MODELING AND SPECIFYING C7 USING SDL

The CCITT specification and description language (SDL) is a formal method for specifying requirements, designing systems and implementing products. This paper describes a major breakthrough in the use of SDL to specify signalling protocols in BT. A significant part of BT's core network signalling, the basic telephony part of signalling system No 7, was re-specified in formal SDL. This demonstrated the suitability of the technique in a real industrial environment and highlighted errors in the existing procurement specifications. Furthermore, the project demonstrated the power of the simulation tools, available for formal SDL, to verify the requirements capture documents before they are used for procurement or design.