IEEE 802.11 wireless LANs use a media access control protocol called
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). While
the name is similar to Ethernet's Carrier Sense Multiple Access with
Collision Detection (CSMA/CD), the operating concept is totally
different.
WiFi systems are the half duplex shared media configurations, where
all stations transmit and receive on the same radio channel. The
fundamental problem of a radio system is that a station cannot hear
while it is sending, and hence it is impossible to detect a collision.
Because of this, the developers of the 802.11 specifications came up
with a collision avoidance mechanism called the Distributed Control Function (DCF).
According to DCF, a WiFi station will transmit only when the channel
is clear. All transmissions are acknowledged, so if a station does not
receive an acknowledgement, it assumes a collision occurred and retries
after a random waiting interval.
The incidence of collisions will increase as the traffic increases or
in situations where mobile stations cannot hear each other.
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