Configuration Options and Protection Mechanisms
point’s buffer is empty. Upon receiving a PS-Poll frame, the access
point may respond with a single queued data frame or it may send an
ACK frame. If the access point responds with an ACK frame, it may
then send the queued data frame at its leisure. Each queued data frame
is sent in response to an additional PS-Poll frame from the station. As
long as there are more queued data frames at the access point, each data
frame sent to the station will have the More Data bit in the Frame
Control field of the MAC header set to 1. The last queued data frame
will have a More Data bit of 0.
FIGURE 4.1
More Data bit
The More Data bit is the method that the 802.11 standard specifies to
ensure that stations empty the access point’s buffer before dozing
again. After emptying the access point’s buffer using the PS-Poll
mechanism, the beacon will no longer show that station’s AID in the
TIM. The station may return to doze mode at its convenience.¹ Figure
4.2 shows a beacon management frame with the TIM indicating that
AID 12 has queued data.
1
IEEE 802.11 – 1999 (R2003) – Section 11.2.1.6
