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Zorluk: Çok zorWireless Networking Standards and Technologies

A systems administrator is optimizing a high-density 5 GHz wireless deployment for a corporate campus located near a municipal airfield. The access points (APs) are configured for 802.11ac (Wi-Fi 5) utilizing 80 MHz channel widths to maximize data throughput. Shortly after deployment, users in specific wings of the building experience sporadic 30- to 60-second complete wireless dropouts, after which the APs are observed operating on narrower 20 MHz channels within a different frequency block. Which of the following wireless technologies is responsible for triggering these automatic channel and bandwidth changes?

  1. Dynamic Frequency Selection (DFS)Cevap
  2. B
    2.4 GHz channel overlap mitigation using non-overlapping channel selection
  3. C
    Layer 3 router boundary fallbacks triggering Layer 2 switch port isolation
  4. D
    Automatic Private IP Addressing (APIPA) failover triggered by high frame loss

Cevap

Dynamic Frequency Selection (DFS) is the mechanism responsible for forcing 5 GHz access points to vacate channels and reduce bandwidth upon detecting radar signals near airfields.
Dynamic Frequency Selection (DFS) is a mandatory feature for Wi-Fi devices operating in certain 5 GHz frequency bands (UNII-2 and UNII-2 Extended). When an AP operating near an airfield detects radar signals, regulatory standards require it to immediately cease transmission on that channel and switch to a non-radar channel. During this process (Channel Availability Check), connected clients experience a brief disconnection, and the AP may fall back to narrower channels (such as 20 MHz) to find clear, non-overlapping spectrum.

Adım Adım Çözüm

1
Analyze the reported symptoms and environment
The deployment uses 5 GHz 802.11ac with 80 MHz channels near an airport, experiencing sudden 30–60 second dropouts and automatic channel/bandwidth reductions.
Airports operate radar equipment in shared portions of the 5 GHz spectrum (UNII-2 and UNII-2 Extended bands).
2
Evaluate the regulatory wireless mechanism governing shared 5 GHz spectrum
Dynamic Frequency Selection (DFS) requires Wi-Fi equipment to continuously listen for radar pulses. If detected, the AP must halt transmission, undergo a Channel Availability Check (CAC) delay (typically 60 seconds), and move to a non-interfering channel.
DFS compliance prevents civilian Wi-Fi networks from interfering with military, weather, or aviation radar systems.
3
Confirm why alternative options do not fit the failure pattern
2.4 GHz channel rules do not govern 5 GHz spectrum; Layer 2/3 wired infrastructure handles frame routing rather than RF frequencies; APIPA handles client IP leasing failures rather than access point radio adjustments.
DFS is the only wireless protocol feature designed specifically for radar detection and dynamic channel reallocation.

Anahtar Kavram

Dynamic Frequency Selection (DFS) in 5 GHz 802.11 Standards
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Wireless Networking Standards and Technologies

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