How Does 9-1-1 Work? – Introduction
Scott Pantall | December 22, 2009
Since I have a month off between semesters at school, I’ve volunteered to help my co-workers understand the information we receive on our maps when a 9-1-1 call is made. But then I thought, why not help everyone understand what happens when you call 9-1-1?
What is 9-1-1 and how did it start?
I don’t really feel like I’m giving good educational value unless I throw some in some history. In 1957, the National Association of Fire Chiefs recommended use of a single number for reporting fires. Then in …..zzzzzzzzzzzzzzzzz… If you want to know the history of 9-1-1, go here1. I’m not going bore you with a history lesson if you don’t want it.
What are the different ways dispatchers received 9-1-1 calls?
The information automatically received by the dispatcher depends on what kind of phone is used to call in…
- Land Line: This is a phone that’s plugged into a wall that’s plugged into the phone system.
- Phase 1 Cell Phone: A cell phone that provides the dispatcher with the telephone number and carrier of the originator of a wireless 911 call and the location of the cell site or base station transmitting the call2.
- Phase 2 Cell Phone: A cell phone that provides all the information that a Phase 1 cell phone provides plus a more precise location specifically, the latitude and longitude of the caller. This information is accurate to within 50 to 300 meters2.
- VOIP: Stands for Voice-Over-Internet-Protocol. This is a fancy way of saying “Using your computer as a phone and the internet as the phone system.”
If you’re still a little confused, don’t worry. We’re going to go over this stuff in much more detail in later posts.
Glossary
I’m including a glossary in the introduction post because becoming familiar with the terms now will help you read the following posts. I am going to try really hard to make this as non-technical as possible, but I’m willing to face the idea that I may fail spectacularly at that.
- MSAG - Master Street Address Guide: Are you a conspiracy theorist who believes there’s a company based in Longmont, Colorado that has a giant database that links almost every land line telephone number to a subscriber, an address and a detailed description of the location of that address? If so, congratulations! You’re right! The MSAG database is how dispatchers know where you’re calling from when you call from a land line.
- PSAP – Public Safety Answering Point: This is the catch-all term for the place where 911 dispatchers receive your call. A PSAP can either belong to a city, county or state-wide entity. There are also regional PSAPs that dispatch for multiple agencies. The important thing to remember is that these are where your 911 call goes.
- Trilateration – Finding the distance between 3 different points to figure out your own location. GPS devices use satellites as their points. Network based phones use cell phone towers as their points. For a visual example, check out this site3.
Up Next: What happens when I call 9-1-1 from a land-line?
Resources
- http://www.nena.org/911-overview-facts
- http://www.fcc.gov/cgb/consumerfacts/wireless911srvc.html
- http://electronics.howstuffworks.com/gadgets/travel/gps1.htm
