CSMA/CA
Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) is very similar to Ethernet's CSMA/CD (Carrier Sense Multiple Access/Collision Detection). The primary difference is that since WLAN radios are half duplex, they can only talk or listen, but not both at the same time. Therefore, 802.11 cannot detect collisions the way that wired Ethernet does using CSMA/CD's collision detection. Rather, 802.11 employs collision avoidance techniques, which, in essence, require the radio to listen before talking.
In addition, after sending a packet, the receiver will respond with an acknowledgement (ACK) frame indicating that the message has been received. If the ACK frame is not received, the sender will assume that the message has been lost and ...
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