The authors present an efficient method for extracting a behavior description of a process (communicating finite state machine), as constrained by a given protocol. In the case where the constrained behavior corresponds to the unconstrained behavior depicted by the process specification, the process is said to be effective. The authors call the derived behavior description a process event graph (PEG). By comparing the PEG with the process specification, they determine whether a process in a protocol is effective. Two extensions to the basic algorithm are given, one to introduce parallelism to reachability analysis and one to detect traces that lead to process blockage. The authors focus initially on the two-process case, and then consider implications of more general protocols.>