Jitter, Jitter Everywhere, But Nary a Packet to Keep

I was looking over the end-to-end discussion on measuring jitter on voice calls on the backbone and came across this little gem: “Jitter – or more precise delay variance – is not important. Only the distribution is relevant”. This dismissive little item of a serious subject is all too commonplace, but misses the point the other researcher was making.

The critic assumes “fixed playout buffer lengths (e.g. from 20 to 200ms)” to calculate overall delay. But do these buffer lengths take into account compressed versus uncompressed audio? If not, the model is faulty right there. The author admits his approach is “problematic” but then assumes that “real-time adaptive playout scheduling” would be better – but then the measurement mechanism becomes part of the measurement, and you end up measuring this instead of the unmodified delay – which doesn’t help the researcher looking at jitter and delay measurements for voice.

But there is a more fundamental disconnect here between our voice-jitter researcher and his jitter-is-irrelevent nemesis – jitter does matter for some communications – it just depends on what problem is being solved. And it is careful definition of the problem that leads to dialogue.

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