When a client station is set for Power Save mode, it will shut down some of the transceiver components for a period of time to conserve power. When the Power Management bit is set to 1, the access point is informed that the client station is using power management, and the access point buffers all of that client's 802.11 frames.
A value of 0 means that no power management is being used, and therefore no buffering is needed.
wlan.fc.pwrmgt == 1
A value of 0 means that no power management is being used, and therefore no buffering is needed.
wlan.fc.pwrmgt == 0
Above the picture from CWAP
Any time a station associates to access point, the station receives an association identifier (AID). The access point uses this AID to keep track of the stations that are associated and the number of the BBS. If the access point is buffering data for a station in Power Save mode, the AID of the station will be seen in in afield of the beacon from know as the traffic indication map.
As shown in the following picture, when access point sends the data to the station, the station needs to know when all of the buffered uni-cast data has been received so that it can go back to sleep. Each unicast frame contains a 1-bit field called the More Data field.
To summarize, the More Data field is used to inform Power Save mode clients that they still have buffered unicast traffic and they should not go back into a doze state.
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