Cisco Systems 7971G-GE, 7970G Monitoring the Voice Quality of Calls

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Cisco Unified IP Phone 7970G/7971G-GE Administration Guide for Cisco Unified Communications Manager 7.0

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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 7-13) or remotely by using Streaming Statistics (see the

“Monitoring the Cisco Unified IP Phone Remotely” chapter).

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.