telecommunications Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...

, common control is a principle of switching

telephone call A telephone call is a connection over a telephone network between the called party and the calling party. First telephone call The first telephone call was made on March 10, 1876, by Alexander Graham Bell. Bell demonstrated his ability to "ta ...

s in an automatic telephone exchange that employs shared control equipment which is attached to the circuit of a call only for the duration of establishing or otherwise controlling the call. Thus, such control equipment need only be provided in as few units to satisfy overall exchange traffic, rather than being duplicated for every subscriber line. In contrast, ''direct control'' systems have subsystems for call control that are an integral part of the switching network. Strowger exchanges are usually direct control systems, whereas crossbar, and electronic exchanges (including all stored program control systems) are common control systems. Common control is also known as indirect control or register control.

History

Early semi-mechanical installations with common control components existed, for example rotary systems in Sweden and France in 1915, and the first

panel switch The Panel Machine Switching System is a type of automatic telephone exchange for urban service that was used in the Bell System in the United States for seven decades. The first semi-mechanical types of this design were installed in 1915 in Newark, ...

es in Newark, New Jersey, also in 1915. The first large-scale, fully automatic, common control switching system deployed in commercial production service was the ''ATlantic'' central office in Omaha, Nebraska, a panel system cut over on December 10, 1921. Other panel offices for Kansas City and New York CIty (''PENnsylvania'') were in planning at the same time and opened shortly after. In 1922, common control was introduced in Strowger-type step-by-step systems,Automatic Electric Company, ''The Automatic Director in Strowger Metropolitan Telephone Systems'', in ''Automatic Telephone'', Volume 10(11-12), November 1922, p.116 resulting in the first installations of Director systems in Havanna, Cuba in 1924, and in London, England in 1927. By the mid-1920s, common control ideas had extended to include marker systems for testing for idle trunks. During the 1960s, common control exchanges became stored program control exchanges,J.G. Van Bosse, F.U. Devetak, ''Signaling in Telecommunication Networks'', 2nd edition (2007), p.111 and by the 1970s they used common-channel signaling in which the channels that are used for signaling are not used for

message A message is a discrete unit of communication intended by the source for consumption by some recipient or group of recipients. A message may be delivered by various means, including courier, telegraphy, carrier pigeon and electronic bus. A ...

traffic (out of band signaling).

References

Telephone exchange equipment {{telephony-stub