[e2e] Are we doing sliding window in the Internet?

Lars Eggert lars.eggert at nokia.com
Mon Jan 7 02:46:47 PST 2008

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On 2008-1-6, at 21:51, ext Christian Huitema wrote:
>> It's important to remember the two reasons for congestion control  
>> from
>> Sally's RFC2914: preventing congestion collapse and establishing some
>> degree of fairness.
> Wait a minute. This is equivalent to saying that continuous  
> stability of the Internet depends on the benevolent cooperation of  
> all Internet users. The implementation of slow start in TCP did  
> indeed prevent the Internet to collapse at a crucial time in its  
> evolution. But that was then. I don't think we can extrapolate the  
> 1988 fix into an everlasting principle, not with a billion hosts on  
> the Internet.

this is taking us pretty far away from the context in which I made the  
statement you quoted above (what we learn from the current CUBIC  
deployment), but anyway:

I'm not saying that end system transport-layer congestion control is  
all that we'll ever need, especially when end systems become selfish.  
But I do think that the stable operation of the Internet has been  
depending and probably is still depending on the majority of the  
traffic being sent over congestion-controlled transport protocols.

If that changes (and my nightmare scenario is that the BitTorrent guys  
realize that they don't need to use the in-kernel TCP stack, all they  
need to use is the TCP packet format), yes, then we do need something  
else, as you say below.

> In that research on "network based" mechanisms, we should accept  
> that end systems will be primarily motivated by their self interest.  
> They are certainly not motivated by a desire to be fair with others.  
> The desire of fairness is a social contract, and I don't think we  
> can assume such a contract when the Internet covers the entire  
> world. If we could, that would indeed be a good thing, we would also  
> have worldwide peace and all that kind of thing. So, we have better  
> assume that end system will try to maximize their individual  
> satisfaction, rather than looking for the common good. If we cannot  
> rely on the benevolent sum of individual behaviors, we need to build  
> mechanisms in the network that help it guarantee its stability.
> In fact, ISP are already attempting to build this "stabilization  
> tools" in their networks. We see various forms of traffic shaping  
> implemented at bottleneck points. We see various tools used to  
> perform "traffic engineering". ISP need to do that if they have any  
> hope of providing some kind of guarantees of service. Many on this  
> list will find those tools crude, or possibly harmful. Fine, but the  
> reaction cannot be to retreat in the ivory tower and leer at those  
> lowly network engineers. Instead of clinging to the illusion that we  
> can entirely solve the problem in an end to end fashion, that all  
> end systems will follow the dictate of the E2E group, maybe we  
> should actually address the problem. What is the best mechanisms to  
> deploy in the Internet to make it immune to variations in end to end  
> algorithms?

I agree with you that there'll need to be something that protects the  
network and other users from selfish end systems, and it will need to  
be a mechanism that doesn't only rely on the cooperation of those end  

But I'm also not convinced that this functionality should completely  
move into the network, which is what I think ISPs are currently  
attempting to do. An architecture that gives incentives to the end  
systems to behave correctly, rather than controlling everything  
network-side, appears more viable to me. (And we've just gotten some  
EU money over the next three years to look at how such a system would  
look in detail.)


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