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Figure: -
TCP state Transition diagram
Note: -
thick solid line is normal state trajectory for a client and the dashed line is
normal
state trajectory for a server
v 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.
v 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.
v A TCP
connection progresses from one state to another in response to events.
v 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.
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