802.11 Protocol Architecture
FIGURE 2.26
CF-Ack + CF-Poll frame (NO DATA)
Null Function frame: This frame is used by a station to notify the
point coordinator that it has not data to transmit. Also, this frame may
be used by stations both in PCF and DCF modes to notify the access
point of its intention to change its power state (awake or asleep).
FIGURE 2.27
Null Function frame (NO DATA)
CF-End frame: This frame is sent by the point coordinator to the BSS
to identify the end of the CFP, which occurs when one of the following
happens:
The CFPDurRemaining time expires
The point coordinator has no frames to transmit and no stations
to poll
FIGURE 2.28
CF-End frame
