Terms And Definitions - Omron CJ Series Connection Manual

2. Terms and Definitions

Term
IP address
Socket
Active open/
Passive open
Keep-alive function
Linger function
Ethernet uses an IP address to perform communications.
The IP address (Internet Protocol address) is an address that is used to
identify a node (host computer or controller, etc.) on the Ethernet.
IP addresses must be set and managed so that they do not overlap.
A socket is an interface that enables the use of the TCP or UDP function
directly from the user program. The socket services enable data
exchange with destination nodes. The CJ-series Programmable
Controller can use the socket services in the following ways:
•Manipulation of a dedicated control bit allocated in the CIO area for
the Ethernet Unit
•Issuing a FINS command (CMND instruction) to an Ethernet Unit
Open processing is executed on each node to connect the TCP socket.
The open method depends on whether the node is opened as a server or
client.
In this document, the method used to open a node as a server is called
"passive open" and the method used to open a node as a client is called
"active open" or "open processing (active)".
When the keep-alive function is used with TCP/IP socket services, the
keep-alive communications frame is used to check the status of the
connection with the destination node (either a server or client) if there are
no communications during the specified time interval.
Checks are executed at a certain interval, and if there is no response to
any of them then the connection is terminated.
This is an option for the TCP socket that enables immediate open
processing using the same port number without waiting until the port
number opens after RST data is sent when the TCP socket closes.
If the linger option is not specified, FIN data will be sent when a TCP
socket is closed, and then approximately 1 minute will be required to
confirm the transmission and perform other closing management with the
destination node. Therefore, it may not be possible to immediately use
TCP sockets with the same port number.
2．Terms and Definitions
Explanation and Definition
2