CCS and SDL

The CCITT Specification and Description Language SDL [CCI88a, SPT87] is intended as a language to write specifications for telecommunication applications, such as telephone exchange control systems. It is widely used within the telecommunications industry. In other areas, such as in process control systems, SDL may find additional applications. Figure 6.1 illustrates the major SDL concepts. An SDL specification consists of states and transitions. Transitions consist of communication actions, decision points and tasks. These elements are connected by means of flow lines; connectors are used to link SDL diagrams together.