2.22 Handshake Protocol

To set up a TCP connection between two hosts, the three-way handshake has to be performed. The name of the procedure stems from the fact that three messages SYN (for synchronization), SYN, and ACK (acknowledgement) have to be exchanged to start the connection. The three-way handshake relies on the fact that in TCP connections all the segments have to be acknowledged to provide a reliable link.

Animation 2.22-1shows the steps of the three-way handshake.

When the handshake is completed, both sides can start sending data. The two processes continually acknowledge the receipt of data.