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.8262/Y.1362 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (01/2015) 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 AND NEXT-GENERATION NETWORKS Internet protocol aspects Transport Timing characteristics of synchronous Ethernet equipment slave clock Recommendation ITU-T G.8262/Y.1362 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.8262/Y.1362 (01/2015) i Recommendation ITU-T G.8262/Y.1362 Timing characteristics of synchronous Ethernet equipment slave clock Summary Recommendation ITU-T G.8262/Y.1362 outlines requirements for timing devices used in synchronizing network equipments that use synchronous Ethernet. This Recommen
8、dation defines the requirements for clocks, e.g., bandwidth, frequency accuracy, holdover and noise generation. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.8262/Y.1362 2007-08-13 15 11.1002/1000/9190 1.1 ITU-T G.8262/Y.1362 (2007) Amd. 1 2008-04-29 15 11.1002/1000/9417
9、 1.2 ITU-T G.8262/Y.1362 (2007) Amd.2 2010-01-13 15 11.1002/1000/10432 2.0 ITU-T G.8262/Y.1362 2010-07-29 15 11.1002/1000/10909 2.1 ITU-T G.8262/Y.1362 (2010) Amd. 1 2012-02-13 15 11.1002/1000/11523 2.2 ITU-T G.8262/Y.1362 (2010) Amd. 2 2012-10-29 15 11.1002/1000/11814 3.0 ITU-T G.8262/Y.1362 2015-0
10、1-13 15 11.1002/1000/12389 Keywords Clock, jitter, synchronization, wander. _ * 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
11、 G.8262/Y.1362 (01/2015) 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-
12、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, establishes the topics for stud
13、y 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 c
14、ollaborative 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 c
15、ertain 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 requ
16、irements. 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 Righ
17、t. 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 received notice of intellectual
18、 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 2015 All rights res
19、erved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. Rec. ITU-T G.8262/Y.1362 (01/2015) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Conventions 3 6 Frequency accuracy 3
20、 6.1 EEC-Option 1 . 3 6.2 EEC-Option 2 . 3 7 Pull-in, hold-in and pull-out ranges 3 7.1 Pull-in range . 3 7.2 Hold-in range 4 7.3 Pull-out range . 4 8 Noise generation . 4 8.1 Wander in locked mode 4 8.2 Non-locked wander 7 8.3 Jitter 7 9 Noise tolerance . 8 9.1 Wander tolerance 9 9.2 Jitter toleran
21、ce 11 10 Noise transfer 14 10.1 EEC-Option 1 . 14 10.2 EEC-Option 2 . 14 11 Transient response and holdover performance . 15 11.1 Short-term phase transient response . 16 11.2 Long-term phase transient response (holdover) . 17 11.3 Phase response to input signal interruptions 19 11.4 Phase discontin
22、uity . 19 12 Interfaces . 20 12.1 External synchronization interfaces . 20 Appendix I Hybrid network elements using STM-N and Ethernet (ETY) interfaces 22 Appendix II Relationship between requirements contained in this Recommendation and other key synchronization-related Recommendations 23 Appendix
23、III List of Ethernet interfaces applicable to synchronous Ethernet 24 Appendix IV Considerations related to synchronous Ethernet over 1000BASE-T and 10GBASE-T . 28 Appendix V Considerations for measuring noise transfer for EEC-Option 2 clocks . 30 Bibliography. 31 iv Rec. ITU-T G.8262/Y.1362 (01/201
24、5) Introduction The synchronous Ethernet method refers to the primary reference clock (PRC) or primary reference time clock (PRTC) distributed method (for instance, based on the global navigation satellite system (GNSS), or the master-slave method using a synchronous physical layer (e.g., ETY, STM-N
25、). These methods are widely implemented to synchronize time division multiplexing (TDM) and mobile backhaul networks. Rec. ITU-T G.8262/Y.1362 (01/2015) 1 Recommendation ITU-T G.8262/Y.1362 Timing characteristics of synchronous Ethernet equipment slave clock 1 Scope This Recommendation outlines mini
26、mum requirements for timing devices used in synchronizing network equipments that support synchronous Ethernet. It supports clock distribution based on the network-synchronous line-code methods (e.g., synchronous Ethernet). This Recommendation allows for proper network operation when a synchronous E
27、thernet equipment clock (EEC) (Option 1 or 2) is timed from another network equipment clock or a higher-quality clock. Included in this Recommendation are requirements for clock accuracy, noise transfer, holdover performance, noise tolerance and noise generation. These requirements apply under the n
28、ormal environmental conditions specified for the equipment. This Recommendation contains two options for synchronous Ethernet. The first option, referred to as “EEC-Option 1“, applies to synchronous Ethernet equipments that are designed to interwork with networks optimized for the 2048-kbit/s hierar
29、chy. These networks allow the worst-case synchronization reference chain as specified in Figure 8-5 of ITU-T G.803. The second option, referred to as “EEC-Option 2“, applies to synchronous Ethernet equipments that are designed to interwork with networks optimized for the 1544-kbit/s hierarchy. The s
30、ynchronization reference chain for these networks is defined in clause II.3 of ITU-T G.813. A synchronous Ethernet equipment slave clock should comply with all of the requirements specific to one option and should not mix requirements between EEC-Options 1 and 2. In the clauses where one requirement
31、 is specified, the requirements are common to both options. It is the intention that EEC-Options 1 and 2 should be harmonized in the future. The intent of the synchronous Ethernet is to interoperate with existing synchronization networks based on ITU-T G.813. Careful consideration should be taken wh
32、en interworking between networks with synchronous Ethernet based on EEC-Option 1 and networks with synchronous Ethernet based on EEC-Option 2. Some synchronous Ethernet network elements (NEs) may have a higher-quality clock. This Recommendation allows for proper network operation when a synchronous
33、Ethernet equipment (EEC-Option 1 or 2) is timed from either another synchronous Ethernet equipment (like option), or from a SDH equipment clock (SEC), or a higher-quality clock. Hierarchical timing distribution is recommended for synchronous Ethernet networks. Timing should not be passed from a sync
34、hronous Ethernet in free-run/holdover mode to a higher-quality clock since the higher-quality clock should not follow the synchronous Ethernet signal during the fault conditions. Certain Ethernet equipments, such as regenerators/repeaters, must provide through-timing capability to transmit timing vi
35、a synchronous Ethernet. These equipments are for further study. More information on synchronous Ethernet can be found in ITU-T G.781, ITU-T G.8261 and ITU-T G.8264. 2 Rec. ITU-T G.8262/Y.1362 (01/2015) 2 References The following ITU-T Recommendations and other references contain provisions which, th
36、rough 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 are therefore encouraged to investigate the possibility of applyin
37、g 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 a stand-alone document, the status of a Recommendation. ITU-T G.
38、703 Recommendation ITU-T G.703 (2001), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T G.781 Recommendation ITU-T G.781 (1999), Synchronization layer functions. ITU-T G.803 Recommendation ITU-T G.803 (2000), Architecture of transport networks based on the synchronous di
39、gital hierarchy (SDH). ITU-T G.810 Recommendation ITU-T G.810 (1996), Definitions and terminology for synchronization networks. ITU-T G.811 Recommendation ITU-T G.811 (1997), Timing characteristics of primary reference clocks. ITU-T G.812 Recommendation ITU-T G.812 (2004), Timing requirements of sla
40、ve 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.825 Recommendation ITU-T G.825 (2000), The control of jitter and wander within digital networks which are based on
41、 the synchronous digital hierarchy (SDH). ITU-T G.8261 Recommendation ITU-T G.8261/Y.1361 (2008), Timing and synchronization aspects in packet networks. ITU-T G.8264 Recommendation ITU-T G.8264/Y.1364 (2008), Distribution of timing information through packet networks. ITU-T G.8272 Recommendation ITU
42、-T G.8272 (2015), Timing characteristics of primary reference time clocks. IEEE 802.3 IEEE Standard 802.3 (2012), IEEE Standard for Ethernet. 3 Definitions The terms and definitions used in this Recommendation are contained in ITU-T G.810. 4 Abbreviations and acronyms This Recommendation uses the fo
43、llowing abbreviations and acronyms: BITS Building Integrated Timing Source BPSK Binary Phase Shift Keying CSMA/CD Carrier Sense Multiple Access with Collision Detection DSL Digital Subscriber Line EC Equipment Clock EEC synchronous Ethernet Equipment Clock Rec. ITU-T G.8262/Y.1362 (01/2015) 3 ESMC E
44、thernet Synchronization Message Channel ETH Ethernet MAC layer network ETY Ethernet PHY layer network GNSS Global Navigation Satellite System MAC Media Access Control MTIE Maximum Time Interval Error NE Network Element NRZ Non-Return to Zero OAM Operations, Administration and Maintenance PAM Pulse A
45、mplitude Modulation PHY Physical (layer) ppm parts per million PRC Primary Reference Clock PRTC Primary Reference Time Clock SDH Synchronous Digital Hierarchy SEC SDH Equipment Clock SSM Synchronization Message Channel SSU Synchronization Supply Unit STM-N Synchronous Transport Module-N TDEV Time De
46、viation TDM Time Division Multiplexing UI Unit Interval UTC Coordinated Universal Time 5 Conventions None. 6 Frequency accuracy 6.1 EEC-Option 1 Under free-running conditions, the EEC output frequency accuracy should not be greater than 4.6 ppm with regard to a reference traceable to a ITU-T G.811 o
47、r ITU-T G.8272 clock. NOTE The time interval for this accuracy is for further study. Values of one month and one year have been proposed. 6.2 EEC-Option 2 Under prolonged holdover conditions, the output frequency accuracy of the different types of node clocks should not exceed 4.6 ppm with regard to
48、 a reference traceable to a primary reference clock, over a time period T of one year. NOTE The time period T applies after 30 days of continuous synchronized operation. 4 Rec. ITU-T G.8262/Y.1362 (01/2015) 7 Pull-in, hold-in and pull-out ranges 7.1 Pull-in range 7.1.1 EEC-Option 1 The minimum pull-
49、in range should be 4.6 ppm, whatever the internal oscillator frequency offset may be. 7.1.2 EEC-Option 2 The minimum pull-in range should be 4.6 ppm, whatever the internal oscillator frequency offset may be. 7.2 Hold-in range 7.2.1 EEC-Option 1 The hold-in range for EEC-Option 1 is not required. 7.2.2 EEC-Option 2 The hold-in range for EEC-Option 2 should be 4.6 ppm, whatever the internal oscillator frequency offset may be. 7.3 Pull-out range 7.3.1 EEC-Option 1 The
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