1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T G.825TELECOMMUNICATIONSTANDARDIZATION SECTOR OF ITU (03/2000) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital networks Quality and availability targets The control of jitter and wander within digital networks which are based
2、 on the synchronous digital hierarchy (SDH) ITU-T Recommendation G.825 (Formerly CCITT Recommendation) ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS G.100G.199 INTERNATIONAL ANALOGUE CARRIER SYSTEM GENERAL
3、 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 SATELLITE LINKS AND INTERCONNECTION
4、WITH METALLIC LINES G.400G.449 COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY G.450G.499 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 fun
5、ctions 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 For further details, please refer to the list of ITU-T
6、Recommendations. ITU-T G.825 (03/2000) i ITU-T Recommendation G.825 The control of jitter and wander within digital networks which are based on the synchronous digital hierarchy (SDH) Summary This ITU-T Recommendation specifies the maximum network limits of jitter and wander that shall not be exceed
7、ed and the minimum equipment tolerance to jitter and wander that shall be provided at any relevant transport or synchronization interfaces which are based on the Synchronous Digital Hierarchy (SDH). The requirements for the jitter and wander characteristics that are specified in this ITU-T Recommend
8、ation must be adhered to in order to ensure interoperability of equipment produced by different manufacturers and a satisfactory network performance. Source ITU-T Recommendation G.825 was revised by ITU-T Study Group 13 (1997-2000) and approved under the WTSC Resolution 1 procedure on 10 March 2000.
9、 Keywords Clocks, Input Jitter Tolerance, Input Wander Tolerance, Network Limits, Output Jitter, Output Wander, Synchronization, Timing. ii ITU-T G.825 (03/2000) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The
10、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 worldwide basis. The World Telecommunication Standard
11、ization Conference (WTSC), 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 WTSC Resolution 1. In some areas of information
12、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 administration and a recognized operating agency. INT
13、ELLECTUAL 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,
14、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 implement this Recommendation. However, implementors ar
15、e cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. Ge3 ITU 2001 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopyin
16、g and microfilm, without permission in writing from the ITU. ITU-T G.825 (03/2000) iii CONTENTS Page 1 Scope. 1 2 References. 1 3 Definitions 2 4 Abbreviations 2 5 Network limits for the maximum output jitter and wander at any hierarchical interface 3 5.1 Network limits for jitter 3 5.2 Network limi
17、ts for wander 4 6 The specification of individual digital equipment 4 6.1 Jitter and wander tolerance for STM-N input ports 4 6.1.1 STM-N input wander tolerance . 6 6.1.2 STM-N input jitter tolerance . 6 6.2 Jitter and wander generation. 10 6.3 Jitter and wander transfer 10 Appendix I Relationship b
18、etween network interface jitter requirements and input jitter tolerance 11 I.1 Network interface jitter requirements. 11 I.2 Input jitter tolerance of network equipment . 12 Appendix II Measurement methodology for output wander of synchronous interfaces 14 Appendix III SDH Line systems and Interwork
19、ing implications . 14 iv ITU-T G.825 (03/2000) Introduction and background In a digital network, jitter and wander accumulate on transmission paths according to the jitter and wander generation and transfer characteristics of each equipment interconnected. This equipment may be different types of mu
20、ltiplexers/demultiplexers, cross-connects, clocks and line systems, for example. An excessive amount of jitter and wander can adversely affect both digital (e.g. by generation of bit errors, slips and other abnormalities) and analogue signals (e.g. by unwanted phase modulation of the transmitted sig
21、nal). The consequences of such impairment will, in general, depend on the particular service that is being carried and the terminating or adaptation equipment involved. It is therefore necessary to set limits on the maximum magnitude of jitter and wander, and the corresponding minimum jitter and wan
22、der tolerance at network interfaces, in order to guarantee a proper quality of the transmitted signals and a proper design of the equipment. These network limits are independent from the particular service that is being carried. ITU-T G.825 (03/2000) 1 ITU-T Recommendation G.825 The control of jitte
23、r and wander within digital networks which are based on the synchronous digital hierarchy (SDH) 1 Scope The scope of this ITU-T Recommendation is to define the parameters and the relevant values that are able to control satisfactorily the amount of jitter and wander present at the SDH network-networ
24、k interfaces (NNI). SDH network interfaces, to which this ITU-T Recommendation is applicable, are defined in terms of bit rates and frame structures in ITU-T Recommendation G.707; their electrical characteristics are described in ITU-T Recommendation G.703 and the optical characteristics in ITU-T Re
25、commendations G.957 and G.691. Additional information regarding the architecture of SDH networks is found in ITU-T Recommendation G.803. Jitter and wander requirements for PDH and synchronization networks are specified in ITU-T Recommendation G.823, for networks based on the first level bit rate of
26、2048 kbit/s, and in ITU-T Recommendation G.824 for networks based on the first-level bit rate of 1544 kbit/s. The jitter and wander control philosophy is based on the need: to recommend a maximum network limit that should not be exceeded at any relevant interface; to recommend a consistent framework
27、 for the specification of individual digital equipment (i.e. jitter and wander transfer, tolerance and generation requirements); to provide sufficient information and guidelines for organizations to measure and study jitter and wander accumulation in any network configuration. 2 References The follo
28、wing ITU-T Recommendations 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 R
29、ecommendation 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. ITU-T Recommendation G.691 (draft), Optical interfaces for s
30、ingle-channel STM-64, STM-256 and other SDH systems with optical amplifiers. ITU-T Recommendation G.703 (1998), Physical/electrical characteristics of hierarchical digital interfaces. ITU-T Recommendation G.707 (1996), Network Node interface for the Synchronous Digital Hierarchy (SDH). ITU-T Recomme
31、ndation G.783 (1997), Characteristics of synchronous digital hierarchy (SDH) equipment functional blocks. ITU-T Recommendation G.803 (2000), Architecture of transport networks based on the synchronous digital hierarchy (SDH). 2 ITU-T G.825 (03/2000) ITU-T Recommendation G.810 (1996), Definitions and
32、 terminology for synchronization networks. ITU-T Recommendation G.811 (1997), Timing characteristics of primary reference clocks. ITU-T Recommendation G.812 (1998), Timing requirements of slave clocks suitable for use as node clocks in synchronization networks. ITU-T Recommendation G.813 (1996), Tim
33、ing characteristics of SDH equipment slave clocks (SEC). ITU-T Recommendation G.823 (2000), The control of jitter and wander within digital networks which are based on the 2048 kbit/s hierarchy. ITU-T Recommendation G.824 (2000), The control of jitter and wander within digital networks which are bas
34、ed on the 1544 kbit/s hierarchy. ITU-T Recommendation G.832 (1998), Transport of SDH elements on PDH networks Frame and multiplexing structures. ITU-T Recommendation G.957 (1999), Optical interfaces for equipments and systems relating to the synchronous digital hierarchy. ITU-T Recommendation O.171
35、(1997), Timing jitter and wander measuring equipment for digital systems which are based on the Plesiochronous Digital Hierarchy (PDH). ITU-T Recommendation O.172 (1999), Jitter and wander measuring equipment for digital systems which are based on the Synchronous Digital Hierarchy (SDH). 3 Definitio
36、ns This ITU-T Recommendation defines the following terms. Additional definitions relating to synchronization networks are provided in ITU-T Recommendation G.810. 3.1 synchronous interface: These interfaces provide an output signal with frequency that is normally traceable to a PRC. 3.2 asynchronous
37、interface: These interfaces provide an output signal with frequency that is not traceable to a PRC and that meets the frequency offset requirements given in ITU-T Recommendation G.703. 3.3 synchronization interface: These interfaces are synchronous and network wander limits are specified using Maxim
38、um Time Interval Error (MTIE) and Time Deviation (TDEV) parameters with values given in this ITU-T Recommendation. 4 Abbreviations This ITU-T Recommendation uses the following abbreviations. Additional abbreviations will be added. CMI Code Mark Inversion ITU-T International Telecommunication Union T
39、elecommunication Standardization Sector MRTIE Maximum Relative Time Interval Error MS-AIS Multiplex Section Alarm Indication Signal MTIE Maximum Time Interval Error NE Network Element NNI Network Node Interface ITU-T G.825 (03/2000) 3 pk-pk Peak-to-Peak RTIE Relative Time Interval Error SDH Synchron
40、ous Digital Hierarchy TDEV Time Deviation TIE Time Interval Error UI Unit Interval UNI User Network Interface 5 Network limits for the maximum output jitter and wander at any hierarchical interface 5.1 Network limits for jitter The limits given in Table 1 represent the maximum permissible levels of
41、jitter at interfaces within a digital network. Jitter as measured over a 60 second interval shall not exceed the limits given in Table 1, when using the specified measurement filters. The limits shall be met for all operating conditions and regardless of the amount of equipment preceding the interfa
42、ce. In general, these network limits are compatible with the minimum tolerance to jitter that all equipment input ports are required to provide. Guidelines for the derivation of the parameters values of Table 1 are given in Appendix I. There is a close relationship between network limits and input t
43、olerance such that the jitter measurement filter cut-off frequencies used in Table 1 have the same values as the jitter tolerance mask corner frequencies used in 6.1. Appendix I provides further information about this relationship. The high-pass measurement filters of Table 1 have a first-order char
44、acteristic and a roll-off of 20 dB/decade. The low-pass measurement filters have a maximally-flat, Butterworth characteristic and a roll-off of 60 dB/decade. ITU-T Recommendation O.172 contains a functional description of equipment appropriate for measurement of jitter in SDH systems. Further specif
45、ications for the frequency response of the jitter measurement function such as measurement filter accuracy and additional allowed filter poles are also given in ITU-T Recommendation O.172. Table 1/G.825 Maximum permissible jitter at network interfaces Interface Measurement bandwidth, 3 dB frequencie
46、s (Hz) Peak-to-peak amplitude (UIpp) 500 to 1.3 M 1.5 STM-1e (Notes 1, 2) 65 k to 1.3 M 0.075 500 to 1.3 M 1.5 STM-1 (Note 4) 65 k to 1.3 M 0.15 1 k to 5 M 1.5 STM-4 (Note 4) 250 k to 5 M 0.15 5 k to 20 M 1.5 STM-16 (Note 4) 1 M to 20 M 0.15 4 ITU-T G.825 (03/2000) Table 1/G.825 Maximum permissible
47、jitter at network interfaces (concluded) Interface Measurement bandwidth, 3 dB frequencies (Hz) Peak-to-peak amplitude (UIpp) 20 k to 80 M 1.5 STM-64 (Note 4) 4 M to 80 M 0.15 (Note 3) NOTE 1 Electrical format CMI-encoded, according to G.703. NOTE 2 For networks deployed with G.813 Option II clocks
48、or G.812 Type II, III or IV clocks, STM-1 requirements apply to STM-1e. NOTE 3 The effect of dispersion and non-linearities on the eye opening and on the choice of this value is for further study. NOTE 4 STM-1 1 UI = 6.43 ns STM-4 1 UI = 1.61 ns STM-16 1 UI = 0.402 ns STM-64 1 UI = 0.100 ns 5.2 Netw
49、ork limits for wander STM-N interfaces are defined as synchronization interfaces. Network limits for wander at synchronization interfaces are specified in ITU-T Recommendation G.823 for networks based on the 2048 kbit/s hierarchy, and in ITU-T Recommendation G.824 for networks based on the 1544 kbit/s hierarchy. 6 The specification of individual digital equipment To help ensure that the interconnection of digital equipment does not result in accumulated jitter that exceeds network limits, the jitter transfer and
