Formal description techniques (FDTs) provide formal and abstract ways to specify what protocols have to do and what features protocols need. Estelle is an FDT defined by the International Organization for Standardization for protocol specifications. We present an incremental protocol design system that contains an incremental protocol verification technique and an Estelle translator. Our incremental protocol design system allows on-line reverification after respecification. That is, instead of verifying respecified (modified) protocols from scratch, the reverification procedure is executed continuously and incrementally at the modification point. Using the translator, Estelle protocol specifications can be translated and interpreted for protocol verification. To meet the requirement of modifying protocol specifications written in Estelle at run time, the Estelle translator allows incremental translation and interpretation of the modified Estelle specification part for incremental verification. To further reduce the number of global states to be explored, the concept of dead and live variables is incorporated into our incremental verification technique. Based on the incremental verification technique and the Estelle translator, an incremental protocol design system (IPDS) is developed on SUN SPARC OPENLOOK work-stations. Using IPDS, protocol designers can analyze the verification results, interactively modify the protocols, and then continue the verification incrementally.
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