[e2e] Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument
David P. Reed
dpreed at reed.com
Mon Nov 2 08:33:06 PST 2009
There are probably also lessons in the evolution from networks that are
synchronized with clocks that must have timing with parts-per-billion
accuracy (the "Bell System" architecture - e.g. SONET) to networks that
allow for internal retiming, buffering, etc.
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
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.
On 11/01/2009 05:10 AM, Jon Crowcroft wrote:
> 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
> 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.
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