A signaling functional model (separated model) that assumes the functional separation of call control (CC) and bearer control (BC) must be considered for B-ISDN because B-ISDN deals with various levels of service quality, various speeds, and various connection configurations. This paper provides the basic structure of the forementioned separated model and the functions of the CC and BC based on actual B-ISDN service specifications. Also, system design guidelines are proposed for connection-type bandwidth selection and interworking between broadband ISDN and narrowband ISDN, which are key issues in the study of B-ISDN signaling protocol.