TCP Three handshakes of

First, let's understand the meaning of the field
SYN=1 The value of indicates that you want to connect
ACK=1 Acknowledgement field ack It works
seq： The sequence number of the packet sent
ack=seq+1： Indicates that the sent data is received , And he wants to send the next packet


The following is my practical example （ The bag grabbing tool is Kelai , The server is QQ）：
After opening the package capturing software, start QQ



You can see local and QQ Three handshakes established between

First step （ I sent it to QQ The data of ）
SYN=1（ I hope to work with you QQ Establishing a connection ）
seq=2605745043 （ I am right. QQ say ： The sequence of packets sent by me is 2605745043 ）
ACK=0（ No confirmation field ）
ack=0 （ Because it is the initiator of establishing the connection, it is 0）



The second step （QQ The data sent to me ）
SYN=1（QQ Hope to establish a connection with me ）
seq=1104303432（QQ Said to me, ：QQ The sequence of packets sent is 1104303432）
ACK=1（ There is a confirmation field, so the value is 1）
ack=seq（ My client ）+1=2605745044（QQ say ： I received the packet sequence sent by your client , And I want you to send the next packet sequence ）



The third step （ I sent it to QQ The data of ）
seq=2605745044（ In Article 2 QQ I hope the order of the packets I send is 2605745044, So I'll send it this time ）
ACK=1（ There is a confirmation field, so the value is 1）
ack=seq（QQ Of ）+1=1104303433（ I received your packet in the order of 1104303432 Your packet , And I hope to receive the next packet ）



Step 4 start communication