Fat tree

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A fat tree.

The fat tree network is a universal network for provably efficient communication.[1] It was invented by Charles E. Leiserson of the Massachusetts Institute of Technology in 1985.[1]

In a tree data structure, every branch has the same thickness, regardless of their place in the hierarchy—they are all "skinny" (skinny in this context means low-bandwidth). In a fat tree, branches nearer the top of the hierarchy are "fatter" (thicker) than branches further down the hierarchy. In a telecommunications network, the branches are data links; the varied thickness (bandwidth) of the data links allows for more efficient and technology-specific use.[citation needed]

Mesh topology and the "hypercube" topology of Connection Machines have communication requirements that follow a rigid algorithm, and cannot be tailored to specific packaging technologies.[citation needed]

Applications in supercomputers[edit]

Supercomputers that use a fat tree network[2] include the Tianhe-2,[3] the Meiko Scientific CS-2, Yellowstone, the Earth Simulator, the Cray X2, the Connection Machine CM-5, and various Altix supercomputers.[citation needed]

Mercury Computer Systems applied a variant of the fat tree topology—the hypertree network—to their multicomputers.[citation needed] In this architecture, 2 to 360 compute nodes are arranged in a circuit-switched fat tree network.[citation needed] Each node has local memory that can be mapped by any other node.[vague] Each node in this heterogeneous system could be an Intel i860, a PowerPC, or a group of three SHARC digital signal processors.[citation needed]

The fat tree network was particularly well suited to Fast Fourier transform computations, which customers used for such signal processing tasks as radar, sonar, and medical imaging.[citation needed]

Related topologies[edit]

In late August 2008, a team of computer scientists at UCSD published a scalable design for network architecture[4] that uses a topology inspired by the fat tree topology to realize networks that scale better than those of previous hierarchical networks. The architecture uses commodity switches that are cheaper and more power-efficient than high-end modular data center switches.

This topology is actually a special instance of a Clos network, rather than a fat-tree as described above. That is because the edges near the root are emulated by many links to separate parents instead of a single high-capacity link to a single parent. However, many authors continue to use the term in this way.


  1. ^ a b Charles E. Leiserson Fat-trees: universal networks for hardware-efficient supercomputing, IEEE Transactions on Computers, Vol. 34 , no. 10, Oct. 1985, pp. 892-901.
  2. ^ Yuefan Deng include "Applied Parallel Computing". 2013. p. 25
  3. ^ Dongarra, Jack (2013-06-03). "Visit to the National University for Defense Technology Changsha, China" (PDF). Netlib. Retrieved 2013-06-17. 
  4. ^ Al-Fares, Loukissas, Vahdat, A Scalable, Commodity Data Center Network Architecture, proceedings of SIGCOMM, 2008.

Further reading[edit]