Terms And Definitions - Omron V330-F Series Quick Start Manual

2. Terms and Definitions

Term
IP Address
Socket
Active and Passive
keep-alive Function
linger function
Ethernet uses IP addresses to achieve communications.
Each IP address (specifically, Internet Protocol address) identifies a
specific node (host computer, controller, etc.) on an Ethernet network,
IP addresses must be set and managed so that they are not duplicated.
A socket is an interface that allows you to directly use TCP or UDP
functions from a user program.
The NJ Series Machine Automation Controller performs socket
communication using standard socket service instructions.
To use socket services, you need to establish a connection with a remote
node and disconnect it after use. In this document, processing for
establishing a connection is referred to as "socket open" or "TCP open"
and for disconnecting it as "socket close" or "close".
You can use the socket services to send and receive arbitrary data to
and from the remote node.
When you open a TCP socket connection with nodes, open processing is
executed for each node.
The method to open a connection differs depending on whether the node
is to serve as a client or server.
In this document, processing to open a connection as a server is referred
to as "passive open" and as a client is referred to as "active open" or
"active open processing".
When a remote node (server or client) does not respond for a set period
of time or longer in TCP/IP socket services, the keep-alive function sends
a communications frame to the node to check the connection status.
If the node does not respond to it, the function performs this check at a
certain interval, and closes the connection if it does not respond to all
check frames.
This is a TCP socket option that sends RST data when the TCP socket is
closed. This enables immediate open processing using the same port
number, without waiting for the port to be opened.
If the linger option is not specified, the controller issues FIN data when
the TCP socket is closed and, after that, performs end control such as a
send data arrival check with the remote node for approximately 1 minute.
Therefore, TCP sockets with the same port number may not be used
immediately.
2. Terms and Definitions
Description/Definition
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