$100 Bounty: Level3/Asterisk/Adtran T.38 Pass-through

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Asterisk Users 14 Comments

We are offering $100 (paid via paypal or check) to the first person who assists us in successfully sending and receiving faxes in the setup described below. Offer expires Dec 31. We are a direct customer of Level 3, there is no other carrier involved.

What we want to work:

Level 3 T.38 TN <-> MSX/Nextone SBC <-> Asterisk <-> Adtran NetVanta w/POTS and T.38 support.

When we replace Asterisk with Kamailio faxes work fine. When we put Asterisk there instead, then faxes fail nearly 100% of the time.

I see the switch to T.38 in the Adtran debug logs. We can originate and terminate T.38 calls in Asterisk using SendFax/ReceiveFax using T.38 so I’m assuming I have my udptl.conf and sip.conf settings correct.

14 thoughts on - $100 Bounty: Level3/Asterisk/Adtran T.38 Pass-through

  • Have you configured the canreinvite=yes in sip peer?

    I am currently off work for two days, but a 100% fail means a configuration problem for sure.


    2012/12/27 Eric Wieling

  • We have set directmedia=yes as well as directmedia=no. There is no NAT involved.

    —–Original Message—

  • We have directrtpsetup=no because the comments in the sample config indicates it does not work in all situations.

    —–Original Message—

  • Last thing to check, just for sanity’s sake:

    t38pt_udptl=yes in sip.conf? It defaults to off.

  • We are using t38pt_udptl=yes,redundancy,maxdatagram@0 Without the maxdatagram we get errors in the CLI. We also tried using FEC instead of redundancy, but no difference.

    —–Original Message—

  • In udptl.conf try the following option

    ; Some VoIP providers will only accept an offer with an even-numbered
    ; UDPTL port. Set this option so that Asterisk will only attempt to use
    ; even-numbered ports when negotiating T.38. Default is no. use_even_ports = yes

    Looking at some old notes other options I set for some devices to be able to pass through T.38 in sip.conf were,

    directmedia=no t38pt_udptl=no

    May be worth checking the following;



  • .


    Hmm, the t38pt_udptl will need to be set to yes, this was set to no for non T.38 capable devices

    I had set faxdetect=no in the peer’s configuration for the T.38 capable device, perhaps this was to prevent an attempt by Asterisk to redirect the call to the fax extension in the dialplan.


  • udptl.conf settings:

    udptlchecksums=no udptlfecentries = 3
    udptlfecspan = 3
    use_even_ports = yes T38FaxUdpEC = t38UDPRedundancy T38FaxMaxDatagram = 400

    sip.conf settings:

    directmedia=yes faxdetect = no t38pt_udptl=yes,redundancy,maxdatagram@0

    —–Original Message—

  • I know you’ve said you tried it both ways, but consensus seems to be that directmedia needs to be =no when using UDPTL.

  • From memory when I was doing this in March 2011 Asterisk would not allow a T.38 connection to successfully establish when canreinvite was set to yes, I did have NAT involved in my testing hence T.38 would be successful when canreinvite=no, the options to use now seeing as canreinvite is deprecated are;

    directmedia=no direcrtpsetup=no

    The T38Fax… options you have in udptl.conf are no longer supported.

    I have the T.38 Fax Gateway patch applied to my installation of
    though I don’t believe this will make any difference as I had got my T.38 relaying working prior to the patch.

    I have in my sip.conf;



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