[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 
queueing delay.

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 
recovery time.

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 
worked best.

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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