How to determine which protocol is being used?

Question

Computer networks

How can I find out what network protocol is being used? For example, there is a stream of bytes, how to find out from these bytes that, for example, the TCP protocol is being transmitted? Is there a reserved sequence or something?

Answer 1

Refine the question. It is necessary to define the protocol at what level, physical, channel, network or transport?
Do we just have a wire from which data flows or do we still intercept IP packets with some kind of data?

Answer 2

and to mirror on the server and there to disassemble a sniffer in any way? in general, you can determine the protocol by bytes, and starting from l2, but knowing their abundance ...

Answer 3

Is the question practical or theoretical? If practical, what do you have (a laptop with a sniffer, some specific device connected to the network, or a .pcap file with a traffic dump), and what should be the output?