Asterisk SCF Goes for Scale in New Open Source VoIP Project

The open source Asterisk project started off as an effort to be an on-premise IP-PBX. Over the years, demand for increasingly scalable and modular approaches for voice communications has grown, which is why a new Asterisk project is being announced this week.

The Asterisk Scalable Communications Framework (SCF) is a new project sponsored by Digium that aims to build an open source VoIP system for large-scale deployments.

“This is motivated by need to be able to provide transparent fault tolerance and give application developers what they need to build the types of things they want to build now, which is primarily not PBX based applications,” Kevin Fleming, Director of Software Technologies at Digium told

Fleming added that SCF is also about providing the ability to scale up or down as conditions and demands change. He noted that Asterisk SCF is a new project and isn’t the same as the Asterisk PBX, though the two efforts will complement each other.

“One of the areas we need to spend time on is figuring out is how tight an integration can we make between SCF and Asterisk and what makes the most sense,” Fleming said.

While scalability is one of the reasons why the SCF project is being created, that doesn’t mean that the regular Asterisk releases won’t benefit from scalability improvements in the near term. Fleming added that, realistically, Asterisk SCF won’t be production-ready for a year or more, and in that time the needs of scale won’t go away.

“There are lots of solutions that already exist for Asterisk that handle large scalability call volumes,” Fleming said. “What I think is really going to be the differentiating factor for SCF will be the ability to grow or shrink scale on demand.”

Fleming explained that with Asterisk SCF, administrators will only have to deploy the components that they actually need. For example, if a big platform had a voting call-in system for a TV show, there would be a need for SIP connectivity, database, call routing and IVR (Interactive Voice Response). In such a scenario, the IVR component may not have the same capacity as the SIP connectivity and the database back end. Fleming noted that with Asterisk SCF, the administrator can spin up as many Amazon EC2 instances as they need just for the IVR component and each one talks to the same SIP and database back end.

“I can just say, I need a hundred more copies of the IVR component and I only need them for four hours tonight,” Fleming said.

For now, Digium does not yet have any formal plans around commercialization of Asterisk SCF. The announcement of the project at this stage is about soliciting community and developer interest and to kick-start the open source project.

“We don’t yet know what all the components of SCF will be,” Fleming said. “A lot of that will come from discussions with potential consumers of the platform.”

Sean Michael Kerner is a senior editor at, the news service of, the network for technology professionals.

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