Asterisk and Double DTMF Digits Issue

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Asterisk Users 3 Comments

I’ve been getting complaints lately that callers to my IVR are pressing a digit once but the system is responding as if they pressed it twice (once for each of two consecutive menus). I’m using an AGI script and logging all DTMF entries – and to the script, at least, it looks like the digit is being pressed twice. The TN being called is a VOIP number (provided by Flowroute) and being forwarded via SIP to my Astersisk server The dtmfmode is set to rfc28333 in sip.conf.

The first time this happened, I figured the caller pressed the number twice without realizing it. It’s happening to too many people for that to be plausible anymore. I also experienced it once myself, months ago, when I entered my tn as 1234567890 and had it read back to me as 1122334455.

Can anyone give me some pointers where to start troubleshooting? Can overloading a system cause such an error?


3 thoughts on - Asterisk and Double DTMF Digits Issue

  • I have seen this before. Upon careful analisys we saw that the far end
    was sending the digits in RFC2833 plus SIP INFO (or Inband, I can’t
    remember). Thus Asterisk detected double digits. The solution was to
    ask the remote end to only send RFC2833.


  • We’ve actually had issues with Flowroute in the past where DTMF was a
    constant issue. My best suggestion for course of action is find another
    provider. NexVortex is pretty solid all around. They also had the quickest
    recourse for when GNAPS went bottoms up last month and sent pretty much all
    VoIP traffic in New England into a tailspin.