Distance-based congestion control mechanism for CoAP in IoT

Designing a scalable and efficient application layer protocols for the Internet of Things (IoT) environment is an ongoing problem. The constrained application protocol (CoAP) offering RESTful services for IoT devices implements a simple congestion control mechanism. This study proposes and analyses the distance-based congestion control CoAP (DCC-CoAP) for the current state of the network and accordingly calculate the future flow rate to handle congestion. The authors' main idea is to use the combination of distance between nodes and round trip time (RTT) measurements which limits the losses of CoAP messages, which is an efficient way to predict the network congestion. The user-defined options, i.e. retransmission counter and timestamp of sent and received CON and ACK messages are introduced for mapping CON to ACK and measure RTT. The comparative analysis of the DCC-CoAP with other congestion control mechanism like default CoAP, CoCoA+ is also highlighted in this study. With low additional computations, future RTT can be measured for avoiding congestion, and retransmission timeout varies with distance to avoid transaction losses. An algorithm with varying data rate has been used in homogeneous and mixed traffic to calculate the parameters in terms of packet delivery ratios, delay and retransmission count.