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 Line 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 stre ...
Initial implementations of Voice over IP telephone systems were not integreated with the 911 system at all, meaning that customers could not even dial 911 in the event of an emergency. However, the Federal Communications Commission has mandated all VoIP providers to provide 911 service, including the E911 feature.
On June 3, 2005, the FCC adopted rules requiring providers of VoIP services that connect with the traditional telephone network to supply E911 capabilities to their customers. The E911 hookup may be directly with the Wirelin ...
A second phase of Enhanced 911 service is to allow a wireless or mobile telephone to be located geographically using some form of radiolocation from the cellular network, or by using a Global Positioning System built into the phone itself.
Radiolocation in cellular telephony uses base stations. Most often, this is done through triangulation between radio towers. The location of the caller or handset can be determined several ways:
angle of arrival (AOA) requires at least two towers, locating the caller at th ...
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, ...
