Combining model checking with simulation-based techniques for protocol verification
Model checking is a powerful technique for verifying properties of systems or protocols, but it often suffers from the state space explosion problem. For protocols such as the Alternating Bit Protocol (ABP) and the Sliding Window Protocol (SWP), increasing parameters such as channel capacities or window sizes leads to a reachable state space that is infeasible for exhaustive model checking. To address this, we propose a technique that combines model checking with simulation relations. We focus on three protocols: the Simple Communication Protocol (SCP), ABP, and SWP. Formalized as state machines, these protocols are presented in decreasing order of abstraction: SCP, ABP, and then SWP, which results in a corresponding increase in reachable states. While SCP is verifiable through direct model checking without state space explosion, the direct application of model checking to ABP and SWP becomes infeasible as their parameter values increase. We demonstrate that ABP satisfies its invariant property by combining model checking on SCP with a simulation relation from ABP to SCP. Furthermore, we demonstrate that SWP satisfies its invariant property through the composition of simulation relations from SWP to ABP and from ABP to SCP, in conjunction with model checking on SCP. These approaches enable the formal verification of protocols with large reachable state spaces by conducting model checking on a significantly smaller state machine.