Throw away your PBX: Why Asterisk may be the VoIP future of your network

Here's your network's dirty little secret: Your private branch exchange (PBX) is old and outdated, and if you want to bring it into the modern era with IP telephony and voice over IP (VoIP), you're going to have to spend a bundle. Specialized switches and hardware and proprietary systems don't come cheap, and they might not even offer all the telephony features you're looking for.

But there is an alternative, as thousands of businesses and network administrators have discovered. The open-source Asterisk PBX has been gaining a big following, offering surprisingly powerful telephony features on inexpensive hardware. Not only has it been saving companies money, but it has also been able to integrate telephony with network applications in ways that previously might not have been possible.

But Asterisk isn't for everyone. And there are issues you need to confront if you plan a move to Asterisk. So here, in a nutshell, is what you need to know about Asterisk, along with advice from those who have already deployed it.

What is Asterisk?

Let's start with the basics: Asterisk is open-source PBX software that runs on a wide variety of operating systems, including Windows, Linux, Mac OS X, OpenBSD, FreeBSD and Sun Solaris. It can run on inexpensive, off-the-shelf hardware, and it includes high-end features such as interactive voice response, voice mail, conference calling, and automatic call distribution and routing that have until now only been available on proprietary PBXs.

It's also exceedingly flexible. New functions can be created by writing scripts in Asterisk's language, by writing modules in C, and by writing scripts in Perl or other languages.

Particularly important is that it handles VoIP calls and works with a variety of VoIP protocols, including the Session Initiation Protocol (SIP) and H.323. It also functions as a gateway between IP phones and the public switched telephone network.

All this means that it can be used to create powerful, programmable PBXs at a low cost, says Joshua Stephens, CEO of Switchvox, a San Diego-based integrator and provider of PBX systems, including many built using Asterisk.

"With Asterisk, you can build any phone system you want. It's irreplaceable when you need custom programming," he says. "It lets you build PBXs with the kinds of features that otherwise would cost many tens of thousands of dollars." In contrast, he says that entire turnkey PBXs based on Asterisk can sell for under $1,000.

Cost is low because it can run on standard, off-the-shelf hardware rather than high-end, proprietary systems. And because it's open-source, licensing fees aren't expensive.

Why you should use Asterisk

The cost factor is one obvious reason for using an Asterisk PBX rather than a proprietary one. But there are other reasons as well, says Dale Laushman, president and CEO of Lakewood, Colo.-based Uptime Group, an IT and VoIP consultancy that has worked extensively with Asterisk.

"Even more important than cost is the flexibility of the system you can build with Asterisk," he contends. "You can make it do just about anything you want. With a traditional PBX, there is a preset number of features, and they're either on or off. With Asterisk, on the other hand, you have your hands on the source code, and you can customize it however you want. It can do things that normal IP PBXs simply can't."

Laushman cites one example of such flexibility -- a PBX his company built for an after-hours urgent-care facility. It was a start-up and needed to hold down costs, but because it provided emergency care, it needed to make sure that every incoming call was answered quickly and was routed to the proper person. So Uptime Group used Asterisk's call-routing flexibility to build a sophisticated system that automatically routes calls to the right health care professional, based on a set of complicated rules.

Incoming calls are first routed to a doctor or nurse on duty at one of the facility's locations. If there is no answer in two rings, it automatically routes to two more people, one on a cell phone and one in the medical office. If neither of those people answer quickly, the call automatically routes to the public 911 emergency system.

"With a traditional, proprietary PBX, you'd have to hire a high-end consultant to do this kind of programming," Laushman says. As for cost, he claims that the facility looked at several proprietary PBXs, which cost "up over six figures," while the one he built for the company based on Asterisk "we put in for less than $30,000 dollars."

Denver-based 5280 Magazine has been using an Asterisk-based PBX for approximately six months, and systems administrator Jeff Panis says the magazine bought the system for its flexibility as well as its relatively low cost. Among the features important to the magazine are that editors and the sales force can use softphones to retrieve their voice mail when they are out of the office.

In addition, voice messages are digitized and sent via e-mail for easy access to them no matter where someone is. The system saves on hardware and licensing costs compared with traditional PBXs, and it saves on staff time as well, because users can make their own changes to their phones with a Web-based interface.

Users can forward incoming calls to external numbers and have incoming calls automatically sent as media files via e-mail automatically, without having to ask an administrator to set up their phones to perform those tasks.

Asterisk can also tie into databases such as MySQL, which is the primary database 5280 Magazine uses for internal application development. The magazine is developing its own team management organization tool for its sales and marketing staff using MySQL, and it will be able to tie its Asterisk-based PBX into that system when the new application is complete.

"A big part of the choice was Asterisk's ability to expand and tie into other systems," Panis says. "Also, with Asterisk, you're not tied to paying big upgrade and licensing fees every time you need to upgrade."

Why you shouldn't use Asterisk

All this doesn't mean that Asterisk is for everyone. In fact, it isn't. To date, it has primarily been used by small and midsize businesses, rather than for large enterprises with multiple offices and divisions in multiple locations. For example, Uptime Group has yet to build a deployment of that size.

"I've heard and read that you can chain Asterisk systems together to make much larger phone systems," Laushman says, but his company has no hands-on experience on doing it.

In addition, building and programming PBXs is not for the faint-hearted; few companies have the expertise to build a system in-house. So companies will have to rely on companies such as the Uptime Group or Switchvox to build systems for them.

Support can be an issue as well. When an Asterisk-based system is installed by a consultant, a support contract will be needed. That means making sure that the company that builds the Asterisk system is solid and will be around for years, in order to provide support.

Finally, there are the cultural issues around using open-source software vs. commercial software. There are companies that still don't trust the open-source model, so any company leery of open source in general will want to stay away from Asterisk.

The future of Asterisk

It's clear that Asterisk is no flash in the pan and is here to stay. Digium Inc. in Huntsville, Ala., is the primary creator of Asterisk and claims that Asterisk has already been downloaded 1 million times. The company also says that there are 130 business partners building Asterisk-based systems worldwide.

Digium also recently closed its first round of venture capital funding, $13.8 million from Matrix Partners, a venture capital firm that manages over $2.5 billion in assets, and has previously invested in businesses including Apple Computer Inc., JBoss Inc. to Sycamore Networks Inc.

So if you're thinking of moving to an IP PBX or upgrading an existing one, commercial-grade PBXs are not your only choice. Ultimately, you may not choose an Asterisk-based system, but it's worth your while to at least give the open-source PBX a first look.

For more information:

Digium's Web site has basic information, downloads, blog posts, etc.

This comprehensive wiki includes news, reference, articles, books, tutorials, forums and other sections.

Trixbox is a tool for Asterisk implementation, formerly called Asterisk@Home

Wikipedia has an entry about the Asterisk PBX.

Preston Gralla is a contributing editor for's Networking Channel and the author of more than 35 books, including How the Internet Works, Windows XP Hacks, and the upcoming Windows Vista in a Nutshell. He has written about technology for more than 20 years, and has published in numerous national magazines and newspapers, ranging from Computerworld to USA Today, the Los Angeles Times, The Dallas Morning News, and CIO Magazine.

Copyright © 2006 IDG Communications, Inc.

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