Direct distance dialing is the traditional North American telephone service that lets subscribers dial long-distance numbers directly. It relies on a hierarchical system of area codes and toll centers to switch the call automatically. The implementation of this system eliminated the need for human operators to manually patch trunk lines together for toll calls.
We need to check the PBX trunk configuration because users are getting busy signals on all DDD calls outside the local exchange.
Also heard as
- direct distance dialing
Related terms
Subscriber trunk dialling
The automated telephone exchange system that allows callers to dial long-distance numbers directly.
Trunk call
A historic long-distance telephone call routed through major intercity exchanges.
Exchange
A physical building or the specific set of telephone numbers routed through it.