"ips " the time , point coordinator must wait to transmit its beacon to let stations know the duration of polling will be in use.
"dcf "distributed coordination function.
When both dcf and pcf is are in use, it makes sense for access point acting as point coordinator to wait for" PIFS" then sends the beacon to let the stations know duration of time during which pcf polling will be used. Upon receiving this beacon, stations that want to transmit using " DCF" will hault their transmission for the duration specified in a beacon . Access point then sends a frame to one station, granting it permission to transmit.
My question is "pifs" makes sense only when both pcf and dcf are in use. When only pcf is in use , access point ( point coordinator) does not need to wait for "pifs" and does not need to send beacon at the end of" pifs" duration to let stations know the duration of polling as there is one pcf method being used, stations know they have to wait for their turn to transmit.
The interframe spaces (SIFS, PIFS, and DIFS) allow 802.11 to control which traffic gets first access to the channel after carrier sense declares the channel to be free. Generally, 802.11 management frames and frames not expecting contention (a frame that is part of a sequence of frames) use SIFS, and data frames use DIFS.