Choke exchange

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[1] 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:

Central office
(NPA–NXX)		Location
202–432Washington, DC
205–741Birmingham, Alabama
206–421Seattle, Washington
212–955New York, New York
213–520Los Angeles, California[2]
818–520
214–787Dallas, Texas
215–263Philadelphia, Pennsylvania
216–578Cleveland, Ohio
225–499Baton Rouge, Louisiana
305–550Miami, Florida
312–591Chicago, Illinois[2]
313–298Detroit, Michigan
314-969

St. Louis, Missouri

337–920Lafayette, Louisiana
401–224Providence, Rhode Island
402–962Omaha, Nebraska
404–741Atlanta, Georgia (770 from 1995-1998)
770–741
410–481Baltimore, Maryland
414–799Milwaukee, Wisconsin
415–478San Francisco, California[2]
416–870, –872Toronto, Ontario[3]
501–433Little Rock, Arkansas
502–571Louisville, Kentucky
504–260New Orleans, Louisiana
512–390Austin, Texas
513–749Cincinnati, Ohio
514–790Montreal, Quebec
585–222Rochester, New York
604–280Vancouver, British Columbia[3]
613–750Ottawa, Ontario
614–821Columbus, Ohio
615–737Nashville, Tennessee
617–931Boston, Massachusetts
651–989Minneapolis/St. Paul, Minnesota
704–570Charlotte, North Carolina
713–390Houston, Texas
714–977Orange County, California[2]
716–644Buffalo, New York
817–787Fort Worth, Texas
901–535Memphis, Tennessee
919–860Raleigh-Durham, North Carolina
619–570San Diego, California

One of the early choke lines (exchanges) was instituted due to a widely advertised contest by a local radio station in the Miami/Fort Lauderdale area. WHYI-FM advertised their "Last Contest". The top prize was an automobile. Since the advertising lasted over a month, there were a very large volume of calls when they announced for people to call in. There were so many calls that the local exchanges ran out of dial tones. This caused major issues since at the time if you had no dial tone, you couldn't dial at all. After it was over, the area emergency services filed complaints, and were heard. Shortly afterward the 305-550 exchange came into being. The first number on it was 305-550-9100 (for Y100 radio station). Due to the issues involved because of the "Last Contest", this may have been what caused the creation of the choke exchanges.

See also

References
  1. Higdon, John (1989-09-25). "Re: Prefix '520' For Los Angeles Radio Stations". Newsgroup: comp.dcom.telecom. Usenet: [email protected].
  2. Higdon, John (1989-09-22). "Re: Prefix '520' For Los Angeles Radio Stations". Newsgroup: comp.dcom.telecom. Usenet: [email protected].
  3. Leibold, David (1990-11-24). "TELECOM Digest Guide to Special Prefixes/Numbers". TELECOM Digest (Mailing list). Retrieved 2010-11-05.
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