Telecommunications Development Based on Message Sequence Charts and SDL

For a long time Message Sequence Charts (MSCs) have been part of auxiliary diagrams within the SDL-recommendations, but only recently their standardization in graphical and textual form has been decided within the CCITT. MSC is a trace language which in its graphical form admits a particularly intuitive representation of system runs in distributed systems. Within a software development process for (tele-)communication systems MSCs are used primarily for the requirements definition describing the required system behaviour in form of traces. However, in practicethe requirements defininition by means of MSCs often was restricted to the specification of few selected system runs, the 'standard cases', since each MSC only describes a partial behaviour. In order to overcome this restriction, composition mechanisms are introduced by means of global and local conditions. Standard building blocks, so called Sequence Chart segments, are defined as means for structuring the composition and to obtain an overview about the specified system. The aim of this paper is to prove the usefulness of these concepts by applying them to the specification of the INRES-service. Beyond that, the power of the composition rules is increased considerably by taking over the asterisk concept from SDL to MSC-conditions.