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, DC204-780Winnipeg, Manitoba 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
References