At the Internet Telephony show in Los Angeles last month, it was fitting that the subject of QoS came up often. During the Wi-Fi conference track, someone joked that the IEEE 802.11e QoS standard “has been six to nine months away - for five to six years.”
Indeed, mid-2005 is now the expected time frame for full 802.11e approval.
However, last month, the Wi-Fi Alliance did begin taking action, by launching a programme it had announced back in May. Just as it did when the sorely needed 802.11i security standard was a while in coming, it began certifying product interoperability among the completed components of the standard so that the industry could begin benefiting from some of the advancements.
In the case of QoS, it is the packet-prioritisation portion - dubbed Wi-Fi Multimedia, or WMM, by the alliance - which is ready for prime time.
Don't be confused, but WMM is the Wi-Fi Alliance's brand for a part of the 802.11e (the part that is "ready") called WME. This is a basic classification and prioritisation scheme, designed by data networking players. The other half of 802.11e is a more sophisticated scheme from voice equipment manufacturers. Read Quality of Service over WLANs , and WLANs need quality for Voice.
Not many products are certified
At this juncture, the only WLAN system to be WMM-certified is Cisco’s Aironet 1200 802.11a/g AP; other certified products are system components, such as Wi-Fi chips and software. However, many Wi-Fi vendors (including Cisco) already support the long-proven Spectralink Voice Priority (SVP) scheme in their APs.
The availability of the WMM capability could allow does makers of consumer-electronics devices such as DVD players and televisions to prioritise types of traffic travelling over Wi-Fi links between their devices.
In addition, AP makers that have not implemented SVP could implement WMM for prioritisation. For voice applications, their customers might still require Spectralink’s SVP server or NetLink Telephony Gateway in their configurations for admission control until the full 802.11e standard, which includes scheduled RF media access and possibly bandwidth provisioning, is implemented.
SVP still has a role
The role of SVP on the wired side is to coordinate the timing of voice calls when sending voice packets to and from an AP. Packets flow isochronously upstream and downstream to eliminate the possibility that traffic will collide.
WMM differs from SVP in that it works across different applications, not just voice. It is based on the IP Differentiated Services model without incurring IP’s overhead, and supports four priority levels.
The priority buckets default to voice as highest, then video, then best effort, then background. The background class, for example, might get print traffic and file downloads. You can, however, customise the settings to suit your own priorities.
What is the Wi-Fi Alliance up to? Read our interview with Wi-Fi Alliance chief Franz Hanzlik.
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