-=> Quoting Dave Hatch to Meng-Shi Lim <=-

 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?

 DH> In the case of this fault, (if that's what it is, no guarantees) this
 DH> won't help.  The theory is sound - but the line degradation once
 DH> triggered is much worse than the line would normally be. 
 DH> There's currently a theory (mine) that the calling tones help trigger
 DH> the problem - I have a line with the problem fairly often, and it
 DH> doesn't happen with either low speed modems, or VFC.  I have yet to
 DH> prove that disabling calling tone will avoid the problem, but it
 DH> appears possible. 

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

Calling tone is disabled by default here and there doesn't seem to be
much difference when I enabled it. I wasn't paying much attention when I
tried this so I need to try a few more times I guess. I'm actually not
quite sure what the calling tone is or does. But, this modem sounds like
it is sending an additional and regular noise down the line when it is
waiting for an answer. ie initiate dial->dial tone->tone
dialling->ringing->BEEP->ringing->BEEP->remote pickup and answer +/-
beep. My external modem doesn't produce this BEEP after dialling. This
beep is independent of the ring of the remote phone and depending on the
timing of when the remote answers the call, can occur during the
handshake period. Depending on the phase of the handshake, this beep can
occasionally stuff up the whole process. Is this the calling tone?

 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?

 DH> This is normal operation for a USR.  I commonly connect on one of my
 DH> nearby hub links at 21600, and then happily log 3650 cps transfers
 DH> both ways on that link. It's fairly conservative in connect speed, but
 DH> 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 ->
 DH> 19200 ->>21600) but I'm not sure about the above.

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

To my surprise it happened here. I forced a connection at 16800 and after
hanging up, ATI6 reported a 24000 connection. It would be nice if I
could force a 14.4k v34 connection and let the modem retrain upwards
(given that the highest speed handshaking often fails here) but for some
reason the modem always connects at 14.4k with v32bis only, although it is
not uncommon to get a fallback from a higher speed v34 connection to a
14.4k v34 speed. Can you force a 14.4k v34 on your modem?

I mainly use this modem for TCP/IP connection and the CPS is never as
high as a ZMODEM transfer on a BBS. However, Win95's system monitor
gives a dynamic reading of the modem's send/receive CPS and from these
one can get a pretty good indication of whether the modem is falling
back or forward.


--- Blue Wave/Max v2.20 [NR]