# Routing Protocols for Mobile Internet of Things (IoT): A Survey on Challenges and Solutions
## 2 Background and Literature Review
### Literature Review  
We note that RPL was designed for static networks, so the introduction of mobility in the network has caused many issues in the functioning of RPL. Authors [28] have surveyed LLN under mobility. Authors have discussed various RPL mobility extensions such as DAG-based Multipath Routing (DMR) [41], Mobility Enhanced RPL (ME-RPL) [42], Co-RPL [43], Mobility Enhanced RPL [44], Modified RPL [45] for Vehicular ad hoc Networks (VANETS), and mRPL [46]. All these protocols supporting mobility properties are discussed such as their directions, metrics, constraints, and messages used for transmission. Furthermore, the discovery of the route, its maintenance and repair mechanism in terms of traffic types, messages trigger, and dissemination of all the protocols are discussed in detail. On the other hand, a survey on RPL enhancement focusing on topology, mobility, and security is done by authors [30]. Discussions are made on dealing with traffic patterns and improving the link quality estimation, in addition, the authors discuss single metric and composite metric OF is discussed. Following, the security threats in RPL such as black and grey hole attacks, sinkhole attacks, Identity-based attacks, wormhole attacks, version number attacks are discussed along with their mitigation. Similarly, various mobility detection methods such as ETX probing, corona mechanism, Kalman filter of Mobility Enhanced RPL [44] are described and  
Figure 2: DODAG Construction process [40]. results are mentioned in terms of responsiveness and energy consumption. Another survey on attacks in RPL was performed by authors [47]. Various RPL attacks such as selective forwarding attack, Sybil attack, Clone ID attack, black hole attack, Wormhole attack, Denial of Service attack, alteration, sinkhole attack, and spoofing attack are discussed and their effects on network parameters are discussed. Methods to counter these attacks were mentioned, such as IDS solution, heartbeat protocol, the global and local repair mechanism of RPL. One more survey was done by authors [48] on security attacks and secure routing protocols in RPL. Classification of attacks was done namely attacks against resources including direct attacks namely flooding attacks, routing table overhead attacks, and indirect attacks comprising an increase in rank attacks, DAG inconsistency attacks, and attacks on the version number. Another classification was made on attacks in topology and attacks on traffic. Various attacks description was given and protocols which can address these attacks were mentioned, such as TRAIL, Markel tree authentication. Another survey performed on RPL is by authors [49]. Different communication paradigms in RPL such as Multi-Point-to-Point, Point-To-Multi-Point, Point-To-Point were discussed. Following, the focus was made on several mechanisms for network management such as fault tolerance, QoS-aware routing, and security in RPL are described. Later RPL performance evaluation with respect to power consumption, packet delay, and packet loss was done by performing simulations. Authors [50] have surveyed various RPL protocols supported by the Contiki operating system. Protocols such as Contiki RPL, GT-RPL, SSCF, Tiny RPL, and DT-RPL are analyzed by performance metrics followed by these protocols; future research directions were also proposed. In addition, routing attacks were studied and security mechanisms proposed to be used in the Contiki network layer are discussed. We note that most of the researchers have done a survey on security attacks on RPL and few of them have performed a survey on evaluating RPL performance under mobility of IoT devices. The authors [28; 30] have proposed solutions for supporting node mobility in RPL but authors failed to classify the solutions into different categories. In addition, the authors have not discussed the strengths, weaknesses, and working principles of each solution. In this research, several issues faced by RPL under mobility are presented and various solutions to those issues are discussed.