DAHDI phantom pickup when ringing

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Asterisk Users 6 Comments


I’ve been experiencing trouble with my DAHDI channels for some time and have
finally decided to try and resolve the issue.

Essentially, the problem I am having is that when a call comes in, and my
DAHDI phones therefore ring, Asterisk thinks that one of the handsets has
picked up to answer the incoming call – whereas in actual fact it is still
on hook. The call then gets instantly dropped (the phone is on-hook, after
all), and the caller has to redial.

Sample log (this is an incoming call from SIP/5555, that was “phantom
answered” by DAHDI/7. There is no time delay between the ‘answered’ line and
the ‘hungup’ line):

6 thoughts on - DAHDI phantom pickup when ringing

  • There has been no reply on this for a few days – is there a more appropriate
    forum I should be utilising, or is it just that nobody else has had these



  • Jonathan Hunter wrote:
    Post the revelent portions of your extension.conf. Maybe you have a
    logic error somewhere.

    Have you tried to move the set from channel 5 to 8 and 7 to 9? (to see
    if one or two of the fxs channels have gone bad in the chan bank?)

    It could also be a power supply issue inside the Zhone that tries to
    ‘trip’ the ringing.

    Lyle Giese
    LCR Computer Services, Inc.

  • My extensions.conf is fairly simple in this regard; I use macro-stdexten:

    exten => s,1,NoOp(‘${CALLERID(NAME)}’ [${CALLERID(NUM)}] calling [${ARG1}])
    exten => s,n,Set(MBOXCONTEXT=****)
    exten => s,n,Dial(${ARG1},30) ; Ring the interface, 30
    seconds maximum
    exten => s,n,MailboxExists(${MACRO_EXTEN}@${MBOXCONTEXT})
    exten => s,n,NoOp(Got mailbox status of ‘${VMBOXEXISTSSTATUS}’)
    exten =>

    and it is called with

    Have you tried to move the set from channel 5 to 8 and 7 to 9? (to see if

    Hmm – not sure how I might determine whether this is the case or not.. It
    only seems to occur on some channels, at the moment.



  • Can you replicate those phantom answers without calling all channels?


    originate DAHDI/7 application Echo

    Does that line answer without you picking up the phone? Or does it
    require a combination of several channels ringing at the same time?

  • Tzafrir,

    Good thinking – I tried this, and also Lye’s suggestion to swap channels.

    When calling just one channel at a time (the command above didn’t work for
    me from the command line – is it a Manager command? Either way, I set up an
    extension to Dial() just that DAHDI channel to test it), I didn’t manage to
    reproduce the problem.

    Admittedly this isn’t an exhaustive test – I may just not have triggered the
    right conditions this time – but it does indicate to me that it has
    something to do with ringing multiple channels at once.

    I then swapped the channels around (5 became 23, and 7 became 14). This
    seemed to work better at first – I was able to make three or four calls
    without any phantom pickups. Sadly, DAHDI/14 then picked up and proved that
    it wasn’t quite fixed 🙂

    We’ve certainly eliminated a couple of things already, which is good…

    Thank you, all, for your continued help!


  • Jonathan Hunter wrote:
    Thinking on this, if the power supply is going bad, reducing the number
    of DAHDI channels in ringing state may help. I am an old telco guy
    having spent 23 years working for the biggest telco in the US in their
    CO’s. I tend to think something funny with the channel bank or the
    channel units. Seen that happen many times working for them.

    I assume the wiring is good and not ‘wet’. If it was underground or in
    a damp environment…

    I would go back to thinking chan bank with FXS channel units, not DAHDI
    channels. It will focus the attention where you have power supplies(-24
    or -48 volt talk battery and ringing current with trip battery
    super-imposed) and all the electronic things that can go wrong with that
    and the detecting of offhook state. It would be easy for the
    electronics to think the phone was offhook when ringing, but not when
    supplying only talk battery when the channel units or power supply goes

    Lyle Giese