Dependability Analysis of Hierarchical Systems with Modular Imperfect Coverage

摘要

We consider the dependability analysis of hierarchical fault tolerant computer based systems in this apaper.The hierarchical nature of the system aids in fault coverage: if an undetected error escapes from one levelof the system, it may be covered or tolerated at a higher level. A fault that remains uncovered through alllevels of the hierarchy, and thus appears at the output, causes immediate system failure despite theremaining redundancy in the system. The difficulty in dependability analysis arises because thedependencies among components and/or modules across the different levels in the hierarchy introduced bysuch modular imperfect coverage have not been addressed in the solution. We offer a means by which toresolve this difficulty.Our analysis approach uses a generalized coverage model for each component. This coverage modeldefines the conditional coverage probabilities associated with each level in the hierarchy. The resultingapproach is applicable to Markov analyses and combinatorial methods such as FT, RBD, or MBDD for theanalysis of both reliability and availability. We present the general approach in terms of a dynamic faulttree, and provide an analysis of a sample hierarchical system.