Constructing protocols with alternative functions

The author describes a method for designing communication protocols which can perform several distinct functions, but are limited to the execution of one function at a time. The construction of such a protocol consists of two steps: (1) developing a component protocol for each function to be included, and (2) integrating the components into the target protocol. The integration involves the resolution of potential component competition and process synchronization problems. A sufficient condition for the safety of the integrated protocol is also discussed. This design method is simple to use and promotes reuse of existing protocols. The construction of two protocols-the call setup phase of a data link control protocol and a portion of the CCITT´s X.21 Recommendation-is demonstrated