1252 Industrial IoT Protocols Overview

1252.1 Industrial IoT Protocols: The OT/IT Convergence

Learning Objectives

By the end of this section, you will be able to:

Distinguish between IT and OT networking requirements
Compare major industrial protocols (OPC-UA, Modbus, PROFINET, EtherCAT)
Understand deterministic networking and real-time requirements
Evaluate protocol selection for different industrial scenarios
Identify Industry 4.0 protocol convergence trends
Design hybrid IT/OT network architectures

1252.2 Prerequisites

Before diving into this chapter, you should be familiar with:

Networking Basics: IP addressing and network fundamentals
IIoT and Industry 4.0: Industrial IoT context and applications
IoT Protocols Overview: General IoT protocol landscape

Related Chapters

Deep Dives: - OPC-UA Fundamentals - OPC-UA architecture and implementation - Modbus Protocol - Modbus RTU and TCP - Industrial Ethernet - PROFINET, EtherCAT, TSN

Context: - IIoT and Industry 4.0 - Industrial IoT overview - WirelessHART - Wireless industrial protocol - ISA100.11a - Industrial wireless standard

Architecture: - M2M Communication - Machine-to-machine patterns - Edge-Fog Computing - Industrial edge architecture

1252.3 For Beginners: IT vs OT Networking

What Makes Industrial Networks Different?

IT (Information Technology) networks are what most people know: - Office computers, phones, web servers - Data moves in bursts (emails, web pages) - A 1-second delay is annoying but acceptable - If a packet is lost, just send it again

OT (Operational Technology) networks control physical processes: - Factory robots, chemical plants, power grids - Data flows continuously (sensor readings, control commands) - A 1-second delay could crash a robot or explode a tank - A lost command could mean product defects or safety hazards

Real-World Example: Imagine you’re controlling a robotic arm that welds car parts: - IT approach: “Move arm to position X” → response in 100-500ms → OK for emails - OT requirement: “Move arm to position X” → response in <1ms → required for precision

Key Insight: Industrial protocols evolved in isolation for 40+ years because standard IT networking (Ethernet, TCP/IP) couldn’t guarantee the timing industrial processes need.

1252.4 The Industrial Protocol Landscape

1252.4.1 Protocol Evolution Timeline

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timeline
    title Industrial Protocol Evolution
    1979 : Modbus RTU
         : Serial RS-485
    1990s : Fieldbus Era
          : CAN, PROFIBUS, DeviceNet
    2000s : Industrial Ethernet
          : PROFINET, EtherNet/IP, EtherCAT
    2008 : OPC-UA
         : Platform-independent
    2016 : TSN Standards
         : IEEE 802.1 Time-Sensitive Networking
    2020s : IT/OT Convergence
          : OPC-UA over TSN, MQTT, cloud integration

Figure 1252.1: Industrial Protocol Evolution Timeline from Modbus to IT/OT Convergence

{fig-alt=“Timeline showing industrial protocol evolution from 1979 Modbus RTU through fieldbus era in 1990s, industrial Ethernet in 2000s, OPC-UA in 2008, TSN standards in 2016, to IT/OT convergence in 2020s with OPC-UA over TSN and cloud integration.”}

Alternative View: Protocol Stack Layers

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graph TB
    subgraph Modern["2020s: Unified IT/OT Stack"]
        M1["Cloud/SCADA Integration"]
        M2["OPC-UA / MQTT"]
        M3["TSN Ethernet"]
        M4["Deterministic Switching"]
    end

    subgraph Mid["2000s: Industrial Ethernet"]
        I1["HMI / SCADA"]
        I2["PROFINET / EtherNet/IP"]
        I3["Standard Ethernet + Extensions"]
        I4["Industrial Switches"]
    end

    subgraph Legacy["1980s-90s: Fieldbus Era"]
        L1["Local HMI"]
        L2["Modbus / PROFIBUS / CAN"]
        L3["RS-485 / RS-232"]
        L4["Serial Wiring"]
    end

    M1 --> M2 --> M3 --> M4
    I1 --> I2 --> I3 --> I4
    L1 --> L2 --> L3 --> L4

    Legacy -.->|"Migration"| Mid
    Mid -.->|"Evolution"| Modern

    style Modern fill:#16A085,stroke:#2C3E50
    style Mid fill:#E67E22,stroke:#2C3E50
    style Legacy fill:#7F8C8D,stroke:#2C3E50

This layered view shows how each era built complete protocol stacks from physical layer to application, with migration paths between generations.

1252.4.2 Protocol Categories

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graph TB
    subgraph Legacy["Legacy Serial Protocols"]
        M1[Modbus RTU]
        M2[Modbus ASCII]
        Prof[PROFIBUS]
    end

    subgraph FieldEth["Fieldbus over Ethernet"]
        MT[Modbus TCP]
        EIP[EtherNet/IP]
        PN[PROFINET]
        EC[EtherCAT]
    end

    subgraph Modern["Modern IT/OT"]
        OPC[OPC-UA]
        MQTT[MQTT + Sparkplug]
        TSN[TSN Ethernet]
    end

    subgraph Wireless["Industrial Wireless"]
        WH[WirelessHART]
        ISA[ISA100.11a]
        Wi-Fi6[Wi-Fi 6 TSN]
    end

    Legacy --> FieldEth
    FieldEth --> Modern
    Modern --> TSN

    style Legacy fill:#7F8C8D,stroke:#2C3E50
    style FieldEth fill:#E67E22,stroke:#2C3E50
    style Modern fill:#16A085,stroke:#2C3E50
    style Wireless fill:#2C3E50,stroke:#16A085

Figure 1252.2: Industrial Protocol Categories: Legacy, Fieldbus, Modern IT/OT, and Wireless

{fig-alt=“Industrial protocol categories showing evolution: Legacy Serial Protocols in gray (Modbus RTU, ASCII, PROFIBUS), Fieldbus over Ethernet in orange (Modbus TCP, EtherNet/IP, PROFINET, EtherCAT), Modern IT/OT in teal (OPC-UA, MQTT+Sparkplug, TSN), and Industrial Wireless in navy (WirelessHART, ISA100.11a, Wi-Fi 6 TSN). Arrows show progression from legacy to modern.”}

1252.5 IT vs OT Requirements

Understanding Industrial Protocol Security

Core Concept: Legacy industrial protocols (Modbus, older PROFIBUS) were designed for isolated networks and have no built-in authentication, encryption, or authorization—any device on the network can read or write any data.

Why It Matters: As industrial networks connect to IT systems and the cloud (IT/OT convergence), this lack of security becomes critical. A compromised IT system could send malicious commands to PLCs controlling physical processes. Defense-in-depth strategies—network segmentation, firewalls, VPNs, and protocol gateways—are essential to protect legacy OT assets.

Key Takeaway: Never expose Modbus TCP (port 502) or similar legacy protocols directly to untrusted networks. Use industrial firewalls and DMZ architectures to create security boundaries, and prefer modern protocols like OPC-UA with built-in security for new deployments.

1252.5.1 Comparison Matrix

Requirement	IT Networks	OT Networks
Latency	10-500 ms acceptable	<1 ms to 10 ms required
Jitter	Variable OK	Must be deterministic
Availability	99.9% (8.7 hrs/year downtime)	99.999% (5 min/year)
Data Model	Flexible, schema-less	Strict, predefined
Security	Defense in depth	Air-gapped historically
Lifecycle	3-5 years	15-30 years
Updates	Frequent, automated	Rare, manual, tested
Traffic Pattern	Bursty	Continuous, cyclic

1252.5.2 The Determinism Challenge

Standard Ethernet is non-deterministic—you can’t guarantee when a packet arrives:

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graph LR
    subgraph Standard["Standard Ethernet"]
        S1[Sensor] --> SW1[Switch Queue<br/>Variable delay]
        SW1 --> PLC1[PLC<br/>1-100ms latency]
    end

    subgraph Realtime["Real-Time Industrial Ethernet"]
        S2[Sensor] --> SW2[TSN Switch<br/>Scheduled queue]
        SW2 --> PLC2[PLC<br/><1ms guaranteed]
    end

    style Standard fill:#c0392b,stroke:#2C3E50
    style Realtime fill:#16A085,stroke:#2C3E50

Figure 1252.3: Standard Ethernet vs Real-Time Industrial Ethernet Latency Comparison

{fig-alt=“Comparison of Standard Ethernet with variable 1-100ms latency through switch queue versus Real-Time Industrial Ethernet with TSN scheduled queue guaranteeing less than 1ms latency. Red highlighting for standard (unreliable), teal for real-time (reliable).”}

1252.5.3 Real-Time Classes

Class	Cycle Time	Jitter	Example Applications
Soft Real-Time	10-100 ms	±10 ms	Building automation, HVAC
Hard Real-Time	1-10 ms	±100 μs	Packaging, assembly lines
Isochronous	<1 ms	±1 μs	Motion control, robotics

1252.6 Major Industrial Protocols

1252.6.1 Protocol Comparison

Protocol	Physical Layer	Typical Cycle	Max Nodes	Primary Use
Modbus RTU	RS-485 Serial	10-100 ms	247	Legacy PLCs, simple sensors
Modbus TCP	Ethernet	5-50 ms	Unlimited	SCADA, HMI integration
PROFINET	Ethernet	1-10 ms	512	Siemens automation
EtherNet/IP	Ethernet	1-10 ms	Unlimited	Rockwell automation
EtherCAT	Ethernet	<100 μs	65,535	High-speed motion control
OPC-UA	TCP/UDP/MQTT	1 ms - 1 s	Unlimited	Enterprise integration

1252.6.2 Protocol Architecture Comparison

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graph TB
    subgraph ModbusArch["Modbus"]
        MC[Master] --> MS1[Slave 1]
        MC --> MS2[Slave 2]
        MC --> MS3[Slave N]
    end

    subgraph ProfiArch["PROFINET"]
        PIO[IO Controller] <--> PD1[IO Device]
        PIO <--> PD2[IO Device]
        PS[Supervisor] -.-> PIO
    end

    subgraph EcatArch["EtherCAT"]
        EM[Master] --> ES1[Slave 1]
        ES1 --> ES2[Slave 2]
        ES2 --> ES3[Slave N]
        ES3 -.-> EM
    end

    subgraph OPCArch["OPC-UA"]
        OC[Client] <--> OS1[Server 1]
        OC <--> OS2[Server 2]
        OS1 <--> OA[Aggregating Server]
        OS2 <--> OA
    end

    style ModbusArch fill:#7F8C8D,stroke:#2C3E50
    style ProfiArch fill:#E67E22,stroke:#2C3E50
    style EcatArch fill:#16A085,stroke:#2C3E50
    style OPCArch fill:#2C3E50,stroke:#16A085

Figure 1252.4: Industrial Protocol Architecture Comparison: Modbus, PROFINET, EtherCAT, OPC-UA

{fig-alt=“Architecture comparison of four industrial protocols: Modbus shows simple master-slave star topology in gray, PROFINET shows IO Controller with devices and optional Supervisor in orange, EtherCAT shows daisy-chain ring topology with single frame passing through all slaves in teal, OPC-UA shows flexible client-server with optional aggregating server in navy.”}

1252.6.3 Protocol Selection Guide

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flowchart TB
    Start[Select Protocol] --> Q1{Cycle Time?}

    Q1 -->|<1 ms| EC[EtherCAT]
    Q1 -->|1-10 ms| Q2{Existing PLC?}
    Q1 -->|>10 ms| Q3{Enterprise Integration?}

    Q2 -->|Siemens| PROF[PROFINET]
    Q2 -->|Rockwell| EIP[EtherNet/IP]
    Q2 -->|Other| MT[Modbus TCP]

    Q3 -->|Yes| OPC[OPC-UA]
    Q3 -->|No| Q4{Legacy?}

    Q4 -->|Yes| MR[Modbus RTU]
    Q4 -->|No| MQTT[MQTT Sparkplug]

    style Start fill:#16A085,stroke:#2C3E50,color:#fff
    style EC fill:#E67E22,stroke:#2C3E50,color:#fff
    style PROF fill:#E67E22,stroke:#2C3E50,color:#fff
    style EIP fill:#E67E22,stroke:#2C3E50,color:#fff
    style MT fill:#E67E22,stroke:#2C3E50,color:#fff
    style OPC fill:#16A085,stroke:#2C3E50,color:#fff
    style MR fill:#7F8C8D,stroke:#2C3E50,color:#fff
    style MQTT fill:#16A085,stroke:#2C3E50,color:#fff

Figure 1252.5: Industrial Protocol Selection Decision Tree Based on Requirements

{fig-alt=“Protocol selection decision tree: Starting with cycle time requirement, sub-1ms leads to EtherCAT, 1-10ms branches by PLC vendor (Siemens→PROFINET, Rockwell→EtherNet/IP, Other→Modbus TCP), greater than 10ms branches on enterprise integration need (Yes→OPC-UA, No→legacy check leading to Modbus RTU or MQTT Sparkplug).”}

1252.7 Modbus Overview

1252.7.1 Modbus Data Model

Modbus uses a simple register-based data model:

Register Type	Address Range	Access	Size	Typical Use
Coils	0-65535	R/W	1 bit	Digital outputs
Discrete Inputs	0-65535	R	1 bit	Digital inputs
Input Registers	0-65535	R	16 bit	Analog inputs
Holding Registers	0-65535	R/W	16 bit	Configuration, outputs

1252.7.2 Modbus RTU vs TCP

Feature	Modbus RTU	Modbus TCP
Physical	RS-485 serial	Ethernet
Speed	9600-115200 baud	10/100/1000 Mbps
Addressing	1-247 (unit ID)	IP address
Max Distance	1200 m	LAN/WAN
Error Check	CRC-16	TCP checksums
Complexity	Simple wiring	IP infrastructure

1252.8 OPC-UA Overview

1252.8.1 OPC-UA Information Model

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graph TB
    subgraph AddressSpace["OPC-UA Address Space"]
        Root[Root]
        Objects[Objects]
        Types[Types]
        Views[Views]

        Root --> Objects
        Root --> Types
        Root --> Views

        Objects --> Server[Server Object]
        Objects --> Device[Device Object]

        Device --> Temp[Temperature<br/>Variable Node]
        Device --> Status[Status<br/>Variable Node]
        Device --> Method[Calibrate<br/>Method Node]

        Types --> BaseType[Base Type]
        Types --> DeviceType[Device Type]
    end

    style AddressSpace fill:#2C3E50,stroke:#16A085
    style Device fill:#E67E22,stroke:#2C3E50,color:#fff
    style Temp fill:#16A085,stroke:#2C3E50,color:#fff
    style Status fill:#16A085,stroke:#2C3E50,color:#fff
    style Method fill:#16A085,stroke:#2C3E50,color:#fff

Figure 1252.6: OPC-UA Address Space Information Model Hierarchy

{fig-alt=“OPC-UA Address Space hierarchy showing Root node branching to Objects, Types, and Views folders. Objects contains Server and Device objects, Device contains Variable nodes (Temperature, Status) and Method node (Calibrate). Types folder contains Base Type and Device Type for type system. Orange highlighting for main device, teal for data nodes.”}

1252.8.2 OPC-UA Services

Service Set	Services	Purpose
Discovery	FindServers, GetEndpoints	Locate servers
Secure Channel	Open, Close, Renew	Establish security
Session	Create, Activate, Close	User sessions
Node Management	AddNodes, DeleteNodes	Modify address space
View	Browse, BrowseNext	Navigate address space
Attribute	Read, Write, History	Access data
Method	Call	Execute methods
Subscription	Create, Modify, Publish	Data change notifications

1252.9 Industrial Ethernet Protocols

1252.9.1 PROFINET Architecture

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graph TB
    subgraph RTClasses["PROFINET Real-Time Classes"]
        NRT[NRT<br/>Non-Real-Time<br/>100ms+]
        RTC[RT<br/>Real-Time<br/>1-10ms]
        IRT[IRT<br/>Isochronous<br/><1ms]
    end

    NRT --> TCP[TCP/IP<br/>Configuration, diagnostics]
    RTC --> RTPN[RT Protocol<br/>Cyclic I/O]
    IRT --> SYNC[Synchronized<br/>Motion control]

    style NRT fill:#7F8C8D,stroke:#2C3E50,color:#fff
    style RTC fill:#E67E22,stroke:#2C3E50,color:#fff
    style IRT fill:#16A085,stroke:#2C3E50,color:#fff

Figure 1252.7: PROFINET Real-Time Classes: NRT, RT, and IRT Communication

{fig-alt=“PROFINET real-time classes: NRT (Non-Real-Time) in gray for 100ms+ configuration and diagnostics over TCP/IP, RT (Real-Time) in orange for 1-10ms cyclic I/O, IRT (Isochronous Real-Time) in teal for sub-1ms synchronized motion control. Shows protocol layering for different timing requirements.”}

1252.9.2 EtherCAT Operation

EtherCAT uses a unique “processing on the fly” approach:

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sequenceDiagram
    participant M as Master
    participant S1 as Slave 1
    participant S2 as Slave 2
    participant S3 as Slave 3

    Note over M,S3: Single Ethernet frame travels through all slaves

    M->>S1: Frame with all data
    Note over S1: Extract input,<br/>insert output<br/>(~1μs delay)
    S1->>S2: Modified frame
    Note over S2: Extract input,<br/>insert output
    S2->>S3: Modified frame
    Note over S3: Extract input,<br/>insert output
    S3->>M: Completed frame

    Note over M: All I/O updated<br/>in single cycle

Figure 1252.8: EtherCAT Processing-on-the-Fly Frame Propagation Sequence

{fig-alt=“EtherCAT operation sequence showing single Ethernet frame traveling from Master through Slaves 1, 2, 3, with each slave extracting its input and inserting its output in approximately 1 microsecond before passing frame to next slave. Final frame returns to Master with all I/O updated in single network cycle.”}

1252.10 IT/OT Convergence Architecture

1252.10.1 Modern Industrial Architecture

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graph TB
    subgraph Cloud["Cloud / Enterprise"]
        ERP[ERP System]
        Analytics[Analytics Platform]
        Historian[Cloud Historian]
    end

    subgraph Edge["Edge / Plant"]
        Gateway[Edge Gateway<br/>OPC-UA Aggregator]
        SCADA[SCADA/HMI]
        MES[MES System]
    end

    subgraph OT["OT Network"]
        PLC1[PLC 1<br/>PROFINET]
        PLC2[PLC 2<br/>EtherNet/IP]
        PLC3[PLC 3<br/>Modbus TCP]
    end

    subgraph Field["Field Devices"]
        S1[Sensors]
        A1[Actuators]
        D1[Drives]
    end

    Cloud <-->|MQTT/AMQP| Edge
    Edge <-->|OPC-UA| OT
    OT <-->|Industrial Protocols| Field

    style Cloud fill:#2C3E50,stroke:#16A085
    style Edge fill:#E67E22,stroke:#2C3E50
    style OT fill:#16A085,stroke:#2C3E50
    style Field fill:#7F8C8D,stroke:#2C3E50

Figure 1252.9: Modern Industrial IT/OT Convergence Architecture with Edge Gateway

{fig-alt=“Modern industrial IT/OT convergence architecture with four layers: Cloud/Enterprise in navy (ERP, Analytics, Historian), Edge/Plant in orange (Gateway with OPC-UA Aggregator, SCADA, MES), OT Network in teal (PLCs with PROFINET, EtherNet/IP, Modbus TCP), and Field Devices in gray (Sensors, Actuators, Drives). MQTT/AMQP connects cloud to edge, OPC-UA connects edge to OT, industrial protocols connect OT to field.”}

1252.10.2 OPC-UA as the Unifying Layer

OPC-UA serves as the bridge between different industrial protocols:

Source Protocol	OPC-UA Gateway	Cloud Integration
Modbus registers	→ OPC-UA variables	→ MQTT topics
PROFINET devices	→ OPC-UA objects	→ REST APIs
EtherCAT slaves	→ OPC-UA methods	→ Time-series DB
S7 Communication	→ OPC-UA address space	→ Analytics

1252.11 Understanding Check

Knowledge Check

Scenario: You’re designing the network architecture for a new automotive assembly plant with: - 50 robot arms (require <1ms cycle time for motion control) - 200 I/O points (sensors, actuators) per station - 10 stations total - SCADA system for monitoring - Cloud analytics for predictive maintenance

Questions:

Which protocol would you use for robot motion control?
How would you integrate SCADA monitoring?
What would connect the OT network to cloud analytics?
What’s the minimum network determinism required?

Auto-Gradable Quick Check

Question: For robot motion control requiring sub-1 ms cycle times and tight synchronization, which industrial protocol is a common choice?

💡 Explanation: B. EtherCAT supports very short cyclic update times and synchronized motion using distributed clocks, making it suitable for deterministic control.

Question: Which technology is commonly used to expose OT data to SCADA/HMI systems in a standardized, vendor-neutral way?

💡 Explanation: B. OPC-UA provides a secure, information-modeled interface for SCADA clients to read/subscribe to OT data exposed by controllers or gateways.

Question: In a layered IT/OT architecture, what protocol is commonly used to publish aggregated telemetry from an edge gateway to cloud analytics?

💡 Explanation: C. MQTT is widely used for efficient publish/subscribe telemetry to cloud services; Sparkplug adds standardized payload/state conventions for IIoT.

Question: What level of determinism is typically required for closed-loop robot motion control?

💡 Explanation: C. Motion control requires predictable cycle times and very low jitter so drives and controllers stay synchronized.

Solution

1. Robot Motion Control: EtherCAT - Sub-1ms cycle time required → EtherCAT (100μs cycles possible) - High node count (50 robots × sensors/drives) → EtherCAT supports 65,535 nodes - Synchronization for coordinated motion → EtherCAT distributed clocks - Alternative: PROFINET IRT (if using Siemens robots)

2. SCADA Integration: OPC-UA - EtherCAT master exposes data via OPC-UA server - SCADA acts as OPC-UA client - Subscriptions for real-time updates (1-10ms) - Historical access for trending

3. Cloud Connectivity: MQTT Sparkplug + Edge Gateway - Edge gateway aggregates OPC-UA data - Publishes to cloud via MQTT Sparkplug B - Data filtering/aggregation at edge (reduce bandwidth) - Cloud historian (InfluxDB, TimescaleDB)

4. Network Determinism Requirements: - Robot control network: Isochronous (<1ms, ±1μs jitter) - SCADA network: Hard real-time (1-10ms OK) - Cloud network: Soft real-time (100ms-1s OK) - Use network segmentation: TSN for robots, standard Ethernet for IT

1252.12 Visual Reference Gallery

Industrial Protocol Visualizations

The following AI-generated diagrams provide additional perspectives on industrial IoT protocols.

1252.12.1 SCADA and Control Systems

DNP3 protocol in SCADA systems showing master station, remote terminal units (RTUs), and intelligent electronic devices (IEDs) communication

DNP3 SCADA

1252.12.2 Industrial Standards

ISA-100.11a wireless industrial network standard showing mesh topology, backbone routers, and gateway to plant control systems

ISA-100.11a

ISA-100.11a usage classes showing Class 0-5 with latency and reliability requirements from emergency shutdown to data logging

ISA Usage Classes

1252.12.3 Industrial Ethernet

Industrial Ethernet protocols comparison showing PROFINET, EtherNet/IP, EtherCAT, and Powerlink with their real-time capabilities

Industrial Ethernet

OPC-UA architecture showing client-server model, information modeling, security layers, and transport bindings for IT/OT integration

OPC-UA Architecture

OPC-UA server implementation showing address space, data access, historical access, alarms and events, and method services

OPC-UA Server

1252.13 Key Takeaways

Summary

OT networks require determinism—guaranteed timing that standard IT networks can’t provide
Legacy protocols persist—Modbus (1979) still dominates simple sensor/actuator integration
Industrial Ethernet evolved from proprietary fieldbus to compete: PROFINET (Siemens), EtherNet/IP (Rockwell), EtherCAT (Beckhoff)
OPC-UA is the unifying layer—platform-independent, secure, designed for IT/OT convergence
TSN (Time-Sensitive Networking) is the future—deterministic standard Ethernet
Choose by cycle time: <1ms → EtherCAT, 1-10ms → PROFINET/EtherNet/IP, >10ms → OPC-UA/MQTT
Layer your architecture: Field protocols → OPC-UA gateway → MQTT → Cloud

1252.13.1 IT/OT Convergence Architecture (Variant View)

This layered architecture diagram shows how industrial protocols integrate IT and OT systems in modern Industry 4.0 deployments:

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graph TB
    subgraph Cloud["Enterprise & Cloud Layer (IT)"]
        ERP["ERP / MES Systems"]
        Analytics["Analytics Platform"]
        DataLake["Data Lake / Historian"]
        Cloud_API["Cloud APIs<br/>REST, GraphQL"]
    end

    subgraph Edge["Edge / Gateway Layer"]
        OPC_GW["OPC-UA Gateway<br/>Protocol Translation"]
        Edge_Compute["Edge Computing<br/>Local Analytics"]
        Security["Security Gateway<br/>Firewall, VPN"]
        MQTT_Bridge["MQTT Bridge<br/>Cloud Connectivity"]
    end

    subgraph Network["Industrial Network Layer"]
        TSN["TSN Switch<br/>Deterministic Ethernet"]
        PROFINET_Net["PROFINET RT/IRT"]
        EtherCAT_Net["EtherCAT Ring"]
        Standard_ETH["Standard Ethernet"]
    end

    subgraph Field["Field Device Layer (OT)"]
        PLC["PLCs<br/>Siemens, Rockwell"]
        Drives["Servo Drives<br/>Motion Control"]
        Sensors["Sensors<br/>Modbus, IO-Link"]
        HMI["HMI Panels"]
    end

    %% Connections
    Cloud_API <-->|"HTTPS/MQTT"| MQTT_Bridge
    Analytics <--> Edge_Compute
    ERP <-->|"OPC-UA"| OPC_GW

    MQTT_Bridge <--> Edge_Compute
    OPC_GW <--> Edge_Compute
    Security <--> Edge_Compute
    Edge_Compute <--> TSN

    TSN <-->|"Prioritized Traffic"| PROFINET_Net
    TSN <-->|"Prioritized Traffic"| EtherCAT_Net
    TSN <--> Standard_ETH

    PROFINET_Net <--> PLC
    EtherCAT_Net <--> Drives
    Standard_ETH <--> HMI
    PLC <-->|"Modbus/IO-Link"| Sensors

    style Cloud fill:#2C3E50,color:#fff
    style Edge fill:#16A085,color:#fff
    style Network fill:#E67E22,color:#fff
    style Field fill:#7F8C8D,color:#fff
    style TSN fill:#fdebd0,color:#2C3E50
    style OPC_GW fill:#d4efdf,color:#2C3E50
    style Edge_Compute fill:#d4efdf,color:#2C3E50
    style Security fill:#d4efdf,color:#2C3E50

Figure 1252.10: IT/OT convergence architecture showing four layers. Cloud/Enterprise Layer (navy) contains ERP, analytics, and data lake systems connected via REST/GraphQL. Edge/Gateway Layer (teal) provides OPC-UA protocol translation, edge computing, and secure MQTT bridging to cloud. Industrial Network Layer (orange) uses TSN switches for deterministic Ethernet supporting PROFINET and EtherCAT traffic. Field Device Layer (gray) includes PLCs, servo drives, sensors (Modbus/IO-Link), and HMI panels. OPC-UA serves as the integration protocol between IT and OT domains. {fig-alt=“Four-layer IT/OT convergence architecture. Cloud Layer: ERP/MES systems, analytics platform, data lake connected via cloud APIs. Edge Layer: OPC-UA gateway for protocol translation, edge computing for local analytics, security gateway (firewall/VPN), MQTT bridge for cloud connectivity. Network Layer: TSN switch providing deterministic Ethernet, PROFINET RT/IRT network, EtherCAT ring topology, standard Ethernet for non-critical traffic. Field Layer: PLCs (Siemens, Rockwell), servo drives for motion control, sensors using Modbus/IO-Link, HMI panels. Vertical connections show protocol transitions: HTTPS/MQTT to cloud, OPC-UA between edge and enterprise, TSN-prioritized traffic to field networks.”}

1252.13.2 Industrial Protocol Cycle Time Comparison (Variant View)

This visualization compares cycle times and suitability across industrial protocols for different application categories:

%%{init: {'theme': 'base', 'themeVariables': {'primaryColor': '#2C3E50', 'primaryTextColor': '#fff', 'primaryBorderColor': '#16A085', 'lineColor': '#E67E22', 'secondaryColor': '#16A085', 'tertiaryColor': '#7F8C8D'}}}%%
graph TB
    subgraph Header["Protocol Selection by Cycle Time"]
        direction LR
        H1["Faster ← Cycle Time → Slower"]
    end

    subgraph Micro["< 100 µs (Isochronous)"]
        EC["EtherCAT<br/>31.25 µs min<br/>Motion control"]
        PNIRT["PROFINET IRT<br/>31.25 µs<br/>Synchronized drives"]
    end

    subgraph Milli1["100 µs - 1 ms"]
        PNRT["PROFINET RT<br/>250 µs - 1 ms<br/>Fast I/O"]
        PLK["Powerlink<br/>100 µs - 1 ms<br/>Synchronized I/O"]
    end

    subgraph Milli10["1 - 10 ms"]
        EIP["EtherNet/IP<br/>1 - 10 ms<br/>Standard automation"]
        MODT["Modbus TCP<br/>5 - 50 ms<br/>Legacy integration"]
    end

    subgraph Soft["> 10 ms (Soft Real-Time)"]
        OPCUA["OPC-UA<br/>1 ms - 1 s<br/>IT/OT integration"]
        MQTT_IND["MQTT + Sparkplug<br/>10 ms - 1 s<br/>Cloud connectivity"]
        HTTP["HTTP/REST<br/>100 ms - 10 s<br/>Configuration, HMI"]
    end

    subgraph Apps["Application Mapping"]
        A1["High-speed motion:<br/>Servo drives, robots<br/>→ EtherCAT, PROFINET IRT"]
        A2["Fast discrete I/O:<br/>Packaging, assembly<br/>→ PROFINET RT, Powerlink"]
        A3["Process control:<br/>Temperature, pressure<br/>→ EtherNet/IP, Modbus TCP"]
        A4["Monitoring & analytics:<br/>SCADA, cloud<br/>→ OPC-UA, MQTT"]
    end

    Micro --> A1
    Milli1 --> A2
    Milli10 --> A3
    Soft --> A4

    style Header fill:#f9f9f9,stroke:#2C3E50
    style Micro fill:#c0392b,color:#fff
    style Milli1 fill:#E67E22,color:#fff
    style Milli10 fill:#16A085,color:#fff
    style Soft fill:#2C3E50,color:#fff
    style Apps fill:#7F8C8D,color:#fff
    style EC fill:#fadbd8,color:#2C3E50
    style PNIRT fill:#fadbd8,color:#2C3E50
    style PNRT fill:#fdebd0,color:#2C3E50
    style PLK fill:#fdebd0,color:#2C3E50
    style EIP fill:#d4efdf,color:#2C3E50
    style MODT fill:#d4efdf,color:#2C3E50
    style OPCUA fill:#d6eaf8,color:#2C3E50
    style MQTT_IND fill:#d6eaf8,color:#2C3E50
    style HTTP fill:#d6eaf8,color:#2C3E50

Figure 1252.11: Industrial protocol comparison by cycle time. Isochronous (<100 µs, red): EtherCAT and PROFINET IRT for motion control and synchronized drives. Fast (100 µs-1 ms, orange): PROFINET RT and Powerlink for fast I/O. Standard (1-10 ms, teal): EtherNet/IP and Modbus TCP for automation. Soft real-time (>10 ms, navy): OPC-UA and MQTT for IT/OT integration and cloud. Application mapping shows high-speed motion needs EtherCAT, discrete I/O uses PROFINET RT, process control uses EtherNet/IP, monitoring uses OPC-UA/MQTT. {fig-alt=“Protocol cycle time comparison chart. Under 100 µs (isochronous, red): EtherCAT (31.25 µs min) and PROFINET IRT (31.25 µs) for motion control and synchronized drives. 100 µs to 1 ms (orange): PROFINET RT (250 µs-1 ms) and Powerlink (100 µs-1 ms) for fast synchronized I/O. 1-10 ms (teal): EtherNet/IP (1-10 ms) and Modbus TCP (5-50 ms) for standard automation and legacy integration. Over 10 ms (soft real-time, navy): OPC-UA (1 ms-1 s), MQTT+Sparkplug (10 ms-1 s), HTTP/REST (100 ms-10 s) for IT/OT integration, cloud connectivity, and configuration. Applications: high-speed motion (servo, robots) needs EtherCAT/PROFINET IRT; fast discrete I/O (packaging, assembly) uses PROFINET RT/Powerlink; process control (temp, pressure) uses EtherNet/IP/Modbus; monitoring and analytics uses OPC-UA/MQTT.”}

1252.14 What’s Next

Continue exploring industrial protocols:

OPC-UA Fundamentals - Deep dive into OPC-UA architecture and services
Modbus Protocol - Modbus RTU and TCP implementation
Industrial Ethernet - PROFINET, EtherCAT, and TSN
IIoT and Industry 4.0 - Industrial IoT context