Power save state and Power consumption state of a Wi-Fi client are two completely different things.
A Wi-Fi client has four power consumption states ordered from highest to lowest power consumption :
- Tx : Active transmission
- Rx : Receiving Wi-Fi frame
- Listen : Searching for Wi-Fi frame (PHY preamble detection)
- Sleep : sleeping
A client wants to maximize the time in sleep state while also meeting its throughput requirements.
There are two power save (PS) states for a Wi-Fi client :
- In PS : AP will buffer unicast frames for client in this state and it will obtain client’s permission before transmitting any unicast frames to client.
- Out of PS : AP can transmit unicast frames to client in this state.
Client can notify AP that it is entering PS state by indicating Power Management (PM)=1 in Frame Control field of MAC header of any frame. Client may decide to go to sleep consumption state upon receiving acknowledgement for its PS notification.
Power save state is simply AP’s view of Wi-Fi client and it has nothing with actual power consumption state of a client. A client may indicate “in PS” state to AP but it may be transmitting or receiving or simply scanning (listening) on different channels.
A client in PS state does NOT imply client in sleep state.
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