Introduction

In railway signaling and communication systems, safety is paramount. The EN 50159 standard outlines how safety-related communication should be handled over transmission systems, even when those systems are not inherently designed for safety.

This standard applies to various transmission environments, from closed systems controlled by railway operators to open networks like the internet or public wireless connections. The goal is to prevent message errors such as corruption, delays, or unauthorized access, ensuring reliable and secure data exchange.

Types of Transmission Systems

EN 50159 classifies transmission systems into three categories:

• Category 1: Closed systems fully controlled by the designer, with fixed configurations.
• Category 2: Semi-open systems where some properties are unknown, but unauthorized access is prevented.
• Category 3: Open systems where security threats, such as hacking and unauthorized access, must be considered.

Common Threats and Safety Measures

Some of the main threats to railway communication systems include:

• Message corruption (data errors due to electromagnetic interference)
• Message delay or loss (leading to train control issues)
• Masquerade attacks (unauthorized entities injecting false messages)

To counter these threats, EN 50159 requires safety mechanisms like:

• Safety codes (e.g., CRC checks, cryptographic signatures)
• Message sequence numbers (to prevent duplication or reordering)
• Time stamps (to detect delays)
• Source/destination identifiers (to verify message authenticity)

Example: Preventing Signal Errors in a Railway Network
Imagine a train control system sending speed limit commands via a wireless network. Without protection, interference or hacking could alter these messages. By applying EN 50159 principles, the system would:

• Use cryptographic authentication to ensure the message is from a trusted source.
• Include a sequence number to prevent message replay attacks.
• Implement error detection codes to catch corruption.

With these measures, even if an attacker tries to send false speed commands, the system will detect and reject them.

Conclusion

EN 50159 is crucial for ensuring safety in railway signaling and control. By following its guidelines, railway operators can mitigate risks and maintain reliable operations, even in open networks.