Win CoAP: A Window-Based Congestion Control Approach for Burst Traffic in IoT Networks

Constrained Application Protocol (CoAP) is a widely used communication protocol in Internet of Things (IoT) networks. Congestion is a major concern in IoT networks because it affects the performance of applications and network reliability. Congestion control (CC) must be employed by the application since CoAP is based on User Datagram Protocol (UDP). IoT devices transfer a burst of data upon event detection. There are suitable features in Non-confirmable (NON) message type of CoAP for burst data transfer. The absence of a CC method for NON message type in CoAP hinders its applicability. OBSERVE defines static rate control for NON messages which is inappropriate for dynamic needs. The Block-wise Transfer also employs static rate control for NON message blocks, resulting in the same limitation. CoAP simple congestion control/advanced (COCOA) provides a dynamic CC method for the NON message type. COCOA employs reliable packets inside the NON message burst at regular intervals to capture network dynamics. Infringement of reliable packets adds up overhead and periodic monitoring caters to insufficient vigilance. In this paper, we propose a window-based dynamic congestion control method called Win CoAP to regulate the burst traffic based on the window of packets. The window size is additively increased on successful delivery and adaptively decreased otherwise. Win CoAP is implemented and validated against COCOA using the Cooja simulator in Contiki OS. We performed extensive simulations using various topologies and burst rates. Win CoAP outperforms COCOA in all analyzed scenarios and can improve the efficiency of event-based applications.