PERFORMABILITY ANALYSIS OF DISTRIBUTED REAL-TIME SYSTEMS

In this paper, an algorithm and a methodology for the performability analysis of repairable distributed real-time systems are presented. The class of distributed real-time work-loads considered consists of concurrent tasks that are repetitive in nature with known cycle and deadline times. A real-time system must be able to meet critical deadlines even when it is not fully operational due to some nonfunctional components. The planning cycle of a real-time distributed system, which normally consists of several task invocations, is first identified. The performability distribution at the end of the planning cycle is determined by repeated convolutions of performability densities between task invocations. These convolution operations are efficiently carried out using the operational properties of Laguerre coefficients. The algorithm numerically determines both moments and distribution of performability in O(N(max)3), where N(max) is the largest size of the state space between any task invocations. To illustrate the overall methodology, a simplified example of a radar system is analyzed and the various performability measures are obtained using the algorithm.