Can P2P applications learn to play fair on networks?

Sun Oct 28 22:10:11 UTC 2007

On Sun, 28 Oct 2007, Sean Donelan wrote:

> If you performed a simple Google search, you would have discovered many
> universities around the world having similar problems.
>
> The university network engineers are saying adding capacity alone isn't 
> solving their problems.

You're welcome to provide proper technical links. I'm looking for ones 
that say that 10GE didn't solve their problem, not the ones saying "we 
upgraded from T3 to OC3 from our campus of 30k student dorms connected 
with 100/100 and it's still overloaded", because that's just silly.

I had someone send me one that contradicts your opinion:

http://www.uoregon.edu/~joe/i2-cap-plan/internet2-capacity-planning.ppt

> Since I know poeple that offer 100/100 to university dorms, and are having
> problems with GE and even 10 GE depending on the size of the dorms, if you
> did a Google search you would find the problem.

Please provide links. I tried googling for instance for <university 
capacity problem p2p 10ge> and didn't find anything useful.

> 1. You are assuming traffic mixes don't change.
> 2. You are assuming traffix mixes on every network are the same.

I'm using real world data from swedish ISPs, each with tens of thousands 
of residential users, including the university ones. I tend to think we 
have one of the highest internet per capita usages in the world unless 
someone can give me data that says something else.

> If you restrict demand, statistical multiplexing works.  The problem is
> how do you restrict demand?

By giving people 10/10 instead of your network can't handle 100/100. Or 
you create a management system that checks port usage and limits the heavy 
users to 10/10, or you use microflow policing to limit uploads to 10, 
especially at times of congestion.

There are numerous ways of doing it that doesn't involve sending RST:s to 
customer TCP sessions or other ways of spoofing traffic.

> What happens when 10 x 100/100 users drive demand on your GigE ring to 99%? 
> What happens when P2P become popular and 30% of your subscribers
> use P2P?  What happens when 80% of your subscribers use P2P?  What happens
> with 100% of your subscribers use P2P?

If 100% of the userbase use p2p, then traffic patterns will change and 
more content will be local.

> TCP "friendly" flows voluntarily restrict demand by backing off when they
> detect congestion.  The problem is TCP assumes single flows, not grouped 
> flows used by some applications.

TCP assumes all flows are created equal, and doesn't take into account 
that a single user can use hundreds of flows, that's correct.

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se