Voice Quality Metric Interpretation
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 LQK scores can vary based on the codec that the Cisco Unified IP Phone uses. The following codecs
provide these maximum MOS LQK scores under normal conditions with zero frame loss:
•
For Cisco Unified Phone 7975G, 7965G, and 7945G:
◦
G.711 gives 4.5 score.
◦
G.722 gives 4.5.
◦
G.728/iLBC gives 3.9.
◦
G.729A/AB gives 3.8.
•
For Cisco Unified Phone 7971G-GE and 7970G:
•
G.711 codec gives 4.5 score.
•
G.729A/AB gives 3.7.
Note
•
CVTQ does not support wideband (7 kHz) speech codecs, as ITU has not defined the extension of
the technique to wideband. Therefore, MOS scores that correspond to G.711 performance are reported
for G.722 calls to allow basic quality monitoring, rather than not reporting an MOS score.
•
Reporting G.711-scale MOS scores for wideband calls through the use of CVTQ allows basic quality
classifications to be indicated as good/normal or bad/abnormal. Calls with high scores (approximately
4.5) indicate high quality/low packet loss, and lower scores (approximately 3.5) indicate low
quality/high packet loss.
•
Unlike MOS, the Conceal Ratio and Concealed Seconds metrics remain valid and useful for both
wideband and narrowband calls.
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:
Cisco Unified IP Phone 7975G, 7971G-GE, 7970G, 7965G, and 7945G Administration Guide for Cisco Unified
Communications Manager 9.0 (SCCP and SIP)
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Troubleshooting and Maintenance
Voice Quality Monitoring