Net:TCP Finite State Machine (FSM)
状态
CLOSED
This is the default state that each connection starts in before the process of establishing it begins. The state is called “fictional” in the standard. The reason is that this state represents the situation where there is no connection between devices—it either hasn't been created yet, or has just been destroyed. If that makes sense.
1. Passive Open
Passive Open: A server begins the process of connection setup by doing a passive open on a TCP port. At the same time, it sets up the data structure (transmission control block or TCB) needed to manage the connection. It then transitions to the LISTEN state.
2. Active Open
Active Open, Send SYN: A client begins connection setup by sending a SYN message, and also sets up a TCB for this connection. It then transitions to the SYN-SENT state.