[Asterisk-Users] TxFax: can't get a fax to destination (log inside)

[Lee Howard]

Steve Underwood wrote:

> TxFAX is doing the right thing, according to the spec. If you don't 
> know how to handle RTN you should disconect. spandsp has not yet been 
> taught how to retrain and retransmit properly.


Okay, so it's not an error.  It's an unimplemented feature.  :-)

> However, this is largely irrelevant. On modern lines a retransmit 
> should be rare.


Yes, agreed.  On a digital receiver I've seen it only 5 times in the 
last week of 672 applicable (non-ECM) faxes... although those statistics 
may be skewed due to the receiver supporting ECM (the vast majority of 
faxes -  - were received with ECM).

> Lately lots of people are reporting this problem to me, and I have not 
> had time to investigate why it happens. Some say it happens with 
> specific machines, and some with all machines.


One of the nice things about ECM is that it generally gives a very 
accurate picture of any Phase C data corruption, and that can help lead 
to an understanding as to the nature of any problems.  It's helped me 
find modem flow-control problems as well as modulator flaws that were 
causing the modulator itself to generate interference.  You may want to 
try running some faxes through your unicall T.31 modem to/from HylaFAX 
to see if the error lies within the common underlying interfaces, or 
whether or not it is something specific to txfax or libtiff.

Lee.