[e2e] Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument
richard at bennett.com
Sat Oct 31 14:46:55 PDT 2009
Dave Eckhardt wrote:
> So it's unclear
> that CSMA/CD was a structural limit of Ethernet--the reality
> is probably more like "It doesn't matter much how you contend
> among a few hosts, but you can't build large networks unless
> you limit contention domains to less than the size of the
> large network", which is almost a tautology.
That's part of the story, but the implications of the switched Ethernet
killing off CSMA/CD Ethernet are much larger, and relate the end-to-end
arguments principle. CSMA/CD Ethernet was an end-point managed system
sharing a dump pipe, while switched Ethernet is a system that deploys
intelligence - switching, flow control, buffering, QoS discrimination,
VLANs - inside the network at multiple points. Switched Ethernet is
scalable, manageable, diagnosable, and future-proof, while CSMA/CD
Ethernet is none of these things. So the competition of CSMA/CD and
Active Switching for markets demonstrates something about which approach
to the design of layer 2 networks is superior.
Now the question that this historical fact raises for me is whether we
can draw any implications from the well-settled outcome of the layer 2
tussle for layer 3 and 4 protocols, given the fact that IP is a very
thin abstraction of the Ethernet layer 2 and that TCP is a vehicle for
resolving problems that are typical of the CSMA/CD Ethernet environment;
I offer that as a realistic assessment of the design choices, realizing
that the official story differs from the reality.
In other words: does the success of Switched Ethernet suggest that it's
better to think of network protocols as units of recursion than as
collections of statically-placed functions that operate once and only
once in the lifetime of a packet?
Information Technology and Innovation Foundation
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