Start-up offers high-capacity WLAN gear

A start-up this week is unveiling a super wireless LAN access point that can offer greater capacity and more coverage than conventional access points.

The Xirrus XS-3900 Wireless LAN Array combines advanced antennas, up to 16 802.11a radios and a wireless-LANs switch in a package that looks like an oversized smoke detector. Xirrus software coordinates the 16 wireless-LAN radios to boost capacity. That's because users can connect to the array on 16 channels at the same time, each channel with a data rate of 54M bit/sec, compared with just one channel on a conventional, one-radio access point.

The effect is somewhat comparable to taping together 16 802.11a access points, but adding a special multi-sector antenna that directs the radio energy thereby extending its range, and adding some clever software that blocks interference between the radios and lets users use adjacent channels, again without interference.

One of the 3900 arrays is being used to cover a two-story, 7,800 square foot classroom building on the campus of the Viewpoint School, an independent K-12 school in Calabasas, Calif. The single array mounted centrally on the second floor ceiling handles coverage for the entire building and extends the wireless LAN roughly 150 feet outside the building, which covers part of the campus, says Paul Rosenbaum, the school's associate headmaster, COO and director of technology.

Previously, the building had four Cisco Aironet access points to cover the same area with adequate performance.

Rosenbaum already is weighing the use of the array in a new 40,000 square foot building under construction because the Xirrus products will reduce WLAN installation and maintenance costs. "Lots of client devices can associate with one [Xirrus] device. That's a huge plus," he says. Using the Xirrus DC power option will eliminate the need to install AC power lines to each array, he says.

"We'll be reducing cabling, the number of switch ports needed in the wiring closets and power cords," he says.

The array comes in four-, eight- and 16-radio models. Picture an 18-inch dinner plate with the radios mounted around the diameter. The array can have up to 12 802.11a radios and up to four dual-frequency radios, which can support either 802.11a or 11b/g clients.

Each radio has a sectorized antenna, which in effect, concentrates the radio's energy in a specific segment, or sector, instead of letting it radiate in all directions as in a conventional access point. By concentrating the energy, the array extends the radio's range, so that at any given distance, the available WLAN throughput is higher than a conventional device. Xirrus executives say that the typical range for an 802.11a access point is less than 100 feet, but the array can reach 175 to 200 feet. The company says the array has about twice the range, at any given data rate, of rival access points from Cisco, Aruba Wireless Networks and Trapeze Networks.

One radio can be designated as a radio monitor, constantly sweeping the airwaves to check signal strength and detect unauthorized WLAN signals.