Why not two or four TCP handshakes

Three times is the minimum number of times to verify that both the client and the server can send and receive data . If there is no third time , The server cannot confirm whether it can send data normally , Only after receiving the third handshake from the client ACK Message can be confirmed .

The third handshake client sends the third handshake ACK After the message , The client thinks the connection has been established , Will maintain the connection on the client , It takes time and space for the operating system to manage these connections . If it's four handshakes , The first thing to think about is the server , The server consumes space and time to maintain these connections , There may be many clients shaking hands with the server , It is not appropriate that all the costs of maintaining these connections are grafted onto the server . The cost of maintaining this connection with three handshakes is borne by the client , It is more reasonable .