Estelle is one of the standardized Formal Description Techniques for the specification of communication protocols and distributed systems. Unfortunately, Estelle is not capable to express real-time requirements or characteristics of services or protocols which is especially important in the context of distributed multimedia systems. In this paper, we introduce an extension to Estelle called Real-Time Estelle that allows to describe real-time systems. We introduce the syntax of the new language and propose both an operational and a descriptive semantics. Examples show the usefulness of the approach. We also discuss ways to implement Real-Time Estelle specifications
