Acceptable Max Jitter value on end point

[swestra01]

Hi All,

  We recently updated to TC7 and are taking a look at the new diagnostic tabs. I see 0% packet loss consistantly on the majority of the calls but I see a large variance in the Max Jitter numbers everywhere from 4 to 63. I was wondering what does that value mean and at what value would you start to see a degraded experience. We have exclusively C40 and Sx20 enpoints.

Thanks, Steven

[Jens Didriksen]

Jitter is the time delay between the arrival of packets. The C-series use a dynamic jitter buffer which varies in size, but doesn't kick in until 20ms (to minimize adding (more) latency to the mix), and it maxes out at 100ms.

The less jitter the better, I only see 0 - 2ms on point-to-point calls on our LAN/WAN (on 2x2.5Gbps link), but that increases quite dramatically with calls hosted on a MCU, in which case I've seen anywhere between 60 and 85ms of jitter, with minimal, if any, impact on the quality. And of course, the iitter is normally higher on calls coming in via the internet.

/jens

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[swestra01]

Ok, so Cisco's jitter is measured in milliseconds. So if I do have a 60 ms or so max jitter, that is really only 2-4 frames depending on call settings. In my thought, that shouldn't really be noticable on the end user side.

[Jens Didriksen]

That's right - you really shouldn't see any noticeable issues specifically caused by jitter, unless you start hitting 100ms or higher - having said that, I have seen the odd glitch at around 80ms when the far-end participant(s) started moving around to quickly. So playing a DVD across the link might not work so well.:)

If you can reduce the jitter, so much the better, but that might not be possible under certain circumstances.

/jens

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