How VQMon works
The IP Deskphone with SIP Software gathers statistics about the current call when VQMon is
enabled. Statistics are also gathered regarding the quality metrics of the current call. The call-
related statistics contain condensed information about the SIP Session Description Protocol (SDP),
the Call ID, the local and remote address, voice quality-related statistics, Zulu times for start-time
and the time the report was sent.
The voice quality-related statistics include jitter, packet loss, delay, burst gap loss, listening R-factor,
R-LQ, R-CQ, MOS-LQ and MOS-CQ. See Table 19: Glossary of RTCP XR metrics on page 143.
More information on each of these metrics is provided in RFC3611 “RTP Control Protocol Extended
Reports (RTCP XR)”.
When the IP Deskphone detects that a particular voice quality metric has exceeded a threshold
(defined in the Device Configuration file), the IP Deskphone sends a message to the server
indicating that there is an issue. If the issue persists, then the IP Deskphone sends another
message indicating that there is an exceeded value at regular intervals. This happens continuously
until the voice quality metric falls below the threshold value. As well, the IP Deskphone can send
regular reports of the voice quality at time intervals defined in the Device Configuration file.
Table 19: Glossary of RTCP XR metrics
Metric Description
Burst A period of high packet losses and / or discards. A
burst is calculated in milliseconds.
Conversational R-factor Voice quality metric based on burst packet loss and
vocoder selection.
Delay One way delay which includes end-to-end delay,
jitter buffer delay and packetization delay. Delay is
calculated in milliseconds.
Inter-arrival jitter The variation in packet arrival times due to
transmission (routing, queuing delay) through the
network. Jitter is calculated in milliseconds.
Listening R-factor Voice quality metric based on burst packet loss,
transmission delay and burst loss.
MIU Media Information Unit. MIU is a concept from
VQMon. An MIU can be any size down to a 10
millisecond (8 sample) block. An MIU means a frame
in the i200x implementation.
MOS Mean Opinion Score. A subjective measurement of
the voice quality of a voice call.
MOS_CQ The VQMon conversational quality MOS score
calculated for a call channel.
MOS_LQ The VQMon listening quality MOS score calculated
for a call channel.
Table continues…
How VQMon works
March 2015 SIP Software for Avaya 1200 Series IP Deskphones-Administration 143
Comments? infodev@avaya.com
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