Technical data

216 • Glossary
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
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
connection 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
direct access to the Internet, indirect access to the network. These can be
systems which are excluded from direct access by a firewall for security
reasons.
A proxy can filter out individual data packets between the Internet and a
local network to increase security. Proxies are also used to limit access to
particular servers.
In addition, proxy gateways can also have a cache function, in which case
they check whether the respective URL address is already available locally
and return it immediately, if necessary. This saves time and costs when there
are multiple accesses. If the URL is not in the cache, the proxy forwards the
request as normal.
The user should not notice the proxy gateway apart from the single
configuration in the web browser. Most web browsers can be configured so
that they use different or no proxy gateways per access method (FTP,
HTTP).