Free CWNA-109 sample questions

Correct answer: Approximately 4.9 meters

The formula for the radius of the first Fresnel zone is r = 17.32 * sqrt((d1*d2)/(f*D)), where d1 and d2 are distances from the ends, D is total distance, and f is frequency in GHz. At the building location (d1=0.5, d2=0.7, D=1.2, f=5), the radius is ~8.15 meters. 60% clearance requires 0.60 * 8.15 = ~4.9 meters. The other options result from common calculation errors.

Correct answers: Excessive Reflection; High Absorption

Metal fixtures cause significant RF reflection, leading to severe multipath where signals arrive at the receiver at different times, causing inter-symbol interference and degrading performance.

Dense stone walls are a primary source of absorption, which converts RF energy into heat, severely attenuating the signal and reducing coverage range.

Correct answer: A high Voltage Standing Wave Ratio (VSWR)

An impedance mismatch between the 50-ohm system (AP and antenna) and the 75-ohm cable causes signal reflections. VSWR is the direct measurement of this reflection and the resulting standing waves. A high VSWR indicates a significant impedance mismatch, which can damage the transmitter and severely degrade performance.

Correct answer: True

Polarization refers to the orientation of the electric field of the RF wave. If the transmitting and receiving antennas have a 90-degree polarization mismatch (e.g., one is vertically polarized and the other is horizontally polarized), the receiving antenna will be unable to efficiently capture the signal energy. This cross-polarization can result in significant signal loss, often exceeding 20 dB, effectively nullifying the link.

Correct answer: The APs are detecting radar signals and initiating DFS events.

U-NII-6 (6.425-6.525 GHz) and U-NII-8 (6.875-7.125 GHz) bands in the 6 GHz spectrum are subject to contention-based protocols to protect incumbent users, which functions similarly to DFS. The naval base is a likely source of incumbent radar signals. When an AP detects these signals, it must vacate the channel immediately and move to a different one, causing the observed disconnects.

Correct answer: It subdivides a channel into smaller RUs and serves multiple users simultaneously within the same transmission opportunity.

The key innovation of OFDMA in 802.11ax is the ability to partition a channel into multiple smaller sub-channels called Resource Units (RUs). This allows an AP to transmit to and receive from multiple clients simultaneously, dramatically reducing contention and latency, which is ideal for high-density environments with many clients sending small packets.

Correct answer: 802.11n

802.11n (Wi-Fi 4) was a major leap forward, introducing several key technologies simultaneously. It was the first standard to mandate MIMO (Multiple-Input, Multiple-Output), introduce 40 MHz channel bonding, and utilize 64-QAM modulation to push data rates significantly higher than previous standards.

Correct answer: RA, TA, DA, SA

In a WDS, all four address fields are used. Address 1 is the Receiver Address (RA) - the next-hop AP. Address 2 is the Transmitter Address (TA) - the sending AP. Address 3 is the Destination Address (DA) - the final server. Address 4 is the Source Address (SA) - the original client. This allows the frame to be routed across the wireless backbone while preserving the original source and final destination MACs.

Correct answer: Unscheduled Automatic Power Save Delivery (U-APSD)

U-APSD, part of WMM-Power Save, is ideal for applications like VoWiFi. It allows the client to sleep between transmissions but can wake up instantly to send voice packets without waiting for a beacon. The AP buffers downlink packets and sends them immediately after receiving an uplink packet from the client, providing both power savings and the low latency required for real-time voice.

Correct answer: The target network has its SSID hidden and the client profile is not configured with the correct SSID.

When an SSID is hidden, APs do not include the SSID in their Beacon frames and will not respond to a broadcast Probe Request (a request with a null SSID field). The client must be configured with the specific SSID in its profile to send a directed Probe Request. If the client sends a broadcast probe, the APs for the hidden network will ignore it, resulting in no Probe Response.