What is network jitter?
Network jitter, a.k.a. packet delay variation (PDV), is a stuttering-like effect in signal quality because of inconsistent packet delays in a data transmission. Each packet in the transmission may be routed differently to its destination causing packets to arrive out of order or not at all (called packet loss). Similar to latency, packet jitter is measured in milliseconds.
Though technology will handle this situation and put the packets back in order, it does cause delays. To illustrate the impact, in cases of high jitter video calls or VoIP, users will experience stuttering video, intermittent voice or dropped calls when speaking to others over the internet.
Jitter vs latency
Network latency (a.k.a lag) is the duration of time it takes a data packet to travel from its source to its destination across a network. Closely related to latency, jitter is a measurement of the variation of delay in a data transmission characteristic of packet-switched networks.
Causes of jitter
Poor network jitter is a real concern for real-time application performance. The quality of a VoIP experience, for instance, quickly deteriorates when jitter is high. This results in choppy calls, and if packet loss is too great, delayed or dropped signals.
Packet loss is when there is overload of network traffic and routers begin discarding data packets in an attempt to manage network latency. Dropped packets will then need to be requested again adding to the delay.
Network congestion is the main cause of packet loss. When routers are unable to direct the flow of network data they buffer packets to relieve traffic. If congestion increases then the overloaded routers begin dropping packets, usually when latency exceeds a delay of 100-200 ms. Ultimately, the common causes behind network congestion are also the likely causes behind most network jitter.
Any or all of the following can contribute to network congestion:
- Exceeding the network’s bandwidth: e.g. simultaneous downloading, streaming, and multiple VoIP sessions
- Inadequate hardware: incompatible, outdated, or damaged network hardware can cause bottlenecks
- WiFi’s signal: walls and other impediments block radio signals causing packet loss
- Software configurations: bugs and improper configuration of network hardware software can cause packet loss
How to calculate network jitter (example)
We can calculate the following seven data point ping sample to find the AvgJitter:
- Obtain a ping sample set (ms): 115, 136, 184, 163, 127, 177, 192
- Find the differences between each consecutive ping sample (see table below).
- Average the differences. Remember to divide the total of the differences by 6 not 7 for the correct average (7 is the number of ping samples, but there are only 6 differences):21+48+21+36+50+15 = 191 ms total of differences191/6 = 31.83 ms
|Latency 1||Latency 2||Difference (ms)|
What is a good average jitter?
In Microsoft’s view, an average network jitter exceeding 30 ms is considered a “poor call”. The specifics of your network will ultimately determine your target number, but keeping your jitter below 30 ms should keep you network in a safe range for maintaining solid QoS.