[Freeswitch-users] Proxy media mode with T.38 re-invite

[Gabriel Kuri]

AFAIK T.38 v2 supports a max speed of 14.4 anyhow, so that's the max
speed you'll ever see in the SDP. T.38 v3 supposedly supports v.34
speeds, however no one that I've seen has implemented it yet - not sure
it's even an official standard?

Yes, in my experience, v.34 capable FAXes do not properly negotiate down
to 14.4 speeds, we've always had to disable v.34 (or whatever the option
is called on your particular make/model to force it down to 14.4 or
slower speeds). We use the Cisco/Linksys ATAs - I've heard there's
better ATAs out there that properly negotiate the FAX down to 14.4 on
the T.30 side of the connection, but never had a chance to play with them.

I'd certainly be interested to hear anyone's experience with T.38
reliability and various combinations of FAX machines and make/model of ATAs.

Gabe

Kristian Kielhofner wrote:
> Gabe,
> 
>   I don't think any of them are plus the T.38 SDP tells me the bitrate
> is 14400, certainly not V.34 speed.
> 
>   Are you saying the machine even trying to negotiate V.34 poses a problem?
> 
> On Thu, Oct 22, 2009 at 2:16 PM, Gabriel Kuri <gkuri at ieee.org> wrote:
>> Out of curiosity, is it a Super G3 (ie v.34) capable FAX? We've had
>> nothing but intermittent problems with Super G3 FAXes over T.38, unless
>> v.34 is strictly turned off on the machine.
>>
>> Gabe
>>
>