- The TCP connection establishment protocol
can be described using
a state transition diagram as
follows:
Explanation of the states:
- CLOSED =
initial state
- The client has
no TCP connection
- The server is not listening for any connection requests
- The client has
no TCP connection
- Listen =
server initialization
- The client has
no TCP connection
- The server is able to process connection requests
- The client has
no TCP connection
- SYN_sent =
client request connection
- the client has
send a
connection request to the
server
- The server has not yet processed the connection request
- the client has
send a
connection request to the
server
- SYN_Recv =
server request connection
- The server has
processed the
client's
connection request and
sends its own
connection request
- The client has not yet processed the server's connection request
- The server has
processed the
client's
connection request and
sends its own
connection request
- ESTABLISHED =
done
- The client has processed the server's connection request
- CLOSED =
initial state
- How to
read the
TCP transistion state diagram:
- The left portion
of the diagram is for the "server"
The right portion of the diagram is for the "client"
- Begin the client
and the server
in the CLOSED state
- The UNIX "listen()" system call
(extern action by the program)
will trigger the external action
Passive open
This event will cause the TCP protocol at the server to enter into the Listen state:
This transistion does not trigger any response....
- When a client program
wants to make a TCP connection,
the client program
will invoke the
UNIX system call "connect()"
The corresponding (external) event is called active open:
This transition will cause a response of transmitting a SYN message to the server
The client TCP protocol enters into the SYN_Sent state.
- When the
SYN message
is received by the server TCP
protocol, it causes the
responses of
sending a
SYN+ACK message
to the client:
The server TCP protocol to enter the SYN_Recv state.
- When the SYN+ACK message
is received by the
client TCP protocol,
it causes the response
of sending a
ACK message to the server:
The client to enter in the EXSTABLISH state (client is done !)
While in the EXSTABLISH state, the TCP protocol will send and receive data messages.
- Finally, when the ACK message
is received by the
server TCP protocol, it causes the server TCP module to
enter in the
EXSTABLISH state:
Now the server can also send data messages to the client...
- The left portion
of the diagram is for the "server"