<html><head><meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0"></head><body>I've also had mixed luck with t.38, but the t.30 fax standard allows only 3 errors; after the third error is detected, the fax is to be cancelled. <div><br></div><div>But working to make t.38 work is worth the effort. The networks have to be phenomenally clean to have a reliable faxing service that works all the time:<br><div><br></div><div>If you're doing 10 pages at 28800 bps, that'll take 350 seconds, and tolerate no more than 0.017% packet loss. That's an unusually clean network. </div><div><br></div><div>If the fax is slower, e.g. 9600 bps, the fax is longer (600 seconds at 9600 bps), so the exposure to errors is greater and the network reliability requirement is higher -- <=0.01% loss allowed. </div><div><br></div><div><span style="background-color:rgba(255,255,255,0)">This assumes errors are randomly distributed; if they come in clusters the requirements are much stricter.</span><br></div><div><br></div><div><br></div><div><br><br>---<div>Mark R Lindsey <div><a dir="ltr" href="mailto:mark@ecg.co">mark@ecg.co</a></div></div><div><a dir="ltr" href="tel:+1-229-316-0013">+1-229-316-0013</a></div><div><a dir="ltr" href="http://ecg.co/lindsey">http://ecg.co/lindsey</a></div><br><br><div>On Sep 30, 2016 at 18:18, Greg Lipschitz <<a href="mailto:Greg@thesummitgroup.com.au" target="_blank">Greg@thesummitgroup.com.au</a>> wrote:<blockquote style="border-left-style:solid;border-width:1px;margin:0px;padding:0px 0px 0px 5px;border-color:#ccc">
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<div>Have you tried the opposite, disable T.38 and use G711a/u for the payload. </div>
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<div>We have had far greater success with the G711a/u RTP. T.38 still seems to be very hit and miss cross devices be it ATA or even a real fax machine. </div>
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<div>Cheers</div>
<div>Greg</div>
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<div id="x_divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> VoiceOps <<a href="mailto:voiceops-bounces@voiceops.org">voiceops-bounces@voiceops.org</a>> on behalf of Nelson Hicks <<a href="mailto:nelsonh@socket.net">nelsonh@socket.net</a>><br>
<b>Sent:</b> Saturday, October 1, 2016 4:47:30 AM<br>
<b>To:</b> <a href="mailto:voiceops@voiceops.org">voiceops@voiceops.org</a><br>
<b>Subject:</b> [VoiceOps] Problems with T.38 fax with Grandstream GXW-4248</font>
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<font size="2"><span style="font-size:10pt">
<div class="PlainText">We have a customer with multiple Grandstream GXW-4248 voice gateways
<br>
that wants to use T.38 for sending and receiving faxes. They are running <br>
the most recent release (1.0.5.16). We have tested this successfully <br>
with other devices, including a Grandstream HT-702 and a Grandstream <br>
GXW-4004, but when configuring the Grandstream GXW-4248 the same way, <br>
the audio from the Grandstream to the fax machine cuts out at the <br>
renegotiation to T.38 and does not resume. When looking at a packet <br>
capture of the fax call, the Re-INVITE appears successful, but the first <br>
and only UDPTL packet sent by the Grandstream is reported as malformed <br>
by Wireshark:<br>
<br>
ITU-T Recommendation T.38<br>
[Stream setup by SDP (frame 510)]<br>
[Stream frame: 510]<br>
[Stream Method: SDP]<br>
UDPTLPacket<br>
seq-number: 32768<br>
primary-ifp-packet<br>
type-of-msg: t30-indicator (0)<br>
something unknown here [too long <br>
integer(per_normally_small_nonnegative_whole_number)]<br>
[Expert Info (Warn/Undecoded): something unknown <br>
here [too long integer(per_normally_small_nonnegative_whole_number)]]<br>
[something unknown here [too long <br>
integer(per_normally_small_nonnegative_whole_number)]]<br>
[Severity level: Warn]<br>
[Group: Undecoded]<br>
[Malformed Packet: T.38]<br>
[Expert Info (Error/Malformed): Malformed Packet (Exception occurred)]<br>
[Malformed Packet (Exception occurred)]<br>
[Severity level: Error]<br>
[Group: Malformed]<br>
<br>
Does anyone have any experience with trying to use T.38 with a <br>
Grandstream GXW-4248?<br>
<br>
Thanks,<br>
<br>
<br>
-- <br>
Nelson Hicks<br>
Network Operations<br>
SOCKET<br>
(573) 817-0000 ext. 210<br>
<a href="mailto:nelsonh@socket.net">nelsonh@socket.net</a><br>
<br>
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