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From: bruce@think.com (Bruce Walker)
Newsgroups: comp.dcom.modems
Subject: Telebit V.32 problems
Keywords: V.32, Telebit, LAPM, MNP, disconnection
Message-ID: <1990Nov8.180824.20867@Think.COM>
Date: 8 Nov 90 18:08:24 GMT
Sender: news@Think.COM
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 43

Since upgrading our dialin modems to the rackmount version of the Telebit
T2500 and handing out a bunch of T1500s for dialups, we have had lots of
problems with connections dropping in V.32 mode.

The problem seems to happen when MNP is turned on ("CONNECT 9600/REL") or
when V.42bis is turned on ("CONNECT 9600/LAPM"), and it is clearly related
to line noise: most of the problems are with long-distance connections or
known-to-be noisy lines, and in situations where connecting without MNP or
LAPM is too noisy for use.

The symptom is a long pause, then a "CONNECT 9600/REL" message (or
occasionally a "CONNECT 9600"), regardless of whether the connection began
with LAPM or MNP.  After a few more seconds, carrier is always dropped.
Sounds as if it is trying to renegotiate in the middle of a session.

This has also happened using FastComm V.32 modems as dialups, so it is not
a T1500-specific problem.  It is also not specific to one or two specific
dialup modems either; I have a bank of 12, and it happens regardless of
which one I use.  PEP never has a problem like this on the same phone
lines.

Telebit technical support had nothing useful to say, other than they didn't
have a record of anyone else reporting it (which I find hard to believe)
and that it is allowed to renegotiate MNP off if there are too many errors
during the session, hence the "CONNECT 9600" message.  I haven't looked at
the protocols, but that must be bogus information, since it completely
defeats the purpose of error correction.

My questions:

	1) Is this a Telebit implementation problem or a fundamental
	   problem in the protocols involved?
	2) Has anyone else seen it on Telebit or other hardware?
	3) What can I do about it?

I am holding off purchases of additional modems until we can do something
about it.  I'll summarize responses.


--
--Bruce Walker
  Thinking Machines Corporation, Cambridge, MA
  bruce@think.com; +1 617 876 1111