“The TCP handshake works like this, with A being the client that is connecting to B:
A: Hi B, I’m A, send number 5.
B: Hi A, I’m B, 5, send number 3.
A: Hi B, I’m A, 3, send number 6. I’d like example.net.
B: Hi A, I’m B, 6, send number 4. Here comes the data: …
After this, A can send data to B and B can send data to A. For each byte of data they send to each other, their numbers increase. This is to keep track of whether all data has been received by the other party, to ensure reliable transmission…”