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<p class=MsoNormal><span style='color:#1F497D'>Correct, I have been able to get
around INVITE glare etc…by tweaking ATA configs, however the problem mainly
lies in UDPTL T3/T38 signaling in the RTP, E.g. TAs keep sending no signal msgs
to the Provider and they don’t sends a DIS back and it then just re-invites for
G711 Pass-though…and that never works…<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'>I have also seen FCS-BAD (HDLC
frame signal) coming from the Provider when UDPTL data is sent.<o:p></o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Justin Randall
[mailto:jrandall@comwave.net] <br>
<b>Sent:</b> Thursday, January 07, 2010 10:40 AM<br>
<b>To:</b> Ujjval Karihaloo; voiceops@voiceops.org<br>
<b>Subject:</b> RE: [VoiceOps] VoIP T38 Fax reliability<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:blue'>Faxing over T.38
from experience has certainly been a better experience than over G711u
bypass. Of course there are some implementations of T.38 that
interoperate with each other better than others. My experience with
AudioCodes, Linksys/Sipura, and Grandstream has been very positive.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:blue'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:blue'>One of the common
potential problems with either approach is the behaviour of the signaling in
response to which end (caller, callee, or both) of the session is responsible for
initiating the re-INVITE for T.38. When supporting wholesale customers it
is not always possible to configure the behaviour of the ATAs/IADs and the only
way to ensure fax will at least always be “detected” is to have one of endpoint
gateways/ATAs/IADs detect fax as the caller and the callee. The next fun
piece to tackle once that’s configured is to ensure that all endpoints properly
support handling SIP 491 Request Pending response codes to avoid a race
condition which can cause INVITE “glare” if one endpoint is configured to
detect faxes and re-INVITE for both caller and callee and the other is set to
detect faxes and re-INVITE on either.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:blue'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:blue'>Regards,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:blue'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:blue'>Justin<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.0pt;color:blue'><o:p> </o:p></span></p>
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<hr size=2 width="100%" align=center>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
voiceops-bounces@voiceops.org [mailto:voiceops-bounces@voiceops.org] <b>On
Behalf Of </b>Ujjval Karihaloo<br>
<b>Sent:</b> Wednesday, January 06, 2010 7:01 PM<br>
<b>To:</b> voiceops@voiceops.org<br>
<b>Subject:</b> [VoiceOps] VoIP T38 Fax reliability</span><span
style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>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.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Any of you folks do T38 and whats the experience like.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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