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.8271/Y.1366 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2016) 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 AND NEXT-GENERATION NETWORKS, INTERNET OF THINGS AND SMART CITIES Internet protocol aspects Transport Time and phase synchronization aspects of packet networks Recommendation ITU-T G.8271/Y.1366 ITU-T G-SERIES RECOMMENDATIONS TRA
3、NSMISSION 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 LINES G.300G.
4、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 DIGITAL TERMINAL
5、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.7999 PACKET OV
6、ER 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 list of ITU-T R
7、ecommendations. Rec. ITU-T G.8271/Y.1366 (07/2016) i Recommendation ITU-T G.8271/Y.1366 Time and phase synchronization aspects of packet networks Summary Recommendation ITU-T G.8271/Y.1366 defines time and phase synchronization aspects in packet networks. It specifies the suitable methods to distrib
8、ute the reference timing signals that can be used to recover the phase synchronization and/or time synchronization according to the required quality. The requirements for the synchronization characteristics that are specified in this Recommendation must be adhered to in order to ensure interoperabil
9、ity of equipment produced by different manufacturers and a satisfactory network performance. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.8271/Y.1366 2012-02-13 15 11.1002/1000/11527 1.1 ITU-T G.8271/Y.1366 (2012) Amd. 1 2013-08-29 15 11.1002/1000/12033 1.2 ITU-T G.8271
10、/Y.1366 (2012) Amd. 2 2015-01-13 15 11.1002/1000/12391 2.0 ITU-T G.8271/Y.1366 2016-07-07 15 11.1002/1000/12812 Keywords Methods and interfaces, time and phase synchronization requirements. * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, f
11、ollowed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T G.8271/Y.1366 (07/2016) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication
12、 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
13、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 so
14、me 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 expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recogniz
15、ed 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 word
16、s “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 RIGHTSITU draws attention to the possibility that t
17、he 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
18、 development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementers are cautioned that this may not represent the latest information and are
19、therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2016 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T G.8271/Y.1366 (07/2016) iii Table of Contents Pag
20、e 1 Scope . 1 2 References . 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Conventions 3 6 The need for time and phase synchronization 3 7 Time and phase synchronization methods 4 7.1 Distributed PRTC . 5 7.2 Packet based methods with timing support of intermediate nodes . 6 8 Network reference
21、 model . 7 8.1 Access section of HRM with PTP/native access IWF 9 9 Time and phase synchronization interfaces 10 Annex A One pulse-per-second (1PPS) time and phase synchronization interface specification 11 A.1 1PPS ITU-T V.11 interface 11 A.2 1PPS 50 phase synchronization measurement interface 17 A
22、ppendix I Time and phase noise sources in time distribution chains . 18 I.1 Noise introduced by a primary reference time clock (PRTC) 18 I.2 Noise introduced by a packet master clock function 18 I.3 Noise introduced by a packet slave clock function 18 I.4 Noise introduced by a telecom transparent cl
23、ock . 18 I.5 Noise introduced by a link 19 I.6 Derivation of delay asymmetry 19 I.7 Characteristics of the noise sources 21 I.8 Time error accumulation in a chain of clocks 23 Appendix II Time and phase end application synchronization requirements . 24 Appendix III Asymmetry compensation for use of
24、different wavelengths . 27 Appendix IV Link and network asymmetry compensation 28 Appendix V Delay asymmetry resulting from interface rate change in PTP-unaware network elements 30 Bibliography. 33 Rec. ITU-T G.8271/Y.1366 (07/2016) 1 Recommendation ITU-T G.8271/Y.1366 Time and phase synchronization
25、 aspects of packet networks 1 Scope This Recommendation defines time and phase synchronization aspects in packet networks. It specifies the suitable methods to distribute the reference timing signals that can be used to recover the phase synchronization and/or time synchronization according to the r
26、equired quality. It also specifies the relevant time and phase synchronization interfaces and related performance. The packet networks that are in the scope of this Recommendation are currently limited to the following scenarios: Ethernet (IEEE 802.3 and IEEE 802.1Q). MPLS (IETF RFC 3031 and ITU-T G
27、.8110). IP (IETF RFC 791 and RFC 2460). The physical layers that are relevant to this specification are the Ethernet media types, as defined in IEEE 802.3. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provi
28、sions 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 Recommendatio
29、ns 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.703 Recommendation ITU-T G.703 (2016), Physica
30、l/electrical characteristics of hierarchical digital interfaces. ITU-T G.810 Recommendation ITU-T G.810 (1996), Definitions and terminology for synchronization networks. ITU-T G.8110 Recommendation ITU-T G.8110/Y.1370 (2005), MPLS layer network architecture. ITU-T G.8260 Recommendation ITU-T G.8260
31、(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 V.11 Recommendation ITU-T V.11/X.27 (1996), Electrical characteristics for balanced double-current intercha
32、nge circuits operating at data signalling rates up to 10 Mbit/s. IEEE 802.1Q IEEE 802.1Q-2014, IEEE Standard for Local and metropolitan area networks Bridges and Bridged Networks IEEE 802.3 IEEE 802.3-2015, IEEE Standard for Ethernet. IEEE 1588 IEEE 1588-2008, Standard for a Precision Clock Synchron
33、ization Protocol for Networked Measurement and Control Systems. . 2 Rec. ITU-T G.8271/Y.1366 (07/2016) IETF RFC 791 IETF RFC 791 (1981), Internet Protocol (IP). http:/www.ietf.org/rfc/rfc0791.txt?number=791. IETF RFC 2460 IETF RFC 2460 (1998), Internet Protocol, Version 6 (IPv6) Specification. http:
34、/www.ietf.org/rfc/rfc2460.txt?number=2460 IETF RFC 3031 IETF RFC 3031 (2001), Multiprotocol Label Switching Architecture. http:/www.ietf.org/rfc/rfc3031.txt?number=3031 3 Definitions The terms and definitions used in this Recommendation are contained in ITU-T G.810, ITU-T G.8260 and IEEE 1588. 4 Abb
35、reviations and acronyms This Recommendation uses the following abbreviations and acronyms: 1PPS One Pulse Per Second CDMA Code Division Multiple Access DCF Dispersion Compensating Fibre FCS Frame Check Sequence FDD Frequency Division Duplex GBAS Ground Based Augmentation System GNSS Global Navigatio
36、n Satellite System GPS Global Positioning System HRPD High Rate Packet Data IP Internet Protocol IRNSS Indian Regional Navigation Satellite System LTE Long Term Evolution LTE-A Long Term Evolution Advanced MAC Medium Access Control MBMS Multimedia Broadcast Multicast Service MBSFN MBMS based on Sing
37、le Frequency Network M2M Machine to Machine NTP Network Time Protocol OTN Optical Transport Network PDV Packet Delay Variation PHY Physical Layer Protocol PRTC Primary Reference Time Clock PSN Packet Switched Network PTP Precision Time Protocol QZSS Quasi-Zenith Satellite System RTT Radio Transmissi
38、on Technology Rec. ITU-T G.8271/Y.1366 (07/2016) 3 SBAS Satellite Based Augmentation System TAI International Atomic Time TDD Time Division Duplexing TD-SCDMA Time Domain Synchronized CDMA T-BC Telecom Boundary Clock T-GM Telecom Grandmaster T-TC Telecom Transparent Clock T-TSC Telecom Time Slave Cl
39、ock UDP User Datagram Protocol UTC Universal Time Co-ordinated UTRA Universal Terrestrial Radio Access WCDMA Wideband CDMA WDM Wavelength-Division-Multiplexing WiMAX Worldwide Interoperability for Microwave Access 5 Conventions Within this Recommendation, the following conventions are used: The term
40、 precision time protocol (PTP) is the protocol defined by IEEE 1588. As an adjective, it indicates that the modified noun is specified in or interpreted in the context of IEEE 1588. The term telecom boundary clock (T-BC) is a device consisting of a boundary clock as defined in IEEE 1588 and with add
41、itional performance characteristics for further study. The term telecom transparent clock (T-TC) is a device consisting of a transparent clock as defined in IEEE 1588 and with additional performance characteristics for further study. The term telecom grandmaster (T-GM) is a device consisting of a gr
42、andmaster clock as defined in IEEE 1588 and with additional performance characteristics for further study. The term telecom time slave clock (T-TSC) is a device consisting of a PTP slave only ordinary clock as defined in IEEE 1588 and with additional performance characteristics for further study. 6
43、The need for time and phase synchronization Time synchronization has traditionally been required to support billing and alarm functions (maintenance or fault isolation). In this context, synchronization must in general be accurate to within hundreds of milliseconds. Another time synchronization appl
44、ication is the monitoring of delays in Internet protocol (IP) networks. In this case, the requirement is accuracy to within some hundreds of microseconds (the actual requirement depends on the application). Stringent time synchronization requirements (i.e., in the range of a few microseconds) apply
45、to the generation of signals over the air interface of some mobile systems, such as CDMA2000 or LTE FDD unicast, when it is required to support synchronous CDMA2000 interworking. Phase synchronization is often needed to support requirements for the air interface of some mobile systems, as in the cas
46、e of time division duplexing (TDD) systems (for instance, LTE TDD), or when supporting multimedia broadcast/multicast service (MBMS). Note that ordinary WCDMA MBMS does not require accurate phase synchronization since it has been specified and designed to work 4 Rec. ITU-T G.8271/Y.1366 (07/2016) pr
47、operly in networks that satisfy the 50 ppb frequency accuracy requirement. This requirement, which is guaranteed by the WCDMA node synchronization function (see b-3GPP TS 25.402), limits phase drift to between 10 and 20 ms. But when MBMS is based on single-frequency network (MBSFN) mode, timing must
48、 be accurate to within a few microseconds. This is because identical waveforms are transmitted simultaneously from multiple cells. The signals from these cells are then combined as the multipath components of a single cell. Terminals must thus perceive the signals of an entire group of transmitting
49、cells as though they came from a single cell. Therefore, all transmissions must be very tightly synchronized and deliver exactly the same content to each base station. The main requirements applicable at the output of the application (e.g., on the radio interface in the case of a wireless application) are summarized in Appendix II. Based on Table II.1, it is possible to classify the applications into classes of requirements, as shown in Table
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