
IEEE 802.11: Medium Access
• Avoid collisions: 2
+
nodes transmitting at same time
• 802.11: CSMA - sense before transmitting
– don’t collide with ongoing transmission by other node
• 802.11: no collision detection!
– difficult to receive (sense collisions) when transmitting due to
weak received signals (fading)
– can’t sense all collisions in any case: hidden terminal, fading
– goal: avoid collisions: CSMA/CA
A
B
C
A
B
C
A’s signal
strength
space
C’s signal
strength
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