1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU G.827.1 (1 1 /2000) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital networks - Quality and availability targets Availa bi I ity performance objectives for end-to-end internation
2、al constant bit-rate digital paths at or above the primary rate ITU-T Recommendation G.827.1 (Formerly CCITT Recommendation) ITU-T G-SERIES RECOMMENDATIONS TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS INTERNATIONAL TELEPHONE CONNECTIONS AND CIRCUITS TRANSMISSION SYSTEMS TNDIVIDUAL CH
3、ARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE SYSTEMS ON METALLIC LINES GENERAL CHARACTERISTICS OF INTERNATIONAL CARRIER TELEPHONE METALLIC LINES COORDINATION OF RADIOTELEPHONY AND LINE TELEPHONY TESTING EQUIPMENTS TRANSMISSION MEDIA CHARACTERISTICS DIGITAL TERMINAL EQUIPMENTS DIGITAL NETWORKS GE
4、NERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER- SYSTEMS ON RADIO-RELAY OR SATELLITE LINKS AND INTERCONNECTION WITH General aspects Design objectives or digital networks Q availabil ets Network capabilities and functions SDH network characteristics Management of transport network SDH radio and
5、satellite systems integration Optical transport networks -II DIGITAL SECTIONS AND DIGITAL LINE SYSTEM G. 100-G. 199 G.200-G.299 G.300-G.399 G.400-G.449 G.450-G.499 G.500-G.599 G.600-G.699 G.700-G.799 G.800-G.899 G. 800-G.809 G.830-G.839 G.840-G.849 G.850-G.859 G.870-G.879 G.900-G.999 G. 860-G. 869 F
6、or further details, please refer to the list of ITU-T Recommendations. ITU-T Recommendation G.827.1 Availability performance objectives for end-to-end international constant bit-rate digital paths at or above the primary rate Summary This Recommendation defines network performance objectives for des
7、cribing end-to-end availability performance of international constant bit-rate digital paths at or above the primary rate. The parameters to which these objectives apply are defined in ITU-T G.827. The objectives given are independent of the physical network supporting the path. Guidance on determin
8、ing expected end-to-end performance using the objectives for path elements is provided in Annex A, and depends on the actual path topology. Source ITU-T Recommendation G.827.1 was prepared by ITU-T Study Group 13 (2001 -2004) and approved under the WTSA Resolution 1 procedure on 24 November 2000. Ke
9、ywords Availability, Availability Objectives, Availability Performance, Availability Ratio, Mean Time Between Digital Path Outages, Outage Intensity, Path Element, Unavailability Ratio. FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of
10、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 worldwide basis. The World Te
11、lecommunication 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 in WTSA Resolution 1. In some
12、 areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with IS0 and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized
13、 operating agency. DJTELLECTUAL 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 Intellec
14、tual 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 implement this Recommendation. Ho
15、wever, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. o 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, i
16、ncluding photocopying and microfilm, without permission in writing fi-om ITU. CONTENTS 1 1.1 1.2 1.3 1.4 2 3 4 5 5.1 5.2 Introduction Purpose . Scope Application of the Recommendation Allocation of end-to-end performance . References Abbreviations . Definitions Availability performance objectives .
17、End-to-end objectives . Apportionment of end-to-end objectives 5.2.1 Allocation to the national portion of the end-to-end path . 5.2.2 Allocation to the international portion of the end-to-end path Annex A . Examples of path topologies and end-to-end availability performance derivations A.l Purpose
18、. A.2 Path topologies . A.3 End-to-end Unavailability A.3.1 Linear topology . A.3.2 Redundant topology A.4 End-to-end Outage Intensity . A.4.1 Linear topology . A.4.2 Redundant topology Page 1 1 1 1 2 2 2 3 4 4 4 5 6 6 6 6 8 8 8 9 9 9 ITU-T Recommendation G.827.1 Availability performance objectives
19、for end-to-end international constant bit-rate digital paths at or above the primary rate 1 Introduction 1.1 Purpose The purpose of this Recommendation is to specify the availability parameters and objectives for end- to-end international constant bit-rate digital paths operating at or above the pri
20、mary rate. The Recommendation should be used: 8 by transmission network planners to determine the required measures and actions within the by the organization responsible for the provision of a path to determine which additional network (e.g. system reliability, maintenance organization, network pro
21、tection techniques); end-to-end actions (such as end-to-end protection switching) are necessary to satisfy Quality of Service objectives; path to ensure that availability requirements are met; 8 a by network operators providing path core elements which make up an international digital 8 by purchaser
22、s of telecommunication capacity. 1.2 Scope This Recommendation is applicable to end-to-end intemational constant bit-rate digital paths operating at or above the primary rate. These paths may be based on the Plesiochronous Digital Hierarchy (PDH), the Synchronous Digital Hierarchy (SDH) or some othe
23、r transport technology. This Recommendation is generic in that it defines parameters and objectives independent of the physical transport network supporting the paths, e.g. optical fibre, radio relay or satellite. The performance objectives are applicable end-to-end over a 27 500 km Hypothetical Ref
24、erence Path as defined in ITU-T G.826 and G.828. The end-to-end availability performance of an international digital path can be calculated from the arrangement of the constituent Path Elements (PES) and their associated objectives. Annex A gives guidance on evaluating end-to-end availability object
25、ives. The availability performance parameters and objectives for PES are defined in ITU-T G.827. In some countries the network may be subdivided into parts which are under the responsibility of different network operators. The partitioning of the objectives between these parts is outside the scope o
26、f this Recommendation. 1.3 Application of the Recommendation This Recommendation is complimentary to ITU-T G.826 and G.828 that define the error performance objectives of the transport network. The performance parameters and definitions applied to paths provided using the ATM layer and the AAL for C
27、BR services (class A, ITU-T 1.362) are for further study. Path end points may be located at users premises. Since the performance objectives are intended to satisfy the needs of the future digital network, it must be recognized that such objectives cannot be readily achieved by all of todays digital
28、 equipment and systems. The intent, however, is to encourage equipment design such that digital paths will satisfy the objectives in this Recommendation. Transport network paths are used to support services such as circuit switched, packet switched and leased line services. The quality of such servi
29、ces, as well as the performance of the network elements belonging to the service layer, is outside of the scope of this Recommendation. 1.4 Allocation of end-to-end performance Allocations of end-to-end performance of CBR paths are derived using the rules laid out in 5.2 which are length and complex
30、ity-based. Detailed allocations of performance to the individual components (lines, sections, multiplexers and cross-connects, etc.) are outside the scope of this Recommendation, but when such allocations are performed, the 5.2 national and international allocations should be achieved. 2 References
31、The following 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; users of this R
32、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. i ITU-T G.827 (2000), Availability parameters and objectives
33、 for path elements of international constant bit-rate digital paths at or above the primary rate. 2 ITU-T G.826 (1 999), Error performance parameters and objectives for international, constant bit rate digital paths at or above the primary rate. 3 ITU-T M.20 (1 992), Maintenance philosophy for telec
34、ommunication networks. 4 ITU-T M. 1010 (1988), Constitution and nomenclature of international leased circuits. 51 ITU-T G.828 (2000), Error performance parameters and objectives for international constant bit-rate synchronous digital paths. 6 ITU-T E.800 (1994), Terms and definitions related to qual
35、ity of service and network performance including dependability. 7 ITU-T E.801 (1996), Framework for Service Quality Agreement. 3 Abbreviations This Recommendation uses the following abbreviations: AR Availability Ratio FS Frontier Station HRP Hypothetical reference path Il3 International Border ICPC
36、E Inter-Country Path Core Element IG International Gateway IPCE International Path Core Element ISC Mo NPCE NPE 01 PAE PDH PE PEP PSE SDH SES SIE SLA SQA UR 4 International Switching Centre Mean Time Between Digital Path Outages National Path Core Element National Path Element Outage Intensity Path
37、Access Element Plesiochronous Digital Hierarchy Path Element Path End Point Path Switching Element Synchronous Digital Hierarchy Severely Errored Second Short Interruption Event Service Level Agreement Service Quality Agreement Unavailability Ratio Definitions This Recommendation defines the followi
38、ng terms: 4.1 path: A path is a transport entity responsible for the integrity of client network information transfer. Paths are terminated at each end by a Path End Point (PEP) (see ITU-T G.827). 4.2 path element: A PE is a portion of a path resulting from partitioning for the purpose of availabili
39、ty management (see ITU-T G.827). The physical realization and topology of the PES are under the responsibility of each network operator. ITU-T G.827 defines the following PES: - National Path Element (NPE); - - 4.3 Three different path categories are distinguished: International Path Core Element (P
40、CE); Inter-Country Path Core Element (ICPCE). path categories: Paths are categorized on the basis of the level of availability performance. e High priority - which will usually consist of high grade equipment and/or some degree of Standard priority - which may or may not have some degree of redundan
41、cy protection. Pre-emptible priority - which may form part of the protection of another path and from redundancy protection. e e which traffic can be dropped if the capacity is required for a high or standard path that has experienced a loss of transmission in one or more of its path elements. NOTE
42、- Customers of network operators may negotiate a defined level of availability for any particular Path by employing the “Framework for Service Quality Agreement“ as defined in ITU-T E.801. 4.4 availability ratio: The Availability Ratio AR, is the proportion of time that an end-to-end Path is in the
43、available state during an observation period. AR is calculated by dividing the total available time during the observation period by the duration of the observation period. The converse of AR, the unavailable ratio, UR, is the proportion of time that an end-to-end Path is in the unavailable state du
44、ring an observation period. UR is calculated by dividing the total unavailable time during the observation period by the duration of the observation period. 4.5 mean time between end-to-end Path outages: The mean time between end-to-end Path outages, Mo, is the average duration of any continuous int
45、erval during which the end-to-end Path is available. Consecutive intervals of planned available time are concatenated. The reciprocal of Mo is defined as the Outage Intensity 01. to 5 Mo F.F.S. F.F.S. F.F.S. 5 Availability performance objectives 5 to 15 15 to 55 55 to 160 160 to 3 500 AR Mo AR Mo AR
46、 Mo AR Mo F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. F.F.S. 5.1 End-to-end objectives Table 1 specifies the end-to-end objectives for a 27 500 km HRP in terms of the parameters defin
47、ed in 5.2 and 5.3. An intemational digital path at or above the primary rate shall meet its allocated objectives for all parameters concurrently. The path fails to meet the availability performance requirement if any of these objectives is not met. The objectives apply to observation periods of one
48、year (365 consecutive days), using a sliding window with 24-hour granularity. Pre-emptible priority Table UG.827.1 - End-to-end availability performance objectives for a 27 500 km international digital HRP at or above the primary rate F.F.S. RateMbith I 1.5 I Digital paths operating at bit-rates cov
49、ered by this Recommendation are carried by transmission systems (digital sections) operating at equal or higher bit-rates. Such systems must meet their allocations of the end-to-end objectives for the highest bit-rate paths which are foreseen to be carried. Meeting the allocated objectives for this highest bit-rate path should be sufficient to ensure that all paths through the system are achieving their objective. For example, in SDH, an STM-1 section may carry a VC-4 path and therefore the STM-1 section should be designed such that it will ensure that the objectives as speci
