Robustness of IoT Application Protocols to Network Impairments

Constrained Application Protocol (CoAP) and Message Queue Telemetry Transport (MQTT) are two IoT application layer protocols that are seeing increased attention and industry deployment. CoAP uses a request-response model and runs over UDP, while MQTT follows a publish-subscribe model running over TCP. For more constrained IoT devices, MQTTSensor Networks (MQTT-SN) provides a UDP-based transport between the sensor and an MQTT-SN gateway, while using TCP between that gateway and the MQTT broker. Quick UDP Internet Connections (QUIC) is a new protocol and although not originally designed for IoT devices, some design features such as reduced connection establishment time may be useful in an IoT environment. Each of these protocols seeks optimizations in features and implementation complexity based on application domains rather than having the full flexibility and adaptability of traditional transport protocols such as TCP. We investigate and analyze four protocols, namely, CoAP, MQTT, MQTT-SN and QUIC, to understand the overhead of obtaining data from an IoT device at a sink to potentially disseminate this data downstream. These constrained IoT devices often operate under challenging, varying network conditions, and it is important to understand the limitations of the protocols in such conditions. Thus, we evaluate the performance of these protocols under varying loss, delay and disruption conditions to identify the most effective environment for their operation and understand the limitations of their dynamic range. Results show that with non-confirmable CoAP a more adaptive wait timer is required; and a more streamlined QUIC protocol may be a potential alternative IoT protocol.