[asterisk-app-dev] Implementing app DIAL using ARI

[Joshua Colp]

Jan Svoboda wrote:
> Hi,
>
> I am currently trying to implement asterisk applications using ARI, and
> came across few problems trying to recreate the DIAL app.
>
> My current approach is the following:
>
> 1. When StasisStart event is received, determine which endpoints to dial
> and create new object, representing the DIAL application in my code,
> passing it the endpoints to call and the originating channel.
>
> 2. Create destination channels from all passed endpoints, listening to
> various events.
> - if at least one destination channel is created, indicate ring to
> originating channel
>
> 3. When one of the destination channels answers:
> - hangup all other destination channels
> - bridge the channel which answered with the originating one
>
> This works and calls can be completed, but the problem is when dialled
> destination channel indicates progress and starts early audio. This can
> be for example in case of a call to mobile phone, which is switched off.
> In this case, there is early audio saying “The called number is
> unavailable at the moment.”.
>
> As there is no other indication apart from the audio message, this leads
> to the caller hearing only the ringing indication and then the call is
> hung up, which makes the misleading impression, that the mobile phone is
> switched on, but does not answer the call.
>
> I have checked the source code of the DIAL app in app_dial.c, and
> noticed, that this is handled specially when there is only one
> destination channel, and that the way it is handled is with
> ast_channel_early_bridge(in, c). Using the DIAL app, this works, and I
> can hear the early audio.

Not really. What actually happens is that since Dial has control of all 
channels involved it can create a primitive bridge inside of itself, 
allowing media to be exchanged back and forth even in an early state. 
Once answer occurs the normal core bridging is invoked.

>
> Bridging the channel early in the app does not seem to be an option,
> since in this case, the channel does not even enter stasis.
>
> Is there any workaround or recommended way to achieve this ? Or is it
> something that yet has to be added to ARI ?

This hasn't been added to ARI yet and thus is not achievable. Until the 
channel is answered you don't have enough control. Ideally what would 
happen is that an early bridge technology would exist and you could then 
throw them into a bridge. The early bridge would do the stuff required 
in an unanswered state and then once answered a smart bridge operation 
would occur and the bridge would transition to a normal simple bridge or 
a native RTP bridge. Heck, it would probably even work in early state in 
normal bridges.

> Another problem is that it seems there is no way to indicate and play
> early audio to the caller. Any attempt to do so seems to answer the
> originating channel and generates ChannelStateChange event with state Up.

This shouldn't happen. Behavior was changed months ago so stuff should 
not explicitly answer. What operation were you doing?

> There is also a problem when playing music on hold to caller. The log
> indicates "Started music on hold”, but there is no audio. This also
> seems to be related to progress not being indicated (and lack of a way
> to do so), because trying it with the PROGRESS app called from the
> dialplan before Stasis works.

Can you file an issue for this? The MOH code should be indicating progress.

Cheers,

-- 
Joshua Colp
Digium, Inc. | Senior Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - US
Check us out at: www.digium.com & www.asterisk.org