Towards automating protocol synthesis and analysis

In OSI (Open Systems Interconnection) Reference Model, a communication protocol is a set of rules governing the interaction and coordination between a number of communicating entities at a certain protocol layer. The purpose of these rules is to provide some intended communication services to the service users, which constitute the next higher layer above the concerned one. The first part of this research is with regard to automating the process of deriving protocol specifications from service specifications. However, the protocol derivation process for an arbitrary communication service appears to be formidably difficult. As a result, we concentrate on a class of communication services whose behavior can be described by a set of directly coupled Finite State Machines (FSMs). For a service specified in this state-transition model, we provide a protocol algorithm which produces the protocol specification from the given service specification automatically once some additional information about the decision options and initiation option is provided by the protocol designer. The provision of the additional information is to ensure that the produced protocol specification is indeed intended by the protocol designer. To enable our algorithm to deal with underlying error-prone communication services, we further devise an error-recovery transformation procedure. The error-recovery transformation procedure consists of three transformation rules applicable to three different patterns of transitions in the synchronizing protocol FSM produced by the protocol derivation algorithm from a service specification. Since every protocol synthesis technique, including ours, has its own limitations imposed by the underlying model and assumptions, protocol analysis (validation and verification) is still needed to ensure the correctness of protocols beyond the expressive power of the underlying model. One of the most effective and mechanizable protocol validation/verification techniques is reachability analysis. However, the global state explosion problem restricts the applicability of reachability analysis to protocols whose global state graphs are not huge. As a result, global state graph reduction techniques are needed for alleviating this problem. In the second part of this research, we propose two such techniques for protocol specification in the Extended Finite State Machine (EFSM) model. The impact of the first global state graph reduction technique on the incremental protocol validation is also examined.