Intelligent networks: British Telecom's first realisation

In 1983 British Telecom (BT) identified a major market potential for Automatic Freephone and Callstream services. An analogue network with extended register translation and call charging facilities, overlaid on the Public Switched Telephone Network (PSTN), was proposed as an interim solution. The Analogue Derived Services Network (ADSN) consisting of 8 fully interconnected switching nodes was brought into limited public service in April 1985 and full public service in July 1985 carrying LinkLine 0800 and LinkLine 0345 traffic. BT awarded a contract to AT&T Network Systems UK for the supply and installation of a Digital Derived Services Network (DDSN) comprising 5ESS-PRX digital switches to be implemented in two distinct phases. Phase 1 involved the supply of 8 digital units utilising CCITT No.7 common channel signalling as replacements for their analogue counterparts. Phase 2 makes provision for an advanced freephone service using an intelligent network architecture.