Any modification of the ERTMS specification is managed via a Change Request (CR). For this purpose, the adopted procedure is the CCM procedure, which describes the whole process for the ERTMS Change Control. The process is explained in the following document:
Backwards Compatibility between Baseline 2 and Baseline 3 (Maintenance Release 1 – MR1 and Release 2 – R2) has been agreed by all stakeholders. This backwards compatibility means that any Baseline 3 R2/MR1 ERTMS onboard subsystem will be able to operate with no technical or operational impact on a B3 R2/B3MR1/Baseline 2 ERTMS trackside.
The Baseline compatibility assessment reports, i.e. the BCA for ETCS B3 MR1 (undertaken by UNISIG and EUG) and BCA for ETCS B3 R2 (undertaken by the Agency), analyse
- the delta between Baseline 2 (2.3.0d) and Baseline 3 MR1 (in the first report),
- the delta between Baseline 3 MR1 and Baseline 3 R2 (in the second report),
and, in both cases, considering backwards compatibility for each individual change identified by a CR. Both BCA reports also include the mitigation measures proposed for the affected trackside, i.e. B3R2, B3MR1 and B2 networks in order to cover the shortcomings detected in 2.3.0d and Baseline 3 MR1.