From GSM to LTE: An Introduction to Mobile Networks and Mobile Broadband

6.8 IEEE 802.11e and WMM—Quality of Service

Within a few years, Wi-Fi has revolutionized networking in offices and homes. Originally, these networks were mainly used for applications such as web browsing and access to files on a local server. Here, high bandwidths are required to transfer data quickly. Other aspects such as a guaranteed bandwidth and jitter were less important.

Today, applications such as VoIP and video streaming have additional requirements. Video streaming, for example, requires, in addition to a high bandwidth, a guaranteed bandwidth and maximum latency to ensure a smooth user experience. VoIP applications have similar requirements. While there is sufficient capacity on the network for all applications using it, such applications will function properly even without additional measures being taken. If, however, a multimedia transmission already requires a significant amount of the available bandwidth while other applications, potentially on other devices, start a file transfer or other bandwidth-intensive operations, it is likely that this transmission will interfere with the multimedia streaming. To prevent such issues, QoS measures were added with IEEE 802.11e. As with other extensions of the standards, there are some parts which must be supported by all devices while the support of others is optional.

To speed up the introduction of the QoS extensions, the Wi-Fi alliance has created the Wi-Fi Multimedia (WMM) specification, which is based on 802.11e. If an ...