To throw in my two cents, we've used SPA3102s that would register
directly to a remote 'fax' server using T.38 with limited success.
Seems like the majority of fax machines would work the majority of
time, but only on short faxes (less then a few pages). The more pages
you sent, the failure rate went up dramatically. We then looked at
AudioCodes devices. The MP2XX series proved to be much more stable then
the SPAs. On the SPAs, we had to make changes on most fax machines
(disable ECM, lower speed to 14.4kbps or less) that we did not need to
make on the AC. In addition, certain fax machines that we could never
get working on the SPAs worked great without any tweaks on the ACs. So
we're using the MP201,202,204 and even 208 for fax ATAs now. My only
pet peeve is that they do not provide any CPC loop disconnect. Even the
Crapstream ATAs would do this. All they can do is play a tone that
defaults to a fast busy but is user selectable. Has caused problems
with a few PBX systems. AudioCodes says they are working on a firmware
fix for this as the hardware supports it. Until that time, we are
looking at the better, albeit more expensive, 100 series which provides
it out of the box.
Personally, I've tested out faxes using an old Sunrocket ATA and G711,
and actually had some limited success with that as well.
-James
Tod Fitch wrote:
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.
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...
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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