This chapter illustrates the use of Z in capturing certain aspects of the state information relevant to a network protocol. Its aim is both to illustrate the applicability of formal specification to realistic computer systems and to demonstrate the use of a formal framework for design. The description covers an abstract design of a network protocol, along the lines of the seven layer network protocol model proposed by the International Standards Organisation (ISO) for Open System Interconnection (OSI). The design is conducted by a kind of refinement, starting from a high level specification. An alternative way of looking at each refinement is as a different abstraction of the protocol. The chapter also shows the kind of proofs that may be required in such refinements and how these may be accomplished.
KeywordsApplication Layer Transport Layer Network Protocol International Standard Organisation Host Computer
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