During **handshaking**, two hosts agree on protocols to be followed during their communication prior to the communication itself. In TCP, **a three-way handshake** takes place during connection establishment.

# Steps

The steps below are the steps involved in the connection establishment:

1. The client (a process that initiates the communication) sends a segment. The segment contains a randomly generated sequence number, and the SYN flag is set.

2. Upon receiving the segment, the server replies with a segment that has the server's sequence number, its window size, an acknowledgment, and the SYN flag set.

3. The client sends its sequence number, its window size, and an acknowledgment.

> The acknowledgment is always equal to the received segment's sequence number plus one.

The illustration below visually represents the steps above:

What is a three-way handshake in TCP?

Steps