A historic telephony routing system that enabled telephone users to place long-distance toll calls without the assistance of a human operator. It relied on hierarchical area codes and automated tandem switches to route the call across regional boundaries. The introduction of this system required massive upgrades to exchange billing equipment to automatically record call duration and distance.
Before subscriber trunk dialling was rolled out to the rural exchanges, you had to ring the operator and ask for the trunk line to London.
Known as STD in the UK and Commonwealth, while the North American equivalent is Direct Distance Dialing (DDD).
Also heard as
- STD
- direct distance dialing
Related terms
STD
Subscriber trunk dialling, the historic system allowing callers to route long-distance calls without an operator.
DDD
Direct distance dialing allows callers to route long-distance calls without an operator.
Telephone exchange
A central system of switches that routes calls between subscribers.
Trunk call
A historic long-distance telephone call routed through major intercity exchanges.