The authors discuss the user-network interface configuration for broadband ISDN and propose an optical passive bus scheme with ATM (asynchronous transfer mode) access, to realize a flexible and expansible customers' premises network. To confirm the feasibility of the optical passive bus, they have studied the transmission efficiency and collision control for ATM multiple access, and they have introduced novel cell-based burst access, frame-phase alignment, and collision-control schemes are introduced. The realization of an optical passive bus scheme and possible application to CCITT standards are described.<<ETX>>