 Remote
connection to Ethernet networks
Use a telephone modem or full duplex radio to give
you a secure connection to a private Ethernet network. You can use
authentication (user name and password – see
below) to insure that only authorized devices log in.
Different
protocols can share a serial port
A PPP connection is effectively a speed reduced
Ethernet network. Ethernet will simultaneously transport multiple
message types (Modbus, SIXNET Universal, html, etc.) – so
will PPP. How many times have you had to give up functionality
because your serial links would only support one protocol? Not
any more!
Low
cost connection to the Internet
Make a dial-up connection into a low cost ISP
(Internet Service Provider) and avoid long distance telephone
charges. Many stations can connect to your central host at the
same time since they appear to be simple Ethernet connections
to your master station. You eliminate the “modem farm”
and all of the maintenance headaches associated with it. Costs
go down and performance of your remote systems goes way up!
Serial
to Ethernet pass through
The PPP add-on also provides “port forwarding”
in the IPm. Port forwarding relays IP messages from one port to
another. When a message is received that does not match the IP
address of this station, port forwarding passes the packet to
the port (Ethernet or PPP-enabled serial port) that is configured
through its subnet mask to accept that IP address. Port forwarding
is a powerful way to pass messages through serial links to provide
remote access to a remote Ethernet network. Multiple hops can
be configured by making the subnet masks at each layer be a subset
of the network segment of the device above it in your connection
topography.
Authenticated
secure connections
PPP connections use a user name and password to
verify that the client seeking to connect to a server is an authorized
user. PPP can therefore be used to increase security by insuring
that unauthorized users cannot access your radio signals and telephone
connections. Since PPP is an additional packeting layer in the
message transmission, it provides an additional layer of protection
as well because it blocks non-PPP devices. It is interesting to
note that with an IPm-based device at each end of a PPP connection,
messages can be sent and received through the “port forwarding”
completely in the clear. This means that existing devices that
for example send Modbus will find the PPP protected link completely
transparent to their operation.
How
to configure PPP in an IPm
Simply select PPP as the protocol for any RS232
port in an IPm. Since the serial port will now act like an Ethernet
connection, it is no longer necessary to select Modbus, SIXNET,
or other individual protocol for that port, because you can now
simultaneously use them all. Each “point-to-point”
connection requires a client (to initiate the connection) and
a server to receive and respond at the other end. Since a PPP
connection is in effect an additional Ethernet port on your IPm,
you will need to assign a subnet mask to the port, so that the
IPm will know which IP addresses to direct to this port. A default
user name and password are assigned to the PPP connection for
your convenience. This default user name already exists in the
IPm’s user list. Most of the other settings in the PPP configuration
window (domain names, DNS servers, …) are only required
by networks that use these features. On simple IPm-to-IPm connections,
you do not need to configure these settings. |
