Siemens IEEE802.11 Tutorial page 33

CSMA/CA + ACK protocol
DIFS
Data
Src
Dest
Other
n
Defer access based on Carrier Sense.
– CCA from PHY and Virtual Carrier Sense state.
n
Direct access when medium is sensed free longer then
DIFS, otherwise defer and backoff.
n
Receiver of directed frames to return an ACK
immediately when CRC correct.
– When no ACK received then retransmit frame after a
random backoff (up to maximum limit).
WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.ppt
SIFS
Contention Window
Ack
DIFS
Backoff after Defer
Defer Access
Next MPDU
Page 33 © Siemens, 2002