Examkin

Question

Difficulty: HardTroubleshooting Wireless Connectivity and Signal Issues

During a wireless network performance audit of a open-plan office, a network administrator observes high frame retransmission rates and latency for clients connected to the 2.4 GHz band. A physical scan reveals that three neighboring access points (APs) mounted along the main corridor are assigned to channels 1, 3, and 6, each operating with a 20 MHz channel width. What is the primary cause of this performance degradation, and how should it be resolved?

  1. The APs are experiencing adjacent-channel interference because channel 3 overlaps with both channels 1 and 6; the APs should be reassigned to non-overlapping channels 1, 6, and 11.Answer
  2. B
    The APs are experiencing co-channel interference due to narrow spacing; increasing the channel width on all APs to 40 MHz will provide higher throughput and eliminate channel congestion.
  3. C
    The client devices are falling back to APIPA addressing due to DHCP scope exhaustion; the DHCP pool prefix must be expanded to handle additional wireless clients.
  4. D
    The Ethernet switch ports connected to the access points are configured for half-duplex operation; updating the switch port settings to full-duplex will eliminate collisions.

Answer

The primary cause is adjacent-channel interference (ACI) caused by assigning overlapping channel 3 alongside channels 1 and 6. The issue is resolved by reconfiguring the access points to operate on standard non-overlapping channels 1, 6, and 11.
In the 2.4 GHz Wi-Fi band (2.412 GHz to 2.472 GHz), 20 MHz wide channels require 25 MHz of spacing between center frequencies to avoid spectral overlap. Channels 1, 6, and 11 are the only three standard non-overlapping channels in regulatory domains adhering to North American standards. Operating an access point on channel 3 causes adjacent-channel interference with APs on channels 1 and 6, as their frequency masks overlap. This interference corrupts frames mid-transmission, causing high retry rates and severe latency. Changing the channel plan to 1, 6, and 11 eliminates adjacent-channel interference.

Step-by-Step Solution

1
Analyze the 2.4 GHz channel assignment layout.
Identified access points running on 2.4 GHz channels 1, 3, and 6.
Each 20 MHz 802.11 channel in the 2.4 GHz ISM band spans 22 MHz of frequency space. Channels separated by fewer than 5 channel numbers share overlapping frequencies.
2
Evaluate the spectrum overlap of channel 3.
Channel 3 center frequency (2422 MHz) overlaps with channel 1 (2412 MHz) and channel 6 (2437 MHz).
Because 802.11 devices on adjacent overlapping channels cannot decode each other's preamble headers reliably for CSMA/CA clear channel assessment, overlapping transmissions cause raw RF noise and packet corruption (adjacent-channel interference).
3
Determine the proper remediation strategy.
Select standard non-overlapping channels 1, 6, and 11 for the 3 APs.
Channels 1, 6, and 11 provide sufficient frequency separation so that adjacent access points operate without spectral overlap.

Key Concept

2.4 GHz Non-Overlapping Channel Selection and Adjacent-Channel Interference (ACI)
Estimated Time:2m 0s
Rate this question

Topics

Troubleshooting Wireless Connectivity and Signal Issues

More questions from this topic