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<font face="Helvetica, Arial, sans-serif">There are probably also
lessons in the evolution from networks that are synchronized with
clocks that must have timing with parts-per-billion accuracy </font>(the
"Bell
System" architecture - e.g. SONET) to networks that allow for
internal retiming, buffering, etc.<br>
<br>
That doesn't mean that it is a fact that IP is a thin layer over such
clock-synchronized networks, which still exist and carry IP traffic.
Nor is TCP designed to be corrective of such networks brittle
unreliability, which leads to rerouting over alternate paths that may
cause transient out-of-order delivery, duplication, and a need to
reallocate resources.<br>
<br>
TCP and IP were designed to handle heterogeneity and best efforts, and
the idea that they were either designed to remedy Aloha or evolved so
that they only run on Ethernet - that is nonsense, a just so story.<br>
<br>
On 11/01/2009 05:10 AM, Jon Crowcroft wrote:
<blockquote cite="mid:E1N4XOe-0000FR-00@mta2.cl.cam.ac.uk" type="cite">
<pre wrap="">There definitely are lessons
in the evolution from
end-mediated contention to
switch-mediated access
in ethernet-land.
The oft-perceived analogy
of the whole internet as a big ethernet,
a huge shared resource
with contention mainly mediated
by end systems, is alluring.
So the move to
net/switch-centric resource allocation/control
in the local,
might suggest some similar move
in the wide area...
until you actually think about the
heterogeneity in the
topology, in capacity and in latency,
of the system -
Plenty of enterprise nets and small ISPs
(e.g. UK size) can consider
a carrier-grade switched ether
control philosophy (e.g.
esp. to replace
complicated MPLS setups:)
but it doesn't subsume/replace e2e
resource sharing -
It doesn't address
multihomeing, multipath, mobility or multicast
in any useful way either...it doesn't
speak to swarms and CDNs much either.
There were other lan technologies
which didn't have built in collapse
as part of the media-sharing protocols
so the lesson wasn't as widely
necessary as the e2e monoculture
pretends (people who built
token and slotted rings
had other views of the world
too:)
On the other hand, it would be instructive
to see how many end&edge systems are now on
wireless ethernet and to see if the balance has
swung back once again in "favour" of
shared media/contention.
aloha
jon
</pre>
</blockquote>
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