Wireless Infrastructure

08:18 AM
Lee Badman
Lee Badman
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You, There! Get Out Of My 2.4 GHz!

The great thing about unlicensed spectrum is the ease with which wireless devices can be implemented. The bad part of unlicensed spectrum? That would be the ease with which wireless devices can be implemented. In the 2.4 GHz ISM band, a growing roster of wireless devices continues to harass and degrade the WLAN space to the dismay of those of us running big wireless environments.

The great thing about unlicensed spectrum is the ease with which wireless devices can be implemented. The bad part of unlicensed spectrum? That would be the ease with which wireless devices can be implemented. In the 2.4 GHz ISM band, a growing roster of wireless devices continues to harass and degrade the WLAN space to the dismay of those of us running big wireless environments.

As you can imagine, a university can be a pretty busy place for not only wireless client traffic, but also for other devices that contend for the same frequency space that 802.11g and the (so far) busiest part of 802.11n use. By name, the 2.4 GHz Industrial, Scientific and Medical band spells trouble for wireless networks. As the RF home for countless devices in all sorts of categories, 2.4 GHz spectrum can be as dirty as Los Angeles on a smoggy day, and trying to preserve the user experience of WLAN clients can be akin to herding cats.

Among the contentious devices found across the wireless landscape I’m charged with are the following: Bluetooth devices of all sorts, microwave ovens, gaming consoles, classroom response systems, lighting systems, cordless telephones, building environmental control systems, wireless video cameras, toy robots and remote control systems. Some are IP-based, and can be artfully stitched into the campus WLAN despite the lack of support for enterprise security protocols. Others are simply noisemakers that need to be managed in other ways. But they all have the potential for detracting from the quality of an expensive, well-planned WLAN environment.

Here’s where many of you are thinking "just move your clients to the less-cluttered 5 GHz band, where 802.11a and 802.11n live on modern dual-band access points." Often, that is easier said than done. Though I have a robust, dual-band 802.11n to offer my clients, many of them show up with devices that only do 2.4 GHz. Overall, about 65% of thousands of clients daily can't do 5 GHz despite it being much cleaner and with the advantage of supporting higher data rates. This includes pretty much the entire explosion of mobile devices, as smartphones and tablets that do 5 GHz wireless are just starting to poke their heads up. On the laptop front, many users still opt for the "Sunday paper special," which typically does not have the dual-band wireless NIC option.

I also use the latest whiz-bang spectrum analysis feature set that Cisco offers (as do pretty much all wireless vendors now). Clean Air does a great job of calling out a wide range of interfering devices that can locally make life tough for wireless clients. But mitigation, as I've written about previously, is a whole other ballgame. Some "rogue" devices can be walked to the door when you show the owner your Deputy Sheriff of Policy badge, while others pull rank and become something you grudgingly have to live with.

So what's it all mean? From a technically philosophical standpoint, these are somewhat strange times to be a WLAN admin. More mobile devices in more hands mean that more eyes are on the wireless network. And performance discontinuities are more apt to be noticed. I have had to explain to a 2.4 GHz classroom response system vendor why its claims of "we don’t interfere with anything, ever!" are false without good channel planning and management. I've been asked to help a contractor figure out why his lighting system won’t configure properly in 2.4 GHz--until he changes channels. I've fended off pitches for wireless video gateways and projectors that are ill-designed for the workplace, and helped a range of folks find alternative solutions to their needs, outside of the 2.4 GHz band.

Chaos is inevitable in 2.4 GHz, but it still needs to be managed as best as it can be. Ideally, all important clients would be in the 5 GHz space while the lesser devices stayed in 2.4 GHz, but that is not likely to be the case for quite a while.

With an ever-changing tapestry of interfering and contending devices forming the backdrop for the busy 2.4 GHz spectrum, keeping the WLAN optimized for performance takes attention and a 10,000-foot understanding of the environment. And sometimes you can't do anything but wait it out while managers talk to managers about why the funky lab equipment or weather station needs to be relocated or swapped for something in the 900 MHz space. It's certainly interesting. But all parties need to remember that "unlicensed" doesn’t mean "self-coordinating," and that the more 2.4 GHz devices that are brought to the party, the harder it is for the network to deliver all it was designed to do.

Lee is a Network Engineer and Wireless Technical Lead for a large private university. He also teaches classes on networking, wireless network administrtaion, and wireless security. Lee's technical background includes 10 years in the US Air Force as an Electronc Warfare ... View Full Bio
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