A choke exchange is a telephone exchange designed to handle many simultaneous call attempts to telephone numbers of that exchange. Choke exchanges are typical used to service telephone phone numbers of talk radio caller and contest lines of radio stations and event ticket vendors.
A central office might only have physical plant resources to handle ca. 8% of allocated telephone numbers, based on historical call traffic averages. A choke exchange has trunk facilities to other exchanges designed in a manner that high call volume is handled through the choke connection rather than overwhelming the rest of the local telephone network. Other local exchanges have a limited number of direct trunks (junctions) to the choke exchange, which may only serve one or more customers, such as a radio station contest line, which may experience many simultaneous calls. But instead of calls being overflowed to main or tandem routes shared with other calls, the unsuccessful callers receive a reorder tone from their local or tandem exchange. If the calls were overflowed to the tandem route, the caller would receive a busy tone from the exchange serving the radio station, and the sudden peak would disrupt calls between other customers.
With common-channel signaling (CCS), e.g., Signalling System No. 7, separate choke exchanges may not be required for these customers.
Examples of choke exchanges in North America have included: