802.11 Protocol Architecture
Acknowledgement (ACK) frame
Clear-to-Send (CTS) frame
The second (or subsequent) fragment of a fragment burst
FIGURE 2.8a
Use of Short Interframe Spaces (SIFS)
PCF IFS (PIFS)
The PIFS is the interval that an access point operating under PCF mode
uses to gain access to the medium before stations using DCF mode.
PIFS provides priority over DIFS because of its shorter time period.
Access points only use PIFS during a CFP to send the initial beacon
and to retransmit frames for which they did not receive an ACK frame.
FIGURE 2.8b
Use of PCF Interframe Spaces (PIFS)
DCF IFS (DIFS)
All stations operating according to the distributed coordination function
use the DIFS interval for transmitting data frames and management
