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Difficulty: Very hardTroubleshooting Wireless Connectivity and Signal Issues

An IT consultant is diagnosing severe throughput degradation and high retransmission rates on a corporate suite's 2.4 GHz wireless network in a multi-tenant office building. A spectrum analyzer capture indicates that a neighboring tenant's unmanaged access point is broadcasting on Channel 4 using a standard 20 MHz channel width. To eliminate adjacent-channel interference and establish total RF spectrum isolation for the corporate suite on the 2.4 GHz band, which channel should the administrator assign to the internal access point?

  1. A
    Reassign the access point to Channel 1
  2. B
    Reassign the access point to Channel 6
  3. Reassign the access point to Channel 11Answer
  4. D
    Configure the connected switch port to half-duplex mode to match wireless frame transmission mechanics

Answer

Assigning the access point to Channel 11 completely isolates the wireless signal from Channel 4's spectral envelope.
In the 2.4 GHz Wi-Fi band, each 20 MHz wide channel requires roughly 22 MHz of channel separation. Channel 4 has a center frequency of 2427 MHz, causing its signal to occupy frequencies from roughly 2416 MHz to 2438 MHz. Channel 1 (2401–2423 MHz) and Channel 6 (2426–2448 MHz) both share overlapping frequency space with Channel 4. Channel 11 (2451–2473 MHz) resides entirely clear of Channel 4's upper limit, providing complete spectral isolation and eliminating adjacent-channel interference.

Step-by-Step Solution

1
Analyze the spectral footprint of the interfering signal on Channel 4.
In 20 MHz 802.11 deployments, Channel 4 operates at a center frequency of 2427 MHz and occupies an RF passband from approximately 2416 MHz to 2438 MHz.
Understanding the exact frequency boundaries of the interference source is required to select a non-overlapping channel.
2
Evaluate candidate 2.4 GHz non-overlapping channels against Channel 4's boundaries.
Channel 1 (2401–2423 MHz) overlaps Channel 4 between 2416 MHz and 2423 MHz. Channel 6 (2426–2448 MHz) overlaps Channel 4 between 2426 MHz and 2438 MHz.
Adjacent-channel interference causes near-far framing errors and unrecoverable packet collisions because radios cannot decode corrupted headers.
3
Verify Channel 11 frequency isolation.
Channel 11 operates at center frequency 2462 MHz with a passband from 2451 MHz to 2473 MHz. Its lowest frequency (2451 MHz) is well above Channel 4's highest frequency (2438 MHz).
Operating above 2438 MHz guarantees complete frequency separation and eliminates adjacent-channel interference.

Key Concept

2.4 GHz Channel Overlap and Spectral Passband Calculation
Estimated Time:2m 0s
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Topics

Troubleshooting Wireless Connectivity and Signal Issues

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