Abstract:
The present invention realizes an Optical Line Terminal (OLT) in an optical access network and a data signal sending method for the optical access network in which the reliability of the network can be assured without increasing the cost of facility investment. The OLT comprises a multiplex control unit for providing a communication path to be used commonly for transmitting data signals for subscriber terminals to communicate with the network, a plurality of optical network interface units, each accommodates the subscriber terminals and provides either a first path connected to the network for transmitting the data signals individually or a second path connected to the multiplex control unit for transmitting the data signals to the network commonly with data signals from other subscriber terminals accommodated in other optical network interface unit, and a path selection control section, which determines for every optical network interface unit to select either the first path or the second path on the basis of path class information in a path management table in which respective path class information for every optical network interface unit have been predetermined and set.

Description:
BACKGROUND OF THE PRESENT INVENTION 
   1. Field of the Present Invention 
   The present invention relates to an optical access network apparatus and its data signal sending method, and more particularly to an OLT (Optical Line Terminal) in an optical access network and a data signal sending method for enabling a subscriber terminal to send a data signal via the OLT to a network. 
   2. Description of the Related Art 
   An xDSL (x-Digital Subscriber Line) is the generic term of ADSL (Asymmetric Digital Subscriber Line), HDSL (High-bit-rate DSL), RADSL (Rate-Adaptive DSL), SDSL (Symmetric DSL), and VDSL (Very-high-bit-rate DSL). This xDSL is a modem technique allowing for the fast packet communications at several tens Megabits/sec at maximum, using the existing subscriber line (ordinary telephone cable made of copper wire) as a transmission line. Due to the introduction of communication services employing the xDSL, a high-speed and always-connected internet access network has become popular and widely spread. 
   However, as the xDSL technology involves the packet communication using the telephone cable, it has a problem that the transmission characteristics and the data transmission speed are affected by the length of the telephone cable, the characteristics of the telephone cable, and the peripheral environmental conditions of wiring path of the telephone cable from a telephone switching office to the subscriber&#39;s premises. 
   Thus, an access network employing the optical technologies has been widely spreading, instead of the access network employing the xDSL technology. The access network employing the optical technologies is an optical access network so called an EPON (Ethernet Passive Optical Network) which employs the Ethernet technologies and realizes the packet communication through an optical cable connected to the subscriber&#39;s premises. The PON technology is recommended in the IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 802.3ah. 
   The optical access network by the EPON is composed of an OLT (Optical Line Terminal) that is installed in the switching center of a communication common carrier, and an ONU (Optical Network Unit) that is installed in the subscriber&#39;s premises. This optical access network is constructed by laying one optical fiber cable to an area in which plural subscribers&#39; premises are locating, connecting a splitter as an optical coupler to the optical fiber cable for splitting an optical path into a plurality of optical paths, and connecting each of split optical cables to respective subscriber&#39;s premises. The optical access network can provide the subscriber with the packet communications of wider band and higher quality than the access network with the metallic cable such as the telephone cable. Particularly, the optical access network is most suitable for an application such as the moving picture contents distribution services. 
   On the other hand, in the communications network, it is necessary to secure the high speed and high quality communications, and it is also important to maintain the reliability of the network by increasing the tolerance or taking measures against the line disturbances. Therefore, the techniques for the dual or redundant configuration of the network have been developed in the optical access network. One of those techniques is disclosed in Japanese Patent Application Laid-Open No. 2003-111116 as a system which performs redundant line selection in order to equalize the frequency of line usage. Also, in Japanese Patent Application Laid-Open No. 2003-318933, a proposal has been made for a system which has a redundant configuration of the active line and the standby line, and diverts a part of data to the standby line when amount of the input data has exceeded beyond the band assured by the active line. 
   The configuration of an optical access network based on the functions of the conventional OLT will be described below. 
   The conventional OLT has a SNI (Service Node Interface) port corresponding to each PON (Passive Optical Network) interface for connection to the network. The OLT accommodates a plurality of PON interfaces (or mounts a plurality of PON interface boards), and their respective SNI ports are connected corresponding one to one to the ports of an L2 (layer 2) switch provided in the network. That is, in a case where the OLT mounts twelve PON interface boards and provides twelve SNI ports, the twelve SNI ports are connected to the L2 switch of the network. 
     FIG. 29  is a system block diagram representing the essence of an example of the conventional optical access network of non-concentrate type. 
   An OLT  101  of the conventional optical access network comprises a control board  102  for controlling the entire apparatus (the OLT  101 ), and n (n is arbitrary integer) PON interface (PON I/F) boards  103   1 ,  103   2 , . . . and  103   n . This conventional optical access network is composed of a network element of subscriber side and a network element of network side. The network element of subscriber side comprises the optical fiber cables  104   1 ,  104   2 , . . . and  104   n  connecting to the respective PON interface boards  103   1 ,  103   2 , . . . and  103   n  in the OLT  101 , the 1×N splitters  105   1 ,  105   2 , . . . and  105   n  for splitting each of the optical fiber cables  104   1 ,  104   2 , . . . and  104   n  into N (N is arbitrary integer) split optical cables for subscribers, not shown, and n×N ONUs  106   11  to  106   1N ,  106   21  to  106   2N , . . . and  106   n1  to  106   nN  connected to the respective 1×N splitters  105   1 ,  105   2 , . . . and  105   n  through the split optical cables. And the network element of network side is configured such that the SNI ports  108   1 ,  108   2 , . . . and  108   n , which are interfaces on the network side of the PON interface boards  103   1 ,  103   2 , . . . and  103   n  in the OLT  101 , are connected to an L2 switch (L2 SW)  109  of the network. 
   In the configuration of the conventional optical access network in  FIG. 29 , data is transmitted or received between the subscriber terminal, not shown, and the network on the paths as indicated by the arrow  111   1 ,  111   2 , . . . and  111   n . That is, data is transmitted or received via the L2 switch  109 , the SNI ports  108   1 ,  108   2 , . . . and  108   n  of the OLT  101 , the PON interface boards  103   1 ,  103   2 , . . . and  103   n , the optical fiber cables  104   1 ,  104   2 , . . . and  104   n  and the ONUs  106   11  to  106   1N ,  106   21  to  106   2N , . . . and  106   n1  to  106   nN . 
   On the other hand,  FIG. 30  is a system block diagram representing the essence of an example of the conventional optical access network of concentrate type. The same parts are given the same numerals throughout  FIGS. 29 and 30 , and the explanation of the same parts is omitted properly. 
   An OLT  121  of the conventional optical access network as shown in  FIG. 30  comprises a multiplex board  122  for controlling the entire apparatus (the OLT  121 ) and multiplexing the data from the subscriber terminals, and n PON interface boards  103   1 ,  103   2 , . . . and  103   n . This conventional optical access network is composed of a network element of subscriber side and a network element of network side. As the configuration of the network element of subscriber side is the same as that shown in  FIG. 29 , the explanation is omitted. The network element of network side is configured such that an SNI port  123  that is an interface on the network side of the multiplex board  122  is connected to the L2 switch  109 . 
   In the configuration of the conventional optical access network as shown in  FIG. 30 , data is transmitted or received on the paths as indicated by the arrow  131  and arrow  132   1 , arrow  131  and arrow  132   2 , . . . , and arrow  131  and arrow  132   n  between the subscriber terminal, not shown, and the network. That is, data is transmitted or received via the L2 switch  109 , the SNI port  123  of the OLT  121 , the PON interface boards  103   1 ,  103   2 , . . . and  103   n , the optical fiber cables  104   1 ,  104   2 , . . . and  104   n  and the ONUs  106   11  to  106   1N ,  106   21  to  106   2N , . . . and  106   n1  to  106   nN . 
   In  FIGS. 29 and 30 , the section of the optical fiber cable between the PON interface boards and the ONUs is called “a PON section”. 
   In the PON system for the optical access network, some measures for providing a duplex system that enables the switching of the PON section at the time of line disturbances have been conventionally proposed. However, no system has been proposed yet for protecting a portion relating to the PON interface boards and the SNI ports at the time of fault. Thereby, the following problems arise. 
   A first problem is that the cost of facility investment is increased when redundant configuration facilities are provided for the network element of network side in the conventional optical access network of non-concentrate type. 
   The conventional OLT  101  of non-concentrate type comprises the SNI ports  108   1 ,  108   2 , . . . and  108   n  corresponding to the PON interface boards  103   1 ,  103   2 , . . . and  103   n , as shown in  FIG. 29 . Therefore, various facilities are required doubly by simply making the apparatus duplex, so that the cost of equipment is increased. 
   A second problem is that the conventional OLT  201  of concentrate type cannot separate the data traffic for transmission depending on the type of subscriber (or subscriber class). To assure the service quality for the respective subscribers, it is required to separate the data traffic for transmission depending on the subscriber class. 
   The conventional OLT  201  of concentrate type concentrates the data traffic for the PON interface boards  103   1 ,  103   2 , . . . and  103   n  in the multiplex board  122  with a single SNI port  123 , as shown in  FIG. 30 , whereby the duplex provision of multiplex board is possible for realizing a redundant configuration. However, the redundant configuration of the multiplex board will cause the complex settings of internal control and troublesome operation for quality assurance in assuring the quality of data depending on the subscriber class. 
   A third problem is that the degree of freedom of setting a path to the network for each subscriber or service is lowered in the both forms of the non-concentrate type and the concentrated type. That is, there are physical separation and logical separation for routing the data corresponding to each subscriber. The physical routing is generally made by the physically independent SNI ports, and the logical routing is generally made by a general VLAN (Virtual Local Area Network) tag. However, these routing methods must accord with a management scheme dependent upon the topology of the OLTs  101  and  121  ( FIGS. 29 and 30 ) connecting to the network. 
   SUMMARY OF THE PRESENT INVENTION 
   An exemplary feature of the present invention is to provide an Optical Line Terminal (OLT) in an optical access network and a data signal sending method for the optical access network in which the reliability of the network can be assured without increasing the cost of facility investment. It is another exemplary feature of the present invention to provide an OLT in an optical access network and a data signal sending method for the optical access network in which the data received from the subscriber terminal can be flexibly routed for each subscriber or each service. 
   The Optical Line Terminal (OLT) according to the present invention comprises a multiplex control unit for providing a communication path to be used commonly for transmitting data signals for subscriber terminals to communicate with the network, a plurality of optical network interface units, each accommodates the subscriber terminals and provides either a first path connected to the network for transmitting the data signals individually or a second path connected to the multiplex control unit for transmitting the data signals to the network commonly with data signals from other subscriber terminals accommodated in other optical network interface unit, and a path selection control section, which determines for every optical network interface unit to select either the first path or the second path on the basis of path class information in a path management table in which respective path class information for every optical network interface unit have been predetermined and set. 
   According to the present invention, the data signal of the subscriber terminal is received via the PON interface, and the path management table is referred to, whereby when this data signal is transmitted to the network, it is possible to select a way of transmitting the data signal, i.e. concentrate or non-concentrate. That is, the path can be flexibly set by arranging the internal data of the OLT without depending on the physical topology between the subscriber and the network. Accordingly, the communication common carrier (or the network provider) can simplify the network path design for the optical access network to a network, whereby the convenience or easiness of the facility maintenance management is improved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary features and advantages of the present invention will become apparent from the following detailed description when taken with the accompanying drawings in which: 
       FIG. 1  is a system block diagram representing the essence of an optical access network according to a first embodiment of the present invention; 
       FIG. 2  is a block diagram representing the specific configuration of an OLT according to the first embodiment; 
       FIG. 3  is a flowchart showing an initialization process of the OLT by an NMS/CLI according to the first embodiment; 
       FIG. 4  is an explanatory view showing the contents of a path management table according to the first embodiment; 
       FIG. 5  is a flowchart showing a process of data communication path selection for the up-stream data to the network according to the first embodiment; 
       FIG. 6  is a system block diagram representing the essence of an optical access network according to a second embodiment of the present invention; 
       FIG. 7  is a block diagram representing the specific configuration of the OLT according to the second embodiment; 
       FIG. 8  is an explanatory view showing the contents of a path management table according to the second embodiment; 
       FIG. 9  is a system block diagram representing the essence of an optical access network according to a third embodiment of the present invention; 
       FIG. 10  is a block diagram representing the specific configuration of the OLT according to the third embodiment; 
       FIG. 11  is an explanatory view showing the contents of a path management table according to the third embodiment; 
       FIG. 12  is a flowchart showing an initialization process of the OLT by the NMS/CLI according to the third embodiment; 
       FIG. 13  is a flowchart showing a process of data communication path selection for the up-stream data to the network according to the third embodiment; 
       FIG. 14  is an explanatory view showing the flow of control signal and data in a first case according to the third embodiment; 
       FIG. 15  is an explanatory view representing how the path selection is performed in accordance with the contents of the path management table according to the third embodiment; 
       FIG. 16  is an explanatory view showing the flow of control signal and data in a second case according to the third embodiment; 
       FIG. 17  is an explanatory view showing the flow of control signal and data in a third case according to the third embodiment; 
       FIG. 18  is an explanatory view showing the flow of control signal and data in a fourth case according to the third embodiment; 
       FIG. 19  is a system block diagram representing the essence of an optical access network according to a fourth embodiment of the present invention; 
       FIG. 20  is a block diagram representing the specific configuration of the OLT according to the fourth embodiment; 
       FIG. 21  is an explanatory view showing the contents of a path management table according to the fourth embodiment; 
       FIG. 22  is a flowchart showing an initialization process of the OLT by the NMS/CLI concerning the setting of a redundant operation mode  712  according to the fourth embodiment; 
       FIG. 23  is a flowchart showing the flow of a process where the line disturbance occurs according to the fourth embodiment; 
       FIG. 24  is a system block diagram representing the essence of an optical access network according to a fifth embodiment of the present invention; 
       FIG. 25  is a block diagram representing the specific configuration of the OLT according to the fifth embodiment; 
       FIG. 26  is an explanatory view showing the contents of a path management table according to the fifth embodiment; 
       FIG. 27  is a flowchart showing an initialization process of the OLT by the NMS/CLI in the fifth embodiment; 
       FIG. 28  is a flowchart showing the flow of a process where the line disturbance occurs at the SNI port of the multiplex control board according to the fifth embodiment; 
       FIG. 29  is a system block diagram representing the essence of an example of the conventional optical access network of non-concentrate type; and 
       FIG. 30  is a system block diagram representing the essence of an example of the conventional optical access network of concentrate type. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will be described below in connection with the five exemplary embodiments. 
   Exemplary Embodiment 1 
     FIG. 1  is a system block diagram schematically representing the essence of an optical access network according to a first embodiment of the present invention. The optical access network  200  of this embodiment constitutes a GEPON (Gigabit Ethernet Passive Optical Network) system as an example. 
   In the optical access network  200  of this embodiment, an OLT  201  comprises a multiplex control board  202  and n (n is arbitrary integer) PON interface (I/F) boards  203   1 ,  203   2 , . . . and  203   n . One ends of the optical fiber cables  204   1 ,  204   2 , . . . and  204   n  are correspondingly connected to the PON interface boards  203   1 ,  203   2 , . . . and  203   n , and the other ends of the optical fiber cables  204   1 ,  204   2 , . . . and  204   n  are connected to the 1×N splitters  205   1 ,  205   2 , . . . and  205   n , and each optical fiber cable is split into N (N is arbitrary integer) optical fiber cables by the 1×N splitter. The split optical fiber cables  206   11  to  206   1N ,  206   21  to  206   2N , . . . and  206   n1  to  206   nN  are connected to the respective ONUs  207   11  to  207   1N ,  207   21  to  207   2N , . . . and  207   n1  to  207   nN . 
   On the network side of the OLT  201 , an SNI port  211  that is an interface on the network side of the multiplex control board  202  and the SNI ports  211   n-1  and  211   n  that are interfaces on the network side of the PON interface boards  203   n-1  and  203   n  are connected to an L2 switch (SW)  212 . 
   Though not shown in  FIG. 1 , an STB (Set Top Box) and a television or personal computer for receiving a large amount of contents broadcasted by a multicast service, and a subscriber terminal such as a VoIP (Voice over IP) service terminal are connected to the ONUs  207   11  to  207   1N ,  207   21  to  207   2N , . . . and  207   n1  to  207   nN . 
   Also, the OLT  201  is connected to an NMS (Network Management System) or a CLI (Command Line Interface) (hereinafter referred to as an NMS/CLI terminal  214 ) for performing the control management of the optical access network. In the drawing, it is shown that the NMS/CLI terminal  214  is directly connected to the OLT  201 , but the NMS/CLI terminal  214  can be connected via a network to the OLT  201  in the actual operation to perform the control management. This NMS/CLI terminal  214  comprises a recording medium, not shown, storing a control program for performing various controls such as the initialization of the OLT  201 , and a CPU (Central Processing Unit) for executing this program. 
   The section composed of the optical fiber cables  204 , the l×N splitter for splitting the optical fiber cables and the optical fiber cables  206  having one ends connected to the splitter  205  is generically referred to as “a PON section”. 
     FIG. 2  is a block diagram representing the specific configuration of the OLT  201 . 
   The component units of the multiplex control board  202  of the OLT  201  are as follows. 
   An NMS communication section  221  (performing the communications with the NMS/CLI terminal  214 , shown in  FIG. 1 , for control management), a CLI control section  222  (performing an interface process with the NMS/CLI terminal  214 ), a universal L2 (layer 2) switch section  223  (performing a data transfer switching process within the multiplex control board for the data input from the subscriber terminal or the network by establishing a switched path), a network communication section  225  (performing the communications with the network with a function of the SNI port  211  of the multiplex control board  202 ), the first to nth PON interface (I/F) communication sections  226   1 ,  226   2 , . . . and  226   n , (performing the communications with the PON interface boards  203   1 ,  203   2 , . . . and  203   n  mounted on the OLT  201 ), and a path management table  227  (storing the path control information for setting the path of data passing through the OLT  201  corresponding to the PON interface board). 
   Also, each of the PON interface boards  203   1 ,  203   2 , . . . and  203   n , mounted on the OLT  201  has the following component units. 
   A multiplex control board communication section  231  (performing the communications with the PON interface (I/F) communication section of the multiplex control board  202 , corresponding to the PON interface board), a network communication section  232  (performing the communications with the network with a function of the SNI ports  211   1 ,  211   2 , . . . and  211   n  of the PON interface boards  203   1 ,  203   2 , . . . and  203   n ), a PON communication section  233  (performing the data communication via the PON section with conforming to the IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 802.3a, and identifying the information contained in the up-stream data packet), an L2 (layer 2) switch section  234  (performing a data transfer switching process within the PON interface board for the data input from the subscriber terminal or the network by establishing a switched path), and a path management table  235  (storing the path control information concerning the PON interface board extracted from the contents of the path management table  227  in the multiplex control board  202 ). 
   Here, in  FIG. 1 , the line for connecting the SNI port directly to the L2 switch  212  of the network, is not shown for the PON interface board  203   1  and  203   2 . On the contrary, in  FIG. 2 , the SNI ports  211   1  and  211   2  are illustrated as if the lines for the SNI ports  211   1  and  211   2  existed in the PON interface board  203   1  and  203   2 . This means that the data received from the subscriber terminal can be controlled to be directly transmitted to the SNI port of the own PON interface board, or concentrated in the multiplex control board  202  and transmitted via the SNI port of the multiplex control board, depending on the settings of the path management table contents for the OLT in this embodiment, as will be described later. 
   The operation of the optical access network as shown in  FIGS. 1 and 2  will be described below. 
   In operating the optical access network according to the present invention, an initialization process for initializing the information required for the OLT  201  is performed beforehand. This initialization process is performed by the NMS/CLI terminal  214  (shown in  FIG. 1 ), and each contents of the path management table  227  in the multiplex control board and the path management table  235  in the respective PON interface boards will be set by this initialization process.  FIG. 3  is a flowchart showing the initialization process for the OLT by the NMS/CLI terminal according to the first embodiment. 
   The OLT  201  monitors the information sent from the NMS/CLI terminal  214  (step S 301 ). If the information having been received is the intra-apparatus path control information (Y), the OLT  201  sets the intra-apparatus path control information received from the NMS/CLI terminal  214  to the path management table  227  in the multiplex control board  202  as contents of the table (step S 302 ). The contents of the path management table  227  includes the intra-apparatus path control information concerning all the PON interface boards mounted on the OLT  201 , as shown in  FIG. 4 . Thereafter, the intra-apparatus path control information corresponding to each PON interface board is extracted from the contents of this path management table  227 , and the intra-apparatus path control information corresponding to each PON interface board is set in the path management table  235  in each PON interface board (step S 303 ). 
     FIG. 4  is an explanatory view showing the table contents of the path management table  227  in the multiplex control board. In the first embodiment, this path management table is called as “a PON interface board path management table”. Contents of the PON interface board path management table  241  include a card number  242 , a card type  243 , and a path class  244 , which are associated. Herein the term “card” means the multiplex control board (MUX/CTL)  202  or each of the PON interface boards  203   1 ,  203   2 , . . . and  203   n  mounted on the OLT  201  as a physical card. The card type  243  indicates the type of card, i.e. MUX/CTL board or PON interface board. This card type  243  is only required for managing the component information of the apparatus, and represented in the general term. In the path class  244 , the “concentrate” indicates “line concentration” which means the data from the subscriber terminals are concentrated at the multiplex control board  202  and transmitted to the network via the SNI port  211  of the multiplex control board  202 , and the “non-concentrate” indicates “line non-concentration” which means the data from the subscriber terminal is not concentrated and transmitted to the network via respective SNI ports  211   1 ˜ 211   n . For example, according to the contents of the PON interface board path management table  241 , the PON interface boards  203   1  to  203   4 ,  203   6  and  203   8  are set as “concentrate” which means the data from the PON interface boards  203   1  to  203   4 ,  203   6  and  203   8  are concentrated in the multiplex control board  202  and transmitted via the SNI port  211  to the network, and the other PON interface boards  203   5 ,  203   7 , 203   m , 203   n-1  and  203   n  are set as “non-concentrate” which means the data from respective PON interface boards  203   5 ,  203   7 ,  203   m ,  203   n-1  and  203   n  is not concentrated and transmitted to the network via respective SNI ports  211   5 ,  211   7 ,  211   m ,  211   n-1  and  211   n . 
   Also, the intra-apparatus path control information corresponding to each PON interface board is extracted from the contents of the PON interface board path management table  241  shown in  FIG. 4  and set in each path management table  235  provided in the respective PON interface boards  203   1 ,  203   2 , . . . and  203   n . For example, “concentrate” is stored as the information indicating the path class  244  in the path management table  235  of the PON interface board  203   1 . 
   Next, a data communication path from the network to the subscriber terminal will be described below. 
   In  FIG. 2 , the network communication section  225  receives data from the network via the SNI port  211  of the multiplex control board  202 , and its data is transferred to the L2 switch section  223 . The L2 switch section  223  has a general FDB (Forwarding Data Base), not shown, managed by the L2 switch section  223  itself for establishing the switched path to transfer the data within the multiplex control board. Therefore, the L2 switch section  223  establishes the switched path to transfer the data from the network communication section  225  to the PON interface communication section  226   x  corresponding to the PON interface board to which the received data is addressed among the first to nth PON interface communication sections  226   1 ,  226   2 , . . . and  226   n  by referring to the general FDB. 
   Then, the PON interface communication section  226   x  sends this data to the multiplex control board communication section  231  provided in the corresponding PON interface board  203   x . Each PON interface board  203  also has a L2 switch section  234  which has a general FDB (Forwarding Data Base), not shown, managed by the L2 switch section  234  itself for establishing the switched path to transfer the data within the PON interface board  203 . Therefore, the L2 switch section  234  establishes the switched path to transfer the data from the multiplex control board communication section  231  to the PON communication section  233 , which is proved in the PON interface board  203   x , by referring to the general FDB. Thereby, the data is transferred via the PON section to the appropriate ONU  207  (see  FIG. 1 ). The above explanation is an example where the data is transferred via the SNI port  211  for the “concentrate” in the down direction. 
   Next, an example where the data is transferred in the down direction using the “non-concentrate” port will be described below. 
   It is assumed that the network communication section  225  of the PON interface board  203   n  receives data in the down direction from the network via the SNI port  211   n  of the PON interface board  203   n . 
   The network communication section  225  transfers its received data to the L2 switch section  234  of the PON interface board  203   n . The L2 switch section  234  establishes the switched path between the network communication section  225  and the PON interface communication section  233  of the PON interface board  203   n  by referring to the general FDB for transferring the data to the PON interface communication section  233 . Thereby, the data is transferred via the PON section to the appropriate ONU  207 . 
   The operation of the L2 switches  223  and  234  as the universal L2 switches is well known to those skilled in the art, and its detailed explanation is omitted. 
   Herein, the operation of the PON communication section  233  conforming to the IEEE802.3ah will be described below. 
   In a network system employing the EPON, one OLT  201  and a plurality of ONUs  207   11  to  207   1N ,  207   21  to  207   2N , . . . and  207   n1  to  207   nN  realize the Point-to-Multipoint Ethernet connection, employing the logical link identifier (LLID: Logical Link Identifier). This logical link identifier is incorporated by two bytes information into the preamble part of a MAC (Media Access Control) frame in the conventional Ethernet, and used in an EPON section (between the OLT  201  and the ONUs  207   11  to  207   1N ,  207   21  to  207   2N , . . . and  207   n1  to  207   nN ). 
   In the EPON section, since the light (optical path) is simply split into a plurality of optical paths, even the frame transmitted from the OLT  201  to the specific ONU  207   nx  will be received by all ONUs  207   n1  to  207   nN . Thus, each of the ONUs  207   n1  to  207   nN  compares the logical link identifier of the frame with the logical link identifier allocated to itself by referring to the preamble part of the frame transmitted from the OLT  201 . As a result, when they are coincide with each other, it is recognized that the frame is addressed to itself, and the frame is taken in as the frame to be received by the ONU  207   nx . On the contrary, when the logical link identifiers are different, the frame is discarded, because the frame is addressed to the other ONU. In this manner, the OLT  201  and the ONU  207   nx  emulate the Point-to-Point communication, employing the logical link identifier. 
   As described above, for the subscriber terminals connected to the ONUs  207   11  to  207   1N  and  207   21  to  207   2N  accommodated in the PON interface boards  203   1  and  203   2  that are used for concentration type, the data is transferred from the network to the subscriber terminals through the paths as indicated by the arrow  251 ,  251   1  and  251   2  as shown in  FIG. 1 . That is, the data is transferred from the network to the subscriber terminals via the L2 switch  212  of the network, the SNI port  211  of the multiplex control board  202 , the multiplex control board  202 , the PON interface boards  203   1  and  203   2 , the PON section corresponding to the PON interface boards  203   1  and  203   2  and the ONUs  207   11  to  207   1N  and  207   21  to  207   2N . 
   On the other hand, for the subscriber terminals connected to the ONUs  207   (n−1)1  to  207   (n−1)N  and  207   n1  to  207   nN  accommodated in the PON interface boards  203   n−1  and  203   n  that are used for non-concentration type, the data is transferred from the network to the subscriber terminals through the paths as indicated by the arrow  251   n−1  and  251   n  as shown in  FIG. 1 . That is, the data is transferred from the network to the subscriber terminals via the L2 switch  212 , the SNI port  211   n−1  and  211   n  of the PON interface boards, the PON interface boards  203   n−1  and  203   n , the PON section corresponding to the PON interface boards  203   n−1  and  203   n  and the ONUs  207   (n−1)1  to  207   (n−1)N  and  207   n1  to  207   nN . 
   In this manner, the data is transmitted in the down direction through the L2 switch process as conventionally well known, regardless of the settings of the intra-apparatus path control information. 
     FIG. 5  is a flowchart showing a process of setting data communication path in the up direction from the subscriber terminal to the network. 
   For the process of setting data communication path from the subscriber terminal to the network, it is supposed that the intra-apparatus path control information has already been set in the OLT  201  through the initialization process explained in  FIG. 3 . 
   For example, it is assumed that the PON interface board  2031 , shown in  FIG. 2 , receives a data packet, at the PON communication section  233 , in the up direction that is transferred from the subscriber terminal to the network (Y at step S 321 ). In this case, the path class parameter stored in the path management table  235  of the PON interface board  203   1  is referred to (step S 322 ). It is confirmed if the path class parameter is set to “concentrate” (Y at step S 323 ). Thus, the L2 switch section  234  of the PON interface board  203   1  establishes the path to transmit the data packet from the PON communication section  233  to the multiplex control board communication section  231  of the PON interface board  203   1  in this example (step S 324 ). Thereby, the multiplex control board  202  receives the data packet in the first PON interface communication section  226   1 , and the L2 switch section  223  establishes the path to transmit the data packet from the first PON interface communication section  226   1  to the network communication section  225  by referring to the path management table  227 , in which the path class corresponding to the PON interface board with the card number “1” is also set to “concentrate”. Then, the network communication section  225  transmits the data packet through the “concentrate” SNI port  211  to the network (step S 325 ). 
   On the other hand, when the PON interface board  203   5  (not shown) receives the data packet at its PON communication section  233 , the path class parameter of the path management table  235  is set to “non-concentrate” (N at step S 323 ). In this case, the L2 switch section  234  of the PON interface board  203   5  establishes the path to transfer the data from the PON communication section  233  to the network communication section  232  of own PON interface board  203   5 . In this case, the network communication section  232  of the PON interface board  203   5  transmits the data packet to the network without intervention of the multiplex control board  202  (step S 326 ). 
   As described above, the data transmitted from the subscriber terminals connected to the ONUs  207   11  to  207   1N  and  207   21  to  207   2N  accommodated within the PON interface boards  203   1  and  203   2  which are to be used for “line concentrate” is transferred from the subscriber terminals to the network through the paths as indicated by the arrow  251   1  and  251   2  to  251 , as shown in  FIG. 1 . That is, the data is transferred from the subscriber terminals to the network via the ONUs  207   11  to  207   1N  and  207   21  to  207   2N , the PON section corresponding to the PON interface boards  203   1  and  203   2 , the PON interface boards  203   1  and  203   2 , the multiplex control board  202 , the SNI port  211  of the multiplex control board  202  and the L2 switch  212 . 
   On the other hand, the data transmitted from the subscriber terminals connected to the ONUs  207   (n−1)1  to  207   (n−1)N  and  207   n1  to  207   nN  accommodated within the PON interface boards  203   n−1  and  203   n  which are to be used for “non-concentrate” is transferred from the subscriber terminals to the network through the paths as indicated by the arrow  251   n  to  251   (n−1)  as shown in  FIG. 1 . That is, the data is transmitted from the subscriber terminals to the network via the ONUs  207   (n−1)1  to  207   (n−1)N  and  207   n1  to  207   nN , the PON section corresponding to the PON interface boards  203   n−1  and  203   n , the PON interface boards  203   n−1  and  203   n , the SNI port  211   n−1  and  211   n  of the PON interface boards, and the L2 switch  212 . 
   In this manner, the data transmission path in the up direction is set based on the contents (path control information) set in the path management table  235  of the PON interface board  203  and the path management table  227  of the multiplex control board  202 . 
   In the first embodiment as described above, the data packet from the subscriber terminal to the network is processed for each PON interface board as a unit mounted on the OLT. Accordingly, to accommodate the ordinary subscribers and the business use (corporate or company) subscribers in the units of the PON interface boards clearly separately, for example, the PON interface boards for accommodating the ordinary subscribers may be set as “concentrate” and the PON interface boards for accommodating the business use subscribers “non-concentrate”. That is, in the first embodiment, the path management table for each PON interface board is provided, and the path is changed or switched inside the OLT by referring to the path management table, whereby the path can be flexibly set without depending on the physical topology between the subscriber terminal and the network, and the data communication quality most adaptable to each subscriber terminal can be easily provided. In this manner, since the data traffic can be physically separated in the first embodiment, the network path design of the network and the optical access network can be simplified. Therefore, it is easier to make the maintenance and operation management of the network elements or system, and the optical access network with higher security can be provided. Further, in the first embodiment, the SNI ports of both the concentrate and non-concentrate types are prepared and the number of SNI ports is reduced, whereby the cost of facility investment for the optical access network is reduced. 
   Exemplary Embodiment 2 
     FIG. 6  is a system block diagram representing the essence of an optical access network according to a second embodiment of the present invention. In the optical access network  200 A according to the second embodiment as shown in  FIG. 6 , the same parts are designated by the same reference numerals or signs as those of the optical access network  200  according to the first embodiment shown in  FIG. 1 , and the explanation of the same parts is omitted properly. In the optical access network  200 A according to the second embodiment, contents of the path management tables of a multiplex control board  202 A and each PON interface board  203 A in an OLT  201 A are slightly different from the path management tables of the multiplex control board  202  and each PON interface board  203  according to the first embodiment. Other points are the same as in the first embodiment. 
     FIG. 7  is a block diagram representing the specific configuration of the OLT according to the second embodiment. The same parts are designated by the same reference numerals or signs throughout  FIGS. 2 and 7 , and the explanation of the same parts is omitted properly. The second embodiment is different from the first embodiment in that in the OLT  201 A, each of a path management table  227 A of the multiplex control board  202 A and a path management table  235 A of each PON interface board  203 A has additional parameters of “a path selection policy and a path selection ID”. In the second embodiment, the path management table is called as “a path management table with a path selection policy”. 
     FIG. 8  is an explanatory view showing the path management table with a path selection policy according to the second embodiment. In the first embodiment, the path class of “concentrate” or “non-concentrate” is set for each of the PON interface boards  203   1 ,  203   2 , . . . and  203   n . However, in the second embodiment, the path class of “concentrate” or “non-concentrate” is set depending on the combination of information of the card type, the path selection policy such as the ONU, the VLAN, the logical link identifier (LLID: Logical Link Identifier) and the protocol, and the path selection ID as shown in  FIG. 8 . 
   In the second embodiment, the initialization of the OLT  201 A is performed by the NMS/CLI  214  in accordance with the same process explained in the first embodiment as shown in  FIG. 3 . 
   In the second embodiment of the present invention, when the NMS/CLI terminal  214  (shown in  FIG. 6 ) performs the initialization of the OLT  201 A by sending the intra-apparatus path control information (step S 302  in  FIG. 3 ), the path management table with path selection policy  241 A as shown in  FIG. 8  is constructed in the path management table  227 A of the multiplex control board  202 A. Also, extracted contents for each PON interface board  203 A is set in the path management table  235 A of each PON interface board  203 A. 
   The data communication path from the network to the subscriber terminal and the data communication path from the subscriber terminal to the network in this state are the same as those of the first embodiment of the present invention. However, the PON interface board  203 A performs the path selection for the data communication path from the subscriber terminal to the network in accordance with a path selection policy  401  for each of the PON interface boards  203 A. And the information to be used as this path selection policy  401  is obtained by referring to the information contained in the data signal received from the subscriber terminal in the PON communication section  233  that performs the communication in the PON section. 
   The path selection policy  401  is employed as the policy for designating what the path selection is performed based on. 
   As shown in  FIG. 8 , in the case of “Card”, the concentrate or non-concentrate path selection is controlled for the card, namely, each of the PON interface boards  203   1 A,  203   2 A, . . . and  203   n A. Also, in the case of“VLAN”, the concentrate or non-concentrate path selection is controlled on a VLAN basis. Particularly, when the VLAN is designated, the ID designated in the parameter of the path selection ID  402  is further referred to. When the path selection policy  401  is “VLAN” and the path selection ID  402  is “10”, the path selection control of “concentrate” is performed for the data of “VLAN ID=10”. 
   Also, when the path selection policy  401  is “ONU”, the concentrate or non-concentrate path selection control is performed for each ONU connected to the PON interface board, and particularly, when the ONU is designated, the ID designated in the parameter of the path selection ID  402  is further referred to. When the path selection policy  401  is “ONU” and the path selection ID  402  is “1”, the path selection control of “concentrate” is performed for the data of “ONU ID=1”. 
   Also, when the path selection policy  401  is “Protocol”, the concentrate or non-concentrate path selection control is performed for each type of protocol handled by the PON interface board, and the type of protocol designated in the parameter of the path selection ID  402  is further referred to. For example, when the path selection policy  401  is “Protocol” and the path selection ID  402  is “PPP” (Point-to-Point Protocol), the data signal handled by the PON interface board is referred to and when data is related with “PPP”, the path selection control of “non-concentrate” is performed. 
   Thus, in the second embodiment, the process for selecting the path for transmitting the data signal to the network is performed inside each PON interface board  203 A based on the information (VLAN class, type of protocol, ID of the ONU, logical link identifier, etc.) contained in the data packet received from the subscriber terminal. That is, in the second embodiment, the path management table with path selection policy is provided, and the path is changed or switched inside the OLT by referring to this path management table with path selection policy, whereby the path can be flexibly set without depending on the physical topology between the subscriber terminal and the network. Therefore, the same effects can be achieved as in the first embodiment, and further the path setting by the logical detail level and the design of network path can be performed, whereby the flexible system can be constructed. 
   Exemplary Embodiment 3 
     FIG. 9  is a system block diagram representing the essence of an optical access network according to a third embodiment of the present invention. In the optical access network  200 B according to the third embodiment as shown in FIG.  9 , the same parts are designated by the same reference numerals or signs as those of the optical access network  200  according to the first embodiment as shown in  FIG. 1 , and the explanation of the same parts is omitted properly. The optical access network  200 B according to the third embodiment is different from the optical access network  200  according to the first embodiment in that a multiplex control board  202 B in an OLT  201 B has a DHCP (Dynamic Host Configuration Protocol) server function, an IGMP (Internet Group Management Protocol) snooping function and an MLD (Multicast Listener Discovery) snooping function, and a path management table with a multiplex control board function valid policy is contained in each of the path management tables of the multiplex control board  202 B and a plurality of PON interface boards  203   1 B,  203   2 B, . . . and  203   n B. In the third embodiment, the path management table is called as “a path management table with a multiplex control board function valid policy”. 
   A different point of the path management table with multiplex control board function valid policy according to the third embodiment from the path management table with path selection policy  241 A according to the second embodiment as shown in  FIG. 8  is that the parameter of “the multiplex control board function valid policy” is used as the policy information indicating whether or not the function provided by the multiplex control board is valid to use. For example, in a case where the multiplex control board  202 B of the third embodiment provides a DHCP (Dynamic Host Configuration Protocol) server function, as will be described later, when the multiplex control board function valid policy parameter is “ON”, the subscriber terminal connecting to the PON interface board  203   x B corresponding to this policy parameter can use the DHCP server function of the multiplex control board, or when the multiplex control board function valid policy parameter is “OFF”, the subscriber terminal cannot use the DHCP server function of the multiplex control board. 
   For example, this means that when the network is constructed by the DHCP but the multiplex control board function valid policy corresponding to the certain PON interface board  203   x B is set to “OFF”, it is required that the DHCP server other than that provided by the multiplex control board is prepared somewhere in the network for the subscriber terminal connecting to the PON interface board  203   x B. 
     FIG. 10  is a block diagram representing the specific configuration of the OLT according to the third embodiment. The same parts are designated by the same reference numerals or signs throughout  FIGS. 2 and 10 , and the explanation of the same parts is omitted properly. In the OLT  201 B, a DHCP server  501 , an IGMP snooping section  502  and an MLD snooping section  503  are newly connected to an L2 switch section  223 B of the multiplex control board  202 B. Also, a path management table  227 B has a path management table with a multiplex control board function valid policy. 
     FIG. 11  is an explanatory view showing the contents of the path management table with multiplex control board function valid policy  511 . The path management table with multiplex control board function valid policy  511  is the same as the PON interface board path management table  241  in the first embodiment as shown in  FIG. 4 , except that the data indicating that the multiplex control board function valid policy  512  is “ON” or “OFF” is additionally provided. 
   The DHCP server  501 , the IGMP snooping section  502  and the MLD snooping section  503  as shown in  FIG. 10  are apparatus examples provided in the multiplex control board  202 B, but not limited to these examples. For example, an apparatus becoming a server such as a PPP server, an RAS (Remote Access Server) or an RADIUS (Remote Authentication Dial-in User Service) server, which is generally employed for the subscriber authentication, may be connected to the L2 switch section  223 B. 
   In the optical access network according to the third embodiment, the multiplex control board  202 B has the server function and the snooping function. Accordingly, the process between the server and the client, which is performed via the network so far, can be performed inside the OLT  201 B in the optical access network. Also, it is new feature of the third embodiment that a path selection control of “concentrate or non-concentrate” in conjunction with utilizing these functions is provided. 
     FIG. 12  is a flowchart for explaining an initialization process of the OLT by the NMS/CLI terminal according to the third embodiment. The OLT  201 B as shown in  FIG. 9  waits to receive the path control information for setting the validity or invalidity of the multiplex control board function from the NMS/CLI terminal  214  (step S 551 ). If the path control information for setting data is received (Y), the validity or invalidity of the multiplex control board function is set in the path management table  227 B of the multiplex control board  202 B ( FIG. 10 ) (step S 552 ). Thereafter, the path control information corresponding to each PON interface board  203 B is extracted, and is set in the path management table  235 B of each PON interface board (shown in  FIG. 10 ) (step S 553 ). The initialization process for other items (card number, card type, path class) in the path management table with multiplex control board function valid policy  511  are already described in the initialization process for the PON interface board path management table  241  according to the first embodiment, as shown in  FIG. 3 , and its illustration is omitted here. 
   The operation of the optical access network  200 B according to the third embodiment will be described below. 
   In the third embodiment, the path management table with multiplex control board function valid policy  511  as shown in  FIG. 11  is constructed in the path management table  227 B. Also, the extracted path control information corresponding to each PON interface board is set in the path management table  235 B of each PON interface board. 
   The data communication path from the network to the subscriber terminal in the third embodiment is the same as that of the first embodiment of the present invention, and its explanation is omitted. 
     FIG. 13  is a flowchart representing a process of setting data communication path from the subscriber terminal to the network in the third embodiment. 
   The PON interface boards  203   1 B,  203   2 B, . . . and  203   n B monitor r the reception of a data packet, at the PON communication section  233 , in the up direction transferred from the subscriber terminal to the network (step S 601 ). If the data packet is received (Y at step S 601 ), the path management table  235 B, which has the contents extracted from the path management table with multiplex control board function valid policy  511 , is referred to (step S 602 ). And it is discriminated which of the following four cases occurs (step S 603 ). 
   First case: the path class  244  is “non-concentrate” and the multiplex control board function valid policy  512  is “OFF”. 
   Second case: the path class  244  is “non-concentrate” and the multiplex control board function valid policy  512  is “ON”. 
   Third case: the path class  244  is “concentrate” and the multiplex control board function valid policy  512  is “OFF”. 
   Fourth case: the path class  244  is “concentrate” and the multiplex control board function valid policy  512  is “ON”. 
   Herein, in the first case, the line is not concentrate, and the additional functions such as the server function and the snooping function by the multiplex control board  202 B are not applied. In the second case, the line is not concentrate, but the additional functions such as the server function and the snooping function by the multiplex control board  202 B are applied. In the third case, the line is concentrate, and the additional functions such as the server function and the snooping function by the multiplex control board  202 B are not applied. In the fourth case, the line is concentrate, and the additional functions such as the server function and the snooping function by the multiplex control board  202 B are applied. 
   For example, in the case of the PON interface board  203   5 B (corresponding to the card number  5  of  FIG. 11 ), if the path management table  235 B is referred to at step S 602 , the path class  244  is “non-concentrate” and the multiplex control board function valid policy  512  is “OFF”, whereby the first case is determined at step S 603 . In this case (N at step S 603 ), the L2 switch section  234  of the PON interface board  203   5 B establishes the switched path between the PON communication section  233  and the network communication section  232  to transfer the received packet to the network communication section  232  of the own PON interface board  203   5 B, which then transmits the packet via the SNI port  211   5 , not shown, to the network (step S 604 ). 
     FIG. 14  is an explanatory view illustrating the first case. Herein, as one example, the communication between the ONU  207   51  and the network is illustrated. In the first case, the packet transmitted from the L2 switch  212  of the network arrives via the SNI port  211   5  at the OLT  201 B, and distributed to the ONU of destination. In this way, the packet  515  composed of the IGMP control signal or data is received by the ONU  207   51 . On the other hand, the packet transmitted from the ONU  207   51  arrives at the OLT  201 B, and is received by the corresponding PON interface board  203   5 B. The received packet is sent directly from the network communication section  232  of the PON interface board  203   5 B via the SNI port  211   5  to the L2 switch  212  of the network. In this way, the packet is not via the multiplex control board  202 B ( FIG. 9 ) in the first case. 
   On the other hand, if it is discriminated at step S 603  that any of the second to fourth cases occurs (Y at step S 603 ) as a result of referring to the path management table  235 B at step S 602  of  FIG. 13 , the L2 switch section  234  of the PON interface board  203   x B establishes the switched path between the multiplex control board communication section  231  and the PON communication section  233  to transfer the received packet to the multiplex control board communication section  231 . And the multiplex control board communication section  231  sends this packet to the corresponding X-th PON interface communication section  226   x  of the multiplex control board  202 B (step S 605 ). If the X-th PON interface communication section  226   x  receives this packet, it is discriminated whether or not the multiplex control board function valid policy  512  in which the card number  242  corresponds to “X” is “ON” by referring to the path management table  227 B (step S 606 ). (Here, the switched path between the X-th PON interface communication section- 226   x  and the path management table  227 B is established by the L2 switch section  223 B.) If the multiplex control board function valid policy  512  is not “ON” but “OFF” (N at step S 606 ), its packet is transmitted from the network communication section  225  of the OLT  201 B to the network (step S 607 ). (Here, the switched path between the X-th PON interface communication section  226   x  and the network communication section  225  is established by the L2 switch section  223 B.) That is, this is the third case corresponding to the PON interface board  203   3 B in which the card number “X” is “3” as seen from  FIG. 11 . 
   On the contrary, if it is discriminated at step S 606  that the multiplex control board function valid policy  512  is “ON” (Y at step S 606 ), the packet received at the X-th PON interface communication section  226   x  is transmitted via the L2 switch section  223 B to the DHCP server  501 , the IGMP snooping section  502  or the MLD snooping section  503 , where the DHCP function by the DHCP server  501  or the IDMP snooping function by the IGMP snooping section  502  is performed (step S 608 ). That is, in the second and fourth cases, since the multiplex control board function valid policy  512  in the path management table with multiplex control board function valid policy  511  of  FIG. 11  is “ON”, the additional functions such as the server function and the snooping function by the multiplex control board  202 B are applied. 
   Thereafter, the path management table with multiplex control board function valid policy  511  is confirmed again depending on which of the PON interface boards  203   1 B,  203   2 B, . . . and  203   n B receives this packet. As a result, if the path class  244  is “concentrate” (Y at step S 609 ), the packet corresponds to the fourth case, the switched path between the X-th PON interface communication section  226   x  and the network communication section  225  is established by the L2 switch section  223 B, and the packet is transmitted from the network communication section  225  of the multiplex control board  202 B to the network (step S 607 ). This is the fourth case corresponding to the PON interface board  203   m B in which the card number “X” is “m” as seen from  FIG. 11 . 
   On the other hand, if the path class  244  is “non-concentrate” (N at step S 609 ), the multiplex control board  202 B returns the packet from the X-th PON interface communication section  226 X to the multiplex control board communication section  231  of the PON interface board  203   x B that has sent the packet (step S 610 ). Then, the L2 switch section  234  of the PON interface board  203   x B establishes the switched path between the multiplex control board communication section  231  and the network communication section  232  of the PON interface board  203   x B to transmit the packet to the network communication section  232 , and the packet is transmitted from there to the network (step S 604 ). This is the second case corresponding to the PON interface board  203   n B in which the card number “X” is “n” as seen from  FIG. 11 . 
     FIG. 15  is an explanatory view representing how to select the path according to the contents of the path management table with multiplex control board valid policy in the optical access network according to the third embodiment. The multiplex control board function valid policy  512  of the path management table with multiplex control board valid policy  511  as shown in  FIG. 11  is used as the policy indicating whether or not the function provided by the multiplex control board  202 B as shown in  FIG. 10  is validated. For example, in the case where the multiplex control board  202 B provides the function as the DHCP (Dynamic Host Configuration Protocol) server  501 , if the multiplex control board function valid policy  512  is “ON”, namely, in the second and fourth cases, the subscriber terminal connecting to the PON interface board  203   x B can use the functions of the DHCP server  501  of the multiplex control board  202 B. On the contrary, in the first and third cases in which the multiplex control board function valid policy  512  is “OFF”, the subscriber terminal connecting to the PON interface board  203   x B cannot use the functions of the DHCP server  501  of the multiplex control board  202 B. For example, this means that when the network is constructed by the DHCP but the multiplex control board function valid policy  512  for the certain PON interface board  203   x B is set to “OFF”, it is required that the DHCP server other than the DHCP server  501  provided by the multiplex control board  202 B is prepared somewhere in the network for the subscriber terminal connecting to the PON interface board  203   x B. 
   In the fourth case in which the path class  244  is “concentrate” and the multiplex control board function valid policy  512  is set to “ON”, the data signal of the subscriber terminal accommodated in the PON interface board  203   x B can use the server function of the multiplex control board  202 B on the path as indicated by numeral  521 , and the data is transmitted via the concentrate SNI port  211  of the multiplex control board  202 B. 
     FIG. 16  is an explanatory view illustrating the second case, corresponding to  FIG. 14 . In the second case, the additional functions of the multiplex control board  202 B can be applied, because the multiplex control board function valid policy  512  is “ON”. Herein, as one example, the communication between the ONU  207   m1  and the network is illustrated. The ONU  207   m1  performs the packet communication with the network via the corresponding PON interface board  203   x B. Since the multiplex control board function valid policy  512  is “ON”, the packet sent from the ONU  207   m1  is received at the PON interface board  203   x B and transmitted to the multiplex control board  202 B (step S 621 ). 
   In the multiplex control board  202 B, the IGMP snooping section  502  performs the IGMP snooping function to peep into the contents of packet which is an IGMP report message (step S 622 ). And, it performs the registration of multicast service for the ONU  207   m1  to the corresponding PON interface board  203   m B according to the contents of the IGMP report message (step S 623 ). Then, the packet is returned to the original PON interface board  203   m B (step S 624 ). This is because the path class  244  is “non-concentrate”. Then, the packet is transmitted from the network communication section  232  of the PON interface board  203   m B via the SNI port  211   m , not shown, to the L2 switch  212  of the network, and is transmitted from there to a desired destination of the network (step S 625 ). 
   When this transmitted packet  532  is received on the network side, the ONU  207   m1  is registered as the delivery destination of the multicast service in accordance with the contents of the IGMP report message (step S 626 ). And the applicable moving picture data is distributed as the multicast packet to the destinations including the ONU  207   m1  (step S 627 ). At this time, the distributed multicast data  533  arrives from the network (L2 switch  212 ) via the SNI port  211   m  of the PON interface board  203   m B of the OLT  201 B, and then is transmitted to the ONU  207   m1  having requested the multicast service. In  FIG. 16 , the signaling section indicated by numeral  541  represents the signaling section for IGMP control signals. 
     FIG. 17  is an explanatory view illustrating the third case, corresponding to  FIGS. 14 and 16 . In the third case, the multiplex control board  202 B is involved in the packet transfer, because the multiplex control board function valid policy  512  is “OFF” but the path class  244  is “concentrate”. Herein, as one example, the packet communication between the ONU  207   11  and the network is illustrated. 
   A packet  561  transmitted from the ONU  207   11  to the network is received by the corresponding PON interface board  203   1 B, and sent to the multiplex control board  202 B (step S 631 ). The additional functions are not applied in the multiplex control board  202 B. Accordingly, the multiplex control board  202 B concentrates the received packet  562  with other packets, not shown, sent on other paths, and transmits the packet  563  from the network communication section  225  of the multiplex control board  202 B via the SNI port  211  to the network (step S 632 ). 
   On the other hand, the packet sent from the network is received by the network communication section  225  of the multiplex control board  202 B, and distributed to the PON interface board  203 B corresponding to the destination. Accordingly, the packet addressed to the ONU  207   11  is distributed to the corresponding PON interface board  203   1 B and transmitted to the ONU  207   11 . 
     FIG. 18  is an explanatory view illustrating the fourth case, corresponding to  FIGS. 14 ,  16  and  17 . In the fourth case, the multiplex control board  202 B is involved at the highest degree, because the path class  244  is “concentrate” and the multiplex control board function valid policy  512  is “ON”. Herein, as one example, the packet communication between the ONU  207   41  and the network is illustrated. The ONU  207   41  communicates the packet  581  which is an IGMP report message with the network via the corresponding PON interface board  203   4 B. Since the multiplex control board function valid policy  512  is “ON”, the packet transmitted from the ONU  207   41  is sent to the multiplex control board  202 B (step S 641 ). 
   In the multiplex control board  202 B, the IGMP snooping section  502  as shown in  FIG. 10  performs the IGMP snooping to peep into the contents of packet (step S 642 ). And, it performs the registration of multicast service for the ONU  207   41  to the corresponding PON interface board  203   4 B according to the contents of an IGMP report message (step S 643 ). Thereafter, the packet is not returned to the original PON interface board  203   4 B because the path class is “concentrate”, but directly transmitted from the network communication section  225  of the multiplex control board  202 B via the SNI port  211  to the network (step S 644 ). Thereby, the packet  583  is transmitted via the L2 switch  212  of the network to a desired destination of the network. 
   When this transmitted packet  583  is received on the network side, the ONU  207   41  is registered as the delivery destination of the multicast service in accordance with the contents of the IGMP report message (step S 645 ). And the applicable moving picture data is distributed as the multicast packet to the destinations including the ONU  207   41  (step S 646 ). At this time, the distributed multicast data  584  arrives from the network (L2 switch  212 ) via the SNI port  211  at the multiplex control board  202 B, and then is transmitted to the PON interface board  203   4 B of the OLT  201 B (step S 647 ). The PON interface board  203   4 B transmits a packet  586  to the ONU  207   41  having requested the multicast service. In  FIG. 18 , the signaling section indicated by numeral  591  represents the signaling section of IGMP control signals. 
   As described above, in the third embodiment of the present invention, the multiplex control board comprises the server function, control information of “concentrate or non-concentrate” is set for each PON interface board, and also control information whether or not the server function of the multiplex control board is used is set. Therefore, the flexible path selection is allowed, and the function of authenticating the subscriber terminal accommodated in the OLT can be configured in a closed form in the optical access network owing to the server function provided by the OLT, as in the first and second embodiments, whereby the security within the optical access network and the operability of the access network are improved. 
   In the third embodiment, the parameters of the path class  244  and the multiplex control function valid policy  512  are combined in the path management table with multiplex control board function valid policy  511 , but the present invention is not limited to this combination. For example, the combinations between the VLAN and the multiplex control board function valid policy  512 , the OLT management number and the multiplex control board function valid policy  512 , and the logical link identifier and the multiplex control board function valid policy  512  are also effective. 
   Exemplary Embodiment 4 
     FIG. 19  is a system block diagram representing the essence of an optical access network according to a fourth embodiment of the present invention. In the optical access network  200 C according to the fourth embodiment as shown in  FIG. 19 , the same parts are designated by the same reference numerals or signs as in the optical access network  200  according to the first embodiment as shown in  FIG. 1 , and the explanation of the same parts is omitted properly. In the optical access network  200 C according to the fourth embodiment, a multiplex control board  202 C in an OLT  201 C and n PON interface boards  203   1 C,  203   2 C, . . . and  203   n C are slightly different from n PON interface boards  203   1 ,  203   2 , . . . and  203   n  according to the first embodiment as shown in  FIG. 1 . Other points are the same as in the first embodiment. 
     FIG. 20  is a block diagram representing the specific configuration of the OLT  201 C according to the fourth embodiment. The multiplex control board  202 C of the OLT  201 C comprises an alarm detection section  701  for detecting the line disturbance at the SNI port  211 . The PON interface boards  203   1 C,  203   2 C, . . . and  203   n C comprise the alarm detection sections  701   1 ,  701   2 , . . . and  701   n  for detecting the corresponding line disturbance at the SNI ports  211   1 ,  211   2 , . . . and  211   n . And, in the fourth embodiment, the path management table is called as “a path management table with first redundant policy”. A path management table  227 C of the multiplex control board  202 C has the path management table with first redundant policy, and the path management table  235 C of each of the PON interface boards  203   1  C,  203   2 C, . . . and  203   n C has the extracted information of the path management table with first redundant policy corresponding to the own PON interface board. The fourth embodiment has a feature that there is a measure for avoiding the line disturbance that occurs at the non-concentrate SNI ports  211   1 ,  211   2 , . . . and  211   n  of the PON interface boards  203   1 C,  203   2 C, . . . and  203   n C, that is, a bypass is provided within the OLT  201 C. 
     FIG. 21  is an explanatory view showing the table format of the path management table with first redundant policy in this embodiment. In the path management table with first redundant policy  711  of this embodiment, comparing with the PON interface board path management table  241  of the first embodiment as shown in  FIG. 4 , the data indicating whether a first redundant operation mode  712  is set to ON or OFF is added. Thereby, the OLT  201 C can perform the path control using the first redundant operation mode  712 . This information (ON or OFF) is set by the NMS/CLI terminal  214  in an initialization process. 
     FIG. 22  is a flowchart showing the initialization process for the OLT by the NMS/CLI terminal to set the first redundant operation mode  712  according to the fourth embodiment. The OLT  201 C monitors the reception of a request for setting the first redundant operation mode from the NMS/CLI terminal  214  (step S 751 ). If the request for setting the first redundant operation mode is received (Y at step S 751 ), this mode setting is performed for the path management table with first redundant policy  711  in the path management table  227 C (step S 752 ). Thereafter, the path control information corresponding to each PON interface board  203 C is extracted from the path management table  227 C, and set in the path management table  235 C of each PON interface board (step S 753 ). The initialization process for other items (card number, card type, path class) in the path management table with first redundant policy  711  is the same as already described in the initialization process for the PON interface board path management table  241  according to the first embodiment, as shown in  FIG. 3 , and its illustration is omitted. 
   When the NMS/CLI terminal  214  has performed the initialization process as described above, the path management table with first redundant policy  711  as shown in  FIG. 21  is constructed in the path management table  227 C. Also, the path management table  235 C of each PON interface board  203 C has the path management information corresponding to the card number  242  of the own PON interface board as the extracted information of the path management table with first redundant policy  711 . 
   The data communication path from the network to the subscriber terminal in the fourth embodiment is the same as that of the first embodiment. Also, the data communication path from the subscriber terminal to the network using the path class information  244  is the same as that of the first embodiment. 
   In the fourth embodiment, a switching function for the data communication path at the time of line disturbance is newly defined. For example, when a line disturbance as indicated by the sign×occurs at the SNI port  211   n  of the OLT  201 C as shown in  FIG. 19 , the data packets to be output from the SNI port  211   n  are switched to be output from the SNI port  211  of the multiplex control board  202 C. 
     FIG. 23  is a flowchart showing a process where the line disturbance occurs at the SNI port  211   n  of the PON interface board  203   n C as shown in  FIG. 19  or  20 . It is assumed that any of the alarm detection sections  701   1 ,  701   2 , . . . and  701   n  in the PON interface boards  203   1 C,  203   2 C, . . . and  203   n C detects a line abnormality such as a link down at the corresponding SNI port (step S 801 ). In this example, it is supposed that a service interruption state (line disturbance) of data transmission or reception is detected at the SNI port  211   n . At this time, the path class information in the path management table  235 C in the PON interface boards  203   n C is switched to refer to the path class  244  of the path setting table  721 . That is, the information of the path class  244  is changed from “non-concentrate” to “concentrate”. And this condition continues during the line disturbance is being detected by the alarm detection section  701   n . 
   Under this condition, when the packet is transmitted from the subscriber terminal, the L2 switch section  234  of the PON interface boards  203   n C refers to the path management table  235 C for establishing the switched path for the destination of the packet to be transmitted (step S 802 ). 
   Herein, the state of first redundant operation mode  712  corresponding to the own PON interface board  203 C is checked. If the first redundant operation mode is “ON” and the path class  244  is changed to “concentrate” (Y at step S 803 ), the L2 switch section  234  of the PON interface boards  203   n C establishes the switched path for the destination of data packet to the multiplex control board communication section  231 . And then, the packet is transmitted to the corresponding nth PON interface communication section  226   n  of the multiplex control board  202 C (step S 804 ). The network communication section  225 C of the multiplex control board  202 C transmits the data packet, which has received from the nth PON interface communication section  226   n  via the switched path established by the L2 switch section  223 , to the network. At this time, the multiplex control board  202 C is informed that the first redundant operation mode “ON” of the corresponding PON interface boards  203   n C is activated and the path class has been changed to “concentrate” by referring to the path management table  227 C. 
   On the other hand, if the first redundant operation mode  712  is set to “OFF” (N at step S 803 ), the L2 switch section  234  of the PON interface board  203 C does not perform the switching operation as described above even if the line disturbance occurs. Therefore, the L2 switch section  234  of the PON interface board  203 C establishes the switched path to transfer the data packet to the network communication section  232 C of the own PON interface board  203 C. At this time, the network communication section  232 C, which has the information that the line disturbance is being detected by the alarm detection section  701 , discards its data packet (step S 805 ). 
   When the line disturbance is restored, the path class information in the path management table  235 C of the PON interface boards  203   n C is referred to as the initial value without referring to the path setting table  721 . That is, the information of the path class  244  is changed from “concentrate” to “non-concentrate” and restored to its original state. Thereby, the data is transmitted from the subscriber terminal to the network via the path in the initial state. 
     FIG. 19  shows a packet transmission or reception path where the line disturbance occurs at the SNI port  211   n  in which the first redundant operation mode  712  in the path management table with first redundant policy is set to “ON”. As shown in  FIG. 19 , an alternate path  731  is concentrated with the other “concentrate” paths  732   1  and  732   2 , whereby the communication is performed with the network via the SNI port  211 . In this way, in this embodiment, the redundant configuration is taken such that the communication path is concentrated in the SNI port  211  of the multiplex control board  202 C when the line disturbance occurs at the SNI port  211   n−1  and  211   n  which are initially “non-concentrate”. Accordingly, there is the effect that the reliability of the optical access network is improved. 
   Exemplary Embodiment 5 
     FIG. 24  is a system block diagram representing the essence of an optical access network according to a fifth embodiment of the present invention. In the optical access network  200 D according to the fifth embodiment as shown in  FIG. 24 , the same parts are designated by the same reference numerals or signs as in the optical access network  200  according to the first embodiment as shown in  FIG. 1 , and the explanation of the same parts is omitted properly. In the optical access network  200 D according to the fifth embodiment, a multiplex control board  202 D in an OLT  201 D and n PON interface boards  203   1 D,  203   2 D, . . . and  203   n D are slightly different from the multiplex control board  202  and n PON interface boards  203   1 ,  203   2 , . . . and  203   n  according to the first embodiment. Other points are the same as in the first embodiment. 
     FIG. 25  is a block diagram representing the specific configuration of the OLT  201 D according to this embodiment. In the fifth embodiment, the path management table is called as “a path management table with second redundant policy”. The path management table with second redundant policy  711 D held in a path management table  227 D of the multiplex control board  202 D is basically the same as the path management table with first redundant policy  711  according to the fourth embodiment as shown in  FIG. 21 , but a path class parameter “protection” is further defined, as will be described later. Also, a path management table  235 D of each PON interface board  203 D holds the extracted information of the path management table  227 D corresponding to the own PON interface board. 
     FIG. 26  is an explanatory view showing the table format of the path management table with second redundant policy for use in the fifth embodiment. As the parameters of the path class  244  in the path management table with second redundant policy  711 D, besides “concentrate” and “non-concentrate” in the fourth embodiment as shown in  FIG. 21 , “protection” is defined. The other points are substantially the same as the path management table with first redundant policy  711  of the fourth embodiment. 
   The optical access network  200 D of the fifth embodiment has a feature that there is a measure for avoiding the line disturbance that occurs at the SNI ports  211  of the multiplex control board  202 D, that is, a bypass is provided in the OLT  201 D, as compared with the optical access network of the fourth embodiment. 
   The second redundant operation mode of the path management table with second redundant policy  711 D is used to indicate whether or not the bypass in the OLT  201 D is effective to secure the data communication path when the line disturbance has occurred at the SNI port. 
   When the second redundant operation mode  712 D is “ON” and the line disturbance occurs at the SNI port  211   x  of the PON interface board  203   x D, the packet data to be passed through the PON interface board  203   x D is transferred to the multiplex control board  202 D which forms a bypass to the network via the SNI port  211 , and the packet data is temporarily concentrated in the multiplex control board  202 D. When the second redundant operation mode  712 D is “OFF” and the line disturbance occurs at the SNI port  211   x  of the PON interface board  203   x D, the packet data passing through the PON interface board  203   x D is not transferred to the multiplex control board  202 D, and the data is interrupted. Also, if the path class for the specific PON interface board  203   x D is set as “protection”, the PON interface board  203   x D with “protection” designated is specified as the redundant communication path when the line disturbance occurs at the SNI port  211  of the multiplex control board  202 D. The packet communication in the concentrate mode is prevented from being interrupted by using the PON interface board  203   x D which provides a redundant SNI port as the bypass, when the line disturbance occurs at the SNI port  211  of the multiplex control board  202 D. 
     FIG. 27  is a flowchart showing an initialization process for the OLT by the NMS/CLI terminal to set the second redundant operation mode  712 D in according to the fifth embodiment. The OLT  201 D monitors the reception of a request for setting the redundant card information and the second redundant operation mode from the NMS/CLI terminal  214  (step S 951 ). If the request for setting the redundant card information and the second redundant operation mode is received (Y at step S 951 ), the redundant card information and the second redundant operation mode is set in the path management table with second redundant policy  711 D in the path management table  227 D (step S 952 ). Thereafter, the information corresponding to the PON interface board  203   1 D,  203   2 D, . . . and  203   n D is extracted from the path management table  227 D, and the path control information corresponding to each PON interface board is set in the path management table  235 D of each PON interface board (step S 953 ). The initialization process for other items (card number, card type, path class) in the path management table with second redundant policy  711 D is the same as already described in the initialization process for the PON interface board path management table  241  in the first embodiment, as shown in  FIG. 3 , and its illustration is omitted. 
   Thereby, the path management table with second redundant policy  711 D is constructed in the path management table  227 D as shown in  FIG. 25 , and the extracted information from the path management table  227 D corresponding to the own PON interface board is set in the path management table  235 D of the PON interface board  203   1 D,  203   2 D, . . . and  203   n D. 
   The data communication path from the network to the subscriber terminal in the fifth embodiment is the same as that of the first embodiment of the present invention. However, when the line disturbance as indicated by the sign×occurs at the SNI port  211  of the OLT  201 D, the L2 switch  212  on the network side shown in  FIG. 24  switches the path for transmitting the data packet from the SNI port  211  to the SNI port  211   n . Therefore, a path switching function at the time of line disturbance is newly defined. Also, the data communication path control from the subscriber terminal to the network using the path class information  244  is the same as in the first embodiment. 
   Thus, the operation where the line disturbance occurs at the SNI port  211  of the multiplex control board  202 D will be described below. 
     FIG. 28  is a flowchart showing a process where the line disturbance occurs at the SNI port for concentration of the multiplex control board  202 D. 
   First of all, it is assumed that an alarm detection section  701  of the multiplex control board  202 D has detected a line abnormality such as a link down at the SNI port  211  (step S 821 ). The multiplex control board  202 D picks up the PON interface board  203 D for which the path class  244  is set to “protection” by referring to the path management table with second redundant policy  711 D (step S 822 ). In the path management table with second redundant policy  711 D as shown in  FIG. 26 , the PON interface board  203   n D has the pass class  244  of “protection”, and the PON interface board  203   n D is selected. And as for the own path class which is corresponding to the card number  242  of “0” in the path management table with second redundant policy  711 D, the redundant path class  841  is set as “Card n” which is the card number to operate as the redundant path (step S 823 ). This means that the PON interface board  203   n D operates as the redundant path indicated by “protection”, and the card number “n” of the PON interface board  203   n D is set. 
   Next, when the second redundant operation mode is “ON” (Y at step S 824 ), the L2 switch section  223  of the multiplex control board  202 D establishes the switched path to transmit the data packet for concentration to the PON interface communication section  226   n  corresponding to “Card n” (step S 825 ). And the PON interface board  203   n D receives the data packet from the multiplex control board  202 D via the multiplex control board communication section  231 . The data packet received at the PON interface board  203   n D is transmitted to the network communication section  232 D from the multiplex control board communication section  231  via the switched path established by the L2 switch section  234  of the PON interface board  203   n D, and then, the data packet is output from the network communication section  232 D to the network via the SNI port  211   n . 
   On the other hand, when the second redundant operation mode  712 D of the path management table with second redundant policy  711 D is “OFF” (N at step s 824 ), the L2 switch section  223  of the multiplex control board  202 D establishes the switched path to transfer the data to the network communication section  225 D. At this time, the network communication section  225 D of the multiplex control board  202 D has the information that the line disturbance is being detected at the SNI port  211  of the OLT  201 D. Accordingly, the data packet is discarded in the network communication section  225 D (step S 826 ). 
   When the line disturbance at the SNI port  211  has restored, the path class  244 , which is corresponding to the multiplex control board  202 D, in the path management table with second redundant policy  711 D is restored (i.e., returns from “Card n” to the original “concentrate”). Thereby, the data communication path from the subscriber terminal to the network returns to the normal path of the SNI port  211 . 
   In this way, in this embodiment, when the fault occurs at the SNI port  211  that is used as the “concentrate” port, the communication path of the data packet is switched to the SNI port  211   n  of the PON interface board  203   n D that is set as “protection” among the PON interface boards  203   1 D,  203   2 D, . . . and  203   n D. Accordingly, the redundant configuration for packet transmission to the network is formed, whereby there is the effect that the reliability of the optical access network is improved. 
   In the first to fifth embodiments as described above, the present invention has been described taking optical access network with the GEPON or EPON as an example, but the present invention is not limited to these embodiments. That is, it is obvious that the present invention may be applied to other communication systems in which the network and the subscriber terminal are connected via the OLT. 
   The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not intended to be limited to the embodiments described herein but is to be accorded the widest scope as defined by the limitations of the claims and equivalents.