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.8273.2/Y.1368.2 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (05/2014) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Packet over Transport aspects Synchronization, quality and availability ta
2、rgets SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Transport Timing characteristics of telecom boundary clocks and telecom time slave clocks Recommendation ITU-T G.8273.2/Y.1368.2 ITU-T G-SERIES RECOMMENDATIONS TRANSMIS
3、SION 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.399 G
4、ENERAL 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 EQUIP
5、MENTS 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 OVER TR
6、ANSPORT 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 Recomm
7、endations. Rec. ITU-T G.8273.2/Y.1368.2 (05/2014) i Recommendation ITU-T G.8273.2/Y.1368.2 Timing characteristics of telecom boundary clocks and telecom time slave clocks Summary Recommendation ITU-T G.8273.2/Y.1368.2 specifies minimum requirements for time and phase for telecom boundary clocks and
8、telecom time slave clocks used in synchronization network equipment that operates in the network architecture as defined in Recommendations ITU-T G.8271, ITU-T G.8271.1, ITU-T G.8275 and ITU-T G.8275.1. It supports time and/or phase synchronization distribution for packet based networks. This versio
9、n of the Recommendation only applies to full timing support from the network. These requirements apply under the normal environmental conditions specified for the equipment. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.8273.2/Y.1368.2 2014-05-14 15 11.1002/1000/12196 _
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.8273.2/Y.1368.2 (05/2014) FOREWORD The International Telecommunication Unio
11、n (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 an
12、d issuing 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 the
13、se 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 expr
14、ession “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 applicab
15、ility) 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
16、Recommendation 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 applicabilit
17、y of 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 th
18、is 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 2014 All rights reserved. No part of this publication may be reproduced, by any means wha
19、tsoever, without the prior written permission of ITU. Rec. ITU-T G.8273.2/Y.1368.2 (05/2014) 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 Physical la
20、yer frequency performance requirements 3 7 T-BC packet layer performance requirements for full timing support from the network . 3 7.1 Constant phase/time error and dynamic time error noise generation . 3 7.2 Noise tolerance . 5 7.3 Noise transfer 5 7.4 Transient response and holdover performance .
21、5 7.5 Interfaces 6 Annex A Telecom boundary clock model 7 Annex B Control of transient due to rearrangements in the synchronous Ethernet network . 8 Annex C Telecom time slave clock requirements 11 C.1 Physical layer frequency performance requirements . 11 C.2 T-TSC packet layer performance requirem
22、ents for full timing support from the network 11 Appendix I Mitigation of time error due to SyncE/SDH transients 15 Appendix II Derivation of T-BC output transient mask due to SyncE/SDH rearrangement . 16 II.1 Background on assumptions for, and derivation of, T-BC output phase error due to a SyncE/S
23、DH rearrangement 16 II.2 T-BC output phase transient masks 20 Appendix III Background to performance requirements of the T-BC 21 III.1 Noise generation requirements . 22 III.2 Noise tolerance . 22 III.3 Noise transfer 23 III.4 Holdover . 25 Appendix IV T-BC dynamic time error noise generation TDEV .
24、 27 Appendix V T-TSC dynamic time error noise generation TDEV 28 Rec. ITU-T G.8273.2/Y.1368.2 (05/2014) 1 Recommendation ITU-T G.8273.2/Y.1368.2 Timing characteristics of telecom boundary clocks and telecom time slave clocks 1 Scope This Recommendation specifies minimum requirements for time and pha
25、se synchronization devices used in synchronization network equipment that operates in the network architecture as defined in ITU-T G.8271, ITU-T G.8271.1 and ITU-T G.8275. It supports time and/or phase synchronization distribution for packet based networks. This Recommendation allows for proper netw
26、ork operation for phase/time synchronization distribution when network equipment embedding a telecom boundary clock (T-BC) and telecom time slave clock (T-TSC) is timed from another T-BC or a telecom grandmaster (T-GM). The current version of this Recommendation addresses only the distribution of ph
27、ase/time synchronization with the full timing support architecture defined in ITU-T G.8275 and the related profile defined in ITU-T G.8275.1; the definition of a T-BC for the future partial timing support architecture is for further study. This Recommendation defines the minimum requirements for tel
28、ecom boundary clocks and telecom time slave clocks in network elements. These requirements apply under the normal environmental conditions specified for the equipment. The current version of this Recommendation focuses on the case of physical layer frequency support. Requirements related to the case
29、 without physical layer frequency support are for further study. This Recommendation includes noise generation, noise tolerance, noise transfer, and transient response for telecom boundary clocks and telecom time slave clocks. This version of the Recommendation was developed based on the simulations
30、 done for time transport via precision time protocol (PTP) and frequency transport via ITU-T G.8262 EEC-Option 1 (and ITU-T G.813 SEC-Option 1 as the requirements are identical). ITU-T G.8262 EEC-Option 2 and ITU-T G.813 SEC-Option 2 are for further study. 2 References The following ITU-T Recommenda
31、tions 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; users of this Recommendation are therefo
32、re 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 Recommendation does not give it, as a stand-a
33、lone document, the status of a Recommendation. ITU-T G.781 Recommendation ITU-T G.781 (1999), Synchronization layer functions. ITU-T G.810 Recommendation ITU-T G.810 (1996), Definitions and terminology for synchronization networks. ITU-T G.813 Recommendation ITU-T G.813 (2003), Timing characteristic
34、s of SDH equipment slave clocks (SEC). ITU-T G.8260 Recommendation ITU-T G.8260 (2012), Definitions and terminology for synchronization in packet networks. ITU-T G.8262 Recommendation ITU-T G.8262/Y.1362 (2010), Timing characteristics of a synchronous Ethernet equipment slave clock. 2 Rec. ITU-T G.8
35、273.2/Y.1368.2 (05/2014) ITU-T G.8264 Recommendation ITU-T G.8264/Y1364 (2008), Distribution of timing information through packet networks. ITU-T G.8271 Recommendation ITU-T G.8271/Y1366 (2012), Time and phase synchronization aspects of packet networks. ITU-T G.8271.1 Recommendation ITU-T G.8271.1/Y
36、.1366.1 (2013), Network limits for time synchronization in packet networks. ITU-T G.8275 Recommendation ITU-T G.8275/Y.1369 (2013), Architecture and requirements for packet-based time and phase distribution. ITU-T G.8275.1 Recommendation ITU-T G.8275.1/Y.1369.1 (2014), Precision time protocol teleco
37、m profile for phase/time synchronization with full timing support from the network. 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defined elsewhere: Definitions related to synchronization are contained in ITU-T G.810 and ITU-T G.8260. 3.2 Terms defined in thi
38、s Recommendation None. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: cTE Constant phase/Time Error dTE Dynamic Time Error EEC synchronous Ethernet Equipment Clock ESMC Ethernet Synchronization Messaging Channel GbE Gigabit Ethernet MTIE Maximum Time
39、Interval Error NE Network Element PEC Packet-based Equipment Clock PPS Pulse Per Second PRC Primary Reference Clock PTP Precision Time Protocol SDH Synchronous Digital Hierarchy SEC SDH equipment slave clock SSM Synchronization Status Message SyncE Synchronous Ethernet T-BC Telecom Boundary Clock TD
40、EV Time Deviation TE Time Error Rec. ITU-T G.8273.2/Y.1368.2 (05/2014) 3 ToD Time of Day T-TSC Telecom Time Slave Clock 5 Conventions None. 6 Physical layer frequency performance requirements Synchronous Ethernet (SyncE) interfaces and synchronous Ethernet equipment clock (EEC) used on the telecom b
41、oundary clock (T-BC) shall meet the performance requirements specified in ITU-T G.8262, and shall generate and process Ethernet synchronization messaging channel (ESMC) messages as specified in ITU-T G.8264. Synchronous digital hierarchy (SDH) interfaces and SDH equipment slave clocks (SECs) used on
42、 the T-BC shall meet the performance requirements specified in ITU-T G.813, and shall generate and process synchronization status message (SSM) messages as specified in ITU-T G.781. 7 T-BC packet layer performance requirements for full timing support from the network See Appendix III for background
43、information on performance requirements of the T-BC. 7.1 Constant phase/time error and dynamic time error noise generation The noise generation of a T-BC represents the amount of noise produced at the output of the T-BC when there is an ideal input reference packet timing signal. Under normal, locke
44、d operating conditions, the time output of the T-BC should be accurate to within the maximum absolute time error (TE) (max|TE|). This value includes all the noise components, i.e., the constant phase/time error (cTE) and the dynamic time error (dTE) noise generation. In order to support different pe
45、rformance requirements at the end application specified in Table 1 of ITU-T G.8271 using different network topologies and network technologies, the maximum absolute time error, the phase/time error and dTE noise generation requirements for T-BCs are divided into two classes: Class A and Class B. At
46、the precision time protocol (PTP) and 1 pulse per second (PPS) outputs, the maximum absolute time error (max|TE|) for Class A and Class B is shown in Table 7-1. This includes all time error components (unfiltered). Table 7-1 Maximum absolute time error (max|TE|) T-BC class Maximum absolute time erro
47、r max|TE| (ns) A 100 ns B 70 ns NOTE The values in Table 7-1 are valid for 1 PPS, 1 gigabit Ethernet (GbE) and 10 GbE interfaces. Above 10 GbE is for further study. The noise generation is divided into two components, the cTE and the dTE noise generation. 7.1.1 Constant phase/time error generation A
48、t the PTP and 1 PPS outputs, the cTE generation for Class A and Class B is shown in Table 7-2. 4 Rec. ITU-T G.8273.2/Y.1368.2 (05/2014) Table 7-2 T-BC permissible range of constant phase/time error T-BC Class Permissible Range of constant phase/time error cTE(ns) A 50 B 20 NOTE 1 The values in Table
49、 7-2 are valid for 1 PPS, 1 GbE and 10 GbE interfaces. Above 10 GbE is for further study. NOTE 2 Constant time error definition and the method to estimate constant time error are defined in ITU-T G.8260. For the purpose of testing the limits in Table 7-2, an estimate of constant time error should be obtained by averaging the time error sequence over 1000 s. 7.1.2 Dynamic time error noise generation For a T-BC Class A or Class B containing
