Abstract:
A fiber to the home FTTH network for convergence of broadcasting and communication is disclosed. The network includes: an OLT for receiving and converting a first predetermined number of broadcast signals and an Ethernet signal into a plurality of converted optical signals, combining the converted optical signals into converged optical signals for subsequent transmission by an optical wavelength division multiplexing method; and an optical network unit (ONU) for classifying the optical signal transmitted from the OLT into the first predetermined number of broadcast signals and the Ethernet signal, switching a second predetermined number of broadcasting signals of the first predetermined number of broadcasting signals according to each SIU by channel selection information contained in upstream Ethernet information, and switching the Ethernet signal to be transmitted to the SIU according to each SIU so as to transmit the switched signal.

Description:
CLAIM OF PRIORITY 
     This application claims priority to an application entitled “FTTH system for convergence of broadcasting and communication through switched broadcasting” filed in the Korean Intellectual Property Office on Sep. 8, 2003 and assigned Serial No. 2003-62856, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a Fiber-To-The-Home (FTTH) network for convergence of broadcasting and communication. 
     2. Description of the Related Art 
     In the prior art, in order to provide for the efficient exchange of an Ethernet signal which is a communication signal, a passive optical network (hereinafter, referred to as a PON) structure. In such a network, there is generally one optical line terminal (hereinafter, referred to as an OLT) that is located at a telephone office. The OLT is subsequently connected to an N number of optical network terminals (hereinafter, referred to as ONTs) that have been installed at homes. 
     In this PON structure, the efficiency of the network increases so much that Ethernet switches in the N number of ONTs share an Ethernet signal from an Ethernet switch in one OLT through a power splitter. In this type of structure, since continuous digital broadcasting signals must be transmitted to all subscribers in a single direction, there has been used a certain method of overlaying optical signals for digital broadcasting onto an Ethernet communication network. 
       FIG. 1  shows a construction for the conventional FTTH network as described above. As shown, an OLT  100  and a plurality of ONTs  200 - 1  to  200 - 3  are connected to each other by a 1×N optical power splitter  111  so as to form the FTTH network. 
     In a conventional network structure such as shown in  FIG. 1 , in order to service digital broadcasting and an Ethernet signal such as an Internet signal/video on demand (VOD) signal simultaneously, the OLT  100  includes an Ethernet switch  106 , an optical transmitter  107 , an optical receiver  108 , and a wavelength division multiplexer  109  and processes the Ethernet signal through these devices. The Ethernet switch  106  switches downstream Ethernet information to each ONT and upstream Ethernet information from each ONT. The optical transmitter  107  generates a downstream optical signal for transmitting the downstream Ethernet information to the ONT. The optical receiver  108  converts an upstream optical signal into an electrical signal so as to transmit the converted signal to the Ethernet switch  106  for further communication with the Intent, or a Video on Demand. The wavelength division multiplexer  109  wavelength division multiplexes the downstream optical signal to transmit the multiplexed signal and receives the upstream optical signal. Also, the OLT  100  includes a Sub Carrier Multiplexing (hereinafter, referred to as an SCM) section  103 , an optical transmitter  104 , an optical amplifier  105  for amplifying an optical signal, and an optical coupler  110  for coupling with an Ethernet signal. The SCM section  103  modulates several digital broadcast channels of a digital broadcasting unit  101 , respectively, from an exterior by a quadrature amplitude modulation (QAM) method, and also multiplexes the modulated channels by an SCM method. 
     The optical transmitter  104  optically modulates the multiplexed broadcast signal. 
     Furthermore, the optical signal transmitted from the optical coupler  110  is classified into an N number of powers by the 1×N optical power splitter  111  and the classified signals are distributed to each ONT. 
     Then, the optical signal that is distributed to the ONT from the optical power splitter is classified into a broadcasting signal and an Ethernet signal via a wavelength division multiplexing demultiplexer  112  for wavelength division multiplexing, which divides signals by wavelength. Further, the broadcasting signal and the Ethernet signal are processed by respective optical receivers  113  and  114 . Herein, the broadcasting signal is transmitted to a set-top box (hereinafter, referred to as an STB)  300  and is passed through an RF filter in the STB  300 . Then, only a desired RF signal is selected and decoded as a high definition television (HDTV) signal to enter a digital TV  500 . 
     Also, the Ethernet signal is transmitted to an Internet/PC  400  through an Ethernet switch  116  which is then provided to a user. An upstream Ethernet signal sent from the user travels through the Ethernet switch  116  and is converted to an optically modulated signal via an optical transmitter  115 . The modulated signal is transmitted to the OLT  100  through the wavelength division multiplexing demultiplexer  112 . 
     The PON structure used for overlaying the conventional digital broadcasting and providing network service as described above has the following problems. 
     Firstly, the PON structure, in which one OLT transmits a signal to the N number of ONTs by means of the power splitting method, has a limitation in the number of the ONTs that can be in communication with the one OLT. According the current technology, since 64 divisions at maximum can be performed in consideration of a power margin, a digital broadcasting signal can be transmitted to 64 ONTs at a maximum by means of one analog optical transmitter. 
     Accordingly, when the number of the ONTs exceeds 64, since another PON system is additionally required as the maximum of the first PON has been exceeded, then the overlay operation must be performed by means of another analog optical transmitter, increasing the costs of the entire system. 
     Further, when 64 divisions at maximum are performed, an expensive optical amplifier, such as an EDFA, must be used next to the optical transmitter in order to increase the intensity of an optical signal and secure a carrier to noise ratio (CNR) for maintaining broadcasting quality. Furthermore, even in a case of a network utilizing an optical transmitter and the optical receiver, an expensive optical transceiver having a good property is required, increasing these costs of the entire system increases. 
     Furthermore, in a case of the conventional overlay method, since the STB receives all broadcastings, the STB of each subscriber requires a subscriber authentication and a real time accounting by a conditional access system (hereinafter, referred to as a CAS) system supporting encryption and decryption. Furthermore, since all broadcasting signals are transmitted to each ONT, an optical line having a large bandwidth must be used. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and a first object of the present invention is to provide a new structure of a FTTH network which provides a service to a plurality of subscribers grouped in a unit of an ONU in a FTTH system, so as to permit the convergence of broadcasting and communications. 
     A second object of the present invention is to provide a FTTH network for the convergence of broadcasting and communications, in which an ONU performs switching for broadcasting and transmits only broadcasting information switched to each subscriber, so that a bandwidth can be efficiently used. 
     A third object of the present invention is to provide a FTTH network for convergence of broadcasting and communication, in which an ONU performs switching for broadcasting and transmits only broadcasting information switched to each subscriber, so that the ONU can perform a subscriber authentication and a real time accounting by a CAS system includes supporting encryption and decryption. 
     A fourth object of the present invention is to provide a FTTH network for convergence of broadcasting and communication which enables a low priced light source operating at a low speed to be used, without using an expensive light source for increasing a transmission speed, because digital broadcastings in all channels are not transmitted to each of the subscribers. 
     In order to accomplish the aforementioned aspects of the present invention, there is provided a FTTH system for the convergence of broadcasting and communications through a switched broadcasting comprising: an OLT for receiving a first predetermined number of broadcasting signals and an Ethernet signal, converting the received signals into optical signals, combining the converted optical signals into optical signals, and transmitting the combined optical signals by an optical wavelength division multiplexing method; an ONU for classifying the optical signal transmitted from the OLT into the first predetermined number of broadcasting signals and the Ethernet signal, converting the classified signals into electrical signals, switching a second predetermined number of broadcasting signals of the first predetermined number of broadcasting signals according to each SIU by means of channel selection information contained in upstream Ethernet information, and switching the Ethernet signal to be transmitted to the SIU according to each SIU so as to transmit the switched signal; and an SIU for converting the signals transmitted from the ONU into electrical signals, transmitting the second predetermined number of broadcasting signals and the Ethernet signal to be transmitted to the subscriber to a corresponding subscriber&#39; terminal, and transmitting the upstream Ethernet information including the upstream Ethernet information for the broadcasting signal to the ONU. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of a conventional FTTH network; 
         FIG. 2  is a block diagram showing an FTTH network for convergence of broadcasting and communication through a switched broadcasting according to a first aspect of the present invention; 
         FIG. 3  is a block diagram showing one construction of an ONU and an SIU in the FTTH network for convergence of broadcasting and communication through the switched broadcasting according another aspect of the present invention; 
         FIG. 4  is a block diagram showing another construction of an ONU and an SIU in the FTTH network for convergence of broadcasting and communication through the switched broadcasting according to the present invention; and 
         FIG. 5  is an exemplary view of a signal time division multiplexed according to the aspect of the invention illustrated in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, preferred aspects of the present invention will be described with reference to the accompanying drawings. The same reference numerals are used to designate the same elements as those shown in other drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention. 
       FIG. 2  is a block diagram showing an FTTH network for convergence of broadcasting and communication through a switched broadcasting according to a first aspect of the present invention. 
     As shown in  FIG. 2 , an OLT  100  and an ONU  600  are connected to each other through one optical fiber, and a downstream output of the ONU  600  is connected to each subscriber interface unit (hereinafter, referred to as an SIU)  700 - 1  or  700 - n  through respective optical fibers, so that a true FTTH network is formed. 
     According to the present invention, this FTTH network structure, in order to service a digital broadcast signal  101  and an Ethernet signal,  102  such as an Internet signal/video on demand (VOD) signal simultaneously, the OLT  100  includes an Ethernet switch  204 , an optical transmitter  205 , an optical receiver  206 , and processes the Ethernet signal through these devices. The Ethernet switch  204  switches a downstream Ethernet signal to be transmitted to each SIU  700 - 1   700 - 1   n  and an upstream Ethernet signal to be transmitted from each SIU. The optical transmitter  205  generates a downstream optical signal for transmitting the downstream Ethernet signal. The optical receiver  206  converts an upstream optical signal into an electrical signal so as to transmit the converted signal further upstream to the Ethernet switch  204 . Furthermore, the OLT  100  includes a synchronous time multiplexing (hereinafter, referred to as an STM) section  201  and an optical transmitter  202 , and the OLT processes a broadcast signal through these devices. The STM multiplexing section  201  respectively multiplexes several digital broadcasting channels by the STM method, and the optical transmitter  202  optically modulates the multiplexed broadcasting signal. Furthermore, the OLT  100  includes a wavelength division multiplexer  203  and combines both the broadcasting signal and the Ethernet signal to transmit the combined signal. The wavelength division multiplexer  203  wavelength division multiplexes the downstream optical signal including the broadcasting signal and the Ethernet signal to transmit the optical multiplexed signal, and receives the upstream Ethernet signal. 
     The ONU  600  includes a wavelength division multiplexing demultiplexer  207  for wavelength division demultiplexing, an STM demultiplexing section  208 , an MPTS switch  209 , an N number of time division multiplexers (hereinafter, referred to as TDMs)  210 - 1  to  210 - n , an Ethernet switch  212 , and an N number of transceivers  211 - 1  to  211 - n . The wavelength division multiplexing demultiplexer  207  divides signals by wavelength, and the STM demultiplexing section  208  STM demultiplexes the wavelength division demultiplexed broadcasting signal to classify the demultiplexed signals into respective digital broadcasting signals. The multiple program transport stream (MPTS) switch  209  receives the digital broadcasting signals classified by the STM demultiplexing section  208  and switches a predetermined number of broadcasting signals to each SIU according to a control signal of the SIU. Each of the TDMs  210 - 1  to  210 - n  time division multiplexes the predetermined number of switched broadcasting signals into one signal so as to transmit the multiplexed signals to each SIU. The Ethernet switch  212  switches the wavelength division demultiplexed downstream Ethernet signals to respective SIUs, transmit channel selection information contained in the upstream Ethernet signal from each SIU to the MPTS switch  209 , and transmit other upstream Ethernet signals to the OLT  100 . Each of the transceivers  211 - 1  to  211 - n  transmit the broadcasting signal and the Ethernet signal switched according to each SIU, and receives an Ethernet signal including a broadcasting selection signal from each SIU. 
     Each of the SIUs  700 - 1  to  700 - n  includes a transceiver  213 , a time division demultiplexer (hereinafter, referred to as a TDDM)  214 , and an Ethernet switch  215 . The transceiver  213  receives the broadcasting signal and the Ethernet signal from the ONU  600 , and transmits the upstream Ethernet signal having channel selection information and a communication signal generated by a subscriber. The TDDM  214  time division demultiplexes the broadcasting signal from the ONU  600  so as to classify the demultiplexed signals into respective broadcasting signals, and transmits the broadcasting signals to an STB  300  of the subscriber. The Ethernet switch  215  receives the channel selection information from the STB  300  of the subscriber and the Ethernet signal from an Internet/personal computer (hereinafter, referred to as a PC)  400 , transmits the received channel selection information and the Ethernet signal to the ONU  600  through the transceiver  213 , and transmit Ethernet information from the ONU  600 , which has been sent through the transceiver  213 , to the STB  300  of the subscriber or the Internet/PC  400 . 
     Hereinafter, an operation in the FTTH network according to the present invention will be described, in comparison with the conventional FTTH network for convergence of broadcasting and communication employing an overlay method. In the prior art, all broadcasting signals are transmitted to respective ONTs. In contrast, in the present invention, all broadcasting signals are transmitted up to the ONU  600 , the channel selection information is received from each SIU, and only a broadcasting signal of a channel selected through switching using the channel selection information is transmitted to the SIU. 
     Therefore, there exists an upstream signal for a broadcasting selection from the SIU, so that an interactive broadcasting service, which is a characteristic of a digital broadcasting, can be performed through the upstream signal. That is, since the channel selection information and information for the interactive broadcasting is simultaneously transmitted, the interactive broadcasting service can be performed. 
     As described above, since the ONU  600  performs the switching for the broadcasting, an authentication and accounting system such as a CAS may be mounted on the ONU  600  and the ONU  600  may perform the switching. Therefore, the ONU  600  may perform an authentication and accounting operation. 
       FIG. 3  is a block diagram showing the ONU and the SIU in the FTTH network for convergence of broadcasting and communication through the switched broadcasting according to one embodiment of the present invention. 
       FIG. 3  is a block diagram showing a construction formed when triplex transceivers are respectively used in the ONU and the SIU in the FTTH network for convergence of broadcasting and communication through the switched broadcasting according to the present invention in  FIG. 2 . 
     As shown in  FIG. 3 , the ONU  600  includes the STM demultiplexing section (not shown), the multiple program transport stream (MPTS) switch  209 , the TDMs  210 - 1  to  210 - n , the Ethernet switch  212 , and the N number of transceivers  211 - 1  to  211 - n . The STM demultiplexing section divides broadcasting signals from the OLT  100 , which are wavelength division multiplexed by the wavelength division multiplexing demultiplexer (not shown) for wavelength division demultiplexing and dividing signals by wavelength, into respective digital broadcast signals. The MPTS switch  209  switches a predetermined number of broadcast signals of the broadcast signals input according to the SIU by a control signal (i.e., channel selection information) from the Ethernet switch  212 . Each of the TDMs  210 - 1  to  210 - n  time division multiplexes the broadcast signals, which have been switched by the MPTS switch  209  according to respective SIUs, into one signal, so as to transmit the multiplexed signal to a corresponding SIU. The Ethernet switch  212  switches the wavelength division demultiplexed downstream Ethernet signals from the OLT  100  to a corresponding SIU, transmits the channel selection information contained in the upstream Ethernet signal from each SIU to the MPTS switch  209 , and transmits other upstream Ethernet signals to the OLT  100 . Each of the transceivers  211 - 1  to  211 - n  transmits the broadcasting signal and the downstream Ethernet signal switched according to each SIU, and receives an upstream Ethernet signal including the channel selection information from each SIU. 
     Herein, each of the transceivers  211 - 1  to  211 - n  utilizes a triplex transceiver including two laser diodes (hereinafter, referred to as LDs)  301  and  302  for downstream transmission and one photo diode (hereinafter, referred to as a PD)  303  for reception. The two LDs  301  and  302  process the broadcast signal and the Ethernet signal, and the PD  303  receives the upstream Ethernet signal. In other words, the broadcast signal and the Ethernet signal are transmitted to the SIU as optical signals having different frequencies. Further, the SIU uses a triplex transceiver including two PDs  306  and  307  for receiving the broadcast signal and the Ethernet signal and one LD  308  for transmitting the upstream Ethernet signal. 
     Each of the SIUs  700 - 1  to  700 - n  includes a transceiver  213 , a time division demultiplexer (TDDM)  214 , and an Ethernet switch  215 . The transceiver  213  receives the broadcast signal and the Ethernet signal from the ONU  600  and transmits the upstream Ethernet signal, which has channel selection information, generated by subscriber. The TDDM  214  time division demultiplexes the broadcast signal from the ONU  600  so as to classify the demultiplexed signals into respective broadcast signals, and transmits the broadcast signals to the STB  300  of the subscriber. The Ethernet switch  215  receives the channel selection information from the STB  300  of the subscriber and the Ethernet signal from the Internet/PC  400 , transmits the received channel selection information and the Ethernet signal to the ONU  600  through the transceiver  213 , and transmits Ethernet information from the ONU  600 , which has been sent through the transceiver  213 , to the STB  300  of the subscriber or the Internet/PC  400 . 
     Hereinafter, an operation in the FTTH will be described. First, N channels of MPTS signals, which are broadcast signals, are switched by the MPTS switch  209  according to channels required by the SIUs  700 - 1  to  700 - n , and the switched signals are transmitted to the TDMs  210 - 1  to  210 - n . At this time, each of the TDMs  210 - 1  to  210 - n  time division multiplexes broadcast channel signals (e.g.,  2  or  3  channel signals) to be transmitted to each SIU according to a specification, and the LD  301  converts the multiplexed channel signals into an optical signal. 
     Meanwhile, the Ethernet signal from the OLT  100  transmitted to the ONU  600  is then transmitted to the LD  302  via the Ethernet switch  212 , and the LD  302  converts the Ethernet signal into an optical signal. 
     Further, the optical signal converted by the LD  301  and the optical signal converted by the LD  302  are combined into one signal through a wavelength division multiplexing coupler WDM  304 . The combined optical signal passes an optical fiber and passes through a wavelength division multiplexing coupler WDM  305  in the SIU  700 - 1  to  700 - n . The wavelength division multiplexing coupler WDM  305  transmits the optical signal to the PDs  306  and  307 , and the PDs  306  and  307  convert the optical signals into electrical signals. 
     Further, the broadcast signal converted by the PD  306  is input to the TDDM  214 , and the TDDM  214  time division demultiplexes the broadcast signal so as to classify the demultiplexed signal according to channels. Then, the TDDM  214  transmits the classified signals to the STB  300 . Further, the Ethernet signal converted by the PD  307  is used to provide an Ethernet service such as an Internet or VOD via the Ethernet switch  215 . Also, information for an interactive broadcasting service can be transmitted to the STB  300 . 
     Herein, when the STB  300  receives a request for a digital broadcast channel change, the STB  300  transmits an Ethernet signal including a channel change protocol (hereinafter, referred to as a CCP) to the ONU  600  through the LD  308 . Then, the ONU  600  performs photoelectric conversion for the Ethernet signal in the PD  303  and transmits the converted signal to the MPTS switch  209  through the Ethernet switch  212  to switch the signal to a desired channel, thereby achieving the channel change. 
       FIG. 4  is a block diagram showing the ONU and the SIU in the FTTH network for convergence of broadcast and communication signals through the switched broadcasting according to another aspect of the present invention. 
     As shown in  FIG. 4 , a structure formed when diplex transceivers are respectively used in the ONU and the SIU in the FTTH network for the convergence of broadcast and communications through the switched broadcasting according to the present invention as illustrated in  FIG. 2 . 
     As shown in  FIG. 4 , the ONU  600  includes the STM demultiplexing section (not shown), the MPTS switch  209 , the Ethernet switch  212 , the TDMs  210 - 1  to  210 - n , and the N number of transceivers  211 - 1  to  211 - n . The STM demultiplexing section divides broadcast signals, which are wavelength division multiplexed by the wavelength division multiplexing demultiplexer (not shown) for wavelength division demultiplexing and dividing signals by wavelength, into a predetermined number of digital broadcast signals. The MPTS switch  209  switches the broadcast signals according to the SIU by a control signal (i.e., channel selection signal) from the Ethernet switch  212 . The Ethernet switch  212  switches the wavelength division demultiplexed downstream Ethernet signals to a corresponding SIU, transmits the channel selection information contained in the upstream Ethernet signal from each SIU to the MPTS switch  209 , and transmits other upstream Ethernet signals to the OLT  100 . Each of the TDMs  210 - 1  to  210 - n  time division multiplexes the broadcast signal, which has been switched by the MPTS switch  209  according to each SIU, and the downstream Ethernet signal, which has been switched by the MPTS switch  209  into one signal so as to transmit the multiplexed signal to a corresponding SIU. Each of the transceivers  211 - 1  to  211 - n  transmits the broadcast signal and the downstream Ethernet signal, which have been time division multiplexed into one signal, to each SIU, and receives an Ethernet signal including the channel selection signal from each SIU. 
     Herein, each of the transceivers  211 - 1  to  211 - n  uses a diplex transceiver including one LD  401  for downstream transmission and one PD  402  for reception. In the present invention, in order to transmit both the broadcast signal and the Ethernet signal to the LD  401 , the Ethernet signal and the broadcasting signal are time division multiplexed into one signal. An example of the multiplexed signal as described above is shown in  FIG. 5 , wherein  501  is MPTS # 1 ,  502  is the MPTS # 2 ,  503  is the MPTS # 3 , and  504  is the high speed Ethernet signal. 
     Referring back to  FIG. 4 , each of the SIUs  700 - 1  to  700 - n  includes a transceiver  213 , a TDDM  214 , and an Ethernet switch  215 . The transceiver  213  receives the broadcast signal and the Ethernet signal as a single time division multiplexed signal from the ONU  600 , and transmits the Ethernet signal having a channel selection signal and a communication signal generated by a subscriber to the ONU  600 . The TDDM  214  time division demultiplexes the broadcast signal and the Ethernet signal from the ONU  600  so as to classify the demultiplexed signals into broadcast signals and Ethernet signals respectively. Further, the TDDM  214  transmits the broadcast signal to the STB  300  of the subscriber and transmits the Ethernet signal to the Ethernet switch  215 . The Ethernet switch  215  receives the channel selection information from the STB  300  of the subscriber and the Ethernet signal for communication from the Internet/PC  400 , transmits the received channel selection information and the Ethernet signal to the ONU  600  through the transceiver  213 , and transmits Ethernet information from the ONU  600 , which has been sent through the TDDM  214 , to the STB  300  of the subscriber or the Internet/PC  400 . 
     Hereinafter, an operation in the FTTH will be described. Firstly, N channels of MPTS signals, which are broadcast signals, are switched by the MPTS switch  209  according to channels required by the SIUs  700 - 1  to  700 - n , and the switched signals are transmitted to the TDMs  210 - 1  to  210 - n . Further, the Ethernet signal transmitted to the ONU  600  is transmitted to the TDMs  210 - 1  to  210 - n  via the Ethernet switch  212 . At this time, each of the TDMs  210 - 1  to  210 - n  time division multiplexes a predetermined number of broadcast signals switched according to each SIU and the Ethernet signal, and the LD  401  converts the multiplexed signal into an optical signal. 
     The converted signal passes an optical fiber and passes through a wavelength division multiplexing coupler  404  in the SIU  700 - 1  to  700 - n . The wavelength division multiplexing coupler WDM  404  transmits the optical signal to the PD  405 , and the PD  405  converts the optical signals into an electrical signal. 
     Further, the signal converted by the PD  405  is inputted to the TDDM  214 , and the TDDM  214  time division demultiplexes the signal. The TDDM  214  classifies the demultiplexed broadcast signal according to channels so as to transmit the classified broadcast signals to the STB  300 . Also, the TDDM  214  transmits the Ethernet signal to the Ethernet switch  215 . Further, the Ethernet signal is used in providing an Ethernet service such as an Internet or VOD via the Ethernet switch  215 . Also, information for an interactive broadcasting service can be transmitted from the Ethernet switch  215  to the STB  300 . 
     Herein, when the STB  300  receives a request for a digital broadcast channel change, the STB  300  transmits an Ethernet signal including a CCP to the ONU  600  through the LD  406 . Further, the ONU  600  performs photoelectric conversion for the Ethernet signal in the PD  402  and transmits the converted signal to the MPTS switch  209  through the Ethernet switch  212  to switch a channel to a desired channel, thereby achieving the channel change. 
       FIG. 5  provides an exemplary view of a signal time division multiplexed according to the aspect of the invention described in reference to  FIG. 4 . 
     As shown in  FIG. 5 , a time slot having the broadcast signal and the Ethernet signal transmitted from the ONU  600  to the SIUs  700 - 1  to  700 - n  includes a predetermined number of broadcast channels  501  to  503  and Ethernet information  504  set in advance. 
     In these aspects of the invention, since a construction of transmitting an Ethernet signal to an STB of a subscriber is for an interactive television, the construction may be omitted without affecting the scope of the present invention. 
     According to the present invention as described above, a service is provided to subscribers grouped in a unit of an ONU in an FTTH network for convergence of broadcast and communications signals, so that the number of subscribers is not limited by a bandwidth. 
     Further, according to the present invention, an ONU in an FTTH network performs switching for broadcasting so as to transmit only the broadcast information switched to each subscriber, so that a bandwidth can be more efficiently used. 
     Further, according to the present invention, an ONU in an FTTH network performs switching for broadcasting and transmits only broadcast information switched to each subscriber, so that the ONU can perform a subscriber authentication and a real time accounting by a CAS supporting encryption and decryption. Therefore, the present invention allows an STB of a subscriber to be liberated from constructing the complicated CAS. 
     Further, according to the present invention, since all channels are not transmitted to each subscriber, a low priced light source operating at a low speed can be used without using an expensive light source for increasing a transmission speed. Therefore, the construction costs for the network can be reduced. 
     While the invention has been shown and described with reference to certain preferred aspects thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.