JP2814514B2 - Ringback tone transmission circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ring-back tone transmission circuit used in a PCM carrier that connects telephones by a direct line.

[Conventional technology]

When telephones are connected to each other via a direct line using a PCM carrier, a system shown in FIG. 3 is generally known. Referring to FIG. 3, when the receiver of the first telephone set 17 is lifted (off-hook), the off-hook is connected to the first PCM.
The terminal device 18 detects the information and transfers the off-hook information to the second PCM terminal device 19. When the second PCM terminal device receives the off-hook information, the second PCM terminal device transmits the ring generator to the second telephone set 20.
Send a call signal from 24. At the same time, a ringback tone is transmitted from the second PCM terminal device 19 to the first telephone set 17 through the first PCM terminal device 8 by the ringback tone generator 23. When the receiver of the second telephone 20 is lifted, the first telephone 17 and the second telephone 20 can talk with each other. Similarly, from the second telephone 20 to the first telephone
Telephone 17 can be called.

FIG. 2 shows a conventional ring-back tone transmitting circuit.

Referring to FIG. 2, the ring back tone transmitting circuit is a PC.
It is provided in the M terminal equipment.

The ringback tone transmission circuit includes a switch 10, a 2-wire / 4-wire (2W / 4W) conversion circuit 11, an encoder 12, and a decoder 15. The switch 10 is connected to a subscriber line input terminal a and is connected to an analog ringback tone generator 16. The encoder 12 is connected to the PCM output terminal 13,
The decoder 15 is connected to the PCM input terminal 14.

When it becomes necessary to send a ringback tone,
The call base operates the switch 10 to connect the output of the ringback tone generator 16 to the 2W / 4W conversion circuit 11. When the ringback tone generator 16 is connected to the 2W / 4W conversion circuit 11, the ringback tone is transmitted from the PCM output terminal 13 to the opposite station via the 2W / 4W conversion circuit 11 and the encoder 12.

On the other hand, if a ringback tone is received,
The 2W / 4W conversion circuit 11 is connected to the subscriber line input terminal 9 by 10, receives a ringback tone via the PCM input terminal 14 and the decoder 15, and supplies the ringback tone to the subscriber line input terminal 9.

[Problems to be solved by the invention]

In the above-mentioned conventional ring-back tone transmitting circuit, when a plurality of call bases are activated at the same time, all of them are connected in parallel to the ring-back tone transmitting circuit. As a result, impedance matching with the subscriber line input terminal of the 2W / 4W conversion circuit becomes impossible, and the transmission level of the ringback tone decreases. In other words, there is a problem that the transmission level fluctuates depending on the number of call bases activated simultaneously.

In addition, considering the case where all the call bases accommodated in the PCM carrier are activated simultaneously, a ringback tone generator having a large output capacity is required. Such a ringback tone generator is problematic in that it is expensive and requires a large installation space.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a ring back tone transmission circuit having no fluctuation in transmission level.

It is another object of the present invention to provide a ringback tone transmitting circuit which does not require an expensive ringback tone and requires a small installation space.

[Means for solving the problem]

According to the present invention, a transmission analog signal from a two-wire subscriber line is converted into a PCM code and transmitted to a digital line as a transmission PCM code, while a reception PC signal from the digital line is transmitted.
A PCM code generator that converts an M code into an analog signal and supplies it as a received analog signal to the two-line subscriber line, and that transmits a ringback tone PCM code; a transmission PCM code and the tone PCM; And a transmission switching means for selectively transmitting the code to the digital line.

〔Example〕

 Next, the present invention will be described with reference to examples.

Referring to FIG. 1, reference numeral 1 denotes a subscriber terminal connected to a subscriber line, 2 denotes a 2W / 4W conversion circuit that converts a voice signal into 2W / 4W, 3 denotes an encoder that converts a voice signal into a PCM code, 4 is a PCM code generator for generating a PCM code in which ringback tone is PCM-coded, 5 is a digital switch for switching between the output of the encoder 3 and the output of the PCM code generator 4, and 6 is for sending the PCM code to the opposite station. Is an input terminal for inputting a PCM code from the opposite station, and 8 is a decoder for decoding the PCM code into an analog signal.

In a normal case (call), a voice signal input from the terminal 1 is input to the encoder 3 through the 2W / 4W conversion circuit 2,
Here, it is encoded into a PCM code. This PCM code is transmitted from the output terminal 6 to the opposite station through the digital switch 5. On the other hand, a PC input from the opposite station via input terminal 7
The M code is converted into an analog signal by the decoder 8 and output to the subscriber terminal 1 through the 2W / 4W conversion circuit 2.

When it becomes necessary to transmit a ringback tone, the digital switch is switched to the PCM code generator 4 side. PCM code generator 4 converts analog ringback tone to PC
An M-coded PCM code is repeatedly generated, and the PCM code is transmitted from the output terminal 6 to the opposite station through the digital switch 5. PC showing ringback tone at opposite station
The M code is input to the input terminal 7, decoded by the decoder 8 into an analog ringback tone of a predetermined level, and output to the subscriber terminal 1 through the 2W / 4W conversion circuit 2. And
From here, it is sent to the subscriber of the opposite station, and the subscriber can confirm that the other party is calling.

〔The invention's effect〕

As described above, in the present invention, a PCM code generator for generating a PCM code in which a ringback tone is PCM-encoded is provided for each ringback tone transmission circuit, and a PCM code of a constant level is provided for each communication path. Can be set to occur. Therefore, the output level of the transmitted ring-back tone is always constant, and as a result, the level does not fluctuate due to the number of simultaneously operating speech paths as in the prior art.

In addition, the digital switch and the PCM code generator can be easily configured with digital circuits, and if IC technology is applied, a low-cost, small, and low-power-consumption one can be easily realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a ringback tone transmitting circuit according to the present invention, FIG. 2 is a diagram showing a conventional ringback tone transmitting circuit, and FIG. 3 is a communication line system using a PCM carrier. FIG. 1,9 …… Subscriber line input terminal, 2,11… 2W / 4W conversion circuit, 3,12
... Encoder, 4 ... Digital switch, 5,13 ... PCM output terminal, 6,14 ... PCM input terminal, 7,15 ... Decoder, 8 ... Ring back tone PCM code generator, 10 … Switcher, 16 …… Analog type ringback tone generator, 17,20 …… Subscriber's telephone, 18,19 …… PCM carrier, 21,24 …… RING signal generator, 22,23 …… Analog type ringback tone generator.

Claims (1)

(57) [Claims] 1. A two-wire / four-wire conversion circuit that receives a transmission analog signal from a two-wire subscriber line and provides a reception analog signal to the two-wire subscriber line. A plurality of communication bases are provided, each of which includes an encoder connected to convert the transmission analog signal into a PCM code and converts the transmission PCM code into a transmission PCM code, and a decoder that converts a reception PCM code from a digital line into an analog signal and converts the analog signal into the reception analog signal. PC
Used for the M transport device, each of the plurality of call bases,
A PCM code generator for generating a tone PCM code in which a ringback tone is PCM encoded, the encoder and the PCM
A ring back tone transmission circuit, comprising: a digital switch connected to a code generator for selectively transmitting the transmission PCM code and the tone PCM code to the digital line.