Calhoun County Consolidated

Dispatch Authority


Serving Our Community One Call at aTime


How Does My Call Get to 9-1-1?


When you call from a phone installed at a residence, business or a pay phone, the phone number of the phone determines which 9-1-1 center you reach. Each 9-1-1 center or Public Safety Answering Point (PSAP) has an enormous list of phone numbers that are designated to come to that center. All of these numbers have a special secondary number on file with the phone company that directs your call to the correct 9-1-1 center for your area.


If you call from a cell phone the procedure is slightly different. Cell phones transmit to the nearest cellular tower and from there to the closest 9-1-1 center. The 9-1-1 center is determined by the location of the cell tower. Sometimes if you are close to a county or state border, you might get the wrong 9-1-1 center. However, the employees there will direct your call to the correct center to get the help you need.


In some locations responses for various types of calls may come from more than one jurisdiction. In those cases you might speak to more than one dispatcher, as each 9-1-1 center involved gathers the information they need.


If you are hearing or speech impaired, Calhoun County Consolidated Dispatch Authority (CCCDA) is equipped with a Text Telephone (TTY) device to allow communication through your TTY device.


The idea behind 9-1-1 is pretty simple: Give people a single, easy-to-remember number to call to receive help during any life-threatening situation. There is no national 9-1-1 system. The answering points and corresponding dispatch services are set up and maintained locally, usually by county, often in a joint effort between local government and any phone companies active in the area. You pay for 9-1-1 with your local taxes and through a surcharge on your phone bill.


In order to be effective, any emergency system needs to do three basic things:


1. Recognize when someone dials the emergency number on any phone (even a pay phone when no coins have been supplied)


2. Route the call to the nearest answering point based on the call's originating location


3. Notify the appropriate agency as quickly as possible so it can respond to the emergency.


This is all that happens in basic 9-1-1 service. In enhanced 9-1-1 service, the answering point's equipment also automatically displays the caller's name and location, making step three above faster and more reliable. Enhanced 9-1-1 (E911) is not the same thing as wireless 9-1-1, but wireless 9-1-1 does require E911 improvements to be in place in order to work. The 9-1-1 system, which has always been based on the public switched telephone network (PSTN) that most of us use every day, has to adapt to constantly evolving technology, including the proliferation of cell phones, VoIP, and the introduction of safety measures like in-vehicle crash notification systems.




Basic 9-1-1 Systems

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.


Enhanced 9-1-1 Systems


Enhanced 9-1-1 is a very similar system, but it has some upgrades and modifications that make the whole process run more smoothly. There's more technology involved - in E911, there's a whole local "9-1-1 network" of collaborative databases that plays a role before the PSAP operator even picks up the call. For an E911 setup, add to the equipment list above:


Automatic Number Identification (ANI) The phone company knows every time you place a call from your phone number - it needs to know for billing purposes. This functionality is adapted to 9-1-1 purposes in E911: When you call 9-1-1 from your phone, the phone company recognizes the emergency number and uses the ANI system to pull up your phone number and send that data with your phone call to the 9-1-1 system.


Automatic Location Identification (ALI) The phone company has a subscriber database matching phone numbers to names and addresses. When your call arrives at the 9-1-1 network, the hub taps into this database to pull up the address that matches your phone number.


Master Street Address Guide (MSAG) The phone company and public safety agencies collaborate to create master maps that match phone numbers, addresses and cross streets to their corresponding PSAP. When you dial 9-1-1, the 9-1-1 network hub uses the MSAG to determine where to route your call.


1.  You dial 9-1-1.


2. The phone company computer recognizes the number, accesses the ANI to get your number and routes the call to the dedicated 9-1-1 switch that acts as a hub for the local network.


3. The network uses your number to get your address from the ALI and uses your address to determine the proper PSAP destination from the MSAG (this is sometimes called selective routing, because the switch uses dynamic data to determine where to send your call instead of blindly routing it to a pre-determined PSAP). In most cases, this all takes a little over one second.


4. Your phone call now carries your phone number and address along with your voice data to the nearest available PSAP. This information is displayed on the call-taker's computer when he or she takes your call.


5. Some PSAPs simultaneously send that ANI/ALI data to the police computer dispatch network to allow for immediate access.


6. If necessary, many PSAPs can transfer your call and your accompanying data to another PSAP.