Specifying Failures and Recoveries in PACSR

The paper presents PACSR, a probabilistic extension of a real-time process algebra ACSR. The extension is built upon a novel treatment of the notion of a resource. In ACSR, resources are used to model contention in accessing physical devices such as processors, memory modules, and communication links, or any other reusable resource of limited capacity. Here, we invest resources with an ability to fail and associate, with every resource, a probability of its failure. The resulting formalism allows us to perform probabilistic analysis of real-time system speci cations in the presence of resource failures. An attractive feature of PACSR is the ability to express failurerecovery actions easily. We perform probabilistic reachability analysis for PACSR speci cations that allows us to compute the probability of occurrence of an undesirable event. We illustrate PACSR speci cation and analysis by means of a telecommunications example.