RFC7252

RFC 7252, titled "The Constrained Application Protocol (CoAP)", is an internet standard that defines a web transfer protocol for use in an Internet of Things (IoT) environment. CoAP is designed to be a lightweight, low-overhead protocol that can operate on resource-constrained devices and networks. It shares many similarities with the Hypertext Transfer Protocol (HTTP) but is optimized for environments where devices have limited processing power, memory, and bandwidth.

The protocol uses a request/response model, similar to HTTP, and supports methods such as GET, POST, PUT, and DELETE. However, CoAP is designed to run over UDP, a connectionless protocol, which reduces overhead compared to HTTP's reliance on TCP. To ensure reliability in the absence of TCP's built-in guarantees, CoAP incorporates mechanisms for message acknowledgment and retransmission. It also defines options for content format negotiation, observe functionality (allowing clients to subscribe to changes in resources), and block-wise transfers for larger payloads.

CoAP is particularly well-suited for machine-to-machine (M2M) communication and is used in various IoT applications, including smart home devices, industrial automation, and environmental monitoring. Its design prioritizes simplicity and efficiency, making it a practical choice for devices that cannot support the full complexity of HTTP.