Maintaining Permanent and Temporary Faults in a Communications System

Permanent and temporary faults can be subdivided into classes with respect to their properties in the electrical domain and the time domain, e.g., sudden solid, marginal, gradual, intermittent. Strategies in the design of the central control of the AXE digital switching system are described. The automatic locating of permanent and temporary faults is based on a modular hardware architecture and strategically located hardware checkers. Field experience is reported. An optimistic approach to include temporary faults in the reliability model of a repairable dual redundant system is discussed. It gives conlderably higher mean time between system failure than the traditional permanent fault model.