Both the client and the server need to know that they can send and receive, so a three-way handshake is required.
Simplify the three-way handshake
From the picture, we can see that the three-way handshake can be simplified as: C initiates the connection request, S confirms the connection, and C confirms the connection. Let’s look at the function of each handshake:
First handshake: S can only accept the packet segment sent by C
Second handshake: C can confirm that S has received the packet segment and can accept the packet segment sent by S
Third handshake: S can confirm that C has received the packet segment