mskuhn@faui09.informatik.uni-erlangen.de (Markus Kuhn) (01/31/91)
I just had an idea that as far as I know hasn't been discussed here: If you want to use OSI protocols on an IBM compatible PC, you will have to buy quite expansive boards (Ethernet, X.25, ISDN, etc.) to conform to one of the established protocol stacks. The only interface that comes with a PC is a serial asyncronous (I think ISO says start-stop-mode instead of asynchronous) RS-232C port that hasn't been supported by any standard so far. But now, I have read that ISO has published an addendum to the HDLC standard that allows HDLC connections on a start-stop-mode line. The X.25 protocol uses a HDLC subset called LAP-B in the data link layer. So the new addendum should allow you to adapt LAP-B and with this X.25 to run on asynchronous ports. In this way, it should be possible to connect every PC over a layer 2 or 3 gateway with the OSI world. This gateway might be a public BBS or a main frame (at universities for example). All the fine OSI services (VT, X.400 UA<->MS, FTAM) would run on PCs via modem lines etc. Has this idea been considered anywhere before? Is it difficult to implement a unix command (lets call it OSI) that switches the terminal line from ASCII to LAP-B. So you login with a OSI terminal emulator at a host, than you enter OSI and switch your terminal program to LAP-B. Or alternatively, you connect to line that has been configured especially for LAP-B and login with the VT protocol. I am a CS student that has more than enough spare time and enthusiasm to implement a small OSI system in this way (public domain of course) on a PC. Unfortunately the standard papers are much to expensive for me. Can anybody give me some technical details of the start-stop HDLC. I am looking forward to any comments on this topic! Markus Kuhn, University Erlangen, Germany