[e2e] Switched Ethernet is Not an End-to-End System; was Protocols breaking the end-to-end argument
detlef.bosau at web.de
Thu Nov 12 08:15:54 PST 2009
O.k., I still don't have an idea, what this argument is all about.
Richard Bennett wrote:
> Classical Ethernet - the co-ax cable-based, Aloha-derived CSMA/CD
> system - is one of the canonical examples of a purely edge-managed
First of all, classical Ethernet is the canonical example of classical
No one was forced to use classical Ethernet, and no one was forced to
avoid classical Ethernet.
The discussion initiated by Salzer, Reed and Clark was _not_, whether or
not a certain network technology should have management capabilies,
leaky bucket facilities, SNMP agents or whatever. Instead, the authors
invite us to carefully
consider, where certain functions, duties, responsibilities should be
placed and where not.
IIRC, Dave Reed told us, there were no such think like an "end to end
principle" some weeks ago.
And in fact, there is none. But it is useful to carefully consider the
placement and separation of concerns and responsibilities. No more, no less.
> It actually hails from the era during which the Internet protocols
> were designed, and expresses a similar set of engineering trade-offs.
And scientists and priests still argue, whether we hail from adam and
eve - or from apes and evolution.
Would this make a difference? Despite of the fact, that mankind should
rather behave like apes (and hopefully, apes still do!), because we
wouldn't have seen thermonuclear weapons and many other "human
When I use a network, my primary interest is not its historical origin
but its use for my problem.
> 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.
You mentioned some examples where some separations of concerns might
have been done in a different way than 1985.
When there are compelling reasons for doing so: Go ahead!
> While we now know that edge-managed LANs and MANs are not the way to
> go, we still use edge-managed protocols to
Typically, it's a good idea to fit a solution to a problem and not the
other way round.
So, first of all, I will have a look at my problem, e.g. how many
systems are to be connected, are there constraints, e.g. I must not use
a wireline connection in a certain scenario and so on, and then I will
make a choice for a certain networking technology.
This may be switched Ethernet - or it may be something different.
Depending on my actual needs and my actual constraints.
> operate the Internet. The Jacobson Algorithm is probably the purest
And I don't see, how switched Ethernet provides an alternative to VJCC.
> The triumph of switched and semi-centralized systems at layer 2
> suggests that it might be beneficial to revisit some of
Excuse me, but where is the triumph of switched Ethernet over VJCC?
> 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 it's always a good idea for IP, not to ignore the lower layers.
(I'm actually writing a very small and tiny network simulator, because
NS2 and other ones are still to big for my purposes and it's quite
appealing to have a small simulator in some few hundred lines of Java,
which simply does its job.
However, it would really spare me quite a few night sessions, if IP
could really ignore the lower layers.)
> 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.
Excuse me, but I don't see your point.
We can well discuss the advantages of circuit switching over packet
switching or the other way round.
However, both have their justification and both are in use for several
And I really don't see the big difference between placing a flow label
into an Ethernet frame or to introduce some
"Flow Switching Over Ethernet Protocol (FSOEP)" to achieve the same goal.
This is a major argument for minor a minor benefit.
Detlef Bosau Galileistraße 30 70565 Stuttgart
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