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I would like to know if it is possible for asterisk to establish a three-way call on an analog line.

Typically, I would like asterisk to call 2 numbers, with the same telephonic line, and connect them together.

For a human, this is already possible on the line I'm using, by following those steps:

  • pick up and dial the 1st number, wait for it to answer,
  • press R (the hook flash) and compose the 2nd number, wait for answer,
  • press R and then 3 so everybody is now in the same conversation.

This is interesting here because the line I'm talking about can make international calls to many destinations without extra charge, so I can use it (as a relay) to call from one country (when travelling) to another without having to ruin myself.

Can asterisk reproduce these steps automatically, and do you know how?

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1 Answer 1

Yes, this is possible with some dialplan scripting.

  • You would want to use the Dial() application to "pick up and dial the 1st number".

  • With a dumb analog line, you might not get any indication that the call was answered by the remote side. You can either have the first callee enter a DTMF digit when they pick up to indicate that it's time to call the next number or try to use call progress detection (callprogress=yes in chan_dahdi.conf). Call progress on analog lines isn't an exact science since it uses DSP techniques to try and determine when the line is ringing, or someone answers, etc..

  • You can use the Flash() dialplan application to send the hook flash.

  • You can use the SendDTMF() dialplan application to dial the 2nd number. Same problem with knowing when the line is answered by the remote side.

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Thank you! Is there any tweaking needed for the Flash() duration? I've heard it can be different between countries. –  Totor Apr 2 '13 at 13:22
    
Yes. What you want is most likely txflash in chan_dahdi.conf. –  sruffell Apr 2 '13 at 17:18
    
I see no mention of txflash, but there is rxflash, is that what you meant? –  Totor Apr 3 '13 at 22:13
    
Sorry. I meant just 'flash'. –  sruffell Apr 4 '13 at 2:14

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