[e2e] traffic engineering considered harmful

David G. Andersen dga at lcs.mit.edu
Tue Jun 12 15:36:46 PDT 2001

Bob Braden just mooed:
>   *>    Resilient Overlay Networks:    http://nms.lcs.mit.edu/ron/
>   *> 
>   *>    Take a small collection of hosts around the 'Net.  They
>   *> can see different paths in and out of various ASs.  Have them
>   *> measure the paths between each other, and if they can establish
>   *> a better route by sending their packets indirectly through another
>   *> member of the overlay, do so.
> Why isn't this the Tragedy of the Commons waiting to happen?

  It might be.  There are a few saving graces, though:

  - The mechanisms used in RON won't scale:
     . The number of inter-node links grows as N^2;  the probe
       traffic would quickly drown most nodes.
     . The routing traffic is reasonably expensive.

Oddly, I think this is a good thing.  It means that you've got to
keep each group of reactive elements small.  If you're careful to avoid
inadvertent synchronization (if you can?), then you may be able to
avoid oscillations from huge groups of reactive elements.

  - These small groups will see different views of the network

I think this is probably the real saving grace.  Since everyone will
have a different set of links available that they choose between,
they won't all be able to overwhelm the same set of "good" links with
their traffic.

However, I don't have a clue if I'm correct about either of these
hypotheses.  And, I think your question had a deeper component
to it ("what if all of the good links get used up") that I don't
completely address in the second point.  If there are enough ants
scrambling along the trails, they _will_ get congested.  The answer
to that boils down to a more fundamental question about the
available bandwidth in the Internet, and its locations relative
to the mandatory bottlenecks people must traverse in getting
from source to destination.  Which is a handwavy way of saying
I don't konw the answer.

work: dga at lcs.mit.edu                          me:  dga at pobox.com
      MIT Laboratory for Computer Science           http://www.angio.net/

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