Resolving Conference Call Reception Problems - Cisco 7937G - Unified IP Conference Station VoIP Phone Administration Manual

Resolving Conference Call Reception Problems

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 conference station uses. The following codecs
provide these maximum MOS LQK scores under normal conditions with zero frame loss:
•
•
A Conceal Ratio of zero indicates that the IP network is delivering frames and packets on time with no
loss.
When you observe significant and persistent changes to metrics, use
troubleshooting information.
Table 9-3
Metric Change
MOS LQK scores decrease
significantly
MOS LQK scores decrease
significantly
Conceal Ratio and Conceal
Seconds increase significantly
Conceal Ratio is near or at zero,
but the voice quality is poor
Voice quality metrics do not account for noise or distortion, only frame loss.
Note
Resolving Conference Call Reception Problems
To ensure optimum performance with the conference station and the external microphones, see
"Guidelines for Best Performance" section on page 3-9
section on page
Cisco Unified IP Conference Station 7937G Administration Guide for Cisco Unified Communications Manager 6.0
9-14
G.711 codec gives 4.5 score
G.719A/ AB gives 3.7 score
Changes to Voice Quality Metrics
3-10.
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 conference station 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.
•
Noise or distortion in the audio channel such as echo or audio
•
levels.
Tandem calls that undergo multiple encode/decode such as
•
calls to a cellular network or calling card network.
Check packet transmit (TxCnt) and packet receive (RxCnt)
counters to verify that voice packets are flowing.
and the
Chapter 9 Troubleshooting and Maintenance
Table 9-3 for general
"Conference Room Setup Examples"
OL-11560-01 Rev. B0