Bridging the gap between formal specification and analysis of communication protocols

Abstract

SDL, Estelle and LOTOS are three high-level formal description techniques (FDT) that have been developed and standardized by the international organizations, the CCITT and ISO respectively, for the specification of industry-strength communication protocols. It is crucial to formally verify an FDT protocol specification before its implementation. Most formal analysis and verification techniques for communication protocols, however, have been based on mathematically simple low-level formulations such as finite state machines (FSM) or extension of this model (EFSM). There is a gap between the low-level formal models and the high-level FDTs in terms of expressive power and verifiability, which prohibits the use of existing state/transition based formal analysis methods, such as reachability analysis, for direct use in the formal verification of the protocols specified in the FDTs. This paper proposes a uniform framework as an approach to bridging the gap through systematic reduction of the FDT protocol specifications to a common intermediate model called the structured system of communicating machines (SSCM) which is an EFSM based, powerful, yet rather simply defined formalism. LOTOS is then used to demonstrate the applicability of the approach by developing a complete set of transformation rules and providing the proof for the semantic perseverance of those transformation rules under a well-defined event trace equivalence.