yaha (Yet Another HFC Article)

Marc Weinstein mhw at fithp
Wed May 15 09:34:36 AEST 1991

As a followup to my own article...

In my last article, I stated that we had created a modem script which
ran from inittab instead of calling uugetty directly.  The script would
apply HFC (and 19200, if needed) and would then exec uugetty.  We have
since found that this is NOT a good idea.

For some reason unknown to us, if uugetty is not called directly from
inittab, it can cause problems.  For instance, after a failed outgoing
call, the uugetty would not see the Carrier Detect go away, and wouldn't
die and get restarted.  So, HFC would never be reapplied.  And, if the
modem was confused, and the far end quit, the modem would stay connected
for much longer because of something strange the hung uugetty would do
to the port.  We were even seeing the port/modem get hung for hours at
a time - when the uugetty was killed manually, everything cleared up.
Very strange.

So, we modified our setup.  We now are back to invoking uugetty directly
from the inittab, and we changed the HFC program to a daemon.  It runs
out of inittab (as a respawn process, just to make sure) and reapplies
HFC every ten seconds (or whatever you like).  This makes it somewhat
asynchronous with the uugetty restart, but it seems to work fine, albeit
not in an ideal fashion.  Things are working much better, and HFC (at 
least at 9600 baud) is working flawlessly.  We're about to try 19200.

Incidentally, for those of you with MNP modems, use MNP4 rather than
MNP5 for sending compressed netnews batches.  Apparently, the MNP5
compression is less efficient than the UNIX compress utility, so it
ends up expanding the number of bytes in the file.  Also, if it's 
possible to set the port speed to the modem higher than the DCE-to-DCE
rate which the modem uses, you can get better than the expected rate.
MNP apparently creates a "pseudo-synchronous" connection between the
modems, and no start and stop bits are needed.  This allows you to
get 20% more throughput on the line (8 bits per byte rather than 10).
But, you have to be able to supply the modem data at a faster rate.

Marc Weinstein
{simon,royko,tellab5}!linac!fithp!mhw		Elmhurst, IL
-or- {internet host}!linac.fnal.gov!fithp!mhw

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