Fat-tree Fat Tree Exchange Network

The network bandwidth is not convergent under the thick tree structure
In the traditional tree network topology, the bandwidth is convergent by layer, and the network bandwidth at the root is much smaller than the sum of all the bandwidth of each leaf.
And the Fat Tree network is more like the real tree, the more the root, the thicker the branches, that is: from the leaves to the root, network bandwidth does not converge. This is the basis for a fat tree architecture to support a nonblocking network.
Figure 2 Comparison of logical topologies between a fat tree network and a traditional network
As shown, in order to achieve no convergence of network bandwidth, each node in the Fat Tree network (except for the root node) needs to ensure that the upstream bandwidth and downlink bandwidth are equal, and each node must provide the ability of wire-speed forwarding to the access bandwidth.
is an example of a physical structure of a 2-yuan 4-storey fat tree (2 yuan: each leaf switch is connected to 2 terminals; 4 Layers: The switches in the network are divided into 4 tiers). All of the physical switches it uses are identical.

Figure 3 Physical topology instance of the Fat Tree architecture
As can be seen, each leaf node is a physical switch, access to 2 terminals; the inner node of the upper layer is composed of 2 physical switches, each logical node is composed of 4 physical switches, and the root node has 8 physical switches.
　　

Thus, the downlink bandwidth and upstream bandwidth are exactly the same for any one logical node. This ensures that the entire network bandwidth is not convergent.

Fat-tree Fat Tree Exchange Network