GATE CS 2016 Set 2 — Question 64

MCQ+2 / -0.67MediumCSMA/CAMedium Access & LANsComputer Networks

Computer Networks → Medium Access & LANs → CSMA/CA

Last updated 5 September 2026

Question

For the IEEE 802.11 MAC protocol for wireless communication, which of the following statements is/are TRUE ? I. At least three non-overlapping channels are available for transmissions. II. The RTS-CTS mechanism is used for collision detection. III. Unicast frames are ACKed.

Correct answer (B) I and III only Solution Statement I is TRUE : In the 2.4 GHz ISM band used by 802.11b/g, there are 11 channels (in the US), and channels 1, 6, and 11 are non-overlapping. Statement II is FALSE : The RTS-CTS (Request to Send / Clear to Send) mechanism is used for collision avoidance (CSMA/CA), specifically to address the hidden terminal problem. Collision detection (CD) is not feasible in wireless networks because the transmitter's own signal would drown out any incoming collision signal (half-duplex nature and high attenuation). Statement III is TRUE : Unlike Ethernet, IEEE 802.11 requires an explicit link-layer acknowledgement (ACK) for every successfully received unicast frame to ensure reliability over the noisy wireless medium. Therefore, only I and III are true. Turn this into a strength. Explore AI-powered practice and doubt support with Success Tracker.

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Correct answer (B) I and III only Solution Statement I is TRUE : In the 2.4 GHz ISM band used by 802.11b/g, there are 11 channels (in the US), and channels 1, 6, and 11 are non-overlapping. Statement II is FALSE : The RTS-CTS (Request to Send / Clear to Send) mechanism is used for collision avoidance (CSMA/CA), specifically to address the hidden terminal problem. Collision detection (CD) is not feasible in wireless networks because the transmitter's own signal would drown out any incoming collision signal (half-duplex nature and high attenuation). Statement III is TRUE : Unlike Ethernet, IEEE 802.11 requires an explicit link-layer acknowledgement (ACK) for every successfully received unicast frame to ensure reliability over the noisy wireless medium. Therefore, only I and III are true.

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