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

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 rely on a shared wireless medium and need a way for many devices to take turns transmitting without stepping on each other. The method used is CSMA/CA, which means stations listen before sending and only transmit when the channel looks free for a short period. If the channel is busy, a station waits a random amount of time (backoff) and then tries again. This avoidance of collisions is crucial in wireless, where detecting collisions is unreliable due to the nature of the radio medium and hidden nodes. To further reduce collisions and coordinate access, many transmissions also use an RTS/CTS handshake to reserve the medium before sending large payloads. The other access methods—TDMA (dividing time into slots), FDMA (dividing by frequency), and CDMA (dividing by codes)—are different ways to share a channel and are not the WLANs’ predominant approach for contention-based access. So CSMA/CA is the standard mechanism that enables multiple stations to contend for the wireless medium.