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 Amendment 1 (08/2017) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Packet over Transport aspects Synchronization, quality and avail
2、ability targets 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 Amendment 1 Recommendation ITU-T G.8272.1/Y.1367.
3、1 (2016) Amendment 1 ITU-T G-SERIES RECOMMENDATIONS 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 INTERNATIO
4、NAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES 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 OPTIC
5、AL SYSTEMS CHARACTERISTICS G.600G.699 DIGITAL 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 DAT
6、A OVER TRANSPORT GENERIC ASPECTS G.7000G.7999 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 F
7、or further details, please refer to the list of ITU-T Recommendations. Rec. ITU-T G.8272.1/Y.1367.1 (2016)/Amd.1 (08/2017) i Recommendation ITU-T G.8272.1/Y.1367.1 Timing characteristics of enhanced primary reference time clocks Amendment 1 Summary Recommendation ITU-T G.8272.1/Y.1367.1 specifies th
8、e requirements for enhanced primary reference time clocks (ePRTCs) suitable 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. Amendment 1
9、 adds a reference, changes a bullet in clause 6.1 and replaces Annex A. History Edition Recommendation Approval Study Group Unique ID* 1.0 ITU-T G.8272.1/Y.1367.1 2016-11-13 15 11.1002/1000/13162 1.1 ITU-T G.8272.1/Y.1367.1 (2016) Amd. 1 2017-08-13 15 11.1002/1000/13325 Keywords Frequency synchroniz
10、ation, 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 ID. For example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T
11、G.8272.1/Y.1367.1 (2016)/Amd.1 (08/2017) 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 permanent or
12、gan 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, establishes the
13、 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 standards are
14、 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 Recommendati
15、on 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 used
16、 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 Intellectu
17、al 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 received no
18、tice 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/. ITU
19、 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 (2016)/Amd.1 (08/2017) iii Table of Contents Page 1 Scope . 1 2 References . 1 3 Definitions 2 4 Abbreviations and acronyms 2 5
20、 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 frequency reference locked 6 8.2 Phase/time hol
21、dover 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 10 Appendix II ePRTC holdover model 12 II.1 Gen
22、eral 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 (2016)/Amd.1 (08/2017) 1 Recommendation ITU-T G.8272.1/Y.1367.1 Timing characteristics of enhanced primary reference time clocks Amendment 1 Editoria
23、l note: This is a complete-text publication. Modifications introduced by this amendment are shown in revision marks relative to Recommendation ITU-T G.8272.1/Y.1367.1 (2016). 1 Scope This Recommendation specifies the requirements for enhanced primary reference time clocks (ePRTCs) suitable for time,
24、 phase and frequency synchronization in packet networks. These requirements apply under the normal environmental conditions specified for the equipment. The ePRTC provides a reference time signal traceable to a recognized time standard (e.g., coordinated universal time (UTC) and also a frequency ref
25、erence. 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 and includes a frequency input directly from an autonomous primary reference clock. The performance of the autonomous primary reference clock
26、 for this particular application is specified in Annex A. An ePRTC provides the reference signal for time, phase, and frequency synchronization for clocks within a network or section of a network. In particular, the ePRTC can also provide the reference signal to the telecom grand master (T-GM) withi
27、n 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 clock are for further study. 2 References The following ITU-T Recommendations and other references contain provisions which, through referen
28、ce 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 possibility of applying the most re
29、cent 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 Recommendation. ITU-T G.703 Recommend
30、ation ITU-T G.703 (2016), 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 Recommendation ITU-T G.811 (1997), Timing characteristics of primary reference clocks
31、. ITU-T G.811.1 Recommendation ITU-T G.811.1 (2017), Enhanced primary reference clock. 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/Y.1366 (2016), Time and phase synchronization aspects o
32、f packet networks. 2 Rec. ITU-T G.8272.1/Y.1367.1 (2016)/Amd.1 (08/2017) 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. 4 Abbreviation
33、s 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 Second PRC Primary Reference Clock PRTC Pr
34、imary 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 ePRTC is characterized by two main aspects
35、: 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 error) the calculation of the maximum time
36、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). No requirement is defined for the constan
37、t 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 performance of the output of the combined e
38、PRTC and T-GM function is for further study. Rec. ITU-T G.8272.1/Y.1367.1 (2016)/Amd.1 (08/2017) 3 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 stan
39、dard (e.g., 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. Normal, locked operating conditions mean that: the ePRTC is fully
40、 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 equipment; the equipment is pr
41、operly 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 authorities; if the referenc
42、e 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 or solar flares. 6.2 Wander in locked
43、 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 (with the use
44、 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 (2016)/Amd.1 (08/2017) Fig
45、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
46、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
47、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 (2016)/Amd.1 (08/2017) 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
48、applicable for 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 r
49、equirements for 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 time 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 out
