[Freeswitch-users] Faxing problems if B leg offers T.38

Tue May 24 04:59:24 MSD 2011

David,

It isn’t the ATA. I’ve tried both the Grandstream HandyTone 502 and
Cisco/Linksys SPA 2102. Same story in both cases.

I had my carrier help me troubleshoot and we can see the SIP request from
the carrier come in. When T.38 is enabled, it is forwarded to the A leg, but
the response from the A leg isn’t forwarded back to the B leg. I can produce
traces that show this. 

When T.38 isn’t enabled, the B leg is sending a T.38 reinvite. FS doesn’t
respond or forward it. So the connection dies.  I have every reason to
believe that I’d be able to send the fax if FS would respond with a 488
indicating T.38 is not acceptable. But instead, all I get is silence. Again,
I can produce traces that demonstrate this.

There’s another similar email  trail out there,
http://freeswitch-users.2379917.n2.nabble.com/T-38-via-UPDATE-request-td3821
994.html, but I’m not certain that they’re related.

Thank you for your help!
Rob 

From: David Ponzone [mailto:david.ponzone at ipeva.fr] 
Sent: Monday, May 23, 2011 6:11 PM
To: FreeSWITCH Users Help
Subject: Re: [Freeswitch-users] Faxing problems if B leg offers T.38

Rob,

perhaps you should not consider T38 is 100% interoperable.

You may tell us what ATA is that, because some of them are nice piece of
junk.

David Ponzone  Direction Technique

email: david.ponzone at ipeva.fr

tel:      01 74 03 18 97

gsm:   06 66 98 76 34

Service Client IPeva

tel:      0811 46 26 26

www.ipeva.fr <BLOCKED::http://www.ipeva.fr/>   -   www.ipeva-studio.com
<BLOCKED::http://www.ipeva-studio.com/> 

Ce message et toutes les pièces jointes sont confidentiels et établis à
l'intention exclusive de ses destinataires. Toute utilisation ou diffusion
non autorisée est interdite. Tout message électronique est susceptible
d'altération. IPeva décline toute responsabilité au titre de ce message s'il
a été altéré, déformé ou falsifié. Si vous n'êtes pas destinataire de ce
message, merci de le détruire immédiatement et d'avertir l'expéditeur.

Le 23/05/2011 à 20:51, Rob Morin a écrit :

I’m having problems faxing if the B leg offers T.38.  Several scenarios, but
always the same result.

First, the architecture

FAX à ATA (T.38 optional) à FS à Carrier  à Destination (Possibly another
carrier (PSTN) and the fax machine)

On my ATA, T.38 is enabled (Auto Detect).

If the destination supports T.38, the Carrier will offer it to Freeswitch.
If the Destination doesn’t support T.38, the B leg doesn’t offer it and the
faxes go through.

I’ve set Freeswitch as:

      <action application="set" data="fax_enable_t38=true"/>

      <action application="export" data="t38_passthru=true"/> 

When that’s the case, and the B leg offers T.38, Freeswitch passes through
the offer and the ATA responds, 3 times. But the response never gets sent to
the B leg, so it terminates the call after about 30 seconds.

When I set Freeswitch as:

      <action application="set" data="fax_enable_t38=false"/>

The B leg still offers T.38 if its other side is capable. Freeswitch doesn’t
pass the offer through and the B leg terminates the call after about 30
seconds.

I’m running on a recent git ( FreeSWITCH Version 1.0.head (git-86d757d
2011-05-17 22-51-47 -0500) ).

I’ve had no success attempting to configure FS as a gateway. Frankly, T.38
“passthrough” has had the most success, mostly when the other ends aren’t
T.38 capable and it stays in G711u.

Is there something else I need to do to enable T.38 in passthrough mode? 

Thank you,
Rob Morin

PS – I can provide tcpdumps of this, or whatever else is necessary.

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