Hmm... I usually run my modem to the serial port on the controller but what if my DB9 cable was terminated with an RJ45 at the other end. With a device server such as a Lantronix UDS-1100, I am able to do this (serial to ethernet conversion) and I will be able to control multiple serial devices with just their IP's without being limited by the number of serial modules on the rack. But of course, on a PC it's just a COM port redirection (through software). But I am not sure if this is even doable for anything other than OEM I/O
This was just an idea I happen to come accross with as I was researching about door access control systems, though.