| 摘要 |
PURPOSE:To use a trunk line in common, and to improve the efficiency of utilization of the circuit, by allowing a higher rank exchange to discriminate a subscriber exchange which has sent out information on the basis of the received information and then to modify a sequence. CONSTITUTION:When a service code for call registration is dialed at a subscriber exchange 2 equipped with a calling-subscriber's number device, a trunk exchange selects a common trunk line to connect a higher rank exchange 4. At this time, the controller 4b of the exchange 4, when detecting the number of received digits exceeding eight, judges that the opposite exchange 2 is equipped with the calling-subscriber's number device 2d and necessary information is all received, and performs succeeding operation. When a service code is sent out of the telephone set 5 of a subscriber exchange 6 which is not equipped with any calling-subscriber's number device, the controller 4b of the exchange 4 detecting the number of received digits being less than five, and switch a network 4a to a key signal receiver 4e, thereby transmitting and receiving necessary information. |
