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 A telephone network is a telecommunications network that connects telephones, which allows telephone calls between two or more parties, as well as newer features such as fax and interne ...

s in an automatic

telephone exchange A telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syst ...

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 exchange Strowger may refer to: * Strowger switch, automatic telephone exchange equipment * Strowger Automatic Telephone Exchange Company, the company that manufactured Strowger switches * Almon Brown Strowger (1839–1902), who invented the principle of ...

s are usually direct control systems, whereas crossbar, and electronic exchanges (including all

stored program control Stored program control (SPC) is a telecommunications technology for telephone exchanges. Its characteristic is that the switching system is controlled by a computer program stored in a memory in the switching system. SPC was the enabling technolog ...

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 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 * ''Di ...

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

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 telecommunication, common-channel signaling (CCS), or common-channel interoffice signaling (CCIS), is the transmission of control information ''(signaling)'' via a separate channel than that used for the messages, The signaling channel usually c ...

in which the channels that are used for

signaling In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...

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