Re: [p2pi] One more proposed definition of fairness...

[Joe Touch <touch at ISI.EDU>]

Nicholas Weaver wrote:
> On Jun 8, 2008, at 10:39 AM, Joe Touch wrote:
> > Nicholas Weaver wrote:
> > > (Buried in a previous mail, but I'd like comments on this separately)
> > > How does the following sound as one possible ideal goal for user- 
> > > fairness:
> > > "Mechanisms to enable the network to enforce traffic such that, in 
> > > the  presence of congestion, a user's congestion control response 
> > > becomes  equivalent to aggregating all traffic from that user into a 
> > > single TCP  stream."
> >
> > See the Congestion Manager or RFC2140 ;-)
> >
> > This is easy to do at the end system, but, AFAICT, impossible to 
> > accomplish anywhere else (users will just grab multiple IP addresses, 
> > e.g.) - or worse, involves violating TCP (or, equivalently, won't work 
> > on encrypted/authenticated streams).
>
>
> I'm a security person.  I have to assume the end systems don't behave 
> right.  But I actually don't think it is impossible to enforce in the 
> network for the local users' ISP.
...
> EG, the ISP can at a single bidirectional point in the network 
> (admittedly keeping lots of state, but...) for a large group of users 
> infer the congestion on each TCP flow,...

That's the point, however, where things stop when someone uses encrypted 
transport layers.

...
> Yes, this is a LOT of engineering work to get right [1], but I believe 
> it is doable, and could accomplish the stated definition of fairness (or 
> something very close to it).

A key question is whether it's worth the state it will take to get 
right. An endpoint might open a few thousand flows just to help overload 
your system ;-)

> Furthermore, you can resist the attacks you mentioned.  Because the ISP 
> can prevent the user from minting new IP addresses (as they control the 
> point of attachment), this prevents address forging.

Sure - the local ISP can prevent that. You can't prevent someone 
accessing multiple ISPs (cable, DSL, etc.), but presumably you don't 
care about that?

Joe

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