Heard of this modem/vax/ultrix/whoknows problem?

[Dean Inada]

Posted for a friend:

From: Kirk Reinholtz <elroy!moc.Jpl.Nasa.Gov!kirk>

Have you seen or heard, on net news perhaps, any discussion of problems
with modems (esp Hayes 2400bps) on 3.0 ultrix on microvaxII, DHV
interface board?  The problem is that sometimes when carrier is dropped
by the remote site w/o the remote site first doing a kill on whatever
shell it has on the local machine the modem shows Rx and Tx lites
constant on and the vax either stops providing cycles to the users (but
does not crash) or gets quite sluggish.  The modem is configured
"shared": used for both dialin and dialout.

TAS put a scope on it and found that the vax was emitting a "Z" every
10ms at the modem, which naturally echoed it back.  The modem was 2400bps
at the time.  This is not the normal getty shouting at modem problem:
the shell on the line does not gather CPU time and does not constantly
die and then come to be reborne.

We swapped modems, we swapped DHV, we even swapped brand of modem: no
substantial impact on the problem, though it does seem like the hayes
is more vulnerable to the malfunction than the other modem we tried
(Telebit).

Thanks!

kirk at mocvax