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ycp

To quickly recap the point of a fat tree: For a normal tree, the H-Tree for example, there is bottleneck (a low bisection bandwidth) through the center node. Basically, if you cut the tree in half, there is only one link between the two halves. To make patch this up and make trees more realistic an option, the fat tree has thicker lines between higher links in tree, representing higher bandwidth. Thus, cutting the Fat Tree in half, will still result in only having one line between the two halves, but that one line will have a higher bandwidth.

uhkiv

Note that the implementation of the fat link between the two roots can vary. For example, the fat link can be implemented by having another set of routers on top of the roots shown here that link to them, and having links from the roots to them to provide higher bandwidth (I believe this was shown in class?). I would also think that indeed having a link with more bandwidth as the picture suggests would be a valid implementation as well.