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 (08/2013) SERIES G: TRANSMISSION SYSTEMS AND 21EDIA, DIGITAL SYSTEMS AND NETWORKS Packet over Transport aspects Quality and availability targets SERIES Y: GLOBAL
2、 INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS 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 MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELE
3、PHONE 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 CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON RA
4、DIO-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 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIGIT
5、AL 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.8000G.8999 Ethernet over Transport aspects G.8000G.80
6、99 MPLS over Transport aspects G.8100G.8199 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 G.8273/Y.1368 (08/2013) i Recommendation ITU-T G.8273/Y.1368 Frame
7、work 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 Recommendations ITU-T G.8271, ITU-T G.8275 and the ITU-T G.8271.x s
8、eries 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 _ * To access the Recommendation, type the URL http:/handle.itu.int/ in the address
9、 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 (08/2013) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications,
10、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 telecommunications on
11、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 the procedure laid dow
12、n 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 a telecommunication
13、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 all of these mandatory
14、 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 RIGHTSITU draws attent
15、ion 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 ITU members or others
16、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 may not represent th
17、e 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 whatsoever, without the prior written permission of ITU. Rec. ITU-T G.8273/Y.1368 (08/20
18、13) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 1 4 Abbreviations and acronyms 1 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 Boundary clocks . 10 A
19、.4 Transparent clocks 12 A.5 Slave clocks 13 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 for systems with transparent clocks 19 B.5 Measurement set-up for s
20、ystems with telecom time slave clock 20 Rec. ITU-T G.8273/Y.1368 (08/2013) 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 t
21、he network architecture defined 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 ti
22、me clocks. 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 Recommendations and other references are subject
23、 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 regularly published. The reference to a document wit
24、hin this Recommendation 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.8260 Recommendation ITU-T G.8260 (2012), Definitions and terminology for synchronizati
25、on in packet networks. ITU-T G.8271 Recommendation ITU-T G.8271/Y.1366 (2012), 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.8272 Recommendation ITU-T G.8272
26、/Y.1367 (2012), Timing characteristics of primary reference time clocks. ITU-T G.8273.2 Recommendation ITU-T G.8273.2/Y.1368.2 (2014), Timing characteristics of telecom boundary clocks and telecom time slave clocks. ITU-T G.8275 Recommendation ITU-T G.8275/Y.1369 (2013), Architecture and requirement
27、s for packet-based time and phase distribution. IEEE 1588-2008 IEEE 1588-2008, Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems. 3 Definitions Definitions related to synchronization are contained in ITU-T G.810 and ITU-T G.8260. 4 Abbreviations an
28、d acronyms This Recommendation uses the following abbreviations and acronyms: 1PPS One Pulse Per Second APTSC Assisted Partial Timing Support Slave Clock 2 Rec. ITU-T G.8273/Y.1368 (08/2013) Cs Caesium cTE constant Time Error DUT Device Under Test FFO Fractional Frequency Offset GM Grandmaster MTIE
29、Maximum Time Interval Error PPS Pulse Per Second PRTC Primary Reference Time Clock PTP Precision Time Protocol SUT System Under Test SyncE Synchronous Ethernet T-BC Telecom Boundary Clock TDEV Time Deviation T-GM Telecom Grandmaster ToD Time of Day T-TC Telecom Transparent Clock T-TSC Telecom Time S
30、lave Clock 5 Conventions Within this Recommendation, the following conventions are used: the term PTP refers to the PTP protocol defined 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
31、 of the timing signal. This Recommendation refers to the ITU-T G.8273.x series of Recommendations. At the time of publication of this document, not all the documents within the series had been approved; they were under study. This means that those documents that remain under study are subject to cha
32、nge. Here is the current working list of titles for the ITU-T G.8273.x series of Recommendations: Recommendation ITU-T G.8273/Y.1368 (2013), Framework of phase and time clocks. Recommendation ITU-T G.8273.1/Y.1368.1 (under study), Timing characteristics of telecom grandmaster clocks. Recommendation
33、ITU-T G.8273.2/Y.1368.2 (2014), Timing characteristics of telecom boundary clocks and telecom time slave clocks. Recommendation ITU-T G.8273.3/Y.1368.3 (under study), Timing characteristics of telecom transparent clocks. Recommendation ITU-T G.8273.4/Y.1368.4 (under study), Timing characteristics of
34、 assisted partial timing support slave clocks. 6 General introduction of phase and time clocks This Recommendation serves 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. Rec. ITU-T G.8273/Y.1368 (08/2013) 3 The foc
35、us of this Recommendation is on packet-based methods for transferring time/phase. Specific methods based on the precision time protocol (PTP) IEEE 1588-2008 are considered. Three generic types of clocks, and one associated device, are associated with PTP: 1) Grandmaster clocks. The implication here
36、is that the clock is a “master“ clock and it receives its timing reference (frequency as well as phase/time) by methods other than packet-based methods. 2) Boundary clocks. The implication here is the clock has an “output“, namely a master clock side and receives its timing reference via PTP from an
37、 upstream master clock (either a grandmaster or another boundary clock). That is, the boundary clock has an “input“, namely a slave clock side and internally transfers time/phase to its master side. A boundary clock provides an auxiliary output (i.e., 1PPS) that reflects the performance of the slave
38、 side. A boundary clock may have an auxiliary input to extract a frequency reference (e.g., synchronous Ethernet). 3) Transparent clocks. Transparent clocks are devices (network elements) that modify the content of PTP packets, permitting the PTP “source“ and PTP “destination“ to factor out the dela
39、y introduced by the device. Strictly speaking a “transparent clock“ is not a clock but a means for providing on-path support for packet-based timing based on PTP. 4) Slave clocks. The implication is that the clock has an “input“ that is packet-based from where it extracts its timing reference (time/
40、phase). The output can be of various formats (e.g., 1PPS), generally not packet-based. A slave clock may have an auxiliary input to extract a frequency reference (e.g., synchronous Ethernet). NOTE Here emphasis is placed on grandmaster, boundary clocks and transparent clocks. Slave clocks are left f
41、or further study. The ITU-T G.8273.x series of Recommendations are expected to define the following; however, it is important to note that as of the date of publication, not all documents mentioned have been approved yet and they are still under study, thus they may be subject to change: Telecom gra
42、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 in Amendment 1 of ITU-T G.8272. Other types of T-GM are for further study and are expected to be s
43、pecified in Recommendation ITU-T G.8273.1/Y.1368.1 (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 toler
44、ance, noise transfer, transient response and 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. The details of T-
45、TC are for further study and are expected to be specified in Recommendation ITU-T G.8273.1/Y.1368.1 (currently under study). Telecom time slave clock specification. The telecom time slave clock (T-TSC) is a device consisting of a slave clock as defined in IEEE1588-2008 with additional performance ch
46、aracteristics. ITU-T G.8273.2 specifies T-TSC. The assisted partial timing support slave clock (APTSC). The details of APTSC are for further study and are expected to be specified in Recommendation ITU-T G.8273.4/Y.1368.4 (currently under study). 4 Rec. ITU-T G.8273/Y.1368 (08/2013) Annex A Testing
47、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 measurement in both cases is time error but
48、for frequency-based measurements the time interval error information is extracted and the typical metrics used are MTIE (maximum time interval error) and TDEV (time deviation). These metrics are appropriate since the absolute value of time error is moot for frequency. In fact, MTIE can be viewed as
49、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 time error as well as the (average) frequency offset. Frequency metrics, such as MTIE, TDEV and FFO can be applied to time/phase clocks and such measurements may have value when assessing the stability of a time cloc
