SUBSET-035 — Specific Transmission Module FFFIS

Scope

The Form Fit Function Interface Specification for Specific Transmission Modules — the adapter architecture that lets an ETCS on-board read legacy Class B national train-protection systems (via an STM) so one vehicle can run seamlessly across ETCS and nationally protected lines.

Europe's migration to ETCS is a decades-long overlay on twenty-plus legacy Class B systems, and SUBSET-035 is the architectural answer: a Specific Transmission Module packages the national system's track-side reading into a standardised interface to the ETCS on-board, which supervises the transitions between levels and systems. The subset specifies the STM control function, the data exchanged over the standardised bus, state machines for connection and supervision hand-over, and the constraints an STM must respect so that national and ETCS supervision never conflict. Mandatory at v4.0.0 under Annex A of the 2023 CCS TSI, it is the daily bread of cross-border fleet projects and of any procurement whose route map mixes ETCS lines with PZB, ATB, KVB, BACC or their peers.