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Cisco Unified IP Phone 7975G Administration Guide for Cisco Unified Communications Manager 7.0 (SCCP and SIP)
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Chapter 9 Troubleshooting and Maintenance
Monitoring the Voice Quality of Calls
Listening quality scores (MOS LQK) relate to the clarity or sound of the received voice signal.
Conversational quality scores (MOS CQ such as G.107) include impairment factors, such as delay, that
degrade the natural flow of conversation.
You can access voice quality metrics from the Cisco Unified IP Phone by using the Call Statistics screen
(see the
“Call Statistics Screen” section on page 7-13
) or remotely by using Streaming Statistics (see the
“Monitoring the Cisco Unified IP Phone Remotely”
chapter).
Using 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 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 gives 4.5
•
G.722 gives 4.5
•
G.728/iLBC gives 3.9
•
G.729 A/AB gives 3.8
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.
