[1] 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.
Early semi-mechanical installations with common control components existed, for example rotary systems in Sweden and France in 1915, and the first panel switches 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.
By the mid-1920s, common control ideas had extended to include marker systems for testing for idle trunks.
[3] This article incorporates public domain material from Federal Standard 1037C.