1、 International Telecommunication Union ITU-T G.8262/Y.1362TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2010) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Packet over Transport aspects Quality and availability targets SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTER
2、NET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Transport Timing characteristics of a synchronous Ethernet equipment slave clock Recommendation ITU-T G.8262/Y.1362 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TE
3、LEPHONE 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
4、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 DIGITAL NETWORKS G.800G.899 DIGITAL SECTIONS AND DIG
5、ITAL 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.
6、8099 MPLS over Transport aspects G.8100G.8199 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.8262/Y.1362 (07/2010) i Recommendation ITU-T G.8262/Y.1362 Timi
7、ng characteristics of a synchronous Ethernet equipment slave clock Summary Recommendation ITU-T G.8262/Y.1362 outlines requirements for timing devices used in synchronizing network equipment that uses synchronous Ethernet. This Recommendation defines the requirements for clocks, e.g., bandwidth, fre
8、quency accuracy, holdover and noise generation. History Edition Recommendation Approval Study Group 1.0 ITU-T G.8262/Y.1362 2007-08-13 15 1.1 ITU-T G.8262/Y.1362 (2007) Amend. 1 2008-04-29 15 1.2 ITU-T G.8262/Y.1362 (2007) Amend.2 2010-01-13 15 2.0 ITU-T G.8262/Y.1362 2010-07-29 15 Keywords Clock, j
9、itter, synchronization, wander. ii Rec. ITU-T G.8262/Y.1362 (07/2010) 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 Sec
10、tor (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 Telecommunication Standardization Assembly (WTSA), which meets ever
11、y 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 information technology which fall within ITU-Ts purview
12、, 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 agency. Compliance with this Recommendation is volunta
13、ry. 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 some other obligatory language such as “must“ and the
14、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 or implementation of this Recommendation may involve t
15、he 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 process. As of the date of approval of this Recommend
16、ation, 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 strongly urged to consult the TSB patent database at http:/w
17、ww.itu.int/ITU-T/ipr/. ITU 2010 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.8262/Y.1362 (07/2010) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Co
18、nventions 3 6 Frequency accuracy 3 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
19、Wander tolerance 9 9.2 Jitter tolerance 11 10 Noise transfer 13 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 . 15 11.2 Long-term phase transient response (Holdover) 16 11.3 Phase response to input signal in
20、terruptions 18 11.4 Phase discontinuity . 18 12 Interfaces. 19 12.1 External synchronization interfaces . 19 Appendix I Hybrid network elements (NEs) using STM-N and Ethernet (ETY) interfaces . 21 Appendix II Relationship between requirements contained in this Recommendation and other key synchroniz
21、ation-related Recommendations 22 Appendix III List of Ethernet interfaces applicable to synchronous Ethernet 23 iv Rec. ITU-T G.8262/Y.1362 (07/2010) Introduction The synchronous Ethernet method refers to the primary reference clock (PRC) distributed method (for instance, based on the global navigat
22、ion satellite system (GNSS), or the master-slave method using a synchronous physical layer (e.g., ETY, STM-N). These methods are widely implemented to synchronize the TDM networks. Rec. ITU-T G.8262/Y.1362 (07/2010) 1 Recommendation ITU-T G.8262/Y.1362 Timing characteristics of a synchronous Etherne
23、t equipment slave clock 1 Scope This Recommendation outlines minimum requirements for timing devices used in synchronizing network equipment that supports synchronous Ethernet. It supports clock distribution based on network-synchronous line-code methods (e.g., synchronous Ethernet). This Recommenda
24、tion allows for proper network operation when an 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 requir
25、ements apply under the normal 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 fo
26、r the 2048-kbit/s hierarchy. 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
27、-kbit/s hierarchy. The synchronization 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 claus
28、es where one requirement 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 consider
29、ation should be taken when interworking between networks with synchronous Ethernet based on EEC-Option 1 and networks with synchronous Ethernet based on EEC-Option 2. Some synchronous Ethernet NEs may have a higher-quality clock. This Recommendation allows for proper network operation when a synchro
30、nous Ethernet equipment (EEC-Option 1 or 2) is timed from either another synchronous Ethernet equipment (like option), or from a SEC, or a higher-quality clock. Hierarchical timing distribution is recommended for synchronous Ethernet networks. Timing should not be passed from a synchronous Ethernet
31、in free-run/holdover mode to a higher-quality clock since the higher-quality clock should not follow the synchronous Ethernet signal during fault conditions. Certain Ethernet equipments such as regenerators/repeaters must provide through-timing capability to transmit timing via synchronous Ethernet.
32、 These equipments are for further study. 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 an
33、d other references are subject 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. T
34、he reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.703 Recommendation ITU-T G.703 (2001), Physical/electrical characteristics of hierarchical digital interfaces. 2 Rec. ITU-T G.8262/Y.1362 (07/2010) ITU-T G.781 R
35、ecommendation ITU-T G.781 (1999), Synchronization layer functions. ITU-T G.783 Recommendation ITU-T G.783 (2006), Characteristics of synchronous digital hierarchy (SDH) equipment functional blocks. ITU-T G.801 Recommendation ITU-T G.801 (1988), Digital transmission models. ITU-T G.803 Recommendation
36、 ITU-T G.803 (2000), 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. ITU-T G.811 Recommendation ITU-T G.811 (1997), Timing characteristics of primary referenc
37、e clocks. ITU-T G.812 Recommendation ITU-T G.812 (2004), Timing requirements 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.822 Recommendation ITU-T G.822
38、(1988), Controlled slip rate objectives on an international digital connection. ITU-T G.823 Recommendation ITU-T G.823 (2000), The control of jitter and wander within digital networks which are based on the 2048 kbit/s hierarchy. ITU-T G.824 Recommendation ITU-T G.824 (2000), The control of jitter a
39、nd wander within digital networks which are based on the 1544 kbit/s hierarchy. ITU-T G.825 Recommendation ITU-T G.825 (2000), The control of jitter and wander within digital networks which are based on the synchronous digital hierarchy (SDH). ITU-T G.8010 Recommendation ITU-T G.8010/Y.1306 (2004),
40、Architecture of Ethernet layer networks. 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), Timing distribution through packet networks. ITU-T Q.551 Recommendation ITU-T Q.551 (2002),
41、Transmission characteristics of digital exchanges. IEEE 802.3 IEEE Standard 802.3-2008, Information technology Telecommunications and information exchange between systems Local and metropolitan area networks Specific requirements Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/C
42、D) Access Method and Physical Layer Specifications. 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 following abbreviations and acronyms: EEC synchronous Ethernet Equipment Clock ETH Ethernet
43、MAC layer network Rec. ITU-T G.8262/Y.1362 (07/2010) 3 ETY Ethernet PHY layer network GNSS Global Navigation Satellite System MTIE Maximum Time Interval Error NE Network Element OAM Operation, Administration and Maintenance PRC Primary Reference Clock SDH Synchronous Digital Hierarchy SEC SDH Equipm
44、ent Clock SSU Synchronization Supply Unit STM Synchronous Transport Module TDEV Time Deviation UI Unit Interval UTC Coordinated Universal Time 5 Conventions This clause is intentionally left blank. 6 Frequency accuracy 6.1 EEC-Option 1 Under free-running conditions, the EEC output frequency accuracy
45、 should not be greater than 4.6 ppm with regard to a reference traceable to a ITU-T G.811 clock. NOTE The time interval for this accuracy is for further study. Values of 1 month and 1 year have been proposed. 6.2 EEC-Option 2 Under prolonged holdover conditions, the output frequency accuracy of the
46、different types of node clocks should not exceed 4.6 ppm with regard to a reference traceable to a primary reference clock, over a time period T of 1 year. NOTE The time period T applies after 30 days of continuous synchronized operation. 7 Pull-in, hold-in, and pull-out ranges 7.1 Pull-in range 7.1
47、.1 EEC-Option 1 The minimum pull-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. 4 Rec. ITU-T G.8262/Y.1362 (07/2010) 7.2 Hold-in range 7.2.
48、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 pull-out range is for further study. A minimum value of 4.6
49、ppm has been proposed. 7.3.2 EEC-Option 2 The pull-out range is not applicable. 8 Noise generation The noise generation of an EEC represents the amount of phase noise produced at the output when there is an ideal input reference signal or the clock is in holdover state. A suitable reference, for practical testing purposes, implies a performance level at least 10 times more stable than the output requirements. The ability of the clock to limit this noise is described by its frequency
