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Re: Congestion control train-wreck workshop at Stanford: Call for Demos
- From: Sean Donelan
- Date: Wed Sep 05 11:16:05 2007
On Wed, 5 Sep 2007, Stephen Stuart wrote:
Operators always define the "user" as the person paying the bill. One
bill, one user.
It's easy to imagine a context where authentication at the application
layer determines "user" in a bill-paying context. Passing that
information into the OS, and having the OS try to schedule fairness
based on competing applications' "guidance," seems like a level of
complexity that adds little value over implementing fairness on a
per-flow basis. In theory, any such notion of "user" is lost once the
packet gets out on the wire - especially when user is determined by
application-layer authentication, so I don't consider 802.1X or the
like to be helpful in this instance.
Money and congestion are aggregated on many different levels. At the dorm
level, money and congestion may be shared on a per-student basis while at
the institution level money and congestion may be shared on a
per-department basis, and on a backbone level money and congestion may be
shared on a per-institution basis.
That's the issue with per-flow sharing, 10 institutions may be sharing a
cost equally but if one student in one department at one institution
generates 95% of the flows should he be able to consume 95% of the
Its fun to watch network engineers' heads explode.
What if the person paying the bill isn't party to either side of the
The person paying the bill is frequently not a party to either side of
individual TCP sessions, that is why you also frequently have disputes
over which TCP session should experience what level of congestion.