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Cisco Unified IP Phone 8941 and 8945 Administration Guide for Cisco Unified Communications Manager 8.5 (SCCP and SIP)
OL-20851-01
Chapter
Monitoring the Voice Quality of Calls
Troubleshooting Tips
When you observe significant and persistent changes to metrics, use Table 9-4 for general
troubleshooting information.
Note Voice quality metrics do not account for noise or distortion, only frame loss.
Using Voice-Quality Metrics
When using 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 also important to distinguish significant changes from random changes in metrics. Significant
changes are scores that change about 0.2 MOS or more and persist in calls that last longer than
30 seconds. Conceal ratio changes indicate a frame loss greater than 3 percent.
The MOS LQK scores can vary based on the codec that the Cisco Unified IP Phone uses. The following
codecs provide these corresponding maximum MOS LQK scores under normal conditions with zero
frame loss for Cisco Unified Phones 8941 and 8945:
• G.711: 4.5 MOS LQK
• G.722: 4.5 MOS LQK
Table 9-4 Changes to Voice Quality Metrics
Metric Change Condition
Conceal Ratio and Conceal
Seconds increase significantly
Network impairment from packet loss or high jitter.
Conceal Ratio is near or at zero,
but the voice quality is poor.
• Noise or distortion in the audio channel such as echo or
audio levels.
• Tandem calls that undergo multiple encode/decode such as
calls to a cellular network or calling card network.
• Acoustic problems coming from a speakerphone,
handsfree cellular phone or wireless headset.
Check packet transmit (TxCnt) and packet receive (RxCnt)
counters to verify that voice packets are flowing.
MOS LQK scores decrease
significantly
Network impairment from packet loss or high jitter levels:
• Average MOS LQK decreases may indicate widespread
and uniform impairment.
• Individual MOS LQK decreases may indicate bursty
impairment.
Cross-check the conceal ratio and conceal seconds for evidence
of packet loss and jitter.
MOS LQK scores increase
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.