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

A J Stiles asterisk_list at earthshod.co.uk
Fri Jun 6 03:14:33 CDT 2014

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).


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