[e2e] Question about propagation and queuing delays

[Puddinhead Wilson]

How is this for a thesis in older times

If the equator and the latitudes was totally
aligned/in  parallel with the plane of the revolution
of the earth is daylight saving times needed?
(neevrmind that latitudes may be ellipses)

;-)
--- Detlef Bosau <detlef.bosau at web.de> wrote:

> David Hagel wrote:
> > 
> > This may sound like a naive question. But if
> queuing delays are so
> > insignificant in comparison to other fixed delay
> components then what
> > does it say about the usefulness of all the
> extensive techniques for
> > queue management and congestion control (including
> TCP congestion
> > control, RED and so forth) in the context of
> today's backbone
> > networks? Any thoughts? Are the congestion control
> researchers out of
> > touch with reality?
> > 
> > - Dave
> 
> 
> It depends.
> 
> One answer is: Yes, they are.
> 
> A more cynical answer is: If a lucky guy joins a PhD
> program, he must 
> find a topic to write about.
> 
> In earlier centuries one wrote a doctoral thesis
> about: "Was Maria 
> virgin until her first intercourse with..., excuse
> me, before she became 
> pregnant?" O.k., now we know about that. Next
> thesis. "Was Maria virgin 
> _during_ her pregnancy?". Even that is clear. Next
> thesis, and this is 
> anatomiclly interetindg, perhaps one could not only
> achieve a D.D. but 
> an M.D. with this: "Was Maria, anatomically correct,
> virgin after she 
> gave birth to Jesus?" And now the most difficult
> one: "Was Maria virgin 
> _during_ the birth of Jesus?"
> 
> No, this is no political incorrect offense to the
> readers, these are 
> topics which were discussed extensivley in the
> Middle Ages, here in 
> Germany and in Italy and in other locations of the
> roman catholic church.
> 
> 
> Nowadays, we are rationalists. Wie don´t debate
> Marias virginity.
> 
> We discuss the importance of timers for congestion
> control. Some months 
> ago, some people from the group around Christoph
> Lindemann published about
> "TCP wit Adaptive Pacing for Multihop Wireless
> Networks" and reckognized 
> latency observation as a new crystall ball for
> congestion forecast and 
> avoidance.
> 
> If this sounds too cyncial: I apologize.
> 
> During the last weeks, I became mad about Edge´s
> paper about adaptive 
> retransmission timeouts.
> 
> And the more I´m thinking about that paper and how
> TCP timers work, the 
> more I become convinced that the insignificance of
> queueing delays, and 
> the consequence that the Internet latency as
> perceived by a flow is 
> nearly constant during the lifetime of a flow, is
> the reason why TCP 
> timers work at all.
> 
> As soon as latencies are subject to large and sudden
> change, prominent 
> example: mobile wide area networks, we talk about
> "spurious timeouts" 
> and other urban legends, which miss the problem.
> 
> The more often I read Edge´s paper and think about
> ist, the more I play 
> around with the actual RTT estimators, the more I´m
> in doubt whether 
> these will work in a network with highly instable
> and quickly changing 
> latencies.
> 
> This is all the more true in mobile wireless
> networks where latencies 
> are due to retransmissions and error recovery
> (without error recovery 
> TCP flows would break down due to retransmission
> collapse in those 
> networks) and therefore subject to change of path
> properties beyound our 
> control.
> 
> It´s not Edge´s approach, which causes the problem.
> 
> It´s our actual approach of RTT estimation which is
> as useful as cast dice.
> 
> So, with respect to your last sentence: We often are
> out of touch with 
> reality, because using our actual TCP timers we use
> an insolid basis for 
> TCP congestion control which by some chance and
> lucky cirumstances holds 
> in contemporary Internet. And when there appear some
> "strange effects" 
> in mobile networks, we are glad about it: "Hurray!
> An effect! A topic 
> for my PhD thesis!"
> Honestly, if you detect fire in your house, you
> certainly will not be 
> glad because you can spare fuel but you will call
> the fire brigade.
> 
> Using instable and inappropriate estimators for mean
> and variance of RTT
> leads to a number of "strange effects", "spurious
> timeouts" is only one 
> if them. However: It´s a symptom. Not the reason. A
> cure must focus at 
> the reason. Not at the symptom.
> 
> Once again: In contemporary Internet with
> neglectible queueing delays 
> and almost constant paths, this is absolutely no
> problem and anything 
> works fine. But falling asleep safe and sound,
> knowing Kah is around is 
> perhaps not the best strategy to solve the imminent
> problem. It´s 
> similar to our German wellfare system, where
> polictians ignored (well 
> known!) problems for decades - and now we face a
> disaster.
> 
> I´m not even convinced that anything is fine in
> wirebound networks.
> Due to some "interesting" discussions here in
> Germany concerning 
> "fastpath" (some new buzzword with ADSL) I had a
> first glance at the ITU 
> recommendation for g.dmt. In fact, we do not _yet_
> use automatic 
> retransmission here. But if we continue to exploit
> extremely noisy lines 
> for high speed data transmission, which appears to
> be promising when you 
> look at the market and which allows me as an
> unemployed person to use 
> the Internet (with my old ISDN dialup account it was
> by far to 
> expensive), things can turn to be different.
> Perhaps, ARQ might be 
> useful fore some line. Perhaps not only at the last
> mile which can be 
> hidden behind a PEP. We discussed ARQ for satellite
> links recently in 
> this list. And then? Will we complain about
> "spurious timeouts" then?
> 
> I apologize when this sounds extremely upset. It´s
> my honest intention 
> not to offense anybody. And if I can contribute an
> approach here, I will 
> do my very best. I sent some rough ideas to some
> people, perhas I will 
> get a feedback about it.
> 
> But either I am to stupid too understand TCP and
> it´s assumptions,
> or there is real danger to get into severe trouble
> when we still ignore 
> the timer issue.
> 
> O.k. I think, I will appl for asylum on the
> falklands or in the 
> antarktis now, since I expect to receive evil
> criticism now.
> 
> I don´t mind. If I´m wrong, I will learn my lesson.
> 
> But at the moment, I´m simply discouraged.
> If I´m wrong, I would appreciate somebody to correct
> me.
> If not, perhpas I can think about a way out. But
> everytime I start my 
> editor on my dated, ten years old P160 with 128
> MByte memory I think: It 
>   does not matter, whatever I write. As long as I do
> not provide 
> 
=== message truncated ===



		
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