The invention relates to a method for establishing a user-network interface in a digital transmission network for a cell-based digital 140 or 155 Mbit/s ATM signal, and a network interface embodying the method. The interface according to the invention comprises an input buffer (22) controlled by a predetermined policing function for receiving the cell-based signal and adapting the transmission speed of the signal to the actual transmission speed of the transmission network; a mapping means (31) for forming cell blocks of N consecutive cells from the cell-based signal and for adding N overhead bytes to each cell block; and a multiplexer (32) for multiplexing the output signal of the mapping means byte by byte into N separate output signals of about 1.5 Mbit/s, 2 Mbit/s, 6 Mbit/s or 8 Mbit/s.