Reliability modelling of time-critical distributed systems

In cost conscious industries, such as automotive, it is imperative for designers to adhere to policies that reduce system resources to the extent feasible, even for safety-critical sub-systems. However, the overall reliability requirement, typically in the order of 10(-9) faults/hour, must be both analysable and met. Faults can be hardware, software or timing faults. The latter being handled by hard-real time schedulability analysis, which is used to prove that no timing violations will occur. However, from a reliability and cost perspective there is a tradeoff between timing guarantees, the level of hardware and software faults, and the per-unit cost for meeting the overall reliability requirement. This paper outlines a reliability analysis method that considers the effect of faults on schedulability analysis and its impact on the reliability estimation of the system. The ideas have general applicability, but the method has been developed with modeling of external interferences of automotive CAN buses in mind. We illustrate the method using the example of a distributed braking system.