Adolfo R. Brandes wrote:
Lee Howard wrote:
The concurrent calls really isn't that big of a deal, either, if
those are your thoughts. The bigger issue seems to be the quality of
the audio as it is delivered to the fax application/modem.
Interesting. The little information I've found on the subject
seemed to imply that Asterisk couldn't handle more than a handful of
fax calls using software DSP. This could also be explained away by
frame slips too, right?
I don't know what a "handful" means, but fax audio is audio just the
same. If Asterisk can handle 30 channels of G.711 then it can handle 30
channels of fax audio. As for the fax application being able to handle
it, I know that HylaFAX can handle it; I'm quite certain that iaxmodem
could; and I suspect that txfax/rxfax could, but I don't know.
The fabled "frame slips" could account for any number of fax-related
problems that users report. Whether or not these things should really
be called frame slips is debatable, but I believe that's how the core
part of Asterisk sees it - kind of like jitter occurring on a PSTN line.
I had begun to get the impression that Sangoma cards were overall
better cards than Digium's. It seems that's not necessarily the case.
Well, the hardware itself is better, yes, from what I understand. But
in my experience that difference doesn't solve the "frame slipping"
issue with the problematic motherboards.
The most success I've seen has been to bridge the call through
Asterisk to a T1 fax modem such as a Patton 2977 or an Eicon Diva
Server with HylaFAX running the modems.
Now THAT is a very good idea! To us, it means that if push comes
to shove, there is a certain method for having IVR and reliable faxing
available during a single call. Thank you! But just to make it
clear, woudn't frame slips enter the picture here too?
If there is "frame slipping" on the Asterisk bridge, yes, that could be
a problem, too. But in the deployments that I've used there was no
so-called frame slipping occurring, so faxing through that bridge was
just fine.
But, if you're referring to "frame slipping" occurring on the fax
modem... no, I've never [ever] seen that happen with either the Patton
2977 or the Eicon Diva Server (or any of a slew of analog multi-modem
hardware)... regardless of motherboard type or sharing of IRQs. I
really do tend to believe that the "frame slipping" problem is with
either the Zap hardware or the Zap driver. I don't know how much common
hardware there is between the Sangoma and the Digium hardware, but I
don't suspect much is common these days, and thus I would tend to look
at the zap drivers first as culprits.
Lee.
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