AudioCodes Mediant 4000 SBC, Руководство пользователя

Страница: 337 / 1037

CHAPTER 17 Quality of Experience
Mediant 4000 SBC | User's Manual
■ Packet Loss: Lost packets are RTP packets that are not received by the voice endpoint.
Packet loss can result in choppy voice transmission.
■ Jitter: Jitter can result from uneven delays between received voice packets. To space evenly,
the device's jitter buffer adds delay. The higher the measurement, the greater the impact of the
jitter buffer's delay on audio quality.
■ Residual Echo Return Loss (RERL): An echo is a reflection of sound arriving at the listener
at some time after the sound was initiated (often by the listener). Echo is typically caused by
delay.
At any given time during a call, a voice metric can be in one of the following color-coded quality
states (as displayed in OVOC):
■ Green: Indicates good call quality
■ Yellow: Indicates fair call quality
■ Red: Indicates poor call quality
When the threshold of a voice metric is crossed, the device changes the alarm severity and
corresponding color-coded quality state of the call:
■ Minor Threshold (Yellow): Lower threshold that indicates changes from Green or Red to
Yellow.
■ Major Threshold (Red): Higher threshold that indicates changes from Green or Yellow to
Red.
The device also uses hysteresis to determine whether the threshold has indeed being crossed.
Hysteresis defines the amount of fluctuation from the threshold in order for the threshold to be
considered as crossed (i.e., change in color state). Hysteresis is used to avoid false reports being
sent by the device. Hysteresis is used only for threshold crossings toward a lesser severity (i.e.,
from Red to Yellow, Red to Green, or Yellow to Green).
The following example is used to explain how the device considers threshold crossings. The
example is based on the MOS of a call, where the Major threshold is configured to 2, the Minor
threshold to 4 and the hysteresis for both thresholds to 0.1:
Table 17-2: Threshold Crossings based on Threshold and Hysteresis
Threshold
Crossing
Calculation
Threshold
based on
Example
Green to
Yellow (Minor
alarm) The change occurs if the measured metric crosses the
configured Minor threshold only (i.e., hysteresis is not used). 4
Green to Red
(Major alarm) The change occurs if the measured metric crosses the
configured Major threshold only (i.e., hysteresis is not used). 2
- 304 -