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Home > Success Center > VoIP & Network Quality Manager (VNQM) > VNQM 4.4 Administrator Guide > Quality of Service metrics > Jitter


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Jitter is a measure of the variation in network latency that results in a loss of synchronization over time. In VoIP phone calls, users experience jitter as distracting noise, clicks, and pops. To ensure acceptable quality of service, network jitter should be located, isolated, and addressed. By using SolarWinds VoIP and Network Quality Manager you can identify areas of your network that may be experiencing synchronization difficulties, and then you can take the necessary action to ensure maximum quality of service on your VoIP network.

SolarWinds VoIP and Network Quality Manager requires you to select a jitter codec to properly configure IP SLAs for your VoIP network. Codecs compute jitter by specifying that IP SLA operations send a number of packets (n), each with a specific size (s), at a set interval (i) between packets, at a determined frequency (f), as shown in the following table.


IP SLA Operation Frequency (f)

Default number of packets (n)

Default packet size (s)

Default interval between packets (i)


Set on each operation as the network test interval


160 + 12 RTP bytes

20 ms



160 + 12 RTP bytes

20 ms



20 + 12 RTP bytes

20 ms

For more information about configurable settings within SolarWinds VoIP and Network Quality Manager, see Configuring VNQM settings.

Based on the Cisco IP SLA operations used by SolarWinds VoIP and Network Quality Manager, jitter codecs G.711a and G.711u can achieve a peak MOS of 4.34. On the same basis, jitter codec G.729a can achieve a peak MOS of 4.06.

SolarWinds VoIP and Network Quality Manager calculates jitter in the following way:

jitterSD = (rttMonLatestJitterOperSumOfPositivesSD + rttMonLatestJitterOperSumOfNegativesSD ) / (rttMonLatestJitterOperNumOfPositivesSD + rttMonLatestJitterOperNumOfNegativesSD)

jitterDS = (rttMonLatestJitterOperSumOfPositivesDS + rttMonLatestJitterOperSumOfNegativesDS) / (rttMonLatestJitterOperNumOfPositivesDS + rttMonLatestJitterOperNumOfNegativesDS)

Jitter = (rttMonLatestJitterOperSumOfPositivesSD + rttMonLatestJitterOperSumOfNegativesSD + rttMonLatestJitterOperSumOfPositivesDS + rttMonLatestJitterOperSumOfNegativesDS) / (rttMonLatestJitterOperNumOfPositivesSD + rttMonLatestJitterOperNumOfNegativesSD + rttMonLatestJitterOperNumOfPositivesDS + rttMonLatestJitterOperNumOfNegativesDS)


SolarWinds VoIP and Network Quality Manager reads one jitter value at a given time, which is calculated based on the SNMP poll. This is an average value. The CLI command is not necessarily executed at the same moment. For this reason, the output of the current CLI commands is not the same as the values displayed in the VNQM charts or in the historical data.

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