| 摘要 |
LINE INTERFACE UNIT A line interface unit is described for controlling receipt and delivery of voice messages over a telephone system having a voice message facility connectible to at least one calling station and a called station via a central office, the calling station having tip and ring lines connected to the central office. The interface unit comprises a first switch connected to the calling station in the tip and ring lines and a second switch connected to the central office in the tip and ring lines, each of the switches having first and second positions and wherein signals on the tip and ring lines are connected directly between the calling station and the central office when each of the switches are in the first position The unit includes a speed-dial circuit for dialing the voice message facility, a speech circuit for issuing a predetermined prompt to the caller at the calling station, monitor circuits for monitoring the tip and ring lines, and detecting circuits for detecting a busy/no answer condition at the called station upon call initiation to the called station, for detecting receipt of a predetermined dual tone multifrequency (DTMF) signal from the calling station and for detecting receipt of a predetermined DTMF signal from the voice message facility. In operation, a control circuit of the line interface unit responds to detection of the busy/no answer condition for switching the first switch from its first position to its second position to connect the speech circuit to the calling station for issuing the prompt. After the prompt is issued, the control circuit responds to receipt of the DTMF signal or receipt of additional coinage from the calling station for switching the second switch from its first position to its second position to connect the speed-dial circuit to the central office for dialing the voice message facility. The control means then responds to any receipt of the DTMF signal from the voice message facility for switching the first and second switches from their respective second positions back to their respective first positions to connect the calling station to the voice message facility. |
