On the Optimum Switch Radix in Fat Tree Networks

Based on a realistic, yet simple cost model, we compute the switch radix that minimizes the cost of a fat tree network to support a given number of end nodes. The cost model comprises two parameters indicating the relative cost of a crosspoint vs. a link, and the crosspoint-independent base cost of a switch. These parameters can be adapted to represent a given technology used to implement links and switches. Based on these inputs, the resulting model allows a quick evaluation of the switch radix that minimizes the overall cost of the network. We demonstrate that the optimum radix depends most strongly on the relative cost of a link, and turns out to be largely independent of the network size. Using a first-order cost bounds analysis based on current CMOS and link technology, our model suggests that the optimum switch radix is in the range of hundreds of ports, rather than the tens of ports being offered today by most commercial switch products.

An extended version of this paper has appeared in: Proc. 2011 IEEE 12th Int'l Conf. on High Performance Switching and Routing "HPSR," Cartagena, Spain (IEEE, July 2011) 44-51

By: C. Minkenberg, R.P. Luijten, G. Rodriguez

Published in: RZ3774 in 2010


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