300-370 · Question #135
After you perform a post-installation RF survey for a customer with ID 339696181, you discover that all areas have at least -67 dBm RSSI, 25 dB SNR, and 10 percent cell overlap. The customer…
The correct answer is A. The cell overlap is too low. Despite good RSSI and SNR, one-way audio on VoWLAN phones often indicates insufficient cell overlap, causing issues with seamless roaming.
Question
After you perform a post-installation RF survey for a customer with ID 339696181, you discover that all areas have at least -67 dBm RSSI, 25 dB SNR, and 10 percent cell overlap. The customer, however, reports one-way audio issues on VoWLAN phones. Which option is a possible cause of the issue?
Exhibit
Options
- AThe cell overlap is too low.
- BThere are coverage black spots.
- CNon Wi-Fi interference causes a high noise floor.
- DThe RSSI is too high.
How the community answered
(54 responses)- A83% (45)
- B6% (3)
- C2% (1)
- D9% (5)
Why each option
Despite good RSSI and SNR, one-way audio on VoWLAN phones often indicates insufficient cell overlap, causing issues with seamless roaming.
For VoWLAN, a 10 percent cell overlap is insufficient for seamless roaming, which can cause one-way audio issues as phones struggle to find a new access point when moving between cells. Industry best practices recommend higher cell overlap (e.g., 15-20%) to ensure smooth client transitions and prevent call quality degradation.
The survey explicitly states 'all areas have at least -67 dBm RSSI', which indicates adequate coverage without black spots.
A high noise floor would result in a lower Signal-to-Noise Ratio (SNR), but the reported SNR of 25 dB is considered good for voice.
An RSSI of -67 dBm is generally considered a good minimum signal strength for VoWLAN and is not 'too high' (implying excessively strong, which isn't the issue).
Concept tested: VoWLAN RF design, cell overlap for roaming
Source: https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Mobility/vowlan/2_5/vowlan_2_5_wlc/vowlan_2_5_chapter3.html
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