Question 4 - CWNP CWAP-404 Real Exam Questions [Jan 2026 Update]

Q: 4

You have installed a new 802.1 lac WLAN configured with 80 MHz channels. Users in one area are complaining about poor performance. This area is currently served by a single AP. You take a spectrum analysis capture in the poor performing are a. While examining the waterfall plot you notice the airtime utilization is higher on the first 20 MHz of the 80 MHz channel when compared to the rest of the channel. What do you conclude?

Options

Correct Answer:

Explanation

In an 802.11ac/ax network configured for wide channels (40/80/160 MHz), the total bandwidth is comprised of a single "primary" 20 MHz channel and one or more "secondary" 20 MHz channels. All management frames (e.g., Beacons, Probe Responses) and control frames must be transmitted on the primary 20 MHz channel. This channel is also used for contention (e.g., RTS/CTS) and for communication with legacy clients that do not support wider channels. Consequently, the primary channel will always exhibit higher airtime utilization than the secondary channels, which are used opportunistically for wide-channel data transmissions. The observation is a normal characteristic of 80 MHz operation.

Why Incorrect

A. The described behavior is a fundamental and expected characteristic of 80 MHz operation, not a sign of misconfiguration.

B. While non-Wi-Fi interference can cause performance issues, the specific pattern of higher utilization on only the primary channel is normal Wi-Fi protocol behavior.

D. If RRM had selected a 20 MHz channel, the AP would only be operating on that single channel, not an 80 MHz channel with varied utilization.

References

1. CWNP, LLC. (2021). CWAP-404 Certified Wireless Analysis Professional Official Study Guide. Sybex. In Chapter 5, "MAC Layer Analysis," the section on "VHT (802.11ac) MAC" explains that the primary 20 MHz channel is used for all management and control frames, leading to higher activity on that specific channel segment within a wider channel bond.

2. IEEE Std 802.11™-2020. (2021). IEEE Standard for Information Technology--Telecommunications and Information Exchange between Systems Local and Metropolitan Area Networks--Specific Requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. In Clause 22.3.13, "Channelization," the standard defines the primary channel for VHT (802.11ac) operations and specifies its mandatory use for certain frame types, which inherently concentrates traffic on it.

3. Coleman, D. D., & Westcott, D. A. (2021). Certified Wireless Network Administrator CWNA-108 Official Study Guide. Sybex. Chapter 10, "802.11ac," details the channel-bonding mechanisms, explicitly stating that the primary channel carries the BSS's beacon frames and is the main channel for contention, explaining the higher utilization.

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