EN 62673:2013

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Metodologija za ocenjevanje in zagotavljanje zagotovljivosti komunikacijskega omrežja (IEC 62673:2013)/Méthodologie pour l’évaluation et l’assurance de la sûreté de fonctionnement des réseaux de communicationMethodology for communication network dependability assessment and assurance33.040.40Podatkovna komunikacijska omrežjaData communication networks03.120.99Drugi standardi v zvezi s kakovostjoOther standards related to qualityICS:Ta slovenski standard je istoveten z:EN 62673:2013SIST EN 62673:2014en01-maj-2014SIST EN 62673:2014SLOVENSKI
STANDARD
EUROPEAN STANDARD EN 62673 NORME EUROPÉENNE
EUROPÄISCHE NORM August 2013
CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B - 1000 Brussels
© 2013 CENELEC -
All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 62673:2013 E
ICS 03.120.01
English version
Methodology for communication network dependability assessment and assurance (IEC 62673:2013)
Méthodologie pour l’évaluation et l’assurance de la sûreté de fonctionnement des réseaux de communication (CEI 62673:2013)
Methodik zur Beurteilung und Sicherstellung der Zuverlässigkeit von Kommunikationsnetzen (IEC 62673:2013)
This European Standard was approved by CENELEC on 2013-07-23. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Foreword The text of document 56/1507/FDIS, future edition 1 of IEC 62673, prepared by IEC/TC 56 "Dependability" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as EN 62673:2013. The following dates are fixed: • latest date by which the document has to be implemented at national level by publication of an identical national standard or by endorsement (dop) 2014-04-23 • latest date by which the national standards conflicting with the document have to be withdrawn (dow) 2016-07-23
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent rights.
Endorsement notice The text of the International Standard IEC 62673:2013 was approved by CENELEC as a European Standard without any modification. In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 61078 NOTE Harmonised as EN 61078. IEC 62198 NOTE Harmonised as EN 62198. IEC 60812 NOTE Harmonised as EN 60812. IEC 60300-3-11 NOTE Harmonised as EN 60300-3-11. IEC 60300-3-1 NOTE Harmonised as EN 60300-3-1. IEC 61165 NOTE Harmonised as EN 61165 SIST EN 62673:2014

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Annex ZA
(normative)
Normative references to international publications with their corresponding European publications
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
NOTE
When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies.
Publication Year Title EN/HD Year
IEC 60050-191
International Electrotechnical Vocabulary (IEV) -
Chapter 191: Dependability and quality of service - -
IEC 60300-3-15
Dependability management -
Part 3-15: Application guide - Engineering of system dependability EN 60300-3-15
IEC 61907
Communication network dependability engineering EN 61907
IEC 62673 Edition 1.0 2013-06 INTERNATIONAL STANDARD NORME INTERNATIONALE Methodology for communication network dependability assessment and assurance
Méthodologie pour l'évaluation et l'assurance de la sûreté de fonctionnement d'un réseau de communication
INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE W ICS 03.120.01 PRICE CODE CODE PRIX ISBN 978-2-83220-871-7
– 2 – 62673  IEC:2013 CONTENTS FOREWORD . 4 INTRODUCTION . 6 1 Scope . 7 2 Normative references . 7 3 Terms, definitions and abbreviations . 7
Terms and definitions . 7 3.1 Abbreviations . 11 3.24 Overview of network dependability methodology . 11
Need for network dependability methods . 11 4.1 Network dependability objectives . 12 4.2 Network service scenarios . 13 4.3 Network dependability assessment strategies . 13 4.4 Network dependability assurance strategies . 14 4.55 Network dependability methodology applications . 15
Network life cycle process . 15 5.1 Life cycle process applications . 15 5.1.1 Risk assessment process applications . 15 5.1.2 Dependability methodology applications . 16 5.1.3 Network dependability performance characteristics . 17 5.2 Network dependability assessment methodology . 18 5.3 Generic dependability analysis and evaluation techniques . 18 5.3.1 Service scenario analysis . 19 5.3.2 Network modelling . 19 5.3.3 Network failure modes, effects and criticality analysis . 20 5.3.4 Network fault insertion test . 21 5.3.5 Failure reporting, analysis and corrective action system . 22 5.3.6 Network dependability assurance methodology . 22 5.4 Scope of dependability assurance methodology applications . 22 5.4.1 Assurance of dependability of service . 23 5.4.2 Assurance of data integrity . 23 5.4.3 Assurance of network performance functions and support process 5.4.4enhancement . 24
Network dependability assurance methods . 24 5.4.5Annex A (informative)
Example of E2E network dependability assessment . 27 Annex B (informative)
Example of full-end network dependability assessment . 33 Annex C (informative)
Evaluation of network dependability performance in field operation . 35 Bibliography . 37
Figure A.1 – A typical example of an E2E network topology . 27 Figure B.1 – A typical example of a full-end network topology . 33 Figure C.1 – Network outage contributions and resultant network service impact . 36
62673  IEC:2013 – 3 –
Table 1 – Summary of network dependability activities and application methods . 17 Table 2 – Summary of network dependability parameters. 18 Table C.1 – Summary of network failure data of a nation-wide public switched telephone network . 35
– 4 – 62673  IEC:2013 INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________
METHODOLOGY FOR COMMUNICATION NETWORK
DEPENDABILITY ASSESSMENT AND ASSURANCE
FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any services carried out by independent certification bodies. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC 62673 has been prepared by IEC technical committee 56: Dependability. The text of this standard is based on the following documents: FDIS Report on voting 56/1507/FDIS 56/1514/RVD
Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. SIST EN 62673:2014

62673  IEC:2013 – 5 – The committee has decided that the contents of this publication will remain unchanged until the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to the specific publication. At this date, the publication will be
• reconfirmed, • withdrawn, • replaced by a revised edition, or • amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it contains colours which are considered to be useful for the correct understanding of its contents. Users should therefore print this document using a colour printer.
– 6 – 62673  IEC:2013 INTRODUCTION Communication network dependability is highly influenced by the design and implementation of the network service functions, which aim to achieve user satisfaction in service performance.
Network evolution, service growth and functional renewal in communications have long been challenges to the providers of network services, not just for the broad range of services now in existence, but also for those service-related activities experienced by the end-users.
To sustain viable business in network services, it is prudent for the communications industry to provide the
– needed network service functions, – adequate network capacity and performance capability, – security of service,
– quality of service, and
– dependability of service.
This International Standard addresses one of the most important issues concerning the assessment and delivery of dependability of service to ensure network service performance. It also addresses the network dependability assurance strategies and methodology applications for enhancing and sustaining network operation. This International Standard describes a generic methodology for dependability assessment and assurance of communication networks. It also provides relevant assessment and assurance methods to support communication networks for dependability engineering application, such as those conforming to IEC 61907 and ITU-T1 Recommendations concerning dependability.
It presents an approach for network dependability analysis and evaluation that ensures dependable network design for effective implementation.
The objective of this standard is to achieve a cost-effective solution for realizing the network dependability performance and to assure the benefits from the network dependability of service operation. ______________ 1 ITU-T: International Telecommunications Union – Telecommunications. SIST EN 62673:2014

62673  IEC:2013 – 7 – METHODOLOGY FOR COMMUNICATION NETWORK
DEPENDABILITY ASSESSMENT AND ASSURANCE
1 Scope
This International Standard describes a generic methodology for dependability assessment and assurance of communication networks from a network life cycle perspective. It presents the network dependability assessment strategies and methodology for analysis of network topology, evaluation of dependability of service paths, and optimization of network configurations in order to achieve network dependability performance and dependability of service. It also addresses the network dependability assurance strategies and methodology for application of network health check, network outage control and test case management to enhance and sustain dependability performance in network service operation. This standard is applicable to network service providers, network designers and developers, and network maintainers and operators for assurance of network dependability performance and assessment of dependability of service. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60050-191, International Electrotechnical Vocabulary (IEV) – Chapter 191: Dependability and quality of service
IEC 60300-3-15, Dependability management – Part 3-15: Application guide – Engineering of system dependability IEC 61907, Communication network dependability engineering 3 Terms, definitions and abbreviations
Terms and definitions 3.1For the purposes of this document, the terms and definitions given in IEC 60050-191 and IEC 61907, as well as the following, apply.
3.1.1communication network system of communication nodes and links that provides transmission of analogue and digital signals EXAMPLES Telecommunications networks, Internet, intranet, extranet, Wide Area Networks (WAN), Local Area Networks (LAN) and computer networking utilizing information technology.
Note 1 to entry: A network has its boundary. All nodes at the network boundary are called ends. In some applications, the term “node” is used instead of “end” as a communication access point to the network, as well as for interconnections between the transmission links. Note 2 to entry: A “backbone” communication network consists of core network and high-speed transmission lines (national or international), connecting between major switching network nodes (interconnection of transmission lines) at various locations in a country or region. SIST EN 62673:2014

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3.1.2dependability network dependability ability to perform as and when required to meet specified communication and operational requirements
3.1.3availability network availability ability to be in a state to perform as required
Note 1 to entry: Availability depends upon the combined characteristics of the reliability, recoverability and maintainability of the network and on the maintenance support performance. Note 2 to entry: Availability may be quantified using appropriate performance measures.
3.1.4reliability network reliability ability to perform as required, without failure, for a given time interval, under given conditions Note 1 to entry: The time interval duration may be expressed in units appropriate to the network concerned. Note 2 to entry: Reliability of a network depends upon the combined characteristics of the reliability, recoverability, maintainability and maintenance support performance of the constituent network elements. Note 3 to entry: Given conditions include aspects that affect reliability, such as: mode of operation, stress levels, environmental conditions, and maintenance. Note 4 to entry: Reliability may be quantified using appropriate performance measures.
3.1.5maintainability network maintainability ability to be retained in, or restored to a state to perform as required under given conditions of use and maintenance Note 1 to entry: Given conditions include aspects that affect maintainability, such as: location for maintenance, accessibility, maintenance procedures and maintenance resources. Note 2 to entry: Maintainability may be quantified using appropriate performance measures.
3.1.6maintenance support network maintenance support provision of resources to maintain a network
Note 1 to entry: Resources include human resources, support equipment, materials and spare parts, maintenance facilities, documentation, information and maintenance information systems.
3.1.7maintenance support performance network maintenance support performance effectiveness of an organization in respect of maintenance support for the network Note 1 to entry: Maintenance support performance may be quantified using appropriate measures.
3.1.8recoverability network recoverability ability to recover from a failure, without corrective maintenance
Note 1 to entry: The ability to recover may or may not require external actions. SIST EN 62673:2014

62673  IEC:2013 – 9 – Note 2 to entry: Recoverability may be quantified using such measures as the probability of recovery within a specified time interval.
3.1.9element network element subsystem or component of a communication network
EXAMPLES Terminals, nodes and switches. Note 1 to entry: A network element may involve human input to perform its service function. Note 2 to entry: Network elements are connected by network links.
3.1.10link network link electrical, wireless or optical connection between network nodes
3.1.11performance network performance ability to provide the service functions related to communications between users
[SOURCE: ITU-T Recommendation I.350:1988][1]2
3.1.12management network management application of organized processes and resources to manage the performance, configuration, accounting, fault, and security activities
3.1.13service function network service function program or application that interacts with the network users or within the network infrastructure to transmit or exchange data and information in the network
Note 1 to entry: A network service function may consist of hardware and software elements, and may involve human interactions for realizing a specific function.
3.1.14network services
provision of network service functions and communication services to the network users Note 1 to entry: Communication services are the network services subscribed by the end-users.
Note 2 to entry: A bearer service is a communication service function that allows transmission of user-information signals between user-network interfaces.
3.1.15quality of service collective effect of service performance that determines the degree of satisfaction of a user of the service
3.1.16network failure loss of ability of a network to perform as required ______________ 2 References in square brackets refer to the Bibliography. SIST EN 62673:2014

– 10 – 62673  IEC:2013 Note 1 to entry: The network failure may be due to, for example, equipment failure, natural disasters or human-caused disturbance.
3.1.17network fault state of inability of a network to perform as required, for internal reason Note 1 to entry: In the context of network operation, a fault may be natural due to an abnormal condition, or malfunction resulting from a network element failure, or induced by external means such as fault injection.
Note 2 to entry: A degraded state in network performance is a situation where one or more performance characteristics do not conform to requirements.
3.1.18service provider organization that provides communication network services EXAMPLES Telephone companies, data carriers, mobile service providers, Internet service providers and cable television operators.
Note 1 to entry: A network carrier or common carrier is an organization that transports a product or service using its facilities or those of other carriers, and offers services to the general public. The term communication carrier refers to various telephone companies that provide local, long distance or value added services.
3.1.19user party that employs the services of a service provider for direct network access Note 1 to entry: A user may be a source or recipient of user information, or both.
Note 2 to entry: In some circumstances, a user of a communication service is also known as a subscriber.
3.1.20integrity
network integrity
ability to ensure that the data contents are not contaminated, corrupted, lost or altered between transmission and reception Note 1 to entry: Throughput is the rate of successful message delivery over a communication channel of a network service.
3.1.21dependability performance network dependability performance ability to provide or demonstrate the performance characteristics of dependability in network operation to achieve network service objectives Note 1 to entry: In the context of this standard, network dependability performance refers to the provision of full-end network services. Note 2 to entry: A full-end network service is the provision of service connectivity established for all transmission and reception ends of a communication network.
3.1.22dependability of service network dependability of service effect of providing the required dependability performance for user communications services
Note 1 to entry: In the context of this standard, network dependability of service refers to the provision of end-to-end (E2E) network services. Note 2 to entry: An end-to-end network service is the provision of service connectivity established between the transmission and reception ends of a communication network.
62673  IEC:2013 – 11 –
3.1.23security of service network security of service effect of providing the required security for user communications services
3.1.24service path network service path connecting path by network links and nodes to establish user communications services
3.1.25service flow network service flow flow of information and data through the service path
3.1.26service scenario operational situation in communication network for provision of network service functions and user service applications
3.1.27network outage state of the network being unable to perform its primary function
Abbreviations 3.2E2E End-to-End FRACAS Failure Reporting, Analysis, Corrective Action System FRU Field Return Unit HAZOP Hazard and operability studies MTTR Mean Time to Restoration of Node/link ND Network Dependability NFIT Network Fault Insertion Test NFMECA Network Failure Modes, Effects and Criticality Analysis OAMP Operations, Administration, Maintenance, and Provisioning OSI Open System Interconnection
QoS Quality of Service RBD Reliability Block Diagram
SLB Service Logic Block 4 Overview of network dependability methodology
Need for network dependability methods 4.1A communication network is a system of systems that interacts with other networks to achieve multiple service performance objectives. A communication network is complex and its constituent systems are constantly changing and evolving. Appropriate methodology and technical approaches are needed for dependability assessment and assurance of the network. From a network dependability assessment perspective, the classical dependability techniques for analysis and evaluation have a limited scope in network application. Existing dependability methods are often unsuitable for modelling complex network topology and difficult for analysis of multiple network configurations and network service paths to provide confidence in the evaluation results. Selective methods such as SLB, NFMECA, and network simulation suitable for network dependability analysis and evaluation can provide effective network solutions. SIST EN 62673:2014

– 12 – 62673  IEC:2013 They have become the essential processes to ensure sustainable network services and dependability performance. A common approach for assurance of network dependability performance and dependability of service is to construct reliable network structure, establish effective routing schemes, provide efficient fault management and network maintenance support, and gather performance data and user feedback for network service evaluation and improvement. The process involves analysis of network service functions for cost-effective implementation, and evaluates value-added network service features for dependability of service enhancement. This approach, though adequate for system life cycle assessment of hardware and software network elements to ascertain dependability performance, is inadequate to deal with routing connectivity of user services in network operation. The traditional assurance approach lacks the responsiveness to react to the market dynamics of adaptive network configurations. This affects the network service objectives to ensure network dependability performance and to guarantee dependability of service in a highly competitive global network business.
There are many dependability methods developed over the years but only a selective few provide efficient methodology appropriate for effective network dependability performance and dependability of service applications. This observation is noted due to the complex nature of network evolution; the innovative topology for development of advanced network service functions, and the unique techniques required for practical dependability methodology applications. Whereas there are many factors that could influence the dependability performance in the network life cycle, the most significant impact would be during the early stages in concept/definition, design/development, and realization/integration. New additions to the existing network would involve scenario analysis of the legacy system during the concept/definition stage prior to investments in subsequent design/development and realization/integration stages. The extent of operation/maintenance, enhancement/renewal and retirement needs should be included in the scenario analysis of the legacy system. Network dependability performance and dependability of service should be continuously monitored, analysed and evaluated for optimization of network operations and provision of revenue generating network services. The network dependability assurance strategies and methodology applications are key contributing factors to enhance and sustain continued provision of network services from a viable business perspective.
Network dependability objectives
4.2The capability of a network to provide users’ communication for continual and uninterrupted service operation is highly dependent on its dependability performance. Dependability implies that the provision of network service functions is trustworthy and capable of performing the desirable service upon demand. To achieve network performance and assure network dependability of service, it is essential to utilize relevant methods for assessment of network dependability. This standard supports the engineering requirements for network design and process implementation, and provides relevant dependability methodology for analysis and evaluation of communication networks. The technical framework of IEC 60300-3-15 on system aspects of dependability and the requirements of IEC 61907 on network dependability engineering apply to this standard. Terms related to communications quality of service are referenced in ITU-T Recommendation G.1000 [2]. In the development and implementation of communication networks, there are several important influencing factors that concern the network operators and service providers to sustain a viable business. They include: • network service functions to satisfy user needs; • network performance capability to meet service demands; • security of service; • quality of service (QoS) [3]; • dependability of service. In the assessment and assurance of network dependability, it should be noted that SIST EN 62673:2014

62673  IEC:2013 – 13 – a) the network functional parameters such as transmission capacity and performance connectivity will degrade with time due to failures and this will affect network dependability; b) the robustness of the network to resist service performance violation due to external intrusion and outage interruption will affect critical network infrastructure protection.
Network service scenarios 4.3There are two network service scenarios of interest to network dependability.
a) Dependability of service of the end-users’ connections for end-to-end (E2E) network services (see Clause A.2) – the objective is to determine the network dependability performance characteristics on E2E network services from the perspective of network end-users. The E2E network service is an essential service to meet end-user needs based on the performance capability of a full-end network in service operation. In the E2E network service scenario, the dependability of service is reliant on the routing schemes and the capability of the network performance associated with the specific service paths selected for the E2E connections. Dependability of service is experienced by the end-users and reflects customer demands and user satisfaction. b) Dependability performance of the entire network for full-end network services (see Clause B.2) – the objective is to determine the network dependability performance characteristics of the entire network from the network operator or the network service provider perspective. A full-end network can operate in a service scenario where the service provider has full control of a private network and has the responsibility to provide network dependability performance adequate for the network services. The full-end network can also operate in a service scenario with multiple service providers each controlling a designated segment of the entire network as in a public switching network. The network operator is responsible for the overall network service performance. Individual service providers are responsible for their contributions of network service performance under the network service level agreements with the network operator in provision of QoS. The two network service scenarios associated with E2E and full-end network service operations are interdependent and complementary. It should be noted that without dependability performance capability, adequate user services could not be achieved or guaranteed; and without user satisfaction of dependability of service, the service provider would experience difficulty in sustaining user service demands and could lose subscriptions; hence affecting network service revenue generation. Relevant network user feedback information gathered and network performance data analysed from these two network service scenarios would facilitate resource planning and control of QoS provision to subscribers or users and maintain dependability of overall network services. Network dependability performance and dependability of service reflect the network service scenarios and operation environments in doing business. This is achieved by means of dependability assessment to ensure dependability performance during network development and dependability assurance to sustain dependability of service during network operation.
The strategies for network dependability assessment and dependability assurance are outlined in 4.4 and 4.5. The dependability methodology and methods for network applications are provided in Clause 5.
Network dependability assessment strategies
4.4Dependability assessment is an appraisal process to determine the status of network performance for delivery of dependability of service. The following describes the network dependability assessment strategies relevant to the network service scenarios.
a) E2E network dependability assessment strategy
The E2E network dependability is influenced by the network topology, the routing schemes and the selection of service paths to achieve user service connections. To assess E2E network dependability, the routing service paths associated with the service scenarios should be analysed. All the equipment and links of each service path should be evaluated SIST EN 62673:2014

– 14 – 62673  IEC:2013 for achievement and delivery of dependability of service. The E2E network dependability assessment covers various network service scenarios in public and private networks.
The assessment strategy for E2E network should consider a technical approach for evaluation of dependability of service. This is due to the multiple service paths that need to be analysed for optimization of dependability of service. The complex nature of the network configuration demands a unique modelling technique and methodology consisting of Service Logic Block (SLB) diagrams (see Clause A.3) to facilitate E2E network dependability of service evaluation.
b) Full-end network dependability assessment strategy
A full-end network operating in a service scenario consists of numerous interacting networks offering various service functions by multiple service providers. Provision of network dependability performance is the collaborative efforts of these service providers under service level agreements for delivery of QoS. The service function reliability of the full-end network can be modelled by the RBD [4] or similar methods. Full-end network dependability assessment can only be practically ascertained after network service implementation by means of field performance survey and customer satisfaction feedback to obtain relevant network performance data. This is due to the complex nature of network evolution where new service functions are continuously being added for performance enhancement and termination of obsolete or unprofitable network services. The public switching network is an example where network dependability performance can be assessed by analysis and evaluation of the reported frequency of user service outages and the outage duration and customer complaints on service impact. The assessment outputs include the categorization of network outages associated with the identified failure causes and their resulting service impact to the network subscribers or users.
A full-end network can be a private network and owned by a single network operator who has full control for provision of the network services. A secured data network consisting of automated teller machines to provide distributed banking services is an example of a private network. To assess the dependability performance of the full-end private network, all the network elements and their relationships should be determined and all relevant dependability performance characteristics evaluated for conformance to established network service performance criteria. The technical processes for network dependability assessment are analysed and evaluated as a system with boundary conditions. For new network development, the network life cycle process should be followed and the dependability engineering activities conducted according to the recommended guidelines from IEC 61907. For network enhancement and renewal projects, it is essential to take into consideration the legacy issues of existing network configurations to optimize renewed network performance. Network performance statistics from field operation should be collected and analysed to validate performance adequacy in meeting network service objectives.
Network dependability assurance strategies
4.5The network dependability assurance strategies are planned activities engaging systematic processes to ensure achievement of network dependability in performance and delivery of customer focused dependability of service. The network dependability assurance strategies reflect the relevant technical domains in network specific applications. They collaborate with network performance management and the routine network maintenance and support activities by providing specific dependability engineering effort. The network specific dependability assurance strategies are summarized from a network operation viewpoint.
a) Delivery of dependability of service to end-users
There are two separate strategic issues concerning the delivery of dependability of service: one is concerning the service contributions from the delivery mechanism of network equipment functions and interoperability in service operation; the other relates to the service delivery of data information as throughput by utilizing the delivery mechanism of the network configuration. The application specific strategies focus on the delivery mechanism and the data integrity. b) Ensuring data integrity
62673  IEC:2013 – 15 –
The data integrity is the foundation for credible information generation and data transmission through the network service paths that represent the delivery mechanism of the network configuration. The data specific strategy is focused on the network dependability performance and the ability to prevent data loss, corruption or security exposure.
c) Enhancement of network performance functions and support processes
The network performance functions and support processes would tend to degrade if not adequately maintained and regularly updated. This would result in gradual degradation in network performance leading to frequent network outages and increased service downtime durations; hence affecting network operation and QoS. The network maintenance support strategy for dependability assurance is to promote continuous improvement to optimize network functions and simplify procedures for network support processes. The technical focus is to enhance critical network performance related dependability characteristics such as recoverability, availability, reliability, maintainability, and maintenance support. Continuous network improvement is essential to sustain viable network service operations and to ensure the satisfaction of end users.
The assurance strategy provides corrective and preventive measures to avoid recurrence of network operation problems.
5 Network dependability methodology applications
Network life cycle process
5.1 Life cycle process applications
5.1.1The applications of network life cycle process involve a series of dependability activities to achieve its performance objectives. The network life cycle stages include concept/definition, design/development, realization/integration, operation/maintenance, enhancement/renewal, and retirement. The relevant application methods for network dependability analysis and evaluation are identified. The objective is to ensure that network dependability requirements are met through judicious applications of relevant methods for assurance of network dependability performance to achieve the required dependability of service.
Individual networks differ from one another due to boundary and service conditions. The network operational scenario relevant to the provision of essential network services should be established. Relevant analysis and evaluation methods should be identified in early network concept design to maximize dependability performance benefits. This process helps assure dependability of service achievement from the network services and the user satisfaction perspectives. The technical approach and process flows are described herein to facilitate methodology applications. Relevant input and output requirements should be identified for network service analysis. Timely response to data collection, analysis and interpretation of evaluation results, and risk assessment as part of the dependability assurance process should form the basis for recommending network dependability improvement.
Risk assessment process applications
5.1.2Risk assessment [5, 6] is the overall process of risk identification, risk analysis, and risk evaluation. A risk assessment provides an understanding of the risk involvement, risk causes and consequences, which are useful inputs to d
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