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  • Sip Trunk and Multitech FaxFinder

    We recently upgraded from PRI/T1 links to a SIP trunk for our provider. In the process of upgrading we lost the ability to receive inbound faxes (for the most part) to our fax finder. It appears a fax will successfully go through at random points but I would say this is 1 out of every 100 faxes. My question is does anyone have a similar setup with an internal fax server using SIP for a provider? If so is there anything special that needs to be setup for faxing?

    FaxFinder - FF240-IP.Rx - Firmware 5.1.6.6
    Mitel Connect - Build:21.86.1828.0

    We also confirmed with our provider that they have enabled T.38 on our connection.

  • #2
    When the faxes fail where do they go? Depending on the type of failure it would change where you look.
    Lance Paddock
    BTX | Business Telephone eXchange
    1(800) 289-0299

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    • #3
      SIP trunks (Telco) and faxes are notorious for failures. So much so that last company I worked for made no guaranties on Fax transmissions on SIP trunks. We strongly suggested using a PRI for fax. I have spent countless hours working with TAC on these issues and TAC basically came back with the same thing, that it is a best effort on these.

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      • #4
        Lance We have had various error messages while tweaking settings with our support partner.
        This is what I have seen so far:
        Normal busy detected
        ResultNegFailed
        ResultNoFax
        Bad destination address
        Null Null

        After doing packet captures with both our provider and Mitel partner they seem to think that the problem lies with a protocol mismatch problem. The strange thing is from what they told us is that they forced it to use just one protocol and they are still negotiating with a different one in the packet capture.


        Soulsanctu I have read this in more than one forums across the internet and am beginning to see why.

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        • #5
          I ended up figuring this out and had a few things going.

          1. The SIP traffic wasn't statically natting back to the provider properly, we had a firewall rule superceeding the rule for the nat that was sending traffic out a different interface then it was sourced from.
          2. The carrier did not have T.38 enabled on our connection.

          Once we fixed these two things faxes started working.

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