JP2911929B2 - Interface circuit in private branch exchange - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Regarding an interface circuit for connecting a private branch exchange (PBX) to a central office line, it detects a tone from the central office line and prevents a malfunction of a tone detector that detects restoration of the central office side. A hybrid unit for converting the audio signal between the central office and the local line into two / four lines, a receiving amplifier for amplifying a signal received from the hybrid unit, and a network for encoding the signal amplified by the amplifier. A codec input unit, a tone detection unit that detects a tone by detecting an amplified signal by the amplifier and sends a detection signal to a local processor, a codec output unit that decodes a code signal from a network side,
A transmitting-side amplifier for amplifying an analog signal from the codec output unit and transmitting the amplified signal to the hybrid unit; and a balancing network for preventing the hybrid unit from sneaking around, between the codec output unit and the transmitting-side amplifier. When the detection signal from the tone detection unit is notified to the local processor, the codec output unit is controlled by the control signal from the local processor, the attenuation unit is activated by the control signal, and the codec output signal is provided. Is attenuated.

[Industrial applications]

The present invention relates to an interface circuit for connecting a private branch exchange (PBX) to an office line.

When an extension subscriber of a private branch exchange (PBX) connects to a subscriber telephone of the central office, the call is transmitted and received through a central office trunk constituting an interface circuit connected to the central office. FIG. 4 shows an example of the connection configuration of the office line trunk in this PBX. In the figure, 31 is an AB line polarity detection circuit, 32 is a Ringer detection circuit, 33 is a DC loop circuit, 34 is a hybrid circuit, 35 is a codec circuit, and 36 is a local processor.

When there is an incoming call from the central office to the PBX, the primary signal inverts the AB line polarity detection circuit 31 to block the transmission, and when a call signal is sent from the office, the ringer detection circuit 32 outputs the call signal. Is detected, the local processor 36 is activated, and the extension subscriber responds to form a DC loop circuit 33, and the communication line is converted into a 2-wire 4-wire through the hybrid circuit 34,
The transmission line and the reception line are separated by the codec circuit 35 and connected to the extension subscriber. In the case of a call termination, a tone (busy tone) is transmitted from the central office side due to the disconnection of the central office, and the internal trunk is restored when the extension subscriber disconnects the connection.

When a call is transmitted from the PBX to the central office, a DC loop circuit 33 for the central office trunk is formed, and a dial signal is sent out.
, The callee response is detected and the call is started. In the case of an end call, the line trunk is restored by disconnection on the PBX side. At this time, if the other party recovers first, a tone (busy tone) is sent from the central office to the PBX, and the PBX detects this tone and immediately releases the office trunk. This is to allow other PBX subscribers to use the office trunk effectively.

That is, when an incoming / outgoing call is made from the PBX to the central office, the off-hook of the other telephone is detected by the loop monitoring of the AB line polarity detection circuit 31, but the on-hook is detected by the hybrid circuit.
The signal is detected by a tone signal detection circuit provided on the receiving side of 34. Conventionally, a PBX subscriber listens tones and hangs up the handset to release the trunk, but recently, the local processor is operated by a tone signal detection circuit to immediately release the trunk.

[Conventional technology]

FIG. 5 shows a tone detection circuit from a station in a conventional line trunk. In the figure, reference numeral 11 denotes a hybrid unit for converting an audio signal from the local line to two-line / four-line conversion, 12 a receiving-side amplifier for amplifying a received signal from the hybrid unit, and 13 a coded signal amplified by the amplifier. A codec input unit for transmitting to the network side; a tone detection unit for detecting a tone of the amplified signal by the amplifier and transmitting a detection signal to a local processor; a codec output unit for decoding a code signal from the network side; Is a transmitting-side amplifier that amplifies an analog signal from the codec output section and transmits the amplified signal to the hybrid section, 17 is a balancing network for preventing looping of the hybrid section, and 18 processes a signal from the tone detection section. 2 shows a local processor that controls a codec unit.

When the tone signal from the line side is received by the hybrid unit 11 due to the on-hook on the line side, the tone signal is amplified by the receiving side amplifier 12, the signal amplified by the codec input unit 13 is coded and passed through the network. Send the call to the handset of the extension telephone. The tone signal amplified by the receiving amplifier 12 is branched at point B and inserted into the tone detector 14. The tone detector 14 detects the on / off ratio of the tone signal,
For a busy tone, for example, a 400 Hz tone signal is turned on for 500 ms,
It detects the intermittent signal of 500 ms off and sends it to the local processor 18. The local processor 18 receives the digitized intermittent signal of 500 ms on and 500 ms off, determines that the busy tone is generated by the office line side off-hook, and releases the office line trunk.

In the case of an incoming connection to an extension subscriber on the PBX side, a ringback tone ringing the extension telephone is sent to the central office. The ringback tone is an on / off intermittent signal of, for example, a 400 Hz signal for one second on and two seconds off, and is output from the codec output unit 15.
And is amplified by the transmission-side amplifier 16 and transmitted from the hybrid circuit 11 to the local line side. The balancing network circuit 17 is a circuit for preventing the sound signal from going from the transmitting side to the receiving side, but also serves to prevent the tone signal from going around.

PBX with automatic answering function for incoming calls from offices,
When there is an incoming call from the office line to the PBX side, when the PBX side automatically answers, a talkie sound "Please add an extension number" is sent to the office line side subscriber. When the local line side subscriber dials the additional number, the extension on the PBX side can be called.
While calling the extension telephone, a ring back tone is transmitted from the codec output unit to the central office. If the line-side subscriber goes on-hook during this call, a busy tone for ending the call is heard from the station.
It is sent to the PBX side. That is, a state occurs in which the ringback tone is transmitted from the codec output unit 15 while the tone signal is being received by the tone detection unit 14 of the PBX.

[Problems to be solved by the invention]

In the conventional trunk line with tone detection function, the ringback tone sent from the PBX goes around, and at point B, the tone that goes around to the busy tone from the station is added, and the tone detection unit 14 detects the tone. There was a problem that it became difficult. At this time, the wrapped waveform is attenuated from the waveform caused by the operation of the balancing network circuit 17, but is not sufficient by itself and the local processor 18 does not release the local trunk due to erroneous detection. Was causing unnecessary waste.

[Means for solving the problem]

FIG. 1 shows a principle configuration diagram of the present invention. In the figure, 1
Is a hybrid unit for converting the audio signal with the local line to two / four-line conversion, 2 is a receiving amplifier for amplifying a signal received from the hybrid unit, 3 is a coded signal amplified by the amplifier and transmitted to the network side. A codec input unit 4 for detecting a tone of an amplified signal by the amplifier and transmitting a detection signal to a local processor; a codec output unit for decoding a code signal from a network side; A transmitting side amplifier for amplifying an analog signal from the section and transmitting the amplified signal to the hybrid section;
Is a balancing device for preventing the hybrid portion from wrapping around.
A network 8 is a local processor that processes a signal from the tone detection unit to control the codec unit, and 9 is an attenuation unit that attenuates an analog signal from the codec output unit in accordance with a control signal from the local processor.

The point added to the conventional example is that an attenuator 9 is provided in front of the codec output unit 5, and while the tone detector 4 detects a busy tone from the local line side, the attenuator 9 is controlled by a control signal from the local processor 8. Is activated to attenuate an amplified signal caused by the ringback tone signal from the codec output unit 5 circulating through the hybrid circuit 1.

[Action]

When the hybrid unit 1 receives a tone signal from the local line side by the on-hook on the local line side, the tone signal is amplified by the receiving side amplifier 2, the signal amplified by the codec input unit 3 is coded, and the signal is coded via the network. Send the call to the handset of the extension telephone. The tone signal amplified by the receiving-side amplifier 2 is branched at a point B and inserted into the tone detector 4. The tone detector 4 detects the on / off ratio of the tone signal,
For a busy tone, for example, a 400 Hz tone signal is turned on for 500 ms,
It detects the intermittent signal of 500 ms off and sends it to the local processor 8. The local processor 8 receives the digitized intermittent signal of 500 ms on and 500 ms off, determines that the busy tone is caused by the off-hook on the line side, and releases the line trunk.

In the case of an incoming connection to an extension subscriber on the PBX side, a ringback tone ringing the extension telephone is sent to the central office. This ringback tone is an on / off intermittent signal of, for example, a 400 Hz signal for 1 second on and 2 seconds off, and is output from the codec output unit 5.
And amplified by the transmission side amplifier 6 and transmitted from the hybrid circuit 1 to the local line side. The balancing network circuit 7 is a circuit for preventing the sound signal from going from the transmitting side to the receiving side, but also serves to prevent the tone signal from going around.

PBX with automatic answering function for incoming calls from offices,
When there is an incoming call from the office line to the PBX side, when the PBX side automatically answers, a talkie sound "Please add an extension number" is sent to the office line side subscriber. When the local line side subscriber dials the additional number, the extension on the PBX side can be called.
While calling the extension telephone, a ring back tone is transmitted from the codec output unit 5 to the central office. If the central office subscriber goes on-hook during this call, a busy tone for ending the call is sent from the office to the PBX. That is, a state occurs in which the ringback tone is being transmitted from the codec output unit 5 while the tone signal is being received by the tone detection unit 4 of the PBX.

In the above state, the tone detection unit 4 sets the tone signal interval to 500 ms on, 500 ms off, and a busy tone of 400 Hz.
Upon receiving the signal, a DC intermittent signal of 500 ms on / off is sent to the local processor 8. At this time, a signal caused by the wraparound of the ringback tone from the codec output unit 5 is added, and the on / off of the DC intermittent signal is spoken. Different from medium tone. The local processor 8 receives the digitized DC intermittent signal, determines that it is a detection notification, sends a control signal to the codec output unit 5, and activates the attenuation unit 9. The ringback tone from the codec output unit 5 is attenuated by the attenuating unit 9 and the signal due to the wraparound is deleted. Therefore, only the intermittent signal of 500 ms on / off is sent to the local processor 8, and the local processor 8 speaks this signal. Judge as medium tone and release line trunk. Therefore, even during the transmission of the ringback tone, the busy tone due to the on-hook from the central office can be reliably received and the central office trunk can be released.

〔Example〕

FIG. 2 shows a block diagram of an embodiment of the present invention. In the figure, 21 is a tone detector, 22 is a codec, 23 is a local processor, and 24 is an attenuator.

When the busy tone from the central office is received by the tone detector 21,
A detection notification signal due to the intermittent DC pulse is sent to the local processor 23. The local processor 23 immediately sends a control signal to the power down terminal PD of the codec 22, activates the attenuator 24 added to the codec 22, controls the wraparound signal, and detects the signal to the CPU of the PBX main body. Make a notification. An intermittent signal of only the busy tone is sent from the tone detecting unit 21 to the local processor 23, and the local processor 23 notifies the CPU of the PBX main body of the detection and notifies the CPU.
, And sends a determination signal to the local processor 23. The local processor 23 receives the decision signal and releases the office trunk.

FIG. 3 shows a detection signal waveform diagram in the above embodiment.
In the figure, (a) is a signal waveform of a busy tone from a local line at point A, (b) is a wraparound waveform of a ringback tone from the codec output side at point A, and (c) is a detection notification at point B. The waveform (d) shows a control signal from the local processor.

In the conventional case where the control signal (d) from the local processor does not come, the busy tone (a) and the ringback tone (b)
Are added, and the waveform (c) of the detection notification signal is transmitted as an unspecified intermittent signal, so that the trunk release processing is not performed. In this embodiment, when the control signal (d) from the local processor is received, the wraparound signal (b) of the ringback tone is attenuated, and only the busy tone (a) is received at the point A. Signal (c) is 500ms
, And the line trunk is released normally.

In the above embodiment, the attenuator 24 is connected to the codec 22.
However, the codec 22 itself may be added to the output side, and the codec itself may be powered off by a power down signal from the local processor.

〔The invention's effect〕

Advantageous Effects of Invention According to the present invention, it is possible to reduce the influence of the wraparound of the tone transmitted by the PBX, and it is possible to accurately and quickly detect the tone from the station. Therefore, it is possible to surely release the trunk of the PBX having the automatic answering function for the incoming call, which is effective for the effective use of the trunk.

[Brief description of the drawings]

1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram of the embodiment, FIG. 3 is a detection waveform diagram of the embodiment, FIG. 4 is a connection configuration example of a local trunk, and FIG. FIG. 2 shows a block diagram of an example. In the figure, 1,11,34 is the hybrid unit, 2,12 is the receiving amplifier, 3,13 is the codec input unit, 4,14,21 is the tone detection unit, 5,15 is the codec output unit, and 6,16 is Transmitting amplifier,
7, 17 are balancing networks, 8, 18, 23, 36 are local processors, 9, 24 are attenuation units, 22, 35 are codecs, 3
1 is an AB line polarity detection circuit, 32 is a ringer detection circuit, 33
Indicates a DC loop circuit.

Continuation of the front page (56) References JP-A-58-81371 (JP, A) JP-A-62-200893 (JP, A) JP-A-63-153993 (JP, A) JP-A-2-224494 (JP) , A) JP-A-2-260791 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04Q 1/54-1/56 H04Q 3/42-3/42 107

Claims (1)

(57) [Claims] An interface circuit for connecting a private branch exchange (PBX) to an office line, comprising: a hybrid unit (1) for converting a voice signal from the office line to two-line / four-line conversion; and a reception signal from the hybrid unit. A receiving-side amplifier (2) for amplification, a codec input unit (3) for encoding an amplified signal from the amplifier and sending it to the network side, and tone-detecting the amplified signal from the amplifier and sending a detection signal to a local processor. A tone detection section (4), a codec output section (5) for decoding a code signal from the network side, and a transmission side amplifier (6) for amplifying an analog signal from the codec output section and transmitting the amplified analog signal to the hybrid section. And a balancing network (7) for preventing the hybrid unit from wrapping around, wherein the codec output unit (5) and the transmission side amplifier (6) are provided. When an attenuator (9) is provided between the local processor (8) and the detection signal from the tone detector (4) is notified to the local processor (8),
An interface circuit in a private branch exchange, wherein a codec output section (4) is controlled by a control signal from the local processor (8), and an attenuator (9) is activated by the control signal to attenuate the codec output signal. .