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.8271.2/Y.1366.2 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 targ
2、ets SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS, NEXT-GENERATION NETWORKS, INTERNET OF THINGS AND SMART CITIES Internet protocol aspects Transport Network limits for time synchronization in packet networks with partial timing support from the network Recommendation ITU-T G
3、.8271.2/Y.1366.2 ITU-T G-SERIES RECOMMENDATIONS 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
4、CARRIER TELEPHONE SYSTEMS ON METALLIC 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 S
5、YSTEMS CHARACTERISTICS G.600G.699 DIGITAL 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 OV
6、ER TRANSPORT GENERIC ASPECTS G.7000G.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 f
7、urther details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.8271.2/Y.1366.2 (08/2017) i Recommendation ITU-T G.8271.2/Y.1366.2 Network limits for time synchronization in packet networks with partial timing support from the network Summary Recommendation ITU-T G.8271.2/Y.1366.2 sp
8、ecifies the maximum network limits of phase and time error that shall not be exceeded. It specifies the minimum equipment tolerance to phase and time error that shall be provided at the boundary of these packet networks at phase and time synchronization interfaces. It also outlines the minimum requi
9、rements for the synchronization function of network elements. Recommendation ITU-T G.8271.2/Y.1366.2 addresses the case of time and phase distribution across a network with packet-based method with partial timing support to the protocol level from the network. History Edition Recommendation Approval
10、 Study Group Unique ID* 1.0 ITU-T G.8271.2/Y.1366.2 2017-08-13 15 11.1002/1000/13324 Keywords Network limits, partial timing support, phase, precision time protocol, synchronization, time. * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, fo
11、llowed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T G.8271.2/Y.1366.2 (08/2017) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communicat
12、ion 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 Wor
13、ld 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
14、 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 expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recog
15、nized 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 w
16、ords “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 tha
17、t 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 Recommendat
18、ion 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 a
19、re 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 whatsoever, without the prior written permission of ITU. Rec. ITU-T G.8271.2/Y.1366.2 (08/2017) iii Table of Conte
20、nts Page 1 Scope . 1 2 References . 2 3 Definitions 3 4 Abbreviations and acronyms 3 5 Conventions 3 6 Network reference model . 4 7 Packet network limits . 4 7.1 Network limits at reference point A and A 4 7.2 Network limit at reference point B . 4 7.3 Network limits at reference point C . 5 Append
21、ix I Deployment scenarios for partial timing support networks . 7 I.1 Assisted partial and partial timing support network use cases . 7 I.2 Full timing support network followed by an assisted partial timing support network or partial timing support network 8 I.3 Partial timing support network follow
22、ed by a full timing support network . 9 I.4 Assisted partial timing support network followed by a partial timing support network 9 I.5 Use of partial timing support network to bridge between two full timing support networks 9 Appendix II Considerations for handling precision time protocol traffic in
23、 networks with partial timing support 10 Appendix III The use of frequency to maintain precise time . 12 Rec. ITU-T G.8271.2/Y.1366.2 (08/2017) 1 Recommendation ITU-T G.8271.2/Y.1366.2 Network limits for time synchronization in packet networks with partial timing support from the network 1 Scope Thi
24、s Recommendation specifies the maximum network limits of phase and time error that shall not be exceeded. It specifies the minimum equipment tolerance to phase and time error that shall be provided at the boundary of these packet networks at phase and time synchronization interfaces. It also outline
25、s the minimum requirements for the synchronization function of network elements. This Recommendation addresses the distribution of time and phase across a network, using the packet-based method with partial timing support to the protocol level from the network. In particular, it applies to the assis
26、ted partial timing support (APTS) and partial timing support (PTS) architectures described in ITU-T G.8275 and the precision time protocol (PTP) profile defined in ITU-T G.8275.2. This Recommendation addresses the following cases. 1) Assisted partial timing support (APTS). In the APTS configuration,
27、 PTP is used as a backup timing source to a local time reference (e.g., primary reference time clock (PRTC) based on the global navigation satellite system (GNSS) for durations up to 72 h. It is not intended to use PTP as the primary timing source. Network requirements take into consideration the dy
28、namic time error (dTE) generated by the network. 2) Partial timing support from the network (PTS). In the PTS configuration, PTP is used as the primary source of time to the end application. In this mode, a local time reference (e.g., GNSS) is not available. Network requirements take into considerat
29、ion the combination of both the constant time error (cTE) and dTE components generated by the network. A network that is based on the architecture defined in ITU-T G.8265, and is designed to meet the network limits for frequency defined in ITU-T G.8261.1, is not designed for the delivery of accurate
30、 time or phase, which requires much lower levels of packet delay variation (PDV) and asymmetry. The network limits specified in this document are for small, well-controlled networks (e.g., in-building or last-mile network segments), which can guarantee that the stringent PDV and asymmetry network li
31、mits are met. Further guidance can be found in Appendix II. The necessary clock specifications are for further study. The packet networks that are in the scope of this Recommendation are currently limited to the following types: Ethernet: IEEE 802.3 and IEEE 802.1Q Multiprotocol label switching (MPL
32、S): IETF RFC 3031 and ITU-T G.8110 Internet protocol (IP): IETF RFC 791 and IETF RFC 2460 The use of other network types are for further study. The physical layer that is relevant to this specification is the Ethernet media types as defined in IEEE 802.3. 2 Rec. ITU-T G.8271.2/Y.1366.2 (08/2017) 2 R
33、eferences 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;
34、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 Recom
35、mendation does not give it, as a stand-alone document, the status of a Recommendation. 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 Recomm
36、endation ITU-T G.8260 (2015), Definitions and terminology for synchronization in packet networks. ITU-T G.8261.1 Recommendation ITU-T G.8261.1/Y.1361.1 (2012), Packet delay variation network limits applicable to packet-based methods (Frequency synchronization). ITU-T G.8265 Recommendation ITU-T G.82
37、65/Y.1365 (2010), Architecture and requirements for packet-based frequency delivery. ITU-T G.8271 Recommendation ITU-T G.8271/Y.1366 (2016), Time and phase synchronization aspects of packet networks. ITU-T G.8271.1 Recommendation ITU-T G.8271.1/Y.1366.1 (2013), Network limits for time synchronizatio
38、n in packet networks. ITU-T G.8272 Recommendation ITU-T G.8272/Y.1367 (2015), Timing characteristics of primary reference time clocks. ITU-T G.8275 Recommendation ITU-T G.8275/Y.1369 (2017), Architecture and requirements for packet-based time and phase distribution. ITU-T G.8275.1 Recommendation ITU
39、-T G.8275.1/Y.1369.1 (2016), 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 (2016), Precision time protocol telecom profile for time/phase synchronization with partial timing suppo
40、rt from the network. 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 1588-2008 IEEE 1588-2008, IEEE Standard for a precision clock synchronization protocol for networked m
41、easurement and control systems. IETF RFC 791 IETF RFC 791 (1981), Internet protocol (IP). IETF RFC 2460 IETF RFC 2460 (1998), Internet Protocol, Version 6 (IPv6) Specification. IETF RFC 3031 IETF RFC 3031 (2001), Multiprotocol label switching architecture. Rec. ITU-T G.8271.2/Y.1366.2 (08/2017) 3 3
42、Definitions 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 cTE constant Time Error dTE dynamic Time Error GNSS Glo
43、bal Navigation Satellite System IWF Interworking Function MPLS Multiprotocol Label Switching PDV Packet Delay Variation PRC Primary Reference Clock PRS Primary Reference Source PRTC Primary Reference Time Clock PTP Precision Time Protocol PTS Partial Timing Support T-BC Telecom Boundary Clock T-BC-P
44、 Telecom Boundary Clock Partial support T-GM Telecom Grandmaster TLV Type Length Variable T-TSC Telecom Time Slave Clock T-TSC-A Telecom Time Slave Clock Assisted T-TSC-P Telecom Time Slave Clock Partial support 5 Conventions Within this Recommendation, the following conventions are used: the term P
45、TP refers to the protocol defined in IEEE 1588-2008. The term telecom boundary clock partial support (T-BC-P) is a device consisting of a boundary clock as defined in IEEE 1588-2008, with only PTS at the protocol level from the network, and with additional performance characteristics for further stu
46、dy. The term telecom time slave clock assisted (T-TSC-A) (e.g., by GNSS) is a device consisting of a PTP slave only ordinary clock as defined in IEEE 1588-2008, assisted by a local time reference clock device, and with additional performance characteristics for further study. The term telecom time s
47、lave clock partial (T-TSC-P) is a device consisting of a PTP slave only ordinary clock as defined in IEEE 1588-2008, with only PTS at the protocol level from the network, and with additional performance characteristics for further study. The terms “dTE“ and “time noise“ are used interchangeably thro
48、ughout this Recommendation to indicate jitter and wander components of the timing signal. 4 Rec. ITU-T G.8271.2/Y.1366.2 (08/2017) 6 Network reference model The general network reference model is described in ITU-T G.8271. 7 Packet network limits This clause defines the network limits that apply to
49、the packet network, i.e., reference points A, B and C in Figures 1 and 2. Figure 1 Reference model for network limits for assisted partial timing support Figure 2 Reference model for network limits for partial timing support The two examples in Figures 1 and 2 are simplified. They represent use cases 1a and 1b in Appendix I. It is highlighted in Appendix I that in some deployment cases, the part of the network located between point C and D may contr
