11e standard may operate during
both the contention and the contention-free periods into which the channel time is typically
partitioned. The AP can access the channel during the contention period by using PIFS, a
shorter waiting requirement than that for stations, to initiate service periods for the stations
with admitted traffic streams [13 ??“ 15]. As a consequence, it is expected that, in practice,
802.11e APs will allocate most of the channel time to contention periods.
Compared to the legacy PCF mechanism, the 802.11e polled access mechanism
results in a polling schedule that better matches the generation of frames in a periodic
traffic stream. This results in superior delay/jitter performance and better channel use
efficiency. The transmission of multiple uplink frames per poll also increases channel use
efficiency.
Relative to contention-based access, scheduled polled access leads to better channel
use efficiency because stations in the same WLAN (that is, stations served by the same AP)
do not contend for the channel, thus eliminating the possibility of collision among them.
The superior delay/jitter performance of polled access in 802.
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