Abstract: A network termination unit to connect a plurality of analog terminals and digital terminals to a U interface of an ISDN telecommunications network. An echo compensator is connected to the U interface to suppress an echo signal produced by the attachment of the terminal device to the U interface. A first bus connects the echo compensator to a communication controller, an a/b interface component block that is compatible with an a/b interface to which an analog terminal is connected, and an S interface component block to which a digital terminal is connected. A processor system, connected to communication controller and a/b interface component block, programs the echo compensator and the S interface component block. B channels of the ISDN telecommunications network are activated and deactivated in response to commands issued by the communication controller. The processor system further evaluates and prepares D channel signalling data for the a/b interface component block.