Bandwidth for High Speed Networks

Identifying unresponsive ows is more straightforward

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Unformatted text preview: xt of the identi cation approach is far from a solved problem; the challenge is to determine if a ow has decreased usage in response to increases in overall packet drop rates 8 . Identifying unresponsive ows is more straightforward in the allocation approach, since here one need only determine if a ow has had signi cantly high drop rates over a long period of time. As a proof of concept we have implemented a simple identi cation and punishment mechanism. First, we examine o -line the last n dropped packets and then monitor the ows with the most dropped packets. Second, we estimate the rate of each of these monitored ows; when a ow's rate is larger than a  a 1, we start dropping all of its packets. Third, we continue to monitor penalized ows, continuing punishment until their arrival rate decreases below b  b 1. Using the parameters a = 1:2, b = 0:6, and n = 100, we applied this algorithm to Simulation 1 in Table 5; the UDP ow was identi ed and penalized in less than 3 seconds. Our task was easy because the identi cation of unresponsive ows can be based on the result packet drops over long periods of time rather than on trying to examine the algorithm detecting whether it actually decreased its rate in response to an increase in the drop rate. Note also that the allocation approach need only distinguish between responsive and unresponsive in the punishment phase, an inherently easier task than distinguishing friendly from unfriendly. In summary, to provide incentives for drop-tolerant ows to use responsive end-to-end congestion control, it may be necessary to identify, and then punish, unresponsive ows. overhead associated with them, and it isn't clear whether, in practice, the overheads are greater or less than the advantages gained. However, one can certainly not claim, as we did above for drop-intolerant applications, that the allocation approach gives drop-tolerant applications a strong incentive to use responsive end-to-end congestion control algorithms. 16 Another possible method, used in ATM ABR, is...
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