In default, the RPL may induce network congestion problems under large-scale and dense networks. Most existing techniques make frequent changes in DODAG structure to avoid congestion issues, but they tend to throughput degradation. Recently, there has been no explicit mechanism to avoid network congestion in the RPL protocol. Most objective functions exploit a simple parent selection mechanism and avoid the DODAG building with bad link quality, large hop count, or large ETX. However, they tend to have a ping-pong effect, and the parent node is switched from one to another.
   If the ping-pong effect occurs on a node, it frequently modifies the DODAG structure. If a node changes its parent due to network congestion, but later, when congestion occurs on its new parent node, it must select its old parent node again if there are no other best candidates. As a result, it tends to poor relay and transmission. It is essential to address the congestion problem between parent nodes and child nodes and avoid the ping-pong effect on RPL, and design an efficient parent-change procedure using game theory strategy.