Essential Guide to Telecommunications, The, Third Edition

Telephone Systems—PBXs, Centrex and Key Systems

When the telephone was first invented in 1876, each person's telephone line was wired directly to another individual user. By 1877, a switchboard was installed in Boston so that each telephone could be wired to the central switchboard instead of to every telephone. When an individual wished to call someone, he or she picked up the telephone handset and asked the operator to connect the call to a particular individual. The operator knew all of the town's business. In 1891, Almon Strowger patented a central office switch where operators were not required to complete each call. Strowger's motivation was privacy: He felt that operators were listening in on his telephone conversations.

What Is a PBX? ...