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WLAN Design

Building a wireless LAN is no easy job. For starters, you must assess your infrastructure's RF environment and map out access point placement to help ensure good performance. Don't be

It all starts with a wireless site survey, where you assess and map out your wireless infrastructure's RF (radio frequency) environment and the placement of your access points to ensure your WLAN performs well. Many handy tools are available to help you in this process, from portable WLAN hardware toolkits to software packages that give you detailed views of coverage areas at your sites, such as Trapeze Networks' RingMaster and the Ekahau Site Survey utility. But these tools can't substitute for knowing just what your wireless users need to get their jobs done.

Mapping It Out

Throughput is a major consideration for your wireless deployment. Consider what types of traffic--e-mail and Web traffic or speed-hungry ERP (enterprise resource planning) or CAD (computer-aided design) applications--will ride across your WLAN most often. Do you need the 54-Mbps speeds of 802.11a and 802.11g, or will 802.11b's 11 Mbps suffice? Either way, network speeds diminish significantly as users wander farther from their access points, so install enough access points to support not only all your users but the speeds at which they need to connect.

A WLAN's advertised speed doesn't exactly correlate to its real-world speed, either. Unlike a switched Ethernet network, a WLAN is a shared medium, much like the hub model of older Ethernet LANs, dividing available throughput rather than providing dedicated speeds to each connected device. This limitation (along with the 50 percent overhead associated with transmitting data over the airwaves) makes throughput planning on your wireless network challenging. It may be tempting to calculate the number of access points you need to install based on the number of users and their minimum bandwidth requirements, but that can limit you down the road when you need more capacity. Overprovision instead. Keep in mind, too, that though 802.11b is getting all the attention these days, 11a soon will become the high-performance WLAN standard of choice, so your infrastructure should support it from day one, or at least be upgradable to it in the near future.

Security is also a major concern, though it typically doesn't factor directly into where you place your access points or how you configure them. Some security solutions diminish throughput with their authentication and encryption methods. It's best to adjust your power outputs and antenna orientation to limit leakage beyond your borders, whether or not you add security.

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