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Protocols

HTTP

The web's request-response protocol, widely used by IoT devices that have enough resources to call a REST API, at the cost of verbose headers and no server push.

HTTP needs no introduction on the web, and many IoT devices simply use it: a gateway POSTs a batch of readings as JSON to a cloud endpoint, or a device polls a REST API for commands. Every language, cloud service and firewall understands it, TLS secures it, and debugging with ordinary web tools is easy.

The costs appear on constrained devices and in real-time use. Text headers add far more overhead than an MQTT frame, each request may require a new TCP and TLS handshake, and the model is strictly client initiated, so a server cannot push a command without the device polling or holding a long connection. HTTP/2 and HTTP/3 reduce some of that overhead, and WebSocket adds a bidirectional channel. For microcontrollers on small batteries, CoAP or MQTT is usually the better fit; see CoAP explained.

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