ACMA WLAN Design 4 — Questions and Answers
Question 1: What is the significance of the 'overlap' percentage between adjacent AP coverage areas in WLAN design?
- Overlap should be 0% to prevent co-channel interference
- 10–15% overlap ensures seamless roaming without excessive interference (Correct answer)
- 50% overlap is required for all enterprise deployments
- Overlap percentage only matters for 2.4 GHz deployments
Correct answer: 10–15% overlap ensures seamless roaming without excessive interference
A 10–15% overlap between adjacent cells ensures clients can roam seamlessly while minimizing co-channel interference.
Question 2: A warehouse deployment requires APs to cover very long aisles between metal shelving. Which antenna configuration is most effective?
- Omnidirectional ceiling-mounted APs above each aisle
- Directional patch antennas mounted at aisle ends pointing down each aisle (Correct answer)
- High-gain omnidirectional antennas mounted on the shelving units
- Dipole antennas mounted horizontally at floor level
Correct answer: Directional patch antennas mounted at aisle ends pointing down each aisle
Directional patch antennas aimed down aisles focus RF energy where it's needed and reduce interference between parallel aisles.
Question 3: Which 802.11 amendment introduced the concept of BSS Coloring to reduce co-channel interference in dense deployments?
- 802.11ac
- 802.11n
- 802.11ax (Wi-Fi 6) (Correct answer)
- 802.11r
Correct answer: 802.11ax (Wi-Fi 6)
802.11ax (Wi-Fi 6) introduced BSS Coloring, which allows devices to differentiate between overlapping BSSs and reduce unnecessary deferrals.
Question 4: What is the purpose of conducting a passive site survey versus an active site survey?
- Passive surveys measure actual throughput; active surveys only measure signal strength
- Passive surveys listen to existing RF environment; active surveys use a test AP to measure coverage (Correct answer)
- Active surveys are done before installation; passive surveys are only done post-installation
- Passive surveys use specialized hardware; active surveys use a smartphone
Correct answer: Passive surveys listen to existing RF environment; active surveys use a test AP to measure coverage
Passive surveys capture existing RF signals and interference without transmitting, while active surveys use a test AP to measure coverage and performance.
Question 5: In a high-density stadium deployment, why are APs typically mounted under seats rather than on the ceiling?
- Under-seat mounting is cheaper and easier to cable
- Ceiling-mounted APs cannot reach 5 GHz frequencies in large venues
- Under-seat mounting provides shorter range and better per-user capacity (Correct answer)
- Building codes require APs to be at floor level in public venues
Correct answer: Under-seat mounting provides shorter range and better per-user capacity
Under-seat AP placement reduces cell size and focuses coverage on individual seating areas, dramatically improving per-user capacity in dense crowds.
Question 6: What does EIRP stand for, and why is it important in WLAN design?
- Effective Isotropic Radiated Power — the total power an antenna system emits in a specific direction (Correct answer)
- Equivalent Internal Radio Protocol — governs how APs communicate internally
- Extended Indoor RF Plan — a document standard for site surveys
- External Interference Reduction Protocol — used by ARM to suppress noise
Correct answer: Effective Isotropic Radiated Power — the total power an antenna system emits in a specific direction
EIRP (Effective Isotropic Radiated Power) combines transmitter output power and antenna gain, and regulatory bodies set maximum EIRP limits for WLAN operation.
Question 7: Which roaming protocol reduces re-authentication delay for wireless clients moving between APs in an Aruba network?
- 802.11k
- 802.11r (Fast BSS Transition) (Correct answer)
- 802.11v
- 802.11u
Correct answer: 802.11r (Fast BSS Transition)
802.11r (Fast BSS Transition) enables clients to pre-authenticate with the target AP before roaming, minimizing handoff delay.
ACMA WLAN Design 4
What is the significance of the 'overlap' percentage between adjacent AP coverage areas in WLAN design?