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Cisco Unified IP Phone Administration Guide for Cisco Unified CallManager 5.1 (SIP), Cisco Unified IP Phones
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Chapter9 Troubleshooting and Maintenance
Monitoring the Voice Quality of Calls
•Concealed Second metrics—Show the number of seconds in which the DSP
plays concealment frames due to lost frames. A severely “concealed second”
is a second in which the DSP plays more than five percent concealment
frames.
•MOS-LQK metrics—Use a numeric score to estimate the relative voice
listening quality. The CiscoUnified IP Phone calculates the mean opinion
score (MOS) for listening quality (LQK) based audible concealment events
due to frame loss in the preceding 8 seconds, and includes perceptual
weighting factors such as codec type and frame size.
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.
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.
You can access voice quality metrics from the CiscoUnified IP Phone by using
the Call Statistics screen (see the “Call Statistics Screen” section on page 7-16 )
or remotely by using Streaming Statistics (see the “Monitoring the Cisco
UnifiedIP Phone Remotely” chapter.
Using 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.