230: Lower limit of maximum tolerable jitter at slave mode equipment input (log-log scale). The graph plots Peak-to-peak jitter (Y-axis) against Frequency (f) in Hz (X-axis). The Y-axis has values 0.05 and 0.5. The X-axis has values 5 Hz, 50 Hz, and 2 kHz. The plot shows a solid line that is horizontal at 0.5 from 5 Hz, then slopes down to 0.05 at 50 Hz, and remains horizontal at 0.05 until 2 kHz. A dashed line extends the slope downwards from the 50 Hz point.
+
+FIGURE 9/V.230
+
+##### **Lower limit of maximum tolerable jitter at slave mode equipment input (log-log scale)**
+
+### 8.3 *Master mode equipment jitter characteristics*
+
+The maximum jitter (peak-to-peak) in the output sequence of a master mode equipment shall be 5% of a bit period when measured using a high pass filter having a cut-off frequency (3 dB point) of 50 Hz and an asymptotic roll off 20 dB per decade. The limitation applies for all data sequences, but for the purpose of demonstrating the compliance of an equipment, it is sufficient to measure jitter with output data sequence consisting of binary ONEs in DV and BV channels and with additional sequence as described in § 8.2.2. c) in DV and BV channels. The limitation applies to the phase of all-zero volt crossings of all adjacent binary ZEROs in the output data sequence.
+
+### 8.4 *Termination of the line*
+
+The interchange circuit pair termination (resistive) should be 100 ohms $\pm$ 5% (see Figure 2/V.230).
+
+### 8.5 *Transmitter output characteristics*
+
+#### 8.5.1 *Transmitter output impedance*
+
+The following requirements apply at interface point $I_A$ (see Figure 2/V.230 for slave mode equipment) and at interface point $I_B$ for master mode equipment (see §§ 4.5 and 8.9 regarding cordage capacitance).
+
+##### 8.5.1.1 *Master mode equipment transmitter output impedance*
+
+- a) When inactive or transmitting a binary ONE, the output impedance, in the frequency range of 2 kHz to 1 MHz, shall exceed the impedance indicated by the template in Figure 10/V.230. The requirement is applicable with an applied sinusoidal voltage of at least 100 mV (r.m.s. value).
+
+*Note* - In some applications, the terminating resistor can be combined with the master mode equipment (see point B of Figure 2/V.230). The resulting impedance is the impedance needed to exceed the combination of the template and the 100-ohm termination.
+
+b) When terminating a binary ZERO, the output impedance shall be $\geq 20$ ohms.
+
+*Note* - The output impedance limit shall apply for two nominal load impedance (resistive) conditions: 50 ohms and 400 ohms. The output impedance for each nominal load shall be defined by determining the peak pulse amplitude for loads equal to the nominal value $\pm 10\%$ . The peak amplitude shall be defined as the amplitude at the midpoint of a pulse. The limitation applies for pulses of both polarities.
+
+
+
+Figure 10/V.230: Master mode equipment impedance template (log-log scale). The graph plots Impedance (Z) in Ohms (Ω) on the y-axis against Frequency in kHz on the x-axis. The y-axis has major ticks at 100, 250, 265, and 2500. The x-axis has major ticks at 2, 20, 106, and 1000. A shaded trapezoidal region represents the impedance limit. The bottom boundary is a horizontal line at Z=250 from 2 kHz to 1000 kHz. The top boundary starts at (2, 250), rises linearly to (20, 2500), remains constant at 2500 until 106 kHz, and then falls linearly to (1000, 250). The area between the top and bottom boundaries is shaded with diagonal lines.
+
+FIGURE 10/V.230
+
+###### Master mode equipment impedance template (log-log scale)
+
+##### 8.5.1.2 Slave mode equipment transmitter output impedance
+
+- a) In the inactive and powered down states or when transmitting a binary ONE, the following requirements apply:
+ - i) the output impedance, in the frequency range of 2 kHz to 1 MHz, should exceed the impedance indicated by the template in Figure 11/V.230. This requirement is applicable with an applied sinusoidal voltage of at least 100 mV (r.m.s. value);
+ - ii) at a frequency of 96 kHz, the peak current which results from an applied voltage of up to 1.2 V (peak value) should not exceed 0.6 mA (peak value).
+
+b) When transmitting a binary ZERO, the output impedance shall be $\geq 20$ ohms.
+
+*Note* - The output impedance limit shall apply for two nominal load impedance (resistive) conditions: 50 ohms and 400 ohms. The output impedance for each nominal load shall be defined by determining the peak pulse amplitude for loads equal to the nominal value $\pm 10\%$ . The peak amplitude shall be defined as the amplitude at the midpoint of a pulse. The limitation applies for pulses of both polarities.
+
+
+
+Figure 11/V.230: Slave mode equipment impedance template (log-log scale). The graph plots Impedance (Z) in Ohms (Ω) on the y-axis against Frequency in kHz on the x-axis. The y-axis has major ticks at 100, 200, 250, and 2500. The x-axis has major ticks at 2, 20, 80, and 1000. A shaded trapezoidal region represents the impedance limit. The bottom boundary is a horizontal line at Z=200 from 2 kHz to 1000 kHz. The top boundary starts at (2, 250), rises linearly to (20, 2500), remains constant at 2500 until 80 kHz, and then falls linearly to (1000, 250). The area between the top and bottom boundaries is shaded with diagonal lines.
+
+FIGURE 11/V.230
+
+###### Slave mode equipment impedance template (log-log scale)
+
+#### 8.5.2 *Test load impedance*
+
+The test load impedance shall be 50 ohms (unless otherwise indicated).
+
+#### 8.5.3 *Pulse shape and amplitude (binary ZERO)*
+
+##### 8.5.3.1 *Pulse shape*
+
+Except for overshoot, limited as follows, pulses shall be within the mask of Figure 12/V.230. Overshoot, at the leading edge of pulses, of up to 5% of the pulse amplitude at the middle of a signal element, is permitted, provided that such overshoot has, at 1/2 of its amplitude, a duration of less than 0.25 $\mu$ s.
+
+##### 8.5.3.2 *Nominal pulse amplitude*
+
+The nominal pulse amplitude shall be 750 mV, zero to peak.
+
+A positive pulse (in particular, a framing pulse) at the output port of master mode and slave mode equipment is defined as a positive polarity of the voltage measured between access leads e to f and d to c respectively (see Figure 20/I.430). (See Table 7/V.230 for the relationship to connector pins.)
+
+#### 8.5.4 *Pulse unbalance*
+
+The "pulse unbalance", i.e., the relative difference in $\int U(t) dt$ for positive pulses and $\int U(t) dt$ for negative pulses shall be $\leq 5\%$ .
+
+#### 8.5.5 *Voltage on other test loads (slave mode equipment)*
+
+The following requirements are intended to assure compatibility with the condition where multiple slave mode equipments are simultaneously transmitting pulses on to a passive bus.
+
+##### 8.5.5.1 400-ohm load
+
+A pulse (binary ZERO) shall conform to the limits of the mask shown in Figure 13/V.230 when the transmitter is terminated in a 400-ohm load.
+
+
+
+The diagram illustrates the transmitter output pulse mask with the following specifications:
+
+- Top width: $5.73 \mu s$
+- Voltage levels: $V = 100\%$ (with $\pm 10\%$ tolerance bands), $50\%$ , $7\%$ , and $0$ (with $\pm 5\%$ tolerance).
+- Inner pulse width at top: $4.17 \mu s$ ( $5.21 - 1.04$ )
+- Nominal pulse width: $5.21 \mu s$
+- Width at 50% level: $4.69 \mu s$ ( $5.21 - 0.52$ )
+- Width at 7% level: $6.25 \mu s$ ( $5.21 + 1.04$ )
+- Base width: $10.42 \mu s$ ( $5.21 + 5.21$ )
+- A $10\%$ vertical tolerance is indicated at the base of the pulse.
+- The diagram is labeled CCITT-64430.
+
+Figure 12/V.230: Transmitter output pulse mask. A diagram showing the voltage-time mask for a binary ZERO pulse. The vertical axis shows voltage levels at 100%, 50%, 7%, and 0%. The horizontal axis shows time durations in microseconds (μs).
+
+*Note* - For clarity of presentation, the above values are based on a pulse width of $5.21 \mu s$ . See § 8.1 for a precise specification of the bit rate.
+
+FIGURE 12/V.230
+
+**Transmitter output pulse mask**
+
+
+
+Graph showing Voltage (%) vs. Time (μs) for an isolated pulse with a test load of 400 ohms. The graph illustrates the nominal pulse with a 50 Ω load and the resulting voltage response over time.
+
+Key parameters and time points:
+
+- 0.1 μs
+- 1.04 μs
+- 0.26 μs
+- 4.1 μs (5.21 - 1.11)
+- 0.47 μs
+- 4.69 μs (5.21 - 0.52)
+- 0.52 μs
+- 5.21 μs
+- 1.25 μs
+- 10.42 μs (5.21 + 5.21)
+
+Voltage levels (V = 100 %):
+
+- 270
+- 160
+- 100
+- 90
+- 50
+- 7
+- 5
+- 0
+- 5
+- 10
+- 20
+
+Additional labels:
+
+- Nominal pulse with 50 Ω load
+- 7 %
+- 5 %
+- 0 %
+- T1808980-89
+
+A graph showing the voltage response of a system to an isolated pulse with a test load of 400 ohms. The vertical axis represents voltage in percent (%), ranging from -20 to 270. The horizontal axis represents time in microseconds (μs), ranging from 0 to 10.42. The graph shows a nominal pulse with a 50 Ω load, which is a rectangular pulse with a width of 5.21 μs and a height of 100%. The actual voltage response is shown as a shaded area, indicating the range of possible values. Key time points and voltage levels are marked: 0.1 μs at 270%, 1.04 μs at 160%, 0.26 μs at 100%, 4.1 μs at 100%, 0.47 μs at 100%, 4.69 μs at 100%, 0.52 μs at 0%, 5.21 μs at 0%, 1.25 μs at 0%, and 10.42 μs at -20%. The voltage levels are also marked: 270%, 160%, 100%, 90%, 50%, 7%, 5%, 0%, -5%, -10%, and -20%. The graph is labeled 'Nominal pulse with 50 Ω load' and 'T1808980-89'.
+
+Note - For clarity of presentation, the above values are based on a pulse width of 5.21 μs. See § 8.1 for a precise specification of the bit rate.
+
+FIGURE 13/V.230
+Voltage for an isolated pulse with a test load of 400 ohms
+
+##### 8.5.5.2 5.6-ohm load
+
+To limit the current flow with two drivers having opposite polarities, the pulse amplitude (peak) with a 5.6-ohm load shall be $\leq 20\%$ of the nominal pulse amplitude.
+
+#### 8.5.6 Unbalance about earth
+
+The following requirements apply under all possible power feeding conditions, under all possible connections of the equipment to ground, and with two 100-ohm terminations across the transmit and receive ports.
+
+##### 8.5.6.1 Longitudinal conversion loss
+
+Longitudinal conversion loss (LCL), which is measured in accordance with Recommendation G.117, § 4.1.3 (see Figure 14/V.230), shall meet the following requirements:
+
+- $10 \text{ kHz} < f \leq 300 \text{ kHz}$ : $\geq 54 \text{ dB}$
+- $300 \text{ kHz} < f \leq 1 \text{ MHz}$ : minimum value decreasing from 54 dB at 20 dB/decade.
+
+
+
+Circuit diagram for measuring longitudinal conversion loss (LCL). The diagram shows an 'Equipment' block with two ports labeled 'REC OR SEND' and 'SEND OR REC'. A 'Power sink 1 (source 1)' is connected to the equipment. A 'Metal foil' is connected to the equipment via a 200 pF capacitor (Note 2) and a 500 ohm resistor. The equipment is connected to a 'Ground (1 m x 1 m metal plate)'. The circuit includes various components: 100 ohm resistors (Note 1), 25 ohm resistors (Note 6), 10 uF capacitors, and inductors L\_G (Note 5). A voltage source U\_G is connected to the equipment. The output is measured as E\_L (rms) (1v) across a 0 ohm resistor. The diagram is labeled CCITT-72502.
+
+The longitudinal conversion loss: $LCL = 20 \log_{10} \left| \frac{E_L}{V_T} \right| \text{ dB}$
+
+The voltages $V_T$ and $E_L$ should be measured within the frequency range from 10 kHz up to 1 MHz using selective test measuring equipment.
+
+The measurement should be carried out in the states:
+
+- deactivated (receive, send).
+- power off (receive, send),
+- activated (receive).
+
+The interconnecting cord shall lie on the metal plate.
+
+*Note 1* - This resistor must be omitted if the termination is already built into the equipment.
+
+*Note 2* - Hand imitation is a thin metal foil with approximately the size of a hand.
+
+*Note 3* - Equipment with metallic housing shall have a galvanic connection to the metal plate. Other equipment with non-metallic housing shall be placed on the metal plate.
+
+*Note 4* - The power cord for mains-powered equipment shall lie on the metal plate and the earth protective wire of the mains shall be connected to the metal plate.
+
+*Note 5* - If there is no power source 1 in the master mode equipment, $R_G$ and $L_G$ are not required.
+
+*Note 6* - This circuit provides a transverse termination of 100 ohms and a balanced longitudinal termination of 25 ohms. Any equivalent circuit is acceptable. However, for equivalent circuits given in Recommendations G.117 and O.121, powering cannot be provided.
+
+FIGURE 14/V.230
+
+##### Receiver input or transmitter output unbalance about earth
+
+8.5.6.2 *Output signal balance*
+
+Output signal balance which is measured in accordance with Recommendation G.117, § 4.3.1 (see Figure 15/V.230), shall meet the following requirements:
+
+- a) *f* - 96 kHz: ≥ 54 dB
+- b) 96 kHz < *f* ≤ 1 MHz: minimum value decreasing from 54 dB at 20 dB/decade.
+
+
+
+Detailed description of Figure 15/V.230: A circuit diagram showing the test setup for measuring output signal balance. The diagram includes an 'Equipment' block containing 'REC' and 'SEND' sections and a 'Power sink 1 (source 1)'. The 'REC' and 'SEND' sections are connected to a network of resistors (100 Ω), inductors (L\_G ≥ 50 mH), and capacitors (≥ 10 μF). A 'Metal foil' is shown connected via a 200 pF capacitor and a 500 Ω resistor to a 'Ground (1 m x 1 m metal plate)'. Various measurement points for V\_T, V\_L, and U\_G are indicated. Notes 1 through 6 are placed at specific points in the circuit to refer to external documentation. The diagram is labeled CCITT - 22512.
+
+Figure 15/V.230 - Transmitter output unbalance about earth
+
+$$\text{Output signal balance} = 20 \log_{10} \left| \frac{V_T}{V_L} \right| \text{ dB}$$
+
+The voltage *VT* and *VL* should be measured within the frequency range from 10 kHz up to 1 MHz using selective test measuring equipment. The measurement should be carried out in the active state. The pulse patterns should contain all binary ZEROs. However, for the purpose of demonstrating the compliance of an equipment, it is sufficient to measure the output signal unbalance about earth with a pulse pattern of continuous frames with at least the B1 and B2 Channels containing all binary ZEROs.
+
+The interconnecting cord shall lie on the metal plate.
+
+*Note* - See notes to this figure in Figure 14/V.230.
+
+FIGURE 15/V.230
+
+**Transmitter output unbalance about earth**
+
+ 8.6 *Receiver input characteristics*
+
+ 8.6.1 *Receiver input imbalance*
+
+ 8.6.1.1 *Slave mode equipment receiver input impedance*
+
+Slave mode equipment shall meet the same input impedance requirements as specified in § 8.5.1.2 a) for the output impedance.
+
+32 Fascicle VIII.1 - Rec. V.230
+
+##### 8.6.1.2 *Master mode equipment receiver input impedance*
+
+In the inactive and powered-down states, the following requirements apply:
+
+- i) The input impedance in the frequency range of 2 kHz to 1 MHz, should exceed the impedance indicated by the template in Figure 11/V.230. This requirement is applicable with an applied sinusoidal voltage of at least 100 mV (r.m.s. value).
+- ii) At a frequency of 96 kHz, the peak current which results from an applied voltage of up to 1.2 V (peak value) should not exceed 0.5 mA (peak value).
+
+*Note* - In some applications, the 100-ohm terminating resistor can be combined with the master mode equipment (see point B of Figure 2/V.230). The resulting impedance is the impedance needed to exceed the combination of the template and the 100-ohm termination.
+
+#### 8.6.2 *Receiver sensitivity - noise and distortion immunity*
+
+Requirements applicable to the equipments for three different interface wiring configurations are given in the following sub-paragraphs. Equipment shall receive, without errors (for a period of at least one minute), an input with a pseudo-random sequence (word length $\geq 511$ bits) in all information channels (combination of BV channel, DV channel and, if applicable, the DV-echo channel).
+
+The receiver shall operate, with any input sequence, over the full range indicated by the waveform mask.
+
+##### 8.6.2.1 *Slave mode equipment*
+
+Slave mode equipment shall operate with the input signals conforming to the waveforms specified in § 8.2.1. For the waveforms in Figures 6/V.230 to 8/V.230, slave mode equipment shall operate with the input signals having any amplitude in the range of + 1.5 dB relative to the nominal amplitude of the transmitted signal as specified in § 8.5.3.2. For signals conforming to the waveform in Figure 5/V.230, operation shall be accomplished for signals having any amplitude in the range of + 1.5 to - 7.5 dB relative to the nominal amplitude of the transmitted signal as specified in § 8.5.3.2. Additionally, the slave mode equipment shall operate with sinusoidal signals having an amplitude of 100 mV (peak-to-peak value) at frequencies of 200 kHz and 2 MHz superimposed individually on the input signals having the waveform shown in Figure 5/V.230.
+
+##### 8.6.2.2 *Master mode equipment for short passive bus (fixed timing)*
+
+Master mode equipment designed to operate with only short passive bus wiring configurations shall operate when receiving input signals indicated by the waveform shown in Figure 16/V.230. Master mode equipment shall operate, with the input signals having any amplitude in the range of + 1.5 dB to - 3.5 dB relative to the nominal amplitude of the transmitted signal as specified in § 8.5.3.2.
+
+##### 8.6.2.3 *Master mode equipment for both point-to-point and short passive bus configurations (adaptive timing)*
+
+Master mode equipment designed to operate with either point-to-point or short passive bus wiring configurations shall operate when receiving input signals indicated by the waveform mask shown in Figure 17/V.230. These master mode equipments shall operate with the input signals having any amplitude in the range of + 1.5 dB to - 3.5 dB relative to the nominal amplitude of the transmitted signal as specified in § 8.5.3.2. These master mode equipments shall also operate when receiving signals conforming to the waveform in Figure 5/V.230. For signals conforming to this waveform, operation shall be accomplished for signals having any amplitude in the range of + 1.5 to - 7.5 dB relative to the nominal amplitude of the transmitted signal as specified in § 8.5.3.2. Additionally, these master mode equipments shall operate with the sinusoidal signals, as specified in § 8.6.2.1, superimposed on the input signals having the waveform in Figure 5/V.230.
+
+
+
+Master's transmit clock Master's transmit clock
+
+Time (clock periods)
+
+-7 % 1 clock period -7 %
+
+Amplitude (normalized)
+
+0 0.5 1.0 1.5 2.0
+
+T1808990-89
+
+Figure 16/V.230: Short passive bus receive pulse waveform mask. The graph shows normalized amplitude (y-axis, -1.0 to 1.0) versus time in clock periods (x-axis, 0 to 2.0). A shaded region indicates the allowed transition area. Above the graph, a timing diagram shows a 'Master's transmit clock' with a '1 clock period' interval. The shaded region is bounded by two vertical lines, each labeled '-7 %' with arrows indicating the width of the shaded area relative to the clock period. The shaded area is centered around the 0.5 and 1.5 clock period marks.
+
+*Note 1* - Shaded area is the region in which pulse transitions may occur.
+
+*Note 2* - The waveform mask is based on the "worst case" configuration shown in Annex C, Figure C-1/V.230 and waveforms ii) and iii) in § 8.2.1. The shaded area of -7% of one clock period accounts for the situation of a single slave mode equipment connected directly to the master mode equipment with a zero length passive bus. However, the waveform mask does not show the higher possible amplitude of framing and DV-channel bit pulses and their associated balancing bits. It should be noted that the above waveform mask does not account for transient effects.
+
+FIGURE 16/V.230
+
+###### Short passive bus receive pulse waveform mask
+
+
+
+Figure 17/V.230: Passive bus receive pulse waveform mask. The graph shows Amplitude (normalized) on the y-axis from -1.0 to 1.0 and Time (clock periods) on the x-axis from 0 to 2.0. A shaded region indicates the allowed pulse transition area. The mask is defined by a series of curves that form a rectangular pulse with rounded edges. The top and bottom edges are flat at approximately 0.75 and -0.75 respectively. The rising and falling edges are defined by curves that start at 0 and reach the nominal levels within 1 clock period. The shaded area is bounded by these curves and extends to ±7% of the nominal amplitude. Above the graph, two 'NT transmit clock' waveforms are shown, each with a period of 1 clock period and a width of 7%.
+
+*Note 1* - Shaded area is the region in which pulse transitions may occur.
+
+*Note 2* - The waveform mask is based on the same "worst case" passive bus configuration as the waveform mask in Figure 16/V.230 except that the permitted round trip delay of the cable is reduced. The shaded area of - 7 % of one clock period accounts for the situation of a single slave mode equipment connected directly to the master mode equipment with a zero length passive bus. However, the waveform mask does not show the higher possible amplitude of framing and DV-channel bit pulses and their associated balancing bits. It should be noted that the above waveform mask does not account for transient effects.
+
+FIGURE 17/V.230
+
+###### **Passive bus receive pulse waveform mask** (Master mode equipment designed to operate with either point-to-point or short passive bus wiring configurations)
+
+##### 8.6.2.4 Master mode equipment for extended passive bus wiring configurations
+
+Master mode equipment designed to operate with extended passive bus wiring configurations shall operate when receiving input signals indicated by the waveform mask shown in Figure 18/V.230. These master mode equipments shall operate with the input signals having any amplitude in the range of + 1.5 dB to - 5.5 dB relative to the nominal amplitude of the transmitted signal as specified in § 8.5.3.2. Additionally, these master mode equipments shall operate with the sinusoidal signals, as specified in § 8.6.2.1, superimposed on the input signals having the waveform shown in Figure 18/V.230. (The above values assume a maximum cable loss of 3.8 dB. Master mode equipment may be implemented to accommodate higher cable loss.)
+
+##### 8.6.2.5 Master mode equipment for point-to-point configurations only
+
+Master mode equipment designed to operate with only point-to-point wiring configurations shall operate when receiving input signals having the waveform shown in Figure 5/V.230. These master mode equipments shall operate with the input signals having any amplitude in the range of +1.5 to -7.5 dB relative to the nominal amplitude of the transmitted signal as specified in § 8.5.3.2. Additionally, these master mode equipments shall operate with the sinusoidal signals, as specified in § 8.6.2.1, superimposed on the input signals having the waveform shown in Figure 5/V.230.
+
+
+
+Figure 18/V.230: Extended passive bus receive pulse waveform mask. The graph plots Amplitude (normalized) on the y-axis (from -1.0 to 1.0) against Time (clock periods) on the x-axis (from 0 to 2.0). A shaded region indicates the area where pulse transitions may occur. The mask shows a series of curves that define the acceptable amplitude range for a pulse transition over time. The shaded area is bounded by a series of curves that start at approximately ±0.6 at time 0, drop to a minimum of about ±0.2 at 0.5 clock periods, and then rise back to ±0.6 by 1.0 clock periods. This pattern repeats, with another shaded region between 1.5 and 2.0 clock periods. The curves are symmetric about the zero-amplitude line.
+
+*Note 1* - Shaded area is the region in which pulse transitions may occur.
+
+*Note 2* - The waveform mask is based on the worst case extended passive bus wiring configuration. It consists of a cable having a characteristic impedance of 75 ohms, a capacitance of 120 nF/km, a loss of 3.8 dB at 96 kHz, four slave mode equipments connected such that the differential delay is at the maximum permitted by § 8.6.3.3. The waveform mask does not show the higher possible amplitude of framing and DV-channel bit pulses and their associated balancing bits. It should be noted that the above waveform mask does not account for transient effects.
+
+FIGURE 18/V.230
+
+###### Extended passive bus receive pulse waveform mask
+
+#### 8.6.3 Master mode equipment receiver input delay characteristics
+
+*Note* - Round trip delay is always measured between the zero-volt crossings of the framing pulse and its associated balance bit pulse at the transmit and receive sides of the master mode equipment (see also Annex A).
+
+##### 8.6.3.1 Master mode equipment for short passive bus
+
+Master mode equipment shall accommodate round trip delays of the complete installation, including slave mode equipment, in the range 10 to 14 $\mu\text{s}$ .
+
+##### 8.6.3.2 Master mode equipment for both point-to-point and passive bus
+
+Master mode equipment shall accommodate round trip delays (for passive bus configurations) in the range 10 to 13 $\mu\text{s}$ .
+
+Master mode equipment shall accommodate round trip delays (for point-to-point configurations) in the range 10 to 42 $\mu\text{s}$ .
+
+##### 8.6.3.3 Master mode equipment for extended passive bus
+
+Master mode equipment shall accommodate round trip delays in the range 10 to 42 $\mu\text{s}$ , provided that the differential delay of signals from different slave mode equipments is in the range 0 to 2 $\mu\text{s}$ .
+
+##### 8.6.3.4 Master mode equipment for point-to-point only
+
+Master mode equipment shall accommodate round trip delays specified in § 8.6.3.2 for point-to-point configurations.
+
+#### 8.6.4 *Unbalance about earth*
+
+Longitudinal conversion loss (LCL) of receiver inputs, measured in accordance with Recommendation G.117, § 4.1.3, by considering the power feeding and two 100-ohm terminations at each port, shall meet the following requirements (see Figure 14/V.230):
+
+- a) $10 \text{ kHz} \leq f \leq 300 \text{ kHz}$ : $\geq 54 \text{ dB}$
+- b) $300 \text{ kHz} < f \leq 1 \text{ MHz}$ : minimum value decreasing from 54 dB with 20 dB/decade.
+
+### 8.7 *Isolation from external voltages*
+
+The electrical environment of interface cable pairs is not specified in this Recommendation.
+
+IEC Publication 479-1, Second Issue 1984, specifies current limitations dealing with human safety. According to that publication, the value of a touchable leakage alternating current measured through a resistor of 2 kOhms is to be limited to 9 mA. The application of this requirement to the user-network interface is not a subject of this Recommendation.
+
+It may be necessary to apportion this value between the number of mains powered equipments connected to the passive bus. A possible maximum value of (touchable) leakage alternating current for each mains powered equipment could be 1 mA. However, it should be noted that leakage current of a fraction of this magnitude may interfere with the satisfactory operation of the equipments.
+
+### 8.8 *Interconnecting media characteristics*
+
+Longitudinal conversion loss of pairs at 96 kHz shall be $\geq 43 \text{ dB}$ .
+
+### 8.9 *Standard GDCI access cord*
+
+A connecting cord designed to connect equipment to a jack on a passive bus cable must meet the requirements specified in Recommendation I.430 for the "standard ISDN basic access TE cord".
+
+## 9 **Power feeding**
+
+Power feeding across the General Data Communication Interface is not required by this Recommendation. All equipment should be capable of operating if power is present in accordance with Recommendation I.430, § 9. In the case of a GDCI application which uses power feed across the interface, power source 2 defined in Recommendation I.430 should be the first choice, followed by either power source 1 or power source 3. Any considerations for operation under restricted power conditions are at the discretion of the application.
+
+## 10 **Interface connector and contact assignments**
+
+The interface connector and contact assignments are the subject of an ISO standard. Table 7/V.230 is reproduced from the Draft International Standard, DIS 8877, dated November 1985. For the transmit and receive leads, pole numbers 3 through 6, the polarity indicated is for the polarity of the framing pulses. For the power leads, pole numbers 1, 2, 7 and 8, the polarity indicated is for the polarity of the d.c. voltages. See Figure 20/I.430 for the polarity of power provided in the phantom mode. In that figure, the leads that are lettered a, b, c, d, e, f, g and h correspond with pole numbers 1, 2, 3, 6, 5, 4, 7 and 8, respectively.
+
+TABLE 7/V.230
+
+### **Pole (contact) assignment for 8-pole connections (plugs and jacks)**
+
+| Pole number | Function | | Polarity |
+|-------------|----------------------|-----------------------|----------|
+| | Slave mode equipment | Master mode equipment | |
+| 1 | Power source 3 | Power sink 3 | + |
+| 2 | Power source 3 | Power sink 3 | - |
+| 3 | Transmit | Receive | + |
+| 4 | Receive | Transmit | + |
+| 5 | Receive | Transmit | - |
+| 6 | Transmit | Receive | - |
+| 7 | Power sink 2 | Power source 2 | - |
+| 8 | Power sink 2 | Power source 2 | + |
+
+*Note* - This reference is only provisional.
+
+# ANNEX A
+
+(to Recommendation V.230)
+
+## **Wiring configurations and round trip delay considerations used as a basis for electrical characteristics**
+
+### A.1 *Introduction*
+
+A.1.1 In § 4 of this Recommendation, two major wiring arrangements are identified. These are point-to-point configuration and a point-to-multipoint configuration using a passive bus.
+
+While these configurations may be considered to be the limiting cases for the definition of the interfaces and the design of the associated equipments, other significant arrangements should be considered.
+
+A.1.2 The values of overall length, in terms of cable loss and delay assumed for each of the possible arrangements, are indicated below.
+
+A.1.3 Figure 2/V.230 is a composite of the individual configurations. These individual configurations are shown in this Annex.
+
+### A.2 *Wiring configurations*
+
+#### A.2.1 *Point-to-multipoint*
+
+A.2.1.1 The point-to-multipoint wiring configuration identified in § 4.2 of this Recommendation may be provided by the "short passive bus" or other configurations such as "extended passive bus".
+
+##### A.2.1.2 *Short passive bus* (Figure A-1/V.230)
+
+An essential configuration to be considered is a passive bus in which the slave mode devices may be connected at random points along the full length of the cable. This means that the master mode equipment receiver must cater for pulses arriving with different delays from various terminals. For this reason, the length limit for this configuration is a function of the maximum round trip delay and not of the attenuation.
+
+A master mode equipment receiver with fixed timing can be used if the round trip delay is between 10 to 14 $\mu$ s. This relates to a maximum operational distance from the master mode equipment in the order of 100-200 m ( $d_2$ in Figure A-1/V.230) [200 m in the case of a high impedance cable ( $Z_c = 150$ ohms) and 100 m in the case of a low impedance cable ( $Z_c = 75$ ohms)]. It should be noted that the slave master equipment connections acts as stubs on the cable, thus reducing the master mode equipment receiver margin over that of a point-to-point configuration. A maximum number of 8 slave mode equipments with connections of 10 m in length are to be accommodated.
+
+The range of 10 to 14 $\mu$ s for the round trip delay is composed as follows. The lower value of 10 $\mu$ s is composed of two bits offset delay (see Figure 3/V.230) and the negative phase deviation of -7% (see § 8.2.3). In this case the slave mode equipment is located directly at the master mode equipment. The higher value of 14 $\mu$ s is calculated assuming the slave mode equipment is located at the far end of a passive bus. This value is composed of the offset delay between frames of two bits (10.4 $\mu$ s), the round trip delay of the unloaded bus installation (2 $\mu$ s), the additional delay due to load of the slave mode equipment (i.e., 0.7 $\mu$ s) and the maximum delay of the slave mode equipment transmitter according to § 8.2.3 (15% = 0.8 $\mu$ s).
+
+
+
+Diagram of a short passive bus configuration. A horizontal line represents the bus. At the left end is a box labeled 'TR' (Terminating resistor). At the right end is a box labeled 'M' (Master). Three boxes labeled 'S' (Slave) are connected to the bus via vertical lines. A dashed line at the far left indicates the start of the bus. A double-headed arrow labeled 'd2' spans the distance from the 'TR' box to the 'M' box. A dashed box labeled 'M' is positioned above the bus line, with a 'Note' label next to it. The reference number 'T1700540-89' is at the bottom right.
+
+TR Terminating resistor
+M Master
+S Slave
+
+*Note* - In principle, the master mode equipment may be located at any point along the passive bus. The electrical characteristics in this Recommendation, however, are based on the master mode equipment located at one end. The conditions related to other locations require confirmation.
+
+FIGURE A-1/V.230
+
+##### Short passive bus
+
+##### A.2.1.3 Extended passive bus (Figure A-2/V.230)
+
+A configuration which may be used at an intermediate distance in the order of 100 m and 1000 m is known as an extended passive bus. This configuration takes advantage of the fact that terminal connection points are restricted to a grouping at the far end of the cable from the master mode equipment. This places a restriction on the differential distance between slave mode equipments. The differential round trip delay is defined as that between zero-volt crossings of signals from different slave mode equipments and is restricted to 2 $\mu$ s.
+
+This differential round trip delay is composed of a slave mode equipment differential delay of 22% or 1.15 $\mu$ s according to § 8.2.3, the round trip delay of the unloaded bus installation of 0.5 $\mu$ s (line length: 25 to 50 m) and an additional delay due to the load of 4 slave mode equipments (0.35 $\mu$ s).
+
+$d_3$ depends on the characteristics of the cable to be used.
+
+The objective for this extended passive bus configuration is a total length of at least 500 m ( $d_4$ in Figure A-2/V.230) and a differential distance between slave mode equipment connection points of 25 to 50 m ( $d_3$ in Figure A-2/V.230). However, an appropriate combination of the total length, the differential distance between slave mode equipment connection points, and the number of slave mode equipments connected to the cable, may be determined by individual Administrations.
+
+
+
+Diagram of an extended passive bus configuration. A horizontal line represents the cable. At the left end, a box labeled 'TR' (Terminating resistor) is connected to the cable. Below the cable, two boxes labeled 'S' (Slave) are connected at different points. The distance between these two slave connection points is labeled 'd3'. At the right end, a box labeled 'TR' is connected to the cable, followed by a box labeled 'M' (Master). The total length of the cable between the two terminating resistors is labeled 'd4'. The reference code 'T1700550-89' is at the bottom right.
+
+TR Terminating resistor
+M Master
+S Slave
+
+FIGURE A-2/V.230
+
+##### Extended passive bus
+
+#### A.2.2 Point-to-point (Figure A-3/V.230)
+
+This configuration provides for one transmitter/receiver only at each end of the cable (see Figure A-3/V.230). It is, therefore, necessary to determine the maximum permissible attenuation between the ends of the cable to establish the transmitter output level and the range of receiver input levels. In addition, it is necessary to establish the maximum round trip delay for any signal which must be returned from one end to the other within a specified time period (limited by DV-echo bits).
+
+A general objective for the operational distance between equipment units is 1.0 km ( $d_1$ in Figure A-3/V.230). It is agreed to satisfy this general objective with a maximum cable attenuation of 6 dB at 96 kHz. The round trip delay is between 10 to 42 $\mu$ s.
+
+
+
+Diagram of a point-to-point configuration. A horizontal line represents the cable. At the left end, a box labeled 'S' (Slave) is connected to the cable, followed by a box labeled 'TR' (Terminating resistor). At the right end, a box labeled 'TR' is connected to the cable, followed by a box labeled 'M' (Master). The total length of the cable between the two terminating resistors is labeled 'd1'. The reference code 'T1700560-89' is at the bottom right.
+
+TR Terminating resistor
+M Master
+S Slave
+
+FIGURE A-3/V.320
+
+##### Point-to-point
+
+The lower value of 10 $\mu\text{s}$ is derived in the same way as for the passive bus configuration. The upper value is composed of the following elements:
+
+- 2 bits due to frame offset ( $2 \times 5.2 \mu\text{s} = 10.4 \mu\text{s}$ , see § 5.4.2.3);
+- maximum 6 bits delay permitted due to the distance between master and slave devices and the required processing time ( $6 \times 5.2 \mu\text{s} = 31.2 \mu\text{s}$ );
+- the fraction (+ 15%) of a bit period due to phase deviation between slave mode equipment input and output (see § 8.2.3, $0.15 \times 5.2 \mu\text{s} = 0.8 \mu\text{s}$ ).
+
+It should be noted that an adaptive timing device at the receiver is required at the master mode equipment to meet these limits.
+
+For the master mode equipment used for point-to-point and passive bus configurations (see § 8.6.3.2), the tolerable round trip delay in passive bus wiring configurations is reduced to 13 $\mu\text{s}$ due to the extra tolerance required for the adaptive timing. Using this type of wiring configuration, it is also possible to provide point-to-multipoint mode of operation at layer 1.
+
+*Note* - Point-to-multipoint operation can be accommodated using only point-to-point wiring. One suitable arrangement is STAR illustrated in Figure A-4/V.230. In such an implementation, bit streams from slave mode equipments must be buffered to provide for operation of the DV-echo channel(s) to provide for contention resolution, but only layer 1 functionality is required. It is also possible to support passive bus wiring configurations on the ports of STARS.
+
+
+
+The diagram illustrates a Star configuration. On the left, two slave devices, labeled 'S', are shown. Each slave is connected to a terminating resistor, labeled 'TR', with a current $I_A$ indicated. Solid lines connect these 'TR' components to a central master device, labeled 'M (STAR)'. The master device also has its own terminating resistor, labeled 'TR', with a current $I_B$ indicated. A dashed line connects the two 'S' devices. The master device 'M' is labeled with the reference number 'T1700570-89'.
+
+Diagram of a Star configuration showing two slave devices (S) connected to a central master device (M) via terminating resistors (TR).
+
+| | |
+|----|----------------------|
+| TR | Terminating resistor |
+| M | Master |
+| S | Slave |
+
+FIGURE A-4/V.230
+
+**Star**
+
+(to Recommendation V.230)
+
+##### SDL representation of a possible implementation of the DV-channel access
+
+
+
+Layer 1 enters the activated state
+
+```
+
+graph TD
+ Start([Layer 1 enters the activated state]) --> Init[X1 = 8
+X2 = 10]
+ Init --> F0[F = 0]
+ F0 --> C0[C = 0]
+ C0 --> Wait([WAIT])
+
+ Wait --> Ebit{E-bit received}
+ Wait --> DataReq{Data request detected and accepted}
+
+ Ebit -- No --> C1{C = 1}
+ C1 -- Yes --> C11{C = 11}
+ C11 -- No --> Cinc[C = C + 1]
+ Cinc --> CX1{C ≥ X1}
+ CX1 -- No --> Wait
+ CX1 -- Yes --> X1val[X1 = 8]
+ X1val --> CX2{C ≥ X2}
+ CX2 -- No --> Wait
+ CX2 -- Yes --> X2val[X2 = 10]
+ X2val --> F1{F = 1}
+ F1 -- No --> Wait
+ F1 -- Yes --> CXi{C ≥ Xi}
+
+ DataReq --> Prio{Priority class?}
+ Prio -- 1 --> i1[i = 1]
+ Prio -- 2 --> i2[i = 2]
+ i1 --> F1
+ i2 --> F1
+
+ CXi -- No --> Wait
+ CXi -- Yes --> SendD[Send 1st data bit D]
+ SendD --> WaitEbit([Wait for E-bit])
+ WaitEbit --> Ebit2{E-bit}
+ Ebit2 --> DE{D = E}
+ DE -- No --> C2{C = 2}
+ DE -- Yes --> MoreD{More D-bit?}
+ MoreD -- No --> CXi
+ MoreD -- Yes --> SendNextD[Send next D-bit]
+ SendNextD --> CXi
+
+ CXi --> End([1])
+
+```
+
+CCITT-60900
+
+D DV-channel bit
+ E DV-echo-channel bit
+ F Flag indicating that frame is pending
+ C Number of consecutive ones detected on the DV-echo-channel
+ X1 Threshold for priority class 1
+ X2 Threshold for priority class 2
+ i Priority class indicator
+
+Flowchart of DV-channel access implementation. The process starts with Layer 1 entering the activated state, setting X1=8, X2=10, F=0, and C=0. It enters a WAIT state. Two main paths are shown: one for 'E-bit received' and another for 'Data request detected and accepted'. The 'E-bit received' path checks if C=1, then C=11, then increments C and checks thresholds X1 and X2. The 'Data request detected and accepted' path checks priority class (1 or 2) and sets F=1. Both paths lead to a decision C ≥ Xi. If yes, it sends the first data bit D and waits for an E-bit. If D=E, it checks for more D-bits and sends them if available. A legend defines variables: D (DV-channel bit), E (DV-echo-channel bit), F (Flag indicating that frame is pending), C (Number of consecutive ones detected on the DV-echo-channel), X1 (Threshold for priority class 1), X2 (Threshold for priority class 2), and i (Priority class indicator).
+
+(to Recommendation V.230)
+
+##### **Test configurations**
+
+In § 8 of this Recommendation, waveforms are shown for testing master and slave mode equipment. This Annex describes configurations, for testing slave mode equipment, which can be used to generate these waveforms (see Figure C-1/V.230). Similar configurations can be used to test master mode equipment.
+
+Table C-1/V.230 gives the parameters for the artificial lines reproduced in Figure C-1/V.230. The artificial lines are used to derive the waveforms. For test configurations ii) and iii), the cable length used corresponds to a signal delay of 1 $\mu$ s.
+
+
+
+**Configuration i) Point-to-point**
+
+**Configuration ii) Short passive bus**
+
+**Configuration iii) Short passive bus**
+
+**Configuration iv) Ideal test signal**
+
+M Master
+S Slave
+
+Four test configurations (i, ii, iii, iv) for testing slave mode equipment. Configuration i) is point-to-point with a master (M) connected to an artificial line (high capacitance, 6 dB) and a 100 Ω resistor, which is then connected to another 100 Ω resistor and a 50 Ω resistor. Configuration ii) is a short passive bus with a master (M) connected to an artificial line (high capacitance) and a 100 Ω resistor, which is then connected to a 7-terminal equivalent input impedance and a 50 Ω resistor. Configuration iii) is a short passive bus with a slave (S) connected to an artificial line (a) high capacitance, b) low capacitance, and a 100 Ω resistor, which is then connected to a 7-terminal equivalent input impedance and a 50 Ω resistor. Configuration iv) is an ideal test signal with a slave (S) connected to two 100 Ω resistors and a 50 Ω resistor.
+
+FIGURE C-1/V.230
+
+##### **Test configurations**
+
+TABLE C-1/V.230
+
+##### **Parameters for the artificial lines**
+
+| Parameters | High capacitance cable | Low capacitance cable |
+|-------------------------|------------------------|-----------------------|
+| R (96 kHz) | 160 ohms/km | 160 ohms/km |
+| C (1 kHz) | 120 nF/km | 30 nF/km |
+| Z 0 (96 kHz) | 75 ohms | 150 ohms |
+| Wire diameter | 0.6 mm | 0.6 mm |
\ No newline at end of file
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+
+
+
+
+ITU logo: a globe with the letters ITU inside, and a lightning bolt striking the globe.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+# ITU-T
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+# V.24
+
+(02/2000)
+
+SERIES V: DATA COMMUNICATION OVER THE
+TELEPHONE NETWORK
+
+Interfaces and voiceband modems
+
+---
+
+**List of definitions for interchange circuits
+between data terminal equipment (DTE) and
+data circuit-terminating equipment (DCE)**
+
+ITU-T Recommendation V.24
+
+(Formerly CCITT Recommendation)
+
+---
+
+# ITU-T V-SERIES RECOMMENDATIONS **DATA COMMUNICATION OVER THE TELEPHONE NETWORK**
+
+| | |
+|-------------------------------------------------------|------------------|
+| General | V.1–V.9 |
+| Interfaces and voiceband modems | V.10–V.34 |
+| Wideband modems | V.35–V.39 |
+| Error control | V.40–V.49 |
+| Transmission quality and maintenance | V.50–V.59 |
+| Simultaneous transmission of data and other signals | V.60–V.99 |
+| Interworking with other networks | V.100–V.199 |
+| Interface layer specifications for data communication | V.200–V.249 |
+| Control procedures | V.250–V.299 |
+| Modems on digital circuits | V.300–V.399 |
+
+*For further details, please refer to ITU-T List of Recommendations.*
+
+# **LIST OF DEFINITIONS FOR INTERCHANGE CIRCUITS BETWEEN DATA TERMINAL EQUIPMENT (DTE) AND DATA CIRCUIT-TERMINATING EQUIPMENT (DCE)**
+
+## **Summary**
+
+This Recommendation applies to the interconnecting circuits being called interchange circuits at the interface between DTE and DCE for the transfer of binary data, control and timing signals as appropriate. This Recommendation also applies to both sides of separate intermediate equipment, which may be inserted between these two classes of equipment.
+
+## **Source**
+
+ITU-T Recommendation V.24 was revised by ITU-T Study Group 16 (1997-2000) and was approved under the WTSC Resolution No. 1 procedure on 17 February 2000.
+
+## FOREWORD
+
+ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the ITU. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics.
+
+The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+The ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, the ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database.
+
+© ITU 2001
+
+All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.
+
+## CONTENTS
+
+| | Page |
+|-------------------------------------------------------------------------|-------------|
+| 1 Scope..... | 1 |
+| 1.1 Range of application ..... | 1 |
+| 1.2 Applicable electrical characteristics..... | 2 |
+| 1.3 Applicable mechanical characteristics ..... | 2 |
+| 1.4 Allocation of functionalities ..... | 2 |
+| 2 Line of demarcation ..... | 2 |
+| 3 Definitions of interchange circuits..... | 2 |
+| 3.1 Circuit 102 – Signal ground or common return ..... | 4 |
+| 3.2 Circuit 102a – DTE common return ..... | 4 |
+| 3.3 Circuit 102b – DCE common return..... | 4 |
+| 3.4 Circuit 102c – Common return ..... | 4 |
+| 3.5 Circuit 103 – Transmitted data ..... | 4 |
+| 3.6 Circuit 104 – Received data..... | 5 |
+| 3.7 Circuit 105 – Request to send ..... | 5 |
+| 3.8 Circuit 106 – Ready for sending ..... | 5 |
+| 3.9 Circuit 107 – Data set ready..... | 5 |
+| 3.10 Circuit 108/1 – Connect data set to line..... | 6 |
+| 3.11 Circuit 108/2 – Data terminal ready..... | 6 |
+| 3.12 Circuit 109 – Data channel received line signal detector..... | 7 |
+| 3.13 Circuit 111 – Data signalling rate selector (DTE source)..... | 7 |
+| 3.14 Circuit 112 – Data signalling rate selector (DCE source)..... | 7 |
+| 3.15 Circuit 113 – Transmitter signal element timing (DTE source) ..... | 7 |
+| 3.16 Circuit 114 – Transmitter signal element timing (DCE source)..... | 8 |
+| 3.17 Circuit 115 – Receiver signal element timing (DCE source)..... | 8 |
+| 3.18 Circuit 116/1 – Back-up switching in direct mode ..... | 8 |
+| 3.19 Circuit 116/2 – Back-up switching in authorized mode ..... | 9 |
+| 3.20 Circuit 117 – Standby indicator ..... | 9 |
+| 3.21 Circuit 118 – Transmitted backward channel data ..... | 9 |
+| 3.22 Circuit 119 – Received backward channel data ..... | 9 |
+| 3.23 Circuit 120 – Transmit backward channel line signal ..... | 9 |
+| 3.24 Circuit 121 – Backward channel ready ..... | 9 |
+| 3.25 Circuit 122 – Backward channel received line signal detector..... | 10 |
+| 3.26 Circuit 125 – Calling indicator ..... | 10 |
+| 3.27 Circuit 126 – Select transmit frequency..... | 10 |
+
+| | Page |
+|---------------------------------------------------------------------|-------------|
+| 3.28 Circuit 128 – Receiver signal element timing (DTE source)..... | 10 |
+| 3.29 Circuit 131 – Received character timing (DCE source) ..... | 10 |
+| 3.30 Circuit 133 – Ready for receiving..... | 11 |
+| 3.31 Circuit 134 – Received data present ..... | 11 |
+| 3.32 Circuit 135 – Received energy present ..... | 11 |
+| 3.33 Circuit 137 – Transmitted character timing (DTE source)..... | 11 |
+| 3.34 Circuit 138 – Transmitted character timing (DCE source)..... | 12 |
+| 3.35 Circuit 140 – Loopback/Maintenance test ..... | 12 |
+| 3.36 Circuit 141 – Local loopback..... | 12 |
+| 3.37 Circuit 142 – Test indicator ..... | 13 |
+| 4 Operational requirements..... | 13 |
+| 4.1 Data circuits and timing circuits ..... | 13 |
+| 4.1.1 Data circuits..... | 13 |
+| 4.1.2 Timing circuits..... | 13 |
+| 4.2 Control and indication circuits..... | 14 |
+| 4.2.1 Operation of circuits 107, 108/1 and 108/2 ..... | 14 |
+| 4.2.2 Circuit 125 – Calling indicator ..... | 15 |
+| 4.2.3 Usage of circuit 126..... | 15 |
+| 4.2.4 Circuit 140 – Loopback/Maintenance Test ..... | 15 |
+| 4.3 Miscellaneous ..... | 15 |
+| 4.3.1 Interrelationship of circuits 103, 105 and 106..... | 15 |
+| 4.3.2 Idle periods ..... | 16 |
+| 4.3.3 Clamping ..... | 16 |
+| 4.4 Circuit failures (electrical) ..... | 17 |
+| 4.5 Provision of interchange circuits in DCEs and DTEs..... | 17 |
+| 4.6 Data flow control ..... | 17 |
+| 4.7 Power-up considerations..... | 17 |
+| 5 References..... | 17 |
+
+## Recommendation V.24
+
+# LIST OF DEFINITIONS FOR INTERCHANGE CIRCUITS BETWEEN DATA TERMINAL EQUIPMENT (DTE) AND DATA CIRCUIT-TERMINATING EQUIPMENT (DCE)
+
+(Geneva, 1964, amended at Mar del Plata, 1968, Geneva, 1972, 1976 and 1980,
+Malaga-Torremolinos, 1984, Melbourne, 1988, Helsinki, 1993, Geneva, 1996 and 2000)
+
+# 1 Scope
+
+## 1.1 Range of application
+
+This Recommendation applies to the interconnecting circuits being called interchange circuits at the interface between DTE and DCE for the transfer of binary data, control and timing signals as appropriate. This Recommendation also applies to both sides of separate intermediate equipment, which may be inserted between these two classes of equipment (see Figure 1).
+
+
+
+T1400030-93
+
+Diagram illustrating the general layout of equipment for V.24 interfaces. It shows a DTE (Data Terminal Equipment) on the left and a DCE (Data Circuit-Terminating Equipment) on the right, connected by a 'Line'. Between them is 'Intermediate equipment (e.g. error control)'. The diagram shows multiple horizontal lines representing data paths. On the left, a 'V.24 interface' is indicated with a downward arrow. On the right, another 'V.24 interface' is indicated with a downward arrow. A 'Line of demarcation' is shown between the DTE and the intermediate equipment. Selections A, B, and C are marked on the lines. Selection A is on the line between DTE and intermediate equipment. Selection B is on the line between intermediate equipment and DCE. Selection C is on the line between DCE and the Line. The diagram is labeled T1400030-93 at the bottom right.
+
+NOTE – Without intermediate equipment, the selections A and B are identical.
+Selection C may be a selection specifically for automatic calling.
+
+**Figure 1/V24 – Illustration of general layout of equipment**
+
+The range of interchange circuits defined in this Recommendation is applicable, for example:
+
+- a) to synchronous and asynchronous data communications;
+- b) to data transmission on leased line service, either 2-wire or 4-wire, either point-to-point or multipoint operation;
+- c) to data transmission on switched network service, either 2-wire or 4-wire;
+
+A DTE/DCE interface conforming to this Recommendation may also be used for attachment to a Public Data Network (PDN). For these cases, additional information on interchange circuit implementation and operational requirements may be found in Recommendations X.20 *bis* and X.21 *bis*.
+
+In any type of practical equipment a selection will be made from the range of interchange circuits defined in this Recommendation, as appropriate.
+
+The actual interchange circuits to be used in a particular DCE are those indicated in the appropriate Recommendation.
+
+The required interchange circuits specified in the DCE Recommendations which make reference to this Recommendation apply only to the DCE side of the interface. Only those circuits necessary to assure satisfactory operation of the application the DTE is intending to support need be controlled or monitored by the DTE (see 4.5 for proper handling of unimplemented circuits).
+
+The usage and operational requirements of certain interchange circuits and the interaction between them are specified in clause 4. For proper operation of the DCE it is important that the guidelines in clause 4 be observed.
+
+## **1.2 Applicable electrical characteristics**
+
+Electrical characteristics for interchange circuits are specified in Recommendations V.10, V.11, V.12, V.28, V.31 and V.31 *bis*.
+
+## **1.3 Applicable mechanical characteristics**
+
+For mechanical characteristics of the interface, refer to ISO/IEC 2110 (25-pole), ISO/IEC 11569 (26-pole), ISO/IEC 13575 (50-pole) or ISO/IEC 4902 (37-pole) as appropriate.
+
+## **1.4 Allocation of functionalities**
+
+The DCE may include signal converters, timing generators, pulse regenerators, and control circuitry, together with equipment to provide functions such as error control, automatic calling and automatic answering. Some of these functions may be implemented in separate intermediate equipment or in the DTE.
+
+# **2 Line of demarcation**
+
+The interface between DTE and DCE is located at a connector, which is the interchange point between these two classes of equipment.
+
+The interface connector will not necessarily be physically attached to the DCE and may be mounted in a fixed position near the DTE.
+
+An interconnecting cable or cables will normally be provided with the DTE. It is recommended to keep the cables as short as possible. Their lengths should be limited by the load capacitance and other electrical characteristics specified in the relevant Recommendation on electrical characteristics (see 1.2).
+
+# **3 Definitions of interchange circuits**
+
+A list of these interchange circuits is presented in Table 1.
+
+NOTE – Compared to earlier versions of this Recommendation, Table 1 and the definitions below summarize fewer interchange circuits, and some circuit numbers are void. Interchange circuits for which no practical application has become known or whose application has ceased have been removed, e.g. the 200-series of interchange circuits for parallel automatic calling in accordance with earlier versions of Recommendation V.25 and interchange circuits relevant for modems employing parallel data transmission in accordance with former Recommendation V.20.
+
+**Table 1/V.24 – Interchange circuits by category**
+
+| Inter-change circuit number | Interchange circuit name | Ground | Data | | Control | | Timing | |
+|-----------------------------|------------------------------------------------|--------|----------|--------|----------|--------|----------|--------|
+| | | | From DCE | To DCE | From DCE | To DCE | From DCE | To DCE |
+| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
+| 102 | Signal ground or common return | X | | | | | | |
+| 102a | DTE common return | X | | | | | | |
+| 102b | DCE common return | X | | | | | | |
+| 102c | Common return | X | | | | | | |
+| 103 | Transmitted data | | | X | | | | |
+| 104 | Received data | | X | | | | | |
+| 105 | Request to send | | | | | X | | |
+| 106 | Ready for sending | | | | X | | | |
+| 107 | Data set ready | | | | X | | | |
+| 108/1 | Connect data set to line | | | | | X | | |
+| 108/2 | Data terminal ready | | | | | X | | |
+| 109 | Data channel received line signal detector | | | | X | | | |
+| 111 | Data signal rate selector (DTE) | | | | | X | | |
+| 112 | Data signal rate selector (DCE) | | | | X | | | |
+| 113 | Transmitter signal element timing (DTE) | | | | | | | X |
+| 114 | Transmitter signal element timing (DCE) | | | | | | X | |
+| 115 | Receiver signal element timing (DCE) | | | | | | X | |
+| 116/1 | Back-up switching in direct mode | | | | | X | | |
+| 116/2 | Back-up switching in authorized mode | | | | | X | | |
+| 117 | Standby indicator | | | | X | | | |
+| 118 | Transmitted backward channel data | | | X | | | | |
+| 119 | Received backward channel data | | X | | | | | |
+| 120 | Transmit backward channel line signal | | | | | X | | |
+| 121 | Backward channel ready | | | | X | | | |
+| 122 | Backward channel received line signal detector | | | | X | | | |
+| 125 | Calling indicator | | | | X | | | |
+| 126 | Select transmit frequency | | | | | X | | |
+| 128 | Receiver signal element timing (DTE) | | | | | | | X |
+| 131 | Received character timing (DCE source) | | | | | | X | |
+| 133 | Ready for receiving | | | | | X | | |
+| 134 | Received data present | | | | X | | | |
+| 135 | Received energy present | | | | X | | | |
+| 137 | Transmitted character timing (DTE source) | | | | | | | X |
+| 138 | Transmitted character timing (DCE source) | | | | | | X | |
+| 140 | Loopback/Maintenance test | | | | | X | | |
+| 141 | Local loopback | | | | | X | | |
+| 142 | Test indicator | | | | X | | | |
+
+## **3.1 Circuit 102 – Signal ground or common return**
+
+This conductor establishes the signal common return for unbalanced interchange circuits with electrical characteristics according to Recommendation V.28 and the d.c. reference potential for interchange circuits according to Recommendations V.10 and V.11.
+
+Within the DTE, this circuit should be brought to one point, and it should be possible to connect this point to protective ground or earth by means of a metallic strap within the equipment. This metallic strap can be connected or removed at installation, as may be required to meet applicable safety regulations or to minimize the introduction of noise into electronic circuitry. Caution should be exercised to prevent the establishment of ground loops carrying high currents.
+
+## **3.2 Circuit 102a – DTE common return**
+
+This conductor is connected to the DTE circuit common return and is used as the reference potential for the unbalanced V.10-type interchange circuit receivers within the DCE.
+
+## **3.3 Circuit 102b – DCE common return**
+
+This conductor is connected to the DCE circuit common return and is used as the reference potential for the unbalanced V.10-type interchange circuit receivers within the DTE.
+
+NOTE – Two arrangements exist for the case where a mixture of V.10 and V.11 circuits is used in the same interface:
+
+- 1) The DTE common return and the DCE common return are both connected to circuit 102. This arrangement is particularly useful where the need to conserve pole assignments is a requirement [10] and [12]. It should, however, be noted that only category 2 receivers as specified in clause 9/V.10 can be used in this case, and that the usable interface cable length may be shorter than specified in Appendix II/V.10.
+- 2) Separate provision is made for the V.10 common return circuits 102a and 102b, and for a d.c. reference potential conductor circuit 102 [11].
+
+## **3.4 Circuit 102c – Common return**
+
+This conductor establishes the signal common return for single-current interchange circuits controlled by contact closure with electrical characteristics according to Recommendation V.31, in cases where a common return is used.
+
+Within the equipment containing the signal source of the interchange circuit, this conductor shall be isolated from signal ground and protective ground, irrespective of whether it is located within the DCE or within the DTE.
+
+## **3.5 Circuit 103 – Transmitted data**
+
+Direction: To DCE
+
+The data signals originated by the DTE:
+
+- 1) to be transmitted via a data channel to one or more remote data stations;
+ - 2) to be passed to the DCE for maintenance test purposes under control of the DTE; or
+ - 3) for the programming or control of serial automatic calling DCEs,
+- are transferred on this circuit to the DCE.
+
+## **3.6 Circuit 104 – Received data**
+
+Direction: From DCE
+
+The data signals generated by the DCE:
+
+- 1) in response to data channel line signals received from a remote data station;
+- 2) in response to the DTE maintenance test signals; or
+- 3) in response to (or as an echo of) programming or control signals from the DTE where a serial automatic calling facility is implemented in the DCE,
+
+are transferred on this circuit to the DTE.
+
+NOTE – The reception conditions for maintenance test signals are specified with circuit 107.
+
+### **3.7 Circuit 105 – Request to send**
+
+Direction: To DCE
+
+Signals on this circuit control the data channel transmit function of the DCE.
+
+The ON condition causes the DCE to assume the data channel transmit mode.
+
+The OFF condition causes the DCE to assume the data channel non-transmit mode, when all data transferred on circuit 103 have been transmitted.
+
+## **3.8 Circuit 106 – Ready for sending**
+
+Direction: From DCE
+
+Signals on this circuit indicate whether the DCE is prepared to accept data signals for transmission on the data channel or for maintenance test purposes under control of the DTE.
+
+The ON condition indicates that the DCE is prepared to accept data signals from the DTE.
+
+The OFF condition indicates that the DCE is not prepared to accept data signals from the DTE.
+
+### **3.9 Circuit 107 – Data set ready**
+
+Direction: From DCE
+
+Signals on this circuit indicate whether the DCE is ready to operate.
+
+The ON condition, where circuit 142 is OFF or is not implemented, indicates that the signal converter or similar equipment is connected to the line and that the DCE is ready to exchange further control signals with the DTE to initiate transfer of data.
+
+The ON condition, in conjunction with the ON condition of circuit 142, indicates that the DCE is prepared to exchange data signals with the DTE for maintenance test purposes.
+
+The OFF condition, in conjunction with the ON condition on circuit 106, indicates that the DCE is ready to exchange data signals associated with the programming or control of serial automatic calling DCEs.
+
+The OFF condition, in conjunction with the OFF condition on circuit 106, indicates:
+
+- 1) that the DCE is not ready to operate in the data transfer phase;
+- 2) that the DCE has detected a fault condition (which may be network or DCE dependent) which has lasted longer than some fixed period of time, such period of time being network dependent; or
+- 3) in switched network operation, that the DCE has detected a disconnect indication from the remote station or from the network.
+
+The OFF condition, in conjunction with the ON condition on circuit 142, indicates that the DCE is involved in tests from the network or remote station.
+
+### **3.10 Circuit 108/1 – Connect data set to line**
+
+Direction: To DCE
+
+Signals on this circuit control switching of the signal-converter or similar equipment to or from the line.
+
+A transition from OFF to ON condition on this circuit causes the DCE to connect the signal-converter or similar equipment to the line.
+
+A transition from OFF to ON condition of this circuit may also be used to initiate a direct call facility for automatic calling DCEs.
+
+The ON condition on this circuit shall maintain the connection but shall not prevent the operation of disconnection functions optionally implemented in the DCE. Examples of such disconnection functions include, but are not limited to, the following:
+
+- loss of line signal (on switched telephone network);
+- implementation of callback facility;
+- depression of a push button at the DCE.
+
+The OFF condition on this circuit, except as noted below, causes the DCE to remove the signal-converter or similar equipment from the line, when the transmission of all data previously transferred on circuit 103 and/or circuit 118 has been completed. In the case where an intermediate function is implemented in the DCE, the DCE may delay the removal of the signal-converter from the line until the protocol requirements of the intermediate function have been satisfied (e.g. outstanding data has been acknowledged or a timeout has occurred).
+
+The OFF condition on this circuit may also be used to direct the DCE to abort or to clear a direct call facility operation (see Recommendation V.25 *bis*).
+
+## **3.11 Circuit 108/2 – Data terminal ready**
+
+Direction: To DCE
+
+Signals on this circuit indicate the status of the DTE.
+
+The ON condition, indicating that the DTE is ready to operate, prepares the DCE to connect the signal-converter or similar equipment to the line.
+
+The DCE may be connected to the line by a supplementary condition. Examples of such supplementary conditions include, but are not restricted to, the following:
+
+- depression of a push button at the DCE;
+- an incoming call in the case of automatic answering;
+- a call request command from the DTE in the case of automatic calling.
+
+The DCE maintains the connection so long as the ON condition persists, except that the ON condition shall not prevent the operation of disconnection functions optionally implemented in the DCE. Examples of such disconnection functions are noted in the definition of circuit 108/1.
+
+The DTE is permitted to present the ON condition on circuit 108/2 whenever it is ready to transmit or receive data.
+
+The OFF condition on this circuit causes the DCE to remove the signal-converter or similar equipment from the line when the transmission to the line of all data previously transferred on circuit 103 and/or circuit 118 has been completed. In the case where an intermediate function is
+
+implemented in the DCE, the DCE may delay the removal of the signal converter from the line until the protocol requirements of the intermediate function have been satisfied (e.g. outstanding data has been acknowledged or a timeout has occurred).
+
+The OFF condition of this circuit may also be used to direct the DCE to abort or to clear a serial automatic calling operation (see Recommendation V.25 *bis*).
+
+## **3.12 Circuit 109 – Data channel received line signal detector**
+
+Direction: From DCE
+
+Signals on this circuit indicate whether the received data channel line signal is within appropriate limits, as specified in the relevant Recommendation for DCE.
+
+The ON condition indicates that the received line signal is within appropriate limits.
+
+Circuit 109 may also be in the ON condition during the exchange of data signals between the DCE and the DTE, associated with the programming or control of serial automatic calling DCEs.
+
+The OFF condition indicates that the received signal is not within appropriate limits. In the case where an intermediate function is implemented in the DCE, the DCE may delay the assertion of an OFF condition on circuit 109, in response to the conditions stated above, until all of the data in its buffers has been transferred to its associated DTE on circuit 104 or a timeout has occurred.
+
+## **3.13 Circuit 111 – Data signalling rate selector (DTE source)**
+
+Direction: To DCE
+
+Signals on this circuit are used to select one of the two data signalling rates of a dual rate synchronous DCE, or to select one of the two ranges of data signalling rates of a dual range asynchronous DCE.
+
+The ON condition selects the higher rate or range of rates.
+
+The OFF condition selects the lower rate or range of rates.
+
+## **3.14 Circuit 112 – Data signalling rate selector (DCE source)**
+
+Direction: From DCE
+
+Signals on this circuit are used to select one of the two data signalling rates or ranges of rates in the DTE to coincide with the data signalling rate or range of rates in use in a dual rate synchronous or dual range asynchronous DCE.
+
+The ON condition selects the higher rate or range of rates.
+
+The OFF condition selects the lower rate or range of rates.
+
+### **3.15 Circuit 113 – Transmitter signal element timing (DTE source)**
+
+Direction: To DCE
+
+Signals on this circuit provide the DCE with signal element timing information.
+
+The condition on this circuit shall be ON and OFF for nominally equal periods of time and the transition from ON to OFF condition shall nominally indicate the centre of each signal element on circuit 103.
+
+## **3.16 Circuit 114 – Transmitter signal element timing (DCE source)**
+
+Direction: From DCE
+
+Signals on this circuit provide the DTE with transmitter signal element timing information.
+
+The condition on this circuit shall be ON and OFF for nominally equal periods of time. The DTE shall present a data signal on circuit 103 in which the transitions between signal elements nominally occur at the time of the transitions from OFF to ON condition of circuit 114.
+
+Where variable transmitter signal element timing is required, the change to a different rate shall occur while this circuit is in the OFF condition. The new rate shall be an integer multiple or fraction of the old rate.
+
+Where it is required to temporarily halt data transmission, this circuit may be held in the OFF condition for a limited period of time. The maximum permissible duration of this condition is for further study. The duration of the OFF condition shall be an integer multiple of the length of a signal element before halting the signal. Signalling on this circuit may then be resumed at the same rate or at a different rate, as specified above.
+
+Where also character or 8-bit byte timing is provided using circuit 138 – *Transmitted character timing (DCE source)*, the change to a different rate on circuit 114 shall occur during the OFF condition that precedes the OFF-to-ON transition which indicates the first bit of a new character or 8-bit byte.
+
+## **3.17 Circuit 115 – Receiver signal element timing (DCE source)**
+
+Direction: From DCE
+
+Signals on this circuit provide the DTE with receiver signal element timing information.
+
+The condition of this circuit shall be ON and OFF for nominally equal periods of time, and a transition from ON to OFF condition shall nominally indicate the centre of each signal element on circuit 104.
+
+Where variable receiver signal element timing is required, the change to a different rate shall occur while this circuit is in the OFF condition. The new rate shall be an integer multiple or fraction of the old rate.
+
+Where it is required to temporarily halt data reception, this circuit may be held in the OFF condition for a limited period of time. The maximum permissible duration of this condition is for further study. The duration of the OFF condition shall be an integer multiple of the length of a signal element before halting the signal. Signalling on this circuit may then be resumed at the same rate or at a different rate, as specified above.
+
+Where also character or 8-bit byte timing is provided using circuit 131 – *Received character timing (DCE source)*, the change to a different rate on circuit 115 shall occur during the OFF condition that precedes the OFF-to-ON transition which indicates the first bit of a new character or 8-bit byte.
+
+### **3.18 Circuit 116/1 – Back-up switching in direct mode**
+
+Direction: To the DCE
+
+Signals on this circuit control switching of the DCE between normal and standby facilities.
+
+The ON condition causes the DCE to connect to the standby facility.
+
+The OFF condition causes the DCE to disconnect from the standby facility, when the transmission to line of all data previously transferred on circuit 103 has been completed, and the DCE then reconnects to the normal facility.
+
+## **3.19 Circuit 116/2 – Back-up switching in authorized mode**
+
+Direction: To the DCE
+
+Signals on this circuit control switching of the DCE between normal and standby facilities.
+
+The ON condition indicates that the DTE is ready to switch from the normal to the standby facility and prepares the DCE to switch to the standby facility when necessary.
+
+The OFF condition causes the DCE to disconnect from the standby facility, when the transmission to line of all data previously transferred on circuit 103 has been completed, and the DCE then reconnects to the normal facility.
+
+### **3.20 Circuit 117 – Standby indicator**
+
+Direction: From DCE
+
+Signals on this circuit indicate whether the DCE is conditioned to operate in its standby mode with the predetermined facilities replaced by their reserves.
+
+The ON condition indicates that the DCE is conditioned to operate in its standby mode.
+
+The OFF condition indicates that the DCE is conditioned to operate in its normal mode.
+
+### **3.21 Circuit 118 – Transmitted backward channel data**
+
+Direction: To DCE
+
+This circuit is equivalent to circuit 103, except that it is used to transmit data via the backward channel.
+
+### **3.22 Circuit 119 – Received backward channel data**
+
+Direction: From DCE
+
+This circuit is equivalent to circuit 104, except that it is used for data received on the backward channel.
+
+## **3.23 Circuit 120 – Transmit backward channel line signal**
+
+Direction: To DCE
+
+This circuit is equivalent to circuit 105, except that it is used to control the backward channel transmit function of the DCE.
+
+The ON condition causes the DCE to assume the backward channel transmit mode.
+
+The OFF condition causes the DCE to assume the backward channel non-transmit mode, when all data transferred on circuit 118 have been transmitted to line.
+
+## **3.24 Circuit 121 – Backward channel ready**
+
+Direction: From DCE
+
+This circuit is equivalent to circuit 106, except that it is used to indicate whether the DCE is conditioned to transmit data on the backward channel.
+
+The ON condition indicates that the DCE is conditioned to transmit data on the backward channel.
+
+The OFF condition indicates that the DCE is not conditioned to transmit data on the backward channel.
+
+## **3.25 Circuit 122 – Backward channel received line signal detector**
+
+Direction: From DCE
+
+This circuit is equivalent to circuit 109, except that it is used to indicate whether the received backward channel line signal is within appropriate limits, as specified in the relevant Recommendation for DCE.
+
+### **3.26 Circuit 125 – Calling indicator**
+
+Direction: From DCE
+
+Signals on this circuit indicate whether a calling signal is being received by the DCE.
+
+The ON condition indicates that a calling signal is being received.
+
+The OFF condition indicates that no calling signal is being received, and this condition may also appear during interruptions of a pulse-modulated calling signal.
+
+### **3.27 Circuit 126 – Select transmit frequency**
+
+Direction: To DCE
+
+Signals on this circuit are used to select the required transmit frequency of the DCE.
+
+The ON condition selects the higher transmit frequency.
+
+The OFF condition selects the lower transmit frequency.
+
+### **3.28 Circuit 128 – Receiver signal element timing (DTE source)**
+
+Direction: To DCE
+
+Signals on this circuit provide the DCE with signal element timing information.
+
+The condition on this circuit shall be ON and OFF for nominally equal periods of time. The DCE shall present a data signal on circuit 104 in which the transitions between signal elements nominally occur at the time of the transitions from OFF to ON condition of the signal on circuit 128.
+
+Where variable receiver signal element timing is required, the change to a different rate shall occur while this circuit is in the OFF condition. The new rate shall be an integer multiple or fraction of the old rate.
+
+Where it is required to temporarily halt data reception, this circuit may be held in the OFF condition for a limited period of time. The maximum permissible duration of this condition is for further study. The duration of the OFF condition shall be an integer multiple of the length of a signal element before halting the signal. Signalling on this circuit may then be resumed at the same rate or at a different rate, as specified above.
+
+### **3.29 Circuit 131 – Received character timing (DCE source)**
+
+Direction: From DCE
+
+Signals on this circuit provide the DTE with received character or 8-bit byte timing information, as specified in the relevant Recommendation for DCE.
+
+Unless otherwise specified in the relevant Recommendation for DCE, the condition of this circuit shall be OFF for nominally the period of the ON condition of circuit 115 – *Receiver signal element timing (DCE source)* which indicates the last bit of a character or an 8-bit byte, and shall be ON at all other times within the period of the character or 8-bit byte.
+
+The centre of the last bit of each character or 8-bit byte will be presented by the DCE on circuit 104 – *Received data* nominally at the time of the OFF to ON transition of circuit 131.
+
+The DCE shall transfer byte timing information on this circuit across the interface at all times that the timing source is capable of generating this information.
+
+Where variable receiver signal element timing is required, also the received character timing will have to be accordingly changed. The change to a different rate shall occur during the ON condition of circuit 131 (see definition of circuit 115).
+
+Where it is required to temporarily halt data reception, this circuit may be held in the ON condition for a limited period of time. The maximum permissible duration of this condition is for further study.
+
+### **3.30 Circuit 133 – Ready for receiving**
+
+Direction: To DCE
+
+Signals on this circuit control the transfer of data on circuit 104, indicating whether the DTE is capable of accepting a given amount of data (e.g. a block of data), specified in the appropriate Recommendation for an intermediate function, for example, error control.
+
+The ON condition shall be maintained whenever the DTE is capable of accepting data, and causes the intermediate equipment or DCE to transfer the received data to the DTE.
+
+The OFF condition indicates that the DTE is not able to accept data, and causes the intermediate equipment or DCE to retain the data.
+
+### **3.31 Circuit 134 – Received data present**
+
+Direction: From DCE
+
+Signals on this circuit are used to separate information messages from supervisory messages, transferred on circuit 104, as specified in the appropriate Recommendation for intermediate equipment, e.g. error control equipment.
+
+The ON condition indicates the data which represents information messages.
+
+The OFF condition shall be maintained at all other times.
+
+### **3.32 Circuit 135 – Received energy present**
+
+Direction: From DCE
+
+Signals on this circuit indicate the presence of energy on the line.
+
+The ON condition on this circuit indicates the instantaneous presence of energy on the line.
+
+The OFF condition on this circuit indicates the absence of energy on the line.
+
+NOTE – For certain applications, this circuit may be used to transfer an indication of the changing instantaneous levels of the received energy in an analogue manner. Details may be found in the appropriate DCE Recommendation.
+
+### **3.33 Circuit 137 – Transmitted character timing (DTE source)**
+
+Direction: From DTE
+
+Signals on this circuit provide the DCE with transmitted character or 8-bit byte timing information, as specified in the relevant Recommendation for DCE.
+
+Unless otherwise specified in the relevant Recommendation for DCE, the condition of this circuit shall be OFF for nominally the period of the ON condition of circuit 113 – *Transmitter signal element timing (DTE source)* which indicates the last bit of a character or an 8-bit byte, and shall be ON at all other times within the period of the character or 8-bit byte.
+
+The DTE shall present the centre of the last bit of each character or 8-bit byte on circuit 103 – *Transmitted data* nominally at the time of the OFF to ON transition of circuit 137 and the beginning of the first bit of each character or 8-bit byte nominally at the time of the OFF to ON transition of circuit 113 which follows the OFF to ON transition of circuit 137.
+
+The DTE shall transfer byte timing information on this circuit across the interface at all times that the timing source is capable of generating this information.
+
+## **3.34 Circuit 138 – Transmitted character timing (DCE source)**
+
+Direction: From DCE
+
+Signals on this circuit provide the DTE with transmitted character or 8-bit byte timing information, as specified in the relevant Recommendation for DCE.
+
+Unless otherwise specified in the relevant Recommendation for DCE, the condition of this circuit shall be OFF for nominally the period of the ON condition of circuit 114 – *Transmitter signal element timing (DCE source)* which indicates the last bit of a character or an 8-bit byte, and shall be ON at all other times within the period of the character or 8-bit byte.
+
+The DTE will present the centre of the last bit of each character or 8-bit byte on circuit 103 – *Transmitted data* nominally at the time of the OFF to ON transition of circuit 138 and the beginning of the first bit of each character or 8-bit byte nominally at the time of the OFF to ON transition of circuit 114 which follows the OFF to ON transition of circuit 138.
+
+The DCE shall transfer byte timing information on this circuit across the interface at all times that the timing source is capable of generating this information.
+
+Where variable transmitter signal element timing is required, also the transmitted character timing will have to be accordingly changed. The change to a different rate shall occur during the ON condition of circuit 138 (see definition of circuit 114).
+
+Where it is required to temporarily halt data transmission, this circuit may be held in the ON condition for a limited period of time. The maximum permissible duration of this condition is for further study.
+
+## **3.35 Circuit 140 – Loopback/Maintenance test**
+
+Direction: To DCE
+
+Signals on this circuit are used to initiate and release loopback or other maintenance test conditions in DCEs.
+
+The ON condition causes initiation of the maintenance test condition.
+
+The OFF condition causes release of the maintenance test condition.
+
+## **3.36 Circuit 141 – Local loopback**
+
+Direction: To DCE
+
+Signals on this circuit are used to control the loop 3 test condition in the local DCE.
+
+The ON condition of circuit 141 causes the establishment of the loop 3 test condition in the local DCE.
+
+The OFF condition of circuit 141 causes the release of the loop 3 test condition in the local DCE.
+
+## **3.37 Circuit 142 – Test indicator**
+
+Direction: From DCE
+
+Signals on this circuit indicate whether a maintenance condition exists.
+
+The ON condition indicates that a maintenance condition exists in the DCE, precluding reception or transmission of data signals from or to a remote DTE.
+
+The OFF condition indicates that the DCE is not in a maintenance test condition.
+
+# **4 Operational requirements**
+
+In the following, operational requirements are given for the usage of interchange circuits. It also explains in further detail the required correlation between interchange circuits, where implemented.
+
+## **4.1 Data circuits and timing circuits**
+
+### **4.1.1 Data circuits**
+
+It is evident that proper data transmission may be impaired when the required condition is not present on an implemented control interchange circuit. Therefore, the DTE shall not transfer, on circuit 103, data which is for transmission to line or for maintenance purposes unless an ON condition is present on all of the following four circuits, where implemented: circuit 105, circuit 106, circuit 107 and circuit 108/1 or 108/2.
+
+The DTE may transfer, on circuit 103, data which is for the programming or control of serial automatic calling DCEs when an ON condition is present on circuits 106 and 108/2, and an OFF condition is present on circuit 107. In this situation, the condition of circuit 105 need not be considered, and may be ON for DTE convenience.
+
+All data transferred on circuit 103 during the time an ON condition is present on all of the above four circuits, where implemented, shall be transmitted by the DCE.
+
+Refer also to 4.2.1 and 4.3.1 below for further explanation.
+
+The DTE shall not transfer data on circuit 118 unless an ON condition is present on all of the following four circuits, where implemented: circuit 120, circuit 121, circuit 107 and circuit 108/1 or 108/2.
+
+All data transferred on circuit 118 during the time an ON condition is present on all of the above four circuits, where implemented, shall be transmitted by the DCE.
+
+### **4.1.2 Timing circuits**
+
+It is desirable that the transfer of timing information across the interface shall not be restricted to periods when actual transmission of data is in progress; however, during intervals when timing information is not transferred across the interface, the circuit involved should be held in the OFF condition.
+
+Accuracy and stability of the signal on circuit 115 as defined in the DCE Recommendations are required only when circuit 109 is ON. Drift during the OFF condition of circuit 109 is acceptable; however, resynchronization of the signal on circuit 115 shall be accomplished as rapidly as possible following the turning ON of circuit 109 for the next transmission as indicated in the relevant DCE Recommendation.
+
+## **4.2 Control and indication circuits**
+
+### **4.2.1 Operation of circuits 107, 108/1 and 108/2**
+
+#### **4.2.1.1 In switched and leased line operations**
+
+Signals on circuit 107 are to be considered as responses to signals which initiate connection to line, e.g. circuit 108/1. However, the conditioning of a data channel, such as equalization and clamp removal, cannot be expected to have been completed when circuit 107 is turned ON.
+
+A configuration option shall be provided within the DCE to select either circuit 108/1 or circuit 108/2 operation.
+
+Under certain test conditions, both the DTE and the DCE may exercise some of the interchange circuits. Thus, when circuits 107, 108/1 or 108/2 are both OFF, the DTE is to ignore the conditions on all other interchange circuits from the DCE, except those on circuit 125 and the timing circuits, and the DCE is to ignore the conditions on all other interchange circuits from the DTE.
+
+During the maintenance phases specified in Recommendation V.54, when the DTE is not involved in the test, circuit 142 is in the ON condition and circuit 107 is in the OFF condition. Circuit 107 shall not respond to circuits 108/1 or 108/2. When the DTE is involved in the test, circuit 142 is in the ON condition and circuit 107 shall respond to circuit 108/1 or 108/2.
+
+#### **4.2.1.2 In leased line operations**
+
+Where circuit 108 is not implemented in the DTE, the condition on this circuit is assumed to be permanently ON.
+
+Where circuit 108 is implemented in the DTE, it shall be implemented as circuit 108/1.
+
+#### **4.2.1.3 In switched line operations**
+
+When the DCE is conditioned for automatic answering of calls, answering of incoming calls occurs only in response to a combination of the calling signal and an ON condition of circuit 108/1 or 108/2.
+
+The OFF condition of circuit 108/1 or 108/2 shall not disable the operation of circuit 125.
+
+When circuit 108/2 is in the ON condition and circuit 107 is in the OFF condition, the DTE may communicate with serial automatic calling DCEs on circuits 103 and 104. This state is recognized by an ON condition on circuit 106.
+
+When circuit 108/1 or 108/2 is turned OFF, it shall not be turned ON again until circuit 107 is turned OFF.
+
+In the case where the DCE turns circuit 107 OFF first, the DTE shall consider the call aborted and shall proceed as described below:
+
+- 1) In the case of circuit 108/1, the DTE shall turn this circuit OFF with minimal delay and shall hold the circuit in the OFF condition for a minimum of 500 ms. After that period of time, the DTE may turn circuit 108/1 back ON either to initiate a new direct call or to respond to an incoming call signalled by circuit 125 coming ON.
+
+The DCE shall not answer an incoming call or initiate a new call until circuit 108/1 has first been turned OFF and then back ON again.
+
+- 2) In the case of circuit 108/2, the DTE shall turn this circuit OFF with minimal delay and shall hold the circuit in the OFF condition for a minimum of 500 ms. After that period of time, the DTE may turn circuit 108/2 back ON either to initiate a new serial automatic calling procedure or to signal the DCE that it is prepared to accept an incoming call.
+
+The DCE shall answer an incoming call or initiate a new call until circuit 108/2 has been turned OFF and then back ON again or after a minimum delay (provisional value 2 s).
+
+#### **4.2.2 Circuit 125 – Calling indicator**
+
+The operation of circuit 125 shall not be impaired or disabled by any condition on any other interchange circuit.
+
+#### **4.2.3 Usage of circuit 126**
+
+Originally, this circuit was defined for operational control of a 2-wire, frequency-divided duplex DCE, such as the Recommendation V.21-type modem. Transmitter and receiver control were separated, so that local testing of both data channels might be performed as national Administrations required.
+
+The modem according to Recommendation V.21 selects the transmit and receive frequencies according to the condition of circuit 125 in switched network operation.
+
+However, the use of circuit 126 may become necessary in certain types of non-centralized multipoint operation, as specified in the relevant DCE Recommendation.
+
+### **4.2.4 Circuit 140 – Loopback/Maintenance Test**
+
+#### **4.2.4.1 Usage of circuit 140**
+
+Circuit 140 can be used in conjunction with coded commands on circuit 103 in accordance with the provisions of Recommendation V.54.
+
+In systems not including the use of circuit 103, i.e. no coded commands, circuit 140 controls only the remote loopback (loop 2).
+
+In systems that involve the use of circuit 103, additional maintenance applications of circuit 140 are possible. These additional applications remain for further study.
+
+#### **4.2.4.2 Interrelationship of circuits 105, 106 and 140**
+
+For automatic control of loop 2 test, circuit 106 is under the control of circuit 140 and circuit 105 is disregarded by the DCE.
+
+## **4.3 Miscellaneous**
+
+### **4.3.1 Interrelationship of circuits 103, 105 and 106**
+
+The DTE signals its intent to transmit data by turning ON circuit 105. It is then the responsibility of the DCE to enter the transmit mode, i.e. be prepared to transmit data, and also to alert the remote DCE and condition it to receive data. The means by which a DCE enters the transmit mode and alerts and conditions the remote DCE are described in the appropriate DCE Recommendation.
+
+When the transmitting DCE turns circuit 106 ON with circuit 107 in the ON condition, the DTE is permitted to transfer data across the interface on circuit 103. By turning ON circuit 106 with circuit 107 ON, it is implied that all data transferred across the interface prior to the time that any one of the four circuits (105, 106, 107 and 108/1 or 108/2) is again turned OFF, will be transferred to the line; however, the ON condition of circuit 106 is not necessarily a guarantee that the remote DCE is in the receive mode. (Depending on the complexity and sophistication of the transmitting signal converter, there may be a delay ranging from less than a millisecond up to several seconds between the time a bit is transferred across the interface until the time a signal element representing this bit is transmitted on the line.)
+
+When the transmitting DCE turns circuit 106 ON, with circuit 107 in the OFF condition, the DTE is permitted to transfer programming or control signals to a serial automatic calling DCE across the interface on circuit 103.
+
+During data transfer, the DTE shall not turn circuit 105 OFF before the end of the last bit (data bit or stop element) is transferred across the interface on circuit 103. Similarly, in certain duplex switched network applications where circuit 105 is not implemented (see the specific DCE Recommendations), this requirement applies equally when circuit 108/1 or 108/2 is turned OFF to terminate a switched network call.
+
+Where circuit 105 is provided, the ON and OFF conditions on circuit 106 during the data transfer phase (i.e. circuit 107 ON) shall be responses to the ON and OFF conditions on circuit 105. Circuit 106 may, however, be turned OFF during the data transfer and test phases independent of the condition of circuit 105 to signal the DTE to interrupt the transfer of data on circuit 103 *transmitted data*, for a finite period of time (e.g. for DCE flow control purposes or DCE/DCE resynchronization). It should be noted that data presented on circuit 103 after circuit 106 turns OFF may be disregarded by the DCE. It should also be noted that circuit 106 may be turned back ON again at any time, provided that circuit 105 is ON at that time. For the appropriate response times of circuit 106, and for the operation of circuit 106 when circuit 105 is not provided, refer to the relevant Recommendation for the DCE.
+
+For serial automatic calling DCEs, the ON and OFF conditions on circuit 106 outside the data transfer phase (i.e. circuit 107 OFF) shall be dependent on the interface state during the automatic call set-up and associated procedures. The transitions on circuit 106 for this application shall be as detailed in Recommendation V.25 *bis*.
+
+When circuit 105 and circuit 106 are both OFF, the DTE shall maintain a binary 1 condition on circuit 103. When circuit 105 is turned OFF it shall not be turned ON again until circuit 106 is turned OFF by the DCE.
+
+NOTE – These conditions also apply to the relationship between circuits 120, 121 and 118.
+
+### **4.3.2 Idle periods**
+
+During intervals when circuit 105 and circuit 106 are in the ON condition and no data are available for transmission, the DTE may transmit binary 1 condition, reversals or other sequences to maintain timing synchronizing, e.g. SYN coded characters, idle characters according to the data link control procedure used, etc.
+
+Specific requirements, where applicable, are stated in the appropriate DCE Recommendations.
+
+### **4.3.3 Clamping**
+
+**4.3.3.1** In all applications the DCE shall hold, where implemented:
+
+- a) circuit 104 in the binary 1 condition when circuit 109 is in the OFF condition; and
+- b) circuit 119 in the binary 1 condition when circuit 122 is in the OFF condition.
+
+**4.3.3.2** In addition, a DCE constrained to half-duplex operation on a 2-wire line shall also hold, where implemented:
+
+- a) circuit 104 in the binary 1 condition and circuit 109 in the OFF condition when circuit 105 is in the ON condition, and for a short time interval (to be specified in Recommendations for DCE) following the ON to OFF transition on circuit 105; and
+- b) circuit 119 in the binary 1 condition and circuit 122 in the OFF condition, when circuit 120 is in the ON condition, and for a short time interval (to be specified in Recommendations for DCE) following the ON to OFF transition on circuit 120.
+
+## **4.4 Circuit failures (electrical)**
+
+A failure condition on one of the following interchange circuits, where implemented, shall be used to detect either a power-off condition in the equipment connected through the interface or the disconnection of the interconnecting cable:
+
+- Circuit 105 – Request to send
+- Circuit 107 – Data set ready
+- Circuit 108/1 – Connect data set to line
+- Circuit 108/2 – Data terminal ready
+- Circuit 120 – Transmit backward channel line signal
+
+The criteria used to determine a failure condition shall be specified in the appropriate Recommendation for electrical characteristics.
+
+The receivers for these circuits shall interpret the power-off condition or the disconnection of the interconnecting cable as an OFF condition on these circuits.
+
+## **4.5 Provision of interchange circuits in DCEs and DTEs**
+
+In some DCE Recommendations optional facilities are defined which require control from the DTE via dedicated circuits. Where the DTE does not provide the respective circuits, these optional facilities cannot be used. The DCE should provide means to disable an option, when necessary, in case the DTE is not equipped with circuitry to control this option. On the other hand, in case the DCE does not provide an option, proper operation of the DTE should not rely on any specific response from the DCE when the DTE activates the control circuit related to that option.
+
+Receiver circuits may be provided in a DTE or a DCE for which no generator is provided in the complementary equipment. Therefore, in cases where a receiver is not connected to a generator, it is suggested that means be provided in the equipment where the receiver is located to inhibit or disregard any possible false triggering of this receiver.
+
+## **4.6 Data flow control**
+
+Some DTE and DCE functionalities rely on the presence of a data flow control mechanism between the DTE and the DCE. Methods for data flow control are described in detail in [9].
+
+## **4.7 Power-up considerations**
+
+During a power-up condition of a DTE or a DCE, the behaviour at the interface towards the complementary equipment is unpredictable. For a short period of time conditions may be assumed that are illegal under normal operational conditions. DTEs and DCEs should therefore be tolerant to illegal conditions and return to normal operation when the illegal condition terminates.
+
+# **5 References**
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published.
+
+- [1] ITU-T Recommendation V.10 (1993), *Electrical characteristics for unbalanced double-current interchange circuits operating at data signalling rates nominally up to 100 kbit/s.*
+
+- [2] ITU-T Recommendation V.11 (1996), *Electrical characteristics for balanced double-current interchange circuits operating at data signalling rates up to 10 Mbit/s.*
+- [3] ITU-T Recommendation V.12 (1995), *Electrical characteristics for balanced double-current interchange circuits for interfaces with data signalling rates up to 52 Mbit/s.*
+- [4] ITU-T Recommendation V.25 (1996), *Automatic answering equipment and general procedures for automatic calling equipment on the general switched telephone network including procedures for disabling of echo control devices for both manually and automatically established calls.*
+- [5] ITU-T Recommendation V.25 bis (1996), *Synchronous and asynchronous automatic dialling procedures on switched networks.*
+- [6] ITU-T Recommendation V.28 (1993), *Electrical characteristics for unbalanced double-current interchange circuits.*
+- [7] CCITT Recommendation V.31 (1972), *Electrical characteristics for single-current interchange circuits controlled by contact closure.*
+- [8] CCITT Recommendation V.31 bis (1984), *Electrical characteristics for single-current interchange circuits using optocouplers.*
+- [9] ITU-T Recommendation V.43 (1998), *Data flow control.*
+- [10] ISO 2110:1989, *Information technology – Data communication – 25-pole DTE/DCE interface connector and contact number assignments.*
+- [11] ISO 4902:1989, *Information technology – Data communication – 37-pole DTE/DCE interface connector and contact number assignments.*
+- [12] ISO/IEC 11569:1993, *Information technology – Telecommunications and information exchange between systems – 26-pole interface connector mateability dimensions and contact number assignments.*
+- [13] ISO/IEC 13575:1995, *Information technology – Telecommunications and information exchange between systems – 50-pole interface connector mateability dimensions and contact number assignments.*
+
+
+
+# ITU-T RECOMMENDATIONS SERIES
+
+| | |
+|-----------------|--------------------------------------------------------------------------------------------------------------------------------|
+| Series A | Organization of the work of the ITU-T |
+| Series B | Means of expression: definitions, symbols, classification |
+| Series C | General telecommunication statistics |
+| Series D | General tariff principles |
+| Series E | Overall network operation, telephone service, service operation and human factors |
+| Series F | Non-telephone telecommunication services |
+| Series G | Transmission systems and media, digital systems and networks |
+| Series H | Audiovisual and multimedia systems |
+| Series I | Integrated services digital network |
+| Series J | Transmission of television, sound programme and other multimedia signals |
+| Series K | Protection against interference |
+| Series L | Construction, installation and protection of cables and other elements of outside plant |
+| Series M | TMN and network maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits |
+| Series N | Maintenance: international sound programme and television transmission circuits |
+| Series O | Specifications of measuring equipment |
+| Series P | Telephone transmission quality, telephone installations, local line networks |
+| Series Q | Switching and signalling |
+| Series R | Telegraph transmission |
+| Series S | Telegraph services terminal equipment |
+| Series T | Terminals for telematic services |
+| Series U | Telegraph switching |
+| Series V | Data communication over the telephone network |
+| Series X | Data networks and open system communications |
+| Series Y | Global information infrastructure and Internet protocol aspects |
+| Series Z | Languages and general software aspects for telecommunication systems |
\ No newline at end of file
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+
+
+
+
+ITU logo: a globe with the letters ITU and a lightning bolt symbol.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+# ITU-T
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+# V.25
+
+(10/96)
+
+SERIES V: DATA COMMUNICATION OVER THE
+TELEPHONE NETWORK
+
+Interfaces and voiceband modems
+
+---
+
+**Automatic answering equipment and general procedures for automatic calling equipment on the general switched telephone network including procedures for disabling of echo control devices for both manually and automatically established calls**
+
+ITU-T Recommendation V.25
+
+(Previously CCITT Recommendation)
+
+---
+
+# ITU-T V-SERIES RECOMMENDATIONS DATA COMMUNICATION OVER THE TELEPHONE NETWORK
+
+- | |
+|--------------------------------------------|
+| 1 – General |
+| 2 – Interfaces and voiceband modems |
+| 3 – Wideband modems |
+| 4 – Error control |
+| 5 – Transmission quality and maintenance |
+| 6 – Interworking with other networks |
+
+*For further details, please refer to ITU-T List of Recommendations.*
+
+# FOREWORD
+
+The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics.
+
+The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993).
+
+ITU-T Recommendation V.25, was revised by ITU-T Study Group 14 (1993-1996) and was approved by the WTSC (Geneva, October 9-18, 1996).
+
+## --- NOTES
+
+1. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+2. The status of annexes and appendices attached to the Series V Recommendations should be interpreted as follows:
+ - an *annex* to a Recommendation forms an integral part of the Recommendation;
+ - an *appendix* to a Recommendation does not form part of the Recommendation and only provides some complementary explanation or information specific to that Recommendation.
+
+© ITU 1997
+
+All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU.
+
+# CONTENTS
+
+| | Page |
+|--------------------------------------------------------------------------------------|-------------|
+| 1 Scope ..... | 1 |
+| 2 Abbreviations and definitions ..... | 2 |
+| 3 Interface procedures at call-originating data station ..... | 3 |
+| 4 Interface procedure at answering data station ..... | 6 |
+| 5 Proposed line procedures ..... | 6 |
+| 6 Manually controlled modem calling automatically controlled modem ..... | 7 |
+| 7 Automatically controlled calling modem calling manually controlled modem ..... | 7 |
+| 8 Disabling of echo suppressors in the case of manually operated data stations ..... | 8 |
+| 9 Notification to ordinary telephone users ..... | 8 |
+| 10 Manual selection of automatic answering, data mode and voice mode ..... | 8 |
+| 11 2100 Hz tone recognition ..... | 8 |
+| References ..... | 9 |
+
+# **AUTOMATIC ANSWERING EQUIPMENT AND GENERAL PROCEDURES FOR AUTOMATIC CALLING EQUIPMENT ON THE GENERAL SWITCHED TELEPHONE NETWORK INCLUDING PROCEDURES FOR DISABLING OF ECHO CONTROL DEVICES FOR BOTH MANUALLY AND AUTOMATICALLY ESTABLISHED CALLS**
+
+*(Mar del Plata, 1968; amended at Geneva, 1972 and 1976;
+revised at Malaga-Torremolinos in 1984 and at Geneva in 1996)*
+
+## **1 Scope**
+
+**1.1** This Recommendation is concerned with the setting-up of a data connection when Data Circuit-terminating Equipment (DCE) comprising automatic answering equipment is used over international circuits. Automatic calling procedures are defined in Recommendations V.25 *bis* and V.25 *ter*.
+
+NOTE – Up to and including the 1988 (*Blue Book*) version, this Recommendation, in addition to what is outlined herein, specified parallel automatic calling equipment using the 200-Series interchange circuits defined in Recommendation V.24, and an associated automatic call set-up protocol. It is the opinion of the ITU-T that both this type of equipment and the associated protocol are out of date, and that more modern techniques and protocols are specified in Recommendations V.25 *bis* and V.25 *ter*. It is therefore not recommended to use this technique for new designs.
+
+Automatic answering equipment used within any single Member's area or between two Members by bilateral agreement is not necessarily constrained by the procedures specified herein. In particular, the use of the 2100 Hz answering tone, as described in this Recommendation, could be substituted by another tone when the equipment is used over circuits not equipped with echo control devices. Similarly, the calling tone could be omitted by bilateral agreements, but attention is drawn to clauses 7 and 8 below.
+
+In addition, the provisions for echo canceller disabling and for a "calling station response" prior to the termination of the answer tone are optional and only applicable to Data Circuit-terminating Equipment (DCE) for which the relevant V-Series Recommendation specifically calls for such provision(s).
+
+**1.2** This Recommendation describes the sequence of events involved in establishing a connection between an automatic calling data station1) and an automatic answering data station for V-Series Recommendations modems specified for general switched telephone network operations.
+
+Consideration is given only to:
+
+- a) the events which affect the interfaces between the data terminal equipment and the data circuit-terminating equipment at the answering data station; and
+- b) the events on the line during establishment of a data call.
+
+Interactions within the data circuit-terminating equipment are not considered, since such consideration is unnecessary for purposes of international standardization.
+
+**1.3** The proposed procedures are intended to be suitable for four types of calls, namely:
+
+- a) automatic calling data station to automatic answering data station;
+- b) manual calling data station to automatic answering data station;
+- c) automatic calling data station to manual answering data station;
+- d) disabling of echo suppressors in the case of manual calling data stations.
+
+---
+
+1) In this Recommendation, the term "data station" is synonymous with the term "terminal installation for data transmission" [1].
+
+- 1.4** The data terminal equipment is responsible for:
+- a) during call establishment:
+ - i) ensuring that the data circuit-terminating equipment is available for operation;
+ - ii) providing the telephone number;
+ - iii) deciding to abandon the call if it is unsuccessfully completed;
+ - b) after call is established:
+ - i) establishing identities;
+ - ii) exchanging such traffic as is appropriate;
+ - iii) initiating disconnect at calling and answering station.
+
+## **2 Abbreviations and definitions**
+
+The following abbreviations are used in this Recommendation:
+
+DCE Data Circuit-terminating Equipment
+DTE Data Terminal Equipment
+
+The following definitions apply to this Recommendation:
+
+**2.1 calling tone:** The tone transmitted from the calling end. The calling tone consists of a series of interrupted 1300 Hz $\pm$ 15 Hz signals (bursts). ON for a duration of not less than 0.5 s and not more than 0.7 s and OFF for a duration of not less than 1.5 s and not more than 2.0 s.2) 3)
+
+**2.2 answering tone:** The tone transmitted from the called end.
+
+NOTES
+
+1 – The answering tone is an uninterrupted 2100 $\pm$ 15 Hz tone with a duration, except when truncated as described in 4.3, of 3.3 $\pm$ 0.7 s.
+
+2 – Recommendation V.8 specifies, for the purpose of starting sessions of data transmission, an amplitude modulated answering tone, ANSam.
+
+**2.3 phase reversals:** Reversals ( $180^\circ$ ) in the phase of the answering tone at intervals of 425 to 475 ms. The reversal in phase shall be accomplished such that the phase is within $180 \pm 10$ degrees in 1 ms, and that the amplitude of the answering tone is not more than 3 dB below its steady state value for more than 400 $\mu s$ .
+
+**2.4 starting signal:** Binary 1, synchronizing signal or equalizer training signal, as specified in the relevant V-Series Recommendation.4)
+
+**2.5 calling station response:** A tone or signal transmitted from the calling DCE in response to its detection, as defined in this Recommendation, of answering tone.4), 5), 6)
+
+**2.6 automatic calling:** A procedure by which a DTE, by use of V.24 interchange circuits, may instruct a DCE to perform the call establishment function. The transmission, from DTE to DCE, of each digit to be dialled is achieved on interchange circuit 103 (see Recommendations V.25 *bis* and V.25 *ter*).
+
+---
+
+2) The calling tone and calling station response should not contain power in the band 2100 $\pm$ 250 Hz.
+
+3) The power levels of the signals specified in this Recommendation shall conform to the levels specified in Recommendation V.2.
+
+4) The calling tone and calling station response should not contain power in the band 2100 $\pm$ 250 Hz.
+
+5) The power levels of the signals specified in this Recommendation shall conform to the levels specified in Recommendation V.2.
+
+6) The specification of the calling station response and the timing of its transmission are the subject of the individual V-Series Recommendation for the DCE involved. The specifications in this Recommendation cover only limitations on its transmission during call establishment.
+
+## 3 Interface procedures at call-originating data station
+
+The description of the complete interface procedures for call initiation at a call-originating data station is not part of this Recommendation. Details may be found in Recommendations V.25 *bis* and V.25 *ter*.
+
+### Event
+
+**3.1** The DTE instructs the DCE to establish a call, and specifies the number to be dialled. Subsequently, circuit 108/2 is in the ON condition (circuit 108/2 may be turned in the ON condition at any time up to and including event 3.6).
+
+**3.2** For half-duplex modems, DTE puts circuit 105 ON if the calling end wishes to transmit first. Circuit 105 can be placed ON at any time up to and including event 3.10.
+
+**3.3** The DCE goes “off-hook”.
+
+**3.4** The telephone system puts dial tone on line.7)
+
+**3.5** The DCE dials the wanted telephone number.
+
+**3.6** The DTE turns circuit 108/2 ON, if not previously ON.
+
+**3.7** If implemented, the DCE transmits the interrupted calling tone to line, as shown in Figures 1, 2 and 3.
+
+
+
+The diagram illustrates the timing of line signals during a call initiation sequence. It features two main horizontal timelines. The top timeline shows a 'Calling tone' (represented by a rectangle) with a duration of 0.5-0.7 s, followed by a 1.5-2 s interval, and then another 'Calling tone' (rectangle) with a duration of 0.5-0.7 s. The bottom timeline shows an 'Answering tone 2100 Hz' (represented by a long rectangle) with a total duration of $3.3 \pm 0.7$ s. This answering tone is divided into segments: 0.4 s, 0.9 s, 0.1-0.6 s, and a 'Tolerance' of $75 \pm 20$ ms. A box labeled 'DCE under control of the DTE, CT 107 ON' is connected to the end of the answering tone. Below the timelines, four boxes provide context for the time intervals: 'Not sufficient to disable echo suppressors' (pointing to the first 0.4 s segment), 'Network interaction time' (pointing to the 0.9 s segment), '2100 Hz detection time' (pointing to the 0.1-0.6 s segment), and 'Gap for recognizing the end of the 2100 Hz answering tone' (pointing to the tolerance segment). A reference code 'T1403050-97/d01' is located at the bottom right of the diagram.
+
+Timing diagram for line signals showing calling and answering tones with various time intervals and annotations.
+
+FIGURE 1/V.25
+Timing of line signals
+
+7) Some countries apply the second dial tone to the line after the initial digit is transferred.
+
+
+
+Calling tone burst truncateda)
+
+≥ 400 ms
+
+Timing at calling data station
+
+Calling tone burst
+
+Calling station response
+
+ANS detected for ≥ 100 ms
+
+DCE under control of the DTE, CT 107 ONb)
+
+ANSc)
+
+Calling station response detected for ≥ 100 ms
+
+Answering
+data station
+connected
+to line
+
+Timing at answering data station
+
+1.8-2.5 s Silent interval
+
+≤ 4.0 sd)
+
+75 ± 20 ms
+
+T1403060-97/d02
+
+Timing diagram for optional calling station response. The diagram shows the sequence of events between a calling data station and an answering data station. At the top, a 'Calling tone burst truncated' is shown with a duration of ≥ 400 ms. Below this, the 'Calling station response' is shown. A vertical line indicates 'ANS detected for ≥ 100 ms'. The 'ANS' (answer tone) is shown as a horizontal bar with a duration of ≤ 4.0 s. The 'ANS' is preceded by a 'Silent interval' of 1.8-2.5 s. The 'ANS' is followed by an 'Answer modem line signal' with a duration of 75 ± 20 ms. The diagram also shows the 'Calling station response detected for ≥ 100 ms' and the 'ANS' detected for ≥ 100 ms. The diagram is labeled 'Timing at calling data station' and 'Timing at answering data station'. A vertical line on the right indicates 'DCE under control of the DTE, CT 107 ON'. The diagram is labeled 'T1403060-97/d02'.
+
+- a) If ANS is detected during a calling tone burst, the burst may be truncated. If it is not truncated, the calling station response must be delayed until at least 400 ms after the end of the burst.
+- b) See 3.10 for exception.
+- c) ANS denotes the answer tone.
+- d) If a calling station response is not received, the answer tone shall continue for $3.3 \pm 0.7$ seconds.
+
+FIGURE 2/V.25
+
+### Timing of line signals – Optional calling station response
+
+- 3.8** a) If the call is answered by a data station, then the answering tone is received by the calling DCE. Echo suppressors and echo cancellers are disabled during coincidence of a silent period in the interrupted calling tone (event 3.7) with the answering tone. The answering tone shall not activate circuits 104 and 109.
+- b) The subsequent action of the DCE and the DTE if no answering tone is detected is beyond the scope of this Recommendation. Details may be found in Recommendations V.25 *bis* and V.25 *ter*.
+
+**3.9** When an answering tone has been received by the DCE for a period of 100 to 600 ms, the interrupted calling tone is discontinued by the DCE as shown in Figures 1, 2 and 3. The DCE transfers control of the connection to circuit 108/2.
+
+
+
+FIGURE 3/V.25
+**Timing of line signals, optional provision for echo canceller disabling
+and for calling station response**
+
+The diagram shows two horizontal timelines: 'Timing at calling data station' and 'Timing at answering data station'.
+
+- Calling station:** Shows a 'Calling tone burst' which can be truncated. After a delay of ≥ 1 s from the end of the burst, the 'Calling station response' begins. This response is under control of the DTE, with CT 107 ON.
+- Answering station:** Starts with a 'Silent interval' of 1.8-2.5 s. This is followed by ANS (answer tone) for a duration τ, then ANS (phase reversed answer tone) for duration τ, where τ = 450 ± 25 ms. A second ANS segment follows. The total duration of these tones is ≤ 4.0 s.
+- Interactions:** ANS is detected by the calling station for ≥ 100 ms. The calling station response is detected by the answering station for ≥ 100 ms. After the calling station response is detected, the answering station waits for a period ≤ τ before switching to 'Answer modem line signal' after a final delay of 75 ± 20 ms.
+
+a) If ANS is detected during a calling tone burst, the burst may be truncated. If it is not truncated, the calling station response must be delayed until at least 1 second after the end of the burst.
+b) See 3.10 for exception.
+c) ANS denotes the answer tone. ANS denotes the answer tone with its phase reversed.
+d) The answer tone duration must be at least 2.6 seconds if a calling station response is not received.
+
+Timing diagram of line signals for echo canceller disabling and calling station response.
+
+The DCE may, as shown in Figures 2 and 3, transmit the calling station response following the detection of a continuation of the answering tone for a period of at least 400 ms after the transmission of the calling tone is terminated. As indicated in Figure 3, the required duration (≥ 1 s) of the continuous 2100 Hz period, which must follow the termination of the calling tone, is longer if the answering tone includes phase reversals to disable echo cancellers.
+
+**3.10** The DCE examines the line to determine the end of the answering tone. The DCE detects an absence of the answering tone for 75 ± 20 ms, and then turns circuit 107 ON:8)
+
+- i) If circuit 105 is ON, the starting signal is put on the line. After its delay as specified in the appropriate V-Series Recommendation, circuit 106 comes ON, and the DTE can then transmit data.
+- ii) If circuit 105 is OFF, the incoming starting signal is recognized, and after its delay as specified in the appropriate V-Series Recommendation, the DCE turns circuit 109 ON to allow the examination of circuit 104 by the DTE.
+- iii) For the duplex modem case, where circuit 105 is not used, the starting signal is put on the line after circuit 107 has been turned ON. The DCE then turns circuits 109 and 106 ON after a delay as specified in the appropriate V-Series Recommendation.
+
+---
+
+8) For some DCEs requiring extended training sequences, the associated V-Series Recommendation may specify that circuit 107 be turned ON at some later time, during the handshake sequence, which is more consistent with the specification in Recommendation V.24 of circuit 107.
+
+**Recommendation V.25 (10/96)** 5
+
+**3.11** The signalling between DTE and DCE to disconnect the call is outside the scope of this Recommendation. Details may be found in Recommendations V.25 *bis* and V.25 *ter*.
+
+NOTE – Where circuit 105 or circuit 120 is not implemented, the timing of circuit 106 or circuit 121 shall be related to circuit 107 and circuit 109 respectively.
+
+## **4 Interface procedure at answering data station**
+
+### **Event**
+
+**4.1** Ringing received on line. The DCE puts circuit 125 ON.
+
+**4.2** a) If circuit 108/2 is ON, the DCE goes “off-hook”.
+b) If circuit 108/1 or circuit 108/2 is OFF, the DCE waits for circuit 108/1 or circuit 108/2 to come ON, and then goes “off-hook”. If circuit 108/1 or circuit 108/2 is not turned ON by the DTE, then the call is not answered.
+
+**4.3** The DCE goes “off-hook”, maintains silence on the line for a period between 1.8 and 2.5 s, then transmits the answering tone for a certain period of time, as shown in Figures 1 and 2.
+
+Where it is intended to disable network echo cancellers [3] as well as echo suppressors [2], phase reversals shall be introduced, as indicated in Figure 3.
+
+The answering tone, with continued reversals in its phase, shall continue for $3.3 \pm 0.7$ s unless a calling station response is received, in which case the answering tone may be discontinued after detection of the response for 100 ms.
+
+For the very special application in which an automatically answering modem is permanently dedicated to receive calls only from acoustically coupled originating stations, the modem may, optionally, extend the duration of the answering tone to ten seconds to compensate for operator reaction time in placing the handset on the acoustic coupler. All other timeouts remain the same, and the protocol is as defined in clause 6. Use of the extended answering tone is restricted expressly to this unique application.
+
+**4.4** At the end of the transmission of the answering tone, the DCE shall provide a silent period for $75 \pm 20$ ms. The DCE puts circuit 107 ON after this silent period.9)
+
+## **5 Proposed line procedures**
+
+The line procedures outlined are applicable to both duplex and half-duplex modems.
+
+Systems which operate in the half-duplex mode and which employ automatic calling equipment shall determine by pre-arrangement which of the two data stations – calling or answering – shall first transmit to the other upon establishment of the data connection. As indicated in clause 3 above, the DTE at the data station which is to transmit first shall put circuit 105 ON, at the appropriate point in the call establishment sequence. For correct operation, it is necessary that the longer response times of circuits 106 and 109 as specified in the appropriate V-Series Recommendation are used during call establishment.
+
+Figures 1, 2 and 3 show the timing of line signals when automatic calling and automatic answering are employed. The sequence of operation is as follows:
+
+On completion of dialling as specified in the appropriate V-Series Recommendation or, where possible, the other end going off-hook, the DCE sends the calling tone to the answering data station.
+
+---
+
+9) For some DCEs requiring extended training sequences, the associated V-Series Recommendation may specify that circuit 107 be turned ON at some later time, during the handshake sequence, which is more consistent with the specification in Recommendation V.24 of circuit 107.
+
+1.8 to 2.5 s after the answering modem is connected to the line (i.e. circuits 125 and 108 are ON), it sends a continuous answering tone for a duration of not more than 4.0 s. If it is intended to disable network echo cancellers as well as echo suppressors, the answering modem shall transmit phase reversals (see Figure 3).
+
+The answering tone propagates towards the calling data station and, during the course of one or two interruptions between bursts of calling tone, causes any echo suppressors in the circuit to disable. If the phase reversals are included in the signal, any echo cancellers in the circuit are also disabled.
+
+The answering tone is recognized by the calling modem 100 ms to 600 ms after its arrival. The calling modem discontinues the calling tone and may transmit a calling station response.
+
+The answering modem, after detecting the calling station response, shall discontinue transmission of the answering tone and shall provide a silent interval of $75 \pm 20$ ms in its transmitted output following the discontinuance of the answering tone and shall then turn circuit 107 ON.10)
+
+The calling modem recognizes the end of the answering tone for a period of $75 \pm 20$ ms. At the end of this interval, the calling modem shall turn circuit 107 ON.
+
+To keep the echo suppressor disabled, it is necessary to ensure that following the $75 \pm 20$ ms silent period after the transmission of the answering tone from the answering modem, which serves to disable the echo suppressor or echo canceller during the silent period in the calling tone, energy is maintained as specified in Recommendation G.164 [2].
+
+During the automatic calling and answering procedures, the echo suppressors will be disabled, and the echo cancellers will be disabled if the required sequence is transmitted. If signal gaps, at the echo suppressor or canceller, exceed 100 ms at any time, e.g. during modem turn-around, they may become re-enabled. This requires that, to maintain the disabled state of echo control devices on circuits with satellite links, the answering modem resumes transmission after the $75 \pm 20$ ms silent period unless a calling station response is received prior to the silent interval and appropriately continued.
+
+## **6 Manually controlled modem calling automatically controlled modem**
+
+The procedure for establishing a call from a manually controlled modem to a modem comprising automatic answering equipment is similar to that from an automatically calling modem, except that no tone is transmitted from the calling modem until the answering modem has answered. The operator dials the required number, hears 2100 Hz returned from the answering modem and then, during the period that 2100 Hz is being received, depresses his data button to connect the modem to line. Circuit 107 comes ON at the time specified in event 3.10.
+
+Where the calling modem is acoustically coupled to the line, placement of the telephone handset on the acoustic coupler is logically equivalent to pressing a “data” button on a permanently installed modem.
+
+Satisfactory disabling of echo suppressors and echo cancellers by the answering tone, however, will require that no speech signals from the microphone at the calling data station enter the telecommunication circuit for a period of at least 1 s during the receipt of the answering tone. This may be accomplished by a handset switch or other appropriate means.
+
+## **7 Automatically controlled calling modem calling manually controlled modem**
+
+An operator answering a call from a modem comprising automatic calling equipment hears the interrupted calling tone of 0.5 to 0.7 s ON and 1.5 to 2.0 s OFF. The data button must be depressed to connect the modem to line. A period of up to 4.0 s of the answering tone is transmitted to the calling modem to disable echo suppressors and/or echo cancellers and to notify the calling modem that the connection is being established. This sequence is followed by data transmission, as required.
+
+---
+
+10) For some DCEs requiring extended training sequences, the associated V-Series Recommendation may specify that circuit 107 be put ON at some later time, during the handshake sequence, which is more consistent with the specification in Recommendation V.24 of circuit 107.
+
+## **8 Disabling of echo suppressors in the case of manually operated data stations**
+
+The procedures as described in clauses 6 and 7 above with regard to the manually operated data stations can obviously be used for disabling echo suppressors and echo cancellers when manual switching from voice conversation to data is required, which is the preferred principle of operation. Considering the type of DCE designed to be used in conjunction with manual connection set-up, it will be necessary to equip the DCE with an answering tone generator. To avoid modifying existing equipment at the data station which receives the answering tone, the following procedure may replace the operation principle of clause 6 above. The operator depresses his data button after the end of the answering tone. The modem which is to transmit the answering tone is to be agreed between the operators while still in the voice mode.
+
+Care must be exercised in cases of half-duplex modems where transmission of data is started from the data station which transmits the answering tone, to avoid mutilation of the initial data.
+
+NOTE – Where, in the half-duplex modem case, disabling of echo suppressors is not required, the answering tone need not be transmitted. However, the delay between circuit 105 and circuit 106 ON conditions should be longer than 100 ms in consideration of the echo suppressor suppression hangover time.
+
+## **9 Notification to ordinary telephone users**
+
+As both automatic calling and automatic answering data stations transmit tones to line during call establishment, a normal telephone user who becomes inadvertently connected to one will receive tone signals for a sufficient duration to indicate clearly to him that he is incorrectly connected.
+
+## **10 Manual selection of automatic answering, data mode and voice mode**
+
+It is recognized that, at the data station, means should be provided to allow the operator to select between automatic and manual answering of calls. If a call is manually answered, voice mode shall be established. Subsequent switching to the data mode shall be performed by the procedure as specified in clause 7 above.
+
+Selection of manual or automatic answering of subsequent calls shall be possible after entering the data mode. As an option, automatic answering may be arranged for all subsequent incoming calls. In this case, manual answering may still be achieved by keeping circuit 108/2 OFF to cause an audible signal to occur at the telephone instrument.
+
+The DCE shall be disconnected from the line whenever circuit 108/1 or circuit 108/2 is turned OFF by the DTE, irrespective of the means employed in establishing the connection.
+
+Procedures for switching to the voice mode between data transmission within the same call shall ensure that circuit 107 is turned OFF while in the voice mode.
+
+## **11 2100 Hz tone recognition**
+
+To protect the 2100 Hz tone detector against faulty operation resulting from interference generated by the interrupted calling tone, the detector may be inhibited during the ON periods of the calling tone.
+
+Additionally, in cases where data circuit-terminating equipment comprising automatic calling equipment is used to set up the call, the 2100 Hz detector must not respond to spurious tones which may arise from speech or service signals during call establishment. It is suggested that the answering tone detection be prevented when the 2100 Hz signal is accompanied by any other signal of comparable level within the ranges 350 Hz to 1800 Hz and 2500 Hz to 3400 Hz.
+
+NOTE – The relative inhibiting signal levels recommended for the echo suppressor disabling tone detector of Recommendation G.164 [2] are a useful guide for 2100 Hz tone detector inhibiting levels.
+
+## References
+
+- [1] CCITT Definition: “Terminal installation for data transmission” in *Terms and Definitions*, Geneva 1988.
+- [2] CCITT Recommendation G.164 (1988), *Echo suppressors*.
+- [3] ITU-T Recommendation G.165 (1993), *Echo cancellers*.
+- [4] ITU-T Recommendation V.24 (1996), *List of definitions for interchange circuits between Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE)*.
+- [5] ITU-T Recommendation V.25 bis (1996), *Synchronous and asynchronous automatic dialling procedures on switched networks*.
+- [6] ITU-T Recommendation V.25 ter (1995), *Serial asynchronous automatic dialling and control*.
+
+# ITU-T RECOMMENDATIONS SERIES
+
+| | |
+|-----------------|----------------------------------------------------------------------------------------------------------------|
+| Series A | Organization of the work of the ITU-T |
+| Series B | Means of expression |
+| Series C | General telecommunication statistics |
+| Series D | General tariff principles |
+| Series E | Telephone network and ISDN |
+| Series F | Non-telephone telecommunication services |
+| Series G | Transmission systems and media |
+| Series H | Transmission of non-telephone signals |
+| Series I | Integrated services digital network |
+| Series J | Transmission of sound-programme and television signals |
+| Series K | Protection against interference |
+| Series L | Construction, installation and protection of cables and other elements of outside plant |
+| Series M | Maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits |
+| Series N | Maintenance: international sound-programme and television transmission circuits |
+| Series O | Specifications of measuring equipment |
+| Series P | Telephone transmission quality |
+| Series Q | Switching and signalling |
+| Series R | Telegraph transmission |
+| Series S | Telegraph services terminal equipment |
+| Series T | Terminal equipments and protocols for telematic services |
+| Series U | Telegraph switching |
+| Series V | Data communication over the telephone network |
+| Series X | Data networks and open system communication |
+| Series Z | Programming languages |
\ No newline at end of file
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+
+
+
+
+ITU logo: a globe with the letters ITU inside, and a lightning bolt striking the globe.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+# ITU-T
+
+TELECOMMUNICATION
+STANDARDIZATION SECTOR
+OF ITU
+
+# V.250
+
+(07/2003)
+
+SERIES V: DATA COMMUNICATION OVER THE
+TELEPHONE NETWORK
+
+Control procedures
+
+---
+
+**Serial asynchronous automatic dialling and
+control**
+
+ITU-T Recommendation V.250
+
+---
+
+# ITU-T V-SERIES RECOMMENDATIONS DATA COMMUNICATION OVER THE TELEPHONE NETWORK
+
+| | |
+|-------------------------------------------------------|--------------------|
+| General | V.1–V.9 |
+| Interfaces and voiceband modems | V.10–V.34 |
+| Wideband modems | V.35–V.39 |
+| Error control | V.40–V.49 |
+| Transmission quality and maintenance | V.50–V.59 |
+| Simultaneous transmission of data and other signals | V.60–V.99 |
+| Interworking with other networks | V.100–V.199 |
+| Interface layer specifications for data communication | V.200–V.249 |
+| Control procedures | V.250–V.299 |
+| Modems on digital circuits | V.300–V.399 |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+# ITU-T Recommendation V.250
+
+# Serial asynchronous automatic dialling and control
+
+## Summary
+
+This version of ITU-T Rec. V.250 integrates Amendment 1 (07/2001), Amendment 2 (03/2002) and Amendment 3 (07/2003) with the 05/1999 version of the Recommendation.
+
+This Recommendation defines commands and responses for use by a DTE to control a V-series DCE using serial data interchange over an asynchronous interface. It contains four elements:
+
+- codifies existing practice in common GSTN-DCE that use the ATtention (AT) command set;
+- defines a format for orderly extension of the AT command set;
+- provides a set for standardized extensions for common functions to identify the DCE, to control the DTE-DCE interface, and to control DCE-DCE protocols (signal conversion, error control and data compression);
+- provides a mapping for these commands into V.25 *bis* frame format for use with DCEs employing synchronous serial interfaces.
+
+## Source
+
+ITU-T Recommendation V.250 was approved on 14 July 2003 by ITU-T Study Group 16 (2001-2004) under the ITU-T Recommendation A.8 procedure.
+
+## Keywords
+
+AT Commands, data modems, data transmission, DCE control.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis.
+
+The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics.
+
+The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1.
+
+In some areas of information technology which fall within ITU-T's purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
+
+## NOTE
+
+In this Recommendation, the expression "Administration" is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words "shall" or some other obligatory language such as "must" and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party.
+
+## INTELLECTUAL PROPERTY RIGHTS
+
+ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process.
+
+As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database.
+
+© ITU 2004
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+# CONTENTS
+
+| | Page |
+|---------------------------------------------------------------------------------------------|-------------|
+| 1 Introduction and scope..... | 1 |
+| 2 References..... | 1 |
+| 2.1 Normative references..... | 1 |
+| 2.2 Informative references..... | 2 |
+| 3 Definitions and abbreviations ..... | 3 |
+| 3.1 Definitions ..... | 3 |
+| 3.2 Abbreviations ..... | 4 |
+| 4 Physical layer..... | 4 |
+| 4.1 Circuits ..... | 4 |
+| 4.2 Character formatting..... | 5 |
+| 4.3 Data rates ..... | 5 |
+| 5 Syntax and procedures ..... | 5 |
+| 5.1 Alphabet ..... | 5 |
+| 5.2 DTE commands lines ..... | 6 |
+| 5.3 Basic Syntax commands..... | 7 |
+| 5.4 Extended Syntax commands..... | 8 |
+| 5.5 Issuing commands ..... | 12 |
+| 5.6 Executing commands..... | 12 |
+| 5.7 DCE responses..... | 13 |
+| 5.8 Manufacturer-specific characteristics..... | 16 |
+| 6 Functions ..... | 17 |
+| 6.1 Generic DCE control ..... | 18 |
+| 6.2 DTE-DCE interface commands..... | 25 |
+| 6.3 Call control ..... | 37 |
+| 6.4 Modulation control commands..... | 48 |
+| 6.5 Error control commands ..... | 60 |
+| 6.6 Data compression commands ..... | 68 |
+| 6.7 DCE testing ..... | 73 |
+| 6.8 PCM DCE commands ..... | 85 |
+| 6.9 V.59 Command (+TMO)..... | 91 |
+| Appendix I – Summary of basic and extended format commands ..... | 93 |
+| Appendix II – DCE configuration, dialling, negotiation and reporting, example session ..... | 95 |
+| Appendix III – Encapsulation of V.250 messages in V.25 bis DCE ..... | 96 |
+| III.1 Scope ..... | 96 |
+| III.2 Encapsulation of V.250 messages ..... | 96 |
+| III.3 Applicable V.250 commands ..... | 96 |
+| III.4 Applicable V.250 responses ..... | 97 |
+
+
+
+# ITU-T Recommendation V.250
+
+# Serial asynchronous automatic dialling and control
+
+# 1 Introduction and scope
+
+This Recommendation is applicable to the interconnection of Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE) employing serial binary data operation via the ITU-T Recs V.100-series interchange circuits.
+
+This Recommendation contains four elements:
+
+- codifies existing practice in common Asynchronous GSTN-DCE that use the ATtention (AT) command set. It identifies the protocol elements, procedures, and behaviours that were found to be held in common among a large portion of DCE manufacturers. It is intended, as much as possible, to preserve compatibility between DCEs and DTEs. Most DCEs implement a number of extensions and behavioural differences beyond the descriptions in this Recommendation; such extensions and differences are explicitly permitted by this Recommendation (see 5.8);
+- defines a format for extension of the AT command set in an orderly fashion. It reserves the "+" command prefix to be used by other standardized extensions, such as those found in ITU-T Recs T.31 and T.32 (Asynchronous Facsimile DCE Control);
+- provides a set of standardized extensions, based on the extended "+" command format. These commands identify the DCE, control the DTE-DCE interface, and control DCE-DCE protocol behaviour (signal conversion, error control and data compression);
+- provides a mapping of the commands defined in this Recommendation into V.25 *bis* frame format for use with DCEs employing synchronous serial interfaces. See Appendix III.
+
+The procedures described for automatic calling equipment conforming to this Recommendation allow interworking with automatic answering equipment conforming to ITU-T Recs V.25 and V.25 *bis*.
+
+# 2 References
+
+## 2.1 Normative references
+
+The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation.
+
+- ITU-T Recommendation Q.23 (1988), *Technical features of push-button telephone sets*.
+- ITU-T Recommendation T.50 (1992), *International Reference Alphabet (IRA) (Formerly International Alphabet No. 5 or IA5) – Information technology – 7-bit coded character set for information interchange*.
+- ITU-T Recommendation V.4 (1988), *General structure of signals of International Alphabet No. 5 code for character oriented data transmission over public telephone networks*.
+- ITU-T Recommendation V.8 *bis* (2000), *Procedures for the identification and selection of common modes of operation between data circuit-terminating equipments (DCEs) and*
+
+*between data terminal equipments (DTEs) over the public switched telephone network and on leased point-to-point telephone-type circuits.*
+
+- ITU-T Recommendation V.24 (2000), *List of definitions for interchange circuits between data terminal equipment (DTE) and data circuit-terminating equipment (DCE).*
+- ITU-T Recommendation V.25 (1996), *Automatic answering equipment and general procedures for automatic calling equipment on the general switched telephone network including procedures for disabling of echo control devices for both manually and automatically established calls.*
+
+Other relevant Recommendations are listed in the Supplement 1 to this Recommendation.
+
+## **2.2 Informative references**
+
+- ITU-T Recommendation T.31 (1995), *Asynchronous facsimile DCE control – Service Class 1.*
+- ITU-T Recommendation T.32 (1995), *Asynchronous facsimile DCE control – Service Class 2.*
+- ITU-T Recommendation V.8 (2000), *Procedures for starting sessions of data transmission over the public switched telephone network.*
+- ITU-T Recommendation V.14 (1993), *Transmission of start-stop characters over synchronous bearer channels.*
+- ITU-T Recommendation V.18 (2000), *Operational and interworking requirements for DCEs operating in the text telephone mode.*
+- ITU-T Recommendation V.21 (1988), *300 bits per second duplex modem standardized for use in the general switched telephone network.*
+- ITU-T Recommendation V.22 (1988), *1200 bits per second duplex modem standardized for use in the general switched telephone network and on point-to-point 2-wire leased telephone-type circuits.*
+- ITU-T Recommendation V.22 bis (1988), *2400 bits per second duplex modem using the frequency division technique standardized for use on the general switched telephone network and on point-to-point 2-wire leased telephone-type circuits.*
+- ITU-T Recommendation V.23 (1988), *600/1200-baud modem standardized for use in the general switched telephone network.*
+- ITU-T Recommendation V.26 bis (1988), *2400/1200 bits per second modem standardized for use in the general switched telephone network.*
+- ITU-T Recommendation V.26 ter (1988), *2400 bits per second duplex modem using the echo cancellation technique standardized for use on the general switched telephone network and on point-to-point 2-wire leased telephone-type circuits.*
+- ITU-T Recommendation V.27 ter (1988), *4800/2400 bits per second modem standardized for use in the general switched telephone network.*
+- ITU-T Recommendation V.32 (1993), *A family of 2-wire, duplex modems operating at data signalling rates of up to 9600 bit/s for use on the general switched telephone network and on leased telephone-type circuits.*
+- ITU-T Recommendation V.32 bis (1991), *A duplex modem operating at data signalling rates of up to 14 400 bit/s for use on the general switched telephone network and on leased point-to-point 2-wire telephone-type circuits.*
+
+- ITU-T Recommendation V.34 (1998), *A modem operating at data signalling rates of up to 33 600 bit/s for use on the general switched telephone network and on leased point-to-point 2-wire telephone-type circuits.*
+- ITU-T Recommendation V.42 (2002), *Error-correcting procedures for DCEs using asynchronous-to-synchronous conversion.*
+- ITU-T Recommendation V.42 bis (1990), *Data compression procedures for data circuit-terminating equipment (DCE) using error correction procedures.*
+- ITU-T Recommendation V.44 (2000), *Data compression procedures.*
+- ITU-T Recommendation V.54 (1988), *Loop test devices for modems.*
+- ITU-T Recommendation V.58 (1994), *Management information model for V-Series DCEs.*
+- ITU-T Recommendation V.59 (2000), *Managed objects for diagnostic information of public switched telephone network connected V-series modem DCEs.*
+- ITU-T Recommendation V.90 (1998), *A digital modem and analogue modem pair for use on the Public Switched Telephone Network (PSTN) at data signalling rates of up to 56 000 bit/s downstream and up to 33 600 bit/s upstream.*
+- ITU-T Recommendation V.91 (1999), *A digital modem operating at data signalling rates of up to 64 000 bit/s for use on a 4-wire circuit switched connection and on leased point-to-point 4-wire digital circuits.*
+- ITU-T Recommendation V.92 (2000), *Enhancements to Recommendation V.90.*
+- ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002, *Information technology – Abstract Syntax Notation One (ASN.1): Specification of basic notation.*
+
+NOTE – See Supplement 1 to this Recommendation for additional informative references.
+
+# 3 Definitions and abbreviations
+
+## 3.1 Definitions
+
+This Recommendation defines the following terms:
+
+**3.1.1 command state:** In Command State, the DCE is not communicating with a remote station, and the DCE is ready to accept commands. Data signals from the DTE on circuit 103 are treated as command lines and processed by the DCE, and DCE responses are sent to the DTE on circuit 104. The DCE enters this state upon power-up, and when a call is disconnected.
+
+**3.1.2 online command state:** In Online Command State, the DCE is communicating with a remote station, but treats signals from the DTE on circuit 103 as command lines and sends responses to the DTE on circuit 104. Depending on the implementation, data received from the remote station during Online Command State may be either discarded or retained in the DCE until Online Data State is once again entered (by a command from the DTE). Data previously transmitted by the local DTE and buffered by the DCE may be transmitted from the buffer to the remote DCE during Online Command State, or it may be discarded or transmission deferred until Online Data State is once again entered. Online Command State may be entered from Online Data state by a mechanism defined in 6.2.9 or by other manufacturer-defined means.
+
+**3.1.3 online data state:** In Online Data State, the DCE is communicating with a remote station. Data signals from the DTE on circuit 103 are treated as data and transmitted to the remote station, and data received from the remote station are delivered to the DTE on circuit 104. Data and control signals are monitored by the DCE to detect events such as loss of the remote connection and DTE requests for disconnection or switching to Online Command State. Online Data State is entered by successful completion of a command to originate or answer a call, by automatically
+
+answering a call, or by a DTE command to return to Online Data State from Online Command State.
+
+**3.1.4 direct mode:** Mode of Online Data State whereby the V.24 circuits 103 (transmit data) and 104 (received data) transfer data at the same rate or rates in use on the DCE-to-DCE communication channels. The DCE does not buffer data in either direction, nor does it implement flow control. For DCE modulation methods that transfer data synchronously, this mode implies the use of V.14 synchronous/asynchronous protocol within the DCE.
+
+**3.1.5 buffered mode:** Mode of Online Data State whereby the V.24 circuits 103 (transmit data) and 104 (received data) transfer data at data rates independent of the rates in use on the DCE-to-DCE communication channels. The DCE buffers the data rate differences as required. Neither error control nor data compression is used. For DCE modulation methods that transfer data synchronously, this mode implies the use of V.14 synchronous/asynchronous protocol within the DCE. For DCE modulation methods that transfer data asynchronously, asynchronous start-stop framing is used on the DCE-to-DCE communications channels.
+
+**3.1.6 leadin:** Commands defined using the extended syntax defined in 5.2.3 begin with a "+" character. The second character is reserved for a particular function or application. That two-character sequence, "+" is the Leadin.
+
+**3.1.7 [...]:** Square brackets are used to indicate that the enclosed items are optional. The square brackets themselves do not appear in the command line.
+
+**3.1.8 <...>:** Angle brackets are used to enclose the names of other syntactical elements. When those elements appear in an actual command line, the actual element is used and the angle brackets are omitted.
+
+All other characters, including "?", "=", parentheses, etc., shall appear in commands as written.
+
+## 3.2 Abbreviations
+
+This Recommendation uses the following abbreviations:
+
+CCITT International Telephone and Telegraph Consultative Committee
+
+IRA International Reference Alphabet (ITU-T Rec. T.50)
+
+ITU-T International Telecommunication Union – Telecommunication Standardization Sector
+
+# 4 Physical layer
+
+The circuits listed in 4.1 are intercepted and controlled by the DCE. The DCE is designed so that it will function properly if only these circuits are connected or implemented. V.24 circuit designators are listed in this clause.
+
+## 4.1 Circuits
+
+Signal Ground (Circuit 102) – Connection of this circuit is required for proper recognition of signals on other circuits.
+
+Transmitted Data (Circuit 103) – While in command state or online command state, data signals are processed by the DCE and not transmitted to the remote station.
+
+Received Data (Circuit 104) – While in command state or online command state, data received from the remote station may be ignored (see 3.1.2 for the definition of online command state), and the DCE generates responses on this circuit.
+
+Data Terminal Ready (Circuit 108/2) – The DCE monitors the effect of changes in the state of this circuit on the operation of the underlying DCE and operates accordingly. For example, if the DCE
+
+responds to an on-to-off transition on this circuit by disconnecting a call, the DCE will act accordingly by returning from online data state to command state.
+
+Received Line Signal Detector (Circuit 109) – The DCE may intercept this signal so that the issuance of result codes can be properly coordinated with transitions on this signal.
+
+Calling Indicator (Circuit 125) – The DCE may intercept this signal so that it can detect network alerting signals and automatically answer, if so conditioned by the appropriate command (S0, see 6.3.8).
+
+## **4.2 Character formatting**
+
+During command state and online command state, data transmitted between the DTE and DCE shall conform to the requirements for start-stop data transmission specified in ITU-T Rec. V.4 and ISO 1177. Parity may be even, odd, mark, space or not used. Each character shall have at least one complete stop element. The DCE should accept commands using any combination of parity and stop elements supported during online data state. These shall include, as a minimum, the following combinations, as defined in Annex B/V.42, each of which consists of ten total bits (including the start element):
+
+- 7 data bits, even parity, 1 stop element;
+- 7 data bits, odd parity, 1 stop element;
+- 7 data bits, space parity, 1 stop element;
+- 7 data bits, mark parity, 1 stop element (7 data bits, no parity bit, 2 stop elements);
+- 8 data bits, no parity, 1 stop element.
+
+During online data state, the DCE shall be transparent to changes in data format; the use of a particular format during command state should not restrict the use of other formats that are supported during online data state. However, DCE responses issued to indicate transition from online data state back to command state are issued using the same format and parity as the last command line issued by the DTE (see 5.7), and the DTE must therefore be prepared to recognize these responses even though the character format may have been changed.
+
+See 6.2.11 for a command to explicitly select the DTE-DCE character format.
+
+## **4.3 Data rates**
+
+The DCE shall be able to accept commands at either 1200 bit/s or 9600 bit/s. It is desirable that the DCE be able to accept commands and automatically detect the rate being used by the DTE at all rates supported by the DCE on the DTE-DCE interface. The DCE may provide a strap, switch, or other facility to define the rate at which the DTE is operating; however, while the rate is so selected, the DCE shall continue to be capable of accepting commands at either 1200 bit/s or 9600 bit/s. See 6.2.10 for a command to explicitly select the DTE-DCE rate.
+
+When operating in the online command state, the DCE is not required to accept commands at other than the online data rate; i.e., the requirement to accept commands at 1200 bit/s or 9600 bit/s does not apply during online command state.
+
+# **5 Syntax and procedures**
+
+## **5.1 Alphabet**
+
+The T.50 International Alphabet 5 (hereinafter cited as "IA5") is used in this Recommendation. Only the low-order seven bits of each character are significant to the DCE; any eighth or higher-order bit(s), if present, are ignored for the purpose of identifying commands and parameters. Lower-case characters (IA5 values from 6/1 to 7/10) are considered identical to their upper-case
+
+equivalents (IA5 values from 4/1 to 5/10) when received by the DCE from the DTE. Result codes from the DCE which are defined in this Recommendation shall be in upper case.
+
+## 5.2 DTE commands lines
+
+In the descriptions that follow, words enclosed in **** are references to syntactical elements defined in this Recommendation. When they appear in a command line, the brackets are not used. Words enclosed in **[square brackets]** represent optional items; such items may be omitted from the command line at the point where they are specified, and when they appear the square brackets are not included in the command line. Other characters that appear in syntax descriptions shall appear in the places shown.
+
+In the following subclauses regarding DTE commands, references are made to responses issued by the DCE which are defined in 5.7. In order to provide a clearer presentation, DCE responses are mentioned in terms of their alphabetic format; the actual response issued will depend on the setting of parameters that affect response formats (e.g., **Q** and **V** commands).
+
+### 5.2.1 Command line general format
+
+A command line is made up of three elements: the prefix, the body, and the termination character.
+
+The command line prefix consists of the characters "**AT**" (IA5 4/1, 5/4) or "**at**" (IA5 6/1, 7/4), or, to repeat the execution of the previous command line, the characters "**A**" (IA5 4/1, 2/15) or "**a**" (IA5 6/1, 2/15).
+
+The body is made up of individual commands as specified later in this Recommendation. Space characters (IA5 2/0) are ignored and may be used freely for formatting purposes, unless they are embedded in numeric or string constants (see 5.4.2.1 or 5.4.2.2). The termination character may not appear in the body. The DCE shall be capable of accepting at least 40 characters in the body.
+
+The termination character may be selected by a user option (parameter **S3**), the default being CR (IA5 0/13).
+
+### 5.2.2 Command line editing
+
+The character defined by parameter **S5** (default, BS [IA5 0/8]) is intended to be interpreted as a request from the DTE to the DCE to delete the previous character; the precise action undertaken is manufacturer-specific. Any control characters (IA5 0/0 through 1/15, inclusive) that remain in the command line after receipt of the termination character shall be ignored by the DCE.
+
+The DCE checks characters from the DTE first to see if they match the termination character (**S3**), then the editing character (**S5**), before checking for other characters. This insures that these characters will be properly recognized even if they are set to values that the DCE uses for other purposes. If **S3** and **S5** are set to the same value, a matching character will be treated as matching **S3** (**S3** is checked before **S5**).
+
+### 5.2.3 Command line echo
+
+The DCE may echo characters received from the DTE during command state and online command state back to the DTE, depending on the setting of the **E** command. If so enabled, characters received from the DTE are echoed at the same rate, parity, and format as received. Echoing characters not recognized as valid in the command line or of incomplete or improperly-formed command line prefixes is manufacturer-specific (see 5.8).
+
+### 5.2.4 Repeating a command line
+
+If the prefix "**A**" or "**a**" is received (IA5 4/1, 2/15 or 6/1, 2/15), the DCE shall immediately execute once again the body of the preceding command line. No editing is possible, and no termination character is necessary. A command line may be repeated multiple times through this mechanism, if desired. Responses to the repeated command line shall be issued using the parity and format of the
+
+original command line, and the rate of the "A/". If "A/" is received before any command line has been executed, the preceding command line is assumed to have been empty (that results in an **OK** result code).
+
+### 5.2.5 Types of DTE commands
+
+There are two types of commands: action commands and parameter commands.
+
+Action commands may be "executed" (to invoke a particular function of the equipment, which generally involves more than the simple storage of a value for later use), or "tested" (to determine whether or not the equipment implements the action command, and, if subparameters are associated with the action, the ranges of subparameter values that are supported).
+
+Parameters may be "set" (to store a value or values for later use), "read" (to determine the current value or values stored), or "tested" (to determine whether or not the equipment implements the parameter, and the ranges of values supported).
+
+### 5.2.6 DTE command syntax
+
+Clause 5.3 defines Basic Syntax DTE commands, which are implemented in common DCE. This Recommendation also defines Extended Syntax DTE commands in 5.4. Commands of either type may be included in command lines, in any order.
+
+## 5.3 Basic Syntax commands
+
+### 5.3.1 Basic Syntax command format
+
+The format of Basic Syntax commands, except for the D and S commands, is as follows:
+
+**[]**
+
+where is either a single character, or the "&" character (IA5 2/6) followed by a single character. Characters used in shall be taken from the set of alphabetic characters.
+
+ may be a string of one or more characters from "0" through "9" representing a decimal integer value. Commands that expect a are noted in the description of the command (see clause 6). If a command expects and it is missing ( is immediately followed in the command line by another or the termination character), the value "0" is assumed. If a command does not expect a and a number is present, an **ERROR** is generated. All leading "0"s in are ignored by the DCE.
+
+Additional commands may follow a command (and associated parameter, if any) on the same command line without any character required for separation. The actions of some commands cause the remainder of the command line to be ignored (e.g., **A**).
+
+See the **D** command for details on the format of the information that follows it.
+
+### 5.3.2 S-parameters
+
+Commands that begin with the letter "S" constitute a special group of parameters known as "S-parameters". These differ from other commands in important respects. The number following the "S" indicates the "parameter number" being referenced. If the number is not recognized as a valid parameter number, an **ERROR** result code is issued.
+
+Immediately following this number, either a "?" or "=" character (IA5 3/15 or 3/13, respectively) shall appear. "?" is used to read the current value of the indicated S-parameter; "=" is used to set the S-parameter to a new value.
+
+**S?**
+
+**S= []**
+
+If the "=" is used, the new value to be stored in the S-parameter is specified in decimal following the "=". If no value is given (i.e., the end of the command line occurs or the next command follows immediately), the S-parameter specified may be set to 0, or an **ERROR** result code issued and the stored value left unchanged. The ranges of acceptable values are given in the description of each S-parameter.
+
+If the "?" is used, the DCE transmits a single line of information text to the DTE. For S-parameters defined in this Recommendation, the text portion of this information text consists of exactly three characters, giving the value of the S-parameter in decimal, with leading zeroes included.
+
+## **5.4 Extended Syntax commands**
+
+### **5.4.1 Command naming rules**
+
+Both actions and parameters have names, which are used in the related commands. Names always begin with the character "+" (IA5 2/15). Following the "+", from one to sixteen (16) additional characters appear in the command name. These characters shall be selected from the following set:
+
+| | |
+|---------------------------|------------------------|
+| A through Z | (IA5 4/1 through 5/10) |
+| 0 through 9 | (IA5 3/0 through 3/9) |
+| ! | (IA5 2/1) |
+| % | (IA5 2/5) |
+| – | (IA5 2/13) |
+| . | (IA5 2/14) |
+| / | (IA5 2/15) |
+| : | (IA5 3/10) |
+| _ | (IA5 5/15) |
+
+The first character following the "+" shall be an alphabetic character in the range of "A" through "Z". This first character generally implies the application in which a command is used or the standards committee that defined it (e.g., command names beginning with "F" are generally associated with facsimile-related standards). See Appendix I for information on first command characters reserved for use by particular standards committees. All other + leadin character sequences are reserved for future standardization by the ITU-T.
+
+The command interpreter in the Data Circuit-terminating Equipment (DCE) considers lower-case characters to be the same as their upper-case equivalents; therefore, command names defined in standards referencing this Recommendation that include alphabetic characters should be defined using only the upper-case characters.
+
+Standards that reference this Recommendation may choose to establish internal naming conventions that permit implicit recognition of a name as an action or as a parameter. For example, the standard could choose to end all action names with an exclamation point ("!"), or all parameter names with a percent sign ("%"). This Recommendation imposes no such conventions, however.
+
+### **5.4.2 Values**
+
+When subparameters are associated with the execution of an action, or when setting a parameter, the command may include specification of values. This is indicated by the appearance of **** in the descriptions below.
+
+**** shall consist of either a numeric constant or a string constant.
+
+#### 5.4.2.1 Numeric constants
+
+Numeric constants are expressed in decimal, hexadecimal, or binary. In standards that reference this Recommendation, the definition of each command shall specify which form is used for values associated with that command; however, such standards may, in introductory information, specify a "default" type of numeric constant that is assumed for commands within that standard that do not explicitly specify the type. Such standards shall also define the minimum and maximum acceptable values.
+
+Decimal numeric constants shall consist of a sequence of one or more of the characters "0" (IA5 3/0) through "9" (IA5 3/9), inclusive.
+
+Hexadecimal numeric constants shall consist of a sequence of one or more of the characters "0" (IA5 3/0) through "9" (IA5 3/h), inclusive, and "A" (IA5 4/1) through "F" (IA5 4/6) inclusive. The characters "A" through "F" represent the equivalent decimal values 10 through 15.
+
+Binary numeric constants shall consist of a sequence of one or more of the characters "0" (IA5 3/0) and "1" (IA5 3/1).
+
+In all numeric constants, the most significant digit is specified first. Leading "0" characters shall be ignored by the DCE. No spaces, hyphens, periods, commas, parentheses, or other generally-accepted numeric formatting characters are permitted in numeric constants; note in particular that no "H" suffix is appended to the end of hexadecimal constants.
+
+#### 5.4.2.2 String constants
+
+String constants shall consist of a sequence of displayable IA5 characters, each in the range from 2/0 to 7/15, inclusive, except for the characters "" (IA5 2/2) and "\" (IA5 5/12). String constants shall be bounded at the beginning and end by the double-quote character (" ", IA5 2/2).
+
+Any character value may be included in the string by representing it as a backslash ("\") character followed by two hexadecimal digits. For example, "\0D" is a string consisting of the single character (IA5 0/13). If the "\" character itself is to be represented in a string, it shall be encoded as "\5C". The double-quote character, used as the beginning and ending string delimiter, shall be represented within a string constant as "\22". Standards that reference this Recommendation may prohibit use of this "\" mechanism if only displayable characters are permitted in string constants in that standard and if the double-quote character is not permitted within string constants; in this case, the "\" character shall be treated as any other IA5 character included within a string constant.
+
+A "null" string constant, or a string constant of zero length, is represented by two adjacent delimiters ("").
+
+Standards that reference this Recommendation shall specify, for each string value, any limitations on the characters that may appear within the string, and the maximum and minimum acceptable string length.
+
+#### 5.4.2.3 Compound values
+
+Actions may have more than one subparameter associated with them, and parameters may have more than one value. These are known as "compound values", and their treatment is the same in both actions and parameters.
+
+A compound value consists of any combination of numeric and string values (as defined in the description of the action or parameter). The comma character (IA5 2/12) shall be included as a separator, before the second and all subsequent values in the compound value. If a value is not specified (i.e., defaults assumed), the required comma separator shall be specified; however, trailing comma characters may be omitted if all associated values are also omitted.
+
+### 5.4.3 Action commands
+
+#### 5.4.3.1 Action execution command syntax
+
+There are two general types of action commands: those that have associated subparameter values that affect only that invocation of the command, and those that have no subparameters.
+
+If subparameters are associated with a command, the definition of the action command shall indicate, for each subparameter, whether the specification of a value for that subparameter is mandatory or optional. For optional subparameters, the definition shall indicate the assumed (default) value for the subparameter if no value is specified for that subparameter; the assumed value may be either a previous value (i.e., the value of an omitted subparameter remains the same as the previous invocation of the same command, or is determined by a separate parameter or other mechanism), or a fixed value (e.g., the value of an omitted subparameter is assumed to be zero). Generally, the default value for numeric subparameters is 0, and the default value for string subparameters is "" (empty string).
+
+The following syntax is used for actions that have no subparameters:
+
+**+**
+
+The following syntax is used for actions that have one subparameter:
+
+**+[=]**
+
+The following syntax is used for actions that have two or more subparameters:
+
+**+[=]**
+
+For actions that accept subparameters, if all subparameters are defined as being optional, and the default values for all subparameters are satisfactory, the Data Terminal Equipment (DTE) may use the first syntax above (i.e., omit the "=" from the action execution command as well as all of the subparameter value string).
+
+If the named action is implemented in the DCE and other relevant criteria are met (e.g., the DCE is in the proper state), the command shall be executed with any indicated subparameters. If **** is not recognized, the DCE issues the **ERROR** result code and terminates processing of the command line. An **ERROR** is also generated if a subparameter is specified for an action that does not accept subparameters, if too many subparameters are specified, if a mandatory subparameter is not specified, if a value is specified of the wrong type, or if a value is specified that is not within the supported range.
+
+#### 5.4.3.2 Action test command syntax
+
+The DTE may test if an action command is implemented in the DCE by using the syntax:
+
+**+=?**
+
+If the DCE does not recognize the indicated name, it shall return an **ERROR** result code and terminate processing of the command line. If the DCE does recognize the action name, it shall return an **OK** result code. If the named action accepts one or more subparameters, the DCE shall send an information text response to the DTE, prior to the **OK** result code, specifying the values supported by the DCE for each such subparameter, and possibly additional information. The format of this information text is defined for each action command; general formats for specification of sets and ranges of numeric values are described in 5.7.1 and 5.7.2.
+
+### 5.4.4 Parameter commands
+
+#### 5.4.4.1 Parameter types
+
+Parameters may be defined as "read-only" or "read-write". "Read-only" parameters are used to provide status or identifying information to the DTE, but are not settable by the DTE; attempting to
+
+set their value is an error. In some cases (specified in the description of the individual parameter), the DCE may ignore attempts to set the value of such parameters rather than respond with an **ERROR** result code, if the continued correct operation of the interface between the DCE and DTE will not be affected by such action. Read-only parameters may be read and tested.
+
+"Read-write" parameters may be set by the DTE, to store a value or values for later use. Read-write parameters may be set, read, and tested.
+
+Parameters may take either a single value, or multiple (compound) values. Each value may be either numeric or string; the definition of the parameter shall specify the type of value for each subparameter. Attempting to store a string value in a numeric parameter, or a numeric value in a string parameter, is an error.
+
+#### 5.4.4.2 Parameter set command syntax
+
+The definition of the parameter shall indicate, for each value, whether the specification of that value is mandatory or optional. For optional values, the definition shall indicate the assumed (default) value if none is specified; the assumed value may be either a previous value (i.e., the value of an omitted subparameter retains its previous value), or a fixed value (e.g., the value of an omitted subparameter is assumed to be zero). Generally, the default value for numeric parameters is 0, and the default value for string parameters is "" (empty string).
+
+The following syntax is used for parameters that accept a single value:
+
+**+=[]**
+
+The following syntax is used for parameters that accept more than one value:
+
+**+=[]**
+
+If the named parameter is implemented in the DCE, all mandatory values are specified, and all values are valid according to the definition of the parameter, the specified values shall be stored. If **** is not recognized, one or more mandatory values are omitted, or one or more values are of the wrong type or outside the permitted range, the DCE issues the **ERROR** result code and terminates processing of the command line. An **ERROR** is also generated if too many values are specified. In case of an error, all previous values of the parameter are unaffected.
+
+#### 5.4.4.3 Parameter read command syntax
+
+The DTE may determine the current value or values stored in a parameter by using the following syntax:
+
+**+?**
+
+If the named parameter is implemented in the DCE, the current values stored for the parameter are sent to the DTE in an information text response. The format of this response is described in the definition of the parameter. Generally, the values will be sent in the same form in which they would be issued by the DTE in a parameter setting command; if multiple values are supported, they will generally be separated by commas, as in a parameter setting command.
+
+#### 5.4.4.4 Parameter test command syntax
+
+The DTE may test if a parameter is implemented in the DCE, and determine the supported values, by using the syntax:
+
+**+=?**
+
+If the DCE does not recognize the indicated name, it returns an **ERROR** result code and terminates processing of the command line. If the DCE does recognize the parameter name, it shall return an information text response to the DTE, followed by an **OK** result code. The information text response shall indicate the values supported by the DCE for each such subparameter, and possibly
+
+additional information. The format of this information text is defined for each parameter; general formats for specification of sets and ranges of numeric values are described in 5.7.1 and 5.7.2.
+
+### **5.4.5 Additional syntax rules**
+
+#### **5.4.5.1 Concatenating commands after extended syntax commands**
+
+Additional commands may follow an extended syntax command on the same command line if a semicolon (";", IA5 3/11) is inserted after the preceding extended command as a separator. The semicolon is not necessary when the extended syntax command is the last command on the command line.
+
+#### **5.4.5.2 Concatenating commands after basic format commands**
+
+Extended syntax commands may appear on the same command line after a basic syntax command without a separator, in the same manner as concatenation of basic syntax commands.
+
+## **5.5 Issuing commands**
+
+All characters in a command line shall be issued at the same data rate, and with the same parity and format.
+
+The DCE shall ignore any command line that is not properly terminated. The DCE may consider 30 seconds of mark idle time between any two characters as an improperly terminated command line. In this case the DCE may or may not generate an **ERROR** message. The DCE shall ignore any characters received from the DTE that are not part of a properly-formatted command line.
+
+If the maximum number of characters that the DCE can accept in the body is exceeded, an **ERROR** result code shall be generated after the command line is terminated.
+
+The DTE shall not begin issuing a subsequent command line until at least one-tenth of a second has elapsed after receipt of the entire result code issued by the DCE in response to the preceding command line.
+
+## **5.6 Executing commands**
+
+Upon receipt of the termination character, the DCE shall commence execution of the commands in the command line in the order received from the DTE. Should execution of a command result in an error, or a character be not recognized as a valid command, execution is terminated, the remainder of the command line is ignored, and the **ERROR** result code is issued. Otherwise, if all commands execute correctly, only the result code associated with the last command shall be issued; result codes for preceding commands are suppressed. If no commands appear in the command line, the **OK** result code is issued.
+
+### **5.6.1 Aborting commands**
+
+Some action commands that require time to execute may be aborted while in progress; these are explicitly noted in the description of the command. Aborting of commands is accomplished by the transmission from the DTE to the DCE of any character. A single character shall be sufficient to abort the command in progress; however, characters transmitted during the first 125 milliseconds after transmission of the termination character shall be ignored (to allow for the DTE to append additional control characters such as line feed after the command line termination character). To insure that the aborting character is recognized by the DCE, it should be sent at the same rate as the preceding command line; the DCE may ignore characters sent at other rates. When such an aborting event is recognized by the DCE, it shall terminate the command in progress and return an appropriate result code to the DTE, as specified for the particular command.
+
+### 5.6.2 Handling of invalid numbers and S-parameter values
+
+The DCE shall react to undefined numbers and S-parameter values in one of three ways:
+
+- 1) issue the **ERROR** result code, and leave the previous value of the parameter unchanged;
+- 2) issue the **OK** result code, and leave the previous value of the parameter unchanged; or
+- 3) issue the **OK** result code, and set the parameter value to the valid value nearest to that specified in the command line.
+
+The description of each command may specify which of these three techniques shall be used to handle invalid parameter values for that command or parameter. If the description does not specify the handling technique, it shall be defined by the manufacturer.
+
+## 5.7 DCE responses
+
+While in command state and online command state, the DCE shall issue responses using the same rate, word length, and parity as the most recently received DTE command line. In the event that no DTE command has yet been received, rate, word length, and parity used will depend on the capabilities of the DCE.
+
+When the DCE transitions from the command state or online command state to the online data state, the result code **CONNECT** should be issued at the bit rate and parity used during the command state. When the DCE transitions from the online data state to the command state or online command state, the result codes should be issued at the bit rate used during the online data state. Thereafter, any unsolicited result codes should use the bit rate and parity of the last command line issued by the DTE to the DCE.
+
+The characters of a response shall be contiguous, with no more than 100 milliseconds of mark idle issued between characters in addition to stop elements.
+
+### 5.7.1 Responses
+
+There are two types of responses that may be issued by the DCE: information text and result codes.
+
+Information text responses consist of three parts: a header, text, and a trailer. The characters transmitted for the header are determined by a user setting (see the **V** command, 6.2.6). The trailer consists of two characters, being the character having the ordinal value of parameter **S3** followed by the character having the ordinal value of parameter **S4**. Information text specified in this Recommendation always consists of a single line; information text returned in response to manufacturer-specific commands may contain multiple lines, and the text may therefore include IA5 CR, LF, and other formatting characters to improve readability.
+
+Result codes consist of three parts: a header, the result text, and a trailer. The characters transmitted for the header and trailer are determined by a user setting (see the **V** command, 6.2.6). The result text may be transmitted as a number or as a string, depending on a user-selectable setting (see the **V** command).
+
+There are three types of result codes: final, intermediate, and unsolicited.
+
+A final result code indicates the completion of a full DCE action and a willingness to accept new commands from the DTE.
+
+An intermediate result code is a report of the progress of a DCE action. The **CONNECT** result code is an intermediate result code (others may be defined by manufacturers). In the case of a dialling or answering command, the DCE moves from command state to online data state, and issues a **CONNECT** result code. This is an intermediate result code for the DCE because it is not prepared to accept commands from the DTE while in online data state. When the DCE moves back to the command state, it will then issue a final result code (such as **OK** or **NO CARRIER**).
+
+Unsolicited result codes (such as **RING**) indicate the occurrence of an event not directly associated with the issuance of a command from the DTE.
+
+Table 1 indicates result codes that shall be implemented by the DCE, their numeric equivalents, and a brief description of the use of each. In clause 6, the description of each command includes the specific result codes that may be issued in relation to that command and the circumstances under which they may be issued.
+
+**Table 1/V.250 – Result codes**
+
+| Result code
(ATV1) | Numeric
(ATV0) | Description |
+|-------------------------------|---------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| OK | 0 | Acknowledges execution of a command |
+| CONNECT | 1 | A connection has been established; the DCE is moving from command state to online data state |
+| RING | 2 | The DCE has detected an incoming call signal from the network |
+| NO CARRIER | 3 | The connection has been terminated or the attempt to establish a connection failed |
+| ERROR | 4 | Command not recognized, command line maximum length exceeded, parameter value invalid, or other problem with processing the command line |
+| NO DIALTONE | 6 | No dial tone detected |
+| BUSY | 7 | Engaged (busy) signal detected |
+| NO ANSWER | 8 | "@" (Wait for Quiet Answer) dial modifier was used, but remote ringing followed by five seconds of silence was not detected before expiration of the connection timer (S7) |
+| CONNECT | Manufacturer-specific | Same as CONNECT, but includes manufacturer-specific text that may specify DTE speed, line speed, error control, data compression, or other status |
+
+### 5.7.2 Extended syntax result codes
+
+Extended syntax result codes may be issued in response to either basic or extended commands, or both. The appropriate responses shall be specified in the definitions of the commands, the responses, or both.
+
+The general format of extended syntax result codes is the same as result codes defined in TIA-602 with regard to headers and trailers. The characters specified in S-parameters **S3** and **S4** shall be used in headers and trailers of extended syntax result codes as they are in basic format result codes. The setting of the "**V**" command shall affect the headers and trailers associated with extended syntax result codes in the same manner as basic format result codes; however, unlike basic format result codes, extended syntax result codes have no numeric equivalent, and are always issued in alphabetic form.
+
+Extended syntax result codes shall be subject to suppression by the "**Q1**" command, as with basic format result codes. The issuance of extended syntax result codes shall not be affected by the setting of the "**X**" command.
+
+Extended syntax result codes may be either final, intermediate, or unsolicited; the type shall be indicated in the definition of the result code.
+
+Extended syntax result codes shall be prefixed by the "+" character to avoid duplication of basic format result codes specified in TIA-602 and by manufacturers. Following the "+" character, the name of the result code appears; result code names shall follow the same rules as command names (see 5.4.1). It is strongly advised that the reservation of the first character of command names noted
+
+in Appendix I also be observed with regard to the assignment of names of extended syntax result codes.
+
+Extended syntax result codes may include the reporting of values. The definition of the result code shall specify whether or not values are appended to the result code, and, if so, how many, their types, and their assumed default values if omitted. When no values are to be reported, the result code appears in the simplest form:
+
+**+**
+
+If a single value is to be reported, the form of the result code shall be:
+
+**+: **
+
+Note that a single space character (ASCII 20h) separates the colon character (ASCII 3Ah) from the ; no space appears between the result code name and the colon. If multiple values are to be reported with the result code, the form is:
+
+**+: **
+
+where follows the rules specified in 5.4.2.3.
+
+### **5.7.3 Information text formats for test commands**
+
+In general, the format of information text returned by extended syntax commands shall be specified in the definition of the command. This clause describes recommended formats for information text returned in response to action test (for actions that accept one or more subparameters) and parameter test commands. The definitions of the responses to such testing commands, as described in the definitions of the associated commands in standards that reference this Recommendation, may use this recommended format or any other suitable format that is adequately specified.
+
+Note that the DCE may insert intermediate characters in very long information text responses, in order to avoid overrunning DTE receive buffers. If intermediate characters are included, the DCE shall not include the character sequences "0 " (3/0, 0/13) or "OK" (4/15, 4/11, 0/13), so that DTE can avoid false detection of the end of these information text responses.
+
+#### **5.7.3.1 Range of values**
+
+When the action accepts a single numeric subparameter, or the parameter accepts only one numeric value, the set of supported values may be presented in the information text as an ordered list of values. The list shall be preceded by a left parenthesis ("(", IA5 2/8), and is followed by a right parenthesis (")", IA5 2/9). If only a single value is supported, it shall appear between the parentheses. If more than one value is supported, then the values may be listed individually, separated by comma characters (IA5 2/12), or, when a continuous range of values is supported, by the first value in the range, followed by a hyphen character (IA5 2/13), followed by the last value in the range. The specification of single values and ranges of values may be intermixed within a single information text. In all cases, the supported values shall be indicated in ascending order.
+
+For example, the following are some examples of value range indications:
+
+- | | |
+|--------------------------|----------------------------------------------|
+| (0) | Only the value 0 is supported. |
+| (1,2,3) | The values 1, 2, and 3 are supported. |
+| (1-3) | The values 1 through 3 are supported. |
+| (0,4,5,6,9,11,12) | The several listed values are supported. |
+| (0,4-6,9,11-12) | An alternative expression of the above list. |
+
+#### 5.7.3.2 Compound range of values
+
+When the action accepts more than one subparameter, or the parameter accepts more than one value, the set of supported values may be presented as a list of the parenthetically-enclosed value range strings described in 5.7.3.1 above, separated by commas. For example, the information text in response to testing an action that accepts three subparameters, and supports various ranges for each of them, could appear as follows:
+
+**(0),(1-3),(0,4-6,9,11-12)**
+
+This indicates that the first subparameter accepts only the value 0, the second accepts any value from 1 through 3 inclusive, and the third subparameter accepts any of the values 0, 4, 5, 6, 9, 11, or 12.
+
+## 5.8 Manufacturer-specific characteristics
+
+This Recommendation describes characteristics universal to a large installed base of DCEs. Most DCEs implement a number of extensions and behavioural differences beyond the descriptions in this Recommendation. The following subclauses mention a few specific and well-known examples of areas in which these extensions and behavioural differences exist. This is not intended to be a comprehensive list; extensions and differences do exist in other areas. This Recommendation is not intended to preclude or limit extensions in these or other areas.
+
+Equipment that implements non-standard commands, values, features, or behaviours, such as described in the following subclauses, shall be capable of being configured, by one or more commands, parameters, or switches, so that the equipment will properly interwork with DTEs that implement only the mandatory provisions of this Recommendation.
+
+### 5.8.1 Extensions
+
+DCEs claiming compliance to this Recommendation often include extensions in a number of areas. This Recommendation does not preclude the use of these extensions; however, the definition of these is totally up to the manufacturer. Other Recommendations may call out extensions as well. Some areas in which extensions exist include:
+
+- 1) command characters and commands consisting of a prefix character followed by one or more characters (however, the "+" prefix is reserved for future use in this and other standards and should not be used for non-standard purposes);
+- 2) command numbers (including additional numbers associated with commands defined in this Recommendation);
+- 3) parameter values (including additional values associated with parameters defined in this Recommendation);
+- 4) S-parameter numbers;
+- 5) S-parameter values (including additional values associated with S-parameters defined in this Recommendation);
+- 6) command line editing characters;
+- 7) result codes;
+- 8) dial string modifiers;
+- 9) syntax extensions to the body of the command line;
+- 10) information responses;
+- 11) mechanisms to exit from online data state and return to command state or online command state (using, for example, particular sequences of characters, timing, or other techniques).
+
+### 5.8.2 Behavioural differences
+
+This Recommendation specifically and intentionally does not describe DCE behaviour in some situations. This is generally due to variations in existing implementations. DTEs must take into account the possibility of differences in the behaviour of various DCEs in particular situations.
+
+The following are some examples of areas in which differences are known to exist. This is not intended to be a comprehensive list; behaviour differences exist in other areas as well:
+
+- 1) handling of unsolicited result codes while a command line is being entered (may be sent, suppressed, deferred, etc.);
+- 2) answering of incoming calls while a command line is being entered (may occur, be deferred, etc.);
+- 3) handling of loss of carrier during online command state [may be reported immediately (and data rate may vary), may be deferred until attempted re-entry into online data state, etc.];
+- 4) handling of undefined command numbers, and S-parameters values (may result in an **ERROR**, clamping of value to the valid range, retention of previous value, etc.);
+- 5) execution time of actions (for example, **Z** command);
+- 6) handling of variations in command line format and editing (for example: "**AT**" in mixed case; length of command line buffer; command line too long; whether or not space characters and control characters are stored in the command buffer; whether or not unrecognized control characters are echoed; echoing of other characters prior to receipt of the "**AT**" prefix; disposition of command lines in which the DTE changed the rate, format, or parity; etc.);
+- 7) displaying of S-parameter values which cannot be expressed as three decimal digits;
+- 8) states of connection establishment (e.g., handshaking) in which attempts to abort a command by transmission of a character to the DCE may not be recognized;
+- 9) handling of additional characters that appear on the same command line after a semicolon that terminates a dial string (see 6.1.1); i.e., whether the additional characters are ignored or processed as commands;
+- 10) carry-over of the effect of **P** and **T** dial modifiers from one dial string to the next.
+
+# 6 Functions
+
+The following descriptions of DCE functions and associated commands include information on both mandatory and optional capabilities. All mandatory commands, parameters, and responses shall be implemented in devices claiming conformance to this Recommendation. If an optional capability is implemented in a DCE, the associated command(s), parameter(s), and response(s) defined in this Recommendation shall be implemented.
+
+For simplicity, the following descriptions use a particular syntax; alternatives may be used when available. For example:
+
+- 1) Result codes are described in terms of their alphabetic format, except in situations where the setting of a parameter directly affects the format (e.g., **V** and **Q** commands). The actual result code issued would depend on the setting of parameters that affect result code formats.
+- 2) The description of the **OK** result code for each command does not mention the fact that the result code will be deferred if any further commands appear on the same command line (see 5.4).
+
+Default values that are specified for some commands have been selected to provide proper operation of the DCE in its initial state. Implementation of the specified defaults is desirable but not mandatory, with the exception of **S3** (which has a mandatory default value of 13). Default values for all parameters supported shall be specified by the manufacturer.
+
+Some DCE functions and associated commands may be subject to national regulations. The manner of handling such restrictions (e.g., elimination of commands, restriction on ranges of accepted values, handling of values outside acceptable ranges, etc.) shall be determined by the manufacturer.
+
+Table I.2 lists all commands contained in the Recommendation, sorted alphabetically.
+
+## 6.1 Generic DCE control
+
+### 6.1.1 Reset to default configuration
+
+#### *Syntax*
+
+**Z**[]
+
+#### *Description*
+
+This command instructs the DCE to set all parameters to their factory defaults as specified by the manufacturer. This may include taking into consideration the settings of hardware configuration switches or non-volatile parameter storage (if implemented). If the DCE is connected to the line, it is disconnected from the line, terminating any call in progress.
+
+All of the functions of the command shall be completed before the DCE issues the result code. The DTE should not include additional commands on the same command line after the **Z** command because such commands may be ignored.
+
+NOTE – Because this command may take into consideration the settings of switches and non-volatile parameter storage, it does not necessarily return the DCE to a "known state". In particular, the DCE may, as a result of execution of this command, be placed in a state in which it appears to not respond to DTE commands, or respond in a completely different format than was being used prior to execution of the command.
+
+#### *Abortability*
+
+This command may not be aborted.
+
+#### *Result codes*
+
+**OK** If is recognized.
+
+**ERROR** If is not recognized or supported.
+
+An **OK** result code for this command is issued using the same rate, parity, and word format as the DTE command line containing the command, but using the new values for parameters that affect the format of result codes (e.g., **Q**, **V**, **S3**, **S4**).
+
+#### *Execution time*
+
+Execution time for this action varies widely depending on manufacturer implementation. The DTE should not assume the amount of time required to execute this command, but await a result code or other positive indication from the DCE that it is ready to accept a command.
+
+#### *Implementation*
+
+Implementation of this command is mandatory. Interpretation of is optional and manufacturer-specific.
+
+### 6.1.2 Set to factory-defined configuration
+
+#### *Syntax*
+
+**&F**[]
+
+#### *Description*
+
+This command instructs the DCE to set all parameters to default values specified by the manufacturer, which may take into consideration hardware configuration switches and other manufacturer-defined criteria.
+
+#### *Abortability*
+
+This command may not be aborted.
+
+#### *Defined values*
+
+- 0** Set parameters to factory defaults.
+- (other)** Reserved for manufacturer proprietary use.
+
+#### *Result codes*
+
+- OK** If value is valid.
+- ERROR** If value is not recognized or not supported.
+
+An **OK** result code for this command is issued using the same rate, parity, and word format as the DTE command line containing the command, but using the factory-defined values for other parameters that affect the format of result codes (e.g., **Q**, **V**, **S3**, **S4**) and dependent upon other commands that may follow on the same command line.
+
+#### *Execution time*
+
+Execution time for this action varies widely depending on manufacturer implementation. The DTE should not assume the amount of time required to execute this command, but await a result code or other positive indication from the DCE that it is ready to accept a command.
+
+#### *Implementation*
+
+Implementation of this command is mandatory. If the value specified is not recognized or implemented, an **ERROR** result code is issued.
+
+### **6.1.3 Request identification information**
+
+#### *Syntax*
+
+**I[]**
+
+#### *Description*
+
+This command causes the DCE to transmit one or more lines of information text, determined by the manufacturer, followed by a final result code. **** may optionally be used to select from among multiple types of identifying information, specified by the manufacturer.
+
+NOTE – The responses to this command may not be reliably used to determine the DCE manufacturer, revision level, feature set, or other information, and should not be relied upon for software operation. In particular, expecting a specific numeric response to an **I0** command to indicate which other features and commands are implemented in a DCE dooms software to certain failure, since there are widespread differences in manufacturer implementation among devices that may, coincidentally, respond with identical values to this command. Software implementors should use **I** commands with extreme caution, since the amount of data returned by particular implementations may vary widely from a few bytes to several thousand bytes or more, and should be prepared to encounter **ERROR** responses if the value is not recognized.
+
+#### *Abortability*
+
+This command is not ordinarily abortable, but may be so in some implementations.
+
+#### *Execution time*
+
+Execution time is dependent on the time required to transmit the information to the DTE. The DTE should not assume the amount of time required to execute this command, but await a result code or other positive indication from the DCE that it is ready to accept a command.
+
+#### *Implementation*
+
+Implementation of this command is optional.
+
+### **6.1.4 Request manufacturer identification (+GMI)**
+
+#### *Syntax*
+
+**+GMI**
+
+#### *Description*
+
+This command causes the DCE to transmit one or more lines of information text, determined by the manufacturer, which is intended to permit the user of the DCE to identify the manufacturer. Typically, the text will consist of a single line containing the name of the manufacturer, but manufacturers may choose to provide more information if desired (e.g., address, telephone number for customer service, etc.).
+
+The total number of characters, including line terminators, in the information text returned in response to this command shall not exceed 2048 characters. Note that the information text shall not contain the sequence "0 " (3/0, 0/13) or "OK" (4/15, 4/11, 0/13), so that DTE can avoid false detection of the end of this information text.
+
+#### *Defined values*
+
+None.
+
+#### *Result codes*
+
+**OK** In all cases.
+
+#### *Execution time*
+
+Execution time is dependent on the time required to transmit the information to the DTE. The DTE should not assume the amount of time required to execute this command, but await a result code or other positive indication from the DCE that it is ready to accept a command.
+
+#### *Abortability*
+
+This command is not abortable.
+
+#### *Implementation*
+
+Implementation of this command is mandatory.
+
+### **6.1.5 Request model identification (+GMM)**
+
+#### *Syntax*
+
+**+GMM**
+
+#### *Description*
+
+This command causes the DCE to transmit one or more lines of information text, determined by the manufacturer, which is intended to permit the user of the DCE to identify the specific model of device. Typically, the text will consist of a single line containing the name of the product, but manufacturers may choose to provide any information desired.
+
+The total number of characters, including line terminators, in the information text returned in response to this command shall not exceed 2048 characters. Note that the information text shall not contain the sequence "0 " (3/0, 0/13) or "OK" (4/15, 4/11, 0/13), so that DTE can avoid false detection of the end of this information text.
+
+#### *Defined values*
+
+None.
+
+#### *Result codes*
+
+**OK** In all cases.
+
+#### *Execution time*
+
+Execution time is dependent on the time required to transmit the information to the DTE. The DTE should not assume the amount of time required to execute this command, but await a result code or other positive indication from the DCE that it is ready to accept a command.
+
+#### *Abortability*
+
+This command is not abortable.
+
+#### *Implementation*
+
+Implementation of this command is mandatory.
+
+### **6.1.6 Request revision identification (+GMR)**
+
+#### *Syntax*
+
+**+GMR**
+
+#### *Description*
+
+This command causes the DCE to transmit one or more lines of information text, determined by the manufacturer, which is intended to permit the user of the DCE to identify the version, revision level or date, or other pertinent information of the device. Typically, the text will consist of a single line containing the version of the product, but manufacturers may choose to provide any information desired.
+
+The total number of characters, including line terminators, in the information text returned in response to this command shall not exceed 2048 characters. Note that the information text shall not contain the sequence "0 " (3/0, 0/13) or "OK" (4/15, 4/11, 0/13), so that DTE can avoid false detection of the end of this information text.
+
+#### *Defined values*
+
+None.
+
+#### *Result codes*
+
+**OK** In all cases.
+
+#### *Execution time*
+
+Execution time is dependent on the time required to transmit the information to the DTE. The DTE should not assume the amount of time required to execute this command, but await a result code or other positive indication from the DCE that it is ready to accept a command.
+
+#### *Abortability*
+
+This command is not abortable.
+
+#### *Implementation*
+
+Implementation of this command is mandatory.
+
+### **6.1.7 Request product serial number identification (+GSN)**
+
+#### *Syntax*
+
+**+GSN**
+
+#### *Description*
+
+This command causes the DCE to transmit one or more lines of information text, determined by the manufacturer, which is intended to permit the user of the DCE to identify the individual device. Typically, the text will consist of a single line containing a manufacturer determined alpha-numeric string, but manufacturers may choose to provide any information desired.
+
+The total number of characters, including line terminators, in the information text returned in response to this command shall not exceed 2048 characters. Note that the information text shall not contain the sequence "0 " (3/0, 0/13) or "OK" (4/15, 4/11, 0/13), so that DTE can avoid false detection of the end of this information text.
+
+#### *Defined values*
+
+None.
+
+#### *Result codes*
+
+**OK** In all cases.
+
+#### *Execution time*
+
+Execution time is dependent on the time required to transmit the information to the DTE. The DTE should not assume the amount of time required to execute this command, but await a result code or other positive indication from the DCE that it is ready to accept a command.
+
+#### *Abortability*
+
+This command is not abortable.
+
+#### *Implementation*
+
+Implementation of this command is optional.
+
+### **6.1.8 Request global object identification (+GOI)**
+
+#### *Syntax*
+
+**+GOI**
+
+#### *Description*
+
+This command causes the DCE to transmit one or more lines of information text, determined by the manufacturer, which is intended to permit the user of the DCE to identify the device, based on the ISO system for registering unique object identifiers. Typically, the text will consist of a single line containing numeric strings delimited by period characters.
+
+The general format of object identifiers is defined in Annex D/X.680, the encoding rules are defined in Annex C/X.680.
+
+The total number of characters, including line terminators, in the information text returned in response to this command shall not exceed 2048 characters. Note that the information text shall not contain the sequence "0 " (3/0, 0/13) or "OK" (4/15, 4/11, 0/13), so that DTE can avoid false detection of the end of this information text.
+
+#### *Defined values*
+
+None.
+
+#### *Result codes*
+
+**OK** In all cases.
+
+#### *Execution time*
+
+Execution time is dependent on the time required to transmit the information to the DTE. The DTE should not assume the amount of time required to execute this command, but await a result code or other positive indication from the DCE that it is ready to accept a command.
+
+#### *Abortability*
+
+This command is not abortable.
+
+#### *Implementation*
+
+Implementation of this command is optional.
+
+### **6.1.9 Request complete capabilities list (+GCAP)**
+
+#### *Syntax*
+
+**+GCAP**
+
+#### *Description*
+
+This extended-format command causes the DCE to transmit one or more lines of information text in a specific format. The content is a list of additional capabilities command +s, which is intended to permit the user of the DCE to identify the overall capabilities of the DCE.
+
+In particular, if the DCE implements a particular DCE control standard that uses Extended Syntax Commands, and if that DCE control standard includes command(s) that indicate general capabilities, the +(s) of those commands shall be reported to the DCE in response to a +GCAP command. See Table 2.
+
+**Table 2/V.250 – Examples of required +GCAP responses**
+
+| +GCAP response | DCE control standard | Description |
+|-----------------------|---------------------------------|----------------------------------------------------------------|
+| +FCLASS | T.class1, +F
or T.class2, +F | Class 1 Facsimile DCE Control
Class 2 Facsimile DCE Control |
+| +MS | +M commands | Modulation Control:
+MS and +MR commands |
+| +MV18S | +MV18 commands | V.18 Modulation Control:
+MV18S and +MV18R |
+| +ES | +E commands | Error Control:
+ES, +EB, +ER, +EFCS, +ETBM |
+| +DS | +D commands | Data Compression:
+DS and +DR |
+
+For example, a data modem that supported all capabilities described in this Recommendation may report:
+
+**+GCAP: +MS, +ES, +DS, +MV18S**
+
+If that example DCE implemented other commands, they shall also be included. If that DCE implemented stubs (e.g., +FCLASS=0 only), it may report +FCLASS as part of its +GCAP response.
+
+The response is not specifically limited as to number of lines of text. Note that the information text shall not contain the sequence "0 " (3/0, 0/13) or "OK" (4/15, 4/11, 0/13), so that DTE can avoid false detection of the end of this information text.
+
+It is not necessary for a DTE to inquire of the +GCAP where the application is specific to a technology, such as facsimile where the +FCLASS command would be sufficient to determine capabilities.
+
+#### *Abortability*
+
+This command is not abortable.
+
+#### *Implementation*
+
+Implementation of this command is mandatory. The response might be null if the DCE lacks specific capabilities commands. A DTE that is aware of a specific DCEs capabilities might elect not to use the +GCAP command.
+
+### **6.1.10 Country of installation (+GCI)**
+
+#### *Parameter*
+
+**+GCI=**
+
+#### *Description*
+
+This extended syntax command is used to indicate and select the country of installation for the DCE. If implemented, the DCE shall use this parameter to select the settings for any operational parameters that need to be adjusted for national regulations or telephone networks. DTE may use this value to determine country-specific functions.
+
+If a DCE supports legal connection in only one country, then that DCE shall report only the T.35 country code for that country in response to a read or test command, and accept only that value for a write command.
+
+#### *Defined values*
+
+ITU-T Rec. T.35 defines 8-bit country codes. Annex A/T.35 lists country codes, with bits 8-1 and the country names. For use with the +GCI parameter, the value shall be the hexadecimal equivalent of the T.35 code, with bit 8 treated as the most significant bit and bit 1 treated as the least significant bit. Example values: 00 for Japan; 0A for Austria; 64 for Lebanon; C4 for Zimbabwe.
+
+#### *Recommended default*
+
+If the DCE is specified for use in only one country, that country code shall be the default. Otherwise, the recommended default is the expected country of sale or first installation. DCE may use hardware means to select the country of installation, in which case the DCE shall use that to determine the default value.
+
+##### *Read syntax*
+
+**+GCI?**
+
+The DCE shall transmit information text which reports the hexadecimal numeric value corresponding to the current setting:
+
+**+GCI:**
+
+e.g., +GCI:3D indicates that the DCE is set for France.
+
+*Test syntax*
+
+**+GCI=?**
+
+The DCE shall transmit information text which reports the list of numerical values corresponding to the country or countries that are supported:
+
+**+GCI:( [, [,...]])**
+
+e.g., +GCI:(20,73,B5) indicates that the DCE can be set for Canada, Mexico or the United States.
+
+*Implementation*
+
+This command shall be implemented in DCE that can be installed in more than one country, and which need to adjust operating parameters in order to function correctly in those countries.
+
+## **6.2 DTE-DCE interface commands**
+
+The parameters defined in this clause control the operation of the interface between the DTE and DCE.
+
+### **6.2.1 Command line termination character**
+
+*Parameter*
+
+**S3**
+
+*Description*
+
+This S-parameter represents the decimal IA5 value of the character recognized by the DCE from the DTE to terminate an incoming command line. It is also generated by the DCE as part of the header, trailer, and terminator for result codes and information text, along with the **S4** parameter (see the description of the **V** parameter for usage).
+
+The previous value of **S3** is used to determine the command line termination character for entry of the command line containing the **S3** setting command. However, the result code issued shall use the value of **S3** as set during the processing of the command line. For example, if **S3** was previously set to 13 and the command line "**ATS3=30**" is issued, the command line shall be terminated with a CR character (IA5 0/13), but the result code issued will use the character with the ordinal value 30 (IA5 2/14) in place of the CR.
+
+*Defined values*
+
+**0 to 127** Set command line termination character to this value.
+
+*Mandatory default setting*
+
+**13** Carriage return character (CR, IA5 0/13).
+
+*Implementation*
+
+Implementation of this parameter is mandatory. If the specified value is not recognized, an **ERROR** result code is issued.
+
+### **6.2.2 Response formatting character**
+
+*Parameter*
+
+**S4**
+
+*Description*
+
+This S-parameter represents the decimal IA5 value of the character generated by the DCE as part of the header, trailer, and terminator for result codes and information text, along with the **S3** parameter (see the description of the **V** parameter for usage).
+
+If the value of **S4** is changed in a command line, the result code issued in response to that command line will use the new value of **S4**.
+
+#### *Defined values*
+
+**0 to 127** Set response formatting character to this value.
+
+#### *Recommended default setting*
+
+**10** Line feed character (LF, IA5 0/10).
+
+#### *Implementation*
+
+Implementation of this parameter is mandatory. If the specified value is not recognized, an **ERROR** result code is issued.
+
+### **6.2.3 Command line editing character**
+
+#### *Parameter*
+
+**S5**
+
+#### *Description*
+
+This S-parameter represents the decimal IA5 value of the character recognized by the DCE as a request to delete from the command line the immediately preceding character (see 5.2.2).
+
+#### *Defined values*
+
+**0 to 127** Set command line editing character to this value.
+
+#### *Recommended default setting*
+
+**8** Backspace character (BS, IA5 0/8).
+
+#### *Implementation*
+
+Implementation of this parameter is mandatory. If the specified value is not recognized, an **ERROR** result code is issued.
+
+### **6.2.4 Command echo**
+
+#### *Parameter*
+
+**E[]**
+
+#### *Description*
+
+The setting of this parameter determines whether or not the DCE echoes characters received from the DTE during command state and online command state (see 5.2.3).
+
+#### *Defined values*
+
+**0** DCE does not echo characters during command state and online command state.
+
+**1** DCE echoes characters during command state and online command state.
+
+#### *Recommended default setting*
+
+**1** DCE echoes characters during command state and online command state.
+
+#### *Implementation*
+
+Implementation of this parameter is mandatory. If the specified value is not recognized, an **ERROR** result code is issued.
+
+### 6.2.5 Result code suppression
+
+#### Parameter
+
+**Q[]**
+
+#### Description
+
+The setting of this parameter determines whether or not the DCE transmits result codes to the DTE. When result codes are being suppressed, no portion of any intermediate, final, or unsolicited result code – header, result text, line terminator, or trailer – is transmitted. Information text transmitted in response to commands is not affected by the setting of this parameter.
+
+#### Defined values
+
+- 0** DCE transmits result codes.
+- 1** Result codes are suppressed and not transmitted.
+
+#### Recommended default setting
+
+- 0** DCE transmits result codes.
+
+#### Result codes
+
+- OK** If value is **0**.
+- (none)** If value is **1** (because result codes are suppressed).
+- ERROR** For unsupported values (if previous value was **Q0**).
+- (none)** For unsupported values (if previous value was **Q1**).
+
+#### Implementation
+
+Implementation of this parameter is mandatory. If the specified value is not recognized, an **ERROR** result code is issued.
+
+### 6.2.6 DCE response format
+
+#### Parameter
+
+**V[]**
+
+#### Description
+
+The setting of this parameter determines the contents of the header and trailer transmitted with result codes and information responses. It also determines whether result codes are transmitted in a numeric form or an alphabetic (or "verbose") form. The text portion of information responses is not affected by this setting.
+
+Table 3 shows the effect of the setting of this parameter on the format of information text and result codes. All references to **** mean "the character with the ordinal value specified in parameter **S3**"; all references to **** likewise mean "the character with the ordinal value specified in parameter **S4**". See Table 3.
+
+**Table 3/V.250 – Effect of V parameter on response formats**
+
+| | V0 | V1 |
+|-----------------------|-----------------------------------------|--------------------------------------------------------------------------------|
+| Information responses | <text><cr><lf> | <cr><lf>
<text><cr><lf> |
+| Result codes | <numeric code><cr> | <cr><lf>
<verbose code><cr><lf> |
+
+#### *Defined values*
+
+- 0** DCE transmits limited headers and trailers and numeric text.
+- 1** DCE transmits full headers and trailers and verbose response text.
+
+#### *Recommended default setting*
+
+- 1** DCE transmits full headers and trailers and verbose response text.
+
+#### *Result codes*
+
+- 0** If value is **0** (because numeric response text is being used).
+- OK** If value is **1**.
+- 4** For unsupported values (if previous value was **V0**).
+- ERROR** For unsupported values (if previous value was **V1**).
+
+#### *Implementation*
+
+Implementation of this parameter is mandatory. If the specified value is not recognized, an **ERROR** result code is issued.
+
+### **6.2.7 Result code selection and call progress monitoring control**
+
+#### *Parameter*
+
+**X[]**
+
+#### *Description*
+
+The setting of this parameter determines whether or not the DCE transmits particular result codes to the DTE. It also controls whether or not the DCE verifies the presence of a dial tone when it first goes off-hook to begin dialling, and whether or not engaged tone (busy signal) detection is enabled. However, this setting has no effect on the operation of the **W** dial modifier, which always checks for a dial tone regardless of this setting, nor on the busy signal detection capability of the **W** and **@** dial modifiers. See Table 4.
+
+**Table 4/V.250 – Defined values for X parameter**
+
+| X<value> | Description |
+|-----------------------|---------------------------------------------------------------------------------------------------------------------------------------------|
+| 0 | CONNECT result code is given upon entering online data state. Dial tone and busy detection are disabled. |
+| 1 | CONNECT result code is given upon entering online data state. Dial tone and busy detection are disabled. |
+| 2 | CONNECT result code is given upon entering online data state. Dial tone detection is enabled, and busy detection is disabled. |
+| 3 | CONNECT result code is given upon entering online data state. Dial tone detection is disabled, and busy detection is enabled. |
+| 4 | CONNECT result code is given upon entering online data state. Dial tone and busy detection are both enabled. |
+
+#### *Implementation*
+
+Implementation of this parameter is mandatory. If the specified value is not recognized, an **ERROR** result code is issued.
+
+### 6.2.8 Circuit 109 (Received line signal detector) behaviour
+
+#### *Parameter*
+
+**&C[]**
+
+#### *Description*
+
+This parameter determines how the state of circuit 109 relates to the detection of received line signal from the distant end. Changing the parameter will take effect immediately in both the command and online command states.
+
+In **&C1** mode of operation, circuit 109 is not turned off until all data previously received from the remote DCE is delivered to the local DTE. However, such buffered data shall be discarded and circuit 109 turned off if the DTE turns off circuit 108 (if **&D1** or **&D2** is set).
+
+#### *Defined values*
+
+- 0** The DCE always presents the ON condition on circuit 109.
+- 1** Circuit 109 changes in accordance with the underlying DCE, which may include functions other than the physical layer functions (e.g., ITU-T Recs V.42, V.110, V.120 and V.13).
+
+#### *Recommended default setting*
+
+- 1** Circuit 109 changes in accordance with the underlying DCE, which may include functions other than the physical layer functions (e.g., ITU-T Recs V.42, V.110, V.120 and V.13).
+
+#### *Implementation*
+
+Implementation of this parameter is mandatory. If the value specified is not recognized, an **ERROR** result code is issued.
+
+### 6.2.9 Circuit 108 (Data terminal ready) behaviour
+
+#### *Parameter*
+
+**&D[]**
+
+#### *Description*
+
+This parameter determines how the DCE responds when circuit 108/2 is changed from the ON to the OFF condition during online data state.
+
+#### *Defined values*
+
+- 0** DCE ignores circuit 108/2.
+- 1** Upon an on-to-off transition of circuit 108/2, the DCE enters online command state and issues an OK result code; the call remains connected.
+- 2** Upon an on-to-off transition of circuit 108/2, the DCE instructs the underlying DCE to perform an orderly cleardown of the call. The disposition of any data in the DCE pending transmission to the remote DCE is controlled by the +ETBM parameter (see 6.5.6) if implemented; otherwise, this data is sent before the call is cleared, unless the remote DCE clears the call first (in which case pending data is discarded). The DCE disconnects from the line. Automatic answer is disabled while circuit 108/2 remains off.
+
+#### *Implementation*
+
+Implementation of this parameter is mandatory. If the value specified is not recognized, an **ERROR** result code is issued. Implementation of defined values 0 and 2 is mandatory; implementation of defined value 1 is optional.
+
+### 6.2.10 Fixed DTE rate (+IPR)
+
+#### *Parameter*
+
+**+IPR=**
+
+#### *Description*
+
+This numeric extended-format parameter specifies the data rate at which the DCE will accept commands, in addition to 1200 bit/s or 9600 bit/s (as required in 4.3). It may be used to select operation at rates at which the DCE is not capable of automatically detecting the data rate being used by the DTE. Specifying a value of 0 disables the function and allows operation only at rates automatically detectable by the DCE. The specified rate takes effect following the issuance of any result code(s) associated with the current command line.
+
+The specified does not apply in online data state if Direct mode of operation is selected.
+
+#### *Defined values*
+
+The value specified shall be the rate in bits per second at which the DTE-DCE interface should operate, e.g., "19 200" or "115 200". The rates supported by a particular DCE are manufacturer-specific; however, the +IPR parameter should permit the setting of any rate supported by the DCE during online operation. Rates which include a non-integral number of bits per second should be truncated to the next lower integer (e.g., 134.5 bit/s should be specified as 134; 45.45 bit/s should be specified as 45). If unspecified or set to 0, automatic detection is selected for the range determined as in 4.3 and the DCE manufacturer, and the character format is also forced to autodetect, +ICF=0 (see 6.2.11).
+
+#### *Recommended default setting*
+
+It is recommended that the default for this parameter be the automatic detection setting (0), which facilitates initial DTE-DCE communications.
+
+##### *Read syntax*
+
+**+IPR?**
+
+The DCE shall transmit a string of information text to the DTE, consisting of:
+
+**+IPR:**
+
+e.g., +IPR:0 if set for automatic rate detection.
+
+e.g., +IPR:9600 if set to 9600 bit/s.
+
+##### *Test syntax*
+
+**+IPR=?**
+
+The DCE shall transmit one or two strings of information text to the DTE, consisting of:
+
+**+IPR:(list of supported autodetectable values)[,(list of fixed-only values)]**
+
+e.g., +IPR:(0,300,1200,2400,4800,9600),(19200,38400,57600)
+
+if the DCE can autodetect up to 9600 bit/s and can support three additional higher fixed rates.
+
+#### *Implementation*
+
+Implementation of this parameter is optional. If the rate specified is not supported by the DCE, an **ERROR** result code shall be returned.
+
+### 6.2.11 DTE-DCE character framing (+ICF)
+
+#### Parameter
+
+**+ICF**=[[,]]
+
+#### Description
+
+This extended-format compound parameter is used to determine the local serial port start-stop (asynchronous) character framing that the DCE shall use while accepting DTE commands and while transmitting information text and result code, if this is not automatically determined; +IPR=0 forces +ICF=0 (see +IPR, 6.2.10). Note that the definition of fixed character format for online data state is for further study.
+
+**** determines the number of bits in the data bits, the presence of a parity bit, and the number of stop bits in the start-stop frame.
+
+NOTE – The semantics of this command are derived from ITU-T Rec. V.58.
+
+**** determines how the parity bit is generated and checked, if present.
+
+#### Defined values
+
+See Table 5.
+
+**Table 5/V.250 – Character format values**
+
+| <format> | Valid numeric values |
+|-----------------------|-------------------------------|
+| 0 | auto detect |
+| 1 | 8 Data; 2 Stop |
+| 2 | 8 Data; 1 Parity; 1 Stop |
+| 3 | 8 Data; 1 Stop |
+| 4 | 7 Data; 2 Stop |
+| 5 | 7 Data; 1 Parity; 1 Stop |
+| 6 | 7 Data; 1 Stop |
+| <parity> | Defined numeric values |
+| 0 | Odd |
+| 1 | Even |
+| 2 | Mark |
+| 3 | Space |
+
+#### Recommended default setting
+
+For : **3**
+
+For : **3**
+
+##### Read syntax
+
+**+ICF?**
+
+The DCE shall transmit a string of information text to the DTE, consisting of:
+
+**+ICF:,**
+
+e.g., +ICF:3,3 for the recommended defaults.
+
+##### Test syntax
+
+###### **+ICF=?**
+
+The DCE shall transmit a string of information text to the DTE, consisting of:
+
+###### **+ICF:(list of supported values),(list of supported values)**
+
+e.g., +ICF:(0-6),(0-3) for all defined values.
+
+#### Implementation
+
+Implementation of this parameter is optional. If the format specified is not supported by the DCE, an **ERROR** result code shall be returned.
+
+### **6.2.12 DTE-DCE local flow control (+IFC)**
+
+#### Parameter
+
+##### **+IFC=[ [,]]**
+
+#### Description
+
+This extended-format compound parameter is used to control the operation of local flow control between the DTE and DCE during the data state when V.42 error control is being used, or when fallback to non-error control mode is specified to include buffering and flow control. It accepts two numeric subparameters:
+
+- ****, which specifies the method to be used by the DTE to control the flow of received data from the DCE; and
+- ****, which specifies the method to be used by the DCE to control the flow of transmitted data from the DTE.
+
+#### Defined values
+
+See Table 6.
+
+**Table 6/V.250 – and values**
+
+| <DCE_by_DTE> | Description |
+|----------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------|
+| 0 | None |
+| 1 | DC1/DC3 on circuit 103; do not pass DC1/DC3 characters to the remote DCE |
+| 2 | Circuit 133 (Ready for Receiving) |
+| 3 | DC1/DC3 on circuit 103 with DC1/DC3 characters being passed through to the remote DCE in addition to being acted upon for local flow control |
+| 4 to 127 | Reserved for future standardization |
+| Other | Reserved for manufacturer-specific use |
+| <DTE_by_DCE> | Description |
+| 0 | None |
+| 1 | DC1/DC3 on circuit 104 |
+| 2 | Circuit 106 (Clear to Send/Ready for Sending) |
+| 3 to 127 | Reserved for future standardization |
+| Other | Reserved for manufacturer-specific use |
+| NOTE – DC1 is IA5 1/1; DC3 is IA5 1/3. | |
+
+#### *Recommended default settings*
+
+For : **2**
+
+For : **2**
+
+##### *Read syntax*
+
+###### **+IFC?**
+
+The DCE shall transmit a string of information text to the DTE, consisting of:
+
+**+IFC:,