[e2e] What's wrong with this picture?
David P. Reed
dpreed at reed.com
Sat Sep 12 12:12:01 PDT 2009
On 09/11/2009 05:41 PM, Lachlan Andrew wrote
> No, IP is claimed to run over a "best effort" network. That means
> that the router *may* discard packets, but doesn't mean that it
> *must*. If the delay is less than the IP lifetime (3 minutes?) then
> the router is within spec (from the E2E point of view). The dominance
> of IP was exactly that it doesn't place heavy "requirements" on the
> forwarding behaviour of the routers.
I disagree with this paragraph. No one ever claimed that IP would run
over *any* best efforts network. One could argue that routers that take
pains to deliver packets at *any* cost (including buffering them for 10
seconds when the travel time over the link between points is on the
order of 1 microsecond, and the signalling rate is > 1 Megabit/sec) are
not "best efforts" but "heroic efforts" networks.
In any case, research topics for future networks aside, the current IP
network was, is, and has been developed with the goal of minimizing
buffering and queueing delay in the network. The congestion control and
fairness mechanism developed by Van Jacobson and justified by Kelly (on
game theoretic grounds, which actually makes a great deal of sense,
because it punishes non-compliance to some extent) is both standardized
and dependent on tight control loops, which means no substantial
It's not the buffer capacity that is the problem. It's the lack of
signalling congestion. And the introduction of "persistent traffic jams"
in layer 2 elements, since the drainage rate of a queue is crucial to
One can dream of an entirely different network. But this is NOT a
political problem where there is some weird idea that layer 2 networks
offering layer 3 transit should have political rights to just do what
they please. It's merely a matter of what actually *works*.
Your paragraph sounds like the statements of what my seagoing ancestors
called "sea-lawyers" people who make some weird interpretation of a
"rule book" that seems to be based on the idea that the design came from
"god" or the "king". Nope - the design came from figuring out what
Now, I welcome a fully proven research activity that works as well as
the Internet does when operators haven't configured their layer 2
components to signal congestion and limit buildup of slow-to-drain
queues clogged with packets.
You are welcome to develop and convince us to replace the Internet with
it, once it *works*.
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