CHAPTER 1.0 - Overview

1.7 E911 Call Flow

The following steps are involved in the E911 emergency call process.

STEP ACTION

1 The county resident requires emergency aid and dials 911.
2 The digits are received in the central office serving the exchange from which the user is dialing.
3 The central office sends the ANI (Automatic Number Identification) to the 911 tandem office.
4 The tandem office finds the associated ESN for the calling telephone number via the TN/ESN table.
5 Based on the ESN, the call is switched, via a dedicated trunk, to the appropriate PSAP.
6 The calling number is displayed (ANI) at the PSAP.
7 The ANI information is sent to the primary and secondary ALI processors for retrieval.
8 The primary or secondary ALI (Automatic Location Information) computer retrieves the ALI data from the database.
9 The ALI computer returns the ALI to the PSAP.
10 The data is received at the PSAP and the information is displayed.
11 The PSAP attendant verifies the telephone number and the street address that has appeared on the screen and obtains information as to which emergency service is needed. The attendant then depresses the button corresponding to the agency requested, e.g., fire or ambulance (one button transfer feature) the call is automatically transferred.
12 The details for each call (calling number, answering attendant's number, time of answer, time of transfer and / or disconnect and the trunk number) are printed after disconnect on a printer at the PSAP.
13 The agency receives the call and a display of the caller's telephone number, name and street address (optional equipment). The PSAP attendant may remain on the line as long as necessary.
14 The agency then dispatches an emergency unit to the caller's address.

STEP	ACTION
1	The county resident requires emergency aid and dials 911.
2	The digits are received in the central office serving the exchange from which the user is dialing.
3	The central office sends the ANI (Automatic Number Identification) to the 911 tandem office.
4	The tandem office finds the associated ESN for the calling telephone number via the TN/ESN table.
5	Based on the ESN, the call is switched, via a dedicated trunk, to the appropriate PSAP.
6	The calling number is displayed (ANI) at the PSAP.
7	The ANI information is sent to the primary and secondary ALI processors for retrieval.
8	The primary or secondary ALI (Automatic Location Information) computer retrieves the ALI data from the database.
9	The ALI computer returns the ALI to the PSAP.
10	The data is received at the PSAP and the information is displayed.
11	The PSAP attendant verifies the telephone number and the street address that has appeared on the screen and obtains information as to which emergency service is needed. The attendant then depresses the button corresponding to the agency requested, e.g., fire or ambulance (one button transfer feature) the call is automatically transferred.
12	The details for each call (calling number, answering attendant's number, time of answer, time of transfer and / or disconnect and the trunk number) are printed after disconnect on a printer at the PSAP.
13	The agency receives the call and a display of the caller's telephone number, name and street address (optional equipment). The PSAP attendant may remain on the line as long as necessary.
14	The agency then dispatches an emergency unit to the caller's address.