That may be a ethernet printer spooler, hard to tell. What would work is an (old) dial-in ethernet modem. I had one I had to leave behind in a move. It had both serial and ethernet connectors that worked even ignoring the modem functions. It was made by one of the big companies in the Mac modem market, maybe Asante.
Edit: apparently these things are called LAN modems, but the one I had allowed serial connection too.
