Anyone have a reliable T.38 Solution

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We are looking to roll a solution that will have the following network layout:

ISDN-PRI < --> Asterisk < --> T.38 < --> ATA < --> Fax

Does version 1.8 with the Digium fax driver have this capability? I
like 1.8 because it is a long term support version.

What ATA’s are people using?

Any working solutions would be great!


16 thoughts on - Anyone have a reliable T.38 Solution

  • I’m using the Linksys PAP2T and the Grandstream with SpanDSP and tx_fax and rx_fax on multiple installations with no problems.

  • What you are looking for is T.38 gateway mode (converting between T.30
    over modems on a TDM circuit and T.38 over UDPTL), and the answer is no:
    Asterisk 1.8 does not have T.38 gateway mode. Asterisk 10 does, and it
    is supported using SpanDSP and res_fax_spandsp. It is not yet supported
    by Digium’s Fax for Asterisk commercial FAX module.

  • On Wed, Jan 4, 2012 at 1:02 AM, David Klaverstyn


    Are you running 10.0 or 1.8?

    Glad to know that the PAP2T has a solid T.38 implementation!


  • I’m using 1.8, but also have 1.4 and 1.2 installs using the same configuration.


  • we are using such a setup:

    Telco < -PRI-> bero*fixBox < -BRI-> Fritz!BoxFon < -analog-> FaxMachine
    +–< -SIP-> Asterisk < -SIP-> Phones
    +– t38modem < -tty-> Hylafax

    The bero*fixBox is has
    one ISDN-PRI and 4 ISDN-BRI ports. The PRI-port is connected to the
    telco, one of the ISDN-BRI ports is connected to an old Fritz!Box Fon which has
    3 (newer ones only 2) analog ports.

    The calls are routed by the bero*fixBox to either the asterisk server or
    the hylafax server based on the DID number.
    The bero*fix box has ~30 softmodems that translate to T.38-SIP which is
    then connected to the t38modem on the hylafax server which handles
    around 70,000 faxpages a month.
    Outgoing (incoming only for test purposes) faxes from our analog fax
    machines are routed by our asterisk server back to the bero*fix box so
    we achive bit-slip-free (and therefore reliable) connection.

    Beronet also has PCI- and PCIe-cards to be directly installed in your
    asterisk server.


  • No PAP2 or PAP2T supports T.38, even though many people will swear that
    they do. For a little while there was some beta code for the PAP2T with
    badly broken T.38 support. Perhaps this is where the “legend of T.38 on
    a PAP2T” started. Of course, on the internet, when someone posts an
    incorrect message many people would like to believe is right, a 1000
    people cite it as proven fact.


  • Thanks for clearing that up. I was getting all excited that I could
    flash the PAP2T; I’ve always used regular voice tones over SIP with
    the PAP2Ts.

  • David Backeberg writes:

    SPA-2102 supports T.38. If you ignore the WAN-port, it is practically a
    PAP2T. The only time you cannot ignore the WAN-port is when doing


  • I ignore the LAN (yellow) port and only use the WAN (blue) port. The LAN
    port has a DHCP server enabled by default. The WAN port is setup with a
    DHCP client. The good thing about using the WAN port is if the settings are
    cleared you won’t have an unknown DHCP server on your network.

    I plug a phone in and dial the below. Then you can configure the rest from
    the web interface.

    **** to enter admin ivr
    7932 enter 1 to enable web interface
    110 will read the WAN address


  • 2012/1/5, Kevin P. Fleming :

    Do you have any idea when Digium’s Fax for Asterisk commercial FAX
    module could roughly become supported ?

  • 2012/1/11, Steve Underwood :

    Not yet ;-)))))))))))
    But the increased fax sending speed (14.4 kbs/s says the datasheet but
    I must be too naive to still read datasheets) may be a feature
    interesting for some.

    By the way, which spandsp version would recommend for asterisk 10 ?
    spandsp-0.0.6pre18.tgz ?

  • There are currently no modem speed differences between res_fax_spandsp
    and res_fax_digium. Both support all commonly-used FAX modems except
    V.34. We do not currently have an estimate on when Fax For Asterisk will
    support T.38 gateway mode (or V.34, for that matter).

  • How is 14.4k an increase? Both spandsp and the Digium modules do 14.4k.
    There is nothing the Digium module does which spandsp does not do, and
    the file handling in spandsp is more flexible.

    spandsp-0.0.6pre18.tgz is currently the right version to use?


  • I didn’t know spandsp could do 14.4k : that’s great !
    So, now I’m realizing how strange my previous question could resonate.

    Thanks for clarifying this.

    2012/1/11, Steve Underwood :