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Research: P Fat Trees

Link speeds in data center fabrics continue to climb, with 10g, 25g, 40g, and 100g widely available, and 400g promised in just a few short years. What isn’t so obvious is how these higher speeds are being reached. A 100g link, for instance, is really four 25g links bundled as a single link at the physical layer. If the optics are increasing in speed, and the processors are increasing in their ability to switch traffic, why are these higher speed links being built in this way? According to the paper under investigation today, the reason is the speed of the chips that serialize traffic from and deserialize traffic off the optical medium. The development of the Complementary metal–oxide–semiconductor, of CMOS, chips required to build ever faster optical interfaces seems to have stalled out at around 25g, which means faster speeds must be achieved by bundling multiple lower speed links.

Mellette, William M., Alex C. Snoeren, and George Porter. “P-FatTree: A Multi-Channel Datacenter Network Topology.” In Proceedings of the 15th ACM Workshop on Hot Topics in Networks, 78–84. HotNets ’16. New York, NY, USA: ACM, 2016. https://doi.org/10.1145/3005745.3005746.

The authors then point out that many data operators Continue reading

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