1、 International Telecommunication Union ITU-T G.8261/Y.1361TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (08/2013) 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 and synchronization aspects in packet networks Recommendation ITU-T G.8261/Y.1361 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIO
3、NS 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 RADIO-RELAY OR SA
4、TELLITE 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 DIGITAL LINE SYSTEM
5、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.8099 MPLS over Tr
6、ansport 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.8261/Y.1361 (08/2013) i Recommendation ITU-T G.8261/Y.1361 Timing and synchroniz
7、ation aspects in packet networks Summary Recommendation ITU-T G.8261/Y.1361 defines frequency synchronization aspects in packet networks. It specifies the maximum network limits of jitter and wander that shall not be exceeded. It specifies the minimum equipment tolerance to jitter and wander that sh
8、all be provided at the boundary of these packet networks at TDM and synchronization interfaces. It also outlines the minimum requirements for the synchronization function of network elements. The requirements for the jitter and wander characteristics that are specified in this Recommendation must be
9、 adhered to in order to ensure interoperability of equipment produced by different manufacturers and a satisfactory network performance. History Edition Recommendation Approval Study Group 1.0 ITU-T G.8261/Y.1361 2006-05-22 15 1.1 ITU-T G.8261/Y.1361 (2006) Cor. 1 2006-12-14 15 2.0 ITU-T G.8261/Y.13
10、61 2008-04-29 15 2.1 ITU-T G.8261/Y.1361 (2008) Amd. 1 2010-07-29 15 3.0 ITU-T G.8261/Y.1361 2013-08-29 15 ii Rec. ITU-T G.8261/Y.1361 (08/2013) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and commu
11、nication 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 a worldwide basis. Th
12、e 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 down in WTSA Resolution
13、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 administration and a
14、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 provisions are met.
15、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 RIGHTS ITU draws attention to the possibili
16、ty 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 outside of the Recom
17、mendation development 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
18、 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.8261/Y.1361 (08/2013) iii Table of Content
19、s Page 1 Scope 1 2 References. 1 3 Definitions 3 3.1 Terms defined elsewhere 3 3.2 Terms defined in this Recommendation . 4 4 Abbreviations and acronyms 5 5 Conventions 6 6 General 7 6.1 Packet network synchronization requirements . 7 6.2 TDM timing requirements 8 6.3 Synchronization network enginee
20、ring in packet networks . 9 6.4 Timing requirements at edge versus timing requirements in core networks 9 6.5 PNT domain and CES domain . 9 7 Reference timing signal distribution over packet networks (PNT domain) . 9 7.1 Plesiochronous and network synchronous methods . 10 7.2 Packet-based methods 11
21、 8 Timing recovery for constant bit rate services transported over packet networks (CES domain) . 12 8.1 Network synchronous operation . 13 8.2 Differential methods . 13 8.3 Adaptive methods . 14 8.4 Reference clock available at the TDM end systems . 14 9 Network limits 15 9.1 CES network limits . 1
22、5 9.2 PNT network limits 19 10 Impact of impairments in the packet network on timing distribution and service clock recovery . 25 10.1 Packet transfer delay and delay variation . 27 10.2 Impacts from packet impairments 31 11 Impact of the reference clock impairment on the service clock recovery 32 1
23、1.1 Impairments for the network synchronous operation methods 32 11.2 Impairments for the differential method . 33 12 Results and consequences of the different synchronization methods over packet network reference models . 34 12.1 CES domain recommendations 34 12.2 PNT domain recommendations 36 Anne
24、x A Proposed network architecture for synchronous Ethernet . 38 iv Rec. ITU-T G.8261/Y.1361 (08/2013) Page A.1 PRC Location . 38 A.2 Limiting jitter and wander of synchronous Ethernet 38 A.3 Considerations on the design of synchronization network based on synchronous Ethernet . 39 A.4 Example of tim
25、ing distribution via synchronous Ethernet . 40 A.5 Interworking of Ethernet and synchronous Ethernet interfaces . 40 Annex B IWF functional partitioning into CES and PNT IWF and network examples . 45 B.1 General . 45 B.2 IWF clocks 47 B.3 Network examples 49 Annex C CES IWF synchronization related r
26、equirements . 51 C.1 Traffic interfaces 51 C.2 Synchronization interfaces . 51 C.3 IWF synchronization function 52 Annex D Network applications and requirements for clocks specified in ITU-T G.8262/Y.1362 . 53 Appendix I Characteristics of Ethernet switches, Ethernet networks, routers and access tec
27、hnologies 54 I.1 Characteristics of Ethernet switches and networks 54 I.2 Delay characteristics of routers 58 I.3 Delay characteristics of access technologies (Microwave nodes, PON, DSL) . 58 Appendix II Stabilization period . 59 Appendix III Considerations on packet-based methods . 60 Appendix IV A
28、pplications and use cases 61 IV.1 Background 61 IV.2 Wireless 61 IV.3 Infrastructure 63 IV.4 Media gateway 63 Appendix V Packet networks reference models . 64 V.1 Ethernet networks models 64 V.2 Other network models 66 Appendix VI Measurement guidelines for packet-based methods . 70 VI.1 Measurement
29、 reference points 70 VI.2 Input traffic characteristics . 71 VI.3 Test topologies for adaptive methods . 72 VI.4 Test Topologies for differential methods . 79 VI.5 Test for two-way protocols . 80 Appendix VII Wander limits in Deployment Case 1 88 Rec. ITU-T G.8261/Y.1361 (08/2013) v VII.1 Limits for
30、 the 2048 kbit/s interface 88 Page VII.2 Limits for the 1544 kbit/s interface 89 Appendix VIII Synchronization status messaging in synchronous Ethernet PHY . 90 Appendix IX IWF examples . 91 Appendix X Considerations on measurement of synchronous Ethernet according to ITU-T methodologies in comparis
31、on with IEEE jitter measurements . 94 Appendix XI Relationship between requirements contained in this Recommendation and other key synchronization related Recommendations . 95 Appendix XII Basic principles of timing over packet networks . 98 XII.1 General . 98 XII.2 Packet delay variation mitigation
32、 by packet selection . 101 XII.3 Comparison of packet-based and synchronous PHY methods . 101 XII.4 Existing standards . 102 Appendix XIII Evaluation of the packet delay variation generation in a network node 103 XIII.1 Introduction 103 XIII.2 General considerations . 103 XIII.3 General configuratio
33、n . 103 Bibliography. 105 Rec. ITU-T G.8261/Y.1361 (08/2013) 1 Recommendation ITU-T G.8261/Y.1361 Timing and synchronization aspects in packet networks 1 Scope This Recommendation defines frequency synchronization aspects in packet networks. It specifies the maximum network limits of jitter and wand
34、er that shall not be exceeded. It specifies the minimum equipment tolerance to jitter and wander that shall be provided at the boundary of these packet networks at TDM and synchronization interfaces. It also outlines the minimum requirements for the synchronization function of network elements. In p
35、articular, two main issues are addressed in this Recommendation: the distribution of a synchronization network clock signal over a packet network (PNT domain), and the distribution of a service clock signal over a packet network (CES domain). NOTE The application of the transport of SDH signals over
36、 packet networks is only partly covered and some aspects are for further study. The packet networks that are in the scope of this Recommendation are currently limited to the following scenarios: Ethernet (IEEE 802.3, IEEE 802.1DTM, IEEE 802.1QTM and IEEE 802.1QayTM) MPLS IETF RFC 3031 and ITU-T G.81
37、10 IP IETF RFC 791 and IETF RFC 2460 The physical layer that is relevant to this Recommendation is the Ethernet media types as defined in IEEE 802.3. Other physical layers can be relevant and may be addressed in a future version of this Recommendation. 2 References The following ITU-T Recommendation
38、s 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 are therefore e
39、ncouraged 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 a stand-alone
40、 document, the status of a Recommendation. ITU-T G.691 Recommendation ITU-T G.691 (2006), Optical interfaces for single channel STM-64 and other SDH systems with optical amplifiers. ITU-T G.702 Recommendation ITU-T G.702 (1988), Digital hierarchy bit rates. ITU-T G.703 Recommendation ITU-T G.703 (20
41、01), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T G.705 Recommendation ITU-T G.705 (2000), Characteristics of plesiochronous digital hierarchy (PDH) equipment functional blocks. ITU-T G.781 Recommendation ITU-T G.781 (2008), Synchronization layer functions. ITU-T G.8
42、03 Recommendation ITU-T G.803 (2000), Architecture of transport networks based on the synchronous digital hierarchy (SDH). ITU-T G.811 Recommendation ITU-T G.811 (1997), Timing characteristics of primary reference clocks. 2 Rec. ITU-T G.8261/Y.1361 (08/2013) ITU-T G.812 Recommendation ITU-T G.812 (2
43、004), 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 (1988), Controlled slip rate objectives on an inter
44、national 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 and wander within digital networks which are based o
45、n 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.957 Recommendation ITU-T G.957 (2006), Optical interfaces for equipments and systems relating to th
46、e synchronous digital hierarchy. ITU-T G.959.1 Recommendation ITU-T G.959.1 (2008), Optical transport network physical layer interfaces. ITU-T G.8010 Recommendation ITU-T G.8010/Y.1306 (2004), Architecture of Ethernet layer networks. ITU-T G.8110 Recommendation ITU-T G.8110/Y.1370 (2005), MPLS layer
47、 network architecture. ITU-T G.8110.1 Recommendation ITU-T G.8110.1/Y.1370.1 (2006), Architecture of Transport MPLS (T-MPLS) layer network. ITU-T G.8260 Recommendation ITU-T G.8260 (2010), Definitions and terminology for synchronization in packet networks. ITU-T G.8261.1 Recommendation ITU-T G.8261.
48、1/Y1361.1 (2012), Packet delay variation network limits applicable to packet-based methods (Frequency synchronization). ITU-T G.8262 Recommendation ITU-T G.8262/Y.1362 (2010), Timing characteristics of synchronous Ethernet equipment slave clock. ITU-T G.8263 Recommendation ITU-T G.8263/Y.1363 (2012)
49、, Timing characteristics of packet-based equipment clocks. ITU-T G.8264 Recommendation ITU-T G.8264/Y.1364 (2008), Timing distribution through packet networks. ITU-T G.8265 Recommendation ITU-T G.8265/Y.1365 (2010), Architecture and requirements for packet-based frequency delivery. ITU-T G.8265.1 Recommendation ITU-T G.8265.1/Y.1365.1 (2010), Precision time protocol telecom profile for frequency synchronization. ITU-T
