[asterisk-users] What if some phone picks up

[Alex Balashov]

Julien Claassen wrote:

> Godd evening!
>    What happens if someone calls and asterisk doesn't "Answer()" itself, but 
> another analog phone does? Can I somehow catch this situation in my dialplan.
>    I have an ISDN line, but with it I got a box with an adapter for good old 
> analog phones. This doesn't seems to be directly connected to the ISDN line 
> asterisk sees. But somehow, it must know, that the call is taken care of. It 
> doesn't answer. So how?
>    I tried the h extension. Would I fair better with looking for BUSY or 
> CONGESTION, or whatever?

On that level, there is no awareness of line appearances or of other 
handsets.  Thus, there is no real way of knowing that another handset 
picked up.  The only thing that changes is that the sending party stops 
signaling the initial address message (in whatever relevant signaling 
technology, i.e. analog FXO/FXS, ISDN Q.931, etc.), so the call is 
aborted.  A call disconnect indicator may or may not be provided.

In SIP, the calling station sends a CANCEL to terminate a dialog to 
which a response was furnished somewhere else.  This can be done using 
branching or multiple call legs.  But these are relatively high-level 
constructs, and as such, don't uniformly exist in physical-layer 
signaling other than in some proprietary digital PBX systems.

So, basically, in your case of ISDN, it really depends on what exactly 
the far end does in response to a pickup on your end from this analog 
adapter device.  You are correct to say that Asterisk does not see the 
handset as being "directly connected" - nothing is "directly" connected 
that way to an ISDN line, because it's ISDN.  Any extension is not going 
to be electrical or physical in nature.

When I get a call abort from the far end (i.e. caller hangs up before 
call is picked up) on a machine with a PRI here, I see messages like 
this (as I have no 'h' extension):

     -- Channel 0/1, span 1 got hangup request, cause 16
     -- Hungup 'IAX2/EBCSDL911-10'
   == Spawn extension (nsx-pstn, NXXXXXXXXX, 2) exited non-zero on 'Zap/1-1'
     -- Hungup 'Zap/1-1'

What do you see when your analog phone picks up?  It may be necessary to 
turn up verbosity on the CLI.

This will (hopefully) help you determine what signaling events have 
which dialplan bindings.

-- Alex

-- 
Alex Balashov
Evariste Systems
Web    : http://www.evaristesys.com/
Tel    : (+1) (678) 954-0670
Direct : (+1) (678) 954-0671
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