Filter
Top Products
7-12
Cisco Unified IP Phone 6901 and 6911 Administration Guide for Cisco Unified Communications Manager 8.5 (SCCP and SIP)
OL-23874-01
Chapter 7 Troubleshooting and Maintenance
Using Voice Quality Metrics
• G.728/iLBC: 3.9 MOS LQK
• G729A/AB: 3.7 MOS LQK
Note • Cisco Voice Transmission Quality (CVTQ) does not support wideband (7 kHz) speech codecs,
because ITU has not defined the extension of the technique to wideband. Therefore, MOS LQK
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 or a low packet loss, and lower scores (approximately 3.5)
indicate low quality or a 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 7-3 for general
troubleshooting information.
Ta b l e 7-3 Changes to Voice Quality Metrics
Metric Change Condition
Conceal Ratio and Conceal
Seconds increase significantly
Network impairment from packet loss or high jitter.
Conceal Ratio is near or at zero,
but the voice quality is poor.
• 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.
• 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
significantly
Network impairment from packet loss or high jitter levels:
• 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.