Going Wi-Fi: A Practical Guide to Planning and Building an 802.11 Network

This specification promises to bring Quality of Service (QoS) to Wi-Fi networks. The 802.11 Working Group realized that the original 802.11 standard and its amendments, a, b, and g, don't provide for an effective mechanism to prioritize traffic. Without such a mechanism, there can't be any strong quality of service, which means that Wi-Fi can't optimize the transmission of audio and video.

The 802.11e Task Group defines QoS by providing classes of service with managed levels of QoS for data, voice, and video applications. It does this by addressing the issue of QoS in the Data Link Layer's MAC sublayer. In particular, the Task Group is working on a prioritized scheme that can be used to ensure that high priority users get more bandwidth allocation than low priority users. To do this, it replaces the Ethernet-like MAC sublayer with a coordinated Time Division Multiple Access (TDMA) scheme, and adds extra error-correction to prioritized traffic. This is accomplished by the use of what is being termed a "hybrid coordination function" (HFC) at the MAC. The HCF uses an enhanced, contention-based channel access method that operates at the computing device concurrently with a polled channel access mechanism that operates at the access point.

Because 802.11e falls within the MAC sublayer, it will be common to all 802.11 PHYs standards (e.g. 802.11a, b, and g) and be backward compatible with all existing wireless LANs based on the 802.11 series of standards. As a result, the lack of a finalized 802.11e specification shouldn't impact a decision on which Wi-Fi flavor to use when deploying a new WLAN. It should be relatively easy to upgrade any existing access points to comply with 802.11e, once it is ratified, through relatively simple firmware upgrades.

Still, 802.11e is critical for service providers who want to offer audio and/or video on demand and/or voice-over-IP service. "You're never going to be able to stream high-quality video from your PC to your TV in the home without Quality of Service. If you want wireless networking to grow beyond resource sharing in the home, you have to ensure quality of service in content delivery," says Barry Davis, Intel's director of platform architecture in the Mobile Communications Division.

Quality of Service also ranks high for enterprises, particularly as voice-over-IP (VoIP) becomes more important in wireless communications.

There have been innumerable delays, thanks to arguments over how many classes of service should be provided and exactly how they should be implemented. However, it appears as if most of the issues have been resolved and that 802.11e might even be ratified by the time you read this.