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.8272.1/Y.1367.1 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (11/2016) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Packet over Transport aspects Synchronization, quality and availability targ
2、ets SERIES Y: GLOBAL INFORMATION INFRASTRUCTURE, INTERNET PROTOCOL ASPECTS, NEXT-GENERATION NETWORKS, INTERNET OF THINGS AND SMART CITIES Internet protocol aspects Transport Timing characteristics of enhanced primary reference time clocks Recommendation ITU-T G.8272.1/Y.1367.1 ITU-T G-SERIES RECOMME
3、NDATIONS TRANSMISSION 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 L
4、INES G.300G.399 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 DIGIT
5、AL TERMINAL EQUIPMENTS 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.79
6、99 PACKET OVER 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 lis
7、t of ITU-T Recommendations. Rec. ITU-T G.8272.1/Y.1367.1 (11/2016) i Recommendation ITU-T G.8272.1/Y.1367.1 Timing characteristics of enhanced primary reference time clocks Summary Recommendation ITU-T G.8272.1/Y.1367.1 specifies the requirements for enhanced primary reference time clocks (ePRTCs) s
8、uitable for time and phase synchronization in packet networks. It defines the error allowed at the time output of the ePRTC. 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
9、.1/Y.1367.1 2016-11-13 15 11.1002/1000/13162 Keywords Frequency synchronization, phase synchronization, primary reference clock, time synchronization. * To access the Recommendation, type the URL http:/handle.itu.int/ in the address field of your web browser, followed by the Recommendations unique I
10、D. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T G.8272.1/Y.1367.1 (11/2016) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telec
11、ommunication 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 Standardization A
12、ssembly (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 technology
13、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. Compliance wit
14、h 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 obligatory
15、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 of th
16、is 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 the dat
17、e 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 consult
18、 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.8272.1/Y.1367.1 (11/2016) iii Table of Contents Page 1 Scope . 1 2 References . 1
19、3 Definitions 1 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 . 2 6.2 Wander in locked mode 3 6.3 Jitter 5 7 Phase discontinuity . 6 8 Transient response and holdover performance . 6 8.1 Transient between time locked and
20、 frequency reference locked 6 8.2 Phase/time holdover based on local frequency reference during loss of phase/time input 6 9 Interfaces . 7 9.1 Phase and time interfaces . 7 9.2 Frequency interfaces . 7 Annex A ePRTC autonomous primary reference clock requirements 9 Appendix I ePRTC functional model
21、 10 Appendix II ePRTC holdover model 12 II.1 General clock model . 12 II.2 Ideal holdover model 12 II.3 ePRTC holdover performance characterization . 13 Bibliography. 15 Rec. ITU-T G.8272.1/Y.1367.1 (11/2016) 1 Recommendation ITU-T G.8272.1/Y.1367.1 Timing characteristics of enhanced primary referen
22、ce time clocks 1 Scope This Recommendation specifies the requirements for enhanced primary reference time clocks (ePRTCs) suitable for time, phase and frequency synchronization in packet networks. These requirements apply under the normal environmental conditions specified for the equipment. The ePR
23、TC provides a reference time signal traceable to a recognized time standard (e.g., coordinated universal time (UTC) and also a frequency reference. Compared to the primary reference time clock (PRTC) as defined in ITU-T G.8272, the ePRTC is subject to more stringent output performance requirements a
24、nd includes a frequency input directly from an autonomous primary reference clock. The performance of the autonomous primary reference clock for this particular application is specified in Annex A. An ePRTC provides the reference signal for time, phase, and frequency synchronization for clocks withi
25、n a network or section of a network. In particular, the ePRTC can also provide the reference signal to the telecom grand master (T-GM) within the network node where the ePRTC is located. This Recommendation defines the ePRTC output requirements. The requirements for the ePRTC integrated with a T-GM
26、clock are for further study. 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 refe
27、rences 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 reference
28、 to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T G.703 Recommendation ITU-T G.703 (2016), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T G.810 Recommendation ITU-T G.810 (1996), Definitions and
29、 terminology for synchronization networks. ITU-T G.811 Recommendation ITU-T G.811 (1997), Timing characteristics of primary reference clocks. ITU-T G.8260 Recommendation ITU-T G.8260 (2015), Definitions and terminology for synchronization in packet networks. ITU-T G.8271 Recommendation ITU-T G.8271/
30、Y.1366 (2016), Time and phase synchronization aspects of packet networks. ITU-T G.8272 Recommendation ITU-T G.8272/Y.1367 (2015), Timing characteristics of primary reference time clocks. 3 Definitions Definitions related to synchronization are contained in ITU-T G.810 and ITU-T G.8260. 2 Rec. ITU-T
31、G.8272.1/Y.1367.1 (11/2016) 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: ePRTC Enhanced Primary Reference Time Clock FM Frequency Modulation GNSS Global Navigation Satellite System MTIE Maximum Time Interval Error NE Network Equipment PPS Pulse Per
32、Second PRC Primary Reference Clock PRTC Primary Reference Time Clock PTP Precision Time Protocol SSU Synchronization Supply Unit T-GM Telecom Grand Master TDEV Time Deviation UTC Coordinated Universal Time 5 Conventions None. 6 Time error, wander and jitter in locked mode The noise generation of an
33、ePRTC is characterized by two main aspects: 1) the constant time error (time offset) at its output compared to the applicable primary time standard (e.g., UTC); 2) the amount of phase error (wander and jitter) produced at its output. For characterization of the second aspect described above (phase e
34、rror) the calculation of the maximum time interval error (MTIE) and the time deviation (TDEV) is useful. Clause 6.1 defines the time error requirements applicable at the output of the ePRTC, which correspond to the combination of the two aspects described above (constant time error and phase error).
35、 No requirement is defined for the constant time error component taken alone, only when it is combined with the phase error. Clauses 6.2 and 6.3 define the wander and jitter requirements applicable at the output of the ePRTC, which correspond to the second aspect described above (phase error). The p
36、erformance of the output of the combined ePRTC and T-GM function is for further study. 6.1 Time error in locked mode Under normal, locked operating conditions, the time output of the ePRTC should be accurate to within 30 ns or better when verified against the applicable primary time standard (e.g.,
37、UTC). For the ePRTC this value includes all the noise components, i.e., the constant time error (time offset) and the phase error (wander and jitter) of the ePRTC. The combined ePRTC and T-GM function is for further study. Rec. ITU-T G.8272.1/Y.1367.1 (11/2016) 3 Normal, locked operating conditions
38、mean that: the ePRTC 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 limited to antenna failures; the environmental conditions are within the operating limits specified for the e
39、quipment; 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., global navigation satellite system (GNSS) signal) is operating within limits, as determined by the relevant operating
40、 authorities; if the reference time signal is operated over a radio system such as GNSS, multipath reflections and interference from other local transmissions, such as jamming, must be minimized to an acceptable level; there are no extreme propagation anomalies, such as severe thunderstorms. 6.2 Wan
41、der in locked mode The wander requirements apply to all the interfaces listed in clause 9.2.2. When the ePRTC 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
42、(with the use of a time standard instead of a frequency standard), should have the following limits shown in Table 1: Table 1 Wander generation (MTIE) MTIE limit (ns) Observation interval (s) 4 0.1 400,000 The resultant requirements are shown in Figure 1. 4 Rec. ITU-T G.8272.1/Y.1367.1 (11/2016) Fig
43、ure 1 MTIE as a function of an observation (integration) interval NOTE 1 For the 1 pulse per second (PPS) output interface, the MTIE mask is applicable for observation intervals greater than or equal to 1 second. When the ePRTC is in the normal, locked mode of operation, the wander, expressed in TDE
44、V, 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 standard), should have the following limits shown in Table 2: Table 2 Wander generation (TDEV) TDEV limit (ns) Observation int
45、erval (s) 1 0.1 30,000 3.33333 105 30,000 300,000 10 300,000 1,000,000 Rec. ITU-T G.8272.1/Y.1367.1 (11/2016) 5 The resultant requirements are shown in Figure 2. Figure 2 TDEV as a function of an observation (integration) interval NOTE 2 For the 1 PPS output interface, the TDEV mask is applicable fo
46、r observation intervals greater than or equal to 1 second. The applicable MTIE and TDEV requirements for the 1 PPS output interfaces are based on the time interval error of the 1 PPS signal taken at one sample per second and without any low-pass filtering. The applicable MTIE and TDEV requirements f
47、or synchronous Ethernet, 2048 kHz, 2048 kbit/s and 1544 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 carrying precision ti
48、me protocol (PTP) messages are for further study. 6.3 Jitter 6.3.1 Output port jitter While most specifications in this Recommendation are independent of the output interface at which they are measured, this is not the case for jitter generation. Jitter generation specifications must utilize existin
49、g specifications that are currently specified differently for different interfaces. These requirements are stated separately for some of the interfaces identified in clause 9. The applicable jitter requirements for 2048 kHz, 2048 kbit/s, 1544 kbit/s, and 10 MHz output interfaces are defined in ITU-T G.811. The intrinsic jitter for the other interfaces identified in clause 9 is for further study. 6.3.2 Input port jitter tolerance The 10 MHz input interface should tolerate
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