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Difficulty: HardTroubleshooting Wireless Connectivity and Signal Issues

During a routine wireless performance audit of a corporate facility, an administrator observes severe packet loss and elevated frame retransmissions among clients connected to 2.4 GHz access points. Signal strength measurements indicate strong coverage (-55 dBm) across all work areas. Inspection of the wireless controller configuration reveals that adjacent access points are operating on channels 1, 2, 4, and 5. Which of the following represents the primary root cause of this connectivity issue?

  1. Adjacent-channel interference resulting from overlapping channel selection in the 2.4 GHz spectrum.Answer
  2. B
    Co-channel interference caused by assigning non-overlapping channels across adjacent coverage cells.
  3. C
    A speed and duplex mismatch on the Ethernet switchport connecting the wireless access point.
  4. D
    DHCP scope exhaustion preventing wireless clients from acquiring valid Layer 3 network configurations.

Answer

Adjacent-channel interference resulting from overlapping channel selection in the 2.4 GHz spectrum.
In the 2.4 GHz spectrum, 802.11 channels are spaced 5 MHz apart but require a 20 MHz signal width (plus sidebands), requiring 25 MHz of total channel spacing to avoid overlap. The standard non-overlapping channels in 2.4 GHz are 1, 6, and 11. Assigning channels 1, 2, 4, and 5 causes adjacent radios to transmit on overlapping frequencies. This results in severe adjacent-channel interference (ACI), leading to unreadable RF energy, packet collisions, high frame retransmissions, and throughput drops despite strong RSSI readings.

Step-by-Step Solution

1
Analyze the reported signal metrics and physical layer status.
The measured signal strength of -55 dBm indicates excellent RF power and eliminates attenuation or distance issues as the root cause.
Signal levels above -65 dBm are generally considered strong for enterprise Wi-Fi environments.
2
Evaluate the 2.4 GHz channel plan against standard 802.11 specifications.
The 2.4 GHz band uses 22 MHz wide channels spaced 5 MHz apart. The only non-overlapping 20 MHz channel plan in North America consists of channels 1, 6, and 11.
Channels 1, 2, 4, and 5 overlap directly in frequency space.
3
Determine the impact of assigning overlapping channels to adjacent access points.
Transmissions on channel 2 bleed into channels 1 and 4, creating elevated noise and frame collisions, which causes clients to retransmit frames and suffer degraded throughput.
Adjacent-channel interference (ACI) cannot be decoded as valid Wi-Fi preamble by neighboring radios, treating it instead as raw RF noise.

Key Concept

2.4 GHz Channel Overlap and Adjacent-Channel Interference (ACI)
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Topics

Troubleshooting Wireless Connectivity and Signal Issues

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