JP2947307B2 - Central office trunk for automatic telephone exchanges - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a central office trunk for an automatic telephone exchange, and more particularly to an office trunk for an automatic telephone exchange having a signal amplifying function for amplifying a call signal from a terminal device.

[0002]

2. Description of the Related Art A conventional line trunk for an automatic telephone exchange having a signal amplifying function (an office trunk accommodated in an automatic telephone exchange) is used for two-way communication signals transmitted between terminals. In contrast, amplification was performed unconditionally.

[0003]

However, in the above-mentioned conventional central office trunk for an automatic telephone exchange, the amplifying device for amplifying the speech signal has an amplification factor such that the gain is constant according to the level of the input signal. In the case of an automatic gain controller (AGC) that automatically adjusts the amplitude, when a modem signal that performs a modulation method including amplitude modulation is input to the amplifier, amplitude information of the modem signal is transmitted to the amplifier by the amplifier. Since it is changed, there is a problem that a bit error may occur in communication between modems (communication between terminal devices) or communication may be disabled.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the disadvantages of the prior art and to achieve good data communication even when a modem signal that uses a modulation method including amplitude modulation is input. An object of the present invention is to provide a central office trunk for an automatic telephone exchange having a function of amplifying a call signal.

[0005]

[Means for Solving the Problems]

A central office trunk for an automatic telephone exchange according to the present invention is a signal amplifier for amplifying a two-way communication signal transmitted between one terminal device and another terminal device in accordance with the level of an input signal. Means, tone detecting means for detecting whether or not a predetermined tone is present in the call signal, and signal amplification of the signal amplifying means when the tone detecting means detects the presence of a tone in the call signal. Control means for stopping the function and outputting the input signal without any change in amplitude. With such a configuration,
It is intended to achieve the above-mentioned object.

[0007]

An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 shows an example of a communication system including a central office trunk for an automatic telephone exchange according to the present invention. This communication system includes one terminal device 9.
And the other terminal device 10, a central office trunk 1 accommodated in an automatic telephone exchange (not shown) which connects these terminal devices 9 and 10 to each other as necessary to enable communication, and the central office trunk 1 Circuit (LC) 6 and time division switch (TDSW) interposed between the terminal and one terminal device 9
7 and a public network (PSTN) 8 interposed between the central office trunk 1 and the other terminal device 10.

[0009] Of these, the office line trunk 1 is a public network (PS).
2-wire to 4-wire conversion circuit (HYB) 2 connected to TN) 8
An auto-gain controller 3 as signal amplifying means for amplifying a two-way communication signal transmitted between one terminal device 9 and the other terminal device 10 according to the level of an input signal; An answer tone detecting circuit (DET) 4 as tone detecting means for detecting whether there is a predetermined tone, that is, an answer tone composed of a 2100 Hz signal, and the answer tone detecting circuit 4 A control device (CPU) 5 is provided as control means for controlling the auto gain controller 3 so as to stop the signal amplification function when it is detected that an answer tone is present.

In this embodiment, it is assumed that a modem that performs amplitude modulation is used as one of the terminal devices 9 and the other terminal device 10.

Next, the overall operation of the embodiment constructed as described above will be described.

First, when a call is made from one terminal device 9 to the terminal device 10 through the subscriber's circuit 6, the time division switch 7, the line trunk 1, and the public network 8, the other terminal device 10 responds. An answer tone from the terminal device 10 arrives at the central office trunk 1 via the public network 8. Then
The answer tone detection circuit 4 constituting the central office trunk 1 detects this answer tone and notifies the control device 5 of the detection result. The control device 5 receives this notification,
The automatic gain controller 3 is controlled to stop the signal amplification function. Thus, the adjustment of the amplification factor according to the input signal level of the auto gain controller 3, that is, the signal amplification function is stopped.

For this reason, since the amplitude information of the modem signal is transmitted between the terminal devices 9 and 10 without any change, good data communication becomes possible. On the other hand, when the answer tone does not reach the trunk 1, the answer tone detecting circuit 4 does not detect the answer tone, so that the signal amplification function of the auto gain controller 3 does not stop.

[0014]

Since the present invention is constructed and functions as described above, according to the present invention, the tone detection means performs the modulation method including the amplitude modulation as one of the response signals to the transmission from the one terminal apparatus. The presence or absence of an answer tone emitted from the terminal device can be detected, and only when this tone is detected by the tone detection unit, the signal amplification function of the signal amplification unit is stopped by the control unit. If no modem signal is input, signal amplification can be performed according to the level of the input signal, and even if a modem signal that uses a modulation method that includes amplitude modulation is input, the modulation method that includes amplitude modulation is used. The amplitude information of the modem signal being transmitted can be transmitted without any change, thereby enabling good data communication. It is possible to provide a no good automatic telephone exchanges for office line trunk conventional called.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 office trunk 3 auto gain controller as call signal amplification means 4 answer tone detection circuit as tone detection means 5 control device as control means 9 one terminal device 10 the other terminal

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04Q 3/42-3/42 107 H04Q 1/54-1/56

Claims (1)

(57) [Claims] 1. A signal amplifying means for amplifying a two-way communication signal transmitted between one terminal device and the other terminal device in accordance with the level of an input signal; Tone detecting means for detecting whether or not the received tone is present, and stopping the signal amplifying function of the signal amplifying means when the tone detecting means detects the presence of the tone in the call signal. Control means for outputting the input signal without changing the amplitude of the input signal.