How systems communicate
No function without communication: interfaces make sure that components of the railway infrastructure are networked effectively.
Each network is only as strong as the nodes that hold it together. This also applies to the networked systems of the railway infrastructure, which has numerous levels and components. Interfaces are therefore crucial to the transmission and exchange of complex data or whole data packets. They form a basis for the functioning of interlockings, monitoring and diagnostic systems, level crossing solutions and signalling equipment. Component manufacturers must therefore ensure that their products can communicate with existing structures and other systems.
Different interface formats are used depending on the solution, requirement and possibilities. A distinction is usually made between parallel interfaces and serial interfaces. The specific features of the two groups include the type and scope of data that can be transmitted, and the possible safety standards and type of data transfer media that can be used (see table).
Interfaces have a determining influence on the depth of information of data.
Simple and direct: parallel interfaces
If application data is output via switching contacts, then an exclusive data connection is needed for each transfer and each direction of transmission. This applies when connecting a sensor to an evaluation unit or when forwarding the evaluated data to a higher-level system. This means that more and more connections need to be installed as the number of components to be integrated rises. The safety of the transmission, which is usually provided via a copper cable, must be classified as outstanding since components are arranged repeatedly on the interface. The likelihood of a short-circuit between the conductors must also be ruled out.
Using these proven, voltage-free hardware interfaces, axle counters and wheel detection systems can, for example, be easily and quickly integrated into electromechanical, relay and electronic interlockings. If an axle counter is exclusively used for train detection, it generally transfers the “clear/occupied” information via a relay interface as an output variable. It receives the “resetting information” via a voltage-free input, such as an optocoupler.
Modern axle counters can be integrated via parallel or serial interfaces.
Multi-directional and flexible: serial interfaces
Serial interfaces offer a range of benefits compared to parallel solutions. These include being able to easily implement decentralised architectures and the bidirectional transmission of various information via a single connection. They are already being used as standard these days in the railway industry for more complex applications. And based on the current trend, it is clear that in future they will be used even more frequently.
Transmission of various application data
To output application data via serial interfaces, at component level it is possible to connect via Ethernet, glass-fibre or radio connections, for instance. In comparison with systems with parallel interfaces, the hardware outlay is significantly less since a common connection can be used for various data. This in itself enables a serial interface to exchange a series of additional information such as direction or speed, in addition to the output of “clear/occupied” or “reset”.
Diagnostic data too can be transmitted in the same way as safety-relevant data when protocol interfaces are used. An additional communication channel therefore does not need to be set up in addition to the actual system connection. When using parallel interfaces, the flexible extension of the data transfer is not possible. In order to do that, specific contacts would have to be set up from scratch for the transmission of each individual piece of information.
A prerequisite for using serial interfaces is that the relevant safety protocols are available. The development outlay required may initially strike the user as being an extra cost factor. However, thanks to rising demand, different protocols specifically developed for railway applications are now already available and can be used for this purpose. The freely available Frauscher Safe Ethernet FSE is an example of this kind of protocol. You can read more about this in the article “Strictly according to protocol”.
Data transfer media
Software interfaces can provide data via various media and networks. Besides fibre optic cables, the media also include radio connections and copper cables. It is crucial that the requirements in accordance with EN 50159 for safety-relevant communication in data transfer systems are taken into consideration in the railway sector. Since Category 3 networks essentially hide the risk of unauthorised access, it is advisable to use Category 2 networks in order to protect the railway infrastructure. These manage without the need for cryptographic protection of the data being transmitted – and with it, an update at short intervals.
Stefan Lugschitz, R&D | Systems Manager, Frauscher Austria
Exploiting the full potential
Existing systems based on hardware interfaces can usually be extended in the future. This is because new components can for instance be integrated via relay interfaces if they are equipped accordingly. But the full potential of data can only be exploited at a cost. While switching contacts demonstrate a very good real-time behaviour due to their extremely short response time, the specific inputs and outputs required due to the exclusivity of the lines, which was described at the start, are very expensive.
When implementing new systems, serial interfaces can provide significant savings since the infrastructure can be used in succession to the transmission of various data. This not only means independence from the respective transmission medium, but also the possibility of a flexible system extension. By using the defined protocol, other components can be integrated with relatively little hardware outlay.
Outlook: networks and clouds
The possibilities that digitalisation offers also lead to increased demands on data processing and storage in the railway sector. The set-up of corresponding network structures is progressing quickly. As is the case in many other sectors, the use of cloud applications is becoming increasingly significant. They are especially impressive when it comes to the preservation and constant availability of data.
The aforementioned demands on safety and availability, which play a vital role here in the railway industry, mean that these developments still face huge challenges. In principle though, we must assume that suitable solutions with regard to diagnostic data will be available sooner rather than later unlike in safety-relevant areas.
Data transmission, data processing and data storage – here too, digitalisation is driving change in the railway industry. There is no shortage of examples of this. Cloud-based data management is already being used in various sectors and increases the potential even further through big data storage, machine learning and cognitive computing. In safety-relevant sectors in particular, these approaches must also go through a series of specific developments.
Focusing on customer benefits
Parallel and serial interfaces offer specific benefits according to requirements. That is why it goes without saying that we should offer all interface variants in the product portfolio in order to cater for all types of integration.
“We want to maximise the benefits to our customers and therefore make our data available via analogue or digital interfaces. Full integration of our systems into higher-level networks is also possible. At integration level 1, the RSR110 wheel sensor emits a separate evaluable sensor signal via an open analogue interface. Our wheel detection systems and axle counters provide data evaluated at Level 2 as information via digital interfaces. In turn, this can then be fully integrated into higher-level architectures at Level 3, via the Frauscher Safe Ethernet FSE protocol or by implementing customer-specific protocols. The disclosure of company know-how will of course give rise to controversy. However, we have made a conscious decision in favour of doing so as we consider the customer benefits to be overriding and want to make sure that our customers can use the systems independently.”
Rudolf Thalbauer, Research & Development Director, Frauscher Austria
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