1、 International Telecommunication Union ITU-T G.8275/Y.1369TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2013) 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 Architecture and requirements for packet-based time and phase distribution Recommendation ITU-T G.8275/Y.1369 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONA
3、L 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 INTERNATIONAL CARRIER TELEPHONE SYSTEMS
4、 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 NETWORKS G.800G.899 DIGITAL SECTIONS AND
5、 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 Ethernet over Transport aspects G.80
6、00G.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.8275/Y.1369 (11/2013) i Recommendation ITU-T G.8275/Y.1369
7、Architecture and requirements for packet-based time and phase distribution Summary Recommendation ITU-T G.8275/Y.1369 describes the architecture and requirements for packet-based time and phase distribution in telecom networks. The architecture described is mainly applicable to the use of IEEE 1588.
8、 Details necessary to utilize IEEE 1588 in a manner consistent with the architecture are defined in other Recommendations. History Edition Recommendation Approval Study Group Unique ID*1.0 ITU-T G.8275/Y.1369 2013-11-22 15 11.1002/1000/12011-en Keywords IEEE1 588, packet synchronization, phase, time
9、. _ *To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T G.8275/Y.1369 (11/2013) FOREWORD The International Telecommunication Union
10、 (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 questions and
11、 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 Recommendations on thes
12、e 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 Recommendation, the expre
13、ssion “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 or applicabi
14、lity) 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 compliance with the R
15、ecommendation 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 applicabilit
16、y 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 not received notice of intellectual property, protected by patents, which may be required to implement th
17、is 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 2014 All rights reserved. No part of this publication may be reproduced, by any means wha
18、tsoever, without the prior written permission of ITU. Rec. ITU-T G.8275/Y.1369 (11/2013) iii Table of Contents Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations and acronyms 2 5 Conventions 2 6 General introduction to packet-based time/phase distribution . 2 6.1 Requirements for packet-
19、based time and phase distribution 3 7 Architecture of packet-based time/phase distribution 3 7.1 Packet-based time and phase distribution . 3 7.2 Time/phase protection aspects 4 7.3 Packet network partitioning 13 8 Security aspects 14 9 Management aspects . 14 Annex A Time/phase models based on ITU-
20、T G.805 15 Appendix I Architecture for time and phase distribution over a packet network providing partial timing support at the protocol level 17 I.1 Architecture for partial timing support . 17 iv Rec. ITU-T G.8275/Y.1369 (11/2013) Introduction Recommendation ITU-T G.8275/Y.1369 describes the gene
21、ral architecture of time and phase distribution using packet-based methods. This Recommendation forms the base architecture for the development of telecom profiles for time and phase distribution. The architecture described covers the case where protocol interaction is at all nodes, between a packet
22、 master clock and a packet slave clock. Details of the necessary profiles are described in other Recommendations. Rec. ITU-T G.8275/Y.1369 (11/2013) 1 Recommendation ITU-T G.8275/Y.1369 Architecture and requirements for packet-based time and phase distribution 1 Scope This Recommendation describes t
23、he general architecture of time and phase distribution using packet-based methods. This version of the Recommendation focuses on the distribution of time and phase using the standard for precision time protocol (PTP) IEEE 1588. The requirements and architecture form a base for the specification of o
24、ther functionalities that are needed to achieve packet-based time and phase distribution in a carrier environment. The architecture described covers the case where protocol interaction is at all nodes, between a packet master clock and a packet slave clock. Details of the necessary profiles are desc
25、ribed in other Recommendations. 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 and other r
26、eferences 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. The refere
27、nce to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.805 Recommendation ITU-T G.805 (2000), Generic functional architecture of transport networks. ITU-T G.810 Recommendation ITU-T G.810 (1996), Definitions and terminology f
28、or synchronization networks. ITU-T G.8260 Recommendation ITU-T G.8260 (2012), Definitions and terminology for synchronization in packet networks. ITU-T G.8261 Recommendation ITU-T G.8261/Y.1361 (2013), Timing and synchronization aspects in packet networks. ITU-T G.8262 Recommendation ITU-T G.8262/Y.
29、1362 (2010), Timing characteristics of a synchronous Ethernet equipment slave clock. ITU-T G.8264 Recommendation ITU-T G.8264/Y.1364 (2008), Distribution of timing information through packet networks. ITU-T G.8265 Recommendation ITU-T G.8265/Y.1365 (2010), Architecture and requirements for packet-ba
30、sed 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 G.8271 Recommendation ITU-T G.8271/Y.1366 (2012), Time and phase synchronization aspects of packet networks. ITU-T G.8271.1 Recommendatio
31、n ITU-T G.8271.1/Y.1366.1 (2014), Network limits for time synchronization in packet networks. ITU-T G.8272 Recommendation ITU-T G.8272/Y.1367 (2012), Timing characteristics of primary reference time clocks. IEEE 1588 IEEE STD 1588 (2008), Standard for a Precision Clock Synchronization Protocol for N
32、etworked Measurement and Control Systems. 2 Rec. ITU-T G.8275/Y.1369 (11/2013) 3 Definitions The terms and definitions used in this Recommendation are contained in ITU-T G.810 and ITU-T G.8260. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: BC Boundar
33、y Clock BMCA Best Master Clock Algorithm EEC Synchronous Ethernet Equipment Clock ESMC Ethernet Synchronization Messaging Channel GM Grand Master GNSS Global Navigation Satellite System LTE Long Term Evolution NTP Network Time Protocol OTN Optical Transport Network PDV Packet Delay Variation PRC Pri
34、mary Reference Clock PRTC Primary Reference Time Clock PTP Precision Time Protocol QL Quality Level SEC SDH Equipment Clock SSM Synchronization Status Message SSU Synchronization Supply Unit T-BC Telecom Boundary Clock T-TC Telecom Transparent Clock T-TSC Telecom Time Slave Clock TC Transparent Cloc
35、k 5 Conventions Within this Recommendation, the term PTP refers to the PTP version 2 protocol defined in IEEE 1588. 6 General introduction to packet-based time/phase distribution The distribution of accurate time and phase is necessary to support certain telecom-based services and in particular the
36、underlying infrastructure. While traditional network synchronization has relied on the accurate distribution of frequency, evolving wireless networks require the distribution of accurate time and phase. As the network evolves from a primarily TDM-based network infrastructure to one using packet-base
37、d technology, the ability to distribute synchronization is also changing. Rec. ITU-T G.8275/Y.1369 (11/2013) 3 In order to enable timing distribution in packet-based networks, the ITU-T developed specifications (ITU-T G.8261, ITU-T G.8262 and ITU-T G.8264) for synchronous Ethernet, which allowed the
38、 use of the Ethernet physical layer to be used as a mechanism to distribute frequency analogous to the methods used with SDH-based network synchronization. In this regard, synchronous Ethernet, by appropriate specification of network equipment clocks provided support for the existing frequency-based
39、 synchronization network over both existing TDM and new packet-based technology. In the absence of the ability to utilize the physical layer, the ITU also developed Recommendations covering frequency distribution using packet-based methods such as precision time protocol (PTP) and network time proto
40、col (NTP). The use of packet-based methods also enabled new frequency synchronization scenarios to be considered. These, as well as other aspects specific to packet-based frequency distribution, resulted in the development of an architectural specification ITU-T G.8265. This Recommendation describes
41、 the architecture for packet-based time and phase distribution. 6.1 Requirements for packet-based time and phase distribution Packet-based mechanisms for time and phase distribution must meet the following requirements: 1) Mechanisms must be specified to allow interoperability between the various ph
42、ase/time clocks defined in this architecture. 2) Mechanisms must permit consistent operation over managed wide area telecom networks. 3) Packet-based mechanisms must allow the synchronization network to be designed and configured in a fixed arrangement. 4) Protection schemes used by packet-based sys
43、tems must be based on standard telecom operational practice and allow telecom time slave clocks (T-TSC) the ability to take phase and time from multiple geographically separate telecom grand master (T-GM) clocks. 5) Phase/time reference source selection based on received phase/time traceability and
44、local priority should be permitted. Automatic establishment of the phase/time synchronization network topology may also be possible. 7 Architecture of packet-based time/phase distribution In contrast to physical layer synchronization, where the significant edges of a data signal define the timing co
45、ntent of the signal, packet-based methods rely on the transmission of dedicated “event packets“. These “event packets“ form the significant instants of a packet timing signal. The timing of these significant instants is precisely measured relative to a master time source, and this timing information
46、 is encoded in the form of a time stamp, which is a machine-readable representation of a specific instance of time. The time stamp is generated via a packet master function and is carried over a packet network to a packet slave clock. A protocol is used between the master and the slave clocks in ord
47、er to adjust for transmission and other delays, resulting in both the master and slave clocks having the same time reference. As time is the integral of frequency, the time stamps can also be used to derive frequency. This case is covered in ITU-T G.8265 and ITU-T G.8265.1. 7.1 Packet-based time and
48、 phase distribution A time reference is initially obtained from a primary reference time clock (PRTC). If the time across the system is required to be referenced to UTC or to some other universal standard source of time, the PRTC itself may require a time reference input such as a GNSS signal. 4 Rec
49、. ITU-T G.8275/Y.1369 (11/2013) For the purposes of time and phase synchronization transport, the packet master delivers its reference to the packet slave clocks using a packet timing signal (see ITU-T G.8260). In order to achieve better accuracy, protocol-level timing support may be used at the various network nodes. Specifically for the IEEE 1588 PTP protocol, these intermediate devices are termed boundary clocks (BCs) or transparent clocks (TCs). The architecture described in thi
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