A connection progresses through a series of states during its lifetime.
The states are: LISTEN, SYN-SENT, SYNRECEIVED, ESTABLISHED, FIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, TIME-WAIT, and the fictional state CLOSED. CLOSED is fictional because it represents the state when there is no TCB, and therefore, no connection. Briefly the meanings of the states are:
LISTEN represents waiting for a connection request from any remote TCP and port. 表示等待来自任何远程TCP和端口的连接请求。是TCP三次握手之前的状态。
SYN-SENT represents waiting for a matching connection request after having sent a connection request.表示发送连接请求后等待匹配的连接请求。是TCP三次握手中的第一次请求发送后的状态
SYN-RECEIVED represents waiting for a confirming connection request acknowledgment after having both received and sent a connection request.表示在接收到并发送了连接请求之后等待确认连接请求确认。是TCP三次握手中的第二次请求发送后的状态
ESTABLISHED represents an open connection, data received can be delivered to the user. The normal state for the data transfer phase of the connection.代表开放连接，接收到的数据可以传递给用户。 连接的数据传输阶段的正常状态。是TCP三次握手中的第三次请求发送后的状态。是一个重要分水岭的状态
FIN-WAIT-1 represents waiting for a connection termination request from the remote TCP, or an acknowledgment of the connection termination request previously sent.表示等待来自远程TCP的连接终止请求，或者等待先前发送的连接终止请求的确认。是TCP四次挥手中的第一次请求发送后的状态
FIN-WAIT-2 represents waiting for a connection termination request from the remote TCP.表示等待来自远程TCP的连接终止请求。是TCP四次挥手中的第二次请求发送后的状态
CLOSE-WAIT represents waiting for a connection termination request from the local user.表示等待本地用户的连接终止请求。是TCP四次挥手中的第四次请求发送后的状态
CLOSING represents waiting for a connection termination request acknowledgment from the remote TCP.表示等待来自远程TCP的连接终止请求确认。
是TCP四次挥手中的第三次请求发送后的状态
LAST-ACK represents waiting for an acknowledgment of the connection termination request previously sent to the remote TCP (which includes an acknowledgment of its connection termination request).表示等待先前发送给远程TCP的连接终止请求的确认（包括对它的连接终止请求的确认）。
TIME-WAIT represents waiting for enough time to pass to be sure the remote TCP received the acknowledgment of its connection termination request.表示等待足够的时间以确保远程TCP收到其连接终止请求的确认。
CLOSED represents no connection state at all.表示完全没有连接状态。
A TCP connection progresses from one state to another in response to events. The events are the user calls, OPEN, SEND, RECEIVE, CLOSE, ABORT, and STATUS; the incoming segments, particularly those containing the SYN, ACK, RST and FIN flags; and timeouts.
Analyse the network trace, the info show us the SYN, Seq AND ACK clearly as below:
Reference Link:
TCPIP_State_Transition_Diagram: https://users.cs.northwestern.edu/~agupta/cs340/project2/TCPIP_State_Transition_Diagram.pdf
TCP connection walkthrough : https://www.youtube.com/watch?v=F27PLin3TV0
当在复杂的环境中面临问题，格物之道需：浊而静之徐清，安以动之徐生。 云中，恰是如此!