1、STD*ITU-T RECMN G-811-ENGL 1777 48b2571 Ob110258 b28 INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU G.81 I (09/97) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital transmission systems - Digital networks - Design objectives f
2、or digital networks Timing characteristics of primary reference clocks ITU-T Recommendation G.811 (Previously CCIlT Recommendation) STDeITU-T RECMN G-BL1-ENGL 1977 qBb2571 Ob40259 5b4 D ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS NTERNATIONAL TELEPHONE
3、 CONNECTIONS AND CIRCUITS NTERNATIONAL ANALOGUE CARRIER SYSTEM 3ENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER- IRANSMISSION SYSTEMS NDIVIDUAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE WITH METALLIC
4、LINES COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY !XANSMISSION MEDIA CHARACTERISTICS 3IGITAL TRANSMISSION SYSTEMS TERMINAL EQlPMENTS SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION General Coding of analogue signals by pulse code modulation Coding of analogue signals by methods o
5、ther than PCM Principal characteristics of primary multiplex equipment Principal characteristics of second order multiplex equipment fincipal characteristics of higher order multiplex equipment Principal Characteristics of transcoder and digital multiplication equipment Operations, administration an
6、d maintenance features of transmission equipment Principal characteristics of multiplexing equipment for the synchronous digital hierarchy Other terminal equipment DIGITAL NETWORKS General aspects Quality and availability targets Network capabilities and functions SDH network characteristics Telecom
7、munications management network DIGITAL SECTIONS AND DIGITAL LINE SYSTEM General Parameters for optical fibre cable systems Digital sections at hierarchical bit rates based on a bit rate of 2048 kbit/s Digital line transmission systems on cable at non-hierarchical bit rates Digital line systems provi
8、ded by FDM transmission bearers Digital line systems Digital section and digital transmission systems for customer access to ISDN Optical fibre submarine cable systems Optical line systems for local and access networks G.100-G.199 G.2004.299 G.300-G.399 G.400-G.449 G.450-G.499 G.700-G.799 G.700-G.70
9、9 G.710-G.719 G.720-G.729 G.730-G.739 G.740-G.749 G.750-G.759 G.760-G.769 G.770-G.779 G.780-G.789 G.790-G.799 G.800-G.899 G.8OO-G. 809 G.820-G.829 G.830-G.839 G.84O-G. 849 G.850-G.859 G.900-G.999 G.900-G.909 G.9104.919 G.920-G.929 G .9 3 04.9 3 9 G.94-G.949 G.950-G.959 G.960-G.969 G.970-G.979 G.980-
10、G.999 For further details, please refer to ITU-T List of Recommendations. STD-ITU-T RECMN G*BLL-ENGL II777 48b259L Ob402b0 28b D ITU-T RECOMMENDATION G.811 TIMING CHARACTERISTICS OF PRIMARY REFERENCE CLOCKS Summary This Recommendation outlines minimum requirements for timing devices used as primary
11、reference clocks in synchronization networks. These networks include Public Switched Telephone Networks (PSTNs) and Synchronous Digital Hierarchy (SDH) networks. Source ITU-T Recommendation G.811 was revised by ITU-T Study Group 13 (1997-2000) and was approved under the WTSC Resolution No. 1 procedu
12、re on the 19th of September 1997. Keywords Clock, Clock Performance Objectives, Clock Performance Parameters, Jitter Performance, Wander Performance. Recommendation G.811 (09197) 1 STD-ITU-T RECMN G*BLL-ENGL 1997 48b257L Ob402bl 112 FOREWORD IT (International Telecommunication Union) is the United N
13、ations Specialized Agency in the field of telecommuni- cations. The ITU Telecommunication Standardization Sector (IT-T) is a permanent organ of the ITU. The IT-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing tel
14、ecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the IT-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members o
15、f the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1. In some areas of information technology which fall within IT-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Administration“ is used fo
16、r conciseness to indicate both a telecommunication administration and a recognized operating agency. INTELLECTUAL PROPERTY RIGHTS The IT draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. The IT
17、takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by IT members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, the ITU hadhad not received notice of intellect
18、ual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. O IT 1998 All rights reserved. No part of this publi
19、cation may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. 11 Recommendation G.811 (09/97) 7 8 9 STD-ITU-T RECMN G-811-ENGL 1777 D 48b257L Ob1102b2 057 D CONTENTS Scope References Defin
20、itions Abbreviations . Frequency accuracy Noise generation . 6.1 Wander 6.2 Jitter Phase discontinuity . Degradation of the performance of a PRC . Interfaces Recommendation G.811 (09197) Page 1 1 2 2 2 2 2 4 4 4 4 . 111 STD-ITU-T RECMN G-811-ENGL 1777 48b2571 Obi02b3 T75 U Recommendation G.811 TIMIN
21、G CHARACTERISTICS OF PRIMARY REFERENCE CLOCKS (revised in 1997) 1 Scope This Recommendation outlines the requirements for Primary Reference Clocks (PRCs) suitable for synchronization supply to digital networks. These requirements apply under the normal environmental conditions specified for digital
22、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, the PRC can also provide the reference signal to the slave clock specified in Recommenda- tion G.812 within the network nodes where the PR
23、C 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 the PRC should be maintained at 1 part in 10“ or better with verification to Coordinated Universal Time (UTC). A PRC may be realized as an auto
24、nomous clock, operating independently of other sources. Alternatively, the PRC may be realized as a non- autonomous clock which is disciplined by UTC-derived precision signals received from a radio or satellite system. In either case, the requirements for long-term accuracy and short-term stability,
25、 as specified in this Recommendation, apply- The long-term accuracy of 1 part in 10“ or better is adequate when a single PRC provides the reference synchronization signal to all other clocks within a network (synchronous mode of operation). In the pseudo-synchronous mode, i.e. not all clocks in the
26、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 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 Re
27、commendations 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; all users of this Recommendation
28、 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. il CCITT Recommendation G.703 (199 1), Physical/electrical characeristics
29、 of hierarchical digital interfaces. Pl ITU-T Recommendation G.783 (1997), Characteristics of Synchronous Digital Hierarchy (SDH) equipment functional blocks. 31 ITU-T Recommendation G.8 1 O ( 1996), Definitions and terminology for synchronization networks. 41 CCITT Recommendation G.812 (1988), Timi
30、ng requirements at the outputs of slave clocks suitable for plesiochronous operation of international digital links. I PI CCIT Recommendation G. 822 ( 1988), Controlled slip rate objectives on an international digital connection. 61 ITU-T Recommendation G.823 (1993), The control of jitter and wander
31、 within digital networks which are based on the 2048 kbith hierarchy. 171 ITU-T Recommendation G.824 (1993), The control of jitter and wander within digital networks which are based on the 1544 kbits hierarchy. i81 ITU-T Recommendation G.825 (1993), The control of jitter and wander within digital ne
32、tworks which are based on the Synchronous Digital Hierarchy SDH). Recommendation G.811 (09/97) 1 3 Definitions The terms and definitions used in this Recommendation are contained in Recommendation G.810. 4 Abbreviations This Recommendation uses the following abbreviations: CMI Coded Mark Inversion F
33、PM Flicker Phase Modulation MTIE Maximum Time Interval Error NE Network Element OAM PLL PRC SDH SEC SSMB STM TDEV UI UTC WFM Operations and Maintenance Phase Locked Loop Primary Reference Clock Synchronous Digital Hierarchy SDH Equipment Clock Synchronization Status Message Byte Synchronous Transpor
34、t Module Time Deviation Unit Interval Coordinated Universal Time White Frequency Modulation 5 Frequency accuracy The maximum allowable fractional frequency offset for observation times greater than one week is 1 part in lo“, over ali applicable operational conditions. 6 Noise generation The noise ge
35、neration of 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 stabilit
36、y. The measures 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 70 of 1/30 seconds. The minimum measurement period for TDEV is
37、twelve times the integration period (T= 127). 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 using the independent clock configuration defined in Figure
38、2dG.810 should have the following limits: MTIE: 0.275 x 10-32 + 0.025 ps for 0.1 1000s 2 Recommendation G.811 (09197) STD-ITU-T RECMN G-ALL-ENGL 1777 9Bb257L Ob1102b5 Ab8 0.01 I The resultant requirements are shown in Figure 1. /I 1000 / I MTI E micro-seconds Figure 1IG.811- MTIE as a function of an
39、 observation (integration) period z The wander, expressed in TDEV, measured using the independent clock configuration defined in Figure 2dG.8 10 should have the following limits: TDEV: 3 ns for 0.1 T I 100s 0.03 T ns for 100 T I 1000s 30 ns for loo0 z 10000s The resultant requirements are shown in F
40、igure 2. TDEV nano-seconds 1 O00 1 O0 30 10 3 1 o. 1 1 10 1 O0 1000 10000 T1310580-97/402 Observation period (seconds) Figure 2/G.811- TDEV as a function of an observation (integration) period z Recommendation G.811 (09/97) 3 6.2 Jitter While most specifications in this Recommendation are independen
41、t of the output interface at which 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
42、identified in clause 8. To be consistent with other jitter requirements, the specifications are in UIpp, where the U1 corresponds to the reciprocal of the bit rate of the interface. The intrinsic jitter at 2048 kIiz and 2048 kbit/s output interfaces as measured over a 60-second interval shall not ex
43、ceed 0.05 UIpp when measured through a single pole band-pass filter with comer 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 comer fre
44、quencies at 10 Hz and 40 kHz. 7 Phase discontinuity Primary reference clocks need a very high 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
45、 result in a lengthening or shortening of the timing signai interval and must not, at the clock output, cause a phase discontinuity in excess of 1/8 UI (this refers to output signals at 1544 kbit/s, 2048 kbitfs or 2048 kHz). 8 If redundancy is applied and a clock frequency departs significantly from
46、 its nominal value, this should be detected and switching to an undegraded oscillator should then be effected. This switching should be accomplished before the MME or TDEV specification is exceeded. Degradation of the performance of a PRC 9 Interfaces The requirements in this Recommendation are rela
47、ted to reference points which may be internal to the equipment or 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 internai reference points, but rather at the exter
48、nal interfaces of the equipment. The output interfaces specified for the equipment in which the PRC clock may be contained are: - 2048 kIiz interfaces according to clause 10lG.703 with additional jitter and wander requirements as specified herein; 1544 kbit/s interfaces according to clause 2/G.703 w
49、ith additional jitter and wander requirements as specified herein; 2048 kbit/s interfaces according to clause 6/G.703 with additional jitter and wander requirements as specified herein; - other interfaces (such as sine wave 8 kHz to 5 MHz) are for further study. Note that not ail of the above interfaces may be implemented on all equipment. - - 4 Recommendation G.811 (09197) ieries A ieries B ieries C ;,ries D series E series F Series G series H Series I Series J Series K Series L Series M Series N Series O Series P Series Q Series R Series S Series T Series U S
