CoAP is a messaging protocol designed for tiny IoT devices that cannot run a full web stack. It works like a simplified version of HTTP but runs over UDP rather than TCP, which cuts connection overhead significantly. It is used when a device has under 100 KB of RAM and a very tight power budget.
In practice, MQTT dominates IoT cloud connectivity. CoAP appears most often at the device-to-gateway link layer in NB-IoT deployments.
- Runs over UDP – no three-way TCP handshake overhead
- Three reliability levels: fire-and-forget, acknowledged delivery, exactly-once
- Supports request-response and publish-subscribe patterns
- Better suited to NB-IoT and constrained LPWAN edge devices than to cloud connectivity