[e2e] Congestion control as a hot topic in IETF

Detlef Bosau detlef.bosau at web.de
Fri Mar 8 11:30:18 PST 2013

Am 08.03.2013 16:54, schrieb Jon Crowcroft:
> In missive <513A04BE.4060505 at web.de>, Detlef Bosau typed:
>   >>> btw, path loss is very real (and not at the antennae)
>   >>no.
>   >>Or can you tell me where the waves have gone? Where the energy has gone?
> this is physics #101 - if you transmit with some power level, and spread that over a distance, guess what, at a
> distance with a signal that is spreading out over a surface, the power level is lower

Good answer :-)

I see, you understood why the power level depends on the distance via a 
sqrt-Function :-)

And that means what?

Merely nothing. When I move around my laptop in my apartment, I use WLAN 
to access my DSL router, the power level will change.
However: Hardly that much that the packet corruption level is affected.

Unfortunately, in my appartment I see up to 8 (eight) WLANs.

So, what do you think affects my data rate notebook - router? Me moving 
around in the apartment or my neighbours surfing the Internet?

In addition, the SNR sinks continuously when moving around. The packet 
corruption ratio doesn't.

It is a theoretical game with numbers.
> eventually the signal (to background noise) is too low level to carry any info in any way distinguishable
>   >>Data corruption is a phenomenon which occurs at the receiver. The
>   >>problem is that the receiver cannot successfully rebuild a packet from
>   >>what he received. The air interface has no idea of which waves are
>   >>travelling along and whether they make any sense at all.
> you're confusing interference with other sources and misreading the honorably Dave Reed

I'm quite sure that I'm not misreading Dave Reed.

> secondly, you are ignoring absorption (e.g. by water vapour which gets a little bit hotter)
> and also _self_ interferance (aka Ricean fading) and scattering (rayleigh fading)

So, a model which correctly describes wireless channels is that flexible 
that it fits anything - and has no use at all.

I don't think I misread Dave Reed - to the contrary, in some particular 
respects I share his anger.


Detlef Bosau
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