This part of IEC 61375 applies to the architecture of data communication systems in open trains, i.e., it covers the architecture of a communication system for the data communication between vehicles of the said open trains, the data communication within the vehicles and the data communication from train to the ground. The applicability of this part of IEC 61375 to the train network technologies allows for interoperability of individual vehicles within open trains in international traffic. The data communication systems inside vehicles are given as recommended solutions to cope with the said TCN. In any case, proof of compatibility between a proposed train backbone and a proposed consist network will have to be brought by the supplier. This part of IEC 61375 may be additionally applicable to closed trains and multiple unit trains when so agreed between purchaser and supplier. NOTE 1 For a definition of open trains, multiple unit trains and closed trains, see Clause 3. NOTE 2 Road vehicles such as buses and trolley buses are not considered in this part of IEC 61375.