# Routing Protocols for Low Power and Lossy Networks in Internet of Things Applications
## 4 Enhanced Routing Solutions for Internet of Things Networks
### Energy Efficiency and QoS Support  
Reliability for data message sending and acceptable latency are requirements of all IoT applications. Due to power restrictions of various IoT devices, it is required that the packet sending task can be executed with the shortest energy expenditure possible. Therefore, a feasible QoS (Quality of Service) and reasonable energy consumption are considered as the most crucial features for all routing protocols for LLNs. Thus, in [87], [PERSON] et al. designed and developed a new cross-layer implementation of RPL, seeking to improve the data transmission reliability. The proposed solution, named RPLca+, is composed of two specialized libraries, the first for link quality estimation and the second for neighbor table management. The goal of the first library is to optimize the RPL operations through a hybrid link-monitoring framework to estimate the link quality with low overheads. Thus, the link quality library is composed of three methods of link quality estimation that are dynamically activated according to the information of the node and the characteristics of the link. The second library consists of a set of techniques for the management of neighbor tables. These techniques describe policies for insertion and replacement of entries in the RPL and IP tables seeking to manage better the neighbor's information considering the memory limitation of the network nodes. Furthermore, the proposed implementation provides a synchronization mechanism between the RPL and IP neighbor tables to improve the consistency of the stored information. This synchronization is done in a unidirectional way in which the inserts and replacements realized in the RPL table are reflected in the IP table, but are not contrary. Finally, it is important to note that the proposal is interoperable with the default RPL implementation since it does not change the RPL control message fields. A routing metric based on the transmission delay and remaining energy was proposed in [53], titled QoS_RPL (Quality of Service RPL). The authors used an Ant Colony Algorithm (ACO) [88] seeking to better fulfill the requirements of energetic efficiency and QoS in LLNs. During routing protocol functioning, the information about energy and delay are piggybacked on the control messages. This information is computed and updated by each node that receives a packet. Furthermore, the approach uses the pheromone (of ACO) as a metric in the process of route selection. The pheromone information is updated whenever a route is used to forward a data packet, realizing the process of path reinforcement. Thus, the most used paths tend to be better evaluated by the proposed approach. However, the authors also implemented negative reinforcement to prevent the use of suboptimal routes and allow the adoption of other possible, better paths. The QoS_RPL has presented the capacity of reducing the delay and consumed energy. Nonetheless, the packet delivery ratio has shown a slight reduction compared with RPL using the ETX metric. \begin{table}
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**Proposal** & **Base Protocol** & **Objectives** & **Description** & **Strengths** & **Weakness** & **Target Applications** \\ \hline LOADEng-CTP [82] & LOADEng & - Permit LOADEng efficiently support MP2P traffic & - Introduces proactive fronting the routing the  
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A novel proposal for improving the network energy balancing seeking to maximize the lifetime of nodes was presented in [49]. The approach is based on RPL, and the authors focused on the creation of a routing solution that considers the estimation of energy consumption. Using a mechanism to measure the Expected Lifetime (ELT) of nodes and exploring multipaths, the proposed approach tries to avoid the use of bottlenecks (nodes with less energy) and equalizes the power consumption.