Abstract: A method of monitoring a digital line signal using a key phone in a private exchange system.

Abstract: A method for controlling and processing a call from one keyphone to a busy keyphone utilizing a keyphone main unit connected to an office line and a plurality of keyphones in a keyphone system, the busy keyphone being connected to a third keyphone, wherein the keyphone main unit receives an input sequence of dialed numbers from the one keyphone; determines when the input sequence is complete; transmits a first display signal to the busy keyphone to cause the busy keyphone to display a message indicating an incoming call from the one keyphone; determines whether the busy keyphone is in a forced off-hook ring mode; transmits a busy tone to the one keyphone when it is determined that the busy keyphone is not in the forced off-hook ring mode; checks for an input signal from an off-hook ring button on the one keyphone; transmits an off-hook ring signal to the busy keyphone when it is determined that the busy keyphone is in the forced off-hook ring mode or when it is determined that the off-hook ring button on the

Abstract: An apparatus for receiving multi-channel caller identification data in a switching system with a path forming portion for forming a path to receive the caller identification data in response to an incoming ring signal from a plurality of central office lines; a multiplexer for selecting one of a plurality of channel signals containing the call identification data and received from the path forming portion; a decoder for sampling an analog signal of a corresponding channel selected by the multiplexer at a predetermined sampling frequency, to thereby convert the analog signal containing the call identification data into a PCM signal; a time switch for switching and outputting the converted PCM signal converted in the decoder and containing the call identification data to a corresponding channel; a demodulator for receiving the PCM signal output through the time switch to thereby demodulate the caller identification data; and a controller establishing a path for the caller identification data in response to the