When auditing IP networks there are three KPIs (Key Performance Indicators) that are paramount to a high performance network.
Packet loss and Latency are important but jitter is the one KPI often overlooked or misunderstood.
Jitter is the deviation in latency and is very commonly seen on the internet rather than on local area networks. For example if you ping www.google.com you may well see response times varying from 53 ms to as much as 63 ms and that is jitter the difference between the minimum and maximum latency. On a LAN for example you will rarely see the jitter as pings to a local server will be 1ms and be pretty constant.
The effect Jitter has on data networks is negligible even across the internet and this is because when traversing the internet TCP/IP is used as the transport protocol. Fortunately, TCP has built in features that mitigate jitter and latency such as reordering of packets and resending any lost packets. However, on voice and video traffic TCPs techniques are not much use as there is little point in sending a real-time voice packet if it was lost in transit. Similarly, real time video streaming does not benefit from packet reordering or resending of packets. Consequently, voice and video require low latency networks with minimal jitter.
If a network has excessive jitter then it probably will not be noticeable during normal data operation. However if you find poor video or voice quality it is something to look out for.
Consequently, when determining the quality of a network to support voice and video, the key factors to look out for is jitter of less than 30ms, anything above that can cause poor performance and poor voice or video quality. There are some ways within LANS and WANS to reduce Jitter, one is to deploy QoS (Quality of Service) another is to prioritize Voice and Video traffic though that normally is done by default. Unfortunately QoS doesn’t work over the internet as you have no control over the intermediately routers that your traffic is passing through or even the route the packets are even taking. However, one solution is to try and at least make sure the source of the jitter is not on your own uplink internet pipe to your ISP, and often the only solution is to increase the bandwidth.