## 4 Performance Experiments
### Throughput and Message Loss Ratio  
To validate the performance of the dual plane architecture, we compared the performance of the proposed system with that of the single plane IoT system developed in our previous research, which processes both user-data and signaling messages in one plane and does not apply the DPDK. For this test, two comparison systems were run on the same hardware condition listed in Table 3. The test messages used in the experiments are user-data messages sent from three types of PHDs to the MN-CSE. For the test, we use PHD simulators to generate large amounts of messages. Each simulator sends its measurements and the MN-CSE forwards the messages to the IN-CSE. First, we conducted a throughput test which indicates the fastest forwarding rate without packet loss at a line speed of 1 Gbps. The throughput was measured repeatedly, while increasing the size of the messages. The result of the evaluation is described in Figure 4. According to Figure 4, the dual plane IoT system outperforms the single plane IoT system considerably, by as much as 250%, 270%, 210%, 190% and 58% for each message size. This result shows that the dual plane architecture proposed in this paper can forward user-data messages at a line speed with messages of 512 bytes or more while the single plane IoT system shows a 34% line rate. Furthermore, it shows much better performance than the single plane IoT system with small size messages. As the benchmark result shows, it is obvious that the proposed architecture is more suited to an IoT environment, in which small messages have to be exchanged very frequently. Next, we measured the message loss rates of each system at a line speed of 1 Gbps while increasing the size of the messages. In a typical network system, NIC line rate represents theoretical performance; actual NIC performance is lower than the theoretical performance due to message processing and packet IO overheads. Therefore, a certain number of messages should be delayed in the receiving queue. A system or gateway that receives messages at too high a rate may experience a full queue. Since the number of newly incoming messages is larger than amount of processed and sent messages, the number of messages delayed in the receiving queue (waiting to be processed and forwarded) will continuously increase. Because a network system has finite buffer memory to hold the queue and cannot expand the buffer memory indefinitely, queue congestion occurs, and the queue becomes full as a result [37]. In this case, the system has no other option than to simply discard excess packets (i.e., packet loss). Therefore, comparison of the packet loss rate provides us with information regarding which architecture is more suitable for a network node. The results of the evaluation are shown in Figure 5. As the result of the evaluation shows, message loss occurs in both single and dual architectures. Figure 3: Overhead ratio. However, the amount of message loss in the dual plane system is much less than in the single plane system, since the dual plane system can handle data messages much faster than the single plane system. The loss rate of the single plane IoT system with a 64-byte message is 72.23%, while that of dual plane is only 9.66%. In addition, a dual plane IoT system does not drop any received messages 512 bytes or more, while the single plane IoT system still drops some of the received messages. This result is due to the high IO performance of DPDK, and the independent message processing approach of the dual plane architecture. Finally, we compared the throughput performance of two different single plane IoT systems: a single plane IoT system without and with DPDK. The former receives and sends messages through the kernel network stack instead of using DPDK, and the latter bypasses the kernel network stack using DPDK. In the test, the throughput was measured with a fixed packet size of 512 bytes, while increasing the number of control messages from 1000 to 40,000.