How much performance capability do companies expect when they deploy a wireless network? Chances are, not enough -- especially as
wireless becomes a mainstream part of the New Data Center infrastructure.
"It's a misconception -- a very common one -- that wireless LAN performance is always poor," says David Newman, a Network World Test Alliance partner and president of Network Test. "People say, 'It's just wireless; what do you expect?' In fact, wireless LANs can be made to perform quite well, but it does involve thinking some about network design."
Here then, courtesy of Newman and other wireless experts, are four tips for optimizing a wireless network and improving application performance.
1. Install more access points than you think are needed.
Having more access points improves reliability, throughput and capacity, says Craig Mathias, principal of Farpoint Group. "People try to get as much range as possible out of access points, and that's the wrong thing to do with any radio-based device," he says. "Back when access points cost a couple thousand bucks, it was a good [money-saving] strategy. But now that they're pretty cheap," usually $400 to $600, that strategy no longer is warranted.
Mathias says he favors optimizing for capacity instead of range. That means making sure there are enough access points to handle users' varying needs. Some users just go on the Internet once in a while and check e-mail, while others run more intensive applications and need more capacity, he says. Determining the right number of access points means studying network-management logs to see what types of applications users are accessing, from where and how often. There is no single answer, and even the rules of thumb aren't very good, he says.
2. Don't place transmitters too far off the ground.
Too often, a network designer takes a transmitter designed to be placed 18 feet to 20 feet above the ground and figures, why not put it 50 feet up and see if it works better, says Leonard Scott, an IS manager for the city of Corpus Christi, Texas. That's not a good idea, and it can cause a number of problems, he says: "When a device is elevated far above the ground, the receiver has difficulty picking up the users on the ground." Twenty feet is about the height of a short utility pole, notes Scott, who has deployed a wireless network that covers Internet access for Corpus Christi residents and the applications used by city employees.
Mistakes in transmitter height aren't restricted to municipal Wi-Fi projects, however. Companies sometimes place transmitters at the top of an atrium in a tall building for aesthetic and security reasons, or because officials think it will result in better coverage, Mathias says. In a warehouse, this strategy might work fine, because the capacity needed typically is low: just enough throughput to scan bar codes and do similar tasks. In an office setting, forcing transmitters to cover longer distances usually backfires; a better option is placing transmitter/receiver devices atop cubicle walls, Mathias says. Wireless signals are designed to radiate laterally, not up and down, he notes.
3. Avoid crowded parts of the spectrum.
Even though major chipset suppliers are phasing out support for the 802.11a WLAN standard, Newman recommends using that standard when possible. "If you have enterprise-class gear today, there's a pretty good possibility it supports [802.11a]. If you can do it, turn it on," he says.
The 802.11a standard helps with optimization because it operates in the little-used 5GHz band and therefore suffers less from interference than the newer 802.11g standard, which operates in the very crowded 2.4GHz band. "Not only is wireless LAN stuff using that band, but so are some cell phones, microwave ovens, cordless phones. There's not enough spectrum for all the devices licensed to use those frequencies," Newman says.
Mathias dismisses those who argue against using the 5GHz band because the radio waves don't go as far as they do in the 2.4GHz band: "If you take my advice -- don't optimize for range, optimize for capacity -- then it doesn't matter," he says.
The draft 802.11n standard, which Mathias says will improve throughout "by a factor of four to five," will operate in the 2.4GHz and 5GHz bands. Thus, enterprises can migrate from 802.11a to 802.11n and still use the 5GHz band.
4. Consider a centralized WLAN architecture.
Deciding whether to use a centralized or a distributed architecture is very much "a religious debate," Newman says. A centralized architecture uses a controller to manage all access points, whereas a distributed architecture requires that access points be managed individually.
"I tend to agree with those who say [centralized is better for optimization], because you can set whatever characteristics you want to set once . . . and they get pushed throughout the enterprise," Newman says. Those characteristics include an access point's radio-frequency settings, as well as QoS mechanisms that prevent delays in voice and video traffic, he says.
Mathias also prefers the centralized approach. With a distributed architecture, you're asking for trouble trying to control every access point and remember every IP address, he says. "I love the centralized approach, and I love the management," he adds.
Companies committed to a distributed architecture have some optimization options, too, Newman says. Vendors such as Colubris Networks argue you can get as much management flexibility with their distributed networks as you could with a centralized setup.
If these four tips aren't enough to maximize the performance of your wireless network, Newman has one final piece of advice: "Use a wire," he says. "Just kidding."
