The Digital Nervous System: EN 61375-3-4 & The Ethernet Consist Network

What is EN 61375-3-4?

EN 61375-3-4 (part of the IEC 61375 series) is the European Standard that specifies the Ethernet Consist Network (ECN). In simple terms, it defines how devices within a single railway vehicle (or a permanently coupled unit, known as a “consist”) communicate using standard Ethernet technology.

As modern trains transform into “data centers on wheels,” legacy fieldbuses like MVB (Multifunction Vehicle Bus) can no longer handle the bandwidth required for video surveillance (CCTV), advanced diagnostics, and Passenger Information Systems (PIS). EN 61375-3-4 solves this by standardizing the use of 100 Mbps or Gigabit Ethernet for on-board communication, ensuring that different subsystems from different manufacturers can exchange data seamlessly over an IP network.

The Role of TRDP (Train Real-time Data Protocol)

Standard office Ethernet (TCP/IP) is not inherently “real-time” enough for critical train control functions like braking or door control. EN 61375-3-4 introduces the Train Real-time Data Protocol (TRDP) to bridge this gap.

• Process Data (PD): TRDP allows for the cyclic, deterministic transmission of critical status variables (e.g., speed, door status) utilizing UDP multicast.
• Message Data (MD): Handles large, non-critical file transfers (e.g., diagnostic logs or database updates) via TCP.
• Interoperability: It provides a common “language” so that a brake computer from Supplier A can talk to a central computer from Supplier B over a standard Ethernet switch.

Network Topology and Redundancy

The standard does not mandate a specific cable layout but strongly recommends topologies that offer high availability. In practice, ECNs are often designed as Ring Topologies. If a cable breaks or a switch fails, the network traffic automatically reroutes in the opposite direction, ensuring no loss of control.

Comparison: MVB (Legacy) vs. ECN (EN 61375-3-4)

The shift from MVB to ECN represents the biggest technological leap in railway avionics in the last 30 years.