| 摘要 |
PURPOSE:To transmit information on a no-charge subscriber call easily and economically by providing a means which allows a terminating trunk ICT to discriminate between a subscriber busy state and a no-charge call by itself without depending upon a common controller marker. CONSTITUTION:If a conventional incoming no-charge telephone set FLT, etc., is connected irregularly instead of a general telepbone set TEL, a relay D does not operate. In this case, a relay M operates to stop a call. In a figure, a talking line is broken at a contact (m) to disable the call, but the relay M starts charging, performs lamp indication,and finds an irregular subscriber while holding the circuit. In inocming to the no-charge telephone set FLT, only a relay G which is not in the figure operates by the indication of the common controller. Consequently, a calling subscriber receives a bush-back signal BT and a called subscriber receives a call signal IR. |
