Abstract: A method is used for transmitting binary information in successive time slots of a time division multiplex frame format in an optical transmission network with a number of terminals and a central unit. At least one optical fiber is connected to the central unit and spreads to the terminals in a tree-like structure via one or more beam splitters and further optical fibers. An address is allocated to each terminal, and synchronization is performed for the transmitting operation of the terminal being phase-locked to the central unit in dependence of the signal delay time between the terminal and central unit. The transmitting level of the terminal is adjusted in dependence upon the line attenuation between terminal and central unit. The frame format has a number of time slots for line-switched information, as well as a number of bits for control and synchronization purposes.