Synopsis
Signalling System 7 is the protocol by which most telephone exchanges communicate and set up calls. This report discusses SS7 and the older MFC/R2 signalling protocols, - ISDN and POTS calls, CLASS services, and Centrex PABX emulation across multiple sites, including with the Asterisk open-source server-based system. Also discussed are PABXs, ‘key systems’, Computer Telephony Integration (CTI) and Number Portability (NP).