Asterisk ARI – What AGI/AMI should have been

Asterisk ARI – for a seasoned AGI/AMI developer like myself, ARI is a serious mind warp. Why is it a mind warp? simple, it’s all the things we wanted AGI to be, and the reliability we wanted AMI to have, minus all the work around we needed to do – in order to get similar functionality in the past.

So, is ARI truly a replacement for AGI/AMI? well… I think the true answer will be NO. Is a replacement for the Asterisk dialplan? well… I think the answer to that is NO as well. “Say, are you messed in the head? first you say “What AGI/AMI should have been”, and then you say it’s not a replacement? – are you mental?” – well, there are a few reasons why I claim it’s not a direct replacement, and I’ll detail these here.

In order to explain, I’ll give a few examples, using the “in-development” PHP ARI wireframe that I’m developing, called Stanley.

Synchronous vs. Asynchronous

ARI by definition is asynchronous. Keeping that in mind, in means that that any command you give it will get queued or spooled in some manner, and return back an immediate result. Just to illustrate it, let’s examine the following code segment:

$this->stasisLogger->notice("Stasis Start");
$lastResult = $this->channels->channel_playback($this->ari_endpoint, $messageData->channel->id, "sound:hello-world");
$this->stasisLogger->notice("Last result: " . $lastResult);
$lastResult = $this->channels->channel_playback($this->ari_endpoint, $messageData->channel->id, "sound:demo-congrats");
$this->stasisLogger->notice("Last result: " . $lastResult);

For all practical purposes, you should regard $this->stasisLogger as a simple logging object, and $this->channels as a model to initiate ARI Channel requests. If you use the above the code, and activate it from with a Stasis application, you would listen to the “hello-world” and “demo-congrats” segments. Now, let us examine the following code segment:

$this->stasisLogger->notice("Stasis Start");
$lastResult = $this->channels->channel_playback($this->ari_endpoint, $messageData->channel->id, "sound:hello-world");
$this->stasisLogger->notice("Last result: " . $lastResult);
$lastResult = $this->channels->channel_playback($this->ari_endpoint, $messageData->channel->id, "sound:demo-congrats");
$this->stasisLogger->notice("Last result: " . $lastResult);
$this->channels->channel_delete($this->ari_endpoint, $messageData->channel->id);

The only difference here is the last line. If you activate this code, you will hear the world “Hello”, immediately followed by a disconnect. “Wait a minute, what just happened? – wasn’t I supposed to hear everything?” – that’s exactly the point, the answer is NO! The asynch nature of ARI will simply queue the first 2 playback requests, while the hangup is performed almost immediately – the playback simply never get to be executed.

In other words, if you need something to be synchronous within the dialplan, you may need to work differently about it. If you are familiar with the Node.JS framework, you are fairly familiar with this issue.

ARI is for writing applications, not IVRs

When the Asterisk team created ARI, their idea was simple: “Don’t manage the queue application, simply write your own”. Same applies for managing multi party conference calls, call origination, etc. In 2009 I wrote a book about AGI programming, where I’ve explained the methodology for “Atomic AGI development“. The concept behind Atomic AGI was to contain small logic units in AGI scripts, and leave most of the heavy lifting to the dialplan. This methodology enables to create scaleable Asterisk platforms at fair ease, and introduce additional technologies, without going about and adding odd things into Asterisk.

ARI is meant to do something similar, in the form where you can go about and create your own logic, contain it into a singular application and activate when you require – for example, rewriting the queue application. One of the first applications that I’ve decided to re-write using ARI was a Radio broadcasting system that I’ve developed in 2006. The problem with that application was that I need to hold about 600 callers in a single queue, and attach them over to the broadcasting booth as required. Of course I needed to enable full call control, caller management, UI and more. Initially, I used MeetMe, MySQL, and AMI to do this. Later on it changed to MeetMe, Redis, AstManProxy and some other tools – but it never seemed to please me. The fact that I needed to maintain 2 MeetMe bridges, one for holding people and one for the actual broadcasting really bugged me. Yes, when Asterisk 1.8 came out I migrated to the Bridge application and yes, I updated bits and pieces here and there, but it was never what I wanted it to be.

When I started playing around with ARI, I said to myself – this is the perfect application to migrate to ARI. The only thing I needed was a simple Stasis application to read my state correctly, and that would be activated once the called is put into the waiting area – so in terms, I’ve developed a very simple queue application.

IVR heavy lifting was done using dialplan, but the actual service was done with ARI.

Blades and Bleeding Edge

Now, before you go about migrating all your existing code to ARI – you must remember this: If you walk on the bleeding edge, expect the blade to cut you here and there. Currently, I hadn’t yet seen any proper ARI wireframe available. I’ve seen some work done with Node.JS and Ruby, but I can’t say that I’ve taken a fancy to any of those. Honestly, my comfort zone is very much PHP and C/C++, what can I say, I’m old school.

When I started building the Stanley wireframe, it was fairly frustrating – simply because not everything was that much clear and clean. In addition, as Asterisk advances, ARI will change and advance as well. What ever you write, make sure it’s modular enough so you can change it as required.

 

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