# Internal Backpressure for Onboard Crospoint-Buffered Switches with Port Multiplexing
## 5 Simulation and Evaluation
### Stochastic Scenario
Because the BP mechanism is not implemented, the system cannot effectively control the rate of data traffic in the face of a high burst length, which leads to the overload of processing cells, thus affecting the throughput. In summary, the relationship between packet delay, the packet loss rate and the throughput rate and the degree of burst reveals the performance differences in different mechanisms in dealing with burst data. Among them, the BP load balance mechanism can effectively improve the throughput of the switching network and reduce the packet loss caused by traffic congestion. The overall performance of BP fine and BP load detection is similar. Then, the influence of unbalance factor \(\omega\) on system performance is analyzed. In this experiment, the length of the ON state is 1200 and the length of the OFF state is 800. We first analyze the effects of \(\omega\) on packet delay under different BP mechanisms. With the increase in \(\omega\), packet delay and the packet loss rate also show an increasing trend. As shown in Figure 9a, it can be found that in the case of the stochastic scenario, when the imbalance factor \(\omega\) increases, some nodes or links may become congestion points due to the aggravation of the non-uniformity of the traffic distribution, resulting in a longer transmission time of data packets in the network. However, it is worth noting that when the BP mechanism is introduced, the added BP strategy may temporarily slow down the sending speed of some streams when adjusting the system speed, so as to avoid traffic congestion and increase the overall packet delay compared to the no-BP mechanism. Among various BP mechanisms, BP load balance, BP fine and BP load detection mechanisms show lower packet delays, and compared to the no-BP structure, the packet delay is only increased by about 3.2-3.6%. This is because these three strategies can effectively balance the load in the system, avoid the excessive congestion of some nodes or links, and thus reduce the waiting time of packets. Secondly, we analyze the influence of \(\omega\) on the packet loss rate under different BP mechanisms. Figure 9b shows that an increase in imbalance factor \(\omega\) will lead to an increase in the packet loss rate. In the case of a high \(\omega\) value, its congestion and overload will be more serious, and packets are more likely to be dropped during transmission. However, after the introduction of the BP mechanism, especially for the BP load balance mechanism, the packet loss rate is significantly reduced compared to that of the no-BP mechanism. Under the stochastic scenario, when \(\omega\) reaches 0.5, the packet loss rate corresponding to the added BP load balance is reduced by 11.9% compared with no-BP. The performance of BP fine and BP load detection is similar. Under the stochastic scenario, the packet loss rate is reduced by about 4% and 5%, respectively, compared to the no-BP scheme. Finally, we analyze the effects of \(\omega\) on throughput under different BP mechanisms. Figure 9c illustrates that an increase in the value of \(\omega\) indicates an increase in the non-uniform traffic distribution; that is, some nodes or links are overloaded while others are relatively idle. By observing the actual simulation data, it can be found that under both deterministic and stochastic scenarios, the overall throughput rate of the system will show a downward trend with an increase in \(\omega\). This is because the non-uniform traffic distribution will cause some key nodes or links to become bottlenecks, limiting the processing capacity of the entire system. When evaluating the effect of different BP mechanisms, the BP load balance mechanism shows good performance in dealing with non-uniform traffic distribution; that is, when \(\omega\) is 0.5, its corresponding throughput rate can reach more than 80%. The performance of the BP fine and BP load detection mechanism is similar. Figure 8: (**a**) The effect of burst length on packet delay under different BP schemes.