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 typically used to service telephone numbers of talk radio caller and contest lines of radio stations and event ticket vendors.

Motivation

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

Examples of choke exchanges in North America have included:

Central office (NPA–NXX)	Location
202–432	Washington, DC
205–741	Birmingham, Alabama
206–421	Seattle, Washington
212–955	New York, New York
213–520	Los Angeles, California
818–520
214–787	Dallas, Texas
215–263	Philadelphia, Pennsylvania
216–578	Cleveland, Ohio
225–499	Baton Rouge, Louisiana
305–550	Miami, Florida
312–591	Chicago, Illinois
313–298	Detroit, Michigan
314–969	St. Louis, Missouri
337–920	Lafayette, Louisiana
401–224	Providence, Rhode Island
402–962	Omaha, Nebraska
404–741	Atlanta, Georgia (770 from 1995 to 1998)
770–741
410–481	Baltimore, Maryland
412–333	Pittsburgh, Pennsylvania
414–799	Milwaukee, Wisconsin
415–478	San Francisco, California
416–870, –872	Toronto, Ontario
501–433	Little Rock, Arkansas
502–571	Louisville, Kentucky
504–260	New Orleans, Louisiana
512–390	Austin, Texas
513–749	Cincinnati, Ohio
514–790	Montreal, Quebec
585–222	Rochester, New York
604–280	Vancouver, British Columbia
613–750	Ottawa, Ontario
614–821	Columbus, Ohio
615–737	Nashville, Tennessee
617–931	Boston, Massachusetts
651–989	Minneapolis/St. Paul, Minnesota
704–570	Charlotte, North Carolina
713–390	Houston, Texas
714–977	Orange County, California
716–644	Buffalo, New York
817–787	Fort Worth, Texas
901–535	Memphis, Tennessee
916–766	Sacramento, California
919–860	Raleigh-Durham, North Carolina
619–570	San 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 a caller had no dial tone, the caller could not 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

• Routing in the PSTN