CONTROL SYSTEM FOR TRUNK LINE

PURPOSE:To obtain a function corresponding to a hooking operation by combining the hooking operation of a telephone set with the storage information of the polarity storage circuit of a trunk line to convert it into instruction information. CONSTITUTION:When an opposite side called through a trunk line 1 by the outgoing of a telephone 4 takes up a telephone transmitter-receiver and answers, (a) and (b) of the trunk line 1 are inverted in their polarity, which is identified in a polarity identification circuit 21 and a polarity storage circuit 51 stores polarity inversion information. When the telephone set 4 which executes outgoing in this action state is made hooking, the pulse information of a cut which a supervisory display circuit part 3 displays is stored in an action display storage circuit 52. A main control circuit part 5 converts it into the information reserving the trunk line 1 based on both information and instructs reservation action control from a trunk line control circuit part control circuit 53 to a reservation control circuit 23. When the polarity of the trunk line 1 isn't inverted the polarity storage circuit 51 stores non-inversion information, so if the telephone set 4 executing outgoing in such state is executed hooking operation the main control circuit part 5 converts it into the action transmitting a flash signal to the trunk line 1 and an instruction is given from a control circuit 53 to a loop control circuit 22.