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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

Even out of the box, without any configuration (to speak of), Asterisk does some pretty impressive things. For example, we'd entered Simon's email address in there somewhere, not really knowing what would happen. We rang his extension, got through to voicemail and left a message. Simon was just thinking to himself, 'I wonder how I access my voicemail' when his machine said, 'You have new mail'. That's right, the message was digitised, attached to an email and sent to him. So we had a system up and running that could handle analog calls and could make a phone ring.

ISDN and VoIP

Having got it to work on analog, the next challenge was to make Asterisk work with ISDN. There were a number of reasons for doing this, most of which revolved around the fact that our office has six incoming ISDN lines, and ISDN does CLI - we had a project in mind that needed this.

However, we had no idea of how hard this would prove to be. The problem wasn't ISDN itself, but rather ISDN cards. Using ISDN from a PC was something that had completely passed us by. Even when, some time in the last millennium, we'd set up ISDN dial-up Internet access, we'd always used routers. So we weren't prepared for the fact there are so many types of card and that they're all so different. Without going into all the horrid details, we ended up buying three different cards from eBay before we found one that worked: a BT Speedway card. Once this was installed, we could make and receive calls over ISDN too.

Now we were ready to tackle VoIP. We found the required configuration, set it up, found some VoIP software (the excellent free version of X-Lite from CounterPath), connected it all up and it just worked. We could dial an internal extension on Asterisk and, since it was connected through our office's exchange, we could dial other extensions and get outside lines. Suddenly, our lives were changed, as VoIP became a reality. Okay, maybe we're getting a bit carried away, but it did make a difference, honest.

First, no matter where we are, we can now pick up a phone and call people in our office without being charged for it - obviously, that is, from anywhere where we have Internet access. Second, we can also make outside calls, via the company exchange, no matter where we are. These two features make life much easier and cheaper when working from home. Third, the combination of Asterisk, VoIP, conventional phone lines and voicemail allows us to cover all bases. You can call our office and someone might answer who's really miles away. If the exchange can't find anyone to answer the call, it can forward it to voicemail so the message gets emailed to the appropriate person.

With Ian based in the US and Simon here in the UK, we can talk to each other very easily and with good quality. Ian can make calls in the UK via our UK office and, if he had the same setup, Simon could equally call out into the US via Ian. Obviously, although we haven't done it yet, we could also connect to a VoIP call service from our Asterisk exchange. If we really wanted to, we could even give up our ISDN lines altogether and just use VoIP. Even if we don't go down this route, the ability to link people together in a private phone network is compelling. Maybe we'll give our clients access so they don't need to pay to call us.

Programming Asterisk

What you have to understand about Asterisk is that it really is a complete 'calling platform' solution, which not only supports phone calls but also phone-based applications. And we don't just mean voicemail, we mean proper IVR (Interactive Voice Response) systems. Now, before you all scream into your copy of PC Pro about why anyone would want to create yet another infernal system where you have to dial '1' for account inquiries, '2' for fault reports and '9' to actually talk to a human being, there's something you need to think about. IVR is expensive, but it can be useful. As a rough guide, the amount of money we've spent so far on everything probably wouldn't buy us a single day of IVR contract programming. We are, after all, programmers - Simon has been writing software for 25 years and has taught other people how to do it for ten - so why can't we program a telephone exchange? It turns out that with Asterisk we can.