Abstract:
There is provided a network management device to manage a network on which an existing optical path is operated, the network management device including: a first receiver configured to receive data related to a measurement result of signal quality of a first optical signal having a first wavelength on the existing optical path; a second receiver configured to receive a request for adding a second optical signal having a second wavelength to the existing optical path; at least one memory configured to store a procedure; and at least one processor configured to execute the procedure of estimating a variation quantity in the signal quality of the first optical signal when the second optical signal is added to the existing optical path based on the data related to the measurement result, when the request is received, and determining whether to add the second optical signal based on results of the estimating.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2015-233268, filed on Nov. 30, 2015, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to an optical communication device and system for network management. 
       BACKGROUND 
       [0003]    In a wavelength division multiplexing (WDM) network, a wavelength may be newly added in some cases. When a new wavelength is added to an existing optical path, it is determined whether a design value of transmission quality in the existing optical path reaches a required value of transmission quality required when the new wavelength is added. For example, the worst value of a parameter for determining transmission quality such as an optical fiber or an optical component is used as the design value. 
         [0004]    When it is determined that the design value of the transmission quality in the existing optical path reaches the required value of the transmission quality, the new wavelength may be added to the existing optical path. On the other hand, when it is determined that the design value of the transmission quality in the existing optical path does not reach the required value of the transmission quality, the transmission quality is ensured by disposing a regenerator (REG) (a regenerative repeater) in the existing optical path in order to add the new wavelength. 
         [0005]    In the WDM network, a light wavelength separating device separates a wavelength A in which a monitoring control signal is carried, and applies the separated monitoring control signal to a monitoring control signal transmission/reception circuit. A technique is known in which an AGC circuit controls an amplifier on the basis of an output of the monitoring control signal transmission/reception circuit and an output of a monitor so as to make a gain of an optical amplifier constant (see, e.g., Japanese Laid-Open Patent Publication No. 2004-173309). 
         [0006]    Related technologies are disclosed in, for example, Japanese Laid-Open Patent Publication No. 2004-173309. 
       SUMMARY 
       [0007]    According to an aspect of the invention, a network management device is configured to manage a network on which an existing optical path is operated, the network management device includes: a first receiver configured to receive data related to a measurement result of signal quality of a first optical signal having a first wavelength on the existing optical path; a second receiver configured to receive a request for adding a second optical signal having a second wavelength to the existing optical path; at least one memory configured to store a procedure; and at least one processor configured to execute the procedure of estimating a variation quantity in the signal quality of the first optical signal when the second optical signal is added to the existing optical path based on the data related to the measurement result, when the request is received, and determining whether to add the second optical signal based on results of the estimating. 
         [0008]    The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
         [0009]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a diagram illustrating an example of a network management system according to an embodiment; 
           [0011]      FIG. 2  is a diagram illustrating an example of a hardware configuration of a network management device according to the embodiment; 
           [0012]      FIG. 3  is a diagram illustrating an example of transmission quality information according to the embodiment; 
           [0013]      FIG. 4A  is a diagram illustrating an example of transmission quality deterioration quantity information due to a nonlinear penalty according to the embodiment; 
           [0014]      FIG. 4B  is a diagram illustrating an example of transmission quality deterioration quantity information due to a nonlinear penalty according to the embodiment; 
           [0015]      FIG. 5A  is a diagram illustrating an example of transmission quality deterioration quantity information due to an OSNR deterioration according to the embodiment; 
           [0016]      FIG. 58  is a diagram illustrating an example of transmission quality deterioration quantity information due to an OSNR deterioration according to the embodiment; 
           [0017]      FIG. 6  is a diagram illustrating an example of user policy information according to the embodiment; 
           [0018]      FIG. 7  is a diagram illustrating an example of a method of prioritizing optical paths addable; 
           [0019]      FIG. 8  is a diagram illustrating an example of updated transmission quality information; 
           [0020]      FIG. 9A  is a diagram illustrating an example of updated transmission quality deterioration quantity information due to a nonlinear penalty; 
           [0021]      FIG. 9B  is a diagram illustrating an example of updated transmission quality deterioration quantity information due to a nonlinear penalty; 
           [0022]      FIG. 10A  is a diagram illustrating an example of updated transmission quality deterioration quantity information due to an OSNR deterioration; 
           [0023]      FIG. 10B  is a diagram illustrating an example of updated transmission quality deterioration quantity information due to an OSNR deterioration; 
           [0024]      FIG. 11  is a flowchart illustrating an example of a process flow in a network management system according to the embodiment; and 
           [0025]      FIG. 12  is a flowchart illustrating an example of a process flow of determining whether an optical path is addable. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0026]    For example, a design value (Q wst ) of transmission quality in an existing optical path is set to 5.5 dB. A required value (Q req ) of transmission quality which is required for an existing optical path when adding a new wavelength to the existing optical path is set to 7.0 dB. In this environment, the design value (Q wst ) of transmission quality does not reach the required value (Q req ) of transmission quality. Accordingly, an REG is disposed in the existing optical path so as to ensure transmission quality and enable the addition of a new wavelength. 
         [0027]    By the way, various units constituting a network have individual differences and actual transmission quality is different from the design value. For example, it is assumed that a noise figure (NF) value of an optical amplifier disposed in an existing optical path is 2.0 dB better than the design value. Then, the transmission quality in the existing optical path is actually 7.5 dB. Since the actual transmission quality in the existing optical path reaches the required value (Q req ) of transmission quality, a new optical path may be added without disposing the REG. 
         [0028]    In this case, when a network is designed using the design value (Q wst ) of transmission quality, an unnecessary REG is disposed in order to newly add an optical path, and thus, network costs increase. 
         [0029]    Hereinafter, an embodiment that enables a network design that is more efficient than a network design using a design value will be described with reference to the accompanying drawings. 
         [0030]    A network management device according to the present disclosure may estimate whether a new wavelength is addable on the basis of a measured value of transmission quality during the operation of an existing optical path.  FIG. 1  is a diagram illustrating an example of a network management system according to the present embodiment. The network management system  100  includes a network management device  110  and a WDM network  120  to be managed by the network management device  110 . The WDM network  120  includes an optical transmitter  121 , optical repeaters  122   a  and  122   b,  and an optical receiver  123 . An optical signal transmitted from the optical transmitter  121  is relayed by the optical repeaters  122   a  and  122   b  and is received by the optical receiver  123 . The optical receiver  123  includes a measuring unit  124 . The measuring unit  124  measures transmission quality of an optical path between the optical transmitter  121  and the optical receiver  123 . The WDM network  120  may have a constitution of an Add/Drop network, a mesh structure, or the like. 
         [0031]    The network management device  110  is a device that manages the WDM network  120 . The network management device  110  includes a first receiver  111 , a second receiver  112 , a memory unit  113 , an estimation unit  114 , a storage unit  115 , a determination unit  116 , and an order unit  117 . The first receiver  111  has an interface that receives a measurement result of the measuring unit  124 . The second receiver  112  receives a request for adding an optical path. Hereinafter, an optical path to be added means that a wavelength is newly added, but may include a path passing through a section (span) that is partially different from an existing optical path. For example, the request for adding an optical path is input by a user. The memory unit  113  stores transmission quality information (which will be described later with reference to  FIG. 3 ), transmission quality deterioration quantity information due to a nonlinear penalty (which will be described later with reference to  FIGS. 4A and 4B ), and transmission quality deterioration quantity information due to an optical signal-to-noise ratio (OSNR) deterioration (which will be described later with reference to  FIGS. 5A and 5B ). When the measurement result is acquired from the first receiver  111 , the memory unit  113  stores the transmission quality information, the transmission quality deterioration quantity information due to a nonlinear penalty, and the transmission quality deterioration quantity information due to an OSNR deterioration which are updated on the basis of the measurement result. 
         [0032]    The determination unit  116  determines whether a new optical path is addable on the basis of the transmission quality information. The storage unit  115  stores user policy information which is used for the determination unit  116  to determine whether a new optical path is addable. When the determination unit  116  determines that an optical path is addable, the order unit  117  transmits a network setting order to set an optical path to the WDM network  120 . 
         [0033]    The transmission quality information includes path information from a certain node element (NE) to another NE and a value indicating the latest (current) transmission quality (Q cur ) correlated with each wavelength. The memory unit  113  stores the transmission quality information for each optical path. When an optical path is added for the first time, the memory unit  113  stores a design value of transmission quality in the transmission quality information. Thereafter, whenever an optical path is added, the memory unit  113  stores the transmission quality information which is updated by the estimation unit  114  on the basis of the measurement result. 
         [0034]    The estimation unit  114  acquires information relating to an optical path to be newly added from the second receiver. The estimation unit  114  estimates a transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) and a transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) on the basis of the transmission quality information. 
         [0035]    The transmission quality deterioration quantity information due to a nonlinear penalty indicates the transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) for each section (span) when adding an optical path. The transmission quality deterioration quantity information due to a nonlinear penalty includes a transmission quality deterioration quantity (ΔQ penalty ) corresponding to a wavelength (λ exp ) of an optical path to be calculated and a wavelength (λ add ) of an added optical path. The transmission quality deterioration quantity (ΔQ penalty ) is estimated by the estimation unit  114 . The memory unit  113  stores the transmission quality deterioration quantity information due to a nonlinear penalty for each fiber input level, each fiber type, and each transmission quality deterioration quantity up to the previous section. The memory unit  113  stores the design value as the transmission quality deterioration quantity information due to a nonlinear penalty until a second optical path is added. Thereafter, whenever an optical path is added, the memory unit  113  stores the transmission quality deterioration quantity information due to a nonlinear penalty which is updated on the basis of the estimation result of the estimation unit  114 . 
         [0036]    The transmission quality deterioration quantity information due to an OSNR deterioration indicates the transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) for each span when adding an optical path. The transmission quality deterioration quantity information due to an OSNR deterioration includes a transmission quality deterioration quantity (ΔQ OSNR ) corresponding to a wavelength (λ exp ) of an optical path to be calculated and a wavelength (λ add ) of an added optical path. The transmission quality deterioration quantity (ΔQ OSNR ) is estimated by the estimation unit  114 . The memory unit  113  stores the transmission quality deterioration quantity information due to an OSNR deterioration for each fiber input level, each wavelength number, and each fiber type. The memory unit  113  stores the design value as the transmission quality deterioration quantity information due to an OSNR deterioration until a second optical path is added. Thereafter, whenever an optical path is added, the memory unit  113  stores the transmission quality deterioration quantity information due to an OSNR deterioration which is updated on the basis of the estimation result of the estimation unit  114 . 
         [0037]    Hereinafter, an operation flow of the network management device  110  will be described in sequence. 
         [0038]    (1) When no optical path is present in a network, the design value is set in the transmission quality information, the transmission quality deterioration quantity information due to a nonlinear penalty, and the transmission quality deterioration quantity information due to an OSNR deterioration which are stored in the memory unit  113 . 
         [0039]    (2) The user inputs information related to an NE of a start point, an NE of an end point, and communication capability of an optical path to be added to the network management device  110 . The second receiver  112  receives the input information. 
         [0040]    (3) The estimation unit  114  estimates a transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) and a transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) which has an influence on an existing optical path by adding an optical path on the basis of the transmission quality information. 
         [0041]    (4) The determination unit  116  determines whether a value obtained by subtracting a transmission quality deterioration quantity (Q add ) due to the addition of an optical path from the current transmission quality (Q cur ) greater than required transmission equality (Q req ). When the value obtained by subtracting a transmission quality deterioration quantity (Q add ) due to the addition of an optical path from the current transmission quality (Q cur ) is greater than the required transmission equality (Q req ), the determination unit  116  determines that the addition of the optical path is enabled. When the value obtained by subtracting a transmission quality deterioration quantity (Q add ) due to the addition of an optical path from the current transmission quality (Q cur ) less than the required transmission equality (Q req ), the determination unit  116  determines that the addition of the optical path is disabled. 
         [0042]    Here, the transmission quality deterioration quantity (Q add ) due to the addition of an optical path is a total sum of estimated values of a transmission quality variation which is estimated when adding a wavelength in an optical path to be added. The transmission quality deterioration quantity (Q add ) due to the addition of an optical path is a sum of the transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) and the transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) which correspond to the added optical path, which are estimated by the estimation unit  114 . The desired transmission quality (Q req ) is a desired value of transmission quality to be secured when adding an optical path and is a value which can be selected from the user policy information stored in the storage unit  115 . The user arbitrarily selects a desired transmission quality (Q req ) on the basis of a required Pre forward error correction (FEC) bit error rate (BER), an idea of a margin, or the like of the user policy. 
         [0043]    (5-1) When it has already been determined that the addition of plural optical paths is enabled, the determination unit  116  prioritizes the optical paths determined to be addable. A higher priority order is given to an optical path which satisfies the input communication capability and has a smaller number of spans in a path connecting an NE of a start point and an NE of an end point. When there are addable optical paths having the same number of spans, a higher priority order is given to an optical path having a shorter wavelength. The method of prioritizing the optical paths using the number of spans and the wavelength is merely an example and the priority order may be set using another method. 
         [0044]    (5-2) The determination unit  116  selects one optical path from the highest priority order side. 
         [0045]    (6) The determination unit  116  estimates an influence on an existing optical path when the optical path determined to be addable in the process (4) or the optical path selected in the process (5-2) is added. The existing optical path to be processed in the process (6) is an optical path passing through a path having one or more spans equal to those of the optical path to be added. The determination unit  116  determines whether a value obtained by subtracting an estimated value (ΔQ det ) of a transmission quality variation estimated when adding a wavelength in an optical path to be added from the current transmission quality (Q cur ) is greater than the desired transmission quality (Q req ). When the subtraction result value is greater than the desired transmission quality (Q req ), the determination unit  116  determines that there is no influence on the existing optical path and determines the corresponding optical path as an optical path to be added. On the other hand, when the subtraction result value is less than the desired transmission quality (Q req ), the determination unit  116  determines the corresponding optical path as a non-addable optical path even if the optical path is determined as an addable one in the process (4). 
         [0046]    (7) When a request for adding plural optical paths is input in the process (2), the estimation unit  114  and the determination unit  116  repeat the processes (2) to (6) on all of the plural optical paths. 
         [0047]    (8) The order unit  117  transmits an order to add the optical path determined to be an optical path to be added in the process (6) to the NEs. The order unit  117  transmits an order to measure the transmission quality after the addition to the optical receiver  124 . 
         [0048]    (9) The transmission quality information, the transmission quality deterioration quantity information due to a nonlinear penalty, and the transmission quality deterioration quantity information due to an OSNR deterioration which are stored in the memory unit  113  are updated on the basis of the estimation result of the estimation unit  114 . 
         [0049]    In this way, the determination unit  116  determines, for each optical path newly added, whether there is no adverse influence on the existing optical path and whether the desired transmission quality can be secured on the basis of the measured value. Accordingly, a network design based on an actual operation is may be made more efficiently than a network design using a design value. The priority orders set in the process (5-1) may be set at the time point where an optical path to be added is input in the process (2). 
         [0050]      FIG. 2  is a diagram illustrating an example of a hardware configuration of the network management device according to the present embodiment, the network management device  110  includes a processor  11 , a memory  12 , a bus  15 , an external memory unit  16 , and a network connector  19 . The network management device  110  may further include an input unit  13 , an output unit  14 , and a medium driver  17  as options. The network management device  110  may be embodied, for example, by a computer. 
         [0051]    The processor  11  functions as the estimation unit  114  and the determination unit  116 . The processor  11  may execute a program stored in the external memory  16  via the memory  12 . The memory  12  functions as the memory unit  113  and the storage unit  115 . The memory  12  also appropriately stores data acquired through the operation of the processor  11  or data used for the process of the processor  11 . The network connector  19  is used for communication with another device, and functions as the first receiver  111  and the order unit  117 . The network connector  19  is used for communication with another device. 
         [0052]    The input unit  13  is implemented by, for example, a button, a keyboard, or a mouse, and the output unit  14  is implemented by a display or the like. The input unit  13  and the output unit  14  function as the second receiver  112 . The bus  15  connects the processor  11 , the memory  12 , the input unit  13 , the output unit  14 , the external memory  16 , the medium driver  17 , and the network connector  19  so as to exchange data therebetween. The external memory  16  stores programs, data, and the like, and supplies the programs, the data, and the like to the processor  11  or the like. The external memory  16  is, for example, an externally attached memory. The medium driver  17  may output the data of the memory  12  or the external memory  16  to a portable recording medium  18  and may read programs, data, and the like from the portable recording medium  18 . Here, the portable recording medium  18  may employ any portable recording medium such as a flexible disk, a magneto-optical (MO) disk, a compact disc recordable (CD-R), or a digital versatile disk recordable (DVD-R). 
         [0053]      FIG. 3  is a diagram illustrating an example of the transmission quality information according to the present embodiment. The network  200  is a network including node elements NE 1  to NE 5 . For example, light input from the node element NE 1  is transmitted in the ring-shaped network  200  such as NE 1 ˜NE 2 ˜NE 3 ˜NE 4 ˜NE 5 −NE 1 . 
         [0054]    Transmission quality information  301  includes path information corresponding to the network  200  and a value indicating the latest (current) transmission quality (Q cur ) correlated with each wavelength. The path information indicates a path of a start point a halfway path an end point. For example, a path of NE 1 ˜NE 5 ˜NE 4 ˜NE 3  indicates that an optical signal transmitted from NE 1  is received by NE 3  via NE 5  and NE 4 . The wavelength (λ) of the transmission quality information  301  is an existing light wavelength. It is assumed that the wavelength of λ 190   1  is the shortest and the wavelength becomes longer in the order of λ# 2 , λ# 3 , and λ# 4 . 
         [0055]    For example, in the latest (current) transmission quality (Q cur ) corresponding to the paths at the wavelength λ# 1 , it can be seen that the transmission quality in three sections of NE 1 ˜NE 5 ˜NE 4 ˜NE 3  is deteriorated as compared to the transmission quality in one section of NE 1 ˜NE 2 . 
         [0056]      FIGS. 4A and 4B  are diagrams illustrating an example of the transmission quality deterioration quantity information due to a nonlinear penalty according to the present embodiment. The transmission quality deterioration quantity information due to a nonlinear penalty,  302   a  to  302   c,  indicates a transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) for each span when adding an optical path. The transmission quality deterioration quantity information due to a nonlinear penalty includes the transmission quality deterioration quantity (ΔQ penalty ) corresponding to a wavelength of an optical path to be calculated (λ exp ) and a wavelength of an optical path to be added (λ add ). The transmission quality deterioration quantity (ΔQ penalty ) is estimated by the estimation unit  114 . The memory unit  113  stores the transmission quality deterioration quantity information due to a nonlinear penalty for each fiber input level, each fiber type, and each transmission quality deterioration quantity up to the previous section. 
         [0057]    The transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) is an estimated value of a transmission quality variation due to a transmission penalty from the first span to the N-th span. The transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) depends on the fiber type or the fiber input level for each span including the order. Accordingly, the transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) may be calculated by sequentially calculating the sum up to the first span, the sum up to the second span, the sum up to the third span, . . . , the sum up to the (N−1)-th span. A specific method of calculating the transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) in the estimation unit  114  will be described below.
       A cumulative total up to the first span: ΔQ penalty1 =f(λ exp , λ add , P in1 , FiberType 1 , 0)   A cumulative total up to the second span: ΔQ penalty2 =f(λ exp , λ add , P in2 /FiberType 2 , ΔQ penalty1 )   A cumulative total up to the third span: ΔQ penalty3 =f(λ exp , λ add , P in1 , FiberType 3 , ΔQpenalty 2 )   A cumulative total up to the (N−1)-th span: ΔQ penalty(N−1) =f (λ exp ), λadd, P in(N−1) , FiberType N−1 , ΔQ penalty(N−2) ),   A cumulative total up to the N-th span: ΔQ penaltyN =f(λ exp , λadd, P inN , FiberType N , ΔQ penalty(N−1) )       
 
         [0063]    Here, N denotes the number of spans of an existing optical path of which the variation will be estimated. P in  denotes the fiber input power of the X-th span of the existing optical path of which the variation will be estimated. FiberType denotes the fiber type of the X-th span of the existing optical path of which the variation will be estimated. Span X denotes a span among the first to N-th spans. 
         [0064]    Finally, the transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) after an optical path is added becomes ΔQ penaltyN . 
         [0065]    The transmission quality deterioration quantity information due to a nonlinear penalty  302   a  is an example in which P in  is −2 dBm/ch, the fiber type is a single mode fiber (SMF), and the transmission quality deterioration quantity (ΔQ penalty ) up to the previous span is 0.0 dB. The transmission quality deterioration quantity information due to a nonlinear penalty  302   a  indicates the transmission quality deterioration quantities ΔQ penaltyN  corresponding to the wavelength (λ exp ) of the optical path to be calculated from the first span to the N-th span and the wavelength (λ add ) of the added optical path. Since the transmission quality deterioration quantity ΔQ penalty  up to the previous span is 0.0 dB, there is no influence on the existing optical path and all the transmission quality deterioration quantities ΔQ penaltyN  are 0 when there is no optical path to be added. 
         [0066]    The transmission quality deterioration quantity information due to a nonlinear penalty  302   b  is an example in which Pin is −2 dBm/ch, the fiber type is an SMF, and the transmission quality deterioration quantity (ΔQ penalty ) up to the previous span is 0.2 dB. The transmission quality deterioration quantity information due to a nonlinear penalty  302   b  indicates the transmission quality deterioration quantities ΔQ penaltyN  corresponding to the wavelength (λ exp ) of the optical path to be calculated from the first span to the N-th span and the wavelength (λ add ) of the added optical path. Since the transmission quality deterioration quantity ΔQ penaltyN  up to the previous span is 0.2 dB, all the transmission quality deterioration quantities ΔQ penaltyN  are 0.2 when there is no optical path to be added. 
         [0067]    The transmission quality deterioration quantity information due to a nonlinear penalty  302   v  is an example in which P in  is −2 dBm/ch, the fiber type is an SMF, and the transmission quality deterioration quantity (ΔQ penalty ) up to the previous span is 0.3 dB. The transmission quality deterioration quantity information due to a nonlinear penalty  302   c  indicates the transmission quality deterioration quantities ΔQ penaltyN  corresponding to the wavelength (λ exp ) of the optical path to be calculated from the first span to the N-th span and the wavelength (λ add ) of the added optical path. Since the transmission quality deterioration quantity ΔQ penalty  up to the previous span is 0.3 dB, all the transmission quality deterioration quantities ΔQ penaltyN  are 0.3 when there is no optical path to be added. 
         [0068]    The transmission quality deterioration quantity information due to each of nonlinear penalties  302   a  to  302   c  is an example and is stored in the memory unit  113  for each combination of P in , the fiber type, and the transmission quality deterioration quantity (ΔQ penalty ) up to the previous span. 
         [0069]      FIGS. 5A and 5B  are diagrams illustrating an example of the transmission quality deterioration quantity information due to an OSNR deterioration according to the present embodiment. The transmission quality deterioration quantity information due to a nonlinear penalty indicates a transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) for each span when adding an optical path. The transmission quality deterioration quantity information due to an OSNR deterioration includes the transmission quality deterioration quantity (ΔQ OSNR ) corresponding to a wavelength (λ exp ) of an optical path to be calculated and a wavelength (X add ) of an optical path to be added. The transmission quality deterioration quantity (ΔQ OSNR ) is estimated by the estimation unit  114 . The memory unit  113  stores the transmission quality deterioration quantity information due to an OSNR deterioration for each fiber input level, and each wavelength number, and each fiber type. 
         [0070]    A specific method of calculating the transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) in the estimation unit  114  will be described below. 
         [0000]      Δ Q   OSNR   =ΔQ   OSNR1   +ΔQ   OSNR2   + . . . ΔQ   OSNR(N−1)   +ΔQ   OSNRN  
 
         [0071]    As indicated, the transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) is the total value of the transmission quality deterioration quantities ΔQ OSNR1  to ΔQ OSNRN  in the spans. The transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) may not be the total value of the transmission quality deterioration quantities in the spans, but may be, for example, a logarithmic value thereof or the like. Then, the transmission quality deterioration quantities ΔQ ISBR1  to ΔQ OSNRN  (for example, referred to as ΔQ OSNRX ) are calculated by g(λ exp , λ add , M λx , P inx , FiberType x ). Here, M λx  denotes the wavelength number of the X-th span of the existing optical path of which the variation will be estimated. 
         [0072]    The transmission quality deterioration quantity information due to an OSNR deterioration  303   a  is an example in which Pin is −2 dBm/ch, the fiber type is an SMF, and M λ  is 1. The transmission quality deterioration quantity information due to an OSNR deterioration  303   a  indicates estimated values of the transmission quality deterioration quantities due to an OSNR deterioration ΔQ OSNRX  corresponding to the wavelength (λ exp ) of the optical path to be calculated in the X-th span and the wavelength (λ add ) of the added optical path. When there is no optical path to be added, there is no influence on the existing optical path and thus, all the transmission quality deterioration quantities ΔQ OSNRX  are 0. 
         [0073]    The transmission quality deterioration quantity information due to an OSNR deterioration  303   b  is an example in which P in  is −2 dBm/ch, the fiber type is an SMF, and M λ is 2. The transmission quality deterioration quantity information due to an OSNR deterioration  303   b  indicates estimated values of the transmission quality deterioration quantities due to an OSNR deterioration ΔQ OSNRX  corresponding to the wavelength (λ exp ) of the optical path to be calculated in the X-th span and the wavelength (λ add ) of the added optical path. When there is no optical path to be added, there is no influence on the existing optical path and thus, all the transmission quality deterioration quantities ΔQ OSNRX  are 0. 
         [0074]    The transmission quality deterioration quantity information due to an OSNR deterioration  303   c  is an example in which Pin is −2 dBm/ch, the fiber type is an SMF, and M λ is 3. The transmission quality deterioration quantity information due to an OSNR deterioration  303   c  indicates estimated values of the transmission quality deterioration quantities due to an OSNR deterioration ΔQ OSNRX  corresponding to the wavelength (λ exp ) of the optical path to be calculated in the X-th span and the wavelength (λ add ) of the added optical path. When there is no optical path to be added, there is no influence on the existing optical path and thus all the transmission quality deterioration quantities ΔQ OSNRX  are 0. 
         [0075]    The transmission quality deterioration quantity information due to an OSNR deterioration  303   a  to  303   c  is an example, and is stored in the memory unit  113  for each combination of Pin, the wavelength number of the X-th span (M λx ), and the fiber type. 
         [0076]      FIG. 6  is a diagram illustrating an example of the user policy information according to the present embodiment. The user policy information  304  is information stored in the storage unit  115 . The user arbitrarily selects desired transmission quality (Q req ) when adding an optical path from combinations of the required Pre FEC BER and an idea of a margin. The determination unit  116  determines whether a new optical path is addable using the selected desired transmission quality (Q req ) 
         [0077]    The required Pre FEC BER is a value which is used to improve performance of an error bit rate due to forward error correction of optical communication. The idea of a margin indicates what margin the user wants to set. Q req  also depends on optical signal types (the bit error rate and modulation methods), performance of the optical transmitter and receiver, and the like. 
         [0078]      FIG. 7  is a diagram illustrating an example of the method of prioritizing optical paths addable. The network  200  is a network including node elements NE 1  to NE 5 . For example, light input from the node element NE 1  is transmitted in the ring-shaped network  200  such as NE 1 ˜NE 2 ˜NE 3 ˜NE 4 ˜NE 5 ˜NE 1 . The network  200  transmits, for example, light of four different wavelengths of λ# 1  to λ# 4 . It is assumed that the wavelength becomes shorter in the order of λ# 1 , λ# 2 , λ# 3 , and λ# 4 . 
         [0079]    An existing optical path  501  is set up as NE 1 ˜NE 2 ˜NE 3 ˜NE 4 , and is an optical path with a wavelength λ# 1 . An existing optical path  502  is set up as NE 2 ˜NE 3 ˜NE 4  and is an optical path with a wavelength λ# 3 . 
         [0080]    Here, four optical paths including the node element NE 1  as a start point and the node element  3  as an end point are added. An added optical path  511  is NE 1 ˜NE 2 ˜NE 3  of which the wavelength is λ# 2 . An added optical path  512  is NE 1 ˜NE 5 ˜NE 4 ˜NE 3  of which the wavelength is λ# 2 . An added optical path  513  is NE 1 ˜NE 2 ˜NE 3  of which the wavelength is λ# 4 . An added optical path  514  is NE 1 ˜NE 5 ˜NE 4 ˜NE 3  of which the wavelength is λ# 4 . 
         [0081]    Then, the determination unit  116  determines whether the added optical paths  511  to  514  are addable (the process (4)). In the process (2), priority orders (an optical path having the smallest number of spans and the shortest wavelength has the highest priority order) may be set on the basis of information of an optical path requested by the user. Then, the priority orders of the added optical paths are given in the order of the added optical path  511 , the added optical path  513 , the added optical path  512 , and the added optical path  514 . 
       [Specific Example of Process (4)] 
       [0082]    Optical paths newly added as NE 1 ˜NE 2 ˜NE 3  are the added optical path  511  and the added optical path  513 . For example, the process of determining whether the added optical path  511  (in NE 1 ˜NE 2 ˜NE 3  with a wavelength λ# 2 ) (the process (4)) is addable will be specifically described below. 
         [0083]    The transmission quality (Q cur ) of the added optical path  511  (in NE 1 ˜NE 2 ˜NE 3  with a wavelength λ# 2 ) is 9.8 ( FIG. 3 ). An optical path having a possibility of new addition as NE 1 ˜NE 2 ˜NE 3  is NE 1 ˜NE 2  with a wavelength λ# 3  (an extension of the existing optical path  502 ) or the added optical path  513  in NE 1 ˜NE 2 ˜NE 3  with a wavelength λ# 4 . 
         [0084]    The estimation unit  114  estimates a transmission quality variation when an optical path in NE 1 ˜NE 2  with a wavelength λ# 3  is added later. First, the estimation unit  114  estimates the transmission quality deterioration quantity due to a nonlinear penalty (ΔQ) due to the wavelength X# 3  of NE 1 ˜NE 2 . Regarding the transmission quality deterioration quantity (ΔQ penalty1 ) of λ# 3  of NE 1 ˜NE 2  (the first span), since no previous span is present, the transmission quality deterioration quantity ΔQ penalty  up to the previous span is 0. The estimation unit  114  estimates the transmission quality deterioration quantity (ΔQ penalty1 ) at the wavelength (λ exp =λ# 2 ) of the optical path to be calculated and the wavelength (λ add =λ# 3 ) of the added optical path to be 0.3 on the basis of the transmission quality deterioration quantity information due to a nonlinear penalty  302   a.  Since the path of NE 1 ˜NE 2  includes one span, the transmission quality deterioration quantity (ΔQ) is 0.3 which is equal to ΔQ penalty1 . 
         [0085]    The estimation unit  114  estimates the transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) due to the wavelength λ# 3  of NE 1 ˜NE 2 . The estimation unit  114  estimates that two wavelengths of the existing optical path  501  and the added optical path  511  (λ exp ) are present in NE 1 ˜NE 2  (the first span), and substitutes 2 into M λ . The estimation unit  114  estimates the transmission quality deterioration quantity (ΔQ OSNR1 ) at the wavelength (λ exp =λ# 2 ) of the optical path to be calculated and the wavelength (λ add =λ# 3 ) of the added optical path to be 0.1 on the basis of the transmission quality deterioration quantity information due to an OSNR deterioration  303   b  (M λ =2). Since the path of NE 1 ˜NE 2  includes one span, the transmission quality deterioration quantity (ΔQ OSNR ) is  0 . 1  which is equal to ΔQ OSNR1 . 
         [0086]    The estimation unit  114  estimates the transmission quality variation (the sum of ΔQ penalty  and ΔQ OSNR ) when an optical path in NE 1 ˜NE 2  with a wavelength λ# 3  is added later to be 0.4. 
         [0087]    Next, the estimation unit  114  estimates a transmission quality variation when an optical path in NE 1 ˜NE 2 ˜NE 3  with a wavelength λ# 4  is added later. First, the estimation unit  114  estimates the transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) due to in the wavelength λ# 4  of NE 1 ˜NE 2 ˜NE 3 . Regarding the transmission quality deterioration quantity (ΔQ penalty1 ) in NE 1 ˜NE 2  (the first span) with λ# 4 , since a previous span is not present, the transmission quality deterioration quantity ΔQ penalty  up to the previous span is 0. The estimation unit  114  estimates the transmission quality deterioration quantity (ΔQ penalty1 ) at the wavelength (λ exp =λ# 2 ) of the optical path to be calculated and the wavelength (λ add =λ# 4 ) of the added optical path to be 0.2 on the basis of the transmission quality deterioration quantity information due to a nonlinear penalty  302   a.    
         [0088]    Regarding the transmission quality deterioration quantity (ΔQ penalty2 ) in NE 2 ˜NE 3  (the second span) with λ# 4 , the transmission quality deterioration quantity ΔQ penalty1  up to the previous span is 0.2. The estimation unit  114  estimates the transmission quality deterioration quantity (ΔQ penalty2 ) at the wavelength (λ exp =λ# 2 ) of the optical path to be calculated and the wavelength (λ add =λ# 4 ) of the added optical path to be 0.4 on the basis of the transmission quality deterioration quantity information due to a nonlinear penalty  302   b.  The transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) is 0.4 which is equal to ΔQ penalty2 . 
         [0089]    The estimation unit  114  estimates the transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) due to the wavelength λ# 4  of NE 1 ˜NE 2 ˜NE 3 . The estimation unit  114  estimates that three wavelengths of the existing optical path  501 , the added optical path  511  (λ exp ), and the wavelength λ# 3  (an extension of the existing optical path  502 ) are present in NE 1 ˜NE 2  (the first span), and substitutes 3 into M λ . The estimation unit  114  estimates the transmission quality deterioration quantity (ΔQ OSNR1 ) at the wavelength (λ exp =λ# 2 ) of the optical path to be calculated and the wavelength (λ=λ# 4 ) of the added optical path to be 0.2 on the basis of the transmission quality deterioration quantity information due to an OSNR deterioration  303   c  (M λ =3). 
         [0090]    The estimation unit  114  estimates that three wavelengths of the existing optical path  501 , the added optical path  511  (λ exp ), and the wavelength λ# 3  (an extension of the existing optical path  502 ) are present in NE 2 ˜NE 3  (the second span), and substitutes 3 into M λ . The estimation unit  114  estimates the transmission quality deterioration quantity (ΔQ OSNR2 ) at the wavelength (λ exp =X# 2 ) of the optical path to be calculated and the wavelength (λ add =λ# 4 ) of the added optical path to be 0.2 on the basis of the transmission quality deterioration quantity information due to an OSNR deterioration  303   c  (M λ =3). The transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) is 0.4 which is equal to the sum of ΔQ OSNR1  and ΔQ OSNR2 . 
         [0091]    Accordingly, the estimation unit  114  estimates the transmission quality variation (the sum of ΔQ penalty  and ΔQ OSNR ) when an optical path in NE 1 ˜NE 2 ˜NE 3  with a wavelength λ# 4  is added later to be 0.8. The estimation unit  114  estimates that the transmission quality deterioration quantities (Q add ) due to the addition of the optical path in NE 1 ˜NE 2  with a wavelength λ# 3  and the added optical path in NE 1 ˜NE 2 ˜NE 3  with a wavelength λ# 4  is 1.2 which is equal to the sum of 0.4 and 0.8. 
         [0092]    Here, when it is assumed that the user selects the required Pre FEC BER (3×10−4) and the idea of a margin (normal) of the user policy, the desired transmission quality (Q req ) is 7.0. 
         [0093]    The deteriorated transmission quality of the added optical path  511  (in NE 1 ˜NE 2 ˜NE 3  with a wavelength λ# 2 ) is 8.6. Since the desired transmission quality (Q req ) satisfies 7.0, the determination unit  116  determines that the added optical path  511  is addable. 
       [Specific Example of Process (6)] 
       [0094]    The estimation unit  114  estimates an influence on an existing optical path when the added optical path  511  (in NE 1 ˜NE 2 ˜NE 3  with a wavelength λ# 2 ) is added (the process (6)). The existing optical paths overlapping with the added optical path  511  in one or more spans include two existing optical paths of the existing optical path  501  and the existing optical path  502 . 
         [0095]    First, the estimation unit  113  estimates an influence on the existing optical path  501  (in NE 1 ˜NE 2 ˜NE 3 ˜NE 4  with a wavelength λ# 1 ). The transmission quality (Q cur ) of the existing optical path  501  (the optical path in NE 1 ˜NE 2 ˜NE 3 ˜NE 4  with a wavelength λ# 1 ) is 7.9 ( FIG. 3 ). 
         [0096]    The estimation unit  114  estimates the transmission quality variation of the existing optical path  501  (in NE 1 ˜NE 2 ˜NE 3 ˜NE 4  with a wavelength X# 1 ) when the added optical path  511  (in NE 1 ˜NE 2 ˜NE 3  with a wavelength X# 2 ) is added later. First, the estimation unit  114  estimates the transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) due to the existing optical path  501  (in NE 1 ˜NE 2 ˜NE 3 ˜NE 4  with a wavelength λ# 1 ). Regarding the transmission quality deterioration quantity (ΔQ penalty1 ) in NE 1 ˜NE 2  (the first span) with λ# 1 , since a previous span is not present, the transmission quality deterioration quantity ΔQ penalty  up to the previous span is 0. 
         [0097]    The estimation unit  114  estimates the transmission quality deterioration quantity (ΔQ penalty1 ) at the wavelength (λ exp =λ# 1 ) of the optical path to be calculated and the wavelength (λ add =λ# 2 ) of the added optical path to be 0.3 on the basis of the transmission quality deterioration quantity information due to a nonlinear penalty  302   a.    
         [0098]    In the transmission quality deterioration quantity (ΔQ penalty2 ) in NE 2 ˜NE 3  (the second span) with λ# 1 , the transmission quality deterioration quantity ΔQ penalty1  up to the previous span is 0.3. The estimation unit  114  estimates the transmission quality deterioration quantity (ΔQ penalty2 ) at the wavelength (λ exp =λ# 1 ) of the optical path to be calculated and the wavelength (λ add =λ# 2 ) of the added optical path to be 0.6 on the basis of the transmission quality deterioration quantity information due to a nonlinear penalty  302   c.    
         [0099]    Since two spans overlap with each other, the transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) is 0.6 which is equal to ΔQ penalty2 . 
         [0100]    The estimation unit  114  estimates the transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) due to the wavelength λ# 1  of NE 1 ˜NE 2 ˜NE 3 . The estimation unit  114  estimates that one wavelength of the existing optical path  501  is present in NE 1 ˜NE 2  (the first span), and substitutes 1 into M λ . The estimation unit  114  estimates the transmission quality deterioration quantity (ΔQ OSNR1 ) at the wavelength (λ exp =λ# 1 ) of the optical path to be calculated and the wavelength (λ add =λ# 2 ) of the added optical path to be 0.1 on the basis of the transmission quality deterioration quantity information due to an OSNR deterioration  303   a  (M λ =1). 
         [0101]    Because two wavelengths of the existing optical path  501  (λ# 1 ) and the existing optical path  502  (λ# 3 ) are present in NE 2  to NE 3  (the second span), the estimation unit  114  substitutes 2 into M λ . The estimation unit  114  estimates the transmission quality deterioration quantity (ΔQ OSNR2 ) at the wavelength (λ exp =λ# 1 ) of the optical path to be calculated and the wavelength (λ add =λ# 2 ) of the added optical path to be 0.1 on the basis of the transmission quality deterioration quantity information due to an OSNR deterioration  303   b  (M λ =2). The transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) is 0.2 which is equal to the sum of ΔQ OSNR1  and ΔQ OSNR2 . 
         [0102]    Accordingly, the estimation unit  114  estimates the transmission quality variation (Q add  (the sum of ΔQ penalty  and ΔQ OSNR ) of the existing optical path  501  when the added optical path  511  is added later to be 0.8. 
         [0103]    Here, when it is assumed that the user selects the required Pre FEC BER (3×10−4) and the idea of a margin (normal) of the user policy, the desired transmission quality (Q req ) is 7.0. 
         [0104]    The deteriorated transmission quality of the existing optical path  501  (in NE 1 ˜NE 2 ˜NE 3  with a wavelength λ# 1 ) is 7.1. Since the desired transmission quality (Q req ) satisfies 7.0, the determination unit  116  determines that there is no adverse influence on the existing optical path  501 . 
         [0105]    In addition, the estimation unit  114  estimates an influence on the existing optical path  502  (in NE 2 ˜NE 3 ˜NE 4  with a wavelength λ# 3 ). The transmission quality (Q cur ) of the existing optical path  502  (in NE 2 ˜NE 3 ˜NE 4  with a wavelength λ# 3 ) is 9.9 ( FIG. 3 ). 
         [0106]    The estimation unit  114  estimates the transmission quality variation of the existing optical path  502  (in NE 2 ˜NE 3 ˜NE 4  with a wavelength λ# 3 ) when the added optical path  511  (in NE 1 ˜NE 2 ˜NE 3  with a wavelength λ# 2 ) is added later. The estimation unit  114  estimates the transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) due to the existing optical path  502  (in NE 2 ˜NE 3 ˜NE 4  with a wavelength λ# 3 ). Regarding the transmission quality deterioration quantity (ΔQ penalty1 ) in NE 2 ˜NE 3  (the first span) with λ# 3 , since a previous span is not present, the transmission quality deterioration quantity ΔQ penalty  up to the previous span is 0. The estimation unit  114  estimates the transmission quality deterioration quantity (ΔQ penalty1 ) at the wavelength (λ exp =λ# 3 ) of the optical path to be calculated and the wavelength (λ add =λ# 2 ) of the added optical path to be 0.3 on the basis of the transmission quality deterioration quantity information due to a nonlinear penalty  302   a.    
         [0107]    Since the number of overlapping spans is one, the transmission quality deterioration quantity due to a nonlinear penalty (ΔQ penalty ) is 0.3 which is equal to ΔQ penalty1 . 
         [0108]    The estimation unit  114  estimates the transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) due to the wavelength λ# 3  of NE 2 ˜NE 3 ˜NE 4 . The estimation unit  114  estimates that two wavelengths of the existing optical path  501  are present in NE 2 ˜NE 3  (the first span), and substitutes 2 into M λ . The estimation unit  114  estimates the transmission quality deterioration quantity (ΔQ OSNR1 ) at the wavelength (λ exp =λ# 3 ) of the optical path to be calculated and the wavelength (λ add =λ# 2 ) of the added optical path to be 0.0 on the basis of the transmission quality deterioration quantity information due to an OSNR deterioration  303   c  (M λ =2). 
         [0109]    Since the number of overlapping spans is one, the transmission quality deterioration quantity due to an OSNR deterioration (ΔQ OSNR ) is 0.0 which is equal to ΔQ OSRN1 . 
         [0110]    Accordingly, the estimation unit  114  estimates the transmission quality variation (Q add  (the sum of ΔQ penalty  and ΔQ OSNR ) of the existing optical path  502  when the added optical path  511  is added later to be 0.3. 
         [0111]    Here, when it is assumed that the user selects the required Pre FEC BER (3×10−4) and the idea of a margin (normal) of the user policy, the desired transmission quality (Q req ) is 7.0. 
         [0112]    The deteriorated transmission quality of the existing optical path  502  is 9.6. Since the desired transmission quality (Q req ) satisfies 7.0, the determination unit  116  determines that there is no adverse influence on the existing optical path  502 . 
         [0113]    Since the addition of the added optical path  511  does not have an adverse influence on any of the existing optical path  501  and the existing optical path  502 , the determination unit  116  determines that the added optical path  511  is addable. 
         [0114]      FIG. 8  is a diagram illustrating an example of updated transmission quality information. The updated transmission quality information  601  is an example obtained after updating the transmission quality information  301  of  FIG. 3  after λ# 2  of NE 1 ˜NE 2 ˜NE 3  has been actually added to the network  200 . When λ# 2  of NE 1 ˜NE 2 ˜NE 3  is actually added to the network  200 , the measuring unit  124  measures the latest transmission quality and transmits the measurement result to the network management device  110 . The memory unit  113  updates the transmission quality information on the basis of the actual measurement result. Then, the memory unit  113  stores a value of the transmission quality at λ# 1  which is updated from 7.9 to 7.7 in the section of NE 1 ˜NE 2 ˜NE 3 ˜NE 4 . The memory unit  113  stores a value of the transmission quality at λ# 2  which is updated from 9.8 to 9.2 in the section of NE 1 ˜NE 2 ˜NE 3 . The memory unit  113  stores a value of the transmission quality at λ# 3  which is updated from 9.9 to 9.8 in the section of NE 2 ˜NE 3 ˜NE 4 . 
         [0115]    Here, there occurs a case in which the actual measurement result is different from the estimation result of the estimation unit  114 . Since the actual measurement result and the estimation result are different from each other, the estimation unit  114  updates the transmission quality deterioration quantity information due to a nonlinear penalty  302   a  to  302   c  and the transmission quality deterioration quantity information due to an OSNR deterioration  303   a  to  303   c.    
         [0116]      FIGS. 9A and 9B  are diagrams illustrating an example of updated transmission quality deterioration quantity information due to a nonlinear penalty. Transmission quality deterioration quantity information  602   a  is an example of the updated transmission quality deterioration quantity information  302   a.  Transmission quality deterioration quantity information  602   b  is an example of the updated transmission quality deterioration quantity information  302   b.  Transmission quality deterioration quantity information  602   c  is an example of the updated transmission quality deterioration quantity information  302   c.    
         [0117]    The estimation unit  114  calculates the transmission quality deterioration quantity on the basis of the actual measurement result, the estimation result, the values set in the transmission quality deterioration quantity information, and the like. Specifically, the estimation unit  114  calculates the transmission quality deterioration quantity using the following equation: (non-updated transmission quality deterioration quantity)×((non-updated transmission quality)−(estimation result))÷((non-updated transmission quality)−(actual measurement result)). 
         [0118]    In the transmission quality deterioration quantity information  602   a , sets of λ add =λ# 2  and λ exp =λ# 1 , λadd=λ# 2  and λ exp =λ add =λ# 3  and λ exp =λ# 2 , and λ add =λ# 4  and λ exp =λ# 2  are updated based on the value calculated by the estimation unit  114  in the above-described processes (4) and (6). With respect to these sets, the estimation unit  114  sets a value proportional by (9.9−9.8)÷(9.9−9.6) times to the transmission quality deterioration quantity information  302   a  on the basis of the value calculated by the estimation unit  114  in the processes (4) and (6). The transmission quality deterioration quantity information  602   a  is updated in places which are used for the above-mentioned calculation, but may be updated in other places in the same way. 
         [0119]    In the transmission quality deterioration quantity information  602   b , a set of λ add =λ# 4  and λ exp =λ# 2  is updated based on the value calculated by the estimation unit  114  in the processes (4) and (6). With respect to this set, the estimation unit  114  sets a value proportional by (9.8−9.2)÷(9.8−8.6) times to the transmission quality deterioration quantity information  302   b  on the basis of the value calculated by the estimation unit  114  in the processes (4) and (6). The transmission quality deterioration quantity information  602   b  is updated in places which are used in the above-mentioned calculation, but may be updated in other places in the same way. 
         [0120]    In the transmission quality deterioration quantity information  602   c  a set of λ add =λ# 2  and λ exp =λ# 1  is updated based on the value calculated by the estimation unit  114  in the processes (4) and (6). With respect to this set, the estimation unit  114  sets a value proportional by (7.9−7.7)÷(7.9−7.1) times to the transmission quality deterioration quantity information  302   c  on the basis of the value calculated by the estimation unit  114  in the processes (4) and (6). The transmission quality deterioration quantity information  602   c  is updated in places which are used in the above-mentioned calculation, but may be updated in other places in the same way. 
         [0121]      FIGS. 10A and 10B  are diagrams illustrating an example of updated transmission quality deterioration quantity information due to an OSNR deterioration. Transmission quality deterioration quantity information  603   a  is an example of the updated transmission quality deterioration quantity information  303   a.  Transmission quality deterioration quantity information  603   b  is an example of the updated transmission quality deterioration quantity information  303   b.  Transmission quality deterioration quantity information  603   c  is an example of the updated transmission quality deterioration quantity information  303   c.    
         [0122]    The estimation unit  114  calculates the transmission quality deterioration quantity on the basis of the actual measurement result, the estimation result, the values set in the transmission quality deterioration quantity information, and the like. Specifically, the estimation unit  114  calculates the transmission quality deterioration quantity by the following equation: (non-updated transmission quality deterioration quantity)×((non-updated transmission quality)−(estimation result))÷((non-updated transmission quality)−(actual measurement result)). 
         [0123]    In the transmission quality deterioration quantity information  603   a  a set of λ add =λ# 2  and λ exp =λ# 1  is updated based on the value calculated by the estimation unit  114  in the processes (4) and (6). With respect to this set, the estimation unit  114  sets a value proportional by (7.9−7.7)÷(7.9−7.1) times to the transmission quality deterioration quantity information  303   a  on the basis of the value calculated by the estimation unit  114  in the processes (4) and (6). The transmission quality deterioration quantity information  603   a  is updated in places which are used in the above-mentioned calculation, but may be updated in other places in the same way. 
         [0124]    In the transmission quality deterioration quantity information  603   b  sets of λ add =λ# 2  and λ exp =λ# 1 , λ add =λ# 2  and λ exp =λ# 3 , and λ add =λ# 3  and X exp =λ# 2  are updated based on the value calculated by the estimation unit  114  in the processes (4) and (6). With respect to the set of λ add =λ# 2  and λ exp =λ# 1 , the estimation unit  114  sets a value proportional by (7.9−7.7)÷(7.9−7.1) times to the transmission quality deterioration quantity information  303   b  for on the basis of the value calculated by the estimation unit  114  in the processes (4) and (6). With respect to the set of λ add =λ# 2  and λ exp =λ# 3 , the estimation unit  114  sets a value proportional by (9.8−9.2)÷(9.8−8.6) times to the transmission quality deterioration quantity information  303   b  on the basis of the value calculated by the estimation unit  114  in the processes (4) and (6). With respect to the set of λ add =λ# 3  and λ exp =λ# 2  the estimation unit  114  sets a value proportional by (9.9−9.8)÷(9.9−9.6) times to the transmission quality deterioration quantity information  303   b  on the basis of the value calculated by the estimation unit  114  in the processes (4) and (6). The transmission quality deterioration quantity information  603   b  is updated in places which are used in the above-mentioned calculation, but may be updated in other places in the same way. 
         [0125]    In the transmission quality deterioration quantity information  603   c , a set of λ add =λ# 4  and λ exp =λ# 2  is updated based on the value calculated by the estimation unit  114  in the processes (4) and (6). With respect to this set, the estimation unit  114  sets a value proportional by (9.8−9.2)÷(9.8−8.6) times to the transmission quality deterioration quantity information  303   c  on the basis of the value calculated by the estimation unit  114  in the processes (4) and (6). The transmission quality deterioration quantity information  603   c  is updated in places which are used in the above-mentioned calculation, but may be updated in other places in the same way. 
         [0126]      FIG. 11  is a flowchart illustrating an example of a process flow in the network management system according to the present embodiment. In  FIG. 11 , it is assumed that there is no optical path in the WDM network  120 . The memory unit  113  stores the transmission quality information, the transmission quality deterioration quantity information due to a nonlinear penalty, and the transmission quality deterioration quantity information due to an OSNR deterioration in which design values are set (operation S 101 ). 
         [0127]    As a process in the case of adding one optical path, the second receiver  112  receives a request for adding one optical path. The estimation unit  114  and the determination unit  115  estimate whether an optical path (one path) to be added and an existing optical path (operation S 102 ) are transmittable. The estimation unit  114  determines whether both the optical path to be added (one path) and the existing optical path are transmittable (operation S 103 ). 
         [0128]    In the case where both the optical path to be added (one path) and the existing optical path are not transmittable (NO in operation S 103 ), the second receiver  112  receives a request for adding another optical path from the user (operation S 104 ). When the request for adding another optical path is received from the user in operation S 104 , the process is repeated from operation S 102 . 
         [0129]    In the case where both the optical path to be added (one path) and the existing optical path are transmittable (YES in operation S 103 ), the order unit  117  transmits an order to add an optical path and an order to measure transmission quality to the node elements NE in the WDM network  120  (operation S 105 ). The measuring unit  124  of the optical receiver  123  measures the transmission quality after a new optical path is added (operation S 106 ). The first receiver  111  receives the measurement result (operation S 106 ). The memory unit  113  stores the transmission quality information, the transmission quality deterioration quantity information due to a nonlinear penalty, and the transmission quality deterioration quantity information due to an OSNR deterioration which are updated on the basis of the measurement result (operation S 107 ). The process is repeated from operation S 102  until operations S 102  to S 107  are completed for all the optical paths input by the user. When operations S 102  to S 107  are completed for all the optical paths input by the user, the network management device ends the process flow. 
         [0130]      FIG. 12  is a flowchart illustrating an example of a process of determining whether an optical path is addable. The process of determining whether an optical path is addable illustrated in  FIG. 12  is a process for describing operation S 102  in  FIG. 11  in more detail. 
         [0131]    The second receiver  112  receives a request for adding one optical path (operation S 201 ). The determination unit  116  determines whether the requested optical path is addable using the estimation result of the estimation unit  114  and extracts an addable optical path. When there are plural addable optical paths, the determination unit  116  prioritizes the optical paths (operation S 202 ). The determination unit  116  selects one optical path having a high priority order (operation S 203 ). 
         [0132]    Based on one existing optical path including the same span as the selected optical path, the determination unit  116  determines whether the selected optical path has an adverse influence on the existing optical path and estimates transmission propriety thereof (operation S 204 ). The determination unit  116  determines whether the based existing optical path is transmittable (operation S 205 ). 
         [0133]    When it is determined that the based existing optical path is not transmittable (NO in operation S 205 ), the determination unit  116  selects an optical path addable having the second highest priority order (operation S 206 ). The determination unit  116  repeats the process from operation S 204  on the optical path selected in operation S 206 . 
         [0134]    When it is determined that the based existing optical path is transmittable (YES in operation S 205 ) and there is an existing optical path having the same span as the selected optical path, the determination unit  116  repeats the process from operation S 204 . When it is determined that the existing optical path of interest is transmittable (YES in operation S 205 ) and there is no existing optical path having the same span as the selected optical path, the determination unit  116  determines an optical path to be added (operation S 207 ). Specifically, the determination unit  116  determines the optical path determined to be addable (operation S 202 ) and not to interfere with the transmission of the existing optical path as an optical path to be added. When the process of operation S 207  is ended, the determination unit  116  ends the process of operation S 102  in  FIG. 11 . 
         [0135]    In this way, the estimation unit  114  may estimate an adverse influence on an existing optical path on the basis of the measured value. The determination unit  116  determines whether there is no adverse influence on an existing optical path and whether desired transmission quality is to be ensured on the basis of the estimation result of the estimation unit  114  for each new optical path. Accordingly, a network design based on actual operation may be made more efficiently than a network design using a design value. 
         [0136]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to an illustrating of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.