CONTINUOUS INBAND TESTING OF TRUNKS WITH AUTOMATIC TRUNK SUBSTITUTION UPON DETECTING A DEFECTIVE TRUNK

摘要

The integrity of a dedicated trunk is checked by providing equipment for periodically transmitting inband test signals in both directions over the trunk. Each of the test signals is a 2,400 Hz signal periodically transmitted over the trunk from the near end. Equipment at the far end responds by returning a 2,600 Hz acknowledgment pulse over the trunk. Filters at both ends of the trunk prevent interference of the test signals with the voice frequency communications thereon. A counter at the near end of the trunk is initialized for each test signal transmitted to the far end and is blocked from counting by each acknowledgment signal returned over the trunk. Upon transmitting two successive test signals to the far end and not receiving acknowledgment signals, the counter is incremented to the count of two and controls an automatic transfer of the voice frequency communications on the dedicated trunk to a spare trunk the integrity of which is similarly checked.