
2. Terms and Definitions
Below is a list of terms used in this manual and their definitions.
IP Address Ethernet communicates using an IP address.
An IP address (Internet Protocol address) is an address for identifying a
node (host computer, controller, etc.) on Ethernet.
IP addresses must be set and managed so that there are no duplicate
addresses on the network.
Socket A socket is an
interface that allows you to directly use TCP or UDP
functions from the user program.
The NJ/NX Series machine automation controller performs socket
communication using the standard socket service instruction.
To use the socket service, you need to establi
sh and disconnect a
connection with the other node. In this document, the establishment
process is called "socket open" or "TCP open", and the disconnection
process is called "socket close" or "close".
Socket service allows you to send and receive arbitrary data with another
node.
Active and Passive
When a TCP socket connection is established, open processing is
executed on each node.
Currently
, the open method differs depending on whether the node
becomes a server or a client.
In this document, processing
when opening as a server is called
"Passive Open", and processing when opening as a client is called
"Active Open" or "Open Processing (Active)".
Keep-alive Function If the TCP / IP socket service does not communicate with the other node
(server or client) for longer than the set time, the keep-alive
communication frame is used to check the connection with the other
node.
If there is no response, confirmation will be performed at regular
intervals, and if there is no response to all confirmations, the connection
will be disconnected.
Linger It is an option of TCP socket that enables open processing by the same
port number immediately without sending RST data at TCP socket close
and waiting for port number release.
If the linger option is not specified, FIN data will be issued when TCP is
closed, and termination management such as delivery confirmation will
be performed with the other node in about 1 minute. For this reason, it
may not be possible to use the TCP socket of the same port number
immediately.