1、 International Telecommunication Union ITU-T G.8261.1/Y.1361.1TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (02/2012) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Packet over Transport aspects Quality and availability targets SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, I
2、NTERNET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Transport Packet delay variation network limits applicable to packet-based methods (Frequency synchronization) Recommendation ITU-T G.8261.1/Y.1361.1 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL
3、 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 CHARACTERISTICS OF INTER
4、NATIONAL 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 DIGITAL NETWOR
5、KS 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.8000G.8999 Et
6、hernet over Transport aspects G.8000G.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.8261.1/Y.1361.1 (02/2012)
7、 i Recommendation ITU-T G.8261.1/Y.1361.1 Packet delay variation network limits applicable to packet-based methods (Frequency synchronization) Summary Recommendation ITU-T G.8261.1/Y.1361.1 depicts synchronization aspects in packet networks. In particular, it specifies the hypothetical reference mod
8、el and the PDV network limits applicable when frequency synchronization is carried via packets and is recovered according to an adaptive clock recovery method as defined in Recommendations ITU-T G.8261 and ITU-T G.8260. It specifies the minimum equipment tolerance to packet delay variation in terms
9、of the metrics defined in Recommendation ITU-T G.8260 at the boundary of these packet networks. History Edition Recommendation Approval Study Group 1.0 ITU-T G.8261.1/Y.1361.1 2012-02-13 15 Keywords PDV, synchronization. ii Rec. ITU-T G.8261.1/Y.1361.1 (02/2012) FOREWORD The International Telecommun
10、ication 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-T is responsible for studying technical, operating and tariff
11、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 study by the ITU-T study groups which, in turn, produce Recommenda
12、tions 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 collaborative basis with ISO and IEC. NOTE In this Recommendati
13、on, 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 certain mandatory provisions (to ensure, e.g., interoperability
14、 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 requirements. The use of such words does not suggest that complian
15、ce 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 claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or
16、 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 property, protected by patents, which may be required to imp
17、lement 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 2012 All rights reserved. No part of this publication may be reproduced, by any
18、means whatsoever, without the prior written permission of ITU. Rec. ITU-T G.8261.1/Y.1361.1 (02/2012) iii Table of Contents Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Conventions 3 6 General 3 7 Network reference model . 3 7.1 Hypothetical reference models . 3 7.
19、2 Reference points for network limits in packet networks 6 8 PDV network limit 8 Bibliography. 10 Rec. ITU-T G.8261.1/Y.1361.1 (02/2012) 1 Recommendation ITU-T G.8261.1/Y.1361.1 Packet delay variation network limits applicable to packet-based methods (Frequency synchronization) 1 Scope This Recommen
20、dation relays synchronization aspects in packet networks. In particular, it specifies the hypothetical reference model (HRM) and the PDV network limits applicable when frequency synchronization is carried via packets and is recovered according to the adaptive clock recovery method as defined in Reco
21、mmendations ITU-T G.8261 and ITU-T G.8260. It specifies the minimum equipment tolerance to packet delay variation in terms of the metrics defined in Recommendation ITU-T G.8260 at the boundary of these packet networks. Two main applications are addressed in this Recommendation: the distribution of a
22、 synchronization network clock signal via a packet based method (e.g., using PTP or NTP packets and using an adaptive approach), and the distribution of a service clock signal over a packet network according to an adaptive clock recovery method (e.g., clock recovery of a circuit emulation service (C
23、ES) using an adaptive method), however the details on the CES network limits are for further study. Both one-way and two-way methods are considered. The packet networks that are in the scope of this Recommendation are currently limited to the following scenarios: Ethernet (IEEE 802.3, IEEE 802.1D, I
24、EEE 802.1 ad, IEEE 802.1Q, IEEE 802.1Qay) MPLS (IETF RFC 3031, ITU-T G.8110) IP (IETF RFC 791 and IETF RFC 2460) The physical layer that is relevant to this specification is the Ethernet media types as defined in IEEE Standard 802.3 2008. Other physical layers can be relevant and may be addressed in
25、 future versions 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 Recommendation. At the time of publication, the editions indicated were valid. All Recommendations an
26、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
27、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.803 Recommendation ITU-T G.803 (2000), Architecture of transport networks based on the synchronous digital hierarchy (SDH). ITU-T G.810 Recommendation ITU-T G.81
28、0 (1996), Definitions and terminology for synchronization networks. 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 wi
29、thin digital networks which are based on the 1544 kbit/s hierarchy. 2 Rec. ITU-T G.8261.1/Y.1361.1 (02/2012) ITU-T G.8110 Recommendation ITU-T G.8110/Y.1370 (2005), MPLS layer network architecture. ITU-T G.8260 Recommendation ITU-T G.8260 (2012), Definitions and terminology for synchronization in pa
30、cket networks. ITU-T G.8261 Recommendation ITU-T G.8261/Y.1361 (2008), Timing and synchronization aspects in packet networks. ITU-T G.8263 Recommendation ITU-T G.8263/Y.1363 (2012), Timing characteristics of packet-based equipment clocks. ITU-T G.8265 Recommendation ITU-T G.8265/Y.1365 (2010), Archi
31、tecture 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 O.172 Recommendation ITU-T O.172 (2005), Jitter and wander measuring equipment for digital systems
32、which are based on the synchronous digital hierarchy (SDH). IEEE 802 IEEE 802-2001, IEEE standard for local and metropolitan area networks: Overview and architecture. IEEE 802.1ad IEEE 802.1adTM-2005, IEEE Standard for local and metropolitan area networks: Virtual bridged local area networks Amendme
33、nt 4: Provider Bridges. IEEE 802.1D IEEE 802.1DTM-2004, IEEE Standard for local and metropolitan area networks: Media Access Control (MAC) Bridges. IEEE 802.1Q IEEE 802.1QTM-2005, IEEE Standard for local and metropolitan area networks: Virtual bridged local area networks. IEEE 802.3 IEEE 802.3-2008,
34、 Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications. IETF RFC 791 IETF RFC 791 (1981), Internet Protocol. IETF RFC 2460 IETF RFC 2460 (1998), Internet Protocol, Version 6 (IPv6) Specification. IETF RFC 3031 IETF RFC 3031 (2001), M
35、ultiprotocol Label Switching Architecture. 3 Definitions The terms and definitions used in this Recommendation are found in ITU-T G.810 and ITU-T G.8260. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: CES Circuit Emulation Service DSL Digital Subscrib
36、er Line Rec. ITU-T G.8261.1/Y.1361.1 (02/2012) 3 DSLAM Digital Subscriber Line Access Multiplexer EEC Ethernet Equipment Clock HRM Hypothetical Reference Model MW Microwave OLT Optical Line Terminal ONU Optical Network Unit OTN Optical Transport Network PDV Packet Delay Variation PEC-M Packet-based
37、Equipment Clock Master PEC-S-F Packet based Equipment Clock Slave Frequency PNT-F Packet Network Timing Function PON Passive Optical Network PRC Primary Reference Clock PTP Precision Time Protocol SEC SDH Equipment Clock SSU Synchronization Supply Unit 5 Conventions None. 6 General The use of packet
38、-based methods as described in ITU-T G.8261 to deliver reference timing signals for the purpose of frequency synchronization, requires the control of the PDV generated in the network in order to meet acceptable performance requirements when using a packet clock with characteristics as specified in I
39、TU-T G.8263. This Recommendation defines the applicable network limits at all relevant points in a network. The network reference models and the related target performance requirements that are considered relevant for this application are described in clause 7. The related PDV limits are specified i
40、n clause 8. 7 Network reference model 7.1 Hypothetical reference models This clause provides hypothetical reference models which are assumed to correspond to the worst-case models for most of the mobile backhaul networks. NOTE The hypothetical reference models defined in this clause are assumed to b
41、e composed with network equipment generating a controlled amount of PDV, compatible with the network limits defined in clause 8. It is known that some network equipment may generate excessive PDV, leading potentially to exceed these PDV network limits. What constitutes a controlled amount of PDV, ho
42、w to determine if particular network equipment are suitable for being considered in these hypothetical reference models, or in a reduced hypothetical reference model, as well as, how to evaluate the level of PDV generated by a network equipment, is for further study. 4 Rec. ITU-T G.8261.1/Y.1361.1 (
43、02/2012) 7.1.1 HRM-1: network using only 1 Gbit/s and 10 Gbit/s connections The HRM-1 is shown in Figure 1 below; it is composed of a 1 Gbit/s link to connect the packet master clock to the first node, 3 10 Gbit/s fibre optical links and 7 1 Gbit/s fibre optical links. It is assumed to correspond to
44、 the worst case model for most of the mobile backhaul networks using only optical fibre connections. The packet delay variation network limits for the HRM-1 are specified in clause 8 of this Recommendation. G.8261.1-Y1361.1(12)_F01PacketmasterclockPacket networkN = 10PacketslaveclockPacket node (e.g
45、., ethernet switch, IP router, MPLS router)10 Gbit/s fibre optical link1 Gbit/s fibre optical linkFigure 1 HRM-1 for packet delay variation network limits NOTE 1 The link between the packet master clock and the first packet node may be 100 Mbit/s instead of 1 Gbit/s. NOTE 2 The link between the last
46、 packet node and the packet slave clock may be 100 Mbit/s instead of 1 Gbit/s in case it is only carrying PTPv2 messages and no data traffic. NOTE 3 The 1 Gbit/s links can be replaced by 10 Gbit/s links in a real deployment, but not the opposite. NOTE 4 The distribution of the links connecting the p
47、acket nodes has no importance (e.g., the 10 Gbit/s links may not always be at the beginning of the packet network); in general however, the 10 Gbit/s links are located in the core network. NOTE 5 Some of the links connecting the packet nodes may be carried over an OTN network, assuming that the PDV
48、generated by these transmission techniques is negligible compared to the PDV generated by the packet nodes of the HRM. Some of the links connecting the packet nodes may also be carried over an SDH network, this is for further study. NOTE 6 It is assumed that no frames larger than 2000 bytes are carr
49、ied over the links of the packet network carrying the PTPv2 messages. NOTE 7 The PTPv2 messages are assumed to be carried with the highest priority, and placed in a strict priority queue in the packet nodes; the other flows using this queue are for further study (it might be assumed that this queue either only contains PTPv2 messages, or that the other data traffic packets going also in this queue are small packets, and that the amount of data in the queue is mu
