Maintenance Techniques in Distributed Communications Switching Systems

The reliability and maintainability design criteria that were a part of large central-control communication systems, have been combined to produce deferred maintenance concepts in fully distributed communication systems. Combining these concepts allows the achievement of a cost-effective life-cycle design for communication switching systems. In a hardware/software environment one should not separate hardware maintainability and software maintainability, nor separate the reliability and maintainability of the system. Reliability models are being developed that reflect a constant rate for transient faults and a decreasing rate for catastrophic faults. The relationship of software bugs to their number and type of manifestation is being defined. Designs for primarily non-attended system sites should include appropriate maintenance concepts in order to be cost effective. If two or more individual repairs can be made with each maintenance visit to a site, the total area maintenance staff can be reduced. Implementation of deferred maintenance techniques can raise the availability level of the services provided, especially for a distributed communication switching system. Several examples of practical techniques for developing deferred maintenance concepts are presented, and topics such as the manning versus non-manning of sites, the time of day effects on state diagrams, centralized maintenance, and computer modeling techniques are discussed. The current and potential maintainability concepts and analysis tools that are discussed in this paper can be used to develop cost-effective maintenance concepts as distributed systems become more prevalent.