Specification and analysis of a data transfer protocol using systems of communicating machines

Abstract

A model for communication protocols called systems of communicating machines is used to specify a data transfer protocol with variable window size (e.g., HDLC), which is an arbitrary nonnegative integer, and to analyze it for freedom from deadlocks. The model uses a combination of finite state machines and variables. This allows the size of the specification (i.e., number of states and variables) to be linear in the window size, a considerable reduction from the pure finite state machine model. A new type of analysis is demonstrated which we call system state analysis. This is similar to the reachability analysis used in the pure finite state model, but it provides substantial simplication by reducing the number of states generated. For example, with the protocol in this paper, if w is the window size, then the global analysis produces O(w5) states, while the system state analysis produces O(w3) states. The system state analysis is then combined with an inductive proof, extending the analysis to all nonnegative integers w.