TCP/IP State Transition Diagram (RFC793)

[mufitsozen]

TCP/IP State Transition Diagram (RFC793)
Gordon McKinney (23 Feb 2002)
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.

SYN-SENT represents waiting for a matching connection request after having sent a connection request.

SYN-RECEIVED represents waiting for a confirming connection request acknowledgment after having both
received and sent a connection request.

ESTABLISHED represents an open connection, data received can be delivered to the user. The normal state
for the data transfer phase of the connection.

FIN-WAIT-1 represents waiting for a connection termination request from the remote TCP, or an
acknowledgment of the connection termination request previously sent.

FIN-WAIT-2 represents waiting for a connection termination request from the remote TCP.

CLOSE-WAIT represents waiting for a connection termination request from the local user.

CLOSING represents waiting for a connection termination request acknowledgment from the remote
TCP.

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).

TIME-WAIT represents waiting for enough time to pass to be sure the remote TCP received the
acknowledgment of its connection termination request.

CLOSED represents no connection state at all.

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.