CompTIA Network+ Question A-17

Which of the following devices implements CSMA/CA virtually through the RTS/CTS protocols?

A. Firewall
B. Router
C. 802.11 AP
D. Switch

Correct Answer: C

802.11 AP is a Wireless Access Point used in a wireless network.
If two computers on a network send data frames at the same time, a collision between the frames can occur. The frames are then discarded and the sending computers will attempt to send the data again.
Carrier sense multiple access with collision avoidance (CSMA/CA) is a protocol used in wireless networks where computers connected to the wireless network attempt to avoid collisions by transmitting data only when the channel is sensed to be “idle”. Carrier Sense Multiple Access/Collision Detect (CSMA/CD) is unreliable in wireless networks because computers connected to the wireless network often cannot see each other so CSMA/CA is a better option for avoiding collisions.
Request to Send/Clear to Send (RTS/CTS) can also be used to mediate access to the wireless network. This goes some way to alleviating the problem of computers not being able to see each other because in a wireless network, the Wireless Access Point only issues a “Clear to Send” to one node at a time.
With RTS/CTS, a Request to Send (RTS) packet is sent by the sending computer, and a Clear to Send (CTS) packet is sent by the intended receiver. This will alert all computers within range of the sender, receiver or both, to not transmit for the duration of the transmission. This is known as the IEEE 802.11 RTS/CTS exchange.