[Asterisk-Users] Fax

[Steve Underwood]

Jason Penton wrote:

>Hi All
>
>I have just a quick question regarding app_txfax for Asterisk. 
>
>When I send a fax from asterisk to a traditional fax machine connected to
>asterisk via the digium analog card everything works perfectly. However the
>same fax machine on the public telephoine network results in errors (looks
>like some sort of training error). 
>
>My asterisk box is connected to the pstn using an ISDN card. I don't mind
>trying to fix this myself but I am puzzled by the different behavior
>experienced when the fax machine is on the digium card and when it is
>connected to our public carrier, and therefore have no idea where to start.
>Would someone (Steve Underwood ;-) )mind at least putting me on the right
>track so I can address this issue?
>
>Thanks in advance Steve
>Jason
>  
>
I don't know why this would fail. An ISDN card should be properly 
synchrinised to the PSTN, and uses A-law or u-law. That should be enough 
to get a good path from the txfax program to the FAX machine. Do you 
have some kind of codec mismatch in your system? Can you try attaching 
an analogue phone in parallel with the FAX machine, and listen to the 
audio? You are probably familiar with how a FAX machine normally sounds, 
so you can probably recognise the bad distortion a codec issue would 
cause. The other thing to listen for is clicks. If there is a timing 
problem, and you have even a single sample slip in the audio stream, a 
modem will not work.

Regards,
Steve