Bandwidth for High Speed Networks

Fred has two variants which we will call fred 1 and

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Unformatted text preview: state, in FRED dropping decisions are based on this ow state. Specifically, FRED preferentially drops a packet of a ow that has either 1 had many packets dropped in the past, or 2 a queue larger than the average queue size. FRED has two variants, which we will call FRED-1 and FRED-2. The main di erence between the two is that FRED-2 guarantees to each ow a minimum number of bu ers. As a general rule, FRED-2 performs better than FRED-1 only when the number of ows is large. In the following data, when we do not distinguish between the two, we are quoting the results from the version of FRED which performed better. DRR De cit Round Robin - This algorithm 20 represents an e cient implementation of the well-known weighted fair queueing WFQ discipline. The bu er management scheme assumes that when the bu er is full the packet from the longest queue is dropped. DRR is the only one of the four to use a sophisticated perow queueing algorithm, and thus achieves the highest degree of fairness. These four algorithms represent four di erent levels of complexity. DRR and FRED have to classify incoming ows, whereas FIFO and RED do not. DRR in addition has to implement its packet scheduling algorithm, whereas the rest all use rst-in- rst-out scheduling. CSFQ edge routers have complexity comparable to FRED, and CSFQ core routers have complexity comparable to RED. We have examined the behavior of CSFQ under a variety of conditions. We use an assortment of tra c sources mainly TCP sources and constant bit rate UDP sources,4 but also some on-o sources and topologies. Due to space limitations, we only report on a small sampling of the simulations we have run.5 All simulations were performed in ns-2 17 , which provide accurate packet-level implementation for various network protocols, such as TCP and RLM 15 Receiver-driven Layered Multicast, and various bu er management and scheduling algorithms, such as RED and DRR. All algorithms used in the simulation, except CSFQ and FRED, were part of the standard ns-2 distribution. Unless otherwise speci ed, we use the follo...
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