tcp 状态图

sync sent

                         (sync m ->)

                                                              sync recved

                         (ack m+1/sync n  <-)

established

                         (ack n+1 ->)

                                                              established

.

.

.

.

.

.

.

.

fin_wait_1

                          (fin ->)

                                                              close_wait

                          (ack <-)

fin_wait_2

                                                              last_ack

                          (fin <-)

time_wait

                          (ack ->)

                                                              closed

 

 

 

1 tcp关闭中的fin只表示本端不再写，但是可以读

2 time_wait发生在主动关闭端； close_wait在被动关闭端

3 time_wait的作用有两个 (1) 确保对端在超时重发fin时可以回复ack    (2)等待本次连接中的最后一个报文在网络中消失。 一般时间在1-4分钟