[Asterisk-Users] Re: Asterisk in production as a fax server, anyone?

[Craig Guy]

In practice I've found that the fax receiving process is sensitive to CPU 
load.  If the load jumps too high you will see half page fax pages or black 
streaky pages mixed with perfectly good pages in a multipage fax.  Things 
that can cause this include running agi scripts or rendering your tiff to 
another format on your * server.

I render my faxes on the * server, however received tiffs are queued so as 
to render them one at a time.  If you get page problems you could try 
rendering them on a dedicated server.

Craig

----- Original Message ----- 
From: "Lee Howard" <faxguy at howardsilvan.com>
To: "Asterisk Users Mailing List - Non-Commercial Discussion" 
<asterisk-users at lists.digium.com>
Sent: Friday, March 31, 2006 3:05 AM
Subject: Re: [Asterisk-Users] Re: Asterisk in production as a fax 
server,anyone?


> 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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