As Enhanced 911 or E911 a legally mandates in the United States by the E911 prescribed service is called, which requires fully automatic transmission of geographic location information of the caller when placing an emergency call.
Basically, one uses here an inverse number search, so that on the basis of number identifier necessarily provided by the network operator the stored number for each address is transmitted. The emergency call receiving it shall rescue coordination center is therefore not dependent on the oral transmission of the site by the often frantic caller or injured.
Enhanced 911 is available in most metropolitan areas of the U.S. and Canada. In some places (for example, Minneapolis / St. Paul ), it is since the early 1980s in use.
In North America, the system uses only if the emergency number 911 is selected. Calls to other numbers, even if they are designated as an emergency number ( engl. emergency telephone number) will not be localized.
Outside the U.S. it's called process caller location ( to German caller location ), with the implementation of the structure and the switching manner of emergency calls varies locally.
Public Safety Answering Point ( PSAP )
Goal of E911 emergency call is a Public Safety Answering Point ( PSAP, dt mutatis mutandis control center ). A local exchange can be used by several PSAPs. Likewise, several exchanges can be assigned to a PSAP. The catchment area of a PSAP depends more on historical, administrative and organizational factors, as technical requirements. Most PSAPs are equipped with a so-called ESN, an individual identification number.
The location information of the caller to the dispatcher in the emergency dispatch usually shown through computer systems on a map. Similarly, the nearest emergency personnel are visualized on that map. In wired emergency calls the stored address from the network operator is displayed in wireless remote emergency calls (eg mobile phones ) geographical coordinates are transmitted. Not all PSAPs have the full functionality of the system.
Enhanced 911 for wired telephony
Based on the E911 mandates U.S. network operators are obliged to forward a caller to the control centers. Based on the caller ID every emergency call an address as well as the ESN is assigned to the relevant control center. This mapping is accomplished using a database function called ALI (Automatic Line Identification). Basically, the entertainment of the ALI database backup to an ILEC with ( Incumbent Local Exchange Carrier ) designated private operator is delegated. Since no specifications are standardized for the ALI database, there are different standards for the ILECs. Is completed, the ALI database in many places by a MSAG database (Master Street Address Guide), containing the street names, address ranges, and other relevant address elements. Operators of local exchanges are connected via at least two DS0 -level state lines to a PSAP or emergency special switching equipment, which are also known as E911 router, since they are connected to the PSAPs via ISUP lines by means of SS7 protocol. This solution is becoming increasingly widespread, as it facilitates the connection between ISUP/SS7 based exchanges to the many proprietary PSAPs.
Analog tailed PSAPs usually use CAMA connections. These are similar to conventional POTS connections, but are at the ability of the transmission of the ANI of a particular caller, extended.
PSAPs that use an older digital connections that use specialized MF connections which transmit the ANI in the wink-start during call setup.
Modernized PSAPs are connected where ISUP/SS7-Leitungen. Here, the ANI is already transmitted in the SS7 setup message.
Data from the ALI database is not transferred over the telephone lines but separate infrastructure.
As ALI failure is referred to the case in which ANI is not sent or the ALI database does not have a corresponding entry has. If necessary, the emergency call is then routed to a PSAP, the ESN has been deposited for each network area. Then the dispatcher in the PSAP must consult the Notrufer according to its location it may show to another PSAP, which is responsible, by site. The network operator shall then any errors in the ALI database to rectify immediately.
The (often competing) local operator ( Competitive local exchange carriers, short CLEC ) interconnection to act ALI database with the local ILEC and complete the ALI database based on the MSAG.