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Cisco Unified IP Phone 7960G/7940G Administration Guide for Cisco Unified Communications Manager 7.0 (SCCP)
OL-15498-01
Chapter 8 Troubleshooting and Maintenance
Monitoring the Voice Quality of Calls
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 Cisco Unified IP 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 Table 8-5 for general
troubleshooting information:
Ta b l e 8-5 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.
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 mobile network or
calling card network.
• Acoustic problems coming from a speakerphone, handsfree mobile phone or wireless headset.
Check packet transmit (TxCnt) and packet receive (RxCnt) counters to verify that voice packets
are flowing.
Voice quality metrics do not account for noise or distortion, only frame loss.