One of them has to run PPP server software, i.e. it has to act like
> the terminal server that an ISP has connected to its dialup modems.
Why not just modem to modem serial? I used to run a BBS and we didn't need no steenkin PPP.
Of course, I suppose it all depends on what exactly OP is trying to do, which he hasn't told us, other than he wants them to "communicate". If he insists on TCP/IP, you may well be right.