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A typical volume of Bell System Practices from the 1970s. The Bell System Practices (BSPs) is a compilation of technical publications which describes the best methods of engineering, constructing, installing, and maintaining the telephone plant of the Bell System under direction of AT&T and Bell Telephone Laboratories. [1]
Centrex is a portmanteau of central exchange, a kind of telephone exchange. It provides functions similar to a PBX, but is provisioned with equipment owned by, and located at, the telephone company premises. [1] Centrex service was first installed in the early 1960s in New York's financial district by New York Telephone.
The voice switching fabric plan was similar to that of the earlier 5XB switch in being bidirectional and in using the call-back principle. [clarification needed] [citation needed] The largest full-access matrix switches (the 12A line grids had partial access) in the system, however, were 8x8 rather than 10x10 or 20x16.
5ESS uses a time-space-time (TST) topology in which the Time-Slot-Interchangers (TSI) in the Switching Modules assign each phone call to a time slot for routing through the CM. CMs perform time-divided switching and are provided in pairs; each module (cabinet) belonging to Office Network and Timing Complex (ONTC) 0 or 1, roughly corresponding ...
Also taking advantage of the superior versatility of 5XB, Centrex was invented as a service package. Later stored program control exchanges allowed more extensive service features. Autovon originally used a four-wire version of 5XB, with a more complex marker to implement its nonhierarchical polygrid routing system.
Template documentation Chart of break up of AT&T into Baby Bells and following merges. The above documentation is transcluded from Template:AT&T chart/doc .
Additional features, such as billing equipment, may also be incorporated into the exchange. The Bell System dial service implemented a feature called automatic number identification (ANI) which facilitated services like automated billing, toll-free 800-numbers, and 9-1-1 service. In manual service, the operator knows where a call is originating ...
Many calling features became available to telephone subscribers after computerization of telephone exchanges during the 1980s in the United States. The services include voicemail, caller ID, call waiting, speed dialing, conference calls (three-way calling), enhanced 911, and Centrex services.