| 摘要 |
PURPOSE:To most stably and effectively operate a circuit, by controlling the operation and no operation of an echo prevention circuit by an ON/OFF control circuit based on the kind of the path information of an input path and an output path and information to be communicated. CONSTITUTION:The central control unit 11 of an exchange controls so that an echo control circuit turns ON the echo preventing circuit 14 when the path A is connected to an extension. When an incoming call arrives at a data terminal not at an extension telephone set from the path A, control such that the echo preventing circuit 14 is turned OFF is performed. The central control unit 11 controls so that the echo preventing circuits of both paths can execute a pass-through operations transparently without adding any processing on call signals.
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