Can a wireless node still buffer packets when its receiver is turned off?
Some wireless nodes perdiodically turn off their radio receivers to save energy. I read somewhere that when the receiver is turned off, the node can still buffer packets. Is this true?
To preserve battery life on small footprint wireless devices, the 802.11 standard defines a Power Save mode. Stations that enter Power Save mode announce their intention to sleep before temporarily shutting down all radio functions, with the exception of a timing function. The timing function wakes the station briefly at regular intervals to listen for AP beacons.
The AP does indeed buffer frames received for a sleeping station. The AP lets all stations know whether unicast frames are pending transmission by sending beacons containing a Traffic Indication Map (TIM). When a sleeping station hears one of those beacons, it leaves Power Save mode, turns its radio back on, and becomes ready to receive buffered frames. A slightly different mechanism is used to deliver buffered broadcast/multicast frames to all stations at specified intervals, known as the DTIM (Delivery Traffic Indication Message) interval.
This was first published in February 2006