Like all technologies with a long history, railroad vehicles were originally controlled by analog controls. However, over time the comfort and the efficiency of the work made it necessary to digitalize many processes, so that, in the best case scenario, they can run automatically.
Furthermore, it also became necessary to look at the operating modes of the individual vehicles in order to analyze them and to find and eliminate possible error sources or defects. Fieldbuses or these requirements have been used for several decades. In the case of railway technology, the Train Communication Network is widely used. This network is composed of a system using two different fieldbuses and is also structured hierarchically.
The Bus and Data Types with the Train Communication Network
The structure of the Train Communication Network provides for two different types of buses and two different types of data. The buses used are
- the MVB and
- the WTB.
The Multifunction Vehicle Bus is originally a vehicle bus, but because of the exclusive use of the Train Communication Network for railway vehicles, this vehicle bus must be seen rather as a fieldbus being used in a vehicle or a group of vehicles coupled to each other.
The Wire Train Bus is a train bus that should be seen as a fieldbus, which can connect different vehicles and can also describe an entire train.
The commonality of these two protocols lies in the synchronous and cyclic data transfer. Furthermore, the messages are source-addressed. This deterministic behavior offers two essential advantages for use of the Train Communication Network.
- Fulfillment of the real-time criteria
- Increase of the fault tolerance
There are also two different types of the data types defined for the Train Communication Network.
- Process data
- Message data
Here, the process data is data that can be characterized as time-critical and which in case of the MVB can be max. 32 bytes. With the WTB, this value is max. 128 bytes. The process data is transferred at regular intervals, where the length of one interval can be between 1 ms and max. 1024 ms.
The message data is considerably longer and includes messages that are transferred only on request. When required, this data is segmented on the respective bus and is always acknowledged afterwards.
Use of the Train Communication Network
This fieldbus system resulted from the work of the International Railway Union in Utrecht and the International Electro technical Commission in Geneva. Both parties tried to standardize a data network able to meet the high demands of a data transfer of rail vehicles. This standard, found in the Train Communication Network, allows interoperability of the rail vehicles.
The interchangeability of the equipment is created by the Train Communication Network, so that the cost efficiency of the technology also shows here. The characteristic of the train bus, one of the two employed fieldbuses, lies in the ability to perform a configuration with each change in the train assembly, so that the position of a vehicle and its characteristics can be recognized and forwarded automatically.
The prospects forthe Train Communication Network
Finding a common standard by the parties took approximately ten years and brought with it a standard recognized today, with the result that the TVN can today be found, and is being used, in thousands of rail vehicles around the world. In addition to the cyclic data transfer by means of the vehicle bus and the train bus, this technology also supports the exchange of messages that are neither demand-oriented, nor time-critical. These include for example the messages for management of the network. These can be sent between any components of a train via the seven-layer stack model with the TCN.
This shows that the decision to develop a separate standard and not to wait for an international fieldbus was correct. Although it is not mandatory that a sub-unit has a standardization, and although naturally other buses exist within a rail vehicle system, it is now generally expected that the data being exchanged between the individual participants is always routed via the TCN.
The Train Communication Network has become a monopoly. Although fieldbuses similar to the technology of the TCN can be found, in most cases they do not solve all tasks given to them, so that only this standard is able to meet stringent requirements. Accordingly, this double fieldbus system has created a successor for analog remote control of vehicles. In addition to saving costs and time, this digitalization of the control has also made it easier to maintain by prevention of failures in the network.