Edit: More about how two towers figure out which cellphones need to be connected to each other
In: Technology
Your phone is constantly listening to different towers, keeping a list of the ones it can hear best. Each tower broadcasts its own identity code (each panel, in fact, has its own code). When you make a call, your phone reaches out to the the tower it hears the best and works its way down the list until one of them accepts the call (all depends who has room, towers *can* be “full” if a lot of people are on their phone at the same time).
Now for the other end. The network doesn’t know exactly *where* you are, but it has a general idea because the network is divided into Local Areas, and each area has its own Local Area Code (LAC). You phone knows what local area it is in; it’s part of the tower’s identity code. When it all of a sudden hears towers with one LAC better than towers with the LAC it had been hearing, it knows (even without GPS) that it has crossed into a new Local Area, so your phone reaches out to the network and sends a Local Area Update message. The network files that information away.
Back to your call. You dial your friend’s number, your phone reaches out to the towers it hears the best, and establishes a connection with the network. It then sends the number you’re trying to call. The network looks up which Local Area your friend’s phone last said it was in, and the entire Local Area, every single tower and panel, sends out a page over a separate channel that all phones are monitoring. The whole Local Area essentially yells, *”Marco!”* Your friend’s phone, which is always listening, reaches out to the tower it can hear the best and says, “*Polo!*” Your friend’s phone establishes a connection with the network through that tower, and now your call is routed to them through the network.
It’s a good deal more complicated than that (and some of my information may be out of date, I haven’t studied this in about 10 years), but that’s the ELI5 version.
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