| 摘要 |
PURPOSE:To offer more appropriate service to the subscriber of an automatic exchange, by informing the vacancy of a subscriber to be set, or a trunk, to a camp-on set subscriber in busy. CONSTITUTION:Assuming that a trunk line incoming call arrives at a camp-on set subscriber 2, the trunk line is connected to the subscriber 2 through a trunk TRK5, resulting a busy state. In such state, by completing a call between a camp-on subscriber 3 to be set, and a call opposite 4, and releasing a link 8, a central control unit CC7 detects the vacancy of the subscriber 3 to be set, and also, recognizes that the set subscriber 2 is in busy, and makes a channel network NW1 close a link between the set subscriber 2, and an alarm tone trunk TNT6, by issuing an instruction to the NW1. By such reason, the set subscriber 2 can recognize the vacancy of the subscriber 3 to be set by listening alarm tone from the TNT6 through the NW1. The set subscriber 2 can select either the continuance of the call with the trunk line, or, connection to the subscriber 3 to be set, while holding the call with the trunk temporarily, by the above alarm.
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