Abstract:
An optical packet switching apparatus includes plural optical switches, an optical switching section that switches a path of an optical packet transmitted thereto according to the switch control signal to output the optical packet, and a control section that takes out a header portion representing a destination of the optical packet transmitted, photoelectrically converts the header to generate the switch control signal according to the destination to transmit the switch control signal to the optical switching section and controls the optical switch. The apparatus further includes a light monitor section that monitors a light quantity level of the optical packet transmitted and a light quantity level of the optical packet to be sent out, and an abnormality recognizing section that recognizes an effective timing of monitoring of the light quantity levels based on the switching control signal, and recognizes an abnormality based on the light quantity levels at the timing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation application of PCT/JP2007/059306, filed on May 1, 2007. 
    
    
     FIELD 
     The present invention relates to an optical packet switching apparatus which transmits an optical packet transmitted thereto to a destination of the optical packet by switching a path. 
     BACKGROUND 
     In order to avoid the bottleneck (limits of bandwidth, signal amount) of the electrical wiring techniques in signal switching in a high speed router, applying an optical packet switch utilizing the high bandwidth characteristics of optical transmission techniques has been studied, and the optical packet switch has been partially introduced. The optical packet switch system which has been introduced so far, once converts an optical signal to an electrical signal to perform switching. Thus, as the bandwidth has been increased, a scale of switch has been expanded. In order to avoid a drastic expansion of the scale of switch, an optical packet switching apparatus which switches an optical packet inputted thereto and sends out the optical packet as it is without converting the optical packet inputted to an electrical signal has been thought. 
       FIG. 1  illustrates an example of an optical packet switching apparatus that is conventionally thought. 
     The optical packet switching apparatus illustrated in  FIG. 1  is a simplified optical packet switching apparatus for the easiness of illustration and description, and includes an input system of two channels and an output system of two channels. 
     The optical packet switching apparatus  10  illustrated in  FIG. 1  includes an optical packet transmission section (OPTS)  20 , an optical switch section (OSS)  30 , an optical monitor section (OMS)  40 , a control section (CTLS)  50  and a center section (CS)  60 . 
     The optical packet transmission section (OPTS)  20  includes two channels of optical transmission lines  211 ,  212  on the input side from which optical packets  701 ,  702  are inputted respectively. The optical packets  701 ,  702  inputted from the respective optical transmission lines  211 ,  212  are separated to headers  701   a ,  702   a  which include destinations and data information(payloads  701   b  and  702   b ) which is main bodies of the optical packets  701 ,  702 . The headers  701   a ,  702   a  and the payloads  702   b ,  702   b  of the optical packets  701 ,  702  are different in the optical wavelength from each other. Optical filters (OF)  221 ,  222  separate the optical packets  701 ,  702  into the headers  701   a ,  702   a  and the payloads  701   b ,  702   b , by using a difference of the wavelength. 
     The headers  701   a ,  702   a  of the optical packets  701 ,  702  are converted into electrical signals by photo detectors (PD)  511 ,  512  for the respective channels provided in the control section (CTLS)  50  to be inputted to an enable signal generation section (ESGS)  513 . 
     In the enable signal generation section (ESGS)  513 , according to destination information written in the headers  701   a ,  702   a , an enable signal for switching plural optical switches (described later) included in an optical switching circuit (OSC)  30  provided in the optical switch section (OSS)  30  is generated to be inputted through six of signal transmission lines  514 - 1 ,  514 - 2 ,  514 - 3 ,  514 - 4 ,  514 - 5 ,  514 - 6  to the optical switching circuit. 
     In contrast, the payloads  701   b ,  702   b  separated by the optical filter (OF)  221 ,  222  are inputted to the optical switch circuit (OSC)  31  of the optical switch section (OSS)  30 . 
       FIG. 2  is a block diagram illustrating a configuration of an optical switching circuit illustrated as one block in  FIG. 1 . 
     The optical switching circuit (OSC)  31  includes two of input ports  311 ,  312 , two of photo couplers  321 ,  322 , two of optical switch modules  331 ,  332  and two of output ports  341 ,  342 . In addition, the two of optical switch modules  331 ,  332  each includes two upstream side optical switches  331 _ 1 ,  331 _ 2  and  332 _ 1 ,  332 _ 2 , one photo couple  331 _ 1  and  332 _ 3 , and one downstream side optical switches  331 _ 4  and  332 _ 4 , respectively. 
     When an optical packet is inputted from the input port  311  of a first channel, the optical packet is divided into two pieces by the photo coupler  321  to be inputted to the optical switch  331 - 1  of the first channel and the optical switch (OSW)  332 _ 1  of a second channel on the upstream side. And, similar to this, when an optical packet is inputted from the input port  312  of a second channel, the optical packet is divided into two pieces by the photo coupler  322  to be inputted to the optical switch  331 - 2  of the first channel and the optical switch  332 _ 2  of the second channel on the upstream side. The optical packets each inputted to the two optical switches  331 _ 1 ,  331 _ 2  of the first channel respectively are, via each of the optical switches  331 _ 1 ,  331 _ 2  when the optical switches  331 _ 1 ,  331 _ 2  are in the on state, further via the photo coupler  331 _ 3 , and furthermore via the optical switch  331 _ 4  when the optical switch  331 _ 4  on the downstream side is on, outputted from the output port  341  of the first channel. 
     In addition, similar to this, the optical packets each inputted to the two optical switches (OSW)  332 _ 1 ,  332 _ 2  of the second channel respectively are, via each of the optical switches  332 _ 1 ,  332 _ 2  when the optical switches  332 _ 1 ,  332 _ 2  are in the on state, further via the photo coupler  332 _ 2 , and furthermore via the optical switch  332 _ 4  when the optical switch  332 _ 4  on the downstream side is in the on state, outputted from the output port  342  of the second channel. 
     Thus, when the first optical switch (OSW)  331 _ 1  on the input side of the first channel and the optical switch (OSW)  331 _ 4  on the output side of the first channel are in the on state, and the second optical switch (OSW)  331 _ 2  of the first channel is in the off state, the optical packet inputted from the input port  311  of the first channel is outputted from the output port  341  of the first channel. When the second optical switch  331 _ 2  on the input side of the first channel and the optical switch (OSW)  331 _ 4  on the output side of the first channel are in the on state, and the first optical switch  331 _ 1  of the first channel is in the off state, the optical packet inputted from the input port  312  of the second channel is outputted from the output port  341  of the first channel. 
     In addition, regarding the second channel, similar to the first channel, when the first optical switch (OSW)  332 _ 1  on the input side of the second channel and the optical switch (OSW)  332 _ 4  on the output side of the second channel are on the on state, and the second optical switch (OSW)  332 _ 2  on the input side of the second channel are in the on state, the packet inputted from the input port  311  of the first channel is outputted from the output port  342  of the second channel. When the second optical switch (OSW)  332 _ 2  and the first optical switch  332 _ 1  on the input side of the second channel is in the off state, the optical packet inputted form the input port  312  of the second channel is outputted form the output port  342  of the second channel. 
     As described above, the optical switching circuit (OSC)  31  includes two of the input ports  311 ,  312  and two of the output ports  341 ,  342 , and may output the optical packet inputted from either one of the two of the input ports  311 ,  312 , from either one of the two of the output ports  341 ,  342 . 
     In addition, the optical switches (OSW)  331 _ 1 ,  331 _ 2 ,  331 _ 4 ,  332 _ 1 ,  332 _ 2 ,  332 _ 4  are connected to six of signal transmission lines  514 _ 1 ,  514 _ 2 ,  514 _ 3 ,  514 _ 4 ,  514 _ 5 ,  514 _ 6  which extend from the enable signal generation section (ESGS)  513  illustrated in  FIG. 1 , respectively. On-off of the respective optical switches (OSW)  331 _ 1 ,  331 _ 2 ,  331 _ 4 ,  332 _ 1 ,  332 _ 2 ,  332 _ 4  is controlled, by the respective enable signals transmitted through the signal transmission lines  514 _ 1 ,  514 _ 2 ,  514 _ 3 ,  514 _ 4 ,  514 _ 5 ,  514 _ 6 . 
     Note that in order to simplify the description, the example in which the output ports are provided two each has been described, however, a case where an optical switching circuit having more input ports or output ports is similar to the example. 
     Returning to  FIG. 1 , the description about the optical packet switching circuit  10  of  FIG. 1  will be continued. 
     The optical packets outputted from each of the output ports  341 ,  342  of the optical switching circuit (OSC)  31  are transmitted through two optical transmission lines  351 ,  352  on the output side, respectively. 
     Note that although the optical transmission lines  351 ,  352  on the output side in  FIG. 1  (and in other figures described later) are illustrated as outputting only the payloads  701   b ,  702   b  of the optical packets  701 ,  702 , actually, new headers are added to the respective payloads  701   b ,  702   b  to be outputted by a configuration not illustrated here. 
     The optical monitor section (OMS)  40  is provided with two input side photo detectors (IPD)  411 ,  412 , where respective light quantities of the optical packets (payloads  701   b ,  702   b ) for the two channels inputted to the optical switch section (OSS)  30  are detected. Light quantity monitor signals detected by the two input side photo detectors (IPD)  411 ,  412  are converted to input monitor values as digital signals by the A/D converter  42 , and are inputted to an input level monitor circuit (ILMC)  515  included in the control section (CTLS)  50 . 
     Similar to this, the optical monitor section (OMS)  40  is provided with two output side photo detectors (OPD)  431 ,  432 , where light quantities of the optical packets (payloads  701   b ,  702   b ) for the two channels outputted from the optical switch section (OSS)  30  are detected. Light quantity monitor signals detected by the two output side photo detectors (OPD)  431 ,  432  are converted to output monitor values as digital signals by the A/D converter  44 , and are inputted to an output level monitor circuit (OLMC)  516  included in the control section (CTLS)  50 . 
     Input level specification values (upper limit value and lower limit value) of the input side optical packet and output level specification values (upper limit value and lower limit value) of the output side optical packet are stored in a register section (RGS)  517  provided in the control section (CTLS)  50 . The input level specification values are inputted to the input level monitor circuit (ILMC)  515  and the output level specification values are inputted to the output level monitor circuit (OLMC)  516 . 
     In the input level monitor circuit (ILMC)  515 , the input monitor value of the input side optical packet inputted from the A/D converter  42  is compared with the input level monitor value received from the register section (RGS)  517  and a comparison result is transmitted to the center section (CS)  60 . 
     Similar to this, in the output level monitor circuit (OLMC)  516 , the output monitor value of the output side optical packet inputted from the A/D converter  44  is compared with the output level specification value received from the register section (RGS)  517 , and a comparison result is transmitted to the center section  60 . 
     The center section (CS)  60  includes an alarm calculation block which collects monitor results in each section to be recorded and outputs an alarm. 
     Note that although the center section  60  is illustrated here as being provided in a single optical packet switching apparatus  10 , single of the center section may be provided for whole plural optical packet switching apparatuses and my be integrally play a role to collect the monitor result and to output the alarm in the plural optical packet switching apparatuses. 
     When the optical packet switching apparatus  10  as illustrated in  FIG. 1  is thought, although it is determined that whether or not the optical quantities of the optical packet on the input side and the optical packet on the output side are satisfied with the references is monitored in the input level monitor circuit (ILMC)  515  and the output level monitor circuit (OLMC)  516 , for the configuration illustrated in  FIG. 1  as it is, it is not known whether it is a timing when the optical packet is currently inputted, and it is not known in what on-off state the optical switches included in the optical switching circuit (OSC)  31  are and through what path the current detected optical packet has passed, and there is a problem that it is difficult to determine whether or not an abnormality occurs. In addition, even though it is determined that an abnormality has occurred, there is a problem that it is difficult to specify whether or not the abnormality is in an optical path or the abnormality is in the detection system for detecting whether or not there is an abnormality. 
     Here, in Japanese Patent Application Laid-open, No. H11-122220, there is disclosed a technique to detect an abnormality of an output level of an optical signal at plural places while the application field is different. However, the technique disclosed in Japanese Patent Application Laid-open, No. H11-122220 also has a problem similar to that explained referring to  FIG. 1 , considering that the application filed of the technique is changed to be applied to an optical packet switching apparatus. 
     In addition, in Japanese Patent Application Laid-open No. H11-8590, there is proposed a technique to control states of plural apparatuses included in an optical transmission system. 
     Further, in Japanese Patent Application Laid-open No. 2005-269668, there is proposed a technique to stabilize a phase of a control signal of an optical switch that demultiplexes an optical multiplexed signal. 
     However, the detection ways described in Japanese Patent Application Laid-open No. H11-8590 and Japanese Patent Application Laid-open No. 2005-269668 may not be applied to an optical packet switching apparatus. 
     In view of the foregoing, it is an object of the present invention to provide an optical packet switching apparatus including means of monitoring that readily detects an abnormality. 
     SUMMARY 
     According to an aspect of the invention, 1. an optical packet switching apparatus inlcudes: 
     an optical switching section that includes an optical switch to switch a path of an optical packet according to an electrical switch control signal, switches the path of the optical packet transmitted thereto according to the switch control signal to output the optical packet; 
     a control section that takes out a header portion representing a destination of the optical packet transmitted thereto, photoelectrically converts the header to generate the switch control signal according to the destination so as to transmit the switch control signal to the optical switching section, and controls the optical switch; 
     a light monitor section that monitors a first light quantity level which is a light quantity level of the optical packet transmitted thereto and a second light quantity level which is a light quantity level of the optical packet to be sent out; and 
     an abnormality recognizing section that recognizes an effective timing of monitoring of the first light quantity level and the second light quantity level based on the switching control signal, and recognizes an abnormality based on the first light quantity level and the second light quantity level at the timing. 
     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 example of an optical switching apparatus conventionally thought; 
         FIG. 2  is a block diagram illustrating a configuration of an optical switching circuit illustrated as one block in  FIG. 1 ; 
         FIG. 3  is a block diagram illustrating an optical packet switching apparatus of a first embodiment according to the invention; 
         FIG. 4  is a block diagram illustrating an internal configuration of an output level abnormality/device abnormality recognizing section (OLADARS)  518  illustrated as one block in  FIG. 3 ; 
         FIG. 5  is a diagram illustrating a relation between a passing timing of the optical packet and on-off of the an enable signal at the output port of the first channel; 
         FIG. 6  is a flow chart illustrating a flow of the processes in the output level abnormality/device abnormality recognizing section (OLADARS) illustrated in  FIG. 4 . 
         FIG. 7  is a block diagram illustrating a second embodiment of the optical packet switching apparatus according to the invention; 
         FIG. 8  illustrates a timing chart at the time when an automatic enable control signal is on; 
         FIG. 9  is a block diagram illustrating a third embodiment of the optical packet switching apparatus according to the invention; 
         FIG. 10  is a block diagram illustrating a configuration of the optical switching circuit in the third embodiment illustrated in  FIG. 9 ; and 
         FIG. 11  is a block diagram illustrating an optical switching circuit of multiple channels. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     As follows, exemplary embodiments of the invention will be explained. 
       FIG. 3  is a block diagram illustrating an optical packet switching apparatus of a first embodiment according to the invention. 
     In  FIG. 3 , elements same as those of the optical packet switching apparatus  10  in  FIG. 1  described above are marked with the same references as those in  FIG. 1  and only different points will be explained. 
     The different points of the optical packet switching apparatus  10 A illustrated in  FIG. 3  from the optical packet switching apparatus  10  illustrated in  FIG. 1  exist in a control section (CTLS)  50 A. The control section (CTLS)  50 A is provided with an output level abnormality/device abnormality recognizing section (OLADARS)  518  instead of an output level monitoring section of the control section (CTLS)  50  in  FIG. 1 , and a register section (RGS)  517 A instead of the register section (RGS)  517  in  FIG. 1 . 
     The register section (RGS)  517  in  FIG. 1  stores input level specification values (upper limit value and lower limit value) which are light quantities of an input optical packet in an input level monitoring circuit  515  and output level specification values (upper limit value and lower limit value) which are references of light quantities of an output packet in an output level monitoring circuit  516 . In contrast, the register section (RGS)  517 A illustrated in  FIG. 3  stores a loss reference value which is a specification value of the light quantity loss while the optical packet passes through the optical switching circuit (OSC)  31  in addition to the input level specification values (upper limit value and lower limit value) and the output level specification values (upper limit value and lower limit value). The loss reference value is a value in which a loss of the optical coupler when the optical coupler is in normality, a loss of the optical switch when the optical coupler is in normal, a loss of the optical fiber connecting them when the optical fibers are in normality and the like are considered. From the register section (RGS)  517 A, the input level specification values are inputted to the input level monitor circuit (ILMC)  515 , and both of the output level specification values and the loss reference value are inputted to the output level abnormality/device abnormality recognizing section (OLADARS)  518 . 
     In addition, an input monitor value representing a light quantity of an input optical packet from an A/D converter  42 , an output monitor value representing a light quantity of an output packet from the A/D converter  44  and enable signals from the enable signal generation section (ESGS)  513 , being equivalent to the enable signals outputted to six of the signal transmission lines  514 _ 1 ,  514 _ 2 ,  514 _ 3 ,  514 _ 4 ,  514 _ 5 ,  514 _ 6 , in addition to the output level specification values and the loss reference values, are inputted to the output level abnormality/device abnormality recognizing section (OLADARS)  518 . 
       FIG. 4  is a block diagram illustrating an internal configuration of an output level abnormality/device abnormality recognizing section (OLADARS)  518  illustrated as one block in  FIG. 3 . 
     The output level abnormality/device abnormality recognizing section (OLADARS)  518  is provided with an enable timing check section (ETCS)  5181 , an input output level difference check section (IOLDCS)  5182 , an output level monitor circuit section (OLMCS)  5183  and an alarm determination section (ADS)  5184 . 
     Enable signals to switch on-off of total six of the optical switches (OSW)  331 _ 1 ,  331 _ 2 ,  331 _ 4 ,  332 _ 1 ,  332 _ 2 ,  332 _ 4 , three each of the them being provided in the optical switch modules  331 ,  332  of two channels illustrated in  FIG. 11 , respectively, are inputted to the enable timing check section (ETCS)  5181  from the enable signal generating section  513 . An enable-on duration of each path is detected as a check effective timing according to a combination of those enable signals in the enable timing check section  5181 . In the input output level difference check section  5182 , the input monitor values for two channels from the A/D converter  42 , the output monitor values for two channels from the A/D converter  44  and the loss reference value from the register section (RGS)  517 A are inputted, calculation of differences between the input monitor values and output monitor values is performed with respect to a path through which an effective packet from the enable timing check section  5181  passes, differences of the monitor values between the input port and the output port for each combination of the input port and the output ports are measured. Difference values as the result of this are compared with the loss reference values, and if the difference values are smaller than the reference values, it is determined that the device of the measurement path measured from the input port to the output port is in normality, and if the difference values are greater than the loss reference values, it is determined that the device of the measurement path is in abnormality, informing the abnormality determination section  5184 . 
     In addition, in the output level monitor circuit section (OLMCS)  5183 , the output monitor values for two channels from the A/D converter  44  and the output level specification values (upper limit value and lower limit value) from the register section (RGS)  517 A are inputted, and a timing when an effective optical packet is outputted from each of the output ports from the enable timing check section  5181  is captured so that the output monitor values for the optical packet outputted from each of the output ports and the output level specification values are compared to be checked, and in a case where the output monitor values are greater than the upper value of the output level specification values, it is determined to be in a high level abnormality, in a case where the output monitor value intermediate between the upper limit value and the lower limit value, it is determined to be in a normality, and in a case where the output monitor values are smaller that the lower limit value, it is determined to be in a low level abnormality, informing the alarm determination section  5184 . 
     Information about whether or not there is an abnormality of the loss level in each of the paths informed from the input output level difference check section  5182  and information about the high level abnormality, low level abnormality and normality of the optical output of each of the paths informed from the output level monitor circuit section (OLMCS)  5183  are considered in a comprehensive manner to determine whether or not there is an abnormality as a whole and what the abnormal place is, and the result is informed to the center section  60 . 
       FIG. 5  is a diagram illustrating a relation between a passing timing of the optical packet and on-off of the an enable signal at the output port of the first channel. 
     In an optical level measurement duration A where the optical switch (OSW)  331 _ 1  (upstream: optical SW( 1 - 1 )) is on, the optical switch (OSW)  331 _ 2  (upstream: optical SW( 1 - 2 ) is off and the optical switch (OSW)  331 _ 4 (downstream: optical SW( 1 - 0 ) is on, of the three optical switches (OSW)  331 _ 1 ,  331 _ 2 ,  331 _ 4 , included in the optical switch module of the first channel illustrated in  FIG. 2 , an optical packet inputted from the input port  311  of the first channel is outputted from the output port  341  of the first channel. Accordingly, in the input-output level difference check section  5182  of the output level abnormality/device abnormality recognizing section (OLADARS)  518  illustrated in  FIG. 4 , a difference between the input monitor value representing a light quantity of the light packet inputted from the input port  311  of the first channel and the output monitor value representing a light quantity of the light packet outputted from the output port  341  of the first channel is obtained to be compared with the loss reference value and it is determined whether or not there is a level abnormality. In the output level monitor circuit section (OLMCS)  5183 , the output monitor value representing a light quantity of the optical packet outputted from the output port  341  of the first channel and the output level specification values (upper limit value and lower limit value) are compared, and the high level abnormality, normality and low level abnormality are determined. 
     Further, in the next optical level measurement duration B, by the enable signals, the optical switch (OSW)  331 _ 1  (upstream: optical SW( 1 - 1 )) is off, the optical switch (OSW)  331 _ 2  (upstream: optical SW( 1 - 2 )) is on and the optical switch (OSW)  331 _ 4  (downstream: optical SW( 1 - 0 )) is on. In this optical level measurement duration B, the optical packet inputted from the input port  312  of the second channel is outputted from the output port  341  of the first channel. Accordingly, a difference between the input monitor values representing a light quantity of the optical packet inputted from the input port  312  of the second channel and the output monitor value representing a light quantity of the optical packet outputted from the output port  341  of the first channel is obtained to be compared with the loss reference value and to be determined whether or not there is a level abnormality. In the output level monitor circuit section (OLMCS)  5183 , the output monitor value representing a light quantity of the optical packet outputted from the output port  341  of the first channel and the output level specification values (upper limit value and lower limit value) are compared, and the high level abnormality, normality and low level abnormality are determined. 
     In the next optical level measurement duration C, by the enable signals, a path equivalent to that in the optical level measurement duration A is formed and an abnormality determination equivalent to that in the optical level measurement duration A is performed. Further, in the next optical level measurement duration D, by the enable signals, a path equivalent to that in the optical level measurement duration B is formed and an abnormality determination equivalent to that in the optical level measurement duration B is performed. 
     Here, an association between the pass timing of the optical packet in the output port of the first channel and the abnormality determination is explained above, and a similar explanation is applied to the output port of the second channel. 
       FIG. 6  is a flow chart illustrating a flow of the processes in the output level abnormality/device abnormality recognizing section (OLADARS) illustrated in  FIG. 4 . 
     In the enable timing check section  5181 , an enable state of each path through which the optical packet of the optical switch circuit (OSC)  31  (see  FIGS. 2 and 3 ) passes is checked based on the enable signal, and when enable is on, that is, a certain path is formed, proceeding to step S 2 , S 3 . 
     In step S 2 , in the output level monitor circuit section (OLMCS)  5183 , with respect to an output port corresponding to a current enable on, the output monitor value and the output level specification values (upper limit value and lower limit value) are compared: 
     when 
     (1) the specification value (lower limit value)&lt;the output monitor values&lt;the specification values (upper limit value), 
     it is determined that the optical output level is in normality; 
     when 
     (2) the output monitor values&gt;the specification value (upper limit value), 
     it is determined to be in a high output level abnormality; and 
     when 
     (3) the specification value (lower limit value)&lt;the output monitor values, 
     it is determined to be in a low output level abnormality. 
     In addition, in the input output level difference check section  5182 , with respect to a combination of input port-output port associated with a current enable-on, a difference between the input monitor value and the output monitor values is obtained and an input output level difference which is the difference is compared with the loss reference value: 
     when 
     (4) the input-output level difference&lt;the loss level reference value, 
     it is determined to be in a loss level normality; and 
     when 
     (5) the input output level difference&gt;the loss level reference value, 
     it is determined to be in a loss level abnormality. 
     When the normality-abnormality is determined in step S 2 , S 3 , the determination results are informed to the alarm determination section  5184 . In the alarm determination section  5184 , the determination results are considered in a comprehensive manner and the alarm determination is performed according to an alarm determination table illustrate in table  1  described below. The alarm determination results are inputted to the center section  30  illustrated in  FIG. 3 , and recording the alarm determination results and outputting an alarm are performed by the center section  60 . 
     
       
         
               
             
               
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Alarm Determination Table 
               
               
                 Alarm Determination 
               
             
          
           
               
                   
                 Loss level check 
               
             
          
           
               
                   
                 Loss level normal 
                 Loss level abnormal 
               
               
                   
                   
               
             
          
           
               
                 Optical output 
                 Optical output 
                 Device normal 
                 Device abnormal 
               
               
                 level check 
                 level normal 
                 Detection 
                 Detection 
               
               
                   
                   
                 circuit normal 
                 circuit normal 
               
               
                   
                 High output 
                 Device normal 
                 Device normal 
               
               
                   
                 level abnormal 
                 Detection 
                 Detection 
               
               
                   
                   
                 circuit abnormal 
                 circuit abnormal 
               
               
                   
                 Low output 
                 Device normal 
                 Device abnormal 
               
               
                   
                 level abnormal 
                 Detection 
                 Detection 
               
               
                   
                   
                 circuit normal 
                 circuit normal 
               
               
                   
               
             
          
         
       
     
       FIG. 7  is a block diagram illustrating a second embodiment of the optical packet switching apparatus according to the invention. Elements same as those in the optical packet switching apparatus  10 A of the first embodiment illustrated in  FIG. 3  are provided the same references as those illustrated in  FIG. 3 . 
     The optical packet switching apparatus  10 B of the second embodiment has a feature in a center section  50 B. After the system is started up, an automatic enable control signal from a register section (RGS)  517 B included in the control section (CTLS)  50 B to an enable signal generating section  513 B turns on. 
     When the automatic enable control signal turns on, in the enable signal generating section  513 B, regardless of a destination address of the header of the optical packet, the enable signal is automatically generated in a fixed pattern. In this time, dummy optical packets are to be continuously inputted. 
       FIG. 8  illustrates a timing chart at the time when an automatic enable control signal is on. 
     When the automatic enable control signal turns on, in the enable signal generating section  513 B, an optical switch (OSW)  331 _ 4  (downstream: optical SW( 1 - 0 ) on the downstream side of the optical switch module  331  of the first channel illustrated in  FIG. 2  is turned on, and at the same time, an enable signal to turn on one optical switch (OSW)  331 _ 1  (upstream: optical SW( 1 - 1 )) on the upstream side of the optical switch module  331  of the first channel is generated. At this time, the other optical switch (OSW)  331 _ 2 (upstream: optical SW( 1 - 2 )) on the upstream side and each of the optical switches (OSW)  332 _ 4 ,  332 _ 1 ,  332 _ 2  (downstream: optical SW( 2 - 0 ), upstream: optical SW( 2 - 1 ), upstream: optical SW( 2 - 2 )) remain off. As described above, in the measurement duration A, a path( 1 ) where the optical packet inputted from the input port  331  of the first channel is outputted from the output port  341  of the first channel is formed. In the output level abnormality/device abnormality recognizing section (OLADARS)  518 B, in the measurement duration A, a difference between the input monitor value and the output monitor value of the path ( 1 ) is obtained. 
     Next, an enable signal is generated such that, this time, of the two optical switches on the upstream side, the optical switches (OSW)  331 _ 1 ,  331 _ 2  (upstream: optical SW( 1 - 1 ), upstream: optical SW( 1 - 2 )) of the optical switch module  331  of the first channel, the one optical switch (OSW)  331 _ 1  (upstream: optical SW( 1 - 1 ) is off and the other optical switch (OSW)  331 _ 2  (upstream: optical SW( 1 - 2 )) is on while the optical switch (OSW)  331 _ 4  (downstream: optical SW( 1 - 0 )) on the downstream side of the optical switch module  331  of the first channel is remained on, and a path ( 2 ) where the optical packet inputted this time from the input port  312  of the second channel is outputted from the output port  341  of the first channel is formed. In the output level abnormality/device abnormality recognizing section (OLADARS)  518 B, a difference between the input monitor value and the output monitor value of the path ( 2 ) in the measurement duration B is obtained. 
     Next, an enable signal is generated to cause the three optical switches (OSW)  331 _ 1 ,  331 _ 2 ,  331   4  (downstream: optical SW( 1 - 0 ), upstream: optical SW( 1 - 1 ), upstream: optical SW( 1 - 2 )) of the first channel all to be on, and this time, to cause the optical switch (OSW)  332 _ 4  (downstream: optical SW( 2 - 0 )) on the downstream side of the optical switch module  332  of the second channel to be on and at the same time to cause the one optical switch (OSW)  332 _ 1  (upstream: optical SW( 2 - 1 )) of the optical switch module  332  of the second channel to be on. At this time, the other optical switch (OSW)  332 _ 2  (upstream: optical SW( 2 - 2 )) remains off. As described above, in the measurement duration C, a path ( 3 ) where the optical packet inputted from the input port  331  of the first channel is outputted from the output port  342  of the second channel is formed, and in the output level abnormality/device abnormality recognizing section (OLADARS)  518 B, a difference between the monitor value and the output monitor value of the path ( 3 ) is obtained in the measurement duration C. 
     Further, next, an enable signal is generated such that, of the two optical switches (OSW)  332 _ 1 ,  332 _ 2  (upstream: optical SW( 2 - 1 ), upstream: optical SW( 2 - 2 )) on the upstream side of the optical switch module  332  of the second channel, this time, the optical switch (OSW)  332 _ 1  (upstream: optical SW( 2 - 1 ) is off and the other optical switch (OSW)  332 _ 2  (upstream: optical SW( 2 - 2 ) is on, while the optical switch (OSW)  332 _ 4  (downstream: optical SW( 2 - 0 ) on the downstream side of the optical switch module  332  of the second channel remains off, and this time, a path ( 4 ) where the optical packet inputted from the input port  312  of the second channel is outputted from the output port  342  of the second channel. In the output level abnormality/device abnormality recognizing section (OLADARS)  518 B, a difference between the input monitor value and the output monitor value of the path ( 4 ) is obtained in the measurement duration D. 
     In the output level abnormality/device abnormality recognizing section (OLADARS)  518 B after calculating these all differences is performed, a loss reference value is obtained by, for example, adding further a margin on a maximum difference value of the difference values. This obtained loss reference value is stored in the register section (RGS)  517 B. 
     In the optical packet switching apparatus  10 B of the second embodiment illustrated in  FIG. 7 , as described above, the loss reference value is obtained at the time when the system is started up. Note that the input level specification values (upper limit vale and lower limit value) and the output level specification values (upper limit vale and lower limit value) are predetermined values, and the predetermined values are stored in the register section (RGS)  517 B in advance. 
     Operations of the enable signal generating section  513 B, the register section (RGS)  517 B and the output level abnormality/device abnormality recognizing section (OLADARS)  518 B are equivalent to the respective operations of the enable signal generating section  513 , the register section (RGS)  517  and the output level abnormality/device abnormality recognizing section (OLADARS)  518  in the first embodiment illustrate in  FIG. 3 . 
       FIG. 9  is a block diagram illustrating a third embodiment of the optical packet switching apparatus according to the invention.  FIG. 10  is a block diagram illustrating a configuration of the optical switching circuit in the third embodiment illustrated in  FIG. 9 . 
     Elements same as those of the optical packet switching apparatus  10 A of the first embodiment described above ( FIG. 3 ) are provided with the same references as those illustrated in  FIG. 3   
     First, an optical switching circuit illustrated in  FIG. 10  will be explained. 
     An optical switching circuit  31 C provided in an optical switching section  30 C of an optical packet switching apparatus  10 C of the third embodiment illustrated in  FIG. 9  includes a system in operation  31 A and a reserve (non-operation) system  31 B. 
     Comparing to the optical switching circuit  31  illustrated in  FIG. 2 , with respect to the system in operation  31 A of the optical switching circuit (OSC)  31 C illustrated in  FIG. 10 , the two photo coupler  321 ,  332  on the input side are to divide each of the optical packets each inputted from the input ports  311 ,  312 , respectively into two pieces in the optical switching circuit (OSC)  31  illustrated in  FIG. 2 , and in contrast, the photo couplers  321 _ 1 ,  322 _ 1  on the input side of the system in operation  31 A illustrated in  FIG. 10  are to divide each of the optical packets inputted from the input ports  311 ,  312 , respectively into four pieces. In addition, the system in operation  31 A is provided with two photo couplers  331 _ 2 ,  332 _ 2  to merge the optical packets outputted from the two optical switch modules  331 A,  332 A of the system in operation  31 A with the optical packets outputted from the two optical modules  331 B,  332 B of the reserve (non-operation) system  31 B, respectively. 
     Internal configuration of each of the optical modules  331 A,  332 A;  331 B,  332 B is equivalent to that of each of the optical modules  331 ,  332 , and since the operation is explained already with reference to  FIG. 2 , only relations of the respective elements will be described. 
     The optical switches (OSW)  331 _ 1 A,  331 _ 2 A,  331 _ 4 A and the photo coupler  331 _ 3 A of the optical switch module  331  A of the system in operation  31 A correspond to the optical switches (OSW)  331 _ 1 ,  331 _ 2 ,  331 _ 4  and the photo coupler  331 _ 3 , respectively. And, similar to this, the optical switches (OSW)  332 _ 1 A,  332 _ 2 A,  332 _ 4 A and the photo coupler  332 _ 3 A of the optical switch module  332 A of the system in operation  31 A correspond to the optical switches (OSW)  332 _ 1 ,  332 _ 2 ,  332 _ 4  and the photo coupler  332 _ 3  of the optical module  332 , respectively. 
     In addition, the reserve (non-operation) system  31 B is similar to the system in operation  31 A. The optical switches (OSW)  331 _ 1 B,  331 _ 2 B,  331 _ 4 B and the photo coupler  331 _ 3 B of the optical switch module  331 B of the reserve (non-operation) system  31 B correspond to the optical switches (OSW)  331 _ 1 ,  331 _ 2 ,  331 _ 4  and the photo coupler  331 _ 3  of the optical module  331  in  FIG. 2 , respectively. And, similar to this, the  332 _ 1 B,  332 _ 2 B,  332 _ 4 B and the photo coupler  332 _ 3 B of the optical switch module  332 B of the reserve (non-operation) system  31 B correspond to the optical switches (OSW)  332 _ 1 ,  332 _ 2 ,  332 _ 4  and the photo coupler  332 _ 3  of the optical module  332  in  FIG. 2 , respectively. 
     Returning to  FIG. 9 , the optical packet switching apparatus  10 C of the third embodiment will be explained. 
     Six signal transmission lines  514 _ 1 ,  514 _ 2 ,  514 _ 3 ,  514 _ 4 ,  514 _ 5 ,  514 _ 6  to transmit the enable signal for on-off control of the optical switches (OSW)  331 _ 1 A,  331 _ 2 A,  331 _ 4 A;  332 _ 1 A,  332 _ 2 A,  332 _ 4 A of the system in operation  31 A illustrated in  FIG. 10  similar to the six transmission lines in the first embodiment illustrated in  FIG. 3  are connected to the enable signal generating section  513 C, and in addition, six signal transmission lines  514 _ 1 B,  514 _ 2 B,  514 _ 3 B,  514 _ 4 B,  514 _ 5 B,  514 _ 6 B to transmit the enable signal for on and off control of the optical switches (OSW)  331 _ 1 B,  331 _ 2 B,  331 _ 4 B;  332 _ 1 B,  332 _ 2 B,  332   4 B of the system in operation  31 B are connected to the enable signal generating section  513 C. 
     In the optical packet switching apparatus  10 C, in the normal state, only the system in operation  31 A of the optical switching circuit (OSC)  31 C is used. Up to this stage, the optical packet switching apparatus  10 C is similar to the optical packet switching apparatus  10 A of the first embodiment illustrated in  FIG. 3 . When an abnormality is detected in the output level abnormality/device abnormality recognizing section (OLADARS)  518 C, the fact that the device abnormality is detected is informed to the enable signal generation section (ESGS)  513 C. The enable signal generation section (ESGS)  513 C turns off all of the optical switches of the system in operation  31 A, and sends the enable signal to the reserve (non-operation) system  31 B to cause the (non-operation) system  31 B to operate substituting the operations operated by the system in operation  31  until that time. 
     Thus, it is possible to immediately recover the operations even if a device abnormality occurs in the optical packet switching apparatus  10 C. 
       FIG. 11  is a block diagram illustrating an optical switching circuit including more multiple channels than the optical switching circuits described above. 
     An optical switching circuit (OSC)  31 D illustrated in  FIG. 11  includes eight input ports and eight output ports, and is provided in the input side with eight photo couplers  3210  which divide an inputted optical packet into eight pieces to send each to each of the optical modules, respectively, and, further, in the downstream side with eight optical switch modules  3310 . Each of the optical switch modules  3310  includes in the input side eight optical switches on the upstream side, and is arranged with one optical coupler  3312  to merge eight inputs into one line on the downstream side of the optical switch modules  3310 , and further, on the downstream side thereof, with one optical switch  3313  of the downstream side. These all optical switches are switched on or off by the enable signals generated according to a destination of the optical packet in the enable signal generating section (see, for example, the enable signal generation section (ESGS)  513 ). 
     Although, the structure of the optical switching circuit (OSC)  31 D illustrated in  FIG. 11  is complicated, since its operation may be easily understood from the operation explanation of the optical switching circuit (OSC)  31  illustrated in  FIG. 2 , a redundant explanation will be saved here. 
     When the optical switching circuit (OSC)  31 D in  FIG. 11  is employed, for example, all the constituent elements of the optical packet switching apparatus  10 A illustrated in  FIG. 3  need to be expanded for eight channels. However, since it is to simply expand the number of channels, and the operations are apparent from the explanation of the optical packet switching apparatus  10 A in  FIG. 3  and like, an explanation about this point is also saved. 
     The present invention may be applied to an optical packet switching apparatus including more, as illustrated in  FIG. 11 , or further more multi channel input and output lines. 
     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 inventions 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.