[e2e] Re: crippled Internet
cannara at attglobal.net
Wed Apr 25 22:15:32 PDT 2001
Randy, the ITU specs are in 6 categories, from "perfect" to "bad". Packet
delays of under 200mS are rated "acceptable", higher are not. Jitter
acceptance really depends on buffering at the ends as well as the delay. So
with 100mS delay you can get away with more jitter than with longer delays.
The reason for a roundtrip spec is that when people actually listen to what
others are saying (unusual, I know), it becomes very annoying when roundtrip
time is near the timing of people's responses to what they just heard (often
resulting in both speaking at once becuase one side thinks the other didn't
Randy Bush wrote:
> > There are ITU specs for jitter and delay in voice that have been used for
> > years in standard telco system design. I should think these would be easily
> > accessible, but I only have a couple of graphs on paper. The basic idea is
> > that 50mS or so of frequent variation in sample arrival time is hard for
> > listeners, and 100mS roundtrip delay becomes annoying in conversations.
> in our universe, the modal delay is pretty much governed by the speed of
> light in fiber and copper plus a few forwarding delays. not a lot we can
> do about it. and i do not understand the meaning of round-trip delay in
> the context of voip, as the phone calls i am on are simultaneous but non-
> correlated one way chanels.
> so the jitter characterization, "50ms or so of frequent variation," would
> seem to be the interesting issue. what is "frequent variation," and how
> should it be measured? i.e. if 3% of the samples are outliers, how they
> are distributed in time would seem to be critical.
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