Serial to ethernet is a rubbish option compared to "real ethernet", do you know how slow the baudrate on serial is ? It's definitely nowhere near 100meg Full Duplex that ethernet offers....not even anywhere near 10Meg half duplex...
" The standard 9-pin serial port can use many different transfer rates. It depends mainly on the hardware, usually a chip called a Uart (universal asynchronous receiver/transmitter.) The speeds start usually at 60 bps and can go to a maximum of 768000 bps. On older PCs the max was 9600 bps, and newer ones average 230,400 bps. "
For Cisco Serial input all that is for is to allow access to the terminal for text output input....
If you want CS, buy a box with a proper ethernet port...a better possibility if ethernet is not available is USB to ethernet adaptors, if the box has USB and driver support...