IoT Protocols for Wireless Communication: MQTT, CoAP, and 6LoWPAN

The Internet of Things (IoT) has witnessed an explosion of connected devices, each generating vast amounts of data. Effective and efficient communication between these devices is crucial for the success of IoT deployments. Wireless communication protocols play a pivotal role in enabling this connectivity. Three prominent protocols widely used in IoT applications are MQTT, CoAP, and 6LoWPAN.

MQTT (Message Queuing Telemetry Transport)

Probably the most widely adopted standard in the Industrial Internet of Things to date, Message Queuing Telemetry Transport is a lightweight publication/subscription type (pub/sub) messaging protocol. Designed for battery-powered devices, MQTT’s architecture is simple and lightweight, providing low power consumption for devices. Working on top of TCP/IP protocol, it has been especially designed for unreliable communication networks in order to respond to the problem of the growing number of small-sized cheap low-power objects that have made their appearance in the network in the recent years.

MQTT is based on subscriber, publisher and broker model. Within the model, the publisher’s task is to collect the data and send information to subscribers via the mediation layer which is the broker. The role of the broker, on the other hand, is to ensure security by cross-checking the authorization of publishers and subscribers. MQTT offers three modes of achieving this (Quality of Service), thanks to which the publisher has the possibility to define the quality of its message: 

Purpose: Primarily designed for machine-to-machine (M2M) communication, MQTT is a lightweight, publish-subscribe protocol.

Key Features:

Publish-Subscribe: Devices publish messages to topics, and subscribers receive messages for those topics.

Asynchronous Communication: Messages are stored in queues, ensuring delivery even if devices are offline.

Small Footprint: MQTT has a small message format and minimal overhead, making it suitable for resource-constrained devices.

Quality of Service (QoS): MQTT offers three QoS levels (at most once, at least once, exactly once) to guarantee message delivery.

CoAP (Constrained Application Protocol)

While the existing Internet infrastructure is freely available and usable for any IoT device, it often proves too heavy and power-consuming for most IoT use cases. Created by the IETF Constrained RESTful Environments working group and launched in 2013, Constrained 

Application Protocol (CoAP) was designed to translate the HTTP model so that it could be used in restrictive device and network environments.

Designed to address the needs of HTTP-based IoT systems, CoAP relies on the User Datagram Protocol (UDP) for establishing secure communication between endpoints. By allowing for broadcasting and multicasting, UDP is able to transmit data to multiple hosts while retaining communication speed and low bandwidth usage, which makes it a good match for wireless networks typically employed in resource-constrained M2M environments. Another thing that CoAP shares with HTTP is the RESTful architecture which supports a request/response interaction model between application endpoints. What is more, CoAP adopts the basic HTTP get, post, put and delete methods, thanks to which ambiguity can be avoided at the time of interaction between clients.

Purpose: Specifically designed for IoT devices with limited resources, CoAP is a RESTful protocol based on HTTP.

Key Features:

RESTful Architecture: CoAP uses HTTP-like methods (GET, PUT, POST, DELETE) for resource interactions.

Lightweight: CoAP is designed to be efficient and consume minimal resources, making it suitable for constrained devices.

UDP-Based: CoAP uses UDP for transport, reducing overhead compared to TCP.

Observational Relationships: CoAP allows devices to establish observational relationships, enabling notifications when resources change.

6LoWPAN (IPv6 over Low-Power Wireless Networks)

6LoWPAN has different features like, support for 64 bit or 16-bit addressing, targeted at low power networks including Bluetooth low energy, header compression for IPv base as well as for UDP headers, network auto configuration and neighbor discovery, support for multicast, unicast, and broadcast, supporting the concept of fragmentation. This makes 6LoWPAN a best suited protocol for IoT.

Purpose: 6LoWPAN adapts IPv6 for use in low-power, low-rate wireless networks, such as those found in IoT deployments.

Key Features:

IPv6 Compatibility: 6LoWPAN provides a seamless transition from IPv6 to constrained wireless networks.

Header Compression: 6LoWPAN employs header compression techniques to reduce packet size and overhead.

Fragmentation and Reassembly: 6LoWPAN can fragment large packets into smaller ones suitable for wireless networks and reassemble them at the receiving end.

Routing Protocols: 6LoWPAN supports various routing protocols, including RPL (Routing Protocol for Low-Power and Lossy Networks), for efficient packet delivery.

Conclusion

The selection of an IoT protocol depends on several factors, including:

Device Constraints: Consider the device’s processing power, memory, and battery life.

Communication Requirements: Evaluate the need for real-time communication, reliability, and security.

Network Topology: Assess the network’s size, structure, and routing requirements.

MQTT, CoAP, and 6LoWPAN offer distinct advantages for IoT communication. MQTT excels in M2M scenarios with it’s publish-subscribe model, CoAP is optimized for resource-constrained devices with its lightweight nature, and 6LoWPAN provides IPv6 compatibility for constrained wireless networks. By carefully considering these factors, developers can choose the most suitable protocol for their IoT applications.