Redundant Control-Unit Communication Using Multipath TCP Failover
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Solution Overview
Problem
Industrial automation systems face issues with communication link interruptions leading to unnecessary service request repetitions and incomplete message transmission, which can cause production plant failures and costly downtime, especially due to high message traffic in redundant communication networks.
Innovation Solution
A method for setting up a redundant communication connection between a failsafe control unit and a communication device using primary and secondary control devices, where two communication connections are established using multipath TCP subflows, with data segments alternately transmitted between them to ensure high availability and minimize downtime.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single communication link is used between control devices, then device complexity is reduced, but reliability deteriorates due to communication interruptions and message loss
Solution Approach 1:
The communication system is segmented into multiple independent communication links (first and second links) between the first and second control devices. Each link operates independently, allowing the system to maintain communication reliability by switching to an alternative link if one fails, while keeping each individual link relatively simple in structure
Solution Approach 2:
The system changes the parameter of communication path redundancy by establishing multiple communication links with different network addresses. The transport protocol dynamically selects and switches between links based on their operational status, transforming a single static communication path into multiple dynamic paths without fundamentally changing the control device architecture
2Reliability
If multiple redundant communication links are established, then reliability is improved, but device complexity increases due to additional communication paths and management overhead
Solution Approach 1:
The transport protocol implements self-service functionality by automatically monitoring the status of multiple communication links and autonomously selecting the operational link for data transmission. The system performs self-diagnosis and self-switching without requiring external intervention or complex manual configuration, reducing the burden on operators while maintaining high availability
Solution Approach 2:
The transport protocol acts as an intermediary layer between the application layer and the physical communication interfaces. It manages the complexity of multiple redundant links by providing a unified interface to upper layers, handling link selection, switching, and status monitoring transparently, thus isolating the complexity from the control logic
3Reliability
If communication links are monitored and switched upon failure, then reliability is improved, but loss of time occurs during link failure detection and switchover
Solution Approach 1:
The system performs preliminary actions by pre-establishing multiple communication links and pre-configuring their network addresses before any failure occurs. The transport protocol maintains ready-state alternative paths and pre-validates their availability, so that when a failure occurs, the switchover can be executed immediately without time-consuming detection or configuration steps
Solution Approach 2:
The transport protocol ensures continuity of useful action by implementing seamless link switching that maintains the communication flow without interruption. The system continuously monitors link status and maintains data transmission on operational links, ensuring that the control communication function continues uninterrupted even during link failures and failover events
Data Source
Figure 1
Figure 2
AI summary
A transport or switching function unit (111, 114) of a communication device (100) establishes two communication connections (110, 120) to a fail-safe control unit (200), which comprises the primary and secondary control devices, using at least one communication network address assigned to a primary control device (201) or a secondary control device (202). Data transmitted via a first communication connection (110) is forwarded from the primary control device to the secondary control device via a first synchronization connection (210). Similarly, data transmitted via a second communication connection (120) is forwarded from the secondary control device to the primary control device via a second synchronization connection (220).