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.811 TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Amendment 1 (04/2016) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital networks Design objectives for digital networks Timing characteristi
2、cs of primary reference clocks Amendment 1 Recommendation ITU-T G.811 (1997) 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-TRAN
3、SMISSION 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 SATELLITE LINKS AND INTERCONNECTION WITH METALLIC LINES G.400G.449 COORDINATION OF RADIO
4、TELEPHONY 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 General aspects G.800G.809 Design objectives for digital networks G.810G.819 Synchronization, quality and availability targets
5、G.820G.829 Network capabilities and functions G.830G.839 SDH network characteristics G.840G.849 Management of transport network G.850G.859 SDH radio and satellite systems integration G.860G.869 Optical transport networks G.870G.879 DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G.900G.999 MULTIMEDIA QUALI
6、TY 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 ACCESS NETWORKS G.9000G.9999 For further details, please refer to the list of ITU-T
7、Recommendations. Rec. ITU-T G.811 (1997)/Amd.1 (04/2016) i Recommendation ITU-T G.811 Timing characteristics of primary reference clocks Amendment 1 Summary Recommendation ITU-T G.811 outlines minimum requirements for timing devices used as primary reference clocks in synchronization networks. These
8、 networks include public switched telephone networks (PSTNs) and synchronous digital hierarchy (SDH) networks. Amendment 1 to Recommendation ITU-T G.811 (1997) adds: A 10 MHz interface and a note in clause 9. 10 MHz jitter specification in clause 6.3. History Edition Recommendation Approval Study Gr
9、oup Unique ID* 1.0 ITU-T G.811 1976-10-08 11.1002/1000/10008 2.0 ITU-T G.811 1980-11-21 11.1002/1000/7783 3.0 ITU-T G.811 1984-10-19 11.1002/1000/4405 4.0 ITU-T G.811 1988-11-25 11.1002/1000/995 4.0 ITU-T G.812 1988-11-25 11.1002/1000/996 5.0 ITU-T G.811 1997-09-19 13 11.1002/1000/4197 5.0 ITU-T G.8
10、12 1998-06-01 13 11.1002/1000/4400 5.1 ITU-T G.811 (1997) Amd. 1 2016-04-13 13 11.1002/1000/12792 6.0 ITU-T G.812 2004-06-13 15 11.1002/1000/7335 * 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. Fo
11、r example, http:/handle.itu.int/11.1002/1000/11830-en. ii Rec. ITU-T G.811 (1997)/Amd.1 (04/2016) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications, information and communication technologies (ICTs). The ITU Telecommu
12、nication 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 Assem
13、bly (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 whic
14、h 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 with th
15、is 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 lang
16、uage 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 this R
17、ecommendation 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 date of
18、 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 the
19、 TSB patent database at http:/www.itu.int/ITU-T/ipr/. ITU 2016 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.811 (1997)/Amd.1 (04/2016) 1 Recommendation ITU-T G.811 Timing characteristics of prim
20、ary reference clocks Amendment 1 Editorial note: This is a complete-text publication. Modifications introduced by this amendment are shown in revision marks relative to Recommendation ITU-T G.811 (1997). 1 Scope This Recommendation outlines the requirements for primary reference clocks (PRCs) suitab
21、le for synchronization supply to digital networks. These requirements apply under the normal environmental conditions specified for digital equipment. A typical PRC provides the reference signal for the timing or synchronization of other clocks within a network or section of a network. In particular
22、, the PRC can also provide the reference signal to the slave clock specified in Recommendation ITU-T G.812 within the network nodes where the PRC is located. This Recommendation defines the PRC output but it does not apply to the output of slave clock directly fed by a PRC. The long-term accuracy of
23、 the PRC should be maintained at 1 part in 1011 or better with verification to coordinated universal time (UTC). A PRC may be realized as an autonomous clock, operating independently of other sources. Alternatively, the PRC may be realized as a non-autonomous clock which is disciplined by UTC-derive
24、d precision signals received from a radio or satellite system. In either case, the requirements for long-term accuracy and short-term stability, as specified in this Recommendation, apply. The long-term accuracy of 1 part in 1011 or better is adequate when a single PRC provides the reference synchro
25、nization signal to all other clocks within a network (synchronous mode of operation). In the pseudo-synchronous mode, i.e. not all clocks in the network have timing traceable to the same PRC, the long-term accuracy is dependent on the number of PRCs in that network. When more than one PRC is used in
26、 a network, a statistical approach is needed to determine the long-term accuracy of each PRC in that network. 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 p
27、ublication, the editions indicated were valid. All Recommendations and other references are subject to revision; all 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 li
28、st of the currently valid ITU-T Recommendations is regularly published. ITU-T G.703 Recommendation ITU-T G.703 (19912016), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T G.783 Recommendation ITU-T G.783 (1997), Characteristics of Synchronous Digital Hierarchy (SDH) equ
29、ipment functional blocks. ITU-T G.810 Recommendation ITU-T G.810 (1996), Definitions and terminology for synchronization networks. ITU-T G.812 Recommendation ITU-T G.812 (1988), Timing requirements at the outputs of slave clocks suitable for plesiochronous operation of international digital links. I
30、TU-T G.822 Recommendation ITU-T G.822 (1988), Controlled slip rate objectives on an international digital connection. 2 Rec. ITU-T G.811 (1997)/Amd.1 (04/2016) ITU-T G.823 Recommendation ITU-T G.823 (1993), The control of jitter and wander within digital networks which are based on the 2048 kbit/s h
31、ierarchy. ITU-T G.824 Recommendation ITU-T G.824 (1993), The control of jitter and wander within digital networks which are based on the 1544 kbit/s hierarchy. ITU-T G.825 Recommendation ITU-T G.825 (1993), The control of jitter and wander within digital networks which are based on the synchronous d
32、igital hierarchy (SDH). 3 Definitions The terms and definitions used in this Recommendation are contained in ITU-T G.810. 4 Abbreviations and acronyms This Recommendation uses the following abbreviations and acronyms: CMI Coded Mark Inversion ePRTC enhanced Primary Reference Time Clock FPM Flicker P
33、hase Modulation MTIE Maximum Time Interval Error NE Network Element OAM Operations and Maintenance PLL Phase Locked Loop PRC Primary Reference Clock SDH Synchronous Digital Hierarchy SEC SDH Equipment Clock SSMB Synchronization Status Message Byte STM Synchronous Transport Module TDEV Time Deviation
34、 UI Unit Interval UTC Coordinated Universal Time WFM White Frequency Modulation 5 Frequency accuracy The maximum allowable fractional frequency offset for observation times greater than one week is 1 part in 1011, over all applicable operational conditions. 6 Noise generation The noise generation of
35、 a PRC clock represents the amount of phase noise produced at its output. A suitable reference, for practical testing purposes, implies a performance level that is more stable than the output requirements. The ability of the clock to limit this noise is described by its frequency stability. The meas
36、ures maximum time interval error (MTIE) and time deviation (TDEV) are useful for characterization of noise generation performance. MTIE and TDEV are measured through an equivalent 10 Hz, first-order, low-pass measurement filter, at a maximum sampling time 0 of 1/30 seconds. The minimum measurement p
37、eriod for TDEV is Rec. ITU-T G.811 (1997)/Amd.1 (04/2016) 3 twelve times the integration period (T = 12). For measurements over longer observation periods, alternative filter bandwidth and sampling time may be required for practical considerations. 6.1 Wander The wander, expressed in MTIE, measured
38、using the independent clock configuration defined in Figure 2a of ITU-T G.810 should have the following limits: MTIE: 0.275 103 + 0.025 s for 0.1 1000 s The resultant requirements are shown in Figure 1. T 1 3 1 0 5 7 0 - 9 7 /d 0 11 E + 0 6 1 E + 0 80 . 0 1 1 1 0 0 1 0 0 0 01 0 0 01 0 01010 . 10 . 0
39、 1M T I Em i c ro -s e c o n d sO b s e r v a t i o n p e r i o d (s e c o n d s )F i gu r e 1/ G .811 M TI E a s a fu n c t i on of an ob s e r v ati o n (i n te gr ati on ) p e r i od FIGURE 1/G. = The wander, expressed in TDEV, measured using the independent clock configuration defined in Figure
40、2a of ITU-T G.810 should have the following limits: TDEV: 3 ns for 0.1 100 s 0.03 ns for 100 1000 s 30 ns for 1000 10 000 s The resultant requirements are shown in Figure 2. 4 Rec. ITU-T G.811 (1997)/Amd.1 (04/2016) T 13 10 58 0- 9 7/ d0 21 0 0 01 0 03010310 . 1 1 10 1 0 0 1 0 0 0 1 0 0 0 0O b s e r
41、 v a t i o n p e r i o d (s e c o n d s )T DE Vn a n o -s e c o n d sF i gu r e 2/G .81 1 T D E V as a fu n c tio n of an ob s e r va ti on ( i n te gr a tion ) p e r i o d FIGURE 2/G.811.D02 = 6.2 Jitter While most specifications in this Recommendation are independent of the output interface at whi
42、ch they are measured, 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 the interfaces identified in clause 8. To be co
43、nsistent with other jitter requirements, the specifications are in UIpp, where the unit interval (UI) corresponds to the reciprocal of the bit rate of the interface. The intrinsic jitter at 2048 kHz and 2048 kbit/s output interfaces as measured over a 60-second interval shall not exceed 0.05 UIpp wh
44、en measured through a single pole band-pass filter with corner frequencies at 20 Hz and 100 kHz. The intrinsic jitter at 1544 kbit/s output interfaces as measured over a 60-second interval shall not exceed 0.015 UIpp when measured through a single pole band-pass filter with corner frequencies at 10
45、Hz and 40 kHz. The intrinsic jitter at 10 MHz output interfaces as measured over a 60-second interval shall not exceed 0.01 UIpp when measured through a single pole band-pass filter with corner frequencies at 20 Hz and 100 kHz. 7 Phase discontinuity Primary reference clocks need a very high level of
46、 reliability and are likely to include replication of the equipment in order to ensure the continuity of the output. However, any phase discontinuity, due to internal operations within the clock, should only result in a lengthening or shortening of the timing signal interval and must not, at the clo
47、ck output, cause a phase discontinuity in excess of 1/8 UI (this refers to output signals at 1544 kbit/s, 2048 kbit/s or 2048 kHz). 8 Degradation of the performance of a PRC If redundancy is applied and a clock frequency departs significantly from its nominal value, this should be detected and switc
48、hing to an undegraded oscillator should then be effected. This switching should be accomplished before the MTIE or TDEV specification is exceeded. Rec. ITU-T G.811 (1997)/Amd.1 (04/2016) 5 9 Interfaces The requirements in this Recommendation are related to reference points which may be internal to t
49、he equipment or network element (NE) in which the PRC is embedded and are therefore not necessarily available for measurement or analysis by the user. Consequently, the performance of the PRC is not specified at these internal reference points, but rather at the external interfaces of the equipment. The output interfaces specified for the equipment in which the PRC clock may be contained are: 2048 kHz interfaces according to clause 10 15 of ITU-T G.703 with additional jitter and wander requi
