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A-7 TCP State Transitions
There are 11 types of TCP connection state.
You can check the TCP state with the TCP connection status that is output by the SktGetTCPStatus
(Read TCP Socket Status) instruction.
The table below shows the TCP states and what each state means.
TCP state
Definition
CLOSED
The connection is closed.
LISTEN
The server is waiting for a connection request (SYN) with a passive open.
SYN SENT
The client sent a connection request (SYN) for an active open and is waiting for acknowl-
edgment (SYN + ACK).
SYN RECEIVED
The server sent an acknowledgment (SYN + ACK) to a connection request (SYN) and is
waiting for acknowledgment (ACK).
ESTABLISHED
A connection is established.
CLOSE WAIT
The server sent acknowledgment (ACK) to a connection close request (FIN) and is wait-
ing for the server application to be ready to close.
FIN WAIT-1
The client sent a connection close request (FIN) and is waiting for acknowledgment
(ACK).
CLOSING
The client and server simultaneously received a connection close request (FIN) and are
waiting for acknowledgment (ACK).
LAST-ACK
The server sent a connection close request (FIN) and is waiting for acknowledgment
(ACK).
FIN WAIT-2
The client is waiting for a connection close request (FIN).
TIME WAIT
The client received acknowledgment (ACK) to a connection close request (FIN) and is
waiting for it to be received and processed by the server.
The TCP state changes as requests and acknowledgments are received from the remote node, and
as TCP socket connection and close instructions are executed in the user program.
When the state changes, a connection request (SYN), close request (FIN), and acknowledgment
(ACK) to those requests are sent to and received from the remote node.
The following figure shows TCP state transitions.
The TCP states are given in
£
in the figure. Between states, the text in the upper row indicates the
condition for the state change, and the text in the lower row indicates the action that is performed at
the state change. (If no action is performed, none is given.)
Example: When SYN and ACK are received in
SYN SENT
state, ACK is sent and the state changes to
ESTABLISHED
.
Appendices
A-60
NJ/NX-series CPU Unit Built-in EtherNet/IP Port User’s Manual (W506)
Summary of Contents for Sysmac NX1P2-10 1 Series
Page 8: ...Manual Structure 6 NJ NX series CPU Unit Built in EtherNet IP Port User s Manual W506...
Page 34: ...Revision History 32 NJ NX series CPU Unit Built in EtherNet IP Port User s Manual W506...
Page 388: ...9 Socket Service 9 34 NJ NX series CPU Unit Built in EtherNet IP Port User s Manual W506...
Page 430: ...12 FTP Client 12 14 NJ NX series CPU Unit Built in EtherNet IP Port User s Manual W506...
Page 569: ...I Index I 1 NJ NX series CPU Unit Built in EtherNet IP Port User s Manual W506 I...
Page 576: ...Index I 8 NJ NX series CPU Unit Built in EtherNet IP Port User s Manual W506...
Page 577: ......