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Designing 'iPad WLANs' poses new, renewed challenges

John Cox | March 26, 2012
Complications that the influx of Apple iPads and iPhones bring to enterprise Wi-Fi networks and wireless LAN administrators are illustrated vividly at The Ottawa Hospital in Ontario.

Universities and colleges in 2008 were already seeing scaling challenges with high-density WLANs, which strained such backend enterprise services as DHCP servers and IP address allocation [see "Wireless LANs face huge scaling challenges"]. The new generation of mobile devices is creating new strains all over again.

Impact on network services

"The impact of smart devices on AAA [authentication, authorization, and accounting] is massive, as these devices don't roam so much as they come online randomly as users take them out and put them away frequently," Lukaszewski says. "You will need a minimum of two times the number of AAA servers that you would need in a laptop-only environment."

Another burden is the use by mobile devices of chatty discovery protocols, especially Apple's Bonjour protocol, based on multicast DNS (MDNS). Bonjour in particular works perfectly fine in a home Wi-Fi network, to find and connect with Apple TV, or an Apple AirPrint printer. But these devices are constantly broadcasting, generating heavy loads across enterprise networks, and doing so at lower data rates than standard data traffic.

The result, says Lukaszewski, is multicast traffic can swell and bog down the WLAN. Aruba this week unveiled software that will filter MDNS traffic, and rival Aerohive announced a solution earlier this month. 

At Ottawa Hospital, CIO Potter is still astonished to find doctors sitting at their desks next to a wired-in PC but using their iPads. When he asks them why, they say "Because [the iPad's] faster," a function of the tablet's instant-on capability and the WLAN's consistent reliability and throughput.


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