TCP three handshakes and four waves (2022.4.18-4.24)

The popular understanding of three handshakes is as follows : The client sends a connection request to the server ( for the first time ), The server receives the information from the client and sends it to the client with verification ( The second time ), The client receives and confirms the verification and sends it to the server ( third time )
Connection request succeeded ;

The text of professional three handshakes is analyzed as follows :
for the first time :
The client initiates... From the server SYN Connect the application and bring your serial port number ( Such as Seq=x), Probably transmitting SYN=1,Seq=x;
The second time :
The server receives the client connection application , send out SYN+ACK( confirm ), The information transmitted to the client is SYN=1,Seq=y( The serial number of the server itself ),ACK=1,ack=x+1;
third time :
The client receives the information from the server and returns it to the client ACK, What is passed to the server is ACK=1,Seq=x+1,ack=y+1; Establishing a connection ;

Four waves are commonly understood as follows : The client completes the task and sends a disconnection request to the server ( for the first time ), The server receives the application but is not ready, and sends a message to the client at this time to make the client wait ( The second time ), Server side
Is fully ready to send a message to the client agreeing to disconnect the application ( third time ), The client disconnects after receiving the disconnection verification request from the server ( The fourth time );

The text of four professional waves is analyzed as follows :
for the first time :
The client sends a disconnection request to the server FIN And bring your serial number ( Such as Seq=u), Probably transmitting FIN=1,Seq=u;
The second time :
The server receives the disconnection application from the client , However, the data may not be completely processed at this time , So let's start with a ACK Confirm that it is sent to the guest server to make it in the state of waiting to be closed , The data transmitted is about :ACK=1,
Seq=v( At this time, the port number in the server state ),ack=u+1;
third time :
The data processing of the server is completed , Formally send to client FIN+ACK notice , There are about FIN=1,ACK=1,Seq=w( At this time, the port number in the server state ),ack=u+1:
The fourth time :
After receiving the message from the server, the client sends it to the server ACK notice , disconnect ; To the server are :ACK=1,Seq=u+1,ack=w+1;