# Performance Analysis of Internet of Vehicles Mesh Networks Based on Actual Switch Models
## 5 Simulation Results
### Network Performance for Different QoS  
This subsection focuses on simulating the relationship between task traffic and network performance metrics. The QoS in the simulation graph represents the traffic of the node initiating the task at each moment. Figure 8 explores the fluctuation of network packet loss rate and task arrival rate under different QoS.  
As shown in Figure 8, initially, the network traffic and task arrival rate exhibit an increasing trend and then change dynamically. This is because under the task QoS and link rate constraints, tasks usually cannot be sent all at once. Consequently, upon the initiation of a task, network traffic experiences a continuous ascent. Subsequently, task transmission persists over time, with new tasks entering the network periodically, thereby the traffic distribution on nodes and links is in a dynamic process.  
When the QoS is 20 Mbps, the average packet loss rate is approximately 3% and the task arrival rate is around 80%. As the QoS increases, the packet loss rate gradually rises, while the task arrival rate declines. This trend stems from the escalating network ingress traffic resulting in the expansion of the node's cache queue. When the cache queue is full, packet loss occurs. Moreover, the higher the QoS is, the easier it is for the cache queue to fill up. In addition, under the same QoS setting, the declining task arrival rate can be attributed to the movement of vehicles causing link disruptions with the change in time, and most of the packets accumulate at the nodes because they cannot be transmitted according to the original routes when the port routing table is not updated. Simultaneously, the reduction in task arrival rate is further influenced by continuous task initiation leading to heightened network traffic over time.  
Figure 9 simulates the variations in the other three metrics with QoS. At lower QoS levels, both the link load ratio and total network traffic exhibit an upward trend with QoS. This is due to the fact that when the QoS is small, the network loses fewer packets, and the total traffic increases with the increase in ingress QoS. Simultaneously, the number of packets forwarded by the nodes increases with the rise in the total number of packets, and thus the link load rate rises. However, at higher QoS settings, the discrepancy between the link load rate and the total network traffic diminishes significantly. This occurrence results from the heightened network packet loss rates in this situation, leading to a small disparity between the number of packets that the nodes can forward after packet loss and the total number of packets carried by the network.  
Figure 8: Packet loss rate and task arrival rate for different QoS.  
For the node load rate, the trend is similar to the other two indicators under higher QoS conditions. The reason for this is the same as analyzed above when a higher degree of packet loss occurs for both vehicles and RSUs. Conversely, under lower QoS settings, the trend in the early stage is similar to the other two indicators. However, in the later stage, the cache queue of vehicle nodes tends to reach capacity due to their smaller cache size compared to RSUs. At this time, a majority of packet losses in the network occur at vehicle nodes, while the RSUs are minimally affected. Therefore, the increased total network traffic primarily originates from RSUs, while the increased packet loss from the vehicles results in a decreased overall node load rate in the network at QoS = 60 Mbps compared to QoS = 20 Mbps.