Voice Quality Metrics; Voice Quality Troubleshooting Tips - Cisco 8821 Administration Manual

Voice Quality Metrics

Related Topics
Phone Statistics, on page 87
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 phone uses. The following codecs provide these MOS
LQK scores under normal conditions with zero frame loss:
• G.711 and G.722 codecs have maximum scores of 4.5
• G.729A/AB codec has a maximum score of 3.8
A Conceal Ratio of zero indicates that the IP network is delivering frames and packets on time with no loss.

Voice Quality Troubleshooting Tips

When you observe significant and persistent changes to metrics, use the following table for general
troubleshooting information.
Table 18: Changes to Voice Quality Metrics
Metric change
MOS LQK scores decrease
significantly
MOS LQK scores decrease
significantly
Conceal Ratio and Conceal
Seconds increase significantly
Cisco Wireless IP Phone 8821 and 8821-EX Administration Guide for Cisco Unified Communications Manager
108
Condition
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.
• Check to see if the phone is using a different codec than expected
(Sender Codec and Rcvr Codec).
• Check to see if the MOS LQK version changed after a firmware
upgrade.
• Network impairment from packet loss or high jitter.
Maintenance