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<div class="moz-cite-prefix">Am 31.08.2014 um 08:24 schrieb Vint
Cerf:<br>
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cite="mid:CAHxHggczR84J-dqZVCcVrH6KRjbJWZ_xqsQ5hPy=coYfeOSLeQ@mail.gmail.com"
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<div dir="ltr">ARPANET used an overly constrained system called
RFNM (request for next message). The mechanism was used to
reserve space at the destination IMP ("get a block" "got a
block").
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<br>
That's what I referred to. <br>
<br>
<br>
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<div>however it was possible to send multiple messages over
different "links" (logical term) and overload the network that
way. It was also possible to overload an intermediate IMP
simply by sending traffic between pairs (source/destination)
that happened to pass through the same intermediate IMP. <br>
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<br>
That's what I missed. And this point is important. <br>
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<div>The Internet protocols did not use these methods and except
for the "congestion encountered" signal, all flow control was
end/to/end which still raised the possibility of intermediate
router congestion. <br>
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<br>
And that's my concern. The only compelling reasons for this seem to
me: a) A concern about possible head of line blocking, b) a lack of
computing power at the nodes. <br>
<br>
As far as I see, both problems can be overcome.<br>
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cite="mid:CAHxHggczR84J-dqZVCcVrH6KRjbJWZ_xqsQ5hPy=coYfeOSLeQ@mail.gmail.com"
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<div>The TCP flow control was an attempt to adjust to signals
from the receiver and signals (dropped packet, congestion
encountered) from intermediate nodes. Packet loss was treated
as a flow control signal leading to backoff of the
retransmission mechanism of TCP. Slow start was a crude way
of sensing where the limits of capacity lay. <br>
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<br>
However, this approach treated the "line" between sender and
receiver, may I say it extremely dense, as a "queueing system where
Little's law applies". <br>
(Which is a bit a contradiction in terms, because EITHER Little's
law applies to a system EXCLUSIVE OR a system suffers from drops.)<br>
<br>
However, one could take this as an approximation. (Which is
sometimes better, sometimes worse. As always in engineering.
Basically, the world is a perfect one - unfortunately, what we
actually have is only an approximation.)<br>
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<div>your claim that there is no congestion with "proper"
implementation may result in lower resource utilization.
Circuit switching dedicates capacity so there is no
congestion, except for the failure to get a circuit ("all
circuits busy" is a congestion signal). But dedicating
capacity removes the implicit statistical multiplexing
advantage of packet switching.</div>
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<br>
That's the very trade off. And I don't advocate circuit switching as
an alternative. The strong shortcoming in circuit switching is the
"fragmentation loss" of resources: Resources are assigned to users
who don't really use them. What I have in mind is basically a flow
layer with flow control (in a sense, Ford and Iyengar had something
similar in mind in 2009) and - to exploit the flexibility of a
packet switched network - an on demand scheduling of resources.<br>
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<div>v</div>
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<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Sat, Aug 30, 2014 at 12:25 PM,
Detlef Bosau <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:detlef.bosau@web.de" target="_blank">detlef.bosau@web.de</a>></span>
wrote:<br>
<blockquote class="gmail_quote">I'm yet to understand the
sitch from the ARPAnet to the Internet in<br>
1983, however, if this happened that way, that an Internet
host sent a<br>
message to its peer using the "message switching system"
(may I call it<br>
that way?) in the ARPAnet, CC would be an "impossible fact".<br>
<br>
(Some German readers might enjoy this little text here:<br>
<a moz-do-not-send="true"
href="http://ingeb.org/Lieder/palmstre.html"
target="_blank">http://ingeb.org/Lieder/palmstre.html</a>)<br>
<br>
In the ARPAnet, congestion was avoided by flow control - and
in fact,<br>
actually, there is nothing like "congestion" when networks
are<br>
implemented correctly.<br>
<br>
To my understanding, "congestion" is an excuse for missing
(or botched)<br>
flow control.<br>
<br>
So, what was the scenario, VJ describes in the congavoid
paper? Up to<br>
know, I always thought, the ARPAnet infrastructure was still
in use,<br>
although adopted by the Internet protocol stack, but I
thought, IP<br>
datagrams were sent like ARPAnet messages?<br>
<span class="HOEnZb"><br>
Detlef<br>
<br>
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</span></blockquote>
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<pre class="moz-signature" cols="72">--
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Detlef Bosau
Galileistraße 30
70565 Stuttgart Tel.: +49 711 5208031
mobile: +49 172 6819937
skype: detlef.bosau
ICQ: 566129673
<a class="moz-txt-link-abbreviated" href="mailto:detlef.bosau@web.de">detlef.bosau@web.de</a> <a class="moz-txt-link-freetext" href="http://www.detlef-bosau.de">http://www.detlef-bosau.de</a>
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