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May 2007
Volume 10 / Number 5
Tech Score
Jeff Hudgins

Can an Asterisk-Based System Scale Out?

By Jeff Hudgins, Columns: Tech Score

Zaptel drivers and Asterisk® software have come a long, long way since their initial release and continue to grow and improve every day. We now see a tremendous number of solutions being deployed that run on Asterisk software. One question that has been raised concerns the scalability of the end solution. So let’s explore the concept of a straightforward VoIP gateway solution and how its scale and flexibility are addressed.


The Hardware Layer

The release of Intel’s 3000 chipset is aimed squarely at the entrylevel server market. It supports single-socket systems but can handle Pentium D and Celeron D as well as Intel’s 3000 series dual and quadcore processors. Platforms based upon this chipset can also support up to four DIMM sockets and up to 8 GB of DDR2 memory. With all of these options, there is ample room for application developers to tune and scale their code for a variety of VoIP gateway functions.

In addition to the server component chip set, provisions are also available for plug-in third-party cards to interface to the public switched telephone network (PSTN). Industry-leading board manufacturers such as Aculab (news - alert) (, Dialogic (news - alert) (, and Digium (news - alert) ( all offer driver support for Asterisk. These cards offer a broad range of protocol support and can scale up to 8 T1/E1 interfaces, if needed.


The Operating System Layer

Asterisk is a complete IP PBX software solution that runs on a variety of operating systems (OS) including Linux, Mac OS X, Open BSD, FreeBSD, and SUN Solaris. A typical Asterisk based VoIP gateway would likely be configured with a Fedora Core or similar operating system.


The Application Layer

In the past, developers purchased an Asterisk Developer’s Kit which included a TDM board with two modules installed. Developers then built their applications working with the Asterisk platform. The recent release of AsteriskNowTM appliance simplifies server application scaleout by eliminating the hassles of installation, configuration, debug, and maintenance. AsteriskNow is a Software Appliance that contains everything you need - the Linux OS, Asterisk, the AsteriskGUI, and all the other software - to build a complete solution, such as a VoIP gateway system. The Asterisk software can be easily configured with a graphical interface. Additionally, the burden of OS kernel versions and package dependencies are eliminated.

So how was the software appliance created? Digium turned to a company called rPath ( and their rBuilderTM product in order to build the AsteriskNow software appliance and Asterisk Business Edition appliance. According to Marty Wesley, Senior Director of Marketing at rPATH, “rBuilder proved to be the easiest way to build the appliances, turning what was several weeks of manual work into a couple of days. In addition, the application now contains field update capability which comes standard in the rPath Appliance Platform.”


The Solution

Integrating the hardware, OS, and application layers into one platform now provides a scalable Asterisk based solution. The figure accompanying this column shows how an ISV or OEM can implement a complete turn-Key VoIP Gateway appliance based upon an AsteriskNow (rBuilder-based) platform.

Final Score

The scale-out of an Asterisk-based system is certainly achievable, but you better be working with industry players that can ensure your success.

Marty Wesley adds: “With the adoption of rBuilder, one of the first things Digium saw was a drop in the number of support calls related to problems with the installation or configuration of Linux. Previously, Digium experienced up to 40% of their support issues that were unrelated to the Asterisk application. Secondly, Digium was able to offer AsteriskNow as a free trial appliance as a lead into their enterprise-grade Asterisk Business Edition. The ease of consumption of AsteriskNow has led to intense interest and trial in the product, averaging over 5,000 downloads a week. The software appliance model opens the door for enterprising VARs to offer specific versions of Asterisk-based appliances. Asterisk can be combined with many other business systems to offer more complete business solutions.”

In the end, combining a software appliance with a robust hardware appliance provides Value Added Resellers and End Users a solution they can leverage right out of the box.

Jeff Hudgins is VP of Engineering at Alliance Systems. (news - alert) For more information, visit the company online at


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