Of the 470,000 Wi-Fi connections made on a recent day at Abilene Christian University, fully 94% used the 2.4GHz band, representing an extreme example of how today's surging number of Wi-Fi clients is crowding the band least able to accommodate them.
At ACU, this is not considered a problem, at least not yet. In part, that's because of careful wireless LAN design and capacity planning. And partly because a goodly percentage of mobile devices that can run on the alternative 5GHz band, do so: on that same day, 47% of the school's laptops and desktops, and two-thirds of its iPads cruised on 5GHz, via either 802.11a or 802.11n.
Yet relatively few of today's Wi-Fi clients support 5GHz.
"The challenge isn't that 5GHz-capable devices are not connecting the 5GHz band, but rather the challenge is there are too few devices that have 5GHz capabilities," says Arthur Brant, ACU's director of networking service. "The 2.4GHz band is congested, a symptom of the number of devices that only operate on that band, and the limitation of its [only] three non-overlapping channels."
A growing concern
This congestion is a growing concern and, in some cases, a problem on college campuses. More schools are rebuilding campus-wide Wi-Fi networks that now are designed for 5GHz. That means more costs, including half as many access points and associated cabling and ports, because the higher frequency doesn't penetrate walls as well. But it also means four to six times the number of non-overlapping channels, much greater capacity, and a clean radio frequency.
At a range of schools, IT staff say 50% to 60% or more of their current Wi-Fi device population, including the tidal wave of smartphones and other mobile devices, are stuck with the 2.4GHz band. [See "Wi-Fi client surge forcing fresh wireless LAN thinking".] Somewhat surprisingly, that's true for many laptop PCs, such as Dell's value-line of Inspiron laptops and its higher performing XPS line, though the latter do offer a $35 upgrade to a dual-band Wi-Fi radio.
"Since most users don't understand the difference, they don't change this option," says John Turner, director for network and systems, at Brandeis University in Waltham, Mass. The Brandeis Wi-Fi network, based on Aruba's dual-band access points, benefits from the growing popularity of Apple Macs. About 50% of the students have them "and will connect on the 5GHz band nicely," Turner says.
"Our jobs would be easier if clients just all did a good job using the 5GHz band and left the 2.4 for other devices, like the [Nintendo] Wii and lower-power devices like smartphones," he says.
But they don't. That's partly because of decisions by radio and device manufacturers and partly due to the 802.11 standard, which from the outset has control of wireless access in the client radio, not the access point. More Wi-Fi brains and control is shifting slowly to the network, as vendors implement optional parts of the IEEE 802.11 standards, and the .11 working group develops new standards. [See "Major Wi-Fi changes ahead"]
At University of Massachusetts/Amherst, the WLAN for campus residence halls has been redesigned for 5GHz (though service on 2.4 is still offered). So far this year, the campus Aruba network has identified 47,000 unique Wi-Fi devices, with just over one-third making use of 5GHz.
The resulting interference levels are high in the residence halls in the 2.4 band, and during peak periods in the evening users on this band see throughput ranging from 5M to 10Mbps. But clients on the 5GHz band, "regularly showed performance in excess of 20Mbps" all day, according to Rick Tuthill and Michael Dickson, network engineers with the school's Office of Information Technologies.
The 2.4GHz junk band
"We would certainly like to see more clients choose 5Ghz when available, because we believe we can deliver a better experience there," says Dan McCarriar, assistant director of network services at Carnegie Mellon University in Pittsburgh. "The general perception in IT, and it matches our experience, is that 2.4GHz has become somewhat of a junk band, with all the consumer Wi-Fi routers and 'hotspot' devices that prefer it." In off-campus sites leased by CMU, "it's not uncommon to see dozens of competing SSIDs and ad-hoc devices operating in 2.4GHz frequencies, causing co-channel and adjacent channel interference and any number of other headaches."
Even where congestion isn't a problem the collection of "junk" on the 2.4 band can bog down performance. "The older equipment slows down the network for everyone, not just the older clients," Turner says.
Gaming systems add another, related set of problems. "These clients, like Xbox, Wii, and TiVo, have very old network cards and don't play well at all with high-speed networks," Turner says. "In fact, Wii consoles require your network to support a very slow data rate - 2Mbps - or they won't even connect! In our enterprise network, those clients hang on to the 2.4 signal for dear life, despite our having access points nearly every 75 feet."
Users with high-throughput 802.11n radios in spiffy new laptops often can't get the most out of that higher throughput, says Marcelo Lew, wireless enterprise administrator at the University of Denver. "You have a Ferrari, but if you are sharing a single-lane road [2.4GHz band] with a lot of other Ferraris, you won't go very fast," he points out. "Now, move the Ferrari to a five-lane highway [5GHz band] and you will be able to move a lot faster."
A better Wi-Fi highway
The IT groups are taking a number of steps both to build the five-lane highway and get clients to use it. As mentioned, many are redesigning their WLANs for 5GHz, creating smaller Wi-Fi cells and boosting capacity in the process, making the 5GHz signal pervasive. Wheaton College in Norton, Mass., is upgrading its dorm network from 802.11abg to dual-band 802.11n, with the access point placement based on 5GHz. "More in-depth shifting of clients to 5GHz will depend on our ability to expand 5GHz coverage," says Steven Hess, Wheaton network administrator.
UMass/Amherst's minimum system requirements for student and faculty include "dual-band Wi-Fi-certified adapter, and before arriving on campus, students are given information on what they can do to "lower the overall noise in the 2.4GHz band," according to Tuthill and Dickson.
Secondly, more of them are switching on the automatic "band-steering" feature that WLAN vendors now support. When a dual-band client radio switches on, it "probes" for a wireless access point. The access point with band-steering temporarily "hides" the 2.4GHz band from the probe. So the client concludes that only 5GHz is available, and then connects using that band. Afterward, it's able to use 2.4 if needed for longer range connectivity.
"In locations with band steering turned off, we have almost no 5GHz usage, says Ethan Sommer, associate director of core services at Gustavus Adolphus College in Saint Peter, Minn. "In our new academic building, where I turned on band steering, I think we have almost 4:1 in favor of 5GHz. I guess we should experiment with turning it on in more places."
Other changes include: setting up a separate SSID for the 5GHz band, and naming it something like "(university name)-fast" to encourage user adoption; and switching off the lower data rates for each connection mode, especially for 11b and 11g.
Many IT staffers say Wi-Fi problems are client-related, often due to aging or badly written drivers. Often, updating the driver fixes the problem. UMass/Amherst is trying out a new program of loaning students who report particular types of network issues a replacement USB Wi-Fi adapter that supports both radio bands. If the adapter solves the problem, the student is encouraged to buy and use the same model.
The influx of Wi-Fi clients that can only use the 2.4GHz band is putting the RF environment under stress. IT groups are responding with better spectrum planning, redesigning WLANs around 5GHz, shifting as many clients as possible to that cleaner band, and using the 2.4GHZ band more efficiently.
"I'd say the 5GHz band is our preferred future," says CMU's McCarriar. "But in the 'bring your own device' environment that many universities have lived in for years, we're ultimately at the mercy of the device vendors doing the right thing in designing and testing their products."
John Cox covers wireless networking and mobile computing for Network World.
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