How does 911 Work
When a call goes out from your phone, your voice isn't the only thing being
transmitted in the network. The phone company switch that serves your phone is
also sending out an Automatic Number Identification (ANI) signal to the
Originally, ANI signaling was designed to assist the phone company in accessing
toll charges for long distance calls. With advances in technology, it was eventually
employed to aid in relaying needed information to the PSAP for 911 response.
How does it work? Within each call, information containing eight digits is
embedded in the signal. These eight digits contain the seven digits of the caller's
local number. The eighth digit is called a Numbering Plan Digit (NPD). NPD is
basically shorthand for the area code of the originating call. Since most 911
tandems rarely dealt with more than two or three area codes, this was an
economical way to relay information with one digit instead of three.
With special equipment, the 911 tandem can read the ANI information and route
the callback number to a digital display at the appropriate PSAP. Armed with this
ANI information, the PSAP has equipment allowing it to request and receive the
caller's physical address or Automatic Location Information (ALI).
With this enhancement, the PSAP is no longer totally dependent on obtaining
location and callback information from the caller. Instead, the dispatcher can
concentrate on helping the caller through the crisis, while instantly passing along
needed information to the correct authorities.
This is how E911 has been working for more than 20 years when dialed from a
wireline phone. With the advent of wireless phones and the need for wireless
911, additional challenges present themselves.
i would also like to add that when you pick your phone up and dile 911 it starts recording instanly this means your being recorded be4 the operaitor
even gets on the line ..if you research a little bit and listen to 911 calls you will see this
[edit on 9-5-2010 by Nephi1337] here is my proof that they are recorded be4 the operaitor gets on the line
[edit on 9-5-2010 by Nephi1337]