Voice Quality Troubleshooting Tips - Cisco 3905 Administration Manual

Voice Quality Metrics
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 SIP Phone 3905:
• G.711: 4.5 MOS LQK
• G729A/AB: 3.7 MOS LQK
Note Cisco Voice Transmission Quality (CVTQ) does not support wideband (7 kHz) speech codecs, because
ITU has not defined the extension of the technique to wideband.
• Reporting G.711-scale MOS scores for wideband calls through the use of CVTQ allows basic-quality
classifications to be indicated as good/normal or bad/abnormal. Calls with high scores (approximately
4.5) indicate high quality or a low packet loss, and lower scores (approximately 3.5) indicate low
quality or a high packet loss.
• Unlike MOS, the conceal ratio and concealed seconds metrics remain valid and useful for both
wideband and narrowband calls.
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 21: Changes to Voice Quality Metrics
Metric Change
Conceal Ratio and Conceal Seconds
increase significantly
Conceal Ratio is near or at zero, but
the voice quality is poor.
Cisco Unified SIP Phone 3905 Administration Guide for Cisco Unified Communications Manager 8.6 (SIP)
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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.
Troubleshooting and Maintenance