What is CoAP and MQTT? List out the key features of CoAP

CoAP (Constrained Application Protocol) and MQTT (Message Queuing Telemetry Transport) are both machine-to-machine (M2M) protocols used in the Internet of Things (IoT) technology.

CoAP is a web transfer protocol that is used in constrained environments. It is designed for use between devices on the same constrained network, between devices and general nodes on the Internet, and between devices on different constrained networks joined by the Internet.

Key features of CoAP include:

1. UDP Binding: CoAP is bound to UDP and optionally to Datagram Transport Layer Security (DTLS), which provides communication security.
2. Asynchronous Message Exchanges: CoAP follows the request/response model but also supports asynchronous communication.
3. Low Overhead: CoAP messages are small in size, which makes the protocol suitable for constrained environments.
4. URI and Content-type Support: CoAP supports URIs and Internet media types.
5. Simple Proxy and Caching Capabilities: CoAP has built-in support for proxy and caching, which is useful in a network of constrained nodes.
6. RESTful Protocol: CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments.

MQTT, on the other hand, is a publish/subscribe messaging protocol designed for lightweight M2M communications. It was designed to minimize network bandwidth and device resource requirements and to ensure reliability in case of intermittent network connections.