Jitter
Description
VoIP jitter occurs when voice packets are sent and received with timing variations. Jitter is effectively a variation of packet delay where delays actually impact the quality of the conversation. Think of jitter as variable delays in packet delivery. Participants will notice delays in the conversations impacted by jitter. As a result, many service providers now account for maximum jitter levels.
Jitter is a more complex problem than latency and packet loss. It's the variation in latency time from one packet to the next. It causes packets to arrive out of order, leaving gaps in the framing sequence of the voice signal. Jitter is at its worst when voice traffic must travel through several routers on the network. The more hops, the worse jitter can get. Different routers, especially those at ISPs, may be configured to queue and forward different kinds of traffic in different ways. Others may be load-balancing, which can contribute to jitter. The chief goal of QoS protocols is to eliminate jitter. Devices called jitter buffers, in endpoints and VoIP servers, can minimize the effect of jitter, too. But, like PLC measures, they do so by increasing latency. (Switching to VoIP By Theodore Wallingford)
Example
- Example audio file - 5% packet discard rate File:Jitter5.wav
- Example audio file - 10% packet discard rate File:Jitter10.wav
- Example audio file - 25% packet discard rate File:Jitter25.wav
Jitter Buffer
For jitter levels under 100 milliseconds then it may be acceptable to increase the jitter buffer size in end-systems or to enable adaptive jitter buffer operation.
For jitter levels over 100 milliseconds then increasing the jitter buffer size to avoid packet discards will introduce significant delay and cause conversational problems; in this case it is preferable to take steps to isolate the source of jitter and eliminate the problem at source.
