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802.11r: Wireless LAN Fast Roaming: Page 2 of 5

Given the need to integrate with 802.11i security and 802.11e QoS standards, developing a workable standard for fast roaming is challenging. Not surprisingly, 11r defines a complex architecture, though one that is not expected to require forklift upgrades of existing hardware. But getting all the software right will be difficult.

Security Is Easy, Mobility Is Hard

The expected deployment of time-sensitive applications like Vo-Fi on enterprise networks is driving 11r. Most Vo-Fi vendors have advocated virtual WLANs dedicated to voice, with WEP encryption often serving as the shaky foundation for privacy and a variety of techniques, largely proprietary, prioritizing voice traffic.

That's yesterday. Tomorrow's Vo-Fi installations will use advanced authentication and dynamic encryption-key techniques made possible by 802.11i and QoS capabilities defined by 802.11e. Unfortunately, upgrading to these standards while still providing fast roaming between APs may be tricky. Full authentication using 802.11i, for example, can create delays of several hundred milliseconds during roaming. The new Fast BSS Transition defined by 802.11r eliminates much of the handshaking overhead.

802.11r provides a no-compromise solution for secure wireless voice, providing fast-roaming transitions of about 50 ms while preserving a device's security and QoS context. It effectively "mobilizes" 802.11i's security services and 802.11e's QoS functions. The increasing number of enterprises that have begun or completed a migration to 802.11i and WPA2 will be poised to take advantage of 802.11r; those with legacy setups will have more to do.