| 摘要 |
PURPOSE:To realize the call-back connection via the dial operation of the incoming extension and with no operation of the operator, thus eliminating a long-time restriction for the operator. CONSTITUTION:When incoming extension EXTA has dialing of ''2'' for calling back, the DA relay of cord B board additional unit ATTAU becomes intermittent. And call-back unit CBU is caught after dialing and via the operation of the CB relay. Then the transmission is given to switch frame SWF, central office trunk COT and cord B board ATT when the receiver of the incoming who heard the DT tone dials called-side extension EXTB to which the receiver wants the ordering. And then the transmission is given to unit CBU being caught through intermittence of the DA relay and marker M to close the channel between EXTA and EXTB. In case EXTA has a call again to the main wire after the ordering, dialing ''2'' is given to break the connection with unit CUB and then to secure the original state. |
