1、 I n t e r n a t i o n a l T e l e c o m m u n i c a t i o n U n i o n ITU-T G.8275/Y.1369 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (08/2017) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Packet over Transport aspects Synchronization, quality and availability targets
2、SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS, NEXT-GENERATION NETWORKS, INTERNET OF THINGS AND SMART CITIES Internet protocol aspects Transport Architecture and requirements for packet-based time and phase distribution Recommendation ITU-T G.8275/Y.1369 ITU-T G-SERIES RECOM
3、MENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS G.200G.299 INDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC
4、 LINES G.300G.399 GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 TRANSMISSION MEDIA AND OPTICAL SYSTEMS CHARACTERISTICS G.600G.699 DIG
5、ITAL TERMINAL EQUIPMENTS G.700G.799 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 MULTIMEDIA QUALITY OF SERVICE AND PERFORMANCE GENERIC AND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.6999 DATA OVER TRANSPORT GENERIC ASPECTS G.7000G.
6、7999 PACKET OVER TRANSPORT ASPECTS G.8000G.8999 Ethernet over Transport aspects G.8000G.8099 MPLS over Transport aspects G.8100G.8199 Synchronization, quality and availability targets G.8200G.8299 Service Management G.8600G.8699 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the l
7、ist of ITU-T Recommendations. Rec. ITU-T G.8275/Y.1369 (08/2017) i Recommendation ITU-T G.8275/Y.1369 Architecture and requirements for packet-based time and phase distribution Summary Recommendation ITU-T G.8275/Y.1369 describes the architecture and requirements for packet-based time and phase dist
8、ribution in telecom networks. The architecture described is mainly applicable to the use of IEEE 1588. Details necessary to utilize IEEE 1588 in a manner consistent with the architecture are defined in other Recommendations. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.
9、8275/Y.1369 2013-11-22 15 11.1002/1000/12011 1.1 ITU-T G.8275/Y.1369 (2013) Amd. 1 2015-01-13 15 11.1002/1000/12396 1.2 ITU-T G.8275/Y.1369 (2013) Amd. 2 2016-04-13 15 11.1002/1000/12814 2.0 ITU-T G.8275/Y.1369 2017-08-13 15 11.1002/1000/13328 Keywords IEEE 1588, packet synchronization, phase, time.
10、 * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T G.8275/Y.1369 (08/2017) FOREWORD The International Telecommunication Union (
11、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 i
12、ssuing 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
13、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-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the express
14、ion “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 applicabili
15、ty) 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 Rec
16、ommendation is required of any party. INTELLECTUAL PROPERTY RIGHTSITU 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 o
17、f claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this
18、Recommendation. However, implementers are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2017 All rights reserved. No part of this publication may be reproduced, by any means whatso
19、ever, without the prior written permission of ITU. Rec. ITU-T G.8275/Y.1369 (08/2017) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Conventions 3 6 General introduction to packet-based time/phase distribution . 3 6.1 Requirements for packet-
20、based time and phase distribution 3 7 Architecture of packet-based time/phase distribution 3 7.1 Packet-based time and phase distribution . 4 7.2 Time/phase protection aspects 5 7.3 Packet network partitioning 14 8 Security aspects 15 9 Management aspects . 15 Annex A Time/phase models based on ITU-
21、T G.805 16 Annex B Inclusion of an external phase/time interface on a PTP clock . 18 Appendix I Architecture for time and phase distribution over a packet network providing partial timing support at the protocol level 20 I.1 Architecture for partial timing support . 20 Appendix II An example of PRTC
22、 switching by the BMCA in a ring network . 24 Appendix III Generic IWF PTP clock 26 Appendix IV Use cases for mapping from PTP clockClass values to quality levels 28 IV.1 Use case I 28 IV.2 Use case II 28 Bibliography. 30 iv Rec. ITU-T G.8275/Y.1369 (08/2017) Introduction Recommendation ITU-T G.8275
23、/Y.1369 describes the general architecture of time and phase distribution using packet-based methods. This Recommendation forms the base architecture for the development of telecom profiles for time and phase distribution. The architecture described covers the case where protocol interaction is at a
24、ll nodes, between a packet master clock and a packet slave clock. Details of the necessary profiles are described in other Recommendations. Rec. ITU-T G.8275/Y.1369 (08/2017) 1 Recommendation ITU-T G.8275/Y.1369 Architecture and requirements for packet-based time and phase distribution 1 Scope This
25、Recommendation describes the general architecture of time and phase distribution using packet-based methods. This version of the Recommendation focuses on the distribution of time and phase using the standard for precision time protocol (PTP) IEEE 1588. The requirements and architecture form a base
26、for the specification of other functionalities that are needed to achieve packet-based time and phase distribution in a carrier environment. The architecture described covers the case where protocol interaction is at all nodes, between a packet master clock and a packet slave clock. Details of the n
27、ecessary profiles are described in other Recommendations. 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 R
28、ecommendations 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 regul
29、arly 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.805 Recommendation ITU-T G.805 (2000), Generic functional architecture of transport networks. ITU-T G.810 Recommendation ITU-T G.810 (1996), Def
30、initions and terminology for synchronization networks. ITU-T G.8260 Recommendation ITU-T G.8260 (2015), Definitions and terminology for synchronization in packet networks. ITU-T G.8261 Recommendation ITU-T G.8261/Y.1361 (2013), Timing and synchronization aspects in packet networks. ITU-T G.8262 Reco
31、mmendation ITU-T G.8262/Y.1362 (2015), Timing characteristics of a synchronous Ethernet equipment slave clock. ITU-T G.8264 Recommendation ITU-T G.8264/Y.1364 (2017), Distribution of timing information through packet networks. ITU-T G.8265 Recommendation ITU-T G.8265/Y.1365 (2010), Architecture and
32、requirements for packet-based frequency delivery. ITU-T G.8265.1 Recommendation ITU-T G.8265.1/Y.1365.1 (2014), Precision time protocol telecom profile for frequency synchronization. ITU-T G.8271 Recommendation ITU-T G.8271/Y.1366 (2016), Time and phase synchronization aspects of packet networks. IT
33、U-T G.8271.1 Recommendation ITU-T G.8271.1/Y.1366.1 (2013), Network limits for time synchronization in packet networks. IEEE 1588 IEEE STD 1588 (2008), Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems. 2 Rec. ITU-T G.8275/Y.1369 (08/2017) 3 Defini
34、tions The terms and definitions used in this Recommendation are contained in ITU-T G.810 and ITU-T G.8260. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: APTS Assisted Partial Timing Support APTSC Assisted Partial Timing Support Clock BC Boundary Cloc
35、k BMCA Best Master Clock Algorithm EEC Synchronous Ethernet Equipment Clock ESMC Ethernet Synchronization Messaging Channel GM Grandmaster GNSS Global Navigation Satellite System HRM Hypothetical Reference Model IWF Inter-working Function LTE Long Term Evolution NTP Network Time Protocol OTN Optical
36、 Transport Network PDV Packet Delay Variation PRC Primary Reference Clock PRTC Primary Reference Time Clock PTP Precision Time Protocol PTS Partial Timing Support QL Quality Level SDH Synchronous Digital Hierarchy SEC SDH Equipment Clock SF Signal Fail SSM Synchronization Status Message SSU Synchron
37、ization Supply Unit T-BC Telecom Boundary Clock T-GM Telecom Grandmaster T-TC Telecom Transparent Clock T-TSC Telecom Time Slave Clock TC Transparent Clock UTC Coordinated Universal Time WCDMA Wideband Code Division Multiple Access Rec. ITU-T G.8275/Y.1369 (08/2017) 3 5 Conventions Within this Recom
38、mendation, the term PTP refers to the PTP version 2 protocol defined in IEEE 1588. 6 General introduction to packet-based time/phase distribution The distribution of accurate time and phase is necessary to support certain telecom-based services and in particular the underlying infrastructure. While
39、traditional network synchronization has relied on the accurate distribution of frequency, evolving wireless networks require the distribution of accurate time and phase. As the network evolves from a primarily TDM-based network infrastructure to one using packet-based technology, the ability to dist
40、ribute synchronization is also changing. In order to enable timing distribution in packet-based networks, the ITU-T developed specifications (ITU-T G.8261, ITU-T G.8262 and ITU-T G.8264) for synchronous Ethernet, which allowed the use of the Ethernet physical layer to be used as a mechanism to distr
41、ibute frequency analogous to the methods used with synchronous digital hierarchy (SDH)-based network synchronization. In this regard, synchronous Ethernet, by appropriate specification of network equipment clocks provided support for the existing frequency-based synchronization network over both exi
42、sting TDM and new packet-based technology. In the absence of the ability to utilize the physical layer, the ITU also developed Recommendations covering frequency distribution using packet-based methods such as PTP and network time protocol (NTP). The use of packet-based methods also enabled new freq
43、uency synchronization scenarios to be considered. These, as well as other aspects specific to packet-based frequency distribution, resulted in the development of an architectural specification ITU-T G.8265. This Recommendation describes the architecture for packet-based time and phase distribution.
44、6.1 Requirements for packet-based time and phase distribution Packet-based mechanisms for time and phase distribution must meet the following five requirements: 1) mechanisms must be specified to allow interoperability between the various phase/time clocks defined in this architecture; 2) mechanisms
45、 must permit consistent operation over managed wide area telecom networks; 3) packet-based mechanisms must allow the synchronization network to be designed and configured in a fixed arrangement; 4) protection schemes used by packet-based systems must be based on standard telecom operational practice
46、 and allow telecom time slave clocks (T-TSC) the ability to take phase and time from multiple geographically separate telecom grandmaster (T-GM) clocks; 5) phase/time reference source selection based on received phase/time traceability and local priority should be permitted. Automatic establishment
47、of the phase/time synchronization network topology may also be possible. 7 Architecture of packet-based time/phase distribution In contrast to physical layer synchronization, where the significant edges of a data signal define the timing content of the signal, packet-based methods rely on the transm
48、ission of dedicated “event packets“. These “event packets“ form the significant instants of a packet timing signal. The timing of these significant instants is precisely measured relative to a master time source, and this timing information is encoded in the form of a time stamp, which is a machine-
49、readable representation of a specific instance of time. The time stamp is generated via a packet master function and is carried over a packet network to a packet slave clock. 4 Rec. ITU-T G.8275/Y.1369 (08/2017) A protocol is used between the master and the slave clocks in order to adjust for transmission and other delays, resulting in both the master and slave clocks having the same time reference. As time is the integral of frequency, the time stamps can also be used to derive frequency. This c
