Siemens IEEE802.11 - Manual (Page 37)

WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.ppt Page 37 © Siemens, 2002
Beacon
Contention Free Period Contention Period
CFP repetition interval
D1+Poll
U1+ACK
D2+Poll
Stations
Access
Point
U2+ACK
CF end
Point Coordination Function (PCF)
n
Optional PCF mode provides alternating contention free and
contention operation under the control of the access point
n
The access point polls stations for data during
contention free period
n
Network Allocation Vector (NAV) defers the contention traffic until
reset by the last PCF transfer
n
PCF and DCF networks will defer to each other
n
PCF improves the quality of service for time bounded data