## 6 Methodology
This assisted in establishing the performance baseline necessary for establishing an overall comparison against the experimental measurements collected in the next stages. The RPL implementation was then examined under different single-attack scenarios in the following evaluation stage. For each setup, multiple attack scenarios were created considering different attack types and attacking nodes. Composite-attack scenarios were then considered in the third stage to run diverse attack scenarios with more than one attacking node. Two different nodes were configured to run the same attack in each scenario considering a different experimental setup at a time. For the final evaluation stage, the same procedure was then repeated except that the two attacking nodes simultaneously run different attack types in each scenario. During each stage and for each scenario, the attack is performed by different nodes of varying properties, in particular node position and neighbor count. This was deemed important for the effective investigation of the variant forms of potential RPL attacks and diverse security effects on RPL performance. The initiation of the attack was configured to be ten minutes after the simulation start time which was set to 50 min. Each simulation run was repeated ten times and the average of the collected results was obtained. The evaluation was based on different network measures which provide effective indications of various network performance parameters. These are categorized as follows:  
- QoS performance: Throughput, Packet Delivery Ratio (PDR), delay, and ETX. - Network stability: Beacon interval and Preferred Parent Change (PPC) rate. - Network overhead: DIO transmission rate and DAO transmission rate. - Energy efficiency: Consumed Energy (CE). The calculation of the average PDR was based on the ratio of the number of received data packets at the UDP server to the number of transmitted data packets at the UDP clients. The throughput was calculated by obtaining the average of the total number of data bits that were successfully transmitted per second. For the delay calculation, the required time for the transmitted data packets to be successfully received by the UDP server was collected and averaged. The calculation of the ETX was based on obtaining the average of the total number of transmissions and retransmissions required for the successful delivery of data packets. Figure 3: Overview of the Evaluation Methodology. The DIO and DAO transmission rates were calculated as the average number of DIO and DAO advertisements being transmitted across the network per minute, respectively. For the calculation of the PPC rate, the total number of changes made by all the nodes to their preferred parent during the entire time of the simulation was divided by the number of nodes and then the average was taken. Beacon interval is an important measure of topology stability as a small beacon interval indicates that more topology updates are being performed in the network. It is the average of the time between two consecutive beacons of all the RPL nodes. The data collected by the \"powertrace\" module were utilized to obtain the time spent in each more state (Transmit, Listen, CPU, and Low-power states). These were then multiplied by their corresponding current consumption levels and the power supply voltage as specified in [52]. The average of the total was then taken for the calculation of energy consumption.