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/Y.1368 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (03/2018) 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 Framework of phase and time clocks Recommendation ITU-T G.8273/Y.1368 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDI
3、A, 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 GENERAL CHARACTERISTIC
4、S 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 EQUIPMENTS G.700G.799 DIGI
5、TAL 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 TRANSPORT ASPECTS G.800
6、0G.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 Recommendations. Rec. ITU-T
7、 G.8273/Y.1368 (03/2018) i Recommendation ITU-T G.8273/Y.1368 Framework of phase and time clocks Summary Recommendation ITU-T G.8273/Y.1368 is a framework Recommendation for phase and time clocks for devices used in synchronizing network equipment that operate in the network architecture defined in
8、Recommendations ITU-T G.8271, ITU-T G.8275 and the ITU-T G.8271.x-series of Recommendations. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.8273/Y.1368 2013-08-29 15 11.1002/1000/12012 1.1 ITU-T G.8273/Y.1368 (2013) Cor. 1 2014-05-14 15 11.1002/1000/12195 1.2 ITU-T G.8273
9、/Y.1368 (2013) Amd. 1 2015-01-13 15 11.1002/1000/12394 1.3 ITU-T G.8273/Y.1368 (2013) Amd. 2 2015-08-13 15 11.1002/1000/12544 2.0 ITU-T G.8273/Y.1368 2018-03-16 15 11.1002/1000/13552 Keywords Phase and time clocks, testing and measurement. * To access the Recommendation, type the URL http:/handle.it
10、u.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/Y.1368 (03/2018) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of
11、 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 Recommendations on them with a view to standardizing t
12、elecommunications 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 approval of ITU-T Recommendations is covered by t
13、he 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 “Administration“ is used for conciseness to indicate both
14、 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 compliance with the Recommendation is achieved when a
15、ll 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 required of any party. INTELLECTUAL PROPERTY R
16、IGHTSITU 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 Intellectual Property Rights, whether asserted by I
17、TU 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. However, implementers are cautioned that this
18、 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 2018 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
19、 G.8273/Y.1368 (03/2018) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 1 4 Abbreviations and acronyms 2 5 Conventions 2 6 General introduction of phase and time clocks . 2 Annex A Testing and measurement of time/phase clocks 4 A.1 Introduction 4 A.2 Grandmaster clocks 7 A.3 B
20、oundary clocks . 10 A.4 Transparent clocks 12 A.5 Slave clocks 13 A.6 Clocks containing media converters . 14 Annex B Phase/time clock equipment specification related measurement methods 15 B.1 Overview 15 B.2 Telecom grandmaster test . 16 B.3 Telecom boundary clock test 18 B.4 Measurement set-up fo
21、r systems with transparent clocks 20 B.5 Measurement set-up for systems with telecom time slave clock 21 Appendix I Variable temperature testing methodology 22 Appendix II Variable temperature holdover testing methodology . 23 Appendix III Synchronous Ethernet transient testing methodology . 24 Bibl
22、iography. 26 Rec. ITU-T G.8273/Y.1368 (03/2018) 1 Recommendation ITU-T G.8273/Y.1368 Framework of phase and time clocks 1 Scope This Recommendation is a framework Recommendation for phase and time clocks for devices used in synchronizing network equipment that operate in the network architecture def
23、ined in ITU-T G.8271, ITU-T G.8275 and the ITU-T G.8271.x-series of Recommendations. This Recommendation serves as a framework for phase and time clocks defined in the ITU-T G.8273.x-series. It includes annexes with detailed testing and measurement methods of phase and time clocks. 2 References The
24、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; users of this
25、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 Recommendation does
26、 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.8260 Recommendation ITU-T G.8260 (2015), Definitions and terminology for synchronization in packet networks. ITU-T
27、 G.8271 Recommendation ITU-T G.8271/Y.1366 (2017), Time and phase synchronization aspects of telecommunication networks. ITU-T G.8271.1 Recommendation ITU-T G.8271.1/Y.1366.1 (2017), Network limits for time synchronization in packet networks. ITU-T G.8272 Recommendation ITU-T G.8272/Y.1367 (2015), T
28、iming characteristics of primary reference 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.8273.3 Recommendation ITU-T G.8273.3/Y.1368.3 (2017), Timing characteristics of telecom trans
29、parent clocks. ITU-T G.8275 Recommendation ITU-T G.8275/Y.1369 (2017), Architecture and requirements for packet-based time and phase distribution. IEEE 1588-2008 IEEE 1588-2008, IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems. 3 Definitions
30、Definitions related to synchronization are contained in ITU-T G.810 and ITU-T G.8260. 2 Rec. ITU-T G.8273/Y.1368 (03/2018) 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: 1PPS One Pulse Per Second APTSC Assisted Partial Timing Support Slave Clock Cs Ca
31、esium cTE constant Time Error DUT Device Under Test ESMC Ethernet Synchronization Message Channel FFO Fractional Frequency Offset GM Grandmaster GNSS Global Navigation Satellite System GPS Global Positioning System MTIE Maximum Time Interval Error PPS Pulse Per Second PRC Primary Reference Clock PRT
32、C Primary Reference Time Clock PTP Precision Time Protocol QL Quality Level SUT System Under Test SyncE Synchronous Ethernet TDEV Time Deviation ToD Time of Day T-BC Telecom Boundary Clock T-BC-A Telecom Boundary Clock Assisted T-BC-P Telecom Boundary Clock Partial support T-GM Telecom Grandmaster T
33、-TC Telecom Transparent Clock 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 precision time protocol (PTP) refers to the PTP protocol defi
34、ned in IEEE 1588-2008. The terms dynamic time error and time noise are used interchangeably throughout this Recommendation to indicate the jitter and wander components of the timing signal. Rec. ITU-T G.8273/Y.1368 (03/2018) 3 6 General introduction of phase and time clocks This Recommendation serve
35、s as a framework for phase and time clocks that have been defined or are to be defined in the ITU-T G.8273.x-series of Recommendations. The focus of this Recommendation is on packet-based methods for transferring time/phase. Specific methods based on the precision time protocol (PTP) IEEE 1588-2008
36、are considered. The ITU-T G.8273.x-series of Recommendations define the following; however, it is important to note that as of the date of publication, there are two documents mentioned below that have not been approved yet, they are still under study, thus they may be subject to change: Telecom gra
37、ndmaster specification. The telecom grandmaster (T-GM) is a device consisting of a grandmaster as defined in IEEE1588-2008 with additional performance characteristics. The details of T-GM are specified ITU-T G.8272. Other types of T-GM are for further study and are expected to be specified in ITU-T
38、G.8273.1 (currently under study). Telecom boundary clock specification. The telecom boundary clock (T-BC) is a device consisting of a boundary clock as defined in IEEE1588-2008 with additional performance characteristics such as noise generation, noise tolerance, noise transfer, transient response a
39、nd holdover. ITU-T G.8273.2 specifies T-BC. Telecom transparent clock specification. The telecom transparent clock (T-TC) is a device consisting of a transparent clock as defined in IEEE1588-2008 with additional performance characteristics. ITU-T G.8273.1 specifies T-TC. Telecom time slave clock spe
40、cification. The telecom time slave clock (T-TSC) is a device consisting of a slave clock as defined in IEEE1588-2008 with additional performance characteristics. ITU-T G.8273.2 specifies T-TSC. Partial timing support telecom boundary clocks (telecom boundary clock partial support (T-BC-P), telecom b
41、oundary clock assisted (T-BC-A) and telecom time slave clocks (telecom time slave clock partial support (T-TSC-P), telecom time slave clock assisted (T-TSC-A). The details of these clocks are for further study and are expected to be specified in ITU-T G.8273.4 (currently under study). 4 Rec. ITU-T G
42、.8273/Y.1368 (03/2018) Annex A Testing and measurement of time/phase clocks (This annex forms an integral part of this Recommendation.) A.1 Introduction Measurement of time/phase behaviour of clocks is substantively different from measurement of frequency behaviour of clocks. The basis for the measu
43、rement in both cases is time error but for frequency-based measurements the time interval error information is extracted and the typical metrics used are maximum time interval error (MTIE) and time deviation (TDEV). These metrics are appropriate since the absolute value of time error is moot for fre
44、quency. In fact, MTIE can be viewed as a stability measure based on peak-to-peak time error (over an observation interval) and the “average“ value is of little consequence. In the case of TDEV, the goal is to characterize the noise processes and consequently it is advantageous to suppress the mean t
45、ime error as well as the (average) frequency offset. Frequency metrics, such as MTIE, TDEV and fractional frequency offset (FFO) can be applied to time/phase clocks and such measurements may have value when assessing the stability of a time clock; such metrics are not sufficient to characterize the
46、time error of a time/phase clock. One such metric that is distinct from frequency metrics is the constant time error. The use of constant, dynamic and frequency metrics to characterize stability of a time/phase clock is for further study. The concentration in this Recommendation is on packet-based m
47、ethods for transferring time/phase. For specificity, methods based on PTP IEEE 1588-2008 are considered. NOTE Here emphasis is placed on grandmaster, boundary clocks and transparent clocks. Slave clocks are left for further study. A.1.1 Master port time-stamp error There are four time stamps that ar
48、e relevant in PTP. These are: Associated with the SYNC message: 1) T1: time-of-departure from master port; 2) T2: time-of-arrival at slave port. Associated with DELAY_REQUEST message: 3) T3: time-of-departure from slave port; 4) T4: time-of-arrival at master port. Of these time stamps, T2 and T3 are
49、 struck at the slave port and are not visible externally (T3 may be visible from some devices). Time stamps T1 and T4 are visible externally. T1 is available in the SYNC (or FOLLOW_UP) message and T4 is available in the DELAY_RESPONSE message. The accuracy of these time stamps is quantified by the difference between the time stamp as struck and the system under test time clock at the actual time-of-departure or time-of-arrival of the SYNC and DELAY_REQ
