Common control

In telecommunications, common control is a principle of switching telephone calls 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 to common control systems, 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, electronic exchanges including all stored program control systems are common control systems. Common control is also known as indirect control or register control.

The first examples of common control deployed on a major scale were the Director telephone system in London and the panel switch, developed and used by the Bell System. Direct control telephone exchanges became rare in the 1960s, leaving only common control ones.

During the 1970s, common control exchanges became stored program control exchanges, and in the 1980s used common-channel signaling in which the channels that are used for signaling are not used for message traffic (out of band signaling).

References

 This article incorporates public domain material from Federal Standard 1037C. General Services Administration. Archived from the original on 2022-01-22. (in support of MIL-STD-188).