categories. One category is the publish-andsubscribe (pub-sub) protocols which connect and publish data to a topic on an intermediary broker. MQTT, AMQP, DDS, and XMPP are examples of pub-sub protocols. The other category is the poll-response or client-server protocols, such as Allen- Bradley, Omron, and Modbus, in which clients continually connect to the server and make requests to determine if any data has changed. Of the two categories, which one should your team choose? To effectively build a highly scalable solution with a high level of efficiency, it is best to adopt a publishsubscribe communication protocol. Rather than connecting applications directly to devices, publish-subscribe protocols decouple devices and allow applications to connect to middleware. Through middleware, the system can connect any application that requires data from any device without placing any heavy demands on the network. From the list of available protocols in the pub-sub category, we highly recommend using MQTT. More than just a protocol, MQTT is the foundation for building new architectures, making IIoT a reality today. MQTT communications protocol While MQTT’s recent emergence into the limelight may suggest that it’s a brand new technology, MQTT has been around for quite some time. In 1999, Dr. Andy Stanford-Clark of IBM and Arlen Nipper invented a messaging protocol that was mainly intended for real-time, oil-and-gas SCADA systems. At the time, operational technology and information technology were two separate worlds. Unlike IT, bandwidth in OT was neither free nor unlimited. In an effort to circumvent the communication limitations of OT, MQTT was designed to be a lightweight, pub-sub protocol that economizes on bandwidth. However, the true value of MQTT is now found in its ability to decouple edge devices from applications that need the data. Traditional poll-response communication protocols can eat a lot of bandwidth without providing any real value. MQTT’s pub-sub method allows devices to put data on message-oriented middleware (MOM). Instead of applications constantly checking devices for any value changes, applications can connect to a MOM and subscribe to the important data that they need, including device state information. Since MQTT has proven to be a formidable communications protocol, its use has gone far beyond the oil and gas industry, and it has emerged as the de facto standard for IIoT and M2M messaging. In the Eclipse Foundation’s 2016 IoT Developer Survey, 80 percent of the respondents chose MQTT as the leading protocol for IIoT. MQTT is becoming more available as manufacturers begin to embed MQTT onto their devices. With so much interest in MQTT, it is safe to say that MQTT is the best choice for your IIoT solution. MQTT the ideal protocol? MQTT has three distinct features that also make it the ideal IIoT protocol: low bandwidth, TLS security, and stateful awareness. Limited bandwidth presents a serious challenge to IIoT, especially for remote locations, which is why MQTT is the perfect solution. It is a lightweight, low-bandwidth communications protocol that uses a pub-sub methodology. Poll-response protocols send and receive a lot of repetitive data which can take up an unnecessary amount of bandwidth. MQTT employs a MOM which decouples devices from applications and thus reduces bandwidth usage. Devices connect directly to a MOM, or in this case the MQTT server, where data is gathered. Applications then connect to the MQTT server, getting an update whenever there are changes to the data. The second important feature is the use of a cryptographic security protocol called Transport Layer Security (TLS), which provides communications security over a computer network. TLS aims to provide privacy and data integrity between two communicating computer applications. It is designed to prevent eavesdropping and tampering. By using TLS, MQTT establishes a secure, private connection via a handshake process. Once a connection is made, data is encrypted and transmitted between the client and the server. If the handshake fails, data is not transmitted. In addition to providing low bandwidth and a high level of security, MQTT has a useful feature called stateful awareness. While current SCADA implementations purely transmit data from devices, MQTT also sends the device state data about the health of the device or network connection. This is important for remote locations because it enables operators to determine if network connections are operational or devices are unavailable. As we dive deeper into the best practices for IIoT, we will discover that stateful awareness is one of the key ingredients to a successful IIoT implementation. Next, let’s look into the importance of stateful awareness and how to implement MQTT. Built-in stateful awareness With its low-bandwidth publish-subscribe methodology and TLS security, MQTT has proven to be a formidable IIoT communication protocol. Another feature that is critical to your IIoT infrastructure is the stateful awareness that is built into MQTT. Stateful awareness is important for SCADA systems, especially for remote installations. Knowing the health of the device and the network connection helps to mitigate any downtime and ensures data is being shared with all levels of an organization. By having stateful awareness, data becomes more stable, Technology 34 industrial ethernet book 11.2017 SOURCE: INDUCTIVE AUTOMATION Cirrus Link MQTT modules leverage a rich feature set and SQL database capabilities to take existing equipment and systems into a robust IIoT infrastructure.
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