On Jun 19 20:56 96, Meng-Shi Lim of 3:635/503 wrote:

ML> Are there any v34 modems out there that allows you to set the fallback
ML> limit of a v34 connection (ie stop the fallback below certain speed) ?
ML> I find that if I enable the fallback option, my 21600 (or higher) v34
ML> connections can sometimes drop down to 7200 or 9600 but I know that the
ML> phone line has never had any problems running at 14.4k v32bis. I just
ML> don't know why it would retrain and drop down so low.

You're receiving "assistance" from Telstra.  So far, cause still unproven.
Seen in a number of places now.   If you get a bidirectional readout,
you'll find that it affected one direction only, with the direction
apparently more or less chosen at random.

ML> Does anyone know what happens if retrain is enabled and fallback is
ML> DISABLED? Does the modem retrain repeatedly at the initial DCE speed
ML> until the line gets so bad that carrier is dropped?

In the case of this fault, (if that's what it is, no guarantees) this won't
help.  The theory is sound - but the line degradation once triggered is
much worse than the line would normally be.

There's currently a theory (mine) that the calling tones help trigger the
problem - I have a line with the problem fairly often, and it doesn't
happen with either low speed modems, or VFC.  I have yet to prove that
disabling calling tone will avoid the problem, but it appears possible.

If you're ambitious, could you try disabling the v8 tones prior to connect,
and report back to us if it helps/fixes/has no effect when there's a known
bad line session on?

ML> Another question: on a 28.8k modem, if the connection is made at less
ML> than 28.8k (eg 21600), can the modem pick up and renegotiate a higher
ML> speed from this point onwards if the quality of the line improves?

This is normal operation for a USR.  I commonly connect on one of my nearby
hub links at 21600, and then happily log 3650 cps transfers both ways on
that link.
It's fairly conservative in connect speed, but the fallforward is excellent.

ML> (Personally I don't think so but you'll never know). I know that the
ML> modem can retrain up and down from the connection speed (eg 21600 ->
19200 ->>21600) but I'm not sure about the above.

Your connect speed vis achieved cps later in the call tell the tale.

Regards,
Dave Hatch.

--- Msgedsq 3.20