CoAP vs. MQTT-SN: Comparison and Performance Evaluation in Publish-Subscribe Environments

The Publish/Subscribe communication pattern has proved to be particularly tailored to the IoT world, with the MQTT protocol being the nowadays standard de-facto for IoT applications. Request/response protocols explicitly designed for the IoT, such as CoAP, have been revised to support also Publish/Subscribe. The purpose of this paper is to perform a comparison between two protocols: MQTT-SN, the version of MQTT thought specifically for sensor networks, and CoAP in its Pub/Sub version, defined in a recent IETF draft. Both protocols are Pub/Sub in nature and based on UDP at the transport layer, allowing therefore a fair comparison of their functionalities. We propose a open-source implementation of the CoAP Pub/Sub version and we compare the two protocols: first from a theoretical perspective and, then, in a simulated environment characterized by varying number of clients and network conditions. Results show that CoAP represents a valid alternative to MQTT-SN for publish-subscribe environments; in particular, CoAP results being the best choice for highly dynamic networks.