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 (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 Time and phase synchronization aspects of telecommunication networks Recommendation ITU-T G.8271/Y.1366 ITU-T G-SERIES RECOMMENDAT
3、IONS 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 LINES
4、 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 DIGITAL T
5、ERMINAL 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 P
6、ACKET 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 list of
7、 ITU-T Recommendations. Rec. ITU-T G.8271/Y.1366 (08/2017) i Recommendation ITU-T G.8271/Y.1366 Time and phase synchronization aspects of telecommunication networks Summary Recommendation ITU-T G.8271/Y.1366 defines time and phase synchronization aspects in packet networks. It specifies the suitable
8、 methods to distribute 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 e
9、nsure interoperability of equipment produced by different manufacturers and a satisfactory network performance. This 2017 edition of the Recommendation integrates G.8271/Y.1366 (2016) Amd.1 (2017) into the base text. It does not add any new technical content. History Edition Recommendation Approval
10、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/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 2.1 ITU-T G.8271/Y.13
11、66 (2016) Amd. 1 2017-08-13 15 11.1002/1000/13322 3.0 ITU-T G.8271/Y.1366 2017-08-13 15 11.1002/1000/13383 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, follow
12、ed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T G.8271/Y.1366 (08/2017) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication tech
13、nologies (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 Telec
14、ommunication 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 ar
15、eas 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 recognized op
16、erating 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 “sh
17、all“ 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 the pr
18、actice 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 deve
19、lopment 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 there
20、fore 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 whatsoever, without the prior written permission of ITU. Rec. ITU-T G.8271/Y.1366 (08/2017) iii Table of Contents Page 1 S
21、cope . 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 5 7.1 Distributed PRTC . 6 7.2 Packet based methods with timing support of intermediate nodes . 7 8 Network reference mode
22、l . 8 8.1 Access section of HRM with PTP/native access IWF 10 9 Time and phase synchronization interfaces 11 Annex A One pulse-per-second (1PPS) time and phase synchronization interface specification 12 A.1 1PPS ITU-T V.11 interface 12 A.2 1PPS 50 phase synchronization measurement interface 18 Appen
23、dix I Time and phase noise sources in time distribution chains . 19 I.1 Noise introduced by a primary reference time clock (PRTC) . 19 I.2 Noise introduced by a packet master clock function . 19 I.3 Noise introduced by a packet slave clock function . 19 I.4 Noise introduced by a telecom transparent
24、clock 19 I.5 Noise introduced by a link . 20 I.6 Derivation of delay asymmetry . 20 I.7 Characteristics of the noise sources . 22 I.8 Time error accumulation in a chain of clocks . 24 Appendix II Time and phase end application synchronization requirements . 25 Appendix III Asymmetry compensation for
25、 use of different wavelengths . 28 Appendix IV Link and network asymmetry compensation 29 Appendix V Delay asymmetry resulting from interface rate change in PTP-unaware network elements 31 Bibliography. 34 Rec. ITU-T G.8271/Y.1366 (08/2017) 1 Recommendation ITU-T G.8271/Y.1366 Time and phase synchro
26、nization aspects of telecommunication networks 1 Scope This Recommendation defines time and phase synchronization aspects in telecommunication networks. It specifies the suitable methods to distribute the reference timing signals that can be used to recover the phase synchronization and/or time sync
27、hronization according to the required quality. It also specifies the relevant time and phase synchronization interfaces and related performance. The telecommunication networks that are in the scope of this Recommendation are currently limited to the following scenarios: Ethernet (IEEE 802.3 and IEEE
28、 802.1Q). MPLS (IETF RFC 3031 and ITU-T G.8110). IP (IETF RFC 791 and RFC 2460). OTN (ITU-T G.709). The physical layers that are relevant to this specification are the Ethernet media types, as defined in IEEE 802.3 and, for OTN, the Optical OCh layer with OTU frame as defined in ITU-T G.709. 2 Refer
29、ences 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; user
30、s 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 Recommend
31、ation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.703 Recommendation ITU-T G.703 (2016), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T G.709 Recommendation ITU-T G.709/Y.1331 (2016), Interfaces for the optical transport network
32、. 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 (2015), Definitions and terminology for synchronization in pack
33、et networks. ITU-T G.8261 Recommendation ITU-T G.8261/Y.1361 (2013), Timing and synchronization aspects in packet networks. ITU-T G.8272 Recommendation ITU-T G.8272/Y.1367 (2015), Timing characteristics of primary reference time clocks. ITU-T V.11 Recommendation ITU-T V.11/X.27 (1996), Electrical ch
34、aracteristics for balanced double-current interchange circuits operating at data signalling rates up to 10 Mbit/s. 2 Rec. ITU-T G.8271/Y.1366 (08/2017) 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 S
35、tandard for Ethernet. IEEE 1588 IEEE 1588-2008, Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems. . 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), Intern
36、et Protocol, Version 6 (IPv6) Specification. http:/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
37、 in ITU-T G.810, ITU-T G.8260 and IEEE 1588. 4 Abbreviations 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 Grou
38、nd Based Augmentation System GNSS Global Navigation 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 Br
39、oadcast Multicast Service MBSFN MBMS based on Single Frequency Network M2M Machine to Machine NTP Network Time Protocol OTN Optical Transport Network PDV Packet Delay Variation Rec. ITU-T G.8271/Y.1366 (08/2017) 3 PHY Physical Layer Protocol PRTC Primary Reference Time Clock PSN Packet Switched Netw
40、ork PTP Precision Time Protocol QZSS Quasi-Zenith Satellite System RTT Radio Transmission Technology 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 Tel
41、ecom Transparent Clock T-TSC Telecom Time Slave Clock 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 Recommenda
42、tion, the following conventions are used: The term 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. 6 The need for time and phase synchronization Time synchronization h
43、as 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 application is the monitoring of delays in Internet protocol (IP) netw
44、orks. 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 to the generation of signals over the air interface of some mobile
45、 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 case of time division duplexing (TDD) systems (for instance, LTE TDD)
46、, 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 properly in networks that satisfy the 50 ppb frequency accuracy requirement. This requirement, which 4 Re
47、c. ITU-T G.8271/Y.1366 (08/2017) 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 be accurate to within a few microseconds. This is because identic
48、al 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 cells as though they came from a single cell. Therefore, all trans
49、missions 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 1 below. NOTE In the case of mobile applications as described in T
