JPH0366862B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention connects a center and a terminal device with a cable, and performs data communication from the center to the terminal device.
The present invention relates to an eavesdropping prevention device in a CATV system, which has a function of preventing eavesdropping on the terminal device side.

[Prior Art] A conventional CATV system is configured as shown in FIG. 1. That is, one center 1 and the terminal devices 28 placed in tens of thousands of households are integrated into one set, and the center 1 and the terminal devices 28 are connected by a coaxial cable. Then, from center 1 to trunk cable 3
is drawn out, and a trunk amplifier 4 and a branch 5 are provided at predetermined locations on the trunk cable 3.

A plurality of branch cables 6 are pulled out from this branch 5, and an extension amplifier 7 and a tap-off 8 are provided at predetermined locations on each branch cable 6. Then, a plurality of branch cables 9 are connected to each tap-off 8.
are pulled out, and the ends of these branch cables 9 are led into each home 2.

A terminal device 28 consisting of a main box 10, a television receiver 11, a control box 12, etc. is installed in each home 2, and the end of the branch cable 9 described above is connected to the main box 10 of this terminal device 28. has been done. Further, the main box 10 is connected to a television receiver 11 and a control box 12, respectively.
In this way, the center 1 and the terminal devices 28 of each home 2 are segmented and connected by the Christmas tree-shaped branching cables 3, 6, and 9.

A receiving antenna 13 is installed outside the center 1, and the receiving antenna 13 is connected to the source group 14.
It is connected to the day modulator 15 inside. The source group 14 includes a video disc player 16,
There are a video tape recorder 17, a studio 18, etc.

The modulation transmitter 19 that receives signals transmitted from the source group 14 consists of two types of systems.
Modulate circuit 20, scramble circuit 21,
There is a system of up converter circuit 22, and a system of IF modulation circuit 23 and up converter circuit 24. Output terminals of up converter circuits 22 and 24 are connected to main cable 3, respectively.

Further, a data transmitter/receiver 25 for communicating with each main box 10 is connected to the trunk cable 3, and a computer 26 is connected to the data transmitter/receiver 25. Furthermore, peripheral devices 27 such as a printer and a display are connected to the computer 26.

Such a CATV system operates as follows.

When the television receiver 11 is turned on and a desired channel is selected by operating the control box 12, the frequency of the channel to be received is converted by the main box 10 to an empty channel that is not on air, and the television receiver is turned on. 11.

The types of channels that can be selected in the control box 12 are divided into groups such as (A) retransmission that receives TV waves as they are, (B) independent programs, and (C) paid programs, and each group can control several channels. I have a total of 20-30
It is now possible to choose the degree.

(A) Retransmission The television waves received by the receiving antenna 13 are demodulated once by the day modulator 15, and
The signal is output to the modulation transmitter 19. The IF modulation circuit 23 modulates the signal, and the up converter circuit 24 increases the modulated signal to a specific frequency. This modulated signal positioned on a specific channel is transmitted to the home 2 via the main cable 3, branch cable 6, and branch cable 9, and is received by the television receiver 11 via the terminal device 28.

(B) Independent programs Weather forecasts, news programs, etc. Video disc player 16, video tape recorder 1
7 and live programs produced in the studio 18 are modulated by an IF modulation circuit 23 and an up converter circuit 24, frequency-converted to a specific channel, and transmitted to the main cable 3. This program is normally free of charge regardless of the number of times it is viewed, the time, etc., and can be viewed by each household 2 for a basic fee paid every month.

(C) Paid programs New movies, specific programs, etc. Video disc player 16, video tape recorder 17
Recorded programs and live programs produced in the studio 18 are modulated by the IF modulation circuit 20, and a specific synchronization signal is added to the image signal by the scrambling circuit 21, so that even if the image is received as it is, it will not turn out to be a normal image. It is processed so that it does not occur. Next, up converter circuit 2
2 increases the frequency to that of a specific channel and sends it out to the trunk cable 3.

When each household 2 wants to receive this pay program, the received signal is demodulated into a normal image signal in the main box 10 and transmitted to the television receiver 11, so that a normal image can be viewed. I can do it. When receiving this pay program, a preset fee is calculated, and a special fee is added to the monthly basic fee and billed.

In this way, in the CATV system, the center 1 and the terminal devices 28 of each home 2 are connected by coaxial cables. However, the CATV system cannot be operated fairly unless it is known which households are receiving which channels at specific times. Therefore, the data transmitter/receiver 25 oscillates a search signal at regular intervals to call the main box 10 of each terminal device 28 with an address number unique to the main box 10. So-called polling is being conducted to find out if there are any.

For this polling, the main box 10 outputs a response signal to the data transmitter/receiver 25 indicating which channel is being received at that time. The response signal received by the data transceiver 25 is data processed by the computer 26 and the results are displayed or printed on the peripheral device 27. Since such polling is performed at regular intervals (several seconds to several minutes), audience ratings and the like can be immediately compiled.

By the way, in this CATV system,
In order to operate the system, it is necessary for the center 1 to know what kind of operating status the terminal device 28 is in. For example, even if a pay program is viewed illegally, if the center 1 is unable to prevent the illegal act, accurate fee collection becomes impossible and system operation cannot be maintained.

In order to prevent this fraudulent act, conventionally, as described above, video signals and downlink data signals are constantly sent from the center 1 to the terminal device 28.
An upstream data signal indicating which channel each terminal device 28 is viewing is sent back to the center 1, and the operating status of each terminal device 28 is grasped based on this upstream data signal.

[Problems to be Solved by the Invention] However, it is possible to interfere with the reception of the differential status search signal included in the downlink data signal by some means, or to check which channel the terminal device 28 in each home 2 is receiving. There is a risk that the return of the upstream data signal in response to the If such interference occurs, it becomes impossible for the center 1 to grasp the operating status of each terminal device 28, and it becomes impossible to prevent eavesdropping.

In view of these drawbacks, the present invention provides a means for determining whether or not a specific signal for searching the operating status within the terminal device is being input, and when the input of this specific signal is interrupted, the terminal device It is an object of the present invention to provide an anti-eavesdropping device for a CATV system that can stop the operation of the device and thereby prevent eavesdropping.

[Means for Solving the Problems] In order to achieve the object, the eavesdropping prevention device of the present invention connects a center and a large number of terminal devices with cables, and transmits video signals and downstream signals from the center to the terminal devices. Sends data signals and controls the operation of each terminal device at the center
A device to prevent eavesdropping in a CATV system,
The terminal device includes a detection means for detecting that the downlink data signal is normally received among the signals sent from the center to the terminal device, and a detection means for detecting that the downlink data signal is not normally received. The present invention is characterized in that it is provided with a timer section that counts a predetermined period of time when the detection means determines that this is the case, and a change means that forcibly changes the image receiving operation of the receiver based on the output of the timer section.

[Operation] In the present invention, two types of signals, a video signal and a downlink data signal, are input to a terminal device in each home. When the reception of the downlink data signal is interrupted for a predetermined period of time, it is determined that the terminal device is not in a normal operating state, and the reception function of the television receiver is changed by the operation of the terminal device according to a command from the center. or stop it. This makes it possible to prevent unauthorized spying based on acts of sabotage.

[Examples] Hereinafter, the present invention will be specifically described by way of examples with reference to FIG. 2.

The branch cable 9 is connected within the main box 10 to a channel converter 31 via a branch 30. An output terminal of this channel converter 31 is connected to the television receiver 11.
A receiving section 32 for receiving a downstream data signal is connected to the branching device 30, and a clock detecting section 33 is connected to the receiving section 32. A timer section 34 is connected to the clock detection section 33, and a tuning signal generation section 35 is further connected to the timer section 34. Further, the aforementioned control box 12 is connected to the tuning section 34, and the output terminal of the tuning signal generating section 35 is connected to the aforementioned channel converter 31.

Next, the operation of this eavesdropping prevention device will be explained.

An operating status search signal is constantly sent from the center 1 at a specific frequency to the terminal devices 28 in each home. This operating status search signal includes a clock.

When the main box 10 is operating properly, the receiving section 32 receives this specific operating status search signal. At this time, the clock detection section 33 detects the clock included in the operating status search signal, and determines that this specific signal is normally received.
does not output a signal. Therefore, the tuning signal generator 35 is controlled by the control box 12 to output a tuning signal corresponding to the selected channel, and causes the channel converter 31 to convert the frequency of the selected channel to a specific channel. The program is output to the television receiver 11 to maintain a state in which the desired program can be viewed.

Here, when the subscriber uses some means to prevent the terminal device 28 from receiving only the downlink data signal in order to perform eavesdropping, the receiving section 32 is unable to receive the frequency of that specific signal. The clock detection section 33 detects the absence of a clock. Then, the detection result is transmitted to the timer section 34.

The timer section 34 outputs an operation stop signal to the tuning signal generating section 35 when the detection signal from the clock detecting section 33 continues for several minutes.
Then, the tuning signal from the tuning signal generating section 35 is forcibly changed to a preset empty channel or a free program channel. This prevents eavesdropping. At this time, since the stop signal from the timer section 34 is given priority over the selection signal from the control box 12, no matter how the control box 12 is operated, the channel selection operation is not possible. Additionally, the timer unit 34 sets a time loss of several minutes;
This is to prevent it from being immediately determined to be an act of eavesdropping in the event that a carrier wave of a specific frequency or a clock cannot be transmitted due to a failure. Center 1 within several minutes set by this timer section 34.
By sending out a specific signal using a spare device inside, the terminal device 28 can continue to watch the desired program regardless of a failure on the center 1 side.

[Effects of the Invention] As explained above, in the eavesdropping prevention device of the present invention, by controlling the operation of the terminal device at the center side, it is possible to prevent acts of eavesdropping on programs caused by illegal means. can do. Since the program cannot be secretly viewed on the terminal device where the act of eavesdropping has been performed, a warning is given to the person committing the act of eavesdropping, and the smooth operation of the CATV system is ensured.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an outline of a CATV system to which the present invention is applied, and FIG. 2 is a block diagram showing the configuration of a terminal device according to the present invention. 1: Center, 3: Trunk cable, 6: Branch cable, 9: Branch cable, 28: Terminal device, 3
0: Branch, 31: Channel converter, 3
2: Receiving section, 33: Clock detection section, 34: Timer section, 35: Tuning signal generation section.

Claims (1)

[Claims] 1. A center and a large number of terminal devices are connected by cables, and video signals and downlink data signals are sent from the center to the terminal devices, so that the operation of each terminal device can be controlled at the center.
An eavesdropping prevention device for a CATV system, which includes a detecting means in the terminal device for detecting that the downlink data signal is normally received among the signals sent from the center to the terminal device; a timer section that counts a predetermined period of time when the detection means determines that the downlink data signal is not normally received; and a change that forcibly changes the image receiving operation of the receiver based on the output of the timer section. The feature is that the means are provided.
Eavesdropping prevention device in CATV system.