| 摘要 |
PURPOSE:To reduce the quantity of software required for a digital switchboard, by transmitting a ring-back tone source in advance to a down-highway of a trunk, and connecting or disconnecting it in the trunk. CONSTITUTION:In case of calling to a message sound source TG from a subscriber SUB, a central processor CPU obtains a sound source start signal TGS and opens a gate GT 3, therefore, a ring-back tone passes through a logical circuit LG through a gate GT 2 forming turning-back line SHT in a talkie trunk TKT and goes into a network NWK by an up-highway U-HW. Accordingly, the SUB knows that the TKT has been caught. By the started TG, a gate GT 1 in the TKT is opened and the GT 2 is closed. Therefore, the ring-back tone is not transmitted to the U-HW, and a message from the TG is transmitted to the U-HW. |
