Experimental evaluation of alternative congestion control algorithms for Constrained Application Protocol (CoAP)

The wide range of IoT applications creates a demand for various types of communication. While both types of communication, unreliable and reliable, are important, it is crucial to extend scalable congestion control in the Internet to cover IoT communication also. Constrained Application Protocol (CoAP), a web transfer protocol for constrained devices and networks proposed by Internet Engineering Task Force (IETF), has optional reliability based on retransmission timeout (RTO) together with exponential RTO backoff to implement a simple basic congestion control mechanism. While the CoAP basic congestion control is simple, it is relatively conservative and potentially inefficient. Hence, there is a need for a more efficient congestion control alternative and CoCoA has been proposed as an option. In this paper we experimentally evaluate the efficiency and scalability of alternative congestion control algorithms for CoAP, including CoCoA and two TCP-based mechanisms. Our results show that while all the alternatives are scalable, they are more aggressive than the default congestion control mechanism of CoAP resulting in more efficient operation particularly at higher congestion level(s).