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Home Video-over-IP Answers Why is jitter important?

Why is jitter important?

Packet inter-arrival jitter is important because it impacts the buffering requirements for all downstream network and video devices, and extreme jitter can lead to anything from lip-sync problems to the loss of packets because of buffer overflow or underflow.  Packet inter-arrival jitter is simply the variation in arrival times for a packet stream that has at least some known packet arrival times.  The industry-accepted standard for calculating and reporting packet inter-arrival jitter is RFC 3550 and its method can be directly applied to any protocol with access to an accurate clock such as MPEG-2 TS.  It is measured and reported in milliseconds rather than in nanoseconds.  For real networks, packet inter-arrival jitter is always going to be much more important than PCR jitter simply because their respective scales are orders of magnitude apart, and the larger scale jitter value will always dwarf the smaller scale jitter value.  This straight-forward measurement can be calculated over any desired measurement interval, is well understood and does not have any of the measurement anomalies that PCR jitter does.

Every video stream is going to have inter-arrival jitter introduced as it travels through the transmission network.  The real question is how much jitter can network devices and video equipment handle before a problem arises? Typical jitter values on a good transmission network are on the order of 1 – 5 milliseconds.  Some video equipment will begin having problems displaying video with as little as 10 ms of jitter and most video equipment will have problems by the time you have 20 ms of introduced jitter.




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