Can P2P applications learn to play fair on networks?

Mon Oct 22 13:12:06 UTC 2007

Sean Donelan wrote:
>
> Much of the same content is available through NNTP, HTTP and P2P. The 
> content part gets a lot of attention and outrage, but network 
> engineers seem to be responding to something else.
>
> If its not the content, why are network engineers at many university 
> networks, enterprise networks, public networks concerned about the 
> impact particular P2P protocols have on network operations?  If it was 
> just a
> single network, maybe they are evil.  But when many different networks
> all start responding, then maybe something else is the problem.
>
> The traditional assumption is that all end hosts and applications 
> cooperate and fairly share network resources.  NNTP is usually 
> considered a very well-behaved network protocol.  Big bandwidth, but 
> sharing network resources.  HTTP is a little less behaved, but still 
> roughly seems to share network resources equally with other users. P2P 
> applications seem
> to be extremely disruptive to other users of shared networks, and causes
> problems for other "polite" network applications.
>
What exactly is it that P2P applications do that is impolite? AFAIK they 
are mostly TCP based, so it can't be that they don't have any congestion 
avoidance, it's just that they utilise multiple TCP flows? Or it is the 
view that the need for TCP congestion avoidance to kick in is bad in 
itself (i.e. raw bandwidth consumption)?

It seems to me that the problem is more general than just P2P 
applications, and there are two possible solutions:

1) Some kind of magical quality is given to the network to allow it to 
do congestion avoidance on an IP basis, rather than on a TCP flow basis. 
As previously discussed on nanog there are many problems with this 
approach, not least the fact the core ends up tracking a lot of flow 
information.

2) A QoS scavenger class is implemented so that users get a guaranteed 
minimum, with everything above this marked to be dropped first in the 
event of congestion. Of course, the QoS markings aren't carried 
inter-provider, but I assume that most of the congestion this thread 
talks about is occuring the first AS?

Sam