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http://www.nwfusion.com/news/2001/1022wlantips.html Rethinking wireless LANs Experts share their tricks and techniques for setting up these increasingly popular nets. By John Cox Network World, 10/22/01 If you're thinking of deploying an 802.11b wireless LAN, you need to change something a lot more important than the network interface cards in end users' laptops. You need to change the way you think. Network World talked with some people who have designed and installed hundreds of wireless LANs to learn about the tricks and techniques of using radio waves instead of cable. Repeatedly, what emerged was the conviction that wireless LANS are more "slippery" than wired LANs. "It's half art and half science, and the former is very hard to teach," says Clark Haynes, senior network engineer with Intermec, where he oversees training for 135 wireless LAN installers. Wireless LANs seem deceptively easy because at first glance you eliminate the cumbersome pulling of Ethernet cable through ceilings and laying out physical connections to every office cubicle. You just plug in the wireless access point, outfit the computers and laptops with wireless interface cards, switch on the 2.4-GHz radios that form the wireless link and - presto! - an instant LAN. What could be easier? A lot, according to experts. "Unfortunately, a lot of customers go that route, then they're caught by surprise at how they've left themselves wide open [to various problems]," says Jeff Schwartz, a technical director with Enterasys Networks' wireless engineering group. The starting point is knowing who your end users are and what kinds of applications they'll be using. Take a look at the applications on the wired LAN as a starting point, these experts say. "We sit down with customers and figure out the bandwidth requirements," Haynes says. "Do you need 11M-bit/sec throughput everywhere? If you're only doing data collection, using bar code scanners, you can go down to 2M bit/sec." The number of users on any access point and the kind of work they perform will affect performance, because wireless LANs are shared, not switched. Users have to share the effective throughput of that wireless link. "You may be able to get 100 users on one access point," Schwartz says. "It depends on what they're doing." When lighting up a university lecture hall, for example, he often sets up two access points, each using a different one of the three 802.11b channels available to it, and they balance the traffic load between them. "Instead of getting 5M bit/sec, users can get about 10," he says. All this data and much more is incorporated into what installers call a site survey. A small team walks through the site, using one or more wireless LAN access points and laptops with wireless cards. This is how you would decide where to put the access points and how many to use. "Experienced installers can just look around and say, 'You'll need one here and here and here,'" Schwartz says. "An extra foot one way or the other can mean the difference between, say, 1M and 2M bit/sec." When positioning the access points, you want overlap between the access points so a mobile user can roam from one place to another and still keep the connection. But you don't want overlap among the three radio channels available to each 802.11b access point: As you pack more access points together in a given area, channel overlap creates contention, cutting overall performance, explains E.J. von Schaumburg, CEO of InvisiNet