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  1. #1
    Junior Member
    Join Date
    Oct 2005
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    12

    Default VOIP Phone Beeps!

    I am running a VOIP phone with Skype. It works well but beeps unpredictably whether I am using it or it's sitting unused. Very annoying and I have run out of ideas. Anyone know of this problem and a cure?

    Cheers

    pburt

  2. #2
    Shows no Fear
    Join Date
    Dec 2005
    Location
    Christchurch
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    34

    Question Re: VOIP Phone Beeps!

    Do you use BroadBand or Dailup ??

    If you use dailup do you have call waiting on you phone line?

  3. #3
    Junior Member
    Join Date
    Oct 2005
    Posts
    12

    Default Re: VOIP Phone Beeps!

    Quote Originally Posted by WhiteWolf4
    Do you use BroadBand or Dailup ??

    If you use dailup do you have call waiting on you phone line?

    I am on broad band. I assume there is a conflict or interference with something on my computer...I just don't know what.

  4. #4
    Shows no Fear
    Join Date
    Dec 2005
    Location
    Christchurch
    Posts
    34

    Cool Re: VOIP Phone Beeps!

    I did find this, it might help

    The problem is due to a poor DTMF detection algorithm in the ATA. When you press a key on your phone, it generates a specific and key-unique DTMF tone that can be detected by whatever the phone is connected to, in this case the ATA. The ATA detects these DTMF frequencies and recognises that a specific key was pressed. Fair enough, not rocket science, but where does the beep come from?

    Complex audio codecs like G723 and G729 do not do well with monotonic and TIME-INVARIANT tones like DTMF tones (frequencies and amplitude does not change over time) - they were specifically designed for encoding voice. DTMF audio tones that are locally encoded and remotely decoded sound garbled due to the compression algorithm. This does not bode well for systems that rely on detecting these tones for whatever reason (e.g. mailbox, PBX, menus etc...).

    The solution is to send the DTMF information in a different format - called "Out-of-band" (OOB) signaling. There are various different ways of sending this key information - the exact method is not important here. When the far end receives this OOB information, it locally REGENERATES a clean and pure DTMF tone based on the key information received (e.g. far end user pressed the '1' key, so play out a '1' DTMF tone). In this case the device regenerating this clean DTMF tone is the PSTN gateway which the ATA is connected to. The PSTN gateway regenerates a clean DTMF tone for the person listening on the PSTN network.

    Problem: if the ATA falsely detects a DTMF tone (i.e. thinking that someone pressed a key), it will send out this OOB information to the PSTN gateway. The PSTN gateway does not know or care that it was a mis-detection, it will blindly regenerate the DTMF tone for the PSTN listener - hence the DTMF beeps during a call.

    The technical jargon for this problem is 'talkoff failure'

    Talkoff testing or passing a 'talkoff test' are necessary requirements for telephone systems that recognize DTMF signaling. There is a standard tape or recording available from Belcore that is used to gauge talkoff performance of any standard DTMF detector. The improper detection that causes this problem means that the ATA most likely would fail a standard talkoff test.

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