WAGO 750 Series Manual page 234

230 • Glossary
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).
R
Repeater
Repeaters are physical amplifiers without their own processing function.
They refresh data without detecting damaged data and forward all signals.
Repeaters are used for longer transmission distances or when the maximum
number of nodes of 64 devices per twisted pair segment is exceeded. A
request from a client to server is a provision to act on a serivce or funtion
call.
Request
A service request from a client which requests the provision of a service
from a server.
Response
The server's reply to a client's request.
RFC specifications
Specifications, suggestions, ideas and guidelines regarding the Internet are
published in the form of RFCs (Request For Comments).
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP