[asterisk-users] Channel is answered by FXO card before callee answered the phone(pick up phone)

Shaun Ruffell sruffell at digium.com
Fri Jun 6 07:53:49 CDT 2014

On Fri, Jun 06, 2014 at 08:28:07AM -0400, John Novack SCII wrote:
> A J Stiles wrote:
> >On Thursday 05 Jun 2014, Mojtaba wrote:
> >>My scenario is (2)
> >After doing some tests with my own hardware, I'm now convinced that this is
> >actually normal behaviour:  As far as Asterisk is concerned, a call is deemed
> >"answered" as soon as the hardware seizes the line.  It is only "not answered"
> >if the line is not available.
> >
> >Which makes sense, because an analogue line has no D-channel.  Once the trunk
> >is acquired successfully, there is no way for a machine to know the state of
> >the call beyond then.  Such supervisory information as there is -- a regular
> >cadence during ringing, possibly a burst of white noise and then a human voice
> >-- is geared towards interpretation by human beings.
> >
> >Moerover, since the tones are different in every country  (and sometimes,
> >between different telephone exchanges in the same country; at one time, the UK
> >was using three sets of supervisory tones depending whether you were on an
> >old-fashioned "clicky-clicky" exchange, an intermediate-generation analogue
> >electronic exchange or System X)  it would not be a trivial task to make sense
> >of them.
> >
> >
> >I think if you want full supervisory information, you are going to need to use
> >some sort of digital telephony technology  (ISDN or GSM).
> >
> This is well known behavior for many years, since the inception of Asterisk/Zaptel
> I wonder why tests had to be run!
> The OP issue was answered several days ago
> His issue was obvious and well stated until another poster confused the issue!

Just to keep it clear for anyone who stumbles on this thread in the
future, this can sometimes work if you set the callprogress=yes
option in chan_dahdi.conf if your country/provider/exchange is

Shaun Ruffell
Digium, Inc. | Linux Kernel Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at: www.digium.com & www.asterisk.org

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