Typical TCP session behavior


What's the typical sequence of events in a TCP connection? Let's say Alice is opening a TCP session with Bob. (Enjoy the sparkling ASCII graphics.)

    Alice         Bob

        (open phase)

    SYN     --->
            <---  SYN+ACK  (no data in packets here)
    SYN+ACK --->

       (data transfer)

    PSH     --->           (PSH packets have data)
            <---  ACK      (Bob is just ACKing without sending data back)
    PSH+ACK --->
            <---  PSH+ACK  (ACKs can be sent along with data)
    PSH+ACK --->
            ...

        (close phase)

    FIN     --->
            <---  FIN+ACK  (also no data in packets here)
    FIN+ACK --->
          (closed)

At this point the connection remains in TIME_WAIT state for a time to prevent stray packets from this connection from being accepted

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Steve VanDevender
Last modified: Thu Jun 24 11:32:21 PDT 2004