Asterisk SCF: Enterprise-class open source VoIP and UC

The new Asterisk SCF framework could transform the open source VoIP software into an enterprise-class unified communications platform with the scalability needed by enterprises and the agility required by the cloud. Digium is reengineering Asterisk's architecture for virtualization, and it will depend on developers to add applications to the framework.

Open source Asterisk VoIP software initially launched in 1999, years before the advent of multi-core processors, server virtualization and cloud computing. Asterisk VoIP software has a significant following, with thousands of developers contributing and enhancing its functionality, but the underlying architecture is best suited for small deployments. Digium, Asterisk’s creator and curator, has recognized that the open source VoIP software needs to be scalable and agile enough to meet the needs of large enterprises. The company is developing a new platform, Asterisk Scalable Communications Framework (SCF), that will meet the requirements of large enterprises and cloud services, as well as open the platform up to a broader range of developers.

The need for scalability in open source VoIP

Asterisk is monolithic in its architecture, built to support a single process or service on one server, according to Steve Sokol, marketing director for Asterisk at Digium. This architecture is fine for small and medium businesses, but it doesn’t scale to meet the needs of a large enterprise. Asterisk was originally designed as a multi-function PBX before the rise of unified communications, so the technology is primarily a voice application. While the Asterisk community has contributed more than 120 helper applications to give Asterisk additional functionality and high availability options, its architecture is still designed to operate within a single physical server. Many Asterisk devotees have used Moore’s law and 10 years of hacking to expand the software beyond its voice-centric, single-server roots. The high availability options, for example, redirect between a master and slave Asterisk VoIP server and require nearly half a minute to failover. However, the single server architecture and its inability to be virtualized and distributed have limited Asterisk's appeal to large-scale enterprises.

Asterisk SCF, due out in late 2011, is a completely reengineered platform that aims to solve the performance, scalability, fault tolerance and extensibility issues inherent in Asterisk VoIP.

“Asterisk SCF is not a PBX or softswitch, but an IP communications network that enterprise-class communications solutions can be built on top of,” Sokol said.

The new Asterisk SCF architecture manages distribution and call control of not only voice traffic, but also any number of media types, including video and instant messaging. Digium has broken Asterisk SCF into individual services or functional blocks, such as media, bridging, video and SIP session management. Enterprises can  deploy each service across multiple virtual or physical servers. This modular design also gives Asterisk SCF its high availability characteristics. Multiple instances of these core services can be deployed between different servers or even different data centers. Vendors and enterprises will be able to integrate applications into Asterisk SCF to provide unified communications solutions, such as call center and interactive voice response (IVR) services. Asterisk SCF will even be a complement to the original Asterisk platform by delivering the SIP interfaces it needs and linking disparate Asterisk services on a common IP communications network.

“Asterisk SCF is something that Digium had to do to go beyond the SMB market. The framework will certainly allow the company and its developer community to take on much larger projects,” said Rob Arnold, senior analyst for enterprise communications at Frost and Sullivan.

Asterisk SCF success will depend on developer community

Asterisk SCF will not be a complete out-of-the-box unified communications solution. Digium will offer a few sample applications to demonstrate the potential of Asterisk SCF, but it will rely on the open source VoIP developer community to build applications that will transform Asterisk into a complete enterprise UC package. Digium hopes to lure more developers by providing application programming interfaces (API) and support for multiple development languages in Asterisk SCF.     

“You shouldn’t need a PhD in Asterisk to develop for SCF,” Sokol said.

Digium has also modified its open source licensing for Asterisk SCF. Based on the GPLv2, developers who release their own code under a similar open source licensing will have open access to Asterisk SCF. However, Digium requires a license if a developer wishes to keep its code propriety.

Will large enterprises embrace open source UC?

While Linux is accepted by many as an enterprise-class open source technology, Asterisk SCF will have to prove itself before large organizations will adopt it as  the backbone of their mission critical unified communications solution.

 “Most enterprises choose best of breed for their UC products, rather than single-source vendor solutions,” Arnold said. “While it may not displace an organization’s primary unified communications solution, Asterisk SCF could find its way into the enterprise for specific solutions.”

Since Asterisk SCF is open source, some vendors may use it as an underlying framework of an otherwise commercial technology. Enterprises may install such Asterisk SCF-based products without even knowing that they are running open source VoIP.

Open source VoIP and UC in the cloud

Asterisk SCF is a unified communications virtualization solution by design, which makes it an ideal technology for cloud deployments. With its added scalability and extensibility, Asterisk SCF  will be attractive to service providers as a low-cost, open source foundation  for multi-tenant, cloud-based virtual call centers and hosted PBX solutions.

“The cloud vendors tend to be more willing to embrace open source software to provide solutions to their customers,” Arnold said.

This was first published in February 2011

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