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I want to use the existing ADSL line to build up the communication between 2 CPUs, but I have only experience with communication through a “normal” TCP/IP network.

Do I have to buy additional cards to put in the 2 racks? I want to transfer 200 signals from one to another, in the both directions, is this possible?

JEPS, ADSL is a digital technology for the transport of speeds up to 8Mbps on a conventional analog telephone line. It is one of the common technologies for connecting PCs to the Internet. I do not know of communications cards for PCs or PLCs that are capable of using ADSL. However, it is possible to purchase ADSL modems with Ethernet TCP/IP interfaces for attachment to computers. The modem is usually capable of sending a message from the computer to a telephone company central office where the ADSL signal is routed to an Internet server.

Therefore, it is possible to use an ADSL connection to send data formatted as a file transfer between two computers, each connected to an ADSL modem via the telephone company central office. If you don't want the data to leave your plant or place it on the Internet, they you cannot send the data via ADSL directly between two computers.

In reply to Dick Caro: I believe the hardware you are referring to is normally known as a DSL router or router/modem. This is an ADSL modem and network router in a single package which is connected to a PC via Ethernet TCP/IP. The router part of the package translates between two otherwise incompatible networks (TCP/IP and ADSL). The modem part of the package does the ADSL communications. Some systems also have wireless communcations built in as well (in which case it may be called a wireless router).

An ADSL router/modem is basically a small embedded computer (usually running a Linux OS) a bit smaller than a paperback book, which you configure via a web interface. They often also include features like a DHCP server, firewalling, various security filters, and ADSL network diagnostics. The settings for these features sometimes have to be adjusted in order for some protocols to work (because some ports may be closed off). The username and password to log onto the ADSL network are normally stored in the router/modem, which automatically logs on to the ADSL nework on power up.

To a PC (or other device) which connects to the Ethernet side of the router/modem, it looks like an ordinary TCP/IP network connection. You just configure your PC to use DHCP (or a fixed IP if that's what you have selected) and the router/modem takes care of the rest. Once they are set up, they are usually pretty trouble free. Since they take care of all the ADSL routing internally, you can usually connect multiple PCs to them via a switch.

There are also devices which are just ADSL modems. These don't have a router and require running special software on the PC in order to make the connection. Pure ADSL modems are often provided by internet service providers who supply the modem as part of the service because the hardware is cheaper. Some of these use Ethernet, but they aren't complete router/modems.