Modems on DHs

[Marc Elvy]

I am having some problems with an autodialer/modem I am using on a 780
running 4.2BSD UNIX, and I am soliciting all help I can get.  I have
a pair of modems (on different Vaxes) that I am running together, and
I cannot seem to get them to hangup properly.  I have a few rather large
programs that manage the modems/dialers and phone lines so that I can
maintain a serial TCP/IP link across the telephone line (at 9600bps),
and I have to have them connected to DHs, because I need the computer
to recognize EIA flow control conventions (which the DZs apparently
ignore).  The software reacts intelligently if the machines crash,
and it is supposed to react intelligently if the remote modem drops
the line.  However, I cannot figure out when the line has been dropped.

I cannot open the tty device unless the modem is putting out DSR,
so I have jumped that pin in the cable.  I would like to watch the
carrier detect signal so I can reset the modem if the line is
droppped, and recognize when a connection has been made.  However,
the ioctl() calls that return the necessary status information seem
to be missing from the DH driver.  I find it hard to believe that
no one has run up against this problem before, so I appeal to anyone
who has written software that recognizes when a connection has been
dropped (or established) for help.

Please send replies directly to ...!harvard!lownlab!elvy or
elvy at harvard.HARVARD.EDU (etc.).


Marc Elvy