System and method for performing telephone line-in-use detection, extension pick-up detection, and remote hang-up detection in a modem

DETAILED DESCRIPTION The present invention overcomes the aforementioned shortcomings associated with the prior art by providing a system and method for performing telephone line-in-use, extension pick-up, and remote hang-up detection in a modem.
These as well as additional advantages of the present invention are achieved by providing automated circuitry in a modem for detecting telephone line events, including whether the telephone line is already in use, whether another telephone extension has been picked-up, and whether the remote party has hung-up.
These telephone line events are detected by monitoring a line voltage and loop current supplied in the telephone line from a central office.
A voltage sensor is connected to the telephone line to detect changes in the line voltage appearing in the telephone line.
The change detected in the line voltage is used by a line-in-use detection circuit to determine if the telephone is already in use.
Interruptions in the loop current are monitored by a remote hang-up detection circuit to determine if the remote party has hung-up.
An extension pick-up circuit is further provided for sensing changes in the telephone loop current in order to determine if a telephone extension has been picked up.
If any of the circuits sense that one of these telephone conditions has occurred, the modem is notified to change its operation accordingly.