Abstract:
An optical wavelength multiplexing device includes: a wavelength selective switch including a first input port for receiving an optical signal, a second input port for receiving a monitoring signal, output ports for outputting the optical signal or the monitoring signal, and an adjustment unit that adjusts a level of the optical signal or the monitoring signal at one of the output ports; a measurement unit that measures an output level of the monitoring signal at one of the output ports; and a control unit that specifies an unused output port of the output ports as a monitoring target port; sets a specific adjustment amount to the monitoring target port; outputs the monitoring signal to the monitoring target port; and determines whether the monitoring target port has an abnormality, based on the output level at the monitoring target port and an estimated output level at the monitoring target port.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2015-083760, filed on Apr. 15, 2015, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to an optical wavelength multiplexing device, an optical transmission device, and an abnormality determination method. 
     BACKGROUND 
     In an optical wavelength division multiplexing (WDM) transmission system, a plurality of optical transmission devices are coupled, and an optical wavelength multiplexed signal obtained by multiplexing optical signals having different optical wavelengths is transmitted between the optical transmission devices. 
     A technology in a related art is discussed in Japanese Laid-open Patent Publication No. 2006-267522. 
     SUMMARY 
     According to an aspect of the embodiments, an optical wavelength multiplexing device includes: a wavelength selective switch that includes a first input port through which an optical signal is input, a second input port through which a monitoring signal corresponding to a monitoring optical signal is input, a plurality of output ports through which the optical signal or the monitoring signal is output, and an adjustment unit that adjusts a level of the optical signal or the monitoring signal output to one of the plurality of output ports; a measurement unit that measures an output level of the monitoring signal at one of the plurality of output ports; and a control unit that controls the wavelength selective switch and the measurement unit; wherein the control unit: specifies an unused output port from among the plurality of output ports as a monitoring target port; sets an adjustment amount of the monitoring target port at a specific adjustment amount; outputs the monitoring signal to the monitoring target port; and determines whether the monitoring target port has an abnormality, based on the output level of the monitoring signal at the monitoring target port, which is measured by the measurement unit, and an estimated output level of the monitoring signal at the monitoring target port when the specific adjustment amount is set. 
     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. 
     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 
         FIG. 1  is a diagram illustrating an exemplary optical transmission system; 
         FIG. 2  is a diagram illustrating an exemplary optical wavelength multiplexing device; 
         FIG. 3  is a diagram illustrating an exemplary function configuration of a central processing unit (CPU) of the optical wavelength multiplexing device; 
         FIG. 4  is a diagram illustrating an exemplary failure determination in a wavelength selective switch (WSS); 
         FIG. 5  is a diagram illustrating an exemplary monitoring processing of the optical wavelength multiplexing device; and 
         FIG. 6  is a diagram illustrating an exemplary evaluation processing of the optical wavelength multiplexing device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Each of the optical transmission devices includes a WSS that optically drops or adds an optical signal having a certain optical wavelength from or to the optical wavelength multiplexed signal. 
     A monitoring signal generated at an internal light source is output from a monitoring signal input port to a monitoring signal output port in the WSS, and the intensity of the monitoring signal, for example, the output level of the monitoring signal is monitored to check the normality of the WSS. Feedback control of the angle of the reflection surface of a corresponding mirror is performed based on the output level of the monitoring signal so that the output level of the monitoring signal having an optical wavelength that is not used for the operation becomes maximum from among optical signals of the optical wavelength multiplexed signal. As described above, the normality of the WSS is checked using the monitoring signal having the unused optical wavelength. 
     For example, the optical transmission device checks the normality of the WSS using a monitoring signal having an unused optical wavelength, but may not check the normality of a port that is not used for the operation. For example, the performance of a port of the WSS may be reduced due to a factor such as a change over time. As a result, in a case in which an unused port has an abnormality when the unused port is used for the operation, a high-quality line guarantee may not be secured at the time of start of the operation in the optical transmission device because the normality of the unused port is not checked. There may be provided that an optical transmission device that checks the normality of an unused port of the WSS, for example, predicts the abnormality in the unused port. 
     The technology discussed herein is not limited to embodiments described below. The embodiments may be combined as appropriate. 
       FIG. 1  is a diagram illustrating an exemplary optical transmission system. In an optical transmission system  1  illustrated in  FIG. 1 , a plurality of optical transmission devices  2  are coupled through optical fibers  3 , and each of the optical transmission devices  2  transmits, through the optical fiber  3 , an optical wavelength multiplexed signal of a WDM scheme, which is obtained by multiplexing optical signals having different optical wavelengths. The optical transmission device  2  includes, for example, an optical wavelength multiplexing device  10  such as a reconfigurable optical add/drop multiplexer (ROADM) that optically drops or adds an optical signal having a certain wavelength from or to the optical wavelength multiplexed signal. 
       FIG. 2  is a diagram illustrating an exemplary optical wavelength multiplexing device. The optical wavelength multiplexing device  10  illustrated in  FIG. 2  includes a first WSS  11 , a second WSS  12 , a small form-factor pluggable (SFP)  13 , an optical channel monitor (OCM)  14 , and a CPU  15 . The first WSS  11  includes a single first input port  11 A, a single second input port  11 B, and M output ports  11 C. The first WSS  11  outputs an optical signal input through the first input port  11 A or the second input port  11 B, to each of the output ports  11 C in a unit of an optical wavelength. The first input port  11 A is an input port for inputting an optical signal such as an optical wavelength multiplexed signal from a downlink. The second input port  11 B is an input port through which a monitoring signal having an optical wavelength different from the optical wavelength multiplexed signal is input. 
     The SFP  13  is a signal source that outputs a monitoring signal. The second WSS  12  includes, for example, N input ports  12 A and a single output port  12 B, and optically combines optical signals from the input ports  12 A, and outputs the combined optical signal to the output port  12 B. The OCM  14  is coupled to first optical dividing units  14 A and a second optical dividing unit  14 B. The first optical dividing unit  14 A is arranged for each of the output ports  11 C of the first WSS  11 , and optically divides a signal output through the output port  11 C. The second optical dividing unit  14 B is arranged for the output port  12 B of the second WSS  12 , and optically divides a signal output through the output port  12 B for the uplink and the OCM  14 . The OCM  14  may be, for example, an optical spectrum analyzer that monitors the output levels of the optical wavelengths at the output ports  11 C of the first WSS  11 , based on the output signals that have been optically divided by the first optical dividing units  14 A, respectively. The output level may be an output power level for each of the optical wavelengths. The OCM  14  monitors the output level of the output port  12 B of the second WSS  12 , based on the output signal that has been optically divided by the second optical dividing unit  14 B. 
     The first WSS  11  includes an attenuator (AU)  11 D that adjusts the output level of the optical signal having each of the optical wavelengths from the first input port  11 A or the second input port  11 B. The second WSS  12  includes an ATT  12 C that adjusts the output level of the optical signal having each of the optical wavelengths from the plurality of input ports  12 A. The CPU  15  controls the entire optical wavelength multiplexing device  10 . 
       FIG. 3  is diagram illustrating an exemplary function configuration of the CPU of the optical wavelength multiplexing device. The CPU  15  illustrated in  FIG. 3  includes a channel equalizer (CHEQ) control unit  20  and a failure control unit  30 . The CHEQ control unit  20  controls the ATT  11 D of the first WSS  11  and the ATT  12 C of the second WSS  12 , based on the monitoring result of the OCM  14 . The CHEQ control unit  20  includes a monitoring light control unit  21 , a level monitoring unit  22 , an ATT amount calculation unit  23 , and an ATT amount setting unit  24 . The failure control unit  30  estimates a failure in the first WSS  11 . 
     The first WSS  11  receives an operating optical signal, from the first input port  11 A, and outputs the received operating optical signal through an operated output port  11 C from among the plurality of output ports  11 C. The first WSS  11  receives a monitoring signal from the second input port  11 B, and outputs the received monitoring signal through an unused output port  11 C from among the plurality of output ports  11 C. The unused output port  11 C is an output port  11 C that is not used for the operation from among the plurality of output ports  11 C. 
     The monitoring light control unit  21  controls the SFP  13  that outputs a monitoring signal. The level monitoring unit  22  monitors the output level of each of the optical wavelengths at the output ports  11 C of the first WSS  11 , through the OCM  14 , and monitors the input level of the monitoring signal input to the first WSS  11 , through the OCM  14 . The level monitoring unit  22  monitors the output level of each of the optical wavelengths at the output port  12 B of the second WSS  12 , through the OCM  14 . The ATT amount calculation unit  23  calculates an ATT amount set to the ATT  11 D of the first WSS  11  so that the output level of each of the optical wavelengths at the operated output ports  11 C, which has been monitored by the level monitoring unit  22 , becomes a target output level. The ATT amount calculation unit  23  calculates an ATT amount set to the ATT  12 C of the second WSS  12  so that the output level of each of the optical wavelengths at the operated output port  12 B, which has been monitored by the level monitoring unit  22 , becomes a target output level. The ATT amount setting unit  24  sets the ATT amount that has been calculated in the ATT amount calculation unit  23 , to the ATT  11 D of the first WSS  11  or the ATT  12 C of the second WSS  12 . For example, the CHEQ control unit  20  performs feedback control by adjusting the ATT amount so that the output level of each of the optical wavelengths of the output ports, which has been monitored by the level monitoring unit  22 , becomes the target output level. 
     The failure control unit  30  includes a setting unit  31 , an estimation unit  32 , an accumulation control unit  33 , an accumulation database (DB)  34 , and a failure determination unit  35 . The setting unit  31  starts monitoring processing at certain intervals. The monitoring processing is processing in which the state of a monitoring target port of the first WSS  11  is monitored. The setting unit  31  specifies an unused output port  11 C from among the plurality of output ports  11 C in the first WSS  11  as a monitoring target port, and sets the ATT amount of the specified monitoring target port at a certain ATT amount. The setting unit  31  may sequentially specify merely an unused output port  11 C from among the plurality of output ports  11 C of the first WSS  11  as the monitoring target port, and may not specify the operated output port  11 C. After the setting unit  31  has set the ATT amount of the monitoring target port at the certain ATT amount, the setting unit  31  outputs a monitoring signal from the SFP  13  to the monitoring target port through the monitoring light control unit  21 . 
     The estimation unit  32  calculates an estimated output level of the monitoring signal at the monitoring target port, based on the input level of the monitoring signal at the second input port  11 B of the first WSS  11  and the certain ATT amount that has been set to the ATT  11 D of the monitoring target port. The estimated output level is the output level at the monitoring target port, which has been calculated from the input level of the monitoring signal and the certain ATT amount. The estimation unit  32  calculates a control error between the output level of the monitoring signal at the monitoring target port, which has been monitored by the level monitoring unit  22 , and the calculated estimated output level of the monitoring signal at the monitoring target port. The control error is a difference between the monitored output level of the monitoring signal and the estimated output level. 
     The accumulation control unit  33  controls the accumulation of the accumulation DB  34 . The accumulation control unit  33  accumulates the port number of the monitoring target port, the control error of the monitoring target port, and the calculated time at which the estimated output level at the monitoring target port has been calculated, in the accumulation DB  34 , as history information. 
     The failure determination unit  35  determines whether the control error exceeds a certain threshold value, for each of the port numbers of the monitoring target ports, with reference to the accumulation DB  34 . The certain threshold value may be a threshold value used to estimate that the control error is caused by an abnormality in the port. The failure determination unit  35  determines an abnormality in the monitoring target port corresponding to the port number when the control error exceeds the certain threshold value for each of the port numbers, associates the port number with the control error, and accumulates the port number and the control error in the accumulation DB  34  as the abnormality. 
     The failure determination unit  35  determines whether a time period in which the abnormality in the monitoring target port has continued exceeds a certain time period, with reference to the accumulation DB  34 . The certain time period may be, for example, three days. When the time period in which the abnormality in the monitoring target port has continued exceeds three days, the failure determination unit  35  determines a failure in the first WSS  11 . When the failure in the first WSS  11  has been determined, the failure determination unit  35  may output a failure alarm to a monitoring terminal in the optical transmission system  1 . The user of the monitoring terminal may recognize the failure in the first WSS  11  of the optical wavelength multiplexing device  10 , through the failure alarm. The failure determination unit  35  may cause an indicator light of the optical wavelength multiplexing device  10  to perform blinking in response to the failure alarm in addition to the output of the failure alarm to the monitoring terminal. The user of the optical transmission device  2  may recognize the failure in the first WSS  11  through the blinking of the indicator light. 
       FIG. 4  is a diagram illustrating an exemplary failure determination of a WSS. In  FIG. 4 , the failure determination of a WSS is performed using a control error based on a relationship between the control error and an elapsed time. For convenience of explanation, monitoring of a monitoring target port is performed, for example, at the same time everyday. The control error in the elapsed time from the first to the sixth days illustrated in  FIG. 4  does not exceed a certain threshold value, which determines the normality of the monitoring target port. The control error in the elapsed time of the seventh and more days exceeds the certain threshold value, which determines an abnormality in the monitoring target port. In the elapsed time from the seventh to the ten days, the time period in which the abnormality in the monitoring target port has continued exceeds the certain time period, for example, three days, so that there is a high probability of the abnormality in the monitoring target port, and a failure in the first WSS  11  may be determined. 
       FIG. 5  is a diagram illustrating an exemplary monitoring processing of the optical wavelength multiplexing device.  FIG. 6  is a diagram illustrating an exemplary evaluation processing of the optical wavelength multiplexing device.  FIG. 5  illustrates an exemplary processing operation of the CPU  15  in the monitoring processing of the optical wavelength multiplexing device  10  illustrated in  FIGS. 2 and 3 . In the monitoring processing illustrated in  FIG. 5 , an unused port from among the plurality of output ports  11 C of the first WSS  11  is monitored as a monitoring target port. The monitoring processing may be executed at certain intervals, for example, at the same time everyday. 
     In  FIG. 5 , the setting unit  31  in the CPU  15  specifies an output port having a port number “1”, from among the plurality of output ports  11 C of the first WSS  11  (Operation S 11 ). The output ports  11 C are identified, for example, between port numbers “1” to “M”. 
     The setting unit  31  determines whether the specified port is an unused port (Operation S 12 ). When the specified port is an unused port (Yes in Operation S 12 ), the setting unit  31  sets the specified port as a monitoring target port (Operation S 13 ). The setting unit  31  controls the SFP  13  to output a monitoring signal to the monitoring target port, through the monitoring light control unit  21  (Operation S 14 ). 
     The setting unit  31  executes the evaluation processing illustrated in  FIG. 6  for the monitoring target port (Operation S 15 ). After the evaluation processing has been executed for the monitoring target port, the CPU  15  determines whether there is an unspecified port from among the output ports  11 C of the first WSS  11  (Operation S 16 ). When there is an unspecified port (Yes in Operation S 16 ), the setting unit  31  specifies the unspecified port (Operation S 17 ). The processing proceeds to Operation S 12  to determine whether the specified port is an unused port. 
     When there is no unspecified port (No in Operation S 16 ), the setting unit  31  ends the processing operation of  FIG. 5 . When the specified port is not an unused port (No in Operation S 12 ), the processing proceeds to Operation S 16  to determine whether there is an unspecified port. 
       FIG. 6  illustrates an exemplary processing operation of the CPU  15  in the evaluation processing of the optical wavelength multiplexing device  10  illustrated in  FIGS. 2 and 3 . In the evaluation processing illustrated in  FIG. 6 , whether there is an abnormality in each of the unused monitoring target ports is determined, and the presence or absence of a failure in the first WSS  11  is evaluated based on the determination result. 
     In  FIG. 6 , the setting unit  31  of the CPU  15  causes the ATT  11 D of the monitoring target port to become active for the first WSS  11 , and sets a certain ATT amount to the ATT  11 D, through the ATT amount setting unit  24  (Operation S 21 ). The setting unit  31  monitors the output level of the monitoring signal at the monitoring target port, through the level monitoring unit  22  (Operation S 22 ). 
     The estimation unit  32  in the CPU  15  obtains the input level of the monitoring signal at the monitoring target port, the output level of the monitoring signal at the monitoring target port, and the certain ATT amount of the first WSS  11 , which has been set to the monitoring target port (Operation S 23 ). 
     The estimation unit  32  calculates an estimated output level at the monitoring target port, based on the input level of the monitoring signal at the monitoring target port and the certain ATT amount that has been set to the monitoring target port (Operation S 24 ). The estimation unit  32  calculates a control error between the output level at the monitoring target port and the estimated output level (Operation S 25 ). 
     The accumulation control unit  33  in the CPU  15  accumulates the control error of the monitoring target port, which has been calculated in the estimation unit  32  and the calculated time, in the accumulation DB  34  (Operation S 26 ). The calculated time may be a date and time in which the estimated output level at the monitoring target port has been calculated in Operation S 24 . 
     The failure determination unit  35  in the CPU  15  determines whether the control error of the monitoring target port exceeds a certain threshold value, with reference to the accumulation DB  34  (Operation S 27 ). When the control error of the monitoring target port exceeds the certain threshold value (Yes in Operation S 27 ), the failure determination unit  35  determines that there is an abnormality in the monitoring target port (Operation S 28 ), associates the port number with the control error, and accumulates the port number and the control error in the accumulation DB  34  as the abnormality (Operation S 29 ). 
     The failure determination unit  35  determines whether a time period in which the abnormality in the monitoring target port has continued exceeds a certain time period, with reference to the accumulation DB  34  (Operation S 30 ). When the time period in which the abnormality in the monitoring target port has continued exceeds the certain time period (Yes in Operation S 30 ), the failure determination unit  35  determines that there is a high probability of the abnormality in the monitoring target port, and determines that there is a failure in the first WSS  11  (Operation S 31 ). The failure determination unit  35  outputs a failure alarm of the first WSS  11  (Operation S 32 ), and ends the processing operation illustrated in  FIG. 6 . The failure determination unit  35  outputs the failure alarm of the first WSS  11  to the monitoring terminal. The user of the monitoring terminal may recognize, in advance, the failure in the first WSS  11  of the optical wavelength multiplexing device  10 , based on the failure alarm output to the monitoring terminal. 
     When the control error of the monitoring target port does not exceed the certain threshold value (No in Operation S 27 ), the failure determination unit  35  determines that the monitoring target port is normal, and ends the processing operation illustrated in  FIG. 6 . When the time period in which the abnormality in the monitoring target port has continued does not exceed the certain time period (No in Operation S 30 ), the failure determination unit  35  ends the processing operation illustrated in  FIG. 6 . 
     The CPU  15  that executes the evaluation processing illustrated in  FIG. 6  sets an unused port as a monitoring target port, outputs a monitoring signal to the monitoring target port, calculates a control error between the actual output level and the estimated output level for each of the monitoring target ports, and estimates an abnormality in the monitoring target port when the control error exceeds the certain threshold value. As a result, the CPU  15  may predict an abnormality in each of the monitoring target ports. 
     The CPU  15  accurately identifies an abnormality in the monitoring target port, and identifies a failure in the first WSS  11  by executing the processing in which whether a time period in which the abnormality in the monitoring target port has continued exceeds the certain time period is determined. The CPU  15  may identify an abnormality in the monitoring target port with high accuracy. 
     When the time period in which the abnormality in the monitoring target port has continued exceeds the certain time period, the CPU  15  identifies the abnormality in the monitoring target port with high accuracy, and outputs a failure alarm for the first WSS  11  to the monitoring terminal. The user of the monitoring terminal may recognize a failure in the first WSS  11  through the failure alarm, and recognize a replacement time of the first WSS  11 . 
     The CPU  15  specifies an unused output port  11 C from among the plurality of output ports of the first WSS  11  as a monitoring target port, sets a certain ATT amount to the specified monitoring target port, and outputs a monitoring signal to the monitoring target port to which the certain ATT amount has been set. The CPU  15  determines an abnormality in the monitoring target port, based on the output level of the monitoring signal at the monitoring target port and the estimated output level of the monitoring signal at the time of setting of the certain ATT amount. An abnormality such as performance reduction caused by a change over time in an unused port of the first WSS  11  or the like may be predicted. 
     The CPU  15  calculates the output level at the monitoring target port as the estimated output level, based on the certain ATT amount and the input level of the monitoring signal at the second input port  11 B. The CPU  15  estimates an abnormality in the monitoring target port, based on the control error between the output level at the monitoring target port and the estimated output level. An abnormality such as a performance reduction caused by a change over time in an unused port of the first WSS  11  or the like may be predicted. 
     The CPU  15  calculates the control error of the monitoring target port at certain intervals, determines an abnormality in the monitoring target port when the control error exceeds the certain threshold value, and determines, when a time period in which the abnormality in the monitoring target port has continued exceeds the certain time period, that there is a high probability of the abnormality in the monitoring target port and there is a failure in the first WSS  11 . The abnormality in an unused port of the first WSS  11  may be predicted with high accuracy, so that the failure in the first WSS  11  may be predicted. The CPU  15  outputs a failure alarm to the monitoring terminal when the failure in the first WSS  11  has been determined. The user may recognize the failure in the first WSS  11  through the failure alarm and recognize a replacement time of the first WSS  11 . 
     The CPU  15  outputs a monitoring signal to the unused port of the first WSS  11 , and estimates an abnormality in the unused port using the output level of the monitoring signal at the unused port or the like. The normality of an optical component such as the OCM  14  or the level monitoring unit  22  that monitors the output level may be checked in addition to the first WSS  11  and an unused port of the first WSS  11 . 
     Whether the control error of the monitoring target port exceeds the certain threshold value is determined, and an abnormality in the monitoring target port is estimated when the control error exceeds the certain threshold value, and here, the estimation timing of an abnormality in the monitoring target port is changed as appropriate by changing the certain threshold value as appropriate. 
     Whether the time period in which an abnormality in the monitoring target port has continued exceeds the certain time period is determined, and the abnormality in the monitoring target port is estimated with high accuracy when the time period in which the abnormality in the monitoring target port has continued exceeds the certain time period, and here, the estimation timing of an abnormality in the monitoring target port is changed as appropriate by changing the certain time period as appropriate. 
     A failure in the first WSS  11  is determined when the time period in which the abnormality in the monitoring target port has continued exceeds the certain time period. For example, control error data of the monitoring target port is accumulated over a certain portion of time, and an abnormality in the monitoring target port or a failure in the first WSS  11  may be determined when the accumulated control error data exceeds a certain first threshold value. 
     The control error data of the monitoring target port is accumulated over a certain time period, the accumulated control error data is averaged over the certain time period, and an abnormality in the monitoring target port or a failure in the first WSS  11  may be determined when the average value exceeds a certain second threshold value. 
     An abnormality in the first WSS  11  is determined when the time period in which the abnormality in the monitoring target port has continued exceeds the certain time period, and here, a failure in the first WSS  11  may be determined a time period in which abnormalities of the plurality of monitoring target ports have continued exceeds the certain time period. 
     The first WSS  11  includes the first input port  11 A through which an operating optical signal is input and the second input port  11 B through which a monitoring signal is input. As the monitoring signal, an optical signal having an optical wavelength different from the operating optical signal is employed, so that crosstalk to the operating optical signal by the monitoring signal may be reduced. 
     For example, in consideration of the crosstalk to the operating optical signal by the monitoring signal, an optical wavelength different from the operating optical signal is set to the monitoring signal. Under an environment in which the crosstalk is not considered in the first WSS  11 , the wavelength of the monitoring signal may be substantially the same as the wavelength of the operating optical signal. 
     All or some of the configuration elements of the units illustrated in the figures may be dispersed or integrated functionally or physically in a unit of a certain group depending on various loads, usage statuses, and the like. 
     All or some of the various processing functions executed in the devices may be executed on a central processing unit (CPU) (or a microcomputer such as a micro processing unit (MPU) or a micro-controller unit (MCU)). All or some of the various processing functions may be executed on a program analyzed and executed by the CPU (or the microcomputer such as the MPU or the MCU) or hardware by wired logic. 
     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 a showing 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.