Using binary decision diagrams for representation and analysis of communication protocols

Abstract

A symbolic representation of a state/transition system based on binary decision diagrams (BDDs) is generally more compact than an explicit representation like a state/transition table. This is due to regular and repetitive patterns occurring in state/transition systems. By exploiting this property, huge state spaces can be represented, and the resulting BDDs can be profitably used for activities such as symbolic model checking and sequential circuit synthesis. This paper shows how such techniques can be applied to communication protocols by presenting a systematic method to build BDD representations from protocol specifications expressed in the ISO standard protocol specification language LOTOS. The method exploits the compositionality of the process algebra of LOTOS to avoid the enumeration of all the states and transitions, takes also data into account, enables building the BDDs in the more convenient disjunctive partitioned form, and can handle any LOTOS specification characterized by a finite LTS. The method consists in partitioning the set of process definitions according to their mutual recursion relationships, building an LTS for each set of mutually recursive process definitions, encoding these LTSs as BDDs which in turn are combined together, according to the process algebraic operators, to obtain the overall BDD representation. An example is used throughout the paper to illustrate the method.