[e2e] Question the other way round:

Jon Crowcroft jon.crowcroft at cl.cam.ac.uk
Sun Nov 17 12:41:07 PST 2013


perfect schedules would work for fixed rate traffic...but in the age of
data nets (eve with packet video and audio) we decided to go with
statistical multiplexing and work conserving, so we keep links busy
whenever packets arrive but we don't know when packets will arrive so we
have to approximate as best we can to having packets arrive when there's
just enough capacity on an output link for the current input flow rate at
any switch so in some sense there's either 0 or 1 packet ahead - in the
fluid flow approximation world, you get infinitesimal slices of packets, so
you can adjust your flow rate to be nearer  a perfect fit - in the discrete
packet world, you are off by edge-of-packet's worth at least - but worse,
the traffic matrix variation over time (and in the presence of wireless and
mobile wibbly wobbly links, the actual output link capacity) vary
unpredictably with time, so your estimates of what you can do are off by as
much as an RTT's worth of  lumpy squeezy stuff (going for R rather than D)-
of course if a lot of sources last a really long time, and the number of
them doesn't vary, and they are all application limited,you might do very
well (i.e. go for D rather than R)

seems ok to me

On Sun, Nov 17, 2013 at 7:13 PM, Sergey Gorinsky
<sergey.gorinsky at imdea.org>wrote:

>   Dear Detlef,
> > The good ol' "Metro Pricing" :-)
>   No. PMP (Paris Metro Pricing) by A. Odlyzko charges different prices for
> the same service. The RD design charges the same price for different
> services.
> > How does your computer share computing time ...
> > It does time slicing...
> > A process scheduler knows about available resources.
>   In networks, the resources of bottlenecks are shared by remote senders.
> Besides, the bottlenecks migrate as the distributed load changes. Not
> knowing which resources to slice makes it difficult to do the slicing.
> Whereas global scheduling of Internet transmission resources is an
> appealing
> idea advocated by a number of (excellent) researchers over a number of
> years, there has not been much concrete progress in this direction. Schemes
> like XCP come the closest, while still staying in the probing
> congestion-control camp.
>   Best regards,
>   Sergey

More information about the end2end-interest mailing list