TCP state machine (part I)
+---------+ ---------\ active OPEN
+---------+<---------\ \ create TCB
passive OPEN | | CLOSE \ \
------------ | | ---------- \ \
create TCB | | delete TCB \ \
| LISTEN | ---------- | |
+---------+ delete TCB | |
----------- | | ------- | V
+---------+ snd SYN,ACK / \ snd SYN +---------+
| |<----------------- ------------------>| |
| RCVD |<-----------------------------------------------| SENT |
| |------------------ -------------------| |
+---------+ rcv ACK of SYN \ / rcv SYN,ACK +---------+
| CLOSE -------------- | | -----------