1、 International Telecommunication Union ITU-T G.8271/Y.1366TELECOMMUNICATION 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, INTER
2、NET PROTOCOL ASPECTS AND NEXT-GENERATION NETWORKS Internet protocol aspects Transport Time and phase synchronization aspects of packet networks Recommendation ITU-T G.8271/Y.1366 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNE
3、CTIONS 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 O
4、R 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 DIGITAL LINE SYS
5、TEM 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 ove
6、r 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.8271/Y.1366 (02/2012) i Recommendation ITU-T G.8271/Y.1366 Time and phase sy
7、nchronization aspects of packet networks Summary Recommendation ITU-T G.8271/Y.1366 defines time and phase synchronization aspects in packet networks. It specifies the suitable methods to distribute the reference timing signals that can be used to recover the phase synchronization and/or time synchr
8、onization according to the required quality. The requirements for the synchronization characteristics that are specified in this Recommendation must be adhered to in order to ensure interoperability of equipment produced by different manufacturers and a satisfactory network performance. History Edit
9、ion Recommendation Approval Study Group 1.0 ITU-T G.8271/Y.1366 2012-02-13 15 ii Rec. ITU-T G.8271/Y.1366 (02/2012) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs).
10、 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. The World Telecommunication Sta
11、ndardization 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 informati
12、on 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 recognized operating agency.
13、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. The words “shall“ or some oth
14、er 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 possibility that the practice or imple
15、mentation 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
16、. As of the 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 u
17、rged 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 means whatsoever, without the prior written permission of ITU. Rec. ITU-T G.8271/Y.1366 (02/2012) iii Table of Contents Page 1 Scope 1 2 Refere
18、nces. 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Conventions 3 6 The need for phase and time synchronization 3 7 Time-phase synchronization methods 4 7.1 Distributed PRTC . 5 7.2 Packet based methods with timing support of intermediate nodes . 6 8 Network reference model . 7 9 Phase/time syn
19、chronization interfaces 9 Annex A One pulse-per-second (1PPS) phase and time synchronization interface specification 10 A.1 ITU-T V.11 interface 10 A.2 1PPS 50 phase synchronization measurement interface 11 Appendix I Time and phase noise sources in time distribution chains . 13 I.1 Noise introduced
20、 by a primary reference time clock (PRTC) 13 I.2 Noise introduced by a packet master clock function 13 I.3 Noise introduced by a packet slave clock function 13 I.4 Noise introduced by a telecom transparent clock . 13 I.5 Noise introduced by a link 14 I.6 Derivation of delay asymmetry 14 I.7 Characte
21、ristics of the noise sources 17 Appendix II Time and phase end application synchronization requirements . 20 Appendix III Asymmetry compensation for use of different wavelengths . 22 Bibliography. 23 Rec. ITU-T G.8271/Y.1366 (02/2012) 1 Recommendation ITU-T G.8271/Y.1366 Time and phase synchronizati
22、on aspects of packet networks 1 Scope This ITU-T Recommendation defines time and phase synchronization aspects in packet networks. It specifies the suitable methods to distribute the reference timing signals that can be used to recover the phase synchronization and/or time synchronization according
23、to the required quality. It also specifies the relevant time and phase synchronization interfaces and related performance. 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, IEEE 802.1ad, IEEE 802.1Q,
24、and IEEE 802.1Qay). MPLS (IETF RFC 3031 and ITU-T G.8110). IP (IETF RFC 791 and RFC 2460). The physical layer that is relevant to this specification is the Ethernet media types, as defined in IEEE Standard 802.3-2005. 2 References The following ITU-T Recommendations and other references contain prov
25、isions 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 encouraged to investigate the possib
26、ility 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 document, the status of a Recommen
27、dation. ITU-T G.810 Recommendation ITU-T G.810 (1996), Definitions and terminology for synchronization networks. 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 i
28、n packet networks. ITU-T G.8261 Recommendation ITU-T G.8261/Y.1361 (2008), Timing and synchronization aspects in packet networks. ITU-T V.11 Recommendation ITU-T V.11/X.27 (1996), Electrical characteristics for balanced double-current interchange circuits operating at data signalling rates up to 10
29、Mbit/s. IEEE 802 IEEE 802-2001, IEEE standard for local and metropolitan area networks: Overview and architecture. 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 metro
30、politan area networks: Virtual bridged local area networks. 2 Rec. ITU-T G.8271/Y.1366 (02/2012) IEEE 802.1ad IEEE 802.1ad-2005, IEEE Standard for local and metropolitan area networks: Virtual bridged local area networks Amendment 4: Provider Bridges. IEEE 802.3 IEEE 802.3-2008, Part 3: Carrier sens
31、e multiple access with collision detection (CSMA/CD) access method and physical layer specifications. IEEE 1588-2008 IEEE Std 1588-2008, Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems. . IETF RFC 791 IETF RFC 791 (1981), Internet Protocol (IP).
32、. IETF RFC 2460 IETF RFC 2460 (1998), Internet Protocol, Version 6 (IPv6) Specification. IETF RFC 3031 IETF RFC 3031 (2001), Multiprotocol Label Switching Architecture. 3 Definitions The terms and definitions used in this Recommendation are contained in ITU-T G.810, ITU-T G.8260 and IEEE 1588-2008.
33、4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: 1PPS One Pulse Per Second CDMA Code Division Multiple Access EEC Ethernet Equipment Clock FDD Frequency Division Duplex GNSS Global Navigation Satellite System GPS Global Positioning System HRPD High Rate
34、 Packet Data HRM Hypothetical Reference Model IP Internet Protocol LTE Long Term Evolution MBMS Multimedia Broadcast Multicast Service MBSFN MBMS based on Single Frequency Network NTP Network Time Protocol PDV Packet Delay Variation PHY Physical Layer Protocol PRTC Primary Reference Time Clock PTP P
35、recision Time Protocol RTT Radio Transmission Technology SCDMA Synchronized CDMA Rec. ITU-T G.8271/Y.1366 (02/2012) 3 SSU Synchronization Supply Unit TDD Time Division Duplexing T-BC Telecom Boundary Clock T-GM Telecom Grandmaster T-TC Telecom Transparent Clock T-TSC Telecom Time Slave Clock WCDMA W
36、ideband CDMA WDM Wavelength-Division-Multiplexing 5 Conventions Within this Recommendation, the following conventions are used: The term precision time protocol (PTP) is the protocol defined by IEEE 1588-2008. As an adjective, it indicates that the modified noun is specified in or interpreted in the
37、 context of IEEE 1588-2008. The term telecom boundary clock (T-BC) is a device consisting of a boundary clock as defined in IEEE1588-2008 and with additional performance characteristics for further study. The term telecom transparent clock (T-TC) is a device consisting of a transparent clock as defi
38、ned in IEEE1588-2008 and with additional performance characteristics for further study. The term telecom grandmaster (T-GM) is a device consisting of a grandmaster clock as defined in IEEE1588-2008 and with additional performance characteristics for further study. The term telecom time slave clock (
39、T-TSC) is a device consisting of a PTP slave only ordinary clock as defined in IEEE1588-2008 and with additional performance characteristics for further study. 6 The need for phase and time synchronization Time synchronization has traditionally been required to support billing and alarm functions (m
40、aintenance or fault isolation). In this context, synchronization must in general be accurate to within hundreds of milliseconds. Another time-synchronization application is the monitoring of delays in IP networks. In this case, the requirement is accuracy to within some hundreds of microseconds (the
41、 actual requirement depends on the application). Stringent time synchronization requirements (i.e., in the range of a few microseconds) apply to the generation of signals over the air interface of some mobile systems, such as CDMA2000 or LTE FDD unicast, when it is required to support synchronous CD
42、MA2000 interworking. Phase synchronization is often needed to support requirements for the air interface of some mobile systems, as in the case of TDD systems (for instance, LTE TDD), or when supporting multimedia broadcast/multicast service (MBMS). Note that ordinary WCDMA MBMS does not require acc
43、urate phase synchronization since it has been specified and designed to work properly in networks that satisfy the 50 ppb frequency accuracy requirement. This requirement, which is guaranteed by the WCDMA node synchronization function (see b-ETSI TS 125 402), limits phase drift to between 10 and 20
44、ms. But when MBMS is based on single-frequency network (MBSFN) mode, timing must be accurate to within a few microseconds. This is because identical waveforms are transmitted simultaneously from multiple cells. The signals from these cells are then combined as the multipath components of a single ce
45、ll. Terminals must thus perceive the signals of an entire group of transmitting cells as though they came from a single cell. Therefore, all transmissions must be very tightly synchronized and deliver exactly the same content to each base station. 4 Rec. ITU-T G.8271/Y.1366 (02/2012) The main requir
46、ements applicable at the output of the application (e.g., on the radio interface in the case of a wireless application) are summarized in Appendix II. Based on Table II.1, it is possible to classify applications into classes of requirements, as shown in Table 1 below. Table 1 Time and phase requirem
47、ent classes Level of accuracy Range of requirements (Note 2) Typical applications 1 1 ms-500 ms Billing, alarms 2 5 s-100 s (Note 1) IP Delay monitoring 3 1.5 s-5 s LTE TDD (large cell) Wimax-TDD (some configurations) 4 1 s-1.5 s UTRA-TDD, LTE-TDD (small cell) 5 x ns-1 s (Note 4) Wimax-TDD (some con
48、figurations) 6 3 km radius) maximum absolute deviation in frame start timing between any pair of cells on the same frequency that have overlapping coverage areas b-3GPP TS 36.133) Rec. ITU-T G.8271/Y.1366 (02/2012) 21 Table II.1 Time and phase end-application requirements Application/ Technology Acc
49、uracy Specification LTE-TDD (home-area base station) 1) 3 s for small cell ( 500 m radius), 1.33 + Tpropagations time difference between Base Stations, where Tpropagationis the propagation delay between the Home BS and the cell selected as the network listening synchronization source. In terms of the network listening synchronization source selection, the best accurate synchronization source to GNSS should be selected. If the Home BS obtain
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