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Case Study: Fast 802.11n Wi-Fi goes to college

High-throughput wireless for students.

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A small New York state college will be the site of the first large-scale wireless LAN based on the draft 802.11n high-throughput standard.

Within the next two weeks, Morrisville State College will start initial testing of thin access points from Meru, plus the vendor's existing 802.11abg devices and early models of its recently announced 11n device, the AP300. Even at this stage, the net is posing intriguing new challenges for Morrisville, Meru and IBM Global Technology Services, the systems integrator for the project.

By the end of September, the college plans to have installed a campus-wide net of some 900 of the 11n access points. The net will also include Meru's recently announced high-end companion controller, the MC5000. Morrisville VP of information services Jean Boland says she expects conservatively that each AP will offer 130 Mbit/s of throughput, shared by whatever number of clients associate to it. That compares with 20-25 Mbit/s for 11a nets, also in the 5GHz band, and 11g nets in the 2.4GHz band.

The actual 11n deployment hinges on the availability of Meru's AP300, announced in April. The school's athletes arrive back on campus on the 10th of August, and Boland plans to have a wireless net ready by them. To do so, the college will deploy Meru's existing 11abg AP as needed, replacing them with the AP300 as it becomes available in late August. In any case, by the end of September, the 1,800 students on this rural campus southwest of Syracuse, will become a living laboratory for 802.11n.

Keeping the cost quiet

Boland won't say how much the project will cost. IT vendors typically have special pricing plans for education customers. And a common practice is to cut some kind of additional discount for being a bleeding edge customer. But the list price for Meru's 11n is still something of a shock: US$1,495, or nearly two times the price of Meru's current high-end 802.11a/b/g AP. Pricing for the new controller is expected to be about $65,000.

Morrisville prides itself on being technology savvy, not to mention bold. In 2003, it scrapped wired phones for students, hitting on a plan to issue Nextel cell phones to all students. It's had a plan for issuing ThinkPad notebooks to incoming freshmen since 1998.

Since 11n is so new to the enterprise, to make it practicable, Morrisville had to figure out how to equip the notebooks so they can access the high-throughput channels.

New students starting in September will be equipped with college-owned Lenovo ThinkPad T61s notebooks, with a built-in 802.11abgn chipset. Those PCs will be configured to access the campus WLAN on the 5GHz band, via one of the two radios in the Meru AP.

The second radio in the AP, on the 2.4 band, will devote one 20 MHz channel to 11b/g clients. The remaining two 20 MHz channels will be blended into one, wider, 40 MHz 11n channel to support clients that may have an 11n plug-in card or USB dongle, which, though still rare, are more likely to be found than comparable client radios in the 5GHz band.

Is the draft standard good enough?

The state-of-the-art WLAN will replace one almost as unique: a 1999 Raytheon Raylink, an 802.11 WLAN, using both frequency hopping and spread spectrum techniques, with a throughput of 2 Mbit/s. With a WLAN at the end of its lifetime, and client adapters nearly impossible to come by, "It was definitely time for a change," says Boland.

"The more we looked at it, the more comfortable we felt with the draft [11n] standard," she says.

There were several reasons. One was the surprisingly swift decision by WLAN vendors to bring out draft 11n products targeted at enterprise networks. Most previous products, using the multiple input multiple output (MIMO) technology that's a key part of 11n, had been aimed at residential APs and routers.

Vendors are convinced that any remaining changes in the 11n standard will be minor and can be dealt by upgrading the code in the AP's firmware.

Second was the greatly increased range and throughput that 11n makes possible, and the expected speed at which 11n will be adopted. Boland didn't want to make a major investment on a WLAN that would become obsolete within two years. "To my mind, anything except 11n will very soon be outdated," she says.

Starting in early 2007, Morrisville talked with WLAN vendors under non-disclosure deals to find out about their 11n product plans, and whether those products would fit the college's demand for a functional net by the end of this summer. The college identified its requirements, dug for information, and ranked the vendors.

Good control of clients

Morrisville IT staff liked Meru's early introduction plans and a number of features in the existing Meru product line. One example, says Morrisville net administrator Matt Barber, is that the Meru controller and APs take charge of the client's interactions with the AP, instead of leaving that in the hands of the client adapter as most rivals do. "[In rival products,] a buggy client or a misconfigured NIC can impact all the other clients on an access point," Barber says. Meru's infrastructure can block that disruption, ensuring optimal performance for the other clients.

IBM got the nod for project manager and systems integrator.

It's a gamble for all of them, with a brand new product, and a draft IEEE standard, as the foundation of a pervasive production WLAN. "We're not risk-averse," says Boland. "We met with our campus president, who's very tech-savvy and supportive. He was very comfortable with it and very supportive of the project." When Boland outlined the project, and what it would deliver, to the year-end faculty meeting in May, the news was greeted, she says, with spontaneous applause.

A first order of business was to test the existing wired net to confirm it could handle the 11n data flows. That's nearly complete, and of 270 Cat5 and Cat5e cable segments tested, only three have had to be replaced.

The switching fabric won't be a problem: two years ago, the campus upgraded to Gigabit Ethernet switches from Enterasys. The Meru 11n APs support 10/100/1000 Ethernet links on the wired side, and the controller uses a Gigabit link to the net.

Much more challenging is the problem of getting more wattage to the high-powered APs. Conventional devices use about 15W, but the 11n devices will use up to 30W, depending on how many radios are used and what combination of 11n and 11abg each radio is running. If power outlets are nearby, that's not a problem. But the preference is to power the AP via the Ethernet cable, power over Ethernet (PoE), so that separate electrical lines don't have to pulled to each access point.

Future plans

The Morrisville net may end up with a three-fold solution, says Mark Wheeler, IBM wireless architect with IBM Global Technology Services. One solution is the new generation of wiring closet power injectors, sometimes called PoE Plus, based on the 802.3AT standard. These products are just now becoming available, though any number of them are still only evaluation units, says Wheeler.

A second option is to use a device that, like a vampire, draws another 15W of power from a second, unused switch port, and combines it with the 15 watts on the port into which the Meru AP is plugged. Obviously that halves the number of ports available for APs on each switch. A third option is mid-span power injectors, which can double the wattage on the cable.

Another issue has been whether to offer 11n on one or both of the available frequency bands, says Wheeler. Initially, the idea was to reserve 11n for the comparatively unused 5GHz band, which besides having less interference also offers more channels, and hence the ability to support denser numbers of clients. The 2.4GHz band would be reserved for legacy 11b/g clients.

That's still the long-term goal for Morrisville. But 11n client adapters are still so rare that the college is looking at offering 11n also on the 2.4 band, where the three non-overlapping bands can be segregated into a 20MHz channel for just 11bg clients, with a 40MHz channel reserved for anyone who can find a 2.4GHz 11n adapter.

The network design is a hampered by not yet having RF design tools that support 11n. IBM and Meru engineers are working around that by deploying the test APs in the next week or so and running a series of tests to evaluate throughput and coverage, and compare the 11n results with the 11a results in the 5GHz range. Wheeler says IBM engineers are creating an AP placement model based on a worst-case set of 5GHz metrics.

"The idea is that if worst-case coverage, based on conventional access points, is the reality, then 11n will improve this," Wheeler says. This placement model will be evaluated during this early testing phase and adjustments made as the engineers glean actual performance data from the 11n gear.

"We expect a one-third increase in range and signal performance in a given area due to MIMO and to spatial and antenna diversity [all used in 11n], compared to 11a," he says.

There are no special security issues raised by 11n. The college will deploy initially using Wi-Fi Protected Access (WPA) and WPA2, which is a full implementation of the 802.11i security standard. Later in 2007 and into 2008, the college will deploy 802.1x-based authentication, with RADIUS servers, covering both wireless and wired clients.


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