Which method manages contention-based access on 802.11 wireless networks such as 802.11n?

Which method manages contention-based access on 802.11 wireless networks such as 802.11n?

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

Answer: (A)

CSMA/CA is the method used to manage access on 802.11 wireless networks. In a shared wireless medium, detecting collisions reliably is difficult, so stations avoid collisions instead of trying to detect them after they happen. They listen first, and if the channel is idle for a DIFS period, they pick a random backoff time and count down while the channel remains idle. When the backoff reaches zero, the station transmits. If the channel becomes busy, they pause the countdown and resume after the channel is idle again. Optional RTS/CTS handshakes can be used to further reduce collisions, especially the hidden-node problem, by reserving the channel before sending large data frames. The other options don’t fit a contention-based approach: CSMA/CD relies on detecting collisions on wired Ethernet, which isn’t reliable in wireless; TDMA schedules access in fixed time slots; FDMA splits access by frequency. Therefore, CSMA/CA best fits how 802.11 handles contention-based access.

CSMA/CA is the method used to manage access on 802.11 wireless networks. In a shared wireless medium, detecting collisions reliably is difficult, so stations avoid collisions instead of trying to detect them after they happen. They listen first, and if the channel is idle for a DIFS period, they pick a random backoff time and count down while the channel remains idle. When the backoff reaches zero, the station transmits. If the channel becomes busy, they pause the countdown and resume after the channel is idle again. Optional RTS/CTS handshakes can be used to further reduce collisions, especially the hidden-node problem, by reserving the channel before sending large data frames. The other options don’t fit a contention-based approach: CSMA/CD relies on detecting collisions on wired Ethernet, which isn’t reliable in wireless; TDMA schedules access in fixed time slots; FDMA splits access by frequency. Therefore, CSMA/CA best fits how 802.11 handles contention-based access.