In basic, the RPL does not consider load balancing issues in the DODAG design process. The adjacent nodes to the root node suffer from congestion, and it tends to poor network performance. Most of the objective functions lack in considering the network traffic transmitted through parent nodes and the size of their subtrees in the parent selection process. It causes an unbalanced tree. Previously, many works have been suggested to tackle this problem by creating different routing metrics and objectives.
   The design of a reliable RPL protocol for IoT is a critical challenge due to the load imbalanced routing and constrained resources of the smart meter nodes. Recently, IoT smart applications allow huge and various numbers of smart meters. With the expansion of network size and nodes, the load imbalancing grows drastically. There are many issues in the provision of reliable RPL routing. By measuring the load imbalance factor and constructing the reliable DODAG structure, the RPL routing performance can be improved.