, 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 USA. Direct control telephone exchanges
became rare in the 1960s, leaving only common control ones.
Note: During the 1980s, common control exchanges became stored program control exchanges, using Common channel signalling in which the channels that are used for signaling, whether frequency bands or time slots, are not used for message traffic.
Source: From Federal Standard 1037C and from MIL-STD-188