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Distributed Reachability Analysis for Protocol Verification Environments

Report ID:
July 1987
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A topic of importance in the area of distributed algorithms is the efficient implementation of formal verification techniques. Many such techniques are based on coupled finite state machine models, and reachability analysis is central to their implementation. SPANNER is an environment developed at
AT&T Bell Laboratories, and is based on the selection/resolution model (S/R) of coupled finite state machines. It can be used for the formal specification and verification of computer communication protocols. In SPANNER, protocols are specified as coupled finite state machines, and analyzed by proving properties of the joint behavior of these machines. In this last step, reachability analysis is used in order to generate the "product" machine from its components, and constitutes the most time consuming part of the verification process. In this paper we investigate aspects of distributing reachability over a local area network of workstations, in order to reduce the time needed to complete the calculation. A key property which we exploit in our proposed design is that the two basic operations performed during reachability, the new state generation, and the state tabulation, can be performed asynchronously, and
to some degree independently. Furthermore, each of these operations can be decomposed into concurrent subtasks. We provide a description of the distributed reachability algorithm we are currently in the process of implementing in SPANNER, and an investigation of the scheduling problems we face.

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