jellinek@candymtn.PARC.xerox.com (Herb Jellinek) (09/09/89)
I'm trying to convince an NCD X terminal to speak SLIP over a pair of Telebit T2500 modems to my Sun-4/330. Substituting a null modem for the modem pair works fine -- the terminal is just about usable at that speed, and I can run X and telnet to my heart's content. Alas, when I put the modems in the circuit, things start off well enough, but deteriorate rapidly. I can open a telnet session to the Sun, but it often hangs just after log-in; output from the Sun no longer echos in the telnet window, even though the HP protocol analyzer I'm using shows that the Sun is busy sending me all sorts of data, which the NCD is ignoring, as well as responding to my keystrokes. Eventually the NCD seems to stop sending anything, and the connection hangs. At that point, I cannot even PING the Sun from the terminal successfully. At times I've even been able to run X applications like Ico, but those die within one or two minutes, running slower and slower until they stop. I've got the Telebits configured for 19200 baud using PEP encoding. I'd like to try them using MNP5 at 9600, but a little piece of paper stuck into my Telebit manual says that that doesn't work yet. Has anyone out there got any suggestions? I'm not too familiar with what's involved with using PEP, or how it might affect synchronization of SLIP packets, but I suspect that that might have something to do with it. Ultimately, though, I'm clueless. I'm running the beta release of Slip 4.0 from Toronto, by the way. Thanks for your help. Herb Jellinek Jellinek@Xerox.com
casey@gauss.llnl.gov (Casey Leedom) (09/18/89)
| From: jellinek@candymtn.PARC.xerox.com (Herb Jellinek) | | I'm trying to convince an NCD X terminal to speak SLIP over a pair of | Telebit T2500 modems to my Sun-4/330. Substituting a null modem for the | modem pair works fine ... Alas, when I put the modems in the circuit, | things start off well enough, but deteriorate rapidly. | | I've got the Telebits configured for 19200 baud using PEP encoding. | I'd like to try them using MNP5 at 9600, but a little piece of paper | stuck into my Telebit manual says that that doesn't work yet. You're probably running into flow control problems. Unfortunately the best I can suggest is that you set up everything to use hardware flow control. That doesn't mean that I think that hardware flow control will actually work - UNIX tty drivers typically don't implement hardware flow control - but it should help prevent any XOFF/XOFF dead lock states which may be hanging you up. After that you'll have to hope that both ends are running the Jacobson/Karels/Karn IP fixes so lost packets don't cause the link to go into failure saturation mode. Also, you should use V.32 even though the MNP compression isn't implemented yet. PEP doesn't work very well in any full duplex application and this is definitely one. By the way, I've used one of the new BETA T2500 PROMs with the MNP compression. Full duplex 19200 is incredible! My Graphon Optimax 200 just loves it! And yes, I have flow control problems also: VAX-11/785, 4.3BSD, DMZ ttys. But most of them appear to be caused by the terminal not being able to keep up with the Telebits! Some may be caused by the T2500 on the VAX dropping CTS (or RTS - I can never keep this stuff straight) and the DMZ driver ignoring the transition. Casey