This Recommendation defines principles and detailed arrangements for the interworking of different networks in order to provide a data transmission service. This Recommendation also specifies, in a general network context, the necessary interaction between elements of user interfaces, interexchange signalling systems and other network functions for the support of data transmission services, telematic services and the OSI connection-mode network service where appropriate. In addition, it defines the principle for realization of international user facilities and network utilities for data transmission services.