Grand Start scheme and loop-start system combined office line trunk circuit, control method of the central office trunk circuit, and the central office trunk circuit control program of

摘要

PROBLEM TO BE SOLVED: To solve the problem that it is difficult to insulate a primary side and a secondary side of a trunk line when realizing a loop start system and a ground start system with the same hardware.;SOLUTION: A central office trunk 3 comprises a DC current detection circuit 31 for detecting a loop current caused by earth from a bi-directional station trunk 2 at a side of a station exchange 1 to a Tip line and minus power supply to a Ring line by a photo-coupler PCDC, a call arrival detection circuit 32 for detecting a calling signal RG supplied from the bi-directional station trunk 2 by a photo-coupler PCRG in call arrival, and a DC sync circuit 33 for loop initiation and loop hold by generating a proper loop current based on a transistor Q for the bi-directional station trunk 2, the earth is detected by a high-resistance detection circuit, so that the central office trunk circuit is provided for both the ground start system and the loop start system, and no auto power source is used for detection at the primary side of the trunk line, thereby easily securing the insulation between the primary side and the secondary side of the trunk line.;COPYRIGHT: (C)2005,JPO&NCIPI