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 (01/2017) 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 Timing characteristics of telecom boundary clocks and telecom time slave clocks Recommendation ITU-T G.8273.2/Y.1368.2 ITU-T G
3、-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 CARRIER TELEPHONE SYSTEM
4、S 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 SYSTEMS CHARACTERISTICS G
5、.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 OVER TRANSPORT GENERIC ASP
6、ECTS 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 further details, please r
7、efer to the list of ITU-T Recommendations. Rec. ITU-T G.8273.2/Y.1368.2 (01/2017) 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
8、for telecom boundary clocks and 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 pa
9、cket based networks. This version 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.1368.2 201
10、4-05-14 15 11.1002/1000/12196 1.1 ITU-T G.8273.2/Y.1368.2 (2014) Amd. 1 2015-01-13 15 11.1002/1000/12395 1.2 ITU-T G.8273.2/Y.1368.2 (2014) Amd. 2 2015-08-13 15 11.1002/1000/12543 2.0 ITU-T G.8273.2/Y.1368.2 2017-01-12 15 11.1002/1000/13109 Keywords Boundary clock, frequency synchronization, phase s
11、ynchronization, slave clock, synchronous Ethernet, time synchronization. * 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.82
12、73.2/Y.1368.2 (01/2017) FOREWORD The International Telecommunication Union (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
13、 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 Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study
14、 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 areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a co
15、llaborative 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 operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain ce
16、rtain 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 “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requi
17、rements. 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 practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right
18、. 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 development process. As of the date of approval of this Recommendation, ITU had not received notice of intellect
19、ual 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 therefore strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2017 All rights
20、reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T G.8273.2/Y.1368.2 (01/2017) 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 Recomm
21、endation . 2 4 Abbreviations and acronyms 2 5 Conventions 3 6 Physical layer frequency performance requirements 3 7 T-BC packet layer performance requirements for full timing support from the network . 3 7.1 Constant time error and dynamic time error noise generation . 4 7.2 Noise tolerance . 6 7.3
22、Noise transfer 6 7.4 Transient response and holdover performance . 7 7.5 Interfaces 9 Annex A Telecom boundary clock model 11 Annex B Control of the phase transient due to rearrangements in the synchronous Ethernet network . 13 Annex C Telecom time slave clock requirements 15 C.1 Physical layer freq
23、uency performance requirements . 15 C.2 T-TSC packet layer performance requirements for full timing support from the network 15 Appendix I Mitigation of time error due to SyncE/SDH transients 22 Appendix II Derivation of T-BC output transient mask due to SyncE/SDH rearrangement . 23 II.1 Background
24、on assumptions for and derivation of T-BC output phase error due to a SyncE/SDH rearrangement 23 II.2 T-BC output phase transient mask . 30 Appendix III Background to performance requirements of the T-BC 33 III.1 Noise generation requirements . 34 III.2 Noise tolerance . 34 III.3 Noise transfer 35 I
25、II.4 Holdover . 37 Appendix IV Consideration on slave clocks embedded in end applications 39 Appendix V Performance Estimation for Cascaded Media Converters acting as T-BCs . 40 V.1 Noise generation . 40 V.2 Noise tolerance . 41 V.3 Noise transfer 41 V.4 Transient response and holdover performance .
26、 41 Rec. ITU-T G.8273.2/Y.1368.2 (01/2017) 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 phase synchronization devices used in synchronization network eq
27、uipment 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 network operation for phase/time synchronization distribution whe
28、n 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 phase/time synchronization with the full timing support archite
29、cture defined in ITU-T G.8275 and the related profile defined in ITU-T G.8275.1. The definition of a T-BC and the T-TSC for the future partial timing support architecture is for further study. This Recommendation defines the minimum requirements for telecom boundary clocks and telecom time slave clo
30、cks 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 without physical layer frequency support (i.e.
31、, the pure PTP case) 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 done for time transpo
32、rt 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. The T-BC requirements are given in clauses 6 and 7 and the T-TSC
33、requirements are given in annex C. NOTE This Recommendation does not modify the physical layer reference chain behaviour, according to ITU-T G.803 and ITU-T G.8261. This Recommendation does not exclude the use of other physical layer clocks (e.g., ITU-T G.812 Type I) within the frequency transport n
34、etwork. The equipment specification of a T-BC assisted by a physical layer equipment clock, other than ITU-T G.8262 option 1, such as ITU-T G.812 Type I, is for further study. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this te
35、xt, 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 therefore encouraged to investigate the possibility of applying the most recent edition
36、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-alone document, the status of a Recommendation. ITU-T G.703 Recommendation ITU-T G
37、.703 (2016), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T G.781 Recommendation ITU-T G.781 (2008), Synchronization layer functions. 2 Rec. ITU-T G.8273.2/Y.1368.2 (01/2017) ITU-T G.803 Recommendation ITU-T G.803 (2000), Architecture of transport networks based on the
38、 synchronous digital hierarchy (SDH). ITU-T G.810 Recommendation 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.813 R
39、ecommendation ITU-T G.813 (2003), Timing characteristics of SDH equipment slave clocks (SEC). ITU-T G.8260 Recommendation ITU-T G.8260 (2015), Definitions and terminology for synchronization in packet networks. ITU-T G.8261 Recommendation ITU-T G.8261/Y.1361 (2013), Timing and synchronization in pac
40、ket networks. ITU-T G.8262 Recommendation ITU-T G.8262/Y.1362 (2015), Timing characteristics of a synchronous Ethernet equipment slave clock. ITU-T G.8264 Recommendation ITU-T G.8264/Y.1364 (2014), Distribution of timing information through packet networks. ITU-T G.8271 Recommendation ITU-T G.8271/Y
41、.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 synchronization in packet networks. ITU-T G.8273 Recommendation ITU-T G.8273/Y.1368 (2013), Framework of phase and time clocks. ITU-T G.8275
42、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 (2016), Precision time protocol telecom profile for phase/time synchronization with full timing support from the network. 3 Def
43、initions 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 this Recommendation None. 4 Abbreviations and acronyms This Recommendation uses the followin
44、g abbreviations and acronyms: cTE Constant Time Error dTE Dynamic Time Error EEC synchronous Ethernet Equipment Clock ESMC Ethernet Synchronization Messaging Channel Rec. ITU-T G.8273.2/Y.1368.2 (01/2017) 3 GbE Gigabit Ethernet MTIE Maximum Time Interval Error NE Network Element PEC Packet-based Equ
45、ipment Clock PPS Pulse Per Second PRC Primary Reference Clock PRTC Primary Reference Time 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 TDEV Time Deviation TE
46、 Time Error ToD Time of Day T-GM Telecom Grandmaster T-TSC Telecom Time Slave Clock 5 Conventions None. 6 Physical layer frequency performance requirements The list of the applicable physical layer frequency interfaces is provided in clause 7.5.2. The following applies for the synchronous Ethernet a
47、nd SDH interfaces: Synchronous Ethernet (SyncE) interfaces and synchronous Ethernet equipment clocks (EECs) used in combination with the telecom boundary clock (T-BC) are specified in ITU-T G.8262 and generate and process Ethernet synchronization messaging channel (ESMC) messages as specified in ITU
48、-T G.8264. Synchronous digital hierarchy (SDH) interfaces and SDH equipment slave clocks (SECs) used in combination with the T-BC are specified in ITU-T G.813 and generate and process synchronization status messages (SSMs) as specified in ITU-T G.781. NOTE The ITU-T G.8273.2 T-BC model does not excl
49、ude the use of other physical layer clocks (e.g., ITU-T G.812 Type I) within the equipment related to the operation between the physical layer input to physical layer output interface behaviour, in accordance to the existing ITU-T G.803 reference chain and ITU-T G.8261 network limits. In such cases, the equipment behaviour related to the interaction between the physical layer input and the PTP output is for further study. 7 T-BC packet layer perfor
