JPH0748762B2 - Three-way calling system for digital communication - Google Patents

Description

The present invention relates to a system for communicating with a network by using a plurality of digital telephones at the same time in a star connection type digital communication system.

[Conventional technology]

In the conventional analog communication, when two or more telephones are connected to one subscriber line and used, they can be used by simply making a branch connection. Moreover, a simple branch connection enables simultaneous use of a plurality of telephones. I was able to talk to the main line using the telephone. However, in digital communication, signal collision occurs and communication cannot be performed simply by branching a digital telephone. When connecting multiple telephones to one line in digital communication, there are a method by bus connection and a method by star connection via a control device. In either method, a plurality of telephones are used at the same time to connect to a curved line. In order to make a telephone call, one telephone needs a means for receiving a plurality of other transmission signals.

As means for this purpose, in the case of star connection type digital communication, as shown in FIG.
Those equipped with 2 _A to _C can be considered. Interface circuits 3 _A ~ _C are those having the function of assembling and fields of a frame of the digital signal, the signal sent to the communication line from the control unit 1 as shown in FIG. 3 is an interface circuit 3 _A
Is multiplexed by _C (frame assembly). Further, the signal sent from the digital telephone (not shown) to the control device 1 through the communication line is in addition to the signal of the voice of the talker (for example, shown as the signal B in FIG. 3). It includes a signal for connection control and the like (for example, represented as a D signal in the third) and a signal indicating a frame configuration (for example, represented as an F signal in the third),
These are disassembled in the interface circuit of the controller.
Then, the transmission signals from the two digital telephones are mixed by the adding circuit, the frame is assembled by the interface circuit 3c, and the frame is transmitted to the network side. Where adder circuit
As 2 _A to _C , a circuit for adding a digital signal as it is by digital signal processing, or a circuit for combining a D / A, A / D converter and an analog adding circuit to once convert it into an analog signal and adding it is considered.

[Problems to be solved by the invention]

However, in the above structure, the above-mentioned 2
There is a problem that the circuit scale becomes large regardless of which kind of circuit is used.

An object of the present invention is to provide a simple three-way call function by using a control device for a star-connection type digital communication system without a large increase in circuit scale.

[Means for solving problems]

The present invention detects a transmission signal in each digital telephone in a digital communication system in which a plurality of digital telephones are connected to a control device by a plurality of multiplexed communication channels formed on a communication line. And a control circuit for determining the presence or absence of a transmission signal based on the output of the detection circuit and notifying the result to the control device through the first communication channel.
Selector switch for switching the connection destination of the second communication channel and a signal for indicating the presence / absence of a transmission signal transmitted from each digital telephone through the first communication channel to switch the connection destination of the second communication channel. The present invention also provides a three-way communication system for digital communication, which has a control circuit for controlling a selector switch. 3
The person-to-person call method refers to a call method in which a plurality of parties make a call to the other party on the system side. Therefore, the total number of parties of the system and the other party is not limited to three.

[Action]

When multiple people are talking on the system side,
When a call is transmitted from any of the digital telephones, the detection circuit of the telephone detects this and the control circuit of the telephone notifies the control device.

The control device monitors the notification from the control circuit of each digital telephone, switches the selector switch based on the notification, and switches the connection destination of the second communication channel (communication channel of the transmission signal or the reception signal). Control.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention, in which 4 is a control device, 5 _A and 5 _B are digital telephones, 3 _A to _C are interface circuits, and SW ₁ to ₃ are selector switches for switching signals. Is. 6 outbound, transmit signals for connection control such as arrival of an incoming call, the control circuit for controlling the switching of the reception and the signal by the selector Sutchi SW ₁ ~ _3, constituted by a microprocessor, a memory, and the like. Reference numeral 7 is an interface circuit. Reference numeral 8 denotes a communication circuit, which is composed of an amplifier for amplifying a transmission signal, a reception signal, etc., a codec for converting the transmission signal, the reception signal, etc. from an analog signal to a digital signal and a digital signal to an analog signal. A detection circuit 9 is connected to the communication circuit 8 and detects whether or not there is a transmission signal having a predetermined magnitude or more. Reference numeral 10 is a control circuit for transmitting and receiving a signal for connection such as transmission and reception, which is composed of a microprocessor and a memory. T is a transmitter and R is a receiver. Other solid lines are signal lines (arrows indicate the direction of signals and thick lines mean bus wiring). Of these, 3 _A to _C , 6 and SW ₁ to ₃ are control devices 4
The elements 7 to 10 and T and R are elements constituting the digital telephones 5 _A and 5 _B. In addition, the communication line has a third
As shown in the figure, two or more channels are formed by the interface circuit, and the connection control signal is transmitted through a channel independent of the transmission / reception signal (hereinafter, the channel transmitting the transmission / reception signal will be Information channel, called the signal channel that transmits the signal for connection control).

The operation of the present invention will be described with reference to FIG. 1. The transmission signal (analog signal) input from the transmitter T is amplified by the speech circuit 8 and converted into a digital signal, which is then transferred to the information channel by the interface circuit 7. The received signal (digital signal) transmitted from the control device 4 to the telephone set 5 _A via the information channel from the control device 4 is transmitted to the control device 4 and the communication circuit 8
Is converted into an analog signal, amplified, and output from the handset R. Further, the control circuit 10 monitors the output of the detection circuit 9 to determine the presence or absence of a transmission signal, and the result is put on the signal channel via the interface circuit 7 and transmitted to the control device 4. The control device 4, the control circuit 6 by audit signal channels telephone 5 _A, 5 _B detects whether during transmission, switching the selector switches SW ₁ ~ _3,
Controlling the connection destination of the information channel output of the interface circuit 3 _A ~ _C.

FIG. 4 is a diagram showing an example of the configuration of the detection circuit 9 of FIG. 1. 11 is an input terminal, 12 is an output terminal, 13 is an amplifier, Tr is a transistor, R ₁ is a resistor, and 14 is a transistor. Is a current mirror circuit, R ₂ is a resistor, and C is a capacitor. In the circuit of FIG. 4, the transmission signal input from the input terminal 11 is amplified by the amplifier 13 and added between the base and emitter of the transistor Tr. When the output signal of the amplifier 13 exceeds the forward voltage between the base and emitter of the transistor Tr, a current flows through the transistor Tr and the current mirror circuit 14, the potential of the output terminal 12 rises, and the output signal of the amplifier 13 decreases. , The potential of the output terminal 12 drops.
The resistors R ₁ and R ₂ and the capacitor C determine the time constant of the change in the output of the output terminal 12.

FIG. 5 is a diagram showing an example of the operation of the control circuit 10 of the telephones 5 _A and 5 _{B. When} the control of the telephone is described with reference to FIG. 5, the output of the detection circuit 9 indicates that there is no transmission (the transmission signal is When a state in which a predetermined signal level is low) is changed to a state in which transmission is performed (the transmission signal is higher than a predetermined signal level), a certain determination is made to the control signal 4 via the signal channel. The signal (hereinafter, this signal is referred to as "S _ON ") is transmitted. On the contrary, when the output of the detection circuit 9 changes from the state with transmission to the state without transmission, another predetermined signal (hereinafter referred to as "S _OFF ") is sent to the control device 4 via the signal channel. Is called) is sent. Note also similar operation in the telephone set 5 _B is performed.

FIG. 6 is a diagram showing an example of the operation of the control circuit 6 of the control device 4, and S _A and S _{B in the} same figure respectively represent signals sent from the telephones 5 _A and 5 _B via signal channels. (When the signal is not sent, it represents the immediately preceding signal held in the memory of the control circuit 6).

The operation of the control device 4 will be described with reference to FIG. The example when the phone 5 _A has started transmitting before the phone 5 _B starts transmission _{(S A = "S ON"} ), the selector switch SW ₁ ~ ₃ is switched, the interface circuit 3 _B, 3 _C transmitted signals information channel interface circuits 3 _a, the signal path for transmitting signals of information channels of the interface circuits 3 _a interface circuit 3 _C is formed. At this time the network and telephone
The transmission signal of the telephone 5 _A is transmitted to 5 _B, and the signal transmitted from the network via the information channel is transmitted to the telephone 5 _A.

Also when the telephone set 5 _B has started transmission _{(S B = "S ON"} ) before the phone 5 _A starts transmission, likewise is switched selector switches SW ₁ ~ _3, the interface circuit 3 _A , 3 _C
The signal of the information channel of the interface circuit 3 _B to
Signal paths for transmitting the signal information channels of the interface circuit 3 _C is formed in the interface circuit 3 _B. At this time, the network and the phone 5 _A is transmitted is transmission signal of the telephone 5 _B, the phone 5 _B signal is sent sent via the information channel from the network.

In addition, phone 5 _{A is in the} state where phone 5 _B has not started talking.
The but when stopping the transmission _{(S A = "S OFF"} ), likewise, transmitted signals information channel interface circuits 3 _A to the interface circuit 3 _C, the interface circuit 3 _A, 3 interface circuit 3 to the _B To carry the signal of the information channel of _C ,
A selector switch and SW1 to SW3 are switched to form a signal bus. Also when the phone 5 _A is the telephone set 5 _B when no start the transmission has stopped transmission _{(S B = "S OFF"} ) , the
Similarly, the interface circuit 3 _C to the interface circuit 3 _B
Transmits the information channel signal of the interface circuit 3 _C , 3
To convey signals information channel interface circuits 3 _C to _B, the selector switch SW1~3 and is switched signal bus is formed.

By the above operation, the information channel signal from the network and the transmission signal from each telephone are
It can reach the network and other telephones.

Further, as can be seen from FIG. 6, regarding the control method of the selector switch, when the transmission of one telephone is not completed and the other telephone does not perform the transmission, the information channel is not switched, Switching the information channel after one phone has finished talking, and when the other phone is not talking, even if one phone finishes talking, that phone is connected to the network and the information channel is retained It is possible to smoothly switch the information channels by taking into consideration such things as doing so.

〔The invention's effect〕

As described above, according to the present invention, in digital telephone communication, without using an adder circuit by a digital signal processing having a large circuit scale or an adder circuit by a combination of a D / A, A / D converter and an analog adder circuit. There is an effect that a three-way call function can be provided by adding a small circuit such as a transmission signal detection circuit mounted on a telephone or a selector switch mounted on a control device. In digital telephone communication, a network interface circuit and a control circuit for controlling these are required in addition to a handset and a call circuit (including a codec for converting an analog signal to a digital signal) only for making a call. However, these circuits are not new necessary circuits for implementing the present invention.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a configuration example of a three-way communication system using an adder circuit, FIG. 3 is a diagram explaining the operation of an interface circuit, and FIG. Is a diagram showing one configuration example of the detection circuit of FIG. 1, FIG. 5 is a diagram showing a control flow of the digital telephone of FIG. 1, and FIG. 6 is a diagram showing a control flow of the control device of FIG. . Interface circuits 3 _A ~ C _...... controller 4 control apparatus ...... embodiment, 5 _A, 5 _B ...... digital telephone, the control circuit 6 ...... controller, interface circuit 7 ...... phone, 8 ... ... speech circuit, 9 ...... detecting circuit, the control circuit 10 ...... telephone, SW ₁ ~ 3 _...... selector switches, T ...... transmitter, R ...... handset.

Claims (1)

[Claims] 1. A control device connected to a digital communication network, and a plurality of digital telephones connected to the digital communication network via the control device. Between the plurality of digital telephones and the control device. Are connected by a communication line composed of a signal channel and an information channel for respectively transmitting a multiplexed control signal and voice signal, and a three-party call is made between the digital communication network and at least two digital telephones. In the system, each of the digital telephones determines a call signal and an interface circuit, a detection circuit that detects a transmission signal, and the presence or absence of a transmission signal based on a detection output of the detection circuit, and the determination result is the interface. And a control circuit for notifying the control device via the signal channel via the circuit, The control device comprises a plurality of interface circuits, a plurality of selector switches for switching the sustaining destination of the transmission signal transmitted from each of the digital telephones through the information channel, and the determination result transmitted through the signal channel. And a control circuit for controlling connection between the plurality of selector switches and the selector switch based on the above, to enable three-way communication.