Cisco CP-7961G-GE Administration Guide - Page 199

Chapter 9 Troubleshooting and Maintenance Monitoring the Voice Quality of Calls 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 Call Statistics Screen, page 7-13) or remotely by using Streaming Statistics (see 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. 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. OL-21011-01 Cisco Unified IP Phone Administration Guide for Cisco Unified Communications Manager 8.0 (SCCP and SIP) 9-15