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Press the Asterisk now

Posted on 22 Nov 2005 at 16:24

Simon Brock and Ian Wrigley look into an open-source VoIP package

The key to programming any system - a user interface, a website or a telephone exchange - is to understand that there will be a sequence of events that you need to be able to see, act upon and deliver events back from. On an IVR platform, the events you need to see are things like 'line ringing', 'button push' and 'hang up', while those you need to deliver back are things like 'answer line', 'play hold music' and 'hang up'. Asterisk provides an API for this called the Asterisk Gateway Interface (AGI), and there are libraries that make it work in most programming languages. From our standpoint, this meant we could write a program in Perl that implemented a full IVR system. Why did we want to do this?

We want a voicemail system that works with our support ticketing system. You call into a support line and it's closed, so you leave a message: the trouble is that any busy helpline has a call centre, which means it gets a reasonable number of calls outside working hours. Normally, these go into a voicemail system and then someone listens to all the messages and transcribes them onto slips of paper. With our system, the voicemails go into a ticketing system - the excellent open-source Request Tracker - where they can be dealt with in a controlled way. More importantly, we put an IVR front-end onto this ticketing system so you can call it up, listen to messages and press '3' to return the call. It's all done with Asterisk and written in Perl.

Asterisk is a great piece of open-source software: it does something useful and allows us to create real phone-based applications that would normally cost thousands of pounds to implement and deploy.

ENTERPRISE LINUX FOR FREE

For a long time, we have, like many others, been using Red Hat Linux. As we all know, a couple of years ago Red Hat changed its pricing model to move away from the cheap volume market and into the enterprise market. This has proven to be a good decision for Red Hat - major manufacturers like Dell and Sun only really talk about Red Hat Linux nowadays. Red Hat continued to give away a version of Linux under the Fedora label, but that's a bleeding-edge product, with typically about a year between major releases. On the other hand, the Enterprise versions have a longer life time and are actively supported. This support comes at what is for Linux a comparatively high price of hundreds of dollars, per year, per machine.

There are alternatives, and one in particular is called Centos, the Community ENTerprise Operating System. Centos is actually the Red Hat source code recompiled and packaged by the community. The people involved in Centos could do this because Red Hat is released under the standard Linux GNU Public Licence, which means it has to make its source code public. As the source code is open, anyone else can compile it and that's what they've done. Obviously, they have to do it in a timely fashion, and they need a network of servers to deliver their files - both reasonably easy to achieve on the Internet. We've been using Centos 3 (which shadows Red Hat Enterprise 3) on half-a-dozen machines for a few months and it's worked well. We're about to move to Centos 4 (based on RHEL4 and runs on kernel 2.6), which is bang up to date. If you want to run Enterprise Linux and don't want to pay - or don't need Red Hat support - go Centos.