A short preface to this is in order.  We didn't include this fix because
we do soft-carrier differently from 4.XBSD and we would have had to
modify the drivers.  Basically acucntrl is the wrong way to do this.  The
kernel should be modified to provide the service which acucntrl is trying
to provide out in user-land; perhaps Chris Torek's multiple interface
scheme is the right way to go ...  This unfortunately doesn't help 4.3BSD
and 2.10BSD people much.

  Following is an UNTESTED fix for /sys/pdpuba/dh.c.  Similar fixes for
dhu.c and dz.c are possible:

*** /tmp/dh.c	Wed Sep  7 03:31:38 1988
--- /sys/pdpuba/dh.c	Thu Aug 18 17:49:17 1988
***************
*** 598,604 ****
  	dm = unit >> 4;
  	tp = &dh11[unit];
  	unit &= 0xf;
! 	if ((dev & 0200) || (dhinfo[dm].ui_flags & (1<<unit)))
  		dhsoftCAR[dm] |= (1<<(unit&0xf));
  	else
  		dhsoftCAR[dm] &= ~(1<<(unit&0xf));
--- 598,604 ----
  	dm = unit >> 4;
  	tp = &dh11[unit];
  	unit &= 0xf;
! 	if (dev & 0200)
  		dhsoftCAR[dm] |= (1<<(unit&0xf));
  	else
  		dhsoftCAR[dm] &= ~(1<<(unit&0xf));

  As stated above, we would far rather see Chris Torek's multiple
interface code installed.  That would allow uucico, tip and any other
programs to simply use the right interface in their opens on the outgoing
modems.  The corresponding fixes to the various tty drivers are
unfortunately fairly extensive.  See Chris for the diffs ...