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TRDP: The Protocol for Interoperable Train Communication

Iris Boss · Systems Engineer· Readin time: 4 min.·7 September 2026

For all systems involved in train operation – such as door control, braking, or air conditioning – to work together smoothly across different manufacturers, they need a shared communication protocol. This is specified in IEC 61375-2-3, Annex A, where the Train Realtime Data Protocol (TRDP) is defined as the standard for train-wide communication.

Origin and Development

TRDP is based largely on the originally proprietary IPTCom protocol from Bombardier Transportation (now Alstom) and was developed with the involvement of all major manufacturers and suppliers of rolling stock – with NewTec playing a leading role. Its further development has since been coordinated by the Train Communication Network Open Source Special Interest Group, or TCNOpen for short, whose current "Full Partners" are Alstom, Siemens, Toshiba, CAF, and NewTec. As a co-developer of TRDP, NewTec was also involved in the evaluation of open TCN protocols commissioned in 2020 as part of the Swiss modernization program "smartrail 4.0," from which TRDP emerged as a suitable protocol for the vehicle bus – an early demonstration of the protocol's practical viability.

TRDP in Detail

TRDP is built on UDP (User Datagram Protocol) – a connectionless transmission protocol with low overhead that enables fast and robust data transfer. TCP is used as well where needed, for non-time-critical data. Two types of data are distinguished:

Process Data (PD): short, time-critical data (max. 1432 bytes) sent cyclically via UDP to one or more recipients (push), or requested on demand (pull)
Message Data (MD): non-time-critical, longer messages transmitted on request

This separation allows both performance-critical control data and more extensive information data to be transmitted efficiently over the same protocol.

TRDP and Safety

TRDP transmission paths are generally regarded as a "black channel" under IEC 61508 – meaning they do not themselves meet the requirements for safety-related applications. For higher safety requirements (up to SIL 2), however, TRDP telegrams can be protected by the additional safety layer SDTv2 (Safe Data Transmission). SDTv2 detects manipulation and errors through checks including the safety code, sequence, latency, protocol and user data version, as well as channel monitoring. With this layer, TRDP meets the requirements of the standard DIN EN 50159:2010 for communication between safety-critical electronic systems on board a train.

TCNOpen: The Open Reference Implementation

To make it easier for manufacturers to integrate TRDP, the TCNOpen initiative provides an open-source implementation in C, hosted on Sourceforge under the Mozilla Public License MPL2. It covers all relevant aspects of TRDP and is modular in structure – separated into PD communication and MD communication – complemented by various example and helper functions that simplify integration into custom projects.

However, some functionalities are only rudimentarily supported by the TCNOpen stack, such as XML-based configuration, train inauguration detection, or thread handling. These functions are typically implemented in an additional high layer on top of the TCNOpen stack, making the official C API more convenient to use and speeding up the development of high-performance TCN applications in accordance with IEC 61375-2-3. This is where NewTec's NTOnTrack TRDP High Layer offers clear advantages.

What This Means for Manufacturers

For train-wide communication via the Ethernet Train Backbone (ETB), TRDP is now mandatory. Increasingly, however, train manufacturers are also requiring TRDP for consist-internal communication via the Ethernet Consist Network (ECN) – an area where CAN has traditionally been widely used.

For component manufacturers, this means in practice: the transition typically happens on a project-specific basis, once a contract requires TRDP in the ECN. This shift involves more than just a software change: it usually requires moving from CAN to Ethernet, which means a new hardware interface as well as adapting the communication software to TRDP.

Manufacturers who make this transition early can participate in more tenders and are immediately ready to deliver for future projects with ECN requirements.

Conclusion

TRDP is the central building block for interoperable train communication – powerful enough to meet today's requirements for flexible train composition, and, with SDTv2, also suitable for applications with higher safety requirements.

As a co-developer of TRDP and an active TCNOpen member, NewTec supports vehicle and component manufacturers in integrating TRDP into their products – from architecture through implementation to conformance and interoperability testing. Learn more about our work in the railway sector on our Railway solutions page.