| 摘要 |
PURPOSE:To facilitate an operation of an originator by connecting an incoming main wire trunk to an incoming register when a trunk line side will not release within a certain period after an extension calling the trunk line has released, and by connecting an optional extension by an additional dial from the trunk line side. CONSTITUTION:Extension telephone sets SUBA and SUBB are connected to a private branch exchange switch SW through an incoming trunk line trunk 1 and a subscriber circuit 2. The switch SW is connected to between the optional telephone sets SUBA and SUBB, or the trunk 1 is connected to the optional telephone sets SUBA and SUBB by a control of a central controller 3. An incoming register 5 is made possible to be connected to the trunk 1, and a trunk line release monitor timer 4 is activated by the controllr 3 when the telephone set calling with the trunk 1 releases. When the trunk 1 will not detect the release of the trunk line side for a certain period, it is judged that a calling party of the trunk 1 at the trunk line side desires an additional dial, and the trunk 1 is connected to the register 5. Finally the additional dial is transmitted by the desire of the originator.
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