Siemens IEEE802.11 - Manual (Page 32)

WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.ppt Page 32 © Siemens, 2002
DIFS
Contention Window
Slot time
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Backoff-Window Next Frame
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SIFS
PIFS
DIFS
Free access when medium
is free longer than DIFS
Busy Medium
CSMA/CA Explained
n
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.
n
Efficient Backoff algorithm stable at high loads.
– Exponential Backoff window increases for
retransmissions.
– Backoff timer elapses only when medium is idle.
n
Implement different fixed priority levels
IFS: Inter Frame Space