Troubleshooting Tips - Cisco 6921 Administration Manual

Monitoring the Voice Quality of Calls

Troubleshooting Tips

When you observe significant and persistent changes to metrics, use
troubleshooting information.
Table 9-4
Metric Change
Conceal Ratio and Conceal
Seconds increase significantly
Conceal Ratio is near or at zero,
but the voice quality is poor.
MOS LQK scores decrease
significantly
MOS LQK scores increase
significantly
Voice quality metrics do not account for noise or distortion, only frame loss.
Note
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 IP Phone 6921, 6941, 6945, and 6961:
•
•
Cisco Unified IP Phone 6921, 6941, 6945, and 6961 Administration Guide for Cisco Unified Communications Manager 8.6 (SCCP and SIP)
9-14
Changes to Voice Quality Metrics
G.711: 4.5 MOS LQK
G.722: 4.5 MOS LQK
Condition
Network impairment from packet loss or high jitter.
• 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.
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.
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.
Table 9-4 for general
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