JPH05167555A - Time division multiplexing device - Google Patents

Abstract

PURPOSE:To make an efficient use of a transmission line by changing the bit rate of transmission digital signal based on whether or not an answer back tone is transmitted in the prescribed time after detecting the connection of the communication lines between analog terminals. CONSTITUTION:When both connection requests on transmission and reception sides are turned on. that is, the connection of an analog communication path is judged, a connection monitoring circuit 23 actuates a timer 25 to count the prescribed time. An answerback tone detection circuit 21 monitors the answerback tone during the period, and when it can not be detected, having a control part 27 to change the sampling rate or the encoding system of A/D, D/A conversion part 15. The control part 27 changes the data rate of a time division multiplexing part 17 according to an analog terminal, and requests the change of the data rate from the multiplexing part 17 to the opposite device as needed. Thus, the efficient use of the transmission line can be realized with simple circuitry.

Description

Detailed Description of the Invention

[0001]

[Industrial applications]

The present invention relates to a time division multiplexer, and in particular, in an apparatus for digitalizing a signal from an analog terminal to perform multiplex communication, by making it possible to change the signal transmission rate according to the type of the analog terminal, The present invention relates to a technique that enables efficient communication with a simple hardware configuration.

[0003]

2. Description of the Related Art In order to transmit a signal from a plurality of analog terminals such as a telephone or a facsimile machine, the signal is digitized and time-division multiplexed, and then transmitted using a high speed digital line or the like. In such a transmission, the data rate of digital data is fixed to a predetermined value depending on the type of each analog terminal. For example, the analog signal of a modem used in a facsimile machine is set to a data rate of about 32 kbps to 64 kbps, and the voice of a telephone set is set to 8 kbps to 32 kbps.
Set to about kbps. In order to use the transmission path efficiently when multiplexing and transmitting data from multiple types of analog terminals, a dedicated analog interface is prepared for the modem to transmit at a high data rate. While telephone voice is transmitted at a relatively low data rate using another analog interface. Alternatively, the analog interface common to the modem and the telephone voice is used, and the minimum data rate that can transmit both the modem and the telephone voice is set to simplify the hardware.

[0004]

Among the above-mentioned conventional time division multiplexers, which use a dedicated analog interface for each type of terminal, the hardware of the device is complicated and large-scale. There was an inconvenience that In addition, in the method of setting the minimum data rate that can be used by each terminal using a common analog interface, signal transmission is performed at a high data rate even when a low data rate such as that of a telephone terminal can be used. Therefore, there is a disadvantage that the use efficiency of the transmission line is deteriorated.

In view of the problems in the above-mentioned conventional apparatus, an object of the present invention is to provide a complicated and large-scale hardware in a time division multiplexing apparatus for digitizing and transmitting signals from a plurality of types of analog terminals. It is to enable efficient signal transmission without using hardware.

[0006]

To achieve the above object, according to the present invention, there is provided a time division multiplexing apparatus for digitizing and transferring signals from a plurality of analog terminals. An A / D and D / A conversion means for digitizing a signal from an analog terminal to generate a digital signal for transmission and converting a digital received signal into an analog signal, and the digital signal for transmission is time-divided. Time division multiplexing and demultiplexing means for demultiplexing and demultiplexing the received time division multiplexed signals, and for detecting that a communication path between a plurality of analog terminals is connected Connection monitoring means, timer means for counting a predetermined time from the time when the communication path between the plurality of analog terminals is connected, and within a predetermined time defined by the timer means. An answer back tone detecting means for determining whether or not an answer back tone is transmitted from one of the plurality of analog terminals, and the answer back tone within a predetermined time from the time when the communication path between the plurality of analog terminals is connected. If is not detected, the control means for reducing the bit rate of the digital signal for transmission,
It is characterized by including.

The bit rate of the transmission digital signal can be reduced by reducing the sampling rate in the A / D and D / A conversion means.

Alternatively, the reduction of the bit rate of the transmission digital signal may be substantially reduced by changing the encoding method of the transmission signal.

[0009]

In the time-division multiplexer having the above structure, the signal from the analog terminal is converted into a digital signal by the A / D conversion means, time-division-multiplexed and transmitted via a high-speed digital line or the like. .. Also, when digitized data from other analog terminals is received,
Time division demultiplexing is performed and D / A conversion is performed and sent to the receiving analog terminal. In this way, communication is performed between a plurality of analog terminals via a high speed digital line or the like.

When performing such communication, the connection monitoring means detects that the communication path between the analog terminals to be communicated is connected, and the answer back tone detection means connects the communication path. It is determined whether or not the answer back tone is transmitted from any of the terminals within a predetermined time from the time point. And if the answer back tone is not detected within a predetermined time, the control means determines that the analog terminal with which communication is performed is a telephone terminal,
The bit rate of the digital signal for transmission is reduced. As a result, the optimum bit rate is set according to the type of analog terminal, the transmission efficiency is improved, and the communication quality required by each terminal can be secured. Further, since it is not necessary to use a dedicated analog interface for each type of terminal, the hardware of the device does not become complicated.

The bit rate of the transmission digital signal may be changed by lowering the sampling rate in the A / D and D / A conversion means, or the transmission signal encoding method may be, for example, PCM.
The bit rate can be substantially changed by changing the system to the ADPCM system or the like. Alternatively, the bit rate may be set to be suitable for the telephone terminal and may be increased when the answer back tone is detected.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a communication system including a time division multiplexing apparatus according to an embodiment of the present invention. The system shown in the figure comprises time division multiplexers 3A and 3B interconnected by a high speed digital line 1.
A private branch exchange 5A, for example, is connected to the time division multiplexing apparatus 3A, and a plurality of analog terminals such as telephones and facsimile machines having a modem are connected to the private branch exchange 5A. In FIG. Only 7A is shown. Similarly, another private branch exchange 5B is also connected to the time division multiplexer 3B, and a plurality of analog terminals are connected to the private branch exchange 5B, but only one telephone terminal 7B is shown in FIG. ing.

In such a communication system, for example, a call is made from the telephone 7A to the telephone 7B, that is, telephone 7A-private branch exchange 5A-time division multiplexer 3A-.
It is assumed that a connection is requested to the high-speed digital line-time division multiplexer 3B-private branch exchange 5B-telephone 7B.
When the telephone 7A is in the off-hook state and the dial input is made to the telephone 7B, the telephone 7
When a ringing tone is sent to B and the telephone set 7B is set off-hook in response to this ringing tone, the private branch exchange 5A
To the private branch exchange 5B. Although such a connection is made by a conventionally known method, the control information necessary for such a connection is provided by the time division multiplexers 3A and 3A.
The data is transmitted at the transmission speed initially set in B.

Immediately after such a connection is made, a time division multiplexer, for example, 3A, receives a frequency component used for answer back tone of the modem from the other terminal, for example, 2100 Hz or 2025 Hz for a predetermined time. Monitor for presence on analog interface.

When it is not possible to confirm that the frequency component used for the answer back tone exists in the analog interface during the predetermined time, the time division multiplexer lowers the sampling rate for analog-digital conversion. Alternatively, the bit rate is substantially reduced by changing the coding method for signal transmission. This is to reduce the transmission data rate and improve the utilization rate of the high-speed digital line when the analog terminal does not require such a high data rate as the telephone terminal does, for example. On the other hand, when it is confirmed that the frequency component used for the answer back tone exists in the analog interface,
Communication is performed at a preset relatively high data rate without performing such a data rate reduction operation.

Concretely, for example, the connection between analog terminals is 64 kbps PCM or 32 kbps immediately after the connection.
When the analog signal used for the answer back tone of the modem is detected within a predetermined time, the data is transmitted at the same data rate and coding method. On the other hand, if the analog signal used for the answer back tone of the modem cannot be detected within the predetermined time, the signal from the telephone terminal is encoded by the ADPCM of 24 kbps or the like for connection.

The data rate can be changed by, for example, A /
This can be done by changing the sampling rate of the D converter and the D / A converter and / or changing the coding method of the signal to be transmitted to substantially change the bit rate. When the answer back tone is detected by one of the time division multiplexers 3A, information indicating that fact is transmitted to the other time division multiplexer 3B using, for example, a supervisory channel, and the time division of the other party is performed. Also in the multiplexer, the data rate of the corresponding communication path can be set.

FIG. 2 shows a concrete configuration example of the time division multiplexer used in the communication system of FIG. The time-division multiplexer shown in FIG. 2 includes an analog interface circuit 11 to which a private branch exchange or a telephone is connected, an analog interface monitor and call control unit 13, and an A / A converter.
A D and D / A converter 15, a time division multiplexer 17,
Ringing tone generation circuit 19, answer back tone detection circuit 21, connection monitoring circuit 23, timer 25, and control unit 2
7 and the like.

A telephone or a modem of a facsimile machine is connected to the analog interface circuit 11 directly or via a private branch exchange or the like. The analog interface monitoring and calling control unit 13 monitors the communication path and transmits a ringing tone for connection and other controls. The answer back tone detection circuit 21 detects whether or not the analog circuit section has a frequency component corresponding to the answer back tone of the modem. In the case of so-called E & M, SS, and SR connection, answer back tone is detected, for example, by monitoring the connection section 29 between the analog interface monitoring and calling control section 13 and the A / D and D / A conversion section 15. Then do it. The time division multiplexing unit 17 time division multiplexes the digitized signals from a plurality of analog terminals, and time division demultiplexes the time division digital signals sent from the time division multiplexing device on the other side to obtain a plurality of signals. To the A / D and D / A converters for the terminal. Further, the control unit 27 changes the sampling rate of the D / A conversion unit 15 to A / D in response to the speed change request from the answer back tone detection circuit 21, or changes the coding method in the time division multiplexing unit 17. This is to perform control to cause it.

In the time division multiplexer of FIG. 2, when the connection monitoring circuit 23 detects that the connection request on the transmitting side and the connection request on the receiving side are turned on, that is, the analog communication path is connected. Timer 25
To start. The timer 25 requests the answer back tone detection circuit 21 to monitor the answer back tone for a predetermined time after starting.

When the answer back tone detection circuit 21 cannot detect the frequency component used for the answer back tone of the modem within this predetermined time, it requests the control unit 27 to change the transmission rate. In response to this request, the control unit 27 changes the sampling rate of the A / D and D / A conversion unit 15 or changes the encoding method. Also,
This request is met by changing the signal increase method in the time division multiplexing unit 17 to substantially change the data rate. In this way, the data rate in one of the time division multiplexers is set according to the type of analog terminal. In addition, the time division multiplexing device on the other side can be requested from the time division multiplexing unit 17 to change the data rate as needed via the supervisory channel.

[0022]

As described above, according to the present invention, it is detected whether the analog terminal connected to the time division multiplexer is a modem that outputs an answer back tone or something else, and the signal is transmitted. Since the speed is selected, it is possible to use the transmission line with high efficiency, and it is not necessary to provide a dedicated analog interface for each analog terminal, which prevents the hardware configuration from becoming complicated and large-scale. It

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a communication system using a time division multiplexing apparatus according to the present invention.

FIG. 2 is a block diagram showing a configuration of a time division multiplexing apparatus according to an embodiment of the present invention.

[Explanation of symbols]

1 High-speed digital line 3A, 3B Time division multiplexer 5A, 5B Private branch exchange 7A, 7B Analog terminal 11 Analog interface circuit 13 Analog interface monitor and call control unit 15 A / D D / A converter 17 Time division multiplexer 19 Ringing tone generation circuit 21 Answer back tone detection circuit 23 Connection monitoring circuit 25 Timer 27 Control section 29 Connection section

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location H04Q 11/04

Claims (3)

[Claims] 1. An A / D and D / A conversion means (15) for digitizing a signal from an analog terminal to generate a digital signal for transmission and converting a digital received signal into an analog signal, said digital for transmission. Time division multiplexing and demultiplexing means (17) for time division multiplexing the signals and demultiplexing the received time division multiplexed signals to generate the digital received signal, and a communication path between a plurality of analog terminals is connected. Connection monitoring means (23) for detecting that a predetermined time has elapsed since the call path between the plurality of analog terminals was connected, and a predetermined time defined by the timer means An answer back tone detecting means (21) for determining whether or not an answer back tone is transmitted from one of the plurality of analog terminals, and the plurality of answer back tone detecting means (21). Control means (27) for changing the bit rate of the digital signal for transmission in accordance with whether or not the answer back tone is detected within a predetermined time from when the communication path between the analog terminals is connected. A time division multiplexing device characterized by: 2. The time division multiplexing according to claim 1, wherein the bit rate of the digital signal for transmission is changed by changing the sampling rate in the A / D and D / A conversion means. apparatus. 3. The bit rate of the transmission digital signal is changed by substantially changing the bit rate by changing the encoding method of the transmission signal. Time division multiplexer.