CWNA

• It physically monitor the traffic on the line.
• If both attempt to transmit after a random time interval, the stations that collided attempt to transmit again
• CSMA/CD is a type of contention protocol.
• It is 802.3

is the principle medium access method employed by IEEE 802.11 WLANs. It is a "listen before talk" method of minimizing (but not eliminating) collisions caused by simultaneous transmission by multiple radios unlike CSMA/CD that deals with network transmissions once collisions have been detected.

access method of 802.11 communications

• period of time that exist between transmission of frames
• Shortest interframe space (SIFI) highest priority
• DCF interframe space (DIFS) lowest priority

• csma/ca mechanism used by listening 802.11 stations.
• When the listening radio hears a frame transmission from another station it looks at the header of the frame and determines weather the Duration/ID fired contains a duration value or an id value

csma/ca is preformed constantly by all stations that are not transmitting or receiving.

• an 802.11 station may contend for the medium during a window of tie know as the contention window.
• the station selects a random backup value

• uses a form of polling.
• Defined by the standard, the medium access method has not been implemented.

hcf defines the use of txops and access categories in edca as well as the use of txops and pulling during hcca

This maintains a prediction of the future traffic on the medium