Congestion control train-wreck workshop at Stanford: Call for Demos

Fred Baker fred at cisco.com
Wed Sep 5 15:53:30 UTC 2007


On Sep 5, 2007, at 8:01 AM, Sean Donelan wrote:

> 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 capacity?

The big problem with this line of reasoning is that the student isn't  
visible at the network layer; at most, the IP address s/he is using  
is visible. If the student has an account at each of the universities  
s/he might be using all of them simultaneously. To the network, at  
most we can say that there were some number of IP addresses  
generating a lot of traffic.

One can do "interesting" things in the network in terms of scheduling  
capacity. My ISP in front of my home does that; they configure my  
cable modem to shape my traffic up and down to not exceed certain  
rates, and lo and behold my families combined computational capacity  
doesn't exceed those rates. One could similar do such things on a per- 
address or per-port basis in an enterprise network. That's where the  
discussion of per-address WFQ came from a decade ago - without having  
to configure each system's capabilities, make the systems using a  
constrained interface share it in some semi-rational manner  
automatically. That kind of thing is actually a lot harder on the end  
system; they don't talk with each other about such things. Can that  
be defeated? Of course; use a different IP address for each  
BitTorrent TCP session for example. My guess is "probably not on a  
widespread basis". That kind of statement might fall in the same  
category as "640K is enough", though.

Can you describe for me what problem you would really like solved?  
Are you saying, for example, that BitTorrent and similar applications  
should be constrained in some way so that the many TCPs from one  
system typically gets no more bandwidth than the single TCP on the  
system next door? Or are you really trying to build constraints on a  
per-user basis?



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