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csfq(1) - Core-St at eless Fair Queueing Bandwidth...

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Core-St at eless Fair Queueing: Achieving Approximately Fair Bandwidth Allocations in High Speed Networks* Ion Stoica Scott Shenker CMlJ Xerox PARC istoicaQcs.cmu.edu [email protected] Hui Zhang CMlJ [email protected] Abstract Router mechanisms designed to achieve fair bandwidth al- locations, like Fair Queueing, have many desirable proper- ties for congestion control in the Internet. However, such mechanisms usually need to maintain state, manage buffers, and/or perform packet scheduling on a per flow basis, and this complexity may prevent them from being cost-effectively implemented and widely deployed. In this paper, we pro- pose an architecture that significantly reduces this imple- mentation complexity yet st,ill achieves approximately fair bandwidth allocations. We apply this approach to an is- land of routers - that is, a contiguous region of the net- work and we distinguish between edge routers and core routers. Edge routers maintain per flow state; they estimate the incoming rate of each flow and insert a label into each packet header based on this estimate. Core routers main- tain no per flow state; they use FIFO packet scheduling aug- mented by a probabilistic dropping algorithm that uses the packet labels and an estimate of the aggregate traffic at the router. We call the scheme Core-Stateless Fair Queueing. We present simulations and analysis on the performance of this approach, and discuss an alternate approach. 1 Introduction A central tenet of the Internet architecture is that conges- tion control is achieved mainly through end-host algorithms. However, starting with Nagle [16], many researchers ob- served that such end-to-end congestion control solutions are greatly improved when routers have mechanisms that allo- cate bandwidth in a fair manner, Fair bandwidth allocation protects well-behaved flows from ill-behaved ones, and al- lows a diverse set of end-to-end congestion control policies Lo co-exist in the network [7]. As we discuss in Section 4, * I’hls research was sponsored by DARPA under contract numbers N66001-96-C-8528, E30602-97-Z-0287, and DABT63-94-C-0073, and by a NSF Carerr Award under grant number NCR-9624979. Addi- tlonal support was provided by Intel Corp., MCI, and Sun Microsys- terns. Views and conclusions contained in this document are those of the authors and should no be interpreted as representing the official poliries, either expressed or implied, of DARPA, NSF, Intel, MCI, Sun, or the U.S. government Q ,998 ACM l-58113~003.l/98/0008.. $5.00 sorne maintain that fair bandwidth allocation’ plays a uer- essary, not just beneficial, role in congestion control [7, 191. Until now, fair allocations were typically achieved by us- ing per-flow queueing mechanisms - such as Fair Queueing [7, 181 and its many variants [2, 10, 20]- or per-flow dropping mechanisms such as Flow Random Early Drop (FRED) [14].
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