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Chapter 9 Troubleshooting and Maintenance
Monitoring the Voice Quality of Calls
You can configure users’ Cisco Unified IP Phones with QRT. When you do so, users can report problems
with phone calls by pressing the QRT softkey. This softkey is available only when the Cisco
Unified IP Phone is in the Connected, Connected Conference, Connected Transfer, and/or OnHook
states.
When a user presses the
QRT
softkey, a list of problem categories appears. The user selects the
appropriate problem category, and this feedback is logged in an XML file. Actual information logged
depends on the user selection, and whether the destination device is a Cisco Unified IP Phone.
For more information about using QRT, refer to
Cisco Unified Communications Manager Features and
Services Guide
.
Monitoring the Voice Quality of Calls
To measure the voice quality of calls that are sent and received within the network, Cisco Unified IP
Phones use these statistical metrics that are based on concealment events. The DSP plays concealment
frames to mask frame loss in the voice packet stream.
•
Concealment Ratio metrics—Show the ratio of concealment frames over total speech frames. An
interval conceal ratio is calculated every 3 seconds.
•
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 Cisco
Unified 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 Cisco Unified IP Phone by using the Call Statistics screen
(see the
“Call Statistics Screen” section on page 7-12
) or remotely by using Streaming Statistics (see the
Monitoring the Cisco Unified IP 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.
