CWS MAC Layer Functions Questions and Answers

Question 1

Which 802.11 MAC layer mechanism is specifically designed to address the hidden node problem by reserving the medium before data transmission?

Accepted Answer

Request to Send/Clear to Send (RTS/CTS)

Answer

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)

Answer

Distributed Coordination Function (DCF)

Answer

Block Acknowledgment (BlockAck)

Question 2

A network administrator is analyzing a wireless packet capture and observes a frame with the 'Type' field set to 01 (Control) and the 'Subtype' field set to 1011. What is the function of this frame?

Accepted Answer

To acknowledge the successful reception of a block of data frames.

Answer

To request that the medium be reserved for transmission.

Answer

To provide a timing signal and announce network information.

Answer

To carry upper-layer data from a client to the distribution system.

Question 3

What is the fundamental channel access method that is a mandatory part of the 802.11 standard, based on the principle of "listen before you talk"?

Accepted Answer

Distributed Coordination Function (DCF)

Answer

Point Coordination Function (PCF)

Answer

Hybrid Coordination Function (HCF)

Answer

Time Division Multiple Access (TDMA)

Question 4

In a high-density Wi-Fi environment, a network engineer wants to reduce the overhead associated with transmitting many small packets. Which 802.11n MAC layer feature allows for combining multiple MAC Service Data Units (MSDUs) into a single frame for transmission?

Accepted Answer

Frame Aggregation (A-MSDU)

Answer

Frame Fragmentation

Answer

Block Acknowledgment

Answer

Request to Send/Clear to Send (RTS/CTS)

Question 5

A battery-powered IoT device needs to conserve as much power as possible. It wakes up periodically to check if the access point has buffered any data for it. Which MAC layer mechanism facilitates this process?

Accepted Answer

The Power Management bit and Traffic Indication Map (TIM)

Answer

The 'Retry' bit in the Frame Control field

Answer

The Network Allocation Vector (NAV)

Answer

The Frame Check Sequence (FCS)

Question 6

Why does the IEEE 802.11 standard use Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) instead of Collision Detection (CSMA/CD) which is used in classic Ethernet?

Accepted Answer

Wireless radios cannot reliably transmit and listen for collisions at the same time.

Answer

CSMA/CD is a proprietary protocol, while CSMA/CA is an open standard.

Answer

CSMA/CA provides higher throughput in all wireless scenarios.

Answer

CSMA/CD requires a centralized controller, which is not present in 802.11 networks.