Structural Models for Specifying Telephone Systems

Two approaches, resource-oriented and constraint-oriented, for structuring telephone systems specifications, are presented. Both approaches express behaviour by collections of communicating processes, using the language LOTOS. However, requirements are distributed differently among processes. Examples are taken from specifications of telephone systems, first basic, and then with features. The features used as examples are call forwarding, originating call screening, and three-way calling. The two structuring methods are compared.