EN 61375-3-3: Shaping Rail’s Interoperable Future

An Introduction to EN 61375-3-3: The CANopen Consist Network (CCN)

EN 61375-3-3 is an international standard that specifies the communication profile for a CANopen Consist Network (CCN) within railway vehicles. It defines the rules, services, and protocols necessary for interoperable data exchange between electronic devices in a fixed or semi-permanent train consist, leveraging the robust and widely adopted CANopen protocol.

As part of the broader EN 61375 series, which governs the Train Communication Network (TCN), this standard provides a cost-effective and reliable solution for non-vital communication. It facilitates the integration of various subsystems like HVAC, door controls, lighting, and passenger information systems from different manufacturers, ensuring they can communicate seamlessly within a defined train unit.

The Role of CCN within the TCN Architecture

The Train Communication Network (TCN) is a hierarchical communication system designed for the complex environment of a modern train. It ensures reliable data flow from the driver’s cab to every connected device across multiple carriages. The CCN operates at a specific level within this hierarchy.

• Train Backbone: This is the highest level of communication, connecting different vehicles or consists. It is typically implemented using the Wire Train Bus (WTB) for time-critical functions or the Ethernet Train Backbone (ETB) for high-bandwidth applications.
• Consist Network: This network level manages communication within a “consist”—a pre-defined group of coupled vehicles that operate as a single unit (e.g., a 3-car EMU). The CANopen Consist Network (CCN) defined by EN 61375-3-3 is one of the standardized technologies for this layer.
• Vehicle Bus: This is the lowest level, handling communication between devices within a single vehicle or carriage. Technologies like CAN, MVB, or Ethernet are commonly used here.

The CCN, therefore, acts as a middle layer, aggregating data from various devices within its consist and communicating with other consists or the train control system via the Train Backbone.

Key Technical Principles of EN 61375-3-3

EN 61375-3-3 does not invent a new protocol; instead, it defines an application profile that tailors the existing CANopen standard (CiA 301) for the specific demands of the railway environment.

Foundation on CANopen Protocol

The standard builds upon the well-established CAN (Controller Area Network) bus for its physical and data link layers and the CANopen protocol for the higher application layers. This provides several inherent advantages:

• Object Dictionary (OD): Each CCN device has an Object Dictionary, which is a standardized data structure holding all configuration parameters, process data, and device functionalities. Communication is achieved by reading from or writing to entries in this dictionary.
• Communication Objects: It utilizes standard CANopen communication objects, including PDOs (Process Data Objects) for fast, real-time data exchange (e.g., sensor status, commands) and SDOs (Service Data Objects) for configuration and diagnostic access.
• Network Management (NMT): NMT services are used to control the state of the network nodes (e.g., start, stop, reset), providing robust network supervision.

The Inauguration Process

A critical function defined by the standard is “inauguration.” When the train is powered on or a consist is reconfigured, the network must automatically discover all connected devices, assign unique addresses, and establish communication paths. This process is managed by a designated “Consist Network Master” and ensures plug-and-play functionality, which is essential for maintenance and operational flexibility in railways.

Physical Layer and Topology

The CCN typically employs a linear bus topology using a shielded twisted-pair cable, which is robust against the electromagnetic interference (EMI) common in railway environments. The standard specifies a fixed baud rate of 125 kbit/s to ensure reliable communication over the maximum defined network length within a consist. Proper termination resistors at both ends of the bus are mandatory to prevent signal reflections and maintain data integrity.

Practical Applications and Benefits of CCN

The CANopen Consist Network is primarily used for non-safety-critical (or non-vital) train functions where reliability and cost-effectiveness are key.

• HVAC Control: Managing air conditioning, heating, and ventilation units across the consist.
• Door Systems: Coordinating the opening, closing, and status monitoring of passenger doors.
• Lighting Control: Centralized control of interior and exterior lighting.
• Passenger Information Systems (PIS): Distributing data for on-board displays and announcements.
• Toilet Systems: Monitoring water levels, occupancy, and system faults.

The primary benefits of adopting EN 61375-3-3 include interoperability between equipment from different suppliers, reduced wiring complexity compared to point-to-point connections, and the use of commercially available off-the-shelf (COTS) CAN components, which lowers development and maintenance costs.

Comparison of TCN Consist Network Technologies

CCN is one of several technologies that can be used for the consist network. The table below compares it with other common alternatives.

Conclusion: The Value of EN 61375-3-3

EN 61375-3-3 plays a vital role in the standardization of modern railway communication systems. By providing a clear and robust framework for a CANopen-based consist network, it enables train builders and operators to create integrated, interoperable, and cost-efficient systems. Its focus on non-vital functions allows more expensive and complex networks like MVB or ECN to be reserved for tasks that require their specific capabilities, leading to an optimized and well-balanced TCN architecture.