An obstacle to the uses of software metrics and size models, which we have developed for measuring the complexity and maintainability of a communication protocol specified in Estelle and for estimating the size of its specification and implementation, is the time-consuming effort in collecting the metrics. To address this problem, a software system called PSAMS (protocol specification assessment and measurement system) for automatically calculating the metrics and sizes of specification and implementation has been developed. This paper describes the design of PSAMS, which provides five functionalities for a communication protocol Estelle specification: exploring its specification, measuring its complexity, assessing its maintainability, estimating its specification size and estimating its implementation size. To demonstrate the usefulness of PSAMS, we have applied it to measure the complexity and maintainability of 10 communication protocol Estelle specifications; the measurement results and decision support information provided by each functionality are presented in this paper. With PSAMS, communication protocol designers and developers are able to assess the complexity of a communication protocol early in the specification stage and have information which helps them manage a communication software project better. Copyright © 2002 John Wiley & Sons, Ltd.