[e2e] Changing dynamics
pekka.nikander at nomadiclab.com
Sat Feb 21 23:31:03 PST 2009
> Most (not all) of these ideas seem to reflect the idea that we
> should operate the net with a lot of internal buffering.
I would rather say the idea is to change how we view the buffering in
> For example, if it were actually a frequent benefit to search
> partway back ... then what would that mean? It would mean that the
> packets are not transiting the network in the US with little or no
> delay ...
But then we would not be considering the fact that not all traffic
requires short delay. AFAICS, the reason why TCP requires short delay
is built-in to TCP; given a different control loop structure (see
Lloyd's and Christian's messages) there could easily be transport
protocols that do not require such short e2e delays.
Taking a higher-layer view, only a small fraction of traffic requires
50..200 ms e2e delay, basically games and "interactive
multimedia" (aka voice :-). Most transaction-like apps (IM, web apps
etc) could tolerate 2000..4000 ms delays, not even speaking about bulk.
> I do think there is a virtue to moving replicated content closer to
> the endpoints. But that is a different thing, and has nothing to do
> with routers and e2e protocols.
I sort-of thought so, too, in the beginning.
Then I realised that changing the way the network handles information
will change the system dynamics, affecting transport and e2e protocols.
> That thing has to do with what we were debating a few weeks ago:
> what Van Jacobson calls "content centric networks" or what Akamai
> does at the app layer, or my point about communications not having
> to be about information that begins with the assumption that
> information is in "one place".
Indeed. That was the starting point. But then, adding a look at the
tends in the price/performance rate changes of the components, the
landscape starts to change.
As a Gedankenexperiment, what if the probability of the data still
being opportunistically cached in the forwarding nodes would be higher
than the "sending" end-node still being up? (Also consider a
"stateless" data source, or a source that has no direct material
interest of knowing if the sink has got the data or not.)
Or another example, I think which you brought forward a few weeks ago,
what if the information in question doesn't have any well defined
"location" but is "smeared" over the network, e.g. due to coding or
being an answer to a question. I presume that it would also have
quite a large effects on how to build routers or transport protocols.
In such a world it is hard to speak about e2e; where is the other end?
Taking a shorter-term time perspective, haven't we learned anything
from the so-called wireless TCP accelerators? There we saw the
effects of the interaction of two (or three) control loops. Now, if
the development of technology makes it a much stronger requirement
than today to prefer local communications to long haul communications,
presumably changing the dynamics (number of interacting control
loops), I surmise that it will have its effects on transport
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