After focusing on communication at field level, the OPC Foundation is continuing a series of activities in the cloud to offer a harmonized solution for process and factory automation that scales from the field to the cloud. The major IoT providers such as AWS, Google Cloud, IBM, Microsoft, SAP and Siemens support this initiative of secure, standardized information exchange in edge-to-cloud applications based on OPC UA.

Stefan Hoppe, President of the OPC Foundation, says: "Many position OPC UA only for 'last mile' communication to the device at field and edge level and intuitively assume MQTT for edge/cloud connectivity." The OPC Foundation also favours MQTT as a protocol in the cloud - but as a subordinate infrastructure for 'OPC UA over MQTT' for the transport of standardized information.

Hoppe explains the reason for this as follows: "MQTT is a payload-agnostic protocol, which means that there is no definition of the message payload and it behaves in a similar way to Modbus back then: certainly very simple - but without a standardized description of the data content. In the age of digitalization, this is no longer state of the art." Hoppe's nightmare scenario: "If all control system manufacturers were to define their own manufacturer-specific mapping to MQTT and other consortia were to do the same - we would end up with a zoo of MQTT mappings!" However, "this would no longer have anything to do with a simple USB interface for machines as a plug & produce solution." Hoppe therefore advocates agreement on a single mapping based on OPC UA.

Arguments in favor of this technological path

First of all, the OPC Foundation published OPC UA PubSub - via UDP and MQTT - in February 2018; OPC UA is the IEC 62541 standard. In recent years, the OPC Foundation has also achieved global acceptance of OPC UA as an open standard for the secure interoperability of production systems across OT and IT networks. There are over 850 registered OPC Foundation members supporting a large, rapidly growing ecosystem of end users, standardization bodies and vendors.

In addition, OPC UA uses a standardized method for defining, recognizing and using information models (IMs) and services that are connected to the production systems. This standardized approach to semantic information exchange avoids vendor lock-in and the costly custom programming required to accommodate non-standard IMs in the cloud.

With the introduction of the UA Cloud Library, OPC UA IMs are globally available to all cloud applications, making it easy for cloud applications to directly utilize OPC UA-based semantic information as well as live data from the edge.

Transport-independent IEC standard

As a transport-independent IEC standard, OPC UA supports two different communication patterns: client/server (via TCP or WebSockets) and publish/subscribe (via UDP or MQTT) to meet the different requirements of the industry - from production systems to edge and cloud scenarios. While the OPC UA client/server-based pattern is easier to use in the environment of transactional behavior à la SCADA/MES plus automation, the more cloud-oriented 'analytics-heavy' application scenario is easier to implement with OPC UA PubSub over MQTT: Data is sent once and is therefore 'forgotten' - handshakes for further actions are not necessary.

Plugfests for quality assurance

Stefan Hoppe, President of the OPC Foundation: "OPC UA is the only harmonized solution for process and factory automation that scales from the field to the cloud."

© OPC Foundation

The OPC Foundation's quality assurance program already covers the OPC UA publish/subscribe communication patterns and is the first cross-vendor multi-cloud standard test. Interoperability workshops with leading PLC providers such as Beckhoff and Siemens, which send OPC UA data from the controller via MQTT, have already begun. The criterion for inclusion in the list of supporters is that the companies either already offer OPC UA over MQTT in their products or that this implementation is on their development roadmap. Initially supporting IT/OT companies include Amazon Web Services, Beckhoff, Google Cloud, IBM, Microsoft, SAP and Siemens.

Further cloud activities

The OPC Foundation is currently working on further projects:

• TheOPC UA Cloud Library: together with CESMII, USA, the joint working group 'The UA Cloud Library' makes it easier for OPC UA information models to be found, shared, researched and used by applications, end users and standardization bodies. Currently, the UA Cloud Library already contains over 70 OPC UA information models created by both individual companies and international standards organizations. There is no larger open library of standardized information models for automation in the world.
• The OPC UA Cloud Federation: Together with DIN, a working group is developing a specification for Industrial Cloud Federation (ICF), which is based on and implemented with OPC UA technology. It describes the communication between endpoints of cloud services and endpoints of devices that are physically located in a production environment. Communication takes place across one or more administrative company boundaries and cloud systems. ICF takes into account both communication from edge components to cloud components and cross-company communication with other cloud systems.

According to documents from the OPC Foundation