A formal approach to reactive systems software: a telecommunications application in ESTEREL

ESTEREL is a formally-defined language designed for programming reactive systems; namely, those that maintain a permanent interaction with their environment. The AT&T 5ESS R telephone switching system is an example of a legacy reactive system. As a case study, we describe an implementation in ESTEREL of one feature of a 5ESS switch; this implementation has been tested in the 5ESS switch simulator. Furthermore, it has been formally verified that this implementation satisfies some safety properties required for telecommunications applications. Our case study provides some evidence that ESTEREL is suitable for programming legacy reactive systems, and that it may afford significant advantages in software development over more traditional programming languages used in industrial settings.