In daily industrial operations, it is common to find scenarios where state-of-the-art machining centers operate side by side with controllers installed 20 or 30 years ago. This coexistence of the new and the old is proof of the long lifecycle of industrial assets, which are designed to function continuously over extended periods.
The problem is that older equipment typically uses communication technologies created when the sole objective was local control on the shop floor, with no expectation of connecting to other systems.
With the advancement of digital transformation, driven by the need to monitor processes in real time, implement predictive maintenance, and integrate operational data into management systems, the limitations of traditional field protocols have become the single greatest challenge to overcome. The demand for structured, accessible data at the corporate level collides directly with the lack of standardization in legacy serial networks.
However, modernization does not require replacing machinery that remains fully operational. The most viable strategy is building technological bridges capable of connecting existing infrastructure to digital ecosystems. This approach extracts maximum performance from active assets while minimizing risks and enabling a gradual transition toward smart factory automation.
What legacy protocols are and why they are still present
Legacy protocols are communication standards developed between the 1970s and 1990s, based on point-to-point serial transmissions or bus topologies. Among the most widely used technologies are Modbus RTU, PROFIBUS (in DP and PA variants), DeviceNet, serial CC-Link, and CANopen. These networks were engineered to ensure that control commands reached actuators and sensors deterministically while resisting electromagnetic interference.
The continued presence of these technologies on the shop floor comes down to operational and economic factors. The reliability and physical robustness demonstrated over decades mean that engineers and technicians trust these networks to handle routine control tasks.
Furthermore, because the equipment relying on these networks boasts a long service life and has long since amortized its initial investment, replacement is hard to justify when the machine continues to perform its core function flawlessly. Maintenance teams are also already thoroughly trained to diagnose and repair these serial networks, bringing extra peace of mind to day-to-day operations.
| Protocol | Primary medium | Typical speed | Application domain |
| Modbus RTU | RS-485 / RS-232 | 9.6 to 115.2 kbps | Variable frequency drives, multimeters, and instrumentation. |
| PROFIBUS DP | RS-485 twisted pair | Up to 12 Mbps | Assembly lines and remote I/O. |
| PROFIBUS PA | Twisted pair (IEC 61158-2) | 31.25 kbps | Continuous process industries and hazardous areas. |
| DeviceNet | CAN cable (Thick/Thin) | 125 to 500 kbps | Sensors, actuators, and motor control centers. |
The massive presence of these networks in existing brownfield installations creates a scenario where automation operates effectively at the field level, yet remains isolated from higher business intelligence layers.
The costs of maintaining infrastructures solely relying on “old” protocols
Maintaining an industrial plant that depends on legacy serial buses creates a series of bottlenecks that grow increasingly severe as the company seeks to boost efficiency and competitiveness.
The first issue is the difficulty of extracting and contextualizing data. Serial protocols operate with raw data structured in numerical registers without metadata. For instance, data received from a meter via Modbus RTU is nothing more than a number stored at a memory address; this requires every variable to be manually mapped and converted within supervisory systems, a time-consuming process that leaves room for errors.
The master-slave architecture typical of legacy networks imposes physical constraints on data sampling. In this model, the controller queries one device at a time sequentially. As new instruments are added to the bus, the network cycle time increases, making the continuous collection of large data volumes, necessary for predictive maintenance algorithms and IIoT solutions, unfeasible.
Cybersecurity represents another critical point. Legacy protocols were created when industrial networks were completely air-gapped. For this reason, they lack native encryption, authentication, or access control mechanisms. When these legacy networks are connected to Ethernet buses without proper isolation, the facility is exposed to risks of unauthorized access and operational disruptions.
Finally, there is the challenge of a shrinking skilled workforce and rising maintenance costs. Younger professionals enter the market trained in IP-based networks, cloud infrastructure, and modern programming languages; this makes finding technicians experienced in physical RS-485 bus diagnostics, termination resistor tuning, and legacy serial network parameterization increasingly difficult. The result is longer downtime whenever communication failures occur.
What modern protocols offer
Transitioning to modern protocols based on Ethernet and open architectures transforms a factory’s communication network into a high-speed, highly integrated infrastructure.
Adopting protocols such as PROFINET, EtherNet/IP, EtherCAT, and Modbus TCP yields transmission rates ranging from 100 Mbps to gigabits per second, eliminating bandwidth bottlenecks and enabling the simultaneous flow of critical control data and diagnostic information.
For data integration between IT and OT systems, open protocols like OPC UA and MQTT can be leveraged. OPC UA provides an object-oriented data structure that transmits information along with its context, such as units of measurement, operating limits, and quality status, ensuring seamless interoperability between equipment from different manufacturers and management software.
Meanwhile, MQTT utilizes an extremely lightweight publish-subscribe (pub/sub) architecture designed for report-by-exception data transmission. This means devices send information only when a state change occurs, optimizing network bandwidth usage and simplifying the transfer of metrics to cloud platforms and Edge Computing systems.
Market studies conducted by HMS Networks reveal that Industrial Ethernet has solidified its dominance in new factory installations, while traditional fieldbuses continue a steady decline, making room for Ethernet solutions and wireless connectivity. See the data below:
Communication type | Adoption in new installations | Main features |
Industrial Ethernet | 79% | High bandwidth, determinism, support for flexible topologies, and native IT integration. |
| Fieldbuses | 17% | Restricted to specific expansions and high maintenance of legacy plants. |
| Wireless networks | 7% | Applied in mobile equipment, remote sensing, and asset monitoring. |
The combination of modern protocols results in scalable networks featuring native support for encryption and security mechanisms, preparing the infrastructure to support advanced applications like predictive analytics without requiring major future overhauls.
How to implement migration in practice
Modernizing an industrial plant’s communication infrastructure should be executed as a planned, continuous process to avoid unscheduled downtime and ensure a clear return on investment at every stage. A successful transition relies on a clear methodology divided into core phases:
Phase 1: Diagnostics and Asset Inventory
The project must begin with a detailed mapping of all installed infrastructure. Every controller, variable frequency drive, sensor, and actuator must be cataloged, recording supported protocols, physical media, connection health, and generated data volumes. This initial assessment prevents surprises during execution and clarifies which devices can remain in service versus those requiring protocol conversion interfaces.
Phase 2: Defining Business Goals and KPIs
Upgrading the network must serve clear business goals. The team must define which Key Performance Indicators (KPIs) will be impacted, whether improving Overall Equipment Effectiveness (OEE), reducing unplanned maintenance downtime, or automating data collection for traceability reporting.
Phase 3: Zones and Conduits Architecture
Based on the guidelines of the IEC 62443 cybersecurity standard, the plant must be segmented into logical security zones that group systems with similar operational and protection requirements. Where data exchange between distinct zones is necessary, conduits controlled by firewalls and gateways are defined, ensuring that a vulnerability in one segment does not compromise the entire facility’s control systems.
Phase 4: Implementation of Industrial Gateways
Deploying protocol conversion gateways and edge computing devices is the key strategy for bridging legacy systems with modern networks without replacing existing controllers. The global industrial gateway market, valued at $1.46 billion in 2024 and projected to reach $2.91 billion by 2033, reflects the widespread adoption of this approach across industrial sectors.
Gateways act as real-time translators: they read serial data from older equipment using protocols like Modbus RTU or PROFIBUS and convert it into modern standards such as OPC UA or MQTT over Ethernet. Simultaneously, edge computers process this data locally, filtering out noise and calculating key operational metrics before sending them to cloud platforms or supervisory systems.
Phase 5: Gradual Validation
During the transition phase, the plant operates in a hybrid format: legacy controllers continue executing critical process control over their original serial networks, while gateways concurrently extract data copies to supply analytics and management platforms. This allows teams to validate data accuracy, test network stability, and train personnel without exposing production to operational risks.
Phase 6: Expansion and Structural Modernization
Once the pilot cell or line is validated, the model is scaled across other areas of the plant. As older equipment reaches the end of its mechanical or electronic lifecycle, it is replaced with newer models featuring native Ethernet connectivity, gradually phasing out intermediate gateways and consolidating a fully modern network architecture.
Learn more: How integration with gateways ensures greater security and fast response in industrial operations
Common mistakes to avoid
Industrial communication modernization projects often fail due to strategic mistakes that could have been foreseen and prevented.
The most dangerous is attempting a complete, immediate replacement of all equipment, the so-called “rip-and-replace” approach. This practice demands massive capital expenditure, forces extended production shutdowns, and introduces high operational risks. The correct approach, as previously noted, prioritizes gradual integration.
Another frequent misstep is rushing the convergence of Information Technology (IT) and Operational Technology (OT) networks without first implementing cybersecurity controls. Connecting legacy networks directly to the corporate network without proper segmentation via firewalls and security zones exposes critical control systems to external threats.
A lack of alignment among IT, automation, engineering, and maintenance teams can also compromise project outcomes. Decisions made exclusively by IT without accounting for real-time shop-floor requirements often result in impractical solutions, just as projects led solely by automation teams may lead to difficult corporate integration.
Finally, choosing closed, proprietary technologies for the new network restricts future expansion. Modernization efforts should prioritize open standards, preserving vendor independence and ensuring long-term compatibility with emerging technologies.
The industrial landscape for the coming years
Upgrading communication protocols establishes the necessary foundation for adopting emerging technologies that will transform industrial management in the coming years. The growth of the global industrial communication market, projected to expand from $23.94 billion in 2025 to $40.14 billion by 2034, demonstrates that investments in network infrastructure remain at the core of corporate strategies.
| Market indicator | Current value & projection | Advantage for an industrial plant |
| Global industrial communication market | US$ 23,94 bi (2025) to US$ 40,14 bi (2034) – 5,91% | Increased investment in connectivity to support digitalization and IIoT. |
| Gateway market | US$ 1,46 bi (2024) to US$ 2,91 bi (2033) – 7,8% | Expansion of retrofit solutions to bridge legacy infrastructures. |
| Hardware segment | 44% of total global market revenue | Strong demand for managed switches, edge gateways, and industrial routers. |
In terms of cybersecurity, compliance with the IEC 62443 standard becomes indispensable as connectivity expands. The standard defines Security Levels (SL), ranging from SL 1 (protection against casual or unintentional access) to SL 4 (protection against highly complex, sophisticated attacks). Migrating to modern protocols makes it possible to implement protection mechanisms such as TLS/SSL traffic encryption, digital certificate authentication, and continuous network anomaly monitoring.
Read more: Why risk analysis is the first step to protecting your plant
The migration process in industrial automation should not be viewed as a radical replacement project, but rather as a natural, continuous evolution of the factory’s technological infrastructure. The transition toward digitalization is fully achievable in industrial plants of any scale, provided it is executed in a planned, gradual manner aligned with core business objectives.
