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Feedback?Learn about the voice quality metrics and voice quality troubleshooting tips of your Cisco Wireless Phone 9821. This Help article is for Cisco Wireless Phone 9821 registered to Cisco Unified Communications Manager (Unified CM).
To measure the voice quality of calls that are sent and received within the network, Cisco IP Phones use the following statistical metrics that are based on R-Factor algorithm using packet loss rate and other network parameters such as codec type and network delay. The DSP plays concealment frames to mask frame loss in the voice packet stream.
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Concealment Ratio metrics
Shows the ratio of concealment frames over total speech frames. An interval conceal ratio is calculated every 3 seconds.
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Concealed Second metrics
Shows the number of seconds in which the DSP plays concealment frames due to lost frames. A severely concealed second is a second in which the DSP plays more than 5 percent concealment frames.
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MOS-LQ and MOS-CQ metrics
Uses a numeric score to estimate the relative voice quality. The phone calculates the mean opinion score (MOS) for listening quality (LQ) and conversational quality (CQ) using an algorithm based on the ITU-T G.107 E-Model. This calculation considers packet loss rate, codec type, and for MOS-CQ, includes additional impairment factors such as network delay.
MOS-LQ scores relate to the clarity or sound of the received voice signal. MOS-CQ scores include delay impairments that degrade the natural flow of conversation.
Concealment ratio and concealment seconds are primary measurements based on frame loss. MOS scores provide a "human-weighted" estimate of voice quality on a scale from 5 (excellent) to 1 (bad), calculated using packet loss rate, codec type, and network delay. While both metrics are affected by packet loss, they are calculated independently and may not always correlate directly.
For information about configuring voice quality metrics for phones, see the Administration Guide for Cisco Unified Communications Manager, Release 15 and SUs.
You can access voice quality metrics on the phone or remotely by using Streaming Statistics.
Voice quality metrics
To use the metrics for monitoring voice quality, note the typical scores under normal conditions of zero packet loss and use the metrics as a baseline for comparison.
It is important to distinguish significant changes from random changes in metrics. Significant changes are scores that change about 0.2 MOS or greater and persist in calls that last longer than 30 seconds. Conceal Ratio changes should indicate greater than 3 percent frame loss.
MOS scores can vary based on the codec that the phone uses. Under normal conditions with zero frame loss, the MOS score (calculate by R-factor) ranges from 1 to 4.5.
A Conceal Ratio of zero indicates that the IP network is delivering frames and packets on time with no loss.
Voice quality troubleshooting tips
When you observe significant and persistent changes to metrics, use the following table for general troubleshooting information.
|
Metric change |
Condition |
|---|---|
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MOS scores decrease significantly |
Network impairment from packet loss or high jitter:
Cross-check with Conceal Ratio and Conceal Seconds for evidence of packet loss and jitter. Check to see if the phone is using a different codec than expected (Sender Codec and Rcvr Codec). |
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MOS-CQ is significantly lower than MOS-LQ | Check the round-trip delay (RTD) as high delay impacts MOS-CQ more than MOS-LQ, and values above 200ms will cause noticeable degradation. |
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Conceal Ratio and Conceal Seconds increase significantly |
|
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Conceal Ratio is near or at zero, but the voice quality is poor |
Check packet transmit (TxCnt) and packet receive (RxCnt) counters to verify that voice packets are flowing. Verify that latency levels remain within the acceptable threshold to prevent degradation of conversational quality. |
Voice quality metrics do not account for noise or distortion. MOS scores primarily reflect the impact of packet loss and delay.
