Which of the following statements are correct about medium access according to C

Question

Which of the following statements are correct about medium access according to CSMA/CA for IEEE 802.11 wireless networks ("WLAN")? DIFS is a time constant that tells how long a node should wait before sending after it has discovered that the channel is busy. A collision is discovered by the sender not receiving an acknowledgement (ACK frame) from the receiver. The RTS/CTS handshake is optional and hence does not need to be used for each frame transmission. Unlike CSMA/CD, a node does not need to listen before sending. The RTS/CTS handshake does not help to deal with the "hidden terminal" problem.

Explanation / Answer

The correct statements are: A and C

A. DIFS is a time constant that tells how long a node should wait before sending after it has discovered that the channel is busy.

(Beacuse transmitter must wait for a channel to be idle for DIFS amount of time before it start to transmit. If the channel is busy it immediately back off the transmission by some amount of time to avoid collision.)

C.The RTS/CTS handshake is optional and hence does not need to be used for each frame transmission.

(Because in wireless network, the Access Point only issues CTS to one node at a time. In wireless 802.11 implementation RTS/CTS does not implement for all transmissions, they must turn off completely or may not use it.)

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