Omfraax

Telecommunication engineer here, specialized in 4G and 5G cellular network.

When several users share the same cell (a cell range typically from 100m to 10kms, depending on population density), they are allocated a specific part of the spectrum and specific time slot by the cell so that they don't interfere. This is done in a very dynamic way : Basically, every millisecond (or even more frequently for 5G), the cell will advertise the phones when and where they should receive/transmit data for the next millisecond. The phones on their side periodically report how much data they need to send and their radio signal level quality to help the cell make the best decision. They can also measure other cells so the network can see the phones moving and change their serving cell.

Now for the 'across the planet' stuff, it's usually no longer through wireless signal but with good ol' optic fibers that the packets are transferred across the core network from the cell to the internet

You can PM or answer this comment if you need more details :)

Imagine a room (the cell) full of people (the phones) with a guy (the base station) in a elevated chair holding a gavel.

The gavel will give you the tempo of the time (in our real world, it's our millisecond)

In front of him you have hundreds of booths with a clerk, currently empty, representing parts of the spectrum.

The guy strikes the gavel : A new time slot begins.

The guy then shouts for everyone to hear a list of names associated with a booth number. That's the control channel.

Immediately after, you see the people who were named go into their booth and listening to a clerk giving them their data. It takes much longer and the clerks in each booth is speaking very fast because you have a lot of data to get. That's your downlink data.

The clerks speaks until the next gavel strike, and then you should leave the booth and listen to the main guy gain.

It's ok for the people to record the clerk and take some time to digest what they listened to. You have four gavel strikes (four time slot) to know if you understood correctly and to notify the guy in the chair by raising your hands. Yes, the guy in the chair knows that and will carefully look for raised hands. If he doesn't see yours when it's your turn, it will redirect the clerk to repeat the same message (or the part of the message that you didn't understand) the next time it schedules you. That's what we called 'HARQ feedback'.

Some other times, it's your turn to talk to the clerk in the booth to send your uplink data (the guy gives you this information when shouting your name like 'John, booth 42, uplink' or 'Jane, booth 15, downlink')

At other times you can also raise your hand with your fingers out to tell the guy how you hear the clerks 0/5 'I can't hear a damn thing' to 5/5 'It's perfectly clear, the clerk can definitely speak faster'. It has been arranged when you entered the room when you should raise your hand for this since the guy in a chair cannot look at everyone in a time slot.

You can also raise your hand when you have something to send in Uplink. It has also been arranged beforehand when you can do that. This is called a Scheduling Request.

By the way, what happens when you enter the room for the first time? The guy doesn't know your name so it cannot give you any data, right ?

Well, actually at the entrance of the room you have a sign that tells you (and tells everyone in fact) that once every 100 gavel strikes, new arrivant can raise their hands. It also gives you other 'rules of the room', like to which network the room belong, etc. This is called 'System Information Boradcast'.

Of course the guy made sure that no-one should raise their hand at this moment. When that happens, the guy looks for raised hands and is able to tell that new arrivants are coming and it will give you a booth where the clerk will give you some information specific for you, like when you can raise your hands to notify the signal quality or your uplink data, or how long lasts the 'control channel' phase, etc. Actually a ton of parameters can be exchenged during this phase.

The clerk will also ask for your name so that the guy can call you when needed. The guy will probably need to speak with his manager (the core network) to check if you have paid your fee to talk in this room (your network subscription).

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Well that' the basics ... hope it isn't too long and still ELI5, but I think it's a really good analogy

Yes exactly, they do.

Concerning this specific issue, you have in 5G the possibility to perform integrity protection on the data plane.

On other main security improvement is the concealment of the IMSI, preventing the use of 'IMSI catcher' impersonating a fake network.