Deadlock detection in communicating finite state machines by even reachability analysis

A network of communicating finite state machines (CFSM) consists of a set of finite state machines which communicate asynchronously with each other over (potentially) unbounded FIFO channels by sending and receiving typed messages. As a concurrency model, CFSMs has been widely used to specify and validate communications protocols. CFSMs is also powerful and suitable for modeling mobile communication systems - a CFSM can naturally model a mobile station in a wireless communication system. The unbounded FIFO channels are ideal for modeling the communication behavior among mobile stations. Fair reachability is a very useful technique in detecting errors of deadlocks and unspecified receptions in networks of (CFSMs) consisting of two machines. The paper extends the classical fair reachability technique, which is only applicable to the class of two-machine CFSMs, to the general class of CFSMs. For bounded CFSMs, the extended fair reachability technique reduces by more than one half the total number of reachable global states that have to be searched in verifying freedom from deadlocks. The usefulness of the new reachability technique, called even reachability, is demonstrated through two examples.