What is Train Communication Network (TCN) railway communication standard

Table of contents

• Table of contents
• Definition
• TCN standard overview
• Core concepts
  • Train composition
  • Network levels: Train backbone \& Consist network
    • Train backbone
    • Consist network
  • Communication technology classes
• Train inauguration as part of train backbone
• Communication patterns
• Communication data clases
  • Service paramentes

Definition

Train Communication Network (TCN) is an international standard network used for communication within train. TCN is specified by the IEC 61375 standard.

The scope is to ensure interoperability and reliable communication between devices on the train and between multiple trains.

TCN standard overview

Core concepts

Train composition

Train is a composition of closed trains, each closed train having one or several consists and each consist having one or several vehicles.

With a maximum number of 63 vehicles.

TCN train structure

Network levels: Train backbone & Consist network

TCN as a hierarchy of two network levels, a train backbone (TB) level and a consist network (CN) level. And consist networks are connected to the TB with train backbone nodes (TBN).

TCN train network

Train backbone

It is a communication network that links all parts of a train., connecting the control networks of each coach/car (train backbone nodes, TBN). It is the main “highway” for data exchange across the entire length of the train, enabling coordinated operations between cars and centrally managed functions.

To configure, it is necessary to:

1. List possible train compositions (“topologies”)
2. Define directions and orientation on vehicle, consist, closed train and train level
3. Do the train inauguration
4. Finally define the implemented TB services

Communication protocols used: Wire Train Bus (WTB) or Ethernet Train Backbone (ETB).

Consist network

It is a communication network that connects the electronic systems within a single vehicle/car/coach (the “consist”). It allows onboard devices and control units in the same car to communicate and share data.

Communication protocols used: Multifunction Vehicle Bus (MVB), CANopen or Ethernet Consist Network (ECN).

Communication technology classes

These network technologies can be classified in two technology classes:

• Bus technology class. Wire Train Bus (WTB), Multifunction Vehicle Bus (MVB) and CANopen.
• Switched technology class. Ethernet Train Backbone (ETB) and Ethernet Consist Network (ECN).

Train inauguration as part of train backbone

The train inauguration protocol is executed in all active TBN whenever a train is formed, vehicles are (dis)connected, or is powered up and determine:

• The sequence of all active TBN in a train (see an example video TTDP, Train Topology Discovery Protocol)
• Orientation of the consist, where a node is located in, with respect to the train orientation.

Train backbone TCN train directions

Depends on the technology of the train backbone: WTB or ETB.

Communication patterns

TCN communication patterns

Communication data clases

TCN defines five main data classes. Detailed service parameter definitions are provided in application-specific communication profiles.

Data class	Description	Service parameters
Supervisor	Data for network operation tasks, like setup or redundancy control
Process	Real-time control and monitoring data	- Data rate ↓ - Cyclic transmission - Latency ↓ - Jitter ↓ - Data integrity ↑ - Safety integrity ↑
Message	Control and monitoring messages	- Data rate ↓ to - - Latency - - Data integrity ↑ - Safety integrity ↑
Stream	Video or voice data packets	- Data rate ↑ - Latency ↓ - Jitter ↓ - Safety integrity ↓
Best effort	Bulk transfers or non-critical activities that must not disrupt other data classes

Service paramentes

Each data class has communication service parameters that define its transmission characteristics.

Service Parameter	Description	Unit
Data packet size	Amount of data transmitted in one packet	number of octets
Data (packet) rate	Number of packets sent per second	bits/s, Kbit/s, Mbit/s
Cycle time	Time between sending two packets (only for cyclically data)	seconds
Latency	Time for a packet to travel from source to sink	seconds
Jitter	Variation in packet transmission time	seconds
Data integrity	Packet arrives without errors	bit error rate (BER)
Safety Integrity	Probability that errors (data corruption, sequence, timing or authentication) will be detected	Probability of dangerous undetected failures per hour (Pdu)