322 • Glossary
Modular I/O System
ETHERNET TCP/IP
MS-DOS
Operating system, which allows all applications direct access to the hard-
ware.
O
Open MODBUS/TCP specification
Specification which establishes the specific structure of a MODBUS/TCP
data packet. This is dependent upon the selected function code or from the
selected function (readin/readout bit or register).
Operating system
Software which links the application programs to the hardware.
P
Ping command
When a ping command (ping <IP address>) is entered, the ping program
ICMP generates echo request packets. It is used to test whether a node is
available.
Port number
The port number, together with the IP address, forms an unambiguous con-
nection point between two processes (applications).
Predictable ETHERNET
The delay time of a message on an ETHERNET network can be predicted.
The measures which have been taken in predictable ETHERNET make it
virtually possible to realize realtime requirements.
Proxy gateway
A proxy gateway (or proxy server, too) allows systems which do not have di-
rect access to the Internet, indirect access to the network. These can be sys-
tems which are excluded from direct access by a firewall for security rea-
sons.