CoAP

CoAP is often described as “a lightweight HTTP over UDP.” That is not wrong, but it only helps you remember the name. It is not enough to judge an implementation, a packet capture, or a debugging session. The real difficulty is that CoAP is not facing browsers and cloud services. It is facing device networks with battery-powered nodes, small memory, lossy links, and constrained packet sizes. In that environment, the HTTP assumptions of reliable connections, long messages, and relatively rich endpoints often do not hold.