Supported system version

A system version supported by the on-board equipment is one of the system versions the on-board equipment is able to operate. By definition, within one of its supported system version numbers X, the on-board equipment always operates one single system version number Y, which is the highest defined in the release of the ETCS specifications the on-board equipment is compliant with. Important note: if within a system version number X at least two values of Y have been defined, the fact that the on-board always operates/supports the highest value Y does not mean that it is not able to handle trackside information using a lower value of Y.