Sojourn Times In Dependability Modeling

We consider Markovian models of computing or communication systems, subject to failures and, possibly, repairs. The dependability properties of such systems lead to metrics that can all be described in terms of the time that the Markov chain spends in subsets of its state space. Some examples of such metrics are MTTF and MTTR, reliability or availability at a point in time, the mean or the distribution of the interval availability in a fixed time interval, and more generally different performability versions of these measures. This chapter reviews this point of view and its consequences, and discusses some new results related to it.