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.8273.3/Y.1368.3 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (10/2017) 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 transparent clocks Recommendation ITU-T G.8273.3/Y.1368.3 ITU-T G-SERIES RECOMMENDATIONS TRA
3、NSMISSION 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.
4、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.600G.699 DIGITAL TERMINAL
5、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 ASPECTS G.7000G.7999 PACKET OV
6、ER 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 refer to the list of ITU-T R
7、ecommendations. Rec. ITU-T G.8273.3/Y.1368.3 (10/2017) i Recommendation ITU-T G.8273.3/Y.1368.3 Timing characteristics of telecom transparent clocks Summary Recommendation ITU-T G.8273.3/Y.1368.3 defines the minimum requirements for telecom transparent clocks (T-TCs). These requirements apply under
8、normal environmental conditions specified for the equipment. This Recommendation includes: clock accuracy, noise generation, noise tolerance, noise transfer, and transient response for T-TCs. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.8273.3/Y.1368.3 2017-10-07 15 11.
9、1002/1000/13327 Keywords PTP, phase and time synchronization, telecom profile, transparent clock. * 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/11.1002/1000/118
10、30-en. ii Rec. ITU-T G.8273.3/Y.1368.3 (10/2017) 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 perm
11、anent 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 Telecommunication Standardization Assembly (WTSA), which meets every four years, establi
12、shes 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 information technology which fall within ITU-Ts purview, the necessary stand
13、ards 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 agency. Compliance with this Recommendation is voluntary. However, the Reco
14、mmendation 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 some other obligatory language such as “must“ and the negative equivalents
15、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 attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed In
16、tellectual 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 process. As of the date of approval of this Recommendation, ITU had not rec
17、eived 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 strongly urged to consult the TSB patent database at http:/www.itu.int/ITU-T/i
18、pr/. ITU 2017 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.8273.3/Y.1368.3 (10/2017) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Ter
19、ms defined in this Recommendation . 2 4 Abbreviations and acronyms 2 5 Conventions 3 6 Physical layer frequency performance requirements 3 7 Packet layer performance requirements 3 7.1 Constant phase/time error and dynamic time error noise generation . 3 7.2 Noise tolerance . 5 7.3 Noise transfer 6
20、7.4 Packet layer transient response and holdover performance 6 8 Interfaces . 6 8.1 Phase and time interfaces . 6 8.2 Frequency interfaces . 7 Annex A Telecom transparent clock functional model 8 Appendix I Traffic load test patterns 10 Appendix II Residence time 12 Bibliography. 13 Rec. ITU-T G.827
21、3.3/Y.1368.3 (10/2017) 1 Recommendation ITU-T G.8273.3/Y.1368.3 Timing characteristics of telecom transparent clocks 1 Scope This Recommendation specifies minimum requirements for time and phase synchronization devices used in synchronizing network equipment, which operates in the network architectu
22、re as defined in ITU-T G.8271 and ITU-T G.8275. It supports time and/or phase synchronization distribution for packet-based networks. The telecom transparent clock (T-TC) must be operating in end-to-end transparent clock (TC) mode. This Recommendation assumes operation within the framework specified
23、 in ITU-T G.8273, and that the physical layer reference chain behaviors given in ITU-T G.803 and ITU-T G.8261 are followed. It is also assumed that the network limits given in ITU-T G.8271.1 are met and that the profile given in ITU-T G.8275.1 is applied. This Recommendation allows for proper networ
24、k operation when a network equipment clock is timed from another network equipment clock or a higher quality clock. This Recommendation defines the minimum requirements for transparent clocks. These requirements apply under normal environmental conditions specified for the equipment. Guidelines for
25、testing are described in Appendix I. This version of the Recommendation focuses on syntonized T-TCs with frequency reference provided by the physical layer based on 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 S
26、EC-Option 2 are for further study. A T-TC without a frequency reference provided by the physical layer is for further study. 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
27、of other physical layer clocks (e.g., ITU-T G.812 Type I) within the frequency transport network. The equipment specification of a T-TC 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 R
28、ecommendations 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 ar
29、e 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 not give it, as
30、a stand-alone document, the status of a Recommendation. ITU-T G.703 Recommendation ITU-T G.703 (2016), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T G.781 Recommendation ITU-T G.781 (2017), Synchronization layer functions. ITU-T G.803 Recommendation ITU-T G.803 (2000)
31、, Architecture of transport networks based on the synchronous digital hierarchy (SDH). ITU-T G.810 Recommendation ITU-T G.810 (1996), Definitions and terminology for synchronization networks. 2 Rec. ITU-T G.8273.3/Y.1368.3 (10/2017) ITU-T G.812 Recommendation ITU-T G.812 (2004), Timing requirements
32、of slave clocks suitable for use as node clocks in synchronization networks. ITU-T G.813 Recommendation 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.
33、 ITU-T G.8261 Recommendation ITU-T G.8261/Y.1361 (2013), Timing and synchronization aspects in packet 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 (2017), Dist
34、ribution of timing information through packet networks. ITU-T G.8271 Recommendation ITU-T G.8271/Y.1366 (2017), Time and phase synchronization aspects of packet networks. ITU-T G.8271.1 Recommendation ITU-T G.8271.1/Y.1366.1 (20173), Network limits for time synchronization in packet networks. ITU-T
35、G.8273 Recommendation ITU-T G.8273/Y.1368 (2013), Framework of phase and time clocks. ITU-T G.8275 Recommendation ITU-T G.8275/Y.1369 (2017), 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 proto
36、col telecom profile for phase/time synchronization with full timing support from the network. 3 Definitions 3.1 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 Th
37、is 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 max|TE| Maximum absolute Time Error MTIE Maximum Time Interval Error NE
38、Network Element Rec. ITU-T G.8273.3/Y.1368.3 (10/2017) 3 PEC Packet-based Equipment Clock PP Packet Processing PPS Pulse Per Second PRTC Primary Reference Time Clock PTP Precision Time Protocol SDH Synchronous Digital Hierarchy SEC SDH equipment slave clock SSM Synchronization Status Message SyncE S
39、ynchronous Ethernet T-GM Telecom Grandmaster T-TC Telecom Transparent Clock TDEV Time Deviation TE Time Error 5 Conventions None. 6 Physical layer frequency performance requirements The list of applicable physical layer frequency interfaces is provided in clause 8.2. The following applies for the sy
40、nchronous Ethernet (SyncE) and synchronous digital hierarchy (SDH) interfaces. Synchronous Ethernet interfaces and synchronous Ethernet equipment clocks (EECs) used in combination with the telecom transparent clock (T-TC) are specified in ITU-T G.8262, and generate and process Ethernet synchronizati
41、on messaging channel (ESMC) messages as specified in ITU-T G.8264. Synchronous digital hierarchy interfaces and SDH equipment slave clocks (SECs) used in combination with the T-TC are specified in ITU-T G.813, and generate and process synchronization status message (SSM) messages as specified in ITU
42、-T G.781. NOTE The T-TC model in this Recommendation does not exclude 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.8
43、03 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 precision time protocol (PTP) output is for further study. 7 Packet layer performance requirements 7.1 Constant phase/time error and dynamic
44、time error noise generation The noise generation of an T-TC represents the amount of noise produced at the output of the T-TC when there is an ideal input reference packet timing signal and, if the T-TC is supporting physical layer frequency reference, an ideal physical layer reference. The noise ge
45、neration is characterized by three parameters: maximum absolute time error (max|TE|), constant phase/time error (cTE) and dynamic time error (dTE) noise generation. 4 Rec. ITU-T G.8273.3/Y.1368.3 (10/2017) To support different performance requirements at the end application specified in Table 1 of I
46、TU-T G.8271 using different network topologies and network technologies, the max|TE|, cTE and dTE noise generation requirements for T-TCs are divided into two classes: Class A and Class B. A T-TC with physical layer support must meet the requirements stated in clauses 7.1.1, 7.1.2 and 7.1.3. 7.1.1 M
47、aximum absolute time error generation The time output of the T-TC should be accurate to within the max|TE|. This value includes all the unfiltered noise components, i.e., the cTE and the dTE noise generation. Table 1 Maximum absolute time error T-TC Class Maximum absolute time error max|TE| (ns) A 1
48、00 ns B 70 ns NOTE The values in Table 1 are valid for 1 Gigabit Ethernet (GbE) and 10 GbE interfaces. Values for signals above 10 GbE or below 1 GbE are for further study. 7.1.2 Constant phase/time error generation At the PTP outputs, the cTE generation for Class A and Class B is shown in Table 2.
49、Table 2 T-TC permissible range of cTE T-TC Class Permissible range of cTE(ns) A 50 B 20 NOTE 1 The values in Table 2 are valid for 1 GbE and 10 GbE interfaces. Values for signals above 10 GbE or below 1 GbE are for further study. NOTE 2 Constant time error and the method to estimate are defined in ITU-T G.8260. For the purpose of testing the limits in Table 2, an estimate of constant time error should be obtained by averaging the time error sequence over 1000 s.
