MQTT and CoAP: IoT Developers dilemma

IoT developers face a wide range of protocol choices in creating applications for the Internet of Things (IoT). These applications need to be able to consume information from a large number of devices. The choice of protocol depends on the use case and where the application will be staged in the software environment.

For machine communication, Two specialized, competing for protocols stand out: Message Queue Telemetry Transport (MQTT) and Constrained Application Protocol (CoAP). They’re each designed to be light-weight and to make cautious use of scarce community sources. Message Queuing Telemetry Transport (MQTT), is old by today’s standards since it dates back to 1999. And the second, Constrained Application Protocol (CoAP), is relatively new and gaining traction.

Both have makes use of, within the appropriate setting, however, the issue is that, as a result of relative infancy of IoT improvement, individuals don’t know precisely what these protocols are or when to make use of them.

MQTT and CoAP support communication from Internet-based resource-rich devices to IoT-based resource-constrained devices. Both CoAP and MQTT implement a lightweight application layer, leaving much of the error correction to message retries, simple reliability strategies, or reliance on more resource-rich devices for post-processing of raw end-node data.

MQTT (Message Queuing Telemetry Transport) Outline

MQTT stands for Message Queue Telemetry Transport. It is a publish/subscribe, extremely simple and lightweight messaging protocol, designed for constrained devices and low-bandwidth, high-latency or unreliable networks. The design principles are to minimize network bandwidth and device resource requirements whilst also attempting to ensure reliability and some degree of assurance of delivery. These principles also turn out to make the protocol ideal of the emerging “machine-to-machine” (M2M) or “Internet of Things” (IoT) world of connected devices, and for mobile applications where bandwidth and battery power are at a premium.

CoAP (Constrained Application Protocol) Outline

Constrained Application Protocol (CoAP) is an Internet Application Protocol for constrained devices. It enables those constrained devices to communicate with the wider Internet using similar protocols. CoAP 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 both joined by the Internet. CoAP is also being used via other mechanisms, such as SMS on mobile communication networks.

CoAP is an application layer protocol that is intended for use in resource-constrained internet devices, such as wireless sensor network nodes. CoAP is designed to easily translate to HTTP for simplified integration with the web, while also meeting specialized requirements such as multicast support, very low overhead, and simplicity. Multicast, low overhead, and simplicity are extremely important for the Internet of Things (IoT) and Machine-to-Machine (M2M) devices, which tend to be deeply embedded and have much less memory and power supply than traditional internet devices have.

Pros of MQTT over CoAP for IoT Developers

Both being open IoT standards, MQTT has certain pros over CoAP; and these are as follows:

Communication Model: MQTT has a highly decoupled publisher and subscriber model, whereas CoAP has an asynchronous communication model.

Maturity and Stability: MQTT is more matured and stable than CoAP.

Transport Layer Protocol: MQTT uses TCP and hence perfect for scenarios where connectivity is required all through, but CoAP uses UDP which ensures effective battery consumption through the connectionless model.

Packet Size: MQTT’s packet size is larger than that of CoAP.

Header: MQTT header is 2 bytes, whereas, CoAP header is 4 bytes.

A number of Message Types: MQTT allow 16 different types of messages, whereas, CoAP allows only 4 types.

Messaging: MQTT supports asynchronous messaging; whereas, CoAP supports both synchronous and asynchronous messaging.

Application Reliability: MQTT has a 3 level application reliability, whereas, CoAP has a 2 level application reliability.

Cons of MQTT over CoAP for IoT Developers

Both being open IoT standards, MQTT also has certain cons when compared to CoAP; and these are as follows:

Transmit Cycles: MQTT has a slower transmit cycle in comparison to CoAP.

RESTful: MQTT is not RESTful, whereas CoAP is RESTful.

Resource Discovery: MQTT works on flexible topic subscriptions; whereas CoAP has a stable resource discovery mechanism.

Encryption: MQTT is unencrypted, but can use TLS/SSL for security and encryption; whereas, CoAP works with DTLS (Data Transport Layer Security).


MQTT and CoAP are rapidly emerging as leading lightweight messaging protocols for the booming IoT market. Each protocol offers unique benefits, and each poses challenges and tradeoffs. Both protocols are being implemented for mesh-networking applications, in which lightweight end nodes are a necessary aspect of almost every network, and for gateway bridging logic to allow inter-standard communication. Contact us at for more detail.