Comparing application layer protocols for the Internet of Things via experimentation

In this paper we compare the performance of three application layer protocols, that are Constrained Application Protocol (CoAP), WebSocket and Message Queuing Telemetry Transport (MQTT), in an Internet of Things (IoT) scenario. The three protocols have been implemented on the same low cost and low complexity hardware platform, suitable for IoT applications. The performance, in terms of protocol efficiency, strictly related to the overhead, and average Round Trip Time (RTT), were experimentally evaluated. In the considered scenario an IoT device was transmitting data to a server and waiting for replies. IEEE 802.11.b/g/n air interface was used for the communication between the IoT device and an Access Point (AP), connected to the final server. Two different settings have been considered: a local area network (LAN) configuration, where the AP and the server were in the same LAN; and a more realistic IoT configuration, where the AP was connected to a remote server via the Internet. Furthermore, in the IoT configuration, two types of Internet connection are considered: a connection established through a home router and another via cellular network. Results show that CoAP achieves the highest protocol efficiency and the lowest average RTT, closely followed by WebSocket. The performance of MQTT protocol strongly depend on the Quality of Service (QoS) profile. Changing the environment, from a LAN network to a realistic IoT scenario, does not significantly impact the protocol efficiency, but has a considerable influence on the average RTT, which increases by a factor of 2 or 3, depending on the protocol. Finally, we give some insights on the impact of routing through a cellular network on the system performance.