What exactly is Jitter?

[bagsta69]

I am sure like myself there are quite a few people who come here experiencing problems and are told to do a pingplotter test and warned about jitter and latency etc etc.

I have had a very vague understanding of what all these things are and got a better understanding of stuff apart from what jitter actually is.

So below is probably one of the easier to understand pieces written about it from the speed test webpage.

Hopefully it will help somebody.

 

Posted on April 13, 2015by Joel Hruska

Now that we’ve covered latency (the amount of time it takes for a block of information, called a packet, to travel across a network) and ping (a test for determining latency), we can discuss a slightly more advanced and extremely important topic — jitter.

 

When computers communicate with each other across a network, whether between a phone and a tablet on the same local network or two computers separated by the entire United States, they do so by sending packets. Some packets, like email, aren’t very latency sensitive. If you’re pulling up the news on a local website, you want the site to load quickly, but it doesn’t necessarily matter if one packet arrives in 20 milliseconds and the next one arrives in 60 milliseconds. The gap between 20ms and 60ms is too small to be noticeable when you’re just reading text.

Other tasks, however, are very latency sensitive — and this is where jitter comes in. If latency equals the time it takes for one packet to move from Point A to Point B, then jitter equals the change in the amount of time it takes for a packet to move from Point A to Point B. Jitter is sometimes referred to as “Packet Delay Variation,” or PDV. This is actually the more precise term, but “jitter” has stuck in certain circles.

Imagine a simple network between two computers. Computer A sends a packet to Computer B every 10ms like clockwork, and Computer B replies to Computer A every 10ms as well. In this case, neither computer is experiencing jitter.

Now, let’s say that Computer A is dispatching packets every 10ms, but the router between A and B is busy handling someone else’s 4K Netflix streaming. As a result, Computer B isn’t receiving packets as quickly or evenly as it was before. Sometimes, the packets arrive after 30ms. Sometimes, multiple packets arrive together — Computer B might get zero packets for 50ms, then five packets all at once.

Again, if you’re just reading news or checking an email, you may never notice the difference. If, on the other hand, you’re watching video or playing a fast-paced game online, you’ll quickly see these lag spikes mount. Your character will freeze for an instant, then teleport across the map. YouTube will suddenly pause to buffer content. (This is obviously a hypothetical, as no one ever has to wait on YouTube to buffer content.)

This sudden surge in jitter/PDV is what players are actually experiencing when they refer to “lag spikes” – the amount of time it takes data to travel between your computer and the server has suddenly shifted. When your position changes dramatically in a manner of seconds, that’s typically a number of client-server communications landing all at once. If you’ve ever gone from full health to dead during an MMO raid or Battlefield game, you can thank jitter.

Controlling jitter is a critical to offering a good online experience. Generally, you know how to deal with slow, regular performance — you can learn to lead your targets in a game (to some extent). And it’s easy to buffer a video on YouTube or Netflix, and then walk away to make popcorn before starting a movie. Dealing with sudden dips and spikes in latency, on the other hand, is absolutely maddening. Regular, low-latency communication is best. But regular high-latency communication beats irregular drops and skips for most applications, most of the time.