How 9-1-1 Works

Basic 9-1-1 Systems

As of 2006, approximately 7 percent of 9-1-1 service is still basic 9-1-1. Here's what this type of call looks like:

  1. You dial 9-1-1.
  2. Your phone company recognizes the number and routes the call to a dedicated 9-1-1 switch that sends the call to the designated PSAP for your area.
  3. The PSAP call-taker (also called an operator or dispatcher) asks what the emergency is, what the location is and for a call-back phone number. The call-taker does not have your number or location information on the screen. He or she actually needs you to provide it. (The PSAP can trace the call and get the information, but that takes longer than you'd think -- in the area of 10 minutes, in some cases -- because it's not built into the basic 9-1-1 system.)
  4. Depending on the emergency, the call-taker uses radio dispatch to alert police, fire and/or EMS to go to the scene.

­In most basic 9-1-1 systems, you're looking at several pieces of equipment (besides the PSTN) t­hat play a crucial role in the process. Some common 9-1-1 equipment includes:

  • Computer-controlled Radio Interface To more quickly dispatch emergency personnel, a PSAP might use a computer-controlled radio system to automatically activate electronic pagers.
  • Computer-aided Dispatch (CAD) A computer mapping program automatically provides directions to the caller's location and identifies any particular hazards or special information the responders might need to know (like road-work detours, flooded streets, that the caller is handicapped, etc.).
  • Recording Equipment PSAPs record everything, including phone calls and all radio communications into and out of the center. In most cases, the recorded data is stored for a minimum of 30 days in the event that police, prosecutors, PSAP managers or call-takers need to review the information. The CAD system can also serve as a full recording setup.
  • Back-up Power PSAPs have back-up generators and uninterruptible power supplies (UPS) in case of a power surges or outages. In most cases, PSAPs can stay online and operational even if the surrounding area has no power.

Next, we'll take a look at how E911 is different.