Diagnostic tests for communicating nondeterministic finite state machines

Systematic test sequence generation for conformance testing of communication protocol implementations, has been an active research area during the last decade. Methods were developed to produce optimized test sequences for detecting faults in such systems. However the application of these methods gives only limited information about the location of detected faults. In this paper we propose a complementary step, which localizes the fault, once detected. It consists of a generalized diagnostic algorithm for the case where distributed system specifications (implementations) are given in the form of communicating nondeterministic finite state machines. Such algorithm localizes the faulty transition once the fault has been detected. The algorithm guarantees the correct diagnosis of any single (output and/or transfer) fault. A simple example is used to demonstrate the functioning of the proposed algorithm. The complexity of each step in the algorithm and hence, the overall complexity are calculated.