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April 16, 2005

Patented Signal Handoff Hype, Promise

By Glenn Fleishman

UCSD did a great job getting into the media this week with a fast Wi-Fi handoff technology: SyncScan drops a Wi-Fi adapter or appliance, like a VoWLAN phone, out of its associated mode for a few milliseconds at a regular, defined interval to check on signal strength. This avoids adapters swapping to a new AP only when signal strength becomes unusable or nearly so.

SyncScan relies on a feature in Atheros’s chipsets that’s available from the open-source madwifi drivers; it’s the same sort of feature (if not the identical one) that allows Atheros’s WLAN switch partners to offer RF monitoring on the same APs that are also handling client data interchange.

Two problems with SyncScan’s approach: first, it requires firmware to be installed on the access point, which is fine for experimentation and open-source projects, but otherwise needs signoff from major firmware developers and their manufacturing partners; second, it’s got that patent-pending label attached, which always has the caveat of causing resistance until fees are revealed.

SyncScan puts all APs within listening range of each other into a synchronized beaconing mode so that the “I’m alive” signals happen at fixed intervals. This allows adapters to only listen at discrete periods and to get a clear idea of precisely what’s happening in the local RF space. But this coordination adds overhead and there has to be a cost to synchronization and the inevitable resynchronization.

One of the IEEE 802.11 groups, 802.11f, was dedicated to fast reassociation through preauthentication—tokens exchanged among APs at Layer 3—but that doesn’t help with fast reassociation on an RF level, or Layer 1.

Posted by Glennf at April 16, 2005 12:37 PM

Categories: Academia, Standards

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