802.11e defines Quality of Service (QoS) for the wireless LAN and The WMM standard is a subset of IEEE 802.11e.
The 802.11e standard includes a method that allows an AP to advertise its load to wireless clients. Specifically, the QBSS element is used to advertise load via beacons. The WMM standard is a subset of IEEE 802.11e.
The QBSS (QOS enhanced basic service set) information element is an 802.11e construct that enables an access point to communicate its channel usage to wireless phones. It is intended to solve the problem of candidate access point selection, or intelligent roaming. It is located in the beacon frames of access points.