1、 International Telecommunication Union ITU-T G.8261/Y.1361TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (04/2008) 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 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 Transport asp
6、ects G.8100G.8199 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 G.8261/Y.1361 (04/2008) i Recommendation ITU-T G.8261/Y.1361 Timing and synchronization aspe
7、cts in packet networks Summary Recommendation ITU-T G.8261/Y.1361 defines 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 shall be provided at t
8、he 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 adhered to in order
9、 to ensure interoperability of equipment produced by different manufacturers and a satisfactory network performance. Source Recommendation ITU-T G.8261/Y.1361 was approved on 29 April 2008 by ITU-T Study Group 15 (2005-2008) under Recommendation ITU-T A.8 procedure. Keywords Clock, jitter, synchroni
10、zation, wander. ii Rec. ITU-T G.8261/Y.1361 (04/2008) 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
11、 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 every four years, es
12、tablishes 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
13、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 voluntary. However, the
14、 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 negative equivalen
15、ts 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 the use of a claime
16、d 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 Recommendation, ITU had 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 2009 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 (04/2008) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 3 3.1 Terms defined elsewhere 3 3.2 Terms defined in th
19、is Recommendation. 3 4 Abbreviations 5 5 Conventions 6 6 General 6 6.1 Packet network synchronization requirements. 7 6.2 TDM timing requirements 8 6.3 Synchronization network engineering in packet networks. 8 6.4 Timing requirements at edge versus timing requirements in core networks 9 6.5 PNT doma
20、in and CES domain . 9 7 Reference timing signal distribution over packet networks (PNT domain) . 9 7.1 Plesiochronous and network synchronous methods. 9 7.2 Packet-based methods 11 8 Timing recovery for constant bit rate services transported over packet networks (CES domain) . 12 8.1 Network synchro
21、nous operation. 12 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. 15 9.2 PNT network limits 20 10 Impact of impairments in the packet network on timing distribution and service clock recovery.
22、 25 10.1 Packet transfer delay and delay variation. 26 10.2 Impacts from packet impairments 31 11 Impact of the reference clock impairment on the service clock recovery 32 11.1 Impairments for the network synchronous operation methods 32 11.2 Impairments for the differential method. 33 12 Results an
23、d consequences of the different synchronization methods over packet network reference models. 34 12.1 CES domain recommendations 34 12.2 PNT domain recommendations 36 Annex A Proposed network architecture for synchronous Ethernet. 38 A.1 PRC Location . 38 iv Rec. ITU-T G.8261/Y.1361 (04/2008) Page A
24、.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 timing distribution via synchronous Ethernet . 40 A.5 Interworking of Ethernet and synchronous Ethernet interfaces . 40 Annex B IWF f
25、unctional partitioning into CES and PNT IWF and network examples. 44 B.1 General . 44 B.2 IWF clocks 45 B.3 Network examples 48 Annex C CES IWF synchronization related requirements . 51 C.1 Traffic interfaces 51 C.2 Synchronization interfaces . 51 C.3 IWF synchronization function 52 Annex D Network
26、applications and requirements for clocks specified in G.8262/Y.1362 53 Appendix I Characteristics of Ethernet switches and networks 54 I.1 Delay characteristics of Ethernet switches . 54 I.2 Characteristics of switched Ethernet networks. 57 Appendix II Stabilization period. 59 Appendix III Considera
27、tions on packet-based methods . 60 Appendix IV Applications 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 67 Appendix VI Measurement guideline
28、s for packet-based methods . 71 VI.1 Measurement reference points 71 VI.2 Input traffic characteristics. 72 VI.3 Test topologies for adaptive methods. 73 VI.4 Test Topologies for differential methods . 80 VI.5 Test for two-way protocols. 81 Appendix VII Wander limits in Deployment Case 1 88 VII.1 Li
29、mits for the 2048 kbit/s interface 88 VII.2 Limits for the 1544 kbit/s interface 88 Appendix VIII Synchronization status messaging in synchronous Ethernet PHY. 89 Appendix IX IWF examples . 90 Rec. ITU-T G.8261/Y.1361 (04/2008) v Page Appendix X Considerations on measurement of synchronous Ethernet
30、according to ITU-T methodologies in comparison with IEEE jitter measurements . 93 Appendix XI Relationship between requirements contained in this Recommendation and other key synchronization related Recommendations . 94 Appendix XII Basic principles of timing over packet networks. 96 XII.1 General .
31、 96 XII.2 Packet delay variation mitigation by packet selection . 99 XII.3 Comparison of packet-based and synchronous PHY methods. 99 XII.4 Existing standards. 100 Bibliography. 101 Rec. ITU-T G.8261/Y.1361 (04/2008) 1 Recommendation ITU-T G.8261/Y.1361 Timing and synchronization aspects in packet n
32、etworks 1 Scope This Recommendation defines 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 shall be provided at the boundary of these packet ne
33、tworks at TDM and synchronization interfaces. It also outlines the minimum requirements for the synchronization function of network elements. In particular, two main issues are addressed in this Recommendation: the distribution of a synchronization network clock signal over a packet network (PNT dom
34、ain), and the distribution of a service clock signal over a packet network (CES domain). NOTE The application of the transport of SDH signals over 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 curre
35、ntly limited to the following scenarios: Ethernet IEEE 802.3, IEEE 802.1D, IEEE 802.1ad, IEEE 802.1Q and b-IEEE P802.1Qay MPLS IETF RFC 3031 and ITU-T G.8110 T-MPLS ITU-T G.8110.1 IP IETF RFC 791 and IETF RFC 2460 The physical layer that is relevant to this Recommendation is the Ethernet media types
36、 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 Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendati
37、on. 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 applying the most recent edition of the Recommendations and other references li
38、sted 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.691 Recommendation ITU-T G.691 (2006), Optical interfaces for single cha
39、nnel 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 (2001), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T G.705 Recommendation ITU-T G.705 (2000),
40、 Characteristics of plesiochronous digital hierarchy (PDH) equipment functional blocks. ITU-T G.803 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
41、 reference clocks. 2 Rec. ITU-T G.8261/Y.1361 (04/2008) 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
42、(SEC). ITU-T G.822 Recommendation ITU-T G.822 (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 Recommendati
43、on ITU-T G.824 (2000), The control of jitter and 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.95
44、7 Recommendation ITU-T G.957 (2006), Optical interfaces for equipments and systems relating to the 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), Architectu
45、re of Ethernet layer networks. ITU-T G.8110 Recommendation ITU-T G.8110/Y.1370 (2005), MPLS layer 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.8262 Recommendation ITU-T G.8262/Y.1362 (2007), Timing
46、characteristics of synchronous Ethernet equipment slave clock (EEC). ITU-T G.8264 Recommendation ITU-T G.8264/Y.1364 (2008), Timing distribution through packet networks. ITU-T O.171 Recommendation ITU-T O.171 (1997), Timing jitter and wander measuring equipment for digital systems which are based on
47、 the plesiochronous digital hierarchy (PDH). ITU-T O.172 Recommendation ITU-T O.172 (2005), Jitter and wander measuring equipment for digital systems which are based on the synchronous digital hierarchy (SDH). ITU-T Y.1411 Recommendation ITU-T Y.1411 (2003), ATM-MPLS network interworking Cell mode u
48、ser plane interworking. ITU-T Y.1540 Recommendation ITU-T Y.1540 (2002), Internet protocol data communication service IP packet transfer and availability performance parameters. ITU-T Y.1561 Recommendation ITU-T Y.1561 (2004), Performance and availability parameters for MPLS networks. ITU-T Y.1731 R
49、ecommendation ITU-T Y.1731 (2006), OAM functions and mechanisms for Ethernet based networks. IEEE 802 IEEE 802-2001, IEEE standard for local and metropolitan area networks: Overview and architecture . Rec. ITU-T G.8261/Y.1361 (04/2008) 3 IEEE 802.1D IEEE 802.1D-2004, IEEE Standard for local and metropolitan area networks: Media Access Control (MAC) Bridges . IEEE 802.1Q IEEE 802.1Q-2005, IEEE Standard for local and metropolitan area networks
