METHOD FOR TESTING WHOLE CHANNEL LOOP BACK TESTING METHOD FOR RELAY AND SWITCHING DEVICE

摘要

PROBLEM TO BE SOLVED: To realize a testing method capable of judging the presence or absence of the necessity of the dispatch of a maintenance staff to a user house, by specifying any defective place when any abnormality is generated in a method for testing a subscriber's line in a ISDN digital communication system. SOLUTION: An ISDN digital subscriber line is provided with a relay 105a, and the relay is provided with a switching device 507. The switching device is provided with a setting part connected to a V/U interface converting part 506 in the relay for setting a return place, and a switch part 508. The switch part 508 has a switch, a passing part 512 connected to a V/T interface converting part and an NT function T point terminating part 304 for allowing signals from the V/T interface converting part and the NT function T point terminating part 304 to pass when the switch is connected to one contact, and a returning part operating for returning the signal from the NT function T point terminating part when the switch is connected to the other contact.