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.8271.1/Y.1366.1 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (10/2017) 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 Recommendation ITU-T G.8271.1/Y.1366.1 ITU-T G-SERIES RECOMMENDATIO
3、NS 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 G
4、.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 TER
5、MINAL 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 PAC
6、KET 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 I
7、TU-T Recommendations. Rec. ITU-T G.8271.1/Y.1366.1 (10/2017) i Recommendation ITU-T G.8271.1/Y.1366.1 Network limits for time synchronization in packet networks Summary Recommendation ITU-T G.8271.1/Y.1366.1 specifies the maximum network limits of phase and time error that shall not be exceeded. It
8、specifies the minimum equipment tolerance to phase and time error that shall be provided at the boundary of packet networks at phase and time synchronization interfaces. It also outlines the minimum requirements for the synchronization function of network elements. This Recommendation addresses the
9、case of time and phase distribution across a network by a packet-based method with full timing support to the protocol level from the network. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.8271.1/Y.1366.1 2013-08-29 15 11.1002/1000/12034 1.1 ITU-T G.8271.1/Y.1366.1 (2013
10、) Amd. 1 2014-05-14 15 11.1002/1000/12194 1.2 ITU-T G.8271.1/Y.1366.1 (2013) Amd. 2 2015-01-13 15 11.1002/1000/12392 2.0 ITU-T G.8271.1/Y.1366.1 2017-10-07 15 11.1002/1000/13323 Keywords Full timing support, network limits, precision time protocol, phase, synchronization, time. _ * To access the Rec
11、ommendation, 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.8271.1/Y.1366.1 (10/2017) FOREWORD The International Telecommunication Union (ITU) is the Unit
12、ed 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 Recommend
13、ations 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 appr
14、oval 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 expression “Administrat
15、ion“ 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 complian
16、ce 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 r
17、equired 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 of claimed Intell
18、ectual 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 Recommendation.
19、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 whatsoever, without th
20、e prior written permission of ITU. Rec. ITU-T G.8271.1/Y.1366.1 (10/2017) iii 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 6 Network reference model . 3 7
21、Network limits 3 7.1 Network limits at reference point A . 4 7.2 Network limits at reference point B . 4 7.3 Network limits at reference point C . 4 7.4 Network limit at reference point D . 6 7.5 Network limit at reference point E . 6 Appendix I Clock models for noise accumulation simulations 7 I.1
22、T-BC models for noise accumulation simulations . 7 I.2 End-to-end TC models for noise accumulation simulations 10 Appendix II HRMs used to derive the network limits 13 II.1 HRM composed of T-BCs 13 II.1.1 HRM without physical layer frequency support from the network 13 II.1.2 HRM with physical layer
23、 frequency support from the network . 15 II.1.3 HRM for cluster-based synchronization . 18 II.2 HRM composed of T-BCs and T-TCs 19 II.2.1 HRM with physical layer frequency support from the network . 19 Appendix III Network limits considerations . 20 III.1 Measurement of network limits in case of dep
24、loyment case 1 . 20 Appendix IV Constant and dynamic time error and error accumulation 23 IV.1 Introduction 23 IV.2 Components of time error . 23 IV.3 Accumulation of time error in a chain of clocks 24 Appendix V Example of design options . 26 V.1 Network limits 26 V.2 Components of time error budge
25、ts . 26 V.3 Failure scenarios . 27 V.4 Time error budget allocation 27 V.5 Operator options . 29 V.6 Further details . 29 iv Rec. ITU-T G.8271.1/Y.1366.1 (10/2017) Appendix VI Mitigation of time error due to synchronous Ethernet transients 32 Appendix VII Maximum relative time error . 33 Appendix VI
26、II Models for budgeting in a chain of microwave devices . 35 Appendix IX Models for Budgeting in a chain of xPON or xDSL devices 38 Rec. ITU-T G.8271.1/Y.1366.1 (10/2017) 1 Recommendation ITU-T G.8271.1/Y.1366.1 Network limits for time synchronization in packet networks 1 Scope This Recommendation s
27、pecifies 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 packet networks at phase and time synchronization interfaces. It also outlines the minimum requiremen
28、ts for the synchronization function of network elements. This Recommendation addresses the case of time and phase distribution across a network with packet-based method with full timing support to the protocol level from the network. The physical layer (PHY) that is relevant to this specification is
29、 the Ethernet media type as defined in IEEE 802.3-2015. 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 Rec
30、ommendations 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 regular
31、ly 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.803 Recommendation ITU-T G.803 (2000), Architecture of transport networks based on the synchronous digital hierarchy (SDH). ITU-T G.810 Recommenda
32、tion ITU-T G.810 (1996), Definitions and terminology for synchronization networks. ITU-T G.812 Recommendation ITU-T G.812 (2004), Timing requirements of slave clocks suitable for use as node clocks in synchronization networks. ITU-T G.823 Recommendation ITU-T G.823 (2000), The control of jitter and
33、wander within digital networks which are based on the 2048 kbit/s hierarchy. ITU-T G.8260 Recommendation ITU-T G.8260 (2015), Definitions and terminology for synchronization in packet networks. ITU-T G.8262 Recommendation ITU-T G.8262/Y.1362 (2015), Timing characteristics of a synchronous Ethernet e
34、quipment slave clock. ITU-T G.8271 Recommendation ITU-T G.8271/Y.1366 (2017), Time and phase synchronization aspects of telecommunication networks. ITU-T G.8272 Recommendation ITU-T G.8272/Y.1367 (2015), Timing characteristics of primary reference time clocks. ITU-T G.8273 Recommendation ITU-T G.827
35、3/Y.1368 (2013), Framework of phase and time clocks. ITU-T G.8273.2 Recommendation ITU-T G.8273.2/Y.1368.2 (2017), Timing characteristics of telecom boundary clocks and telecom time slave clocks. ITU-T G.8275 Recommendation ITU-T G.8275/Y.1369 (2017), Architecture and requirements for packet-based t
36、ime and phase distribution. 2 Rec. ITU-T G.8271.1/Y.1366.1 (10/2017) IEEE 802.3-2015 IEEE 802.3-2015, IEEE standard for Ethernet. IEEE 1588-2008 IEEE 1588-2008, IEEE standard for a precision clock synchronization protocol for networked measurement and control systems. 3 Definitions 3.1 Terms defined
37、 elsewhere This Recommendation uses the terms and definitions contained in ITU-T G.810 and ITU-T G.8260. 3.2 Terms defined in this Recommendation None. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: CPRI Common Public Radio Interface DSLAM Digital Sub
38、scriber Line Access Multiplexer EEC Ethernet Equipment Clock GNSS Global Navigation Satellite System GPON Gigabit-capable Passive Optical Network HRM Hypothetical Reference Model LTE Long-Term Evolution MTIE Maximum Time Interval Error OLT Optical Line Terminal ONT Optical Network Terminal OSC Optic
39、al Supervisory Channel OTN Optical Transport Network PHY Physical layer PLL Phase-Locked Loop PPS Pulse Per Second PRC Primary Reference Clock PRTC Primary Reference Time Clock PTP Precision Time Protocol RE Radio Equipment REC Radio Equipment Control RT-DSLAM Remote Terminal-Digital Subscriber Line
40、 Access Multiplexer SDH Synchronous Digital Hierarchy SSM Synchronization Status Message SSU Synchronization Supply Unit T-BC Telecom Boundary Clock Rec. ITU-T G.8271.1/Y.1366.1 (10/2017) 3 TDD Time Division Duplex TDEV Time Deviation TE Time Error T-GM Telecom Grand Master T-TC Telecom Transparent
41、Clock T-TSC Telecom Time Slave Clock VCO Voltage Controlled Oscillator xDSL x-type Digital Subscriber Line xPON x Passive Optical Network 5 Conventions Within this Recommendation, the following conventions are used: the term precision time protocol (PTP) refers to the PTP protocol defined in IEEE 15
42、88-2008. The terms dynamic time error (TE) and time noise are used interchangeably throughout this Recommendation to indicate jitter and wander components of the timing signal. 6 Network reference model The general network reference model is described in ITU-T G.8271. 7 Network limits The following
43、main (i.e., worst case) scenarios have been identified and are considered in the definition of the relevant network limits: deployment case 1: time distribution chain with telecom time slave clock (T-TSC) integrated into the end application and end application with a distributed architecture. In thi
44、s case, the performance specification of the T-TSC is outside the scope of ITU-T G.8273.2. deployment case 2: time distribution chain with a T-TSC external to the end application and end application with a distributed architecture. NOTE a specific equipment implementation may also be based on implem
45、enting a telecom boundary clock (T-BC) function (instead of a T-TSC function) and delivering the phase/time reference to the end application via a phase/time synchronization distribution interface. In this case, the performance specification of the T-TSC is defined in ITU-T G.8273.2. The deployment
46、cases are shown in Figure 7-1. 4 Rec. ITU-T G.8271.1/Y.1366.1 (10/2017) Figure 7-1 Time synchronization deployment cases NOTE An example of distributed architecture is the case of mobile applications where the base stations have the base band unit also called radio equipment control (REC) connected
47、remotely to the radio units also called radio equipment (RE). In this case, a point to point connection (e.g., via fibre) is assumed and chain topologies are possible. The TE budget applicable to this connection is assumed to be 150 ns; the details on the chain topology are for further study. 7.1 Ne
48、twork limits at reference point A The network limits applicable at reference point A, i.e., at the output of the primary reference time clock (PRTC), are specified in ITU-T G.8272. In particular, according to ITU-T G.8272, the maximum absolute TE is: |TE| 100 ns NOTE This limit is applicable under n
49、ormal, locked operating conditions. The limit under failure conditions at the PRTC is for further study. Dynamic TE network limits applicable at reference point A are also specified in ITU-T G.8272. 7.2 Network limits at reference point B In the case of a telecom grand master (T-GM) integrated into the PRTC, the network limits applicable at reference point B are the same as the limits applicable at reference point A. In the case of a T-GM ext
