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+![ITU logo: A globe with a lightning bolt and the letters ITU.](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+ITU logo: A globe with a lightning bolt and the letters ITU.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**Q.115.0**
+
+(12/2002)
+
+SERIES Q: SWITCHING AND SIGNALLING
+
+Clauses applicable to ITU-T standard systems – Logic and protocols for the control of signal processing network elements and functions
+
+---
+
+**Protocols for the control of signal processing network elements and functions**
+
+ITU-T Recommendation Q.115.0
+
+---
+
+# 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   |
+| General clauses                                                                                | Q.100-Q.109   |
+| Transmission clauses for signalling                                                            | Q.110-Q.114   |
+| <b>Logic and protocols for the control of signal processing network elements and functions</b> | <b>Q.115</b>  |
+| Abnormal conditions                                                                            | Q.116-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 |
+
+For further details, please refer to the list of ITU-T Recommendations.
+
+## **ITU-T Recommendation Q.115.0**
+
+# **Protocols for the control of signal processing network elements and functions**
+
+## **Summary**
+
+Echo Cancellation and Voice Quality Enhancement have become a necessity not only in Circuit Switched Networks (wired and wireless) but also in Next Generation Networks. Signal processing network elements and functions are provided on a per-call basis to guarantee QoS for voice calls. This Recommendation describes the protocols to control, on a per-call basis, the signal processing functions. The protocols described in this Recommendation include TDM-based as well as IP-based protocol versions for TDM networks and IP networks.
+
+## **Source**
+
+ITU-T Recommendation Q.115.0 (2002) was prepared by ITU-T Study Group 11 (2001-2004) and approved under the WTSA Resolution 1 procedure on 29 December 2002.
+
+## **Keywords**
+
+Automatic Level (Gain) Control, Echo cancellation, Echo control, Noise Reduction, Voice Quality Enhancement.
+
+## 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 2003
+
+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 .....                                             | 1 |
+| 4   | Abbreviations and acronyms .....                              | 2 |
+| 5   | Conceptual model .....                                        | 2 |
+| 6   | Network scenarios .....                                       | 3 |
+| 6.1 | TDM: Standalone SPNE.....                                     | 3 |
+| 6.2 | VoIP: SPNE integrated in or external to a media gateway ..... | 4 |
+| 7   | Protocols .....                                               | 5 |
+| 7.1 | TDM .....                                                     | 5 |
+| 7.2 | VoIP.....                                                     | 5 |
+
+
+
+# Protocols for the control of signal processing network elements and functions
+
+# 1 Scope
+
+Echo Control (e.g., echo cancellation) and Voice Quality Enhancement (e.g., voice enhancement device) have become a necessity not only in Circuit Switched Networks (wired and wireless) but also in Next Generation Networks. Signal processing network elements and functions are provided on a per-call basis to guarantee QoS for voice calls. This Recommendation describes the protocols to control on a per-call basis the signal processing functions. The protocols described in this Recommendation include TDM-based as well as IP-based protocol versions for TDM networks and IP networks.
+
+The signal processing function specific logic, i.e. the logic that decides on the need for a signal processing function and the number of signal processing functions to be provided for a call, is defined in ITU-T Recs Q.115.x.
+
+# 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.
+
+- [1] ITU-T Recommendation Q.52 (2001), *Signalling between international switching centres and stand-alone echo control devices*.
+- [2] ITU-T Recommendation Q.55 (1999), *Signalling between signal processing network equipment (SPNE) and international switching centres (ISC)*.
+- [3] ITU-T Recommendation Q.56 (2001), *Signalling between signal processing network equipment (SPNE) and international switching centers over an IP network*.
+- [4] ITU-T Recommendation H.248 (2000), *Gateway Control Protocol*.
+- [5] ITU-T Recommendation G.173 (1993), *Transmission planning aspects of the speech service in digital public land mobile networks*.
+
+# 3 Definitions
+
+This Recommendation defines the following terms:
+
+- 3.1 signal processing function specific logic:** A functional entity (part of call control) that decides if a signal processing function is required for this call.
+- 3.2 signal processing function:** A functional entity; examples are echo cancellation, noise reduction, automatic level (gain) control, etc.
+- 3.3 signal processing network element:** A physical entity that contains one or more signal processing functions assigned to one or more E1/T1 facilities.
+
+# 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations:
+
+|       |                                                                                       |
+|-------|---------------------------------------------------------------------------------------|
+| CAS   | Channel associated signalling                                                         |
+| CCF   | Call Control Function                                                                 |
+| ECD   | Echo Control Device                                                                   |
+| ECF   | Echo Control Function (echo cancellation, echo suppression)                           |
+| E1    | A transmission link operating at 2048 kbit/s, supporting 30 or 31 64 kbit/s channels. |
+| IP    | Internet Protocol                                                                     |
+| LAN   | Local Area Network                                                                    |
+| MG    | Media Gateway                                                                         |
+| MGC   | Media Gateway Controller                                                              |
+| QoS   | Quality of Service                                                                    |
+| SPF   | Signal Processing Function                                                            |
+| SPFCF | SPF Control Function                                                                  |
+| SPFSF | SPF Switching Function                                                                |
+| SPFSL | SPF Specific Logic                                                                    |
+| SPNE  | Signal Processing Network Element                                                     |
+| TDM   | Time Division Multiplex                                                               |
+| T1    | A transmission link operating at 1544 kbit/s supporting 24 speech channels.           |
+| VoIP  | Voice over IP                                                                         |
+
+# 5 Conceptual model
+
+For each signal processing function SPF there exists a signal processing function specific logic added to call/bearer control; see Figure 1. Any SPF is provided on a per-call basis. A master slave relation exists between the SPF switching function and the SPF control function.
+
+![Figure 1/Q.115.0 – Conceptual methodology model. A diagram showing three planes: Functional plane, Physical plane, and VoIP plane. Functional plane contains SPFSF, SPFCF, and CCF/BCF (with SPFSL). Physical plane contains EXCHANGE, SPNE, and MG. VoIP plane contains MGC and SPNE. Connections include IP, TDM, and relationships 'r'. A note indicates SPF may be provided in the MG or a standalone SPNE.](ebff22fb5dd6f50a90e44dca0f82f285_img.jpg)
+
+The diagram illustrates the conceptual methodology model across three planes:
+
+- Functional plane:** Contains SPFSF, SPFCF, and CCF/BCF (which includes SPFSL). SPFSF and SPFCF are connected by a relationship 'r'. CCF/BCF is connected to SPFSF by a dashed mapping line.
+- Physical plane:** Contains EXCHANGE, SPNE, and MG. EXCHANGE is connected to SPNE by a solid TDM line. EXCHANGE is connected to MGC in the VoIP plane by a dashed mapping line. SPNE is connected to MG by a solid IP line.
+- VoIP plane:** Contains MGC and SPNE. MGC is connected to MG by a solid IP line. SPNE is connected to MG by a solid TDM line.
+
+Mapping lines (dashed) connect functional entities to physical entities: SPFSF to EXCHANGE, SPFCF to SPNE, and CCF/BCF to EXCHANGE. A note indicates that SPF may be provided in the MG or in a standalone SPNE.
+
+**Legend:**
+
+- Physical /virtual connection
+- r Relationship between communicating pairs of functional entities
+- - - - Mapping
+
+Q.115.0\_F01
+
+Figure 1/Q.115.0 – Conceptual methodology model. A diagram showing three planes: Functional plane, Physical plane, and VoIP plane. Functional plane contains SPFSF, SPFCF, and CCF/BCF (with SPFSL). Physical plane contains EXCHANGE, SPNE, and MG. VoIP plane contains MGC and SPNE. Connections include IP, TDM, and relationships 'r'. A note indicates SPF may be provided in the MG or a standalone SPNE.
+
+**Figure 1/Q.115.0 – Conceptual methodology model**
+
+In the VoIP scenario where the MG controls the SPFs provided in a standalone (external) SPNE, the MG has an application protocol interworking function (H.248 SPNE package ↔ Q.52/Q.55/Q.56).
+
+# 6 Network scenarios
+
+## 6.1 TDM: Standalone SPNE
+
+Echo suppressors and echo cancellers provided as standalone equipment are considered to be a first generation of SPNE. The protocol to control standalone echo control devices is defined in ITU-T Rec. Q.52; see Figure 2.
+
+A platform providing one or more signal processing functions is referred to as SPNE. The protocols to control standalone SPNEs are defined in ITU-T Recs Q.55 and Q.56; see Figure 2.
+
+![Figure 2/Q.115.0 – TDM scenarios and the control protocols. The diagram shows two scenarios. The top scenario shows an EXCHANGE connected to an ECD via E1, T1 lines. The EXCHANGE contains a box 'a' (SPFSF) and the ECD contains a box 'b' (SPFCF) within an ECF. A callout box 'Q.52' points to the connection. The bottom scenario shows an EXCHANGE connected to an SPNE via E1, T1 lines. The EXCHANGE contains a box 'a' (SPFSF) and the SPNE contains a box 'b' (SPFCF) within SPFs. A callout box 'Q.55' points to a 'CAS, SS7, LAN' connection between 'a' and the SPNE. Another callout box 'Q.56' points to a connection between the SPNE and an IP network (represented by an oval). A legend at the bottom left defines 'a' as SPFSF and 'b' as SPFCF. The label 'Q.115.0_F02' is in the bottom right.](a5ee5c23b6dc52ec1d724b76d5a5f58f_img.jpg)
+
+Q.115.0\_F02
+
+a SPFSF  
+b SPFCF
+
+Figure 2/Q.115.0 – TDM scenarios and the control protocols. The diagram shows two scenarios. The top scenario shows an EXCHANGE connected to an ECD via E1, T1 lines. The EXCHANGE contains a box 'a' (SPFSF) and the ECD contains a box 'b' (SPFCF) within an ECF. A callout box 'Q.52' points to the connection. The bottom scenario shows an EXCHANGE connected to an SPNE via E1, T1 lines. The EXCHANGE contains a box 'a' (SPFSF) and the SPNE contains a box 'b' (SPFCF) within SPFs. A callout box 'Q.55' points to a 'CAS, SS7, LAN' connection between 'a' and the SPNE. Another callout box 'Q.56' points to a connection between the SPNE and an IP network (represented by an oval). A legend at the bottom left defines 'a' as SPFSF and 'b' as SPFCF. The label 'Q.115.0\_F02' is in the bottom right.
+
+**Figure 2/Q.115.0 – TDM scenarios and the control protocols**
+
+## 6.2 VoIP: SPNE integrated in or external to a media gateway
+
+H.248 is the media gateway protocol used between a media gateway controller and a media gateway in the decomposed architecture. The H.248 SPNE package defined in this Recommendations allows the control of signal processing functions; see Figure 3.
+
+![Figure 3/Q.115.0 – VoIP Gateway (decomposed architecture); H.248 SPNE package (as defined in this Recommendation) is the control protocol. The diagram shows a Media Gateway Controller (MGC) connected to two Media Gateways (MG). The top MG is connected to an SPNE unit containing SPFs (Signal Processing Functions) labeled 'a' (SPFSF) and 'b' (SPFCF). The bottom MG is also connected to an SPNE unit with SPFs labeled 'b' (SPFCF). Both MGs are connected to an IP network via routers. The MGC is connected to the top MG via an H.248 SPNE package. The top MG is connected to the bottom MG via a Q.52, Q.55 package. The IP network is shown as a circle containing three routers. A legend indicates: 'a' SPFSF, 'b' SPFCF, and a double-headed arrow for interworking.](cfef993dcc8fb513de79eb1f93cf26ae_img.jpg)
+
+Figure 3/Q.115.0 – VoIP Gateway (decomposed architecture); H.248 SPNE package (as defined in this Recommendation) is the control protocol. The diagram shows a Media Gateway Controller (MGC) connected to two Media Gateways (MG). The top MG is connected to an SPNE unit containing SPFs (Signal Processing Functions) labeled 'a' (SPFSF) and 'b' (SPFCF). The bottom MG is also connected to an SPNE unit with SPFs labeled 'b' (SPFCF). Both MGs are connected to an IP network via routers. The MGC is connected to the top MG via an H.248 SPNE package. The top MG is connected to the bottom MG via a Q.52, Q.55 package. The IP network is shown as a circle containing three routers. A legend indicates: 'a' SPFSF, 'b' SPFCF, and a double-headed arrow for interworking.
+
+**Figure 3/Q.115.0 – VoIP Gateway (decomposed architecture); H.248 SPNE package (as defined in this Recommendation) is the control protocol**
+
+# 7 Protocols
+
+## 7.1 TDM
+
+The protocol to control standalone Echo Control Devices is defined in ITU-T Rec. Q.52.
+
+The protocols (protocol family, including CAS, SS7 and LAN) to control one or more SPF of a SPNE is defined in ITU-T Rec. Q.55. If a "public" IP network is used for the transport of the control signalling, then ITU-T Rec. Q.56 could be used.
+
+## 7.2 VoIP
+
+This clause describes the Signal Processing Network Equipment (SPNE) package for H.248. It allows a Media Gateway Controller to control the SPFs of a SPNE equipment either integrated into or attached to a Media Gateway. The SPNE equipment may include echo cancellation (without non linear processor), automatic level control, noise reduction and frequency equalization.
+
+### SPNE Control Package
+
+PackageID: spne, (-----)
+
+Version: 1
+
+Extends: TDM Package (tdmc (0x000d) Version 1
+
+This package defines properties and events for SPNE functions controlled by or integrated into a media gateway. Note that echo cancellers associated with media gateways are assumed to be compliant with ITU-T Rec. G.168 as indicated in ITU-T Rec. G.177.
+
+Logic that determines which SPNE function is enabled or disabled during a call is outside the scope of this Recommendation.
+
+### 7.2.1 Properties
+
+#### **Non Linear Processing**
+
+PropertyID: nlp (0x0003)
+
+Controls the non-linear processing property of an ECD on the TDM termination.
+
+Type: enumeration
+
+Possible Values:
+
+DISABLE (0x0000)
+
+ENABLE (0x0001)
+
+Defined in: LocalControlDescriptor
+
+Characteristics: Read/Write
+
+#### **Comfort Noise Injection**
+
+PropertyID: cni (0x0004)
+
+This controls the comfort noise injection function of the ECD on the TDM termination.
+
+Type: enumeration
+
+Possible Values:
+
+DISABLE (0x0000)
+
+ENABLE (0x0001)
+
+Defined in: LocalControlDescriptor
+
+Characteristics: Read/Write
+
+#### **Automatic Level Control**
+
+PropertyID: alc (0x0005)
+
+This provides control information for incoming automatic level control on the TDM termination.
+
+Type: enumeration
+
+Possible Values:
+
+DISABLE (0x0000)
+
+ENABLE TYPE 0 (0x0001)
+
+ENABLE TYPE 1 (0x0002)
+
+ENABLE TYPE 2 (0x0003)
+
+ENABLE TYPE 3 (0x0004)
+
+Defined in: LocalControlDescriptor
+
+Characteristics: Read/Write
+
+#### **Frequency Equalization**
+
+PropertyID: fe (0x0006)
+
+This controls the frequency equalization function of a TDM termination. The characteristics of the frequency equalization type is determined and configured by manufacturer and/or carrier.
+
+Type: enumeration
+
+Possible Values:
+
+DISABLE (0x0000)  
+ENABLE TYPE 0 (0x0001)  
+ENABLE TYPE 1 (0x0002)  
+ENABLE TYPE 2 (0x0003)  
+ENABLE TYPE 3 (0x0004)
+
+Defined in: LocalControlDescriptor
+
+Characteristics: Read/Write
+
+#### **Noise Reduction**
+
+PropertyID: in-nrd (0x0007)
+
+This controls the incoming noise reduction function of a TDM termination. The characteristics of the incoming noise reduction function type is determined and configured by manufacturer and/or carrier.
+
+Type: enumeration
+
+Possible Values:
+
+DISABLE INCOMING (0x0000)  
+ENABLE INCOMING TYPE 0 (0x0001)  
+ENABLE INCOMING TYPE 1 (0x0002)  
+ENABLE INCOMING TYPE 2 (0x0003)  
+ENABLE INCOMING TYPE 3 (0x0004)
+
+Defined in: LocalControlDescriptor
+
+Characteristics: Read/Write
+
+PropertyID: out-nrd (0x0009)
+
+This controls the outgoing noise reduction function of a TDM termination. The characteristics of the outgoing noise reduction function type is determined and configured by manufacturer and/or carrier.
+
+Type: enumeration
+
+Possible Values:
+
+DISABLE OUTGOING (0x0000)  
+ENABLE OUTGOING TYPE 0 (0x0001)  
+ENABLE OUTGOING TYPE 1 (0x0002)  
+ENABLE OUTGOING TYPE 2 (0x0003)  
+ENABLE OUTGOING TYPE 3 (0x0004)
+
+Defined in: LocalControlDescriptor
+
+Characteristics: Read/Write
+
+Events: None
+
+Signals: None
+
+Statistics: None
+
+### **7.2.2 Procedures**
+
+#### **Echo Cancellation**
+
+When a MGC determines, through Q.115.1 echo control logic, a need to provide an echo control device (ECD) on a connection, it initiates a command to the MG. The MG, upon receipt of a property with the ECD indication, enables the echo control device associated with the specified termination if the value is ENABLE, or disables the echo control device if the value is DISABLE.
+
+#### **Non Linear Processing**
+
+Echo cancellers include a function called a non-linear processor (NLP). This operates as a smart attenuator, and eliminates residual echo during periods when only one party is speaking. In some cases the NLP function is automatically enabled when the ECD is enabled, however, in other network configurations, it is beneficial to speech quality to disable the NLP independent of the ECD. A network operator may determine that the NLP should be disabled for certain calls. When a MGC determines a requirement for disabling the NLP associated with a termination, it will send this package to the MG. How the MGC determines the requirement for use of the NLP is outside the scope of this Recommendation.
+
+#### **Automatic Level Control**
+
+When a MGC determines a requirement for automatic level control of the media stream, it will send a package to a MG to enable a selected Type ALC associated with the termination. How the MGC determines the requirement for use of the ALC is outside the scope of this Recommendation.
+
+#### **Frequency Equalization**
+
+When a MGC determines a requirement for frequency equalization of the media stream, it will send a property to a MG to enable a selected type of FE associated with the termination. How the MGC determines the requirement for use of the FE is outside the scope of this Recommendation.
+
+#### **Noise Reduction**
+
+When a MGC determines to insert a Noise Reduction Device/Function to reduce the amount of unwanted noise, it will enable a NRD associated with the termination by sending a property to the MG. How the MGC determines the requirement for use of the NRD is outside the scope of this Recommendation.
+
+
+
+## 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                                                   |
+| <b>Series Q</b> | <b>Switching and signalling</b>                                                                                                |
+| 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                                                           |