<Tr> <Td> </Td> <Td> This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations . Please help to improve this article by introducing more precise citations . (January 2013) (Learn how and when to remove this template message) </Td> </Tr> <P> In telecommunication, a common control is an automatic telephone exchange arrangement in which the control equipment necessary for the establishment of connections is shared by being associated with a given call only during the period required to accomplish the control function for the given call . The first examples deployed on a major scale were the Director telephone system in London and the panel switch in the Bell System . Direct control telephone exchanges became rare in the 1960s, leaving only common control ones . </P> <P> Systems which have control subsystem as an integral part of the switching network itself were known as direct control switching systems . Systems in which the control subsytem is outside the switching network are known as Common control systems . 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 . </P> <P> During the 1970s, common control exchanges became stored program control exchanges, using in the 1980s common - channel signaling in which the channels that are used for signaling are not used for message traffic . </P>

Difference between common control and direct control switching system
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