Abstract: According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT) 2 or a standard telephone (STT) 4 as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals 2 and 4 as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU) 12.

Abstract: According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT) 2 or a standard telephone (STT) 4 as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals 2 and 4 as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU) 12.

Abstract: According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT) 2 or a standard telephone (STT) 4 as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals 2 and 4 as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU) 12.

Abstract: According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT) 2 or a standard telephone (STT) 4 as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals 2 and 4 as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU) 12.

Abstract: According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT) 2 or a standard telephone (STT) 4 as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals 2 and 4 as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU) 12.

Abstract: According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT) 2 or a standard telephone (STT) 4 as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals 2 and 4 as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU) 12.

Abstract: According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT) 2 or a standard telephone (STT) 4 as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals 2 and 4 as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU) 12.

Abstract: According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT) 2 or a standard telephone (STT) 4 as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals 2 and 4 as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU) 12.

Abstract: According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT) 2 or a standard telephone (STT) 4 as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals 2 and 4 as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU) 12.

Abstract: According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT) 2 or a standard telephone (STT) 4 as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals 2 and 4 as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU) 12.

Abstract: According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT) 2 or a standard telephone (STT) 4 as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals 2 and 4 as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU) 12.

Abstract: According to this invention, a digital key telephone system connected to an analog public network NW having a function of transmitting a ringing signal including identification information of a calling line through a subscriber line (CO line), accommodating a plurality of extension lines each connected to a digital key telephone (DKT) 2 or a standard telephone (STT) 4 as an extension terminal, and having a function of switching and connecting the subscriber line to the plurality of extension lines or the extension lines to each other includes a called party storage means storing, in advance, information representing the correlation between the calling line and the extension terminals 2 and 4 as a called terminal. When a ringing signal arrives from the analog communication network NW, calling line identification information (caller ID) contained in the ringing signal is detected by a calling line identification information interface unit (RCIU) 12.

Abstract: A bell signal generating circuit for a key telephone set. A dc component of a pulse signal is removed by a photo-coupler to generate a first signal. A high frequency component of the first signal is removed by a filter to generate a second signal. A differential amplifier amplifies the second signal to generate a bell signal. To the differential amplifier, a dc supply voltage based on the dc signal in synchronism when the pulse signal is applied.

Abstract: A telephone line interface circuit for connecting telephone equipment provided with internal speech lines having predetermined DC impedance to external telephone lines, comprising a rectifying circuit connected with the telephone lines for rectifying the DC voltage coming from the telephone lines; a dial pulse sending circuit which makes connection and disconnection between the output terminals of the rectifying circuit and the internal speech lines for sending dial pulses to the telephone lines; and a polarity inversion detecting circuit which discriminates th evoltage relationship between the telephone lines and the internal speech lines for detecting the polarity inversion of the DC voltage coming from the telephone lines.

Abstract: A digital communication apparatus in which time slots need not be switched, comprises a single channel highway in which a plurality of time slots are time-divisionally multiplexed, and first and second transmitting/receiving units connected to the highway. The first transmitting/receiving unit transmits a first signal supplied from a first terminal to the second transmitting/receiving unit through the highway using a first time slot designated from the plurality of time slots. The second transmitting/receiving unit outputs the first signal transmitted from the first transmitting/receiving unit through the highway using the designated first time slot to a second terminal. A second signal from the second terminal is transmitted to the first transmitting/receiving unit through the highway using a designated second time slot.

Abstract: A key telephone system comprising a terminal device and a main apparatus which exchanges speech signals with the terminal device, the terminal device having a loudspeaking circuit for providing a predetermined amount of loss to either one of first speech signals selected to be transmitted to the main apparatus and second speech signals received from the main apparatus to prevent howling in a loudspeaking conversation mode, said system comprising: a first communication unit provided in the terminal device, for sending the first speech signals to the main apparatus through a first channel and receiving the second speech signals from the main apparatus through a second channel separated from the first channel; second communication unit provided in the main apparatus and connected to the first communication unit, for receiving the first speech signals from the first communication unit through the first channel and sending the second speech signals to the first communication unit through the second channel; in the

Abstract: In a digital key telephone system through which extension-to-extension calls can be made and incoming calls can be transferred between a master main installation and plural slave main installations, the master and slave main installations are interconnected through digital interface units provided for each installation in order to transmit and receive speech data and control data in digital code between the installations. The digital interface unit of the master main installation first designates an address of the slave main installation to which data are to be transmitted before data transmission, while the digital interface unit of the slave main installation receives data transmitted from the master main installation after address designation. Further, the addresses of the slave main installations can be designated together or separately.

Abstract: A telephone system which allows external releasing of a holding state set by a holding operation of a telephone set. A signal receiving circuit of the system receives a holding-state releasing signal such as a DTMF signal or the like sent from a central office line to release the hold state of the telephone set on the basis of an output of the circuit.

Abstract: A loud-speaker telephone set includes a switching control circuit to attenuate the incoming signal, during transmission, and to attenuate the outgoing signal, during reception, in order to prevent feedback from the loud-speaker to the microphone. An automatic gain control circuit is added which detects at least one of the incoming signal level and the outgoing signal level and which adjusts the attenuation of both the incoming and outgoing signals so as to reduce the attenuation change between reception and transmission below 20 dB and eliminate the unpleasant sensation, to a user, of large attenuation changes.