IEEE 802.11 MAC Protocol:CSMA/CA 802.11 sender 1 if sense channel idle for DIFS then sender receiver transmit entire frame(no CD) 2 if sense channel busy then DIFS start random backoff time timer counts down while channel idle data transmit when timer expires if no ACK,increase random backoff interval,repeat 2 SIFS 802.11 receiver ACK if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) 6:Wireless and Mobile Networks 6-206: Wireless and Mobile Networks 6-20 IEEE 802.11 MAC Protocol: CSMA/CA 802.11 sender 1 if sense channel idle for DIFS then transmit entire frame (no CD) 2 if sense channel busy then start random backoff time timer counts down while channel idle transmit when timer expires if no ACK, increase random backoff interval, repeat 2 802.11 receiver - if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) sender receiver DIFS data SIFS ACK