On Mon, Oct 24, 2011 at 10:42 AM, John Leslie <john@xxxxxxx> wrote:
Mikael Abrahamsson <swmike@xxxxxxxxx> wrote:I'm embarrassed to admit I don't know which Brian Rosen meant: perhaps
> 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?
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 fineI'm pretty sure what I've observed mobile-to-mobile exceeds Brian's
> with 400ms RTT (this is a quite common delay just talking mobile
> phone-to-phone even in the same city),
criteria...
_I_ certainly notice before 500 msec RTT-plus-codec.
> but people really start to notice around 500-700ms RTT. 1 second RTT
> is really noticable, but still workable with some practice.
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.
Exactly!
> It's hard to have a heated argument over more than 400-500 ms RTT
> though,
It wouldn't be IETF without an occasional heated-discussion!
> so it depends on what kind of discussions are to be had :P
There's no reason why ground/sea based fibre needs to exceed about
> 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,
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. :^(
(I'm guessing you mean a single-central-server through which all
> at least if the system is located at the same place or fairly close
> to the venue
audio passes.)
I don't honestly know how flexible the various vendor systems are
> (at least so the signal doesn't have to be bounced half way around
> the world before it's sent to the final > destination).
in that respect. I would like to believe they are capable of more
intelligent switching than that...
--
John Leslie <john@xxxxxxx>
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