[VoiceOps] VoIP T38 Fax reliability

Richey mylists at battleop.com
Wed Jan 6 21:04:02 EST 2010

We are having good luck with the Cisco 2431 and Adtran TA900 series with
faxing.    We won't touch faxing if the customer is not OnNet with us.
The best success is if you have A to Z control of the customer's connection.


-----Original Message-----
From: voiceops-bounces at voiceops.org [mailto:voiceops-bounces at voiceops.org]
On Behalf Of Gabriel Kuri
Sent: Wednesday, January 06, 2010 7:15 PM
To: Ujjval Karihaloo
Cc: voiceops at voiceops.org
Subject: Re: [VoiceOps] VoIP T38 Fax reliability

It seems to be hit and miss, certainly not 100%, but better than trying to
use either PCMU or PCMA over the commodity Internet for FAXing. PCMU/PCMA
might work over a local private LAN with QoS enabled and the jitter down to
almost nothing. The biggest issue I've seen with T38 is the ATA's inability
to properly negotiate a Super-G3 fax down to G3 or slower speeds. In our
experience, you need to disable the Super-G3 feature of the FAX machine to
slow it down to either 14.4 or 9600 and disable ECM. Many of the newer FAX
machines have a "VoIP Compatibility" mode which essentially slows it down to
9600 and disables ECM.

We predominantly use Cisco/Linksys/Sipura ATAs, but would like to hear if
anyone has better experiences with other ATAs, particularly in business
environments where there's potentially a lot of FAXing.


On Wed, Jan 6, 2010 at 6:00 PM, Ujjval Karihaloo <ujjval at simplesignal.com>
> I know this a thorn in everyones flesh, I would like to know of 
> experiences with T38 Voip Faxing. We have had good and bad. Those that 
> don't work just don't and they don't even want to troubleshoot and 
> just switch over to an Analog line for Fax. We mostly use AudioCodes and
Sipura T38 ATAs.
> Any of you folks do T38 and whats the experience like.
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