Centrex is a portmanteau of central exchange, a kind of

telephone exchange A telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syst ...

. It provides functions similar to a PBX, but is provisioned with equipment owned by, and located at, the telephone company premises. Centrex service was first installed in the early 1960s in New York's financial district by New York Telephone. As of 2003, it was estimated that there were 20 million Centrex lines installed worldwide by 20 telephone companies, with the most installations in the United States (15 million), Canada (2 million), and the United Kingdom (1 million). This accounted for approximately 5% of all installed business telephone lines, worldwide. In terms of user-visible features, Centrex and PBX are similar. Features include: *

Direct inward dialing Direct inward dialing (DID), also called direct dial-in (DDI) in Europe and Oceania, is a telecommunication service offered by telephone companies to subscribers who operate a private branch exchange (PBX) system. The feature provides service for ...

(DID) * Automatic routing of calls to obtain lowest cost * Call pick-up groups *

Call forwarding Call forwarding, or call diversion, is a telephony feature of all telephone switching systems which redirects a telephone call to another destination, which may be, for example, a mobile or another telephone number where the desired called party is ...

Conference calling A conference call is a telephone call in which someone talks to several people at the same time. The conference call may be designed to allow the called party to participate during the call or set up so that the called party merely listens into ...

Automatic call distribution An automated call distribution system, commonly known as automatic call distributor (ACD), is a telephony device that answers and distributes incoming calls to a specific group of terminals or agents within an organization. ACDs direct calls based ...

(ACD) *

Call detail recording In computer science, a record (also called a structure, struct, or compound data) is a basic data structure. Records in a database or spreadsheet are usually called "rows". A record is a collection of ''fields'', possibly of different data typ ...

Phasing out

In the United States, the usage of Centrex lines has fallen from 16.5 million in 2002 to 10.7 million in 2008 as users transition to IP-PBX (through VoIP). Centrex continues to be used by large institutions, government agencies, and universities as most of the equipment has already been paid for, though leasing Centrex lines may be more expensive.

References

{{telecommunications Telephone service enhanced features Telephone exchanges