ACMA Wireless Networking Fundamentals & Technologies 5 — Questions and Answers
Question 1: What is co-channel interference (CCI) in wireless networking?
- Interference between overlapping channels with partially shared frequencies
- Interference between two APs operating on the same channel within range of each other (Correct answer)
- Noise introduced by non-Wi-Fi devices such as microwaves
- Signal degradation caused by multipath reflections
Correct answer: Interference between two APs operating on the same channel within range of each other
Co-channel interference occurs when two or more APs use the same channel and their coverage areas overlap, forcing clients to compete for the same medium.
Question 2: In 802.11 WMM (Wi-Fi Multimedia), which Access Category has the highest priority?
- AC_BK (Background)
- AC_BE (Best Effort)
- AC_VI (Video)
- AC_VO (Voice) (Correct answer)
Correct answer: AC_VO (Voice)
AC_VO (Voice) has the highest QoS priority in WMM, using the shortest AIFSN and CWmin values to minimize latency for voice traffic.
Question 3: What is the effect of increasing the channel width from 20 MHz to 80 MHz in 802.11ac?
- It reduces the number of non-overlapping channels and increases throughput (Correct answer)
- It increases the number of non-overlapping channels and reduces throughput
- It has no effect on throughput but reduces interference
- It only applies to the 2.4 GHz band
Correct answer: It reduces the number of non-overlapping channels and increases throughput
Wider channels carry more subcarriers and increase throughput, but consume more spectrum and reduce the number of available non-overlapping channels.
Question 4: Which physical layer characteristic determines the maximum theoretical data rate of an 802.11 link?
- Transmit power and antenna gain only
- Channel width, modulation scheme, coding rate, and number of spatial streams (Correct answer)
- SSID broadcast interval and beacon rate
- The IP MTU size configured on the AP
Correct answer: Channel width, modulation scheme, coding rate, and number of spatial streams
The PHY data rate is a product of channel width (subcarrier count), modulation and coding scheme (MCS), and the number of spatial streams used.
Question 5: What does the 802.11k standard enable in a wireless network?
- Fast roaming by pre-authenticating with the target AP
- Radio resource measurement and neighbor reporting to assist client roaming decisions (Correct answer)
- Opportunistic key caching to reduce re-authentication time
- Downlink MU-MIMO scheduling by the AP
Correct answer: Radio resource measurement and neighbor reporting to assist client roaming decisions
802.11k provides mechanisms for APs and clients to exchange radio resource measurements and neighbor AP lists, helping clients make better-informed roaming decisions.
Question 6: Which term describes the phenomenon where a wireless signal arrives at the receiver via multiple paths due to reflections, causing amplitude and phase variations?
- Doppler shift
- Multipath fading (Correct answer)
- Free-space path loss
- Absorption
Correct answer: Multipath fading
Multipath fading occurs when reflected copies of a signal arrive at slightly different times and phases, causing constructive or destructive interference at the receiver.
Question 7: In an Aruba network, what is the primary function of the Air Monitor (AM) mode on an AP?
- Serving client traffic while scanning for rogues in the background
- Dedicating the AP exclusively to WIDS/WIPS monitoring, scanning all channels for threats (Correct answer)
- Providing mesh backhaul connectivity between remote APs
- Operating as a spectrum analyzer only for 6 GHz channels
Correct answer: Dedicating the AP exclusively to WIDS/WIPS monitoring, scanning all channels for threats
An AP in Air Monitor mode does not serve client traffic and instead dedicates all resources to scanning channels for rogue APs, security threats, and RF environment data.
ACMA Wireless Networking Fundamentals & Technologies 5
What is co-channel interference (CCI) in wireless networking?