Northwestern University is getting rid of its old TDM phone switches not in response to a groundswell of demand for communications options unique to its new VoIP system, but to be ready for the day when that groundswell hits.

“In some sense we are buying potential," says David Carr, director of telecommunications and networking for Northwestern, about the move to Nortel VoIP switches.

Most of the university’s 18,000 phone users on two campuses say they’d be happy with phone service just as it is, according to a poll by Carr. Others are ready to embrace VoIP, but for a limited set of features that can help them do their jobs better right away.

Click to see: Diagram of Northwestern's resilient VoIP network

The new capabilities include mobility and presence integrated with applications, but Carr says users weren't looking for a specific application.

Time for upgrades

As part and parcel of the VoIP project, which started in 2003 with a review of ways to upgrade two Nortel SL 100 phone switches, the university discovered it needed to upgrade its wiring closets, stress-test its network, address QoS and consider network admission control. “They all get wrapped together," Carr says.

The two carrier-grade SL-100 phone switches, one at the university’s Chicago campus and one at its campus in Evanston, Ill., were about 20 years old.

The goal was to collapse the two separate switches into a single logical switch to reduce management complexity, he says. The school also didn’t want to replace all its digital phones at once.

It decided to upgrade to the Nortel CS 2100 VoIP switch, which supports both VoIP and TDM, so users would not be forced to switch their handsets for VoIP phones. “Those who wanted to take advantage of the VoIP value proposition could do so, and those that were happy continuing to use their current telephony features and services could do so. It allowed the community to migrate at its own pace," Carr says.

The university has installed a CS 100 at the Chicago campus and expects to have one installed at the Evanston campus next month. Until then the school has 250 IP phones working on a trial basis. “Beyond that we’re waiting until we finish these upgrades," he says.

The university is keeping the line side of the TDM switches that the twisted-pair wires plug into. The trunk side and the core of the switch are all IP and include an interface that marries the TDM access lines to the VoIP core.