Performance study of the constrained application protocol in lossy networks

The Constrained Application Protocol (CoAP) is a lightweight core protocol used for communication between devices in the Internet-of-Things. The CoAP standard defines a simple congestion control mechanism based mainly on retransmissions after timeouts and a binary exponential back-off procedure with randomization. However, the default parameters of this mechanism can affect negatively the efficiency of the protocol in severe network conditions. In this paper, we propose new exact mathematical models to study the performance of CoAP in lossy networks. This study provides useful insights in order to tune CoAP parameters and also highlights CoAP properties and limitations so that future better mechanisms can be designed adequately.