Is QoS approval holding up 802.11a phone delivery?

* Vendors may await 802.11e to ship 802.11a phones

I could'a had a V-8 recently during a conversation with a voice-over-Wi-Fi expert. If you've read this newsletter for very long, you've probably noticed that I frequently bemoan the relative scarcity of 802.11a deployments in general (so many channels, so little time!). I also kvetch about the near-absence of commercially available 802.11a phones.

The chicken-and-egg situation hit me like a brick. The 802.11a handsets will likely appear following the finalization of the ever-elusive 802.11e QoS standard, now due this fall.

802.11a brings flexible configuration options for Vo-Fi installations. Its 21 available nonoverlapping channels (depending on geography) offer the ability to set aside some number of those channels for voice without interference worries (at least from each other).

Isn't it likely that the 802.11a phone makers are awaiting ratification of the full 802.11e standard before they unleash their 802.11a handsets? Why go back and build QoS into an 802.11b phone, which will soon be passé from a bandwidth point of view? In fact, maybe the absence of industry-standard Wi-Fi QoS explains why there are so few 802.11a clients deployed in general.

The Wi-Fi Alliance has already been certifying client devices for interoperability with what it calls the Wireless Multimedia (WMM) portion of the 802.11e spec. WMM prioritizes packets into four classes: voice as highest, then video, then best effort, then background, such as print traffic and file downloads (though you can change priorities around, if you want).

Still to get the final seal of approval is the scheduled access (SA) component, which builds call admission control into the Wi-Fi QoS equation. This allows the wireless access point to become a scheduling device, determining how much time to allocate to each associated client and whether there is capacity for a "new" client device that wishes to associate with it.

Such deterministic behavior also offers important battery efficiencies: if the client knows when its turn will come to transmit and receive, it can power down at other times to conserve power.

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Copyright © 2005 IDG Communications, Inc.

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