TCP Three-way Handshake
Before transmitting data using TCP, three packets are sent to synchronize data communications between the two hosts.
The two hosts synchronize their initial sequence numbers (ISN). These sequence numbers ensure that the communications are assembled in the proper order and that no missing packets exist.
When a synchronization is sent, it is abbreviated SYN. When an acknowledgement is sent, the abbreviation is ACK.
The three-way handshake actually has four steps:
- Host 1 sends SYN packet to Host 2. (first data packet)
- Host 2 ACK packet from Host 1. (second data packet)
- Host 2 includes its SYN data for Host 1. (second data packet)
- Host 1 ACK packet from Host 2. (third data packet)