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Cisco Unified IP Phone 7962G and 7942G Administration Guide for Cisco Unified Communications Manager 7.0
OL-15483-01
Chapter 9 Troubleshooting and Maintenance
Monitoring the Voice Quality of Calls
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.
Troubleshooting Tips
When you observe significant and persistent changes to metrics, use
Table 9-5
for general
troubleshooting information:
Table 9-5
Changes to Voice Quality Metrics
Metric Change
Condition
MOS LQK scores decrease
significantly
Network impairment from packet loss or high jitter:
•
Average MOS LQK decreases could indicate widespread
and uniform impairment.
•
Individual MOS LQK decreases indicate bursty
impairment.
Cross-check with Conceal Ratio and Conceal Seconds for
evidence of packet loss and jitter.
MOS LQK scores decrease
significantly
•
Check to see if the phone is using a different codec than
expected (RxType and TxType).
•
Check to see if the MOS LQK version changed after a
firmware upgrade.
Conceal Ratio and Conceal
Seconds increase significantly
•
Network impairment from packet loss or high jitter.
