T.38 fax not quite working

Discussion in '3CX Phone System - General' started by instantexpert, Apr 22, 2011.

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  1. instantexpert

    Dec 2, 2008
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    After over 15 years of continuous operation, my old US Robotics Courier modem finally died. I went looking for the alternative to the old and, apparently, discontinued 3CX fax send driver. I don't need receive or routing service as MaxEmail does that for me for $9/month.

    I followed these instructions:

    After a bit of pain, I got it working through my Patton gateway but not through my NexVortex/Cogent VOIP line. I abandoned RelayFax because their licensing/costs were more than I wanted to pay. In additional searching, I found this product:


    They are difficult to setup on 64-bit windows due to driver issues but, once I sorted that all out, I now have a fax solution that integrates with the 3CX PBX and cost $111USD for the t38faxvoip product and $99USD for the Eltima virtual COM port. If anyone else tries this, DO NOT use the alternative Eterlogic port. Only the built in virtual com port (useful for 32 bit only) and the Eltima virtual com ports are supported for use with Microsoft Fax service.

    So, in the end, I have a system that functions for sending faxes through 3CX to my Patton gateway but when I try to send a fax through my VOIP line the call gets dropped. I have included the trace from NexVortex. Can anyone point me in the direction of solving this problem. Is it in the FaxVoip software (I had the same problem with RelayFax) or the 3CX PBX? FWIW, I'm using the latest v9 of 3CX.

    Thank you,

    reINVITE with T.38 was sent to your 3CX system and it didn't respond to the reINVITE with T38 codec. and as a result the request times out

    (time in GMT)
    U 2011/04/22 19:47:30.980869 ->
    INVITE sip:13122558757@ SIP/2.0..Record-Route: <sip:131225
    58757@;nat=yes;ftag=gK0bda9f72;lr=on>..Record-Route: <sip
    :;lr=on;ftag=gK0bda9f72>..Via: SIP/2.0/UDP;b
    ranch=z9hG4bKe1ae.9405e66.0..Via: SIP/2.0/UDP;branch=z9hG4bKe1
    ae.3b1aed95.0..Via: SIP/2.0/UDP;branch=z9hG4bK0bBa1813b5e
    0a32e9cd..From: <sip:13122558758@cogentvoip.com>;tag=gK0bda9f72..To: "DMC,
    Inc." <sip:13122558757@cogentvoip.com>;tag=a95af507..Call-ID: NGQxMmM3MTRjN
    mIzMTNmNTE4MmNmOGQ5ZmE5MTQ1ZTg...CSeq: 18920 INVITE..Max-Forwards: 16..Allo
    OPTIONS..Accept: application/sdp, application/isup, application/dtmf, appli
    cation/dtmf-relay, multipart/mixed..Contact: <sip:13122558758@
    :5060>..Supported: timer..Session-Expires: 3600;..m=image 28010 ud
    ptl t38..a=T38FaxVersion:0..a=T38MaxBitRate:14400..a=T38FaxRateManagement:t

    no response from the 3CX PBX and the reINVITE request times out and the call fails to complete. Please make sure your system is setup for T.38 codec for fax
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  2. davidbenwell

    davidbenwell Active Member

    Apr 27, 2010
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    does your VoIP provider support T.38?
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