1、 STDSITU-T RECMN X-137-ENGL 1997 = 48b2.591 Ob39742 O92 INTERNATIONAL TELECOMMUNICATION UNION ITU=T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU X.137 (08/97) SERIES X: DATA NETWORKS AND OPEN SYSTEM COMMUNICATION Public data networks - Network aspects Availability performance values for public da
2、ta networks when providing international packet-switched services ITU-T Recommendation X.137 (Previously CCIlT Recommendation) STD-ITU-T RECMN X-Ll7-ENGL 1997 m 48b259L Ob39743 T29 ITU-T X-SERIES RECOMMENDATIONS DATA NETWORKS AND OPEN SYSTEM COMMUNICATION PUBLIC DATA NETWORKS Services and facilities
3、 Interfaces X. l-X. 199 X.1-X. 19 X.20-X.49 II Transmission. signalling and switching x.50-X.89 Maintenance Administrative arrangements Model and notation Service definitions Connection-mode protocol specifications Connectionless-mode protocol specifications PICS proformas Protocol Identification .
4、Security Protocols Layer Managed Objects Conformance testing General Satellite data transmission systems MESSAGE HANDLING SYSTEMS DIRECTORY OS1 NETWORKING AND SYSTEM ASPECTS OPEN SYSTEM INTERCONNECTION INTERWORKING BETWEEN NETWORKS Networking Efficiency Naming, Addressing and Registration Abstract S
5、yntax Notation One (ASN.l) OS1 MANAGEMENT Systems Management framework and architecture Management Communication Service and Protocol Structure of Management Information Management functions SECURITY OS1 APPLICATIONS Commitment, Concurrency and Recovery Transaction processing Remote operations OPEN
6、DISTRIBUTED PROCESSING X . 1 50-X. 179 X. 180-X.199 X.200-X.299 X.200-X.209 X.210-X.2 19 X.220-X.229 X.230-X.239 X.240-X.259 X.260-X.269 X.270-X.279 X.280-X.289 X.290-X.299 X.300-X.399 X.300-X.349 X.350-X.399 X.400-X.499 X.500-X.599 X.600-X.699 X.600-X.629 X.63eX.649 X.650-X.679 X.680-X.699 X.700-X.
7、799 X.700-X.709 X.710-X.719 X.720-X.729 X.730-X.799 X.800-X.849 X.850-X.899 X.850-X.859 X.860-X.879 X.880-X.899 X.900-X.999 II For further details, please refer to ITU-T List of Recommendations. ITU-T RECOMMENDATION X.137 AVAILABILITY PERFORMANCE VALUES FOR PUBLIC DATA NETWORKS WHEN PROVIDING INTERN
8、ATIONAL PACKET-SWITCHED SERVICES Summary This Recommendation provides availability parameters and associated worstzase objectives within the X. 130-Series Recommendations on PSPDN performance. Source ITU-T Recommendation X.137 was revised by ITU-T Study Group 7 (1997-2000) and was approved under the
9、 WTSC Resolution No. 1 procedure on the 9th of August 1997. Recommendation X.137 (08/97) 1 STD-ITU-T RECMN XSL37-ENGL L977 48b257L Ob37745 8T1 FOREWORD ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of telecommuni- cations. The ITU Telecommunication
10、 Standardization Sector (ITU-T) is a permanent organ of the ITU. The 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 Standardization Confe
11、rence (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 of the IT-T is covered by the procedure laid down in WTSC Resolution No. 1. In some area
12、s 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 oper
13、ating agency. INTELLECTUAL PROPERTY RIGHTS The ITU 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 takes no position concerning the evidence, validity or applicability of claimed Intell
14、ectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, the ITU had/had not received notice of intellectual property, protected by patents, which may be required to implement this Recommen
15、dation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. O ITU 1997 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mec
16、hanical, including photocopying and microfilm, without permission in writing from the ITU. 11 Recommendation X.137 (08/97) CONTENTS 1 Introduction and scope . 2 References 3 Abbreviations . 4 Availability function 5.1 service availability definition Definition of mean time between service outages .
17、. Related parameters . : Annex A - Sampling estimation of availability parameters Procedures for estimating service availability _I . Procedures for estimating mean time between service outages Annex B - Representative end-to-end availability performance . Definition of the example end-to-end connec
18、tions . End-to-end availability performance for the Type 1 and Type 2 configuration examples . 5 Availability parameters 5.2 5.3 Values . 5.4 A.l Test of availability A.2 A.3 A.4 SPRT methodology . B.l B.2 Recommendation X.137 (08197) Page 1 3 4 4 5 5 6 6 7 8 8 10 10 11 14 14 15 iii STD-ITU-T RECMN
19、X-137-ENGL 1997 48b2.591 Ob39747 b74 m Speed Accuracy Dependability Access _ - User information Rec. Rec. transfer X.135 X.136 Recommendation X.137 AVAILABILITY PERFORMANCE VALUES FOR PUBLIC DATA NETWORKS WHEN PROVIDING INTERNATIONAL PACKET-SWITCHED SERVICES (revised in 1997) 1 Introduction and scop
20、e 1.1 This Recommendation is the fourth in a series of four Recommendations (X.134 to X.137) that define performance parameters and values for international packet-switched data communication services. Figure 1 illustrates the scope of these four Recommendations and the relationships among them. - R
21、ec. X.134 1 Networksection 1 (Packet network) Circuit section DTE DSE (Rec. X.25 or Rec. X.75) e Figure 1m.137 - Packet-switched semce performance description framework Recommendation X.137 (08/97) 1 STD-ITU-T RECMN X.137-ENGL 1477 = 48b32593 0b34748 500 National A National B International A 1.2 Rec
22、ommendation X. 134 divides a virtual connection into basic sections whose boundaries are associated with X.25 and X.75 interfaces; defines particular collections of basic sections, called virtual connection portions, for which performance values will be specified; and defines a set of Packet-layer r
23、eference Events (PES) which provides a basis for performance parameter definition. The basic sections consist of network sections and circuit sections. They are delimited, in each case, by physical Data Terminal Equipment (DTE) or Data Switching Equipment (DSE) interfaces. Two types of virtual conne
24、ction portions are identified national portions and international portions. Each PE is defined to occur when a packet crossing a section boundary changes the state of the packet layer interface. Terrestrial connection via an access network section. Connection via an access network section with one s
25、atellite circuit; or via an access network section and one or more transit network sections. Connection via a direct terrestrial internetwork section. 1.3 For comparability and completeness, packet-switched network performance is considered in the context of the 3 x 3 performance matrix defined in R
26、ecommendation X.140. Three protocol-independent data communication functions are identified in the matrix: access, user information transfer, and disengagement. These general functions correspond to call Set-up, data (and interrupt) transfer, and call clearing in packet-switched virtual call service
27、s conforming to Recommendations X.25 and X.75. Each function is considered with respect to three general performance concerns (or performance criteria”): speed, accuracy, and dependability. These express, respectively, the delay or rate, degree of correctness, and degree of certainty with which the
28、function is performed. International B 1.4 Recommendation X.135 defines protocol-specific speed of service parameters and values associated with each of the three data communication functions. Recommendation X. 136 defines protocol-specific accuracy and dependability parameters and values associated
29、 with each function. X.135 and X.136 parameters are called “primary parameters” to emphasize their direct derivation from packet layer reference events. Connection via two satellite circuits and one transit network section; or via one satellite circuit and two or more transit network sections. 1.5 A
30、n associated two-state model provides a basis for describing overall service availability. A specified availability function compares the values for a subset of the primary parameters with corresponding outage thresholds to classify the service as ”available” (no service outage) or “unavailable” (se
31、rvice outage) during scheduled service time. This Recommendation specifies the availability function and defines the availability parameters and values that characterize the resulting binary random process. 1.6 Two availability parameters are defined in this Recommendation: service availability and
32、mean time between service outages. Each parameter can be applied to any basic section or portion of a virtual connection. This generality makes the parameters useful in performance allocation and concatenation. 1.7 This Recommendation specifies availability values for national and international port
33、ions of two types (seeTable 1). Performance values for data terminal equipment are not specified, but the parameters defined in this Recommendation may be employed in such specification to assist users in establishing quantitative relationships between network performance and quality of service (see
34、 Recommendation X. 140). Table iX.137 - Virtual connection portion types for which performance values are specifieda) Portion type - Typical characteristics a) The values specified for Type B portions also apply to virtual connection portions not explicitly identified as Type A or Type B. 2 Recommen
35、dation X.137 (08197) STD-ITU-T RECMN X.137-ENGL 1977 4862571 0b37749 q47 1.8 Worst-case values for each of the two availability parameters are specified below for each virtual connection portion type identified in Table 1. The term “worst case” means that these values should be met during any hour o
36、f the day in the worst-performing virtual connection portion used in providing international packet-switched service. The performance of a virtual connection portion may be better than the worst-case values specified in this Recommendation. Design objectives that take into account more demanding use
37、r applications and network performance, and connectivity enhancements are for further study. Numerical methods for combining individual portion performance values to estimate end-to-end performance are also provided in this Recommendation. DTE to DTE values for two particular hypothetical reference
38、connections are derived using these methods in Annex B. 2 References The following ITU-T Recommendations, and other references contain provisins which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, .the editions indicated were valid. All Re
39、commendations and other references are subject to revision; all 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 list of the currently valid ITU-T Recommendations is re
40、gularly published. - ITU-T Recommendation X.l (1996), International user classes of service in, and categories of access to, public data networks and Integrated Services Digital Networks (ISDN). - IT-T Recommendation X.2 ( 19961, International data transmission services and optional user facilities
41、in public daia networks and ISDNs. - ITU-T Recommendation X.25 (1996), Interface between Data Terminal Equipment (DTE) And Data Circuit- Terminating Equipment (DCE) for terminals operating in the packet mode and connected to public daia networks by dedicated circuit. - ITU-T Recommendation X.75 (199
42、6), Packet-switched signalling system between public networks providing data transmksion services. - ITU-T Recommendation X.96 (1993), Call progress signals in public data networks. - ITU-T Recommendation X. 1 10 (1996), International routingprinciples and routingplan for public data networks. - ITU
43、-T Recommendation X. 134 (1997), Portion boundaries and packet-layer reference events: Basis for defining packet-switched performance parameters. - ITU-T Recommendation X. 135 (1 997), Speed of service (delay and throughput) performance values for public data networks when providing international pa
44、cket-switched services. - ITU-T Recommendation X.136 (1997), Accuracy and dependability performance values for public data networks when providing international packet-switched services. - ITU-T Recommendation X.138 (1997), Measurement of performance values for public data networks when providing in
45、ternational packet-switched seuvices. - IT-T Recommendation X. 139 (1 997), Echo, drop, generator and test DTEs for measurement of performance values in public data networks when providing international packet-switched services. - CCITT Recommendation X. 140 (1992), General qualiS) of service parame
46、ters for communication via public data networks. - ITU-T Recommendation X.213 (1995), Information technology - Opens Systems Interconnection -Network service definition. - CCITT Recommendation X.323 (1988), General arrangements for interworking Behueen Packet-Switched Public Data Networks (PSPDNs).
47、Recornmendation X.137 (08/97) 3 STD-ITU-T RECMN X.137-ENGL 1997 m LiBb2571 b39750 Lb9 W Availability decision parameters Call set-up Failure Probability (cfp) Call set-up Error Probability (cep) Throughput Capacity (tc) Residual Error Ratio (rer) Reset Probability (rp) Reset Stimulus Probability (rs
48、pl, rspz) Premature Disconnect Probability (pdp) Premature Disconnect Stimulus Probability (pdsp I, pdsp2) 3 Abbreviations This Recommendation uses the following abbreviations: cep Call set-up Error Probability cfp Call set-up Failure Probability DCE Data Circuit-terminating Equipment DSE Data Switc
49、hing Equipment DTE Data Terminal Equipment MTBSO Mean Time between Service Outages MTTSR Mean Time to Service Restoral OS1 Open Systems Interconnection pdp Premature Disconnect Probability pdsp Premature Disconnect Stimulus Probability PE Packet-layer reference Event rer Residual Error Ratio rp Reset Probability rsP Reset Stimulus Probability SPRT Sequential Probability Ratio Test tc Throughput Capacity Outage criteria (cfp + cep) 0.9 tc 10-3 (rspl + rp + rspz) 0.015 (pdspl + pdp + pdsp2) 0.01 4 Availability function Eight performance parameters from Recommen
