Supported Protocols¶
This page lists what is shipped and working today. It contains no roadmap items: a protocol appears here only when the released software actually speaks it.
How Flowgate connects¶
Flowgate is OPC UA first. Every Flowgate node runs an embedded OPC UA server, and nodes chain to each other over OPC UA Reverse Connect, so the OT network never needs an inbound firewall rule. Anything that can present an OPC UA server is collectable without a dedicated connector. For systems that cannot, Flowgate ships protocol connectors, and the RetroBridge companion product bridges classic and field protocols into the same chain.
See Chaining and Reverse Connect for how nodes link up, and What is Flowgate for the platform overview.
Flowgate protocols¶
| Protocol | Direction | Notes |
|---|---|---|
| OPC UA (server) | Serves data out | Embedded in every node. Live values, subscriptions, writes, historical access, and the node's management surface. Security policies and client certificate handling are covered in Certificate Management. |
| OPC UA (client) | Collects data in | Connects to external OPC UA servers: PLCs, gateways, historians, simulators. Browse, subscribe, read, write. |
| OPC UA Reverse Connect | Node to node | The chain transport between Flowgate nodes. The more protected node dials outward; no inbound rule at the OT boundary. Store and forward runs over this link. |
| MQTT 3.1.1 (subscribe) | Collects data in | Subscribes to broker topics and maps messages into the tag space. Username, password, and TLS supported. |
| MQTT 3.1.1 (publish) | Sends data out | Publishes tag updates as JSON messages, plain or gzip compressed, with durable store and forward delivery. Includes provider presets for Azure IoT Hub (SAS token authentication, TLS 8883 or WebSocket 443) and AWS IoT Core (X.509 mutual TLS). |
| Sparkplug B | Sends data out | Publishes as a Sparkplug edge node: birth and death certificates, NDATA and DDATA, and rebirth on request. Verified against AWS IoT Core and Azure Event Grid MQTT; see Sparkplug B to cloud MQTT brokers. |
| Apache Kafka | Both | Producer and consumer connectors for an external Kafka cluster. Opt-in: Kafka is a backbone for high-throughput and fan-out sites, never a required component. |
| HTTP / REST | Sends data out | Posts tag updates to an HTTP endpoint as JSON, with retry. |
Protocols added by RetroBridge¶
RetroBridge is a separate H2 Innovations product that runs as a node in the same chain and is managed from the same console. It carries the protocols that classic and field devices speak. A RetroBridge node serves everything it collects as OPC UA, so from Flowgate's side it looks like any other node.
| Protocol | Direction | Platforms | Notes |
|---|---|---|---|
| OPC UA (server) | Serves data out | Windows and Linux | Every RetroBridge node runs the same embedded OPC UA server as a Flowgate node: everything it collects is served as OPC UA, with the same security policies and certificate handling. |
| OPC UA Reverse Connect | Node to node | Windows and Linux | A RetroBridge node links into a Flowgate chain by dialing outward to a parent Flowgate node's Reverse Connect listener, so no inbound firewall rule is needed at its boundary. It joins as a leaf: other nodes do not chain below it. |
| OPC Classic DA | Collects data in | Windows only | Wraps an OPC Classic DA server (for example Matrikon or other vendor DA servers) through a supervised bridge process. The DA server must run on the same machine as RetroBridge today. |
| Modbus TCP | Collects data in | Windows and Linux | Reads a Modbus TCP device: a PLC, RTU gateway, or meter. |
| Emerson ROC Plus | Collects data in | Windows and Linux | Polls a ROC Plus device (FloBoss 107 class) over TCP. RetroBridge acts as the ROC master, driven by an authored point map. |
| DNP3 | Collects data in | Windows and Linux | Polls an Emerson FB3000 outstation over TCP. RetroBridge acts as the DNP3 master, with automatic point discovery from the poll response. |
Why OPC Classic DA is Windows only
OPC Classic DA is built on COM, a Windows technology. RetroBridge on Linux offers the other three protocols; the DA connector simply does not appear there.
What this means for other systems¶
Many products expose an OPC UA server as an option, and Flowgate collects from any of them with no product-specific connector. Validation results against specific third-party clients, servers, and cloud services are listed under Interoperability.