Wireless LANs Create Opportunities And Challenges For School Districts

The different variants of 802.11 wireless networks offer different speeds, coverage and performance, so school districts have to decide which version best suits their needs.

It all starts on the walls and ceilings. That’s where you mount your wireless access points, running an Ethernet cable back to your local area network (LAN). Then you just cart in some notebooks with wireless network cards and, presto, you’re on the Web with no strings attached.

If only it were so simple.

School districts that have installed wireless LANs (WLANs) say 802.11b Wi-Fi initiatives involve heaps of planning, regular tweaking and constant attention to security.

“We spent a lot of time figuring out the best way to implement this technology,” says Nancy Toll, technology coordinator for the School District of Hudson in Hudson, Wis. “It had to fit into our larger network and give us campus-wide coverage.”

Hudson now has 14 carts, each stocked with 15 wireless notebooks, for the seven schools in its district. But before even implementing wireless connectivity, the district determined it needed a beefed-up wide area network.

“We had to add a second T-1 line to our district because of the additional demand, and we’re going to need another upgrade fairly soon, probably a T-3,” Toll says. “Our network gets a lot more use now.”

At Consolidated High School District 230 in Orland Park, Ill., Technology Coordinator Darrell Walery paid particular attention to antenna placement when setting up a district-wide Wi-Fi network. “The bottleneck for us is at the local access point,” he says.

Like most school systems, Orland Park uses the 802.11b standard for its network. According to most experts, you can expect throughput problems after 25 or so devices patch into a single access point.

“We wanted to make sure every classroom could hook up to at least three access points,” Walery says. “Just as with a hard-wired network, you want to create a certain amount of redundancy.”

Ken Dulaney, a wireless analyst for Stamford, Conn.-based Gartner, preaches the need to map user density. “It’s a shared medium,” he says. “A dense cluster of users can really cause a problem if you haven’t planned for it.”

Of course, that redundancy also touches on one of the chief problems with an 802.11b WLAN: It’s a crowded band. 802.11b broadcasts across three nonoverlapping channels on the 2.4 gigahertz (GHz) frequency. It shares that frequency with wireless phones, personal digital assistants and even microwave ovens.

Congestion often becomes a problem, resulting in device interference and diminished performance.

“There comes a point where you’ve just got too much activity and interference on that frequency and no amount of access points can save you,” notes Chris Kozup, an analyst with META Group in Stamford, Conn.

Hudson’s Toll engineered an innovative solution to that problem: She put the access points on the carts themselves.

“The access points are only plugged in and operating when the carts are in use,” she says. “It cuts down on interference, and it helps with security because the network’s not always open.”

Her reports indicate that having cart-based access points has helped alleviate bottlenecks and allows the school system to deploy the technology without having to invest in additional infrastructure, which would increase overhead costs.

The cart-based access point solution hasn’t solved all of Hudson’s Wi-Fi challenges, however. “We’re seeing the bottleneck in our point-to-point wireless feed between buildings,” Toll says. “In fact, we’re looking for a higher speed point-to-point solution to fix that.”

School buildings may also cause problems for WLANs because of the many walls between classrooms. In general, users and experts both agree that the typical 300-foot coverage distance for open areas, such as cubicle workspaces, does not apply to schools with dividing walls.

Supply and Demand

Another way to improve your throughput is to limit what classroom users can do with the notebooks. Toll chose not to load all of the software usually found on a hard-wired lab desktop onto the notebooks. For example, video applications are not allowed on Hudson’s wireless devices.

Orland Park’s Walery believes it’s only a matter of time before streaming video becomes essential in the classroom. That will require new technology, such as the 802.11g standard, ratified last summer by the New York-based Institute of Electrical and Electronics Engineers.

The 802.11g standard broadcasts on the same frequency and is backward-compatible with the 802.11b standard, but it offers superior throughput. The maximum speed for 802.11b is 11 megabits per second (Mbps). 802.11g can transmit as much as 54Mbps.

Walery cautions that migration won’t be easy and will likely be costly. “If you’re not going to connect the whole network to the new standard, it doesn’t make a lot of sense,” he says. “So we’re looking to extend the life of our current system as long as we can.”

Experts also stress the difference between the actual speed of wireless networks and the advertised speed.

For instance, Toll says her 802.11b system runs around 4Mbps, which is less than half of the advertised rate.

Dulaney’s research at Gartner corroborates Toll’s experience. The speed is “generally half the quoted link rate on the box and then goes down, dependent on distance from the transmitter and how many users you’ve got,” he explains.

Dulaney further cautions that if you mix an 802.11g network with an 802.11b network, the result is degraded performance. The combination will cut the 802.11g throughput to a quarter of its advertised speed, around 13Mbps. “If you want the higher speed, go to 802.11a and bypass g,” he notes.

The 802.11a standard broadcasts across less crowded bands, typically between 5GHz and 6GHz on 12 nonoverlapping channels. Because it uses a different frequency, it can be deployed alongside an older network without having the two compete for precious bandwidth.

In early tests after its 2001 release, 802.11a did not come close to the coverage range of 802.11b, but experts say that, while the performance degrades after 150 feet, the speed is still superior at the 300-foot distance generally associated with 802.11b.

META Group’s Kozup expects that dual-and (a/b) access points will hit the market in force in 2004 and quickly become competitively priced.

Siege Mentality

While wireless carts allow teachers to incorporate technology with the classroom lesson plans, a WLAN does create a security hassle for the IT staff.

“Schools are one of the places where you have hostile users,” Orland Park’s Walery says. “Students can get sophisticated fairly quickly, and they’ll figure out ways to hack into your system.”

He’s seen it happen. “We had a case where some students had stolen a wireless card and modified it,” he recalls. “They attached an extra antenna and were out in the parking lot probing the network when we caught them.”

Orland Park will be adding a new router for added security. Those who wish to use the WLAN will first need to log on to that network and then on to the school system’s main network.

Until this year, Wi-Fi security standards were fairly ineffectual when it came to stopping hackers or blocking eavesdroppers, but META’s Kozup believes the Wi-Fi Protected Access (WPA) standard will change that.

WPA requires encrypted data between the client and the access point and allows the access point to run its own WLAN user authentication. He also notes that better wireless network management software will be hitting the market soon.

“The wired side doesn’t know what the wireless side is doing, and the wireless side doesn’t know what the wired side is doing,” Kozup says. “They’re just passing packets per the Ethernet standard. If you can get better insight into how it all works together, it will improve everything from performance to security.”

Oct 12 2006

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