[asterisk-users] fax / t38 gateway

[JR Richardson]

>  The folks that devloped the fax V.protocols took into acount typical
> copper problems like noise or echo. But what they never conceived of as
> even being possible is that a call might shift around in the time
> domain. Thanks to jitter/latency, the delay time of a call can change in
> the middle of the call. That isn't possible with copper technologies.
> This makes faxing over even G.711 a dice roll.
>
> IMO, with a sufficiently large buffer and a rock-solid quartz clocking
> system that goes way beyond what is typically seen, it might be
> theoretically possible to send a fax over VOIP.

Hi All,

This is a good discussion.  I can support most of the findings here as
I have recently spent a lot of time in the lab with T38 equipment from
several vendors.  Interoperability is a toss up, some ATA's only work
with the parent vendor gateways, some gateways are more forgiving and
work with Asterisk, some ATA's work straight out of the box, others
require a PHD to configure, etc.....

What I ended up with for a rock solid "ON-NET" T38 gateway to T38 fax
ATA is the Audiocodes Mediant 1000 with Audiocodes ATA's (MPXXX).  I
emphasis on-net because I control my environment end-to-end from
PSTN-Data Center-T1's-Customer-QOS LAN.  I was able to reliably push
100's of faxes, multi page, single page, high density, high
resolution, natted ATA's, various scenarios successful.

I was very excited about T38 and was convinced this was the solution I
would build on.  So I took one of the ATA's home to test over the
Internet (great connection, low hops to my datacenter, low latency,
low jitter, lots of bandwidth) and was very disappointed when I could
not get more than a 3 page fax through without errors.  I started
getting protocol and various page errors.  I tweaked every T38
parameter that Audiocodes had with zero improvement.

So I have to say, my confidence in T38 is very low, at least where
open Internet connections are being used.  I'm now going to look at
some other technology, fax over HTTPS.  I will be testing the FaxBack
products to see how they stack up.

JR
---------------------
JR Richardson
Engineering for the Masses