CONNECTING SYSTEM OF PRIVATE BRANCH EXCHANGE

PURPOSE:To increase the quantity of process for a common controller and to decrease the number of switching of a channel switch network, by connecting a call from an extension to an extension mutual connecting trunk and transmitting a dial signal to a common controller via this trunk. CONSTITUTION:An extension mutual connecting trunk OIOT includes a supplying function of the call current plus the gate functions for the monitor of state of the circuit loop current and each tone signal of the call signal, ringing tone, howler tone and busy tone respectively. When a call is generated from an extension telephone TELi, a common controller CC detects this call and connects it to the trunk OIOT via a channel switch network SW. The trunk OIOT transmits the dial tone to the TELi, and then the TELi transmits the dial signal. Thus the trunk OIOT receives the dial signal and gives it to a device CC. Then the talking state is secured between the telephones TELi and TELj after the device CC discriminates the extension to be connected to the TELj.