Highlighting Some Shortcomings of the CoCoA+ Congestion Control Algorithm

The Constrained Application Protocol (CoAP) is expected to be the de-facto standard application protocol for the future Internet of Things (IoT). Future IoT devices will be interconnected by networks characterized by high packet error rates and low throughput. For this reason, congestion control will be crucial to ensure proper and timed communication in these networks. In this context, CoCoA+, an advanced congestion control for CoAP, is currently under standardization. In this work, we present a critical analysis of CoCoA+ by means of simulation, and highlight some of its shortcomings and pitfalls. We considered a typical scenario with an increasing traffic load due to an increasing number of CoAP requests. We show how CoCoA+ may be characterized by many spurious retransmissions at some offered loads close to congestion.