When someone calls me on my cell phone how does the phone system know where I am (which cell phone tower I am closest to?)
Is there some kind of database that keeps track of where everyone is? That seems like it would not work because of all the changes with people driving around.
Also if I go to Europe or outside the US that would make matters even more complicated. I assume it would take longer for a call to reach me outside the US.
I am not a cell phone engineer…oh…wait…never mind.
I’m more on the digital side than the signalling side of cell phones…(surprise!)…but…
There’s a mapping of all available cell towers. Your phone is talking to one of them. It maintains a periodic connection, so it can receive pages in case you get an incoming call or text message.
The network has an idea of how close your phone is to the other towers based on signal strength. As the signal strength changes on the tower you are camped on and the ones nearby, the network will instruct your phone to start talking to a different tower.
The process repeats as you move.
If you turn your phone off, and turn it on in a new area, it goes through a scanning sequence to identify a usable tower. Then the process starts again.
The delay in a call if you are overseas would come mostly from transferring the data to your location, not from identifying where you are.
Technically, I’m not an engineer anyway…just a simple computer science guy who happens to work in an engineering field…
-D/a
I work for a regional cell phone provider that uses CDMA technology (think Verizon or Sprint–I do not work for either of those companies). This information may differ from companies that use GSM technology (think AT&T or T-Mobile).
A cell phone uses three different identifiers to help it do it’s job–MDN, MIN, and MSID. The MDN is your cell phone number. The MIN is the network identifier that may or may not be the same as your cell number. The MSID is the system identifier that is unique to your service provider and geographic area.
Your cell phone will search for the closest tower that matches the MSID it is programmed with. My provider’s MSID is 4112, so my phone will search for a tower that has that identifier. Once it finds that tower it will broadcast it’s MDN, telling the tower that that particular number is in it’s service area.
The tower in turn transmits that information to the MTSO, or Mobile Telephone Switching Office. The MTSO is the “brains” of the whole system. When a call for your number comes to the MTSO it directs that call to the tower that last reported your number. The tower then delivers the call to your phone.
This is a basic overview of how the system works. If you want more detail let me know and I can expand on this information. Please keep in mind that I am not an engineer or have any formal training in this field. This is info that I learned from others while on the job.