[Asterisk-Users] RFD: With echo and other distortion, can ulaw/alaw line quality ever be good enough for faxing?

[Ryan Thrash]

Still way to early to tell any definitive results, but here's my 
preliminary observations:

1) Forget faxing through an ATA for now. If you need echo canceling for 
voice quality, it kills faxing. Otherwise, you can get faxing to work, 
sometimes with echo canceling turned off. It would be nice to 
enable/disable echo canceling on a per extension basis instead of 
globally (think 100 DIDs on 23 channels...).

2) PRI T1 -> T100P -> TDM10B -> Analog fax appears to work fine with 
minimal configuration!

I'd be interested in working/testing the fax side of the equation. It 
really *should* work in Asterisk. I find your comment below about echo 
canceling changes particularly interesting. We have multiple daily 
complaints of echo at the office, despite the fact that voice calls 
come in on a T1 PRI. The theory as I've been told is that you 
*shouln't* need echo canceling with a T1. My experience is totally the 
opposite. I wonder if there's something I could get Allegiance to 
tweak? I feel for you on the tech support response... got a very 
similar one myself.

HTH,
Ryan Thrash

On May 5, 2004, at 2:35 PM, Darren Nickerson wrote:

> Folks,
>
> The silence was deafening ... I had a few private replies but overall 
> I'd
> have to conclude that most people on this list aren't interested in 
> faxing
> thru Asterisk. You're all probably jazzed about VoIP and fax is 
> forgotten
> for now ;-)
>
> We have learned the answer to _one_ of the questions I asked below - 
> the
> Adit channel bank's gain controls can be usefully applied to adjust 
> each of
> the incoming telephone lines independently, and by combining the 
> Adit's gain
> setting with Asterisk's, fun and good things can be made to happen ;-)
>
> Another interesting observation is that echo can be seen visually when 
> using
> ztmonitor. Muting one side of the call (the RX side), and speaking 
> from my
> handset I can see my voice appear stongly on the TX side, and then I 
> can see
> the echo appearing on the RX side at an attenuated level, but it 
> follows my
> voice perfectly ;-)  I spend half a day talking to myself, and I have 
> to
> say, for the first time in ages I was running out of things to say! :-)
>
> In other interesting news, updating zapel from CVS seems to have made 
> things
> significantly better. I had CVS from about 4 weeks ago previously, so
> perhaps something was amiss. We can actually get faxes transmitting 
> now, and
> although they fail about 30% of the time, this is definitely progress.
>
> Another data point, is that MARK3 echo cancellation is audibly worse 
> under
> our particular conditions. We're using MARK2 with the aggressive option
> enabled, and while occasional flares of distorted (but attenuated) 
> echo can
> be heard, it's much easier to have conversations with customers! I'm
> disappointed nobody commented on the echo cancelation options in the
> source... I can only assume nobody actually knows the origins of any 
> of them
> any more, and the other ones are mostly anachronisms that are no longer
> useful, and MARK2 is the clear winner.
>
> Unfortunately, the news from Digium's technical support is not good. 
> Here's
> what they had to say in response to our inquiry about faxing:
>
> "Faxing in asterisk is only at varied levels of support and is
> definitely not at a production level.  However, if you wish to work on
> this we wouldn't mind at all :-).  The source code is of course free
> to your disposal."
>
> I'm not sure I understand that this support rep is saying to me ... 
> we've
> had much success faxing from one PRI to another with them both 
> connected to
> Asterisk via a TE400P. Asterisk doesn't even break a sweat. We're 
> rarely
> getting the theoretical maximum of 33,600 that we can get with a T1 
> loopback
> though, so something's slightly amiss, but it's only when we try to go 
> out
> to the PSTN that things start to fall apart badly.