Defining, analysing and implementing communication protocols using attribute grammars

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Abstract
A new approach to describing communication protocols is introduced. In the style of a formal language, the protocol is considered as the set of all legal sequences of symbols that can be exchanged by the communicating processes. Although context free grammars cannot adequately describe such sequences, it is shown that attribute grammars may be used. Examples are given which show that common protocol features such as interleaving, windowing and flow control can be described by attribute grammars. It is shown how deadlock-proneness of a protocol can be formalised as a property of its attribute grammar specification, and the undecidability of deadlock-proneness for arbitrary grammars is proved. An algorithm is given for determining whether a protocol is deadlock-prone in the decidable case. A method of automatically implementing protocols from their specifications is described. The implementation takes the form of a pair of communicating attributed pushdown automata. These are based on LR(0) parsers, with attribute evaluation being performed in parallel with the parse; attribute values are used to help direct the parse. Consideration is also given to the handling of errors.

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