Passive Testing - A Constrained Invariant Checking Approach

Passive testing of a network protocol is the process of detecting faults in the protocol implementation by passively observing its input/output behaviors (execution trace) without interrupting the normal network operations. In observing the trace, we can focus on the most expected relevant properties of the protocol specification by defining some invariants on the specification and checking them on the trace. While intuitive extraction of the invariants from the protocol requirements with respect to the control portion of the protocol system is relatively simple, taking the data portion into account is difficult. In this paper we propose algorithms for checking the correctness of given invariants on the specification and extracting the required constraints on the variables (data portion). Once we generate the constraints for a given invariant, we can check if the execution trace is confirmed by the specification with respect to the invariant and its constraints. We show the applicability of the algorithm on a case study: the simple connection protocol (SCP).