Real-time networking yielding minimal delay, maximal throughput, and access of fairness, has been becoming essential for supporting real-time applications. Design and analysis of these networks and protocols have been informal and ad hoc. Such informal methods not only lead to ambiguities but also result in timed-consuming redesign should errors occur. This paper presents a prototype workstation, called Communication Protocol Analyzer and Simulator System (CPASS), aimed at the modelling, verification, analysis, and simulationfor real-time networks by means of a formal and automated approach. The system is based on an extended finite state machine model, called SDLN (a variant of SDL). It is composed of six components: Network Topology Editor, SDLN/GR Editor, Protocol Verifier and Analyzer, SDLN-to-C Compiler, Simulator, and Statistical Generator and Comparator. The paper first presents the syntax and semantics of SDLN. The paper then describes the functionality of each component of CPASS. An example of a token ring network is used to illustrate the complete processes of modelling, analysis and simulation throughout the paper.