[asterisk-dev] Looking for definitive answer for Busy() vs. Hangup() when used on a non-answered PRI channel

[Richard Mudgett]

On Thu, Jul 10, 2014 at 10:57 AM, Justin Killen <
jkillen at allamericanasphalt.com> wrote:

>  Hi,
>
>
>
> I’m using freepbx, and I’ve gotten myself into a bit of an argument (
> http://issues.freepbx.org/browse/FREEPBX-7706) about when to use Busy()
> vs. Hangup(17).  The conversation boils down to the fact that in a certain
> condition within the freepbx dialplan, an incoming PRI call runs the
> application Playtone(busy) followed by Busy(20).  My issue here is that
> PRI_CAUSE never gets set, so the calling phone doesn’t ever ring busy, it
> just rings normally.  I should note that this call is never Answer()’d.
> The stance of the freepbx team member is that calling Busy() should be all
> that an application needs to do – they shouldn’t have to worry about
> writing special code depending on the type of the underlying channel.  I
> can’t say that I disagree with that, especially after viewing the official
> docs, which describe Busy() as:
>
>
>
> "This application will indicate the busy condition to the calling channel."
>
>
>
> This to me implies that calling Busy() on a PRI channel should internally
> set PRI_CAUSE = 17.
>
>
>
> What I’m really looking for here is a definitive answer as to what should
> change here, either:
>
> a)       Dialplans be required to check channel status and run
> playtones/busy on answered channels or hangup(17) on non-answered channels
>
> or
>
> b)      Busy(), when called on a non-answered channel, should set the
> PRI_CAUSE (or whatever other appropriate variable for the channel)
>
>
>
>
>
> Lastly, I should mention that I’ve posted this to the users group, and
> although I have gotten workarounds, I have not been able to get a
> definitive answer on how this actually *should* work, only on how it *does
> *work and how to work around it.
>

The Hangup(), Busy(), and Congestion() applications are not equivalent
in their behaviours even though some channel drivers treat Busy() as
Hangup(17) and Congestion() as Hangup(34).  The Hangup() application
always sets the cause code and immediately begins hangup
procedures.  The Busy() and Congestion() applications send a control
frame to the channel driver to handle as it sees fit and then the
application waits with optional timeout for the far end to hangup the call.
For chan_dahdi PRI, this behaviour is configurable in chan_dahdi.conf to
work either way when the Busy()/Congestion() applications are used.
The default is to send the inband busy/congestion tone rather than send
the cause code 17/34 so a caller can hear the tone and hangup.

Excerpt from chan_dahdi.conf.sample file:

; PRI Out of band indications.
; Enable this to report Busy and Congestion on a PRI using out-of-band
; notification. Inband indication, as used by Asterisk doesn't seem to work
; with all telcos.
;
; outofband:      Signal Busy/Congestion out of band with RELEASE/DISCONNECT
; inband:         Signal Busy/Congestion using in-band tones (default)
;
; priindication cannot be changed on a reload.
;
;priindication = outofband

Richard
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