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<div class="moz-cite-prefix">Am 13.12.2012 15:57, schrieb Jim
Gettys:<br>
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cite="mid:CAGhGL2AFHw+5KkngML-aRymsCDtNfpesAWSL+f0bpKBgMzkJpg@mail.gmail.com"
type="cite">
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<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Thu, Dec 13, 2012 at 6:15 AM,
Eggert, Lars <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:lars@netapp.com" target="_blank">lars@netapp.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote">
<div class="im">On Dec 12, 2012, at 16:38, Detlef Bosau <<a
moz-do-not-send="true" href="mailto:detlef.bosau@web.de">detlef.bosau@web.de</a>>
wrote:<br>
> My central question at the moment is: Do we have
stationary packet delivery times on mobile wireless links?<br>
<br>
</div>
</blockquote>
<div>Not sure what you mean by "stationary".</div>
<div><br>
</div>
<div>This crossed my radar screen:</div>
<div><br>
</div>
<div><a moz-do-not-send="true"
href="http://conferences.sigcomm.org/sigcomm/2012/paper/cellnet/p1.pdf">http://conferences.sigcomm.org/sigcomm/2012/paper/cellnet/p1.pdf</a></div>
<div><br>
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</blockquote>
<br>
And there you find <br>
<br>
<blockquote type="cite">Simply speaking, the static value could be
too<br>
small in large BDP (Bandwidth-Delay Product) links but too large<br>
in small BDP links.<br>
</blockquote>
<br>
And if you compare this to the "BDP Definition" as used e.g. in <br>
<br>
<blockquote type="cite">@article{ meyer,<br>
author ="Michael Meyer and Joachim Sachs and Markus Holzke",<br>
title ="{Performance Evaluation of A TCP Proxy in WCSMA
Networks}",<br>
journal ="IEEE Wireless Communications",<br>
year = "2003",<br>
month = "October"<br>
}<br>
</blockquote>
<br>
you see, what I'm talking about.<br>
<br>
Particularly, as the quoted paper uses the GPRS link's gross data
rate for the calculation of the "Bandwidth-Delay Product", a term
which is, decently spoken, complete nonsense in the context of
mobile wireless networks.<br>
<br>
I have to apologize for being upset, if you knew me a bit closer,
you would surely understand my attitude.<br>
<br>
If you have a look hat Little's paper (I think it's commonly known
that the "Bandwidth-Delay Product" is the CS "conception" of
Little's Theorem, of course used with the "CS conception" of the
term "bandwidth", which was a subject of discussion in this list
some weeks ago, you'll find that this is an equation between several
expectations.<br>
<br>
The average (i.e. expected) number of jobs in a queueing system
equals the product of the average (i.e. expected) arrival rate times
the avarage (i.e. expected) sojourn time. <br>
<br>
As TCP employs a self clocking mechanism for clocking out sent
packets and the delivery times in mobile links are non stationary (I
did not ask for papers, because this were an open question, that
mobile link's delivery times are not stationary is obvious, however
the people I talk to don't believe me, this is a cause for my anger)
neither the arrival rate nor the sojourn time have an expectation,
hence Little's theorem simply does not apply here.<br>
<br>
More simply: When you offer lots of load to a wireless interface (be
it window- or rate-controlled, this doesn't make a difference) and
the delivery time suffers from a sudden increase (I well know the
lots of paper with Gilbert-Markov-Models and "link outages" - what
is a "link outage" in mobile wireless networks? We work with mobile
wireless networks for 20 years now and many guys still think in the
black and white manner of a link being up or down! Although a simple
look into the standards will tell you that e.g. for a GPRS link the
.95 quantile for the delivery of 1024 byte packet varies (depending
on the chosen QoS class and the link's properties) from 7 seconds to
375 seconds.<br>
<br>
And please note the meaning of 0.95 quantile. When the mentioned 6
minutes are over, it may well be that your packet is lost and no one
told you about that.<br>
<br>
So, when the delivery time suffers from a sudden increase - why do
we wonder about buffer bloats then?<br>
<br>
And when delivery times of, say, a HSDPA interfaces vary on a time
range from some few milliseconds, why do we wonder, that TCP sending
sockets seeing a RTT of, say, 50 ms, do not timely adapt?<br>
<br>
I first discussed this issue with academics in Germany 6 years ago,
they did not believe me. I noted that the term BDP is completely
inappropriate for mobile networks, no one believed me. For some
reasons which don't belong here, I cannot afford papers at visible
conferences and when I submit papers on that issue to conferences or
papers, no one believes me.<br>
<br>
I'm frequently taken for an idiot and rejected and offended - and
when I claim, rain would consist of water, no one believes me.<br>
<br>
On the one hand, I'm glad to see this paper.<br>
<br>
On the other hand, I'm extremely upset and I hardly can describe my
anger and bitterness here, although this must not be part of this
list. But I'm only a human being, so I cannot ignore my emotions.<br>
<br>
Detlef <br>
<br>
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