Protocols For IoT: MQTT, CoAP, and More

Devices in homes and factories speak with simple rules. Two popular choices are MQTT and CoAP, each with its own strengths. This guide explains how they work and how to pick the right protocol for your project.

MQTT: a light, brokered option MQTT uses a publish-subscribe model. Sensors publish messages to topics, and a central broker forwards them to subscribers. This setup fits telemetry, remote control, and apps that need reliable delivery in tight networks. QoS levels 0, 1, and 2 let you tune speed and reliability. Keep-alive pings help detect broken links, and TLS protects data in transit. When used well, MQTT scales from a few devices to thousands.

Best for: telemetry streams, device control, and deployments with a central broker.

Example: a temperature sensor publishes to home/livingroom/temperature with QoS 0.

CoAP: a compact REST-like approach CoAP runs over UDP and follows a simple request/response style. It also offers an Observe feature to stream updates and supports multicast for efficiency. This makes CoAP a good fit for constrained networks and local gateways. Security is provided with DTLS on top of UDP.

Best for: local sensing, smart devices talking to a gateway, and apps that fit REST patterns.

Example: a smart bulb exposes a resource at coap://gateway/lights/1 to turn on or off.

Other options and practical tips Beyond MQTT and CoAP, you can consider MQTT-SN for tiny devices on non-IP networks, HTTP/REST for cloud-friendly APIs, or DDS for real-time data sharing in larger systems.

  • MQTT-SN for very small devices
  • HTTP/REST in cloud scenarios
  • CoAP Observe for streaming data

Choosing a protocol depends on network type, power, latency, and security. Many projects use a gateway that translates between protocols: sensors use MQTT or CoAP locally, and the gateway forwards data to the cloud via MQTT or HTTP.

Example scenario: a smart thermostat uses CoAP to report status to a local hub, then the hub publishes the data to the cloud with MQTT.

Key ideas for success

  • Start with the network and device limits, then pick MQTT, CoAP, or a gateway strategy.
  • Plan security early: TLS for MQTT, DTLS for CoAP, strong authentication.
  • Keep configurations simple: predictable topics or resources aid maintenance and growth.

Key Takeaways

  • MQTT and CoAP cover most IoT needs; choose based on network, power, and deployment scale.
  • Security (TLS/DTLS, proper keys) should be designed from day one.
  • Gateways that translate between protocols simplify large, mixed deployments.