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Bandwidth for High Speed Networks

The averaging constants k used in estimating the ow

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Unformatted text preview: wing parameters for the simulations in this section. Each output link has a capacity of 10 Mbps, a latency of 1 ms, and a bu er of 64 KB. In the RED and FRED cases the rst threshold is set to 16 KB, while the second one is set to 32 KB. The averaging constants K used in estimating the ow rate, K used in estimating the fair rate, and Kc used in making the decision of whether a link is congested or not are all set to 100 ms unless speci ed otherwise. The general rule of thumb we follow in this paper is to choose these constants to be roughly two times larger than the6 maximum queueing delay i.e., 64KB=10Mbps = 51.2 ms. Finally, in all topologies the rst router on the path of each ow is always assumed to be an edge router; all other routers are assumed without exception to be core routers. We simulated the other four algorithms to give us benchmarks against which to assess these results. We use DRR as our model of fairness and use the baseline cases, FIFO and 4 This source, referred to as UDP in the remainder of the paper, has xed size packets and the packet interarrival times are uniformly distributed between 0:5  avg; 1:5  avg, where avg is the average interarrival time. 5 A fuller set of tests, and the scripts used to run them, is available at http: www.cs.cmu.edu ~istoica csfq 6 It can be shown that by using this rule an idle link that becomes suddenly congested by a set of identical UDP sources will not experience bu er over ow before the algorithm detects the congestion, as long as the aggregate arrival rate is less than 10 times the link capacity see 22 . UDP-1 - UDP-10 DRR CSFQ FRED RED FIFO 1.4 Allocated Bwdth. / Ideal Bwdth. 1.2 UDP-K1 - UDP-K10 Sinks TCP/UDP-0 Source TCP/UDP-0 Sink Gateway 1 Gateway ... ... ... Gateway Gateway 0.8 Sources 0.6 UDP-1 UDP-10 UDP-11 UDP-20 ... UDP-K1 UDP-K10 0.4 0.2 0 5 10 15 20 Total Number of Flows 25 30 Figure 4: The normalized bandwidth of a TCP ow that competes with N , 1 UDP ows sending at twice their allocated rates, as a function of N . RED, as repr...
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