1、 International Telecommunication Union ITU-T G.8260TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 2(05/2014) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Packet over Transport aspects Synchronization, quality and availability targets Definitions and terminology f
2、or synchronization in packet networks Amendment 2: Amendment to the definition of time error Recommendation ITU-T G.8260 (2012) Amendment 2ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 GENERAL C
3、HARACTERISTICS 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 RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WI
4、TH 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 DIGITAL LINE SYSTEM G.900G.999 MULTIMEDIA QUALITY OF SER
5、VICE 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.8099 MPLS over Transport aspects G.8100G.8199 Synchro
6、nization, quality and availability targets G.8200G.8299Service 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.8260 (2012)/Amd.2 (05/2014) i Recommendation ITU-T G.8260 Definitions and terminology for synchroni
7、zation in packet networks Amendment 2 Amendment to the definition of time error Summary Amendment 2 to Recommendation ITU-T G.8260 (2012) augments definition 3.1.20, “time error“. History Edition Recommendation Approval Study Group Unique ID*1.0 ITU-T G.8260 2010-08-12 15 11.1002/1000/10907 2.0 ITU-
8、T G.8260 2012-02-13 15 11.1002/1000/11521 2.1 ITU-T G.8260 (2012) Amd. 1 2013-08-29 15 11.1002/1000/12016 2.2 ITU-T G.8260 (2012) Amd. 2 2014-05-14 15 11.1002/1000/12189 _ *To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Reco
9、mmendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T G.8260 (2012)/Amd.2 (05/2014) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies
10、 (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 a worldwide basis. The World Telecommunica
11、tion 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 down in WTSA Resolution 1. In some areas of i
12、nformation 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 administration and a recognized operating
13、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 provisions are met. The words “shall“ or
14、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 RIGHTS ITU draws attention to the possibility that the practice
15、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 outside of the Recommendation development
16、 process. As of the date of approval of this Recommendation, ITU had 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 the latest information and are therefore strong
17、ly 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.8260 (2012)/Amd.2 (05/2014) 1 Recommendation ITU-T G.8260 Defin
18、itions and terminology for synchronization in packet networks Amendment 2 Amendment to the definition of time error Replace definition 3.1.20, which currently reads: 3.1.20 time error (Based on ITU-T G.810): Constant time error: With reference to the time error model provided in ITU-T G.810, the con
19、stant time error is the term x0. Constant time error estimate: Given a time error sequence x(n); n = 0,1,(N1), an estimate of the constant time error is the average of the first M samples of the time error sequence. M is obtained from the observation interval providing the least value for TDEV as co
20、mputed for the given time error sequence. If a frequency offset is present then a linear regression method in accordance with Appendix II of ITU-T G.823 can be applied. Considerations for measurement data containing transients is for further study. NOTE In some cases due to the frequency components
21、of the noise of the signal being measured it might be difficult to identify a stable, consistent observation interval. These cases must be addressed case by case. With the following new definition: 3.1.20 time error: The time error of a clock with respect to a time standard is the difference between
22、 the time of that clock and the time indicated by the time standard. A model for expressing the time error of a clock is described in clause I.3 of ITU-T G.810. Constant time error: With reference to the time error model provided in clause I.3 of ITU-T G.810, the constant time error (cTE) of a synch
23、ronized clock is the term x0. Constant time error estimate: Given a time error sequence x(n); n = 0,1,(N1), an estimate of the constant time error is the average of the first M samples of the time error sequence. M is obtained from the observation interval providing the least value for TDEV as compu
24、ted for the given time error sequence. If a frequency offset is present then a linear regression method in accordance with Appendix II of ITU-T G.823 can be applied. Considerations for measurement data containing transients is for further study. NOTE In some cases due to the frequency components of
25、the noise of the signal being measured it might be difficult to identify a stable, consistent observation interval. These cases must be addressed case by case. Dynamic time error: With reference to the time error model provided in clause I.3 of ITU-T G.810, the dynamic time error (dTE) of a synchron
26、ized clock is the random noise component, i.e., () ()nomreftt2. The shape of the dTE component may be expressed using the time interval error function TIE(t, ), and characterized using the related metrics MTIE and TDEV, although the offset from zero of the TIE function may vary depending on the time
27、 t when the measurement starts. Maximum absolute time error: The maximum absolute time error (max|TE|) of a synchronized clock is the maximum absolute value of the time error function. Printed in Switzerland Geneva, 2014 SERIES OF ITU-T RECOMMENDATIONS Series A Organization of the work of ITU-T Seri
28、es D General tariff principles Series E Overall network operation, telephone service, service operation and human factors Series F Non-telephone telecommunication services Series G Transmission systems and media, digital systems and networks Series H Audiovisual and multimedia systems Series I Integ
29、rated services digital network Series J Cable networks and transmission of television, sound programme and other multimedia signals Series K Protection against interference Series L Construction, installation and protection of cables and other elements of outside plant Series M Telecommunication man
30、agement, including TMN and network maintenance Series N Maintenance: international sound programme and television transmission circuits Series O Specifications of measuring equipment Series P Terminals and subjective and objective assessment methods Series Q Switching and signalling Series R Telegra
31、ph transmission Series S Telegraph services terminal equipment Series T Terminals for telematic services Series U Telegraph switching Series V Data communication over the telephone network Series X Data networks, open system communications and security Series Y Global information infrastructure, Internet protocol aspects and next-generation networks Series Z Languages and general software aspects for telecommunication systems
