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Open source packs free IP telephony

Dec 16, 20025 mins
LinuxNetworkingOpen Source

Open source IP telephony software packages are helping users move away from the traditional world of proprietary office phone systems, PBXs with closed operating systems and expensive specialty components.

Users also are taking advantage of Linux for running IP voice. Observers say open source telephony software packages – many as good as commercial products – are further opening the world of packetized voice.

The open source Linux platform is a growing part of the computer telephony infrastructure at Sitel Worldwide, an Omaha, Neb., a company that runs call center operations for customers such as Cox Communications, Verizon and Mitsubishi Motors. Sitel has deployed Linux servers running the company’s call center application and database to more than 20 of its call center sites worldwide.

The Dell PowerEdge 2650 servers, which run a Red Hat Linux and an Oracle Enterprise Server database, interact with Nortel circuit-switched PBX systems at the sites, providing call center applications such as “screen-pops” or windows with customer information brought up through caller ID technology.

Scott Clark, director of systems at Sitel, says he is pleased with the stability of Linux in the company’s call centers, especially because many sites are in far-flung locations with no onsite technical support.

Unlike Web, file or print servers – the traditional role of Linux in many companies – Sitel’s Linux boxes are running an application that operates in real-time with the company’s call-routing infrastructure, which requires zero downtime.

“The [Linux] servers are rock-solid, and you don’t have to mess with them,” once they’re deployed, he says.

Sitel uses several IBM RS/6000 servers running AIX in its central data center, but Clark found that distributing RS/6000 servers to all its call centers would be cost-prohibitive. With Linux he says he saved about $9,000 per server as opposed to using IBM/AIX boxes.

Sitel also uses Red Hat Linux servers to run its call-recording application, a package called TantaComm Dart, which records customer service calls for Sitel’s credit card and banking customers, and stores the data for seven years – a requirement by law for those industries.

For users comfortable with open source software and have a do-it-yourself mindset, there are many options for deploying Linux and other types of free software in a voice-over-IP (VoIP) or computer telephony environment.

Two open source software packages that provide Session Initiation Protocol (SIP) and H.323 protocol gateway support are available for free from Vovida and Columbia University’s computer science department.

Vovida, a company that Cisco acquired in 2000, offers a Linux-based telephony server that can provide protocol translation for H.323, Media Gateway Control Protocol and SIP, and a SIP proxy and conferencing server.

free SIP-H.323 gateway is available from Columbia’s Web site. The software translates traffic among devices using these two protocols, allowing SIP- and H.323-based phones switches to live on the same network.

Both software packages have been tested and deployed at Menlo College in Atherton, Calif., which uses a mix of Cisco CallManager IP PBXs, Cisco phones, other vendors’ SIP phones and SIP-enabled PCs around its campus.

Patrick Olson, formerly the CIO at Menlo College, who oversaw the VoIP technology installation at the school, says the open source SIP software from Columbia was a good complement to the network.

“I liked [Columbia’s SIP-H.323 gateway] best,” Olson says. “The Cisco CallManager keeps track of all the telephone numbers, and you simply add each SIP phone as an H.323 phone in the CallManager and let the gateway connect the phone to the CallManager. The signaling gateway takes care of [SIP] registration.”

Olson says this lets SIP products from third-party vendors such as Pingtel, be deployed on the CallManagers, which do not support SIP natively, he adds.

Other open source packages for computer telephony H.323 networking include Bayonne and the OpenH323 Project.

Bayonne is a telephony application server that runs on Linux and can be used in areas such as interactive voice response, integrating voice features into a Web site or as a small corporate voice mail system.

Free VoIP

Some open source projects for Linux-based IP telephony servers.


A Linux-based telecommunications application server of the GNU project for developing telephony applications such as voice mail and IVR systems.

SIP-H.323 Signaling Gateway

Developed at Columbia University, the gateway maps SIP and H.323 addresses to each other, letting devices supporting these protocols work on the same network.

OpenH323 Project

An open source project that has developed a variety of H.323-based telephony applications for Linux, such as a H.323/public switched telephone network gateway, H.323 softphone and a conferencing server.


An open source effort responsible for VOCAL, a Linux-based telephony server that can provide H.323, MGCP and SIP protocol mapping, and a SIP proxy and conferencing server. Also runs on Windows, Solaris and FreeBSD servers.

The OpenH323 Project has software available for building Linux-based gateway servers to act as a bridge between an H.323 network and the public phone network. The project also has software on its Web site for a Linux-based H.323 softphone application and a conferencing server based on H.323 and Linux.

But there’s an element of “installer beware” with these packages, experts say.

“Like all open source software, these kind of packages have their pros and cons,” says Mike Hommer, lab manager at Miercom, an IP telephony testing and consulting firm and a Network World Global Test Alliance member.

Cost is an obvious plus, because the packages are free. But getting the right driver support for specialized telecom gear can sometimes be difficult, and could be more time-consuming and costly than buying a preconfigured commercial product, other observers say.

Having a staff that is experienced with programming and how the open source community works is essential to any project involving free software, says Mark Lesswing, vice president for the Center for Realtor Technology at the National Association of Realtors. Lesswing has helped his organization integrate several open source software rollouts.

“You have to be prepared to do a lot of bug fixing and even some pretty extensive coding yourself,” when taking on any piece of free software, Lesswing says.