[asterisk-users] TDM Fax

[Steve Underwood]

On 08/17/2012 06:08 AM, Eric Wieling wrote:
> Has anyone experimented with increasing the DAHDI chunk size in improve fax reliability?  If so, did it help, hurt, or not make any difference?
>
I haven't found issues related to the DAHDI chunk size. The main thing 
which used to hurt FAXing with Asterisk before Digium launched their own 
FAX software was the timing within Asterisk, which they refused to fix 
at that time (although independent patches were available). With the 
launch of FFA they changed chan_dahdi so on a FAX call the buffering 
should change to make the flow of transmitted audio a lot more elastic. 
People just tolerate some hiccups in voice calls, but hate latency. 
Modem signals must be rigidly timed, but a bit more latency is OK. This 
change fixed the main issue affecting all the FAX solutions around. If 
that switch in the buffering mode is not happening on your system for 
some reason it can badly affect the reliability of FAXes.

Steve