Skip to content
Protocols

CoAP

The Constrained Application Protocol, an IETF standard that brings REST-style request and response to tiny devices over UDP with very small headers.

CoAP, defined in RFC 7252 by the IETF, gives constrained devices the familiar web model: GET, PUT, POST and DELETE on URIs, response codes, content types, caching and proxies that can translate to and from HTTP. It runs over UDP with a four-byte header, adds its own optional reliability through confirmable messages, and supports observe, a mechanism for a client to subscribe to changes in a resource.

Because it is request and response rather than broker based, CoAP suits device management and direct device-to-device calls, and it is the transport under LwM2M. Security comes from DTLS rather than TLS. The trade-off against MQTT is the absence of a central hub for fan-out and buffering, and the fact that UDP passes through NATs and firewalls less predictably. CoAP explained covers the details.

Part of the IoT Glossary. Spotted an error or a missing term? Tell us.