Broadband Related > ADSL Issues

Latency and jitter figures from AA speedtester

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Weaver:
After I converted today to using a small switch as a VLan MUX to talk to my four modems I recorded some numbers with AA speedtester.

The latency (is this round trip? or one way?) was 90 ms and the jitter was 49.5 ms. Do those seem a bit high? I thought the latency was around 40ms.

The jitter could be to do with alternating between different modems which run at rather different speeds. Is that right?

aesmith:
Our latency according at A&A is around 40ms, that's for a similar but shorted 21CN line (53dB) synch rate currently 4243k and interleaving or 64 down 8 up.  The same line has RTT of around 25ms with interleaving off.

Weaver:
@aesmith exactly. That is the figure I am used to seeing.

So not sure what was going on with the numbers from that speedtester.

And now it appears that that has gone away, and the huge jitter is a lot less. Currently speedtester2.aa.net.uk is giving:
    Ping = 48.34
    Jitter = 10.37
at Downstream = 10.21 / Upstream = 1.62

Perhaps it was a duff result before, because of alien traffic perhaps ?

The other difference that I can think of is that line speeds have improved and the lines’ downstream performance figures are all very close, upstream not so?

Could the ‘jitter’ figure be affected by that kind of disparity?

I would have thought that quirks of the two routers’ packet scheduling designs (the router at AA and my own Firebrick at my end) wouod affect the jitter figures for me. Does that make sense? I am thinking that if I were designing a router of this ilk I could aim for minimised jitter as opposed to maximising throughout or other priorities if that is what one wanted to do.

Does a poor jitter value mess up some voip systems?

niemand:
The default buffer for many VoIP services is 50ms so it's tolerant to some level of interesting network conditions.

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