Can P2P applications learn to play fair on networks?

Iljitsch van Beijnum iljitsch at muada.com
Fri Oct 26 07:38:49 UTC 2007


On 25-okt-2007, at 18:50, Sean Donelan wrote:

> Comcast's network is QOS DSCP enabled, as are many other large  
> provider networks.  Enterprise customers use QOS DSCP all the  
> time.  However, the net neutrality battles last year made it  
> politically impossible for providers to say they use QOS in their  
> consumer networks.

And generating packets with false address information is more  
acceptable? I don't buy it.

The problem is that ISPs work under the assumption that users only  
use a certain percentage of their available bandwidth, while (some)  
users work under the assumption that they get to use all their  
available bandwidth 24/7 if they choose to do so. Obviously the two  
are fundamentally incompatible, which becomes apparent if the number  
of high usage users starts to fill up available capacity to the  
detriment of other users.

I don't see any way around instituting some kind of traffic limit.  
Obviously that can't be a peak bandwidth limit because that way ISPs  
would have to go back to selling 56k connections. (Still enough to  
generate 15 GB or so per month in one direction.) So it has to be a  
traffic limit. But then what happens when a customer goes over the  
limit? I think in the mobile broadband business such customers are  
harassed to leave. That's a good business practice if you can get  
away with it, but the Verizon case shows that you probably can't in  
the long run. So after a customer goes over the traffic limit, you  
still need to give them SOME service but it must be a reduced one for  
some time so the customer doesn't keep using up more than their share  
of available bandwidth. One approach is to limt bandwidth. The other  
is dumping that user in a lower traffic class. If there is a  
reasonable amount of bandwidth available for that traffic class, then  
the user still gets to burst (a little) so this gives them a better  
service level. I don't see how this logic violates net neutrality  
principles.

> Until P2P applications figure out how to play nicely with non-P2P  
> network uses, its going to be a network wreck.

And how exactly do you propose that they do that?

My answer is: set a different DSCP. As I said before, at least one  
popular BitTorrent client can already do that. And if ISPs like  
Comcast already have diffserv-enabled networks, this seems like a no- 
brainer to me. Don't forget that the first victim of an overloaded  
last mile link is the user of that link themselves: if they let their  
torrents rip at max speed, they get in the way of their own  
interactive traffic.



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