If your VoIP provider is setup for T.38 then you may have an issue.
For in-bound faxes you are in control: If you don't allow T.38 then it
will stay with whatever codec you have negotiated. Which should be
g711. For out-bound faxes you are at the mercy of your VoIP provider's
setup. The receiving (provider's) side of the VoIP connection can
detect that a fax is being sent and attempt a re-invite using T.38.
The PAP2T does not support T.38.
I switched to using a Grandstream HT502 which claims support for T.38
but still haven't gotten it to work through my Astlinux box. My
provider claims better operation if you have the ATA directly register
with them. The Asterisk logging with debug on claims a rejected codec
but I don't know if that is Asterisk complaining or if it is my ATA. I
haven't yet bothered looking at the traffic with Wireshark to figure
out exactly what is going on.
Net result: If your provider does not do T.38 then you can probably
get faxes to work using the g711 codec. I have maybe a 95% fax success
rate with that type of operation. Not good enough for a heavy business
use but good enough for my needs. If the provider re-invites to T.38
then you may have a 0% success rate (my experience). I believe that
the specs call for graceful fall back to the voice codec if the T.38
invite fails but I haven't seen that happen (two different VoIP
providers). If anyone knows how to get this to work I would dearly
like to know.
-Tod
On May 27, 2010, at 6:34 AM, David Kerr wrote:
I should add that the PAP2T I have is one that I got through
Nextalarm.com which is customized to support alarm/security system
monitoring over the internet (VoIP). The ATA is customized to
connect one of the analog lines into their systems, the other line
is available to configure for my own use (after you get the admin
password from them). I mention this because it is possible that the
customization included work to improve the A to D conversion
process, not just hard wiring one of the lines to nextalarm's
systems...
https://nextalarm.com/do/customer/productDetail?id=17
David
On Thu, May 27, 2010 at 9:28 AM, David Kerr <[email protected]> wrote:
The answer is "it depends." I have had success with a fax machine
connected to a linksys PAP2T ATA and routing through vitelity as the
SIP trunk provider (with Astlinux in-between). I have had complete
failure with an older Linksys/Sipura SPA-2002 and the same SIP trunk.
I have both a PAP2T and SPA-2002 connected to my system and the
audio quality is noticeably better on the PAP2T. In particular
there is a lot of background hiss from the SPA-2002 that is not
present on the PAP2T. That may also suggest that the dynamic range
of the SPA-2002 is not as strong as the PAP2T. Both the background
hiss and a compressed dynamic range would explain why analog fax
does not work well.
In addition to good A to D conversion, which the PAP2T seems to
handle well, you then have to deal with the characteristics of SIP/
VoIP. You may have to fiddle with settings like jitter buffer and
echo cancelling and you want a high quality trunk provider.
Good luck.
David
On Thu, May 27, 2010 at 8:17 AM, Tom Chadwin <[email protected]
> wrote:
Slightly OT...
With an uncustomized 0.7.2 (1.4) on a net5501 with a berofix PRI,
what is
the easiest way to attach an analogue fax which currently uses one
DDI on
the UK PRI? Will an ATA work?
Thanks
Tom
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