Siemens IEEE802.11 - Manual (Page 33)

WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.ppt Page 33 © Siemens, 2002
Ack
Data
Next MPDU
Src
Dest
Other
Contention Window
Defer Access Backoff after Defer
DIFS
SIFS
DIFS
CSMA/CA + ACK protocol
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).