The Panel Dial Telephone Switching System Douglas A. Kerr Issue 6 June 15, 2018
The panel dial telephone switching system Douglas A. Kerr Issue 6 June 15, 2018 ABSTRACT In the 1910s, AT&T, the parent of the Bell Telephone System, anxious to reduce the stupendous labor costs of manual telephone switching (especially in large metropolitan areas), and realizing that the most prominent available switching system (the Strowger system) had serious limitations of its use in such areas, undertook the development from the ground up of a switching system based on many entirely new concepts. This system, the panel dial switching system, came to be the mainstay of the Bell System’s program of mechanizing telephone service in many of the largest cities in the U.S. In this article, we will learn of the evolution of this system, of the unique mechanisms around which it revolves, and of the implications of its basic operational principle, known as common control. Considerable detail in system operation is given, although not usually at the circuit level, except where necessary to illustrate an important concept. 1 HISTORICAL CONTEXT 1.1 The telephone industry in 1910 By 1910, the telephone industry in the United States was well on the way to its “classical” structure, which existed until about 1984. The Bell Telephone System, owned by American Telephone and Telegraph Company (AT&T), was becoming the major force in the industry, and provided local telephone service in most of the nation’s largest cities (often after acquiring existing locally-owned telephone companies, sometime several competing ones in the same city, whose operations had to be harmonized and consolidated). In about 1907, AT&T adopted the slogan, “One Policy, One System, Universal Service”.
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