Improving Protocol Passive Testing through 'Gedanken' Experiments with Finite State Machines

This paper is devoted to study the use of 'gedanken' experiments with Finite State Machines (FSMs) for protocol passive testing optimization. We discuss how the knowledge obtained from the state identification of an implementation under test (IUT) can be utilized for effective IUT monitoring. Differently from active testing techniques, such identification is performed by only observing the IUT behavior. If the state identification is possible (at least partially), then this fact allows to reduce the number of properties (test purposes) to be checked at certain execution point(s). Correspondingly, this allows to simplify and/or accelerate, i.e. improve the monitoring process by verifying the system behavior only at critical states against the appropriate set of properties associated with a given state. The paper discusses which 'gedanken' experiments can be considered for this purpose and how they can be derived for various specifications of communication protocols. The results presented in the paper are followed by an illustrative protocol example that demonstrates the efficiency of the proposed approach.