JP2001326916A - Streamed noise monitoring system and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restore the communication failure by detecting a communication failure due to the noise of an incoming transmission channel, and specifying the occurrence part of a noise in a bidirectional CATV network having a tree- like configuration. SOLUTION: When a center station side automatically detects that the communication failure occurred, it firstly discriminates whether or not the failure is caused by the noise. The noise is measured by a noise measuring instrument provided in the center station, and the gate switch of an amplifier for main line branch is sequentially interrupted when the communication failure is the failure by the noise, and the occurrence part of the noise is specified by detecting decrease of the quantity of noise measured at the time. Next, an incoming signal is interrupted and the noise is suppressed by controlling the gate switch of the amplifier for main line branch of the specified part. Besides, the gate switch intercepting the incoming signal is turned to passage when the disappearance of the noise is confirmed, the communication of all subscriber terminals is normalized, and thus the communication failure is restored automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for detecting a communication failure due to noise generated on an uplink transmission line in a tree-structured network such as a bidirectional CATV system. The present invention relates to a system and a device for quickly identifying and restoring a communication failure.

[0002]

2. Description of the Related Art FIG. 1 shows a configuration diagram of a conventional bidirectional CATV system. .., 2A, 2B,... Are trunk branch amplifiers. The trunk branch amplifiers are branched into two transmission paths by a branching device provided in each trunk branch amplifier, and are sequentially connected to the trunk branch amplifier to form a tree-like structure. A network consisting of transmission paths that spread over The lowest transmission line is
It is connected to the subscriber's terminal 3 via a tap-off 4 for drawing into each home.

Reference numeral 2 denotes a CATV center station, for example, a head end 21, a cable modem 22, which is a CATV communication device, a status monitor 23, a terrestrial antenna 24 for receiving terrestrial broadcasting, and a satellite wave for receiving satellite broadcasting. It comprises a receiving antenna 25. The cable modem 22 is connected to the Internet (not shown) via a router 26. PC 31 of subscriber's terminal 3
Are the cable modem 32 in the terminal 3, the tap-offs 4,
Alternatively, it is connected to the cable modem 22 in the center station 2 via a plurality of trunk branch amplifiers and the head end 21, and performs communication via the cable modem 22 in the center station 2.

In general, in a CATV system, an optical transceiver is provided at the head end 21 of the center station 2, an optical fiber is wired from the optical transceiver, and an optical transceiver is disposed ahead of the optical transceiver, from which a coaxial cable is connected. ing. Signals from the head end 21 are passed through the main branch amplifiers cascade-connected to the coaxial cable to the subscriber terminal 3.
Will be delivered to Here, the conversion part from the optical fiber to the coaxial cable, that is, the optical transceiver, is called a node.

Usually, there is a relation of (number of nodes) = (number of first-stage main branch amplifiers). The main-stage branch amplifier 1A is connected to the transmission line branched into two by the branching device.
B and 2A are connected respectively, and further, a trunk branch amplifier is connected to each of the number of trunk branch amplifiers 1B and 2A via a transmission line. It has a so-called tree structure in which the number of transmission paths increases as the number of layers increases.

FIG. 1 shows two transmission lines connected to the first-stage main branch amplifier 1A from the head end 21 via a node and extending in a tree shape. These two lines are representatively shown. As shown, in practice, many more similar systems are provided, with each first stage mains branch amplifier connected to the head end 21 via a respective node,
A plurality of tree-shaped transmission paths are configured.

[0007] The cable modem 22 of the center station 2 is connected to the Internet via a router 26, for example. Alternatively, a dedicated server can be provided in the center station 2 to provide a bulletin board and services such as video on demand. Here, FIG. 2 shows a connection relationship between the status monitor 23 and the main branch amplifier 1A.
A block configuration of the control signal will be exemplified.
The illustrated trunk branch amplifier 1A is located at the first branch point of the tree-shaped transmission line, and is a first-stage trunk branch amplifier. Therefore, the node 10 is connected to the input side of the trunk branch amplifier 1A. Other main branch amplifiers connected downstream of the main branch amplifier 1A do not include the node 10, but have the same configuration in other respects.

The status monitor 23 is a control CPU.
231, a monitor 232 for displaying or printing the status of each trunk branch amplifier, a printer 233, and a CPU 2
An RF modem 234 converts a control signal output from the control signal 31 into a signal flowing on a communication path or vice versa. The main branch amplifier 1A includes a splitter 11 for splitting a control signal from a transmission line, a splitter 12 for splitting a downlink communication signal into two transmission lines, and a splitter 13 for joining two uplink communication signals. A CPU 17 for control, an RF modem 16 for converting a signal flowing on a transmission path and outputting a control signal to the CPU 17 or vice versa, and a CPU
Gate switch for up signal 14 controlled by 17
And 15 are included.

The control of the gate switches 14 and 15 of the main branch amplifier 1A by the status monitor 23 is performed using the main branch amplifier control band in the upstream frequency band A and the downstream frequency band B. Generally, as shown in FIG.
The frequency band of the signal flowing on the transmission line is 10 to 55 MHz
The low frequency part and the high frequency part of 70 to 770 MHz are used, and the low frequency side is used for the upstream signal used for communication by the subscriber,
The high frequency side is used for downstream signals such as broadcasting. Further, the high frequency portion of the upstream low frequency band A is used for the amplifier monitoring signal W1, and the low frequency portion is used for the data communication D1.
Assigned to 1. In the high frequency band B for downlink, W2 for amplifier monitoring signal and D2 for data communication are allocated.

Therefore, in the main branch amplifier 1A, the gate switch is controlled by the amplifier monitor signal included in the down signal. Status monitor 23 and main branch amplifier 1A
In the inter-communication, in addition to the control signal of the gate switch, information on the state (for example, input / output level, temperature, power supply voltage, etc.) of the main branch amplifier 1A is exchanged. In the above configuration, when the subscriber terminal 3 performs uplink communication, the upstream signal from each subscriber terminal flows into the trunk branch amplifier 2A via the tap-off 4 and flows into the upstream signal from another subscriber terminal. While being transmitted to the upstream main branch amplifier 1A, it communicates with a predetermined communication destination.

Conventionally, when a communication failure occurs, first, the cable modem 22 detects the occurrence of the failure from the communication state, and then determines whether the failure is due to a failure of the device or the like, or Humans had determined whether the noise was superimposed. As a result, when the noise is a cause of the communication failure, the gate switch of the trunk branch amplifier is manually opened and closed sequentially by operating the status monitor 23, and the location of the failure is identified by measuring the noise amount. Was.

In addition, restoration of communication in the system has been realized by shutting off a gate switch in an amplifier located immediately upstream of the specified noise generation point, and eliminating influence on other paths. Here, upstream refers to the head end 21 side, and downstream refers to the subscriber terminal 3 side. In addition, as a method of automatically detecting the superposition of noise and avoiding this, a trunk line amplifier itself is provided with a function for measuring the amount of noise, the location where noise is generated is identified, and the trunk line that detects an increase in the amount of noise is detected. A method of separating a branch amplifier from a communication path has been proposed (see Japanese Patent Application Laid-Open No. 10-178628).

[0013]

However, in the case of specifying and restoring a noise generation location by the former human naval tactics,
Since the location where the noise occurs is identified after the person in charge knows the communication failure, a considerable time lag occurs between the occurrence of the failure and the isolation and recovery of the location where the noise occurs.

Also, regarding the location of noise generation, a person must manually close each gate switch of the main branch amplifier temporarily to confirm whether noise is included in the upstream communication signal during that time. did not become. Further, when opening the gate switch of the trunk branch amplifier which was shut off at the time of restoration, the gate switch is temporarily opened, and after manually checking that no noise is generated, the gate switch is opened.

Also, in the latter method of automatically detecting the superposition of noise, the cost of the trunk branch amplifier itself becomes expensive because each trunk branch amplifier is provided with a function of detecting a communication failure, and the existing CATV network is expensive. However, there is a problem that capital investment is increased in order to incorporate it into the system. Therefore, the present invention can easily detect a communication failure due to ingress noise generated on an uplink transmission line in a tree-structured network such as a bidirectional CATV system, and quickly and easily specify a noise generation location. It is an object of the present invention to be able to recover from a communication failure.

[0016]

In order to solve the above problems, according to the present invention, when a center station automatically detects that a communication failure has occurred, the failure first occurs due to noise. Identify whether or not. The noise is measured by a noise measuring device provided in the center station. If the communication failure is caused by the noise, the location where the noise is generated is specified by sequentially controlling the gate switches of the main branch amplifier. Next, by controlling the gate switch of the specified main branch amplifier, the upstream signal is cut off to suppress noise. If the disappearance of noise can be confirmed, the signal is passed through the gate switch that blocks the upstream signal, the communication of all the subscriber terminals is normalized, and the communication failure is automatically restored.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The overall configuration of an embodiment according to the present invention will be described. FIG. 4 is a configuration diagram showing a configuration of the bidirectional CATV system according to the present embodiment. FIG.
Here, the same reference numerals are given to the same parts as the configuration of the bidirectional CATV system shown in FIG.

In FIG. 4, a center station 2 of the bidirectional CATV system includes a head end 21, a cable modem 22, which is a CATV communication device, a status monitor 23,
A terrestrial antenna 24 for receiving terrestrial broadcasting, a satellite wave receiving antenna 25 for receiving satellite broadcasting, a control device 27,
It comprises a noise measuring device 28. The subscriber terminal 3 is connected to a transmission line formed in a tree shape and a head end 21 of the center station 2 at the end of the transmission line via a tap-off 4 for drawing in to each home. The terminal 3 is connected to the cable modem 22 of the center station 2 and the router 2.
6 is connected to the Internet (not shown).

The upstream signal from the subscriber terminal 3 is input to the cable modem 22 via the main branch amplifiers 1A and 2A having functions of controlling the tap-off 4, the gate switch, and the head end 21. Here, the difference between the center station 2 in the present embodiment and the center station 2 in the bidirectional CATV system shown in FIG. 1 is that the center station 2 receives communication failure information from the cable modem 22 and performs noise measurement with a spectrum analyzer or the like. And a control device 27 for controlling the status monitor 23 based on a signal from the noise measuring device 28.

The status monitor 23 includes a subscriber terminal 3
In addition to the signal of the band D1 used for communication, the upstream signal including the signal of the band W1 used for the control signal and the like by the system side is input. The status monitor 23 records network-like arrangement information (connection-related information) such as the number of trunk branch amplifiers connected to each node and the vertical relationship. Also, the cable modem 22, the noise measuring device 2
8. The status monitor 23 is controlled by the control device 27.

FIG. 4 shows an example in which one cable modem 22 is provided. However, when a plurality of cable modems are connected between the headend 21 and the router 26, FIG. , A plurality of cable modems 22-1, 22-2, 22-3.
It is also possible to select one from .. and sequentially measure the amount of noise contained in the upstream communication signal passing through the cable modem by the noise measuring device 28.

FIG. 6 shows a block diagram of the control device. 6, the same parts as those in FIG. 4 are denoted by the same reference numerals. The control device 27 includes a communication failure information receiving unit 271, a noise determination unit 272, an amplifier control unit 273, an information display / storage unit 274, and a control unit 275. When the communication failure information is detected by the cable modem 22, the failure information is sent to the control unit 275 via the communication failure information receiving unit 271.

The amount of noise obtained by the noise measuring device 28 is input to a noise determination unit 272 and compared with a predetermined threshold value to determine whether or not the failure is caused by noise.
The result of the determination is sent to the control unit 275. The amplifier control section 273 performs open / close control of the gate switch 15 of each main branch amplifier based on the connection relation information of the main branch amplifier stored in the information display / storage section 274. The information display / storage unit 274 includes a communication failure occurrence state and a noise amount obtained through the control unit 275, a control state of the main branch amplifier,
It is for storing connection relationship information of the main branch amplifier and the like managed by the status monitor 23, displaying the information on a monitor screen, or outputting on paper.

Next, the operation of the system according to the present embodiment having the above configuration will be described. When a communication failure occurs, the cable modem 22 having a communication failure detection function detects this and sends a communication failure detection signal to the control device 27. As a method of detecting a communication failure, there is a method of detecting a communication failure by monitoring a link level of data flowing on a transmission line of the cable modem 22 itself.
In addition, the cable modem 22 constantly checks information that affects communication such as a bit error rate (BER), and outputs a communication failure detection signal to the control device 27 when this value exceeds a predetermined threshold. It is also possible to adopt a method of connecting an external device that can perform the operation. As the control device 27, for example, a CPU can be used.

Here, since the cable modem 22 has only the function of detecting a communication failure, it is necessary at this stage to determine whether the communication failure is caused by noise or equipment failure. Can not. After receiving the communication failure detection signal, control device 27 instructs noise measuring device 28 to measure the amount of noise included in the uplink communication signal. The noise measuring device 28 measures the amount of noise contained in a band used by the cable modem 22 for communication or in a band where the influence of noise is likely to occur in other bands.

As a result of the measurement, if the uplink signal contains noise equal to or greater than a preset threshold, the noise determination unit 27
2 judges that noise affecting communication on the uplink transmission path is occurring, and outputs a noise detection signal to the control unit 275. The noise measuring device 28 can be realized by measuring the floor level and peak value of noise using, for example, a spectrum analyzer or the like. A threshold value is obtained from a normal value obtained from an average value over a long period of time, and the measured value is compared with the threshold value. For example, when the threshold value is exceeded a predetermined number of times within a predetermined time, it can be determined that noise is occurring. In addition, as the threshold value, a floor level or a maximum peak value of noise at which a communication failure actually occurs may be experimentally obtained in advance through experiments or the like.

Upon receiving the noise detection signal from the noise determination unit 272, the control unit 275 controls the opening / closing of the gate switch of each trunk branch amplifier connected to each node. By controlling the shutoff / opening of these gate switches, the upstream signal can be selectively shut off. At this time, by measuring the change in the amount of noise, it is possible to specify the location of the noise.

Referring now to FIG. 4, a description will be given of a specific example of specifying a noise generation location in a bidirectional CATV system configured in a tree shape having many systems. For example, it is assumed that noise is generated between the subscriber terminal 3 and the gate switch d of the main branch amplifier 2A. When the cable modem 22 detects a communication failure, the noise meter 28 measures the amount of noise. If the amount of noise is equal to or greater than a preset threshold, the noise determination unit 272 determines that the noise has caused a communication failure, and starts a specific process of a noise generation location.

Therefore, first, it is checked which node connected to the head end 21 has the noise source.
Now, since the CATV system is operated, all the gate switches of the trunk branch amplifiers connected after each node are all open (on state where signals pass), so that the first stage trunk branch amplifier at each node is opened. Both of the two gate switches 14 and 15 are sequentially cut off (OFF state in which a signal is blocked) for each node. In the case of FIG. 4, both gate switches a and b of the first stage main branch amplifier 1A are shut off.

In this specific example, it is assumed that a noise source exists at the first node among a plurality of nodes connected to the head end 21, so that both the gate switches a and b of the first-stage main branch amplifier 1A are shut off. As a result, noise to this node is not input to the noise measuring device 28. Therefore, the measurement amount of the noise measuring device 28 is smaller than the noise amount at the start of the noise occurrence location specifying process. By detecting this decrease in the amount of noise, it is possible to specify that there is a noise source in the system related to the first node.

Next, for the specified node, the gate switches a and b in the first-stage main branch amplifier 1A are controlled from being cut off to being opened, so that the noise measuring device 28 can measure the ingress noise. And the first-stage mains branch amplifier 1
Control the gate switches of A and gate switches a and b
Temporarily shut off one of them. Here, the gate switch a
Is temporarily cut off, there is no noise source in the transmission line of the main branch amplifiers 1B, 2B,... Connected under the gate switch a side, so that the noise is measured by the noise measuring device 28. There is no change in the amount of noise.

Further, when the other gate switch b is temporarily shut off, the amount of noise measured by the noise measuring device 28 after the shutoff is smaller than before the shutoff. As a result, it can be seen that a noise source exists under the gate switch b. Here, after storing the information of the gate switch b, the gate switch b is controlled to be returned to the open state. Since it has been found that a noise source exists under the gate switch b, control is now performed on the gate switches c and d of the main branch amplifier 2A under the control. Current,
Gate switches c and d are open. Therefore,
For example, the gate switch c is controlled to temporarily shut off. At this time, since there is no noise source under the control of the gate switch c side, there is little change in the measured noise amount.

On the other hand, when the gate switch d is controlled and temporarily shut off, the measured noise amount is significantly reduced. Here, when the measured noise amount is significantly reduced, it can be specified that noise is generated under the control of the gate switch d side. However, even if the gate switch d is cut off (the gate switch c is also cut off), the measured noise amount does not decrease and if there is no change, if there is no change between the main branch amplifier 1A and the main branch amplifier 2A. , It can be specified that noise is occurring.

Further, when the noise generation point is located downstream, the gate switch of the subordinate trunk branch amplifier that is sequentially located downstream is controlled, and the same processing is performed to specify the noise generation point. Note that even if one of the two gate switches in the first-stage trunk branch amplifier of each node is sequentially shut off to detect whether there is a noise source on the transmission path under the gate switch, no matter which node It can be determined whether or not the occurrence location exists. However, shutting off both of the gate switches in the first-stage trunk branch amplifier of the node and detecting a reduction in the amount of noise enables a determination as to which node has a noise-occurring portion earlier.

In order to specify each node, it is not necessary to shut off the gate switch in order from the end, and the past noise occurrence frequency may be stored, and for example, the shutoff control may be performed in descending order of frequency. Alternatively, it is also possible to preferentially perform cut-off control on a fault that has recently occurred. Further, the determination as to whether or not the noise amount is reduced is made, as described above, when the amount of noise reduced by the open / close control of the gate switch is equal to or greater than a predetermined threshold value, or a predetermined threshold value that does not cause a communication failure. As compared with, it may be determined that the amount of noise has decreased when the noise amount becomes smaller than the predetermined threshold value.

In the above-described specific example, the number of noise generation points is assumed to be one, but there is a possibility that noises may be generated in a plurality of systems at the same time. In such a case, when the gate switch of each node is turned off, it is only necessary to sequentially detect a decrease in the measured noise amount and store the detected node. The process of specifying the noise generation location at the node may be performed each time the detection is performed, or the process of specifying the noise generation location of each node may be performed sequentially after all the detections are performed.

In this way, even if there are noise occurrence locations in a plurality of nodes, it is possible to sequentially determine. The identification of the noise occurrence location in each node determined to have the noise occurrence location is performed for each node in the above-described procedure. In the specific example described above, the method of specifying one node (or the first-stage main branch amplifier) or the gate switch to identify the noise generation location has been described. It can also be realized by opening only the first-stage main branch amplifier or the gate switch.

In this case, when the criterion of the measured noise amount is different from the above, the measured noise amount is increased to a predetermined value or more compared to the noise amount before controlling the first-stage main branch amplifier or the gate switch. Means that noise is generated below the currently opened first stage main branch amplifier or at the gate switch.If there is only an increase below the predetermined value, that is, if there is no change in the amount of noise, open the current That is, no noise is generated at the node or the gate switch.

Further, it is not always necessary to completely shut off the upstream signal, and it is also possible to measure the amount of noise after attenuating it to a certain degree or more. Next, with reference to the flowcharts shown in FIGS. 7 and 8, a case where a noise amount that does not cause a communication failure is set as a predetermined threshold, and a case where it is determined that the noise is reduced when the noise amount is less than the predetermined threshold is considered. explain. Note that the predetermined threshold is empirically determined from the floor level and peak value of noise, and is determined according to the network scale and the like.

The processing flow performed by the control device 27 when a communication failure occurs will be described in detail. Here, FIG.
FIG. 8 mainly shows the noise generation location specifying process.
This shows the recovery process. The noise occurrence location specifying process will be described with reference to the process flow of FIG. During operation of the two-way CATV system, the cable modem 22 detects a communication failure and transmits communication failure information to the communication failure information receiving unit 27.
1 (step S1).

The control unit 275 instructs the noise measurement unit 28 to perform noise measurement from the noise determination unit 272 to determine whether the communication failure is caused by noise. Then, the noise amount included in the uplink signal measured by the noise measuring device 28 is obtained by the noise determination unit 272 (step S2). It is determined whether the acquired noise amount is noise causing a communication failure (step S3). If the noise amount is smaller than a predetermined threshold value based on the average noise amount in normal times (N), the communication failure that has occurred is a factor other than noise, such as a device failure. Is determined to be a communication failure due to noise, because the noise source has disappeared while the location of the noise has been specified, or has attenuated to a level that does not affect communication. The process ends (step S16).

If the acquired noise amount is equal to or larger than the predetermined threshold value (Y), it is determined that the communication failure is due to noise, and the process of specifying the location where the noise occurs is performed. Here, the automatic detection of the communication failure by the cable modem 22 is used as the start timing of the noise measurement. However, besides this, for example, when the system administrator presses the start button at any timing at which the user wants to measure the noise, It is also possible to execute this processing.

Normally, a plurality of nodes are connected to the cable modem 22, and FIG. 4 shows only two nodes for convenience. During operation of the bidirectional CATV system, all the gate switches in many trunk branch amplifiers connected below each node are open. The control device 27 first uses the amplifier control unit 273 to control the first node, which is one of the nodes connected to the headend 21 in large numbers.
In the node, the gate switches a and b of the first-stage main branch amplifier 1A are controlled, and the two gate switches a and b are controlled.
Are shut off together (step S4). Thereby, the upstream signal at the first node is cut off. If there is a noise generation point downstream of the first node, this ingress noise will also be cut off.

At this time, the control unit 275
At 72, it is determined whether the amount of noise measured by the noise measuring device 28 decreases (step S5). If there is no noise generation point downstream of the first node,
The noise amount acquired from the noise measuring device 28 is equal to or greater than a predetermined threshold (N). In this case, it is determined that there is no noise generation point downstream of the first node, and the process proceeds to a process of specifying the noise generation point for the next node.

When proceeding to the process of specifying the location of the noise at the next node, the node that has been processed before, that is, in the example of FIG. 4, the two gate switches of the first stage main branch amplifier of the first node are both controlled. Switch from shutoff to open. Next, also for the next node, similarly to the processing in step S4, the gate switch of the first-stage main branch amplifier 3A is controlled, and both the gate switches e and f are shut off (step S6). As a result, the upstream signal at the next node is cut off.

Then, the process of step S5 is performed. According to the example of FIG. 4, since a noise generation point exists downstream of the first node, when both the gate switches a and b of the first-stage main branch amplifier 1A are shut off, the noise determination unit 27
Since it is determined in step 2 that the noise amount obtained from the noise measuring device 28 is less than the predetermined threshold, the control unit 275 specifies the main branch amplifier 1A having the noise generating node (Y in step S5).

When the main branch amplifier in which the noise is generated is specified, any one of the two gate switches provided in the main branch amplifier is controlled by the amplifier control unit 273 and cut off. (Step S
7). According to the example of FIG. 4, one of the gate switches a and b of the first-stage main branch amplifier 1A is cut off, for example, a.

In this case, too, the control device 27 executes step S5.
Similarly to the above, the noise determination unit 272 determines whether the noise amount is less than the predetermined threshold (step S8). According to the example of FIG. 4, when the gate switch a of the first-stage main branch amplifier 1A is shut off, the noise amount acquired from the noise measuring device 28 remains at or above the predetermined threshold (N). Therefore, based on the information stored in the information display / storage unit 274, the control unit 275 determines whether or not there is a gate switch that has not been shut off in the first-stage main branch amplifier 1A (step S9).

Since the gate switch a of the first-stage main branch amplifier 1A has been shut off, another gate switch b needs to be shut off ("Yes" in step S9). Therefore,
The amplifier control unit 273 shuts off the other gate switch b (Step S10). At this time, the gate switch a
Is controlled to switch from cut-off to open. Then, the process returns to step S8. According to the example of FIG. 4, when the gate switch b is cut off, the upstream signal from the main branch amplifier 2A is cut off, so that the noise amount acquired from the noise measuring device 28 becomes less than the predetermined threshold (Y). Thus, it is determined that the noise generating point exists on the gate switch b side.

Next, since there is a possibility that noise is generated further downstream, the control unit determines whether there is a trunk branch amplifier under the gate switch based on the information stored in the information display / storage unit 274. A decision is made (step S11).
According to the example of FIG. 4, the main branch amplifier 2A is connected to the gate switch b (Y). Main line branch amplifier 2A
By controlling one of the two gate switches c and d, for example, to cut off c (step S1).
2). Even when the gate switch c is shut off, the process proceeds to step S8, and it is determined whether the amount of noise acquired from the noise measuring device 28 is less than a predetermined threshold. At this time, since the acquired noise amount is equal to or larger than the predetermined threshold (N in step S8), it is determined that there is no noise generation part on the gate switch c side.

Since the main branch amplifier 2A has another gate switch d ("Yes" in step S9),
Proceeding to step S11, the other gate switch d of the main branch amplifier 2A is shut off. Also at this time, the gate switch c is controlled to switch from cutoff to open. Proceeding to step S8, if it is determined that the amount of noise acquired from the noise measuring device 28 is less than the predetermined threshold (Y of step S8), the process proceeds to step S11 to determine whether there is a main branch amplifier under the gate switch d side. . Since there is no trunk branch amplifier under the control (N in step S11), it can be specified here that there is a noise generating part in the transmission line on the gate switch d side of the main branch amplifier 2A. The control unit 275 determines that the process has been completed (step S13).

By the way, in the example of FIG. 4, there is shown a case where there is a noise generating portion on the transmission line on the gate switch d side of the main branch amplifier 2A. For example, between the first stage main branch amplifier 1A and the main branch amplifier 2A. There may be a place where noise is generated. In this case, even if the other gate switch d is turned off in step S10, the noise amount acquired from the noise measuring device 28 remains at or above the predetermined threshold because there is a noise generation point upstream of the main branch amplifier 2A ( N in step S8). Then, the gate switch d is controlled and opened again.

The process further proceeds to step S9, at which time
Since there is no gate switch to be cut off in the main branch amplifier 2A ("NO" in step S9), it can be specified that there is a noise generation location upstream of the main branch amplifier 2A, and the process of specifying the noise generation location ends (step S13). ). After the noise generation location is specified as described above, the specified gate switch is controlled and the upstream signal is blocked by the amplifier control unit 273 (step S14). When a noise generation location is specified downstream of the trunk branch amplifier, the gate switch is kept shut off, and an upstream signal from the gate switch downstream is shut off.
Further, when a noise generation location is specified upstream of the main branch amplifier, the gate switch of the upstream main branch amplifier is switched from cut-off to open after detecting a decrease in the amount of noise. The switch is controlled to shut off, and an upstream signal from downstream of the gate switch is shut off.

Here, the location where the noise is generated is specified, and in connection with this specification, the information on the gate switch that is kept shut or the gate switch that has been shut off is stored in the information display / storage unit 274 (step S15). The information related to the specified gate switch is stored, and the process of specifying the location of the noise occurrence ends (step S16).

As described above, when the process of specifying the location of the noise has been completed, the control device 27 keeps shutting off the upstream signal from the gate switch by maintaining the shutoff of the specified gate switch, and continues to shut off the other gate switches. Is released, the communication of the cable modem 22 is normalized.
Information on which gate switch is blocked is
It is also stored on the status monitor 23.

The recovery process will be described with reference to FIG. If it is stored in the information display / storage unit 274 that there is a gate switch that has been shut off (step S20), the gate switch that has been shut off is periodically opened for a short period of time, and the noise amount during that period is measured. . Note that a counter A is provided in the control unit 275 to measure a time interval at which the gate switch is temporarily opened.

After normalizing the cable modem 22, the control device 27 first initializes the counter A to 0 (step S21). Next, the count A is incremented by one (step S22). The count is further increased, and every time the count exceeds a predetermined interval, for example, 10 counts (step S23), the gate switch that blocks the up signal is temporarily opened (step S24). This count value can be appropriately set as needed.

When the gate switch is controlled and opened, the noise amount measured by the noise measuring device
72 is obtained (step S25). At this time, if there is a noise amount equal to or more than the predetermined threshold value (Y), it is determined that noise continues to be generated, the gate is shut off again (step S26), and the counter A is reset to 0 (step S26).
21).

If the measured noise amount is less than the predetermined threshold value in step S25 (N), it is determined that the noise source that has occurred has disappeared or has been attenuated to a level that does not affect communication. , Keep the gate switch open. As a result, the upstream signal is released from the interruption.
At the same time, the information related to the gate switch that has been turned off is deleted from the storage (step S27). Here, the restoration process ends (step S28).

As described above, according to the present embodiment, when a communication failure occurs, it can be determined whether the failure is caused by noise, and the gate switch of the main branch amplifier is cut off from the upstream side. Since the control is performed, it is possible to easily specify a noise generation location. If it is caused by noise, the gate switch of the main branch amplifier located immediately upstream of the transmission line where the noise is generated is shut off to reduce the effect of noise contamination on the transmission line where no failure has occurred. The least difficult to stop.

When a noise generation location is specified and cut off, the amount of noise is periodically measured and automatically restored only when it is determined that there is no noise. The stop time of the transmission line is hardly minimized, and the influence on other normally operating transmission lines can be minimized. Further, since the noise amount is measured not at the amplifier unit on the transmission line but at the center station side, the existing amplifier can be used as it is. As a result, it is possible to reduce the cost when introducing the present apparatus into the currently operating system.

[0062]

According to the present invention, in a tree-structured network such as a bidirectional CATV system, a communication failure due to ingress noise generated on an upstream transmission path can be easily detected, and a noise generation location can be quickly detected. And easily identified,
Communication failure can be recovered.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration diagram of a conventional bidirectional CATV system.

FIG. 2 is a diagram showing a block configuration diagram of a status monitor and a main branch amplifier.

FIG. 3 is a diagram illustrating a use state of a frequency band in an uplink communication signal and a downlink communication signal.

FIG. 4 is a diagram showing a configuration diagram of a bidirectional CATV system according to the present embodiment.

FIG. 5 is a diagram showing a configuration diagram of a bidirectional CATV system when a plurality of cable modems are connected.

FIG. 6 is a diagram showing a block diagram of a control device.

FIG. 7 is a diagram showing a flow of a noise occurrence location specifying process and a normalizing process according to the present embodiment.

FIG. 8 is a diagram showing a flow of a recovery process according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Main line branch amplifier 10 ... Node 11, 12, 13 ... Branching device 14, 15 ... Gate switch 16, 234 ... RF modem 17, 231 ... CPU2 ... Center station 21 ... Head end 22, 22-1 to 22-3 ... cable modem 23 ... status monitor 24 ... terrestrial wave receiving antenna 25 ... satellite wave receiving antenna 26 ... router 27 ... control device 271 ... communication failure information receiving unit 272 ... noise determination unit 273 ... amplifier control unit 274 ... information display / storage unit 275 control unit 28 noise measuring device 3 subscriber terminal 31 personal computer 32 cable modem 4 tap-off 5 selector switch

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H04N 17/00 F-term (Reference) 5C061 BB13 CC03 5C064 BA01 BA07 BB10 BC12 BC14 BD01 BD07 5K030 GA12 HC13 JA10 MA01 MA04 MB04 MB20 MC07 MC08 MC09 MD01 5K033 AA06 BA07 CB06 DA01 DA16 DB01 DB20 DB21 EA02 EA04 EA06 EB02 EB08 5K035 AA01 BB02 DD01 EE04 JJ02 LL03 LL04

Claims (7)

[Claims] An ingress noise monitoring system in a tree-type two-way communication network having a plurality of transmission paths by a plurality of branching means, comprising: a communication fault detecting means for detecting a communication fault at an uppermost stream of the network; Noise amount detecting means for detecting an amount of noise in an upstream signal transmitted to the uppermost stream of the network; and when the communication error detecting means detects a communication error, the amount of noise detected by the noise amount detecting means is predetermined. Control means for determining that the communication failure is a communication abnormality due to ingress noise when the value is equal to or greater than the value. 2. The branching means has a gate switch for blocking or opening an upstream signal for each of a plurality of connected transmission lines, and when the control means determines that the communication is abnormal due to the ingress noise, a gate is provided. The switch performs an open / close control of an upstream signal of the transmission line, and specifies a gate switch located at the most downstream side among gate switches whose noise amount detected by the noise amount detection means is less than a predetermined value when cut off. The ingress noise monitoring system according to claim 1. 3. The ingress noise monitoring system according to claim 2, wherein the control unit maintains a state in which the specified gate switch is shut off. 4. The method according to claim 1, wherein the control means includes: an order from a gate switch located upstream to a gate switch located downstream;
4. The ingress noise monitoring system according to claim 2, wherein the gate switch is controlled to shut off and open in an order based on a frequency of specifying the gate switch in the past. 5. 5. The control means controls the gate switch in the shut-off state to open / close every predetermined time, and holds the gate switch in the open state if the noise amount in the open state is less than a predetermined value. The ingress noise monitoring system according to claim 3, wherein when the amount of noise is equal to or more than a predetermined value, the ingress state is maintained. 6. An ingress noise monitoring device for monitoring ingress noise in a tree-type two-way communication network having a plurality of transmission paths by a plurality of branching means, wherein an upstream in a transmission path located at an uppermost stream of the network. A noise determination unit that determines whether the amount of noise in the signal is less than a predetermined value; a communication failure information receiving unit that receives communication failure information of the network; and an upstream signal for each of a plurality of transmission paths connected to the branching unit. A gate switch control unit that controls a gate switch that shuts off or opens, if the noise amount is equal to or more than a predetermined value when the communication failure information is received, the gate switch performs shutoff / opening control of an upstream signal of a transmission path for the gate switch. Then, the gate switch located at the most downstream position is specified among the gate switches in which the amount of noise when the gate switches are sequentially shut off is less than a predetermined value. Both ingress noise monitoring apparatus; and a control means for holding the gate switch is the identified cut-off state. 7. A storage device for storing a gate switch held in a cut-off state, wherein the control unit controls the gate switch in the cut-off state to be turned on and off every predetermined time, and 7. The ingress noise monitoring and control device according to claim 6, wherein the gate switch is kept open when the noise amount is less than a predetermined value, and is held in a shut-off state when the noise amount is equal to or more than the predetermined value.