[e2e] Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument
richard at bennett.com
Wed Nov 11 16:08:26 PST 2009
Classical Ethernet - the co-ax cable-based, Aloha-derived CSMA/CD system
- is one of the canonical examples of a purely edge-managed network. It
actually hails from the era during which the Internet protocols were
designed, and expresses a similar set of engineering trade-offs.
Thirty-five years after the design of Ethernet, we've dropped the purely
edge-managed approach to building layer 1 and 2 networks in favor of
somewhat more centralized systems: Switched Ethernet, DOCSIS, DSL,
Wi-Max, and Wi-Fi are the leading examples. These systems aren't purely
centralized, of course; they're more like multiply-centralized meshes
than either edge-managed or core-managed systems.
While we now know that edge-managed LANs and MANs are not the way to go,
we still use edge-managed protocols to operate the Internet. The
Jacobson Algorithm is probably the purest example.
The triumph of switched and semi-centralized systems at layer 2 suggests
that it might be beneficial to revisit some of the design tradeoffs at
layer 3 if for no other reason than to bring them up-to-date. In
principle, IP isn't supposed to care what's happening at layer 2, but in
practice it makes a great deal of difference; this is one reason that
people design networks nowadays with the express intention of being good
for IP; e.g., MPLS.
That's the general idea.
Detlef Bosau wrote:
> Richard Bennett wrote:
>> 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?
> I've just had a very first glance at this discussion. (Thanks god, I
> first wrote the post by Joe....)
> However, I'm a bit curious what this discussion is all about.
> Many of us enjoy Switched Ethernet, me too. However, what is the very
> issue with switched Ethernet from the end to end arguments point of view?
> And second: Shall switched Ethernet replace TCP/IP?
> If not: What is this argument all about?
> Just curious.
Information Technology and Innovation Foundation
More information about the end2end-interest