Abstract:
Communication of a terminal accessing a network by using a static IP address is cut off. A packet transfer device includes plural ports, a protocol processing unit and a control unit. An IP address distribution request by a DHCP protocol from a client terminal is transferred to a DHCP server, and an application of the IP address distribution is received. At that time, the packet transfer device stores information (IP address, MAC address) of the client terminal into a storage unit. Besides, information (IP address, MAC address) of the client terminal is stored into the storage unit also from an ARP packet by ARP resolution by the client terminal or ARP resolution by the packet transfer device itself. When the IP addresses of the stored DHCP packet and the ARP packet coincide with each other, port filtering is performed to the client terminal having transmitted the ARP packet.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an Optical Network Unit (ONU) management method and an optical line termination, and particularly to an ONU management method and an optical line termination in a Passive Optical Network (PON) system including an Optical Line Termination (OLT) and an ONU or an Optical Network Termination (ONT).  
         [0003]     2. Description of the Related Art  
         [0004]     At present, as a realization method of an access network with high speed broad band, the introduction of a PON system has been advanced. The PON system is a network system in which plural user side units (ONU: Optical Network Unit) and one station side unit (OLT: Optical Line Termination) are connected in star configuration by an optical splitter and optical fibers, and communication is performed between the units of the OLT-ONU.  
         [0005]     As the PON system, an ATM-PON system in which communication is performed in a PON section based on an Asynchronous Transfer Mode (ATM) communication system is standardized by the ITU-T Recommendation G.983 series (see, for example, the ITU-T Recommendation G.983.1). Besides, a Gigabit-capable Passive Optical Networks (GPON) system is standardized by the ITU-T Recommendation G.984 series.  
         [0006]     For example, in the ATM-PON system, as described in the ITU-T Recommendation G.983.1, in order to establish communication between OLT-ONU and to perform ONU connection, a series of processings called the ranging flow is performed. The ranging flow processing is such a function that distances between OLT-ONU are measured, transmission timings of up signals from the ONUs to the OLT are determined for the respective ONUs, and collision of the up signals is prevented. When the distances are measured in the ranging flow processing, in order to prevent the collision of ONU responses at the time of the measurement, it is necessary to cause the ONUs to respond one by one. For that purpose, a unique serial number of the ONU is used. That is, the ONU serial number is designated to specify the ONU which may respond. In the OLT, a number (identifier) for ONU identification, called a PON-ID, is assigned to an ONU whose ONU serial number has been found and whose distance has been also measured, and after that, the ONU is specified by the PON-ID, and a message is exchanged between the OLT-ONU.  
         [0007]     Although the ONU identifier is described as “PON-ID” in the after-mentioned ITU-T Recommendation G.983.1, there is a case where it is described as “ONT-ID” or “ONU-ID” according to documents.  
         [0008]     The unique serial number of the ONU is defined by information of 64 bits, and it is defined such that the 32 upper bits indicate a vender ID (fixed value for each vender) to represent a vender, and the 32 lower bits indicate a vender definition part which can be arbitrarily defined by the vender. For example, in the vender definition part of 32 bits, “manufacturing date and serial number are assigned”, or “all of the 32 bits are made serial number”, so that the respective ONUs have different serial numbers and the ONUs can be identified.  
         [0009]     In the ranging flow processing, the ONU connection is performed using the unique serial number of the ONU. As the ONU connection method, for example, two methods (Method A, Method B) are described in 8.4.1.1 of the ITU-T Recommendation G.983.1. The Method A is a method in which for example, the serial number of the ONU is registered from an operation system (OpS) to the OLT. The Method B is a method in which for example, the serial number of the ONU is not registered from an operation system to the OLT.  
         [0010]     In the case of the Method B, although the ONU serial number is not registered to the OLT from the operation system, in order to establish the communication between the OLT-ONU, it is necessary for the OLT side to specify the serial number of the ONU. Thus, a procedure is required in which the OLT side searches for the ONU serial number. The search of the ONU serial number is such that various bit patterns (for example, several lower bits, etc.) are simply tried among 64-bit patterns of the ONU serial number, and the bit pattern consistent with the serial number of the connected ONU is found by the presence/absence of the response from the ONU. The ITU-T Recommendation G.983.1 III.2 describes an example of the search method of the ONU serial number.  
         [0011]     Besides, there is known a system in which when a current system of plural ONUs constituting a redundant configuration and a spare system are switched over, a switch at the ONT side is set, so that the same ONU identifier is used after and before the switching (see, for example, JP-A-2005-45566). There is also known a system in which in a redundant configuration, a current system and a spare system have the same subscriber unit information (serial number) (see, for example, JP-A-2003-244179).  
         [0012]     When the ranging flow processing is performed and the PON-ID is assigned to the connected ONU, the subsequent message between the OLT-ONU is exchanged by specifying the ONU with the PON-ID. Thus, in the case where setting is performed individually for the ONU, it is expected that the individual setting data is correlated with the PON-ID and is stored. Under such circumstances, for example, in the case where a failure occurs in an ONU, and the ONU is replaced, it is desired that the PON-ID assigned before the replacement is assigned also to an ONU after the replacement, and the individual setting data before the replacement is succeeded and set.  
         [0013]     According to the ITU-T Recommendation G. 983.1, the procedure of the ONU replacement is not specified. In case the Method A of the ITU-T Recommendation G. 983.1, that is, the method of previously registering the ONU serial number from the OLT is adopted, since the serial number of the new ONU is known at the OLT side also at the time of the ONU replacement, the ONU serial number of the storage data has only to be rewritten. However, in order to actually perform this method, it is necessary to perform such complicated management that at the time of the ONU replacement, an ONU installation worker and an operation system administrator communicate with each other in real time, and the new ONU serial number is inputted from the operation system to the OLT, or the ONU serial number is previously informed to the operation system administrator, and the ONU with the serial number is certainly distributed to the user as the replacement destination.  
         [0014]     In case the Method B of the ITU-T Recommendation G.983.1, that is, the method in which the ONU serial number is not registered from the OLT is adopted, the OLT searches for the ONU serial number by some method and automatically performs the ONU connection. At this time, when the ONU is simply replaced and the new ONU is connected, the PON-ID is newly assigned, and the storage data before the replacement can not be succeeded. Alternatively, it becomes necessary to manually set data again.  
         [0015]     Besides, in the method disclosed in JP-A-2005-45566, the setting of the switch and the like are required at the ONU side. In the method disclosed in JP-A-2003-244179, it is necessary that the current system and the spare system have the same serial number.  
         [0016]     In view of the above circumstances, the present invention has an object to provide an ONU management method and an optical line termination, in which in a PON system, ONU connection is performed without registering a serial number of an ONU from an operation system to an OLT, and the same PON-ID as that before the ONU is replaced is assigned to a new ONU after the replacement. Besides, another object of the invention is that setting data before replacement is succeeded also after the replacement.  
         [0017]     Another object of the invention is to eliminate the necessity that in a PON system, at the time of ONU installation or replacement, an ONU installation worker and an operation system administrator communicate with each other in real time, and an ONU serial number is inputted from an operation system to an OLT. Besides, another object of the invention is to eliminate the necessity that ONU setting data is set again after ONU replacement, and to enable the ONU replacement to be facilitated.  
       SUMMARY OF THE INVENTION  
       [0018]     In order to achieve the above objects, in a PON system and an ONU management method of the invention, an OLT includes an area (PON-ID state) where a management state of a PON-ID is stored, an area (PON-ID management table) where the PON-ID and a serial number of a connected ONU are made to correspond to each other and are stored, and an area (delete ONU table) where the PON-ID and an ONU serial number of a delete object are made to correspond to each other and are stored, and when an ONU replacement instruction is received, the PON-ID management state is set to be under ONU replacement, the PON-ID is stored, the PON-ID assigned to the ONU of the replacement object is assigned to an ONU newly connected during the ONU replacement, and the PON-ID before the replacement is assigned to the ONU after the replacement. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  shows an example of the whole system configuration of a PON system.  
         [0020]      FIG. 2  is a block configuration view showing an example of an OLT.  
         [0021]      FIG. 3  shows an example of a structure of a PON-ID management table.  
         [0022]      FIG. 4  shows an example of a structure of a delete ONU table.  
         [0023]      FIG. 5  shows an example of a definition of a PON-ID state.  
         [0024]      FIG. 6  shows an example of a flowchart of an ONU connection main process.  
         [0025]      FIG. 7  shows an example of a flowchart of an ONU connection process.  
         [0026]      FIG. 8  shows an example of a flowchart of the ONU connection process.  
         [0027]      FIG. 9  is a flowchart showing the outline of a ranging flow processing in the ITU-T Recommendation G.983.1.  
         [0028]      FIG. 10  shows an example of a flowchart of an ONU connection recovery process.  
         [0029]      FIG. 11  shows an example of a flowchart of an ONU delete process.  
         [0030]      FIG. 12  shows an example of a flowchart of an ONU replacement process.  
         [0031]      FIG. 13  shows an example of a flowchart of an ONU setting process.  
         [0032]      FIG. 14  shows an example of a sequence. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     Hereinafter, embodiments of the present invention will be described with reference to the drawings.  
         [0000]     (Hard Structure)  
         [0034]      FIG. 1  shows an example of the whole system configuration of a PON system in an embodiment.  
         [0035]     The PON system includes, for example, an OLT  40 , plural ONUs ( 60 - 1  to  60 - n ), an optical splitter  50 , and optical fibers  140  and  150 . Besides, the PON system can include an operation system (OpS)  10 , a switching hub  20 , an initial setting terminal  80 , and subscriber terminals  70 .  
         [0036]     In  FIG. 1 , the OLT  40  is connected to the plural ONUs ( 60 - 1  to  60 - n ) through the optical fibers ( 140 ,  150 - 1 ,  150 - n ) and the optical splitter  50 . The optical splitter  50  equally distributes an optical signal, which has been transmitted to the optical fiber  140  from the OLT  40 , to the plural connected ONUs ( 60 - 1  to  60 - n ). Besides, the optical splitter multiplexes optical signals transmitted from the plural ONUs ( 60 - 1  to  60 - n ) to the optical fibers ( 150 - 1  to  150 - n ) and transfers them to the OLT  40 . The respective ONUs ( 60 - 1  to  60 - n ) are connected to the subscriber terminals ( 70 - 1  to  70 - n ) through lines ( 160 - 1  to  160 - n ) of Ethernet® or the like.  
         [0037]     The ONU may be an optical network termination such as an ONT. The PON system may include plural OLTs  40  and  41 . At this time, the ONUs, the optical fibers and the optical splitter are provided for each of the OLTs as shown in  FIG. 1 .  
         [0038]     The operation system  10  to perform the management and setting of the PON system is connected to the OLTs ( 40 ,  41 ) through lines ( 100 ,  110 ,  111 ) of Ethernet® or the like and the switching hub  20  to perform transfer of Ethernet® frames.  
         [0039]     The initial setting terminals ( 80 ,  81 ) can be used for performing, as the pre-stage of connection of the operation system  10 , initial setting of various parameters and the like at the time of initial setting of the OLTs ( 40 ,  41 ), and is connected to the OLTs through, for example, lines ( 130 ,  131 ) of serial cables or the like.  
         [0040]     The OLTs ( 40 ,  41 ) are connected to the Internet  30  through lines ( 120 ,  121 ) of Ethernet® or the like, and enable provision of services, such as Internet access, to the subscriber terminals ( 70 - 1  to  70 - n ,  71 - 1  to  71 - n ).  
         [0041]     For example, in the ATM-PON system, the ONUs ( 60 - 1  to  60 - n ,  61 - 1  to  61 - n ) are installed, and before the services are started to the subscriber, in order to establish communication between the OLTs ( 40 ,  41 )-ONUs ( 60 - 1  to  60 - n ,  61 - 1  to  61 - n ), ONU connection is performed in accordance with, for example, the procedure described in the ITU-T Recommendation G.983.1. In the case where the Method B of the ITU-T Recommendation G.983.1 is used for the connection of the ONU, it is necessary that the OLT searches for the ONU serial number (unique number) to specify the serial number of the ONU, and performs the connection. In this embodiment, also at the time of replacement of the ONU due to an ONU failure or the like, the serial number of the ONU after the replacement is not registered from the OLT, and the ONU connection is automatically performed.  
         [0042]     In the following description, although the ATM-PON system will be described as an example, the invention can be similarly applied to another system such as a GPON system.  
         [0043]      FIG. 2  is a block configuration view showing an example of the OLT  40  in this embodiment. The OLT  40  shown in  FIG. 2  includes a control network interface unit  410  connected to the operation system  10  or the switching hub  20 , a main signal network interface unit  420  connected to the Internet  30 , a serial interface unit  430  connected to the initial setting terminal  80 , an optical interface unit  490  connected to the ONU  60  through, for example, the optical fiber  140  and the optical splitter  50  and including E/O conversion and O/E conversion, a PON control unit  480  connected to the optical interface unit  490  and to perform a PON control, and an OLT control unit  440  to perform a control of the OLT.  
         [0044]     The OLT control unit  440  includes a CPU  450 , a non-volatile memory  460 , and a volatile memory (RAM)  470 . As the non-volatile memory  460 , although a flash memory can be used as an example, an EPROM (Erasable Programmable ROM) or an EEPROM (Electro Erasable Programmable ROM) may be used.  
         [0045]     The non-volatile memory  460  stores, for example, a program code  461 , a PON-ID state (state management unit)  462 , a PON-ID management table (connection management table)  463 , and a delete ONU table (delete management table)  464 . The program code  461  is an OS or an application to be executed by the CPU  450 , and at the time of start, it is loaded from the non-volatile memory  460  into the volatile memory  470 . A main control process  471 , an ONU connection main process  472 , an ONU connection recovery process  473 , an ONU delete process  474 , an ONU replacement process  475 , an ONU connection process  476 , an ONU setting process  477  and the like are part of the program code  461 . The main control process  471  is a main routine to perform an OLT control, and starts the ONU connection main process  472  as the need arises. The respective processes will be described later in detail.  
         [0000]     (Memory Structure)  
         [0046]      FIG. 3  shows an example of the structure of the PON-ID management table  463  in this embodiment. The PON-ID management table  463  is such a table that in this embodiment, an ONU serial number is searched, and the found ONU serial number is made to correspond to “PON-ID” and is stored.  
         [0047]     In  FIG. 3 , the PON-ID management table  463  includes a flag area  4631  to indicate whether the PON-ID has been already assigned, an area  4632  to store the serial number of the ONU  60  to which the PON-ID is assigned, and an area  4633  where individual setting for the ONU is stored. The individual setting includes a setting parameter necessary for providing services to a user by using the ONU  60 , and management data used for the ONU management, and any information and data may be used. As an example of the individual setting, the setting of, for example, a maximum bandwidth assigned to the ONU  60 , a network address (IP address), a user name of the ONU  60  and the like are conceivable. In addition to these, suitable information concerning the communication of the ONU and/or user may be used.  
         [0048]     In the example of  FIG. 3 , an area to store the PON-ID itself is not provided. This is because when the memory address and the PON-ID are made to correspond to each other, the area to store the PON-ID is not required. Here, the PON-ID is an identifier (ID) to specify the ONU  60  as a message object uniquely when a message is sent from the OLT  40  to the ONU  60 , and is the ID assigned from OLT  40  at the time of the establishment of communication between the OLT-ONU and after the serial number of the ONU  60  is specified by the OLT  40 . Since the example of  FIG. 3  is a configuration example of a case in which 64 (0 to 63) ONUs at the maximum are connected, the areas up to PON-ID # 63  are shown. An area to store the PON-ID may be provided.  
         [0049]     With respect to the PON-ID assignment flag  4631 , an example is shown in which in the case where the PON-ID has already been assigned, the value “1” is stored, and in the case of not assigned, the value “0” is stored. However, a method in which the PON-ID assignment flag  4631  is not provided can be adopted by making such a definition that in the case of not assigned, a value (for example, all are 0 or null code) previously determined in the ONU serial number storage area  4632  is stored.  
         [0050]      FIG. 4  shows an example of the structure of the delete ONU table  464  in this embodiment. The delete ONU table  464  is such a table that in this embodiment, when an ONU delete instruction or an ONU replacement instruction is received from the operation system  10  or the initial setting terminal  80 , the serial number of the ONU as the delete or replacement object is made to correspond to the “PON-ID” and is stored. Although the ONU delete instruction from the operation system  10  or the initial setting terminal  80  can be performed with the PON-ID, it may be performed with the ONU serial number itself. In  FIG. 4 , the delete ONU table  464  includes a delete object ONU serial number storage area  4641  as an area to store the ONU serial number of the delete or replacement object.  
         [0051]     In the example of  FIG. 4 , an area to store the PON-ID itself is not provided. This is because when the memory address and the PON-ID are made to correspond to each other, the area to store the PON-ID is not required. Since the example of  FIG. 4  is the structural example of the case in which 64 (0 to 63) ONUs at the maximum are connected, the areas up to PON-ID # 63  are shown. An area to store the PON-ID may be provided.  
         [0052]     In the delete object ONU serial number storage area  4641 , for example, in the case where the instruction of “deletion of ONU of PON-ID # 3 ” is received from the operation system  10 , the ONU serial number to which the PON-ID # 3  is assigned is stored into the area corresponding to PON-ID # 3 . A previously determined value (for example, all are 0 or null code) is stored in the area corresponding to the PON-ID which is being used (delete or replacement instruction is not received). Incidentally, for example, the operation system  10  receives the notification of ONU replacement from a subscriber or the like, and can specify the PON-ID.  
         [0053]     For example, a time lag can occur between the time when the OLT  40  receives the replacement instruction from the operation system  10  and the time when the ONU installer actually removes the ONU as the replacement object and connects a new ONU. Since the OLT  40  periodically searches for a serial number also in this period, in the state where the serial number is deleted from the PON-ID management table  463 , the ONU before the replacement is recognized as the new ONU, and the connection processing is performed. Then, the OLT  40  refers to the ONU deletion table  464 , and in the case where the searched serial number is stored, it is regarded as the serial number of the ONU of the replacement object or delete object, and the connection processing or the like is not performed.  
         [0054]      FIG. 5  is an explanatory view of an example of the definition of the PON-ID state  462  in this embodiment. In this embodiment, the PON-ID state  462  takes one of three states of “ONU is being replaced”, “there is PON-ID to be assigned” and “there is no PON-ID to be assigned”, and indicates the management state of the PON-ID.  
         [0055]     The example of  FIG. 5  is the example of the case in which 64 ONUs at the maximum are connected, and it is defined that the PON-ID state  462  indicating “ONU is being replaced” takes, for example, a value of 0 to 63. That is, the case of “PON-ID state  462 =3” means such a situation that the replacement instruction of PON-ID # 3  is received, and the replacement has not yet been ended. Besides, it is defined that in the case where the 64 ONUs are connected, and the assignment of PON-ID # 0  to # 63  has been completed, the state is made “there is no PON-ID to be assigned”, and a value “255” is taken. Further, it is defined that in the case where less than 64 ONUs are connected, the state is made “there is PON-ID to be assigned”, and a value of from “64” to “254” is taken. Incidentally, suitable values other than the above values can be defined as the values corresponding to the respective states.  
         [0000]     (Flowchart)  
         [0056]     Next, the operation of this embodiment will be described.  
         [0057]      FIG. 6  shows a flowchart of an example of the ONU connection main process  472  in this embodiment. The ONU connection main process  472  is a process to perform new connection, deletion, replacement, and connection recovery of an ONU.  
         [0058]     The ONU connection main process  472  is started from the main control process  471  at the time of OLT start. In the following description, respective processes can be executed by the CPU  450 . In addition to this process, the CPU  450  receives instructions of “ONU deletion”, “ONU replacement”, “ONU setting” and the like at suitable timing. These instructions can be stored in, for example, a queue.  
         [0059]     In the ONU connection main process  472 , the PON-ID management table  463  is searched, and it is judged whether or not at least one PON-ID has already been assigned (S 1  of  FIG. 6 ). In the case where the assignment has already been made, the information stored in the PON-ID management table  463  is used, and the ONU connection recovery process  473  is executed to recover the ONU connection (S 2  of  FIG. 6 ).  
         [0060]     Since the ONU connection recovery process  473  is the process in which the connection at the time of the former start is recovered at the time of OLT start, it has only to be performed once at the time of the OLT start.  
         [0061]     Next, in the ONU connection main process  472 , it is judged whether or not the “ONU deletion” instruction is received from the operation system  10  or the initial setting terminal  80  (S 3  of  FIG. 6 ). In the case where the “ONU deletion” instruction is received, the ONU delete process  474  is executed (S 4  of  FIG. 6 ).  
         [0062]     Next, it is judged whether or not the “ONU replacement” instruction is received from the operation system  10  or the initial setting terminal  80  (S 5  of  FIG. 6 ). In the case where the “ONU replacement” instruction is received, the ONU replacement process  475  is executed (S 6  of  FIG. 6 ).  
         [0063]     Next, the PON-ID state  462  is read, and it is judged whether or not the PON-ID state  462  indicates “there is PON-ID to be assigned” or “ONU is being replaced” (S 7  of  FIG. 6 ). In this embodiment, as shown in  FIG. 5 , it is judged whether the PON-ID state has a value of 64 to 254. In the case where the PON-ID state  462  indicates “there is PON-ID to be assigned” or “ONU is being replaced”, the ONU connection process  476  is executed (S 8  of  FIG. 6 ). In the case where the PON-ID state  462  indicates “there is no PON-ID to be assigned”, it means that the ONUs up to the maximum number are connected.  
         [0064]     Next, it is judged whether or not the “ONU setting” instruction is received from the operation system  10  or the initial setting terminal  80  (S 9  of  FIG. 6 ). In the case where the “ONU setting” instruction is received, the ONU setting process  477  is executed (S 10  of  FIG. 6 ).  
         [0065]     Next, in the ONU connection main process  472 , return is made to the judgment (S 3  of  FIG. 6 ) as to whether or not the “ONU deletion” instruction is received, and the subsequent processing is repeated. By repeating this processing, the ONU connection main process can deal with the additional connection, replacement, deletion, and setting of an ONU which is being used.  
         [0066]     Incidentally, the order of the processing of S 3 , S 5 , S 7  and S 9  of  FIG. 6  may be changed.  
         [0067]      FIGS. 7 and 8  show flowcharts of an example of the ONU connection process  476 . The ONU connection process  476  of step S 8  is the process to perform the new connection of the installed ONU.  FIG. 9  is a rough flowchart up to the ONU connection in the ranging flow processing described in the ITU-T Recommendation G.983.1. Since the ranging flow is described in the ITU-T Recommendation G.983.1, its explanation will be omitted.  
         [0068]     In the ONU connection process  476 , a processing up to the ONU serial number acquisition (S 903  of  FIG. 9 ) is performed in the ranging flow processing by the Method B based on the ITU-T Recommendation G.983.1 (S 801  of  FIG. 7 ). In the ranging flow by the Method B, since the ONU connection is performed without registration of the serial number of the ONU  60  from the OLT  40 , the search processing of the ONU serial number is required. In this embodiment, a known technique can be used as the search method of the ONU serial number. Here, when there is a newly connected ONU  60 , the serial number thereof is acquired.  
         [0069]     Next, it is judged whether the ONU serial number has been acquired (S 802  of  FIG. 7 ). In the case where the ONU serial number has not been acquired (No route of S 802  of  FIG. 7 ), it means that a new ONU has not been connected during one cycle of the ONU serial number search, and accordingly, the ONU connection process  476  is ended.  
         [0070]     In the case where the ONU serial number has been acquired (Yes route of S 802  of  FIG. 7 ), it is judged whether or not the acquired ONU serial number exists in the delete ONU table  464  (S 803  of  FIG. 7 ). In the case where the acquired ONU serial number exists in the ONU delete table  464  (Yes route of S 803  of  FIG. 7 ), since the ONU is the delete object, the ONU connection is not performed, and in order to continue the ONU search processing from the subsequent bit pattern, return is made to the ONU serial number search processing (S 801  of  FIG. 7 ). For example, in the case where the ONU itself is still connected although the instruction of “ONU” deletion is received, the serial number search is made by the foregoing ranging flow, however, the connection processing is not performed for the ONU. In the case where the acquired ONU serial number does not exist in the delete ONU table  464  (No route of S 801  of  FIG. 7 ), since the ONU is a newly connected ONU, the PON-ID state  462  is next read, and it is judged whether or not the PON-ID state  462  indicates “ONU is being replaced” (S 804  of  FIG. 8 ). For example, as shown in  FIG. 5 , it is judged whether the PON-ID state is a value of 0 to 63.  
         [0071]     In the case where the PON-ID state  462  indicates “ONU is being replaced” (Yes route of S 804  of  FIG. 8 ), the value of the PON-ID state  462  is set to be the PON-ID value which is assigned to the ONU whose serial number has now been acquired (S 805  of  FIG. 8 ). For example, the PON-ID state  462  indicates a value “3”, “3” is set as an “assigned PON-ID value”.  
         [0072]     In the case where the PON-ID state  462  does not indicate “ONU is being replaced” (No route of S 804  of  FIG. 8 ), the PON-ID management table  463  is searched, and one of non-assigned PON-ID values is set as the “assigned PON-ID value” (S 806  of  FIG. 8 ). The non-assigned PON-ID is the PON-ID indicating that the PON-ID assignment flag  4631  indicates a value “0”. In another method, the connection ONU serial number  4632  of the PON-ID management table  463  is the PON-ID indicating a previously determined value (for example, all are 0 or null code).  
         [0073]     Next, the processings (S 904  to S 906  of  FIG. 9 ) subsequent to the PON-ID setting of the ranging flow processing described in the ITU-T Recommendation G.983.1 are carried out (S 807  of  FIG. 8 ). By these processings, the ONU  60  and the OLT  40  are connected.  
         [0074]     Next, in the PON-ID management table  463 , a value “1”, which indicates that assignment has been made, and the acquired ONU serial number are respectively stored in the PON-ID assignment flag  4631  and the connection ONU serial number  4632  at the same PON-ID row as the “assigned PON-ID value”, and the PON-ID management table  463  is updated (S 808  of  FIG. 8 ).  
         [0075]     Next, in the delete ONU table  464 , the delete object ONU serial number  4641  at the same PON-ID row as the “assigned PON-ID value” is deleted (initialized) from the table (S 809  of  FIG. 8 ). This “S 809 ” processing is a correspondence processing at the time of ONU replacement. In the case where the ONU replacement instruction is received, the ONU serial number as the delete object and before the replacement is stored in the delete object ONU serial number  4641  at the PON-ID row of the delete ONU table  464 . When the ONU replacement is performed, the PON-ID is assigned to the new ONU after the replacement, and the ONU serial number of the delete object is deleted from the delete ONU table  464 .  
         [0076]     Next, the PON-ID management table  463  is searched, and it is judged whether there is room for the PON-ID (whether there is a non-assigned PON-ID) (S 810  of  FIG. 8 ). For example, reference is made to the PON-ID assignment flag, and when there is “0” indicating the non-assignment, it is judged that there is room. In the case where there is room (Yes route of S 810  of  FIG. 8 ), the PON-ID state  462  is made to have a value (for example, a value of 64 to 254) indicating “there is PON-ID to be assigned” and is stored (S 811  of  FIG. 8 ). In the case where there is no room (No route of S 810  of  FIG. 8 ), the PON-ID state  462  is made to have a value (for example, 255) indicating “there is no PON-ID to be assigned” and is stored (S 811  of  FIG. 8 ). This is the end of the ONU connection process.  
         [0077]      FIG. 10  shows a flowchart of an example of the ONU connection recovery process  473 . The ONU connection recovery process  473  of step S 2  of  FIG. 6  is such a process that the OLT is once started and after the ONU connection is performed, in the case where the OLT is restarted, the connection of the ONU is recovered in accordance with the setting stored in the past.  
         [0078]     In the ONU connection recovery process  473 , respective pieces of the information of the PON-ID management table  463  are read (S 201  of  FIG. 10 ). Next, the ranging flow processing (for example, S 901 , S 903  to S 906  of  FIG. 9 ) by the Method A based on the ITU-T Recommendation G.983.1 is performed for the ONU  60  to which the PON-ID has been assigned (S 202  of  FIG. 10 ).  
         [0079]     Although the ONT connection method in this embodiment is made the Method B, in the ONU connection recovery process  473 , since the ONU serial number has already been stored in the PON-ID management table  463 , it is possible to perform the ONU connection by the same procedure as the Method A.  
         [0080]     Next, it is judged whether or not the ranging flow processing has been performed for all the ONUs  60  to which the PON-IDs have already been assigned (S 203  of  FIG. 10 ). When there is an ONU  60  to which the PON-ID has been assigned and whose processing has not been performed (No route of S 203  of  FIG. 10 ), return is made to the processing of S 201 , and the processing is repeated. When the processing has been made for all the ONUs to which the PON-IDs have been assigned (Yes route of S 203  of  FIG. 10 ), the ONU connection recovery process  473  is ended.  
         [0081]      FIG. 11  is a flowchart of an example of the ONU delete process  474 . The ONU delete process  474  of step S 4  of  FIG. 6  is a process to delete the registration of the once connected ONU when the ONU  60  is removed due to, for example, termination of contract.  
         [0082]     The ONU delete process  474  receives, from the operation system  10  or the initial setting terminal  80 , the ONU delete instruction to specify the ONU to be deleted. At this time, the way of specifying the ONU of the delete object may be such that it is specified by the PON-ID, or it is specified by the ONU serial number, and in the ONU delete process  474 , the PON-ID is reversely obtained from the ONU serial number of the PON-ID management table  463 .  
         [0083]     In the ONU delete process  474 , the serial number of the delete object ONU is stored in the PON-ID row of the delete ONU table  464  (S 401  of  FIG. 11 ). As the serial number of the delete object ONU, the serial number acquired from the PON-ID management table  463  can be used based on, for example, the PON-ID specified by the ONU delete instruction. Next, in the PON-ID management table  463 , the PON-ID assignment flag  4631 , the connection ONU serial number  4632 , and the individual setting  4633  at the PON-ID row as the delete object are initialized (S 402  of  FIG. 11 ).  
         [0084]     Next, the PON-ID state  462  is read, and it is judged whether or not the PON-ID state  462  indicates “ONU is being replaced” (S 403  of  FIG. 11 ). In the case where the PON-ID state  462  does not indicate “ONU is being replaced” (No route of S 403  of  FIG. 11 ), a vacancy (non-assignment) ought to occur in the PON-ID assignment by the ONU deletion, an update is made such that the PON-ID state  462  indicates “there is PON-ID to be assigned” (S 404  of  FIG. 11 ), and the ONU delete process  474  is ended.  
         [0085]     In the case where the PON-ID state  462  indicates “ONU is being replaced” (Yes route of S 403  of  FIG. 11 ), the ONU delete process  474  is ended. The ONU replacement process  475  of step S 6  of  FIG. 6  is a process to replace the ONU when the ONU goes wrong.  
         [0086]      FIG. 12  shows a flowchart of an example of the ONU replacement process  475 .  
         [0087]     In the ONU replacement process  475 , the ONU replacement instruction to specify the ONU to be replaced is received from the operation system  10  or the initial setting terminal  80 . At this time, the way of specifying the ONU of the replacement object may be such that it is specified by the PON-ID, or it is specified by the ONU serial number, and in the ONU replacement process  475 , the PON-ID is reversely obtained from the ONU serial number of the PON-ID management table  463 .  
         [0088]     In the ONU replacement process  475 , the serial number of the replacement object ONU is stored in the PON-ID row of the delete ONU table  464  (S 601  of  FIG. 12 ). As the serial number of the replacement object ONU, based on the specified PON-ID, a number acquired from the PON-ID management table  463  can be used.  
         [0089]     Next, in the PON-ID management table  463 , the PON-ID assignment flag  4631  and the connection ONU serial number  4632  at the PON-ID row as the replacement object are initialized and stored (S 602  of  FIG. 12 ). At this time, since the ONU is replaced, the individual setting  4633  is not initialized and is held.  
         [0090]     Next, the PON-ID state  462  is updated to indicate “ONU is being replaced” and is stored (S 603  of  FIG. 12 ), and the ONU replacement process  475  is ended. For example, the value of the specified PON-ID is stored in the PON-ID state  462 .  
         [0091]      FIG. 13  is a flowchart of an example of the ONU setting process  477 . The ONU setting process  477  of step S 10  of  FIG. 6  is a process to set and store individual data relevant to the ONU.  
         [0092]     In the ONU setting process  477 , data content to be set in the ONU is received from the operation system  10  or the initial setting terminal  80 . The data content includes, for example, a network address, a maximum bandwidth, a user name and the like. At this time, the way of specifying the ONU of the data setting object may be such that it is specified by the PON-ID, or it is specified by the ONU serial number, and the PON-ID is reversely obtained from the ONU serial number of the PON-ID management table  463  in the ONU setting process  477 .  
         [0093]     In the ONU setting process  477 , the data setting is performed for the ONU  60  having the PON-ID in accordance with the instruction from the operation system  10  or the initial setting terminal  80 , and the data content (S 1001  of  FIG. 13 ).  
         [0094]     Next, in the ONU setting process  477 , the setting content is stored in the individual setting  4633  at the PON-ID row of the PON-ID management table  463  (S 1002  of  FIG. 13 ).  
         [0095]      FIG. 14  shows an example of the transition sequence of the PON-ID state  462 , the PON-ID management table  463 , and the delete ONU table  464  in accordance with the flowcharts of the embodiment. In  FIG. 14 , for simplification, an explanation will be mad while it is assumed that the maximum connection number of ONUs is two, and the ONU serial number is 1 byte.  
         [0096]     A state  501  of  FIG. 14  indicates an initial state, the PON-ID state  462  indicates “there is PON-ID to be assigned”, and the others indicate initial values. A state  502  of  FIG. 14  indicates a state in which one ONU having an ONU serial number 0x0A is connected, the operation is performed in accordance with the ONU connection process of  FIGS. 7 and 8 , and “XXX” is set as the individual setting in accordance with the ONU setting process of  FIG. 13 . A state  503  of  FIG. 14  indicates a state in which one ONU having an ONU serial number 0x0B is additionally connected, the operation is performed in accordance with the ONU connection process of  FIGS. 7 and 8 , and “YYY” is set as the individual setting.  
         [0097]     A state  504  of  FIG. 14  indicates a state in which the delete instruction of the ONU of PON-ID # 1  is made, and the operation is performed in accordance with the ONU delete process of  FIG. 11 . In the ONU delete process, the individual setting (XXX) is also deleted. A state  505  of  FIG. 14  indicates a state in which the replacement instruction of the ONU of PON-ID # 2  is made, and the operation is performed in accordance with the ONU replacement process of  FIG. 12 . In the ONU replacement process, the individual setting (YYY) is not deleted.  
         [0098]     A state  506  of  FIG. 14  indicates the result of an operation in which the ONU having the ONU serial number 0x0B is replaced by a new ONU having an ONU serial number 0x0C, and the operation is performed in accordance with the ONU connection process of  FIGS. 7 and 8 . Here, there is indicated a state in which the individual setting data “YYY” before the replacement is succeeded to the ONU (serial number 0x0C) after the replacement.  
         [0099]     In the embodiment 1, although the ONU management method in the ATM-PON system has been described as an example, the invention can be applied to an ONU management method in a GPON system, or another PON system.  
         [0100]     According to the embodiment, in the PON system, it is not necessary that at the time of ONU installation or replacement, an ONU installation worker and an operation system administrator communicate with each other, and the ONU serial number is inputted from the operation system to the OLT, or the ONU setting data is set again after the ONU replacement, and the ONU replacement can be facilitated.  
         [0101]     According to the invention, the ONU management method and the optical line termination can be provided in which in the PON system, the ONU connection is performed without registering the serial number from the operation system to the OLT, and the same PON-ID as that before the replacement of the ONU is assigned to the new ONU. Besides, according to the invention, the setting data before the replacement can be succeeded also after the replacement.  
         [0102]     According to the invention, in the PON system, it becomes unnecessary that at the time of ONU installation or replacement, the ONU installation worker and the operation system administrator communicate with each other in real time, and the ONU serial number is inputted from the operation system to the OLT. Besides, according to the invention, it is not necessary to set the ONU setting data again after the ONU replacement, and the ONU replacement can be facilitated.