Disjoint Flows

We first look at the number of disjoint flows that can be supported by SSCH. All nodes in this experiment are in communication range of each other, and therefore two flows are considered disjoint if they do not share either endpoint. Ideally, SSCH should utilize the available bandwidth on all the channels on increasing the number of disjoint flows in the system. We evaluate this by varying the number of nodes in the network from 2 to 30 and introducing a flow between disjoint pairs of nodes -- the number of flows varies from 1 to 15.

Figure 9: Disjoint Flows: The throughput of each flow on increasing the number of flows.

Figure 10: Disjoint Flows: The system throughput on increasing the number of flows.

Figure 9 shows the average per-flow throughput, and Figure 10 shows the total utilized system throughput. IEEE 802.11a performs marginally better when there is just one flow in the network. When there is more than one flow, SSCH significantly outperforms IEEE 802.11a.

An increase in the number of flows decreases the per-flow throughput for both SSCH and IEEE 802.11a. However, the drop for IEEE 802.11a is much more significant. The drop for IEEE 802.11a is easily explained by Figure 10, which shows that the overall system throughput for IEEE 802.11a is approximately constant.

It may seem surprising that the SSCH system throughput has not stabilized at 13 times the throughput of a single flow by the time there are 13 flows. However, this can be attributed to SSCH's use of randomness to distribute flows across channels. These random choices do not lead to a perfectly balanced allocation, and therefore there is still unused spectrum even when there are 13 flows in the system, as shown by the continuing positive slope of the curve in Figure 9.