JP5451097B2 - Terminal network control device and data communication system - Google Patents

Description

  The present invention relates to a data communication system for transmitting data from a terminal device such as a meter through a communication line between a terminal network control device and a center device.

  Electricity, gas, water, etc. are indispensable energy for companies and general households, and safe and reliable supply and management to a huge number of users is a daily issue for suppliers. In the era of liberalization competition, suppliers are required to improve operational efficiency, save costs, and improve customer service.

  Against this background, regular meter visits to users and checking of terminal devices are a heavy burden for suppliers, and may require a balance for users. It was. For this reason, a data communication system that automatically performs meter reading and checking from a remote location using a public telephone line to which most users are subscribed has been introduced, and is beginning to spread to ordinary households. In particular, the development and popularization of automatic remote meter reading and automatic remote diagnosis in the field of city gas and LP gas, where safety effects are important, are remarkable.

  In a conventional data communication system that performs automatic meter reading, a terminal network control device to which a meter is connected and a center device are communicably connected via a telephone line, for example. When a call signal is input to the terminal network control device through the telephone line, the terminal network control device counts ringing due to the call signal. When the number of calls reaches a predetermined number, the terminal network control device determines that the meter reading is being called from the center device, and transmits data to the center device by transmitting to the terminal. At this time, the terminal network control device reads the value of the meter and transmits the data to the center device side.

  Here, communication equipment such as a telephone and a facsimile machine is connected to the terminal network control device. The telephone and the facsimile apparatus are located behind (downstream) the terminal network control apparatus with respect to the line. Disadvantage that if the telephone or facsimile connected to the downstream side of the terminal network control device in response to a call from the center device goes off-hook, the telephone line becomes busy and the center device cannot call the terminal network control device. was there.

  In order to solve this problem, Patent Document 1 describes that when the number of calls reaches a predetermined value, the downstream side of the terminal network control device is disconnected. Patent Document 2 describes that when the number of detections of the bell ringing signal matches the set value, a loop is performed, and when the ID signal is detected and matched, it goes on-hook and communication is started by the second ID signal. Further, when the number of detections of the bell call signal does not match the set value, the line is monitored in a high impedance state, and if an ID signal is detected, a loop is made and communication is performed by disconnecting the rear communication device. In Patent Document 3, if the number of ringing detections of the bell ringing signal is equal to or greater than a set value, data is transmitted to the center device by activation on the terminal side after a predetermined time.

  In Patent Document 4, when a call signal is detected and the communication device goes off-hook, the communication device itself goes off-hook, and a signal transmitted from the communication device is blocked by a filter circuit provided between the communication device and the center device. The presence or absence of an ID signal is detected.

  Further, in Patent Document 5, when the number of call detections of a call signal is less than a set value and the telephone connected to the downstream side of the terminal network control device goes off-hook, the line is monitored for a certain time. If an ID signal from the center apparatus is received during that time, data transmission is performed by activation of the terminal side.

JP-A-5-236141 JP-A-8-237385 JP-A-10-79799 JP 2007-228071 A JP 2004-201157 A

  As described above, when detecting the number of detections of the call signal, if the communication device goes off-hook before the call signal reaches a predetermined value, the terminal network control device is not connected to the communication line. ID signal from cannot be received. Therefore, the terminal network control device cannot perform data communication with the center device.

  Further, when the answering machine or the facsimile apparatus is off-hook by a calling signal, these communication devices transmit a talkie sound or a FAX communication sound by voice synthesis. Further, when the facsimile apparatus goes off-hook in response to the calling signal, it transmits a response signal such as a confirmation signal or a tone signal. There is a possibility that the response signal transmitted from such a communication device is congested with the ID signal from the center device. The terminal network control device cannot identify the ID signal and cannot communicate with the center device. Here, when the terminal network control device is provided with a filter circuit, it is possible to attenuate the voice band signal to improve the SN ratio of the ID signal and to easily identify the ID signal. However, a filter circuit must be added, which increases the cost.

  In particular, when a communication device that responds to a call signal of a super G3 standard facsimile apparatus is connected downstream of the terminal network control apparatus, the transmission side facsimile apparatus and the reception side facsimile apparatus determine the communication speed. Negotiate to do. When the facsimile apparatus goes off-hook by the call signal, the terminal network control apparatus enters a high impedance loop state and is connected to the communication line in order to monitor the line for a certain period of time. At this time, if the negotiation period of the facsimile device and the monitoring period coincide, the negotiation cannot be performed correctly due to the high impedance loop of the terminal network control device, and the facsimile device cannot transmit or receive at an appropriate speed or quality. I can't.

  In view of the above, the present invention makes it possible to receive an identification signal from the center device without disconnecting the communication device from the communication line, and enables data communication with the center device without obstructing the use of the communication device. An object of the present invention is to provide a terminal network controller.

  The present invention is a terminal network control apparatus having a control unit that controls data communication with a center apparatus through a communication line, to which a terminal apparatus and a communication apparatus are connected, and the communication apparatus is in a state of being connected to the communication line When the communication device goes off-hook by the calling signal, the control unit monitors the identification signal from the center device for a predetermined monitoring time while the communication device is connected to the communication line and the device is connected to the communication line. Is.

  During the monitoring of the identification signal, the communication device is kept connected to the communication line. Therefore, the communication device can transmit a necessary response signal, and when the call is made to the communication device, the communication device can be used as it is.

  When the control unit detects the identification signal from the center device, the control unit communicates with the center device so that the communication device is disconnected from the communication line. When the identification signal is not detected, the control unit communicates with the communication device. While maintaining the state of being connected to the line, the apparatus is brought into a state of being disconnected from the communication line. When detecting the identification signal from the center device, the control unit transmits a response signal to the center device after the transmission of the identification signal is completed. That is, when the terminal network control device starts communication with the center device, it responds in accordance with the operation of the center device, and does not interfere with the operation of the center device.

  By the way, a communication device connected to a communication line sends a response signal off-hook. In order to reliably detect the identification signal without being disturbed by the response signal, the monitoring time is set according to the response signal. That is, the monitoring time is set to a time longer than the transmission time of the response signal sent when the communication device goes off-hook.

  Therefore, the terminal network control device can reliably detect the identification signal in a period in which the response signal from the communication device and the identification signal are not congested. Specifically, there is a no-signal period between response signals sent in order from the communication device. This no-signal period always appears within the monitoring time. The control unit detects the identification signal during the no-signal period.

  The terminal network control device and the center device constitute a data communication system that performs data communication through a communication line. The center device that has called the terminal network control device transmits an identification signal when detecting the off-hook of the communication device, and the terminal network control device starts monitoring the identification signal after detecting the off-hook of the communication device, When the identification signal is detected, the communication device is disconnected from the communication line and communicates with the center apparatus. The terminal network control device starts monitoring the identification signal after detecting the off-hook of the communication device. When the identification signal from the center device is not detected, the terminal network control device maintains the state where the communication device is connected to the communication line. Is disconnected from the communication line. The transmission time of the identification signal of the center device is set longer than the transmission time of the response signal.

  In addition, the terminal network control device includes a connection circuit that connects the device itself to the communication line, an off-hook detection circuit that detects an off-hook of the communication device, and a communication device to enable communication with the center device. A rear connection switching circuit for switching between a state connected to the communication line and a state disconnected from the communication line, and the control unit. The control unit controls each circuit to monitor the identification signal and perform data communication with the center device.

  According to the present invention, it is possible to monitor the presence or absence of an identification signal from the center apparatus while the communication device is connected to the communication line. If it is not a call from the center device, the communication device can respond to the call, so that the use of the communication device is not hindered.

Overall configuration diagram of data communication system of the present invention Block diagram showing schematic configuration of terminal network controller The figure which shows the operation | movement flow of the data communication system with respect to the call from a center apparatus. The figure which shows the operation | movement flow of the data communication system with respect to the call from a center apparatus. The figure which shows the operation | movement flow of the data communication system with respect to the call from the facsimile machine of a super G3 specification.

  A data communication system of this embodiment is shown in FIG. The data communication system performs data communication such as automatic meter reading between the center side and the terminal side. In the center device 1, a host device 2 comprising a computer is connected to a center network control device 3, and the center network control device 3 is connected to the terminal side device 7 through a public telephone line 4 as a communication line and its exchanges 5 and 6. Connected to the terminal network control device 8.

  The terminal network control device 8 is connected to a communication device 9 such as a telephone and a facsimile device, and is connected to a terminal device such as a meter 10, a sensor, and a contact device. The communication device 9 is connected to the rear side (downstream side) of the terminal network control device 8 with respect to the telephone line 4.

  The terminal network control device 8 communicates with the meter 10, for example, and acquires necessary meter reading data. Then, the terminal network control device 8 transmits meter reading data to the center device 1 in response to a meter reading request from the center device 1 or by a terminal call. The communication device 9 is generally a telephone, but includes a facsimile machine with a telephone function, an answering machine, and a super G3 facsimile machine. A plurality of communication devices 9 may be connected to the terminal network control device 8.

  As shown in FIG. 2, the terminal network control device 8 includes a loop & high impedance loop circuit 21, a communication circuit 23, a control unit 24, a meter interface circuit 25, a paging signal detection circuit 22, a rear connection switching circuit 27, an off-hook detection circuit. 26.

  The terminal network control device 8 is connected to a telephone line 4, and a loop & high impedance loop circuit 21 and a communication circuit 23 are connected to the telephone line 4, and each circuit 21, 23 includes a CPU, ROM, and RAM. Connected to the control unit 24.

  The communication circuit 23 has a modem function for mutually modulating / demodulating between a data signal and an audible frequency signal flowing through the telephone line. The meter 10 is connected to the meter interface circuit 25 via a connection terminal. The meter interface circuit 25 is responsible for the interface between the meter 10 and the control unit 24, and exchanges data.

  The off-hook detection circuit 26 is connected between the telephone line 4 and the communication device 9, detects whether the communication device 9 is used, that is, off-hook or on-hook, and outputs a detection signal to the control unit 24. The rear connection switching circuit 27 is configured by a relay, and is interposed between the on-hook detection circuit 26 and the communication device 9. The rear connection switching circuit 27 is controlled by the control unit 24 and switches between a connected state in which the communication device 9 is connected to the telephone line 4 and a disconnected state in which the communication device 9 is disconnected from the telephone line 4. When the communication device 9 is in the disconnected state, the communication device 9 is connected to the control unit 24 through the rear connection switching circuit 27. Thereby, the control unit 24 can directly detect the off-hook of the communication device 9.

  The call signal detection circuit 22 detects a 16 Hz call signal transmitted from the telephone line 4. The loop & high impedance loop circuit 21 is a connection circuit that closes the telephone line 4 to make a loop state or a high impedance loop state (half-loop state). When the terminal network control device 8 enters a loop state or a high impedance loop state with respect to the telephone line 4, the terminal network control device 8 is connected to the telephone line 4 and can communicate with the center device 1.

  The loop state is a state in which the terminal network control device 8 is connected to the telephone line 4 with a low impedance, for example, 50Ω to 300Ω. The high impedance loop state is a state in which the telephone line 4 is connected with a higher impedance, for example, several kΩ. In the high-impedance loop state, less power is being monitored than in the loop state. Further, there is an advantage that it is difficult to hinder a call of the communication device 9 that is off-hook.

  The control unit 24 controls each circuit described above to perform data communication with the center apparatus 1 and enables communication via the telephone line 4 by the communication device 9. In addition, since these controls are well-known techniques, detailed description is abbreviate | omitted.

  Then, the terminal network control device 8 operates according to the behavior of the communication device 9 so that automatic meter reading of the meter 10 can be reliably performed by a call from the center device 1. Therefore, the control unit 24, when receiving a call signal from the telephone line 4, a function of counting the number of calls by the call signal, a function of detecting whether the communication device 9 is off-hook when the number of calls is less than a predetermined number of times, When an off-hook of the communication device 9 is detected, the communication device 9 has a function of connecting itself to the telephone line 4 and a function of monitoring the telephone line 4 while the communication device 9 is connected to the telephone line 4. In addition, the control unit 24 has a function of monitoring the telephone line 4 when the communication device 9 does not go off-hook and the telephone line 4 is connected to the telephone line 4 when the calling number of calling signals exceeds a predetermined number. . The control unit 24 monitors the identification signal from the center device 1 for a predetermined monitoring time.

  When the control unit 24 receives the identification signal addressed to itself from the center device 1, the control unit 24 disconnects the communication device 9 to perform data communication with the center device 1 and does not receive the identification signal addressed to itself. It has a function of canceling the connection with the telephone line 4, stopping the monitoring of the telephone line 4, and setting the standby state. Even if the terminal network control device 8 is in the standby state, the communication device 9 is maintained in the connected state.

  In the center apparatus 1, when the host apparatus 2 calls the terminal network control apparatus 8 and detects an off-hook of the terminal side apparatus 7, the host apparatus 2 transmits an identification signal to the terminal network control apparatus 8 through the center network control apparatus 3. The host device 2 outputs an identification signal for a fixed time.

  Next, an operation in the data communication system when the terminal network control device 8 is called will be described. When a call signal is input to the terminal network control device 8 through the telephone line 4, the call signal detection circuit 22 detects the call signal. First, the control unit 24 determines whether or not the ringing number (calling number) by the calling signal is equal to or greater than the predetermined number N. If less than N, the control unit 24 determines whether or not the communication device 9 is off-hook based on the output from the off-hook detection circuit 26.

  If the communication device 9 is off-hook, the control unit 24 drives the loop & high impedance loop circuit 21 to put the telephone line 4 into a high impedance loop state and monitors the telephone line 4. That is, the control unit 24 detects the presence / absence of a signal flowing through the telephone line 4 through the loop & high impedance loop circuit 21 and the communication circuit 23.

  If the communication device 9 does not go off-hook and the number of ringing is N or more, the control unit 24 determines that the call is from the center device 1 and the terminal network control device 8 goes off-hook. Then, the control unit 24 puts its own device in a loop state with respect to the telephone line 4, monitors the telephone line 4, and detects a signal transmitted. Note that the control unit 24 controls the loop and high impedance loop circuit 21 so as to be in a high impedance loop state when monitoring the identification signal and in a loop state when performing data communication.

  The control unit 24 receives a signal from the telephone line 4 and monitors whether it is an identification signal from the center device 1. When the control unit 24 identifies that the identification signal is an ID signal addressed to itself, the control unit 24 operates the rear connection switching circuit 27. The communication device 9 is disconnected from the telephone line 4. The control unit 24 starts communication with the center device 1. When the communication with the center device 1 is completed, the terminal network control device 8 goes on-hook and puts the communication device 9 in a state of being connected to the telephone line 4.

  When the ID signal addressed to itself cannot be received even after the monitoring time has elapsed, the monitoring is timed out, and the control unit 24 determines that the call is not from the center device 1. That is, a call to another terminal network control device 8 or a call to the communication device 9. The control unit 24 cancels the high impedance loop state and ends the process. When the call is for the communication device 9, the communication device 9 responds and performs communication thereafter.

  In monitoring the identification signal, the control unit 24 determines whether the ID included in the received ID signal matches the own ID. As the ID signal, for example, a push button signal (PB signal) from the center device 1 or a data communication signal can be used.

  When a PB signal is used as the ID signal, at least one of A, B, C, and D that does not exist in the push button of the telephone may be used. These A, B, C, and D signals are the fourth column of the 4 × 4 matrix, that is, the coordinates (1, 4), (2, 4), (3, 4), on the operation unit of the telephone. Although corresponding to (4, 4), there is no push button at these coordinate points. Therefore, it is not input from the operation unit of the telephone, and it can be surely confirmed that the ID signal is from the center apparatus 1.

  As the identification signal instead of the ID signal, in addition to the PB signal and the data communication signal, an audio signal, that is, an audio signal having a content such as “I will perform meter reading now” may be used. Further, a combination of these PB signal, data communication signal, and audio signal may be used. When a voice signal is transmitted, if a PB signal or a data communication signal is transmitted before and after the voice signal, the terminal side device 7 can surely recognize the ID as compared with the case of only the voice signal.

  By the way, when the communication device 9 goes off-hook, the communication device 9 transmits a response signal. When the communication device 9 is a facsimile machine, a called station identification signal is transmitted as a response signal. This response signal is transmitted from 2.6 seconds to 4 seconds, and after that, there is always a non-signal period during which 75 msec is silent as FAX communication.

  Therefore, the monitoring time and the transmission time of the identification signal are set so that the terminal network control device 8 can reliably detect the identification signal from the center device 1. The monitoring time is set to a time longer than the transmission time of the response signal. The time for the center device 1 to transmit the identification signal is also set to be longer than the response signal transmission time. That is, the monitoring time is set from 4 seconds to 6.5 seconds, and the transmission time of the identification signal is set to 4 seconds or more. It is preferable to set the monitoring time longer than the transmission time of the identification signal. Further, the upper limit of the monitoring time, that is, the monitoring end timing is determined according to the transmission signal of the external facsimile apparatus sent through the telephone line 4. When the monitoring is completed, the terminal network control device 8 is released from the state connected to the telephone line 4, and the facsimile device can correctly receive the transmission signal.

  For example, when the transmission time from the center apparatus 1 is 5 seconds and the time required for recognition of the identification signal is 50 msec, the transmission time of the response signal is 2.6 seconds to 4 seconds. , At least 50 msec can be recognized in the no-signal period. Thereby, the identification signal can always be detected within the monitoring time. Therefore, even when the communication device 9 is connected to the telephone line 4, the control unit 24 can reliably receive the identification signal without being disturbed by the response signal of the communication device 9. As a result, the terminal network control device 8 can perform data communication with the center device 1 in response to the call of the center device 1.

  By the way, in the terminal network control device in Japanese Patent Application Laid-Open No. 2007-104269, when the communication device goes off-hook within a predetermined number of calls, the main control device temporarily disconnects the communication device from the telephone line, The telephone line is monitored for a certain period of time in the loop state. If the ID signal from the center device is received during this fixed time, data communication with the center device is started with the communication device disconnected. Here, the communication device is disconnected from the telephone line so that the ID signal can be received.

  As described above, if the transmission time of the identification signal from the center device 1, the monitoring time of the terminal network control device 8, and the time for recognizing the identification signal are set based on the response time of the communication device 9, the communication device 9 is temporarily set. Thus, the identification signal can be reliably received without being separated.

  The control unit 24 always maintains the communication device 9 connected to the telephone line 4 except during communication with the center device 1. Thereby, it is possible to prevent the operation of the communication device 9 that transmits a response signal when a call signal is received from being hindered. When not calling from the center device 1, the user can use the communication device 9.

  When the communication device 9 is a facsimile machine, there are a super G3 FAX and a G3 FAX. The communication procedure differs between the two. However, the terminal network control device 8 can monitor the identification signal without hindering the communication of the facsimile device regardless of the facsimile device of any standard.

  Specifically, when the communication device 9 is a G3 standard facsimile machine, the operation flow is as shown in FIG. The center device 1 dials the terminal network control device 8 for meter reading (104). A call signal flows from the switching center 6 to the terminal side (105), and the facsimile apparatus which is the terminal network control device 8 or the communication device 9 detects the call signal (106). First, the facsimile machine makes an off-hook response (107). This off-hook is detected by the off-hook detection circuit 26 (108), and the control unit 24 of the terminal network control device 8 recognizes the off-hook of the communication device 9 and operates the loop & high impedance loop circuit 21. The terminal network control device 8 enters a high impedance loop state, and monitoring of the identification signal is started (112).

  The center side apparatus 1 is transmitted with the polarity inversion of the line due to the off-hook in the terminal side apparatus 7 (109). The center network control device 3 detects a call response (110), and upon receiving this detection, the host device 2 instructs transmission of an ID signal as an identification signal. The center network control device 3 starts transmitting the ID signal (111). The transmission time is 5 seconds.

  At this time, the facsimile apparatus starts a CED signal for FAX communication at substantially the same timing (113). This response signal is transmitted between 2.6 seconds and 4.0 seconds. Note that the start time and transmission time of the CED signal vary widely depending on the type of the facsimile apparatus, but they fall within the range of 2.6 seconds to 4.0 seconds. Therefore, the ID signal from the center apparatus 1 and the CED signal from the facsimile apparatus are congested on the telephone line. As described above, during the transmission of the response signal, the control unit 24 of the terminal network control device 8 cannot recognize the ID signal from the relationship of SN even though the ID signal is being monitored.

  When the facsimile apparatus finishes transmitting the CED signal for a maximum of 4 seconds, a no-signal period of 75 msec in which no communication is performed is generated (114). During this no-signal period, the terminal network control device 8 can recognize the ID signal for at least 50 msec. Therefore, during this time, the control unit 24 can detect a call from the center device 1 (115).

  After detecting the ID signal, the control unit 24 operates the rear connection switching circuit 27 to disconnect the facsimile apparatus from the telephone line 4 (116). The facsimile apparatus transmits a DIS signal as a response signal in accordance with the regulations (114). However, since the facsimile apparatus is disconnected from the telephone line 4, this response signal is not sent to the telephone line 4.

  The control unit 24 stops monitoring the ID signal (118), sets a loop state for the telephone line 4, and then transmits a response signal to the center apparatus 1 (119). When the center device 1 detects this response signal (120), it starts data communication with the terminal network control device 8 (121). When the data communication is completed, the control unit 24 of the terminal network control device 8 operates the loop & high impedance loop circuit 21 to release the loop state, puts the own device into a standby state, and sets the rear connection switching circuit 27 The facsimile machine is connected to the telephone line 4 by operating.

  Some facsimile apparatuses do not send a response signal immediately after being off-hooked. That is, as shown in FIG. 4, after the center apparatus 1 transmits an ID signal (211), the facsimile apparatus starts transmitting a response signal (213). At this time, the control unit 24 of the terminal network control device 8 can detect the ID signal before transmitting the CED signal (215). Thereafter, the terminal network control device 8 can normally communicate with the center device 1.

  As described above, the timing at which the response signal is transmitted after the communication device 9 goes off-hook may be different. However, when the control unit 24 detects the off-hook of the communication device 9, the monitoring start timing is determined so as to start monitoring the identification signal. On the other hand, the center apparatus 1 normally transmits an identification signal when about 1 second to 2 seconds have elapsed after detecting polarity reversal due to off-hook on the terminal side. For this reason, transmission of the identification signal is started slightly later than the monitoring start timing. Considering these delays in the start timing, by setting the monitoring time longer than the transmission time of the identification signal and the transmission time of the response signal, the identification signal can always be detected within the monitoring time.

  Next, FIG. 5 shows an operation flow when the communication device 9 is a super G3 standard facsimile apparatus. Unlike the G3 standard, the super G3 FAX protocol is ITU-T (International Telecommunication Union) Complies with 34 Recommendations. The communication protocol is half-duplex communication in the G3 standard, but the super G3 standard is full-duplex communication. Also, the communication speed of the G3 standard is a maximum of 14.4 kbps, while the super G3 standard is a high speed of 33.6 kbps. Therefore, depending on the noise and impedance of the line, the communication speed is lowered and communication is impossible.

  In particular, when an equalizer adjustment signal is transmitted from the calling side facsimile apparatus to the receiving side facsimile apparatus, if there is an impedance imbalance or noise, negotiation will not be successful and FAX communication will be impossible. At this important timing, if the terminal network control device 8 controls the line in a high impedance state for detecting the ID signal, there is a possibility that FAX communication becomes impossible. Therefore, the monitoring of the ID signal may be completed before the negotiation period starts. The monitoring end timing is determined so as to exclude the negotiation period, and based on this, the upper limit of the monitoring time is determined. Therefore, the monitoring time is set between 4 seconds and 6.5 seconds. The monitoring ends before the negotiation period.

  In FIG. 5, the calling side facsimile apparatus of the Super G3 standard calls the facsimile apparatus of the terminal side apparatus. When the facsimile apparatus is off-hook in response to this call, the control unit 24 detects this off-hook and starts monitoring the ID signal (312). The facsimile apparatus transmits a response signal (313). When the calling facsimile apparatus detects a response from the terminal side, a CM signal + CJ signal (311), INFOOa signal (314), equalizer adjustment signal (316), and MPh signal (318) are determined after a while. Sequentially transmit at the same timing. The receiving facsimile apparatus also sequentially transmits the INFOOc signal (315) and the MPh signal (319) at a determined timing.

  The monitoring of the terminal network control device 8 ends before the negotiation period (317) starts. Since the high-impedance loop state of the terminal network control device 8 is released, the facsimile apparatus connected behind the terminal network control device 8 can correctly transmit and receive signals through the telephone line 4 and can reliably perform negotiation. Both facsimile apparatuses can perform high-speed FAX communication by determining communication conditions.

  Here, in the case of a call from the center apparatus 1, the identification signal of the center apparatus 1 is transmitted during the non-signal period of the facsimile apparatus. The terminal network control device 8 can detect the identification signal during the no-signal period, and can perform data communication with the center device 1. Therefore, the terminal network control device 8 can be equipped with not only a G3 standard facsimile machine but also a super G3 standard facsimile machine.

  In addition, this invention is not limited to the said embodiment, Of course, many corrections and changes can be added to the said embodiment within the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Center apparatus 4 Telephone line 8 Terminal network control apparatus 9 Communication apparatus 10 Meter 21 Loop & high impedance loop circuit 22 Call signal detection circuit 23 Communication circuit 24 Control part 25 Meter interface circuit 26 Off-hook detection circuit 27 Back connection switching circuit

Claims (7)

A terminal network control apparatus having a control unit for controlling data communication with a center apparatus through a communication line, to which a terminal apparatus and a communication apparatus are connected, wherein the communication apparatus connected to the communication line is When off-hook, the control unit monitors the identification signal from the center device for a predetermined monitoring time with the device connected to the communication line while the communication device is connected to the communication line .
The monitoring time is set to a time longer than the transmission time of the response signal transmitted when the communication device goes off-hook. There is a non-signal period between response signals sequentially transmitted from the communication device. A terminal network control device that detects an identification signal during a signal period . When the control unit detects the identification signal from the center device, the control unit communicates with the center device so that the communication device is disconnected from the communication line. When the identification signal is not detected, the control unit is switched to the communication line. 2. The terminal network control apparatus according to claim 1, wherein the terminal apparatus is placed in a state in which the connection with the communication line is released while maintaining the connected state. 3. The terminal network control device according to claim 2, wherein when the control unit detects an identification signal from the center device, the control unit transmits a response signal to the center device after transmission of the identification signal is completed. A data communication system in which a terminal device and a terminal network control device to which a communication device is connected and a center device perform data communication through a communication line, and the terminal network control device is a communication device in a state of being connected to the communication line. When off-hook by the call signal, the communication device is connected to the communication line while the communication device is connected to the communication line, and the identification signal from the center device is monitored for a predetermined monitoring time ,
The monitoring time is set to a time longer than the transmission time of the response signal transmitted when the communication device goes off-hook, and there is a no-signal period between response signals sequentially transmitted from the communication device. A data communication system , wherein an identification signal is detected during a no-signal period . The center device that has called the terminal network control device transmits an identification signal when detecting the off-hook of the communication device, and the terminal network control device starts monitoring the identification signal after detecting the off-hook of the communication device, 5. The data communication system according to claim 4, wherein when the identification signal is detected, the communication apparatus is disconnected from the communication line and communicates with the center apparatus. The terminal network control device starts monitoring the identification signal after detecting the off-hook of the communication device. When the identification signal from the center device is not detected, the terminal network control device maintains the state where the communication device is connected to the communication line. 6. The data communication system according to claim 5 , wherein the connection to the communication line is released. 7. The data communication system according to claim 5 , wherein a transmission time of the identification signal of the center device is set longer than a transmission time of the response signal.

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