What’s up with QoS for Wi-Fi?

What’s the deal with 802.11e, the ever-emerging IEEE wireless LAN standard for Wi-Fi quality-of-service mechanisms?

After all, 802.11e is starting to become important now, with the growing excitement about voice-over-IP (VoIP) over WLANs. But 11e’s expected ratification date is up in the air.

IEEE 802.11e working group participants indicate they are at an impasse on certain technology specifications, in part because different types of companies are members. For example, along with traditional Wi-Fi network equipment makers, I’m told that businesses like HDTV companies, whose products have different wireless QoS requirements, are involved.

While working group members duke it out, a subset of the 802.11e draft specification, Wireless Multimedia Extensions (WME), is under development. It is analogous to Wi-Fi Protected Access (WPA), a subset of the full 802.11i security spec required for Wi-Fi Alliance certification today. At press time, the alliance wasn’t officially saying whether it is considering requiring WME support for certification, though alliance members indicate that Wi-Fi interoperability testing will begin during the first half of next year.

Taking a tip from 802.11i, the WME effort seems aimed at preventing the market fragmentation that occurs when multiple, non-interoperable pre-standard technologies get deployed. WME’s primary author is from Microsoft, but about 10 companies are contributing to the spec, including Cisco and the primary WLAN chip vendors.

When WME and/or 802.11e are in place, the client device and the access point infrastructure are in sync about how to handle queuing, channel access, collision avoidance and other functions. So you don’t have to specially configure the infrastructure to recognize a VoIPoWLAN phone and to treat traffic from that device accordingly.

WME uses four priority levels in negotiating communication between wireless access points and client devices. A few noteworthy points in the latest WME specification, published in July:

* For reasons of forward-compatibility with 802.11e, WME devices will not advertise 802.11e capability unless they also support those features independently.

* While the specifications are based on those proposed for 802.11e, the working group won’t track changes in 802.11e and update the WME specification. Rather, the working group intends to freeze the WME

specification ASAP.

* WME will use only Enhanced Distribution Coordination Function, which supports the concept of traffic categories, for wireless station communication. Stations with lower-priority traffic must wait longer than

those with high-priority traffic before trying to access the wireless medium.