Abstract:
Provided is an optical relay system ( 10 ) which is capable of suppressing wasteful power consumption of an entire system to a low level. The optical relay system ( 10 ) includes a plurality of relay devices ( 30 ) and a network control device ( 20 ). The network control device ( 20 ) causes an optical signal to be regenerated by a regenerative repeater ( 35 ) within the relay device ( 30 ) existing at an upstream of the relay device ( 30 ) reporting that the optical signal has deteriorated by a degree exceeding a predetermined level. Further, the network control device ( 20 ) causes the regenerative repeater ( 35 ) to stop regenerating the signal in a case where deterioration of the signal remains within an allowable range even when the regenerative repeater ( 35 ) stops regenerating the signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese application JP 2010-130893 filed on (Jun. 8, 2010), the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     The present application relates to an optical relay system which relays an optical signal by wavelength division multiplexing. 
     An optical add/drop multiplexer (OADM) which adds/drops a partial wavelength of a plurality of wavelengths that are multiplexed is introduced into a node device within an optical network which uses wavelength division multiplexing (WDM). Further, in recent years, introduction of a wavelength selective switch (WSS) is underway as a device capable of switching a path of an optical signal having an arbitrary wavelength. By building a network using the wavelength selective switch, it is possible to easily change the path of the optical signal even in the network configured only by the optical signal. 
     However, compared with a network which relays an optical signal by converting the optical signal into an electrical signal, the optical network which relays the optical signal as it is raises a problem that deterioration of the optical signal accumulates. Therefore, in a case of performing a long-distance transmission of the optical signal, it is necessary to perform signal regeneration by using a relay device to temporarily convert the optical signal into the electrical signal. Japanese Patent Application Laid-open No. 2009-147913 (hereinafter, referred to as “Patent Document 1”) discloses a wavelength selective switch incorporating a regenerative repeater which performs signal regeneration by converting an optical signal into an electrical signal. 
     SUMMARY OF THE INVENTION 
     However, according to the technology disclosed in Patent Document 1, when the path of the optical signal is changed from an initial stage in which an optical network is built, there may be a case where there is a change in a distance by which the optical signal is transmitted without the intermediation of the regenerative repeater, which causes quality of the optical signal to deteriorate, and hence the received signal cannot be decoded. It cannot be decided where to locate the regenerative repeater in the new path without examining deterioration degrees of signal quality within respective relay devices. 
     Therefore, even when the wavelength selective switch is used to rapidly switch a relay path of the optical signal, there is no guarantee that the optical signal is appropriately transmitted in the path after the change until completion of the examination of the deterioration degrees of the signal quality within the respective relay devices, and hence it is impossible to gain an advantage that the wavelength selective switch facilitates path switching. 
     Further, there is an idea of constantly regenerating the optical signal by using all the relay devices all of which are provided with regenerative repeaters in order to handle all kinds of path change, but the regeneration may be performed even in a situation in which the regeneration is unnecessary, which leads to wasteful power consumption of the regenerative repeater. In addition, a plurality of optical signals having multiplexed wavelengths pass through each of the relay devices, and hence the wasteful power consumption increases when the regenerative repeaters for all the wavelengths are constantly operated on all the relay devices. 
     The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to suppress wasteful power consumption of an entire optical relay system to a low level by operating a regenerative repeater when an optical signal needs to be regenerated. 
     In order to achieve the above-mentioned object, according to the present invention, an optical signal is regenerated by a regenerative repeater within a relay device at an upstream of a relay device reporting that the optical signal has deteriorated by a value equal to or higher than a predefined threshold value. 
     For example, the present invention provides an optical relay system, which relays an optical signal by wavelength division multiplexing, including: 
     a plurality of relay devices each of which relays the optical signal; and 
     a network control device which controls each of the plurality of relay devices,
         each of the plurality of relay devices including:
           a wavelength selective switch;   a deterioration degree measuring section which measures a deterioration degree of the optical signal having each wavelength and notifies the network control device of the measured deterioration degree along with a signal ID which identifies the corresponding optical signal and a relay device ID which identifies the own relay device; and   a regenerative repeater which regenerates the optical signal corresponding to the signal ID when a regeneration instruction including the signal ID is received from the network control device,   
           the network control device including:
           an equipment information retaining section which retains, for each of relay device IDs, a regenerative repeater ID which identifies the regenerative repeater included in the relay device corresponding to the each of the relay device IDs and use information which indicates whether or not the regenerative repeater is in use;   a relay path retaining section which retains, for each of signal IDs, information which identifies an order in which the optical signal is relayed by a plurality of the relay devices existing on a relay path of the optical signal corresponding to the each of the signal IDs and the relay device IDs of the plurality of the relay devices existing on the relay path of the optical signal;   a threshold value retaining section which retains a threshold value of the deterioration degree which is allowed for the optical signal having the each wavelength;   a deterioration degree retaining section which retains, for each of the signal IDs, the deterioration degree notified with regard to the optical signal corresponding to the each of the signal IDs, in association with the relay device ID of the relay device that has notified the deterioration degree;   a deterioration degree collecting section which stores the deterioration degree notified from each of the plurality of relay devices in the deterioration degree retaining section in association with the signal ID and the relay device ID which have been notified along with the deterioration degree; and   a regenerative repeater allocation management section which executes a regenerative repeater allocation processing for each of the signal IDs,   
               

     in which the regenerative repeater allocation management section is configured to, in the regenerative repeater allocation processing: 
     reference the deterioration degree retaining section and the threshold value retaining section, for each of the signal IDs, to extract the relay device ID associated with the deterioration degree equal to or higher than the threshold value from the deterioration degree retaining section when the relay device that has notified the deterioration degree equal to or higher than the threshold value exists; 
     identify the relay device IDs of the relay devices existing upstream of the relay device having the extracted relay device ID on the relay path of the optical signal corresponding to the each of the signal IDs from within the relay path retaining section; 
     select the relay device ID of the relay device including an unused regenerative repeater among the identified relay device IDs from within the equipment information retaining section; and 
     transmit, to the relay device corresponding to the selected relay device ID, the regeneration instruction including the signal ID of the optical signal having the deterioration degree notified as being equal to or higher than the threshold value. 
     According to the present application, by operating the regenerative repeater when the optical signal needs to be regenerated, it is possible to suppress wasteful power consumption of the entire optical relay system to a low level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a system configuration diagram illustrating a configuration of an optical relay system according to an embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating an example of a functional configuration of a relay device; 
         FIG. 3  is a block diagram illustrating an example of a functional configuration of a network control device; 
         FIG. 4  is a diagram illustrating an example of a structure of data stored in an equipment information retaining section; 
         FIG. 5  is a diagram illustrating an example of a structure of data stored in a path information retaining section; 
         FIG. 6  is a conceptual diagram illustrating a distribution of deterioration degrees across a relay path of an optical signal whose signal ID is “S 004 ”; 
         FIG. 7  is a diagram illustrating an example of a structure of data stored in a priority retaining section; 
         FIG. 8  is a diagram illustrating an example of a structure of data stored in a replacement information retaining section; 
         FIG. 9  is a flowchart illustrating an example of an operation of the network control device; 
         FIG. 10  is a flowchart illustrating an example of a first regenerative repeater allocation processing (S 200 ); 
         FIG. 11  is a conceptual diagram for describing a flow of the optical signal relayed within the optical relay system; 
         FIG. 12  is a diagram illustrating an example of a structure of data of a list created in a process of the first regenerative repeater allocation processing; 
         FIG. 13  is a flowchart illustrating an example of a replacement information creating processing (S 220 ); 
         FIG. 14  is a conceptual diagram for describing a process for creating replacement information; 
         FIG. 15  is a conceptual diagram for describing the process for creating the replacement information; 
         FIG. 16  is a flowchart illustrating an example of a replacement processing (S 230 ); 
         FIG. 17  is a flowchart illustrating an example of a second regenerative repeater allocation processing (S 300 ); 
         FIG. 18  is a conceptual diagram for describing the optical signal caused to flow through the optical relay system before the relay path is changed; 
         FIG. 19  is a flowchart illustrating an example of a regeneration stopping processing (S 310 ); 
         FIG. 20  is a conceptual diagram for describing a process for the regeneration stopping processing; 
         FIG. 21  is a conceptual diagram for describing the process for the regeneration stopping processing; and 
         FIG. 22  is a hardware configuration diagram illustrating an example of a computer which realizes functions of the network control device. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, an embodiment of the present invention is described with reference to the accompanying drawings. 
       FIG. 1  is a system configuration diagram illustrating a configuration of an optical relay system  10  according to the embodiment of the present invention. The optical relay system  10  includes a plurality of terminal devices  13 , a plurality of relay devices  30 , and a network control device  20  which controls the respective relay devices  30 . 
     The respective terminal devices  13  are, for example, connected to a plurality of communication devices  11  via access lines  12  such as metal cables. Further, the plurality of relay devices  30  are provided between the terminal devices  13 , and optical fiber cables are used for connections between the terminal device  13  and the relay device  30  and between the relay device  30  and the relay device  30 . Further, the respective terminal devices  13  and the respective relay devices  30  communicate with the network control device  20  via a management network (indicated by the dotted lines of  FIG. 1 ) such as metal cables. 
     Each of the relay devices  30 , which includes a wavelength selective switch (WSS), receives an optical signal obtained by multiplexing optical signals having a plurality of wavelengths via the optical fiber cable, and separates the received optical signal into the optical signals having the respective wavelengths. Then, according to an instruction issued from the network control device  20 , the relay device  30  again multiplexes the optical signals having the respective wavelengths for each of the other relay devices  30  or each of the terminal devices  13  that is a transmission destination, and sends out the multiplexed optical signal to another of the relay devices  30  or the terminal device  13 . 
     Further, each of the terminal devices  13  and the relay devices  30  measures a deterioration degree of the optical signal having each wavelength received from another terminal device  13  or another relay device  30 , and notifies the network control device  20  of the measured deterioration degree via the management network. Further, when a regeneration instruction that specifies the optical signal having a specific wavelength is received from the network control device  20  via the management network, in relaying the optical signal having each wavelength received from another terminal device  13  or another relay device  30 , each of the relay devices  30  regenerates and sends out the optical signal having the wavelength specified by the regeneration instruction from among the optical signals having the respective wavelengths. 
     When the network control device  20  is notified of the deterioration degrees of the optical signals having the respective wavelengths from each of the terminal devices  13  and the relay devices  30  via the management network, with regard to the optical signal whose deterioration degree is equal to or higher than a predetermined level, the network control device  20  transmits the regeneration instruction that specifies the above-mentioned optical signal to any one of the relay devices  30  located on a relay path of the above-mentioned optical signal. 
       FIG. 2  is a block diagram illustrating an example of a functional configuration of the relay device  30 . The relay device  30  includes a plurality of demultiplexers  31 , a wavelength selective switch (WSS)  32 , a plurality of multiplexers  33 , a deterioration degree measuring section  34 , a regenerative repeater  35 , and a communication section  36 . 
     Each of the demultiplexers  31 , which is provided for each of the terminal device  13  of a relay source and the other relay devices  30  to which the own relay device  30  is connected via the optical fiber cables, separates the optical signal received from the terminal device  13  or another relay device  30  into the optical signals having the respective wavelengths, and sends the optical signals to the WSS  32 . 
     The WSS  32  sends the optical signal having each wavelength received from each of the demultiplexers  31  to any one of the multiplexers  33  according to an instruction received from the network control device  20  via the communication section  36 . Further, when the optical signal is being regenerated by the regenerative repeater  35 , the WSS  32  sends the optical signal regenerated by the regenerative repeater  35  to the multiplexer  33  in place of the optical signal before regeneration thereof. 
     Each of the multiplexers  33 , which is provided for each of the terminal device  13  of a relay destination and the other relay devices  30  to which the own relay device  30  is connected via the optical fiber cables, multiplexes the optical signals having the respective wavelengths output from the WSS  32 , and sends out the multiplexed optical signal to the terminal device  13  of the relay destination or another relay device  30 . 
     The deterioration degree measuring section  34  measures the deterioration degree of the optical signal having each wavelength obtained by separation by the demultiplexer  31  at regular timings, for example, every hour or at a timing at which a quality measuring instruction is received from the network control device  20  via the communication section  36 . Then, the deterioration degree measuring section  34  sends quality information to the network control device  20  via the communication section  36 , the quality information including the measured deterioration degree, a signal ID which identifies the optical signal to be subjected to the measurement, and a relay device ID which identifies the own relay device  30 . 
     In this embodiment, the term “deterioration degree” represents a numerical value indicating a degree of deterioration in quality of the optical signal and assuming a higher numerical value for the optical signal having worse quality. In this embodiment, the deterioration degree is, for example, the reciprocal of a signal-to-noise ratio (SNR). 
     The regenerative repeater  35  extracts the optical signal having a wavelength corresponding to a signal ID from the WSS  32  when the regeneration instruction including the signal ID is received from the network control device  20  via the communication section  36 , regenerates the optical signal, and returns the regenerated optical signal to the WSS  32 . Further, when a regeneration stopping instruction including a signal ID is received from the network control device  20  via the communication section  36 , the regenerative repeater  35  stops the regeneration being executed for the optical signal corresponding to the signal ID. 
     The communication section  36  communicates with the network control device  20  via the management network, and sends the regeneration instruction and the regeneration stopping instruction, which are received from the network control device  20  via the management network, to the regenerative repeater  35 . Further, the communication section  36  sends the quality measuring instruction, which is received from the network control device  20  via the management network, to the deterioration degree measuring section  34 , and transmits the quality information, which is received from the deterioration degree measuring section  34 , to the network control device  20  via the management network. 
       FIG. 3  is a block diagram illustrating an example of a functional configuration of the network control device  20 . The network control device  20  includes a communication section  21 , a path changing section  22 , a deterioration degree collecting section  23 , a path information retaining section  24 , a priority retaining section  25 , a regenerative repeater allocation section  26 , a replacement information retaining section  27 , an equipment information retaining section  28 , and a threshold value retaining section  29 . The communication section  21  communicates with the terminal device  13  and the relay device  30  via the management network. 
     The equipment information retaining section  28  retains, as illustrated in, for example,  FIG. 4 , in association with a relay device ID  280  which identifies each of the relay devices  30 , a regenerative repeater ID  281  which identifies the regenerative repeater  35  included in the relay device  30 , use information  282  which indicates whether or not the regenerative repeater  35  is in use, and a signal ID  283  which identifies the optical signal having a wavelength being regenerated by the regenerative repeater  35  in a case where the regenerative repeater  35  is in use. The relay device ID  280  and the regenerative repeater ID  281  are registered in advance in a stage in which each of the relay devices  30  is installed. The use information  282  stores “unused” as a default value. 
     The threshold value retaining section  29  retains a threshold value of the deterioration degree which is allowed for each optical signal having each wavelength. In this embodiment, the threshold value retaining section  29  retains one threshold value. It should be noted that, as another mode, in a case where the deterioration degree that is allowed for the optical signal having each wavelength differs according to the wavelength, in a case where the relay devices  30  and the terminal devices  13  have different capabilities to decode the optical signal, or other such cases, different threshold values may be provided according to the wavelength, the relay device  30 , or the terminal device  13 . 
     The path information retaining section  24  retains, as illustrated in, for example,  FIG. 5 , in association with a signal ID  240  which identifies the optical signals having each wavelength, a relay device ID  241  of the relay device  30  which relays the optical signal. Further, in association with the signal ID  240  and the relay device ID  241 , the path information retaining section  24  retains a deterioration degree  242  of the optical signal corresponding to the signal ID  240 , which has been notified from the relay device having the relay device ID  241 . 
     In this embodiment, the relay device IDs of the relay devices  30  which relay the corresponding optical signal are stored in the relay device ID  241  in an order in which the corresponding optical signal is relayed. The information on the signal ID  240  and the relay device ID  241  is set when the relay path of each optical signal is decided by an administrator of the optical relay system  10 . 
       FIG. 6  is a conceptual diagram illustrating a distribution of the deterioration degrees  242  across the relay path of the optical signal of which the signal ID  240  is “S 004 ” in the information within the path information retaining section  24  exemplified in  FIG. 5 . In  FIG. 6 , the black circle indicates a value of the deterioration degree notified from each of the terminal devices  13  and the relay devices  30 . The optical signal of which the signal ID  240  is “S 004 ” is relayed to a relay device  30 E via a relay device  30 D after being output from a terminal device  13 A, regenerated by a regenerative repeater  35   e  within the relay device  30 E, and further relayed to a terminal device  13 B via a relay device  30 F and a relay device  30 G. 
     The priority retaining section  25  retains, as illustrated in, for example,  FIG. 7 , in association with a signal ID  250  which identifies the optical signal having each wavelength, a priority  251  of the optical signal. The information within the priority retaining section  25  is set in advance by the administrator of the optical relay system  10 . 
     The replacement information retaining section  27  retains replacement information  270  as illustrated in, for example,  FIG. 8 . Stored in the replacement information  270 , in association with a signal ID  271  which identifies the optical signal having each wavelength, are an in-use device ID  272  which indicates the relay device ID of the relay device  30  including the regenerative repeater  35  that is regenerating the optical signal and a replacement device ID  273  which indicates the relay device ID of the relay device  30  including another regenerative repeater  35  that can replace the regenerative repeater  35  in regenerating the optical signal. 
     Next,  FIG. 9  and the subsequent figures are referenced to describe operations of the other functional blocks of the network control device  20 .  FIG. 9  is a flowchart illustrating an example of an operation of the network control device  20 . The network control device  20  starts the operation illustrated in this flowchart at a predetermined timing, for example, when power is turned on. 
     First, the deterioration degree collecting section  23  determines whether or not the quality information has been received from the terminal device  13  or the relay device  30  via the communication section  21  (S 100 ). When the quality information has been received (S 100 : Yes), the deterioration degree collecting section  23  stores the deterioration degree included in the quality information in the path information retaining section  24  in association with the signal ID and the relay device ID that are included in the received quality information (S 101 ), and again executes the processing illustrated in Step S 100 . 
     On the other hand, when the quality information has not been received (S 100 : No), the regenerative repeater allocation section  26  determines whether or not a timing to examine the deterioration degree of the optical signal in each of the terminal devices  13  and the relay devices  30  has been reached (S 102 ), determines whether or not a reception error including a signal ID has been notified from the terminal device  13  via the communication section  21  (S 103 ), and determines whether or not an instruction to reallocate the regenerative repeater has been received from the administrator of the optical relay system  10  through an input device  17  (S 104 ). The timing to examine the deterioration degree of the optical signal is, for example, every hour. 
     When the timing to examine the deterioration degree of the optical signal has been reached (S 102 : Yes), when the reception error has been notified (S 103 : Yes), or when the instruction to reallocate the regenerative repeater has been received (S 104 : Yes), the regenerative repeater allocation section  26  executes a first regenerative repeater allocation processing described later (S 200 ), and the deterioration degree collecting section  23  again executes the processing illustrated in Step S 100 . 
     On the other hand, when the timing to examine the deterioration degree of the optical signal has not been reached (S 102 : No), when the reception error has not been notified (S 103 : No), and when the instruction to reallocate the regenerative repeater has not been received (S 104 : No), the path changing section  22  determines whether or not an instruction to change the relay path has been received from the administrator of the optical relay system  10  through the input device  17  (S 105 ). When the instruction to change the relay path has not been received (S 105 : No), the deterioration degree collecting section  23  again executes the processing illustrated in Step S 100 . 
     When the instruction to change the relay path has been received (S 105 : Yes), the path changing section  22  instructs each of the subject terminal devices  13  and relay device  30  to change the relay path according to the instruction issued by the administrator of the optical relay system  10  via the communication section  21  (S 106 ). Then, the path changing section  22  changes the relay device ID of the relay device  30  on the relay path retained within the path information retaining section  24  with regard to the optical signal to be subjected to the changing of the path (S 107 ). 
     Subsequently, the path changing section  22  transmits the quality measuring instruction to each of the terminal devices  13  and the relay devices  30  via the communication section  21  (S 108 ). Then, the deterioration degree collecting section  23  receives the quality information from the terminal device  13  or the relay device  30  via the communication section  21 , and stores the deterioration degree included in the quality information in the path information retaining section  24  in association with the signal ID and the relay device ID that are included in the received quality information (S 109 ). Then, the regenerative repeater allocation section  26  executes a second regenerative repeater allocation processing described later (S 300 ), and the deterioration degree collecting section  23  again executes the processing illustrated in Step S 100 . 
       FIG. 10  is a flowchart illustrating an example of the first regenerative repeater allocation processing (S 200 ). 
     First, the regenerative repeater allocation section  26  sets a replacement information creation flag, which indicates that replacement information needs to be created, to “1” (S 201 ), and references the priority retaining section  25  to select one signal ID of the optical signal having the highest priority from among the unselected optical signals (S 202 ). 
     Subsequently, the regenerative repeater allocation section  26  references the path information retaining section  24  and the threshold value retaining section  29  to determine whether or not the signal ID selected in Step S 202  is associated with the deterioration degree equal to or higher than the threshold value (S 203 ). When the signal ID selected in Step S 202  is not associated with the deterioration degree equal to or higher than the threshold value (S 203 : No), the regenerative repeater allocation section  26  executes the processing illustrated in Step S 207 . 
     On the other hand, when the signal ID selected in Step S 202  is associated with the deterioration degree equal to or higher than the threshold value (S 203 : Yes), the regenerative repeater allocation section  26  extracts one relay device ID associated with the deterioration degree equal to or higher than the threshold value from the path information retaining section  24 . It should be noted that in a case where the signal ID selected in Step S 202  is associated with a plurality of deterioration degrees equal to or higher than the threshold value, the regenerative repeater allocation section  26  extracts, from the path information retaining section  24 , one relay device ID of the relay device located at the most upstream on the relay path of the optical signal corresponding to the signal ID selected in Step S 202  from among the relay device IDs associated with the deterioration degrees equal to or higher than the threshold value. 
     Subsequently, the regenerative repeater allocation section  26  references the path information retaining section  24  to create a list in which the relay device IDs of the relay devices located at an upstream of the relay device having the extracted relay device ID on the relay path of the optical signal corresponding to the signal ID selected in Step S 202  are stored in association with the signal ID selected in Step S 202  (S 204 ). 
     For example, as illustrated in  FIG. 11 , in a situation in which the optical signal of which signal ID is “S 001 ” is being transmitted from the terminal device  13 A to the terminal device  13 B by being relayed via the relay device  30 D, the relay device  30 E, the relay device  30 F, a relay device  301 , and a relay device  30 J in the stated order, when the deterioration degree notified from the relay device  301  is equal to or higher than the threshold value, the regenerative repeater allocation section  26  creates a list  40  as illustrated in, for example,  FIG. 12 . It should be noted that in  FIG. 11 , a box within each of the relay devices  30  represents the regenerative repeater  35 , and the black-filled box indicates that the regenerative repeater  35  is in use. 
     Stored in the list  40  in association with a signal ID  41  selected in Step S 202  are relay device IDs  42 , in other words, the relay device ID “ 30 D” of the relay device  30 D, the relay device ID “ 30 E” of the relay device  30 E, and the relay device ID “ 30 F” of the relay device  30 F that are located at the upstream of the relay device  301  on the relay path of the optical signal corresponding to the signal ID  41 . 
     Subsequently, the regenerative repeater allocation section  26  references the equipment information retaining section  28  to determine whether or not the relay device  30  including the unused regenerative repeater  35  exists among the relay devices  30  corresponding to the relay device IDs within the list created in Step S 204  (S 205 ). 
     In the example of  FIG. 11 , the optical signal whose signal ID is “S 002 ” is being regenerated by a regenerative repeater  35   f  within the relay device  30 F whose relay device ID is “ 30 F”, the optical signal whose signal ID is “S 004 ” is being regenerated by the regenerative repeater  35   e  within the relay device  30 E whose relay device ID is “ 30 E”, and the optical signal whose signal ID is “S 005 ” is being regenerated by a regenerative repeater  35   d  within the relay device  30 D whose relay device ID is “ 30 D”. 
     The above-mentioned situation is also understood from the information within the equipment information retaining section  28  exemplified in  FIG. 4 . By referring to  FIG. 4 , it is understood that the regenerative repeaters  35  within the relay devices  30  corresponding to the relay device IDs “ 30 D”, “ 30 E”, and “ 30 F” stored in the list  40  exemplified in  FIG. 12  are all in use. 
     When the relay device  30  including an unused regenerative repeater  35  exists (S 205 : Yes), the regenerative repeater allocation section  26  transmits the regeneration instruction including the signal ID selected in Step S 202  to the relay device  30  including the unused regenerative repeater  35  via the communication section  21  (S 206 ). It should be noted that in a case where a plurality of relay devices  30  including the unused regenerative repeater  35  exist, the regenerative repeater allocation section  26  transmits the regeneration instruction including the signal ID selected in Step S 202  to the relay device  30  that is located on the relay path at the upstream of the relay device  30  that has reported the deterioration degree equal to or higher than the threshold value and at the most downstream from among the relay devices  30  including the unused regenerative repeater  35  (in other words, the relay device  30  located on the relay path at the closest upstream of the relay device  30  that has reported the deterioration degree equal to or higher than the threshold value). 
     Subsequently, the regenerative repeater allocation section  26  determines whether or not the signal IDs of all the optical signals have been selected in Step S 202  (S 207 ). When there is an unselected signal ID (S 207 : No), the regenerative repeater allocation section  26  again executes the processing illustrated in Step S 202 . On the other hand, when the signal IDs of all the optical signals have been selected (S 207 : Yes), the regenerative repeater allocation section  26  ends the first regenerative repeater allocation processing illustrated in this flowchart. 
     When it is determined in Step S 205  that the relay device ID of the relay device  30  including the unused regenerative repeater  35  does not exist in the list created in Step S 204  (S 205 : No), the regenerative repeater allocation section  26  determine whether or not the replacement information creation flag is set to “1” (S 208 ). When the replacement information creation flag is not set to “1” (S 208 : No), the regenerative repeater allocation section  26  executes the processing illustrated in Step S 210 . 
     On the other hand, when the replacement information creation flag is set to “1” (S 208 : Yes), the regenerative repeater allocation section  26  executes a replacement information creating processing described later (S 220 ), and sets the replacement information creation flag to “0” (S 209 ). When the replacement information creating processing described later is executed, the information as illustrated in, for example,  FIG. 8  is stored into the replacement information retaining section  27 . By referring to the replacement information retaining section  27 , it is possible to identify the relay device  30  including the regenerative repeater  35  that can be replaced by another unused regenerative repeater  35  in regenerating the optical signal. 
     Subsequently, the regenerative repeater allocation section  26  references the replacement information retaining section  27  in which the information created in Step S 220  is registered to determine whether or not the relay device  30  including the regenerative repeater  35  that can be replaced exists within the list created in Step S 204  (see  FIG. 12 ) (S 210 ). Specifically, the regenerative repeater allocation section  26  determines whether or not anyone of the relay device IDs within the list created in Step S 204  is registered as an in-use device ID within the replacement information retaining section  27  in which the information created in Step S 220  is registered. 
     When the relay device  30  including the regenerative repeater  35  that can be replaced exists within the list created in Step S 204  (S 210 : Yes), the regenerative repeater allocation section  26  executes a replacement processing for replacing the relay device  30  registered as the in-use device ID within the replacement information retaining section  27  by another relay device  30  corresponding to a replacement device ID associated with the in-use device ID in regenerating the optical signal (S 230 ). Details of the replacement processing are described later. Then, the regenerative repeater allocation section  26  sets the replacement information creation flag to “1” (S 211 ), and executes the processing illustrated in Step S 207 . 
     When the relay device  30  including the regenerative repeater  35  that can be replaced does not exist within the list created in Step S 204  (S 210 : No), the regenerative repeater allocation section  26  displays an error to the effect that the deterioration of the signal cannot be resolved due to absence of another regenerative repeater  35  that can be allocated on a display device (not shown) or the like along with the signal ID selected in Step S 202  (S 212 ), and executes the processing illustrated in Step S 207 . 
     By the execution of the first regenerative repeater allocation processing illustrated in this flowchart, when the deterioration degree of the optical signal becomes equal to or higher than the threshold value in the relay device  30  on the relay path of each optical signal, if the relay device  30  including the unused regenerative repeater  35  exists on the relay path, the regenerative repeater allocation section  26  assigns the regenerative repeater  35  to thereby lower the deterioration degree of the optical signal. 
     Further, when the deterioration degree of the optical signal becomes equal to or higher than the threshold value, even when the relay device  30  including the unused regenerative repeater  35  does not exist on the relay path, as long as the regenerative repeater  35  that is in use on the relay path can be replaced by another regenerative repeater  35 , the regenerative repeater allocation section  26  can lower the deterioration degree of the optical signal by assigning the regenerative repeater  35  that has become unused by the replacement. 
       FIG. 13  is a flowchart illustrating an example of the replacement information creating processing (S 220 ). 
     First, one unselected signal ID is further selected from among the signal IDs unselected in Step S 202  (S 221 ), and the relay device ID associated with the selected signal ID is extracted from the path information retaining section  24 . Then, the regenerative repeater allocation section  26  references the equipment information retaining section  28  to determine whether or not the extracted relay device ID is associated with use information indicating that the regenerative repeater  35  is in use, to thereby determine whether or not the optical signal corresponding to the selected signal ID is being regenerated by the regenerative repeater  35  of any one of the relay devices  30  on the relay path (S 222 ). 
     When the optical signal corresponding to the selected signal ID is not being regenerated by the regenerative repeater  35  of any one of the relay devices  30  on the relay path (S 222 : No), the regenerative repeater allocation section  26  executes the processing illustrated in Step S 229 . 
     On the other hand, when the optical signal corresponding to the selected signal ID is being regenerated by the regenerative repeater  35  of any one of the relay devices  30  on the relay path (S 222 : Yes), the regenerative repeater allocation section  26  calculates the deterioration degrees of the respective relay devices  30  on the relay path on the assumption that the regeneration by the regenerative repeater  35  is stopped (S 223 ). 
     For example, consideration is given to a case where the deterioration degrees measured in the respective relay devices  30  on the relay path with regard to the optical signal whose signal ID is “S 004 ” are distributed as indicated by, for example, the black circles of  FIG. 6 . In the example of  FIG. 6 , the optical signal is being regenerated by the regenerative repeater  35   e  within the relay device  30 E. 
     First, the regenerative repeater allocation section  26  calculates a difference Δd 1  between the deterioration degree of the optical signal before the regeneration (black circle of  FIG. 6 ) and the deterioration degree thereof after the regeneration (white circle of  FIG. 6 ) in the relay device  30 E regenerating the optical signal. It should be noted that the deterioration degree before the regeneration (black circle of  FIG. 6 ) is a value measured by the deterioration degree measuring section  34  within the relay device  30 E. Further, the deterioration degree after the regeneration, which is predefined as a regeneration capability of each regenerative repeater  35 , is used as the deterioration degree after the regeneration (white circle of  FIG. 6 ). 
     Then, as illustrated in, for example,  FIG. 14 , the regenerative repeater allocation section  26  calculates first virtual deterioration degrees (white squares of  FIG. 14 ) by adding the calculated difference Δd 1  to the deterioration degrees measured by the relay device  30 F, the relay device  30 G, and the terminal device  13 B that are located on the relay path at a downstream of the relay device  30 E including the regenerative repeater  35   e  executing the regeneration. 
     Subsequently, the regenerative repeater allocation section  26  references the path information retaining section  24  and the equipment information retaining section  28  to extract the regenerative repeater IDs of the unused regenerative repeaters  35  from among the relay devices  30  on the relay path of the optical signal corresponding to the signal ID selected in Step S 221 . Then, the regenerative repeater allocation section  26  selects one regenerative repeater ID that is unselected from among the extracted regenerative repeater IDs (S 224 ), and calculates the distribution of the deterioration degrees measured in the respective relay devices  30  obtained in a case where the regeneration is performed by the regenerative repeater  35  corresponding to the selected regenerative repeater ID (S 225 ). 
     For example, in the distribution of the deterioration degrees including the first virtual deterioration degrees calculated as described with reference to  FIG. 14 , the regenerative repeater allocation section  26  calculates a difference Δd 2  between the deterioration degrees, as illustrated in  FIG. 15 , obtained in a case where the regeneration is performed by the relay device  30 G including an unused regenerative repeater  35   g . Then, the regenerative repeater allocation section  26  calculates a second virtual deterioration degree by subtracting the calculated difference Δd 2  from the first virtual deterioration degree calculated with regard to the terminal device  13 B located on the relay path at the downstream of the relay device  30 G. 
     For example, in the example of  FIG. 15 , at a timing at which the calculation performed in Step S 225  is finished, the measured deterioration degrees are employed for the relay device  30 D and the relay device  30 E, the first virtual deterioration degrees calculated in Step S 223  are employed for the relay device  30 F and the relay device  30 G, and the second virtual deterioration degree calculated in Step S 225  is employed for the terminal device  13 B. 
     Subsequently, the regenerative repeater allocation section  26  determines whether or not all the deterioration degrees calculated in the respective relay devices  30  on the relay path are lower than the threshold value retained by the threshold value retaining section  29  (S 226 ). When any one of the deterioration degrees calculated in the respective relay devices  30  on the relay path is equal to or higher than the threshold value retained by the threshold value retaining section  29  (S 226 : No), the regenerative repeater allocation section  26  executes the processing illustrated in Step S 228 . 
     When all the deterioration degrees calculated in the respective relay devices  30  on the relay path are lower than the threshold value retained by the threshold value retaining section  29  (S 226 : Yes), in other words, when the regenerative repeater  35  canoe replaced by another regenerative repeater  35 , the regenerative repeater allocation section  26  stores the relay device ID of the relay device  30  including the regenerative repeater  35  assumed to be stopped in Step S 223  as the in-use device ID and the relay device ID of the relay device  30  including the regenerative repeater  35  corresponding to the regenerative repeater ID being selected in Step S 224  as the replacement device ID, in the replacement information retaining section  27  in association with the signal ID being selected in Step S 221  (S 227 ). 
     Subsequently, the regenerative repeater allocation section  26  determines whether or not all the unused regenerative repeaters  35  on the relay path have been selected in Step S 224  (S 228 ). When there is an unselected regenerative repeater  35  (S 228 : No), the regenerative repeater allocation section  26  again executes the processing illustrated in Step S 224 . On the other hand, when all the unused regenerative repeaters  35  on the relay path have been selected (S 228 : Yes), the regenerative repeater allocation section  26  determines whether or not all the signal IDs unselected in Step S 202  have been selected (S 229 ). 
     When there is an unselected signal ID among the signal IDs unselected in Step S 202  (S 229 : No), the regenerative repeater allocation section  26  again executes the processing illustrated in Step S 221 . On the other hand, when all the signal IDs unselected in Step S 202  have been selected (S 229 : Yes), the regenerative repeater allocation section  26  ends the replacement information creating processing illustrated in this flowchart. 
     By the execution of the replacement information creating processing illustrated in this flowchart, in the case where each optical signal is being regenerated, the information for identifying the relay device  30  including the regenerative repeater  35  that can be replaced by another unused regenerative repeater  35  in the regeneration can be created and registered in the replacement information retaining section  27 . 
       FIG. 16  is a flowchart illustrating an example of the replacement processing (S 230 ). 
     First, the regenerative repeater allocation section  26  selects one relay device ID registered as the in-use device ID within the replacement information retaining section  27  in which the information created in Step S 220  is stored, from within the list created in Step S 204  (S 231 ). 
     For example, when the list as illustrated in  FIG. 12  is created in Step S 204 , and when the information as illustrated in  FIG. 8  is created in Step S 220  and stored in the replacement information retaining section  27 , the regenerative repeater allocation section  26  selects, for example, “ 30 D” as the relay device ID within the list  40  which is also registered as the in-use device ID within the replacement information retaining section  27 . 
     Subsequently, the regenerative repeater allocation section  26  references the replacement information retaining section  27  to select one replacement device ID associated with the relay device ID selected in Step S 231  (S 232 ). In the example illustrated in  FIG. 8 , the regenerative repeater allocation section  26  selects, for example, “ 30 G” as the replacement device ID associated with the relay device ID selected in Step S 231 . 
     Subsequently, the regenerative repeater allocation section  26  transmits the regeneration instruction including the signal ID associated with the replacement device ID selected in Step S 232  to the relay device  30  corresponding to the above-mentioned replacement device ID (S 233 ). In the example illustrated in  FIG. 8 , the regenerative repeater allocation section  26  transmits the regeneration instruction including “S 005 ” as the signal ID to the relay device  30 G whose relay device ID is “ 30 G” via the communication section  21 . 
     Subsequently, the regenerative repeater allocation section  26  transmits the regeneration instruction including the signal ID being selected in Step S 202  to the relay device  30  corresponding to the relay device ID selected in Step S 231  (S 234 ), and the regenerative repeater allocation section  26  ends the replacement processing illustrated in this flowchart. In the list  40  exemplified in  FIG. 12 , the relay device ID is stored in association with the signal ID being selected in Step S 202 , and hence the regenerative repeater allocation section  26  transmits the regeneration instruction including “S 001 ” exemplified in  FIG. 12  as the signal ID to the relay device  30  whose relay device ID is “ 30 D” via the communication section  21 . 
     By the execution of the replacement processing illustrated in this flowchart, even when the unused regenerative repeater  35  does not exist on the relay path, the regenerative repeater allocation section  26  can replace any one of the regenerative repeaters  35  on the relay path by another unused regenerative repeater  35  in the regeneration, and hence it is possible to secure one unused regenerative repeater  35  on the relay path. 
     Next, the second regenerative repeater allocation processing (S 300 ) is described.  FIG. 17  is a flowchart illustrating an example of the second regenerative repeater allocation processing (S 300 ). Here, as described with reference to  FIG. 9 , the second regenerative repeater allocation processing (S 300 ) is executed in the case where the relay path of the optical signal has been changed by the administrator of the optical relay system  10 . 
     For example, as illustrated in  FIG. 18 , it is assumed that when the optical signal whose signal ID is “S 001 ”, “S 002 ”, and “S 003 ” is being transmitted from the terminal device  13 A to the terminal device  13 B by being relayed via a relay device  30 A, the relay device  30 F, a relay device  30 B, and a relay device  30 C, failures have occurred in an optical line between the relay device  30 A and the relay device  30 F and an optical line between the relay device  30 C and the terminal device  13 B. 
     Then, it is assumed that the administrator of the optical relay system  10  has changed the relay paths of the optical signals “S 001 ”, “S 002 ”, and “S 003 ” through the input device  17  in such a manner as illustrated in  FIG. 11 . It should be noted that the optical signal whose signal ID is “S 002 ” is regenerated by the regenerative repeater  35   f  within the relay device  30 F before and after the change of the relay paths. 
     Further, the optical signal whose signal ID is “S 004 ” or “S 005 ” is being transmitted from the terminal device  13 A to the terminal device  13 B by being relayed via the relay device  30 D, the relay device  30 E, the relay device  30 F, and the relay device  30 G without the change of the relay path. Further, the optical signal whose signal ID is “S 004 ” is being regenerated by the regenerative repeater  35   e  within the relay device  30 E, and the optical signal whose signal ID is “S 005 ” is being regenerated by the regenerative repeater  35   d  within the relay device  30 D. 
     The description is given by returning to  FIG. 17 . In the second regenerative repeater allocation processing illustrated in  FIG. 17 , processings denoted by the same reference symbols as in the first regenerative repeater allocation processing illustrated in  FIG. 10  are the same, except for the following points, as the processings described with reference to  FIG. 10 , and hence description thereof is omitted. 
     When it is determined in Step S 203  of the second regenerative repeater allocation processing illustrated in  FIG. 17  that the signal ID selected in Step S 202  is not associated with the deterioration degree equal to or higher than the threshold value (S 203 : No), the regenerative repeater allocation section  26  executes a regeneration stopping processing described later (S 310 ). 
       FIG. 19  is a flowchart illustrating an example of the regeneration stopping processing (S 310 ). 
     First, the regenerative repeater allocation section  26  references the equipment information retaining section  28  with regard to the signal ID being selected in Step S 202  to determine whether or not the regenerative repeater  35  that is in use for regenerating the optical signal corresponding to the signal ID exists (S 311 ). To give the description by taking as an example the optical signal whose signal ID is “S 002 ” in the optical relay system  10  after the change of the relay path illustrated in  FIG. 11 , the optical signal is being regenerated by the regenerative repeater  35   f  within the relay device  30 F whose relay device ID is “ 30 F” in the optical relay system  10  after the change of the relay path. 
     Subsequently, the regenerative repeater allocation section  26  references the equipment information retaining section  28  to determine whether or not the regenerative repeater  35  that is regenerating the optical signal of the signal ID being selected in Step S 202  can be stopped (S 312 ). For example, in the optical relay system  10  after the change of the relay path illustrated in  FIG. 11 , it is assumed that the deterioration degrees measured by the respective terminal devices  13  and relay devices  30  on the relay path of the optical signal “S 002 ” exhibit a distribution as illustrated in, for example,  FIG. 20 . 
     The regenerative repeater allocation section  26  calculates a difference Δd 3  between the deterioration degree of the optical signal before the regeneration (black circle of  FIG. 20 ) and the deterioration degree thereof after the regeneration (white circle of  FIG. 20 ) in the relay device  30 F regenerating the optical signal. It should be noted that the deterioration degree before the regeneration (black circle of  FIG. 20 ) is a value measured by the deterioration degree measuring section  34  within the relay device  30 F. Further, the deterioration degree after the regeneration, which is predefined as the regeneration capability of each regenerative repeater  35 , is used as the deterioration degree after the regeneration (white circle of  FIG. 20 ). 
     Then, as illustrated in, for example,  FIG. 21 , the regenerative repeater allocation section  26  calculates the first virtual deterioration degree (white squares of  FIG. 21 ) on the assumption that the regeneration by the regenerative repeater  35   f  is stopped by adding the calculated difference Δd 3  to the deterioration degrees measured by the relay device  30 G and the terminal device  13 B that are located on the relay path at the downstream of the relay device  30 F including the regenerative repeater  35   f  executing the regeneration. 
     Then, the regenerative repeater allocation section  26  determines whether or not all the calculated first virtual deterioration degrees are lower than the threshold value retained within the threshold value retaining section  29 . When all the calculated first virtual deterioration degrees are lower than the threshold value retained within the threshold value retaining section  29 , the regenerative repeater allocation section  26  determines that the regenerative repeater  35   f  assumed to be stopped is the regenerative repeater  35  that can be stopped. 
     When the regenerative repeater  35  regenerating the optical signal corresponding to the signal ID being selected in Step S 202  can be stopped (S 312 : Yes), the regenerative repeater allocation section  26  transmits the regeneration stopping instruction including the signal ID to the relay device  30  including the regenerative repeater  35  via the communication section  21  (S 313 ). 
     Subsequently, the regenerative repeater allocation section  26  modifies the use information on the regenerative repeater  35  registered in the equipment information retaining section  28  in association with the relay device ID of the relay device  30  to “unused”, and deletes the signal ID associated with the regenerative repeater  35  (S 314 ), and the regenerative repeater allocation section  26  ends the regeneration stopping processing illustrated in this flowchart. 
     When the regenerative repeater  35  that is in use for regenerating the optical signal corresponding to the signal ID being selected in Step S 202  does not exist (S 311 : No), or when the regenerative repeater  35  regenerating the above-mentioned optical signal cannot be stopped (S 312 : No), the regenerative repeater allocation section  26  ends the regeneration stopping processing illustrated in this flowchart. 
     By the execution of the regeneration stopping processing, the relay path is changed to cause a change in a loss on the path, and it is possible to cancel the allocation of the regenerative repeater  35  to the optical signal whose regeneration has become unnecessary. Accordingly, wasteful power consumption of the entire optical relay system  10  can be suppressed to a low level. 
       FIG. 22  is a hardware configuration diagram illustrating an example of a computer  50  which realizes functions of the network control device  20 . The computer  50  includes a central processing unit (CPU)  51 , a random access memory (RAM)  52 , a read only memory (ROM)  53 , a hard disk drive (HDD)  54 , a communication interface (I/F)  55 , an input/output interface (I/F)  56 , and a media interface (I/F)  57 . 
     The CPU  51  operates based on a program stored in the ROM  53  or the HDD  54 , and performs control of each component. The ROM  53  stores a boot program executed by the CPU  51  at the startup of the computer  50 , a program depending on hardware of the computer  50 , and the like. 
     The HDD  54  stores a program executed by the CPU  51 , data used by the program, and the like. The communication interface  55  receives data from the terminal device  13  or the relay device  30  via the management network and sends the data to the CPU  51 , while transmitting data generated by the CPU  51  to the terminal device  13  or the relay device  30  via the management network. 
     The CPU  51  controls an output device including a display and a printer and an input device including a keyboard and a mouse via the input/output interface  56 . The CPU  51  acquires data from the input device via the input/output interface  56 . Further, the CPU  51  outputs the generated data to the output device via the input/output interface  56 . 
     The media interface  57  reads a program or data stored in a recording medium  58 , and provides the program or data to the CPU  51  via the RAM  52 . The CPU  51  loads the program from the recording medium  58  onto the RAM  52  via the media interface  57 , and executes the loaded program. The recording medium  58  is, for example, an optical recording medium such as a digital versatile disc (DVD) or a phase change rewritable disk (PD), a magneto-optical recording medium such as a magneto-optical disk (MO), a tape medium, a magnetic recording medium, or a semiconductor memory. 
     The CPU  51  of the computer  50  executes the program loaded onto the RAM  52  to thereby realize the respective functions of the communication section  21 , the path changing section  22 , the deterioration degree collecting section  23 , and the regenerative repeater allocation section  26 . Stored in the ROM  53  or the HDD  54  are data items included within the path information retaining section  24 , the priority retaining section  25 , the replacement information retaining section  27 , the equipment information retaining section  28 , and the threshold value retaining section  29 . 
     The CPU  51  of the computer  50  executes those programs by reading the programs from the recording medium  58 , but as another example, the CPU  51  may acquire those programs from another device via a communication line. 
     The embodiment of the present invention has been described above. 
     As apparent from the above description, according to the optical relay system  10  of this embodiment, when the optical signal needs to be regenerated, the operation of the regenerative repeater  35  allows the wasteful power consumption of the entire system to be suppressed to a low level. 
     It should be noted that the present invention is not limited to the above-mentioned embodiment, and various modifications can be made within the scope of the gist. 
     For example, in the above-mentioned embodiment, one regenerative repeater  35  is provided within each of the relay devices  30 , but the present invention is not limited thereto, and two or more regenerative repeaters  35  may be provided within each of the relay devices  30 . It should be noted that, also in this case, the regeneration of the optical signal that needs to be regenerated can be realized by the plurality of relay devices  30  on the relay path, and hence the number of the regenerative repeaters  35  within each of the relay devices  30  can be further reduced than in the conventional technology (for example, the number of the regenerative repeaters  35  within each of the relay devices  30  is set to be smaller than the number of all the signals) 
     Further, any system is applicable as long as the regeneration of the optical signal that needs to be generated within any one of the relay devices  30  on the relay path can be realized by the regenerative repeater  35 , and hence any system is applicable as long as the regenerative repeater  35  is provided within any one of the relay devices  30  on the relay path of the optical signal that needs to be regenerated even when the relay device  30  that does not include the regenerative repeater  35  exists on the relay path.