Siemens IEEE802.11 Tutorial page 32

CSMA/CA Explained
Free access when medium
is free longer than DIFS
DIFS
Busy Medium
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Reduce collision probability where mostly needed.
– Stations are waiting for medium to become free.
– Select Random Backoff after a Defer, resolving contention
to avoid collisions.
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Efficient Backoff algorithm stable at high loads.
– Exponential Backoff window increases for
retransmissions.
– Backoff timer elapses only when medium is idle.
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Implement different fixed priority levels
WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.ppt
DIFS
Contention Window
PIFS
SIFS
Backoff-Window
Slot time
IFS: Inter Frame Space
Next Frame
Page 32 © Siemens, 2002