Open source tools such as Asterisk and SIP Enterprise Router are facing their biggest test yet at the University of Pennsylvania, where deployment of 15,000-seat VoIP network based on these open source IP telephony servers is rolling along.

The Philadelphia-based Ivy League university currently has over 1,250 Session Initiation Protocol (SIP) IP phones on desktops, tied to a back end based on SIP Express Router -- an open source VoIP call-control and routing stack, and Asterisk for voice mail messaging.

Deke Kassabian, the university's senior technology director for information systems and computing, plans to grow that installed base by a factor of more than 10 over the next five years. Driving the project is the desire to get off costly Centrex monthly fees and infrastructure, and the promise of an open source, standards-based VoIP infrastructure that provides superior integration and control.

"If we can run one modern IP network for voice, video and data …. there's a clear win," Kassabian says. "If we provide business telephony internally, less money leaves the university."

The infrastructure Kassabian and his team built is designed for high-availability VoIP, with redundant connections to IP call and feature servers, PSTN and IP telephony service provider (ITSP) point-of-presence links. Two data centers on campus host redundant clusters of Asterisk boxes, SIP proxy servers, and media/messaging feature servers. Phones on the network can register to and access any set of servers. "In this way, there's no single failure, and no single site failure that would take out the servers," Kassabian says.

For outbound calling, UPenn is using a mix of VoIP and PSTN services. For long distance service and other calls, UPenn is plugging its campus VoIP network directly into a SIP trunking service from Level 3. A pair of dedicated Cisco 3600 routers also support PSTN links for local calls, and as a back for ITSP service.

Optical fiber supporting multiple wavelengths of Gbps Ethernet over dense wavelength division multiplexing links UPenn's campus to a carrier hotel in Philadelphia, which provides ISP and SIP trunking services. A Session Border Controller sits at the edge of UPenn's VoIP network and peers with SBCs from Level 3 to connect campus SIP endpoints to IP and PSTN endpoints beyond the university.