STD meaning in Telecommunication ?

Subscriber trunk dialling (STD), also known as subscriber toll dialing, is a telephone numbering plan feature and telecommunications technology for the dialing of trunk calls by telephone subscribers without the assistance from switchboard operators.

Switching systems to enable automatic dialling of long distance calls by subscribers were introduced in the United Kingdom on 5 December 1958. The system used area codes that were based the letters in a towns name. A ceremonial first call was made by Queen Elizabeth II from Bristol to Edinburgh.

A similar service, built on crossbar equipment, using regionally structured numbering, rather than alphanumeric codes, was experimentally introduced by P&T in Ireland in 1957, with the first services being in Athlone. A full service was rolled out in 1958, initially to exchanges in Cork and then Dublin and its hinterland and gradually to all areas with automatic exchanges.

The term ‘STD call’ was once commonly used in the UK, Ireland, Australia, India, and parts of South East Asia, but it may be considered archaic today, or possibly even no longer be understood. Other less technical terms like ‘national calling,’ ‘long distance calling’ and so on are now more commonly used. The distinction between local and long distance / STD calls is also no longer relevant to many users, as calls are charged at flat or bundled rates. It is also necessary to dial area codes on most (or all) calls, especially from mobile phones, so they are considered part of the number.

Terms such as ‘area code’, ‘prefix’ or ‘national dialling code’ tends to be used in place of STD code in the U.K. and in Ireland.