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Difficulty: HardTroubleshooting Wireless Connectivity and Signal Issues

Users in a newly renovated office space report severe latency and frequent packet loss while connected to the wireless network. A network technician measures the Received Signal Strength Indicator (RSSI) on an affected client device and records a strong signal reading of −55 dBm-55\text{ dBm}. However, the Signal-to-Noise Ratio (SNR) is measured at only 8 dB8\text{ dB}, leading to high retransmission rates. Which of the following is the most likely cause of this performance degradation?

  1. A high ambient noise floor caused by non-802.11 RF interference in the environmentAnswer
  2. B
    Correct deployment of non-overlapping channels 1, 6, and 11 on adjacent 2.4 GHz access points
  3. C
    DHCP scope exhaustion forcing client devices to self-assign APIPA addresses
  4. D
    A full-duplex mismatch on the Ethernet link between the wireless access point and switch

Answer

A high ambient noise floor caused by non-802.11 RF interference in the environment
Signal-to-Noise Ratio (SNR) represents the difference between the received signal strength (RSSI) and the background noise floor. Given an RSSI of −55 dBm-55\text{ dBm} and an SNR of only 8 dB8\text{ dB}, the noise floor is calculated to be −63 dBm-63\text{ dBm}, which is significantly higher than the acceptable baseline of −90 dBm-90\text{ dBm}. This high noise floor is caused by ambient non-802.11 RF interference, causing corruption of transmitted frames and elevated retransmission rates despite strong transmitter signal power.

Step-by-Step Solution

1
Analyze the reported physical layer Wi-Fi metrics
The measured RSSI is −55 dBm-55\text{ dBm} (indicating strong signal power) and the SNR is 8 dB8\text{ dB} (indicating poor signal quality).
Signal-to-Noise Ratio is defined as SNR=RSSI−Noise Floor\text{SNR} = \text{RSSI} - \text{Noise Floor}.
2
Calculate the environmental noise floor level
Noise Floor=−55 dBm−8 dB=−63 dBm\text{Noise Floor} = -55\text{ dBm} - 8\text{ dB} = -63\text{ dBm}.
Enterprise Wi-Fi networks typically require an SNR of 20 dB20\text{ dB} or higher and operate with a healthy noise floor between −90 dBm-90\text{ dBm} and −95 dBm-95\text{ dBm}.
3
Determine the root cause of the elevated noise floor
An elevated noise floor at −63 dBm-63\text{ dBm} points directly to high ambient RF noise created by non-802.11 interference sources.
External RF noise raises the overall background noise floor, shrinking the SNR gap even when the access point radiates a strong signal.

Key Concept

Signal-to-Noise Ratio (SNR) and Noise Floor Troubleshooting
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Topics

Troubleshooting Wireless Connectivity and Signal Issues

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