## 6 Simulation and Results
### Robustness Against Malicious Nodes  
In order to validate the blockchain based collaboration protocol against agents that intentionally or accidentally submit false information, recurring simulation experiments have been conducted. A blockchain platform agnostic consensus protocol (i.e., it can be implemented on any blockchain platform that provides smart contracts support e.g., Ethereum, Hyperledger, Corda) is proposed. As the protocol failure probability is independent of any specific implementation of the blockchain, we have conducted a simulation experiment to evaluate this probability. The goal was to estimate the probability that information of a path-message has been falsified, without this being noticed, under specific parameters such as:  
* malicious nodes population
* maximum path-message length  
Figure 5: DDoS detection for 10,000 IoT devices (all records).  
number of state checks committed at each agent  
For all scenarios, the population of nodes was set to 1000. The population of malicious nodes has been varied between 100, 200, and 300. The maximum path-message length has been set to values 10, 20, and 30. The number of checks committed at each agent have been gradually increased from 2 to 7. The resulting probabilities that malicious nodes can falsify information while going undetected are depicted in Tables 5-7 for all different parameters' values. Specifically, each table shows the results obtained for each one of the three different cases with respect to the population of malicious nodes.  
Figure 8: 300 malicious nodes.  
Figure 6: 100 malicious nodes.  
Figure 7: 200 malicious nodes.  
Our approach exhibits some qualitative advantages, with respect to other collaborative DDoS detection techniques, presented in literature. While conducting a quantitative comparison was not applicable, we opted for identifying the main characteristics that each one of the published methods demonstrates. The comparison has been made upon the following main points:  
* **Integrity:** Integrity is related to whether the proposed approach defends the integrity of the exchanged information and thus the validity of the detection results.
* **Availability:** Availability relates to the robustness of the proposed systems with respect to possible failures for a limited number of nodes. It describes the ability of proposed systems to remain available in such cases.
* **Responsiveness:** Responsiveness describes the ability of systems to timely detect possible attacks and produce corresponding alerts.
* **Scalability:** Scalability corresponds to whether the proposed systems can be scaled to protect larger gateways federations, without becoming inefficient.  
An analysis of eight previous research efforts (traditional ones and blockchain based ones) along with the approach presented herein has been conducted. According to this analysis, a comparison depicted in Table 8 has been attempted. While our approach is blockchain based, it adheres to layer 2 scaling paradigm [33] that enables building an efficient decentralized application, which does not suffer from low transaction rates and other related issues. Our methodology utilizes the state channels approach [34] and enables agents to collaborate in a safe and efficient way. Our system is the only one that can offer integrity, availability, and responsiveness guaranties and at the same time maintain these offerings even for relatively larger networks of nodes.