A simulation based approach for estimating the reliability of distributed real-time systems

Designers of safety-critical real-time systems are often mandated by requirements on reliability as well as timing guarantees. For guaranteeing timing properties, the standard practice is to use various analysis techniques provided by hard real-time scheduling theory. However, in many cost conscious industries, such as automotive, it is imperative that the designers also adhere to policies that reduce system resources to the extent feasible. From a reliability and cost perspective there is a trade-off between timing guarantees, the level of hardware and software faults, and the per-unit cost. By allowing occasional deadline misses, less costly hardware may be used, while still meeting the overall reliability requirement. This paper presents analysis based on simulation, that considers the effects of faults and timing parameter variations on schedulability analysis, and its impact on the reliability estimation of the system. We look at a wider set of scenarios than just the worst case considered in hard real-time schedulability analysis. The ideas have general applicability, but the method has been developed with modelling the effects of external interferences on the Controller Area Network (CAN) in mind. We illustrate the method by showing that a CAN interconnected distributed system, subjected to external interference, may be proven to satisfy its timing requirements with a sufficiently high probability, even in cases when the worst-case analysis has deemed it non-schedulable.