802.11 Protocol Architecture
Polling
Stations have an option of being pollable. A station can indicate its
desire for polling using the CF Pollable subfield within the Capability
Information field of an Association Request frame. A station can
change its pollability by issuing a reassociation request frame. The
point coordinator maintains a polling list of eligible stations that may
receive a poll during the CFP. The point coordinator will send a CF-
Poll frame to at least one station during each CFP when there are
entries in the polling list. A subset of the stations on the polling list
will be polled, in order, by ascending AID.
Frame Types
After sending the beacon frame, the point coordinator may then
transmit any of several frame types after waiting one SIFS interval. All
functions use SIFS during the CFP except the initial PIFS before the
first beacon and any error conditions such as a lack of an ACK frame.
There are four types of data frames that carry data and four types that
do not. The Simple Data frame is illustrated below. Figures 2.20 –
2.23 show those data frame types that carry data:
Simple Data
Data+CF-Ack
Data+CF-Poll
Data+CF-Poll+CF-Ack
Figures 2.24 – 2.27 show those data frames that do not carry data:
CF-Ack
CF-Poll
CF-Ack+CF-Poll
Null Function
Simple Data frame: This point coordinator frame is directed from the
access point's point coordinator to a particular station. If the point
coordinator does not receive an acknowledgement frame from the
