Applies to data communication in open trains, that is covers data communication between vehicles of the said open trains and data communication within the vehicles of the said open trains. Allows for interoperability of individual vehicles within open trains in international traffic. May also be applicable to closed trains and multiple unit trains when so agreed between purchaser and supplier. This edition includes the following significant technical changes with respect to the previous edition: technical amendments in clauses 2, 3 and 4 where some inconsistencies were removed.