telecommunications Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...

, common control is a principle of switching

telephone call A telephone call, phone call, voice call, or simply a call, is the effective use of a connection over a telephone network between the calling party and the called party. Telephone calls are the form of human communication that was first enabl ...

s in an automatic

telephone exchange A telephone exchange, telephone switch, or central office is a central component of a telecommunications system in the public switched telephone network (PSTN) or in large enterprises. It facilitates the establishment of communication circuits ...

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 (the ''PENnsylvania exchange'') 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 Director may refer to: Literature * ''Director'' (magazine), a British magazine * ''The Director'' (novel), a 1971 novel by Henry Denker * ''The Director'' (play), a 2000 play by Nancy Hasty Music * Director (band), an Irish rock band * ''D ...

systems in Havana, 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 A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. ...

are not used for

message A message is a unit of communication that conveys information from a sender to a receiver. It can be transmitted through various forms, such as spoken or written words, signals, or electronic data, and can range from simple instructions to co ...

traffic (out of band signaling).

References

{{FS1037C MS188 Telephone exchange equipment