| 摘要 |
<p>A ring-trip circuit monitors the voltage developed across a source resistor coupled to one of the leads of the subscriber line circuit, regardless of the ringing frequency of the ringing voltage applied to the line circuit, and irrespective of the polarity of the DC loop current developed in the line. In response to detecting a prescribed threshold level of the source resistor voltage - indicating that the customer has answered the call, the ring-trip circuit provides a digital output that is read by the control equipment of the central office to terminate the ringing voltage.</p> |
