Cisco 8831NR Administration Manual page 146

Voice Quality Monitoring
Note Concealment ratio and concealment seconds are primary measurements based on frame loss while MOS LQK
scores project a "human-weighted" version of the same information on a scale from 5 (excellent) to 1 (bad)
for measuring listening quality.
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.
For information about configuring voice quality metrics for conference phones, see the Cisco Unified
Communications Manager System Guide, "Cisco Unified IP Phones" chapter, "Phone Features" section.
You can access voice quality metrics from the conference phone by using the Call Statistics screen or remotely
by using Streaming Statistics.
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 conference phone uses. The following codecs provide
these maximum MOS LQK scores under normal conditions with zero frame loss:
• G.711 codec gives 4.5 score
• G.719A/ AB gives 3.7 score
A Conceal Ratio of zero indicates that the IP network is delivering frames and packets on time with no loss.
When you observe significant and persistent changes to metrics, use the following table for general
troubleshooting information.
Table 38: Changes to Voice Quality Metrics
Metric Change
MOS LQK scores decrease significantly
MOS LQK scores decrease significantly
Cisco Unified IP Conference Phone 8831 and 8831NR Administration Guide
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Troubleshooting and Maintenance
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 conference phone is using a
different codec than expected (RxType and
TxType).
• Check to see if the MOS LQK version changed
after a firmware upgrade.