# Modeling Intelligent Control Switch IEC 61850 Based Substation Automation Communication
## 6 Results and Discussion
### Scenario I  
The buffer size of the switch is set to 2 Mbits and can be expressed as packets numbers as follows:  
\[2\;\text{Mbits}=\;\frac{2\times 10^{6}}{1518\times 8}\;=\;164\;\text{ packets} \tag{5}\]  
The simulation parameters that are used for this scenario are shown in Table 1. The number of the drop packets increase dramatically with time because the generation time of the events is faster than the processing time of the CPU, as shown in Figure 10. In turn, that will increase the time of the packets (events) in the FIFO buffer, and if the waiting time of the packets inside the buffer exceeded the dead-time tag, the buffer will drop those packets to accommodate the new coming packets. In other words, this traffic will cause delay in receiving the acknowledgement packets from the processor. After a certain period of time, if the acknowledgement packet is missed (not received), the packet is assumed to be lost or dropped. However, the capability of forwarding packets is collapsed after the period of 400 ms, as the switch becomes hardly able to cope with the network congestion, as shown in Table 2. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Inter-Event Time (ms)** & **Buffer Capacity** & **Service Time of Processor (ms)** \\ \hline
4 ms & 164 & 20 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Switch architecture parameters for one buffer. Figure 9: Switch controller architecture in SimEvents. However, increasing the buffer size was an option in this scenario. Accordingly, two buffers with identical capacity size (2 Mbits) were used to reduce the drop packets in the network. The parameter specifications of the two buffers scenario are tabulated in Table 3. Figure 11 shows the number of dropped packets by installing two buffers in the switch. By using two buffers, the number of the drop packets are minimized, because of providing more room to accommodate the incoming packets. For instance, the minimum number of drop packets occurred in the time of 200 ms was 72 packets, in contrast with the one buffer scenario, where the drop packets were 236 packets. On the other hand, the maximum number of drop packets occurred in the time of 1 s was 1622 packets. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Simulation Time** & **Number of Generated** & **Number of Drop** & **Percentage of Drop** \\  & **Packets from 8 Ports** & **Packets** & **Packets** \\ \hline
200 ms & 400 & 236 & 59\% \\
400 ms & 800 & 636 & 79\% \\
600 ms & 1200 & 1036 & 86.3\% \\
800 ms & 1600 & 1436 & 89.75\% \\
1 s & 2000 & 1822 & 91.1\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Drop packets percentage of single buffer. Figure 11: Number of drop packet using two buffers switch. Figure 10: Single buffer drop packets of the switch. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Inter-Event Time (ms)** & **Buffer Capacity** & **Service Time of Processor (ms)** \\ \hline
4 ms & \(2\times 164\) & 20 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Two buffers scenario parameter specifications. By analyzing these results, we concluded that the two buffers in the switch show a significant performance in reducing the number of the drop packets compared with the one buffer case, as shown in Table 4. The percentage of the drop packets between these two architectures is illustrated in Figure 12. As can be seen, the percentage of the drop packets in the time 200 ms of the two buffers is 18% whereas with the one buffer it is 41%. Furthermore, in the worst case at time 1 s, the two buffers reduced the drop packets to 81.1%, as compared with the one buffer, 91.1%. Figure 13 depicts the reduction percentage of the drop packets in both cases of scenario one. However, the system will collapse after exceeding the first second, due to severe congestion in the network. In addition, the number of drop packets increases during the network congestion. Accordingly, misbehaving congestion can directly affect the network reliability and security.