RaSTA Protocol Stack

About the Client and the Project

The ongoing digitalization in the railway sector presents new challenges for infrastructure operators. In particular, the integration and communication between different systems demand high standards of safety and efficiency.

In this context, SBB participated in the European initiative EULYNX, which aims to standardize interfaces and signaling systems.

To this end, SBB implemented a Proof of Concept (PoC), with CSA acting as a close partner in the integration of the Rail Safe Transport Application (RaSTA) protocol stack.

Our Services

As part of modernizing its railway infrastructure and introducing EULYNX architectures, SBB evaluated the possibility of running both safety-critical and non-safety-critical applications on the same embedded platform.

A key component is the RaSTA protocol stack—a safety-critical communication stack that ensures reliable and standards-compliant data transmission between interlocking systems and object controllers. The development was carried out according to railway standards EN50128, EN50126, and EN50159, and complied with the highest Safety Integrity Level (SIL4).

CSA was responsible for the complete development and integration of the RaSTA protocol stack for SBB, based on Aviotech’s SCORPOS platform. As part of the project, all system components were developed according to the V-model—including specification, implementation, verification, and validation.

An important part was the integration of the stack onto the dual-channel SCORPOS platform, with spatially and temporally separated partitions, allowing multiple applications to run independently and deterministically.

The RaSTA stack is also split across two partitions: Safety and Retransmission Layer (SIL4) and Redundancy Layer (Basic Integrity). Physically, each channel uses an Ethernet interface with one RaSTA channel. This channel is continuously monitored by a heartbeat. Additionally, TCP/IP, TLS, and OPC-UA were implemented on further partitions.
 
The entire development process was accompanied by thorough technical documentation and concluded with a successful TÜV inspection report at the end of 2022.

The project results were also presented by SBB at the EUG Safety Conference in October 2022.

Thanks to these comprehensive services, CSA was able to effectively support SBB in developing a SIL4-compliant system and ensure that all safety-critical requirements were fully met.

More details can be found in the following blog post:
Successful development and integration of an SIL4 protocol stack for the rail industry

Created Value

Thanks to CSA’s expertise in embedded software, standards, and project management, an approval-ready reference implementation of the RaSTA protocol stack was efficiently realized for SBB. This enables SBB to gain key insights into the EULYNX standard as well as develop requirement specifications based on it. The use of the RaSTA stack in a PoC also proves the feasibility of the requirements.

Together with SBB, CSA made a significant contribution to the modernization of railway infrastructure through the successful implementation.

In addition, an open-source RaSTA stack reference implementation is publicly available:
https://github.com/SchweizerischeBundesbahnen/sbb-rasta-stack