Performability modeling of N version programming technique

Abstract

The paper presents a detailed, but efficiently solvable model of the N version programming for evaluating reliability and performability over a mission period. Employing a hierarchical decomposition we reduce the model complexity and provide a modeling framework for evaluating the NVP failure and execution time behavior and the operational environment, as well. The failure and execution rates are treated as random variables and the operational profile is analyzed on the microstructure level, looking at probabilities of occurrence, failure and execution rates for each partition of input space. The reliability submodel that represents per run behavior of NVP, includes both functional failures and timing failures thus resulting in system reliability which accounts for performance requirements. The successive runs are modeled by the performance submodel, that represents the iterative nature of the software execution. Combining the results of both submodels, we assess the performability over a mission period that represents the collective effect of multiple system attributes on the NVP effectiveness.