# Trust and Mobility-Based Protocol for Secure Routing in Internet of Things
## 3 Related Work
### Trust-Based Security Solutions  
Trust-based approaches and trust modelling are feasible methods to countermeasure the security attacks in IoT networks. To make the system more reliable and trustworthy for users, trust modelling can be applied to the development of functional measures. Trust embedded in IoT networks and routing is significant for stability and security. This can enable network maintenance, particularly with a rise in the number of connected devices. In IoT networks and routing, trust-based approaches have not been thoroughly explored and pose a vital field of research, especially from the perspective of security. Additionally, the importance of trust models for IoT network and routing security, as explained by [14], indicates their implications. The measurements of trust can be based on device or application and depend on the purpose and idea of the system [53]. Ref. [54] mentions that the trust metrics are based on either social or quality-of-service (QoS) properties. Correspondingly, nodes' mobility is an important aspect to be considered while selecting and analysing the trust metrics in IoT. In a mobile IoT environment, contextual information involves device location as one of the metric categories. For instance, devices with known locations are more trustworthy than others. Similarly, the mobility-based metrics are helpful in trust computations. Thisconcept is used more commonly in the case of VANETs. For example, in the trust model proposed by [55], time, location, and distance are considered important trust metrics. A trust-based mechanism for RPL security, SecTrust [25], is proposed. It specifies its own OF to establish trust in RPL. The network efficiency and packet loss rate are evaluated considering the Rank and Sybil attacks. Similarly, a SecTrust revision is proposed [56] to evaluate Blackhole attacks. In addition, refs. [27; 57] proposed a trust model for IoT, using QoS, quality-of-P2P-communication (QPC), and contextual knowledge for trust evaluation. The model is evaluated for Rank, Blackhole, and Sybil attacks in RPL. A trust-aware and cooperative routing protocol, MRTS, is proposed by [26]. Trust calculation in MRTS is carried out by adding ETX metric. Their proposed approach is effective for packet delivery ratio (PDR), energy consumption, throughput, and node rank change. However, MRTS uses an IDS approach for attack detection and isolation, which is computationally expensive and requires a hardware security chip embedded in each node [58]. These approaches have a common research gap regarding the lack of consideration for mobility of nodes. Only [27] considers the mobility of nodes, but their evaluation is limited to sender nodes' mobility. Ref. [59] presents a security protocol for trust management in IoT networks, but its focus is not on the routing attacks and nodes' mobility. The methods proposed in [46] insert a dummy packet in the network to mitigate the packet dropping attacks. The insertion of dummy packets creates high overhead, and this approach does not consider RPL-specific attacks. Thus, the existing trust models are not adequate from the perspective of mobile IoT environments. For attack detection and defence against malicious nodes, the trust-based approach is easily adaptable to IoT scenarios. It is also scalable at any node density level and can cope well with network size growth or shrinkage [60]. Moreover, it is important to select adequate trust metrics for an efficient security approach for RPL-based IoT. In the existing literature, the trust models proposed for routing security in IoT lack some features, such as consideration of IoT node mobility, heterogeneity in IoT environments, adaptability to IoT networks and routing, and the consideration of RPL-specific attacks. Furthermore, trust dynamics and network performance are not taken into account in some of the presented solutions. However, some of them focus solely on network performance and routing behaviour, neglecting to address routing attacks and security concerns.