Evaluating the Impact of RPL Control Overhead on Network Performance

In IoT-LLN networks, RPL is a widely used routing protocol. RPL provides a lightweight and efficient way to route packets between devices in LLNs, creating a mesh network topology. For network bootstrapping and maintenance purposes, it periodically transmits DIO, DIS, DAO, and DAO-ACK packets. The lower-layer 6TiS CH protocol uses only a single minimal cell in a slotframe to transfer control messages. This increases the transmitting control messages' queue size. The packets in the transmission queue that have been waiting for a long time are removed from the queue. Network-associated nodes transfer control messages simultaneously, which causes the collision. Because of these issues, nodes waiting to join the network are not receiving the required control messages, and remain unassociated. Network-associated nodes must receive the DIO packets regularly to update the network topology information. If these nodes do not receive the DIO packets, it causes unnecessary parent-switching measures. Extensive simulations were done using Contiki-NG's COOJA simulator with varying network sizes, slotframe lengths, and hop sequences. Increased network size, slotframe lengths, and hop sequence caused more control message collisions, and parent-switching.