On Mon, Oct 24, 2011 at 10:42 AM, John Leslie <[email protected]> wrote: > Mikael Abrahamsson <[email protected]> wrote: > > On Mon, 24 Oct 2011, John Leslie wrote: > > > >> 150 milliseconds is a real challenge to accomplish worldwide, though > >> it's quite achievable within one continent. I expect IETF folks could > >> learn to work with 250 milliseconds. > > > > Are these numbers RTT or one-way? > > I'm embarrassed to admit I don't know which Brian Rosen meant: perhaps > he'll elaborate. He may well have meant one-way delay plus codec delay > plus application delay. >
The speed of light in optical fibers (index of refraction ~ 1.5) means that the one way time from any place on Earth to its antipode must be >~ 100 milliseconds, so I think that the above must be one way times. 300 to 400 milliseconds to the antipodes and back (i.e., RTT) is pretty realistic (say, US to Australia*). To that has to be added codec delays (each frame of 30 fps video represents ~30 msec);100+ msec one way video codec delays are common. If you add all of that up, you get enough latency that it begins to be noticeable, even in a formal meeting, for links such as US-India and US-Australia. Regards Marshall *The closest to truly antipodal pair of places I know of in common use are Hawaii to South Africa. If anyone has measured RTTs for that I would be curious to know them. > According to figures I've seen in other contexts, most people are fine > > with 400ms RTT (this is a quite common delay just talking mobile > > phone-to-phone even in the same city), > > I'm pretty sure what I've observed mobile-to-mobile exceeds Brian's > criteria... > > > but people really start to notice around 500-700ms RTT. 1 second RTT > > is really noticable, but still workable with some practice. > > _I_ certainly notice before 500 msec RTT-plus-codec. > > I don't think I agree that 1 second RTT-plus-codec is workable in > groups where any of a half-dozen folks might speak at any time. > > > It's hard to have a heated argument over more than 400-500 ms RTT > > though, > > Exactly! > > > so it depends on what kind of discussions are to be had :P > > It wouldn't be IETF without an occasional heated-discussion! > > > Ground/sea based fiber optical cable networks rarely give more than > > 500ms RTT, so anyone fairly well connected to the worldwide Internet > > via ground based infrastructure should be able to participate with > > less than 1s RTT including encoding delays etc, > > There's no reason why ground/sea based fibre needs to exceed about > 200 msec RTT; but buffer-bloat does cause this sometimes. In practice, > business-level Internet is likely to add 100 msec to this, and cable > Internet can add considerably more. :^( > > > at least if the system is located at the same place or fairly close > > to the venue > > (I'm guessing you mean a single-central-server through which all > audio passes.) > > > (at least so the signal doesn't have to be bounced half way around > > the world before it's sent to the final > destination). > > I don't honestly know how flexible the various vendor systems are > in that respect. I would like to believe they are capable of more > intelligent switching than that... > > -- > John Leslie <[email protected]> > _______________________________________________ > Ietf mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/ietf >
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