Which two MAC modes are described as coexisting in 802.11 WLANs?

Which two MAC modes are described as coexisting in 802.11 WLANs?

• A. PCF-mode and DCF-mode
• B. CSMA/CA-mode and TDMA-mode
• C. OFDM-mode and DSSS-mode
• D. MAC-layer mode and PHY-layer mode

Answer: (A)

In 802.11 WLANs you have two MAC access methods: the distributed coordination function (DCF), which is the standard contention-based method where devices listen before transmitting using CSMA/CA, and the point coordination function (PCF), a polling-based method where the access point coordinates who can transmit during a contention-free period. These two can coexist because 802.11 defines both, with the AP able to manage a CFP (contention-free period) using PCF while the rest of the time devices contend for the medium under DCF. PCF provides a more controlled, time-sensitive access, while DCF handles typical traffic through contention. The other options mix up concepts: TDMA is not the MAC mode used in 802.11, and PHY modes like OFDM/DSSS or linking MAC to PHY layers aren’t describing coexisting MAC access methods.

In 802.11 WLANs you have two MAC access methods: the distributed coordination function (DCF), which is the standard contention-based method where devices listen before transmitting using CSMA/CA, and the point coordination function (PCF), a polling-based method where the access point coordinates who can transmit during a contention-free period. These two can coexist because 802.11 defines both, with the AP able to manage a CFP (contention-free period) using PCF while the rest of the time devices contend for the medium under DCF. PCF provides a more controlled, time-sensitive access, while DCF handles typical traffic through contention. The other options mix up concepts: TDMA is not the MAC mode used in 802.11, and PHY modes like OFDM/DSSS or linking MAC to PHY layers aren’t describing coexisting MAC access methods.