ACMA Wireless Fundamentals 5 — Questions and Answers
Question 1: What is the primary advantage of using 5 GHz over 2.4 GHz for wireless deployments?
- Better wall penetration and longer range
- More available channels and less interference (Correct answer)
- Lower equipment cost and wider client support
- Higher transmit power limits from the FCC
Correct answer: More available channels and less interference
The 5 GHz band offers up to 25 non-overlapping 20 MHz channels in the US and experiences far less interference from consumer devices.
Question 2: In an 802.11 infrastructure BSS, which device is responsible for coordinating access to the wireless medium?
- The wireless client with the strongest signal
- The RADIUS server
- The Access Point (AP) (Correct answer)
- The Mobility Controller
Correct answer: The Access Point (AP)
In infrastructure mode, the AP coordinates medium access and acts as the central point for all client communications.
Question 3: What technology introduced in 802.11ac Wave 2 allows an AP to transmit to multiple clients simultaneously using separate spatial streams?
- SU-MIMO
- MU-MIMO (Correct answer)
- OFDMA
- TxBF
Correct answer: MU-MIMO
MU-MIMO (Multi-User MIMO) was introduced in 802.11ac Wave 2, allowing an AP to transmit to multiple clients simultaneously in the downlink.
Question 4: Which 802.11 feature reduces power consumption by allowing a client to enter a sleep state and buffer frames at the AP?
- WMM Power Save (U-APSD)
- Dynamic Frequency Selection (DFS)
- Target Wake Time (TWT) (Correct answer)
- Transmit Beamforming (TxBF)
Correct answer: Target Wake Time (TWT)
Target Wake Time (TWT), introduced in 802.11ax/Wi-Fi 6, allows clients and APs to negotiate specific times for data exchange, dramatically reducing power consumption.
Question 5: What is a co-channel interference (CCI) in Wi-Fi, and why does it degrade performance?
- Interference from a device on an adjacent channel that partially overlaps
- Interference from multiple APs sharing the same channel within range (Correct answer)
- Signal degradation caused by excessive AP transmit power
- Noise introduced by non-Wi-Fi devices on the same frequency
Correct answer: Interference from multiple APs sharing the same channel within range
CCI occurs when multiple APs on the same channel overlap, forcing devices to compete for airtime and increasing contention and retransmissions.
Question 6: In Aruba's architecture, what operating mode allows an AP to function without a controller by running all intelligence locally on the AP?
- Tunnel mode
- Remote AP mode
- Instant AP (IAP) mode (Correct answer)
- Monitor mode
Correct answer: Instant AP (IAP) mode
Aruba Instant APs operate without a physical controller — one AP in the cluster acts as a virtual controller, running locally on the AP hardware.
Question 7: What is the significance of the DIFS (DCF Interframe Space) in 802.11 medium access?
- It is the time an AP waits before sending a Beacon frame
- It is the mandatory idle period a station must wait before initiating a transmission (Correct answer)
- It defines the gap between frames in a block acknowledgment session
- It determines the duration of the random backoff timer
Correct answer: It is the mandatory idle period a station must wait before initiating a transmission
DIFS is the minimum time a station must sense the medium as idle before initiating a data transmission in DCF mode.
ACMA Wireless Fundamentals 5
What is the primary advantage of using 5 GHz over 2.4 GHz for wireless deployments?