Choke exchange

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A choke exchange is a telephone exchange designed to limit the effect of high numbers of simultaneous call attempts to that exchange. Typical phone numbers on choke exchanges include radio station talk radio caller and contest lines[1] and event ticket vendors.

Based on typical call volumes, two exchange buildings might only have 800-1000 connections for an entire prefix of 10,000 numbers, based on historical averages that about 8% of all lines are in use at one time. A choke exchange differs in that it has a much higher connection formula, and more reliability in the event of severely high call volumes.

The choke exchange is connected to other exchanges in such a way that even high call volume will be 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 like a radio station contest line, which may experience a large number of simultaneous calls. But instead of calls being overflowed to main or tandem routes shared with other calls, the unsuccessful callers receive the reorder tone from their local or local tandem exchange. If the calls were overflowed to the tandem route, the caller would receive busy tone from the exchange serving the radio station, and the sudden peak would disrupt calls between other customers.

With common-channel signaling (CCS), like Signalling System No. 7, separate choke exchanges may not be required for these customers.

Examples of choke exchanges in North America have included:

See also[edit]


  1. ^ Higdon, John (1989-09-25). "Re: Prefix '520' For Los Angeles Radio Stations". Newsgroupcomp.dcom.telecom. Usenet: 
  2. ^ a b c d Higdon, John (1989-09-22). "Re: Prefix '520' For Los Angeles Radio Stations". Newsgroupcomp.dcom.telecom. Usenet: 
  3. ^ a b Leibold, David (1990-11-24). "TELECOM Digest Guide to Special Prefixes/Numbers". TELECOM Digest (Mailing list). Retrieved 2010-11-05.