Grid, torus and Clos [5] network topologies have been studied. Figure 1 shows how a 400 node 2-dimensional grid network can be constructed. Each packet switch has 16 on-board connections to traffic nodes and four external connections to each of its four nearest neighbours.
Figure 1: : A 400 node 2-dimensional grid network
A 256 node 3-stage folded Clos network is shown in figure 2. The centre stage of the Clos consists of the switch modules described above. Each terminal stage switch connects with groups of two links to every switch in the centre stage.
Figure 2: : A 256 node Clos network
Grid style networks are easier to physically implement, since connections are all between adjacent switches, while Clos topologies have the constraint that each switch in the centre stage must be connected to every switch in the terminal stage.
The third topology which has been studied is the torus. A torus is similar to a grid which has its edge links wrapped around to connect to the opposite side of the network.