OBM <--> Telebit incompatibility: SUMMARY

[Thad P Floryan]

All this talk about Telebits "doing" bit shaving is interesting, but reading
the description of the visible effects of the problem reminds me of something
else that caused the IDENTICAL problems 10 years ago at 1200baud and for which
a sound technical explanation (AND FIX) existed:

	speed tolerance mismatch when calling Racal-Vadic Triple-Modems, model
	3467, which operated in 103 mode (0-300 bps), 212A mode (1200 bps) and
	VA3400 mode (also a nominal 1200 bps).

My 212A modems (then) had NO problems calling anywhere except to one site, and
that particular site had ONLY the Vadic modems.

Vadic modems had the misfeature of an on-board jumper which would select the
"nominal 1200 bps" to be EITHER the ranges:

	1186 to 1204 bps, or
	1196 to 1219 bps

212A modems' bit rates are specified as 1182 to 1212 bps.

>From the factory, Vadic modems were set to the "1196 to 1219 bps" range and,
of course, worked fine with other Vadic modems.

But if one called using a 212A modem into a Vadic (or vice versa), the bit rate
variation would cause complete garbling after about 20 characters or so, and
rendered the connection useless due to the cumulative effects of the 0.6% bit
rate difference.

So, my conjecture is that the problem may not be "bit shaving" but, in fact,
something like a bit rate mismatch.  Hmmm, wonder where the Vadic engineers
went after Vadic went belly up?  :-)   [ NOTE that Vadic was in Santa Clara
and Telebit was in Cupertino (2 miles away) and is now in Mountain View, about
4 miles from the old Vadic site ]

In any event, I had to "fight" that site admin for quite a while; he kept
insisting his modems worked fine for him (sure, all his were Vadics) and that
any "problem" had to be in my modem.  Finally convinced him to RTFM, and he
THEN adjusted that jumper on his Vadics, and all worked fine since.

Now that same site has Codex modems which are ALSO improperly configured (by
the SAME guy, sigh) regarding its multi-mode handshake decoding sequence
"song-and-dance" as to what to set its modulation technique to be.  Sigh.
Causes real problems using V.32/V.42 and, I hear, Telebit (ah, the irony :-).

My modems again can call ANY site in the WORLD with no problems; only that one
site has the problem, and I'm still dorking-around getting that guy to "fix"
HIS problem; to be fair, he's been going out of his way to assist me regarding
remote tests, etc., but I believe I could solve that problem if he'd just loan
me the manual for a day and I read it to see how to configure Codex modems,
and then DO it.

For what it's worth, the "site" to which I'm referring is the same one that
was mentioned in John Ruckstuhl's (ruck at sphere.UUCP) anecdote re:

	... said, essentially, "I *won't* carry it because I don't see that it
	is beneficial to HP".  I wrote back asking him to reconsider, hoping
	that he wouldn't apply a criterion to unix-pc that he wouldn't apply
	to, say, rec.arts.tv.soaps.  This logic, and a "spirit of USENET"
	appeal failed to persuade him.

And yet, that site, HP-Labs (Palo Alto) does carry alt.sex.pictures and, of
course, alt.sex.bondage.  Obviously pornography and kinky sex IS important
to HP-Labs, right?  :-)

The above is NOT meant to cast aspersions on Hewlett-Packard.  It's just that
every company has its share of obstinate people.

Thad Floryan [ thad at cup.portal.com ]