Wireless 11n net becomes a high-bandwidth way of life

An American university has 720 access points supporting 3,000 users on its high-throughput wireless LAN

The 11n net also makes possible their weekly bowling night: every Thursday, they meet with other friends for pizza and rolling virtual strikes via their wireless Nintendo Wii gaming consoles.

The main problems they've run into are due to a lack of what they call "network education" -- simple, practical explanations from the Morrisville IT department on how to best use the network, on issues with software drivers, on Microsoft Vista and the like.

The WLAN has been a major addition to the college's compact infrastructure. The data center houses about 50 rack-mounted servers, mainly from IBM, a HP storage area network, and an Enterasys data network of M7 core switches and hundreds of C2 wiring closet switches, linked via a gigabit fiber backbone. A 90Mbps data link joins the college to the Internet. The voice network is based on a Nortel PBX, recently updated. The main software applications include Banner's student information system, with attendant Oracle database, Microsoft Exchange for e-mail, and the WebCT course management software (now part of Blackboard).

The 11n access points are wired into the nearest Ethernet switch, and talk to one of six Meru controllers in the data center. The access points draw power either from a nearby outlet, using adapters the MSC IT staff call "wall warts," or via Power-over-Ethernet from the switch, based on the existing 802.3af standard.

Using PoE creates some limitations for the dual-radio Meru devices, as it does with most other 802.11n vendors. That's because in most cases, to run both 11n radios at full power with all antennas, requires about twice the wattage possible with existing 802.3af systems. The Meru access points have 3 pairs of external antenna wands, to transmit and receive the two spatial streams created by the Atheros 11n chipset (future chipsets will have three or even more streams). The access point constantly selects the two pairs of wands that provide the best signal for those streams.

The access point can sense when PoE is used and in effect shuts off one of the three antenna pairs, which can lower signal quality and range somewhat. In one limited test, Morrisville used power injectors to boost the juice to a group of access points, similar to the level that the pending 802.3at standard will introduce. They found that the number of access points that could "hear" each other jumped by 25 per cent to 30 per cent. That jump can translate into greater signal strength, the need for fewer access points, or more access point choice for wireless clients, according to MSC's Matt Barber.

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