  Recently, the demand for multimedia applications is dramatically increased,
which in turn increases the portion of video traffic on the Internet. The video
streams, which require stringent Quality of Service (QoS), are expected to
occupy more than two-thirds of web traffic by 2019. IEEE802.11e has introduced
HCF Controlled Channel Access (HCCA) to provide QoS for delay-sensitive
applications including highly compressed video streams. However, IEEE802.11e
performance is hindered by the dynamic nature of Variable Bit Rate (VBR) video
streams in which packet size and interval time are rapidly fluctuating during
the traffic lifetime. In order to make IEEE802.11e able to accommodate with the
irregularity of VBR video traffic, many approaches have been used in the
literature. In this article, we highlight and discuss the QoS challenges in
IEEE802.11e. Then, we classify the existing QoS approaches in IEEE802.11e and
we also discuss the selection of recent promising and interesting enhancements
of HCCA. Eventually, a set of open research issues and potential future
directions is presented.
