Enhanced 911 or E911 service is a North American telephone network (NANP) feature of the 911 emergency-calling system that automatically associates a physical address with the calling party's telephone number. List of VOIP 911 Service Providers.
This is generally done by a form of reverse telephone directory that is supplied by the telephone company as a computerized file. Computer software makes an association between the callers' line and a street address. This provides emergency responders with the location of the emergency without the person calling for help having to provide it. This is often useful in times of fires, break-ins, kidnapping, and other events where communicating your location is difficult or impossible.
The system only works in North America if the emergency telephone number 911 is called. Calls made to other telephone numbers, even though they may be listed as an emergency telephone number may not permit this feature to function correctly.
Outside the United States this type of facility is often called caller location, though its implementation is dependent on how the telephone network processes emergency calls.
The location information provided is normally integrated into emergency dispatch center's computer-assisted dispatch or CAD system, to provide the dispatcher with an on screen street map that highlights the caller's position and the nearest available emergency responders. For Wireline E911, the location is an address. For Wireless E911, the location is a coordinate. Not all PSAPs have the Wireless and Wireline systems integrated.
Each telephone company (LEC) has at least two redundant DS0-level (that is, 64 kbit/s, or voice quality) trunks connecting each host office telephone switch to each PSAP. These trunks are either directly connected to the PSAPs or they are connected to a telephone company central switch that intelligently distributes calls to the PSAPs. These special switches are often known as 911 Selective Routers. Their use is becoming increasingly more common as it simplifies the interconnection between newer ISUP/SS7-based host office switches and the many older PSAP systems. ...
This is generally done by a form of reverse telephone directory that is supplied by the telephone company as a computerized file. Computer software makes an association between the callers' line and a street address. This provides emergency responders with the location of the emergency without the person calling for help having to provide it. This is often useful in times of fires, break-ins, kidnapping, and other events where communicating your location is difficult or impossible.
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History
A pioneering system was in place in Chicago by the mid-1970s providing both police and fire departments access to the source location of emergency calls. Enhanced 911 is currently deployed in most metropolitan areas in the United States and Canada.The system only works in North America if the emergency telephone number 911 is called. Calls made to other telephone numbers, even though they may be listed as an emergency telephone number may not permit this feature to function correctly.
Outside the United States this type of facility is often called caller location, though its implementation is dependent on how the telephone network processes emergency calls.
Public Safety Answering Point (PSAP)
The final destination of a E911 call (where the 911 operator sits) is a Public Safety Answering Point (PSAP). There may be multiple PSAPs within the same exchange or one PSAP may cover multiple exchanges. The territories covered by a single PSAP is based more on historical and legal police considerations rather than telecommunications issues. Most PSAPs have a regional ESN, a number identifying the PSAP.The location information provided is normally integrated into emergency dispatch center's computer-assisted dispatch or CAD system, to provide the dispatcher with an on screen street map that highlights the caller's position and the nearest available emergency responders. For Wireline E911, the location is an address. For Wireless E911, the location is a coordinate. Not all PSAPs have the Wireless and Wireline systems integrated.
Wireline Enhanced 911
There is special privacy legislation that permits emergency operators to obtain the caller's information. This information is gathered by mapping the calling phone number to an address and ESN in a database. This database function is known as ALI, Automatic Location Identification. The database is generally maintained by the Incumbent Local Exchange Carrier (ILEC) under contract by the PSAP. Each ILEC has their own standards for the formatting of the database. Most ALI databases have a companion database known as the MSAG, Master Street Address Guide. The MSAG describes the exact spelling of streets, street number ranges, and other address elements.Each telephone company (LEC) has at least two redundant DS0-level (that is, 64 kbit/s, or voice quality) trunks connecting each host office telephone switch to each PSAP. These trunks are either directly connected to the PSAPs or they are connected to a telephone company central switch that intelligently distributes calls to the PSAPs. These special switches are often known as 911 Selective Routers. Their use is becoming increasingly more common as it simplifies the interconnection between newer ISUP/SS7-based host office switches and the many older PSAP systems. ...