Enhancing Bidirectional Modbus TCP ↔ RTU Gateway Performance: A UDP Mechanism and Markov Chain Appro
AUDP and Markov-based reliability enable a lightweight Modbus UDP–RTU gateway with TCP-level stability and low latency.
WIZnet - W5500
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Enhancing Modbus Gateway Performance with AUDP and W5500: A Markov-Chain–Driven Approach
As industrial networks continue to evolve, modern IIoT systems increasingly rely on a wide mix of heterogeneous devices and communication protocols. Among them, Modbus remains one of the most widely deployed due to its simplicity and extensive legacy base. However, bridging Modbus RTU (serial) and Modbus TCP/UDP (Ethernet) efficiently is far from trivial—particularly when real-time responsiveness is required.
The recent paper “Enhancing Bidirectional Modbus TCP ↔ RTU Gateway Performance: A UDP Mechanism and Markov Chain Approach” addresses this problem by rethinking the transport layer itself. The authors identify a long-standing issue: traditional Modbus TCP-to-RTU gateways suffer from the inherent overhead of the TCP stack, while UDP, though extremely fast, lacks the reliability mechanisms necessary for industrial applications.
AUDP: Adding Reliability to UDP Without Sacrificing Speed
UDP’s appeal lies in its connectionless nature—no handshake, no session maintenance, and minimal overhead. These characteristics make it ideal for low-latency systems, but they also introduce vulnerabilities such as packet loss, incorrect frame matching, and unpredictable behavior under network jitter.
To address this, the authors propose AUDP (Advanced UDP), which incorporates four reliability mechanisms directly at the application layer:
- CRC-16 verification for data integrity
- Retransmission mechanism to recover from packet loss
- Transaction ID matching to eliminate mis-association of responses
- Exponential backoff to avoid congestion during retries
What makes the paper stand out is not merely these mechanisms, but the mathematical rigor used to justify them. Through Markov chain modeling, the study quantifies the effects of packet loss, retransmission probability, and delay distributions to determine how reliability and latency behave over time.
Rather than claiming that “UDP is faster,” the research demonstrates why and how UDP can be made reliable enough for industrial-grade communication.
Why the WIZnet W5500 Was Chosen as the Ethernet Core
One of the most significant engineering choices in the proposed gateway is the selection of the WIZnet W5500 Ethernet controller. This is not a trivial decision—the W5500 sits at the heart of the system, enabling the theoretical improvements of AUDP to translate into real, measurable performance gains.
The paper explicitly highlights the W5500’s role:
“The W5500 serves as the core for Ethernet access, integrating a hardware-based TCP/UDP/IP stack… It incorporates 32 KB of dual-port SRAM and supports up to 8 hardware sockets.”
— Sensors 2025, 25, 3861, p.7
This selection is technically significant for several reasons.
1. Hardware-Offloaded TCP/IP Stack → Minimal MCU Load
The gateway uses an STM32F103 MCU. Instead of burdening the MCU with protocol handling, the W5500 processes IP, UDP, and TCP entirely in hardware.
This frees the MCU to focus on:
- Modbus RTU parsing
- AUDP logic
- CRC validation
- Transaction ID management
For a real-time system with tight timing constraints, this division of labor is crucial.
2. Deterministic, High-Performance UDP Handling
The reliability enhancements of AUDP rely heavily on predictable UDP behavior.
W5500’s hardware sockets provide:
- Stable cycle-to-cycle latency
- Minimal jitter
- High throughput without CPU intervention
This consistency forms a clean experimental baseline for the study’s Markov chain modeling.
3. 32 KB Internal Buffer for Robust Request–Response Flows
Modbus gateways often exchange a high frequency of short frames.
W5500’s internal buffer helps prevent:
- Overflow during burst traffic
- Data loss during MCU processing
- Timing drift under load
This contributes directly to the system’s real-time reliability.
4. Simple SPI Integration with DMA
The gateway uses SPI with DMA for zero-overhead transfers.
W5500’s straightforward SPI interface (up to 80 MHz) enables:
- Low CPU usage
- High throughput
- Minimal implementation complexity
This simplicity is beneficial both for research prototyping and industrial deployment.
5. Industrial-Grade Stability
The W5500 combines a built-in PHY with low power consumption and proven link stability—factors that align well with IIoT deployment requirements.
In short, W5500 is not merely an Ethernet chip; within the context of this study, it is the enabler that makes high-speed, reliable AUDP-based Modbus communication experimentally feasible.
Experimental Outcomes: AUDP vs. UDP vs. TCP
The study’s experiments validate the theoretical claims:
Under 30% packet loss and 10% out-of-order traffic:
- AUDP achieves ~17 ms average request–response latency
- UDP is fast but unreliable
- TCP experiences severe latency spikes due to congestion control
Under 20% packet loss:
- Conventional Modbus UDP success rate: 77.4%
- Modbus AUDP success rate: >98%
This is a substantial improvement and clearly demonstrates that AUDP can meet industrial reliability requirements without incurring TCP-level latency penalties.
Conclusion: A Balanced Fusion of Hardware, Software, and Theory
What makes this research noteworthy is the balance it strikes between:
- Transport-layer theory (Markov chains)
- Application-layer protocol design (AUDP)
- Hardware architecture (W5500 + STM32)
The W5500’s deterministic hardware behavior provides a stable foundation on which AUDP’s reliability mechanisms can operate. Combined with rigorous mathematical modeling and real-world experiments, the result is a Modbus gateway architecture that significantly advances what UDP-based industrial communication can achieve.
As demand grows for real-time IIoT networking, studies like this highlight the importance of pairing appropriate hardware choices with well-designed protocol enhancements. The W5500’s hardware UDP engine proves particularly well-suited to this role, enabling both academic exploration and practical adoption of high-performance Modbus gateways.