In my previous post I’ve announced the bootstrapping of a new PHP project, called “Project Stanley”. Project Stanley was an attempt at creating a Asterisk ARI developer kit, based upon the PHP programming language (yes, I call it a programming language).

Shortly after initiating the development and reaching a point where our code was actually able to do something, we realized that we’ve gone the wrong way. The wire frame we’ve created relied heavily on the Ellislabs CodeIgniter MVC framework. Now, don’t get me wrong, I love CodeIgniter – but, it was the wrong choice. It was wrong, because we were locking our developers into an MVC structure, that truly isn’t needed for something like this.

So, we’ve stopped working on Project Stanley (you can still find it on github if you really want to) and we migrated the code into the PHPARI project. PHPARI is a cleaner approach to providing a simple, to the point, ARI developer kit using PHP. It relies on 2 PHP external libraries – PHPWS and PEST.

PHPWS is a WebSocket client implementation in PHP, while PEST is a REST client implemented in PHP. Both are actively maintained and had been tested by multiple projects as stable and battle tested. We’ve also enabled PHPARI in packagist, you can look it up for installation. Make sure you use the dev-master part of the package, not the dev-develop – it’s unstable and may actually contain broken code.

What do the following have in common: Skype, Viber, Whatsapp, Line2, Tango and Kakao? Yes, there are all OTT apps for your mobile phone that enable you to communicate with your peers. Skype, Viber, Line2, Tango and Kakao actually enable you to call one another. Each one dominates a section of the world, where Kakao and Line2 are dominant in the far east, Viber dominates Japan and Eastern Europe and Skype kind’a says: “Look at me bit**es, I’m all of you combined”.

What do the following have in common: VoipDiscount, Nymgo, WiCall, VoIPstunt, Vox Mobile, Cloud Roam, Skuku? All of these are VoIP Mobile OTT apps, similar to the above and yet – no one truly heard about these or is using them. Each one of the above is more or less a replica of the previous one, maybe with one or more added features – but all in general are the same pitch and bit**, make cheap calls over VoIP via our service.

So, what does it all mean? it means one simple thing, no one truly cracked the formula to make money on the Mobile VoIP OTT business – everybody is still looking for the killer business model/VoIP OTT Application. What is the right way? providing low cost calls? providing business oriented services? providing simple roaming solutions? maybe bundling roaming data plans and SIM cards? or maybe, all of these are sooooooo passe that the world just says: “Stop fu**ing about and create some truly new, change how think and how we work completely. Paying 1 or 2 dollars more per month, I’m not gonna change my service for that – it’s pointless.”

So, what are the true killer apps that will truly say: “this is a game changer, from this point onward, VoIP OTT will no longer be the same!” – Here is a list that I believe will make the difference:

1. Make calls completely social – Phone numbers are so 18th century, they are pointless

2. Make your phone aware – Presence and availability is key

3. Drop the stupid things – call recording, visual voicemail, funny sounds, funky tones – stop the bullshit, give me proper services than stupid features

4. Make your service reliable – stop behaving like a website operator and thing like Ebay, every minute your service is down or affected by bad service you are loosing money

5. Make work, then make pretty – application design is important, product design is important, but not more than the product itself

6. Invest in support and monitoring – relying on your suppliers to do it for you is stupid and childish

7. Only blame yourself! – when something fu**s up, it means that you did your job wrong and you cut corners. Don’t start blaming your colleagues or your contractors, they are only doing what you asked them to do

And most importantly, remember the following statement: “I’ve seen the furthest, because I sat on the shoulders of giants.” – don’t tell the world how you’re going to obliterate Whatsapp and Skype, look at them, strive to be them, and then do it better.

I wish all of you good luck.

One of the biggest questions in the world of Asterisk is: “How many concurrent channels can be sustained with an Asterisk server?” – while many had tried answering the question, the definitive answer still alludes us. Even the title of this post says “3500 concurrent channels with Asterisk” doesn’t really say much about what really happend. In order to be able to understand what “concurrent channels” really means in the Asterisk world, let us take a look at some tests that were done in the past.

Asterisk as a Signalling Only Switch

This scenario is one of the most common scenarios in the testing world, and relies upon the basic principle of allowing media (RTP) to traverse from one end-point to the other, while Asterisk is out of the loop regarding anything relating to media processing (RTP). Examine the following diagram from one of the publicly available OpenSER manuals:

Direct Media Path between phones via a SIP Proxy

Direct Media Path between phones via a SIP Proxy

As you can see from the above, the media path is established between our 2 SIP endpoints.

This classic scenario had been tested in multiple cases, with varying codec negotiations, varying server hardware, varying endpoints, varying versions of Asterisk – no matter what the case was, the results were more or less the same. Transnexus had reported being able to sustain over 1,200 concurrent channels in this scenario, which makes perfect sense.

Why does it make sense? very simple, as Asterisk doesn’t manage or mangle RTP packets, Asterisk performs less work and the server also consumes less resources.

Asterisk as a Media Gateway

Another test that people had done numerous times is to utilize Asterisk a Media Gateway. People used it as a SIP to PSTN gateway, SIP to IAX2 gateway, even as a SIP to SIP transcoder gateway. In any case, the performance here varied immensly from one configuration to another, however, they all relied on a simple call routing mechanism of routing calls between endpoints and allowing Asterisk to handle media proxy tasks and/or handle codec translation tasks.

Depending on the tested codec, I’ve seen reports of sustain over 300 concurrent channels of media on a single server, while other claim for around the 140 concurrent channels mark – this again mostly relied on various hardware/software/network configurations – so there is nothing new in there.

These tests tell us nothing

While these tests are really nice in the theoretical plane of thinking, it doesn’t really help us in the design and implementation of an Asterisk system – no matter if it is an IVR system, a PBX system or a time entry phone system for that matter – it simply doesn’t provide that kind of information.

The Amazon EC2 performance test

In my previous post, Rock Solid Clouded Asterisk, I’ve discussed the various mathmatics involved in calculating the RoI factors of utilizing Cloud computing. One thing the article didn’t really tell us, did it really work?

Well, here are some of the test results that we managed to validate:

  • Total number of Asterisk based Amazon EC2 instances used: 24
  • Total number of concurrent channels sustained per instances (including media and logic): 80
  • Average length of call: 45 seconds
  • Total number of calls served: 2.84 Million dials
  • Test length: approximately 36 hours

According to the above data, each server was required to dial an approximate 3300 dials every hour. So, let’s run the math again:

  • 3300 Diales per hour
  • 55 Dials per minute
  • As each call is an average of 45 seconds, this means that each gateway generates 20 calls
    per second, and within 4 seconds fills the 80 channels limit per server.

According to the above numbers that we’ve measured, each of the Amazon EC2 instances used was utilized to about 50% of its CPU power, while consuming a load average of 2.4, which was mostly caused by I/O utilization for SIP and RTP handling.


When asking for the maximum performance of Asterisk, the question is incorrect. The correct question should be: “What is the maximum perfromance of Asterisk, utilizing X as the application layout?” – where X is the key factor for the performance. Asterisk application performance can vary immensly from one application to another, while both appear to be doing the exact same thing.

When asking your consultant or integrator for the top performance, be sure to include your business logic and application logic in the Asterisk server, so that they may be able to better answer your question. Asterisk as Asterisk is just a tools, asking for its performance is like asking how many stakes a butcher’s knife can cut – it’s a question of what kind’a steaks you intend on cutting.

This post is somewhat a combination of posts from previous posts, mainly, the posts about virtualization and my latest posts about the utilization of Amazon EC2. As some of you may know, a part of what I do at GreenfieldTech is develop various API’s for the Asterisk Open Source PBX systems. Two of these API’s are the IVR API and the Dialer API. This post if called “Rock Solid Clouded Asterisk” as it will describe the latest production environment that I’ve implemented, using these API’s and Amazon EC2 virtualization framework.

The network diagram

Our implementation consisted of the following general schematic:

Network Diagram

Network Diagram

The application logic was based upon a JAVA based web-service, implementing the XML-RPC server side of the IVR API, and a dialer management system that controlled the dialer API located on the remotely located dialers – hosted on Amazon EC2 instances. For simplicity, and we were very much aware this would reduce the overall capacity, we’ve located both the dialer framework and the IVR API execution on each of the servers, while allowing the server s to communicate internally.

Some constraints

As much as we wanted to run many Amazon AMI instances, we were limited to running 5 elastic IPs with a single Amazon AWS account. As a result, we’ve registered 5 accounts, and executed a total of 24 AMI instances with 24 elastic IP’s.

An additional constraint we had realised, but had no way of actually knowing its limitation was the actual number of concurrent calls per server. Initially, we’ve reached the following numbers and configuration on a physical server:

  • Intel Quad Core XEON
  • 2GB RAM
  • 1GB Network Uplink
  • CentOS 5.2 64bit
  • Total capacity: 120 concurrent calls of Dialer+IVR on a single server

Per our theory, if we managed to reach a similar capacity using amazon c1.medium instances, we would be very happy.

The results

After conducting a test utilizing a single AMI instance, we’ve reached the following results:

  • Dual Core instance (c1.medium)
  • 180GB Disk Storage
  • 8GB of RAM
  • Fedora Core 8 32bit
  • Total capacity: 80 concurrent calls of Dialer+IVR on a single instance

A decrease of 33% in comparison to the performance observed on a physical server. Ok, so we weren’t all that happy with these results, until we started doing the financial math, realising that using Amazon EC2 with that Dialer+IVR framework would yield a savings of almost 80% in operational costs.

Doing the math

The normal co-located option

Our aim was to reach a capacity of around 2800 concurrent channels. Per the normal physical setup, our hardware requirements would be to use at least 24 servers. At a price of 1500$ per server, that sums up to a total of 36,000$. Adding the time required to install 24 servers, the overall expense for 24 servers would be around the 42,000$ mark. To sustain a total of 2800 concurrent calls, using the g711 codec, we would be required to carry a total of 300Mbps internet uplink – basically talking about 10,000$ of bandwidth.

So, taking all of the above into consideration, we will need a total of 52,000$ just to maintain the hardware installation and operational cost. Taking into consideration that the system would be used at full for no more than a period of 30 hours, we end up with a total of: 1733$ per hour.

The Amazon EC2 option

Now, let’s calculate for Amazon EC2:

2800 concurrent channels translates into 35 instances. Price per c1.medium instance per hour is 0.2$. So, rack that up and you get: 210$ for operating 35 instances for 30 hours.

Elastic IP costs are 0.01$ per hour per server – a total of 10.5$ for 30 hours.

Bandwidth costs are 0.17 per each GB, so according to 300Mbps for 30 hours, with each call duration at 1 minute sums up to be: 5M of data per call. Calculating 2800 concurrent channels for 30 hours gives: 25,200,00 MB, or 25TB of traffic. According to Amazon, first 10TB are at 0.17$ per GB, and then the price goes down. So, let’s take a worst case of 0.17$ per GB. A total of 4284$ for operating 30 hours.

A total of: 4,468 US Dollars, Price per hours calculated at: 148$.

The savings

Per the task at hand, the utilization of Amazon EC2 yielded a savings of 92%

So, is Amazon EC2 good for any usage?

The answer is a definite NO! If your requirement is for a system that works 24×7, like a PBX system or a call center, then your utilization of Amazon EC2 would be identical to leasing a co-located server at any of the world wide co-location providers. If your application is of sporadic nature, or is utilized for short bursts of time, Amazon EC2 is a wonderful tool for lowering your overall expenses. Sure, it will require some work to get running, but the overall savings is more than worth-while.