The Industrial Internet of Things (IIoT), also known as Industry 4.0, is a paradigm shift in industrial production that is leading to what has been called the fourth industrial revolution. It is spurred on by the availability of low-cost computer processors, networks, and sensors. The goal is to use data gathered from the networked industrial components to further automate and optimize the facility’s operations.
At one time the communication protocol you would use on your IIoT network was primarily determined by the vendor whose control system you were using. According to automationworld.com, that has recently changed with the introduction of open technologies for industrial communication which can communicate with any device on your network. You want to be able to access all data at all times for timely analysis and action.
You now have multiple choices when it comes to the communication protocol you employ on your network. Your choice will be based on the needs of your enterprise and the strengths and weaknesses of each protocol. AMQP, CoAP, DDS, RTI Connext DDS, MQTT, and ZeroMQ are the most popular protocols available.
Let’s see how these protocols fit in with your IIoT goals. Some protocols offer distinct advantages in certain situations. Here are some points to consider.
What Communication Interaction Pattern Will Be Used?
You may be using a tightly coupled reply-request interaction for the control portion of your system, while the data plane of the system is more likely to use a publish/subscribe model that is loosely coupled. CoAP has limited capabilities with the publish/subscribe model, and is best suited for a control system. The MQTT protocol does not support reply-request interaction and therefore would not be suitable for your control infrastructure’s communication protocol. DDS is a protocol that supports both interaction patterns.
Other patterns that may be encountered are the one-to-many and many-to-one forms of communication which are supported by all popular protocols. Queueing, or point to point messaging, is less broadly supported and if you need that capability then AMQP or XMPP may be the right protocol for your system.
What Are Your System Interoperability Requirements?
Varying levels of interoperability concerning data exchange between applications and subsystems is offered by each communication protocol. Based on your needs you can choose a protocol that offers foundational (MQTT), structural (AMQP, XMPP), or full semantic interoperability (DDS, CoAP). Your receiving IT system’s ability to interpret data can be dependent on this choice.
Structural interoperability ensures that the messages exchanged are syntactically correct. With semantic operability, devices can exchange meaningful messages and act on the information exchanged.
What Are Your Data Exchange and Connectivity Requirements?
You may need the ability to exchange data between devices. You also may be going from device to cloud or between two cloud instances when developing your Industrial IoT communications infrastructure. CoAP works well for wireless sensors on devices and network gateways but cannot communicate with the cloud without an HTTP bridge. The MQTT protocol is designed to facilitate message propagation throughout enterprise web servers and mobile devices. AMQP and DDS are the most versatile, enabling full interoperability between devices, as well as device-to-cloud and between clouds.
Do You Have Quality Of Service Requirements?
What we are talking about here is the ability to distinguish differences in your real-time data. Data gathered from certain sensors may be able to be collected periodically with no impact to the system if a set timeframe is met. Alarm messages operate with no timeframe, but require immediate and guaranteed delivery.
Some protocols, such as MQTT, AMQP and CoAP, provide some basic quality of service (QoS) support. Protocols like XMPP and HTTP rely strictly on the underlying TCP/IP transport layer for messaging. DDS is the protocol that offers the most robust QoS capabilities, allowing applications to tune the IIoT’s communication behavior to meet specified requirements.
This allows for the prioritization of messages and complete control over the regulated flow of messages through your system. Using DDS you can define QoS policies on both the consumer and producer side of a message. These include parameters such as deadline, transport priority, reliability and many more to tailor your system to your specific needs.
What Are Your Plans For Expanding Your IIoT Network?
If scalability is an issue, then the protocols that support the publish/subscribe interaction model may be the best fit for your enterprise. In particular for the many-to-one and one-to-many models, protocols such as DDS that do not require brokers and directly support peer-to-peer communication works well and is extremely scalable. If your short term plans are to expand your system to encompass other facilities or processes, then this may be an important factor in choosing a protocol.
What Level Of Security Do You Require?
Your security needs may vary. It may take a back seat in situations where you have strong physical security in place or where the data being moved is of no value to outsiders. Basic data encryption at the transport level is provided by all of these communication protocols. Some, like AMQP and MQTT, allow for another level of security through TLS/SSL connections.
The DDS protocol provides an extensive security framework for IIoT systems. It specifies a complete end-to-end Authentication, Authorization and Accounting security architecture and allows for configuring the security parameters on a per data flow basis.
Which Protocol Should You Choose?
There is no clear cut answer to the question of which communication protocol is right for your company’s implementation of the Industrial Internet of Things. You must take a hard look at the system you intend to build and focus on points where the choice of protocol can make a difference to your final solution. You must also face the fact that with legacy equipment involved, you may need to employ several different communication protocols to gain the full functionality that you desire from your system.
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