BS EN 61907:2010 pdf download – Communication network dependability engineering
5 Network dependability implementation
5.1 Dependability engineering applications
5.1.1 Management of network dependability Dependability is a technical discipline that is managed by engineering principles and practices. The dependability management systems [1 ] 1 and guidelines  are used in this standard for formulation of dependability management strategies and general application of technical approaches for implementation of dependability elements and tasks. Additional management processes are introduced to address network specific management issues. Dependability management involves project planning, resource allocation, dependability task assignments, monitoring and assurance, measurement of results, data analysis and continual improvement. Dependability activities should be conducted in conjunction with other technical disciplines to attain the necessary synergistic effects and add values to the project outcomes. Project tailoring is emphasized for cost-effective management of network projects. Where applicable, life cycle cost analysis  and risk assessment [1 1 ] should be used for resource allocation and optimization for evaluation of acquisition and ownership costs. From a communication network management perspective, dependability management should be an integral part of the network management process with relevant dependability activities to support development and implementation of network service functions throughout the life cycle and network evolution. Network management is the execution of the set of management processes for planning, controlling, allocating, deploying, coordinating, maintaining and monitoring the resources of a network. From an engineering perspective, a network can be viewed as a complex system consisting of multiple interconnecting systems. The technical processes in IEC 60300-3-1 5 are used to describe the network life cycle stages for project implementation. The network life cycle stages are modified to accommodate the process descriptions of network evolution and technology convergence, optimization and renewal, obsolescence and retirement. Network management process and dependability related activities for each network life cycle stage are presented in Annex B.
5.1 .2 Network dependability attributes
The basic set of network dependability attributes is derived from a network performance perspective. Other attributes may be added for specific applications.
a) Availability Network availability reflects the users’ requirements from three aspects: – the network has the ability to perform as and when required; – the network service functions should not be affected by network faults; – the network can recover as quickly as possible when a network fault affects its service functions.
Network reliability can be improved by using redundancy technology and protection mechanisms. For a network with high reliability requirements, the protection of multipoint faults should be considered. The manifestation of faults becomes more critical for complex network operation, especially with the continued usage of obsolete equipment that may have compatibility problems.
c) Maintainability Maintainability reflects the ease of restoring a network to an operating state following a fault, or from a degraded state of network performance operation. The incorporation of redundancy in design and fault management capability into the network can affect maintainability performance. For example, remote fault management where fault identification and corrective action are carried out by remote intervention, can shorten maintenance time.
d) Maintenance support performance Maintenance support performance is dependent on the provision and management of resources to perform maintenance activities. Network dependability design requires an approach to reduce the complexity of network equipment for maintenance, easy access for active maintenance during network operation, standardized maintenance procedures, network fault identification and traceability, and perfected spare parts management system. This approach applies to hardware and software as well as to human functions for maintenance support performance and design consideration.
e) Recoverability Recoverability in service performance is dependent on the design of network architecture, fault-tolerant protection mechanisms, access for maintenance and self-healing features incorporated into the network functions. The means of achieving restoration may be automatic or by external actions.
f) Integrity Integrity infers that the network is stable and robust, and able to maintain consistency in performance and use. Network integrity provides security and protection for information transfer in network performance and service functions.