OPC UA

showstack / protocols / opc-ua

Also called OPC Unified Architecture, IEC 62541.

The OPC Foundation's platform-independent, service-oriented standard for structured, secured data exchange between industrial and building systems, from simple tag reads to full information models over TCP, UDP, WebSockets or MQTT/AMQP. In venues it is the practical bridge where show control needs to read or write into building management, HVAC or facility-automation systems.

Device managementOpenOPC FoundationVerified

Management Housekeeping, no deadline

Discovery, monitoring, configuration, backups, updates. Useful, and none of it has a deadline of its own.

What kills it. Nothing kills it. That is the problem: with no deadline it has no manners, and it will happily starve everything that does have one. Putting it on a show VLAN is the commonest self-inflicted wound in the industry.

Why this one, and not what the category suggests. Industrial monitoring and configuration. Its safety-rated siblings do the commanding.

The four flows, and why the model is worth having →

Ports

tcp/4840 OPC UA TCP binary protocol (opc.tcp://) default endpoint/discovery port

What goes wrong

The specification text is free to read at reference.opcfoundation.org, but the identically-numbered IEC 62541 standard document must be purchased from the IEC Webstore if a compliance paper trail specifically needs the ISO/IEC-badged version.

OPC UA supports both classic client/server (request-response over TCP binary) and newer pub/sub patterns over very different transports (UDP, MQTT, AMQP); two devices that both claim "OPC UA support" are not guaranteed to share a transport/pattern without checking which profile each one implements.

Security is optional per-endpoint (None/Sign/SignAndEncrypt policies can all be offered by the same server), so a server discovered and connected without checking its security policy list may be handing data over completely unencrypted even though the standard itself supports strong security.

What speaks OPC UA (4)

Product	Direction	Notes
CODESYS CODESYS Group	bidirectional	Standard integration for exposing controller state.
Medialon Control System Medialon (Barco)	bidirectional	OPC UA for industrial integration.
TwinCAT Beckhoff Automation	bidirectional	The usual way state is exposed upward to other systems.
Beckhoff CX5140 Embedded PC Beckhoff Automation	bidirectional	Exposing state upward to show systems.

Open source implementations

open62541 — C, MPL-2.0
asyncua (formerly python-opcua / FreeOpcUa) — Python, LGPL-3.0-or-later

Typical use

Bridging show control or venue automation into building management systems (BMS/HVAC) via a shared OPC UA server
Exposing PLC and industrial-machinery data models to higher-level monitoring/dashboarding software
Vendor-neutral integration layer between different automation vendors' equipment in fixed installations

Sources

OPC UA TCP well-known address, port 4840 (opc.tcp://localhost:4840/UADiscovery) — OPC Foundation primary
Update for IEC 62541 (OPC UA) Published — OPC Foundation primary
OPC Unified Architecture (first released 2006, IEC 62541, free specification download, transports) — Wikipedia
open62541 — open source implementation of OPC UA (IEC 62541), Mozilla Public License v2.0 — open62541 project

Understand the mechanism

Code on a show

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