Mobile Wi-Fi clients are surging on wireless LANs. The growth is forcing IT groups to adapt to a new, more dynamic RF environment and rethink WLAN design.
Carnegie Mellon University, which saw 1,000 brand-new Wi-Fi clients appear on its campus wireless LAN this past semester, is experiencing the kind of device surge that's forcing IT groups all over to adapt to a new, more dynamic radio environment.
IDC reports that twice as many smartphones and tablets, nearly all with Wi-Fi, will ship compared to laptops this year. The number of Wi-Fi certified handsets in 2010 was almost 10 times the number certified in 2007, according to the Wi-Fi Alliance. Tablets, e-readers and portable audio devices are helping to drive this growth.
The result is a very different wireless environment in terms of radio behaviors, Wi-Fi implementations, applications, usage and traffic compared to just a year or two ago. This raises a different set of issues from simply managing these mobile devices with tools from vendors like MobileIron and Zenprise.
BACKGROUND: Major Wi-Fi changes ahead
One complex result is that Wi-Fi infrastructures have to become more sensitive to mobile Wi-Fi clients. That's not easy because the IEEE 802.11 wireless LAN standard puts the client in charge of connections, the opposite of a cellular network where the infrastructure takes charge of the client's behavior. (This is changing with new IEEE standards and clever vendor engineering. See "Major Wi-Fi changes ahead.")
It's also increasingly common for users to have two -- or more -- Wi-Fi devices, such as a laptop and smartphone, and to use them both at once.
In a typical week this past spring at Simon Fraser University in Burnaby, British Columbia, Canada, network statistics showed about 22,000 unique users. About 14,000, or two-thirds of the total, had only one MAC address, indicating a single client. That means roughly one-third of the users had two or more MAC addresses; nearly 5,400 had two, and just over 1,000 had three, according to Craig Simons, a manager with the school's network operations group.
Many schools report that the vast majority of the traffic they see with these new clients is Web traffic, and much of that is video related -- watching YouTube or streaming movies or TV shows from Netflix.
What's more, the new mobile devices really are mobile: Users may be streaming music or video or making VoIP or video calls over Wi-Fi while on the go. By contrast, although laptops are portable, in practice they're usually stationary when being used.
The price of new radio behaviors
The new devices have new radio characteristics, which bring a mix of costs and benefits. There's a huge variability in how client radios behave. Even if they support 802.11n, they may do so only on one frequency, 2.4GHz, limiting channel selection, and use only one antenna, limiting throughput. Real-world tests of mobile clients show dramatic differences in performance. [See "Smartphones, tablet Wi-Fi performance varies widely"]
Driver software varies. Some iPad 2 users complained of Wi-Fi problems, which lessened with later firmware updates, for example. Other devices, though not personal mobile clients, can impact WLANs in unexpected ways with badly written software. "Wireless projectors, printers, and the like have network stacks that are quite poorly implemented," says Simon Fraser's Simons. "Printers will grab a DHCP address but also take the next 30 or so. In the meantime, people are buying this equipment and just expect it to work."
Joe McBreen, CIO for St. Vrain Valley School District, in Longmont, Colo., north of Denver, remembers being astonished at seeing an iPad's Wi-Fi performance change dramatically in high school classrooms. "You can be holding the iPad, walking around the room, tilt it, and the performance nosedives: Your browsing speed plummets," he says. "The [user's] experience varies depending on how it's held in your hand and oriented."
That particular problem was compensated for after the district replaced its Cisco-based WLAN with equipment from Ruckus Wireless, whose access points make use of a multi-component antenna that can tailor the Wi-Fi signal to each client device.
Some IT managers report that mobile devices are more "aggressive" in Wi-Fi behavior than laptops, often grabbing an access point and hanging on to it, when it should shift to another one. "We see iOS holding on to an access point for longer than we would like," says David Morton, director of mobile communications at the University of Washington in Seattle. (Such idiosyncrasies are true for Android and other mobile operating systems as well, he adds). "And there are fewer tweaks we can do on the device side, so we have to address it from the infrastructure side."
At the same time, there is sometimes greater uniformity in mobile device radios than in laptops, with fewer Wi-Fi chipsets and driver combinations. "We suspect that we will see fewer 'unknown client' problems [as a result]," Morton says.
Changing usage patterns
The new Wi-Fi clients are creating different usage patterns. A student using only a laptop typically creates short bursts of data being transferred, with long "silences" between them, Morton says. But now, a student could be streaming music via Pandora on a smartphone, or streaming video to a tablet, while working on the laptop. "Pandora doesn't take a lot of bandwidth, but it does access the air a lot, with a lot of small packets," Morton says. "The way Wi-Fi works, you have to get access to air. If a lot of [client] devices are doing this at the same time, it's inefficient to send lots of little packets versus larger packets."
"Real-time communications is likely to take off in a much bigger way very soon," Morton says. "We're seeing VoIP and [Apple] Facetime and other forms of video chat are all on top of the regular ebb and flow of the Web-type traffic we've seen in the past."
"When the [class] bell sounds, students come out of classes, whip out their phones and start texting, surfing or Facebooking," St. Vrain Valley's McBreen says. During lunch break, students would move around the cafeteria hunting for the best Wi-Fi signal, a behavior McBreen found striking as an example of the importance students place on being always connected and communicating.
And not just outside the classroom. Increasingly, teachers are introducing real-time curricula designed for mobile devices, asking a group of 300-400 students to surf to YouTube to watch a video, or participate on the spot in online polls or surveys. "We want to support that, but we're not there yet," Simon Fraser's Simons says.
Trying to "get there" itself, the University of Ottawa in Ontario, Canada, recently hosted a test by Aruba Networks, the school's WLAN vendor. Aruba set up four high-end 11n access points to see how 100 Apple iPads would perform simultaneously running a series of mainly education applications, all of them with some kind of video content. In the test, the iPads sustained throughput of about 1Mbps. The Aruba infrastructure pushed all the tablets to the 5GHz band, and spread them evenly over the access points.
But not all mobile clients, even if they have an 11n radio adapter, support 5GHz: For space, power conservation and pricing reasons, any number of mobile devices run 11n only on 2.4GHz, unable to exploit the higher frequency's additional channels and less interference for optimal throughput. Simon Fraser for example, offers 11n throughput only on the 5GHz band, to lure students to associate on the higher frequency. But 80% either stick with or are stuck on 2.4Ghz.
"We are just going to have to wait for the market to catch up," Simons says.
In the meantime, the client explosion is causing an IT rethink in WLAN design. [see "Tips for navigating the evolving wireless LAN landscape"]
John Cox covers wireless networking and mobile computing for Network World.
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