Modular Verification of Computer Communication

Programs that implement computer communications protocols can exhibit extremely complicated behavior, and neither informal reasoning nor testing is reliable enough to establish their correctness: In this paper we discuss the application of modular program verification techniques to protocols. This approach is more reliable than informal reasoning, but has an advantage over formal reasoning based op finite-state models: the complexity of the proof need not grow unmanageably.as the size of the program increases. Certain tools of concurrent program verification that are especially useful for protocols’ are presented: history varigbles that record sequences of input and output’values, temporal logic for expressing properties that must hold in a future system state (such as eventual receipt of a message), and module specification and composition rules. The use. of these techniqqe5 is illustrated by verifying two data transfer protocols frow ‘the literature: the alternating bit protocol and a protocol proposed by Stenning. ’ ’