[asterisk-users] Problems receiving some faxes in T.38

[David Backeberg]

On Wed, May 20, 2009 at 6:58 AM, Santiago Gimeno
<santiago.gimeno at gmail.com> wrote:
> We have been working with the ReceiveFax application for some weeks now in
> order to receive faxes in T.38 and it works fairly well, but there are some
> faxes that for some reason we are not able to receive correctly.
>
> The asterisk version we are using is 1.6.0.6 with spandsp-0.0.5pre4 and the
> asterisk machine is behind a CISCO mediaGW to be able to communicate with
> the PSTN.

That's very similar to a setup I made. And I was troubleshooting
similar problems. Let me ask you a question:

Are you quite confident that the inbound faxes that fail are going to
succeed on an ordinary fax machine?

In my case I was able to crank through my logs, and trace that the
failing calls were people who were calling a fax line by mistake, or
wardialers, or clients with lousy fax configurations where those faxes
also fail to our 'real' fax machines.

When we stopped counting the 'never going to work anyway' faxes in our
fax success calculations we had nearly perfect success rates.

And here's my debugging tip. Pick a number that always fails, change
the Cisco dialpeer to send those as ordinary audio fax passthrough, no
t.38, use asterisk with monitor to record them, and watch whether they
ever succeed. I'm willing to be my two cents that they don't.