OSI model

This one is not generally seen by software, which mostly operates starting from OSI layer 2.

A good project to see UARTs at work in all their beauty is to connect two Raspberry Pis via UART, and then:

Part of the beauty of this is that you can just connect both boards directly manually with a few wire-to-wire connections with simple jump wire. Its simplicity is just quite refreshing. Sure, you could do something like that for any physical layer link presumably...

Remember that you can only have one GNU screen connected at a time or else they will mess each other up: unix.stackexchange.com/questions/93892/why-is-screen-is-terminating-without-root/367549#367549

On Ubuntu 22.04 you can screen without sudo by adding yourself to the dialout group with:

The frequency range of Wi-Fi, which falls in the microwave range, is likely chosen to allow faster data transfer than say, FM broadcasting, while still being relatively transparent to walls (though not as much).

This can be seen with Wireshark very clearly for example, just make a ping and disssemble it.

There is no userland process for it, it is handled directly by the Linux kernel: unix.stackexchange.com/questions/439801/what-linux-process-is-responsible-for-responding-to-pings/768739#768739