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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.
DCO-SE (Line Switch 10,000 lines, software enhanced, class features, centrex, etc.) DCO-RLS (Remote Line Switch, controlled by hosts above) RLS 1000 (Pedestal mount cabinet 1000 lines in a subdivision - required multiple T-1's to host)
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.
The first version of the new hand telephone sets was marked by AT&T as D-76869, a specification type for small quantities of new equipment. The device was described by George K. Thompson of the American Telephone and Telegraph Company (AT&T) in United States patent No. 1508424 of 1924, without showing the handset that was still in development. [10]
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From the 1960s, a simulated PBX, known as Centrex, provided similar features from the central telephone exchange. A PBX differs from a key telephone system (KTS) in that users of a key system manually select their own outgoing lines on special telephone sets that control buttons for this purpose, while PBXs select the outgoing line automatically.