Wireless LANs face huge scaling challenges

Philippe Hanset is wondering about the intersection of the Slingbox and the campuswide wireless LAN at University of Tennessee at Knoxville, where he's IT manager.

A vendor has been industriously selling the Slingbox  to incoming students, who set it up in their dorm rooms where they have cable TV service. The WLAN then lets them stream TV programs to their notebooks anywhere on campus. Imagine a hit like "American Idol" streaming wirelessly to hundreds of student notebooks.

"This could be challenging," Hanset acknowledges, with masterful understatement.

The development is typical of the new scaling challenges facing WLAN administrators as WLANs continue to grow in size, in number of users, and in more demanding applications. With big WLAN deployments, higher education is a kind of ground zero for many of these issues. (Compare enterprise WLAN products.)

Early WLANs focused on growing the number of access points to cover a given area. But today, many wireless administrators are focusing more attention on scaling capacity.

That focus is a broad one, calling for a deeper understanding of what access points are capable of, and paying more attention to scaling back-end systems, servers and networks.

The rise of high-density WLANs

"We've been used to 20 to 50 wireless users in an area, with another 20 to 50 maybe 50 or 100 feet away," says Brad Noblet, a former college IT director, at Dartmouth and Harvard, who’s now an independent consultant, BN Consulting. The assumption: few users, who wanted just e-mail access or Web searching.

Click to see: Text list of scaling wireless LANs

Low-density WLANs are giving way to high-density ones, with new challenges for network administrators. "When we first put this [WLAN] in three years ago, there were few wireless clients," says John Turner, director of network and systems at  Brandeis University, in Waltham, Mass. "Now everyone has a laptop."

The scaling challenges include ensuring adequate wireless, and wired, bandwidth for the applications being served to wireless users. "These scaling issues are becoming more and more apparent where lots of folks show up and you need to make things happen," Noblet says.

What has to happen is that lots of clients have to associate with an access point, get an IP address, be authenticated, get enough bandwidth (wireless and wired) for their applications, and behave themselves as network citizens.

Configure access points for capacity, not access

Noblet urges network administrators to configure access points for performance (or capacity), rather than for access. He's found some access points are configured without any limits on the number of client associations. If a large group of users coalesce around an access point, they'll find slow associations or none at all. "What it's really about is understanding the throughput performance of a particular data stream," Noblet says.

But everyone agrees that capacity planning at the level of the access point is more art than science. "When I speak on this topic, I always emphasize that we, the IT professionals, not the vendors are the ones who best understand the user and application scenarios we'll be dealing with in our deployments," says Dan McCarriar, assistant director of network services at Carnegie Mellon University (CMU) in Pittsburgh.