Cisco Systems 6921 manual Troubleshooting Tips, Metric Change Condition

Chapter

Monitoring the Voice Quality of Calls

Troubleshooting Tips

When you observe significant and persistent changes to metrics, use Table 9-4for general troubleshooting information.

Table 9-4 Changes to Voice Quality Metrics

Metric Change	Condition
Conceal Ratio and Conceal	Network impairment from packet loss or high jitter.
Seconds increase significantly
Conceal Ratio is near or at zero,	• Noise or distortion in the audio channel such as echo or
but the voice quality is poor.	audio 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.
MOS LQK scores decrease	Network impairment from packet loss or high jitter levels:
significantly	• Average MOS LQK decreases may indicate widespread
	and uniform impairment.
	• Individual MOS LQK decreases may indicate bursty
	impairment.
	Cross-check the conceal ratio and conceal seconds for evidence
	of packet loss and jitter.
MOS LQK scores increase	• Check to see if the phone is using a different codec than
significantly	expected (RxType and TxType).
	• Check to see if the MOS LQK version changed after a
	firmware upgrade.

Note Voice quality metrics do not account for noise or distortion, only frame loss.

Using Voice-Quality Metrics

When using 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 also important to distinguish significant changes from random changes in metrics. Significant changes are scores that change about 0.2 MOS or more and persist in calls that last longer than 30 seconds. Conceal ratio changes indicate a frame loss greater than 3 percent.

The MOS LQK scores can vary based on the codec that the Cisco Unified IP Phone uses. The following codecs provide these corresponding maximum MOS LQK scores under normal conditions with zero frame loss for Cisco Unified Phones 6921, 6941, 6945, and 6961:

•G.711: 4.5 MOS LQK

•G.722: 4.5 MOS LQK

	Cisco Unified IP Phone 6921, 6941, 6945, and 6961 Administration Guide for Cisco Unified Communications Manager 8.5 (SCCP and SIP)
9-14	OL-23769-01