| 摘要 |
PURPOSE:To freely apply the extension of a PBX by an additional dial through a private branch exchange (PBX) dial in by providing a register for receiving an extension designating signal and an additional dial signal and a circuit for converting the extension designating signal in a storage program control type private branch exchange. CONSTITUTION:An incoming call is received from a public network 4 and the register 5 is trapped, the extension designating signal is stored in the register and this extension designating signal is converted into a conversion number or discriminating information for the additional dial by the expansion table of an extension designating signal converting circuit. When the addition dial discriminating information is ADD=1, a receiving completion signal is transmitted, thereafter, a secondary response signal is spuriously transmitted after a fixed timing, and the public network and the PBX1 can be called and that the additional dial is enable is informed to a calling subscriber by the connection of a talkie 2. Then, the PBX 1 connects the register 5 with a central office 3 and enters the preparation for receiving a PB signal from the calling subscriber of the public network. At the time of receiving the additional dial number, it is connected to an extension 7 or an exclusively used line 6 by the similar processing to the conventional connection of the reception of calling for the exclusively used line.
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