Rethinking wireless LANs
Experts share their tricks and techniques for setting up these increasingly popular nets.
 
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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, a wireless net integrator in Chicago. In dense deployments, positioning access points and channels can get tricky, he says.
There is a range of antenna designs to tackle this problem. Think of radio as light, "shining" on or through a site, and think of antennas as flashlights, which direct and focus the light. The standard antenna creates a spherical spread of radio waves, or a "beach ball," von Schaumburg says. But other designs will flatten the spread, so it runs horizontally across one floor of a building. Others create a spread in the shape of a pizza wedge, or a 180-degree spread.
Be prepared to make changes in your placement plan.
Intermec's Haynes worked on one project for a Las Vegas resort-casino in which the casino management team wanted to install wireless clocks on 30 floors in each of two towers.
The first plan called for four access points on each floor. But the hardware and cabling costs to tie these into the LAN were prohibitive. The second plan was to mount the access points outside the building, lighting up the interior. But that didn't work because the windows were covered with a reflective coating.
Finally, Haynes' team placed access points in the elevator shafts. But the casino managers realized the placement would void their warranty with the elevator manufacturer.
"So we went back and placed the access points in the air shafts," Haynes recalls, with satisfaction. "They acted like cannons: You could be anywhere in the hotel and the signal fired through these shafts. We put just one radio in each tower."
Checking out the client devices is also key.
"Look to see what kinds of computers they have and their operating systems," says Vinny Gullotta, head network engineer for LANocracy, a New Canaan, Conn., wireless net installer. "Every computer is different. This isn't actually a problem, but it can cause little kinks in the installation or force me to do additional troubleshooting."
One very important step is ensuring the various client devices have the appropriate drivers for a wireless LAN.
Security concerns about wireless LANs have been well-documented recently, and new issues seem to pop up weekly. The experts we interviewed said security requirements for wireless LANs vary with the data being transmitted and the site itself.
Careful use of antenna designs will limit how much of the radio signal "leaks" beyond the building's perimeter.
Gullotta finds that a most corporate customers never bother to turn on the Wired Equivalent Protocol (WEP) encryption, which is part of the 802.11b standard. They leave themselves wide open to "war driving" or "stumbling" - a hacker driving around with a wireless-equipped laptop, searching for open wireless connections. WEP is far from foolproof, he acknowledges.
"However, it's definitely more difficult to get into a network that uses WEP than into one that's not," he says.
Once your wireless LAN is in place, expect to do some fine-tuning, the experts say.
At one hospital, the wireless LAN erratically collapsed in just one area. Schwartz arrived, ready to conduct a full signal-strength analysis with a spectrum analyzer, until he found the staff had put the access point on top of a microwave oven.
He moved it a few feet and the network came back up.
Don't overlook the obvious Experts say the key to a successful wireless LAN implementation is doing the basics. These include:
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