[VoiceOps] FAX over VOIP networks

[Brent Paddon]

I've spent more time playing with fax over IP networks than I would care to
remember.  Here's what we ended up doing (in Australia anyway).

Typically we use cheap little linksys PAP-2T ATA's and have found these to
work perfectly.

1/ ensure there is as low a latency as possible and zero jitter.  We run QoS
on private tails so this isnt too hard.
2/ we dont run T38 but instead ensure that all codecs in use along the
entire path are g711A (711A is the PSTN standard here)
3/ Ensure there is NO transcoding going on anywhere - even between 711u and
711a - this will break faxing if there is
4/ In the linksys PAP-2T the FXS port gain settings need changing from
defaults - we've found -1.5db to work well

This last bit has been very important, otherwise for us the Linksys was
providing too 'loud' a signal to the fax machine and would break faxing
after say a page or two max.   Using these settings, we have customers who
send long (15-20) page faxes regularly with no problems.  Additionally so
far we havent had to change any fax machine settings, presumably the fax
machines are simply training down to a speed they are happy with but we
haven't spent much time looking at what they do in this regard - faxing
works and thats all we cared about.

Brent

On Sat, Aug 29, 2009 at 3:03 AM, Scott Berkman <scott at sberkman.net> wrote:

>  Agreed.
>
>
>
> The key really is g.711 (usually u-law) and low (read no) latency/jitter
> unless you can fully interop T.38 across the network.  Most fax machines
> will auto-negotiate to the lower speeds when needed, but low to middle end
> Brother machines may be a major exception as they often have a poor T.30
> implementation.
>
>
>
>                 -Scott
>
>
>
> *From:* voiceops-bounces at voiceops.org [mailto:
> voiceops-bounces at voiceops.org] *On Behalf Of *Kenny Sallee
> *Sent:* Friday, August 28, 2009 12:06 PM
> *To:* voiceops at voiceops.org
> *Subject:* [VoiceOps] FAX over VOIP networks
>
>
>
> So the last thread on T38 made me want to start a thread on FAX over IP via
> an ATA or something like the Adtran TA900 series.
>
>
>
> From our experience, to be most successful w/ FAX over IP of any sort we've
> found that if you:
>
>
>
> 1.) Set baud to lowest setting fax can handle
>
> 2.) Lower print quality settings if possible
>
> 3.) Make sure to force G711
>
> 4.) Disable ECM and VAD on fax/modem tone detection
>
>
>
> And then cross your fingers fax's are successful and consistent.  Anyone
> else have other experiences or suggestions?
>
> Kenny
>
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>


-- 
--
Brent Paddon

Director | Over the Wire Pty Ltd brent.paddon at overthewire.com.au |
www.overthewire.com.au
Phone: 07 3847 9292 | Fax: 07 3847 9696 | Mobile: 0400 2400 54 | Direct: 07
3503 4807
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