[VoiceOps] VoIP T38 Fax reliability

Carlos Alcantar carlos at race.com
Wed Jan 6 22:18:40 EST 2010

Send and pray that what we say with faxing over voip lol.

Carlos Alcantar
Race Telecommunications, Inc.
101 Haskins Way
South San Francisco, CA 94080
P: 650.649.3550 x143
F: 650.649.3551
E: carlos at race.com

-----Original Message-----
From: voiceops-bounces at voiceops.org
[mailto:voiceops-bounces at voiceops.org] On Behalf Of Alex Balashov
Sent: Wednesday, January 06, 2010 6:36 PM
To: voiceops at voiceops.org
Subject: Re: [VoiceOps] VoIP T38 Fax reliability

On 01/06/2010 07:15 PM, Gabriel Kuri wrote:

> 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.

Agreed about T.38 vs. analog pass-through.

> 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.

There's been an enormous explosion of Super G3 machines in the last few 
years;  asking users to disable SG3 is not really tenable.

Fax over IP is one of those things that, like anything else, can be 
gotten to work passably with enough spiritual commitment.  But it's just

not worth it.  Hand the customers some resale analog lines or what have 
you and be done with it.

Alex Balashov - Principal
Evariste Systems
Web     : http://www.evaristesys.com/
Tel     : (+1) (678) 954-0670
Direct  : (+1) (678) 954-0671
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