1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T G.827TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (09/2003) SERIES G: TRANSMISSION SYSTEMS AND MEDIA, DIGITAL SYSTEMS AND NETWORKS Digital networks Quality and availability targets Availability performance parameters and objectives for end-to-end inter
2、national constant bit-rate digital paths ITU-T Recommendation G.827 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.20
3、0G.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 RADIOTELEPHONY AND LINE TE
4、LEPHONY G.450G.499 TESTING EQUIPMENTS G.500G.599 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 capabilit
5、ies 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 QUALITY OF SERVICE AND PERFORMANCE GENERIC A
6、ND USER-RELATED ASPECTS G.1000G.1999 TRANSMISSION MEDIA CHARACTERISTICS G.6000G.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.827 (09/2003) i ITU-T Recommendation G.827 Availability per
7、formance parameters and objectives for end-to-end international constant bit-rate digital paths Summary This Recommendation defines network performance parameters and objectives for the path elements and end-to-end availability of international constant bit-rate digital paths. These parameters are i
8、ndependent of the type of physical network supporting the end-to-end path, e.g., optical fibre, radio relay or satellite. Guidance is included on methods for improving availability and calculating the end-to-end availability of a combination of network elements. Source ITU-T Recommendation G.827 was
9、 approved on 13 September 2003 by ITU-T Study Group 13 (2001-2004) under the ITU-T Recommendation A.8 procedure. Keywords Availability, availability objectives, availability performance, availability ratio, unavailability ratio. ii ITU-T Rec. G.827 (09/2003) FOREWORD The International Telecommunicat
10、ion Union (ITU) is the United Nations specialized 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 vi
11、ew to standardizing telecommunications on a worldwide 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 Recommenda
12、tions is covered by the procedure laid down in 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 concise
13、ness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation
14、 is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language 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. INTE
15、LLECTUAL 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, w
16、hether 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 are
17、 cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2004 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. G.827 (09/2
18、003) iii CONTENTS Page 1 Introduction 1 1.1 Scope 1 1.2 Purpose . 1 1.3 Application of this Recommendation. 2 2 References. 2 3 Abbreviations 3 4 Definitions 4 4.1 Availability. 4 4.2 End-to-end paths. 5 4.3 Path elements 5 4.4 Path element categories 6 4.5 Performance level categories 7 5 Length ca
19、tegories 7 6 Availability parameters. 8 6.1 Availability ratio and unavailability ratio. 8 6.2 Mean time between outages and outage intensity 9 7 Availability objectives 9 7.1 End-to-end availability . 9 7.2 End-to-end objectives. 9 7.3 Availability objectives for path elements. 10 8 Related availab
20、ility parameters. 11 Annex A Examples of path topologies and end-to-end path availability calculations . 12 A.1 Purpose . 12 A.2 Path topologies . 12 A.3 End-to-end unavailability calculations. 13 A.4 Large-scale telecommunication networks 16 Appendix I Bibliography 17 Appendix II Calculations and s
21、ervice levels supporting the end-to-end availability objectives 18 ITU-T Rec. G.827 (09/2003) 1 ITU-T Recommendation G.827 Availability performance parameters and objectives for end-to-end international constant bit-rate digital paths 1 Introduction This Recommendation is part of a set of Recommenda
22、tions that define the end-to-end transmission performance of the international telecommunications transport network. The performance definitions are based upon a 27 500 km Hypothetical Reference Path (HRP) defined in ITU-T Rec. G.826. 1.1 Scope This Recommendation specifies the availability paramete
23、rs and their objectives for path elements and end-to-end international constant bit rate (CBR) digital paths. These paths are based on the Plesiochronous Digital Hierarchy (PDH) as defined in ITU-T Rec. G.705, the Synchronous Digital Hierarchy (SDH) as defined in ITU-T Rec. G.707 or the Optical Tran
24、sport Network (OTN) technology as defined in ITU-T Rec. G.709. Future revisions of this Recommendation may consider the availability specification of other transmission technologies. The availability parameters and their objectives are independent of the transmission media supporting the path, e.g.,
25、 optical fibre, radio relay or satellite. The availability objectives are considered to be complementary to the error performance objectives defined in ITU-T Recs G.821, G.826, G.828 and G.8201. Packet or cell-based transport technologies are covered by other ITU-T Recommendations such as X.137 and
26、I.357. The availability performance for switched connections in the ISDN is defined in ITU-T Rec. I.355. The objectives given in this Recommendation may be used as a basis for the negotiation of enhanced performance, between the customer and the service provider, via a Service Level Agreement (SLA)
27、as described in ITU-T Recs E.800 and E.801. This Recommendation calls up other Recommendations for details about particular transport technologies such as measurement points and conditions and testing strategies. These Recommendations are for networks in general, including path protection arrangemen
28、ts: ITU-T Rec. G.805; for terrestrial optical fibre cable systems: ITU-T Recs G.872 and G.911; for microwave radio-relay transmission systems: ITU-R Recs F.1492 and F.1493; for satellite systems: ITU-R Rec. S.579-5; for details of the control protocol employed to switch between main and protection p
29、aths in SDH transport systems: ITU-T Recs G.841 and G.842. 1.2 Purpose This Recommendation is intended to be useful to: purchasers of telecommunication capacity; transmission-network-planners, to determine the required infrastructure to support the telecommunication service offering; 2 ITU-T Rec. G.
30、827 (09/2003) organizations responsible for the supply of capacity, to determine what additional end-to-end support may be needed (such as end-to-end protection switching) to fulfil the contracted quality of service objectives; network operators providing the network elements, to ensure that the con
31、tracted availability objectives are met; national public network supervisory bodies. 1.3 Application of this Recommendation This Recommendation defines the availability of international end-to-end CBR digital paths based upon the availability of their constituent path elements. A path is constructed
32、 using path elements that meet availability objectives obtained using the principles specified in 7.2. The designer will assemble the path elements into the path such that the path will meet the Table 2 objectives. The path may include various protection topologies; examples are given in Annex A. Th
33、e characteristics of path elements depend upon their length, their location in the end-to-end circuit and their quality category. More detailed analysis of their availability down to network operator domains, server layers, subnetworks or access groups is outside the scope of this Recommendation. Te
34、chniques for improving the end-to-end availability by employing additional protection network elements are described in Annex A. The availability is calculated from unity minus the unavailability. Note that one or both of the end-to-end paths end points may be located at the users premises. Annex A
35、also gives detailed guidance on methodologies for evaluating the end-to-end availability. In some cases, an international telecommunications circuit may be provided by a group of private network operators. Then, the customer must negotiate the availability objectives required between these network o
36、perators to establish a SLA contract possibly using the performance specified in this Recommendation as guidance. 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
37、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 li
38、st 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 E.800 (1994), Terms and definitions related to quality of service and net
39、work performance including dependability. 2 ITU-T Recommendation E.801 (1996), Framework for Service Quality Agreement. 3 ITU-R Recommendation F.1492 (2000), Availability objectives for real digital radio-relay links forming part of the international portion constant bit rate digital path at or abov
40、e the primary rate. 4 ITU-R Recommendation F.1493 (2000), Availability objectives for real digital radio-relay links forming part of national portion constant bit rate digital path at or above the primary rate. ITU-T Rec. G.827 (09/2003) 3 5 ITU-T Recommendation G.705 (2000), Characteristics of ples
41、iochronous digital hierarchy (PDH) equipment functional blocks. 6 ITU-T Recommendation G.707/Y.1322 (2000), Network node interface for the synchronous digital hierarchy (SDH). 7 ITU-T Recommendation G.709/Y.1331 (2003), Interfaces for the Optical Transport Network (OTN). 8 ITU-T Recommendation G.805
42、 (2000), Generic functional architecture of transport networks. 9 ITU-T Recommendation G.821 (2002), Error performance of an international digital connection operating at a bit rate below the primary rate and forming part of an Integrated Services Digital Network. 10 ITU-T Recommendation G.826 (2002
43、), End-to-end error performance parameters and objectives for international, constant bit-rate digital paths and connections. 11 ITU-T Recommendation G.828 (2000), Error performance parameters and objectives for international, constant bit-rate synchronous digital paths. 12 ITU-T Recommendation G.82
44、01 (2003), Error performance parameters and objectives for multi-operator international paths within the Optical Transport Network (OTN). 13 ITU-T Recommendation G.841 (1998), Types and characteristics of SDH network protection architectures. 14 ITU-T Recommendation G.842 (1997), Interworking of SDH
45、 network protection architectures. 15 ITU-T Recommendation G.872 (2001), Architecture of optical transport networks. 16 ITU-T Recommendation G.911 (1997), Parameters and calculation methodologies for reliability and availability of fibre optic systems. 17 ITU-T Recommendation I.355 (2000), ISDN 64 k
46、bit/s connection type availability performance. 18 ITU-T Recommendation I.357 (2000), B-ISDN semi-permanent connection availability. 19 ITU-R Recommendation S.579-5 (2001), Availability objectives for a hypothetical reference circuit and a hypothetical reference digital path when used for telephony
47、using pulse code modulation, or as part of an integrated services digital network hypothetical reference connection, in the fixed-satellite service. 20 ITU-T Recommendation X.137 (1997), Availability performance values for public data networks when providing international packet-switched services. 3
48、 Abbreviations This Recommendation uses the following abbreviations: AR Availability Ratio CBR Constant Bit Rate CP Customer Premises FS Frontier Station HRP Hypothetical Reference Path IB International Border 4 ITU-T Rec. G.827 (09/2003) ICPCE Inter-Country Path Core Element IG International Gatewa
49、y IPCE International Path Core Element Mo Mean time between outages MTTR Mean Time To Restore NPCE National Path Core Element NPE National Path Element OI Outage Intensity OTN Optical Transport Network PDH Plesiochronous Digital Hierarchy PE Path Element PEP Path End Point SA Service Availability SDH Synchronous Digital Hierarchy SES Severely Errored Second SLA Service Level Agreement TIC Terminal International Centre U Unavailability UR Unavailability Ratio Failure rate Restoration rate 4 De
