The Sliding-Window Protocol in CSP

A formal specification and proof of correctness is given of the sliding­ window protocol using the notation of Communicating Sequential Pro­ cesses. First the stop-and-wait protocol is defined; its correetne8S, that it forms a I-place buffer, is almost evident. Next the alternating-bit protocol is defined and described in terms of the stop-and-wait proto­ col, and its correctness deduced. Finally the sliding-window protocol is described in terms of the alternating-bit protocol and its correctness deduced accordingly. The protocols are refined, and implemented in occam. The paper has two thrusts: that modularity of a specification helps to structure proofs about it (in this case, proofs that the protocols implement bUffers); and that refinement in CSP leads to structured, correct implementations in occam.