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Cisco Unified IP Phone 6921, 6941, 6945, and 6961 Administration Guide for Cisco Unified Communications Manager 8.5 (SCCP and SIP)
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Chapter
Monitoring the Voice Quality of Calls
Procedure
Step 1 While powering up the phone, press and hold #.
Step 2 When the light on the mute button and handset light strip turns off and all other lights (line button,
headset button, speakerphone button and select button) stay green, press 123456789*0# in sequence.
When you press 1, the lights on the line buttons turn red. The light on the select button flash when a
button is pressed.
If you press the buttons out of sequence, the lights on the line button, headset button, speakerphone
button, and select button turn green. You will need to start over and press 123456789*0# in sequence
again.
After you press these buttons, the phone goes through the factory reset process.
Do not power down the phone until it completes the factory reset process, and the main screen appears.
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.
• Mean Opinion Score (MOS) for Listening Quality (LQK) Voice Metrics—Uses a numeric score to
estimate the relative voice-listening quality. The Cisco Unified IP Phones calculate the MOS LQK
based audible-concealment events due to a frame loss in the preceding 8 seconds and includes
weighting factors such as codec type and frame size.
MOS LQK scores are produced by a Cisco-proprietary algorithm, the Cisco Voice Transmission
Quality (CVTQ) index. Depending on the MOS LQK version number, these scores may comply 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. A Conceal
Ratio of zero indicates that the IP network is delivering frames and packets on time with no loss.
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 7-8) or remotely by using Streaming Statistics (see the
Monitoring the Cisco Unified IP Phone Remotely chapter).