300-425 · Question #4
A wireless engineer is performing a post verification of a wireless network. Which two metrics does the engineer verify to ensure that the wireless network can support voice services? (Choose two.)
The correct answer is B. The client device must have at least an -67 dBm RSSI. D. The rate of retransmitted packets must be 20 percent or below. Cisco wireless voice design requires a minimum -67 dBm RSSI at the client and a retransmission rate at or below 20% to ensure acceptable call quality.
Question
A wireless engineer is performing a post verification of a wireless network. Which two metrics does the engineer verify to ensure that the wireless network can support voice services? (Choose two.)
Options
- AThe coverage area must have a noise floor that does not exceed -87 dBm.
- BThe client device must have at least an -67 dBm RSSI.
- CThe rate of retransmitted packets must be 15 percent or below.
- DThe rate of retransmitted packets must be 20 percent or below.
- EThe client device must have at least an -65 dBm RSSI.
How the community answered
(45 responses)- A2% (1)
- B91% (41)
- C4% (2)
- E2% (1)
Why each option
Cisco wireless voice design requires a minimum -67 dBm RSSI at the client and a retransmission rate at or below 20% to ensure acceptable call quality.
The noise floor threshold for voice is typically -85 dBm or better, not -87 dBm - a noise floor of -87 dBm would actually be acceptable, but this is not one of the two primary metrics Cisco cites.
Cisco recommends a minimum RSSI of -67 dBm at the client device to ensure sufficient signal margin for voice traffic, which is highly sensitive to packet loss and jitter.
A 15% retransmission rate threshold is more stringent than the Cisco standard recommendation of 20%, making this value incorrect for the defined specification.
A retransmission rate of 20% or below is the Cisco-recommended threshold for voice-capable wireless networks, as higher retransmission rates introduce latency and jitter that degrade call quality.
While -65 dBm represents a stronger signal than -67 dBm, the Cisco recommended minimum for voice is -67 dBm - -65 dBm is not the stated design threshold.
Concept tested: Wireless voice network post-verification metrics
Source: https://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/Mobility/vowlan/41dg/vowlan41dg-book/vowlan_ch3.html
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