Latency in SolarWinds VNQM

With respect to VoIP, latency is a measure of the difference in time between when one caller speaks and when the other caller hears what the first has said. Excessive network latency can cause noticeable gaps and synchronization loss in transmitted conversations, particularly when VoIP is used with other types of data, as in a video conference. If these gaps become large enough, callers may find that they inadvertently interrupt each other while conversing.

Network Service Assurance operations measure latency by sequentially applying four different time stamps to a single test packet in the following way:

1. Time stamp T1 is applied to a test packet as it leaves the source router.
2. Time stamp T2 is applied as the test packet arrives at the target router.
3. Time stamp T3 is applied as the test packet leaves the target router to return to the source.
4. Time stamp T4 is applied when the test packet returns to the source.

Network Service Assurance operations provide four separate measures of latency by computing differences among the four time stamps in the following way.

Latency measure	Calculation
Round trip time	T4 – T1
Source-to-target latency	T2 – T1
Target processing latency	T3 – T2
Target-to-source latency	T4 – T3

Latency is computed for both source-to-target and target-to-source directions to account for asynchronous network behavior, providing a more detailed picture of the overall network latency.

VoIP and Network Quality Manager calculates latency in the following way:

MinLatencySD = milli/microseconds equivalent of rttMonLatestJitterOperOWMinSD

MinLatencyDS = milli/microseconds equivalent of rttMonLatestJitterOperOWMinDS

AvgLatencySD = milli/microseconds equivalent of rttMonLatestJitterOperOWAvgSD

AvgLatencyDS = milli/microseconds equivalent of rttMonLatestJitterOperOWAvgDSMaxLatencySD = milli/microseconds equivalent of rttMonLatestJitterOperOWMaxSD

MaxLatencyDS = milli/microseconds equivalent of rttMonLatestJitterOperOWMaxDS

MinLatency = milli/microseconds equivalent of rttMonLatestJitterOperRTTMin

AvgLatency = if rttMonLatestJitterOperNumOfRTT == 0 then 0

else

(milli/microseconds equivalent of rttMonLatestJitterOperRTTMin) / rttMonLatestJitterOperNumOfRTT

MaxLatency = milli/microseconds equivalent of rttMonLatestJitterOperRTTMax

rttMonLatestJitterOperOWMinSD	1.3.6.1.4.1.9.9.42.1.5.2.1.35
rttMonLatestJitterOperOWMinDS	1.3.6.1.4.1.9.9.42.1.5.2.1.39
rttMonLatestJitterOperOWAvgSD	1.3.6.1.4.1.9.9.42.1.5.2.1.49
rttMonLatestJitterOperOWAvgDS	1.3.6.1.4.1.9.9.42.1.5.2.1.50
rttMonLatestJitterOperOWMaxSD	1.3.6.1.4.1.9.9.42.1.5.2.1.36
rttMonLatestJitterOperOWMaxDS	1.3.6.1.4.1.9.9.42.1.5.2.1.40
rttMonLatestJitterOperRTTMin	1.3.6.1.4.1.9.9.42.1.5.2.1.4
rttMonLatestJitterOperNumOfRTT	1.3.6.1.4.1.9.9.42.1.5.2.1.1
rttMonLatestJitterOperRTTMin	1.3.6.1.4.1.9.9.42.1.5.2.1.4
rttMonLatestJitterOperRTTMax	1.3.6.1.4.1.9.9.42.1.5.2.1.5