A compositional approach for designing multifunction time-dependent protocols

We propose a framework based on the model of timed extended finite state machines for building communication protocols which perform several functions, where each function corresponds to a component protocol. For parallel composition, we specify a conjunctive relation which requires that the execution of events in two component protocols be synchronized. We also propose a predicate strengthening technique to refine the composite protocol in a stepwise manner while preserving the invariants of the component protocols. For sequential composition, we present a set of constraints, alternating, ordering and disabling, on the actions of the component protocols, and give sufficient conditions for the composite protocol to retain the safety properties such as freedom from unspecified receptions and freedom from deadlocks. Our sufficient conditions are weaker than those given an previous works.