High Education Tackles The Problem Of Wi-Fi Capacity - InformationWeek

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4/28/2006
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High Education Tackles The Problem Of Wi-Fi Capacity

Colleges are finding ways to meet the wireless computing demands of large concentrations of students--and businesses could learn a thing or two from them.

Have Laptop, Will Connect
Northern Michigan University in Marquette experienced the challenge of providing adequate wireless performance in a dense environment where creating microcells, even on nonoverlapping channels, wasn't enough in an open area. The university, which has a mandatory laptop program, has in its Jamrich Hall 36 classrooms on the upper floor and three lecture halls on the lower level that seat 350 people each. Thirty-six access points in the hall serve about 800 wireless connections at peak times, a 1-to-22 ratio of access points to clients. Although that's not unusually high, it doesn't reflect the fact that each lecture hall hosts just three access points for up to 250 students at one time--averaging 50 to 80 active clients per access point, assuming effective load balancing. Even for the most robust enterprise wireless products, this volume poses a scalability problem.

David Maki, director of technical services, found that after 15 wireless clients were associated with a Cisco Aironet 1200 series access point, it would become unstable, making it impossible to scale online learning in a lecture hall environment. Adding access points on other channels and turning down their power helped, but the first-generation generic wireless cards in students' newer laptops didn't automatically trim their power output levels as previous models did, and the power asymmetry led the wireless clients in one lecture hall to interfere with the laptops in the neighboring hall.

Maki deployed Airespace's thin access point system, which worked well enough that he could reach 75 users over two average classrooms, but the performance degradation that exists in mixed 802.11b/g environments and the occasional quirks left him less than satisfied.

The Wireless Crowd, barchartMaki bought a Meru Wireless LAN Controller and several multiband access points from Meru Networks. Contrary to the conventional deployment of adjacent access points with nonoverlapping channels, Meru uses a single channel for all its access points. By using an advanced centralized coordination system to control when its access points transmit, and leveraging 802.11 features such as network allocation vectors and related concepts to control when clients transmit, the LAN controller is able to maintain good performance even in very dense environments. Meru's system also is able to use its upstream control mechanisms to virtually separate 802.11b and 802.11g clients, so the typical performance degradation that occurs in mixed environments is avoided.

Overall system capacity problems are addressed by deploying additional access points on nonoverlapping channels. Since the Meru deployment, Maki says he hasn't looked back. He can have as many as 100 clients on an access point, and the presence of 802.11b clients doesn't drive down the performance of 802.11g clients.

Universities, with their compact living quarters and student-filled lecture halls, are facing the challenges of dense wireless deployments--channel selection, co-channel interference, power asymmetry, and wireless client scalability. Businesses can expect similar challenges as their wireless networks mature.

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