| 摘要 |
In private telephone branch exchanges with subscriber stations which output their dialling information in accordance with the voice frequency dialling method with or without accompanying signal, conversion of the dialling information is necessary in the case of exchange traffic when a different type of dialling is used in the public telephone network. At the same time, it must be prevented that voice frequency signals of interfering duration can enter the public network. This is required even if, with the same type of dialling in the public network and in the private branch exchange, selection code interpretation takes place in the latter. For this purpose, an immediate interruption, if possible, of the connecting path between the private branch exchange and the exchange is required after the occurrence and during the output of the dialling digits. To achieve this, a switch (S) is provided in the connecting path, which switch is opened either by a first disconnect signal derived from a current change occurring in the case of push-button voice frequency dialling with accompanying signal when a dialling digit is sent out in the relevant subscriber line loop or by a second disconnect signal derived from the excessive voltage occurring as a result of the said current change in the circuit extending from the subscriber station (TN) via the switching network (KF) to the digit input circuit (WS) or by a third disconnect signal generated with the occurrence of frequencies corresponding to a dialling signal in the digit input circuit (WS). <IMAGE>
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