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.8272/Y.1367 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (01/2015) 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 AND NEXT-GENERATION NETWORKS Internet protocol aspects Transport Timing characteristics of primary reference time clocks Recommendation ITU-T G.8272/Y.1367 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SY
3、STEMS 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 INTERNAT
4、IONAL 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 NETWORKS
5、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 Ether
6、net 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 Recommendations. Rec. ITU-T G.8272/Y.136
7、7 (01/2015) i Recommendation ITU-T G.8272/Y.1367 Timing characteristics of primary reference time clocks Summary Recommendation ITU-T G.8272/Y.1367 specifies the requirements for primary reference time clocks (PRTCs) suitable for time, phase and frequency synchronization in packet networks. It defin
8、es the error allowed at the time output of the PRTC. These requirements apply under the normal environmental conditions specified for the equipment. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.8272/Y.1367 2012-10-29 15 11.1002/1000/11817 1.1 ITU-T G.8272/Y.1367 (2012)
9、Amd. 1 2013-08-29 15 11.1002/1000/12013 2.0 ITU-T G.8272/Y.1367 2015-01-13 15 11.1002/1000/12393 _ * 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/11.1002/1000/11
10、830-en. ii Rec. ITU-T G.8272/Y.1367 (01/2015) 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 permane
11、nt 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, establishe
12、s 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 standard
13、s 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 Recomme
14、ndation 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 equivalents are
15、 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 of this Recommendation may involve the use of a claimed Intel
16、lectual 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 not receiv
17、ed 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/ipr/
18、. ITU 2015 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.8272/Y.1367 (01/2015) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 2 3.1 Terms defined elsewhere 2 3.2 Terms defi
19、ned in this Recommendation . 2 4 Abbreviations and acronyms 2 5 Conventions 2 6 Time error, wander and jitter in locked mode 2 6.1 Time error in locked mode . 3 6.2 Wander in locked mode 3 6.3 Jitter 5 7 Holdover . 5 8 Phase discontinuity . 5 9 Interfaces . 5 9.1 Phase and time interfaces . 5 9.2 Fr
20、equency interfaces . 6 Appendix I Measuring the performance of a PRTC or a PRTC combined with T-GM . 7 I.1 Factors influencing the performance of a GNSS-based PRTC 7 I.2 Phase wander measurement 7 I.3 Time error measurements . 9 Appendix II PRTC functional model 13 Appendix III Information exchanged
21、 over the time interface . 15 Appendix IV PRTC locations . 16 Rec. ITU-T G.8272/Y.1367 (01/2015) 1 Recommendation ITU-T G.8272/Y.1367 Timing characteristics of primary reference time clocks 1 Scope This Recommendation specifies the requirements for primary reference time clocks (PRTCs) suitable for
22、time, phase and frequency synchronization in packet networks. These requirements apply under the normal environmental conditions specified for the equipment. A typical PRTC provides the reference signal for time, phase and frequency synchronization for other clocks within a network or section of a n
23、etwork. In particular, the PRTC can also provide the reference signal to the telecom grand master (T-GM) within the network nodes where the PRTC is located. The PRTC provides a reference time signal traceable to a recognized time standard (e.g., coordinated universal time (UTC). UTC can be obtained
24、from a UTC time laboratory registered at Bureau International des Poids et Mesures (BIPM) (e.g., a national UTC time lab) or, most commonly, from a global navigation satellite system (GNSS). This Recommendation defines the PRTC output requirements. The accuracy of the PRTC should be maintained as sp
25、ecified in this Recommendation. This Recommendation also covers the case where a PRTC is integrated with a T-GM clock. In this case it defines the performance at the output of the combined PRTC and T-GM function, i.e., the precision time protocol (PTP) messages. 2 References The following ITU-T Reco
26、mmendations 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; users of this Recommendation are t
27、herefore 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 Recommendation does not give it, as a s
28、tand-alone document, the status of a Recommendation. ITU-T G.703 Recommendation ITU-T G.703 (2001), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T G.810 Recommendation ITU-T G.810 (1996), Definitions and terminology for synchronization networks. ITU-T G.811 Recommendat
29、ion ITU-T G.811 (1997), Timing characteristics of primary reference clocks. ITU-T G.8260 Recommendation ITU-T G.8260 (2012), Definitions and terminology for synchronization in packet networks. ITU-T G.8271 Recommendation ITU-T G.8271/Y.1366 (2012), Time and phase synchronization aspects of packet ne
30、tworks. ITU-T G.8273 Recommendation ITU-T G.8273/Y.1368 (2013), Framework of phase and time clocks. IEEE 1588-2008 IEEE Std 1588-2008, Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems. 2 Rec. ITU-T G.8272/Y.1367 (01/2015) 3 Definitions 3.1 Terms d
31、efined elsewhere This Recommendation uses the following terms defined elsewhere: Definitions related to synchronization are contained in ITU-T G.810 and ITU-T G.8260. 3.2 Terms defined in this Recommendation None. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and
32、acronyms: 1PPS 1 Pulse-Per-Second GNSS Global Navigation Satellite System GPS Global Positioning System MTIE Maximum Time Interval Error PRC Primary Reference Clock PRTC Primary Reference Time Clock PTP Precision Time Protocol RF Radio Frequency SSU Synchronization Supply Unit T-GM Telecom Grand Mas
33、ter TDEV Time Deviation ToD Time of Day UTC Coordinated Universal Time 5 Conventions None. 6 Time error, wander and jitter in locked mode The noise generation of a PRTC is characterized by two main aspects: the constant time error (time offset) at its output compared to the applicable primary time s
34、tandard (e.g., UTC); the amount of phase error (wander and jitter) produced at its output. For characterization of the second aspect described above (phase error) the calculation of the maximum time interval error (MTIE) and the time deviation (TDEV) is useful. Clause 6.1 defines the time error requ
35、irements applicable at the output of the PRTC, which corresponds to the combination of the two aspects described above (constant time error and phase error). No requirement is defined for the constant time error component taken alone; it is combined with the phase error and not separately measurable
36、. Clauses 6.2 and 6.3 define the wander and jitter requirements applicable at the output of the PRTC, which correspond to the second aspect described above (phase error). Rec. ITU-T G.8272/Y.1367 (01/2015) 3 The performance specified in clauses 6.1 and 6.2 also applies to the output of the combined
37、PRTC and T-GM function when integrated into a single piece of equipment. Therefore, there is no additional allowance for the inclusion of the T-GM function. NOTE Optimization of the noise inside the equipment is possible by combining the two functions. Therefore, the total noise of equipment that in
38、tegrates the PRTC and T-GM can be the same as equipment that only contains the PRTC. 6.1 Time error in locked mode Under normal, locked operating conditions, the time output of the PRTC, or the combined PRTC and T-GM function, should be accurate to within 100 ns or better when verified against of th
39、e applicable primary time standard (e.g., UTC). For the PRTC this value includes all the noise components, i.e., the constant time error (time offset) and the phase error (wander and jitter) of the PRTC. For the combined PRTC and T-GM function the same applies, except the samples are processed using
40、 the method specified in ITU-T G.8273 to address timestamp quantization. Normal, locked operating conditions mean that: the PRTC is fully locked to the incoming reference time signal, and is not operating in warm-up; there are no failures or facility errors in the reference path, including but not l
41、imited to antenna failures; the environmental conditions are within the operating limits specified for the equipment; the equipment is properly commissioned and calibrated for fixed offsets such as antenna cable length, cable amplifiers and receiver delays; the reference time signal (e.g., GNSS sign
42、al) is operating within limits, as determined by the relevant operating authorities; if the reference time signal is operated over a radio system such as a GNSS, multipath reflections and interference from other local transmissions, such as jamming, must be minimized to an acceptable level; there ar
43、e no extreme propagation anomalies, such as severe thunderstorms. 6.2 Wander in locked mode When the PRTC is in the normal, locked mode of operation, the wander, expressed in MTIE, measured using a similar configuration as the synchronized clock configuration defined in Figure 1a of ITU-T G.810 (wit
44、h the use of a time standard instead of a frequency standard), should have the following limits: Table 1 Wander generation (MTIE) MTIE limit s Observation interval s 0.275 103 + 0.025 0.1 273 The resultant requirements are shown in Figure 1. 4 Rec. ITU-T G.8272/Y.1367 (01/2015) G . 8 2 7 2 - Y . 1 3
45、 6 7 ( 1 2 ) _ F 0 110.10.011 e 1 1 e + 0 1 e + 1 1 e + 2 1 e + 3 1 e + 4 1 e + 5 1 e + 6 1 e + 7 1 e + 8O b s e r vat i on i n t e r val s M T I E s mFigure 1 MTIE as a function of an observation (integration) period NOTE 1 For the 1 pulse-per-second (1PPS) output interface, the MTIE is applicable
46、above a 1 second observation period. When the PRTC is in the normal, locked mode of operation, the wander, expressed in TDEV, measured using a similar configuration as the synchronized clock configuration defined in Figure 1a of ITU-T G.810 (with the use of a time standard instead of a frequency sta
47、ndard), should have the following limits: Table 2 Wander generation (TDEV) TDEV limit ns Observation interval s 3 0.1 100 0.03 100 1 000 30 1 000 10 000 The resultant requirements are shown in Figure 2. G . 8 2 7 2 - Y . 1 3 6 7 ( 1 2 ) _ F 0 21003010310.1 1 10 100 1 000 10 000O b s e r vat i on i n
48、 t e r val s T D E V n s Figure 2 TDEV as a function of an observation (integration) period NOTE 2 For the 1PPS output interface, the TDEV is applicable above a 1 second observation period. The applicable MTIE and TDEV requirements for 1PPS output interfaces are based on the time interval error of t
49、he 1PPS signal taken at one sample per second and without any low-pass filtering. Rec. ITU-T G.8272/Y.1367 (01/2015) 5 The applicable MTIE and TDEV requirements for 2 048 kHz, 2 048 kbit/s and 1 544 kbit/s output interfaces are measured through an equivalent 10 Hz, first-order, low-pass measurement filter, at a maximum sampling time 0 of 1/30 seconds. The applicable MTIE and TDEV requirements for an Ethernet interface carr
