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Jitter is a submeasurement of latency. All packets traveling through a network experience some delay. But those delays aren't always uniform. Some transmissions take longer than others. Jitter reflects the difference between those delays.
While low latency is always good, consistent latency is especially important to applications such as voice over IP (VoIP). To that end, a low jitter measurement means latency on your network is consistent.
While network latency can be measured easily through a variety of simple tools -- among them, the common ping command -- the ingredients to accurately measure jitter are more comprehensive, usually requiring the use of commercial products.
Many of those require a license or annual subscription. If your jitter measurement needs are short term, determine if vendors offer a 15- or 30-day trial.
If your needs are limited, consider a unified communications as a service provider, like RingCentral, which offers a web portal that enables you to measure jitter, latency and voice quality from your location to the RingCentral cloud. Simply download the basic -- and free -- client, and start your test. Results are delivered within minutes. The RingCentral offering is based on the NetQCheck network test engine from network app and performance management assessment company Visualware Inc.
Pingman Tools' PingPlotter Professional Edition network monitoring and troubleshooting tool is another option, although jitter reporting isn't available via its free or standard editions.
For detailed testing and modeling of applications, The Tolly Group uses Ixia's IxChariot suite of simulated applications. These run between endpoints that can be located anywhere in the world. The simulated VoIP applications report statistics that include jitter. IxChariot is designed for serious testing, however, and is not geared toward those companies needing to check on the jitter of a given connection.
Finally, many network management vendors offer jitter monitoring as part of their product suites. There are a variety of ways to measure jitter, but it's important you find the option that works best for you.