Why MQTT Is Important for Edge-to-cloud Connectivity
The Industrial Internet of Things (IIoT) is enabling digital transformation by connecting Operation Technology (OT) machines and devices to Information Technology (IT) systems, thus adding new value and bringing new benefits to many different industries, such as smart manufacturing, smart energy, and many more.
Amidst this digital transformation revolution, connectivity is playing a crucial role as IIoT applications require more bandwidth to integrate edge devices with cloud applications. Furthermore, engineers need to learn how to connect hundred thousands of devices that use a variety of different industrial protocols, as well as manage security concerns as more and more devices are being connected to the Internet.
A number of new connectivity technologies have emerged to keep pace with new developments in the IIoT. For example, Time-Sensitive Network (TSN) has been developed to enable the transmission of deterministic data over standard Ethernet networks. OPC UA focuses on unifying the variety of languages between different devices on shop floors. Most significantly, Message Queuing Telemetry Transport (MQTT) has come forth as the preferred publish-and-subscribe messaging protocol to enable machine-to-machine communication or bring data from the edge into cloud and enterprise systems.
The Emergence of MQTT
When an automation engineer connects sensors, machines, or edge computers to the cloud for data collection and data analysis, the common communication protocol through the Internet is HTTP/HTTPs. This protocol is widely used in computer networks and the Internet. However, HTTP/HTTPs is a so-called request-response pattern protocol that requires both the client and server to be online at the same time to ensure that data is transmitted and received successfully. For IIoT applications, such as solar farms, water and wastewater management plants, and oil pipelines, it might be impossible for devices to maintain a strong enough connection with the network to receive the required data. Therefore, this request-response pattern is not suitable for such applications.
MQTT was first developed in 1999 by IBM and Cirrus Link and was accepted as an ISO standard in 2013. It is designed to transmit data from oil pipelines in the desert, so it needs bandwidth-efficient, lightweight, and low battery consumption. MQTT’s publish-subscribe pattern is tailor-made for situations where devices are not guaranteed to be connected to the network at the same time.
Compared with HTTP/HTTPs, MQTT uses publish-subscribe pattern (see figure below) to exchange messages. As illustrated in the figure, an MQTT system comprises one broker and several clients, where clients can either be publishers or subscribers. Publishers send data to the broker in the form of MQTT packets, which consist of a topic and a payload. The broker then distributes the data to subscribers based on the topics they have expressed interest in.
Other Benefits of MQTT
Compared with other protocols, MQTT also brings other advantages that make it a perfect match for IoT applications. The advantages include:
MQTT clients only publish data to the broker when certain conditions are met (e.g., a warning signal could indicate that the temperature of a particular device is too high). This event-driven capability saves energy or battery consumption on the device itself. It also saves money since only one-way communication is needed to complete data transmissions.
With this publish-subscribe behavior, machines only need to establish a connection with the broker instead of connecting directly to each other, saving a significant amount of time on handshaking. Since one broker is dedicated to handling the communication between all the machines, data transmission is more reliable.
Security is always the biggest concern when we connect devices to the Internet. MQTT broker supports account names and passwords to prevent unauthorized clients from connecting to the broker to subscribe to topics. MQTT also supports TLS encryption for data transmissions to greatly minimize the chance that data will get hacked during transmissions.
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