# Routing Protocols for Low Power and Lossy Networks in Internet of Things Applications
## 4 Enhanced Routing Solutions for Internet of Things Networks
### RPL Objective Functions  
The RPL protocol uses objective functions to determine the network topology and the process of preferred parent selection. In its RFC document, RPL does not mandate the use of a specific OF and suggests that this choice should be made based on the application requirements. However, IETF has defined two initial OFs, OF0 and MRHOF, which can attend to simple routing requirements. Nonetheless, these OFs can present some limitations, e.g., they do not consider energy information during route selection. Thus, several works have proposed alternative OFs for RPL considering different routing metrics. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Proposal** & **Base Protocol** & **Objectives** & **Description** & **Strengths** & **Weaknesses** & **Target Applications** \\ \hline RPLCa+ [87] & RPL & - Improves the reliability of data delivery in RPL & - Improves the reliability of data taking management & - Cross-layer approach for link quality estimation and routing table management & - Provides the policies for the management of routing tables improves the packet delivery rate & - Persons implementation overhead increases the energy consumption & - Advanced metering infrastructure \\ \hline QoS\_RPL[53] & RPL & - Improves energy efficiency and QoS in LINs & - Composite routing metric based on delay, remaining energy, and pheromomes (ACO) & - Reduces the delay and energy consumption & - Decreased the packet delivery rate & - Can Provoise a disturbance in the load balancing & - Not specified the load balancing increases the control & - Not specified \\ \hline multiEILT-RPL[49] & RPL & - Maximizes the network lifetime and creates an energy energy balanced topology & - Computes the expected node lifetime and uses a multipath RFL modification & - Increases the node lifetime and prevents the early necessity of routing topology reconfiguration & - Increase the memory usage modifies the structure of default RFL control messages & - Not specified \\ \hline ERGID[89] & SPEED & - Provides low delay and load balancing for emergency response applications & - Uses the estimation of global delay of nodes and information about the energy consumption & - Choose routes based on global information about the global information about the energy consumption & - Uses a high number of control messages to maintain delay information updated packet loss rate without increasing energy consumption & - Uses a high number of control messages to maintain delay information updated packet loss rate without increasing energy consumption & - Employency response applications and routing table update & - Employency response applications \\ \hline LOADng+ NDM[90] & LOADng & - Reduces problems caused by local failures in the nodes or radio interferences & - Creates a set of alternative neighbor disjoint routes & - The main scheme can be adapted for different routing protocols & - Does not consider any information about energy consumption or link quality in the route selection & - Does not consider any information about energy consumption or link quality in the route selection & - Not specified \\ \hline \hline \multirow{2}{*}{FQA + FSRRC[91]} & \multirow{2}{*}{DD} & - Improves QoS and energy efficiency in IoT networks & - Designs a new tag-reading protocol integrated with a fuzzy system-based route classifier that uses four routing metrics to define the path quality & - Consistency IoT devices equipped with RFID readers & - The approach is based on fuzzy systems that can be complex for IoT devices & - The approach is based on fuzzy systems that can be complex for IoT devices & - Asplifications that exploit RFID and LIN devices & - Applications that exploit RFID and LIN devices \\ \hline \end{tabular}
\end{table} 
Table 5: Comparison among studied approaches for energy efficiency and QoS support. The Energy-Aware Objective Function (EAOF) was introduced in [96].