flexfax: Zyxel U-1496E RTN errors

[Jim Stosick <jws@lindy.stanford.edu>]

I just installed Hylafax v4.0pl2, and am using it with a Zyxel U-1496E
V6.19 fax modem.

I found that we were getting quite a few RTN (retrain negative) errors
when using this modem in Class 2.0 mode.

In some cases the receiving fax machine was in our own location, so
line errors are unlikely.  I installed the Hylafax tag line patch to
eliminate that bug as a potential cause but the problem continued.

I found that using the modem in Class 2 (rather than Class 2.0) mode
has eliminated this problem.  We have now sent several hundred faxes
in Class 2 mode with only one RTN error failure.  The logs show that in
Class 2 mode there is an extra handshaking step at the end of a page
which is not present in Class 2.0 mode.  Perhaps this extra step
avoids some timing problem present in the Zyxel Class 2.0 firmware.

I found other reports of the RTN problem in the mailing list archive, 
but no reported solution.  Perhaps the information on the Hylafax web 
site about the Zyxel U-1496E should be updated to suggest using Class 2 
mode with this modem.