UIC Leaflet 755-2: Ground-to-Train Radio Systems – Data Transmission Protocols

What is UIC Leaflet 755-2?

UIC Leaflet 755-2 is an essential technical specification titled “Ground-to-train radio systems – Data transmission.” While Leaflet 751-2 focuses on the radio frequency and physical hardware, 755-2 is dedicated to the logical layer—defining how information is packaged, addressed, and transmitted over the air.

In modern Infrastructure Management, voice communication alone is insufficient. UIC 755-2 enables Data Exchange for critical functions like train identification, status reporting, and emergency signaling. By standardizing these protocols, it ensures Interoperability, allowing a locomotive to communicate its digital status to a foreign network’s control center.

Core Messaging and Data Protocols

The leaflet dictates the structure of the digital messages sent between the Rolling Stock and the ground stations. This ensures that the “language” used by the machines is consistent:

• Train Identification: Standardized formats for transmitting the train number and vehicle ID to the dispatcher.
• Status Codes: Preset digital codes for common operational messages (e.g., “Ready for departure,” “Passing signal at danger,” or “Mechanical fault detected”).
• Addressing Modes: Protocols for selective calling, allowing a dispatcher to send data to a specific train, a group of trains, or all trains in a defined geographical area.
• Priority Handling: Mechanisms that ensure safety-critical data (like an emergency stop command) takes precedence over routine operational data.

Interface and Transmission Characteristics

UIC 755-2 also defines the Interface Requirements between the radio terminal and the train’s internal data systems (such as the train bus):

• Error Correction: Implementation of Forward Error Correction (FEC) and Cyclic Redundancy Checks (CRC) to ensure that data remains intact despite the electromagnetic interference common in the Rail Environment.
• Transmission Rates: Definition of baud rates and modulation schemes optimized for low-latency delivery of safety commands.
• Acknowledgment Logic: Standardized “handshaking” procedures where the receiving station must confirm the receipt of critical data packets.

Impact on Operational Safety

The protocols defined in UIC 755-2 are the backbone of automated safety features. For example, if a driver triggers a “General Emergency” signal, the 755-2 protocol ensures that every radio in the vicinity receives the digital trigger instantly, regardless of the manufacturer of the onboard unit. This provides a level of Operational Safety that voice communication cannot match in speed or reliability.

Comparison: Voice-Only vs. Data-Integrated (UIC 755-2) Systems