How do you create your protocol?

Question

Computer networks

Here is, for example, mail.ru agent. They have their own data transfer protocol. How do they create it, what are they attached to? After all, the data goes on the same wire. Accordingly, according to the general, lower in the chain, TCP / UDP protocol. It turns out here the case is of the type - "Protocol on the protocol"?
And can you call data encryption with your own algorithm (and decryption at the reception) your protocol? Though they will be transferred through the same HTTP.

Answer 1

lower down the chain, TCP/UDP protocol.

Exactly. We read about the OSI model.
If, within the framework of your protocol, you also describe how the key exchange takes place, etc. then yes.

Answer 2

You have a direct road here - https://en.wikipedia.org/wiki/%D0%A1%D0%B5%D1%82%D...