ITU-T G 8264-2017 Distribution of timing information through packet networks (Study Group 15).pdf

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.8264/Y.1364 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (08/2017) 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, NEXT-GENERATION NETWORKS, INTERNET OF THINGS AND SMART CITIES Internet protocol aspects Transport Distribution of timing information through packet networks Recommendation ITU-T G.8264/Y.1364 ITU-T G-SERIES RECOMMENDATIONS TRANS

3、MISSION 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.39

4、9 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 EQ

5、UIPMENTS 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 OVER

6、 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 Rec

7、ommendations. Rec. ITU-T G.8264/Y.1364 (08/2017) i Recommendation ITU-T G.8264/Y.1364 Distribution of timing information through packet networks Summary Recommendation ITU-T G.8264/Y.1364 outlines aspects of distribution of timing information through packet networks and initially focuses on Ethernet

8、 networks. A number of methods may be used to transfer frequency which may be physical-layer based or protocol-layer based. This Recommendation provides information on architectural aspects of timing flows in Ethernet networks which will form the basis for future work related to time and phase trans

9、fer. This Recommendation specifies the synchronization status message (SSM) protocol and formats for use with synchronous Ethernet. Adherence to the SSM formats specified in this Recommendation is required in order to ensure interoperability between synchronous Ethernet equipment involved in frequen

10、cy transfer. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.8264/Y.1364 2008-10-29 15 11.1002/1000/9420 1.1 ITU-T G.8264/Y.1364 (2008) Cor. 1 2009-11-13 15 11.1002/1000/10433 1.2 ITU-T G.8264/Y.1364 (2008) Amd. 1 2010-09-22 15 11.1002/1000/10927 1.3 ITU-T G.8264/Y.1364 (2

11、008) Cor. 2 2012-02-13 15 11.1002/1000/11526 1.4 ITU-T G.8264/Y.1364 (2008) Amd. 2 2012-02-13 15 11.1002/1000/11525 2.0 ITU-T G.8264/Y.1364 2014-05-14 15 11.1002/1000/12192 2.1 ITU-T G.8264/Y.1364 (2014) Amd. 1 2015-01-13 15 11.1002/1000/12390 2.2 ITU-T G.8264/Y.1364 (2014) Amd. 2 2016-04-13 15 11.1

12、002/1000/12810 3.0 ITU-T G.8264/Y.1364 2017-08-29 15 11.1002/1000/13321 Keywords ESMC, packet timing, physical timing, synchronization, synchronous Ethernet. _ * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations

13、 unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T G.8264/Y.1364 (08/2017) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU

14、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. The World Telecommunication Standardizat

15、ion 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 1. In some areas of information techno

16、logy 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 recognized operating agency. Complianc

17、e 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. The words “shall“ or some other obliga

18、tory 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 RIGHTSITU draws attention to the possibility that the practice or implementation

19、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 Recommendation development process. As of th

20、e date of approval of this Recommendation, ITU had not 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 co

21、nsult the TSB patent database at http:/www.itu.int/ITU-T/ipr/. 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.8264/Y.1364 (08/2017) iii Table of Contents Page 1 Scope . 1 2 References . 1

22、 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defined in this Recommendation . 2 4 Abbreviations and acronyms 3 5 Conventions 5 6 Packet network architectures 5 6.1 Network layers and synchronization 6 6.2 Layer network performance impacts on synchronization. 6 7 Timing flows . 6 8 Functi

23、onal blocks 7 9 Next generation timing architectures 9 9.1 Current synchronization based on SDH . 9 9.2 Synchronization performance . 9 9.3 Network evolution 9 9.4 Next generation synchronization networks 9 10 Frequency transfer using synchronous Ethernet . 10 10.1 Synchronous Ethernet: General 10 1

24、0.2 Operation modes . 11 11 SSM for synchronous Ethernet . 12 11.1 Packet-level SSM . 12 11.2 Sync selection based on SSM . 13 11.3 SSM for synchronous Ethernet: Format and protocol 13 11.4 ESMC PDU extensions 20 11.5 Interworking with existing synchronization networks . 20 11.6 SSM for clocks with

25、enhanced holdover 20 12 Use of synchronous Ethernet in a multi-operator context 20 12.1 Timing transparent transport of synchronous Ethernet client signals 21 12.2 Synchronization service provided by the carrier operator based on an interface providing a physical timing reference (generation of sync

26、hronous Ethernet interface) . 22 13 Synchronization management aspects 23 Annex A Reference source selection mechanism . 24 A.1 Requirements 24 A.2 Inputs 24 A.3 Internal oscillator 24 iv Rec. ITU-T G.8264/Y.1364 (08/2017) Page A.4 Internal physical timing flows Frequency ETY 24 A.5 Selection mechan

27、ism 24 A.6 Synchronization status message selection 25 A.7 Hybrid equipment selection function . 25 Appendix I Examples of timing flows 27 Appendix II Functional models based on ITU-T G.805 and ITU-T G.809 29 II.1 Background . 29 II.2 Application of ITU-T G.805 to the IWF 29 II.3 Timing information

28、transported over layer networks . 30 II.4 Functional model of Ethernet physical layer timing 31 II.5 Functional model for differential and adaptive methods 31 Bibliography. 34 Rec. ITU-T G.8264/Y.1364 (08/2017) 1 Recommendation ITU-T G.8264/Y.1364 Distribution of timing information through packet ne

29、tworks 1 Scope This Recommendation outlines the requirements on Ethernet networks with respect to frequency transfer. It specifies the synchronization status message (SSM) transport channel namely the Ethernet synchronization messaging channel (ESMC), protocol behaviour and message format. A number

30、of methods may be used to transfer frequency which may be physical-layer based or protocol-layer based. The method used will be dependent on the actual architecture and what may be supported. This Recommendation focuses on physical layer synchronization. The physical layer that is relevant to this R

31、ecommendation is the Ethernet media types defined in IEEE 802.3. Other physical layers may also be relevant and may be addressed, along with other packet technologies, in future versions of this Recommendation. This Recommendation also details the required architecture in formal modelling language.

32、Timing flows are used to describe where and how time and timing will flow through the architecture. Such flows describe what is functionally allowed as an acceptable timing source. Such a source may only be available for use within the equipment or may be available outside as a client service. 2 Ref

33、erences 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 and other references are subject to revision; us

34、ers 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. The reference to a document within this Recomme

35、ndation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.709 Recommendation ITU-T G.709/Y.1331 (2016), Interfaces for the optical transport network. ITU-T G.781 Recommendation ITU-T G.781 (2017), Synchronization layer functions. ITU-T G.803 Recommendation ITU-T G.

36、803 (2000), Architecture of transport networks based on the synchronous digital hierarchy (SDH). ITU-T G.805 Recommendation ITU-T G.805 (2000), Generic functional architecture of transport networks. ITU-T G.809 Recommendation ITU-T G.809 (2003), Functional architecture of connectionless layer networ

37、ks. ITU-T G.811 Recommendation ITU-T G.811 (1997), Timing characteristics of primary reference clocks. 2 Rec. ITU-T G.8264/Y.1364 (08/2017) 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 Reco

38、mmendation 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 international digital connection. ITU-T G.823 Recommendation ITU-T G.823 (2000), The control of jitter and wander within dig

39、ital 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 on the 1544 kbit/s hierarchy. ITU-T G.825 Recommendation ITU-T G.825 (2000), The control of jitter and wander within dig

40、ital networks which are based on the synchronous digital hierarchy (SDH). ITU-T G.8010 Recommendation ITU-T G.8010/Y.1306 (2004), Architecture of Ethernet layer networks. ITU-T G.8261 Recommendation ITU-T G.8261/Y.1361 (2013), Timing and synchronization aspects in packet networks. ITU-T G.8262 Recom

41、mendation ITU-T G.8262/Y.1362 (2015), Timing characteristics of a synchronous Ethernet equipment slave clock. IEEE 802 IEEE 802-2014, IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture. IEEE 802.1AX IEEE 802.1AX-2014, IEEE Standard for Local and Metropolitan Area Netwo

42、rks Link Aggregation. IEEE 802.3 IEEE 802.3 (2015), IEEE Standard for Ethernet 3 Definitions 3.1 Terms defined elsewhere This Recommendation uses the following terms defined elsewhere: 3.1.1 network clock ITU-T G.8261: The clock generating the network clock signal. 3.1.2 service clock ITU-T G.8261:

43、The clock generating the service clock signal. 3.2 Terms defined in this Recommendation This Recommendation defines the following terms: Rec. ITU-T G.8264/Y.1364 (08/2017) 3 3.2.1 Ethernet synchronization message channel: The logical channel carrying the synchronization status message (SSM) code rep

44、resenting the quality level of the synchronous Ethernet equipment clock (EEC), which is bonded to the physical layer. The structure of the channel is provided by an organizational specific slow protocol (OSSP). 3.2.2 non-sync operation mode: A synchronous Ethernet interface configured in non-synchro

45、nous mode is an interface that, for the receive side, does not pass the recovered clock to the system clock and is therefore not a candidate reference to the synchronization selection process. It does not process the Ethernet synchronization messaging channel (ESMC) that may be present and therefore

46、 cannot extract the quality level (QL) value. On the transmit side, its output frequency might be synchronized to the synchronous Ethernet equipment clock (EEC), but this remains unknown to the receive interface at the other termination of the link. Indeed, an interface in non-synchronous mode opera

47、tion does not generate an ESMC and therefore does not transmit a QL. Such an interface does not participate to the synchronization network and is functionally identical to an asynchronous interface, as defined in IEEE 802.3. 3.2.3 synchronous operation mode: A synchronous Ethernet interface can be c

48、onfigured in synchronous operation mode. Its receive side is able to extract the frequency of its input signal and pass it to a system clock (a synchronous Ethernet equipment clock (EEC) or a better quality clock. It processes the Ethernet synchronization messaging channel (ESMC) and extracts the qu

49、ality level (QL). This signal can now be used as a candidate frequency reference. The transmit part of the interface is locked to the output timing of the system clock and generates the ESMC to transport a QL. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: AAL1 Asynchronous transfer mode Adaptation Layer 1 AI Adapted Information ATM Asynchronous Transfer Mode BITS Building Integrated Timing Supply BS Base Stati