JP2008311877A - Catv system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the number of optical fibers that constitute an optical transmission path in an FTTH communication system, and to facilitate introduction of the communication system. <P>SOLUTION: This CATV system 1A comprises an optical coupler 14 which is installed in a cluster cell S<SB>C</SB>and is connected to a head end 2 via an optical transmission line 4, for branching an optical signal containing broadcasting data transmitted from the head end 2; a node device 13 in a mini cell S<SB>M</SB>having an amplifier 15 for amplifying the optical signal branched by the optical coupler 14 for rebranching, and a converter 16, which is connected to the head end 2 via the optical transmission line 4, for mutually converting the optical signal containing two-way communication data transmitted to and received from the head end 2 and the optical signal transmitted to and received from subscriber facility 3; and an optical coupler 19, which is connected between the node device 13 and a plurality of subscriber accommodations 3, for branching/combining the optical signal transmitted and received between the node device 13 and the subscriber facility 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a CATV system for connecting a head end and subscriber equipment through an optical transmission line.

In recent years, an FTTH (Fiber To The Home) communication system that connects a central station such as a telephone station or a center station of a CATV system and equipment in a subscriber's home via an optical fiber has begun to be introduced. The FTTH communication system includes an SS (Single Star) system in which a subscriber's home and a central office are connected one-to-one using an optical fiber, and an optical coupler extending from the central office on the subscriber's home side. A PDS (Passive Double Star) system is known in which a subscriber's house and a central office are connected in an N-to-1 manner by branching into a plurality of optical fibers by using a network, but it is easy to introduce from a cost standpoint. The PDS method is becoming mainstream (see Patent Document 1 below).
JP 2003-101560 A

  In this PDS system, since it is difficult to use an active circuit element on the subscriber's home side from the viewpoint of securing a stable power source, etc., an optical fiber using an optical coupler which is a passive element on the subscriber's home side is used. Branched. Here, since the optical signal transmitted through the optical fiber is deteriorated due to the level fluctuation or signal delay according to the transmission distance, the number of branches in the optical coupler for each optical fiber is limited (for example, The maximum number of branches is 32 at a transmission distance of 10 km, and the maximum number of branches is 16 at a transmission distance of 20 km. Therefore, a considerable number of optical fibers must be laid according to the number of subscribers on the transmission line connecting the central office to the subscriber's premises, leading to an increase in communication system introduction costs and introduction man-hours. It will be.

  Accordingly, the present invention has been made in view of such problems, and provides a CATV system that facilitates the introduction of a communication system by reducing the number of optical fibers constituting an optical transmission line in an FTTH communication system. For the purpose.

  In order to solve the above problems, a CATV system of the present invention is a CATV system in which a head end and a plurality of subscriber facilities are connected by branching an optical transmission line by an optical coupler. A first optical coupler that is connected to the head end via an optical transmission line and branches a first optical signal including broadcast data transmitted from the head end; Is connected to the head end via an optical transmission line, and an amplifying unit for amplifying and re-branching the first optical signal branched by the first optical coupler. A plurality of node devices in a cell having a conversion unit that mutually converts a second optical signal including bidirectional communication data to be transmitted / received to / from a third optical signal to be transmitted / received to / from subscriber equipment, No Connected between de device and a plurality of subscriber equipment, and a second optical coupler for branching / combining the third optical signal transmitted and received between the node devices and the subscriber equipment.

  According to such a CATV system, the first optical signal including the broadcasting data transmitted from the head end via the optical transmission line is branched by the first optical coupler in the cell and branched. The optical signal is amplified and re-branched by the amplification unit of the node device in the cell and transmitted to the subscriber equipment side. In addition, an optical signal including bidirectional communication data transmitted and received between the head end and the subscriber equipment is mutually converted between two optical signals across the node equipment, and between the node equipment and a plurality of subscriber equipment. The optical signal transmitted / received in is split / combined by the second optical coupler in the cell. As a result, the optical device for broadcasting is actively amplified and branched using the node device installed in the cell in the CATV system, and the optical signal for bidirectional data communication is passively transmitted by the optical coupler. Actively interconverts between the branched / synthesized optical signal and another optical signal, so that even if the transmission distance is long, the number of subscriber facilities for each optical fiber constituting the optical transmission line is effective. Can be increased. In particular, the node device in the CATV system can easily solve the problem of securing the power supply by amplifying and converting the optical signal.

  A switching device connected between the head end and the node device in the cell, for selecting bidirectional communication data addressed to the node device from the second optical signal and transmitting the data to the node device as a fourth optical signal; It is preferable that the conversion unit converts the fourth optical signal transmitted from the switching device into a third optical signal.

  In this case, even if the distance between the head end and the node device is long, it is connected to the head end without increasing the number of optical fibers in the optical transmission path between the head end and the switching device. The number of subscriber facilities can be ensured more reliably. At the same time, since an optical signal including only data addressed to a certain node device is transmitted to the corresponding node device, efficient data communication can be performed between the switching device and the node device.

  Further, the conversion units of the plurality of node devices are connected to each other in a cascade manner, and the conversion unit of one of the plurality of node devices sends the second optical signal to the conversion unit of the other node device. It is also preferable to relay.

  By adopting such a configuration, even when the distance between the head end and the node device is long, the head end is not increased without increasing the number of optical fibers in the optical transmission path between the head end and the node device. The number of subscriber facilities to be connected can be ensured more reliably. Further, since the second optical signal is transmitted and received between all the node devices in the cell and the head end by the relay function in the node device, the optical cable routing distance in the cell is further shortened.

  Still further, the switching device is connected to the head end via the duplexed first optical transmission line and the second optical transmission line, and is transmitted via the first optical transmission line. It is also preferable to switch the connection so that the second optical signal is received via the second optical transmission line when an abnormality is detected in the optical signal.

  In this way, even if a failure occurs in the optical transmission line, the failure is automatically detected, and the switching device switches the optical transmission line for transmitting and receiving the optical signal. Data communication can be restored to a normal state.

  Furthermore, the optical transmission line has a duplexed first and second optical transmission line, and the plurality of node devices convert the first to Nth (N is an integer of 2 or more) node devices. Are connected in order in cascade, and the conversion units of the first and N-th node devices are connected to the first optical transmission line and the second optical transmission line, respectively. The conversion unit of the first node device receives the second optical signal from the first optical transmission line, relays it in turn to the Nth node device, and the conversion units of the second to Nth node devices When an abnormality of the second optical signal relayed from the first to (N-1) th node devices is detected, the second optical signal is received from the second optical transmission line, and the first node is sequentially It is also preferable to relay towards the device.

  In this case, even if a failure occurs in either the first or second optical transmission line, the failure is automatically detected, and the optical transmission line for transmitting and receiving the optical signal is switched by the node device and the optical signal is switched. Since the relay direction of the optical signal between the node devices is changed to the opposite direction, the data communication between the head end and the subscriber equipment can be immediately restored to the normal state.

  According to the CATV system of the present invention, the number of optical fibers constituting the optical transmission line in the FTTH communication system can be reduced and the introduction of the communication system can be facilitated.

  Hereinafter, preferred embodiments of a CATV system according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

[First Embodiment]
FIG. 1 is a diagram showing a connection configuration of a CATV system 1A according to the first embodiment of the present invention. The CATV system 1A receives a broadcast program received by an antenna (not shown) from a headend 2 installed in a central office of a cable television company or the like, and a subscriber facility 3 such as a set-top box installed in a subscriber's house. It is a communication system which transmits toward. The CATV system 1A is also connected to a communication network N composed of an Internet network, a telephone network, and the like, and packet data for telephone communication and Internet communication transmitted and received between the communication network N and the subscriber equipment 3 (both Data communication function for relaying data for communication). The CATV system 1A employs an FTTH system in which the head end 2 and the subscriber equipment 3 are connected by an optical transmission line including an optical fiber. In the following description, regarding the connection relationship of equipment, the head end 2 side is “upstream”, the subscriber equipment 3 side is “downstream”, and the optical signal transmission direction is from the subscriber equipment 3 to the head end 2. The “upward direction” is the side, and the subscriber equipment 3 side from the head end 2 is the “downward direction”.

Here, the subscriber station 3, a plurality for each area to the position of the subscriber's home (e.g., 200 households) are collectively formed minicells S _M, form a cluster cells S _C that minicells S _M is further more together is doing. And, in between the subscriber equipment 3 and the head end 2, the optical transmission path 4 is laid for each cluster cells S _C. In this optical transmission line 4, two optical fibers f _a1 and f _a2 are installed as the working optical line on the same route, and the two optical fibers f _b1 and f _b2 are the same as the backup optical line. And an optical transmission line 4b installed along the route.

  The head end 2 includes a broadcast optical transmission device 5 that has a transmission function for broadcasting data including a broadcast program, and a communication optical transmission device 6 that has a transmission / reception function for bidirectional communication data.

This broadcast optical transmission apparatus 5 passively converts two optical transmitters 7a and 7b that convert broadcast data into optical signals and outputs the optical signals output from the optical transmitters 7a and 7b. The two optical couplers 8a and 8b branch to the optical signal. Optical coupler 8a of the broadcasting optical transmission device 5 is connected to an optical fiber f _a1, and sent to the downstream side the optical signal branched through the optical fiber f _a1, the optical coupler 8b is connected to an optical fiber f _b1 The branched optical signal is transmitted to the downstream side through the optical fiber _fb1 . Thus, optical transmission device 5 for broadcasting, an optical signal containing broadcast data, is branched for each cluster cells S _C, via the optical fiber 2 that has been duplexed f _a1, f _b1 downstream To the side.

The communication optical transmission device 6 includes two media converters 9a and 9b. The media converter 9a is connected to the communication network N and the optical fiber f _a2 , and the media converter 9b is connected to the communication network N and the optical fiber f _b2 . The media converters 9a and 9b convert electrical signals including communication data addressed to the plurality of subscriber facilities 3 received from the communication network N into optical signals according to the LAN communication system, and convert the optical signals to the optical fiber f. It transmits to the downstream side via _a2 and _fb2 . As this predetermined communication method, for example, a LAN communication method such as CSMA / CD method is used. The media converters 9a and 9b receive optical signals including communication data transmitted from the plurality of subscriber facilities 3 toward the communication network N via optical fibers f _a2 and f _b2, and The signal is converted back into an electric signal suitable for the communication network N side. Thus, communication optical transmission device 6 includes a transmitting and receiving an optical signal, via _the two optical fibers f _{a2, f} b2 which is duplexed with the cluster cells S _C including two-way communication data To do.

The downstream end of the optical fiber _{f a1, f b1} of the optical transmission path 4, the optical switch 11 installed in the cluster cells _{S C} is connected, the optical transmission path 4 of the optical fiber _{f a2, f b2} the downstream end, LAN switch (switching device) 12 installed in the cluster cells S _C is connected.

The optical switch 11, the optical coupler 8a of the head end 2 through an optical fiber _{f a1, f b1,} connected to 8b, two optical signals transmitted via the optical fiber _{f a1, f b1,} selectively It has a function of switching and transmitting to the downstream side. The optical switch 11 outputs an optical signal from the optical fiber _fa1 to the downstream side in a normal state. On the other hand, the optical switch 11 monitors the optical input level of the two optical signals from the head end 2, and when the optical input level of the optical signal from the optical fiber f _a1 decreases, the optical signal from the optical fiber f _b1. Is switched to output downstream.

LAN switch 12, the optical fiber _{f a2,} via the _{f b2} headend 2 media converters 9a, is connected to 9b, distributing / combining the optical signal transmitted and received between the media converters 9a, 9b and minicell _{S M} This is an active switching hub device. The LAN switch 12 (details will be. Described below) a plurality of node devices provided for each minicell S _M and 13, are connected via a plurality of optical fibers f _c which is laid in the cluster cells S _C Yes. Then, the LAN switch 12 receives the optical signal including the uplink communication data from the plurality of node devices 13, combines the uplink communication data included in these optical signals, and regenerates the optical signal. Transmit to media converter 9a, 9b side. Furthermore, LAN switch 12, media converter 9a, and receives the optical signal including the downlink communication data from 9b, distribute these downlink communication data, each minicell S _M by referring to the destination address To do. LAN switch 12, the optical signal including the downstream communication data distribution regenerated every minicell S _M, and transmits it to those optical signals to the appropriate node device 13. Specifically, the downlink communication data in which the node device 13 is designated as the transmission destination is distributed so as to be selected for the node device 13. Here, between the LAN switch 12 and the node device 13, the same LAN communication method as that between the LAN switch 12 and the media converters 9a and 9b is used.

The LAN switch 12 has a function of detecting a network failure in an optical signal transmitted / received to / from the media converter 9a via the optical fiber _fa2, and when an abnormality of the optical signal is detected, It also has a function of switching the connection with the head end 2 so that an optical signal is transmitted to and received from the media converter 9b via the fiber _fb2 . As a protocol for realizing such a switching function, for example, link aggregation is used.

The optical coupler 14 is a passive optical device that is installed to correspond to the optical transmission path 4, which is duplicated in the cluster cells S _C. The optical coupler 14 is connected to the optical switch 11 via the optical fiber f _d, the optical signal including the broadcast data from the optical switch 11 is transmitted to the downstream side, branches to a plurality of node devices 13. Here, the optical coupler 14 via a plurality of optical fibers f _e which is laid in the cluster cells S _C, is connected to a plurality of node devices 13 provided for each minicell S _M, split optical signal _Are transmitted to the node device 13 via these optical fibers _fe .

The node device 13 includes an amplifying unit 15 that performs an amplification function of an optical signal including broadcasting data, and a conversion unit 16 that performs a conversion function of a communication method of an optical signal including bidirectional communication data. The amplifying unit 15 is connected to the output of the optical coupler 14 via the optical fiber _fe , amplifies the level of the optical signal transmitted from the optical coupler 14, and again branches the amplified optical signal to the subscriber equipment 3. Send to. For example, an EDFA (Erbium Doped Fiber Amplifier) is used as an amplifier constituting the amplifying unit 15. The optical signal transmitted from the amplifying unit 15 passes through an optical fiber provided between the node device 13 and the subscriber equipment 3 and an optical coupler for branching the optical fiber, and is subordinate to the node device 13. It is transmitted simultaneously to a plurality of subscriber facilities 3.

The conversion unit 16 of the node device 13 includes a LAN switch 17 and two OLTs (Optical Line Terminals) 18a and 18b. LAN switch 17, the optical signal transmitted from the LAN switch 12 via an optical fiber _{f c} demodulates the downlink communication data, and distributes the downstream communication data for two OLT18a, 18b Output. Specifically, the downlink communication data in which the subscriber equipment 3 under the OLTs 18a and 18b is designated as the transmission destination is distributed and output to the OLTs 18a and 18b. Also, LAN switch 17, OLT18a, modulates the optical signal after synthesizing the uplink communication data transmitted from 18b, and transmits the optical signal to the LAN switch 12 via an optical fiber _{f c.}

OLT18a node device 13, 18b is a facility for supporting a plurality of subscriber station 3 located within the minicell _{S M,} each of the optical signals transmitted and received between the subscriber station 3 OLT18a, 18b and Data communication control such as control of bandwidth allocation to the subscriber equipment 3 is performed. The OLTs 18a and 18b are connected between an optical signal transmitted / received between the node device 13 and the head end 2 and an optical signal transmitted / received between the node device 13 and the subscriber equipment 3 by the LAN communication method. Thus, the communication methods are mutually converted. Note that a PON (Passive Optical Network) method, which is a communication method for optical access lines, is used between the node equipment 13 and the subscriber equipment 3, and the OLTs 18a and 18b actively distribute / The communication method is converted between the LAN communication method to be combined and the PON method that passively branches / synthesizes the optical signal.

  Between the OLTs 18a and 18b and the subscriber equipment 3, an optical coupler 19 is connected at a node of an optical fiber having a tree shape. The optical coupler 19 branches the optical signal including the downlink communication data transmitted from the OLTs 18 a and 18 b toward the subscriber equipment 3 and also includes the uplink communication data transmitted from the subscriber equipment 3. The signals are combined and transmitted to the OLTs 18a and 18b.

According to the CATV system 1A described above, the optical signal including the broadcast data transmitted via the optical transmission path 4 that is duplicated from the head end 2, is branched by the optical coupler 14 in the cluster cells S _C , branched optical signals are transmitted to the subscriber station 3 side is re-branched after being amplified by the amplification unit 15 of the node device 13 in the mini-cell S _M. An optical signal including bidirectional communication data transmitted / received between the head end 2 and the subscriber unit 3 is an optical signal in the upstream LAN communication system and a downstream PON system across the node device 13. It is mutually converted between optical signals. Further, the optical signal transmitted and received between the subscriber station 3 to the node device 13 is branched / combined by the optical coupler 19 which is installed in the mini-cell S _M. Thus, by using the node device 13 which is installed in the mini-cell S _M of the CATV system 1A, with branches actively amplify optical signals for broadcasting, an optical signal for bidirectional data communication, optical coupler PON system optical signal that is passively branched / combined by the PON system and LAN communication system optical signal that is actively switched are mutually converted, so that even if the transmission distance is long, one optical transmission path is configured. The number of subscriber facilities for each optical fiber can be effectively increased.

  Specifically, when the head end and the subscriber equipment are connected by the PON system, the maximum number of branches per optical cable is 32 when the transmission distance is 10 km or less, and a cell including 1000 households is used. A 64-core optical cable is required for housing. Similarly, when the transmission distance is 20 km or less, the maximum number of branches per optical cable is 16, and a 126-core optical cable is required to accommodate cells including 1000 households. On the other hand, according to the CATV system 1A, it is possible to accommodate one cluster cell including about 1200 households with a four-core optical fiber including two optical transmission lines between the head end and the cluster cell. Become.

  Further, in a conventional HFC type (Hybrid Fiber / Coaxial system) CATV system, a node device installed in a cell employs a method of actively converting a signal between an optical cable and a coaxial cable. Therefore, when the configuration of the CATV system 1A is adopted to replace the system from the HFC type to the FTTH system, it is possible to easily solve the problems of securing the power source and securing the installation space. In addition, the number of new optical fiber installations during system replacement can be minimized.

  Further, by connecting the head end 2 and the node device 13 via the LAN switch 12, even if the distance between the head end 2 and the node device 13 is long, the optical fiber of the optical transmission line 4 is used. The number of subscriber facilities connected to the head end 2 can be more reliably ensured without increasing the number of the subscribers. At the same time, since an optical signal including only data addressed to a certain node device 13 is selectively transmitted to the corresponding node device 13, efficient data communication can be performed between the LAN switch 12 and the node device 13.

  Further, even when a failure occurs in the optical transmission line 4 by the LAN switch 12, the failure is automatically detected and the optical transmission lines 4a and 4b for transmitting / receiving optical signals are switched, so that the head end 2 can be immediately joined. The data communication between the person facilities 3 can be restored to the normal state.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. FIG. 2 is a diagram showing a connection configuration of the CATV system 1B according to the second embodiment of the present invention. CATV system 1B is different from the node device 33a installed in the mini-cell _{S M,} 33b, 33c, 33d are duplexed optical transmission line 4a, that it has a 4b switching function of the first embodiment.

As shown in the drawing, the downstream end of the cluster cells S and the optical coupler 34a connected to the downstream end of the optical fiber f _a1 of the optical transmission path 4a is in _C, the optical transmission line 4b optical fiber f _b1 And an optical coupler 34b connected to each other. These optical couplers 34a, 34b, respectively, head-end 2 from the optical transmission line 4a, the optical signal including the broadcast data transmitted through the 4b, cluster cells S _C plurality of which are laid in an optical fiber f _g, branching toward the _{f h.}

The node device 33a further includes an optical switch 35 connected to the upstream side of the amplification unit 15. This optical switch 35 is connected to the downstream ends of the two optical fibers f _g and f _h , and outputs an optical signal from the optical fiber f _g to the downstream amplification unit 15 in a normal state. On the other hand, the optical switch 35 has a function of monitoring the optical input level from the optical fiber optical fiber f _g, when the optical input level of the optical signal from the optical fiber f _g is lowered, from the optical fiber f _h It switches so that an optical signal may be output to the downstream amplification part 15. FIG. Similarly, the node devices 33b, 33c, and 33d also have an optical switch 35 built therein. With this optical switch 35, even if a network failure occurs in the optical transmission line 4 or the optical couplers 34a and 34b fail, the reception of broadcast data in the subscriber facility 3 can be immediately restored to a normal state. it can.

Further, the four LAN switches 37 of the node devices 33a, 33b, 33c, and 33d are provided between the downstream end of the optical fiber f _a2 of the optical transmission line 4a and the downstream end of the optical fiber f _b2 of the optical transmission line 4b. Are connected in a cascaded manner. That is, the downstream end of the optical fiber _fa2 is connected to the LAN switch 37 of the node device 33a, and the LAN switch 37 of the node device 33a, the LAN switch 37 of the node device 33b, the LAN switch 37 of the node device 33c, and the node The LAN switch 37 of the device 33d is connected in series in this order, and the downstream end of the optical fiber _fb2 is further connected to the LAN switch 37 of the node device 33d. Each LAN switch 37 receives the optical signal including the downlink communication data transmitted from the optical transmission line 4a side, distributes the communication data to the two OLTs 18a and 18b, and outputs them simultaneously. The optical signal is sequentially relayed toward the node device on the subsequent stage side. Here, a node device connected to the optical transmission path 4a side is referred to as a “front-stage side” node device, and a node apparatus connected to the optical transmission path 4b side is referred to as a “rear-stage side” node device.

Further, each LAN switch 37 combines the uplink communication data transmitted from the OLTs 18a and 18b, and then outputs an optical signal including the communication data to the optical output port on the preceding stage side (optical fiber _fa2 side). To do. Furthermore, the LAN switch 37 also has a function of sequentially relaying an optical signal including uplink communication data received from the downstream node device toward the upstream node device.

The LAN switch 37 also has a function of switching a route for transmitting and receiving an optical signal including bidirectional communication data from the optical transmission path 4a to the optical transmission path 4b when an abnormality is detected in the optical transmission path 4a. Specifically, each LAN switch 37 operates as follows when an abnormality is detected in an optical signal transmitted / received via the optical transmission line 4a. That is, the LAN switch 37 switches the optical input port so as to receive the optical signal including the downlink communication data transmitted from the rear stage side (the optical transmission line 4b side), and simultaneously transmits the optical signal to the node on the front stage side. Relay in turn towards the device. Further, each LAN switch 37 combines the uplink communication data transmitted from the OLTs 18a and 18b, and then outputs an optical signal including the communication data to the optical output port on the rear stage side (optical fiber _fb2 side). Switch to Further, the LAN switch 37 switches so that the optical signal including the uplink communication data received from the upstream node device is sequentially relayed to the downstream node device. At this time, an abnormality in the optical signal can be detected based on control information exchanged in the optical signal.

According to the CATV system 1B described above, even if the distance between the head end 2 and the node devices 33a, 33b, 33c, 33d is long, the head end 2 and the node devices 33a, 33b, 33c, 33d The number of subscriber equipment connected to the head end 2 can be more reliably ensured without increasing the number of optical fibers in the optical transmission line between. Further, since the second optical signal to and from all the node devices and the head-end in the cluster cells S _C by the relay function in the node apparatus is transmitted and received, the routing distance of the optical cable in the cluster cells S _C is shorter .

  Further, even if a failure occurs in any of the optical transmission paths 4a and 4b, the failure is automatically detected, and the optical transmission path 4 for transmitting and receiving optical signals is switched by the node devices 33a, 33b, 33c, and 33d. At the same time, the relay direction of the optical signal between the node devices 33a, 33b, 33c, and 33d of the optical signal is changed to the reverse direction, so that the data communication between the headend 2 and the subscriber equipment 3 is immediately restored to the normal state. be able to.

  In addition, this invention is not limited to embodiment mentioned above. For example, the number of optical fibers, the number of branches by optical couplers, or the number of devices such as node devices and optical couplers in this embodiment are merely examples, and can be changed to various numerical values.

  The optical transmission path is not limited to a duplexed four-core optical cable, and may be an optical transmission path including only a two-core optical cable for broadcast data and communication data. Further, the optical signal including the broadcasting data and the optical signal including the communication data may be multiplexed and transmitted / received by wavelength division multiplexing (WDM) on a single optical fiber.

It is a figure which shows the connection structure of the CATV system concerning 1st Embodiment of this invention. It is a figure which shows the connection structure of the CATV system concerning 2nd Embodiment of this invention.

Explanation of symbols

S C _... cluster cells, S M _... minicells, 1A, 1B ... CATV system, 2 ... headend, 3 ... subscriber equipment, 4, 4a, 4b ... optical transmission line, 12 ... LAN switch (switching device), 13, 33a, 33b, 33c, 33d ... node devices, 14, 19, 34a, 34b ... optical couplers, 15 ... amplifying unit, 16 ... converting unit.

Claims (5)

A CATV system for connecting a head end and a plurality of subscriber facilities by branching an optical transmission line with an optical coupler,
A first optical signal that is installed in a cell including a plurality of subscriber houses and is connected to the head end via the optical transmission path and that includes broadcast data transmitted from the head end is branched. A first optical coupler that
An amplifying unit connected to the first optical coupler and amplifying and re-branching the first optical signal branched by the first optical coupler, and connected to the head end via the optical transmission line And a conversion unit that mutually converts a second optical signal including bidirectional communication data to be transmitted / received to / from the head end and a third optical signal to be transmitted / received to / from the subscriber equipment. A plurality of node devices in the cell;
A second optical coupler connected between the node device and the plurality of subscriber facilities, for branching / combining the third optical signal transmitted / received between the node device and the subscriber facilities;
A CATV system comprising: Connected between the head end and the node device in the cell, and selects the bidirectional communication data addressed to the node device from the second optical signal to the node device as a fourth optical signal. A switching device for transmitting,
The converter converts the fourth optical signal transmitted from the switching device into the third optical signal;
The CATV system according to claim 1. The conversion units of the plurality of node devices are connected to each other in a cascade manner, and the conversion unit of one node device of the plurality of node devices is directed to the conversion unit of another node device. Relay the optical signal of
The CATV system according to claim 1. The switching device is connected to the head end via a first optical transmission line and a second optical transmission line that are duplicated, and is transmitted via the first optical transmission line. When an abnormality is detected in the optical signal, the connection is switched to receive the second optical signal via the second optical transmission line;
The CATV system according to claim 2. The optical transmission line has a duplexed first and second optical transmission line,
In the plurality of node devices, the conversion units of first to Nth (N is an integer of 2 or more) node devices are sequentially connected in a cascade manner, and the conversion units of the first and Nth node devices Are respectively connected to the first optical transmission line and the second optical transmission line,
The converters of the first to (N-1) th node devices receive the second optical signal from the first optical transmission line and relay the signals sequentially to the Nth node device;
When the conversion unit of the second to N-th node devices detects an abnormality in the second optical signal relayed from the first to N-1th node devices, the second optical transmission line Receiving the second optical signal from and relaying in turn to the first node device,
The CATV system according to claim 3.

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