1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T G.813TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (03/2003) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital networks Design objectives for digital networks Timing characteristics of SDH equipment slave clocks (SEC) ITU-T
2、Recommendation G.813 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
3、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 TESTING EQUIPMENTS G.500G.59
4、9 TRANSMISSION MEDIA 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 Quality and availability targets G.820G.829 Network capabilities and functions G.830G.839 SDH network charac
5、teristics 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 QUALITY OF SERVICE AND PERFORMANCE G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.
6、6999 DIGITAL TERMINAL EQUIPMENTS G.7000G.7999 DIGITAL NETWORKS G.8000G.8999 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. G.813 (03/2003) i ITU-T Recommendation G.813 Timing characteristics of SDH equipment slave clocks (SEC) Summary This Recommendation outlines
7、minimum requirements for timing devices used in synchronizing network equipment that operate according to the principles governed by the Synchronous Digital Hierarchy (SDH). This 2003 revision of ITU-T Rec. G.813 includes, in addition to a few editorial points, two technical points: An update in 8.2
8、 b) of the jitter tolerance for Option 2 that has already been published in ITU-T Rec. G.813 Corrigendum 1 in 2001. The introduction of STM-64 jitter generation values for Options 1 and 2 in clause 7.3. Source ITU-T Recommendation G.813 was revised by ITU-T Study Group 15 (2001-2004) and approved un
9、der the WTSA Resolution 1 procedure on 16 March 2003. Keywords Clock performance objectives, Clock performance parameters, Jitter performance, SDH equipment clock, Wander performance. ii ITU-T Rec. G.813 (03/2003) FOREWORD The International Telecommunication Union (ITU) is the United Nations special
10、ized agency in the field of telecommunications. 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 standardizing telecommunications on a w
11、orldwide 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 covered by the procedure laid down i
12、n 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 indicate both a telecommunication adm
13、inistration and a recognized operating agency. INTELLECTUAL 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 appli
14、cability 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 notice of intellectual property, protected by patents, which may be required to imple
15、ment 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. ITU 2003 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prio
16、r written permission of ITU. ITU-T Rec. G.813 (03/2003) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 2 4 Abbreviations 2 5 Frequency accuracy 3 6 Pull-in, hold-in, and pull-out ranges. 3 6.1 Pull-in range . 3 6.2 Hold-in range 3 6.3 Pull-out range . 3 7 Noise generation . 3 7.1 Wander i
17、n locked mode 4 7.2 Non-locked Wander 6 7.3 Jitter 7 8 Noise tolerance . 8 8.1 Wander tolerance 8 8.2 Jitter tolerance 11 9 Noise transfer 13 10 Transient response and holdover performance. 14 10.1 Short-term phase transient response. 14 10.2 Long-term phase transient response (Holdover) 16 10.3 Pha
18、se response to input signal interruptions 18 10.4 Phase discontinuity. 18 11 Interfaces. 19 Appendix I Guidance on the relationship between network limits and input noise tolerances 19 I.1 Option 1 network limits 19 I.2 Option 2 network limits 19 Appendix II Considerations on bandwidth requirements,
19、 noise accumulation and payload wander accumulation 20 II.1 Introduction 20 II.2 Relevant network requirements and assumptions for Option 1 20 II.3 Relevant network requirements and assumptions for Option 2 23 ITU-T Rec. G.813 (03/2003) 1 ITU-T Recommendation G.813 Timing characteristics of SDH equi
20、pment slave clocks (SEC) 1 Scope This Recommendation outlines requirements for timing devices used in synchronizing network equipment that operate according to the principles governed by the Synchronous Digital Hierarchy (SDH). These requirements apply under the normal environmental conditions speci
21、fied for the SDH equipment. In normal operation, SDH equipment contains a slave clock traceable to a primary reference clock. In general, the SDH equipment clock (SEC) will have multiple reference inputs. In the event that all links between the master and the slave clock fail, the equipment should b
22、e capable of maintaining operation (holdover) within prescribed performance limits. The SEC is part of the SDH equipment, the functions of which are specified in ITU-T Rec. G.783 as the Synchronous Equipment Timing Source (SETS). Slave clocks used in SDH equipment must meet specific requirements in
23、order to comply with network jitter requirements for plesiochronous tributaries. This Recommendation contains two options for the SEC. The first option, referred to as “Option 1,“ applies to SDH networks optimized for the 2048 kbit/s hierarchy. These networks allow the worst-case synchronization ref
24、erence chain as specified in Figure 8-5/G.803. The second option, referred to as “Option 2,“ applies to SDH networks optimized for the particular 1544 kbit/s hierarchy that includes the rates 1544 kbit/s, 6312 kbit/s, and 44 736 kbit/s. The synchronization reference chain for these networks is defin
25、ed in Appendix II. An SDH equipment slave clock should comply with all of the requirements specific to one option and should not mix requirements between Options 1 and 2. In the clauses where one requirement is specified, the requirements are common to both options. It is the intention that Options
26、1 and 2 should be harmonized in the future. Careful consideration should be taken when interworking between networks with SECs based on Option 1 and networks with SECs based on Option 2. This Recommendation defines the minimum requirements for clocks in SDH NEs. However, some SDH NEs may have a high
27、er quality clock. This Recommendation allows for proper network operation when a SEC (Option 1 or 2) is timed from another SEC (like option), or a higher quality clock. Hierarchical timing distribution is recommended for SDH networks. Timing should not be passed from a SEC in free-run/holdover mode
28、to a higher quality clock since the higher quality clock should not follow the SEC signal during fault conditions. 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
29、 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 references listed below. A l
30、ist 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. 1 ITU-T Recommendation G.703 (2001), Physical/electrical characteristics of hierarchical digita
31、l interfaces. 2 ITU-T Recommendation G.783 (2000), Characteristics of synchronous digital hierarchy (SDH) equipment functional blocks. 2 ITU-T Rec. G.813 (03/2003) 3 ITU-T Recommendation G.801 (1988), Digital transmission models. 4 ITU-T Recommendation G.803 (2000), Architecture of transport network
32、s based on the synchronous digital hierarchy (SDH). 5 ITU-T Recommendation G.810 (1996), Definitions and terminology for synchronization networks. 6 ITU-T Recommendation G.811 (1997), Timing requirements of primary reference clocks. 7 ITU-T Recommendation G.812 (1998), Timing requirements of slave c
33、locks suitable for use as node clocks in synchronization networks. 8 ITU-T Recommendation G.822 (1988), Controlled slip rate objectives on an international digital connection. 9 ITU-T Recommendation G.823 (2000), The control of jitter and wander within digital networks which are based on the 2048 kb
34、it/s hierarchy. 10 ITU-T Recommendation G.824 (2000), The control of jitter and wander within digital networks which are based on the 1544 kbit/s hierarchy. 11 ITU-T Recommendation G.825 (2000), The control of jitter and wander within digital networks which are based on the synchronous digital hiera
35、rchy (SDH). 12 ITU-T Recommendation Q.551 (2002), Transmission characteristics of digital exchanges. 3 Definitions The terms and definitions used in this Recommendation are contained in ITU-T Rec. G.810. 4 Abbreviations This Recommendation uses the following abbreviations: CMI Coded Mark Inversion F
36、PM Flicker Phase Modulation MTIE Maximum Time Interval Error NE Network Element OAM Operation 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 Tim
37、e Deviation UI Unit Interval UTC Coordinated Universal Time WFM White Frequency Modulation ITU-T Rec. G.813 (03/2003) 3 5 Frequency accuracy a) Option 1 Under free-running conditions, the SEC output frequency accuracy should not be greater than 4.6 ppm with regard to a reference traceable to a G.811
38、 clock. NOTE The time interval for this accuracy is for further study. Values of 1 month and 1 year have been proposed. b) Option 2 Under free-running conditions, the SEC output frequency accuracy should not be greater than 20 ppm. Note that payload performance is not guaranteed for a fractional fre
39、quency deviation with a magnitude greater than 4.6 ppm. However, Operations and Maintenance (OAM) functionality shall be supported when a SEC is performing at the minimum accuracy. 6 Pull-in, hold-in, and pull-out ranges 6.1 Pull-in range a) Option 1 The minimum pull-in range should be 4.6 ppm, what
40、ever the internal oscillator frequency offset may be. b) Option 2 The minimum pull-in range shall be 20 ppm, whatever the internal oscillator frequency offset may be. 6.2 Hold-in range a) Option 1 The hold-in range for Option 1 is not required. b) Option 2 The minimum hold-in range shall be 20 ppm,
41、whatever the internal oscillator frequency offset may be. 6.3 Pull-out range a) Option 1 The pull-out range is for further study. A minimum value of 4.6 ppm has been proposed. b) Option 2 The pull-out range is not specified. 7 Noise generation The noise generation of a SEC represents the amount of p
42、hase noise produced at the output when there is an ideal input reference signal or the clock is in holdover state. A suitable reference, for practical testing purposes, implies a performance level at least 10 times more stable than the output requirements. The ability of the clock to limit this nois
43、e is described by its frequency stability. The measures MTIE and Time Deviation (TDEV) are useful for characterisation 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 0of 1/30 seconds. The m
44、inimum measurement period for TDEV is twelve times the integration period (T = 12). 4 ITU-T Rec. G.813 (03/2003) 7.1 Wander in locked mode a) Option 1 When the SEC is in the locked mode of operation, the MTIE measured using the synchronized clock configuration defined in Figure 1a/G.810 should have
45、the limits in Table 1, if the temperature is constant (within 1K): Table 1/G.813 Wander generation (MTIE) for Option 1 with constant temperature MTIE limit Observation interval 40 ns 0.1 100 s The resultant requirements are shown by the thin solid line in Figure 1. G.813_F010.1 1.0 10 100 1000(const
46、. temp.)(var. temp.)MTIE ns10110001006340Observation interval s113150Figure 1/G.813 Wander generation (MTIE) for Option 1 ITU-T Rec. G.813 (03/2003) 5 When the SEC is in the locked mode of operation, the TDEV measured using the synchronized clock configuration defined in Figure 1a/G.810 should have
47、the limits in Table 3, if the temperature is constant (within 1K): Table 3/G.813 Wander generation (TDEV) for Option 1 with constant temperature TDEV limit Observation interval 3.2 ns 0.1 15 s, exceed the following limit: T(S) = (a1+ a2) S + 0.5 b S2+ c ns where: a1= 50 ns/s (see Note 1); 2= 2000 ns
48、/s (see Note 2); b = 1.16 104ns/s2(see Note 3); c = 120 ns (see Note 4). This limit is subject to a maximum frequency offset of 4.6 ppm. The behaviour for S 1 Hz Wander accumulation in a synchronization distribution chain; SEC accumulation 1 Hz 1 s maximum phase transients due to automatic timing re
49、storation 1 Hz From this it is concluded that the bandwidth of the SEC should be in the range 1-10 Hz. ITU-T Rec. G.813 (03/2003) 23 II.3 Relevant network requirements and assumptions for Option 2 II.3.1 Clock bandwidth requirements The following considerations were taken into account in determining the maximum bandwidth of a G.813 clock used in networks based on the G.824 1544 kbit/s hierarchy: 1544 kbit/s facilities from the G.824 hierarchy used for synchronization distribution may experience a
