Bandwidth for High Speed Networks

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Unformatted text preview: Intel Corp., MCI, and Sun Microsystems. Views and conclusions contained in this document are those of the authors and should no be interpreted as representing the o cial policies, either expressed or implied, of DARPA, NSF, Intel, MCI, Sun, or the U.S. government. Hui Zhang CMU [email protected] some maintain that fair bandwidth allocation1 plays a necessary, not just bene cial, role in congestion control 7, 19 . Until now, fair allocations were typically achieved by using per- ow queueing mechanisms such as Fair Queueing 7, 18 and its many variants 2, 10, 20 or per- ow dropping mechanisms such as Flow Random Early Drop FRED 14 . These mechanisms are more complex to implement than traditional FIFO queueing with drop-tail, which is the most widely implemented and deployed mechanism in routers today. In particular, fair allocation mechanisms inherently require the routers to maintain state and perform operations on a per ow basis. For each packet that arrives at the router, the routers needs to classify the packet into a ow, update per ow state variables, and perform certain operations based on the per ow state. The operations can be as simple as deciding whether to drop or queue the packet e.g., FRED, or as complex as manipulation of priority queues e.g., Fair Queueing. While a number of techniques have been proposed to reduce the complexity of the per packet operations 1, 20, 21 , and commercial implementations are available in some intermediate class routers, it is still unclear whether these algorithms can be cost-e ectively implemented in high-speed backbone routers because all these algorithms still require packet classi cation and per ow state management. In this paper we start with the assumption that 1 fair allocation mechanisms play an important, perhaps even necessary, role in congestion control, and 2 the complexity of existing fair allocation mechanisms is a substantial hindrance to their adoption. Both of these points are debatable; developments in router technology may make such algorithms rather inexpensive to implement, and there may be solutions to congestion control that do not require fair allocation we discuss this point more fully in Sec...
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