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Two wireless LANs better than one, Carnegie Mellon says

802.11n wireless net decision explained by university

By , Network World
December 11, 2007 08:19 AM ET

Network World - Carnegie Mellon University has launched a massive upgrade of its campus-wide wireless LAN . . . and chosen two WLAN vendors to supply the 802.11n infrastructure for it.

The decision runs counter to almost every large-scale wireless deployment, where a company in effect standardizes on one vendor. CMU IT staff are well aware that the choice of Aruba Networks for the academic buildings and common areas, and Xirrus for the outlying ring of dormitories, poses a unique set of challenges.

And they’re confident they can handle them. Since 1994, CMU has had an extensive WLAN, called Wireless Andrew. Originally developed for wireless research purposes, it has greatly expanded over the campus and parts of downtown Pittsburgh. The last upgrade in the late 1990s adopted 802.11b equipment in the 2.4-GHz band from Lucent. It’s this equipment that the new network, dubbed Wireless Andrew 2.0, will replace in 2008.

The university didn’t set out with a dual-vendor solution in mind, says Dan McCarriar, assistant director of network services for CMU’s computing services group. A request for proposals drew six submissions from 11 vendors. During the assessment process, CMU staff gradually realized that Aruba and Xirrus both offered specific features that could meet different requirements. And it became gradually clearer that the 2.0 version of the network should adopt the high-throughput WLAN IEEE draft standard, 802.11n.

“This was definitely a unique decision for us, even having been in the wireless game for a long time,” McCarriar says. “In the end, though, I believe we selected two technologies that best address the different usage patterns we see around campus.” CMU staff were intrigued, he says, by the idea of using different products for different purposes.

CMU decided Aruba offered very strong security, in addition to its range of features, and Xirrus offered optimal capacity with its Wi-Fi Arrays. “Traditionally, academic nets have been very open,” McCarriar says. “But we’ve been tightening down on security.” Aruba recently partnered with Bradford Systems to offer a network access control (NAC) policy manager.

Capacity was especially an issue in dormitory areas, and in some classroom spaces. “We know capacity issues well,” McCarriar says. “Use patterns vary widely in offices, classrooms and dorms, some with high-capacity ‘flashpoints’ at different times of the day. Mix these patterns with emerging bandwidth hungry applications, and you have potential problems.” Xirrus’s high-capacity gear has been the foundation for networks such as the Interop show network.

Aruba and Xirrus have very different approaches. Aruba has a conventional controller-based architecture: thin access points that work with a separate WLAN switch (or “controller”), which handles authentication, security, administration and similar tasks. It scored high in Network World ClearChoice tests a year ago. Xirrus bundles the controller with four, eight or 16 access points, and a special sectored directional antenna, into a single package.

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