Path-based calculation of MTTFF, MTTFR and asymptotic unavailability with the stochastic process algebra tool CASPA

CASPA is a stochastic process algebra tool for performance and dependability modelling, analysis and verification. It is based entirely on the symbolic data structure MTBDD (Multi-Terminal Binary Decision Diagram) which enables the tool to handle models with very large state space. This paper describes an extension of CASPA’s solving engine for path-based approximation of MTTFF (Mean Time To First Failure), MTTFR (Mean Time To First Recovery) and asymptotic unavailability by MTBDD algorithms. To keep the paper self-contained, we briefly recall a symbolic variant of the k-shortest-path algorithm of Azevedo et al., which works in conjunction with a symbolic variant of Dijkstra’s shortest path algorithm. A non-trivial case study illustrates the use of this kind of pathbased analysis and compares the path-based unavailability calculation to the results from standard Markovian analysis. This work is based on the paper Symbolic calculation of k-shortest paths and related measures with the stochastic process algebra tool CASPA [6]