Bandwidth for High Speed Networks

In what follows we borrow heavily from 7 3 and there

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Unformatted text preview: ion scenario so that the TCP ow starts after all the RLM ows then it receives less than half of its fair share. This hysteresis in the RLM versus TCP behavior was rst pointed out to us by Steve McCanne 15 . 4.2 Two Approaches There are, in the literature, two general approaches to addressing the problem of unfriendly ows. The rst is the allocation approach. Here, the router itself ensures that bandwidth is allocated fairly, isolating ows from each other so that unfriendly ows can only have a very limited impact on other ows. Thus, the allocation approach need not demand that all ows adopt some universally standard endto-end congestion control algorithm; ows can choose to respond to the congestion in whatever manner best suits them without unduly harming other ows. Assuming that ows prefer to not have signi cant levels of packet drops, these allocation approaches give an incentive for ows to use endto-end congestion control, because being unresponsive hurts their own performance. Note that the allocation approach does not provide an incentive for ows to be TCP-friendly an example of an alternative end-to-end congestion control algorithm is described in 13 , but does provide strong incentives for drop-intolerant applications to use some form of end-to-end congestion control.10 Of course, the canonical implementations of the allocation approach, such as Fair Queueing, all require signi cant complexity in routers. Our goal in this paper was to present a more scalable realization of the allocation approach. The problem of unfriendly ows can be addressed in another manner. In the identi cation approach, as best exempli ed by 8 , routers use a lightweight detection algorithm to identify unfriendly ows, and then explicitly manage the bandwidth of these unfriendly ows. This bandwidth management can range from merely restricting unfriendly ows to no more than the currently highest friendly ow's share11 to the extreme of severely punishing unfriendly ows by dropping all of their packets. This approach relies on the ability to accurately identify unfriendly ows with relatively lightweight router mechanisms. This is a daunting task. Below we discuss the process...
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