Engineering Resources • Reference Table
Industrial Protocol Selection Matrix
A one-page comparison of the industrial protocols you are most likely to meet in the field, written for engineers choosing a protocol for a new project or making sense of an inherited one. Scroll the table sideways on a phone; the decision sequence below it is the short version.
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How to read this table: rows describe the base protocol as published by its steward organization. Real deployments vary by device profile, firmware, and configuration - a protocol having a security feature does not mean your devices implement it or that it is turned on. Confirm anything load-bearing against the steward’s current specification, linked in the sources at the bottom.
The Matrix
| Protocol | Transport | Comms model | Report by exception | Time-stamping | Security | Typical use |
|---|---|---|---|---|---|---|
| Modbus RTUModbus Organization | Serial (RS-485, RS-232) | Client/server (historically master/slave); one client polls | No - polled only | None in the protocol; timestamps are applied by the polling host | None in the protocol | Simple field devices, power meters, VFDs, legacy RTUs, across nearly every industry |
| Modbus TCPModbus Organization | Ethernet, TCP port 502 | Client/server; polled | No | None in the protocol | None in the base protocol; the Modbus Organization publishes a TLS-secured variant | PLC-to-SCADA links, gateways, plant Ethernet networks |
| DNP3 (IEEE 1815)DNP Users Group | Serial and TCP/IP | Master/outstation, including unsolicited responses | Yes - a core strength, with event buffering in the outstation | Yes - events are time-stamped at the outstation | Secure Authentication defined in the standard; commonly deployed with TLS | Electric utilities, water/wastewater, oil and gas pipelines |
| OPC UAOPC Foundation | opc.tcp binary, HTTPS; PubSub extension over UDP or MQTT | Client/server with subscriptions, plus optional pub/sub | Yes - subscriptions report monitored items on change | Yes - source and server timestamps in the data model | Built in: X.509 certificates, signing, encryption, user authentication | Cross-vendor integration, manufacturing, moving data from controls to IT systems |
| MQTT + SparkplugOASIS (MQTT); Eclipse Foundation (Sparkplug) | TCP, typically with TLS, via a central broker | Publish/subscribe | Yes - Sparkplug is explicitly report-by-exception, with birth and death messages for state | Yes - Sparkplug metrics carry timestamps | TLS plus broker authentication (credentials or certificates) | IIoT telemetry, oil and gas field SCADA, large fleets of remote sites |
| EtherNet/IPODVA | Standard Ethernet; TCP and UDP (CIP) | Producer/consumer: cyclic implicit I/O plus explicit messaging | Not typical - I/O data is produced cyclically | Time synchronization available via CIP Sync | CIP Security defines TLS/DTLS protection; adoption varies by device | Discrete manufacturing, machine control, Rockwell-centric plants |
| HARTFieldComm Group | 4-20 mA loop with a superimposed digital signal; WirelessHART for mesh networks | Master/slave; up to two masters on wired HART | Limited - wired HART is polled; burst mode lets a device publish continuously | Not in the wired protocol | Minimal in wired HART; WirelessHART encrypts traffic | Smart transmitters and valve positioners, device configuration and diagnostics in process industries |
| BACnetASHRAE (Standard 135) | BACnet/IP, MS/TP over RS-485, BACnet/SC over TLS-secured WebSockets | Client/server services | Yes - change-of-value (COV) subscriptions | Supported in objects such as trend logs and event notifications | BACnet/SC adds TLS; older transports are commonly deployed unsecured | Building automation, HVAC, campus energy management |
How to Choose - a Decision Sequence
Worked in order, these questions settle most protocol decisions:
- Inventory what your devices already speak. Protocol choice is usually constrained by installed hardware long before it is a matter of preference.
- On constrained or metered links (cellular, satellite), prefer report-by-exception protocols such as DNP3 or MQTT Sparkplug to cut traffic and cost.
- If you need sequence-of-events with timestamps applied at the source, shortlist DNP3 and OPC UA.
- If many systems need the same data, a pub/sub architecture (MQTT) or OPC UA decouples data producers from consumers instead of multiplying poll loads.
- For building systems, BACnet is the established default in that domain.
- For machine-level control, use the native protocol of the controller family - for example, EtherNet/IP in Rockwell environments.
- Let security requirements veto. If certificate-based authentication or encryption is mandatory end to end, shortlist protocols with those features built in rather than planning to bolt on wrappers later.
- Remember gateways. It is common practice to run a simple field protocol locally (often Modbus) and translate at an edge gateway to MQTT or OPC UA for the backhaul - you rarely need one protocol to do everything.
Notes and Caveats
- Terminology: the Modbus Organization now uses client/server for what older documentation calls master/slave. Both terms describe the same polling relationship.
- “Security features exist” and “security is enabled on your network” are different facts. Audit what is actually configured.
- HART occupies a different niche than the others: it rides on the 4-20 mA measurement loop, so it usually complements rather than competes with the network protocols in this table.
- Standards evolve. Treat this page as a map, and the steward documents below as the territory.
Sources & Standards
Each protocol is stewarded by an organization that publishes the authoritative specification:
- Modbus Organization - Modbus RTU, Modbus TCP, and the TLS-secured Modbus/TCP variant.
- DNP Users Group - DNP3, standardized as IEEE 1815.
- OPC Foundation - the OPC UA specification family, including PubSub.
- MQTT (OASIS) - the MQTT specification, standardized at OASIS.
- Eclipse Foundation - home of the Sparkplug specification working group.
- ODVA - EtherNet/IP, CIP, CIP Sync, and CIP Security.
- FieldComm Group - HART and WirelessHART.
- ASHRAE - BACnet, published as ASHRAE Standard 135.
Speaking Your Protocol
The matrix stands on its own - bookmark it for the next kickoff meeting. If you want your existing devices on one dashboard, Merobix connects across the major protocol families listed here.