| 摘要 |
PURPOSE:To prevent the effect of the service interruption as well as the collision between the originating and incoming calls by making talking circuit correspond to the state of the exchange before answering to the called subscriber to use it as the incoming circuit for the public telephone. CONSTITUTION:At the incoming time, terminal L10 and L9 are inverted to + and - polarites respectively. And relay RR is actuated to ring bell BB. When the caller resigns halfway, relay RR is released. With confirmation of the answer of the called subscriber through the exchange, terminal L9 and L10 are turned to + and - polarities respectively. Relay RR keeps actuation, and bell BB stops ringing. When the call is over via talking SC1 and the called subscriber is hooked on, relay RR is released and then the originating call control is carried out through originating call control circuit CC2. In this case, the operation of RR is made to correspond to the function of the exchange under on-hook state uniformly. And at the off-hook time, the switching is over between the terminating circuit and the originating circuit. |
