The Digital Backbone: UIC Leaflet 752 Data Transmission

Introduction to UIC Leaflet 752

Long before the public internet became secure enough for critical infrastructure, European railways needed a way to share data instantly—whether for seat reservations, freight tracking, or timetable updates. UIC Leaflet 752, titled “General regulations concerning the establishment and technical operating of international data transmission,” established the rules for this private digital highway.

This leaflet governs the famous HERMES (High Efficiency Railway Manager Electronic System) network, a closed and secure Wide Area Network (WAN) that connects the IT centers of different national railways (e.g., DB to SNCF), ensuring that operational data flows reliably across borders.

Snippet Definition: What is UIC 752?

UIC Leaflet 752 is a technical regulation that defines the administrative and technical conditions for establishing data transmission links between railway undertakings. It specifies the requirements for the availability, security, and management of the international network (originally based on X.25, now largely IP/MPLS) known as HERMES, managed by Hit Rail.

The HERMES Network

The core subject of UIC 752 is the management of the interconnection points between railways.

• Purpose: To create a “Railway Intranet” isolated from the public internet, protecting critical traffic from DDoS attacks or interception.
• Management: The network is technically managed by Hit Rail, a company formed by European railway operators to oversee compliance with UIC 752.
• Evolution: While UIC 752 originally specified legacy protocols like X.25, modern implementations utilize secure IP VPNs and MPLS (Multiprotocol Label Switching) technologies to handle high-bandwidth applications like video monitoring and real-time signaling data.

Technical Requirements

UIC 752 sets strict Service Level Agreements (SLAs) for the data links:

1. Availability and Reliability

The network must operate 24/7/365. The leaflet defines redundancy requirements, ensuring that if one physical cable is cut (e.g., between France and Germany), traffic is automatically rerouted through another path (e.g., via Belgium) without data loss.

2. Protocol Independence

The “pipe” defined by UIC 752 must be agnostic to the content. It carries everything from legacy mainframe messages to modern XML (TAF-TSI) files.

Comparison: UIC 752 vs. UIC 917

It is essential to distinguish between the road (Network) and the trucks (Messages).

Operational Context

Today, UIC 752 remains relevant as the governance framework for the TSI (Technical Specifications for Interoperability) data exchange. When a freight train crosses from Poland to Germany, the “Train Composition Message” travels over the secure links defined by UIC 752/Hit Rail, ensuring that the German infrastructure manager knows exactly what hazardous goods are on board before the train arrives.