1、 International Telecommunication Union ITU-T G.8272/Y.1367TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (10/2012) 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 Timing characteristics of primary reference time clocks Recommendation ITU-T G.8272/Y.1367 ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECT
3、IONS 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 OR
4、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 SYSTE
5、M 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 over
6、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.8272/Y.1367 (10/2012) i Recommendation ITU-T G.8272/Y.1367 Timing characterist
7、ics 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 and phase synchronization in packet networks. It defines the error allowed at the time output of the PRTC. These requirements apply u
8、nder the normal environmental conditions specified for the equipment. History Edition Recommendation Approval Study Group 1.0 ITU-T G.8272/Y.1367 2012-10-29 15 ii Rec. ITU-T G.8272/Y.1367 (10/2012) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in t
9、he 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 issuing Recommendations on them with a view to stan
10、dardizing 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 these topics. The approval of ITU-T Recommendations is c
11、overed 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 expression “Administration“ is used for conciseness to in
12、dicate 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 applicability) and compliance with the Recommendation is achi
13、eved 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 Recommendation is required of any party. INTELLECTUAL
14、 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 applicability of claimed Intellectual Property Rights, whether a
15、sserted 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 this Recommendation. However, implementers are caution
16、ed 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 2013 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU
17、. Rec. ITU-T G.8272/Y.1367 (10/2012) iii Table of Contents Page 1 Scope 1 2 References. 1 3 Definitions 1 4 Abbreviations and acronyms 1 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 4 7 Phase/Time holdover 4
18、 8 Phase discontinuity . 4 9 Interfaces. 5 9.1 Phase and time interfaces . 5 9.2 Frequency interfaces . 5 Appendix I Measuring the performance of a PRTC . 6 I.1 Factors influencing the performance of a GNSS-based PRTC 6 I.2 Phase wander measurement 6 I.3 Time error measurements . 7 Appendix II PRTC
19、functional model 10 Appendix III Information exchanged over the time interface . 12 Appendix IV PRTC locations . 13 Rec. ITU-T G.8272/Y.1367 (10/2012) 1 Recommendation ITU-T G.8272/Y.1367 Timing characteristics of primary reference time clocks 1 Scope This Recommendation specifies the requirements f
20、or primary reference time clocks (PRTCs) suitable for time and phase 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 synchronization and/or phase synchronization
21、for other clocks within a network or section of a network. In particular, the PRTC can also provide the reference signal to the “Telecom Grand Master“1within the network nodes where the PRTC is located. The PRTC provides a reference time signal traceable to a recognized time standard (e.g., UTC). Th
22、is Recommendation defines the PRTC output requirements. The accuracy of the PRTC should be maintained as specified in this Recommendation. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Rec
23、ommendation. 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 recent edition of the Recommendations and other refe
24、rences 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 Recommendation ITU-T G.703 (2001), Physical/electrical char
25、acteristics 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. ITU-T G.8260 Recommendation ITU-T G.8260 (2012),
26、 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 networks. 3 Definitions Definitions related to synchronization are contained in ITU-T G.810 and ITU-T G.8260. 4 Abbreviations
27、and acronyms This Recommendation uses the following abbreviations and acronyms: GNSS Global Navigation Satellite System GPS Global Positioning System _ 1“Telecom Grand Master“ is currently under study within ITU-T. 2 Rec. ITU-T G.8272/Y.1367 (10/2012) MTIE Maximum Time Interval Error PRC Primary Ref
28、erence Clock PRTC Primary Reference Time Clock SSU Synchronization Supply Unit TDEV Time Deviation UTC Coordinated Universal Time 5 Conventions None. 6 Time error, wander and jitter in locked mode The noise generation of a PRTC clock is characterized by two main aspects: the constant time error (tim
29、e offset) at its output compared to the applicable primary time standard (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 d
30、eviation (TDEV) is useful. Clause 6.1 defines the time error requirements 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,
31、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 PRTC, which correspond to the second aspect described above (phase error). 6.1 Time error in locked mode Under normal, locked operating conditions, the time ou
32、tput of the PRTC should be accurate to within 100 ns or better when verified against the applicable primary time standard (e.g., UTC). 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. Normal, locked operati
33、ng 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 limited to antenna failures. The environmental conditions are within the operating limits specif
34、ied 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 signal) is operating within limits, as determined by the relevant operating authorities. If the ref
35、erence time signal is operated over a radio system such as a global navigation satellite system (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 thunder
36、storms. Rec. ITU-T G.8272/Y.1367 (10/2012) 3 6.2 Wander in locked mode When the PRTC clock 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 of a
37、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. G.8272-Y.1367(12)_F0110.10.011e1 1e+0 1e+1 1e+2 1e+3 1e+4 1e+5 1e+6 1e+7
38、1e+8Observation interval sMTIE sFigure 1 MTIE as a function of an observation (integration) period NOTE 1 For the 1PPS output interface, the MTIE is applicable above a 1 second observation period. When the PRTC clock is in the normal, locked mode of operation, the wander, expressed in TDEV, measured
39、 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: Table 2 Wander generation (TDEV) TDEV limit ns Observation interval s 3 0.1 100 0.03 100 1 0
40、00 30 1 000 10 000 4 Rec. ITU-T G.8272/Y.1367 (10/2012) The resultant requirements are shown in Figure 2. G.8272-Y.1367(12)_F021003010310.1 1 10 100 1 000 10 000Observation interval sTDEV nsFigure 2 TDEV as a function of an observation (integration) period NOTE 2 For the 1PPS output interface, the T
41、DEV 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 the 1PPS signal taken at one sample per second and without any low-pass filtering. The applicable MTIE and TDEV requirements for 2 048 k
42、Hz, 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 0of 1/30 seconds. 6.3 Jitter While most specifications in this Recommendation are independent of the output interface at which they are m
43、easured, this is not the case for jitter production; jitter generation specifications must utilize existing specifications that are currently specified differently for different interface rates. These requirements are stated separately for some of the interfaces identified in clause 9. The applicabl
44、e jitter requirements for 2 048 kHz, 2 048 kbit/s and 1 544 kbit/s output interfaces are defined in ITU-T G.811. The intrinsic jitter for the other interfaces identified in clause 9 is for further study. 7 Phase/Time holdover When a PRTC clock loses all its input phase and time references, it enters
45、 the phase/time holdover state. Under these circumstances, the PRTC clock may either rely on the holdover of a local oscillator, or on an optional external input frequency reference traceable to a primary reference clock (PRC), or on a combination of both. This requirement bounds the maximum excursi
46、ons in the output timing signal. Additionally, it restricts the accumulation of the phase movement during input signal impairments or internal disturbances. The phase/time holdover requirements applicable to a PRTC are for further study. 8 Phase discontinuity The phase discontinuity for a PRTC is fo
47、r further study. Rec. ITU-T G.8272/Y.1367 (10/2012) 5 9 Interfaces The requirements in this Recommendation are related to reference points which may be internal to the equipment or NE in which the PRTC is embedded and are therefore not necessarily available for measurement or analysis by the user. C
48、onsequently, the performance of the PRTC is not specified at these internal reference points, but rather at the external interfaces of the equipment. Note that not all of the interfaces below need to be implemented on all equipment. 9.1 Phase and time interfaces The output phase and time interfaces
49、specified for the equipment in which the PRTC clock may be contained are: 1PPS interface, as defined in Annex A of ITU-T G.8271 for a measurement interface. Other interfaces are for further study. 9.2 Frequency interfaces In addition to phase and time interfaces, frequency interfaces may be used. The output frequency interfaces specified for the equipment in which the PRTC clock may be contained are: 2 048 kHz interfaces acco
