The IEEE has finally approved a quality of service specification for WLANs, although there remains plenty of opportunity for further argument.
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, a maker of voice over Wi-Fi systems. The standard is a set of technologies for prioritisng traffic and preventing packet collisions and delays, which should improve the experience of users making VoI calls and watching video over wireless LANs.
Mitchell-Brown 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 WMM (Wi-Fi Multimedia), which has already been adopted by several wireless LAN vendors.
On wireless LANs 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 combines 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 prioritise certain traffic types, but it may not be the right standard for doing QOS 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, "anyone has the ability to mark e-mail as high-importance," he said. In larger deployments more control will have to reside in centralised servers or network mechanisms, he said.
As a result, the process of standardising priority in wireless LANs may be just beginning, Germanow said. Vendors such as Meru Networks 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 wireless LAN 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 (QoS) guarantees on wireless LANs is still limited, Germanow said.
Ruckus Wireless, a maker of wireless LAN gear optimised for voice and video in home use, believes 802.11e is limited in that 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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