Which medium access protocol do WLANs predominantly rely on for contention-based access?

• A. CSMA/CA
• B. TDMA
• C. FDMA
• D. CDMA

Answer: (A)

WLANs share the wireless medium using a contention-based approach that relies on listening before transmitting and using a randomized backoff to reduce the chance of collisions. This is CSMA/CA—carrier sense multiple access with collision avoidance. In wireless, you can’t reliably detect collisions while you’re transmitting, so devices avoid collisions in advance by waiting for a free channel and then backing off if it was busy. The collision avoidance aspect can include mechanisms like RTS/CTS to further mitigate hidden-node problems.

Other schemes like TDMA, FDMA, or CDMA allocate resources in time, frequency, or codes rather than letting stations contend and back off. They’re not the typical contention-based access method used by WLANs, which is why CSMA/CA is the best fit here.