COAP vs MQTT: Protocol Comparison

This article compares the Constrained Application Protocol (COAP) and Message Queue Telemetry Transport (MQTT) protocols, highlighting their key differences.

COAP Protocol

• Full Name: Constrained Application Protocol
• Specified in RFC 7252; an open IETF standard.
• A highly efficient RESTful protocol, easily proxied to/from HTTP.
• Utilizes an embedded web transfer protocol (coap://).
• Employs an asynchronous transaction model.
• Binds with UDP, offering reliability and multicast support.
• Uses familiar methods like GET, POST, PUT, and DELETE.
• URI support is included.
• Features a small, simple 4-byte header.
• Supports binding to UDP, SMS, and TCP.
• DTLS-based PSK, RPK, and certificate security.
• Utilizes a subset of MIME types and HTTP response codes.
• Includes a built-in discovery mechanism.

MQTT Protocol

Figure 1 depicts a simple broker-based MQTT protocol architecture. Key features include:

• Operates over TCP.
• Uses SSL/TLS for security.
• Defines various message types like CONNECT, PUBLISH, SUBSCRIBE, DISCONNECT, etc.
• Utilizes Username/Password within the ‘connect’ message.
• Payload agnostic, meaning it encrypts the payload regardless of its content.
• Typically uses port 1883.

COAP vs MQTT: Feature Comparison

The following table compares features of COAP and MQTT: