Asterisk PBX: Open Source VoIP Branches Out

Telephony is generally regarded as a mission critical business service, and any downtime can be costly in terms of lost productivity and lost business: Most companies want their phones to be a dial-tone service. And since the PBX is the heart of a corporate telephone system, you'd imagine it would not be something that the company would want to scrimp and save on. No one ever got fired, in other words, for buying a Cisco PBX.

Which is why the Asterisk open source PBX is quite surprising. Running on Linux on standard PC hardware with suitable PCI interface cards, it works as a PBX with extra telephony features like voice mail and conferencing, working with analog phones and standards-based IP phones for VoIP telephony. And it's certainly no geek plaything. You could run your own home PBX using Asterisk, certainly, but a single machine can handle raw call volumes in the low thousands, or about 120 channels with echo cancellation and transcoding. And by using built-in peering technology you can link up multiple Linux boxes to make a PBX serving a hundred thousand users.

Many enterprises run Linux in their data centers, so why not an open source PBX?

In practice most corporations' needs are more modest, so in theory you could download Asterisk and have a fully working PBX for the cost of a Linux box (which you may already have lying around), the interface cards you need (perhaps $1,500 for a T1 card) and G.729 codec licenses at $10 per channel – around $5,000 could do it. Or you could buy a Cisco system to meet the same needs for a few tens of thousands of dollars.

But although low prices are good and higher prices are, well, not good, no-one in their right mind is going to implement a large PBX just because it is cheap.

An open source PBX like Asterisk is in demand because it's almost infinitely customizable, says Mark Spencer, the original creator of Asterisk and president of Digium, the primary developer and sponsor of Asterisk, and supplier of interface cards and support for the software. "In the telecoms business the advantage of customization is at a premium. People like phones to work exactly how they want," he says. "It's not just about money, its about being able to add features. If you have a Cisco system, only Cisco can change the code. We see big companies using Asterisk because nothing else solves their particular problem, and they don't want to be beholden to a particular vendor."

What if you don't have the expertise to implement Asterisk in-house? The answer is that, as with Linux, there are plenty of resellers who can provide a solution – which might include Digium hardware, Asterisk software, integration services and support.

The open source model is now fairly well understood and trusted, so there should really be no reason in principal why companies shouldn't trust their phone systems to the open source community. After all, many enterprises run Linux in their data centers, so why not an open source PBX? But for those companies that are not happy with the idea, Digium offers a Asterisk Business Edition. This is a $795 package with a version of Asterisk tested for over 240 simultaneous calls per server. It includes the PBX functionality and features (including voice mail, VoIP and TDM capabilities and VoIP/TDM integration) of the open source version, but also includes a technical manual and quick start guide, upgrades and support, and a commercial license with legal protections. It is not the bleeding edge, but it is stable and tested.

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That's all very well and good, but at the end of the day Digium is a small private company with about forty employees which has, according to Spencer, been profitable for a few years. So with the Business Edition you are not exactly in the hands of huge corporation like Cisco that you can be sure isn't going to go away. If Digium hardware became unavailable, what would you do?

The answer, and an implicit endorsement of Asterisk, was announced on September 20: Digium's Asterisk Business Edition is to incorporate support for Intel's Intel NetStructure and Intel Dialogic products from November. This provides an alternative to Digium's hardware. Intel says the on-board media processing capabilities of its modular products means that calls require less overhead from the CPU (central processing unit) of the PBX PC. Support for a range of analog and digital network interface boards is intended, the company says.

What does all this mean for the average corporation? PBXs age, and VoIP is becoming increasingly prevalent. So sooner or later it's likely you are going to be looking at replacing your existing system, or integrating your analogue system with digital telephony. Cost is certainly a factor, but reliability, feature sets and flexibility are likely to be more significant things which influence your buying decision. So it's certainly worth noting that there are open source PBX solutions out there, along with commercial versions backed by, or at least linked to, large corporations like Intel.

And no one ever got fired for saving money, did they?