Table of Contents
Question
Which of the following 802.11 fames is used to receive data packers by a STA working, in power-saving mode?
A. RTS
B. CTS
C. ACK
D. PS-Poll
Answer
D. PS-Poll
Explanation
The correct answer is D. PS-Poll.
PS-Poll is a type of 802.11 frame that is used by a station (STA) working in power-saving mode to receive data packets from an access point (AP). Power-saving mode is a feature that allows a STA to conserve battery power by switching to a low-power state when it is not transmitting or receiving data.
When a STA enters power-saving mode, it sends a null data frame to the AP with the power management bit set to 1, indicating that it is going to sleep. The AP then buffers any data packets that are destined for the STA until it wakes up. The AP also sets the traffic indication map (TIM) bit in the beacon frames that it broadcasts periodically, indicating that it has buffered data for the STA.
When the STA wakes up, it listens for the beacon frames from the AP and checks the TIM bit. If the TIM bit is set to 1, it means that the AP has buffered data for the STA. The STA then sends a PS-Poll frame to the AP, requesting one data packet at a time. The AP responds with a data frame containing the requested packet and sets the more data bit to indicate whether there are more packets buffered for the STA. The STA acknowledges the data frame with an ACK frame and repeats the process until it receives all the buffered packets or goes back to sleep.
The other options are incorrect because:
- A. RTS. This is false because RTS stands for request to send, which is a type of 802.11 frame that is used by a STA to initiate a data transmission and reserve the wireless medium for a specified duration. RTS is not used to receive data packets by a STA working in power-saving mode.
- B. CTS. This is false because CTS stands for clear to send, which is a type of 802.11 frame that is used by an AP or another STA to respond to an RTS frame and grant permission for the data transmission. CTS is not used to receive data packets by a STA working in power-saving mode.
- C. ACK. This is false because ACK stands for acknowledgment, which is a type of 802.11 frame that is used by an AP or a STA to confirm the successful reception of a data frame. ACK is not used to receive data packets by a STA working in power-saving mode, but rather to acknowledge them after receiving them.
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