With wireless LANs starting to be used for more than just data traffic, quality of service is getting taken more seriously.

Some wireless voice-over-IP (VoIP) vendors have created simple proprietary schemes to give voice priority on WLANs. That's critical for voice because without it the quality of calls erodes quickly.

Separately, the IEEE's 802.11e task group is finalizing work on a QoS standard that will let WLAN administrators set a range of priorities for different kinds of packets and control the time intervals between transmitted packets. The ability to schedule traffic flows is critical in transforming a WLAN from a network that hopes for the best to a network that guarantees delivery.

But, as with so much else in WLANs, none of this will be easy or quick.

Dartmouth College in Hanover, N.H., is experiencing a growing need for QoS as its campuswide WLAN gains users and traffic, says Brad Noblet, director of technical services. This fall, Dartmouth - like many other schools with extensive WLANs - was hammered by a range of aggressive network viruses. The Nachia virus, for example, sent out surges of Internet Control Message Protocol (ICMP) messages, fast and repeatedly, over a range of addresses.

The Cisco access points that Dartmouth uses had a vulnerability in some software versions that caused them to stop forwarding traffic when receiving ICMP packets. "Without QoS, you can get head-of-the-line blocking and dropped packets," Noblet says. Dartmouth has worked with Cisco and WLAN switch vendor Aruba Wireless Networks to correct any vulnerabilities and improve the ability to set traffic priorities.

The basic idea behind WLAN QoS is to handle traffic streams based on what kind of packets they are, such as voice, data or video. Class-of-service features categorize the traffic, and QoS features set priorities for delivery.

"There needs to be a mechanism to define traffic types, and then you can set [network] policies against [those types]," Noblet says. "You want to make sure there's no interruption in your voice traffic: You need to make sure that every 20 milliseconds voice traffic gets passed along. Otherwise you drop packets."

"QoS is needed in wireless LANs as more voice and video applications are rolled out," says Lynn Lucas, director of product marketing for Proxim. "I just received a [request for quote] from a university that is requiring support for 24 simultaneous videostreams per classroom. We believe this usage of video over the WLAN network will increase."

A QoS capability also will let network executives manage WLAN bandwidth, which is quickly consumed by voice and multimedia applications, or just big file transfers.

"A lot of our users stream [music or other] files," he says. "They could consume a lot of the access point's bandwidth, which today is really pretty limited. In the best case with 802.11b, we have about 6 megabits per second, tops, of useable bandwidth."

Some vendors, such as SpectraLink and Symbol Technologies, have introduced their own QoS techniques that let access points and client devices such as wireless VoIP phones give voice traffic priority on a network. A number of WLAN equipment vendors, including Proxim and Trapeze Networks, have licensed the SpectraLink protocol to support wireless voice applications.

"[With these schemes] you can boost voice traffic to the highest level of priority, but they don't deal with the problem of getting the packet [time] intervals correct," says Jacob Jorgensen, president and CEO of Broadstone Networks, a start-up beginning trials of an appliance designed to introduce QoS in WLANs. "[Simple prioritization] works in a lightly loaded environment, but in moderate to heavy loads it doesn't work well."

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