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In the late 90’s some
states started to require that E911 functionality be provided for
when installing PBX telephone systems2. Regulations and requirements very by state.
In Washington State, PBX phone systems are required to be
E911 compatible in certain circumstances when installed in schools,
or when installed in multi-tenant office buildings.3 This enables an emergency services operator
to know not only the address of a caller, but also the building
(if there are multiple buildings), floor and suite or room number
from which a call originated. This
information enables faster response to emergencies and helps to
eliminate confusion about a caller’s exact location. The Asterisk® Open Source PBX provides a cost effective way
of achieving E911 compatibility when used in conjunction with a
telephone carrier that offers E911 database management services
to its customers. This
database management service consists of a reverse directory maintained
by the customer, but residing with the carrier, that associates location
information to private (DID) telephone numbers
that the customer uses. In order for E911 to function on an Asterisk PBX, each extension phone must be assigned a 10-digit DID number. This DID number is then registered with the telephone carrier (or contracted ALI database service provider) along with the location of the phone. An ISDN PRI link connects the Asterisk PBX to the carrier. This digital link utilizes a dedicated signaling channel (D-Channel) to handle call setup and signaling. It is the D-Channel that enables E911 functionality through the carrier. When a 911 call is placed on the PBX, Asterisk needs to be programmed to set the outbound CallerID (ANI) for the call to the registered DID for the calling extension. When the call reaches the Public Safety Answering Point (PSAP) this ANI number is matched with the DID number and location information which was pre-registered with the carrier (or contracted ALI database service provider). The exact location of the caller is then displayed to the emergency services operator. The same method may
also be used with Asterisk to provide E911 service when subscribing
to services from an E911 enabled VoIP Internet Telephony
Service Provider (ITSP). Asterisk offers a cost effective way to implement E911 services, increasing safety and security within an organization. Even organizations that are not legally required to implement E911 can greatly benefit from its implementation. About
the Asterisk® Open Source PBX
Asterisk is a complete PBX in software. It runs on Linux and provides all of the features you would expect from a PBX and more. Asterisk does voice-over-IP (VoIP) in multiple protocols, and can interoperate with almost all standards-based telephony equipment using relatively inexpensive hardware. For more about Asterisk click here. About VoiceIP SolutionsVoiceIP Solutions is
a telephone systems integrator specializing in Asterisk Open Source
PBX telephone systems. We
are a full service IT communications provider serving Washington
State and internationally through a network of IT consultants and
service providers. To see how VoiceIP Solutions may be able to help
your organization, please see our website at http://www.voiceipsolutions.com/.
Asterisk® is a trademark of Digium, Inc. |
Enhanced
911 service or E911, is a North American telephone network
feature that automatically associates the physical address of a
caller with the calling party's telephone number. This is generally
done using a form of reverse telephone directory that is supplied by
the telephone company. This provides emergency responders with the
location of the emergency without the person calling for help having
to provide it.
