Congestion control train-wreck workshop at Stanford: Call for Demos

Thu Sep 6 14:32:07 UTC 2007

> On Wed, 5 Sep 2007, Stephen Stuart wrote:
> >
> > [...]
> 
> If there is no congestion, then this conversation serves no purpose.
> I'd like one infinite improbability drive too.

Sure. When mine arrives, I'll drop it into my matter replicator so you
can have one. :-)

> > Let's say our example student is capable of generating 95% of flows by
> > virtue of having access to 95% of the IP endpoints in the example
> > network. How do you envision the OS notion of "user" helping you
> > implement a per-user notion of fairness on the backbone?
> 
> That's why I don't think operators care about "users" or "endpoints" but
> they do care about who is paying the bills.  Operators care about the 
> relative "fairness" between bill payers, not flows, sessions or users.
> 
> Suppose MIT has a /8, Harvard as a /16; if MIT figured out they could get 
> more backbone bandwidth than Harvard by multiplexing its "flows" across 
> more addresses, and starving Havard students of backbone capacity. 
> Suppose Harvard was paying for 50% of the backbone cost, while poor
> MIT could only afford to pay for 10% of the backbone cost.
> 
> If the congestion point was always at the backbone edge, you might be
> able to accomplish this by making Harvard's connection bigger than MIT's
> connection.  But lets imagine instead, during periods of little congestion
> you want both Harvard and MIT to use as much of the backbone as they can, 
> and only when there is congestion do you want to "share" the backbone 
> congestion "fairly" between them.

Yes, that's the notion that I was trying to convey. 

I agree that operators don't care about users, my reason for steering
the conversation back toward them is that what kicked this sub-thread
off was the assertion that knowledge of user by the OS at a TCP
endpoint could somehow provide relevant information for resource
allocation in a network such that congestion is divided among
users. Techniques for trying to impose how congestion is "fairly"
shared among flows exist and aren't what we're talking about. Could a
technique be developed that used a notion of "user" in a network?
(From Fred's reply, I think that's what we're talking about.) I'd
argue that if it could it would be complex and therefore unsuitably
fragile in a service provider environment, and would lose all
relevance the moment a congestion point at an administrative boundary
was crossed.

Stephen