How 911 works?

Answer 1

NENA, the National Emergency Number Association estimates that approximately 240 Million calls to 9-1-1 are made to each year in the US.

How does my call get to the Public Safety Answer Point or PSAP?

How do I send the location information for a particular caller to the PSAP?

How a 911 call gets to the PSAPLet's break a 9-1-1 call into smaller pieces to understand the actual call flow Behind the Scenes.

• Someone dials 9-1-1 on their telephone.
• The call is sent out over telephone lines to the Local Exchange Carrier or LEC.
• When the LEC receives the call, it translates on the dialled digits of 9-1-1 and immediately passes this call to a specialized component in the network Called a 9-1-1 Tandem or Selective Router.
• The Selective Router is a specialized Central Office switch usually dedicated to handle 9-1-1 traffic. When a call arrives, the Caller ID of the caller is examined and matched against a special database called the Master Street Address Guide or MSAG. Based on this database lookup, the PSAP responsible for servicing this number is returned based on the provisioned street address and number.
• The Selective Router then sends this call to the appropriate PSAP down specialized E911 trunks for further handling where they receive both the original caller ID as well as the voice of the caller.

What the 911 call taker seesThe PSAP then uses specialized equipment to extract the caller ID from the call and performs another database query to the Automatic Number Identification database usually maintained by the LEC. The LEC then returns the result of the lookup with the matching Automatic Location Identification or ALI record information that is in turned displayed on the call takers terminal screen. Along with the location information, additional information is provided to the call taker that will assist in dispatching the call.

Additional information such as the responsible Police, Fire and EMS agencies are noted where a PSAP services multiple communities, and in the case of Cellular callers specific X Y coordinates are returned representing the location of the caller.