Re: Low resulation : retrain negative

[Didier Gautheron <dgautheron@magic.fr>]

Hi

Michael Mller wrote:
> 
> --> [8:+FPTS: 2]                     # I normally get +FPTS: 3 =>ok
> --> [SEND recv RTN (retrain negative)# what does it mean exactly ?
> <-- [6:AT+FK\r]
> --> [9:+FHNG: 50]
> REMOTE HANGUP: Unspecified Transmit Phase D error
> ...
> 
It's easy for a fax to check the data received for conformity with T4.
and if quality is poor
in phase D (at the end of a page) the remote fax could answer :
RTP retrain positive: the page is ok but the remote fax wants to
renegotiate speed for next page
RTN retrain negative: the page is not ok and have to be retransmit after
speed renegotiation if (a big if) the local modem have the capability to
do it.

This problem - remote sends and RTN even when the page seems ok - isn't
uncommon.
May be a new option in sendfax could deal with it (i.e. don't resend on
a RTN ). 

We noticed this problem always on the same faxs with other problems
(class 1 modem):
remote fax is disconnecting without notice after training succeed.
black dots at the page's top
first lines are missing.
too many white lines at the top.

Looks like remote has problems with the first EOL.

And we're testing a workaround:
In T30 specs
>             Note 3 -  Transmission  of  signals  utilizing  the  modulation  system  of
>         Recommendation  V.21  channel  No.  2  should  be  followed   by   a   delay   of
>         75  20 milliseconds before the  signalling,  utilizing  a  different  modulation
>         system commences (e.g. the delay between DCS and  the  Recommendation  V.27  ter,
>        V.29, V.33 or V.17 training sequence).
>               Note 4 - The transmission of signalling utilizing  the  modulation  systems
>         of Recommendations V.27 ter, V.29, V.33 or V.17 should be followed by a delay  of
>         75  20 milliseconds before the  signalling,  utilizing  a  different  modulation
>         system, commences (e.g. the delay between RTC and MPS).
And HylaFAX does it

And in the "FAX MODEM SOURCEBOOK - WILEY" Andrew Margolis wrote 
> The latest version of T.30 includes a recommandation that there should be a wait of 75 ms after > receiving any T.30 signals before sending data at any of the higher speeds.
 So we do it we add a new delay (actually we are testing 2 things : a
delay after training succeed - in test -, and sending a stream of 1
after the second AT+FTM=96 - not tested yet -).

And all problems vanish (maybe) !