Editing Common control (section)

{{more citations needed|date=January 2013}}

In [[telecommunications]], '''common control''' is a principle of switching [[telephone call]]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.<ref>{{Cite book
|url=http://archive.org/details/bellsystem_No5CrossbarVol1EquipmentApplicationsMay63
|title=No. 5 Crossbar Volume 1: Equipment Applications May 63|last=Western Electric Co.
|date=1963-05-01
}}</ref>  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]]s 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.