Train Communication Network (TCN)
The Train Communication Network is the family of onboard data networks standardised in IEC 61375 that connects the control units, sensors and subsystems of a train. It includes the Ethernet Train Backbone linking vehicles or consists and the Ethernet Consist Network within them, alongside the older MVB and WTB buses.
How it works
Within a vehicle or fixed consist, the Ethernet Consist Network (ECN) or the older Multifunction Vehicle Bus (MVB) connects the traction, brake, door, HVAC and passenger systems to the Train Control and Management System. Between consists, the Ethernet Train Backbone (ETB) or the older Wire Train Bus (WTB) links the units together and discovers the train's composition automatically when vehicles are coupled.
The Train Real-time Data Protocol (TRDP) runs on top of the Ethernet networks to exchange process data and messages between devices. Modern trains increasingly consolidate control, diagnostics, CCTV and passenger information onto the same Ethernet infrastructure, separated by VLANs and gateways.
Why it matters for security
Moving onboard control to Ethernet and IP has made trains far more capable and far more connected, but the underlying protocols were designed for reliability rather than security and typically lack authentication. Anyone with access to the onboard network, whether through a maintenance port, a compromised passenger system or the train-to-ground link, can potentially observe or inject control traffic.
Because trains are coupled and uncoupled, visit different depots and are maintained by multiple suppliers, the onboard network's boundaries are hard to enforce. Standards such as IEC 62443 and IEC 63452 treat the TCN as a system requiring zoning and monitoring, and rolling stock security programs increasingly deploy onboard sensors to watch it.
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