| 摘要 |
PURPOSE:To make service to the called extension possible by using the main wire in case of leased circuit originating route trunk all busy. CONSTITUTION:When a calling extension dials the leased circuit originating number, the earth is given to terminal 7 by the dial number expansion tree, and the leased circuit originating route TT relay is operated, and it is checked whether leased circuit trunks are all busy or not by its contact tt; and in case of busy, the earth is given to terminal TAB' by the leased circuit trunk group, and the trunk all busy indication TAB relay is operated. By the operation of the TAB relay, the operation route of the TT relay is switched to the main wire originating route relay to operate the main wire originating route COT relay. |
