| 摘要 |
The lines or stations of a multi-line office telephone system are sequentially examined to detect a hold tone signal of a specified frequency or frequencies on one or more of the lines. The lines are examined for increasingly longer time periods in accordance with the type of energy sensed at each line. If the line is not active or connected in a first brief period, the scanner then proceeds to examine the next line for a hold tone signal. If wide-band energy is not detected on the line in a second, longer period, the examination of the line is terminated and the scan process is continued to the next line. If wide-band energy above a threshold is detected on the line in a third, still longer period, the detected energy is further examined to determine whether this energy includes a valid hold tone signal. If a hold tone signal is detected on a line, the line is scanned again to detect the removal of the hold tone signal therefrom, whereupon a hold status is assigned to the line.
|
