Information About Unscheduled Automatic Power Save Delivery
Unscheduled automatic power save delivery (U-APSD) is a QoS facility that is defined in IEEE 802.11e that extends the battery life of mobile clients. In addition to extending the battery life, this feature reduces the latency of traffic flow that is delivered over the wireless media. Because U-APSD does not require the client to poll each individual packet that is buffered at the access point, it allows delivery of multiple downlink packets by sending a single uplink trigger packet.
U-APSD is enabled automatically when WMM is enabled.