1、Report No. 24 A Technical ReportonNovember 1993 Network Survivability Performance Prepared byT1A1.2Working Group on Network Survivability PerformanceCommittee T1 is sponsored by the Alliance for Telecommunciations Industry Solutions(formerly the Exchange Carriers Standards Association)Accredited by
2、American National Standards InstituteCopyright 1994 by Alliance for Telecommunications IndustrySolutions All rights reserved.No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher.A Technical Re
3、port onNetwork Survivability PerformanceAbstractThis Technical Report provides information on the network survivabilityperformance of telecommunications networks. Although techniques,parameters and methods needed to study network survivabilityperformance are defined, recommended parameter objectives
4、 are notestablished.Document T1A1.2/93-001R3Prepared by T1A1.2Working Group on Network Survivability PerformanceForewordThis report addresses the growing concerns from the telecommunica-tions community about the survivability of telecommunicationsnetworks, including the services provided. It is inte
5、nded to provide abasis for designing and operating telecommunications networks to meetusers expectations regarding network survivability.The intended audience of this report includes providers, users and regu-lators of telecommunications networks and services, as well astelecommunications equipment
6、providers.Suggestions for improvement of this report are welcome. They shouldbe sent to the Alliance for Telecommunications Industry Solutions,Suite 500, 1200 G Street NW., Washington, DC 20005.Working Group T1A1.2 (formerly T1Q1.2) on Network Survivability,which developed this report had the follow
7、ing officers and participants:Chair: A. ZolfaghariVice-Chair and Chief Editor: F. KaudelEditors: J. Cassano M. PettyR. Doverspike J. YuristyG. Koerner F. ZamoraJ. Lord A. ZolfaghariS. MakrisActive Participants:T. Adcock M. Kanotz M. PettyR. Arsaga C. Karpewicz T. PillaiL. Barker F. Kaudel R. PintoN.
8、 Barlett G. Koerner A. ReillyF. Burns B. Lollar L. SayadianJ. Cassano J. Lord T. SoejimaM. Daneshmand S. Makris J. SosnoskyR. Doverspike H. Mar E. TurnerF. Ellefson J. McDonough R. WallerW. Grover M. Mostrel G. WilliamsH. Holton S. Nadkarni J. YuristyJ. James D. Nak F. ZamoraR. Jensen C. Pack A. Zol
9、faghariiTable of Contents0. Executive Summary. 11. Purpose, Scope, Application and Outline 21.1 Purpose. 21.2 Scope 1.3 Application. 31.4 Outline2. Related Work .2.1 Committee T1 Standards Work 32.2 International Standards Work 42.3 Other Domestic Forums and Committees 2.4 U.S. NSTAC Task Force Work
10、 . 53. Introduction 63.1 User Categories 84. Framework for Quantifying and Categorizing Service Outages . 94.1 Service Outage Parameters 104.2 Service Outage Categories . 115. Framework for Classifying Network Survivability Techniques and Measures. 125.1 Physical Layer 145.2 System Layer 155.3 Logic
11、al Layer .5.4 Service Layer . 175.5 Summary 6. Network Survivability Techniques 186.1 Physical Layer 206.2 System Layer 216.2.1 Point-to-Point Systems with Automatic Protection Switching. 216.2.2 Rings .6.2.2.1 Unidirectional Ring 226.2.2.2 Bidirectional Ring.6.2.2.3 Line Protection Switched Ring .
12、236.2.2.4 Path Protection Switched Ring . 256.3 Logical Layer . 266.3.1 DCS Reconfiguration Strategies. 266.3.1.1 Detection and Notification 276.3.1.2 Identification. 276.3.1.3 Path (Route) Selection 276.3.1.4 Rerouting 306.3.1.5 Normalization .6.3.1.6 Summary of DCS Reconfiguration Methods 306.4 Se
13、rvice Layer . 316.4.1 Circuit Switching 316.4.1.1 Size Limits ii6.4.1.2 Dynamic Routing 316.4.1.3 Reconfiguration 326.4.1.4 Network Management 326.4.1.5 Multi-Serving6.4.2 Packet Switching 326.4.3 Common Channel Signaling. 336.4.3.1 Service Layer Architecture for MTP 336.4.3.2 Service Layer Architec
14、ture for SCCP. 376.4.3.3 Manual Traffic Management Controls . 386.4.3.4 Relationship of Software Diversity to CCSN Reliability . 386.5 Integrated Techniques 427. Network Survivability Performance Analysis . 447.1 Network Survivability Characterization 7.2 Network Survivability Analysis Model . 447.2
15、.1 Given Occurrence of Failure Survivability Model . 447.2.2 Random Occurrence of Failure Survivability Model . 457.2.3 Application of GOF and ROF Models 457.3 GOF Network Survivability Measures 467.3.1 Service Layer Examples . 477.3.2 Logical and System Layer Examples . 487.4 ROF Network Survivabil
16、ity Measures. 507.4.1 Service Layer Examples . 507.4.1.1 Circuit Switching 7.4.1.2 Packet Switching 517.4.1.3 Common Channel Signaling. 517.4.2 Logical and System Layer Examples . 557.5 Qualitative Assessment of Network Survivability Techniques . 578. Suggestions to General Industry 589. Recommendat
17、ions to Standards Organizations . 599.1 Recommendations for Committee T1 9.2 Recommendations for Future T1A1.2 Work . 5910. Summary 5911. Bibliography 6012. Definitions . 6413. Abbreviations and Acronyms 66Appendix A. Telecommunications Service Priority. 67Appendix B. Example Network Survivability A
18、nalyses and Assessments 70Appendix B.1 Bidirectional Ring Survivability Example 70Appendix B.2 Network Survivability Assessment Example 71Appendix C. User Expectations . 73Appendix C.1 U.S. Government User Expectations . 73Appendix D. Tolerance Categories for Restoration Times 76Index 8110. Executiv
19、e SummaryAs a result of growing concerns from the telecommunications community, thisTechnical Report has been developed to address the survivability oftelecommunications networks, including the services provided.The report is needed to provide a common understanding and common assessmenttechniques f
20、or network survivability. It provides a basis for designing andoperating telecommunications networks to meet users expectations regardingnetwork survivability. The intended audience of this report includes providers,users and regulators of telecommunications networks and services, as well astelecomm
21、unications equipment suppliers. The report also provides a foundationfor continuing industry activities in this area.Terminology to characterize network survivability is provided. In particular,network survivability is defined to be: (i) the ability of a network to maintain orrestore an acceptable l
22、evel of performance during network failures by applyingvarious restoration techniques, and (ii) the mitigation or prevention of serviceoutages from network failures by applying preventative techniques. Networksurvivability includes other industry terms, such as “network integrity” and“network reliab
23、ility,” and is related to “network availability.”A framework for quantifying service outages is developed. The parameters for thisframework are the unservability of services affected by the network failure, theduration of the outage, and the extent of the failure (e.g., geographical area,population,
24、 or network). Categories of service outage are outlined. The categoriesdepend on type of user, network and service. Types of users include carriers,residential customers, government agencies, educational and medical institutions,as well as business and financial customers.A four-layer framework is d
25、escribed for classification of network survivabilitytechniques in telecommunication networks. These layers are physical, system,logical and service. In addition to providing a common basis for describing andcomparing techniques, the framework identifies layer(s) responsible for reacting tothe variou
26、s types of failures and their interaction.Techniques available to network providers to enhance the survivability of theirtelecommunications networks at each layer are described. Two basic approachesto compare survivability techniques and evaluate network survivabilityperformance are given. The first
27、 approach (Given Occurrence of Failure, or GOF)uses a conditional approach and defines survivability measures for a networkassuming that given failures have occurred. The second approach (RandomOccurrence of Failure, or ROF) uses probability of network failure and, possibly,Technical Report No. 242r
28、ates of repair and/or restoration, to calculate various measures of networkunservability or loss.Suggestions are given for the general industry. Key suggestions are outlined here: quantify service outages with the framework described herein, use the terminology defined herein for describing network
29、survivability,including network reliability and network integrity, use the layered network survivability framework described herein forclarifying failure survivability analyses, objectives and methods, plan survivability jointly (e.g., interexchange carrier and exchange carrierinterworking), and use
30、 the performance measures defined herein to compare survivabilitytechniques and to evaluate network survivability performance.Recommendations are also given for future standards work. Key recommendationsare outlined here: better quantification of the qualifying regions for service outage categories,
31、 validation of traffic characteristics, analysis of user expectations of network survivability performance,planning, engineering and operations guidelines for network survivabilityperformance, and standardization of network survivability performance measures.1. Purpose, Scope, Application and Outlin
32、e1.1 Purpose As a result of growing concerns from the telecommunicationscommunity, this Technical Report has been developed to address the survivabilityof telecommunications networks, including the services provided. The report is aresponse to the need for a common understanding of, and assessment t
33、echniquesfor, network survivability, including availability, integrity, and reliability. It alsoprovides a basis for designing and operating telecommunications networks to meetusers expectations for network survivability. Further this report provides afoundation for continuing industry activities in
34、 the subject area.1.2 Scope This Technical Report focuses on the survivability of both publicand private networks and covers a wide range of potential users. Two frameworksare established: the first for quantifying and categorizing service outages, and thesecond for classifying network survivability
35、 techniques and measures. Theperformance of network survivability techniques is considered; however,Technical Report No. 243recommended objectives for network survivability performance are not established.Recommendations are made for continuing work on this topic.1.3 Application The intended audienc
36、e of this Technical Report includesproviders, users, and regulators of telecommunications networks, and services, aswell as suppliers of telecommunications equipment. Network provider personnel including designers, planners, traffic engineers, and individuals in charge ofoperations, maintenance, man
37、agement and administration can use this TechnicalReport to quantify and enhance the survivability of their networks. This TechnicalReport also provides a service outage framework that can help users communicateto the providers their expectations of service and a framework that allows networkprovider
38、s to specify their requirements for network survivability.Telecommunications equipment suppliers can use this Technical Report to guidethe design and building of equipment to improve network survivability.1.4 Outline Section 2 and Appendix A review related work. Several aspectsof Operations, Adminis
39、tration and Maintenance (OA network survivability has two components: (i) the ability of anetwork to maintain or restore an acceptable level of performance during networkfailures by applying various restoration techniques, and (ii) the mitigation orprevention of service outages from network failures
40、 by applying preventativetechniques. Preventative techniques can reduce the need for restoration techniques.Depending on the type and scope of the failures, which can range from affectingvery large geographic areas to a single customer, service restoration times canrange from many days to millisecon
41、ds.The type and scope of service outages, occurring from both natural and human-caused network failures, are categorized in Section 4 as being one of catastrophic,major or minor. These categories are based on the impact of the failure on users.For minor failures, network restoration can be automatic
42、 and virtually transparentto the user. However, for catastrophic and major events affecting largepopulations, some service may be restored automatically, but most service will berestored manually and as quickly as possible, based upon availability of personneland replacement facilities.A framework f
43、or quantifying and categorizing service outages in specific terms hasbeen developed in Section 4. The parameters of this framework are: (i) theUnservability (U) of some or all of the provided service affected by the failure; (ii)the Duration (D) during which the service outage exists, and (iii) the
44、Extent (E) inTechnical Report No. 248terms of the geographical area, population and traffic volumes affected by thenetwork failure. Throughout this report, this framework will be referred to as the(U, D, E) triple.To lessen the occurrence and the degree of such service outages, survivabilitytechniqu
45、es have included redundancy of networks and systems, provisioning ofhighest reliability systems, good preventative maintenance, monitoring andsurveillance, manual response, and optimized restoration and repair techniques.Survivability techniques are being developed, based on intelligent and efficien
46、ttechnology, that provide the potential and capability to develop new andpreemptive techniques for network survivability. Innovative developments in alllayers and elements of networks are making it technically and practically possibleto cope with many types of network failures. When this is coupled
47、with well-planned reactive techniques such as readiness and contingency planning (DisasterRecovery), the structure is in place for the capability to provide a full spectrum ofnetwork survivability. The information contained within this Technical Report canhelp to provide a focus and impetus for ensu
48、ring the survivability performance ofnetworks and services in general, as well as a base for enhanced networksurvivability techniques for special applications needs.3.1 User Categories This section lists a range of telecommunications networkusers, and groups them into categories based on broad funct
49、ional or service relatedcharacteristics.User concerns have been heightened by telecommunications failures that havedramatized the vulnerability of telecommunications networks to fires, viruses,software errors, optical fiber/metallic cable cuts, power failures and other natural orhuman-caused accidents.Users have unique requirements and expectations for uninterrupted service,depending on the user type, service value and subscription cost. To meet theseuser expectations, service providers may make use of: specific networkconfigurations, dynamic routing, restoration tech
