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Difficulty: HardTroubleshooting Wireless Connectivity and Signal Issues

An enterprise network engineer is investigating severe throughput degradation and excessive frame retransmissions on a newly installed 2.4 GHz wireless network servicing an open-plan office. A site survey reveals that three neighboring access points with overlapping coverage areas are configured as follows:

- Access Point North: Channel 1, 20 MHz channel width
- Access Point Center: Channel 3, 20 MHz channel width
- Access Point South: Channel 5, 20 MHz channel width

Which administrative action will most effectively eliminate the performance bottleneck caused by adjacent-channel interference?

  1. Reassign the access point channels to 1, 6, and 11 respectively.Answer
  2. B
    Expand the channel width on all access points from 20 MHz to 40 MHz.
  3. C
    Configure an IP Helper address on the default gateway to assist client DHCP binding.
  4. D
    Change the uplink switchport duplex settings connected to the access points to half-duplex.

Answer

Reassigning the access point operating channels to 1, 6, and 11 eliminates adjacent-channel interference by enforcing non-overlapping 20 MHz frequency spacing in the 2.4 GHz spectrum.
In 2.4 GHz Wi-Fi deployments, 20 MHz wide channels require 25 MHz of center-frequency separation to operate without overlapping. Channels 1, 6, and 11 are the standard non-overlapping channels. Reconfiguring adjacent access points from channels 1, 3, and 5 to channels 1, 6, and 11 removes adjacent-channel interference (ACI), preventing RF noise and high packet retransmission rates.

Step-by-Step Solution

1
Analyze the existing 2.4 GHz channel configuration.
Channels 1, 3, and 5 overlap directly with each other because standard 20 MHz 2.4 GHz channels require a 25 MHz separation (5 channel numbers apart) to avoid overlapping.
Channels 1, 3, and 5 cause partial spectrum overlap, leading to severe adjacent-channel interference (ACI) where radio receivers cannot effectively decode frames.
2
Identify standard non-overlapping channels for the 2.4 GHz Wi-Fi spectrum.
In the 2.4 GHz spectrum (802.11b/g/n), the three primary non-overlapping channels are 1, 6, and 11.
Using channels 1, 6, and 11 ensures complete frequency separation between neighboring access points.
3
Select the remediation action that enforces non-overlapping channel separation.
Reconfiguring the access points to channels 1, 6, and 11 eliminates ACI.
Eliminating ACI stops packet corruption at the physical layer, drastically reducing retransmission rates and restoring throughput.

Key Concept

2.4 GHz Non-Overlapping Channel Assignment & Adjacent-Channel Interference
Estimated Time:2m 0s
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Topics

Troubleshooting Wireless Connectivity and Signal Issues

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