[e2e] A note on entropy Re: Are our models correct? Re: Just a very quick remark on system theory Re: Why don't we talk about segments/objects instaead of layers? Re: Lost Layer?

Andrew Mcgregor andrewmcgr at google.com
Fri Feb 21 14:01:56 PST 2014

You still need a model of the link's distribution of forwarding, to allow
any useful end-to-end conclusions.  That can be done, but of course those
distributions are often fairly pathological for wireless links.

On 22 February 2014 08:22, Detlef Bosau <detlef.bosau at web.de> wrote:

> Am 21.02.2014 18:10, schrieb Andrew Mcgregor:
> > You didn't read the paper I was pointing you at then.  It models the
> > window, and all the timers, and includes provision for cwnd clamping and
> > various other optional features of TCP.
> >
> > The limitations you point out are indeed things that happen in naiive
> > models.  Not all models are that naiive.
> Where I run into trouble with the paper you pointed to is the non
> decreasing level of entropy in closed systems.
> I think the model of Hui is a quite straight forward interpretation of
> However, I encountered the most severe problems with wireless networks
> where you will fail to interpret the propagation of information as a
> "transport" of energy which is continuously conveyed between buffers /
> increasing the level of entropy.
> Perhaps the most important lesson I learned during the past 14 years is
> that there is no reasonable way to model mobile networks.
> Meanwhile, I think it is not even necessary to "model" links from a
> congestion control perspective to model links for a simple reason:
> Congestion does not occur on a link but on switching nodes.
> So the idea is to focus on the nodes - and not primarily on the links
> (which are reasonably dealt with by schedulers.)

Andrew McGregor | SRE | andrewmcgr at google.com | +61 4 1071 2221

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