Contemporary Controls CTRLink EIAR-10T, User Manual, Page: 13 / 78

Description of Functions
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3 Description of Functions
3.1 General Description of Functions
The Internet Access Router provides a local Ethernet based on TCP/IP
the transition to another IP network via a PPP connection (long-distance
data transmission).
This transition is normally provided via the internal modem integrated
into the router (56k Analog Modem or ISDN Modem, see Chapter 6).
This grants all clients integrated into the network access to a remote
PPP server (Internet provider, in-house monitoring computer) via a
single interface.
In this case, the connection is only established when necessary (IP
packets addressed externally) and is cleared if not used for a longer
period.
Additionally, an authorised computer may establish a direct PPP
connection to the router via its integrated modem. By using this
connection, the router can be monitored and configured.
Since the router shows a transparent behaviour with such a direct PPP
connection, the clients working in the Ethernet can be addressed
directly, and TCP/IP-based services, such as Telnet or FTP, can be
used.
In addition, it is possible to establish a VPN connection via the Internet.
A configurable firewall software is preinstalled, protecting the Ethernet
from unauthorised access from outside.
3.2 Functioning of "Dial on Demand"
As already mentioned, the Internet Access Router only establishes a
connection to the Internet if required ("on demand").
This situation arises if the router receives an IP packet from your
Ethernet, which possesses a target address outside the Ethernet.
At this time, the router checks whether there is already a modem
connection. If this is not the case, the router will dial a number specified
by you using the internal or external modem. Then, a PPP program
becomes active to establish an IP connection using the PPP protocol
(Point-to-Point).