IT Technology: What is Jitter in Networking

Simply said, time difference in packet inter-arrival time to their destination can be called jitter. Jitter is specific issue that normally exists in packet networks and this phenomenon is usually not causing any communication problems. TCP/IP is responsible for dealing with the jitter impact on communication. On the other hand, in VoIP network environment, or better say in any bigger environment today where we use IP phones on our network this can be a bigger problem. When someone is sending VoIP communication at a normal interval (let’s say one frame every 10 ms) those packets can stuck somewhere in between inside the packet network and not arrive at expected regular peace to the destined station. That’s the whole jitter phenomenon all about so we can say that the anomaly in tempo with which packet is expected and when it is in reality received is jitter.

In this image above, you can notice that the time it takes for packets to be send is not the same as the period in which the will arrive at the receiver side. One of the packets encounters some delay on his way and it is received little later than it was asumed. Here are the jitter buffers entering the story. They will mitigate packet delay if required. VoIP packets in networks have very changeable packet inter-arrival intervals because they are usually smaller than normal data packets and are therefore more numerous with bigger chance to get some delay.

In order to have the chance to better tune the jitter correction, best practice is to enumerate packets who arrive late and with that base data calculate a ratio of those packets and packets that are successfully transferred. With that ratio you can better adapt the jitter buffer to some predictable number of late arriving packets. This is the best way to tune jitter buffer. Although it can maybe some time be confusing but the jitter and total delay are not even close to be the same thing. Having a lot of jitter in network will probably increase the total delay to, but it must not be the case. It will usually mean that because more jitter means that you need bigger jitter buffer to be able to compensate the unpredictable packet network packet flow behavior.

The buffers are not endlessly big. In case of heavy jitter situation it is better to drop some packets or have fixed size buffer instead of creating delays in the jitter buffers itself. The main reason for the last sentence is that if you did a good job in planing and designing the network infrastructure with all the best practice and recommendations, the probability to have jitter issues is minimal. In that kind of network jitter is normally not a big problem.

You can se if there is some jitter in your network using RTP timestamps in Cisco IOS. Cisco IOS has by default those buffers set like a dynamic queue. This queue will change its size depending on the packet timing and tempo when arriving to destination. Almost all other vendors use static jitter buffers, Cisco deduced that dynamic jitter buffer with some enhancement in the design is the best way to use the buffer for VoIP transferring networks.


Reference:
WHAT IS JITTER IN NETWORKING?
http://howdoesinternetwork.com/2013/jitter