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WLAN quality-of-service specification approved

Posted by iTech - 2005-10-10

A specification that could improve voice and video on wireless LANs has received approval from the Institute of Electrical and Electronics Engineers Inc., ending a long standards-setting process but possibly setting the stage for more work on the problem.

The standards board of the full IEEE approved the 802.11e specification for publication in late September, according to Geri Mitchell-Brown, Wi-Fi strategist at SpectraLink Corp., a maker of voice over Wi-Fi systems. The standard is a set of technologies for prioritizing traffic and preventing packet collisions and delays, which should improve the experience of users making voice-over-IP (VoIP) calls and watching video over WLANs.

Mitchell-Brown said she expects vendors and the Wi-Fi Alliance to adopt specific elements of the standard as appropriate for common demands by users. The Wi-Fi Alliance has adopted a subset of the standard, called Wi-Fi Multimedia (WMM), which has already been adopted by several WLAN vendors.

On WLANs that are based on standard 802.11, all users share the network's capacity, and no packet gets priority over any other. This isn't usually a problem with typical data applications such as exchanging e-mail and browsing the Web, but with voice calls and streaming video, packets have to get across the network at the right time.

The 802.11e specification allows packets to gain priority by defining four traffic classes, each with its own queue. By default, they would be for voice, video, best-effort and background, said Ben Guderian, vice president for market strategies and industry relations at SpectraLink. The definitions of the four classes could be changed from the default. To identify the class of each packet, the standard uses markers similar to ones used in wired Ethernet, he added. Seeing those markers, an access point could give voice packets top priority for transmission, followed by video, and so on, he said.  

That piece can be used with other mechanisms for preventing collisions between packets, Guderian added. Another key element of the standard is a way of timing communications with client devices that's intended to conserve battery life in handheld devices, he said.

The new standard is a good start, according to IDC analyst Abner Germanow.

"It's a fairly good standard for small wireless LAN deployments where you have a need to prioritize certain traffic types, but it may not be the right standard for doing QoS [quality of service] in large-scale enterprise environments," Germanow said.

The problem with 802.11e is that it puts the power to request priority in the client, Germanow said. As a result, he said, "anyone has the ability to mark e-mail as high-importance." In larger deployments, more control will have to reside in centralized servers or network mechanisms, Germanow said.

As a result, the process of standardizing priority in WLANs may be just beginning, Germanow said. Vendors such as Meru Networks Inc. already offer mechanisms better suited to large enterprises, and it's likely that vendors will try to put more advanced technology into another standard that would go into WLAN gear alongside 802.11e, he said.

However, the new standard is good enough for now, because the use of applications that need quality-of-service guarantees on WLANs is still limited, Germanow said.

Ruckus Wireless Inc., a maker of WLAN gear optimized for voice and video in home use, believes 802.11e is limited because it puts all voice calls into the same queue, and likewise with video streams. This may work fine in some cases, but homes with multiple Wi-Fi phones and Internet TV viewers need additional tools to maintain high quality on all those sessions, company officials have said.

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