JPH1169336A - Cable modem device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cable modem device which automatically stops the transmission output of a terminal when one of plural terminals, which is connected to a CATV line, becomes an abnormal transmission state and which considerably reduces adverse effect on the operation of a CATV communication system. SOLUTION: When information showing 'during transmission' is continuously inputted to a microcomputer circuit 7 from a detection circuit 5 showing the transmission operation state of a transmission RF circuit 3 even if information showing a reception state does not exist from a detection circuit 6 showing the operation state of a LAN interface circuit 4, namely, even if data is not received from a personal computer 30, the microcomputer circuit 7 judges the abnormality of the transmission RF circuit 3 and compulsorily stops the transmission operation of the transmission RF circuit 3. Thus, an adverse effect on the other terminal unit on the operation of the CATV communication system, which occurs by continuous abnormal transmission, can be suppressed to a minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CATV communication system for performing bidirectional communication between a data communication device on the receiving side and a center on the transmitting side using a CATV line, and modulates data from the data communication device on the receiving side. Then, when transmitting to the transmitting side through the CATV line, it is checked whether the data transmission state is normal, and if it is determined that the data transmission state is abnormal,
The present invention relates to a cable modem device that does not adversely affect other normal cable modems connected to a CATV line.

[0002]

2. Description of the Related Art Hitherto, a bidirectional data transmission system using a CATV (cable television) transmission line has been developed and applied to services such as video on demand. On the other hand, a CATV line has a larger capacity for data transmission than a telephone line. Therefore, a CATV line is used to construct a network using a CATV line, for example, a high-speed transmission from a personal computer (hereinafter, a personal computer) of a subscriber terminal to the Internet or the like. A data communication service that can access the Internet has been developed.

In this service, an interface between a CATV line called a cable modem device and a network line is installed at a subscriber's house, and a personal computer, for example, is connected to the cable modem device. This allows the user to use services such as the Internet. Between the cable modem device and the personal computer, for example, IEEE80
By using the Ethernet system compatible with the 2.3 standard, a transmission capacity of 10 Mbps can be easily realized.

FIG. 5 shows a CAT including a cable modem device.
FIG. 2 is a block diagram illustrating a schematic configuration of a V broadcast system.

[0005] Referring to FIG.
Is a server device 24 connected to the video supply device 22, the external network 23, a signal conversion circuit 25 connected to the server device 24, and a modulated video signal from the video supply device 22 and a signal from the signal conversion circuit 25. It is provided with a mixing / demultiplexing circuit 26 for mixing the modulated data signal or for separating the mixed video signal and data signal from the CATV line 27.

[0006] In the CATV broadcasting center 21, a video signal accompanying a normal broadcasting service such as terrestrial broadcasting and satellite broadcasting is modulated from a video supply device 22 and mixed / demultiplexed by a mixing / demultiplexing circuit 26.
And then transmitted to the CATV line 27. C
The ATV line 27 is composed of a hybrid of an optical cable and a coaxial cable, and is connected to a plurality (two in the illustrated case) of subscriber terminals 28.

The CATV broadcasting center 21 is provided with a server device 24 connected to an external network 23 such as the Internet. The server device 24 manages subscribers, security with the outside, and network management. And so on.

On the downstream of the signal conversion circuit 25 connected to the server device 24, data generation, modulation processing and frequency conversion of the CATV communication system are performed, supplied to the mixing / demultiplexing circuit 26, and output to the CATV line 27. Is done.

The upstream signal transmitted from the subscriber terminal 28 is subjected to demodulation of upstream data and conversion of server format data by a signal conversion circuit 25 via a CATV line 27 through a mixing / demultiplexing circuit 26. Then, it is supplied to the server device 24.

On the other hand, in the subscriber terminal 28, the broadcast signal transmitted from the CATV line 27 is received by the CATV home terminal 31 and subjected to channel selection processing and demodulation processing, and then reproduced by the television receiver 32. I do.

The downstream signal sent from the broadcasting center 21 via the CATV line 27 is subjected to demodulation processing by the cable modem device 29, control data for the cable modem is extracted, and the connected data is transmitted. Necessary data is supplied to a personal computer 30 as a communication device. As the cable 33 between the cable modem device 29 and the personal computer 30, a twisted pair cable having a transmission capacity of 10 Mbps based on the Ethernet 10BASE-T is used.

On the other hand, the upstream data transmitted from the personal computer 30 is subjected to a modulation process by the cable modem device 29, and is transmitted as an upstream signal through the CATV line 27 through the CATV line.
The broadcast is sent to the broadcast center 21.

As described above, this CATV broadcasting system is different from the conventional subscriber terminal in that not only the CATV home terminal 31 receives the broadcast signal from the broadcasting center 21 but also the cable modem device 29 of each terminal aggressively. Can be transmitted to the broadcast center 21 at the same time.

Communication between the broadcast center 21 and the subscriber terminal 28 is performed for each of the uplink and downlink data by QPSK modulation having frequency bands of 1.5 MHz and 6 MHz, respectively, as shown in FIG. It is carried out.

The transmission and reception data transmission rates of the cable modem apparatus 29 are 2 Mbps and 2 Mbps, respectively.
8 Mbps. This is because the transmission rate at the time of downlink, that is, at the time of reception is designed to be higher in consideration of the large amount of information at the time of reception such as the Internet.

The communication data format is the same for both uplink and downlink. As shown in FIG. 7, a certain unit time is divided into one frame, and a continuous data stream is formed in this frame.

The outline of the configuration can be divided into FS (frame sync), terminal control signal, and subframe area (subframes 1 to n). FS indicates the beginning of the frame. The terminal control signal is transmitted to the subscriber terminal 28 to which the broadcast center 21 is connected.
Is an area where the subscriber 28 is controlled by a downlink signal.
And the subscriber terminal called by the uplink signal responds to the response request at a designated timing. Thus, communication between the broadcast center 21 and the subscriber terminal 28 is established. The terminal control signal also notifies the transmission timing of the uplink signal by the downlink signal.

The transmission of a packet is started so as to start from the head of a subframe for both uplink and downlink. If the packet does not fit in one subframe, the continuation of the packet is transmitted to the next subframe. In addition, control information of the uplink packet is also added to the downlink signal, and the subscriber terminal 28 controls the output of the uplink packet based on this information and performs transmission.

The transmission of uplink data from the subscriber terminal 28 to the broadcasting center 21 will be described in more detail. For transmission of uplink data, it is necessary to change the transmission output of the modem depending on the distance between the subscriber terminal 28 and the broadcasting center 21 (because the signal attenuation rate varies according to the distance between the terminal and the center). So) subscriber terminal 2
8 to the broadcasting center 21 so that all the upstream data signals arrive at the center 21 at the same level.
It is a mechanism to control the gain with. For this purpose, the control information of the uplink packet is added to the downlink signal of the subframe.

The center 21 notifies a plurality of terminals of the transmission timing of the uplink signal in the downlink terminal control signal. As a result, the terminal 28
The upstream packet is transmitted to the center at an appropriate timing in the subframe area of one upstream frame. If the information is normally received by the center 21, a response indicating this is returned to the terminal side. However, Center 2
In response to the notification of the uplink transmission timing issued from 1 to the terminal 28, since the plurality of terminals all have a fair transmission timing (right), the plurality of terminals transmit the uplink packet at once to the center 21. , A data collision occurs.

Therefore, Ethernet uses CSMA / CD (carrier sensing multiple access / access) as its access method.
Each terminal 28 checks the state of the LAN (the presence or absence of a carrier) before transmitting the uplink data, and transmits the uplink data only when the terminal 28 is idle. This retransmission timing is adjusted by a random number for each terminal 28 to avoid collision.

The problem here is that if one of the plurality of terminals 28 fails and enters a continuous transmission state, that terminal 28
Interferes in time with the frequency band in which it is transmitting, and the data transmitted by the other terminals 28 cannot be transmitted to the center 21 correctly, causing a problem in the operation of the CATV communication system.

For example, for one upstream frame, a subframe 1 from a normal terminal first, for example, 101010.
Is received by the center 21 and a faulty terminal is generated, the subframe 2 becomes, for example, 11111
1 are received, and the subframes 3 are all 1 like the data C such as 111111.
Are continuously received, and the data B, C,... Continue in a state where the last error check code is not normal. This is Center 21
From the point of view, all data other than the first data A are received by the center side in a state that there is no abnormality. Even in this way found to be abnormal in the center 21 the terminal side occurs, placed left sent data can not be identified or on any device abnormality since all abnormalities has occurred, a particular failure terminal There is a problem that it takes a very long time and effort to recover the system, in combination with the time and effort required.

[0024]

As described above, conventionally,
If a terminal connected to the CATV communication system breaks down and continuous transmission is performed, transmission data of other normal terminals connected to the same system is also destroyed, which has a serious effect on system operation. There was a problem.

In view of the above, the present invention provides a cable modem device capable of automatically stopping the transmission output of a terminal in an abnormal transmission state to minimize the adverse effect on system operation. The purpose is to do so.

[0026]

According to the first aspect of the present invention,
On the receiving side, disposed between the CATV line and the data communication device, the data from the data communication device is modulated and transmitted to the transmitting side through the CATV line, while the data is modulated on the transmitting side and transmitted through the CATV line. A cable modem device for demodulating data and transmitting the data to the data communication device, receiving data output from the data communication device through a communication device side interface,
Transmitting means for modulating and transmitting the signal to the CATV line; first detecting means for detecting a state of a transmitting operation of the transmitting means; and second detecting means for detecting a state of a data receiving operation of the communication device side interface And, while controlling the operation of the normal transmission in the communication device side interface and the transmission means, while comparing and determining the detection result from the first detection means and the detection result from the second detection means,
A control unit that outputs a transmission stop signal to the transmission unit when it is determined that the transmission state is continuously performed from the transmission unit in a state where data is not received from the data communication device. It was done.

According to the first aspect of the present invention, even though there is no information indicating the reception state from the second detection means indicating the operation state of the communication device side interface, that is, the communication device side interface receives data from the data communication device. If the information indicating that the transmitting means is transmitting is continuously input from the first detecting means indicating the state of the transmitting operation of the transmitting means to the control means even though the transmitting means has not been received, The transmission operation of the transmission means is forcibly stopped upon determining that the transmission is abnormal. As a result, it is possible to minimize adverse effects on other terminal devices in the operation of the CATV communication system, which are caused by continuous abnormal transmission.

According to the second aspect of the present invention, C
It is arranged between an ATV line and a data communication device, modulates data from the data communication device and transmits it to the transmitting side through the CATV line, and modulates data transmitted at the transmitting side and transmits through the CATV line. A cable modem device for demodulating and transmitting the data to the data communication device, comprising receiving data output from the data communication device through a communication device side interface, modulating the data, and
Transmitting means for transmitting to an ATV line; first detecting means for detecting a state of a transmitting operation of the transmitting means; second detecting means for detecting a state of a data receiving operation of the interface on the communication device side; A first interface for controlling a normal transmission operation in the device-side interface and the transmission unit;
And comparing the detection result from the first detection means with the detection result from the second detection means, and transmitting from the transmission means in a state where data is not received from the data communication device. A second control unit that outputs a transmission stop signal to the transmission unit when it is determined that the states are continuously performed.

According to the second aspect of the present invention, the first aspect is provided.
According to the invention, the control means, for example, one microcomputer circuit performs the control of the normal transmission and the control of the transmission abnormality determination and the control of the transmission stop based on the abnormality, so that the control of the normal transmission is performed by the first control means, for example. The main microcomputer circuit performs the transmission abnormality determination and the control of the transmission stop based on the abnormality in the second control means, for example, the sub-microcomputer circuit. Thus, even if an abnormal transmission state occurs, the sub-microcomputer circuit can detect this and forcibly stop the transmission operation of the transmission means.

According to a third aspect of the present invention, in the cable modem device according to the second aspect, the first control means is constituted by a microcomputer circuit, and the second control means is provided by the first control means.
To adjust the time to the detection signal from the detecting means
And a delay circuit for delaying the detection signal from the detection means, and comparing the delay signal from the delay circuit with the detection signal from the first detection means, in a state where no data is received from the data communication device. When the transmission state is continuously performed from the transmission unit, the transmission unit outputs a transmission stop signal to the transmission unit.

According to the third aspect of the present invention, the second control means can be realized only by connecting a delay circuit and a comparison circuit to signal lines from the first and second detection means. Compared to the case where the second control means is configured by a software (programming) such as a microcomputer,
The addition of a simple circuit can reliably prevent an abnormal state without being affected by software.

According to the fourth aspect of the present invention, C
It is arranged between an ATV line and a data communication device, modulates data from the data communication device and transmits it to the transmitting side through the CATV line, and modulates data transmitted at the transmitting side and transmits through the CATV line. A cable modem device for demodulating and transmitting the data to the data communication device, comprising receiving data output from the data communication device through a communication device side interface, modulating the data, and
Transmitting means for transmitting to the ATV line, detecting means for detecting the state of the transmitting operation of the transmitting means, control means for controlling the normal transmission operation in the communication device side interface and the transmitting means, and data by the detecting means The elapsed time of transmission is measured after detecting the start of transmission, and the elapsed time is compared with the time required for the maximum packet length. If the time required for the maximum packet length is exceeded, a transmission stop signal is sent to the transmission means. And a timer comparing means for outputting.

In the fourth aspect of the present invention, the maximum value of the amount of data transmitted at one time is usually the same as the maximum packet length. The timer comparing means is operated to compare the transmission elapsed time with the time required for the maximum packet length. If a longer transmission elapsed time is required, it is determined that the transmission is abnormal and the transmission of the transmission means is forcibly stopped.

[0034]

Embodiments of the present invention will be described with reference to the drawings. The following cable modem device 10 according to the embodiment of the present invention uses the CATV shown in the conventional example (FIG. 5).
It is used in place of the cable modem device 29 in the subscriber terminal 28 in the broadcasting system.

FIG. 1 is a block diagram showing a cable modem device according to a first embodiment of the present invention.

In FIG. 1, a cable modem device 10
Is a mixer / demultiplexer 1 connected to the CATV line 27, a receiving RF circuit 2 as a receiving means, a transmitting RF circuit 3 as a transmitting means, and L as a communication device side interface.
AN interface (LAN I / F) circuit 4 and the first
, An RF transmission state detection circuit 5 as a detection means, a data reception detection circuit 6 as a second detection means, and a microcomputer circuit 7 as a control means. The LAN interface circuit 4 in the cable modem device 10 includes a personal computer 3 as a data communication device.
0 is externally connected. As the cable 33 between the cable modem device 10 and the personal computer 30, a twisted pair cable having a transmission capacity of 10 Mbps based on Ethernet 10BASE-T is used.

For example, a QPSK-modulated RF signal is input / output to / from the mixer / demultiplexer 1 via a CATV line 27. The receiving RF circuit 2 has a QPS
An RF signal which is K-modulated and transmitted through the CATV line 27 is received, QPSK demodulated, and output to the LAN interface circuit 4. The transmission RF circuit 3 transmits a data signal from the personal computer 30 to a LAN interface circuit 4.
Input, QPSK modulated and CA signal as RF signal
Send to TV line 27.

The RF transmission state detection circuit 5 is provided with the transmission RF
The state of the transmission operation of the circuit 3 (the presence or absence of transmission) is detected and output to the microcomputer circuit 7. The data reception detection circuit 6 detects the state of the data reception operation of the LAN interface circuit 4 (presence or absence of data reception) and outputs it to the microcomputer circuit 7.

The microcomputer circuit 7 is composed of a microcomputer, and controls the reception RF circuit 2, the transmission RF circuit 3, and the LAN interface circuit 4 to control signals 7
A to 7C are generated to control the normal transmission / reception operation in each circuit, and the detection result from the RF transmission state detection circuit 5 and the detection result from the data reception detection circuit 6 are compared and determined. If it is determined that the transmission RF circuit 3 is in the continuous transmission state even though no data is received from the transmission RF circuit 3, the transmission RF circuit 3 generates a transmission stop command 7D to the modulation circuit of the transmission RF circuit 3, Control for forcibly stopping the transmission of the message.

In the configuration shown in FIG. 1, the current transmission operation status is transmitted from the transmission RF circuit 3 to the RF transmission status detection circuit 5. Based on this, the RF transmission state detection circuit 5
Determines the presence or absence of transmission, and transmits the determination result to the microcomputer circuit 7. On the other hand, the current reception operation state is transmitted from the LAN interface circuit 4 to the data reception detection circuit 6, based on which the data reception detection circuit 6 determines the presence or absence of reception, and transmits the determination result to the microcomputer circuit 7. The microcomputer circuit 7 compares the presence or absence of transmission from the RF transmission state detection circuit 5 with the presence or absence of reception from the data reception detection circuit 6, and the data reception detection circuit 6 does not transmit the data reception state. (No reception) Despite RF
If the data receiving state from the transmission state detection circuit 5 has continued for a certain period of time (there is transmission), it is determined that the transmission RF circuit 3 is abnormal, and a transmission stop command 7D is issued to the transmission RF circuit 3. , The transmission of the transmission RF circuit 3 is forcibly stopped. As a result, it is possible to prevent the operation of the CATV communication system from being hindered, and to improve the reliability of the cable modem device.

FIG. 2 is a block diagram showing a cable modem device according to a second embodiment of the present invention.

In FIG. 2, the same parts as those in FIG. In the embodiment of FIG.
1 is that one microcomputer circuit 7 as a control means in FIG. 1 performs normal transmission / reception control and transmission abnormality determination and transmission stop control based on the abnormality. In this embodiment, normal transmission / reception control is performed, and transmission abnormality determination and transmission stop control based on the transmission abnormality determination are performed by another microcomputer circuit 9 as second control means. That is, the microcomputer circuit 7 controls the normal transmission / reception operation in the LAN interface circuit 4 and the transmission RF circuit 3, and the microcomputer circuit 9 determines the transmission operation state (the presence or absence of transmission) from the RF transmission state detection circuit 5. The state of the reception operation from the data reception detection circuit 6 (presence or absence of reception) is compared and determined, and although the data is not received from the personal computer 30 which is a data communication device (no reception), the transmission RF circuit 3 is not transmitted. If the transmission state continues for a certain period of time (there is transmission), it is determined that the transmission RF circuit 3 is abnormal, and a transmission stop command 7D is generated for the transmission RF circuit 3 and the transmission RF circuit 3 Forcibly stop sending. Other configurations are the same as those in FIG.

Thus, similar to the embodiment of FIG.
While it is possible to prevent the operation of the ATV communication system from being hindered, the main microcomputer circuit 7 serving as the first control means for performing various operation controls may run out of control and transmit RF signals.
Even if the circuit 3 cannot be controlled and abnormal continuous transmission occurs, the sub-microcomputer circuit 9 as the second control means can detect the abnormality and forcibly stop the transmission operation of the transmission RF circuit 3. Thus, the reliability of the cable modem device can be improved.

FIG. 3 is a block diagram showing a cable modem device according to a third embodiment of the present invention.

In FIG. 3, the same parts as those in FIG. In the embodiment of FIG. 3, FIG.
The difference is that a comparison operation circuit 11 having a simple hardware configuration is used instead of the sub-microcomputer circuit 9 as the second control means for performing the transmission abnormality determination and the transmission stop control based on the transmission abnormality determination. The comparison operation circuit 11
, A delay circuit for delaying a detection signal (a signal indicating the presence or absence of reception) from a data reception detection circuit 6 as a detection means, and a delayed detection signal from the delay circuit and an RF transmission state detection circuit 5 as a first detection means. Is compared with the detection signal (signal of transmission presence or absence), and when the two detection signals do not match each other, or when the data is not received from the personal computer 30 as a data communication device (no reception), the transmission RF signal is output. Circuit 3
And when the transmission state is continuously performed (there is a transmission), a comparison circuit that outputs a transmission stop signal to the transmission RF circuit 3 is configured.

Here, the reason for providing the above-mentioned delay circuit is as follows.
There is a time delay before the data signal from the personal computer 30 is sent to the transmission RF circuit 3 via the LAN interface circuit 4 (this is because the data signal is temporarily stored in a buffer in the LAN interface circuit 4 and the transmission RF circuit 3
Before the data signal reaches the transmission RF circuit 3, the LAN interface circuit 4
Although the data reception detection circuit 6 connected to the data reception detection circuit 6 detects that the data has been received and supplies a detection result indicating the presence of the reception to the comparison operation circuit 11 as one of the comparison inputs, the transmission R
In the RF transmission state detection circuit 5 connected to the F circuit 3, a state occurs in which a detection result indicating that there is transmission cannot be obtained, and the comparison operation circuit 11 determines that the comparison result does not match in the comparison operation, and outputs the transmission stop signal 7 D. The signal is output to the transmission RF circuit 3 and the circuit 3 is stopped. Therefore, the comparison operation circuit 11 is provided with a delay circuit for delaying the detection signal from the data reception detection circuit 6 and adjusting the time with the detection signal from the RF transmission state detection circuit 5 in addition to the comparison circuit. I have. (In the configuration using the sub-microcomputer circuit 9 of FIG. 2, unlike the embodiment of FIG. 3, the timing of the two detection signals to be compared can be easily adjusted in the microcomputer circuit 9. It is not particularly necessary to provide a delay circuit.) As a result, as in the embodiment of FIG. 1, it is possible to prevent the operation of the CATV communication system from being hindered, but as in the embodiment of FIG. First to take control
Even if the main microcomputer circuit 7 as the control means runs out of control and cannot control the transmission RF circuit 3 and enters an abnormal continuous transmission state, the comparison arithmetic circuit 11 as the second control means detects the abnormality. As a result, the transmission operation of the transmission RF circuit 3 can be forcibly stopped, and the reliability of the cable modem device can be improved. Further, in the embodiment of FIG. 3, a simple circuit (a delay circuit and a comparison circuit)
And the abnormal state can be reliably prevented without being affected by software as in the case where the microcomputer circuit 9 is used as the second control means as shown in FIG.

FIG. 4 is a block diagram showing a cable modem device according to a fourth embodiment of the present invention.

In FIG. 4, the same parts as those in FIG. In the embodiment of FIG. 4, FIG.
The difference from this is that the data reception detection circuit 6 is deleted and a timer comparison circuit 12 is provided in place of the comparison operation circuit 11. Other configurations are the same as those in FIG.

The timer comparison circuit 12 measures the elapsed time of transmission after the start of data transmission is detected by the RF transmission state detection circuit 5, and uses the measured time as a timer threshold (for example, the time required for the maximum packet length). ), And outputs a transmission stop signal to the transmission RF circuit 3 when the threshold value is exceeded. Here, since the maximum length of one packet in the LAN is 1518 bytes, the maximum packet length is specifically 151 bytes.
It indicates the time required to transmit 8 bytes, and this time or a time obtained by adding α to this time is set as the threshold value of the timer. The time set as the timer threshold is the time required for transmitting 1518 bytes as described above, but this time varies depending on the transmission speed of the uplink data of the cable modem device in the CATV communication system. Of course. In the present embodiment, the transmission speed of the uplink data of the cable modem device is 2 Mbps. The threshold value of the timer can be set in the timer comparison circuit 12 in advance, or can be set by the microcomputer circuit 7 so that the set value can be changed.

In the configuration shown in FIG. 4, the RF transmission state detection circuit 5 as the detection means detects the state of the transmission operation of the transmission RF circuit 3, and the RF transmission state detection circuit 5 When it is determined that transmission has started, a timer start signal is supplied to the timer comparison circuit 12. As a result, the timer of the timer comparison circuit 12 operates, measures the transmission elapsed time, and compares the measured time with the timer threshold. If the transmission continues abnormally and the transmission elapsed time exceeds the threshold value of the timer (for example, the time required for the maximum packet length), it is determined that the transmission is abnormal and the transmission stop signal 7 is output from the timer comparison circuit 12.
D is generated, and the transmission operation of the transmission RF circuit 3 is forcibly stopped.

As a result, as in the embodiment of FIG.
While it is possible to prevent the operation of the ATV communication system from being hindered, as in the case of FIG. 2, the main microcomputer circuit 7 as the first control means for performing various operation controls runs out of control and the transmission RF circuit 3 Even if the transmission is not controlled, the timer comparison circuit 12 can detect the abnormality and forcibly stop the transmission operation of the transmission RF circuit 3 even if the state becomes abnormal continuous transmission. Improvement can be achieved. Further, in the present embodiment,
There is an advantage that the data reception detection circuit 6 can be eliminated as compared with the embodiment of FIG.

Note that, in addition to the configuration of each embodiment of FIGS. 1 to 4 described above, the microcomputer circuit 7, the microcomputer circuit 9, the comparison operation circuit 11, and the timer comparison circuit 12 in each embodiment include a transmission error. When the transmission stop signal is output as "1", the transmission stop signal is supplied to the microcomputer circuit 7, and the microcomputer circuit 7 turns on a display means (not shown) such as an LED in response to the signal. The transmission abnormality is notified to the user, or is input to the personal computer 30 via the LAN interface circuit 4 from the microcomputer circuit 7 based on the transmission stop signal.
May display a transmission error occurrence on a screen of a display device (not shown) based on the software.

[0053]

As described above, according to the present invention, CA
In the TV communication system, the transmission output of the subscriber terminal in the abnormal transmission state is automatically stopped, and the adverse effect on the system operation can be minimized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a cable modem device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a cable modem device according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a cable modem device according to a third embodiment of the present invention.

FIG. 4 is a block diagram showing a cable modem device according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram showing a general CATV communication system.

FIG. 6 is a diagram showing an uplink / downlink frequency band of an RF signal used in a CATV communication system.

FIG. 7 is a diagram showing an uplink / downlink communication data format.

[Explanation of symbols]

3: RF transmission circuit (transmission means) 4: LAN interface circuit (communication device side interface) 5: RF transmission state detection circuit (first detection means) 6: data reception detection circuit (second detection means) 7: microcomputer Circuit (first control means) 9 ... sub-microcomputer circuit (second control means) 10 ... cable modem device 11 ... comparison operation circuit 12 ... timer comparison circuit 27 ... CATV line 30 ... PC (data communication equipment)

Claims (4)

[Claims] 1. A receiving side, which is disposed between a CATV line and a data communication device, modulates data from the data communication device and transmits the data to the transmitting side through the CATV line, and modulates data on the transmitting side. What is claimed is: 1. A cable modem device for demodulating data transmitted through a CATV line and transmitting the demodulated data to said data communication device, comprising: receiving data output from said data communication device through a communication device side interface;
Transmitting means for transmitting to the V line; first detecting means for detecting a state of a transmitting operation of the transmitting means; second detecting means for detecting a state of a data receiving operation of the communication device-side interface; While controlling the normal transmission operation in the device-side interface and the transmission unit, the detection result from the first detection unit and the detection result from the second detection unit are compared and determined, and the data communication device And control means for outputting a transmission stop signal to the transmission means when it is determined that the transmission state is continuously performed from the transmission means in a state in which the transmission means is not received. Cable modem device. 2. A receiving side, which is disposed between a CATV line and a data communication device, modulates data from the data communication device and transmits the data to the transmitting side through the CATV line, and modulates the data on the transmitting side. What is claimed is: 1. A cable modem device for demodulating data transmitted through a CATV line and transmitting the demodulated data to said data communication device, comprising: receiving data output from said data communication device through a communication device side interface;
Transmitting means for transmitting to the V line; first detecting means for detecting a state of a transmitting operation of the transmitting means; second detecting means for detecting a state of a data receiving operation of the communication device-side interface; A first control unit for controlling a normal transmission operation in the device-side interface and the transmission unit; and comparing and determining a detection result from the first detection unit with a detection result from the second detection unit; A second control unit that outputs a transmission stop signal to the transmission unit when it is determined that the transmission state is continuously performed from the transmission unit in a state where data is not received from the data communication device; A cable modem device comprising: 3. The first control means is constituted by a microcomputer circuit, and the second control means detects a signal from the second detection means so as to adjust a time to a detection signal from the first detection means. A delay circuit for delaying a signal, and comparing a delay signal from the delay circuit with a detection signal from the first detection means,
And a comparison circuit that outputs a transmission stop signal to the transmission unit when the transmission state is continuously performed from the transmission unit in a state where data is not received from the data communication device. The cable modem device according to claim 2, wherein: 4. A receiving side disposed between a CATV line and a data communication device, modulating data from the data communication device and transmitting the modulated data to the transmitting side through the CATV line, and modulating the data on the transmitting side. What is claimed is: 1. A cable modem device for demodulating data transmitted through a CATV line and transmitting the demodulated data to said data communication device, comprising: receiving data output from said data communication device through a communication device side interface;
Transmitting means for transmitting to a V line; detecting means for detecting a state of a transmitting operation of the transmitting means; control means for controlling a normal transmission operation in the communication device-side interface and the transmitting means; data by the detecting means The elapsed time of transmission is measured after detecting the start of transmission, and the elapsed time is compared with the time required for the maximum packet length. If the time required for the maximum packet length is exceeded, a transmission stop signal is sent to the transmission means. A cable modem device comprising a timer comparing means for outputting.