System for controlling the isdn activation sequence

A digital subscriber line formed by terminal equipment ,(3), a network control device (NT) including a plurality of the terminal equipment, and an exchange terminal (1). In a waiting state of the digital subscriber line, the network control device (NT) is placed in a state which can only receive a signal. A sending portion of the network control device is driven when, at a call from the terminal equipment (3), the terminal control device receives a line activation signal from the exchange equipment (1) and when, at an incoming state from the state from the exchange terminal (1), the terminal control device receives a line activation from the exchange equipment. The synchronization pattern signal is sent from the sending portion to the exchange terminal (1) so that the synchronization of the exchange terminal is established.