| 摘要 |
PURPOSE:To prevent ineffective operation, with a PB extension connected to a DP main trunk which foresees that the special service specific to the PB main trunk can not be used. CONSTITUTION:When a PB extension EXT makes a call and if the catching of a vacant PB main trunk COT1 is unsuccessful, a central controller CC tries to select a DP main trunk COT2. If the catching of the COT2 is successful, a PB sender RST relay T is operated via a relay driver RC and returns a special signaltone SPT to the EXT via a relay A. The EXT knows that the call connection is done to a DP main trunk CL2 through the detection of a special signal tone returned for a prescribed time and gives up the use of special service specific to the PM trunk CL1. Further, the selection number of PB signal format transmitted from the EXT is processed at the RST, converted into a dial pulse form and transmitted to the main trunk CL2. |
