A STATE-DEPENDENT RELIABILITY MODEL AND ITS APPLICATIONS

FASTAR(SM) is a fast automatic restoration system for restoring AT&T DS3 services (in the event of a cable failure). Its deployment has helped to reduce restoration times significantly. Reliable operations throughout a cable failure event is the key to the success of the restoration process. Since the hardware components involved during restoration vary, the traditional reliability block diagram is too simplistic to capture the state dependent system availability. In this paper we propose a state dependent reliability model that incorporates both state transition and reliability block diagrams. This model is designed to handle a general cable cut case which usually results in multiple reroute paths. We demonstrate how the model works using a typical example. The primary application of the model is to support the AT&T FASTAR program in meeting its very high availability design criterion.