ring and support. be sent to the customer with the regular bill or transmitted on a data link directly to the customer. The next logical step is wide area Centrex. This makes it possible for the user to configure a highly featured wide area virtual private network while retaining an exceptional level of flexibility. Wide 35.3 Development of the Centrex market area Centrex draws on a database of users, identifying their location, and privileges, giving them the full range of Centrex business services at all sites. It amounts to a virtual private managed network By the 1960s AT&T, the North American PTO, had achieved univer- operated by the telephone company retaining the availability sal POTs service. They then looked for new market opportunities possible only on the PSTN. and Centrex was born. First generation analogue Centrex services The telecommunications revolution has SO far served the business were highly acceptable by the standards of the day, and, by the start user within the office environment. Extension of the wide area of the 1970s, 20% of the business market used Centrex. This then Centrex concept through intelligent networks brings the networked slumped as AT&T chose to focus on the PBX business to protect its office environment into the home and also brings the home worker position in anticipation of divestiture. Centrex recovered sharply into the mainstream business community through shared facilities. following the divestiture of AT&T and the introduction of more Any user, wherever he or she is, can have access to the range of highly featured digital Centrex such as that on the Northern Telecom DMS. Today, every Bell Operating Company has experienced services which would previously have been available only in the office environment on the corporate network. growth in Centrex services, which once again handles close on 20% The advantages of Centrex for the business and domestic con- of North American business telecommunications sumer are clear, such as variety of features, low investment, protec- I