Identification of one of a bunch of clients connected to one server

Question

Computer networks

There is a server. It has a server program that opens a specific port. Clients are connected to the program, which remain hanging - to keep the connection. Let's say there are a hundred of them, and each of them has a unique serial number, which is transmitted when connected or upon request, it doesn't matter. How can I contact a specific customer if I know their serial number?

Answer 1

Dictionary id->socket?
It's actually a very general question.