Cisco CP-7942G Administration Guide - Page 168

Monitoring the Voice Quality of Calls Chapter 9 Troubleshooting and Maintenance 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. MOS LQK scores can vary based on the codec that the Cisco Unified IP Phone uses. The following codecs provide these maximum MOS LQK scores under normal conditions with zero frame loss: • G.711 gives 4.5 • G.722 gives 4.5 • G.728/iLBC gives 3.9 • G.729 A/AB gives 3.8 Note • CVTQ does not support wideband (7 kHz) speech codecs, as ITU has not defined the extension of the technique to wideband. Therefore, MOS scores that correspond to G.711 performance are reported for G.722 calls to allow basic quality monitoring, rather than not reporting an MOS score. • Reporting G.711-scale MOS scores for wideband calls through the use of CVTQ allows basic quality classifications to be indicated as good/normal or bad/abnormal. Calls with high scores (approximately 4.5) indicate high quality/low packet loss, and lower scores (approximately 3.5) indicate low quality/high packet loss. • Unlike MOS, the Conceal Ratio and Concealed Seconds metrics remain valid and useful for both wideband and narrowband calls. A Conceal Ratio of zero indicates that the IP network is delivering frames and packets on time with no loss. Troubleshooting Tips When you observe significant and persistent changes to metrics, use Table 9-5 for general troubleshooting information: Table 9-5 Changes to Voice Quality Metrics Metric Change MOS LQK scores decrease significantly MOS LQK scores decrease significantly Conceal Ratio and Conceal Seconds increase significantly Condition Network impairment from packet loss or high jitter: • Average MOS LQK decreases could indicate widespread and uniform impairment. • Individual MOS LQK decreases indicate bursty impairment. Cross-check with Conceal Ratio and Conceal Seconds for evidence of packet loss and jitter. • Check to see if the phone is using a different codec than expected (RxType and TxType). • Check to see if the MOS LQK version changed after a firmware upgrade. • Network impairment from packet loss or high jitter. 9-16 Cisco Unified IP Phone 7962G and 7942G Administration Guide for Cisco Unified Communications Manager 7.0 OL-15483-01