Hello Attila
Let me try to make the concept a little clearer for you. Jitter is the deviation from true periodicity. True periodicity is the attribute of being completely periodic. In other words, true periodicity is achieved when the time between events remains exactly the same.
Translating that to the receiving of packets, if you receive 10 packets, and you receive them at
intervals of exactly 29 milliseconds every time, then you have a jitter of zero. This is because there has been zero deviation from true periodicity.
Now if you receive 10 packets at varying time intervals, then there is a deviation, therefore there is jitter. But the most challenging question is, how do you measure it? Well, the truth is that there are different ways to measure it. If you want to get academic, take a look at the various metrics you can use to measure jitter here.
When using a utility like ping to measure it, you must take several issues into consideration. Are you measuring the jitter of the round-trip ping or of the arrival of packets at the destination? Are you measuring jitter over a period of time, or over a certain number of packets? Are you measuring the jitter of each packet compared to the previous and next packet or compared to all of the packet arrival intervals? ΅What is the value of the true periodicity that you are comparing arrival times to, the average or some absolute value? These are questions that must be answered before you manually measure jitter.
The links you shared make some assumptions before they actually do the calculations, assumptions that they don’t make clear from the beginning. However, the purpose of these manual calculations of jitter is not really to monitor a real network. This would not be useful in any way. But the purpose is to gain a deeper understanding of what jitter is.
Ultimately, you should use network monitoring tools to gain a view of the real jitter on a network to determine if it is causing problems that need fixing. More info on jitter and measuring and dealing with it using various tools can be found in these lessons:
I hope this has been helpful!
Laz