Dialling (telephony)

Dialling, (dialing in US English), is the action of initiating a telephone call by operating the rotary dial or the telephone keypad of a telephone.

Prior to Strowgers invention of SXS, rotary switch in 1891, telephone connections involved cranking a handle to generate a voltage that operated a bell on the remote operator's board; the operator would then on the line to the subscriber and speak to them, they would then raise a voltage on the recipients phone, alerting them of an incoming call. When this was acknowledged, the operator would patch the two subscribers together using a lead terminating in a jack plug.

Under Strowger's system that was first introduced commercially in La Porte, Indiana the number was dialled using two telegraph keys. The subscriber tapped eight times on one, then three times on the second to 'dial' the number 83. When this was introduced into Albion, New York in 1899 – the keys had been replaced by a rotary dial.

From 1912, the British General Post Office, which also operated the British telephone system, installed several automatic telephone exchanges from several vendors in trials at Darlington on 10 October 1914 (rotary system), Fleetwood (relay exchange from Sweden), Grimsby (Siemens), Hereford (Lorimer) and Leeds (Strowger). The BPO selected the Strowger switches for small and medium cities and towns. However, the selection of switching systems for London and other large cities was not decided until the 1920s, when the Director telephone system was adopted. The Director systems used SXS switches for destination routing and number translation facilities similar to the register used in common-control exchanges. Using similar equipment as in the rest of the network was deemed beneficial and the equipment could be manufactured in Britain.

Introduced to the public in 1963 by AT&T, Touch-Tone dialing greatly shortened the time of initiating a telephone call. It also enabled direct signaling from a telephone across the long-distance network using audio-frequency tones, which was impossible with the rotary dials that generated digital direct current pulses that had to be decoded by the local central office.

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