Open source PBX calls on telecoms

The Asterisk open-source platform touts increased flexibility that proprietary products cannot offer, allowing users to integrate their own applications.

Faced with the high cost of buying a traditional telephone system, Digium CEO Mark Spencer made use of his own programming skills to create Asterisk, an open-source alternative.

Spencer had helmed a company called Linux Support Services, when he decided to create an open source-based PBX in 1999 and dubbed it, Asterisk. He then changed the name of the Huntsville, U.S.-based company to Digium, shifting its focus to provide support and consulting services for the Asterisk open-source platform. PBX, or private branch exchange, is a telephone system which resides within a company and is used to connect calls between users in the organization as well as callers from external phone lines.

According to a Digium spokesperson, the company's Asterisk-based products provide significant cost savings compared to proprietary telephony systems. The open source tool also touts increased flexibility that proprietary products cannot offer.

"Digium's products not only offer a complete VoIP (voice over Internet Protocol) solution, but can provide companies with a 'hybrid' solution combining legacy equipment with VoIP applications," the spokesperson said.

Brian Capouch, assistant professor of computer science at the Saint Joseph's College in Indiana, said Asterisk is largely popular because of its ability to integrate legacy telephony protocols. Capouch lectures in networking, open source and wireless technologies, and has helped implement an Asterisk system for the school. "Its real success comes from its wide support for different kinds of technologies," he said, during an interview last year with IT Conversations, a U.S.-based podcast channel.

Capouch estimated that organizations that deploy Asterisk could save 15 to 20 percent of what they would normally spend on a legacy telephony system.

Disclaimer requested

While Asterisk is licensed under the GNU Public License (GPL), Digium asked developers who contribute to the Asterisk code base to include a disclaimer so that the company can use the developers' codes in its proprietary products.

Under the GPL, source code can only be integrated with other codes that are governed by the same license. That provision is necessary for such software to remain free from proprietary constraints, according to the authors of GPL.

Brian Capouch, Saint Joseph's College's assistant professor of computer science, said: "[Digium's] justification is that [it] gave away the code--[the company's] primary intellectual property. But there are a number of GPL purists in the crowd who feel that's not the way to do it."

"There is a lively debate in the Asterisk community on whether that disclaimer does more good than harm, though generally, the community sees this as a way to pay back Mark Spencer for creating [Asterisk]," Capouch said.


    Today, Digium's customers hail from a broad spectrum of industries ranging from contact centers and research companies, to universities and government bodies. Presently, there are over 1 million Asterisk users, in addition to 130 vendors and 500 contributors who support the platform, according to Digium.

    The company's customers include the University of Pennsylvania (Upenn) in the United States and the German city of Pforzheim, an area known for its black forest cakes and traditional cuckoo-clocks. Upenn deployed Asterisk last year, and had worked with Digium to extend the open source system with a unified messaging platform that pulls messages from e-mail and voice inboxes into a single data repository.

    Officials at Pforzheim implemented Asterisk to deliver VoIP (voice over Internet Protocol) capabilities to users of the municipality's network. But it was the ability to combine its own applications with Asterisk that the German city decided to go with the open source platform.

    Andreas Hurst, the city's director of Internet technology, said in a media statement: "Making the biggest difference for our organization is the possibility to integrate collaboration services and business applications with voice. That is the greatest difference between the VoIP Asterisk solution and other traditional systems. With Asterisk, we have more functionality available than we had with the traditional telephony system."

    Digium's spokesperson also acknowledged that some customers prefer to support Asterisk deployments on their own. But "as the creators of Asterisk, we strongly recommend companies work with us and our certified partners to ensure the best solution for their needs," she said.

    According to Capouch, there is "great interest" in the open source system from countries where telecoms monopolies charge exorbitant call rates, or in places where VoIP regulatory issues have yet to be evolved.

    "Once someone comes up to speed with the technology that underlies Asterisk, it really comes close to replacing an entire telephone switch," he said. "We're finding people putting Asterisk servers and completely doing away with their local [telephone] service that they are getting in their country."

    Plans are already underway to add video and instant messaging features to the platform, Capouch said. The Inter-Asterisk Exchange (IAX) Protocol, developed by Digium, is already used in some Asterisk-compatible video phones, he added.