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

[Peter Steinbach]

I have the same problem with a freeswitch GIT version ~ 1 week old.
A leg is a Patton resp. Hylafax via tty modem, B-leg is another Patton.

When the B leg offers T.38 by a reinvite:

  * Freeswitch sends a "trying"
  * the Freeswitch console shows the B leg's SDP with T.38
  * Then  nothing happens for ~30 sec
  * Then the B-leg cancels the request and the call is terminated.

Grepping the network traffic I can see that Freeswitch will never answer
the Reinvite request. This also happens if a leg is T.30 (hylafax tty
modem), so this is not a behaviour of forwarding the t.38 SDP to the
A-leg and waiting for an answer.

I saw a similar behaviour in http://jira.freeswitch.org/browse/FS-5181
but the solution there was to fallback to T.30.

Is there any solution so far or any hint how to overcome this?

Best regards
Peter



On 06/02/11 19:57, Anthony Minessale wrote:
> start by proving them and post them in a jira with full console traces
> with sofia global siptrace on and pcaps etc
>
> then wait for us to get to them or email consulting at freeswitch.org for
> expedition
>
> On Wed, May 25, 2011 at 11:56 AM, Rob Morin <rmorin at blie-ent.com> wrote:
>> Thank you.
>>
>>
>>
>> So, I believe that there are two potential problems, fixing either of which
>> will allow me to send faxes.
>>
>>
>>
>> 1.       When T.38 is enabled in passthrough mode and the B leg offers T.38,
>> Freeswitch needs to forward the invite and the responses. Currently it isn’t
>> forwarding the response back to the B leg.
>>
>> 2.       When T.38 is not enabled and the B leg offers T.38, Freeswitch
>> needs to respond with a 488 indicating T.38 is not acceptable.  Currently it
>> doesn’t respond at all.
>>
>>
>>
>> How would I go about making or requesting these fixes?
>>
>> Thank you,
>> Rob
>>
>>
>>
>> From: David Ponzone [mailto:david.ponzone at ipeva.fr]
>> Sent: Wednesday, May 25, 2011 11:11 AM
>>
>> To: FreeSWITCH Users Help
>> Subject: Re: [Freeswitch-users] Faxing problems if B leg offers T.38
>>
>>
>>
>> Rob,
>>
>>
>>
>> On my test box, I run a GIT from 05-02, and I don't have any issue.
>>
>> But I just did the test, and the call flow is different from yours.
>>
>>
>>
>> When I send a fax with my endpoint (Zoiper Softphone), I got the remote fax
>> tone, and then my Zoiper sends the T38-REINVITE, not the remote gateway.
>>
>> So I guess there are 2 possible call flows, because I remember in some
>> circumstances, the remote sends the RE-INVITE.
>>
>>
>>
>> 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  -   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 25/05/2011 à 13:18, Rob Morin a écrit :
>>
>> Is the fact that I was previously running the snapshot from 25 March
>> adequate to meet this test?
>>
>>
>>
>> From: Rob Morin [mailto:rmorin at blie-ent.com]
>> Sent: Tuesday, May 24, 2011 10:50 AM
>> To: 'FreeSWITCH Users Help'
>> Subject: Re: [Freeswitch-users] Faxing problems if B leg offers T.38
>>
>>
>>
>> I can, if someone can tell me where to get the snapshot.  I looked
>> at files.freeswitch.org and didn’t see one.
>>
>>
>>
>> Prior to updating to the 5-17 snapshot, I was having the same problems with
>> the 3-25 snapshot that I was using.
>>
>>
>>
>> Thank you,
>>
>> Rob
>>
>>
>>
>> From: David Ponzone [mailto:david.ponzone at ipeva.fr]
>> Sent: Tuesday, May 24, 2011 1:47 AM
>> To: FreeSWITCH Users Help
>> Subject: Re: [Freeswitch-users] Faxing problems if B leg offers T.38
>>
>>
>>
>> Rob,
>>
>>
>>
>> following Yehavi's comment, could you downgrade your GIT version to a
>> previous version, like one month old ?
>>
>>
>>
>> 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  -   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 24/05/2011 à 02:59, Rob Morin a écrit :
>>
>>
>>
>> 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-td3821994.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  -   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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>>
>>
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>>
>>
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>
>


-- 
With kind regards
Peter Steinbach 

Telefaks Services GmbH
mailto:lists (att) telefaks.de
Internet: www.telefaks.de

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