Design and Evaluation of a Rate-Based Congestion Control Mechanism in CoAP for IoT Applications

CoAP is an application protocol that provides standardisedRESTful services for IoT devices. Since COAP messagesare encapsulated into UDP datagrams, COAP specificationprovides: i) optional reliability mechanisms through retransmissions,and ii) simple congestion control mechanisms based onretransmission timeouts. Recent studies have demonstrated thatthese congestion control schemes may significantly underperformwhen operating with bursty traffic. To address these limitations,in this paper we propose COAP-R, an alternative solution forregulating the sending rate of CoAP sources, which adopts arate-based approach for traffic control. Key features of COPARare: i) to leverage the tree-based routing structure of IoTnetworks to estimate the maximum throughput that can beobtained on the bottleneck link of every upward route, and ii)to perform in a distributed manner a max-min fair allocation ofavailable network capacity on the basis of estimated bottleneckbandwidths. The proposed approach is evaluated by means ofsimulations considering a scenario in which traffic is generatedin bursts, for instance as consequence of events detected bysensors. Our simulations demonstrate that the proposed approachensures a fair allocation of network resources, and leads to a 40%decrease of the data collection delays when compared to COAP.