Abstract:
A relaying method of an optical signal of a hybrid relaying apparatus in a gigabit passive optical element includes: selecting and receiving any one of a first serial electrical signal corresponding to a downlink wavelength division multiplexing-passive optical line terminal (WDM-PON OLT) optical signal and a second serial electrical signal corresponding to a downlink gigabit passive optical network optical line terminal (GPON OLT) optical signal; modulating the downlink serial electrical signal to a downlink GPON transmission convergence (GTC) frame; extracting control information for uplink transmission from the downlink GTC frame; converting the downlink GTC frame into the downlink serial electrical signal; and converting the converted serial electrical signal into an optical signal and transmitting the converted optical signal in a GPON OLT optical transceiver.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2009-0119957 filed in the Korean Intellectual Property Office on Dec. 4, 2009, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to a relaying apparatus in a gigabit passive optical network and a relaying method using the same. 
         [0004]    (b) Description of the Related Art 
         [0005]    A passive optical network (PON) technology is one of fiber to the home (FTTH) technologies proposed to effectively supply a bandwidth required for a subscriber terminal. The PON technology is classified into TDM-PON using a time division multiplexing (TDM) method and WDM-PON using a wavelength division multiplexing (WDM) method. The TDM-PON includes broadband PON (BPON), Ethernet PON (EPON), and gigabit PON (GPON), as examples. The BPON provides an asynchronous transfer mode (ATM) service as a method that is standardized by the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) G.983.x. The BPON is not suitable for an internet protocol (IP)-based service, and provides a bandwidth of 622 Mb/s (megabits per second) at a maximum. The EPON provides only an Ethernet service as a method that is standardized by the Institute of Electrical and Electronics Engineers (IEEE) 802.3ah. The EPON provides a bandwidth of the maximum uplink/downlink of 1.25 Gb/s (gigabits per second). The GPON provides a maximum uplink bandwidth of 1.244 Gb/s and a downlink bandwidth of 2.488 Gb/s as a method that is standardized by the ITU-T G.984.x in order to solve a problem of the bandwidth of the BPON and receive various multi-protocols, for example, ATM, TDM (time division multiplexing), and Ethernet service. In recent years, an optical network has been required to provide a bandwidth of 1 Gb/s or more in order to provide various multimedia contents, for example, IPTV (IP television), VoD (video on demand), games, etc. to subscribers, and the GPON satisfying this is in the limelight. 
         [0006]    The GPON can service a maximum transmission distance of 20 Km as a point to multipoint network structure to share one optical line terminal (OLT) through a splitter in which 64 optical network units (ONUs) are passive elements. In general, the OLT is positioned at a central office and the ONU is positioned in a subscriber&#39;s home or a subscriber&#39;s terminal box. In the GPON, since a plurality of subscribers share the bandwidth through a time domain, the bandwidth that the subscribers can use is reduced as the number of subscribers increases. Accordingly, the GPON is suitable for a small-sized network and is not suitable for a large-sized network having hundreds of subscribers or more. 
         [0007]    In recent years, as extension of a service area has been an issue, a method that is capable of servicing a transmission distance of 60 Km has been evaluated. For this, the long-reach PON (LR-PON) based on the GPON, which provides a long-reach service to a remote node of a trunk optical fiber section by using an active element-based relaying apparatus, has been standardized in the ITU-T G.984.6. In the LR-PON, since the number of central offices can be reduced, it is possible to save management and maintenance costs of the network. 
         [0008]    Meanwhile, the WDM-PON that is one of the PON technologies provides service to subscribers in different wavelengths. Since a bandwidth of 1 Gb/s per wavelength is provided, each subscriber can receive a bandwidth of 1 Gb/s. However, since there are few services using a wide bandwidth, the WDM-PON has comparatively poorer bandwidth using efficiency than the GPON. Further, since the WDM-PON has light sources (laser diode, LD) having different wavelengths for each subscriber, the implementation cost of the WDM-PON is high and it is difficult to manage the WDM-PON. 
         [0009]    Therefore, a hybrid GPON structure applying the WDM-PON to a relaying trunk network section of the GPON is being researched. In the hybrid GPON, optical signals having a single wavelength outputted from each OLT port are converted into a plurality of wavelengths through the WDM-PON and transmitted through a long-reach single trunk optical fiber. Each of the transmitted optical signals are separated from the remote node and thereafter converted into an optical signal having a single wavelength and transmitted to the ONUs. That is, ONUs of a maximum 64 branches can receive the single wavelength. Accordingly, the hybrid GPON can solve a problem in the bandwidth using efficiency of the WDM-PON and can provide a service to a large number of subscribers by using the single trunk optical fiber. Further, since different light sources are used for each ONU group, it is possible to save implementation cost of a large-scale network at the time of implementing the large-scale network. Accordingly, the hybrid GPON is suitable for construction of a large-scale network and long-reach transmission. 
         [0010]      FIG. 1  is a diagram showing a known wavelength division multiplexing/time division multiplexing (WDM/TDM) hybrid optical network. 
         [0011]    Referring to  FIG. 1 , the WDM/TDM hybrid optical network includes TDM-PONs  100 ,  130 , and  140 , a hybrid OLT  110 , and a hybrid relaying apparatus  120 . The TDM-PON includes a TDM-PON OLT  100 , a splitter  130 , and a TDM-PON ONU  140 . The TDM-PON includes N TDM-PON OLTs  100  and N splitters  130  corresponding thereto, and includes a plurality of TDM-PON ONUs  140  branched from each splitter  130 . The hybrid OLT  110  includes a TDM-PON optical transceiver (TDM-PON TRx)  111 , a WDM-TDM matcher (WTA)  112 , a WDM-PON optical transceiver (WDM-PON TRx)  113 , and a WDM wavelength branching multiplexer (WDM MUX)  114 . Each of the TDM-PON optical transceiver  111 , the WDM-TDM matcher  112 , and the WDM-PON optical transceiver  113  of the hybrid OLT  110  may be provided in N numbers to correspond to N TDM-PON OLTs  100 . The hybrid relaying apparatus  120  includes a WDM wavelength branching multiplexer (WDM MUX)  124 , a WDM-PON optical transceiver (WDM-PON TRx)  123 , a WDM-TDM matcher (WTA)  122 , and a TDM-PON optical transceiver (TDM-PON TRx)  121 . Each of the TDM-PON optical transceiver  123 , the WDM-TDM matcher  122 , and the TDM-PON optical transceiver  121  of the hybrid relaying apparatus  120  may be provided in N numbers to correspond to N TDM-PON OLTs  100 . The hybrid OLT  110  may be positioned at the central office and the hybrid relaying apparatus  120  may be positioned at the remote node RN. The hybrid OLT  110  and the hybrid relaying apparatus  120  enable long-reach transmission and high branching in comparison with the known TDM-PON, for example, the GPON. 
         [0012]    In downlink transmission, an optical signal of λ dT  is transmitted to the TDM-PON optical transceiver  111  of the hybrid OLT  110  from the TDM-PON OLT  100  and is converted into an electrical signal, and the WDM-TDM matcher  112  matches the electrical signal with the WDM-PON optical transceiver  113 . N WDM-PON optical transceivers  113  generate optical signals having different wavelengths λ d1 , λ d2 , . . . , λ dN  from the electrical signal, and one WDM wavelength branching multiplexer  114  connected with N WDM-PON optical transceivers  113  multiplexes the optical signals having different wavelengths and transmits them to the hybrid relaying apparatus  120 . The WDM wavelength branching multiplexer  124  of the hybrid relaying apparatus  120  branches the optical signals having different wavelengths. N WDM-PON optical transceivers  123  convert the optical signals having different wavelengths into the electrical signal, and the WDM-TDM matcher  122  matches the electrical signal with the TDM-PON optical transceiver  121 . The TDM-PON optical transceiver  121  converts the electrical signal into the optical signal of λ dT . The splitter  130  transmits the optical signal of λ dT  to the plurality of TDM-PON ONUs  140  branched from the splitter  130 . 
         [0013]    In uplink transmission, an optical signal of λu T  is transmitted to the TDM-PON optical transceiver  121  of the hybrid relaying apparatus  120  from the TDM-PON ONU  140  and is converted into the electrical signal, and the WDM-TDM matcher  122  matches the electrical signal with the WDM-PON optical transceiver  123 . N WDM-PON optical transceivers  123  generate optical signals having different wavelengths λ u1 , λ u2 , . . . , λ uN  from the electrical signal, and the WDM wavelength branching multiplexer  124  multiplexes the optical signals having different wavelengths and transmits them to the hybrid OLT  110 . The WDM wavelength branching multiplexer  114  of the hybrid OLT  110  branches the optical signals having different wavelengths. N WDM-PON optical transceivers  113  convert the optical signals having different wavelengths into the electrical signal, and the WDM-TDM matcher  112  matches the electrical signal with the TDM-PON optical transceiver  111 . The TDM-PON optical transceiver  111  converts the electrical signal into the optical signal of λ UT . The optical signal of λ uT  is transmitted to the TDM-PON OLT  100 . 
         [0014]    The WDM/TDM hybrid optical network shown in  FIG. 1  enables a high branching rate and long-reach transmission in comparison with the TDM-PON or WDM-PON. However, the optical signal that the TDM-PON ONU  140  uplink-transmits is transmitted in a burst in accordance with the TDM method. Therefore, the hybrid relaying apparatus  120  needs a control signal for converting a burst optical signal into the electrical signal. Further, in the section using the WDM-PON technology, the optical signal is continuously transmitted, but when the optical signal is transmitted in the burst like the known WDM-TDM hybrid optical network, an error may be generated. Further, since the WDM-TDM matcher  122  of the hybrid relaying apparatus  120  provides only a matching function using the electrical signal, an additional device and an additional channel are required to collect state monitoring information of the TDM-PON optical transceiver  121  and the WDM-PON optical transceiver  123  of the hybrid relaying apparatus  120 . System complexity is increased due to the additional device and channel. 
         [0015]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY OF THE INVENTION 
       [0016]    The present invention has been made in an effort to provide a relaying apparatus for providing high branching and long-reach transmission in a gigabit passive optical network, and a relaying method using the same. 
         [0017]    An exemplary embodiment of the present invention provides a relaying method of an optical signal in a hybrid relaying apparatus of a gigabit passive optical element including: selecting and receiving a first downlink electrical signal corresponding to a downlink wavelength division multiplexing-passive optical line terminal (WDM-PON OLT) optical signal and a second downlink electrical signal corresponding to a downlink gigabit passive optical network optical line terminal (GPON OLT) optical signal; modulating the downlink electrical signal to a downlink GPON transmission convergence (GTC) frame; extracting control information for uplink transmission from the downlink GTC frame; converting the downlink GTC frame into the downlink electrical signal; converting the converted downlink electrical signal into an optical signal in a GPON OLT optical transceiver; and transmitting the converted optical signal to a GPON ONU. 
         [0018]    The relaying method of an optical signal may further include: extracting an uplink burst optical signal by using the extracted control information, converting the extracted burst optical signal into the serial electrical signal, modulating an uplink GTC frame from a burst electrical signal, converting the modulated burst GTC frame into a continuous GTC frame, converting the continuous GTC frame into an electrical signal, and converting the converted electrical signal into the selected OLT optical signal. 
         [0019]    Another embodiment of the present invention provides a hybrid relaying apparatus in a gigabit passive optical network including: a GPON framer modulating any one of a first downlink electrical signal corresponding to a downlink wavelength division multiplexing-passive optical line terminal (WDM-PON OLT) optical signal and a second downlink electrical signal corresponding to a downlink gigabit passive optical network optical line terminal (GPON OLT) optical signal to a downlink GPON transmission convergence (GTC) frame, extracting control information for uplink transmission from the downlink GTC frame, and converting the downlink GTC frame into an electrical signal or extracting a burst uplink GTC frame by using extracted control information and converting the extracted frame into a continuous GTC frame; and a GPON OLT optical transceiver converting the converted electrical signal into an optical signal. 
         [0020]    According to an embodiment of the present invention, a relaying apparatus provides high branching and a long-reach service. Further, control information is extracted from a signal in downlink transmission to be used for uplink transmission, and the state of an optical transceiver in the relaying apparatus may be transmitted to a central office without an additional channel or device. In addition, the relaying apparatus according to the embodiment of the present invention may be used as a WDM/GPON hybrid relaying apparatus using WDM-PON in a trunk optical fiber section or used as a GPON reach extender in accordance with a relaying mode. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a diagram showing a known wavelength division multiplexing/time division multiplexing (WDM/TDM) hybrid optical network; 
           [0022]      FIG. 2  is a diagram showing a hybrid optical network according to an embodiment of the present invention; 
           [0023]      FIG. 3  is a detailed block diagram of a hybrid relaying apparatus  600  according to an embodiment of the present invention; 
           [0024]      FIG. 4  is a flowchart illustrating a downlink transmission method of a hybrid relaying apparatus  600  according to an embodiment of the present invention; 
           [0025]      FIG. 5  is a flowchart illustrating an uplink transmission method of a hybrid relaying apparatus  600  according to an embodiment of the present invention; 
           [0026]      FIG. 6  is a diagram illustrating an output of a relaying mode control signal for selecting a relaying mode of a hybrid relaying apparatus  600  according to an embodiment of the present invention; 
           [0027]      FIG. 7  is a block diagram illustrating a structure of a GPON framer  650  according to an embodiment of the present invention; 
           [0028]      FIG. 8  is a flowchart illustrating a processing method of a downlink signal passing through a GPON framer  650 ; 
           [0029]      FIG. 9  is a flowchart illustrating a processing method of an uplink signal passing through a GPON framer  650 ; 
           [0030]      FIG. 10  is a diagram illustrating processing of an uplink GTC frame according to an embodiment of the present invention; and 
           [0031]      FIG. 11  illustrates a method for monitoring states of optical transceivers in a hybrid relaying apparatus  600  according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0032]    In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
         [0033]    In the specification, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
         [0034]      FIG. 2  is a diagram showing a hybrid optical network according to an embodiment of the present invention. 
         [0035]    Referring to  FIG. 2 , the hybrid optical network includes a GPON system  200 , a hybrid OLT  300 , and a hybrid relaying apparatus  400 . The GPON system  100  includes N GPON OLTs  210 , N splitters  220  corresponding thereof, and a plurality of GPON ONUs  230  branched from each splitter  220 . Each splitter  220 , for example, may have 64 branches. The hybrid OLT  300  includes a GPON ONU optical transceiver (GPON ONU TRx)  310 , an OLT relaying apparatus  320 , a WDM-PON OLT optical transceiver (WDM-PON OLT TRx)  330 , a MUX/DEMUX device  340 , and a seed light source device  350 . The hybrid relaying apparatus  400  includes an arrayed waveguide grating (AWG)  440 , a WDM-PON ONU optical transceiver (WDM-PON ONU TRx)  430 , a GPON framer  420 , and a GPON OLT optical transceiver (GPON OLT TRx)  410 . N GPON OLTs  210  and the hybrid OLT  300  may be positioned at a central office, and the hybrid relaying apparatus  400  may be positioned at a remote node. 
         [0036]    The hybrid OLT  300  uses GPON ONU optical transceivers  310 , OLT relaying apparatuses  320 , and WDM-PON OLT optical transceivers  330  of the same number (i.e., N) as the GPON OLT  210  in order to adopt the WDM-PON technology without changing a hardware device of the GPON system  200 . The GPON ONU optical transceiver  310  is, one to one, connected with the WDM-PON OLT optical transceiver  330  through the OLT relaying apparatus  320 . The GPON ONU optical transceiver  310  is connected with the GPON OLT  210  corresponding thereto through an optical line. The GPON ONU optical transceiver  310  converts an optical signal of λ dT  transmitted from the GPON OLT  210  and transmits the electrical signal to the WDM-PON OLT optical transceiver  330 , or converts the electrical signal transmitted from the WDM-PON OLT optical transceiver  330  into an optical signal of λ uT  and transmits the optical signal to the GPON OLT  210 . The OLT relaying apparatus  320  relays the electrical signal between the GPON ONU optical transceiver  310  and the WDM-PON OLT optical transceiver  330 . N WDM-PON OLT optical transceivers  330  convert the electrical signals received from the GPON ONU optical transceivers  310  corresponding thereto into optical signals having different wavelengths λ d1 , . . . , λ dN  or convert optical signals having different wavelengths λ u1 , . . . , λ uN  into electrical signals and transmit the electrical signals to the corresponding GPON ONU optical transceivers  310 . The seed light source device  350  generates an independent wavelength to be used to generate optical signals having different wavelengths in N WDM-PON OLT optical transceivers  330 . The MUX/DEMUX device  340  multiplexes the optical signals λ d1 , . . . , λ dN  received from N WDM-PON OLT optical transceivers  330 , or demultiplexes the multiplexed optical signals λ u1 , . . . , λ uN  and may transmit them to N WDM-PON OLT optical transceivers  330 . 
         [0037]    The optical signals λ d1 , . . . , λ dN  having different wavelengths are multiplexed in the MUX/DEMUX device  340 , and thereafter are transmitted to the hybrid relaying apparatus  400  through a trunk optical fiber  500 . Further, the multiplexed optical signals λ u1 , . . . , λ uN  having different wavelengths transmitted from the hybrid relaying apparatus  220  through the trunk optical fiber  500  are demultiplexed in the MUX/DEMUX device  340 . A section of the trunk optical fiber  500  may have a long range of 30 Km. When the WDM technology is applied to the trunk optical fiber section, as many trunk optical fibers as the number of wavelengths are not used but one trunk optical fiber is used, thereby saving network construction cost. 
         [0038]    The hybrid relaying apparatus  400  uses the WDM-PON ONU optical transceiver  430  and the GPON OLT optical transceiver  410  corresponding to the GPON OLT  210 , and the WDM-PON ONU optical transceiver  430  and the GPON OLT optical transceiver  410  are connected with the GPON framer  420 . The arrayed waveguide grating (AWG)  440  selects a predetermined wavelength from the optical signal transmitted through the trunk optical fiber  500 . The optical signal having the predetermined wavelength is transmitted to the corresponding GPON ONU  230  through the corresponding WDM-PON ONU optical transceiver  430 , the GPON framer  420 , the GPON OLT optical transceiver  410 , and the splitter  220 . That is, the hybrid relaying apparatus  400  converts one optical signal among the optical signals having different wavelengths in the trunk optical fiber  500  into a downlink wavelength of the GPON OLT  210 , or converts an uplink wavelength of the GPON ONU  230  to a predetermined wavelength. The GPON framer  420  performs re-amplify, re-shape, and re-time (3R) optical-electrical-optical conversion for the signal received from the GPON OLT optical transceiver  410  or the WDN-PON ONU optical transceiver  430 . In the downlink transmission, the GPON framer  420  extracts control information from the downlink optical signal to be used for the uplink transmission. 
         [0039]    Herein, the WDM-PON OLT optical transceiver  330  and the WDM-PON ONU optical transceiver  430  may use, for example, a reflective semiconductor optical amplifier (RSOA) method, which is a wavelength utilizing method. According to the RSOA method, the WDM-PON ONU optical transceiver  430  of the hybrid relaying apparatus  400  remodulates the downlink-transmitted optical signal to be used for the uplink-transmitted optical signal. In this case, since the WDM-PON ONU optical transceiver  430  of the hybrid relaying apparatus  400  does not need an additional light source, the WDM-PON ONU optical transceiver  430  may be implemented independently to the wavelength. Consequently, since one kind of broad-spectrum light source (BLS) is installed at the central office, construction cost is saved. 
         [0040]      FIG. 3  is a detailed block diagram of a hybrid relaying apparatus  600  according to an embodiment of the present invention,  FIG. 4  is a flowchart illustrating a downlink transmission method of a hybrid relaying apparatus  600  according to an embodiment of the present invention, and  FIG. 5  is a flowchart illustrating an uplink transmission method of a hybrid relaying apparatus  600  according to an embodiment of the present invention. For convenience of description, it is assumed that N is 2 in  FIGS. 3 to 5 . 
         [0041]    Referring to  FIG. 3 , the hybrid relaying apparatus  600  includes GPON ONU optical transceivers  610 - 1  and  610 - 2 , WPON ONU optical transceivers  620 - 1  and  620 - 2 , serial signal selectors  630 - 1  and  630 - 2 , a control processor  640 , a GPON framer  650 , burst clock and data recoveries (CDRs)  660 - 1  and  660 - 2 , and GPON OLT optical transceivers  670 - 1  and  670 - 2 . 
         [0042]    Referring to  FIGS. 3 and 4 , the GPON ONU optical transceivers  610 - 1  and  610 - 2  convert the optical signal received from the GPON OLT  210  positioned at the central office into a serial electrical signal and transmit the serial electrical signal to the serial signal selectors  630 - 1  and  630 - 2  (S 400 ). The WDM-PON ONU optical transceivers  620 - 1  and  620 - 2  convert the optical signal received from the GPON OLT  210  positioned at the central office through the GPON ONU optical transceiver  310 , the WDM-PON OLT optical transceiver  330 , and the AWG  440  into the serial electrical signal, and transmit the serial electrical signal to the serial signal selectors  630 - 1  and  630 - 2  (S 410 ). 
         [0043]    The serial signal selectors  630 - 1  and  630 - 2  select the serial electrical signal transmitted from the GPON ONU optical transceivers  610 - 1  and  610 - 2  or select the serial electrical signal transmitted from the WDM-PON ONU optical transceivers  620 - 1  and  620 - 2  depending on a relaying mode (S 420 ), and transmit the selected serial electrical signal to the GPON frame  650  (S 430 ). The hybrid relaying apparatus  600  may take a GPON relaying mode or a WDM-PON relaying mode. When the hybrid relaying apparatus  600  takes the GPON relaying mode, the serial signal selectors  630 - 1  and  630 - 2  select the serial electrical signal transmitted from the GPON ONU optical transceivers  610 - 1  and  610 - 2 . At this time, the hybrid relaying apparatus  600  may be used as a GPON reach extender of the re-amplify, re-shape, and re-time (3R) optical-electrical-optical converting method according to the ITU-T G.984.6 standard. When the hybrid relaying apparatus  600  takes the WDM-PON relaying mode, the serial signal selectors  630 - 1  and  630 - 2  select the serial electrical signal transmitted from the WDM-PON ONU optical transceivers  620 - 1  and  620 - 2 . At this time, the hybrid relaying apparatus  600  may be used as the WDM-PON-based hybrid relaying apparatus adopting the WDM technology in the trunk optical fiber section. The serial signal selectors  630 - 1  and  630 - 2  may select the serial electrical signal depending on the relaying mode by selecting, for example “0” or “1”. The relaying mode may be determined by the central office. For example, the relaying mode may be remotely determined by the control signal received from the central office. Further, the relaying mode may be determined by a network provider. 
         [0044]    The GPON framer  650  converts the serial electrical signal into a parallel signal (S 440 ) and modulates the parallel signal to a GPON transmission convergence (GTC) frame to extract the control information (S 450 ). After the control information is extracted, the GPON framer  650  converts a downlink GTC frame into the serial electrical signal again (S 460 ). The control information may include uplink band allocation information, for example, information on an estimated arrival time of the uplink GTC frame. Further, the control information may include information relating to the burst control signal requiring the GPON OLT optical transceivers  670 - 1  and  670 - 2  and the burst CDRs  660 - 1  and  660 - 2  in the uplink transmission, for example, an effective section of the burst optical signal. 
         [0045]    The GPON framer  650  transmits the serial electrical signal to the GPON OLT optical transceivers  670 - 1  and  670 - 2  (S 470 ), and the GPON OLT optical transceivers  670 - 1  and  670 - 2  convert the serial electrical signal into the optical signal (S 480 ) and transmit the optical signal to the GPON ONU  230  through the splitter  220  (S 490 ). 
         [0046]    Referring to  FIGS. 3 and 5 , the GPON OLT optical transceivers  670 - 1  and  670 - 2  receives the burst optical signal from the GPON ONU  230  through the splitter  220  (S 500 ), and convert the burst optical signal into the serial electrical signal by using the control information received from the GPON framer  650  (S 510 ). The control information may include the information on the effective section of the burst optical signal. 
         [0047]    The GPON OLT optical transceivers  670 - 1  and  670 - 2  transmit the serial electrical signal to the burst CDRs  660 - 1  and  660 - 2  (S 520 ), and the burst CDRs  660 - 1  and  660 - 2  convert the serial electrical signal into a burst parallel electrical signal (S 530 ). At this time, the burst CDRs  660 - 1  and  660 - 2  may convert the serial electrical signal by using the control information received from the GPON framer  650 . 
         [0048]    The GPON framer  650  receives the burst parallel electrical signal from the burst CDRs  660 - 1  and  660 - 2  (S 540 ), modulates the burst parallel electrical signal to the uplink GTC frame (S 550 ), and processes the uplink GTC frame (S 560 ). That is, the GPON framer  650  converts the uplink GTC frame of a burst mode into the uplink GTC frame of a continuous mode. A section in the uplink GTC frame of the burst mode without data is filled with a preamble. Further, when the central office requests the state monitoring information of the hybrid relaying apparatus  600 , the GPON framer  650  inserts an OMCI packet into the uplink GTC frame in response thereto. For this, the GPON framer  650  needs to be ranged to the GPON OLT  210 . The GPON framer  650  converts the uplink GTC frame into the serial electrical signal (S 570 ) and transmits the serial electrical signal to the serial signal selectors  630 - 1  and  630 - 2  (S 580 ). 
         [0049]    The serial signal selectors  630 - 1  and  630 - 2  transmits the serial electrical signal to the GPON ONU optical transceivers  610 - 1  and  610 - 2  or the WDM-PON ONU optical transceivers  620 - 1  and  620 - 2  depending on the relaying mode (S 550 ). When the GPON relaying mode is taken, the serial signal selectors  630 - 1  and  630 - 2  transmit the serial electrical signal to the GPON ONU optical transceivers  610 - 1  and  610 - 2 . When the WDM-PON relaying mode is taken, the serial signal selectors  630 - 1  and  630 - 2  transmit the serial electrical signal to the WDM-PON ONU optical transceivers  620 - 1  and  620 - 2 . The serial signal selectors  630 - 1  and  630 - 2  may select the serial electrical signal depending on the relaying mode by selecting, for example “0” or “1”. 
         [0050]    The GPON ONU optical transceivers  610 - 1  and  610 - 2  or the WDM-PON ONU optical transceivers  620 - 1  and  620 - 2  convert the serial electrical signal into the optical signal and transmit the optical signal to the GPON OLT  210 . 
         [0051]      FIG. 6  is a diagram illustrating an output of a relaying mode control signal for selecting a relaying mode of a hybrid relaying apparatus  600  according to an embodiment of the present invention. 
         [0052]    In  FIG. 6 , for convenience of description, one serial signal selector  630  is shown, and it is assumed that in the serial signal selector  630 , two ports are provided in each of the uplink transmission and the downlink transmission and only one port of two ports is used. 
         [0053]    Referring to  FIG. 6 , the serial signal selector  630  includes a downlink selection unit  632  and a downlink selection unit  634 . The downlink selection unit  632  includes four transmission logic units  632   a ,  632   b ,  632   c , and  632   d  and two multiplexers  632   e  and  632   f , and the uplink selection unit  634  includes four transmission logic units  634   a ,  634   b ,  634   c , and  634   d  and two multiplexers  634   e  and  634   f . The transmission logic units  632   a  to  632   d  and  634   a  to  634   d  are logic units used to transmit the serial electrical signal, and for example, may be current mode logic (CML) units. 
         [0054]    The transmission logic unit  632   a  transmits the received GPON ONU serial electrical signal to input No. “0” of the multiplexers  632   e  and  632   f , and the transmission logic unit  632   b  transmits the received WDM-PON ONU serial electrical signal to input No. “1” of the multiplexers  632   e  and  632   f . The multiplexers  632   e  and  632   f  transmit the outputs to the transmission logic units  632   c  and  632   d , the transmission logic unit  632   c  transmits the downlink serial electrical signal corresponding to the output to the GPON framer  650 , and the transmission logic unit  632   d  transmits the downlink serial electrical signal corresponding to the output to the GPON framer  650  or the other device. 
         [0055]    The transmission logic unit  634   c  receives the uplink serial electrical signal from the GPON framer  650  and transmits the received uplink serial electrical signal to input No. “0” of the multiplexers  634   e  and  634   f , and the transmission logic unit  634   d  receives the uplink serial electrical signal from the GPON framer  650  or the other device and transmits the received uplink serial electrical signal to No. “1” of the multiplexers  634   e  and  634   f . The multiplexers  634   e  and  634   f  transmit the outputs to the transmission logic units  634   a  and  634   b , respectively, the transmission logic unit  634   a  outputs the output as the WDM-PON ONU serial electrical signal, and the transmission logic unit  634   b  outputs the output as the GPON ONU serial electrical signal. 
         [0056]    In this case, the multiplexers  632   e ,  632   f ,  634   e , and  634   f  operate in response to control signals SELA 0 , SELA 1 , SELB 0 , and SELB 1  and output a signal of input No. “1” when the corresponding control signals SELA 0 , SELA 1 , SELB 0 , and SELB 1  have a value of “1” and output a signal of input No. “0” when the corresponding signals have a value of “0”. The transmission logic units  632   a ,  632   b ,  632   c , and  632   d  operate in response to control signals ENA 0 , ENA 1 , ENB 0 , and ENB 1 , and output the input signal when the corresponding control signals ENA 0 , ENA 1 , ENB 0 , and ENB 1  have the value of “1” and interrupt the input signal when the corresponding control signals ENA 0 , ENA 1 , ENB 0 , and ENB 1  have the value of “0”. 
         [0057]    The GPON framer  650  transmits the control signals SELA 0 , SELA 1 , SELB 0 , SELB 1 , ENA 0 , ENA 1 , ENB 0 , and ENB 1  to the serial signal selector  630 . The control signals SELA 0 , SELA 1 , SELB 0 , SELB 1 , ENA 0 , ENA 1 , ENB 0 , and ENB 1  may be received from the central office. The central office can monitor the state of the hybrid relaying apparatus  600  through the OMCI packet inserted into the uplink GTC frame, and can select and direct a proper relaying mode. The central office can direct the relaying mode to the GPON framer  650  by using a mode switch or a control processor. 
         [0058]    The relaying mode control signal transmitted to the serial signal selector  630  is shown in Table 1. 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Relaying mode 
                 ENA0 
                 SELA0 
                 ENB0 
                 ENB1 
               
               
                   
               
             
             
               
                 WDM-PON relaying mode 
                 1 
                 1 
                 1 
                 0 
               
               
                 GPON relaying mode 
                 1 
                 0 
                 0 
                 1 
               
               
                   
               
             
          
         
       
     
         [0059]    In the downlink transmission, since one output port is not used, ENA 1  and SELA 1  output “0” at all times. In the uplink transmission, since one input port is not used, SELB 0  and SELB 1  output “0” at all times. 
         [0060]    When the control signal represents “1”, the serial signal selector  630  operates in the GPON relaying mode, and when the relaying mode control signal represents “0”, the serial signal selector  630  operates in the WDM-PON relaying mode. 
         [0061]      FIG. 7  is a block diagram illustrating a structure of a GPON framer  650  according to an embodiment of the present invention,  FIG. 8  is a flowchart illustrating a processing method of a downlink signal passing through a GPON framer  650 , and  FIG. 9  is a flowchart illustrating a processing method of an uplink signal passing through a GPON framer  650 . 
         [0062]    Referring to  FIG. 7 , the GPON framer  650  includes a reception I/O interface module  651 , a downlink GTC frame processing module  652 , an uplink GTC frame processing module  653 , a transmission I/O interface module  654 , and a SERDES module  655 . The reception I/O interface module  651  includes a clock generation unit  651 - 1 , data reception units  651 - 2  and  651 - 3 , and data transmission units  651 - 4  and  651 - 5 . The transmission I/O interface module  654  includes a clock generation unit  654 - 1 , data reception units  654 - 2  and  654 - 3 , and data transmission units  654 - 4  and  654 - 5 . 
         [0063]    Referring to  FIGS. 7 and 8 , the reception I/O interface module  651  receives a serial data signal of 2.488 Gb/s (S 800 ), and recovers data and a clock from the serial data signal (S 810 ). The reception I/O interface module  651  applies an external reference clock, i.e., 155.52 MHz, to the clock generation unit  651 - 1  in order to recover the serial data signal. The reception I/O interface module  651  extracts a parallel 16-bit data signal and a recovery clock, i.e., 155.52 MHz, by using the reference clock. Since the recovery clock is used in the GPON framer  650 , the recovery clock may also be an internal clock. 
         [0064]    The reception I/O interface module  651  transmits the recovery clock and the 16-bit data signal to the downlink GTC frame processing module  652  (S 820 ), and the downlink GTC frame processing module  652  demultiplexes the downlink GTC frame through the recovery clock and the 16-bit data signal and extracts the control information from the downlink GTC frame (S 830 ). 
         [0065]    The downlink GTC frame processing module  652  transmits the 16-bit data signal to the transmission I/O interface module  654  (S 840 ), and the transmission I/O interface module  654  converts the 16-bit data signal into the serial signal of 2.488 Gb/s and outputs the serial signal (S 850 ). At this time, since the transmission I/O interface module  654  uses only a data transmission unit, the clock generation unit  654 - 1  may a recovery clock rather than the reference clock. 
         [0066]    As such, in the downlink transmission, the GPON framer  650  of the hybrid relaying apparatus  600  recovers the data and clock by using the reference clock and downlink-transmits the data signal by using the recovery clock. 
         [0067]    Referring to  FIGS. 7 and 9 , the burst CDRs  660 - 1  and  660 - 2  receive the serial data signal of 1.244 Gb/s (S 900 ), and recovers the clock and data from the serial data signal (S 910 ). At this time, the burst CDRs  660 - 1  and  660 - 2  may use the reference clock of 155.52 MHz from the outside in order to recover the clock and data. The reference clock used by the burst CDRs  660 - 1  and  660 - 2  may be the recovery clock recovered in the downlink transmission in the GPON framer  650 . The burst CDRs  660 - 1  and  660 - 2  may extract a parallel 4-bit data signal and a clock of 311.04 MHz from the serial data signal of 1.244 Gb/s. 
         [0068]    The burst CDRs  660 - 1  and  660 - 2  transmit the recovery clock and the 4-bit data to the SERDES module  655  (S 920 ), and the SERDES module  655  converts a 4-bit data signal into a 8-bit data signal (S 930 ) and transmits the converted signal to the uplink GTC frame processing module  653  (S 940 ). The uplink GTC frame processing module  653  processes the 8-bit data signal by using the recovery clock recovered in the downlink transmission (S 950 ), and transmits the 8-bit data signal to the transmission I/O interface module  654  (S 960 ). 
         [0069]    The transmission I/O interface module  654  converts and outputs the 8-bit data signal received from the uplink GTC frame processing module  653  into the serial data signal of 1.244 Gb/s (S 970 ). 
         [0070]    As such, since the clock recovered in the downlink transmission is used for the uplink transmission, the uplink transmission synchronized with the GPON OLT  210  is available. 
         [0071]      FIG. 10  is a diagram illustrating processing of an uplink GTC frame according to an embodiment of the present invention. 
         [0072]    Referring to  FIG. 10 , the uplink GTC frame is the burst signal. That is, data is transmitted from each GPON ONU with the burst, such that a partial section without data is provided. The uplink GTC frame processing module  653  may insert the preamble into a partial section without data. At this time, the GPON framer  650  can find a partial section without data from the control information extracted from the downlink GTC frame in the downlink transmission. Accordingly, the uplink GTC frame outputted from the uplink GTC frame processing module  653  may be a continuous signal. As a result, the continuous signal may be transmitted in the section to which the WDM-PON technology is applied. A delay time for the uplink GTC frame processing module  653  to process the uplink GTC frame may be taken. 
         [0073]      FIG. 11  illustrates a method for monitoring states of optical transceivers in a hybrid relaying apparatus  600  according to an embodiment of the present invention. 
         [0074]    Referring to  FIG. 11 , the GPON framer  650  periodically or aperiodically monitors the GPON ONU optical transceiver  610 , the WDM-PON ONU optical transceiver  620 , and the GPON OLT optical transceiver  670  through an  120  interface. The control processor  640  collects the state monitoring information of the GPON ONU optical transceiver  610 , the WDM-PON ONU optical transceiver  620 , and the GPON OLT optical transceiver  670  from the GPON framer  650 . When the central office requires the state monitoring information of the GPON ONU optical transceiver  610 , the WDM-PON ONU optical transceiver  620 , and the GPON OLT optical transceiver  670 , the control processor  640  inserts the state monitoring information into the OMCI packet and transmits the OMCI packet to the GPON OLT  210  through the uplink frame. The OMCI packet may be inserted into a partial section of the uplink frame. For this, the GPON framer  650  needs to be ranged to the GPON OLT  210 . Ranging the GPON framer  650  and the GPON OLT  210  is performed in the control processor  640 . 
         [0075]    The above-mentioned exemplary embodiments of the present invention are not embodied only by an apparatus and method. Alternatively, the above-mentioned exemplary embodiments may be embodied by a program performing functions, which correspond to the configuration of the exemplary embodiments of the present invention, or a recording medium on which the program is recorded. 
         [0076]    While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.