Automatic Power Save Delivery (APSD)

In IEEE 802.11 wireless LANs, automatic power save delivery (APSD) is a mechanism that aims to reduce power consumption by the devices connected in the network. It was originally introduced to IEEE 802.11e in 2005.


APSD is generally deployed in infrastructure BSS (basic service set). In infrastructure BSS, there is are access points (APs) which are basically wireless routers forming the base stations for access. All the wireless devices i.e. clients communicate with each other through the APs. When a client has frames to send it sends the frames to the corresponding AP along with the destination address. The AP then sends the frames to the corresponding devices.

In APSD, the AP buffers frames and sends them to a client device immediately after the client device has delivered its frames to the AP. The client device then go to a hibernation state until it has more frames waiting to be delivered, thus reducing power usage. The method waves away the need to poll for each frame. This not only reduces polling time, but is also energy efficient.

Types of APSD

APSD defines two delivery mechanisms −

  • U-APSD (Unscheduled – Automatic Power Save Delivery)
  • S-APSD (Scheduled – Automatic Power Save Delivery)

Updated on: 19-Nov-2019


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