Telecommunication software validation using a synchronous approach

Telephone services and features provide a challenging application domain for the development and the validation of real-time software. This paper reviews our experiment on incremental validation of services and features which has been carried out in collaboration with CNET-France Telecom. Because of the well-known "feature interaction problem", telephone software can be considered as safety-critical software, and must exhibit qualities such as correctness and safety with very high assurance. For this class of software, the requirements engineering phase usually ends in a formal specification which is provided in some logic; therefore, the validation can be performed in a very rigorous and formal way using proof tools and/or specification-based testing techniques. Much critical software is reactive: it continuously reacts with its environment at its own speed. Therefore, it must satisfy some strong temporal causalities between external events, in order to bring about or maintain the desired relationships in the environment. We have developed a new approach for specification-based testing of synchronous reactive software and its associated environment. The specification language is LUSTRE, which is both a temporal logic and a synchronous data-flow programming language. We have successfully modelled a telecommunication system as a reactive software system; this allowed us to extensively apply our testing approach to this type of software. A synchronous model of a telecommunication system is described. A specification of the model is then given and the validation work is presented.