Automatic Power Save Delivery (APSD)

In IEEE 802.11In IEEE, Automatic Power Save Transmission (APSD) in wireless LAN is a mechanism designed to reduce the power consumption of connected devices in the network. It was first introduced in2005Year introduced IEEE 802.11e.

Technology

APSD is typically deployed in infrastructure BSS (Basic Service Set). In infrastructure BSS, there are some Access Points (APs), which are essentially wireless routers that make up the access base station. All wireless devices (i.e., clients) communicate with each other through APs. When a client has frames to send, it sends the frames along with the target address to the corresponding AP. Then, the AP sends the frames to the corresponding device.

In APSD, the Access Point (AP) buffers frames and sends them to the client device immediately after sending them to the client device. Then, the client device enters a sleep state until more frames are waiting to be sent, thereby reducing power consumption. This method eliminates the need for polling each frame. Not only does it reduce polling time, but it also saves energy.

APSD types

APSD defines two transmission mechanisms-

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

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