January 17, 2005 (Computerworld) -- When Erlanger Health System began deploying VoIP technology in 2002, it wanted to simplify and lower the cost of moving phones when employees changed locations.
Since then, however, the 28-hospital system, based in Chattanooga, Tenn., has added wireless VoIP phones so caregivers can communicate when mobile. It's also testing multimedia IP applications to improve scheduling efficiency and eventually allow physicians to conduct patient consultations via videoconference, says John Haltom, Erlanger's network director.
IP PBXs, unlike their proprietary circuit-switched counterparts, convert phone numbers to IP addresses. IP addresses can be assigned automatically by Dynamic Host Configuration Protocol servers when phones come online and even when users "log in" to remote phones on the VoIP network.
Moving IP phones requires little more than unplugging them from the back of a PC or Ethernet switch port and plugging them in elsewhere.
"We figured initial savings were about $40 per phone deployed, based on converging the cabling infrastructures for the computing and phone systems," says Haltom. "But those savings are not nearly as significant as when users move a second and third time."
In the circuit-switched world, moving entails PBX line-card changes, programming and technician time for changing cabling cross-connects, he explains. The whole process can take several days.
Designing for Reliability
Erlanger is moving its IP phone population to Nortel Networks' Communication Server 1000E IP PBX over five years. The facility selected the Nortel system for its reliability.
The two other vendor contenders at the time of selection -- Avaya (Erlanger's incumbent supplier) and Cisco Systems -- both based their IP PBXs on Windows servers.
"We couldn't see banking telephony on Windows," Haltom says. "We couldn't control viruses on our [Windows-based] PCs," which made the system unsuitable for Haltom's goal of 99.999%, or "five 9s," uptime.
Windows for telephony "is a religious and cultural issue," observes Areg Gharakhanian, a vice president at Vanguard Communications Corp., a call center and IP telephony consultancy in Morris Plains, N.J.
"Windows has a reputation for being less reliable than Linux or Unix, but the Windows-based IP PBXs have fail-over mechanisms. The biggest issue has to do with software patches," Gharakhanian says. "The more Windows servers you have for fail-over, the more patching you have to do."
Erlanger's VoIP project slowed when wireless phones entered the picture. Adding Nortel wireless gear shifted the redundancy and power requirements from the centralized data center to distributed wiring closets. Here, wireless LAN switches connect to ceiling-mounted radio access points. The access points bridge traffic from mobile VoIP phones to the wireless switches, which connect to the corporate network and IP PBX.
Erlanger wanted a common power-management and redundancy scheme for managing the entire distributed VoIP system, including the wireless access points and wired IP phones.
"Adding wireless required us to take a big step backwards and look at pushing redundancy, power and air conditioning -- taken for granted in the computer room -- out to the wiring closets," says Haltom. "This is a massive infrastructure effort for mission-critical services. Anyone who doesn't look at it this way is making a big mistake." Erlanger needed its vendor to evolve to meet this requirement, says Haltom. Nortel offered 24-port power-over-Ethernet hubs for the wiring closet, but at the time they didn't support dual power feeds, he says. "If the power supply died, 24 users fell off the face of the earth. That wasn't a five-9s environment," Haltom says.
Then the Nortel Passport 8300 Ethernet Switch arrived with fully redundant power-over-Ethernet components for powering wired IP phones and wireless access points. The hospital system could then implement full redundancy in the wiring closet.
Hybrid Network for E-911
A hybrid VoIP/time division multiplexing (TDM) architecture has two IP PBXs and eight TDM phone switches. For emergency 911 services on the wired network, Haltom says, all PBXs collapse back to the TDM architecture. The TDM PBXs hook to the public-safety answering point in the municipality that's geographically closest.
Wireless emergency calling is less straightforward. Nortel buys equipment from other manufacturers and customizes its WLAN switches, access points and IP handsets. While the wireless switch software can triangulate a phone call to a handset within a few meters of an access point, no integration has yet been done to communicate that location information to the Nortel IP PBX. The IP PBX, in turn, would pass it along to a public-safety answering point, Haltom explains.
At press time, Erlanger was finishing an 18-month beta test with the Nortel Multimedia Communication Server 5100, which enables presence-management-based functions for about 500 users.
Presence management applications converge VoIP, data, video, instant messaging and location tracking across wired and wireless networks to display users' whereabouts and status. Users click on another user's entry to set up instant messaging, a mobile call, VoIP call or videoconference session.
Eventually, Haltom would like to combine the Multimedia Communication Server 5100 with a computer on a portable audio/video cart. Doctors, who have trouble finding time to see all the patients on their rosters, could consult from home or other locations via videoconference, he says.
Wexler is a freelance writer in California's Silicon Valley. Contact her at joanie@jwexler.com.
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