Figure 4 also shows that the throughput of Clos and 2-dimensional grid networks does not scale linearly with network size under random traffic, the per node throughput is reduced as the network size increases. Figure 5 shows saturation network throughput for different sizes of Clos and 2-dimensional grid networks under random and systematic traffic for 64 byte packets. Systematic traffic involves fixed pairs of nodes sending to each other. For the grid this traffic pattern involves communication between nodes attached to nearest neighbour switches. The performance of the Clos under systematic traffic is independent of the choice of pairs. For random traffic, contention at the destinations and internally to the network reduces the network throughput compared to that obtained for systematic traffic, where there is no destination contention. The fall off in performance from systematic to random traffic is more pronounced for the grid than the Clos.
Figure 5: Throughput versus network size for Clos and grid networks
Figure 4: Per node throughput for 2-dimensional grid and Clos networks under
random traffic