## 7 Results
Although it had less overall impact than VN attacks, Tables 4 and 5 show that the rank attacks led to 9-25% less PDR and throughput in addition to 28-90% additional delay and ETX considering all three experimental setups. The rank attacks also led to noticeable increases in the PPC rate and energy consumption as shown in Figure 4a,b and Figure 8a,b, respectively. However, the WP attack came next to the VN attacks when it comes to the impact on network overhead. It resulted in higher control packet transmissions than in the cases of rank and replay attacks. Compared to these attacks, 15-53% additional transmissions were incurred by the WP attacks in single- and composite-attack scenarios considering all three setups as presented in Figure 6a,b and Figure 7a,b. The least effective routing attack among those under consideration was the replay attack considering single- and composite-attack scenarios in all the setups. It resulted in a less adverse impact on QoS performance by up to 7% and lower control traffic by up to 22 control packets per minute compared to the other attacks. The replay attacks also had a less adverse effect on network stability and energy consumption but with very close results to those of the WP attacks. Nevertheless, the replay attacks can still be regarded as harmful RPL routing attacks with noticeable adverse impacts on network overhead and stability, particularly in composite-attack scenarios and large-scale setups. In hybrid-attack scenarios, the results show that the combination of VN-rank attacks had the most significant impact on QoS performance and network stability considering all the setups. These attacks incurred pronounced degradation of the QoS performance with more than 19% reductions in PDR and throughput in addition to more than 48% increases in delay and ETX as indicated in Table 6. The PPC rate increased to 38 changes/node on average and the consumed energy reached a considerably high figure of almost 20,000 joules during the hybrid VN-rank attacks as shown in Figures 4c and 8c, respectively. However, combining the VN and WP attacks led to close results with a higher impact on network overhead. For example, Figures 6c and 7c show that this combination incurred 791 control packets per minute in S3, adding more than 16 control packets per minute compared to the results of the hybrid VN-rank attacks. Considering all the setups, it can be seen that combining the VN attack with either rank or WP attacks yields the most effective attack strategies to target standard RPL networks. Next to these hybrid attacks in the order of effectiveness were the combinations of VN and replay attacks as well as rank and WP attacks. These attacks resulted in degraded QoS performance with more than 13% reductions in PDR and throughput in addition to more than 34% increases in delay and ETX as indicated in Table 6. They also incurred high network overhead with the transmission of up to 791 control packets per minute as shown in Figures 6c and 7c. Figure 8c shows that they caused high energy consumption of up to 17,262 joules. However, these two combinations of hybrid attacks were less effective than the composite VN attacks, particularly for network overhead and energy consumption. Figures 6b and 7b show that composite VN attacks resulted in up to 19 additional control packets per minute and Figure 8b shows that they led to up to 1191 additional joules. Regarding QoS performance and network stability, composite VN attacks still had a higher impact but with very close results to the aforementioned hybrid attacks. Similarly, the results also show that the composite rank and composite WP attacks were more effective than some of the hybrid attacks. For example, the composite rank attack resulted in more degraded QoS measurements and higher energy consumption than the hybrid VN-replay, rank-replay, and WP-replay attacks. The composite WP attack also incurred higher network overhead compared to the hybrid WP-replay and rank-replay attacks.