Carnegie Mellon: Leaders in Wireless Technology

Since then, the network, whimsically named “Wireless Andrew” in honor of the university's two founders, Andrew Carnegie and Andrew Mellon, has grown to support more than 8,000 people. The WLAN users tote their notebook PCs and personal digital assistants (PDAs) around the 4 million square feet of interior space on the 105-acre campus, enjoying 11 megabits-per-second (Mbps) access just about everywhere.

CMU Director of Network Services Charles Bartel, who is responsible for Wireless Andrew, describes the network as both “a test bed and a field of dreams.” A combination of research grants and an avid high-tech community at the science-centric university has yielded an advanced WLAN that continues to grow today, even though its journey hasn't always been smooth.

Coverage Versus Capacity

One of Bartel's original challenges – and one that vexes WLAN administrators to this day – was deciding whether to strive for maximum coverage or maximum capacity. “The 802.11b-type access point running in the 2.4 gigahertz [GHz] range has only three distinct channels to design for,” he says. “So we tried to provide as much coverage as we could, while watching out for co-channel overlap problems that limit throughput.

“The result is that the WLAN is thinner than what we would like. Even though we have 100 percent coverage, we may be talking about only 1Mbps to 2Mbps at the outer edges of some of that coverage.”

Today, Bartel focuses on positioning more access points in places where he thinks there will be especially intense demand for capacity, while keeping in mind that there is no standards-based load-balancing scheme for access points. Vendors have come up with various proprietary techniques to load-balance across a given space, but Bartel is wary of embracing too many proprietary solutions for a WLAN that must serve so many people and so many types of devices.

His bottom line: Strive for 100 percent coverage even if that means thin spots in some locations around campus. Having a slow connection is an annoyance, but having no access is a lot worse.

Taking Measurements

Bartel likes to joke about the fact that “the first four letters of wireless spell ‘wire.'” Too often, he says, WLAN designers forget that every access point will have to be connected to a CAT5 or CAT6 drop, and installing them costs money. He advocates taking extensive radio interference measurements throughout a building rather than doing a lot of paper planning before a wireless installation.

Bartel points out that even though it's cheaper to pull wire before drywall is up, his team waits until after the building is completed, furnished and mostly occupied before testing and measuring for a wireless design.

It's impossible to know how a WLAN will truly perform until a building is full of the things that can interfere with connectivity. These include furniture, wall coverings and human bodies, which Bartel calls “6-foot-high columns of water moving through space.” That's why his team takes measurements both when buildings are empty and when they're full of people.

It's also important to make sure blueprints indicate how high the access points should be positioned. At CMU, one construction team didn't understand why data jacks had to be positioned 6 feet off the floor. So they repositioned them at floor level, which was an expensive mistake.

“On a wired network, you have a physical connection so you can probe it easily,” adds Peter Bronder, CMU's manager of network engineering. “With wireless, you're talking about radio signals, so you can no longer be at your desk to look for interference. You've got to get out in the field and start sniffing the airwaves to get an accurate picture.”

“To actually pinpoint the location where interference is coming from,” Bronder explains, “it sometimes requires going on the site to sniff around, perhaps with a directional antenna attached to a sniffing device.

“An ongoing challenge after the initial installation is that there are always renovations going on or someone has moved office furniture around a room, so that requires another site visit to see what's going on.”

A good way to budget for a WLAN installation, according to Bartel, is to add up the costs of the access points, cabling and installation, as well as the power to keep them running, and then divide that number by the square footage being covered. At CMU, the price almost always works out to about $1 per square foot.

“Tell us how big the building is,” Bartel says, “and we'll multiply [the number of square feet] by $1 and hold that allocation to build what we think we'll need to do wireless there.”

An Eye on the Future

With Wi-Fi standards changing so quickly, WLAN administrators have to build for today while keeping an eye on tomorrow.

“We talk with different vendors to get a feel for where the industry is headed,” says Larry Gallagher, CMU's manager of data communications. “We're always interested in partnering with a vendor and reducing our costs by offering development work or something that will help them better market their product.”

Bartel's current wireless focus is on 802.11a (for point-to-point speed) and 802.11g, but he adds, “In about a year, we're going to see speeds up to 500Mbps with 802.11n.”

He calls 802.11n “a wild card” that could leapfrog 802.11a in terms of widespread deployment depending on when 802.11n is finally ratified – his best guess is early 2007 – and how soon after that the first hardware comes out. The lesson is that no WLAN is ever truly complete because physical plants always change and the network technology always improves.

Bartel reminds WLAN administrators to keep planning on a continual basis and to remember that “students are getting a better educational experience because they have access to information whenever and wherever they need it.”

And that's the bottom line at any institution of higher learning.