Filter
Top Products
CG-EWCG-001 Wireless E911 Guide
Issue 3, January 6, 2004 Overview of E911
1. Overview of E911
1.1 Definition of E911
"911" has been designated in the United States as the number to be used by the public to summon
emergency aid or to report a crime, fire or accident. Its main purpose is to make it easier for people in time
of emotional stress to contact the proper emergency agency. An important advantage of 911 emergency
service is improved (reduced) response time.
The original 911 service, known as Basic 911 (B911), routes a call to one centralized answering location.
The attendant at the answering location obtains the pertinent information that identifies the call and the
caller’s need. The attendant then determines the appropriate agency and dials the number to transfer
the caller to that agency.
Enhanced 911 service, or E911, is a full featured electronic system that provides three (3) major
enhancements to Basic 911 service:
1.1.1 Selective Routing
Electronically routes 911 emergency calls to the proper Public Safety Answering Point (PSAP) based
on the Emergency Service Number (ESN) code that has been assigned to the cell site address or the
longitude/latitude of the caller’s location. This may be accomplished by assigning "pseudo-ANI"
telephone numbers to each face of each antenna in order to designate a fixed location for the serving
area. Some wireless solutions allow the assignment of a pseudo-ANI telephone number to a specific
PSAP rather than an antenna face. An ESN is assigned to the "pseudo-ANI" telephone numbers during
database record processing and is assigned from the Master Street Address Guide (MSAG) based on
the address. Some solutions may dynamically assign the ESN based upon the longitude/latitude of the
caller’s location. Wireless Carriers must work with the local governmental agencies and agree on call
routing, ESN assignments, and MSAG valid addresses. This process is described later in this document.
Wireless Carriers should identify selective routing capabilities for premises based ALI systems and make
arrangements to deliver wireless calls directly to the PSAP in those cases where selective routing is not
utilized. See Premises Based ALI Systems below.
1.1.2 Automatic Number Identification (ANI)
Provides the PSAP with the 7-digit pseudo-ANI telephone number representing the antenna face which
received the wireless 9-1-1 call or the pseudo-ANI PSAP routing number, depending on the wireless
solution implemented. Interfaces utilizing Feature Group D signaling between the E911 selective routing
tandem and the PSAP may be capable of sending 10-digit ANI or 10-digit ANI and 10-digit call back
number to the PSAP. Pseudo-ANI numbers must be assigned from the wireless carrier’s number range and
must be geographically valid for the E911 selective routing tandem service area.
1.1.3 Automatic Location Identification (ALI)
Provides the PSAP with cell site location information associated with the pseudo-ANI. Phase 1 compliance
also requires ALI to contain the wireless subscribers call back number. This may be accomplished by the
Page 1