SonicOS 7.0 Access Points

Configuring IEEE802.11r Settings for Secure Fast Roaming

Many deployed implementations of IEEE 802.11 WiFi have effective ranges of only a few hundred meters, so, to maintain communications, devices in motion need to hand-off from one access point to another. In an automotive environment, this could easily result in a hand-off every five to ten seconds.

Hand-offs are already supported under the existing standard. The fundamental architecture for hand-offs is identical for 802.11 with and without 802.11r: the mobile device is entirely in charge of deciding when to hand-off and to which access point it wishes to hand-off. In the early days of 802.11, hand-off was a much simpler task for the mobile device. Only four messages were required for the device to establish a connection with a new access point (five if you count the optional “I'm leaving” message [deauthentication and disassociation packet] the client could send to the old access point). However, as additional features were added to the standard, including 802.11i with 802.1X authentication and 802.11e or WMM with admission control requests, the number of messages required went up dramatically. During the time these additional messages are being exchanged, the mobile device's traffic, including that from voice calls, cannot proceed, and the loss experienced by the user could amount to several seconds. Generally, the highest amount of delay or loss that the edge network should introduce into a voice call is 50 ms.

802.11r undoes the added burden that security and quality of service added to the hand-off process and restores it to the original four-message exchange. In this way, hand-off problems are not eliminated, but at least are returned to the status quo.

The primary application currently envisioned for the 802.11r standard is voice over IP (VOIP) through mobile phones designed to work with wireless Internet networks, instead of (or in addition to) standard cellular networks.

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