Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!zaphod.mps.ohio-state.edu!mips!ultra!rmg
From: rmg@ultra.com (Rich Geiger)
Newsgroups: comp.dcom.modems
Subject: V.22bis modems confused by T2500 V.32 answer tones?
Message-ID: <1990Jul10.210044.2650@ultra.com>
Date: 10 Jul 90 21:00:44 GMT
Reply-To: rmg@ultra.com (Rich Geiger)
Organization: Ultra Network Technologies
Lines: 38


We recently installed two Telebit T2500's on the dailup lines into our
Unix system. We have noticed that some types of V.22bis modems (2400
bps) are having difficulties connecting at 2400bps when they dial in.
Based on various experiments, it appears that the T2500's V.32 answer
tones are being misinterpreted by some V.22bis modems; they seem to
respond to the V.32 tones rather than waiting for the T2500 to
downshift to the V.22bis tones. This seems to be a mariginal behavior;
with the afflicted modems, it will happen *most* of the time, but
occasionally they will wait for the coreect tones and get a proper
V.22bis connection.

I have tried adjusting the T2500's S92 register ("V.32 AC Transmit
Duration") down to the minimum (300 milliseconds), but that didn't
seem to make any difference.

If we disable V.32 on the Telebits, so that they answer directly with
V.22bis tones, the modems are always able to connect.

Calling modems that I have seen have the problem:

  Everex Evercom 24+
  Touchbase Systems Worldport 2400

Calling modems that I have never seen have the problem:

  Everex 2400E
  Practical Peripherals PM2400SA

Is this a known/common problem? Is unrealistic to expect that most
V.22bis modems will not be confused by the V.32 answer tones?  Are
there any workarounds?


-- 
 - Rich Geiger
Ultra Network Technologies / 101 Daggett Drive / San Jose CA 95134
rmg@ultra.com  ...!ames!ultra!rmg  (408) 922-0100 [w]  (408) 739-7911 [h]