Abstract: A digital subscriber line formed by terminal equipment, a network control device including a plurality of the terminal equipment, and an exchange terminal. In a waiting state of the digital subscriber line, the network control device 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, the terminal control device receives a line activation signal from the exchange equipment and when, at an incoming state from the state from the exchange terminal, 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 so that the synchronization of the exchange terminal is established.

Abstract: In this invention, a call control information of a subscriber's line is compiled into a packet form, is transferred via a network of a digital switch board to a signal control device, and digital data is also transferred via the network to a handler. Accordingly, a signal from a digital subscriber is efficiently processed, and an analog subscriber is also accommodated so that a call control in the same way as for the digital subscriber is made possible for the analog subscriber.

Abstract: A digital subscriber line formed by terminal equipment, a network control device including a plurality of the terminal equipment, and an exchange terminal. In a waiting state of the digital subscriber line, the network control derive 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, the terminal control device receives a line activation signal from the exchange equipment and when, at an incoming state from the state from the exchange terminal, 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 so that the synchronization of the exchange terminal is established.

Abstract: A digital exchange system including exchange terminals, a digital network, and a bit rate conversion unit located therebetween. The bit rate conversion unit operates to match low bit-rate channel signals with high bit-rate channel signals acceptable by the digital network, by multiplexing a plurality of the outgoing low bit-rate channel signals. The bit-rate conversion unit operates, on the other hand, to demultiplex the incoming multiplexed low bit-rate channel signals.