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+# Recommendation **ITU-T G.1051 (03/2023)**
+
+SERIES G: Transmission systems and media, digital systems and networks
+
+Multimedia Quality of Service and performance – Generic and user-related aspects
+
+# --- **Latency measurement and interactivity scoring under real application data traffic patterns**
+
+![ITU logo](0538daaa5583c23e17db3a12f2281a55_img.jpg)
+
+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.
+
+ITU logo
+
+## ITU-T G-SERIES RECOMMENDATIONS **TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS**
+
+|                                                                                                                                              |                      |
+|----------------------------------------------------------------------------------------------------------------------------------------------|----------------------|
+| INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS                                                                                             | G.100–G.199          |
+| GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS                                                                  | G.200–G.299          |
+| INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES                                                      | G.300–G.399          |
+| GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES | G.400–G.449          |
+| COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY                                                                                            | G.450–G.499          |
+| TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS                                                                                       | G.600–G.699          |
+| DIGITAL TERMINAL EQUIPMENTS                                                                                                                  | G.700–G.799          |
+| DIGITAL NETWORKS                                                                                                                             | G.800–G.899          |
+| DIGITAL SECTIONS AND DIGITAL LINE SYSTEM                                                                                                     | G.900–G.999          |
+| <b>MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE – GENERIC AND USER-RELATED ASPECTS</b>                                                      | <b>G.1000–G.1999</b> |
+| TRANSMISSION MEDIA CHARACTERISTICS                                                                                                           | G.6000–G.6999        |
+| DATA OVER TRANSPORT – GENERIC ASPECTS                                                                                                        | G.7000–G.7999        |
+| PACKET OVER TRANSPORT ASPECTS                                                                                                                | G.8000–G.8999        |
+| ACCESS NETWORKS                                                                                                                              | G.9000–G.9999        |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+# Recommendation ITU-T G.1051
+
+# Latency measurement and interactivity scoring under real application data traffic patterns
+
+## Summary
+
+An important aspect of the data transmission performance of networks are data transfer times and resulting answering delay in real-time, interactive scenarios. Latency and reactivity are becoming even more essential for new interactive and real-time applications as e.g., in augmented reality but also in Industry 4.0 or automotive use.
+
+Latency and resulting reactivity must be measured in a scenario that emulates the application and use case to be evaluated. This requires first a data transfer profile (traffic pattern) that is considered as equivalent to the application so that the relevant latency and reactivity can be measured. Second, the resulting influence of latency to a certain application can be described by an interactivity scoring model. This model is not a general one, rather, it is individually scaled for each of the use cases like e.g., e-Gaming or real-time drone control and is focused on scoring transport with a simplified, parametrizable model approach, it does not target individual application behaviours.
+
+## History
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID*                                                                |
+|---------|----------------|------------|-------------|---------------------------------------------------------------------------|
+| 1.0     | ITU-T G.1051   | 2023-03-01 | 12          | <a href="http://handle.itu.int/11.1002/1000/15468">11.1002/1000/15468</a> |
+
+## Keywords
+
+Data traffic patterns, interactivity, latency, round-trip time.
+
+---
+
+\* To access the Recommendation, type the URL <http://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID. For example, <http://handle.itu.int/11.1002/1000/11830-en>.
+
+## 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/software copyrights, 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 appropriate ITU-T databases available via the ITU-T website at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2023
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|      |                                                                                                                                                                                  | Page |
+|------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|------|
+| 1    | Scope .....                                                                                                                                                                      | 1    |
+| 2    | References.....                                                                                                                                                                  | 1    |
+| 3    | Definitions .....                                                                                                                                                                | 1    |
+| 4    | Abbreviations and acronyms .....                                                                                                                                                 | 2    |
+| 5    | Conventions .....                                                                                                                                                                | 2    |
+| 6    | Introduction.....                                                                                                                                                                | 2    |
+| 7    | Test method to obtain two-way latency .....                                                                                                                                      | 2    |
+| 7.1  | Approach to obtain two-way latency .....                                                                                                                                         | 2    |
+| 7.2  | Extending the approach to asymmetrical traffic.....                                                                                                                              | 3    |
+| 7.3  | Guidelines to derive traffic patterns from real applications .....                                                                                                               | 4    |
+| 8    | Latency test results and metrics.....                                                                                                                                            | 5    |
+| 8.1  | Per-packet two-way latency.....                                                                                                                                                  | 5    |
+| 8.2  | Packet delay variation .....                                                                                                                                                     | 5    |
+| 8.3  | Inter-packet delay variation .....                                                                                                                                               | 5    |
+| 8.4  | Lost packets .....                                                                                                                                                               | 6    |
+| 9    | Interactivity prediction model and related test case definition.....                                                                                                             | 6    |
+| 9.1  | Principles of the generic interactivity model approach.....                                                                                                                      | 6    |
+| 9.2  | Parametrization of an interactivity model.....                                                                                                                                   | 7    |
+| 9.3  | Guidelines for application grouping.....                                                                                                                                         | 8    |
+| 9.4  | Guidelines for defining test cases.....                                                                                                                                          | 8    |
+|      | Annex A – Computational structure of a generic interactivity model approach.....                                                                                                 | 9    |
+| A.1  | Introduction.....                                                                                                                                                                | 9    |
+| A.2  | Modelling approach for perceived interactivity of interactive applications ...                                                                                                   | 9    |
+| A.3  | Consideration of lost and discarded packets and packet delay variation in<br>the model.....                                                                                      | 10   |
+| A.4  | Conclusion .....                                                                                                                                                                 | 12   |
+|      | Appendix I – Example generic traffic patterns and model parameters according to<br>Annex A .....                                                                                 | 14   |
+| I.1  | Principle of application emulation and model parameters.....                                                                                                                     | 14   |
+| I.2  | Examples for application emulation and interactivity score computation.....                                                                                                      | 14   |
+|      | Appendix II – Parameter implementation according to Annex A based on subjective<br>results for cloud gaming considering a real example application on client and<br>server ..... | 20   |
+| II.1 | Introduction.....                                                                                                                                                                | 20   |
+| II.2 | Traffic patterns.....                                                                                                                                                            | 20   |
+| II.3 | Guidance for adaptation.....                                                                                                                                                     | 21   |
+| II.4 | Parameters for approximation subjective scores for cloud gaming .....                                                                                                            | 22   |
+|      | Bibliography .....                                                                                                                                                               | 25   |
+
+
+
+# Recommendation ITU-T G.1051
+
+# Latency measurement and interactivity scoring under real application data traffic patterns
+
+# 1 Scope
+
+The scope of this Recommendation is to specify a method to measure continuously data two-way latency and loss for a defined observation period. The basis for this method can be IETF's Two-Way Active Measurement Protocol (TWAMP). The typical symmetrical fixed-rate stream method will be modified to reflect situations in today's telecommunication networks including mobile scenarios and typical interactive use cases. The measurement approach is designed to also cover 5G URLLC configurations.
+
+In this approach, a scalable UDP packet stream is sent from and reflected by a far-end server back to the measurement client, e.g., from a smartphone or modem device to a server in the network or a second device.
+
+Based on the results of the latency, latency variation and loss measurements, a generic approach for a model describing interactivity as a single figure of merit is developed. Because the measurement results and the interactivity model depend on the chosen traffic pattern emulating an application, there will be clear rules to derive traffic patterns and corresponding model configurations as well as defined traffic patterns and formulas for popular applications (by applying the defined rules). This allows an immediate application of the measurement approach and enables later extension for new, arising applications.
+
+# 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 Y.1540] Recommendation ITU-T Y.1540 (2019), *Internet protocol data communication service – IP packet transfer and availability performance parameters*.
+- [3GPP TS 23.501] 3GPP TS 23.501 (2020), *System architecture for the 5G system (5GS)*.
+- [IETF RFC 5357] IETF RFC 5357 (2008), *A two-way active measurement protocol (TWAMP)*.
+- [IETF RFC 5481] IETF RFC 5481 (2009), *Packet delay variation applicability statement*.
+- [IETF RFC 6038] IETF RFC 6038 (2010), *Two-way active measurement protocol (TWAMP) reflect octets and symmetrical size features*.
+
+## 3 Definitions
+
+None.
+
+## 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|       |                                          |
+|-------|------------------------------------------|
+| 5QI   | 5G Quality of Service Identifier         |
+| ACR   | Absolute Category Rating                 |
+| DL    | Downlink direction in mobile connection  |
+| HD    | High Definition (video)                  |
+| IP    | Internet Protocol                        |
+| IPDV  | Inter-Packet Delay Variation             |
+| MOS   | Mean Opinion Score                       |
+| MTU   | Maximum Transmission Unit                |
+| PDV   | Packet Delay Variation                   |
+| QoS   | Quality of Service                       |
+| RTT   | Round-Trip Time                          |
+| TWAMP | Two-Way Active Measurement Protocol      |
+| UDP   | User Datagram Protocol                   |
+| UDPST | User Datagram Protocol Speed Test        |
+| UL    | Uplink direction in mobile connection    |
+| URLLC | Ultra-Reliable Low-Latency Communication |
+
+## 5 Conventions
+
+None.
+
+# 6 Introduction
+
+This Recommendation describes the technical realization of two-way delay measurements, how to apply this approach to emulate real application traffic and how to obtain the metrics and results from this measurement.
+
+The introduced measurement method considers specific characteristics of mobile networks and, in general, dynamically adjusted and load-dependent networks and connections.
+
+This Recommendation also gives advice on how to derive load and traffic patterns from real applications as well as for adjusting the scalable interactivity model to the target use case or application.
+
+One realization of an on-the-top model to predict interactivity of the tested connection is described in Annex A.
+
+# 7 Test method to obtain two-way latency
+
+## 7.1 Approach to obtain two-way latency
+
+A typical approach to obtain two-way latency is sending packets to a reflecting unit in the network and measuring the time between sending and receiving the corresponding packets. Time stamps for each packet from the sending and reflecting unit are required to obtain the key performance indicators (KPIs) defined in this Recommendation.
+
+As an established example, the TWAMP methodology and protocol can be considered, as defined in [IETF RFC 5357]; additional notes can be found in [IETF RFC 6038]. It is based on a UDP packet stream of packets of pre-defined size and frequency. The packets are sent to a reflecting server that sends the packet back to the sending client, where the received reflected packet can be assigned to a sent packet by an ID. The difference of the sending and receiving time stamps are reported as two-way latency. The TWAMP protocol according to IETF is defined and – depending on the vendor – supported by infrastructure components such as routers and IP-gateways.
+
+In addition to two-way packet latency, the TWAMP methodology also supports the calculation of one-way packet-delay variation (PDV), separated into uplink and downlink directions, as well as the detection of lost packets based on packet sequence numbers.
+
+The amount of data to transmit and the resulting data rate can be specified by packet size and sending frequency. This allows an emulation of data stream characteristics as produced by real applications.
+
+Other methods to obtain packet round-trip time (RTT) and one-way delay jitter and packet loss in sufficient temporal resolution can also be used such as that based on the UDPST method as described in [b-IETF] and is available under [b-OB-UDPST].
+
+## 7.2 Extending the approach to asymmetrical traffic
+
+A pure reflection of received packets by a reflecting unit leads to widely identical and symmetrical data streams in direction to and from the reflecting unit. Each sent packet triggers a reflected packet of the same size. Consequently, packet size and frequency and the resulting data rate are the same. This symmetrical traffic is a special case and does not emulate most real applications, where the traffic is asymmetrical, meaning different in each direction.
+
+Additional notes about the method as specified in [IETF RFC 6038] are focused on achieving absolutely symmetrical traffic; the received packets are reflected exactly back to the sender. Consequently, the amount of data requested to transmit is the same in the send and receive directions.
+
+The definition of additional TWAMP features in [IETF RFC 6038] has already foreseen the possibility to define the size of the reflected packets<sup>1</sup>.
+
+A different size of the reflected packet generates asymmetrical traffic; the reflected packet stream can result in a higher or lower bitrate. It must be noted that this way the asymmetrical traffic is only achieved by varying the packet size, not the packet frequency.
+
+There can be implementations realized, where also the packet frequency varies in either direction. A received packet at the reflecting unit can trigger sending multiple packets instead of one. It depends on the implementation and the target traffic pattern to be emulated whether these packets are sent in an equidistant way or as bursts.
+
+Vice versa, there might also be implementations where multiple received packets at the reflecting unit trigger less or just one packet to be sent back to the client side. Also, in this case the targeted traffic pattern defines the parameters of asymmetry.
+
+If the reflected packet must carry a higher number of bytes than the sent one, the packet is extended by random bits. This is the more usual case (uplink rate < downlink rate). If the reflected packet must be smaller, the payload is cut to the target size, where the lower limit is the header information of the packet for its identification.
+
+Alternative methods as UDPST as described in [b.1] also offer techniques to realize different load per direction resulting in a desired asymmetrical traffic pattern.
+
+---
+
+<sup>1</sup> The implementation is not part of [IETF RFC 6038] and is left to the implementor. Preferably, the implementation carries the information of how many octets should be reflected in each packet. Thus, the asymmetry of the traffic can be defined per packet as highest granularity.
+
+## 7.3 Guidelines to derive traffic patterns from real applications
+
+When creating a traffic pattern, the goal is to derive an archetype traffic pattern that is representative for the target application. This should usually cover the main usage scenarios of a group of similar applications such as 'high-interactive e-Gaming' or 'remote drone control'. Alternatively, the traffic pattern could also be targeted to an individual application and use case.
+
+First, the traffic created by several representative real applications should be analysed. The IP trace should be recorded in the different phases of application usage, for example initializing phase, active interaction, passive use and trailing phase. For all applications, use cases and usage phases, the traffic should be analysed regarding uplink and downlink bitrate, packet size and frequency.
+
+#### 7.3.1 Temporal structure of traffic patterns
+
+The next step is the definition of a traffic pattern by segments of different bitrates. The proportion of bitrates and their profile vs time should be driven by the real use but in a shorter overall duration (e.g., 10 s to 15 s, where segment duration can be down to 1 s). The order of the segments should resemble the real-time profile, e.g., start with an initializing phase and not a highly interactive phase. In asymmetrical traffic scenarios, the uplink and downlink bitrates can differ and have a different proportion for each segment.
+
+#### 7.3.2 Controlling data rate by packet size and frequency
+
+The packet stream realized e.g., by TWAMP as in [IETF RFC 5357] and [IETF RFC 6038] is considered an emulation of a traffic pattern of a real application. This load is not only defined by an average or short-term bitrate but rather by the underlying packet sizes and frequency. Packet size and frequency can be different for individual applications even the resulting bitrate is the same. Some applications may send small packets in higher frequency, while others send larger packets but in lower frequency.
+
+Therefore, the target bitrates for the segments have to be broken into the parameters' packet size and packet sending frequency. The packet size is limited to the range between the minimum defined by the header size of all transport protocols including the TWAMP header and the maximum defined e.g., by TWAMP as in [IETF RFC 6038] (~65 000 bytes). Within this range, the packet size and frequency should be set to resemble the real application traffic.
+
+Packet sizes exceeding one maximum transmission unit (MTU) will be split into multiple MTUs transmitted and received sequentially. The receiving side will then assemble the incoming MTUs to one UDP packet. It should be noted that the latency and the corresponding PDVs are calculated based on the reception of the latest MTU forming this individual packet. Furthermore, a packet is counted as lost if a single MTU is lost or erroneous.
+
+This consideration of oversized packets will result in data streams close to a real application. An oversized packet is split into several MTUs but these MTUs are transferred directly one after another as a bulk of MTUs. After transmitting, there can be a pause until the next oversized packet is split and transmitted. The more bursty data traffic on lower layers is closer to resembling the reality for those applications.<sup>2</sup>
+
+One additional restriction applies to the packet frequency if TWAMP as in [IETF RFC 5357] is used: The defined packet frequency applies for uplink and downlink traffic within one segment, because of the round-trip nature of the measurement. Packets are only reflected at the server side, not multiplied nor discarded. Thus, the packet frequency in both directions is identical.
+
+---
+
+<sup>2</sup> A typical example application is UHD video streaming, where single frames are packetized but exceed the MTU size and are split. Nevertheless, the entire packet (video frame) is considered as lost if the transport of a single MTU fails.
+
+# 8 Latency test results and metrics
+
+## 8.1 Per-packet two-way latency
+
+The realization of the described two-way latency measurement method allows the determination of the latency of each individual sent and received UDP packet. As a result of the measurement, the vector  $D(i)$ , where  $D$  is the latency of an individual packet  $i$  for a measurement interval, is available for detailed analysis.
+
+As statistical aggregation metrics of  $D(i)$  quantiles are recommended:
+
+- Delay  $D(i)$  50<sup>th</sup> percentile (median)
+- Delay  $D(i)$  10<sup>th</sup> percentile (approximation for the shortest reachable latencies in practice)
+
+An arithmetic average as statistical mean for characterization of the latency in a measurement interval cannot be recommended, since individual extreme latencies dominate this average. Measured packet latencies follow a so-called heavy-tailed distribution with reduced meaning of arithmetic averages.
+
+## 8.2 Packet delay variation
+
+In line with [ITU-T Y.1540] and [IETF RFC 5481], the packet delay of an individual packet is rated to the minimal packet latency and is defined as:
+
+$$PDV(i) = D(i) - D(\min) \text{ where } PDV(i) \in \mathbb{R}^+$$
+
+where  $D(i)$  is the individual latency of one packet and  $D(\min)$  is the minimum individual latency of all packets in the measurement interval.
+
+PDV values can only be zero or positive, and quantiles of the PDV distribution are direct indications of delay variation.
+
+This vector  $PDV(i)$  is used to calculate the:
+
+- $PDV$  50<sup>th</sup> percentile (median)
+- $PDV$  99.9<sup>th</sup> percentile (approx. maximum)
+
+The PDV is a relative measure with respect to the packet with the shortest latency. This enables the provision of the PDV per direction, as no time synchronization is needed for relative measures. Based on the timestamps of sending at client side and receiving at server side, the uplink one-way PDV can be computed. Likewise, based on the timestamps of sending at server side and receiving at client side the downlink one-way PDV can be derived. Consequently, PDV is available as:
+
+- $PDV_{CS}$  one-way (client to server)
+- $PDV_{SC}$  one-way (server to client)
+
+In principle and if needed, also the resulting two-way PDV (client to server and return) can be obtained from the available timestamps.
+
+## 8.3 Inter-packet delay variation
+
+In line with [IETF RFC 5481], the inter-packet delay variation (IPDV)<sup>3</sup> of an individual packet is rated to the delay of the previous packet and is defined as:
+
+$$IPDV(i) = D(i) - D(i - 1) \text{ where } i \in N$$
+
+where  $D(i)$  is the individual delay of one packet.
+
+IPDV values can be both negative and positive, and percentiles of the IPDV distribution are direct indications of delay variation.
+
+---
+
+<sup>3</sup> Please note that IPDV is also used as an abbreviation for IP-packet delay variation in other contexts.
+
+This vector  $IPDV(i)$  is used to calculate the:
+
+- $IPDV_{>0}$  34.1<sup>th</sup> percentile (standard deviation under assumption of normal distribution)
+- $IPDV_{>0}$  99.9<sup>th</sup> percentile (approx. maximum)
+
+Here  $IPDV_{>0}$  denotes the vector of all positive values of IPDV.
+
+The IPDV is a relative measure with respect to the previous packet. This enables the provision of the IPDV per direction, as no time synchronization is needed for relative measures. Based on the timestamps of sending at client side and receiving at server side, the uplink one-way IPDV can be computed. Likewise, based on the timestamps of sending at server side and receiving at client side the downlink one-way IPDV can be derived. Consequently, IPDV is available as:
+
+- $IPDV_{CS}$  one-way (client to server)
+- $IPDV_{SC}$  one-way (server to client)
+
+In principle and if needed, additionally the resulting two-way IPDV (client to server and return) can be obtained from the available timestamps.
+
+## 8.4 Lost packets
+
+Packets which are not received on the IP-interface of client or server side are counted as lost.
+
+This covers more than lost packets that are actually lost, in particular:
+
+- Not sent packets: Packets that could not leave the client device due to uplink congestion and being discarded by the device kernel after timeout.
+- Lost packets: Packets that were lost during transmission or could not leave the reflecting server due to downlink congestion and being discarded by the server kernel after timeout. Lost packets can be determined at the reflecting server side as well as at the receiving client. Lost packets can be reported for either one-way separately or two-way.
+- Erroneous packets: Packets that were corrupted after arriving back at the client device.<sup>4</sup>
+
+An overall indicator as the ratio of lost packets  $P_L$  can be computed simply by:
+
+$$P_L = \text{number of lost packets} / \text{number of all packets sent by the application}$$
+
+The packet loss  $P_L$  can also be calculated per direction separately if the underlying method allows it.
+
+$$P_{L\_CS} = \text{number of lost packets at server side} / \text{number of all packets sent by the client application}$$
+
+$$P_{L\_SC} = \text{number of lost packets at client receiving side} / \text{number of all packets sent by the server}$$
+
+# 9 Interactivity prediction model and related test case definition
+
+### 9.1 Principles of the generic interactivity model approach
+
+Obtaining latency, PDV, IPDV and packet loss opens the possibility to create a prediction model for perceived interactivity for individual applications or application classes. An application class could be, for example, HD video chat or online gaming, where the effect of delay, jitter and loss on perception is comparable in between the individual realizations of the application.
+
+The basic concept of scoring interactivity is that the latency and number of lost and unusable packets determine the interactivity perceived by a user. Two-way packet latency gives information on how fast a response to an action originated at the client user device is received back at the device side. In
+
+---
+
+<sup>4</sup> Please note that usually the IP kernel of the operating system discards corrupted packets below the IP interface level. When tracing packets at IP level, corrupted packets are seen as lost.
+
+addition, disqualified packets are missing information for the user's application. They can be lost packets as in clause 8.4 or packets considered as discarded by exceeding a delay limit. Those lost and discarded packets are defined as disqualified packets.<sup>5</sup> Whether disqualified packets can be interpolated by the application or only lead to temporary distortions, pausing while using the application or even stopping the application completely depends on the application itself and its implementation.
+
+To receive results for latency and ratio of disqualified packets as close to a real application as possible, the packet stream – especially in data-rate and traffic pattern – should emulate the targeted application in use.
+
+Latency of the received packets and number of disqualified packets determine the perceived interactivity, but the influence on the perceived interactivity of an application or use case depends on the target application and the expectation of the user.
+
+Consequently, there will not be one single prediction model for interactivity, but rather individual ones for different applications. Considering the huge number of potential applications, a generic and scalable approach is developed and described in this Recommendation.
+
+Therefore, the following principles are anticipated:
+
+- Same input parameter types for derived interactivity models
+- Same computational structure of the interactivity model
+- Classification of applications and use cases in application types or groups having same or similar expectations of the user
+- Parametrization of the computational model structure to one specific application type or group
+
+Considering the principles above, a fast realization of prediction models is achievable and because of clear application grouping and a transparent approach, the results stay comparable within and across application groups. One example of a model for the computation of an interactivity score based on the principles described above is given in Annex A.
+
+## **9.2 Parametrization of an interactivity model**
+
+#### **9.2.1 Subjective testing**
+
+The most obvious approach to parametrization is the use of data obtained by subjective testing of the application that should be predicted by the interactivity model. Human subjects have to use the application in its interactive stage under different defined channel conditions regarding latency, jitter and loss and to score the perceived interactivity. Based on the results, the best fitting parameters for the above-described model can be derived.
+
+The advantage of this approach is the direct link to human scores of a real application and thus the ability to correctly reflect the priority/weight of different network degradations. Disadvantages are that the application has to exist and that the outcome of the test refers to this dedicated application and it is hardly possible to generalize unless also evaluating how other competing applications behave, which does not have to be done with fully subjective tests. Furthermore, the ambition of a test user in an experimental set-up may not be fully comparable with a real use of the application, where the interests of the user are different.
+
+---
+
+<sup>5</sup> Considering packets exceeding the delay budget as unusable and discarded reflects real-time applications, where delayed packets cannot be considered for e.g., rendering a media stream.
+
+#### 9.2.2 Best practice parametrization
+
+Best practice parametrization models perceive interactivity based on anticipated thresholds for a given application or use case. These anticipated thresholds are derived from expected performance in certain environments while using the application. Basic considerations can be at which latency a perceived degradation of latency starts (e.g., an interactivity score of 90 of 100) and at which latency the perceived interactivity drops significantly (e.g., an interactivity score of 60 of 100, would relate to MOS  $\sim$  3 in a five-point absolute category rating (ACR) test) and/or where the application becomes unusable in practice. In addition, the influence of packet loss and serious packet delay variation should be estimated. This estimation considers known or assumed packet loss and buffering strategies. Examples for best practice parametrization are shown in Appendices I and II..
+
+### 9.3 Guidelines for application grouping
+
+In principle, an individual traffic pattern and interactivity model can be defined for each application or use case. However, there are applications and use cases resulting in very similar patterns and model parameters. For comparability and practical use, it is helpful to test applications and use cases under the same conditions if the traffic shape and/or model parameters are similar.
+
+Traffic pattern similarity should be given in
+
+- Temporal structure of traffic pattern;
+- Applied bit rates.
+
+Model parameter similarity should be given in
+
+- Delay budget for the application;
+- Perceptual influence of packet latency;
+- Degradation by packet latency variations and especially disqualified packets.
+
+The use of the same defined traffic pattern and set of model parameters for different applications is not limited to similar appearance or use; applications can be treated the same although they have a different use, as long as they share the similarities above.
+
+## 9.4 Guidelines for defining test cases
+
+The results obtained by the test method, such as two-way latency, PDV, IPDV and packet loss, depend on the traffic emulated, for example, on bitrate and packet size. Therefore, the measurement of latency must take place under equivalent traffic conditions as in the target application for which latency scores should be obtained.
+
+If the measurement results will be used to estimate the interactivity of an application type, the parametrization of this model must also consider the characteristics of the targeted application such as sensitivity to packet loss, defined delay budget and dependency on latency.
+
+Considering this, a test case for deriving a prediction of interactivity is mainly defined by the used traffic or bitrate profile including packet size and frequency, and – if applied – the model parameters to estimate perceived interactivity. A packet with a two-way latency exceeding the defined delay budget is considered as disqualified, meaning discarded due to late arrival by the emulated application.
+
+Limits for latency of different application classes, grouped by the standardized 5QI value, are given by [3GPP TS 23.501]. These limits apply to network delays. They are preferable to use if the emulated application matches, otherwise best practice assumptions or actual discarding limits of the applications are practicable.
+
+Examples of traffic patterns and corresponding model parameters for a model as described in Annex A are presented in Appendix I.
+
+## Annex A
+
+## Computational structure of a generic interactivity model approach
+
+(This annex forms an integral part of this Recommendation.)
+
+### A.1 Introduction
+
+This annex describes a model for estimation of perceived interactivity. As perceived interactivity strongly depends on the application class, the computational model must be parametrized for dedicated application classes and their demands.
+
+The model is based on the obtained two-way latency per packet from simulated data traffic in a network or transport centric approach.
+
+The basic idea of this model realization is a simple consideration of the application's client and server and its scalable construction across many different application cases. Even though this will not perfectly match each individual application, its main advantage is the comparability between individual settings and modelled test cases due to the same modelling approach being taken.
+
+### A.2 Modelling approach for perceived interactivity of interactive applications
+
+The basic assumption of modelling perceived interactivity is its monotonous dependency on data latency. The shorter the data transport time is, the shorter the response time in an interactive application is and the more interactive the use of the application is perceived to be.
+
+However, this dependency is not a simple linear function; rather there are saturation areas at both tails of the function, where no further change in perception happens even if the latency changes.
+
+A valid approximation of this non-linear dependency is a logistic (sigmoid) function.
+
+$$f(t) = 1 - \frac{1}{1 + e^{-\frac{1}{b}(t-a)}}$$
+
+where  $a$  defines the horizontal shift on the  $t$ -axis and  $b$  the gradient.
+
+For a parametrization that matches the value range of positive latencies and a scaling by  $f_0$  to a maximum score value of  $f_p(0) = f_{max}$ , the following formula is applied:
+
+$$f_p(t, i) = \frac{f_{max}}{f_0} \left( 1 - \frac{1}{1 + e^{-\frac{1}{b}(t_i-a)}} \right) \text{ for } t > 0 \text{ with } f_0 = 1 - \frac{1}{1 + e^{\frac{a}{b}}}$$
+
+where  $t$  is the packet latency in milliseconds,  $i$  is the indicator of the packet,  $a$  defines the shift of  $f_p(t, i)$  directly on the  $t$ -axis in milliseconds and  $b$  defines the gradient of  $f_p(t, i)$ , where larger values of  $b$  make  $f_p(t, i)$  less steep.
+
+The scaling factor  $f_0$  guarantees the maximum score value at  $t = 0$ . In case, the upper saturation area of the  $f_p(t, i)$  starts in the range of  $t > 0$ , the  $f_0$  will be close to 1.0. If  $f_0 \rightarrow 1$ , the parameter  $a$  defines the latency value where the perceived interactivity has fallen to almost 50% of  $f_{max}$ .
+
+In cases where per-packet two-way latency can be obtained, the logistic function can be applied to each individual packet latency. Here, the value  $f_p(t, i)$  is computed for each individual packet  $i$  and its latency  $t$ . The aggregated interactivity based on latencies  $I_L$  for an observation period is the average of all  $f_p(t, i)$ :
+
+$$I_L = \frac{1}{N} \sum_{i=1}^N \frac{f_{max}}{f_0} \left( 1 - \frac{1}{1 + e^{-\frac{1}{b}(t_i-a)}} \right)$$
+
+In cases where the per-packet two-way latency cannot be obtained in the test set-up or higher order statistics appear more applicable, the principle of the logistic weighting can be applied to the median of the two-way latencies as a single value input into the function.
+
+$$I_{L-CG} = \frac{f_{max}}{f_0} \left( 1 - \frac{1}{1 + e^{-\frac{1}{b}(RTT_{MEDIAN} - a)}} \right)$$
+
+with  $RTT_{MEDIAN}$  = Median delay of all packets sent by the application
+
+If using the alternative method, the parameters  $a$  and  $b$  may differ from the per-packet application of the sigmoid function.
+
+![Figure A.1: A graph titled 'Logistic weighting of two-way latency (Example)'. The y-axis is labeled f(t) and ranges from 0 to 100. The x-axis is labeled 'Two-way latency/ms' and ranges from 0 to 160. A solid black curve starts at f(t) = 100 at x = 0 and decreases towards 0 as x increases. The curve passes through (60, 50). A legend in the top right corner specifies a = 60, b = 15, and f_max = 100. The text 'G.1051(23)' is in the bottom right corner.](cbc4516eb885829fe8c9dabc0946dcbe_img.jpg)
+
+Figure A.1: A graph titled 'Logistic weighting of two-way latency (Example)'. The y-axis is labeled f(t) and ranges from 0 to 100. The x-axis is labeled 'Two-way latency/ms' and ranges from 0 to 160. A solid black curve starts at f(t) = 100 at x = 0 and decreases towards 0 as x increases. The curve passes through (60, 50). A legend in the top right corner specifies a = 60, b = 15, and f\_max = 100. The text 'G.1051(23)' is in the bottom right corner.
+
+Figure A.1 – Example of a logistic weighting function for two-way latency
+
+If seen from an quality of experience (QoE) perspective, first, parameter  $a$  shifts the latency value, where the decrease of perceived interactivity depending on latency starts along the  $t$ -axis. In case  $f_0$  is close to 1.0, parameter  $a$  directly defines the latency where the predicted interactivity is decreased to 50% of the maximum reachable score. Second,  $b$  determines the sensitivity of the user, means the range of latency, where the perceived interactivity is decreasing from almost maximum to close to zero. Both parameters are depending on the expectation of the user to the application used.
+
+![Figure A.2: Two side-by-side graphs titled 'Logistic weighting of two-way latency (Example)'. The left graph shows three curves for different values of parameter 'a' (60, 90, 120) with b = 15 and f_max = 100. The right graph shows three curves for different values of parameter 'b' (7, 15, 25) with a = 60 and f_max = 100. Both graphs have f(t) on the y-axis (0-100) and 'Two-way latency/ms' on the x-axis (0-160). The text 'G.1051(23)' is in the bottom right corner of the right graph.](011fecb4a85637472f0c697a6cbdb15d_img.jpg)
+
+Figure A.2: Two side-by-side graphs titled 'Logistic weighting of two-way latency (Example)'. The left graph shows three curves for different values of parameter 'a' (60, 90, 120) with b = 15 and f\_max = 100. The right graph shows three curves for different values of parameter 'b' (7, 15, 25) with a = 60 and f\_max = 100. Both graphs have f(t) on the y-axis (0-100) and 'Two-way latency/ms' on the x-axis (0-160). The text 'G.1051(23)' is in the bottom right corner of the right graph.
+
+Figure A.2 – Parametrization of the logistic weighting function for two-way latency
+
+### A.3 Consideration of lost and discarded packets and packet delay variation in the model
+
+#### A.3.1 Disqualified packets
+
+The defined packet loss  $P_L$  reports packets which are not received and cannot be used by the application. In addition to that, a real application will also discard packets which are heavily delayed
+
+and are not received in time. This maximum accepted delay for packets depends on the application and e.g., internal queuing and buffering mechanisms. In general, the more real-time capability an application has to provide, the shorter the acceptable delay. Packets received later than the maximum delay are discarded by the application and would not be usable for a real and running application, for example, for media rendering.
+
+For predicting a perceived interactivity, discarded packets count as lost packets ( $P_L$ ) and are counted cumulatively as disqualified packets. This covers in particular:
+
+- Not sent packets: Packets that could not leave the client device due to uplink congestion and being discarded by the device kernel after timeout.
+- Lost packets: Packets that were lost during transmission or could not leave the reflecting server due to downlink congestion and being discarded by the server kernel after timeout. Lost packets can be determined at the reflecting server side as well as at the receiving client. Lost packets can be reported for either one-way separately as well as for two-way.
+- Erroneous packets: Packets that were corrupted after arriving back at the client device.
+
+as considered in clause 8.4 as lost packets, and additionally
+
+- Discarded packets: Packets that were received back after a pre-defined timeout at the client device. This timeout, also called delay budget, emulates discarding by a real application because of too long a delay. The timeout is specified and defined according to the maximum acceptable latency for the target application and forms one parameter of emulation of the application.
+
+From an application's point of view, no differentiation is needed between the individual causes of not considering a packet as received. An overall indicator such as the ratio of disqualified packets  $P_{DQ}$  is seen as sufficient at application level.
+
+$$P_{DQ} = \text{number of disqualified packets} / \text{number of all packets sent by the application}$$
+
+As a consequence, all packets considered as usable by the application are defined as qualified packets.
+
+#### A.3.2 PDV considering delay budget
+
+In clause 8.2, the packet delay variation (PDV) is defined. The PDV is derived from the received packet stream without considering discarding due to the applied delay budget. As for prediction of the perceived interactivity a delay budget is applied, the PDV of the incoming packet stream does not reflect anymore the packet delay variation to be considered by the emulated application.
+
+To reflect the packet delay variation within the applied delay budget, the formula of PDV is applied to packet delays considering only the qualified packets according to clause A.3.2.1 and defined as  $PDV_Q$ . In the further modelling, the standard deviation across all  $PDV_Q$  values is defined as  $PDV_{sQ}$ .
+
+The  $PDV_{sQ}$  describing delay variation from client to server and return can be calculated based on two-way latencies, where the time difference between sending a packet and receiving back its reflection is measured.
+
+If the two-way PDV cannot be obtained, alternatively the standard deviation of PDV or IPDV can be computed individually per link direction.<sup>6</sup> Here, IPDV and resulting  $IPDV_{sQ}$  are measured for either direction separately and the average of the standard deviations of IPDV in the uplink and downlink direction is considered as substitute of two-way  $PDV_{sQ}$ . If using the per-link computation, the parameter  $u$  may differ from that defined for two-way  $PDV_{sQ}$ .
+
+---
+
+<sup>6</sup> This separation into IPDV per link is also required in case of asymmetrical traffic patterns using different packet frequencies in each direction. There is no one-to-one relation between sent and received packets which is the pre-condition for a two-way PDV or two-way IPDV.
+
+#### A.3.3 Consideration of disqualified packets and two-way PDV in the interactivity model
+
+In addition to latency, it is anticipated that delay variation and number of disqualified packets also contribute to perceived interactivity. To simplify, both indicators are considered as degrading factors  $D_{PDV}$  and  $D_{DQ}$  by multiplication:
+
+$$IntAct = I_L \times D_{PDV} \times D_{DQ}, \text{ with } D_{PDV} = 1 - PDV_{SQ} / u, \text{ and } D_{DQ} = 1 - v P_{DQ}$$
+
+In the expression above,  $PDV_{SQ}$  is the standard deviation across all  $PDV_Q$  values,  $P_{DQ}$  is the ratio of disqualified packets, and  $u$  and  $v$  are parameters that determine the impact of the degradations on interactivity. Alternatively,  $PDV_{SQ}$  can also be used as descriptor for the standard deviation of  $IPDV_Q$ .
+
+The multiplication with the contributors  $0 < D_{PDV} < 1$  and/or  $0 < D_{DQ} < 1$  will also decrease the maximum value  $IntAct_{max} < I_{Lmax}$ . It means even if latency is very short, if packets are disqualified the maximum score for perceived interactivity can no longer be reached.
+
+For example, a median  $PDV_{SQ}$  of 20 ms will lead to a degrading factor  $D_{PDV} \sim 0.85$  if  $u = 130$ , and a ratio of disqualified packets of 5% ( $P_{DQ} = 0.05$ ) to a degrading factor  $D_{DQ} = 0.65$  if  $v = 7$ .
+
+The influence of  $PDV_{SQ}$  and  $P_{DQ}$  to the weighting function is illustrated in Figure A.3.
+
+![Figure A.3: Logistic weighting of two-way latency (Example). The graph shows three curves representing the weighting function f(t) against two-way latency in ms. The solid line represents the baseline function. The dashed line shows the effect of PDV_SQ = 20 ms and u = 130. The dotted line shows the effect of P_DQ = 5% and v = 7. The parameters used are a = 60, b = 15, and f_max = 100.](dc0cec98faa3ead994c1b171cb56265d_img.jpg)
+
+The figure is a line graph titled "Logistic weighting of two-way latency (Example)". The y-axis is labeled  $f(t)$  and ranges from 0 to 100. The x-axis is labeled "Two-way latency/ms" and ranges from 0 to 160. There are three curves: a solid line, a dashed line, and a dotted line. The solid line starts at 100 at 0 ms and decreases towards 0 as latency increases. The dashed line starts at approximately 85 at 0 ms and follows a similar downward path, crossing the solid line. The dotted line starts at approximately 65 at 0 ms and also decreases, crossing both the solid and dashed lines. Arrows point from labels to the curves: "PDV<sub>SQ</sub> = 20 ms, u = 130" points to the dashed line, and "P<sub>DQ</sub> = 5 %, v = 7" points to the dotted line. A legend in the top right corner specifies parameters:  $a = 60$ ,  $b = 15$ , and  $f_{max} = 100$ . A small code "G.1051(23)" is in the bottom right corner.
+
+Figure A.3: Logistic weighting of two-way latency (Example). The graph shows three curves representing the weighting function f(t) against two-way latency in ms. The solid line represents the baseline function. The dashed line shows the effect of PDV\_SQ = 20 ms and u = 130. The dotted line shows the effect of P\_DQ = 5% and v = 7. The parameters used are a = 60, b = 15, and f\_max = 100.
+
+Figure A.3 – Example of influence of  $PDV_{SQ}$  and  $P_{DQ}$  to the logistic weighting function
+
+Generally, the above-mentioned formula is applied to the entire observation period (e.g., 10 s). To result in a higher temporal granularity, the formula can also be applied to shorter sub-intervals of 1 s, for example.
+
+### A.4 Conclusion
+
+The described computational formula is a simplified, generic approach to retrieve perceived interactivity from latency measurements with the advantage of transparent scalability. The logistic weighting function to estimate a perceived interactivity value from two-way latency measurements ensures a monotonous behaviour and can model perceptual saturation areas at both boundaries of the scale similar to typical perceptual weightings. Degrading effects of delay jitter (derived from  $PDV_{SQ}$ ) and disqualified packet loss ( $P_{DQ}$ ) are considered by simple multiplicative scaling factors. Multiplicative scaling retains the monotonous behaviour and does not change the saturation areas and their cut-off positions.
+
+There may be more accurate formulas for perceived interactivity and individual model structures for dedicated applications, but those definitions require more investigations and are for further study.
+
+## Appendix I
+
+## Example generic traffic patterns and model parameters according to Annex A
+
+(This appendix does not form an integral part of this Recommendation.)
+
+### I.1 Principle of application emulation and model parameters
+
+There are many individual traffic patterns when using an application. They depend on the application itself, the phase in the application (e.g., the gaming scene) and the interaction by the user.
+
+Instead of exactly simulating an individual pattern, a more generalized approach is chosen. At first, applications are classified under consideration of similar use and resulting load, e.g., video chat applications or gaming. For those classes of applications, an analysis of real traffic when using the most common applications of each class was made. The derived patterns do not just represent an average bitrate, rather they emulate some statistical characteristics of the real patterns such as the relative occurrence of data rates (e.g., 50% ~100 kbit/s, 30% ~500 kbit/s and 20% ~2 Mbit/s) as well as typical temporal behaviour in a simple way by e.g., incorporating peaks or longer steady transport.
+
+This principle will load the network statistically in a similar way to a real application of this class and leads to latencies as they can be expected when running this type of application.
+
+These example traffic patterns and the resulting two-way latency values, the measured PDV and packet loss can also be used to estimate a perceived interactivity for this application class by applying a computational interactivity model as described in Annex A.
+
+The model as in Annex A is based on measurements on the transport layer; the measurements do not consider the application itself with respect to specific treatments of transport problems such as packet loss concealment or predictive media rendering, for example, as in video or gaming. The examples given in this appendix are parametrized by applying limits and thresholds defined by 3GPP for individual use cases and might be more challenging than subjective experience including real applications with error treatment.
+
+### I.2 Examples for application emulation and interactivity score computation
+
+#### I.2.1 Example high-interactive 'e-Gaming real-time'
+
+The example traffic pattern for emulating high-interactive e-gaming is derived from heavy multiplayer games. It covers an initializing phase (low-bit-rate) without interaction, a sustainable phase with motion and interaction, the loading of a new game instance as a bit rate peak, a longer sustainable phase of high interaction with up to several hundreds of players and a (low-bit-rate) trailing phase with fewer players and medium interaction. The set bit rates for the phases were taken from real, demanding multiplayer games and represent also in its relative duration and sequence a real gaming session but compressed into a duration of 10 s.
+
+The chosen packet size is 100 bytes sent in a frequency of 125 to 1250 packets per second and the pattern is the same in uplink and downlink, meaning each packet is reflected in the same size. In [3GPP TS 23.501] a maximal one-way latency for online real-time gaming of 50 ms is defined (5QI class 3), the two-way latency therefore should not exceed 100 ms and forms the delay budget for this test case.
+
+![Figure I.1: Example of traffic pattern 'e-Gaming real-time'. The graph shows Data rate/kbit/s on the y-axis (0 to 2000) versus Time/s on the x-axis (0 to 10). The traffic pattern is a step function: 0-1s at 100 kbit/s, 1-2s at 300 kbit/s, 2-3s at 1000 kbit/s, 3-7s at 300 kbit/s, and 7-10s at 100 kbit/s. A label 'up-and downlink' is placed above the 300 kbit/s segment. The code 'G.1051(23)' is in the bottom right corner.](5ed9189841659dfb01f809b8e3b21f74_img.jpg)
+
+Figure I.1: Example of traffic pattern 'e-Gaming real-time'. The graph shows Data rate/kbit/s on the y-axis (0 to 2000) versus Time/s on the x-axis (0 to 10). The traffic pattern is a step function: 0-1s at 100 kbit/s, 1-2s at 300 kbit/s, 2-3s at 1000 kbit/s, 3-7s at 300 kbit/s, and 7-10s at 100 kbit/s. A label 'up-and downlink' is placed above the 300 kbit/s segment. The code 'G.1051(23)' is in the bottom right corner.
+
+**Figure I.1 – Example of traffic pattern 'e-Gaming real-time'**
+
+For parametrization of the interactivity model as described in clause 9.2.2, the following principles are used: A fluent video stream produces 60 frames per second (fps), a movie 24. It is assumed that degradation starts if the channel adds a two-way delay of ~30 ms (two frames delay for 60 fps). Furthermore, a degradation to 60 of 100 for the interactivity score is assumed in case of a two-way delay added by the channel of ~60 ms (four frames for 60 fps). These thresholds can be seen as challenging but refer to highly interactive gaming applications in high speed networks as in 5G URLLC.
+
+In addition, it is anticipated that a  $PDV_{SQ}$  of 30 ms reduces the interactivity as defined by latency by another 10% ( $D_{PDV} = 0.9$ ) and a ratio of disqualified packets of 5% reduces the perceived interactivity by 20% ( $D_{DQ} = 0.8$ ).
+
+The parametrization of the model:
+
+$$IntAct = I_L \times D_{PDV} \times D_{DQ}$$
+
+with  $D_{PDV} = 1 - PDV_{SQ} / u$ ,  $D_{DQ} = 1 - v P_{DQ}$  and  $I_L = \frac{1}{N} \sum_{i=1}^N \frac{f_{max}}{f_0} \left( 1 - \frac{1}{1 + e^{-\frac{1}{b}(t_i - a)}} \right)$
+
+is resulting in:
+
+| Parameter | $f_{max}$ | $a$ | $b$ | $u$ | $v$ |
+|-----------|-----------|-----|-----|-----|-----|
+| Value     | 100       | 61  | 14  | 120 | 4   |
+
+![Figure I.2: Interactivity score 'eGaming' graph. The y-axis is 'Interactivity score' from 0 to 100. The x-axis is 'RTT/ms' from 0 to 400. Two curves are shown: a solid line for PDV_SQ = 40 ms and a dashed line for P_DQ = 2%. Both curves start at 100 and drop to 0 by RTT 150 ms.](60e9207be66a64332619bb4b667fe67b_img.jpg)
+
+Figure I.2 is a line graph titled "Interactivity score 'eGaming'". The y-axis is labeled "Interactivity score" and ranges from 0 to 100 in increments of 10. The x-axis is labeled "RTT/ms" and ranges from 0 to 400 in increments of 50. Two curves are plotted: a solid line representing  $PDV_{SQ} = 40 \text{ ms}$  and a dashed line representing  $P_{DQ} = 2 \%$ . Both curves start at an interactivity score of 100 at 0 ms RTT and decrease sharply, reaching a score of 0 at approximately 150 ms RTT. The dashed line ( $P_{DQ} = 2 \%$ ) shows a slightly higher interactivity score than the solid line ( $PDV_{SQ} = 40 \text{ ms}$ ) for RTT values between 25 ms and 100 ms.
+
+Figure I.2: Interactivity score 'eGaming' graph. The y-axis is 'Interactivity score' from 0 to 100. The x-axis is 'RTT/ms' from 0 to 400. Two curves are shown: a solid line for PDV\_SQ = 40 ms and a dashed line for P\_DQ = 2%. Both curves start at 100 and drop to 0 by RTT 150 ms.
+
+G.1051(23)
+
+**Figure I.2 – Example parametrization for real-time gaming according to Annex A**
+
+#### I.2.2 Example 'Remote drone control'
+
+An example traffic pattern for emulating remote drone control through video illustrates steady but highly asymmetrical traffic, where a low-bit-rate stream of control commands is transferred in uplink to the drone, while the controlling device receives a continuous high bitrate video stream. There are no individual phases with different bit rates; the profile is seen as constant over the observation period. For simplification, the frequency of small uplink control packets and received images is set to the same value. This enables the use of the packet reflection approach as described in [IETF RFC 6038].
+
+The bit rate profile for real-time drone control consists of a 10 s constant 300 kbit/s in uplink and 25 Mbit/s in downlink as defined in use-case scenario 4 ('Remote unmanned aerial vehicle controller through 4k HD video') in [b-3GPP TS 22.125].
+
+Although for the example 'Drone control' the downlink video resolution is chosen to be 4K HD, lower video rates are possible. The example emphasizes the large difference in scale that is possible between uplink and downlink data rate, e.g., 20 times more traffic.
+
+![Figure I.3: Traffic pattern 'Drone control' graph. The y-axis is 'Data rate/kbit/s' from 0 to 30. The x-axis is 'Time/s' from 0 to 10. A solid line at 25 Mbit/s represents the downlink, and a dashed line at 300 kbit/s represents the uplink.](5adf12d50dfea82178ca002a2c48641b_img.jpg)
+
+Figure I.3 is a line graph titled "Traffic pattern 'Drone control'". The y-axis is labeled "Data rate/kbit/s" and ranges from 0 to 30 in increments of 5. The x-axis is labeled "Time/s" and ranges from 0 to 10 in increments of 1. Two lines are plotted: a solid line representing the downlink at 25 Mbit/s and a dashed line representing the uplink at 300 kbit/s. The downlink line is constant at 25 Mbit/s across the entire 10-second duration. The uplink line is constant at 300 kbit/s across the entire 10-second duration. The downlink data rate is significantly higher than the uplink data rate.
+
+Figure I.3: Traffic pattern 'Drone control' graph. The y-axis is 'Data rate/kbit/s' from 0 to 30. The x-axis is 'Time/s' from 0 to 10. A solid line at 25 Mbit/s represents the downlink, and a dashed line at 300 kbit/s represents the uplink.
+
+G.1051(23)
+
+**Figure I.3 – Example of traffic pattern 'drone control'**
+
+The chosen packet size in uplink is 300 bytes sent in a frequency of 125 packets per second and the corresponding packet size in downlink is 25 000 bytes, meaning each packet is reflected in a much larger size. In [b-3GPP TS 22.125] a maximal one-way latency for remote control of 20 ms unmanned aerial vehicle to a terminating unmanned aerial vehicle is defined. The two-way latency therefore should not exceed 40 ms and this value forms the delay budget for this test case.
+
+For parametrization of the interactivity model as described in clause 9.2.2, the following principles are used: A commercial consumer drone reaches 60 km/h average maximum velocity. This results in a flying distance of ~1.6 cm/ms. A beginning degradation (90 of 100 for the interactivity score) can be anticipated at a delay of visual feedback of 10 ms (flying distance ~16 cm), a severe degradation (60 of 100 for the interactivity score) can be assumed for 20 ms and the begin of an unusable two-way delay at > 30 ms (flying distance > 50 cm).
+
+The additional influence of  $PDV_{SQ}$  and disqualified packets is also more severe than for e-gaming. It is anticipated that a  $PDV_{SQ}$  of 5 ms reduces the interactivity as defined by latency by another 10% ( $D_{PDV} = 0.9$ ) and a ratio of disqualified packets of 1% reduces the perceived interactivity already by 20% ( $D_{DQ} = 0.8$ ).
+
+The parametrization of the model is resulting in:
+
+| Parameter | $f_{max}$ | $a$ | $B$ | $u$ | $v$ |
+|-----------|-----------|-----|-----|-----|-----|
+| Value     | 100       | 22  | 6   | 40  | 20  |
+
+![Figure I.4: A line graph titled 'Interactivity score 'Drone control''. The y-axis is 'Interactivity score' from 0 to 100. The x-axis is 'RTT/ms' from 0 to 400. A solid blue curve starts at (0, 100) and drops sharply to 0 at approximately 50 ms RTT. Two points on the curve are highlighted with arrows: 'PDV_SQ = 5 ms' points to a score of approximately 90 at 10 ms RTT, and 'P_DQ = 1%' points to a score of approximately 75 at 20 ms RTT. The graph includes a grid. A small label 'G.1051(23)' is in the bottom right corner.](65f66758012e229247953202e8adf35d_img.jpg)
+
+Figure I.4: A line graph titled 'Interactivity score 'Drone control''. The y-axis is 'Interactivity score' from 0 to 100. The x-axis is 'RTT/ms' from 0 to 400. A solid blue curve starts at (0, 100) and drops sharply to 0 at approximately 50 ms RTT. Two points on the curve are highlighted with arrows: 'PDV\_SQ = 5 ms' points to a score of approximately 90 at 10 ms RTT, and 'P\_DQ = 1%' points to a score of approximately 75 at 20 ms RTT. The graph includes a grid. A small label 'G.1051(23)' is in the bottom right corner.
+
+Figure I.4 – Example parametrization for drone control according to Annex A
+
+#### I.2.3 Examples 'Interactive remote meeting' and 'Video chat HD'
+
+An example traffic pattern for emulating interactive remote meetings with sharing visual information such as live camera streams, desktop sharing and presentations (with change of content) is emulated by steady, sustainable phases of 500 kbit/s symmetrical traffic and two short intervals of 2000 m peaks, where content change (e.g., new slide) happens. This can be seen as a simplified traffic shape typical for several popular remote meeting tools. This example applies asymmetrical traffic, where one peak is applied in uplink, the other one in downlink. It emulates short peaks in either direction.
+
+![Figure I.5: Traffic pattern 'Interactive remote meeting'. A line graph showing data rate in kbit/s over time in seconds. The y-axis ranges from 0 to 2000 kbit/s in increments of 200. The x-axis ranges from 0 to 10 seconds in increments of 1. The graph shows two data series: 'uplink' (dashed line) and 'downlink' (solid line). The uplink starts at 500 kbit/s at 0s, jumps to 2000 kbit/s at 2s, and returns to 500 kbit/s at 3s. The downlink starts at 500 kbit/s at 0s, jumps to 2000 kbit/s at 7s, and returns to 500 kbit/s at 8s. Both series remain at 500 kbit/s until 10s. A label 'G.1051(23)' is in the bottom right corner.](9ce50bc10864dc86e1cdee4be08f1897_img.jpg)
+
+Figure I.5: Traffic pattern 'Interactive remote meeting'. A line graph showing data rate in kbit/s over time in seconds. The y-axis ranges from 0 to 2000 kbit/s in increments of 200. The x-axis ranges from 0 to 10 seconds in increments of 1. The graph shows two data series: 'uplink' (dashed line) and 'downlink' (solid line). The uplink starts at 500 kbit/s at 0s, jumps to 2000 kbit/s at 2s, and returns to 500 kbit/s at 3s. The downlink starts at 500 kbit/s at 0s, jumps to 2000 kbit/s at 7s, and returns to 500 kbit/s at 8s. Both series remain at 500 kbit/s until 10s. A label 'G.1051(23)' is in the bottom right corner.
+
+**Figure I.5 – Example of traffic pattern 'interactive remote meeting'**
+
+The chosen packet size is 1000 bytes, which is typical for video content. The packet sending frequency is then derived to be 62 packets/s during the sustainable phases and 250 packets/s in the high bit rate phases. An example for a 'video chat HD' application is a similar use case, but it relies on live camera video and transmitting the participant videos in high resolution and the main focus is visual interaction and feedback between people. According to real video chat applications, there is a short initial (set-up) phase followed by a sustainable phase where the video link is established.
+
+![Figure I.6: Traffic pattern 'Video chat HD'. A line graph showing data rate in kbit/s over time in seconds. The y-axis ranges from 0 to 2000 kbit/s in increments of 200. The x-axis ranges from 0 to 10 seconds in increments of 1. The graph shows a single data series labeled 'up-and downlink'. The series starts at 500 kbit/s at 0s, jumps to 1000 kbit/s at 2s, and remains at 1000 kbit/s until 10s. A label 'G.1051(23)' is in the bottom right corner.](45329c7d9aa2bd1290af5b2027f08d7e_img.jpg)
+
+Figure I.6: Traffic pattern 'Video chat HD'. A line graph showing data rate in kbit/s over time in seconds. The y-axis ranges from 0 to 2000 kbit/s in increments of 200. The x-axis ranges from 0 to 10 seconds in increments of 1. The graph shows a single data series labeled 'up-and downlink'. The series starts at 500 kbit/s at 0s, jumps to 1000 kbit/s at 2s, and remains at 1000 kbit/s until 10s. A label 'G.1051(23)' is in the bottom right corner.
+
+**Figure I.6 – Example of traffic pattern 'video chat HD'**
+
+The chosen packet size is again 1000 bytes, which is typical for video content. The packet sending frequency is then derived to be 62 packets/s during the sustainable phases and 125 packets/s in the high bit rate phases. The traffic pattern is symmetrical, meaning the packet size and frequency are the same for uplink and downlink.
+
+The applicable delay budget is identical for both types of video application. In [3GPP TS 23.501], a maximal one-way latency for conversational video of 150 ms is defined (5QI class 2), the two-way latency therefore should not exceed 300 ms and this value forms the delay budget for this test case.
+
+These two examples of applications and traffic shapes have similar constraints regarding perceived interactivity and as an example, the applicable interactivity uses the same parameters for both applications and traffic shapes.
+
+For parametrization of the interactivity model as described in clause 9.2.2, the following principles are used: While running a video chat with interactions and feedback, a two-way delay of 100 ms can be seen as the length of a spoken syllable, a beginning degradation is anticipated for this range (90 of 100 for the interactivity score). The interactions become very difficult in case of a response delay  $> 250$  ms.
+
+It is further expected that while using an interactive remote meeting, a user may have more relaxed expectations on packet delay variations than for e-gaming but is more sensitive in case of lost or disqualified packets because video meetings are usually based on unreliable transmission and missed frames are visible as image distortions.
+
+To reflect this, it is anticipated that a  $PDV_{SQ}$  of 25 ms reduces the interactivity as defined by latency by another 10% ( $D_{PDV} = 0.9$ ) and a ratio of disqualified packets of 1% reduces the perceived interactivity already by 30% ( $D_{DQ} = 0.7$ ).
+
+The parametrization of the model is resulting in:
+
+| Parameter | $f_{max}$ | $a$ | $b$ | $u$ | $v$ |
+|-----------|-----------|-----|-----|-----|-----|
+| Value     | 100       | 215 | 50  | 150 | 30  |
+
+![Figure I.7: A line graph titled 'Interactivity score 'RemoteMeeting', 'Video Chat HD''. The y-axis is 'Interactivity score' from 0 to 100. The x-axis is 'RTT/ms' from 0 to 400. Three curves are shown: a solid line (baseline), a dashed line for PDV_SQ = 25 ms, and a dotted line for P_DQ = 1%. All curves decrease as RTT increases. The dotted line is the lowest, followed by the dashed line, and then the solid line.](0245dc88c1db93181871e732bc0655dd_img.jpg)
+
+The graph shows the interactivity score for 'RemoteMeeting' and 'Video Chat HD' as a function of RTT/ms. The baseline curve (solid line) starts at 100 at 0 ms RTT. The curve for  $PDV_{SQ} = 25$  ms (dashed) starts at 90. The curve for  $P_{DQ} = 1\%$  (dotted) starts at 70. All curves converge towards 0 as RTT approaches 400 ms.
+
+| RTT/ms | Baseline (Solid) | $PDV_{SQ} = 25$ ms (Dashed) | $P_{DQ} = 1\%$ (Dotted) |
+|--------|------------------|-----------------------------|-------------------------|
+| 0      | 100              | 90                          | 70                      |
+| 100    | 95               | 85                          | 65                      |
+| 200    | 80               | 65                          | 45                      |
+| 300    | 45               | 35                          | 20                      |
+| 400    | 10               | 8                           | 5                       |
+
+Figure I.7: A line graph titled 'Interactivity score 'RemoteMeeting', 'Video Chat HD''. The y-axis is 'Interactivity score' from 0 to 100. The x-axis is 'RTT/ms' from 0 to 400. Three curves are shown: a solid line (baseline), a dashed line for PDV\_SQ = 25 ms, and a dotted line for P\_DQ = 1%. All curves decrease as RTT increases. The dotted line is the lowest, followed by the dashed line, and then the solid line.
+
+**Figure I.7 – Example parametrization for remote meeting and video chat according to Annex A**
+
+## Appendix II
+
+## Parameter implementation according to Annex A based on subjective results for cloud gaming considering a real example application on client and server
+
+(This appendix does not form an integral part of this Recommendation.)
+
+### II.1 Introduction
+
+Subjective tests show that subjects are less sensitive to delay and delay jitter in a real gaming situation than the 3GPP thresholds define. There can be many reasons, but in subjective testing the actual application on server and client are considered.
+
+Even though the model described in Annex A is based on measurements on the transport layer and the measurements do not consider the application itself, the model in Annex A can be parametrized to approximate the subjective perception as in subjective tests.
+
+The given examples in this Appendix II are parametrized by a real gaming situation, while the parameters in Appendix I are based on QoS limits. The subjects played a CS\_GO FPS game of 90 seconds match rounds over a Steam Link connection. Consequently, the example parameters in this appendix differ from those given in Appendix I, because the model approximate subjective scores include a real application and its gaming situation.
+
+### II.2 Traffic patterns
+
+#### II.2.1 Packet pattern temporal structure
+
+The recorded packets show that the pattern is mostly tied to the video and audio frame rate. The 120 Hz frame rate and the 50 Hz audio frame rate have the shortest common period of 100 ms, when 12 videoframes and five audio frames are transmitted. This has been noticed from the fact that periodical video and audio frame bursts are transmitted one after each other with a common denominator period of 100 ms. However, the common period can be approximated quite accurately with a 40 ms period comprising five video frames and two audio frames.
+
+The packets recorded on DL show that a video frame is represented by six packets and audio frame by two packets when now network impairments was applied. The last packets of each of these two packet burst types (video frames, audio frames) vary typically between 500 and 800 bytes, and the other packets are of full MTU size. The total size should depend on codecs, resolution and compression rate.
+
+From both DL and UL recorded packets it can also be seen that there is in both directions an acknowledgement mechanism causing transmission of smaller single packets in between bursts.
+
+In addition to the transmission of the apparent acknowledgements, the recorded UL packets show that the frame rate is present, and it shows that user input is transmitted at this rate.
+
+UL packet recording also shows a packet appearing approximately at 50 Hz, which likely is audio input from the user's microphone.
+
+It should be noted that modern algorithms for prioritizing traffic in network nodes analyse the pattern of the traffic. Therefore, in order to closely mimic the real cloud game service, it is important that the traffic characteristics reflect the presence of audio and video streams and the extra packets indicating a real-time transmission.
+
+Table II.1 presents the DL and UL packets patterns basic characteristics represented by packet size and number, based on the analysis of the recorded UL and DL packets described above.
+
+**Table II.1 – Packets patterns characteristics**
+
+| <b>Network condition: No degradations</b> |        |           |        | <b>Network condition: worst case</b> |        |           |        |
+|-------------------------------------------|--------|-----------|--------|--------------------------------------|--------|-----------|--------|
+| <b>UL</b>                                 |        | <b>DL</b> |        | <b>UL</b>                            |        | <b>DL</b> |        |
+| Packets/s                                 | kbit/s | Packets/s | kbit/s | Packets/s                            | kbit/s | Packets/s | kbit/s |
+| ~150                                      | ~140   | ~1100     | ~10000 | ~700                                 | ~620   | ~600      | ~3500  |
+
+As already mentioned above, dividing the packet pattern into temporal sub-segments of 40 ms is expected to be accurate enough. However, to handle the different number of packets per link direction the protocol of choice needs to support, or be extended to support, the concept of bursts (in this case frames) instead (or in addition to) of the single packet concept. This results in two-way measurements such as RTT on the frame burst level instead of the single packet level, but only for the first packet on the respective link.
+
+### II.3 Guidance for adaptation
+
+#### II.3.1 Number of adaptations per link
+
+The different packet patterns for DL can be created by adjusting the number of packets representing the video where the traffic is represented by one to five packets of MTU size. Consequently, the DL can be represented by five patterns.
+
+Packet loss (PL) affects the packet patterns by increasing packets per second and bit/s from the server or from the client. Only a high PL significantly affects the amount of extra traffic, but the interactivity reaches very low subjective interactivity at far lower packet losses and thus the PL impact on the packet pattern can be ignored. The exception would be when RTT is low enough (depending on service's settings) for a re-transmission mechanism to handle high rates of PL with much smaller impact on interactivity. However, that low RTT is not the case for today's mobile networks when the service is running at 120 Hz, and thus that exception case can also be ignored.
+
+For UL the effect of packet loss is much more dramatic, a 5% packet loss rate can yield a doubled packet/bit rate. However, the UL traffic is, compared with DL, using much less of the maximum capacity of the link, and therefore UL adaptation for PL can be ignored.
+
+Large spikes in the delay were in the recorded traffic observed to cause a large increase in uplink traffic, possibly warranting a different packet pattern in those cases. Generally though, the traffic amount is still low versus the link capacity and that UL traffic is still, compared with DL, using much less of the maximum capacity of the link. Thus, the UL adaptation for jitter spikes can be ignored.
+
+#### II.3.2 Adaptation pace
+
+The adaptation of the packet patterns should correspond to the adaptation during the active gaming time (game match) of 90 seconds (value used in the subjective test). A resolution for the measurements on gaming performance over mobile networks within the context of a drive test, needs to ensure a balance between the following:
+
+- drive test real-time characteristic
+- feasible (practical) adaptation scheme of the tested service to the network conditions
+- expected behavioural changes of the tested service's (aka gaming) interactivity depending on the network conditions
+
+Based on these, a measurement time window of 10 s is reasonable. During the 10 s a 40 ms (or 100 ms as mentioned above) packet pattern is played repeatedly. Within each time window of 10 s, a decision on the adaptation is made after 8–9 s based on the network condition.
+
+### II.4 Parameters for approximation subjective scores for cloud gaming
+
+#### II.4.1 Interactive subjective test
+
+For parametrization of the interactivity model as described in Annex A subjective scores are used in accordance with clause 9.2.1.
+
+The basis of parametrization is an interactive subjective test set-up in a lab-controlled environment. The test used 31 subject gamers (males=29 and females=2) who met the requirement of having experience with playing games, either on computers or smartphones, and of being of age 18 or older. The subjects provided answers to the cloud gaming questionnaire as defined in [b-ITU-T G.1072].
+
+The subjects played a CS\_GO FPS game of 90 seconds match rounds. The reason for the game selection relies on the fact that the scope is to provide a generic quality testing solution for one of the most popular video gaming genres played on mobile devices, using technology typical for delivering these, and at the same time addressing the most demanding video game genres for mobile networks in the sense of being most sensitive to the mobile network performance. In this way operators can optimize and troubleshoot their network for the worst scenarios, and thus pre-empt and avoid customer dissatisfaction for both the most demanding as well as the less demanding games.
+
+For each gamer, each of the match rounds have been altered by 30 individual network conditions defined by a set of network metrics. Both the network metrics as well as their values and combinations are selected to meaningfully describe the impact of the mobile network performance on the cloud gaming service based on an interactive subjective pre-test run with a small number of gamers, different from the group used in the full-scale test. The following network metrics are defined as follows:
+
+- i) **RTT (delay)** as the median time the system delivers and receives back a packet, referred to as "static" delay.
+- ii) **Jitter** defined as two types of delay variations which show different effect on the Steam Link streaming.
+  - **Random jitter** frequent with small delay changes (IPDV) from packet to packet.
+  - **Jitter spikes** characterized by amplitude values  $\geq 50$  ms and possibility of frequency between 0.01–1 Hz.
+- iii) **Packet loss** as lost packets during transmission or packets which cannot leave the reflecting server due to downlink congestion and being discarded by the server after timeout.
+
+The network conditions have been created using NetEm emulators and a summary is presented in Table II.2.
+
+**Table II.2 – Mobile network conditions**
+
+| Network metric           | No. of conditions | Values                                                                                 |
+|--------------------------|-------------------|----------------------------------------------------------------------------------------|
+| RTT                      | 7                 | 2*, 25, 50, 100, 200, 300, 400 ms                                                      |
+| PL (per link)            | 4                 | 0, 5, 25, 45% with RTT=2 ms*                                                           |
+| PL (per link) with RTT   | 9                 | PL (0.2, 1, 5%), each with RTT/(25, 50, 100 ms)                                        |
+| Jitter spikes (per link) | 6                 | Jitter spikes with amplitudes values of (25, 100, 750 ms), applied every (5, 15, 45 s) |
+| Random jitter (per link) | 4                 | Avg=25 ms, stdev=3, 6, 9, 12 ms                                                        |
+
+\* An RTT of 2 ms is used as reference for a "clean" condition to be simulated with NetEm.
+
+The target value used for the function parameterization as in Annex A for the cloud gaming over mobile networks use case is selected to be the answer to the question regarding the overall QoE [b-ITU-T G.1072]. The decision for this approach is based on the outcome of an interactive test for
+
+which the results show that the perceived overall QoE describes the interactivity experience as impacted by all the gaming quality dimensions. In addition, this is also empowered by the usage of a specific game with a specific resolution which is acting as a normalization to a reference video-audio quality, and consequently making the overall QoE an interactivity score.
+
+#### II.4.2 Function parametrization according to Annex A
+
+The principal formula for perceived interactivity is as described in Annex A
+
+$$IntAct = I_L \times D_{PDV} \times D_{DQ}$$
+
+The parameter  $I_L$  is calculated as  $I_{L-CG}$  by
+
+$$I_{L-CG} = \frac{f_{max}}{f_0} \left( 1 - \frac{1}{1 + e^{-\frac{1}{b}(RTT_{MEDIAN} - a)}} \right)$$
+
+with  $RTT_{MEDIAN}$  = Median delay of all packets sent by the application
+
+The consideration of packet delay jitter is considered by standard deviation if IPDV is used. By standard deviation is meant the average of standard deviation of IPDV on DL and standard deviation of IPDV on UL.
+
+$$IPDV(i) = D(i) - D(i-1), \text{ and}$$
+
+$$D_{IPDV} = 1 - \frac{IPDV_{STDEV}}{u}$$
+
+Finally, the effect of packet loss is modified compared to Annex A, because the 3GPP RTT specified limit (RTT = 100 ms) does not reflect when interaction with the service (cloud gaming in this case) is not possible per se, since packets are rarely late for a critical moment, and users adapt to latency which anyway is handled by  $I_L$ .
+
+The proposed modification is to consider a limit of 100 ms for disqualification on large jitter (IPDV) values in order to capture the fact that large delay spikes disrupt the ability to interact. The reasoning for this is that tests showed that delay spikes start to affect at 50 ms and can have very noticeable effect at 1500 ms, and these jitter spikes are not captured by the median value of PDV.
+
+In addition, it is proposed that DQ term is used to describe the packet loss. Therefore, the  $D_{DQ}$  term becomes:
+
+$$D_{DQ-CG} = 1 - v \times P_{DQ}$$
+
+$$\text{with } P_{DQ} = \frac{P_{JS}}{T_{MeasureWindow}} + \overline{P_{L-CS} + P_{L-SC}}$$
+
+$$\text{and } P_{JS} = \max(IPDV) \text{ , if } \max(IPDV) \geq DQ_{LIMIT}$$
+
+$$= 0, \text{ otherwise}$$
+
+where by JS is denoted the jitter spike, and  $DQ_{LIMIT}=50$  ms
+
+These modification results in a combining formula as
+
+$$IntAct \text{ for } CG = f_{offset} + f_{max} \times I_{L-CG} \times D_{IPDV} \times D_{DQ-CG}$$
+
+The parameters  $a$ ,  $b$ ,  $u$  and  $v$  to be applied for approximating scores as obtained in the introduced subjective test set-up are:
+
+| Parameter | $a$ | $b$ | $u$ | $v$ |
+|-----------|-----|-----|-----|-----|
+| Value     | 213 | 91  | 25  | 7   |
+
+![Figure II.1: Interactivity score 'CloudGaming' graph. The Y-axis is 'Interactivity score (ACR)' from 1.0 to 5.0. The X-axis is 'RTT/ms' from 0 to 600. Three curves are shown: a solid line for P_DQ-CG = 2%, and two dashed lines for IPDV_STDDEV = 5 ms. All curves show a decreasing trend as RTT increases.](a2dcc4a0703102026ec86e82caa4985e_img.jpg)
+
+The graph titled "Interactivity score 'CloudGaming'" shows the relationship between RTT/ms (X-axis, 0 to 600) and Interactivity score (ACR) (Y-axis, 1.0 to 5.0). Three curves are plotted: a solid line representing  $P_{DQ-CG} = 2\%$ , and two dashed lines representing  $IPDV_{STDDEV} = 5\text{ ms}$ . All curves show a decreasing trend as RTT increases, starting from an ACR of 5.0 at 0 ms RTT and approaching 1.0 at 600 ms RTT.
+
+| RTT/ms | $P_{DQ-CG} = 2\%$ (Solid Line) | $IPDV_{STDDEV} = 5\text{ ms}$ (Dashed Lines) |
+|--------|--------------------------------|----------------------------------------------|
+| 0      | 5.0                            | 4.7                                          |
+| 100    | 4.5                            | 4.0                                          |
+| 200    | 3.8                            | 3.2                                          |
+| 300    | 3.0                            | 2.4                                          |
+| 400    | 2.3                            | 1.8                                          |
+| 500    | 1.8                            | 1.4                                          |
+| 600    | 1.5                            | 1.1                                          |
+
+G.1051(23)
+
+Figure II.1: Interactivity score 'CloudGaming' graph. The Y-axis is 'Interactivity score (ACR)' from 1.0 to 5.0. The X-axis is 'RTT/ms' from 0 to 600. Three curves are shown: a solid line for P\_DQ-CG = 2%, and two dashed lines for IPDV\_STDDEV = 5 ms. All curves show a decreasing trend as RTT increases.
+
+**Figure II.1 – Example of interactivity score for 'cloud gaming'**
+
+It should be noted that  $f_{offset}$  is set to 1.0 and  $f_{max}$  to 4.0 to scale the output into a five-point ACR scale as in the underlying subjective test.
+
+## Bibliography
+
+- [b-ITU-T G.1072] Recommendation ITU-T G.1072 (2020), *Opinion Model Predicting Gaming Quality Of Experience For Cloud Gaming Services*.
+- [b-3GPP TS 22.125] 3GPP TS 22.125 (2019), *Unmanned Aerial System (UAS) support in 3GPP*.
+- [b-IETF] IETF Draft IPPM Capacity Protocol (2022), *Test protocol for one-way IP capacity measurement*. <https://datatracker.ietf.org/doc/html/draft-ietf-ippm-capacity-protocol-04>
+- [b-OB-UDPST] OB-UDPST (2023), OB-UDPST. <https://github.com/BroadbandForum/obudpst>
+
+
+
+
+
+## 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                                                                                                                  |
+| <b>Series G</b> | <b>Transmission systems and media, digital systems and networks</b>                                                                                       |
+| 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                                                                                      |

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+
+
+# Recommendation**ITU-T G.698.5 (01/2024)**
+
+SERIES G: Transmission systems and media, digital systems and networks
+
+Transmission media and optical systems characteristics –  
+Characteristics of optical systems
+
+---
+
+## **Multichannel DWDM applications with single-channel optical interfaces in the O-band**
+
+![ITU logo](0538daaa5583c23e17db3a12f2281a55_img.jpg)
+
+The logo of the International Telecommunication Union (ITU) is located in the bottom right corner. It features a blue globe with white grid lines and the letters 'ITU' in a bold, blue, sans-serif font.
+
+ITU logo
+
+## ITU-T G-SERIES RECOMMENDATIONS
+
+## Transmission systems and media, digital systems and networks
+
+|                                                                                                                                              |                    |
+|----------------------------------------------------------------------------------------------------------------------------------------------|--------------------|
+| INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS                                                                                             | G.100-G.199        |
+| GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS                                                                  | G.200-G.299        |
+| INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES                                                      | G.300-G.399        |
+| GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES | G.400-G.449        |
+| COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY                                                                                            | G.450-G.499        |
+| TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS                                                                                       | G.600-G.699        |
+| General                                                                                                                                      | G.600-G.609        |
+| Symmetric cable pairs                                                                                                                        | G.610-G.619        |
+| Land coaxial cable pairs                                                                                                                     | G.620-G.629        |
+| Submarine cables                                                                                                                             | G.630-G.639        |
+| Free space optical systems                                                                                                                   | G.640-G.649        |
+| Optical fibre cables                                                                                                                         | G.650-G.659        |
+| Characteristics of optical components and subsystems                                                                                         | G.660-G.679        |
+| <b>Characteristics of optical systems</b>                                                                                                    | <b>G.680-G.699</b> |
+| DIGITAL TERMINAL EQUIPMENTS                                                                                                                  | G.700-G.799        |
+| DIGITAL NETWORKS                                                                                                                             | G.800-G.899        |
+| DIGITAL SECTIONS AND DIGITAL LINE SYSTEM                                                                                                     | G.900-G.999        |
+| MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE – GENERIC AND USER-RELATED ASPECTS                                                             | G.1000-G.1999      |
+| TRANSMISSION MEDIA CHARACTERISTICS                                                                                                           | G.6000-G.6999      |
+| DATA OVER TRANSPORT – GENERIC ASPECTS                                                                                                        | G.7000-G.7999      |
+| PACKET OVER TRANSPORT ASPECTS                                                                                                                | G.8000-G.8999      |
+| ACCESS NETWORKS                                                                                                                              | G.9000-G.9999      |
+
+For further details, please refer to the list of ITU-T Recommendations.
+
+# Recommendation ITU-T G.698.5
+
+## Multichannel DWDM applications with single-channel optical interfaces in the O-band
+
+## Summary
+
+Recommendation ITU-T G.698.5 provides optical parameter values for physical layer interfaces of dense wavelength division multiplexing (DWDM) systems primarily intended for mobile fronthaul and metro applications in the O-band, optimized for 10-km and 20-km transmission distances. Applications are defined using optical interface parameters and values for single-channel interfaces of multichannel wavelength division multiplexing (WDM) optical systems in point-to-point applications. This Recommendation uses a system architecture comprising a head-end equipment (HEE) connecting to the tail-end equipment (TEE) through a black link. For mobile fronthaul applications, the HEE is in a central office while the TEE is in a remote antenna site. A single bidirectional transmission fibre is used in the black link to connect the HEE to the TEE. This version of the Recommendation includes bidirectional single-fibre WDM applications at 25 Gbit/s per channel with a nominal optical channel frequency spacing of 800 GHz.
+
+## History \*
+
+| Edition | Recommendation | Approval   | Study Group | Unique ID          |
+|---------|----------------|------------|-------------|--------------------|
+| 1.0     | ITU-T G.698.5  | 2024-01-13 | 15          | 11.1002/1000/15792 |
+
+## Keywords
+
+25G, application codes, black link, metro networks, multivendor, O-band, optical interfaces, optical networks, WDM.
+
+---
+
+\* To access the Recommendation, type the URL <https://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID.
+
+## 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/software copyrights, 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 appropriate ITU-T databases available via the ITU-T website at <http://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2024
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|                                                              | Page |
+|--------------------------------------------------------------|------|
+| 1 Scope.....                                                 | 1    |
+| 2 References.....                                            | 1    |
+| 3 Definitions .....                                          | 2    |
+| 3.1 Terms defined elsewhere .....                            | 2    |
+| 3.2 Terms defined in this Recommendation.....                | 2    |
+| 4 Abbreviations and acronyms .....                           | 3    |
+| 5 Conventions .....                                          | 3    |
+| 6 Classification of optical interfaces.....                  | 3    |
+| 6.1 Applications.....                                        | 3    |
+| 6.2 Reference points .....                                   | 4    |
+| 6.3 Nomenclature .....                                       | 5    |
+| 7 Transverse compatibility .....                             | 5    |
+| 8 Parameter definitions .....                                | 5    |
+| 8.1 General information.....                                 | 6    |
+| 8.2 Interface at point SS .....                              | 7    |
+| 8.3 Optical path from S <sub>s</sub> to R <sub>s</sub> ..... | 7    |
+| 8.4 Interface at point RS.....                               | 8    |
+| 9 Parameter values .....                                     | 8    |
+| 10 Optical safety considerations.....                        | 9    |
+
+
+
+# Recommendation ITU-T G.698.5
+
+## Multichannel DWDM applications with single-channel optical interfaces in the O-band
+
+# 1 Scope
+
+The purpose of this Recommendation is to provide optical interface specifications towards the realization of transversely compatible bidirectional dense wavelength division multiplexing (DWDM) systems in O-band, primarily intended for mobile fronthaul and metro applications.
+
+This Recommendation defines and provides values for optical interface parameters of point-to-point WDM applications on single-mode optical fibres through the use of the black link approach with both of the propagation directions sharing the same optical fibre end-to-end.
+
+This Recommendation uses a system architecture comprising a head-end equipment (HEE) connecting to the tail-end equipment (TEE) through a black link. For mobile fronthaul applications, the HEE is in a central office while the TEE is in a remote antenna site. A single bidirectional transmission fibre is used in the black link to connect the HEE to the TEE. This version of the Recommendation includes bidirectional single-fibre WDM applications at 25 Gbit/s per channel with a nominal optical channel frequency spacing of 800 GHz.
+
+For the applications in this version of the Recommendation, the black link does not contain optical amplifiers.
+
+This Recommendation describes bidirectional WDM systems that include the following features:
+
+- Operating wavelength band: the O-band;
+- Nominal optical channel frequency spacing: 800 GHz;
+- Nominal bit rate of signal channel: 25 Gbit/s;
+- Nominal transmission distances: 10 km and 20 km;
+- Maximum capacity: 6 bidirectional channels (at 12 wavelengths) at 25 Gbit/s.
+
+Specifications are organized according to application codes.
+
+# 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 G.650.2] Recommendation ITU-T G.650.2 (2015), *Definitions and test methods for statistical and non-linear related attributes of single-mode fibre and cable*
+- [ITU-T G.652] Recommendation ITU-T G.652 (2016), *Characteristics of a single-mode optical fibre and cable*.
+- [ITU-T G.664] Recommendation ITU-T G.664 (2012), *Optical safety procedures and requirements for optical transmission systems*.
+- [ITU-T G.671] Recommendation ITU-T G.671 (2019), *Transmission characteristics of optical components and subsystems*.
+
+- [ITU-T G.694.1] Recommendation ITU-T G.694.1 (2020), *Spectral grids for WDM applications: DWDM frequency grid.*
+- [ITU-T G.698.1] Recommendation ITU-T G.698.1 (2023), *Multichannel DWDM applications with single-channel optical interfaces.*
+- [ITU-T G.698.4] Recommendation ITU-T G.698.4 (2023), *Multichannel bi-directional DWDM applications with port agnostic single-channel optical interfaces.*
+- [ITU-T G.709.4] Recommendation ITU-T G.709.4/Y.1331.4 (2020), *OTU25 and OTU50 short-reach interfaces.*
+- [ITU-T G.957] Recommendation ITU-T G.957 (2006), *Optical interfaces for equipments and systems relating to the synchronous digital hierarchy.*
+- [ITU-T G.959.1] Recommendation ITU-T G.959.1 (2018), *Optical transport network physical layer interfaces.*
+- [ITU-T G.972] Recommendation ITU-T G.972 (2020), *Definition of terms relevant to optical fibre submarine cable systems.*
+- [IEC 60825-1] IEC 60825-1:2014, *Safety of laser products – Part 1: Equipment classification and requirements.*
+- [IEC 60825-2] IEC 60825-2:2021, *Safety of laser products – Part 2: Safety of optical fibre communication systems (OFCS).*
+
+# 3 Definitions
+
+## 3.1 Terms defined elsewhere
+
+This Recommendation uses the following terms defined elsewhere:
+
+- 3.1.1 Term defined in [ITU-T G.650.2]
+  - differential group delay.
+- 3.1.2 Terms defined in [ITU-T G.671]:
+  - channel insertion loss;
+  - channel spacing;
+  - reflectance;
+  - ripple.
+- 3.1.3 Term defined in [ITU-T G.694.1]:
+  - frequency grid.
+- 3.1.4 Term defined in [ITU-T G.957]:
+  - transverse compatibility.
+- 3.1.5 Terms defined in [ITU-T G.959.1]:
+  - optical tributary signal;
+  - optical tributary signal class NRZ 25G.
+- 3.1.6 Term defined in [ITU-T G.972]
+  - dense wavelength division multiplexing (DWDM).
+
+## 3.2 Terms defined in this Recommendation
+
+This Recommendation defines the following term:
+
+**3.2.1 receiver sensitivity:** The minimum value of average received power at point R to achieve a  $1 \times 10^{-10}$  BER.
+
+# 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|                |                                                                   |
+|----------------|-------------------------------------------------------------------|
+| BER            | Bit Error Ratio                                                   |
+| DWDM           | Dense Wavelength Division Multiplexing                            |
+| FEC            | Forward Error Correction                                          |
+| HEE            | Head-End Equipment                                                |
+| NRZ            | Non-Return to Zero                                                |
+| OD             | Optical Demultiplexer                                             |
+| OM             | Optical Multiplexer                                               |
+| R <sub>s</sub> | Single-channel reference point at the black link tributary output |
+| S <sub>s</sub> | Single-channel reference point at the black link tributary input  |
+| TEE            | Tail-End Equipment                                                |
+| WDM            | Wavelength Division Multiplexing                                  |
+
+# 5 Conventions
+
+None.
+
+# 6 Classification of optical interfaces
+
+## 6.1 Applications
+
+This Recommendation provides the physical layer parameters and values for single-channel interfaces of WDM multichannel optical systems in physical point-to-point single-fibre applications. These WDM systems are primarily intended to be used in mobile fronthaul and metropolitan area networks for a variety of clients, services and protocols.
+
+The specification method in this Recommendation uses a black link approach which means that optical interface parameters for only (single-channel) optical tributary signals are specified at the HEE and the TEE. Additional specifications are provided for the black link parameters such as maximum attenuation, chromatic dispersion, ripple and polarization mode dispersion. The configurations in Figures 6-1 and 6-2 may coexist at the two ends of the black link and, as such, share the same application code. Implementers need to take care to coordinate the connection type of the transceiver and the black link.
+
+Figure 6-1 shows the linear black link approach for bidirectional transmission applications with two fibres connecting to each transceiver according to the wavelength channel plan specified in clause 8.2.2. For mobile fronthaul applications, the HEE is in a central office while the TEE is in a remote antenna site.
+
+![Figure 6-1: Linear black link approach for bidirectional transmission applications with two fibres connecting to each transceiver. The diagram shows a central 'Black link' containing a 'Fibre' for 'Bidirectional transmission'. On the left, an 'HEE' (Head-End Equipment) contains multiple transceivers, each with an 'Rx' (Receiver) and 'Tx' (Transmitter). Each transceiver is connected to the black link via two optical demultiplexers (OD/OM). The top transceiver's 'Tx' is connected to the black link through an OD/OM, and its 'Rx' is connected through another OD/OM. The bottom transceiver follows the same pattern. On the right, a 'TEE' (Terminal Equipment) also contains transceivers with 'Tx' and 'Rx' connected to the black link via OD/OMs. Reference points are marked: 'R_s' (Receiver signal input) and 'S_s' (Signal output) at each transceiver's interface with the black link. The diagram is labeled 'G.698.5(24)'.](a5ee5c23b6dc52ec1d724b76d5a5f58f_img.jpg)
+
+Figure 6-1: Linear black link approach for bidirectional transmission applications with two fibres connecting to each transceiver. The diagram shows a central 'Black link' containing a 'Fibre' for 'Bidirectional transmission'. On the left, an 'HEE' (Head-End Equipment) contains multiple transceivers, each with an 'Rx' (Receiver) and 'Tx' (Transmitter). Each transceiver is connected to the black link via two optical demultiplexers (OD/OM). The top transceiver's 'Tx' is connected to the black link through an OD/OM, and its 'Rx' is connected through another OD/OM. The bottom transceiver follows the same pattern. On the right, a 'TEE' (Terminal Equipment) also contains transceivers with 'Tx' and 'Rx' connected to the black link via OD/OMs. Reference points are marked: 'R\_s' (Receiver signal input) and 'S\_s' (Signal output) at each transceiver's interface with the black link. The diagram is labeled 'G.698.5(24)'.
+
+**Figure 6-1 – Linear black link approach for bidirectional transmission applications with two fibres connecting to each transceiver**
+
+Figure 6-2 shows the linear black link approach for bidirectional transmission applications with one fibre connecting to each transceiver according to the wavelength channel plan specified in clause 8.2.2.
+
+![Figure 6-2: Linear black link approach for bidirectional transmission applications with one fibre connecting to each transceiver. This diagram is similar to Figure 6-1 but shows a single fibre connecting each transceiver's 'Tx' and 'Rx' to the central 'Black link' via a single OD/OM unit. The 'HEE' and 'TEE' components and the internal 'Fibre' for 'Bidirectional transmission' remain the same. Reference points 'R_s' and 'S_s' are also indicated at the interfaces.](e6df2733626a85205c1db682e6259c46_img.jpg)
+
+Figure 6-2: Linear black link approach for bidirectional transmission applications with one fibre connecting to each transceiver. This diagram is similar to Figure 6-1 but shows a single fibre connecting each transceiver's 'Tx' and 'Rx' to the central 'Black link' via a single OD/OM unit. The 'HEE' and 'TEE' components and the internal 'Fibre' for 'Bidirectional transmission' remain the same. Reference points 'R\_s' and 'S\_s' are also indicated at the interfaces.
+
+**Figure 6-2 – Linear black link approach for bidirectional transmission applications with one fibre connecting to each transceiver**
+
+## 6.2 Reference points
+
+The system architecture comprises a HEE connecting to the TEE through a black link. The HEE houses a set of transmitters and receivers. A single bidirectional fibre or a pair of fibres is used to connect a pair of head-end transmitter (Tx) and receiver (Rx) with one or two ports of the black link. Both the HEE-side optical demultiplexer (OD) / optical multiplexer (OM) and the TEE-side OD/OM are considered to be part of the black link. The connection between the HEE-side OD/OM and the TEE-side OD/OM is bidirectional.
+
+The reference points in Figure 6-1 and Figure 6-2 are defined as follows:
+
+- $S_s$  is a single-channel reference point at the black link tributary input;
+- $R_s$  is a single-channel reference point at the black link tributary output.
+
+At the  $S_s$  interface, a single-channel signal enters the black link from an optical transmitter.
+
+At the  $R_s$  interface, a single-channel signal exits the black link towards an optical receiver.
+
+## 6.3 Nomenclature
+
+The application code notation is constructed as follows:
+
+$Lc-s-dD-y-tz$
+
+where:
+
+- L is the indicator of WDM applications defined in this Recommendation.
+- c is the number of channels.
+- s is a number giving the channel spacing in 100 GHz:
+  - 8 indicating 800 GHz spacing
+- d is a number indicating the span distance in km, such as:
+  - 10 indicating short-haul up to 10 km distance;
+  - 20 indicating short-haul up to 20 km distance.
+- D is the indicator of unidirectional or bidirectional transmission:
+  - B bidirectional transmission.
+- y indicates the highest class of optical tributary signal supported:
+  - 9 indicating NRZ 25G.
+- t indicates the configuration supported by the application code. In the current version of this Recommendation, the only value used is:
+  - D indicating that the black link does not contain any optical amplifiers.
+- z indicates the fibre types. In the current version of this Recommendation, the only value used is:
+  - 1 indicating ITU-T G.652 fibre.
+
+# 7 Transverse compatibility
+
+This Recommendation specifies parameters in order to enable transverse (i.e., multivendor) compatible line systems for point-to-point applications at single-channel reference points  $S_s$  and  $R_s$ .
+
+The single-channel reference points  $S_s$  and  $R_s$  are intended to make multiple tributary interfaces of WDM TEEs transversely compatible with the HEE. In this case, tributary signal transmitter ( $T_x \lambda_i$ ) and receiver ( $R_x \lambda_i$ ) pairs may be from different vendors. Thus, TEE, black link and HEE suppliers are not necessarily the same.
+
+# 8 Parameter definitions
+
+The parameters in Table 8-1 are defined at the interface points and the definitions are provided in the clauses below.
+
+**Table 8-1 – Physical layer parameters for multichannel bidirectional WDM applications**
+
+| Parameter                                                              | Units | For HEE to TEE defined in: | For TEE to HEE defined in: |
+|------------------------------------------------------------------------|-------|----------------------------|----------------------------|
+| <b>General information</b>                                             |       |                            |                            |
+| Bit-rate/line coding of optical tributary signals                      | –     | 8.1.1                      | 8.1.1                      |
+| Maximum bit-error ratio                                                | –     | 8.1.2                      | 8.1.2                      |
+| Fibre type                                                             | –     | 8.1.3                      | 8.1.3                      |
+| <b>Interface at point S<sub>s</sub></b>                                |       |                            |                            |
+| Maximum mean channel output power                                      | dBm   | 8.2.1                      | 8.2.1                      |
+| Minimum mean channel output power                                      | dBm   | 8.2.1                      | 8.2.1                      |
+| Minimum central frequency                                              | THz   | 8.2.2                      | 8.2.2                      |
+| Maximum central frequency                                              | THz   | 8.2.2                      | 8.2.2                      |
+| Maximum spectral excursion                                             | GHz   | 8.2.3                      | 8.2.3                      |
+| Minimum channel extinction ratio                                       | dB    | 8.2.4                      | 8.2.4                      |
+| Eye mask                                                               | –     | 8.2.5                      | 8.2.5                      |
+| <b>Optical path from S<sub>s</sub> to R<sub>s</sub></b>                |       |                            |                            |
+| Maximum channel insertion loss                                         | dB    | 8.3.1                      | 8.3.1                      |
+| Minimum channel insertion loss                                         | dB    | 8.3.1                      | 8.3.1                      |
+| Maximum ripple                                                         | dB    | 8.3.2                      | 8.3.2                      |
+| Chromatic dispersion range                                             | ps/nm | 8.3.3                      | 8.3.3                      |
+| Minimum optical return loss at S <sub>s</sub>                          | dB    | 8.3.4                      | 8.3.4                      |
+| Maximum discrete reflectance between S <sub>s</sub> and R <sub>s</sub> | dB    | 8.3.5                      | 8.3.5                      |
+| Maximum differential group delay                                       | ps    | 8.3.6                      | 8.3.6                      |
+| Maximum inter-channel crosstalk at R <sub>s</sub>                      | dB    | 8.3.7                      | 8.3.7                      |
+| Maximum interferometric crosstalk at R <sub>s</sub>                    | dB    | 8.3.8                      | 8.3.8                      |
+| <b>Interface at point R<sub>s</sub></b>                                |       |                            |                            |
+| Maximum mean channel input power                                       | dBm   | 8.4.1                      | 8.4.1                      |
+| Minimum mean channel input power                                       | dBm   | 8.4.1                      | 8.4.1                      |
+| Receiver sensitivity                                                   | dBm   | 8.4.2                      | 8.4.2                      |
+| Maximum optical path penalty                                           | dB    | 8.4.3                      | 8.4.3                      |
+| Maximum reflectance of receiver or optical network element             | dB    | 8.4.4                      | 8.4.4                      |
+
+## 8.1 General information
+
+### 8.1.1 Bit-rate/line coding of optical tributary signals
+
+The bit-rate/line coding of optical tributary signals is defined in [ITU-T G.959.1].
+
+### 8.1.2 Maximum bit-error ratio
+
+The maximum bit-error ratio is defined in [ITU-T G.698.1].
+
+### 8.1.3 Fibre type
+
+Currently, the only single-mode optical fibre type is that defined in [ITU-T G.652].
+
+## 8.2 Interface at point Ss
+
+### 8.2.1 Maximum and minimum mean channel output power
+
+The mean channel output power is defined in [ITU-T G.959.1].
+
+### 8.2.2 Minimum and maximum central frequency
+
+The central frequency is defined in [ITU-T G.698.1].
+
+For each optical channel, different ranges of frequencies are used in the head end (HE) to tail end (TE) and TE-to-HE directions. The channel frequencies in the two directions are paired.
+
+In application codes L12-8-10B-9-D1 and L12-8-20B-9-D1, the nominal bidirectional optical channel frequencies and their pairing are set according to Table 8-2.
+
+**Table 8-2 – Nominal bidirectional optical channel frequencies and their pairing for L12-8-10B-9-D1 and L12-8-20B-9-D1 applications codes**
+
+| Bidirectional channel | From HEE to TEE      |                         |                         | From TEE to HEE      |                         |                         |
+|-----------------------|----------------------|-------------------------|-------------------------|----------------------|-------------------------|-------------------------|
+|                       | Channel index (Note) | Central frequency (THz) | Central wavelength (nm) | Channel index (Note) | Central frequency (THz) | Central wavelength (nm) |
+| 1                     | $f_2$                | 235.4                   | 1273.54                 | $f_1$                | 236.2                   | 1269.23                 |
+| 2                     | $f_4$                | 233.8                   | 1282.26                 | $f_3$                | 234.6                   | 1277.89                 |
+| 3                     | $f_6$                | 232.2                   | 1291.10                 | $f_5$                | 233.0                   | 1286.66                 |
+| 4                     | $f_7$                | 231.4                   | 1295.56                 | $f_8$                | 230.6                   | 1300.05                 |
+| 5                     | $f_{10}$             | 229.0                   | 1309.14                 | $f_9$                | 229.8                   | 1304.58                 |
+| 6                     | $f_{12}$             | 227.4                   | 1318.35                 | $f_{11}$             | 228.2                   | 1313.73                 |
+
+NOTE –  $f_m = 237.0 - 0.8 \times m$  (THz),  $m = 1$  to 12; each pair of channels on the same row in Table 8-2 can share a single bidirectional fibre to reach their corresponding HEE/TEE Tx/Rx.
+
+### 8.2.3 Maximum spectral excursion
+
+The maximum spectral excursion is defined in [ITU-T G.698.1].
+
+### 8.2.4 Minimum channel extinction ratio
+
+The minimum channel extinction ratio is defined in [ITU-T G.698.1].
+
+### 8.2.5 Eye mask
+
+The eye mask is defined in [ITU-T G.959.1].
+
+## 8.3 Optical path from Ss to Rs
+
+### 8.3.1 Maximum and minimum channel insertion loss
+
+The channel insertion loss is defined in [ITU-T G.698.1].
+
+### 8.3.2 Maximum ripple
+
+The ripple is defined in [ITU-T G.698.1].
+
+### 8.3.3 Chromatic dispersion range
+
+This parameter defines the range between the minimum and the maximum values of the optical path chromatic dispersion that the system shall be able to tolerate.
+
+### 8.3.4 Minimum optical return loss at Ss
+
+The minimum optical return loss is defined in [ITU-T G.959.1].
+
+### 8.3.5 Maximum discrete reflectance between Ss and Rs
+
+The maximum discrete reflectance is defined in [ITU-T G.959.1].
+
+### 8.3.6 Maximum differential group delay
+
+The maximum differential group delay is defined in [ITU-T G.698.1]
+
+### 8.3.7 Maximum interchannel crosstalk at Rs
+
+The interchannel crosstalk is defined in [ITU-T G.698.1].
+
+### 8.3.8 Maximum interferometric crosstalk at Rs
+
+The interferometric crosstalk is defined in [ITU-T G.698.1].
+
+## 8.4 Interface at point Rs
+
+### 8.4.1 Maximum and minimum mean channel input power
+
+The mean channel input power is defined in [ITU-T G.959.1].
+
+### 8.4.2 Receiver sensitivity
+
+The receiver sensitivity is defined in [ITU-T G.698.1].
+
+### 8.4.3 Maximum optical path penalty
+
+The maximum optical path penalty is defined in [ITU-T G.698.1].
+
+### 8.4.4 Maximum reflectance of receiver or optical network element
+
+The maximum reflectance of receiver is defined in [ITU-T G.698.1]
+
+# 9 Parameter values
+
+Table 9-1 shows parameter values for L12-8-10B-9-D1 and L12-8-20B-9-D1 application codes.
+
+**Table 9-1 – Optical specifications for 10-km and 20-km application codes L12-8-10B-9-D1 and L12-8-20B-9-D1**
+
+| Parameter                                         | Units | L12-8-10B-9-D1                                     | L12-8-20B-9-D1 |
+|---------------------------------------------------|-------|----------------------------------------------------|----------------|
+| General information                               |       |                                                    |                |
+| Maximum numbers of channels                       | –     | 12                                                 |                |
+| Bit-rate/line coding of optical tributary signals | –     | 25.78125 Gb/s $\pm$ 100 ppm / 25G NRZ              |                |
+| Maximum bit error ratio (Note 1)                  | –     | $10^{-12}$                                         |                |
+| Fibre type                                        | –     | G.652                                              |                |
+| <b>Interface at point Ss</b>                      |       |                                                    |                |
+| Maximum mean channel output power                 | dBm   | 5.5                                                | 5.5            |
+| Minimum mean channel output power                 | dBm   | 0                                                  | 2              |
+| Central frequencies of all the channels           | THz   | $f_m = 237.0 - 0.8 \times m, m = 1 \text{ to } 12$ |                |
+| Central frequencies of the HE-to-TE channels      | –     | $f_2, f_4, f_6, f_7, f_{10}, f_{12}$               |                |
+
+**Table 9-1 – Optical specifications for 10-km and 20-km application codes L12-8-10B-9-D1 and L12-8-20B-9-D1**
+
+| Parameter                                                                                                                                                                         | Units | L12-8-10B-9-D1                    | L12-8-20B-9-D1 |  |  |
+|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------|-----------------------------------|----------------|--|--|
+| Central frequencies of the TE-to-HE channels                                                                                                                                      | –     | $f_1, f_3, f_5, f_8, f_9, f_{11}$ |                |  |  |
+| Maximum spectral excursion                                                                                                                                                        | GHz   | $\pm 200$                         |                |  |  |
+| Minimum channel extinction ratio                                                                                                                                                  | dB    | 3.5                               |                |  |  |
+| Eye mask                                                                                                                                                                          | –     | NRZ 25G Ratio                     |                |  |  |
+| <b>Optical path from point S<sub>s</sub> to R<sub>s</sub></b>                                                                                                                     |       |                                   |                |  |  |
+| Maximum channel insertion loss (Note 2)                                                                                                                                           | dB    | 10.7                              | 15.9           |  |  |
+| Minimum channel insertion loss (Note 2)                                                                                                                                           | dB    | 2.5                               | 2.5            |  |  |
+| Maximum ripple                                                                                                                                                                    | dB    | 2                                 |                |  |  |
+| Chromatic dispersion range                                                                                                                                                        | ps/nm | –50 to +15                        | –100 to +30    |  |  |
+| Minimum optical return loss at S <sub>s</sub>                                                                                                                                     | dB    | 20                                |                |  |  |
+| Maximum discrete reflectance between S <sub>s</sub> and R <sub>s</sub>                                                                                                            | dB    | –26                               |                |  |  |
+| Maximum differential group delay                                                                                                                                                  | ps    | 10.3                              |                |  |  |
+| Maximum inter-channel crosstalk at R <sub>s</sub>                                                                                                                                 | dB    | –25                               |                |  |  |
+| Maximum interferometric crosstalk at R <sub>s</sub>                                                                                                                               | dB    | –45                               |                |  |  |
+| <b>Interface at point R<sub>s</sub></b>                                                                                                                                           |       |                                   |                |  |  |
+| Maximum mean channel input power                                                                                                                                                  | dBm   | 3                                 | 3              |  |  |
+| Minimum mean channel input power                                                                                                                                                  | dBm   | –10.7                             | –13.9          |  |  |
+| Maximum optical path penalty (Note 3)                                                                                                                                             | dB    | 2                                 | 2.5            |  |  |
+| Receiver sensitivity (Note 4)                                                                                                                                                     | dBm   | –12.7                             | –16.4          |  |  |
+| Maximum reflectance of optical network element                                                                                                                                    | dB    | –26                               |                |  |  |
+| NOTE 1 – The BER for these application codes is required to be met only after RS10(528,514) has been applied, as in the OTU25u-RS FEC specification in [ITU-T G.709.4].           |       |                                   |                |  |  |
+| NOTE 2 – The channel insertion loss refers to the trunk optical path loss, containing the cabled optical fibre attenuation, connection and splice loss, and OM/OD insertion loss. |       |                                   |                |  |  |
+| NOTE 3 – The optical path penalty contains the penalties from chromatic dispersion, PMD, crosstalk and FWM.                                                                       |       |                                   |                |  |  |
+| NOTE 4 – The receiver sensitivity is measured with transmitter set at the maximum power and with the minimum optical return loss of the black link.                               |       |                                   |                |  |  |
+
+# 10 Optical safety considerations
+
+See [ITU-T G.664], [IEC 60825-1] and [IEC 60825-2] for optical safety considerations.
+
+
+
+
+
+## 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                                                                                                                  |
+| <b>Series G</b> | <b>Transmission systems and media, digital systems and networks</b>                                                                                       |
+| 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                                                                                      |

marked/G/T-REC-G.7721.1-202508-I_PDF-E/raw.md

@@ -0,0 +1,723 @@
+
+
+# Recommendation
+
+# **ITU-T G.7721.1 (08/2025)**
+
+SERIES G: Transmission systems and media, digital systems and networks
+
+Data over Transport – Generic aspects – Transport network control aspects
+
+---
+
+# **Data model of synchronization management**
+
+![ITU logo](84a1d09fb489061482111515543b60dc_img.jpg)
+
+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 G-SERIES RECOMMENDATIONS **Transmission systems and media, digital systems and networks**
+
+|                                                                                                                                              |                      |
+|----------------------------------------------------------------------------------------------------------------------------------------------|----------------------|
+| INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS                                                                                             | G.100-G.199          |
+| GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS                                                                  | G.200-G.299          |
+| INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES                                                      | G.300-G.399          |
+| GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES | G.400-G.449          |
+| COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY                                                                                            | G.450-G.499          |
+| TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS                                                                                       | G.600-G.699          |
+| DIGITAL TERMINAL EQUIPMENTS                                                                                                                  | G.700-G.799          |
+| DIGITAL NETWORKS                                                                                                                             | G.800-G.899          |
+| DIGITAL SECTIONS AND DIGITAL LINE SYSTEM                                                                                                     | G.900-G.999          |
+| MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE – GENERIC AND USER-RELATED ASPECTS                                                             | G.1000-G.1999        |
+| TRANSMISSION MEDIA CHARACTERISTICS                                                                                                           | G.6000-G.6999        |
+| DATA OVER TRANSPORT – GENERIC ASPECTS                                                                                                        | G.7000-G.7999        |
+| General                                                                                                                                      | G.7000-G.7099        |
+| <b>Transport network control aspects</b>                                                                                                     | <b>G.7700-G.7799</b> |
+| PACKET OVER TRANSPORT ASPECTS                                                                                                                | G.8000-G.8999        |
+| ACCESS NETWORKS                                                                                                                              | G.9000-G.9999        |
+
+*For further details, please refer to the list of ITU-T Recommendations.*
+
+# Recommendation ITU-T G.7721.1
+
+# Data model of synchronization management
+
+## Summary
+
+Recommendation ITU-T G.7721.1 specifies the synchronization information models and data models for transport network elements (NEs) to support specific interface protocols and specific management and control (MC) functions.
+
+The information models are interface protocol neutral and specified using the unified modelling language (UML).
+
+The data models are interface protocol specific and are directly derived from these information models. The specific data models considered in this Recommendation include, but are not limited to, yet another next generation (YANG) data models.
+
+The specific MC functions for synchronization covered by this Recommendation are specified in Recommendations ITU-T G.8265.1, ITU-T G.8275.1 and ITU-T G.8275.2.
+
+The precision time protocol (PTP) telecom profile YANG modules defined in this Recommendation augments:
+
+- The PTP YANG module defined in IETF RFC 8575 for the management of the precision time protocol (PTP) defined in IEEE 1588-2008.
+- The PTP-TT YANG module defined in IEEE 1588e-2024 for the management of the precision time protocol (PTP) defined in IEEE 1588-2019, with the inclusive language.
+
+The UML information model and YANG data model in this version of the Recommendation covers the PTP telecom profiles defined in Recommendations ITU-T G.8265.1, ITU-T G.8275.1 and ITU-T G.8275.2.
+
+Amendment 1 updates the Recommendation to align the data model for PTP telecom profile with the latest editions of PTP Telecom Profiles Recommendations (i.e., ITU-T G.8265.1 Edition 4.1, ITU-T G.8275.1 Edition 4.2 and ITU-T G.8275.2 Edition 3.2).
+
+This revision updates ITU-T G.7721.1 to add the YANG data model for SyncPhy in alignment with the data set defined in Recommendation ITU-T G.781 Edition 5.2 and the SyncPhy information model defined in Recommendation ITU-T G.7721.
+
+## History\*
+
+| Edition | Recommendation               | Approval   | Study Group | Unique ID          |
+|---------|------------------------------|------------|-------------|--------------------|
+| 1.0     | ITU-T G.7721.1               | 2022-06-06 | 15          | 11.1002/1000/14915 |
+| 1.1     | ITU-T G.7721.1 (2022) Amd. 1 | 2024-12-07 | 15          | 11.1002/1000/16149 |
+| 2.0     | ITU-T G.7721.1               | 2025-08-22 | 15          | 11.1002/1000/16398 |
+
+## Keywords
+
+Data model, management, synchronization.
+
+---
+
+\* To access the Recommendation, type the URL <https://handle.itu.int/> in the address field of your web browser, followed by the Recommendation's unique ID.
+
+## FOREWORD
+
+The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, and 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/software copyrights, 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 appropriate ITU-T databases available via the ITU-T website at <https://www.itu.int/ITU-T/ipr/>.
+
+© ITU 2025
+
+All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU.
+
+## Table of Contents
+
+|                                                                                   | Page |
+|-----------------------------------------------------------------------------------|------|
+| 1 Scope.....                                                                      | 1    |
+| 2 References.....                                                                 | 1    |
+| 3 Definitions .....                                                               | 2    |
+| 3.1 Terms defined elsewhere .....                                                 | 2    |
+| 3.2 Terms defined in this Recommendation.....                                     | 2    |
+| 4 Abbreviations and acronyms .....                                                | 2    |
+| 5 Conventions .....                                                               | 3    |
+| 5.1 Information modelling conventions .....                                       | 3    |
+| 6 Synchronization functions .....                                                 | 3    |
+| 6.1 Precision time protocol (PTP) telecom profiles .....                          | 3    |
+| 6.2 SyncPhy functions .....                                                       | 3    |
+| 7 Synchronization management information models .....                             | 3    |
+| 7.1 PTP telecom profiles management information model .....                       | 4    |
+| 7.2 SyncPhy management information model.....                                     | 11   |
+| 7.3 Synchronization UML information models.....                                   | 11   |
+| 8 Synchronization data models .....                                               | 11   |
+| 8.1 Synchronization YANG data models .....                                        | 11   |
+| Annex A – Management conformance for PTP telecom profiles YANG data models .....  | 13   |
+| A.1 Configuration of optional YANG data nodes.....                                | 13   |
+| A.2 Reporting values in the operational datastore .....                           | 13   |
+| Annex B – Using the IETF PTP YANG data model for ITU-T PTP telecom profiles ..... | 15   |
+| Appendix I – YANG deviation example for the PTP YANG data model.....              | 16   |
+| Bibliography.....                                                                 | 17   |
+
+Electronic attachment: The UML information model, the YANG data model described in clauses 7 and 8 and the ptp deviation example YANG module described in Appendix I.
+
+
+
+# Recommendation ITU-T G.7721.1
+
+## Data model of synchronization management<sup>1</sup>
+
+# 1 Scope
+
+This Recommendation specifies the synchronization information models and data models for transport network elements (NEs) to support specific interface protocols and specific management and control (MC) functions.
+
+The specific MC functions for synchronization covered by this Recommendation are specified in [ITU-T G.8265.1], [ITU-T G.8275.1] and [ITU-T G.8275.2].
+
+The information models are interface protocol neutral and specified using the unified modelling language (UML). The information models of this Recommendation are derived through pruning and refactoring from the [ITU-T G.7711] core information model and the [ITU-T G.7721] synchronization base information model.
+
+The data models are interface protocol specific and are directly derived from these information models. The specific data models considered in this Recommendation include, but are not limited to, yet another next generation (YANG) data models.
+
+The precision time protocol (PTP) telecom profile YANG module defined in this Recommendation augments:
+
+- The PTP YANG module defined in [IETF RFC 8575] for the management of the precision time protocol (PTP) defined in [IEEE 1588-2008].
+- The PTP-TT YANG module, defined in [IEEE 1588e-2024] for the management of the precision time protocol (PTP), defined in [IEEE 1588-2019], with inclusive language.
+
+The UML information model and YANG data model in this version of the Recommendation covers the PTP telecom profiles defined in [ITU-T G.8265.1], [ITU-T G.8275.1], and [ITU-T G.8275.2].
+
+Amendment 1 updates the Recommendation to align the data model for PTP telecom profile with the latest editions of PTP telecom profiles Recommendations (i.e., [ITU-T G.8265.1] Edition 4.1, [ITU-T G.8275.1] Edition 4.2 and [ITU-T G.8275.2] Edition 3.2).
+
+This revision updates ITU-T G.7721.1 to add the YANG data model for SyncPhy in alignment with the data set defined in [ITU-T G.781] Edition 5.2 and the SyncPhy information model defined in [ITU-T G.7721].
+
+# 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 G.781] Recommendation ITU-T G.781 (2024), *Synchronization layer functions for frequency synchronization based on the physical layer*.
+
+---
+
+<sup>1</sup> This Recommendation includes an electronic attachment containing the UML information model, the YANG data model described in clauses 7 and 8 and the ptp deviation example YANG module described Appendix I.
+
+- [ITU-T G.7711] Recommendation ITU-T G.7711 (2025), *Generic protocol-neutral information model for transport resources*.
+- [ITU-T G.7721] Recommendation ITU-T G.7721 (2025), *Management requirement and information model for synchronization*.
+- [ITU-T G.8265.1] Recommendation ITU-T G.8265.1/Y.1365.1 (2022), *Precision time protocol telecom profile for frequency synchronization*.
+- [ITU-T G.8275.1] Recommendation ITU-T G.8275.1/Y.1369.1 (2022), *Precision time protocol telecom profile for phase/time synchronization with full timing support from the network*.
+- [ITU-T G.8275.2] Recommendation ITU-T G.8275.2/Y.1369.2 (2022), *Precision time protocol telecom profile for phase/time synchronization with partial timing support from the network*.
+- [IEEE 1588-2008] IEEE Std 1588<sup>TM</sup>-2008, *IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems*.
+- [IEEE 1588-2019] IEEE Std 1588<sup>TM</sup>-2019, *IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems*.
+- [IEEE 1588e-2024] IEEE Std 1588e<sup>TM</sup>-2024, *IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems Amendment: MIB and YANG Modules*.
+- [IETF RFC 7950] RFC 7950 (2016), *The YANG 1.1 Data Modeling Language*.
+- [IETF RFC 8340] RFC 8340 (2018), *YANG Tree Diagrams*.
+- [IETF RFC 8342] RFC 8342 (2018), *Network Management Datastore Architecture (NMDA)*.
+- [IETF RFC 8343] RFC 8343 (2018), *A YANG Data Model for Interface Management*.
+- [IETF RFC 8575] RFC 8575 (2019), *YANG Data Model for the Precision Time Protocol (PTP)*.
+
+# 3 Definitions
+
+## 3.1 Terms defined elsewhere
+
+None.
+
+## 3.2 Terms defined in this Recommendation
+
+None.
+
+# 4 Abbreviations and acronyms
+
+This Recommendation uses the following abbreviations and acronyms:
+
+|      |                                    |
+|------|------------------------------------|
+| CASC | Configuration and Switch Control   |
+| LTP  | Logical Termination Point          |
+| NE   | Network Element                    |
+| PTP  | Precision Time Protocol            |
+| TT   | Time transmitter and Time receiver |
+| UML  | Unified Modelling Language         |
+| YANG | Yet Another Next Generation        |
+
+# 5 Conventions
+
+## 5.1 Information modelling conventions
+
+### UML modelling conventions
+
+See [ITU-T G.7711] clause 5.1.
+
+### Model artefact lifecycle stereotypes conventions
+
+See [ITU-T G.7711] clause 5.2.
+
+### Forwarding entity terminology conventions
+
+See clause 5.3 of [ITU-T G.7711].
+
+### Conditional package conventions
+
+See clause 5.4 of [ITU-T G.7711].
+
+### Pictorial diagram conventions
+
+See clause 5.5 of [ITU-T G.7711].
+
+# 6 Synchronization functions
+
+This clause identifies the synchronization functions that are modelled by the information model and data models of this Recommendation.
+
+## 6.1 Precision time protocol (PTP) telecom profiles
+
+The precision time protocol (PTP) is defined in [IEEE 1588-2008] and in [IEEE 1588-2019].
+
+ITU-T has developed a set of PTP telecom profiles, as listed in Table 6-1.
+
+**Table 6-1 – ITU-T PTP telecom profiles**
+
+| ITU-T PTP telecom profiles                                               | Reference        |
+|--------------------------------------------------------------------------|------------------|
+| Frequency synchronization                                                | [ITU-T G.8265.1] |
+| Phase/time synchronization, with full timing support from the network    | [ITU-T G.8275.1] |
+| Phase/time synchronization, with partial timing support from the network | [ITU-T G.8275.2] |
+
+## 6.2 SyncPhy functions
+
+ITU-T has developed the following frequency synchronization based on the physical layer (SyncPhy) datasets in [ITU-T G.781]:
+
+- defaultDS: defines members for the default device attributes of a physical layer clock.
+- currentDS: defines members for the current device attributes of a physical layer clock.
+- parentDS: defines members for the clock source attributes of a physical layer clock.
+- portDS: defines members for the port attributes of a physical layer port.
+
+The information model of this Recommendation for SyncPhy functions aligns with the SyncPhy model defined in [ITU-T G.7721].
+
+# 7 Synchronization management information models
+
+This clause contains the unified modelling language (UML) information model of the synchronization functions identified in clause 6. The information model is derived through pruning and refactoring
+
+the [ITU-T G.7711] core information model and the [ITU-T G.7721] synchronization base information model.
+
+There are two synchronization management information models, one for the ITU-T PTP telecom profiles, and one for SyncPhy.
+
+## 7.1 PTP telecom profiles management information model
+
+Considering backward compatibility with the PTP telecom profile module defined in the first version of this Recommendation, three models are defined:
+
+- PTP telecom profile types module, which provides common definitions used by the PTP-time transmitter and time receiver (TT) telecom profile module and the PTP telecom profile module.
+- PTP telecom profile module, which augments the IETF PTP model, defined in [IETF RFC 8575], supports only implementations of the ITU-T PTP telecom profiles based on [IEEE 1588-2008].
+- PTP-TT telecom profile module, which augments the IEEE PTP-TT model, defined in [IEEE 1588e-2024] using inclusive language, and which supports the implementations of ITU-T PTP telecom profiles based on [IEEE 1588-2008] or on [IEEE 1588-2019].
+
+The scenarios of PTP telecom profiles YANG are summarized in Table 7-1.
+
+**Table 7-1 – Scenarios of PTP telecom profiles YANG**
+
+|                     | Base specification | Base YANG                            | YANG augmentations                              |
+|---------------------|--------------------|--------------------------------------|-------------------------------------------------|
+| <b>Scenario I</b>   | [IEEE 1588-2008]   | ietf-ptp<br>[IETF RFC 8575]          | itut-ptp-telecom-profile<br>[ITU-T G.7721.1]    |
+| <b>Scenario II</b>  | [IEEE 1588-2008]   | ieee1588-ptp-tt<br>[IEEE 1588e-2024] | itut-ptp-tt-telecom-profile<br>[ITU-T G.7721.1] |
+| <b>Scenario III</b> | [IEEE 1588-2019]   | ieee1588-ptp-tt<br>[IEEE 1588e-2024] | itut-ptp-tt-telecom-profile<br>[ITU-T G.7721.1] |
+
+It is worth noting that the first version of this Recommendation supports only Scenario I, and that:
+
+- migration from Scenario I to either Scenario II or Scenario III is non-backward compatible because the migration from the IETF PTP model, defined in [IETF RFC 8575] and IEEE PTP-TT model, defined in [IEEE 1588e-2024], is not backward compatible;
+- migration from Scenario II to Scenario III is backward compatible.
+
+For the implementations of ITU-T PTP telecom profiles developed after Edition 1.1 (12/2024) of this Recommendation, it is recommended to use the PTP-TT telecom profile module.
+
+It is worth noting that the names of the YANG data nodes defined in [IETF RFC 8575] and in Edition 1.0 of this Recommendation use the legacy terminology, while the names of the YANG data nodes defined from Edition 1.1 onwards of this Recommendation use the new terminology.
+
+The users of the itut-ptp-telecom-profile YANG data model are assumed to be familiar with both terminologies, as described in Appendix XII of [ITU-T G.8275].
+
+### 7.1.1 PTP telecom profile types module
+
+The PTP telecom profile types module provides common definitions used by the PTP-TT telecom profile module and the PTP telecom profile module.
+
+#### 7.1.1.1 Required object classes and relations
+
+An overview of the PTP telecom profile types UML is illustrated in Figure 7-1 (also available in the electronic attachment).
+
+![Figure 7-1 – PTP telecom profile types UML overview. This UML diagram shows the relationships between several classes: PtpTelecomProfileType, PtpTlpDeviceType, G.8265.1_DeviceType, G.8275.1_DeviceType, PtpProfileVersion, and PtpTlpProfileIdentifier. It also shows two default packages, CommonPtpTlpDefaultDsPac and CommonPtpTlpDefaultDsPac, with their respective attributes and associations. Associations are labeled with 'PruneAndRefactor' and 'CommonPtpTlpDefaultDsPacRealizesPtpTlpDefaultDsPac'.](e9314c83043183351ed74908e9bf2f90_img.jpg)
+
+Figure 7-1 – PTP telecom profile types UML overview. This UML diagram shows the relationships between several classes: PtpTelecomProfileType, PtpTlpDeviceType, G.8265.1\_DeviceType, G.8275.1\_DeviceType, PtpProfileVersion, and PtpTlpProfileIdentifier. It also shows two default packages, CommonPtpTlpDefaultDsPac and CommonPtpTlpDefaultDsPac, with their respective attributes and associations. Associations are labeled with 'PruneAndRefactor' and 'CommonPtpTlpDefaultDsPacRealizesPtpTlpDefaultDsPac'.
+
+Figure 7-1 – PTP telecom profile types UML overview
+
+NOTE – The conformance level (when different from CONDITIONAL), default value and value range of the attributes are defined in the relevant PTP telecom profile Recommendations, particularly in clause A.2 of [ITU-T G.8265.1], clause A.2 of [ITU-T G.8275.1] or clause A.2 of [ITU-T G.8275.2].
+
+#### 7.1.1.2 Required attributes and operations
+
+This clause shows (from Table 7-2 to Table 7-6) how the required attributes and operations defined in [ITU-T G.7721] are pruned or refactored for the management of the PTP telecom profile types module.
+
+Table 7-2 – PTP attributes for data types
+
+| Data types in [ITU-T G.7721]                                                                                             | PTP telecom profile types |
+|--------------------------------------------------------------------------------------------------------------------------|---------------------------|
+| PtpTelecomProfileType                                                                                                    | Refactored (copied)       |
+| PtpTlpDeviceType                                                                                                         | Pruned (Note)             |
+| G.8265.1_DeviceType                                                                                                      | Pruned (Note)             |
+| G.8275.1_DeviceType                                                                                                      | Pruned (Note)             |
+| G.8275.1_DeviceType                                                                                                      | Pruned (Note)             |
+| PtpProfileVersion                                                                                                        | Refactored (copied)       |
+| PtpTlpProfileIdentifier                                                                                                  | Pruned (Note)             |
+| NOTE – Different pruning and refactoring rules for the PTP telecom profile module and the PTP-TT telecom profile module. |                           |
+
+Table 7-3 – PTP attributes for CommonPtpDefaultDsPac
+
+| Attributes in [ITU-T G.7721]                                                                                                                                | PTP telecom profile types |
+|-------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------|
+| maxStepsRemoved (Note 1)                                                                                                                                    | Pruned (Note 1)           |
+| instanceEnable (Note 1)                                                                                                                                     | Pruned (Note 1)           |
+| All other attributes                                                                                                                                        | Pruned (Note 2)           |
+| NOTE 1 – Different pruning and refactoring rules for the PTP telecom profile module and the PTP-TT telecom profile module.                                  |                           |
+| NOTE 2 – All the other attributes are pruned because already defined in both [IEEE 1588e-2024] PTP-TT YANG model and in the [IETF RFC 8575] PTP YANG model. |                           |
+
+**Table 7-4 – PTP attributes for CommonPtpTlpDefaultDsPac**
+
+| Attributes in [ITU-T G.7721]                                                                                             | PTP telecom profile types |
+|--------------------------------------------------------------------------------------------------------------------------|---------------------------|
+| deviceType                                                                                                               | Pruned (Note)             |
+| localPriority                                                                                                            | Refactored (copied)       |
+| profileIdentifier                                                                                                        | Pruned (Note)             |
+| NOTE – Different pruning and refactoring rules for the PTP telecom profile module and the PTP-TT telecom profile module. |                           |
+
+**Table 7-5 – PTP attributes for CommonPtpPortDsPac**
+
+| Attributes in [ITU-T G.7721]                                                                                                                                | PTP telecom profile types |
+|-------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------|
+| timeTransmitterOnly                                                                                                                                         | Pruned (Note 1)           |
+| portEnable                                                                                                                                                  | Pruned (Note 1)           |
+| All other attributes                                                                                                                                        | Pruned (Note 2)           |
+| NOTE 1 – Different pruning and refactoring rules for the PTP telecom profile module and the PTP-TT telecom profile module.                                  |                           |
+| NOTE 2 – All the other attributes are pruned because already defined in both [IEEE 1588e-2024] PTP-TT YANG model and in the [IETF RFC 8575] PTP YANG model. |                           |
+
+**Table 7-6 – PTP attributes for CommonPtpTlpPortDsPac**
+
+| Attributes in [ITU-T G.7721] | PTP telecom profile types |
+|------------------------------|---------------------------|
+| localPriority                | Refactored (copied)       |
+| sf                           | Refactored (copied)       |
+| syncReceiptTimeout           | Refactored (copied)       |
+| delayRespReceiptTimeout      | Refactored (copied)       |
+| notTimeTransmitter           | Refactored (copied)       |
+| monitorSender                | Refactored (copied)       |
+| monitorReceiver              | Refactored (copied)       |
+| sfLotm                       | Refactored (copied)       |
+| sfUnusable                   | Refactored (copied)       |
+| sfSu                         | Refactored (copied)       |
+
+### 7.1.2 PTP telecom profile module
+
+#### 7.1.2.1 Required object classes and relations
+
+The management of the precision time protocol (PTP), defined in [IEEE 1588-2008], is provided by the PTP YANG data model, defined in [IETF RFC 8575].
+
+To assist the PTP telecom profile UML pruning and refactoring and to ensure that the translated PTP telecom profile YANG data model can augment seamlessly the PTP YANG data model, the PTP YANG data model, defined in [IETF RFC 8575], has been reverse-engineered into UML form.
+
+Figure 7-2 (also available in the electronic attachment) provides an overview of the PTP UML model, reverse-engineered from the PTP YANG data model defined in [IETF RFC 8575], and of the Spec object classes of the PTP telecom profile UML model, defined in this Recommendation.
+
+![UML overview diagram of the PTP telecom profile. It shows a hierarchy of object classes. Green classes (e.g., PtpTelecomProfileType, PtpTlpDeviceType) are from the PTP YANG data model. Magenta classes (e.g., PtpTelecomProfile, PtpTlpDevice) are from the Interface YANG data model. Blue classes (e.g., PtpTelecomProfileType, PtpTlpDeviceType) are from the PTP telecom profile UML model. The diagram includes associations, inheritance, and composition relationships between these classes.](af7916c89a458fdab6c3f443217388ae_img.jpg)
+
+UML overview diagram of the PTP telecom profile. It shows a hierarchy of object classes. Green classes (e.g., PtpTelecomProfileType, PtpTlpDeviceType) are from the PTP YANG data model. Magenta classes (e.g., PtpTelecomProfile, PtpTlpDevice) are from the Interface YANG data model. Blue classes (e.g., PtpTelecomProfileType, PtpTlpDeviceType) are from the PTP telecom profile UML model. The diagram includes associations, inheritance, and composition relationships between these classes.
+
+G.7721.1(25)
+
+**Figure 7-2 – PTP telecom profile UML overview**
+
+NOTE 1 – The green object classes are from the PTP UML model, reverse-engineered from the PTP YANG data model defined in [IETF RFC 8575]; the magenta object class is from the Interface UML model, reverse-engineered from the Interface YANG data model defined in [IETF RFC 8343], and the blue object classes are from the PTP telecom profile UML model, defined in this Recommendation.
+
+NOTE 2 – The conformance level (when different from CONDITIONAL), default value and value range of the attributes are defined in the relevant PTP Telecom Profile Recommendations, particularly in clause A.2 of [ITU-T G.8265.1], clause A.2 of [ITU-T G.8275.1] or clause A.2 of [ITU-T G.8275.2].
+
+A PTP instance supports one and only one PTP telecom profile; a network element (NE) may support one or multiple PTP instances, each of the instances can represent the same or different PTP profiles.
+
+#### 7.1.2.2 Required attributes and operations
+
+This clause shows (from Table 7-7 to Table 7-11) how the required attributes and operations defined in [ITU-T G.7721] are pruned or refactored for the management of PTP telecom profiles module.
+
+**Table 7-7 – PTP attributes for data types**
+
+| Data types in [ITU-T G.7721] | PTP telecom profile |
+|------------------------------|---------------------|
+| PtpTelecomProfileType        | Pruned (Note 1)     |
+| PtpTlpDeviceType             | Refactored (Note 4) |
+| G.8265.1_DeviceType          | Refactored (Note 4) |
+| G.8275.1_DeviceType          | Refactored (Note 3) |
+| G.8275.1_DeviceType          | Refactored (Note 4) |
+| PtpProfileVersion            | Pruned (Note 1)     |
+| PtpTlpProfileIdentifier      | Pruned (Note 2)     |
+
+NOTE 1 – Pruned because already refactored in the CommonPtpTlpDefaultDsPac object class.  
+NOTE 2 – Refactored as profile, profileVersion and profileIdentifier attributes of the PtpTlpDefaultDsPac object data class, for backward compatibility with G.7721.1 v1.0.  
+NOTE 3 – Refactored as G.8275.1\_ClockType and without the T-TC enumeration literal, for backward compatibility with G.7721.1 v1.0.  
+NOTE 4 – Refactored as clockType, G.8265.1\_ClockType and G.8275.2\_ClockType, for backward compatibility with G.7721.1 v1.0.
+
+**Table 7-8 – PTP attributes for PtpDefaultDsPac**
+
+| <b>Attributes in [ITU-T G.7721]</b>                                                                                                      | <b>PTP telecom profile</b> |
+|------------------------------------------------------------------------------------------------------------------------------------------|----------------------------|
+| maxStepsRemoved                                                                                                                          | Refactored (Note 1)        |
+| instanceEnable                                                                                                                           | Refactored (Note 1)        |
+| All other attributes                                                                                                                     | Pruned (Note 2)            |
+| NOTE 1 – Copied, because not defined in the IETF RFC 8575 PTP YANG model.<br>NOTE 2 – Already defined in [IETF RFC 8575] PTP YANG model. |                            |
+
+**Table 7-9 – PTP attributes for PtpTlpDefaultDsPac**
+
+| <b>Attributes in [ITU-T G.7721]</b>                                                                                                                                                                                                                                                                             | <b>PTP telecom profile</b> |
+|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------|
+| deviceType                                                                                                                                                                                                                                                                                                      | Refactored (Note 1)        |
+| localPriority                                                                                                                                                                                                                                                                                                   | Pruned (Note 2)            |
+| profileIdentifier                                                                                                                                                                                                                                                                                               | Refactored (Note 3)        |
+| NOTE 1 – Refactored as clockType, for backward compatibility with G.7721.1 v1.0.<br>NOTE 2 – Pruned because already refactored in the CommonPtpTlpDefaultDsPac object class.<br>NOTE 3 – Refactored as profile, profileVersion and profileIdentifier attributes, for backward compatibility with G.7721.1 v1.0. |                            |
+
+**Table 7-10 – PTP attributes for PtpPortDsPac**
+
+| <b>Attributes in [ITU-T G.7721]</b>                                                                                                                                                                                                                                             | <b>PTP telecom profile</b> |
+|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------|
+| timeTransmitterOnly                                                                                                                                                                                                                                                             | Refactored (Note 1)        |
+| portEnable                                                                                                                                                                                                                                                                      | Refactored (Note 2)        |
+| All other attributes                                                                                                                                                                                                                                                            | Pruned (Note 3)            |
+| NOTE 1 – Refactored as masterOnly, for backward compatibility with G.7721.1 v1.0 and not defined in the IETF RFC 8575 PTP YANG model.<br>NOTE 2 – Copied, because not defined in the IETF RFC 8575 PTP YANG model.<br>NOTE 3 – Already defined in IETF RFC 8575 PTP YANG model. |                            |
+
+**Table 7-11 – PTP attributes for PtpTlpPortDsPac**
+
+| <b>Attributes in [ITU-T G.7721]</b>                                                 | <b>PTP telecom profile</b> |
+|-------------------------------------------------------------------------------------|----------------------------|
+| localPriority                                                                       | Pruned (Note)              |
+| sf                                                                                  | Pruned (Note)              |
+| syncReceiptTimeout                                                                  | Pruned (Note)              |
+| delayRespReceiptTimeout                                                             | Pruned (Note)              |
+| notTimeTransmitter                                                                  | Pruned (Note)              |
+| monitorSender                                                                       | Pruned (Note)              |
+| monitorReceiver                                                                     | Pruned (Note)              |
+| sfLotm                                                                              | Pruned (Note)              |
+| sfUnusable                                                                          | Pruned (Note)              |
+| sfSu                                                                                | Pruned (Note)              |
+| NOTE – Pruned because already refactored in the CommonPtpTlpPortDsPac object class. |                            |
+
+### 7.1.3 PTP-TT telecom profile module
+
+#### 7.1.3.1 Required object classes and relations
+
+The management of the precision time protocol (PTP) with inclusive language, defined in [IEEE 1588-2019], is provided by the PTP-TT YANG data model, defined in [IEEE 1588e-2024].
+
+To assist the PTP telecom profile UML pruning and refactoring and to ensure that the translated PTP telecom profile YANG data model can augment seamlessly the PTP YANG data model, the PTP YANG data model, defined in [IEEE 1588e-2024], has been reverse-engineered into UML form.
+
+Figure 7-3 (also available in the electronic attachment) provides an overview of the PTP UML model, reverse-engineered from the PTP YANG data model defined in [IEEE 1588e-2024], and of the Spec object classes of the PTP telecom profile UML model, defined in this Recommendation.
+
+![Figure 7-3 – PTP-TT telecom profile UML overview. This UML diagram shows the structure of the PTP-TT telecom profile. It includes several object classes: PtpTelecomProfileType (blue, Enumeration), PtpTlpDeviceType (blue, DataType), G.8265.1_DeviceType (blue, Enumeration), G.8275.1_DeviceType (blue, Enumeration), and PtpProfileVersion (blue, DataType). It also shows relationships like 'PtpTelecomProfileTypeRealizesPtpTelecomProfileType' and 'PtpTlpDeviceTypeRealizesPtpTlpDeviceType'. Attributes and references are listed within the classes, such as 'localPriority', 'twoStepFlag', 'delayRequestTimeout', and 'masterSender'.](9b6b5924b48bf2fd5f347f88f06f45b3_img.jpg)
+
+Figure 7-3 – PTP-TT telecom profile UML overview. This UML diagram shows the structure of the PTP-TT telecom profile. It includes several object classes: PtpTelecomProfileType (blue, Enumeration), PtpTlpDeviceType (blue, DataType), G.8265.1\_DeviceType (blue, Enumeration), G.8275.1\_DeviceType (blue, Enumeration), and PtpProfileVersion (blue, DataType). It also shows relationships like 'PtpTelecomProfileTypeRealizesPtpTelecomProfileType' and 'PtpTlpDeviceTypeRealizesPtpTlpDeviceType'. Attributes and references are listed within the classes, such as 'localPriority', 'twoStepFlag', 'delayRequestTimeout', and 'masterSender'.
+
+Figure 7-3 – PTP-TT telecom profile UML overview
+
+NOTE 1 – The green object classes are from the PTP UML model, reverse-engineered from the PTP YANG data model defined in [IEEE 1588e-2024]; the magenta object class is from the Interface UML model, reverse-engineered from the Interface YANG data model defined in [IEEE 1588e-2024], and the blue object classes are from the PTP telecom profile UML model, defined in this Recommendation.
+
+NOTE 2 – The conformance level (when different from CONDITIONAL), default value and value range of the attributes are defined in the relevant PTP Telecom Profile Recommendations, particularly in clause A.2 of [ITU-T G.8265.1], clause A.2 of [ITU-T G.8275.1] or clause A.2 of [ITU-T G.8275.2].
+
+A PTP instance supports one and only one PTP telecom profile; a network element (NE) may support one or multiple PTP instances, each of the instances can represent the same or different PTP profiles.
+
+#### 7.1.3.2 Required attributes and operations
+
+This clause shows (from Table 7-12 to Table 7-16) how the required attributes and operations defined in [ITU-T G.7721] are pruned or refactored for the management of the PTP-TT telecom profile module.
+
+Table 7-12 – PTP attributes for data types
+
+| Data types in [ITU-T G.7721] | PTP-TT telecom profile |
+|------------------------------|------------------------|
+| PtpTelecomProfileType        | Pruned (Note)          |
+| PtpTlpDeviceType             | Refactored (copied)    |
+| G.8265.1_DeviceType          | Refactored (copied)    |
+| G.8275.1_DeviceType          | Refactored (copied)    |
+| G.8275.1_DeviceType          | Refactored (copied)    |
+| PtpProfileVersion            | Pruned (Note)          |
+
+**Table 7-12 – PTP attributes for data types**
+
+| <b>Data types in [ITU-T G.7721]</b>                                                    | <b>PTP-TT telecom profile</b>    |
+|----------------------------------------------------------------------------------------|----------------------------------|
+| PtpTlpProfileIdentifier                                                                | Refactored (copied)localPriority |
+| NOTE – Pruned because already refactored in the CommonPtpTlpDefaultDsPac object class. |                                  |
+
+**Table 7-13 – PTP attributes for PtpDefaultDsPac**
+
+| <b>Attributes in [ITU-T G.7721]</b>                            | <b>PTP-TT telecom profile</b> |
+|----------------------------------------------------------------|-------------------------------|
+| maxStepsRemoved                                                | Pruned (Note)                 |
+| instanceEnable                                                 | Pruned (Note)                 |
+| All other attributes                                           | Pruned (Note)                 |
+| NOTE – Already defined in [IEEE 1588e-2024] PTP-TT YANG model. |                               |
+
+**Table 7-14 – PTP attributes for PtpTlpDefaultDsPac**
+
+| <b>Attributes in [ITU-T G.7721]</b>                                                    | <b>PTP-TT telecom profile</b> |
+|----------------------------------------------------------------------------------------|-------------------------------|
+| deviceType                                                                             | Refactored (copied)           |
+| localPriority                                                                          | Pruned (Note)                 |
+| profileIdentifier                                                                      | Refactored (copied)           |
+| NOTE – Pruned because already refactored in the CommonPtpTlpDefaultDsPac object class. |                               |
+
+**Table 7-15 – PTP attributes for PtpPortDsPac**
+
+| <b>Attributes in [ITU-T G.7721]</b>                            | <b>PTP-TT telecom profile</b> |
+|----------------------------------------------------------------|-------------------------------|
+| timeTransmitterOnly                                            | Pruned (Note)                 |
+| portEnable                                                     | Pruned (Note)                 |
+| All other attributes                                           | Pruned (Note)                 |
+| NOTE – Already defined in [IEEE 1588e-2024] PTP-TT YANG model. |                               |
+
+**Table 7-16 – PTP attributes for PtpTlpPortDsPac**
+
+| <b>Attributes in [ITU-T G.7721]</b>                                                 | <b>PTP-TT telecom profile</b> |
+|-------------------------------------------------------------------------------------|-------------------------------|
+| localPriority                                                                       | Pruned (Note)                 |
+| sf                                                                                  | Pruned (Note)                 |
+| syncReceiptTimeout                                                                  | Pruned (Note)                 |
+| delayRespReceiptTimeout                                                             | Pruned (Note)                 |
+| notTimeTransmitter                                                                  | Pruned (Note)                 |
+| monitorSender                                                                       | Pruned (Note)                 |
+| monitorReceiver                                                                     | Pruned (Note)                 |
+| sfLotm                                                                              | Pruned (Note)                 |
+| sfUnusable                                                                          | Pruned (Note)                 |
+| sfSu                                                                                | Pruned (Note)                 |
+| NOTE – Pruned because already refactored in the CommonPtpTlpPortDsPac object class. |                               |
+
+## 7.2 SyncPhy management information model
+
+The G.7721.1 SyncPhy management information model is not defined. The G.7721.1 SyncPhy YANG data model is directly derived from the [ITU-T G.7721] SyncPhy UML model through a combined process of pruning, refactoring and translation.
+
+## 7.3 Synchronization UML information models
+
+The UML information models defined in this Recommendation can be downloaded from [this](#) link.
+
+This zip file contains the following folders:
+
+- The G.7721.1\_v1.1 folder, which contains the following:
+  - The .project file
+  - The .di, .notation, and .uml files of the itut-ptp-telecom-profile-types model
+  - The .di, .notation, and .uml files of the itut-ptp-telecom-profile model
+  - The .di, .notation, and .uml files of the itut-ptp-tt-telecom-profile model
+  - The Diagrams folder, which contains PNG images of the UML diagrams in the above models.
+  - The Doc folder, which contains the data dictionaries (DDs) and the DD templates of the above models.
+  - The UmlProfiles folder, which contains the UML profiles that define the properties of the UML artifacts.
+- The G.7711\_v4.0 folder, which contains the [ITU-T G.7711] Core information model, which is imported by the G.7711.1 models above.
+- The IetfModels\_v1.2 folder, which contains the UML information –models, reverse-engineered from the IETF YANG data models, which are imported by the G.7721.1 models above.
+- The IeeeModels\_v1.2 folder, which contains the UML information models, reverse-engineered from the IEEE YANG data models, which are imported by the G.7721.1 models above.
+
+The UML information models above have been developed using the Papyrus 2020-06 modelling tool, which is available at [b-Eclipse-Papyrus]. The installation guide for Eclipse and Papyrus can be found in [b-ONF TR-515].
+
+To load the ITU-T G.7721.1 UML models into a Papyrus workspace, follow the steps below:
+
+- In the *Project Explorer* / right click / *Import* / *General* / *Projects from Folder or Archive* / *Next* / *Archive* / *Select* the G.7721.1 zip file / *Open* / *Select* the folders of the models to be loaded (Note) / *Finish*
+
+NOTE – If an UML model imported by the G.7721.1 models above already exist in the workspace, should not be selected for loading.
+
+# 8 Synchronization data models
+
+This clause contains the interface-protocol-specific data models of the synchronization functions identified in clause 6. These data models are translated from the interface-protocol-neutral UML information specified in clause 7.
+
+## 8.1 Synchronization YANG data models
+
+The YANG data models defined in this Recommendation can be downloaded from [this](#) link.
+
+The zip file includes the following files:
+
+- The .yang and .tree files of the itut-ptp-telecom-profile-types module
+- The .yang and .tree files of the itut-ptp-telecom-profile module
+- The .yang and .tree files of the itut-ptp-tt-telecom-profile module
+- The .yang and .tree files of the itut-sync-phy module
+
+The YANG data models specified in this Recommendation use the YANG 1.1 language specified in [IETF RFC 7950]. The tree format specified in [IETF RFC 8340] is used for the YANG data model tree representation. The YANG data models specified in this Recommendation conform to the network management datastore architecture specified in [IETF RFC 8342].
+
+The PTP telecom profile YANG data model, as defined in this clause, augments the PTP YANG data model, as defined in [IETF RFC 8575], to manage PTP instances which are compliant with the ITU-T telecom profiles, as outlined in clause 6.1.
+
+Since the PTP YANG data model defined in [IETF RFC 8575] supports only the management of the PTP implementations based on the [IEEE 1588-2008] version, the PTP telecom profile YANG data model, defined in this Recommendation, supports only the management of the PTP telecom profile implementations which are based on the [IEEE 1588-2008] version.
+
+Since the PTP YANG data model, as defined in [IETF RFC 8575], has a broader scope than the management of the ITU-T PTP telecom profile instances, Annex B provides some guidelines on how the PTP YANG data model shall be used to manage the ITU-T PTP telecom profile instances.
+
+The YANG model of this Recommendation is translated from the interface-protocol-neutral UML information provided in clause 7.3. The translation is done with the assistance of the Open-Source translation tooling xmi2yang, which is developed according to [b-ONF TR-531] mapping guidelines.
+
+At the time of publication of this Recommendation, the xmi2yang mapping tool is still a work in progress. Therefore, manual modifications on the tool-generated yang are necessary.
+
+## Annex A
+
+## Management conformance for PTP telecom profiles YANG data models
+
+(This annex forms an integral part of this Recommendation.)
+
+The YANG data models defined in [IETF RFC 8575], [IEEE 1588e-2024] and in this Recommendation defines almost all the data nodes as optional, to accommodate different conformance requirements that depend on the PTP profile being used.
+
+The only mandatory data nodes in the YANG data modules defined in this Recommendation are those which define which PTP telecom profile and device type apply to a given PTP instance, when it is configured to support any PTP telecom profile.
+
+The ITU-T PTP telecom profiles Recommendations, which are listed in clause 6.1, define for each dataset members the default value, the value range and the operational conformance (mandatory, optional or not used), which depend on the configured PTP telecom profile and device type.
+
+### A.1 Configuration of optional YANG data nodes
+
+With the exception of the PTP telecom profile and device type, all the YANG data nodes which correspond to configurable dataset members are optional to be configured in the running data store.
+
+When a YANG data node, which corresponds to a configurable and mandatory dataset member, is not configured in the running datastore, the system shall apply the default value, defined for the corresponding dataset member.
+
+When a YANG data node, which corresponds to a configurable, optional and supported dataset member, is not configured in the running datastore, the system shall apply the default value, defined for the corresponding dataset member.
+
+NOTE – As required in section 5.3 of [IETF RFC 8342], the system always reports, within the operational datastore, the values in use, regardless of the default value definition.
+
+When a YANG data node, which corresponds to a configurable, optional and not supported dataset member, is configured in the running datastore, the system shall either reject the configuration and reply with an error message, or accept the configuration, not apply it and reply with a warning message. The warning or the error message shall notify the client that the optional dataset member is not supported by the system.
+
+When a YANG data node, which corresponds to a configurable and not used dataset member, is configured in the running datastore, the system shall either reject the configuration and reply with an error message, or accept the configuration, not apply it and reply with a warning message. The warning or the error message shall notify the client that the dataset member is not supported by the configured PTP telecom profile.
+
+When a YANG data node, which corresponds to a configurable dataset member, is configured, in the running datastore, with value outside the range defined for the corresponding dataset member, the system shall reject the configuration and reply with an error message.
+
+### A.2 Reporting values in the operational datastore
+
+As required in section 5.3 of [IETF RFC 8342], the system shall always report, within the operational datastore, the values of the YANG data nodes in use.
+
+Therefore, the system shall report, within the operational datastore, the values of the YANG data nodes, which correspond to mandatory dataset members as well as to optional and supported dataset members. The system shall not report, within the operational datastore, the values of the YANG data
+
+nodes which correspond to not used dataset members as well as to optional and not supported dataset members.
+
+The PTP telecom profile implementation shall ensure that the values of the reported YANG data nodes are within the range defined for the corresponding dataset member.
+
+# Annex B
+
+## Using the IETF PTP YANG data model for ITU-T PTP telecom profiles
+
+(This annex forms an integral part of this Recommendation.)
+
+The YANG conformance guidelines for PTP telecom profiles provided in Annex A are generic and apply when either the IETF PTP YANG data model, defined in [IETF RFC 8575], or the IEEE PTP-TT YANG data model, defined in [IEEE 1588e-2024], are used, together with the PTP YANG data models, defined in this Recommendation, to manage PTP telecom profiles.
+
+This annex provides additional guidelines which are applicable only when the IETF PTP YANG data model, defined in [IETF RFC 8575], is used, together with the PTP YANG data models, defined in this Recommendation, to manage PTP telecom profiles.
+
+The PTP YANG data model in [IETF RFC 8575] defines some default values, using YANG default statements, which differ from the default values defined for the corresponding dataset members by the ITU-T PTP telecom profile Recommendations.
+
+It is not appropriate to allow the system to override the default values defined by YANG default statements. It is therefore recommended that an implementation of the PTP telecom profile YANG data model does not implement the YANG default statements within the PTP YANG data model, defined in [IETF RFC 8575], and reports this using the YANG deviation statements, as defined in section 5.6.3 of [IETF RFC 7950].
+
+Since section 7.20.3 of [IETF RFC 7950] does not allow including YANG deviation statements in standard YANG modules, the definition of these YANG deviation statements is implementation specific. Appendix I provides some guidelines on how deviation statements could be written to report that the YANG default statements in the PTP YANG data model, defined in [IETF RFC 8575], are not implemented.
+
+Moreover, the PTP YANG data model in [IETF RFC 8575], and its augmentations in this Recommendation, support write operations for some attributes which corresponds to static or dynamic dataset members.
+
+When a writable YANG data node, which corresponds to a static or dynamic dataset member, is configured in the running datastore, the system shall reject the configuration and reply with an error message, notifying the client that the static or dynamic dataset members are not configurable.
+
+## Appendix I
+
+## **YANG deviation example for the PTP YANG data model**
+
+(This appendix does not form an integral part of this Recommendation.)
+
+Annex B recommends that an implementation of the PTP telecom profile YANG data model, as defined in clause 8.1.1, also reports, using YANG deviation statements, that the YANG default statement of the PTP YANG data model, defined in [IETF RFC 8575], are not implemented.
+
+Since section 7.20.3 of [IETF RFC 7950] does not allow including YANG deviation statements in standard YANG modules, the definition of these YANG deviation statements is implementation specific.
+
+This appendix provides some guidelines on how these deviation statements could be written by providing, as an example, the `itut-ptp-deviation-example` YANG module which only declares that the YANG default statements of the PTP YANG data model, defined in [IETF RFC 8575] are not supported.
+
+The `itut-ptp-deviation-example` YANG module example (`itut-ptp-deviation-example@2021-09-30.yang`) can be downloaded from [this](#) link.
+
+# Bibliography
+
+- [b-Eclipse-Papyrus] Papyrus Eclipse UML Modelling Tool. <https://www.eclipse.org/papyrus>. Accessed on 17-Nov-2025.
+- [b-ONF TR-515] Papyrus Guidelines 1.3 (2018) [https://opennetworking.org/wp-content/uploads/2018/08/TR-515\\_Papyrus\\_Guidelines\\_v1.3-1-1.pdf](https://opennetworking.org/wp-content/uploads/2018/08/TR-515_Papyrus_Guidelines_v1.3-1-1.pdf). Accessed on 17-Nov-2025.
+- [b-ONF TR-531] UML to YANG Mapping Guidelines (2018) [https://opennetworking.org/wp-content/uploads/2018/08/TR-531\\_UML-YANG\\_Mapping\\_Gdls\\_v1.1-1-1.pdf](https://opennetworking.org/wp-content/uploads/2018/08/TR-531_UML-YANG_Mapping_Gdls_v1.1-1-1.pdf). Accessed on 17-Nov-2025.
+
+
+
+
+
+# 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                                                                                                                  |
+| <b>Series G</b> | <b>Transmission systems and media, digital systems and networks</b>                                                                                       |
+| 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                                                                                      |

marked/T/T-REC-T.0-199607-I_PDF-E/raw.md

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+
+
+![ITU logo: a globe with the letters ITU and a lightning bolt symbol.](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+ITU logo: a globe with the letters ITU and a lightning bolt symbol.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**T.0**
+
+(07/96)
+
+**TERMINALS FOR TELEMATIC SERVICES**
+
+---
+
+**CLASSIFICATION OF FACSIMILE TERMINALS  
+FOR DOCUMENT TRANSMISSION OVER  
+THE PUBLIC NETWORKS**
+
+**ITU-T Recommendation T.0**
+
+(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 T.0, was revised by ITU-T Study Group 8 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 3rd of July 1996.
+
+# --- NOTE
+
+In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency.
+
+© ITU 1996
+
+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.
+
+# **SUMMARY**
+
+Recommendations T.2 and T.3 define Group 1 and Group 2 facsimile terminals respectively; such stand-alone terminals have not been manufactured for many years and Group 3 facsimile terminals are the only type being used on the GSTN.
+
+In recognition of this market situation, Study Group 8 has agreed to delete references to Groups 1 and 2 in Recommendations T.4 and T.30.
+
+In order to be consistent and to minimize the possibility of any confusion, it is proposed that this Recommendation be amended to delete references to Group 1 and Group 2 terminals and also to use consistent terminology.
+
+
+
+# CLASSIFICATION OF FACSIMILE TERMINALS FOR DOCUMENT TRANSMISSION OVER THE PUBLIC NETWORKS
+
+*(Geneva, 1976; amended at Geneva, 1980;  
+Malaga-Torremolinos, 1984, Melbourne, 1988 and in 1996)*
+
+**1** For document facsimile transmission by international communications carried on the public networks there is a need for providing sufficient operating speeds to meet users' requirements.
+
+**2** Users' requirements may best be served at the present time by classifying the following four basic categories of document facsimile terminal.
+
+## 2.1 Terminals for use over the public telephone network
+
+Group 3 (see Note)
+
+A terminal which incorporates means for reducing the redundant information in the document signal prior to the modulation process and which can achieve a transmission time less than 1 minute for a typical typescript document of ISO A4 size via a telephone-type circuit. The terminal may incorporate bandwidth compression of the line signal.
+
+NOTE – This terminal has been standardized in Recommendation T.4.
+
+## 2.2 Terminals for use over the public data networks
+
+Group 4 (see Note)
+
+A terminal which incorporates means for reducing the redundant information in the document signal prior to transmission mainly via Public Data Networks (PDNs). The apparatus will utilize procedures applicable to the PDN and will assure an essentially error-free reception of the document.
+
+NOTE – This terminal has been standardized in Recommendations T.6, T.503, T.521 and T.563.
+
+**3** The users will choose among these terminals, in accordance with their needs and the facilities afforded by the connection and the network.
+
+**4** Procedures for Group 3 document facsimile transmission in the public switched telephone network should be in accordance with Recommendation T.30.
+
+**5** Procedures for Group 4 document facsimile transmission should be in accordance with Recommendations T.62, T.62 *bis*, T.70 and T.90.
+
+**6** Annex A contains definitions for terms used in the T-Series Recommendations applicable to facsimile terminals.
+
+# Annex A
+
+## Definitions for terms used in the T-Series Recommendations applicable to facsimile terminals
+
+(This annex forms an integral part of this Recommendation)
+
+The following definitions apply to Recommendations T.1 and T.4:
+
+**A.1 dead sector** (Recommendation T.1): In drum terminals, that portion of the drum surface the scanning time of which cannot be used for picture signal transmission.
+
+**A.2 drum factor** (Recommendation T.1): In drum terminals, the ratio of the usable scanning length of the drum to its diameter.
+
+**A.3 facsimile** (Series T): The process of scanning a document (page), converting the image scanned into electrical signals for transmission to a remote receiver and the conversion of the received signals to produce a copy of the image originally scanned.
+
+**A.4 factor of cooperation** (Recommendation T.1): The product of the total scanning line length and the scanning density.
+
+**A.5 flat-bed transmitter** (Recommendation T.1): A terminal in which the original document is placed flat and scanned line by line.
+
+**A.6 index of cooperation** (Recommendation T.1): Quotient of the factor of cooperation divided by the quantity  $\pi$ . In the case of a drum terminal, the index of cooperation is also equal to the product of the drum diameter and the scanning density.
+
+**A.7 judder, longitudinal** (Recommendation T.1): Effect due to the irregular rotation of the drum or helix causing, on the reproduced picture, slight waviness or breaks in lines that are regular on the original document.
+
+**A.8 judder, transverse** (Recommendation T.1): Effect due to irregularity of the scanning pitch resulting in concurrent overlapping and underlapping in the reproduced picture.
+
+**A.9 nominal black (white)** (Recommendation T.1): Level or frequency of the signal corresponding to a pure black (white).
+
+**A.10 pel** (Series T): A contraction of “picture element”.
+
+**A.11 phasing** (Recommendation T.1): At the receiver, ensuring the exact coincidence of the midpoint of the scanning field, with the corresponding point at the transmitter so as to ensure the correct positioning of the picture on the recording medium.
+
+**A.12 phasing signal** (Recommendation T.1): A signal sent by the transmitter for phasing purposes.
+
+NOTE – Phasing is known as “phase white (black)” if the phasing signal is a black (white) signal of which a short interruption corresponding to the white (black) is sent during the lost time.
+
+**A.13 phototelegraphy** (Recommendation T.1): Method of reception of facsimile telegraphy which is chiefly intended for the reproduction of graded tonal densities and in which a photographic process is used at the receiver.
+
+**A.14 picture element** (Recommendation T.4):
+
+a) *at transmission:*
+
+The part of the area of the original document which coincides with the scanning spot at a given instant and which is of one intensity only, with no distinction of the details that may be included.
+
+b) *at reception:*
+
+The area of the finest detail that can be effectively reproduced on the recording medium.
+
+**A.15 reproduction ratio** (Recommendation T.1): The ratio of the linear dimensions of the reproduced document to the corresponding dimensions of the original document.
+
+**A.16 resolution** (Series T): A measure of the capability for delineating picture detail. In Group 3 and Group 4 facsimile transmission resolution is expressed as picture elements or pels per mm (horizontal resolution) and lines per mm (vertical resolution).
+
+**A.17 scanning density** (Recommendation T.1): Number of scanning pitches per unit length.
+
+**A.18 scanning line** (Recommendation T.1): The area explored by the scanning spot in one sweep from one side to the other of the scanning field.
+
+**A.19 scanning pitch** (Recommendation T.1): The distance between the corresponding edges of two consecutive scanning lines.
+
+**A.20 skew** (Recommendation T.4): A defect in reproduction in which lines that should be at right-angles to the scanning direction are inclined to it, owing to a difference between the scanning speeds at transmission and reception.
+
+**A.21 synchronization** (Recommendation T.1): The establishment of equal scanning line frequencies at the transmitter and receiver.

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+
+
+![ITU logo: a globe with the letters ITU and a lightning bolt symbol.](2dfa6ac3edfe874f68aa0cbccaa42322_img.jpg)
+
+ITU logo: a globe with the letters ITU and a lightning bolt symbol.
+
+INTERNATIONAL TELECOMMUNICATION UNION
+
+**ITU-T**
+
+TELECOMMUNICATION  
+STANDARDIZATION SECTOR  
+OF ITU
+
+**T.10 *bis***
+
+**TERMINAL EQUIPMENT AND PROTOCOLS FOR  
+TELEMATIC SERVICES**
+
+---
+
+**DOCUMENT FACSIMILE TRANSMISSIONS  
+IN THE GENERAL SWITCHED TELEPHONE  
+NETWORK**
+
+**ITU-T Recommendation T.10 *bis***
+
+(Extract from the *Blue Book*)
+
+---
+
+# NOTES
+
+1 ITU-T Recommendation T.10 *bis* was published in Fascicle VII.3 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.
+
+# **DOCUMENT FACSIMILE TRANSMISSIONS IN THE GENERAL SWITCHED TELEPHONE NETWORK**
+
+*(Mar del Plata, 1968; amended at Geneva, 1972, 1976 and 1980)*
+
+## **1 Type of circuits to be used**
+
+Since circuits of the general telephone network and the station lines of telephone subscribers should be capable of being used for document facsimile transmissions on the general network, the circuits to be used are those of the general switched network which have 2-wire terminals at both ends of the facsimile station.
+
+*Note* – For the actual document transmission, which is one-way, there is no need to cater for the disabling of echo suppressors. Compandors do not seem detrimental to document facsimile transmission.
+
+## **2 Overall loss**
+
+The conditions for overall transmission loss are the same as those for circuits of the general switched telephone network.
+
+## **3 Modulation**
+
+Equipment conforming to Recommendation T.2 or Recommendation T.3 may be used. In the case of Recommendation T.2 equipment, frequency modulation shall be used.
+
+## **4 Power**
+
+In order to avoid the risk that facsimile signals be disturbed, e.g. by dial pulses transmitted over adjacent channels or by noise, it is important that the sending level should be as high as possible, provided, however, that it shall not exceed  $-13$  dBm0 on the trunk circuit for frequency-modulation equipment conforming to Recommendation T.2 or that the mean power in any hour, in one direction of transmission, shall not exceed 32 microwatts ( $-15$  dBm0) at the zero relative level point of the trunk circuit for equipment conforming to Recommendation T.3.
+
+The maximum power output of the transmitting apparatus into the line shall not exceed 1 mW whatever the frequency.
+
+## **5 Amplitude and phase distortion**
+
+Equipment conforming to Recommendation T.2 should not require any special treatment. However, equipment conforming to Recommendation T.3 may require both amplitude and phase distortion correction on certain connections.