Cisco 7921G Administration Guide - Page 199

Chapter 10 Troubleshooting the Cisco Unified Wireless IP Phone 7921G Resolving Voice Quality and Roaming Problems You can access voice quality metrics remotely by using Streaming Statistics (see Chapter 9, "Monitoring the Cisco Unified Wireless IP Phone Remotely." 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. 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 codec gives 4.5 score • G.729A/ AB gives 3.7 score 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 10-1 for general troubleshooting information. Table 10-1 Changes to Voice Quality Metrics Metric Change Condition MOS LQK scores decrease significantly 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. MOS LQK scores decrease significantly • 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. Conceal Ratio and Conceal Seconds increase significantly • Network impairment from packet loss or high jitter. Conceal Ratio is near or at zero, • Noise or distortion in the audio channel such as echo or audio but the voice quality is poor levels. • Tandem calls that undergo multiple encode/decode such as calls to a cellular network or calling card network. • Acoustic problems coming from a speakerphone, handsfree cellular phone or wireless headset. Check packet transmit (TxCnt) and packet receive (RxCnt) counters to verify that voice packets are flowing. OL-15985-01 Cisco Unified Wireless IP Phone 7921G Administration Guide for Cisco Unified Communications Manager Release 7.0 10-13