Using Voice Quality Metrics - Cisco 7931G - Unified IP Phone VoIP Administration Manual

Chapter 9 Troubleshooting and Maintenance

Using Voice Quality Metrics

Note
Cisco Unified IP Phone 7931G Administration Guide for Cisco Unified Communications Manager 6.0
OL-12457-01
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:
G.711 codec gives 4.5 score
•
G.729A/ AB gives 3.8 score
•
G.728/iLBC gives 3.9 score
•
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.
Monitoring the Voice Quality of Calls
9-23