OPC UA (OPC Unified Structure) is a platform-independent, service-oriented, open, and safe communication structure. It allows interoperability of commercial automation units, methods, and software program functions from completely different distributors. The OPC UA data mannequin defines the codes and codecs for exchanging information utilizing varied transport protocols.
The identical basis developed OPC UA and its predecessor, Open Platform Communications (OPC), however they’re considerably completely different. The inspiration continues to develop OPC UA to create an structure that’s extra fascinating than the unique OPC communications and extra in keeping with the wants of evolving industrial automation.
The OPC Basis launched the primary model of the OPC UA specification in 2006, and as of in the present day, OPC UA is at model 1.05. Along with the Shopper-Server (Subscriptions) mannequin, OPC UA features a Pub-Sub mechanism, which permits pushing JSON specs (additionally utilizing the standard-defined binary specification – UADP) over the UDP protocol, MQTT protocol, or AMQP protocol.
By way of the quick, safe, and dependable transport channel offered by the MQTT protocol, OPC UA can instantly use the web for information switch whereas retaining the important thing advantages of OPC UA’s end-to-end safety and standardized information modeling.
Options of OPC UA
- Practical equivalence – All OPC Basic specs map to the UA, and the OPC UA consists of the DA, A&E, and HDA performance present in OPC Basic:
| Performance | Descriptions |
|---|---|
| Discovery | Discover accessible OPC servers in your native PC and/or community |
| Tackle area | All information is represented hierarchically (e.g. information and folders), permitting OPC shoppers to find and make the most of easy and sophisticated information buildings |
| On-demand | Learn and write information/data based mostly on entry rights |
| Subscription | Monitor information/data and report exceptions when values change past the shopper’s settings |
| Occasion | Shopper-based settings notify necessary data |
| Technique | Purchasers can execute packages based mostly on strategies outlined on the server, and so forth. |
- Safety – Message encryption, authentication, and auditing, one of the vital necessary concerns for a corporation when selecting a expertise commonplace is safety. OPC UA addresses safety by offering a set of controls when passing by means of firewalls:
| Performance | Descriptions |
|---|---|
| Transport | A lot of protocols are outlined, offering choices reminiscent of ultra-fast OPC binary transfers or the extra basic SOAP-HTTPS |
| Session encryption | Info is transmitted securely with 128-bit or 256-bit encryption ranges |
| Message Signature | The signature should be similar when the message is acquired as when it’s despatched. |
| Sequencing Knowledge Packages | Recognized message replay assaults eradicated by means of sequencing |
| Authenticate | Every UA shopper and server is recognized by an OpenSSL certificates, which supplies management over how functions and methods join to one another. |
| Person management | Purposes can require person authentication (login credentials, certificates, and so forth.) and may additional prohibit or improve person entry to permissions and handle area “views”. |
| Audits | Logging of person and/or system exercise to supply an entry audit path |
- Complete Info Modelling: The OPC UA Info Modeling Framework, used to outline complicated data, converts information into data. It permits modeling and lengthening even probably the most complicated multi-level buildings by means of totally object-oriented performance, with the aptitude to outline information sorts and buildings in configuration information.
Info Mannequin for OPC UA
The OPC UA data mannequin, the handle area, is a community of nodes and references forming a structured graph.
Objects in an ordinary type are represented within the handle area, the place mannequin parts are referred to as nodes. The handle area represents objects and their elements as a set of nodes, described by attributes and linked by references. OPC UA modeling is all about creating nodes and references between nodes.
Object Mannequin
OPC UA makes use of objects as the premise for representing information and actions within the processing system. Variables, occasions, and strategies are interconnected by reference inside objects.
Node Mannequin
- Attributes describe nodes, and completely different node courses have completely different units of attributes. The definition of a node class consists of defining attributes, so the handle area doesn’t embrace attributes.
- A Reference represents a relationship between nodes. An occasion of a node of the reference sort that exists within the handle area defines a reference.
- Generic properties of the node mannequin
Reference Mannequin
The supply node is the node containing the reference, and the goal node is the referenced node. The referenced goal node might be in the identical handle area because the supply node, or within the handle area of one other OPC server, and even the goal node might be non-existent.
Node Varieties
An important node classes in OPC UA are objects, variables, and strategies.
- Object nodes: Customers use object nodes to type handle areas, and these nodes don’t comprise information. They use variables to reveal values for objects. Customers can use object nodes to group administration objects, variables, or strategies; variables and strategies all the time belong to an object.
- Variable node: Variable node represents a price. The info sort of the worth depends upon the variable. The shopper can learn, write, and subscribe to the worth.
- Technique node: The strategy node represents a way within the server that the shopper calls and receives the outcome. The enter parameters and the output outcome are within the type of variables as a part of the strategy node. The shopper specifies the enter parameters and will get the output outcome after the decision.
Why Bridge OPC UA to MQTT?
MQTT is a light-weight, environment friendly, and dependable messaging protocol for IoT, utilizing a publish-and-subscribe mannequin to help real-time communication. MQTT is well-suited for resource-constrained environments, particularly situations requiring environment friendly energy and bandwidth use.
Constructed on MQTT 3.1.1, SparkplugB ensures versatile, environment friendly primary information modeling for industrial IoT by means of an industry-established specification. SparkPlugB achieves robust interoperability and community state consciousness, because of MQTT’s wonderful design.
OPC UA and MQTT have a sure diploma of performance overlap, however their use of situations may be very completely different:
- OPC UA facilitates seamless communication amongst various tools and methods within the {industry} through the use of a standardized language.
- MQTT effectively handles real-time sensor information over the Web, addressing low bandwidth and unreliable community situations in IoT functions. Its learn/publish mechanism affords exceptional flexibility in utilization.
In industrial situations, MQTT excels at messaging in distributed methods, whereas OPC UA focuses on offering interoperability. OPC UA abstracts and aggregates enterprise information, and MQTT facilitates seamless, distributed information alternate with its robust connectivity capabilities.
OPC UA over MQTT
The Pub-Sub mannequin proposed by the OPC Basis within the newest specification of OPC UA permits information adjustments to be pushed to subscribers utilizing the MQTT Dealer.
Pub-Sub safety is a little more complicated than that in shopper/server, and the specification isn’t as detailed. In an MQTT community, safety is predicated on SSL/TLS, and the dealer can outline application-level authentication along with enabling SSL/TLS for transport.
In precept, these safety fashions are both all or nothing for each subscriber and writer that may be part of the community. The continuing standardization of OPC UA remains to be a piece in progress, and it stays unclear how you can greatest map the wealthy OPC UA data mannequin to MQTT.