This standard addresses the interworking and interoperability between ANSI-41 MAP[1] and GSM MAP[4] based networks in the support of subscribers roaming between networks. The interworking and interoperability functionality of the services, information flows, and message mappings are specified. This standard consists of four volumes: Volume 0 - Overview and Interworking Reference Model, Volume 1 - Service Descriptions, Volume 2 - Information Flows, and Volume 3 - Message Mappings. This is Volume 0, an overview of the Interworking and Interoperability Function (IIF) and the associated network reference model.