Glossary of E911 Terms

Here's a quick-reference guide to help you understand the most frequently used E911 terms.

Automatic Location Identification (ALI)
Working with ANI, the use of a database to associate a physical location with a telephone number.

Automatic Number Identification (ANI)
The 10-digit telephone number that is used to retrieve ALI information from a database at the PSAP.

Dynamic ALI (D-ALI)
The 10-digit telephone number that is used to route and retrieve ALI information from a database to be viewed at the PSAP Emergency Services Gateway (ESGW) Sends an incoming 9-1-1 call to the appropriate Selective Router and on to the appropriate PSAP.

Emergency Services Query Key (ESQK)
An optional add-on to E911 Manager which provides visual and audible notification of a 9-1-1 call in progress including the calling number and location to subscriber workstations

Emergency Services Routing Number (ESRN)
See ANI

Enhanced 911 (E911)
An advanced form of 9-1-1 services. The telephone number out-pulsed with a 9-1-1 call is cross-referenced with the local enhanced 9-1-1 database resulting in the address and exact location within the building being displayed to the PSAP.

Local Exchange Carrier (LEC)
Local telephone company also known as a Local Service Provider (LSP).

Master Street AddressGuide (MSAG)
An MSAG ledger is used by a municipality to assign a particular police, fire, or rescue agency to a given street and number range. The MSAG also specifies the particular location/address format that the jurisdiction maintaining the MSAG expects data to be displayed for locations under its emergency services jurisdiction.

Public Safety Answering Point (PSAP)
The institution that answers 9-1-1 calls and dispatches the appropriate emergency care providers.

Public Switched Telephone Network (PSTN)
The concentration of the world's public circuit-switched telephone networks, in much the same way that the Internet is the concentration of the world's public IP-based packet-switched networks. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital, and now includes mobile as well as fixed telephones.

Selective Router 
The node in the emergency services network that performs enhanced call routing for E911 calls. Usually operated by the LEC.

Voice over Internet Protocol (VoIP)
The routing of voice conversations over the Internet or any other IP-based network. The voice data flows over a general-purpose packet-switched network, instead of traditional dedicated, circuit-switched voice transmission lines.

VPC
VoIP Positioning Center.