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

Christian Huitema huitema at windows.microsoft.com
Sun Jan 6 11:51:10 PST 2008

> 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.

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?

-- Christian Huitema

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