Using Voice Quality Metrics - Cisco 7941G - Unified IP Phone VoIP Administration Manual

Monitoring the Voice Quality of Calls
Note

Using Voice Quality Metrics

Cisco Unified IP Phone 7961G/7961G-GE and 7941G/7941G-GE for Cisco Unified Communications Manager 6.1
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MOS LQK scores are produced by a Cisco proprietary algorithm, Cisco Voice
Transmission Quality (CVTQ) index. Depending on the MOS LQK version
number, these scores might be compliant with the International
Telecommunications Union (ITU) standard P.564. This standard defines
evaluation methods and performance accuracy targets that predict listening
quality scores based on observation of actual network impairment.
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.
You can access voice quality metrics from the Cisco Unified IP Phone by using
the Call Statistics screen (see the
or remotely by using Streaming Statistics (see the
Unified IP Phone Remotely
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.729A/ AB gives 3.7
•
Chapter 9
"Call Statistics Screen" section on page
chapter).
Troubleshooting and Maintenance
Monitoring the Cisco
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