N10-009 Question 160
Single answerChannels: Channel width, Non-overlapping channels, Regulatory impacts (802.11h)A network administrator is redesigning Wi-Fi in a European office that uses several 5 GHz access points. Users report intermittent disconnects in conference rooms near windows facing a nearby weather radar installation. To increase capacity, the administrator had previously configured 80 MHz channels on all APs. After a site survey, the administrator wants to reduce interference and stay compliant with regional regulations while maintaining stable service. Which action is the BEST choice?
- A
Reconfigure the 5 GHz APs to use narrower 20 or 40 MHz channels and ensure DFS/TPC features required by 802.11h are enabled
- B
Move all APs to channel 6 on 2.4 GHz because it is a non-overlapping channel and will avoid radar-related interruptions
- C
Disable 802.11h support so the APs will remain on their assigned 5 GHz channels even when radar is detected
- D
Increase transmit power on the 80 MHz 5 GHz channels so clients can maintain signal strength during radar events
Show answer and explanation
Correct answer: A
Explanation
The best answer is to reduce channel width and keep 802.11h-related protections active. In a dense enterprise WLAN, narrower channels such as 20 MHz or 40 MHz often provide better practical performance than 80 MHz because they allow more usable channel planning and reduce contention. In the 5 GHz band, some channels are subject to DFS requirements because they share spectrum with radar systems. IEEE 802.11h was introduced to help WLAN devices meet these regulatory requirements, including Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC). If radar is detected, compliant APs must vacate the channel rather than remain fixed on it. This behavior is particularly relevant in Europe under ETSI regulatory rules and is reflected in vendor WLAN best practices and Wi-Fi design guidance. For comparison, 2.4 GHz non-overlapping channels such as 1, 6, and 11 are important, but shifting a business deployment to 2.4 GHz is usually not the best way to solve 5 GHz DFS-related instability.
- A. Correct.
Correct. In 5 GHz deployments, wider channels such as 80 MHz provide more throughput but consume more spectrum and increase the chance of overlap with DFS channels that may be affected by radar detection. In Europe, regulatory rules commonly require DFS and TPC behavior on certain 5 GHz channels, which is addressed by 802.11h. Reducing channel width to 20 or 40 MHz can improve channel reuse and reduce co-channel interference in multi-AP environments, while keeping 802.11h-related compliance features enabled helps the WLAN respond properly to radar events.
- B. Incorrect.
Incorrect. Channel 6 is one of the three commonly used non-overlapping channels in 2.4 GHz, but moving a multi-AP office deployment from 5 GHz to 2.4 GHz would usually reduce overall capacity and increase contention because 2.4 GHz has fewer usable non-overlapping channels. It also does not address the design goal of maintaining stable, scalable service in a dense office environment.
- C. Incorrect.
Incorrect. 802.11h exists specifically to support regulatory compliance in 5 GHz bands, including DFS and transmit power control where required. Disabling it to ignore radar detection would be noncompliant and could interfere with protected systems such as weather radar. This option reflects a dangerous misconception that stability can be improved by bypassing regulatory requirements.
- D. Incorrect.
Incorrect. Increasing transmit power does not prevent DFS-triggered channel changes caused by radar detection. In fact, higher power can worsen cell overlap and co-channel interference in dense deployments. 802.11h includes transmit power control to manage power appropriately, not simply maximize it.