Abstract:
A transmission device that is coupled to a mesh network includes a memory, and a processor coupled to the memory, configured to detect an another transmission device in the mesh network, which receives a first data signal that is same as a second data signal requested to the transmission device, and branch the first data signal to the transmission device from the detected another transmission device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2013-208451 filed on Oct. 3, 2013, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to a transmission device, a transmission system, and a transmission method. 
     BACKGROUND 
     With an increase in demand for communication, a high-speed optical transmission scheme has been standardized. For example, the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) recommendation G.709 defines a scheme of an Optical Transport Network (OTN) operating at about 1.25 to 100 Gbps. 
     Optical transmission in the OTN is performed such that a plurality of client signals is accommodated in an optical signal in a format called an Optical channel Transport Unit (OTU) frame, so that transmission of data having large capacity may be performed. As the client signal that is accommodated in the OTU frame, there are a Synchronous Digital Hierarchy (SDH) frame, a Synchronous Optical NETwork (SONET) frame, and an Ethernet (registered trademark) frame. 
     The client signals are respectively accommodated for Optical Data Units (ODU) that are multiplexed in the OTU frame. The bandwidth type of the ODU is defined by “ODUk” (k=0, 1, . . . ). For example, an ODU0 is a unit of data of 1.25 Gbps, and an ODU1 is a unit of data of 2.5 Gbps, and an ODU2 is a unit of data of 10 Gbps. 
     The OTN technology achieves transmission of data having large capacity in the unit of the ODU, so that contents such as a video and music may be provided to a user with high quality and multi-channel when the OTN technology is applied to a broadcast distribution system. 
     Regarding the broadcast distribution technology, for example, Japanese Laid-open Patent Publication No. 10-294729 discloses a connection procedure that is used to find by rearrangement a path for multirate/multicast traffic through an SDH cross-connect with sub-network connection protection. In addition, Japanese Laid-open Patent Publication No. 2005-192213 discloses a network-based data distribution scheme in which data to be distributed to a plurality of destination links is replicated in a physical layer in a network-based communication system. 
     SUMMARY 
     According to an aspect of the invention, A transmission device that is coupled to a mesh network includes a memory, and a processor coupled to the memory, configured to detect an another transmission device in the mesh network, which receives a first data signal that is same as a second data signal requested to the transmission device, and branch the first data signal to the transmission device from the detected another transmission device. 
     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 a structure of a transmission system according to an embodiment; 
         FIG. 2  is a diagram illustrating a structure of a transmission device according to a first embodiment; 
         FIG. 3  is a diagram illustrating a structure of an OTU frame; 
         FIG. 4  is a diagram illustrating a structure of an overhead; 
         FIG. 5  is a diagram illustrating a structure of a TCMi area; 
         FIG. 6  is a table illustrating an example of a content of a first identification information storage unit; 
         FIG. 7  is a table illustrating an example of a content of a bandwidth information storage unit; 
         FIG. 8  is a diagram illustrating a structure example of control information; 
         FIG. 9  is a diagram illustrating an application example of the first embodiment; 
         FIG. 10  is a diagram illustrating an application example of the first embodiment; 
         FIG. 11  is a diagram illustrating an application example of the first embodiment; 
         FIG. 12  is a diagram illustrating an application example of the first embodiment; 
         FIG. 13  is a flowchart illustrating an operation of a request-side transmission device according to the first embodiment; 
         FIG. 14  is a flowchart illustrating an operation of a non-request side transmission device according to the first embodiment; 
         FIG. 15  is a diagram illustrating a structure of a transmission device according to a second embodiment; 
         FIG. 16  is a table illustrating an example of a content of a management table; 
         FIG. 17  is a diagram illustrating an application example of the second embodiment; 
         FIG. 18  is a diagram illustrating an application example of the second embodiment; 
         FIG. 19  is a flowchart illustrating an operation of a request side transmission device according to the second embodiment; 
         FIG. 20  is a flowchart illustrating an operation of a non-request side transmission device according to the second embodiment; 
         FIG. 21  is a diagram illustrating a transmission instruction signal that is transmitted from a reception device; and 
         FIG. 22  is a flowchart illustrating detection processing of a data signal of the request side transmission device. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     When a failure occurs in a transmission path in a network, the transmission path is switched from the work side path to the protection side path by an Automatic Protection Switching (APS) function. As a scheme that achieves the APS function, for example, there are 1+1 protection, a Uni-directional Path Switched Ring (UPSR), an Optical-UPSR (0-UPSR), and a Bi-directional Line Switched Ring (BLSR). 
     In the broadcast distribution system, transmission of real-time data such as a video and music is performed, so that it is desirable that the transmission path is switched rapidly. When the APS function is achieved by the above-described scheme, it is desirable that a bandwidth of the protection side path is obtained beforehand along the transmission path from a distribution server to a reception device on the user side. This is applied to a case of a mesh network in addition to a ring network. 
     A connection between nodes of the mesh network is complicated as compared with the ring network. Therefore, in the case of the mesh network, setting processing of the transmission path is complicated, so that it is difficult to switch a transmission path rapidly. In addition, in a case of a network that is layer 2 or above such as the Ethernet, the transmission of data is dynamically switched by packet forwarding processing based on destination information that is included in a frame, so that the setting processing of the transmission path is not executed. 
     However, as the above-described OTN, in a case of a network of a layer 1, the setting processing of a transmission path is executed, so that it is desirable that the setting processing is completed rapidly. In addition to the case of switching of the transmission path, the rapid setting processing is desired in a case in which a transmission path from the distribution server to the reception device on the user side is newly set. 
     The embodiments discussed herein are made in view of the above-described problems, and a transmission device, a transmission system, and a transmission method are provided in which a transmission path of broadcast distribution may be set rapidly. 
       FIG. 1  is a diagram illustrating a structure of a transmission system according to an embodiment. The transmission system includes a server  90 , a network management system  92 , a plurality of receive devices (client devices)  91 , and a mesh network  8 . The network  8  includes a plurality of transmission devices  1  that are interconnected to each other, and through which a data signal DT that has been input from the server  90  is transmitted to the plurality of reception devices  91 . 
     The server  90 , the plurality of transmission devices  1 , and the plurality of reception devices  91  are interconnected to each other through optical fibers. Each of the transmission devices  1  is connected to a network management system  92  that manages the network  8 . In  FIG. 1 , “(1-1)” to “(3-3)” indicate node numbers in the network. 
     The server  90  distributes, for example, a data signal DT such as a video and music, to the plurality of reception devices  91 , through the network  8 . That is, the data signal DT is a broadcast signal to be transmitted to the plurality of reception devices  91 . The broadcast signal may be transmitted to all of the reception devices  9  that are connected to the server  90 , or may be transmitted to some of the reception devices  91  through the network  8 . In  FIG. 1 , to the network  8 , merely one data signal DT is transmitted, but data signals having a plurality of types may be respectively transmitted though different transmission paths. 
     In the example, it is assumed that transmission paths of a data signal DT, which is from the server  90  to the reception devices  91 , are paths passing through the following nodes of (1) to (3). 
     (1): nodes (1-1), (2-1), and (3-1) 
     (2): nodes (1-1), (1-2), (2-2), and (3-2) 
     (3): nodes (1-1), (1-2), (1-3), (2-3), and (3-3) 
     The network management system  92  sets each of the above-described transmission paths and a bandwidth of the data signal DT, to each of the transmission devices  1 . 
     The reception device  91  is, for example, a set-top box that is installed at a user&#39;s house of delivery service of a video, music, and the like. The reception device  91  receives a data signal DT that is broadcasted and delivered from the server  90 . 
     The transmission device  1  is connected to the network  8 , and for example, based on the OTN technology that is defined by the ITU-T recommendation G.709, a data signal DT is mapped onto an OTU frame and transmitted. In addition, the transmission device  1  is not limited to such a case, and a data signal DT may be transmitted by a further scheme. 
     As described below, the transmission devices  1  of adjacent nodes (3-1) to (3-3) of each of the reception devices  91  reset autonomously transmission paths of a data signal DT when the data signal DT is not allowed to be received due to occurrence of a failure. In addition, the above-described transmission device  1  autonomously sets the transmission path of the data signal DT in response to a transmission instruction of the data signal DT from the reception device  91  when the reception device  91  is added to the transmission system. That is, the above-described transmission device  1  sets a transmission path of a data signal DT that has been requested to the transmission device  1 . 
     Due to the setting of the transmission path, the transmission device  1  detects a further transmission device  1  that has received a data signal DT that is identical to the data signal DT that has been requested to the transmission device  1 , and transmits the data signal DT to branch to the transmission device  1  from the detected transmission device  1 . In addition, the transmission device  1  transmits the branched data signal DT to the reception device  91 . As a result, the transmission device  1  may transmit the data signal DT from the detected further transmission device  1  to the reception device  91  while saving the effort of setting of the transmission path that ranges from the server  90  that is the transmission source of the data signal DT to the reception device  91 . 
     There is no difference between the configurations of the transmission devices  1 , but in the following description, for convenience of description, the transmission device  1  to which a data signal DT has requested is referred to as “request side transmission device”, and a further transmission device  1  is referred to as “non-request side transmission device”. In addition, in the following description, a transmission path in the transmission system is referred to as “route”. For example, the transmission device  1  of the node (3-2) illustrated in  FIG. 1  is connected to the routes #1 to #4, and from among the routes, the route #4 is a transmission path with the reception device  91 . In addition, in the following description, a transmission direction or reception direction of each signal is indicated by a route. 
     First Embodiment 
       FIG. 2  is a diagram illustrating a structure of the transmission device  1  according to a first embodiment. The transmission device  1  includes a plurality of reception processing units  10 , a plurality of the transmission processing units  11 , a switch unit  13 , and a control unit  14 . The transmission device  1  further includes a bandwidth information storage unit  130 , a first identification information storage unit  131 , a transmission side (client side) ODU processing unit  120 , a data extraction unit  121 , a data transmission unit  122 , a failure detection unit  123 , and a second identification information storage unit  124 . 
     The reception processing unit  10  and the transmission processing unit  11  are provided for each of the routes. In the case of the transmission device  1  of the node (3-2) illustrated in  FIG. 1 , as illustrated in  FIG. 2 , the reception processing unit  10  and the transmission processing unit  11  that correspond to each of the routes #1 to #3 are provided. In addition, for the route #4 on the reception device  91  side, the transmission side (client side) ODU processing unit  120 , the data extraction unit  121 , and the data transmission unit  122  are provided. 
     The reception processing unit  10  includes an OTU reception unit  100 , a separation unit  101 , and a plurality of reception side ODU processing units  102 , and executes reception processing of an OTU signal S that has been received from the corresponding route. The OTU signal S is formed, for example, by an OTU frame that is defined by the ITU-T recommendation G.709. 
       FIG. 3  is a diagram illustrating a structure of an OTU frame. An OTU frame  60  includes an overhead area, a payload area, and a Forward Error Correction (FEC) area. “OH” in  FIG. 3  indicates an overhead. 
     The overhead area includes a frame alignment signal (FAS) overhead, an OTU overhead, an ODU overhead, and an optical channel payload unit (OPU) overhead. The FAS overhead is used for frame-synchronizing in the reception processing. Each of the OTU overhead and the ODU overhead includes monitoring information and control information. In addition, the FEC area includes the error-correcting code. 
     The payload area accommodates a plurality of ODU frames  61  so that the plurality of ODU frames  61  are multiplexed. The number of accommodated ODU frames  61  is determined based on a bandwidth of the OTU signal S, that is, the above-described ODUx. For example, when the bandwidth of the OTU signal S is the ODU2 (10 Gbps), the four ODU frames  61  of ODU1 (2.5 Gbps) may be accommodated. 
     The ODU frame  61  includes an overhead area and a payload area. Similar to the OTU frame  60 , the overhead area includes a FAS overhead, an OTU overhead, an ODU overhead, and an OPU overhead. In addition, the payload area accommodates a client signal. The client signal is a target signal that is transmitted and received by a user, and in the example, the client signal corresponds to the above-described data signal DT. 
       FIG. 4  is a diagram illustrating an overhead. In  FIG. 4 , “Row” and “Byte” respectively correspond to “Row” and “Byte” in  FIG. 3 . 
     The ODU overhead includes REServed (RES), Path Monitoring (PM) &amp; Tandem Connection Monitoring (TCM), a TCM Activation/deactivation Control Channel (ACT), TCM 1 to 6, and a Fault Type &amp; Fault Location reporting channel (FTFL). The ODU overhead further includes PM, Experimental (EXP), GCC 1 and 2, and an Automatic Protection Switching coordination channel (APS)/Protection Communication Channel (PCC). The details of the above-described parameters are defined by the ITU-T recommendation G.709. 
     Referring to  FIG. 2  again, when the received OTU signal S includes control information, the OTU reception unit  100  extracts the control information and outputs the extracted control information to the control unit  14 . The control information is inserted, for example, into the GCC 1 and 2, the RES, or the like in the OTU frame  60 . As described later, the control unit  14  executes processing that is related to setting of a transmission path of a data signal DT in accordance with a content of the control information. 
     The separation unit  101  separates one or more ODU frames  61  from the OTU frame  60 . The separated and obtained ODU frames  61  are respectively input to the plurality of reception side ODU processing units  102 . Each of the plurality of reception side ODU processing units  102  executes the reception processing of the ODU frame  61 . In addition, the reception side ODU processing unit  102  extracts signal identification information from the ODU frame  61  and writes the extracted signal identification information into the first identification information storage unit  131 . 
     The signal identification information is specific information that is used to identify a data signal DT. The data signal DT is accommodated in each of the ODU frames, so that an ODU signal Sd may be distinguished by referring to the signal identification information. The signal identification information may be included, for example, in the TCMi area (i=1 to 6) of the ODU overhead of the ODU frame  61  (see  FIG. 4 ). 
       FIG. 5  is a diagram illustrating a structure of a TCMi area. Each of the TCM 1 to 6 includes a Trail Trace Identifier (TTI) and a Bit Interleaved Parity (BIP)-8. In addition, each of the TCM1 to 6 further includes Backward Error Indication (BEI) i/Backward Incoming Alignment Error (BIAE) i, Backward Defect Indication (BDI) i, and a Status (STAT) i (i=1 to 6). 
     The TTI includes a Source Access Point Identifier (SAPI), a Destination Access Point Identifier (DAPI), and signal identification information. The signal identification information is inserted into the ODU frame  61  by the server  90 . 
       FIG. 6  is a table illustrating an example of a content of the first identification information storage unit  131 . For example,  FIG. 6  illustrates a case in which signal identification information of the data signal DT that has been received from the route #1 is “Music_Channel_1”, and signal identification information of the data signal DT that has been received from the route #2 is “Video_Channel_1”. As described above, the signal identification information may be represented using a given name, a sign, and a number. 
     The reception side ODU processing unit  102  may periodically extract the signal identification information each time the ODU frame  61  is received. For example, when the ODU frame  61  that includes the identical signal identification information is not received for a certain time period, the signal identification information stored in the first identification information storage unit  131  is autonomously deleted. Therefore, the control unit  14  may detect a data signal DT received by the transmission device  1 , with reference to the signal identification information of the first identification information storage unit  131 . 
     After the reception side ODU processing unit  102  has extracted the signal identification information, the reception side ODU processing unit  102  outputs the ODU frame  61  to the switch unit  13  as an ODU signal Sd. The switch unit  13  is a cross-connect switch that connects the reception processing unit  10  and the transmission processing unit  11 . 
     The transmission processing unit  11  includes a plurality of transmission side ODU processing units  110 , a multiplexing unit  111 , and an OTU transmission unit  112 . The reception side ODU processing unit  102  and the transmission side ODU processing units  110  and  120  are connected to each other through the switch unit  13 . 
     The switch unit  13  cross-connects the reception side ODU processing unit  102  and the transmission side ODU processing units  110  and  120  in accordance with cross-connect setting from the control unit  14 . Therefore, the control unit  14  may transmit an ODU signal Sd that has been received from each of the routes, to a given route, by setting the switch unit  13 . 
     The switch unit  13  cross-connects the reception side ODU processing unit  102  to the transmission side ODU processing units  110  and  120 , by one-to-one relationship (see symbol d1) or one-to-many relationship (see symbols d2 and d3). Therefore, the switch unit  13  may cause one ODU signal Sd to branch and output the branched signal to the plurality of routes. 
     Each of the plurality of transmission side ODU processing units  110  executes transmission processing of an ODU signal Sd. The ODU signal Sd for which the transmission processing has been executed is input to the multiplexing unit  111 . The multiplexing unit  111  multiplexes the ODU frames  61  of a plurality of ODU signals Sd, and outputs the ODU frames  61  to the OTU transmission unit  112 . 
     The OTU transmission unit  112  generates the OTU frame  60 , and accommodates the ODU frames  61  that have been multiplexed by the multiplexing unit  111 , in a payload area of the OTU frame  60 . 
     In addition, the OTU transmission unit  112  inserts control information that has been generated by the control unit  14  into the OTU frame  60 , in response to an instruction from the control unit  14 . As described above, for example, the control information is inserted into the GCC 1 and 2 or RES in the header. The OTU transmission unit  112  transmits the OTU frame  60  to the corresponding route as an OTU signal S. 
     From among ODU signals Sd from the routes, an ODU signal Sd that includes a data signal DT transmitted to the reception device  91  is input from the switch unit  13  to the transmission side ODU processing unit  120 . When failure information is included in the ODU frame  61 , the transmission side ODU processing unit  120  extracts the failure information from the ODU frame  61  and outputs the extracted failure information to the failure detection unit  123 . The failure information is included in the header of the ODU frame  61 . 
     The failure detection unit  123  detects a transmission path failure, for example, based on an Alarm Indication Signal (AIS) of the failure information. In this case, the state of the transmission path becomes a state in which the transmission is not allowed to be performed, so that a data signal DT is not included in the ODU frame  61 . 
     In addition, the transmission side ODU processing unit  120  extracts signal identification information from the ODU frame  61 , and writes the extracted signal identification information into the second identification information storage unit  124 . For example, as described above with reference to  FIG. 5 , the signal identification information is included in the TCMi area of the ODU overhead. Similar to the first identification information storage unit  131 , the second identification information storage unit  124  stores signal identification information of a data signal DT received by the reception device  91 , for each of the routes of the transmission source (see  FIG. 6 ). 
     The transmission side ODU processing unit  120  may extract the signal identification information each time the ODU frame  61  is received, or periodically. The signal identification information stored in the second identification information storage unit  124  is held in order to reset the transmission path of a data signal DT when the data signal DT is not received due to occurrence of a transmission path failure. Therefore, the control unit  14  may detect a data signal DT that is not received due to the transmission path failure, that is, a requested data signal DT, by referring to the signal identification information of the second identification information storage unit  124 . 
     The data extraction unit  121  extracts a data signal DT from the payload area of the ODU frame  61 . The extracted data signal DT is input to the data transmission unit  122 . The data transmission unit  122  transmits the data signal DT to the reception device  91 . 
     The bandwidth information storage unit  130  stores a used bandwidth and an unused bandwidth for each of the routes, based on information that is input from the switch unit  13 . In  FIG. 7 , an example of a content of the bandwidth information storage unit  130  is illustrated. 
     The used bandwidth and the unused bandwidth are represented as a bandwidth (ODUx) of the ODU frame  61  that is accommodated in the payload area of the OTU frame  60  and the number of ODU frames  61 . For example, in the OTU frame  60  that is transmitted to the route #1 (here, it is assumed that the frame is the ODU2), three ODU0 are used, and five ODU0 are unused. 
     The control unit  14  may determine a bandwidth of a data signal DT that is transmitted to the reception device  91  and determine whether or not a transmission path of a requested data signal DT is set, with reference to the bandwidth information storage unit  130 . A content of the bandwidth information storage unit  130  may be written from the network management system  92 . 
     The control unit  14  is, for example, an arithmetic processing device such as a central processing unit (CPU), and controls an operation of the transmission device  1 . When occurrence of a transmission path failure is notified from the failure detection unit  123 , the control unit  14  executes resetting processing of a transmission path of a data signal DT. Initial setting of the transmission path is executed, for example, for the switch unit  13  of each of the transmission devices  1  by the network management system  92 . 
     In the setting processing of a transmission path, the control unit  14  generates various pieces of control information, and outputs the generated information to the OTU transmission unit  112 . The OTU transmission unit  112  inserts the input control information into the ODU overhead of the OTU frame  60 , and transmits the frame to a further transmission device  1 . In addition, the control unit  14  obtains the control information that has been transmitted from the further transmission device  1 , from the OTU reception unit  100 . 
       FIG. 8  is a diagram illustrating control information. The control information includes, for example, a header of 4 bytes, signal identification information of 32 Bytes, a control code of 1 Byte, a bandwidth code of 2 Bytes, and a Cyclic Redundancy Check (CRC) value of 2 Bytes. 
     The header includes a specific data pattern that is used to identify control information by the OTU reception unit  100 . A data pattern of the header is not limited, but for example, may be “0x5A5A5A5A”. Here, “0x” indicates a hexadecimal number. 
     The signal identification information indicates a data signal DT that is a setting target of a transmission path. The control code indicates a content by the control information. When the control code is “0x00”, the control information is invalid, that is, it is indicated that the any processing is not executed. 
     When the control code is “0x01”, the control information indicates a request of a data signal DT from the request side transmission device  1 . The requested data signal DT is determined by the signal identification information. In the following description, an OTU signal S that includes control information in which the control code is “0x01” is referred to as “request signal”. 
     When the control code is “0x02”, the control information indicates a response from the non-request side transmission device  1  for the request signal. In the following description, an OTU signal S that includes control information in which the control code is “0x02” is referred to as “response signal”. 
     When the control code is “0x03”, the control information indicates that reception of a requested data signal DT has been completed in the request side transmission device  1 . In the flowing description, an OTU signal S that includes the control information in which the control code is “0x03” is referred to as “completion notification signal”. 
     When the control code is “0x04”, the control information indicates that a completion notification signal has been confirmed in the non-request side transmission device  1 . In the following description, an OTU signal S that includes control information in which the control code is “0x04” is referred to as “notification confirmation signal”. 
     The bandwidth code indicates a bandwidth of a requested data signal DT, and is used in the case of a request signal. When the bandwidth code is “0x00”, a bandwidth of the requested data signal DT is invalid (for example, a bandwidth value in which processing is not allowed be performed). 
     When the bandwidth code is “0x01”, a bandwidth of the requested data signal DT is the ODU0 (1.25 Gbps). When the bandwidth code is “0x02”, a bandwidth of the requested data signal DT is the ODU1 (2.5 Gbps). When the bandwidth code is “0x03”, a bandwidth of the requested data signal DT is the ODU2 (10 Gbps). When the bandwidth code is “0x04”, a bandwidth of the requested data signal DT is an ODU Flex (flexible bandwidth depending on a client signal). Here, “0x05” to “0xFF” are used as a spare. 
     The CRC value is an error detection symbol that is used to detect a data error of a header, signal identification information, a control code, and a bandwidth code. The control unit  14  may correct an error of 1 Bit or 2 Bits that occurs in the control information using the CRC value. 
     In the setting of a transmission path, the processing of the control unit  14  is different between the request side transmission device  1  and the non-request side transmission device  1 . The control unit  14  of the request side transmission device  1  detects the non-request side transmission device  1  that has received a data signal DT that is identical to the data signal DT that has been requested to the transmission device  1 , and transmits the data signal DT to branch from the detected non-request side transmission device  1  to the transmission device  1 . On the other hand, the control unit  14  of the non-request side transmission device  1  transmits the received data signal to branch to the request side transmission device  1  when the non-request side transmission device  1  is detected by the request side transmission device  1 . In the following description, the detailed operations of the control units  14  of the request side transmission device  1  and the non-request side transmission device  1  are described respectively. 
     In the request side transmission device  1 , the control unit  14  obtains signal identification information of a data signal DT that is not allowed to be received due to a transmission path failure, from the second identification information storage unit  124 , when occurrence of a transmission path failure or the like is notified from the failure detection unit  123 . In addition, the control unit  14  obtains bandwidth information (ODUx and the like) of the data signal DT, from the bandwidth information storage unit  130 . The control unit  14  generates a request signal that includes the obtained signal identification information and bandwidth information, and transmits the generated request signal to routes other than the route on the reception device  91  side. 
     On the other hand, in the non-request side transmission device  1 , the control unit  14  refers to the signal identification information of the first identification information storage unit  131  when reception of a request signal is notified from the OTU reception unit  100 . In addition, the control unit  14  determines whether or not the transmission device  1  has received a requested data signal DT, based on the signal identification information that is included in the request signal. In addition, the control unit  14  determines whether or not a bandwidth of the requested data signal DT is obtained, based on the bandwidth code included in the request signal, with reference to the bandwidth information storage unit  130 . 
     When the control unit  14  receives the data signal DT, and the bandwidth is obtained, the control unit  14  sets the switch unit  13  so that the data signal DT is caused to branch to the request side transmission device  1 . As a result, the switch unit  13  cross-connects the reception side ODU processing unit  102  and the transmission side ODU processing units  110  and  120  so that the ODU signal Sd including the data signal DT is caused to branch to two routes (see symbols d2 and d3). One of the two routes is the original transmission destination (transmission destination before the transmission path failure occurs) of the ODU signal Sd that includes the requested data signal DT, and the other route is a route that is destined for the request side transmission device  1 . 
     In addition, the control unit  14  generates a response signal, and transmits the generated response signal to the request side transmission device  1 . At that time, signal identification information included in the response signal corresponds to signal identification information included in the received request signal. 
     In addition, the control unit  14  may obtain a bandwidth, but forwards a received request signal to a further transmission device  1  other than the request side transmission device  1  when the transmission device  1  does not receive a data signal that is identical to the requested data signal DT. At that time, the control unit  14  replicates the request signal that has been notified from the OTU reception unit  100 , and outputs the replicated request signal to the OTU transmission unit  112 . In this case, even in the subsequent processing, similarly, the control unit  14  replicates further control information and forwards the replicated control information, and when a branched data signal DT is further received, the control unit  14  sets the switch unit  13  so that the data signal DT is forwarded to the request side transmission device  1 . 
     In the request side transmission device  1 , when reception of a response signal is notified from the OTU reception unit  100 , the control unit  14  sets the switch unit  13  so that an ODU signal Sd (data signal DT) that has been transmitted from the non-request side transmission device  1  that is the transmission source of the response signal is transmitted to the reception device  91 . At that time, the switch unit  13  cross-connects the reception side ODU processing unit  102  of the route of the transmission source of the response signal to the transmission side ODU processing unit  120  of the route on the reception device  91  side. In addition, the data transmission unit  122  transmits a data signal DT that has been transmitted from the non-request side transmission device  1 , to the reception device  91 . 
     When response signals are received from the plurality of non-request side transmission devices  1 , the control unit  14  controls a data signal DT of the transmission device  1  that has transmitted a response signal that is received earliest, to branch to the transmission device  1 . That is, the control unit  14  selects a data signal DT that has been transmitted from the transmission device  1  that is the transmission source of the response signal that is received earliest, from among data signals DT that have been transmitted from the plurality of non-request side transmission devices  1 . Therefore, the control unit  14  transmits a completion notification signal to a further non-request side transmission device  1  that has transmitted a data signal DT in response to the request signal in order to stop the transmission. As a result, conflict of transmission of data signals DT between the plurality of non-request side transmission devices  1  is avoided, so that wasteful use of a bandwidth may be avoided. 
     In the non-request side transmission device  1 , when reception of a completion notification signal is notified from the OTU reception unit  100 , the control unit  14  sets the switch unit  13  so that branching of an ODU signal Sd that includes a data signal DT that is identical to the requested data signal DT is stopped. For example, the control unit  14  sets the switch unit  13  so that cross-connect of the transmission side ODU processing units  110  and  120  that correspond to the route of the request side transmission device  1  from among two routes that are branch destinations of the ODU signal Sd is released. After completion of the setting, the control unit  14  generates a notification confirmation signal, and transmits the generated notification confirmation signal to the request side transmission device  1 . 
     An application example of the embodiment is described below with reference to  FIGS. 9 to 12 . In the example, it is assumed that the transmission device  1  of the node (3-2) is the request side transmission device  1 . 
     As illustrated in  FIG. 9 , when a transmission path failure F occurs in the transmission path between the node (1-2) and the node (2-2), the transmission device  1  of the node (2-2) transmits a notification signal such as an AIS, to the request side transmission device  1 . Here the example of a failure includes a transmission path failure F, but the failure is not limited to such an example, and may include a further failure such as a device failure of the transmission device  1 . 
     When the request side transmission device  1  detects occurrence of a transmission path failure F by the failure detection unit  123 , the request side transmission device  1  transmits a request signal REQ to the routes #1 to #3 in order to detect a further transmission device (non-request side transmission device)  1  that has received a data signal DT that is identical to a data signal DT that is not allowed to be received. The route #4 is a route destined for the reception device  91 , so that a request signal is not transmitted to the route #4. 
     The transmission devices  1  of the nodes (3-1) and (3-3) receive a data signal DT that is identical to the requested data signal DT, so that the request signal REQ is processed in the transmission device  1 . On the other hand, the transmission device  1  of the node (2-2) does not receive the data signal that is identical to the requested data signal DT, so that a request signal REQ is forwarded to the transmission devices  1  of the adjacent nodes (2-1) and (2-3). 
     As illustrated in  FIG. 10 , each of the transmission devices  1  of the nodes (2-1), (2-3), (3-1) and (3-3) that have received the request signal REQ transmits a response signal RSP to the request side transmission device  1 . In addition, each of the transmission devices  1  of the nodes (2-1), (2-3), (3-1), and (3-3) transmits a requested data signal DT to branch to the request side transmission device  1 , by the setting of the switch unit  13 . At that time, the transmission device  1  of the node (2-2) forwards the data signal DT and the response signal RSP from each of the transmission devices  1  of the nodes (2-1) and (2-3), to the request side transmission device  1 . 
     As illustrated in  FIG. 11 , based on the setting of the switch unit  13 , the request side transmission device  1  transmits a data signal DT of the transmission device  1  that has transmitted a response signal RSP received earliest (hereinafter referred to as “earliest transmission device”), from among the response signals RSP received from the plurality of non-request side transmission devices  1 , to the reception device  91 . In the example, it is assumed that the transmission device  1  of the node (3-1) is the earliest transmission device  1 . 
     In addition, the request side transmission device  1  transmits a completion notification signal NTF, to the non-request side transmission devices  1  other than the earliest transmission device  1 , that is, the transmission devices  1  of the nodes (2-1), (2-3), and (3-3). At that time, the transmission device  1  of the node (2-2) forwards the completion notification signal NTF to the transmission devices  1  of the nodes (2-1) and (2-3). 
     As illustrated in  FIG. 12 , the non-request side transmission device  1  that has received the completion notification signal NTF stops transmission of a data signal DT to the request side transmission device  1 . After the transmission is stopped, the non-request side transmission device  1  transmits a notification confirmation signal CNF, to the request side transmission device  1 . When the request side transmission device  1  receives the notification confirmation signal CNF, the request side transmission device  1  stops the transmission of completion notification signal NTF. As described above, the request side transmission device  1  resets a transmission path of the data signal DT that is not allowed to be received due to a transmission path failure F. 
       FIG. 13  is a flowchart illustrating an operation of the request side transmission device  1  according to the first embodiment. The processing illustrated in the flowchart is executed by the control unit  14  when a transmission path failure is detected by the failure detection unit  123 . 
     First, the control unit  14  transmits a request signal REQ to each of the routes (Step St 1 ). At that time, the control unit  14  obtains signal identification information of a requested data signal DT from the second identification information storage unit  124 , obtains a bandwidth of the requested data signal DT from the bandwidth information storage unit  130 , and generates a request signal REQ. 
     The control unit  14  determines the presence or absence of reception of a response signal RSP from a further transmission device  1  (Step St 2 ). When a response signal RSP is not received within a certain time period after transmission of the request signal REQ (No in Step St 2 ), the control unit  14  notifies the network management system  92  of setting failure of a transmission path (Step St 8 ). 
     On the other hand, when a response signal RSP is received within the certain time period after transmission of the request signal REQ (Yes in Step St 2 ), the control unit  14  refers to signal identification information of a route of a transmission source of the earliest response signal RSP, from among the plurality of response signals RSP (Step St 3 ). As described above, the signal identification information is stored in the first identification information storage unit  131 , for each of the routes. 
     The control unit  14  detects whether or not signal identification information of a data signal DT that has been requested to the transmission device  1  is stored in the first identification information storage unit  131  (Step St 4 ). That is, the control unit  14  determines whether or not an ODU signal including a requested data signal DT is transmitted from a further transmission device  1  that has received a request signal REQ to the transmission device  1 , with reference to the first identification information storage unit  131 . 
     When signal identification information of the requested data signal DT is not detected within the certain time period (No in Step St 4 ), the control unit  14  notifies the network management system  92  of setting failure of a transmission path (Step St 8 ). In this case, instead of notification of the setting failure, in the control unit  14 , the flow returns to the processing Step St 3 , and the control unit  14  may detect signal identification information of a transmission source route of a further response signal RSP. 
     When signal identification information of the requested data signal DT is detected within the certain time period (Yes in Step St 4 ), the control unit  14  transmits a data signal DT included in an ODU signal Sd that has been transmitted from the transmission device  1  that is the transmission source of a response signal RSP, to the reception device  91  (Step St 5 ). At that time, the control unit  14  sets the switch unit  13  so that the reception side ODU processing unit  102  of the reception processing unit  10  of the route of the transmission device  1  is cross-connected to the transmission side ODU processing unit  120  of the route on the reception device side. As a result, a transmission path that ranges from the detected further transmission device  1  to the reception device  91  is set, so that the transmission of the data signal DT, which has been interrupted due to the transmission path failure F, is resumed. 
     The control unit  14  transmits a completion notification signal NTF, to a route of a transmission source of a further response signal RSP (response signal RSP other than the earliest response signal RSP) (Step St 6 ). That is, the control unit  14  transmits a completion notification signal NTF to the transmission device  1  other than the transmission device  1  that is a transmission source of the requested data signal DT. The completion notification signal NTF is kept to be transmitted for a certain time period. When one response signal RSP is merely received, the processing is not executed, and in the control unit  14 , the processing ends. 
     The control unit  14  determines the presence or absence of reception of a notification confirmation signal CNF from the transmission device  1  that is the transmission destination of the completion notification signal NTF (Step St 7 ). Here, the control unit  14  made the determination for each of the corresponding transmission devices  1 . 
     When a notification confirmation signal CNF is not received within the certain time period (No in Step St 7 ), the control unit  14  notifies the network management system  92  of setting failure of a transmission path (Step St 8 ). On the other hand, when notification confirmation signal CNF is received within the certain time period (Yes in Step St 7 ), the control unit  14  stops transmission of the completion notification signal NTF (Step St 9 ). As described above, the request side transmission device  1  executes the setting processing of a transmission path. 
     On the other hand,  FIG. 14  is a flowchart illustrating an operation of the non-request side transmission device  1  according to the embodiment. When the control unit  14  receives a request signal REQ (Yes in Step St 10 ), the control unit  14  refers to signal identification information of each of the routes (Step St 11 ). 
     The control unit  14  detects whether or not signal identification information of the requested data signal DT is stored in the first identification information storage unit  131  (Step St 12 ). That is, the control unit  14  detects whether or not the transmission device  1  has received a data signal DT that is indicated by signal identification information included in the request signal REQ (data signal that is identical to the requested data signal DT), with reference to the first identification information storage unit  131 . 
     When signal identification information of the requested data signal DT is detected (Yes in Step St 12 ), the control unit  14  checks the presence or absence of a available bandwidth that is used to transmit the requested data signal DT to a transmission source route of the request signal REQ, with reference to the bandwidth information storage unit  130  (Step St 13 ). That is, the control unit  14  determines whether or not a bandwidth indicated by a bandwidth code that is included in the request signal REQ is obtained for the corresponding route, with reference to the bandwidth information storage unit  130 . 
     When there is no available bandwidth (No in Step St 13 ), in the control unit  14 , the processing ends. On the other hand, when there is a available bandwidth (Yes in Step St 13 ), the control unit  14  transmits a response signal RSP to the route of the transmission source of the request signal REQ (Step St 14 ). 
     As described above, the non-request side transmission device  1  searches for signal identification information that corresponds to the signal identification information included in the request signal REQ, from pieces of signal identification information that are used to identify a data signal DT that has been received by the transmission device  1 . In addition, when the corresponding signal identification information is found, the non-request side transmission device  1  transmits a response signal RSP to the request side transmission device  1 . Therefore, the request side transmission device  1  easily detects a further transmission device  1  that has received a data signal DT that has been requested to the transmission device  1  with reference to the comparison result of the pieces of signal identification information. 
     The control unit  14  controls a data signal DT that is identical to the requested data signal DT (ODU signal Sd) to branch, and transmits the branched data signal to the route of the transmission source of the request signal REQ (Step St 15 ). At that time, the control unit  14  sets the switch unit  13  so that the data signal DT that is identical to the requested data signal DT (ODU signal Sd) is caused to branch to the original route and a route that is destined for the request side transmission device  1  (see symbols d2 and d3 in  FIG. 2 ). 
     The control unit  14  determines the presence or absence of reception of a completion notification signal NTF from the request side transmission device  1  (Step St 16 ). When a completion notification signal NTF is not received within a certain time period (No in Step St 16 ), in the control unit  14 , the processing ends. 
     On the other hand, when a completion notification signal NTF is received within the certain time period (Yes in Step St 16 ), the control unit  14  stops transmission of a requested data signal DT (ODU signal Sd) to the route of the transmission source of the request signal REQ (Step St 17 ). At that time, the control unit  14  sets the switch unit  13  so that the requested data signal DT (ODU signal Sd) is merely transmitted to the original route. 
     The control unit  14  transmits a notification confirmation signal CNF to the route of the transmission source of the request signal REQ (Step St 18 ). In the control unit  14 , the processing ends. 
     On the other hand, when signal identification information of the requested data signal DT is not detected (No in Step St 12 ), the non-request side transmission device  1  operates as a forward device that forwards control information and a data signal DT (ODU signal Sd). The operation corresponds to an operation of the transmission device  1  of the node (2-2) illustrated in  FIGS. 9 to 12 . 
     First, the control unit  14  checks the presence or absence of a available bandwidth that is used to transmit a requested data signal DT to a transmission source route of a request signal REQ, with reference to the bandwidth information storage unit  130  (Step St 19 ). The processing is similar to the above-described processing of Step St 13 , and may be integrated with the processing of Step St 13 , and, for example, the integrated pieces of processing may be executed after Step St 10 . 
     When there is no available bandwidth (No in Step St 19 ), in the control unit  14 , the processing ends. On the other hand, when there is a available bandwidth (Yes in Step St 19 ), the control unit  14  forwards the request signal REQ to the routes other than the route of the transmission source of the request signal REQ (Step St 20 ). 
     As described above, when signal identification information that corresponds to the signal identification information included in the request signal REQ is not found, the non-request side transmission device  1  forwards the request signal REQ to a further transmission device  1 . Thus, the request side transmission device  1  may detect a further transmission device  1  that has received a data signal that is identical to the requested data signal DT even when the transmission device  1  of the adjacent node does not receive a data signal that is identical to the requested data signal DT. 
     The control unit  14  determines the presence or absence of reception of a response signal RSP (Step St 21 ). When a response signal RSP is not received within a certain time period (No in Step St 21 ), in the control unit  14 , the processing ends. On the other hand, a response signal RSP is received within the certain time period (Yes in Step St 21 ), the control unit  14  forwards the received response signal RSP, to the route of the transmission source of the request signal REQ (Step St 22 ). 
     The control unit  14  refers to signal identification information of the route of the transmission source of the response signal RSP (Step St 23 ). The control unit  14  detects whether or not signal identification information of the requested data signal DT is stored in the first identification information storage unit  131  (Step St 24 ). That is, the control unit  14  detects whether or not the transmission device  1  has received a data signal DT that is indicated by the signal identification information included in the request signal REQ (data signal that is identical to the requested data signal DT), with reference to the signal identification information of the first identification information storage unit  131 . 
     When signal identification information of the requested data signal DT is not detected (No in Step St 24 ), in the control unit  14 , the processing ends. On the other hand, when signal identification information of the requested data signal DT is detected (Yes in Step St 24 ), the control unit  14  forwards the requested data signal DT (ODU signal Sd), to the route of the transmission source of the request signal REQ (Step St 25 ). At that time, the control unit  14  sets the switch unit  13  so that the requested data signal DT (ODU signal Sd) is transmitted to the route of the transmission source of the request signal REQ. 
     The control unit  14  determines the presence or absence of reception of a completion notification signal NTF (Step St 26 ). When a completion notification signal NTF is not received within a certain time period (No in Step St 26 ), in the control unit  14 , the processing ends. On the other hand, a completion notification signal NTF is received within the certain time period (Yes in Step St 26 ), the control unit  14  forwards the received completion notification signal NTF, to the route of the transmission source of the response signal RSP (Step St 27 ). 
     The control unit  14  determines the presence or absence of reception of a notification confirmation signal CNF (Step St 28 ). When a notification confirmation signal CNF is not received within a certain time period (No in Step St 28 ), in the control unit  14 , the processing ends. On the other hand, a notification confirmation signal CNF is received within the certain time period (Yes in Step St 28 ), the control unit  14  forwards the received notification confirmation signal CNF, to the route of the transmission source of the completion notification signal NTF (Step St 29 ). As described above, the non-request side transmission device  1  executes the setting processing of a transmission path. 
     As described above, in the embodiment, the control unit  14  of the request side transmission device  1  transmits a request signal REQ including signal identification information that is used to identify a data signal DT that has been requested to the transmission device  1 , to a further transmission device  1 . In addition, when the control unit  14  receives a response signal RSP for the request signal REQ, from the further transmission device  1 , the control unit  14  detects a further transmission device  1  that has received a data signal DT that is identical to the data signal DT that has been requested to the transmission device  1 . 
     In the transmission device  1  according to the embodiment, even when a node configuration is unknown in the network  8 , a further transmission device  1  that has received a data signal that is identical to the requested data signal DT may be detected by the response signal RSP for the request signal REQ. 
     Second Embodiment 
     In the above-described embodiment, the control unit  14  detects a further transmission device  1  that has received a data signal that is identical to a requested data signal DT by a response signal RSP for a request signal REQ, but the embodiment is not limited to such an example. For example, as described below, the control unit  14  may further rapidly detect a further transmission device  1  that has received a data signal that is identical to the requested data signal DT using a management table that manages identification information of the transmission device  1 . 
       FIG. 15  is a diagram illustrating a structure of the transmission device  1  according to the embodiment. In  FIG. 15 , the same symbol is assigned to a configuration that is similar to the configuration in  FIG. 2 , and the description is omitted herein. 
     The transmission device  1  includes the plurality of reception processing units  10 , the plurality of the transmission processing units  11 , the switch unit  13 , and a control unit  14   a . The transmission device  1  further includes the bandwidth information storage unit  130 , the first identification information storage unit  131 , the transmission side ODU processing unit  120 , the data extraction unit  121 , the data transmission unit  122 , the failure detection unit  123 , the second identification information storage unit  124 , and a management table storage unit (storage unit)  132 . 
     Differently from the first embodiment, in the request side transmission device  1 , the control unit  14   a  does not transmit a request signal REQ to the routes, and merely transmits a request signal REQ to the detected further transmission device  1  with reference to the management table storage unit  132 . Further processing of the control unit  14   a  (processing and the like of the response signal RSP) is similar to the control unit  14  according to the first embodiment. 
     The management table storage unit  132  stores a management table of device identification information that is used to identify a further transmission device  1  that has received a data signal DT that is identical to the data signal DT that has been requested to the transmission device  1 . A content of the management table is set, for example, by the network management system  92 . In  FIG. 16 , an example of a content of the management table is illustrated. 
     In  FIG. 16 , “node” indicates a node number of the transmission device  1 , and “signal identification information” indicates signal identification information of a data signal DT that has been requested to the transmission device  1 . In addition, “request target node” indicates a node number (device identification information) of a transmission destination of a request signal REQ, and “route” indicates a route of the node, which is viewed from the transmission device  1  that is indicated by the above-described “node”. In addition, “request target node” is associated with “priority level” for each of the devices, and the associated node and priority level are stored. Here, “priority level” becomes high as the number is small. The node number corresponds to the node number illustrated in  FIG. 2 . 
     For example, in the node (3-2), when a data signal DT of “Video_Channel_1” is not received due to a transmission path failure, the control unit  14   a  transmits a request signal REQ to the transmission device  1  of the node (3-1) of the route #1. In addition, in the node (3-1), when a data signal DT of “Video_Channel_1” is not received due to a transmission path failure, the control unit  14   a  transmits a request signal REQ to the transmission device  1  of the node (3-2) of the route #3. 
     In addition, when a further transmission device  1  that has been detected based on “request target node” is not allowed to cause a data signal DT to branch to the transmission device  1 , the control unit  14   a  further detects a further transmission device  1  the priority level of which is lower than the priority level of the detected further transmission device  1 , based on “request target node”. That is, when the transmission device  1  of the detected request target node is not allowed to cause a data signal DT (ODU signal Sd) to branch to the transmission device  1  due to a failure or the like, the control unit  14   a  detects a transmission device  1  the priority level of which is lower than the detected further transmission device  1 , and transmits a data signal DT to branch. 
     For example, in the node (3-2), when a data signal DT is not transmitted from the transmission device  1  of the node (3-1) in which “priority level” is “1”, the control unit  14   a  transmits a request signal REQ to the transmission device  1  of the node (3-3) in which “priority level” is “2”. In addition, in the node (3-1), when a data signal DT is not transmitted from the transmission device  1  of the node (3-2) in which “priority level” is “1”, the control unit  14   a  transmits a request signal REQ to the transmission device  1  of the node (3-3) in which “priority level” is “2”. 
     An application example of the embodiment is described below with reference to  FIGS. 17 and 18 . In the example, it is assumed that the transmission device  1  of the node (3-2) is the request side transmission device  1 . 
     As illustrated in  FIG. 17 , when a transmission path failure F occurs in the transmission path between the node (1-2) and the node (2-2), the transmission device  1  of the node (2-2) transmits a notification signal such as an AIS to the request side transmission device  1 . When the request side transmission device  1  detects occurrence of a transmission path failure F by the failure detection unit  123 , the request side transmission device  1  refers to the management table of the management table storage unit  132  in order to detect a further transmission device (non-request side transmission device)  1  that has received a data signal DT that is not allowed to be received. 
     In the example, when it is assumed that the node of the request side transmission device  1  is the node (3-2), and signal identification information of a data signal DT that is not allowed to be received due to a transmission path failure F is “Video_Channel_1”, “request target node” is the node (3-1), and the route correspond to the route #1 (see  FIG. 6 ). Thus, the control unit  14  of the request side transmission device is transmits a request signal REQ to the transmission device  1  of the node (3-1) of the route #1. 
     As illustrated in  FIG. 18 , the transmission device  1  of the node (3-1) that has received a request signal REQ receives a data signal that is identical to the requested data signal DT, so that the transmission device  1  of the node (3-1) transmits a response signal RSP to the request side transmission device  1 . In addition, the transmission device  1  of the node (3-1) transmits the data signal DT to branch to the request side transmission device  1  by the setting of the switch unit  13 . 
     In addition, the request side transmission device  1  transmits the data signal DT that has been transmitted from the transmission device  1  of the node (3-1), to the reception device  91 , by the setting of the switch unit  13 . As described above, the request side transmission device  1  resets a transmission path of a data signal DT that is not allowed to be received due to the transmission path failure F. 
       FIG. 19  is a flowchart illustrating an operation of the request side transmission device  1  according to the embodiment. The processing illustrated in the flowchart is executed by the control unit  14   a  when a transmission path failure is detected by the failure detection unit  123 . 
     The control unit  14   a  detects a further transmission device  1  that has received a data signal that is identical to the requested data signal DT, with reference to the management table of the management table storage unit  132  (Step St 31 ). At that time, the control unit  14   a  detects the transmission device  1  having the highest “priority level”. The control unit  14   a  may detect a further transmission device  1  rapidly with reference to the management table. 
     The control unit  14   a  transmits a request signal REQ to the route of the detected transmission device  1  (Step St 2 ). At that time, the control unit  14   a  refers to “route” that is stored in the management table. 
     The control unit  14   a  determines the presence or absence of reception of a response signal RSP from the transmission device  1  that is the transmission destination of the request signal REQ (Step St 33 ). When a response signal RSP is received within a certain time period after the transmission of the request signal REQ (Yes in Step St 33 ), the control unit  14   a  refers to the signal identification information of the route of the transmission source of the response signal RSP (Step St 34 ). 
     The control unit  14   a  detects whether or not signal identification information of a data signal DT that has been requested to the transmission device  1  is stored in the first identification information storage unit  131  (Step St 35 ). That is, the control unit  14   a  determines whether or not an ODU signal including the requested data signal DT is transmitted from a further transmission device  1  that has received a request signal REQ, to the transmission device  1 , with reference to the first identification information storage unit  131 . 
     When signal identification information of the requested data signal DT is detected within the certain time period (Yes in Step St 35 ), the control unit  14   a  transmits the data signal DT included in the ODU signal Sd that has been transmitted from the transmission device  1  that is the transmission source of the response signal RSP, to the reception device  91  (Step St 36 ). At that time, the control unit  14   a  sets the switch unit  13  so that the reception side ODU processing unit  102  of the reception processing unit  10  of the route of the transmission device  1  is cross-connected to the transmission side ODU processing unit  120  on the reception device  91  side. As a result, a transmission path that ranges from the detected further transmission device  1  to the reception device  91  is set, so that the transmission of the data signal DT, which has been interrupted due to the transmission path failure F, is resumed. 
     In addition, when the response signal RSP is not received (No in Step St 33 ), or when a data signal DT that is identical to the above-described data signal DT is not detected (No in Step St 35 ), the control unit  14   a  detects a further transmission device  1  having a lower priority level (priority level “2”) from the management table (Step St 37 ). 
     When a further transmission device  1  is detected (Yes in Step St 37 ), the control unit  14   a  executes the processing from Step St 32  again. Thus, even when the detected further transmission device  1  is not allowed to cause a data signal DT to branch to the transmission device  1  due to a transmission path failure or the like, the request side transmission device  1  may detect a further transmission device  1 , and transmits a data signal DT to branch to the transmission device  1 . 
     On the other hand, when a further transmission device  1  is not detected (No in Step St 37 ), the control unit  14   a  notifies the network management system  92  of setting failure of a transmission path (Step St 38 ). As described above, the request side transmission device  1  executes the setting processing of a transmission path. 
       FIG. 20  is a flowchart illustrating an operation of the non-request side transmission device  1  according to the embodiment. When the control unit  14   a  receives a request signal REQ (Yes in Step St 41 ), the control unit  14   a  determines whether or not the request signal REQ is destined for the transmission device  1  (Step St 42 ). Here, destination information that indicates the destination of the request signal REQ may be included, for example, in the ODU header of the OTU frame  60  (GCC 1 and 2, or RES). 
     When the request signal REQ is destined for the transmission device  1  (Yes in Step St 42 ), the control unit  14   a  determines the presence or absence of an available bandwidth that is used to transmit a requested data signal DT to a transmission source route of the request signal REQ (Step St 43 ). That is, the control unit  14   a  determines whether or not a bandwidth that is indicated by a bandwidth code included in the request signal REQ is obtained for the corresponding route, with reference to the bandwidth information storage unit  130 . 
     When there is no available bandwidth (No in Step St 43 ), in the control unit  14   a , the processing ends. On the other hand, when there is a available bandwidth (Yes in Step St 43 ), the control unit  14   a  transmits a response signal RSP to the route of the transmission source of the request signal REQ (Step St 44 ). 
     The control unit  14   a  controls a data signal that is identical to the requested data signal DT (ODU signal Sd) to branch, and transmits the branched data signal to the route of the transmission source of the request signal REQ (Step St 45 ). At that time, the control unit  14   a  sets the switch unit  13  so that the requested data signal DT (ODU signal Sd) branches to the original route and a route that is destined for the request side transmission device  1  (see symbols d2 and d3 in  FIG. 2 ). 
     On the other hand, when the received request signal REQ is not destined for the transmission device  1  (No in Step St 42 ), the non-request side transmission device  1  operates as a forward device that forwards control information and a data signal DT (ODU signal Sd). 
     First, the control unit  14   a  determines the presence or absence of a available bandwidth that is used to transmit a requested data signal DT to a transmission source route of a request signal REQ, with reference to the bandwidth information storage unit  130  (Step St 46 ). The processing is similar to the above-described processing of Step St 43 , and may be integrated with the processing of Step St 43 , and for example, the integrated pieces of processing may be executed after Step St 41 . 
     When there is no available bandwidth (No in Step St 46 ), in the control unit  14   a , the processing ends. On the other hand, when there is a available bandwidth (Yes in Step St 46 ), the control unit  14   a  forwards the request signal REQ to a route that is a destination indicated by the destination information (Step St 47 ). 
     The control unit  14   a  determines the presence or absence of reception of a response signal RSP (Step St 48 ). When the control unit  14   a  does not receive a response signal RSP within a certain time period (No in Step St 48 ), the processing ends. On the other hand, when the control unit  14   a  receives a response signal RSP within a certain time period (Yes in Step St 48 ), the control unit  14   a  forwards the received response signal RSP to the route of the transmission source of the request signal REQ (Step St 49 ). 
     The control unit  14   a  refers to signal identification information of the route of the transmission source of the response signal RSP (Step St 50 ). The control unit  14   a  detects whether or not signal identification information of the requested data signal DT is stored in the first identification information storage unit  131  (Step St 51 ). That is, the control unit  14   a  detects whether or not the transmission device  1  has received a data signal DT that is indicated by the signal identification information included in the request signal REQ, with reference to the first identification information storage unit  131 . 
     When signal identification information of the requested data signal DT is not detected (No in Step St 51 ), in the control unit  14   a , the processing ends. On the other hand, when signal identification information of the requested data signal DT is detected (Yes in Step St 51 ), the control unit  14   a  forwards the requested data signal DT (ODU signal Sd) to the route of the transmission source of the request signal REQ (Step St 52 ). At that time, the control unit  14   a  sets the switch unit  13  so that the requested data signal DT (ODU signal Sd) is transmitted to the route of the transmission source of the request signal REQ. As described above, the non-request side transmission device  1  executes the setting processing of a transmission path. 
     As described above, in the embodiment, the request side transmission device  1  includes the management table storage unit  132  that stores a node number (device identification information) that is used to identify a further transmission device  1  that has received a data signal DT that has been requested to the transmission device  1 . The control unit  14   a  detects a further transmission device  1  that has received a data signal DT that has been requested to the transmission device  1 , based on the node number. 
     Thus, in the embodiment, a further transmission device  1  that has received a data signal DT that has been requested to the transmission device  1  may be detected further rapidly based on the node number of the management table storage unit  132 , which has been set beforehand. 
     In addition, in the embodiment, the control unit  14   a  transmits a request signal REQ merely to the detected transmission device  1 , so that communication after reception of a response signal RSP is not performed differently from the first embodiment. Therefore, in the embodiment, the setting processing of a transmission path may be simplified. 
     In the above-described embodiment, the request side transmission device  1  detects a further transmission device  1  that has received a data signal DT that is not allowed to be received due to a transmission path failure F (requested data signal DT) when a failure occurs, but the embodiment is not limited to such as example. 
     As illustrated in  FIG. 21 , the request side transmission device  1  may detect a further transmission device  1  that has received a data signal DT that has been requested to the transmission device  1  when a transmission instruction signal CMD that is used to instruct transmission of a data signal DT is received from the reception device  91 . In such a case, for example, it is assumed that a new reception device  91  is added to the transmission system. 
     In this case, prior to detection of a further transmission device  1  that has received a data signal DT, the request side transmission device  1  determines whether or not the transmission device  1  has received the data signal.  FIG. 22  is a flowchart illustrating detection processing of a data signal DT of the request side transmission device in such a case. 
     In the control units  14  and  14   a , when a transmission instruction signal CMD is received from the reception device  91  (Yes in Step St 61 ), the control unit refers to signal identification information of each of the routes that are stored in the first identification information storage unit (Step St 62 ). When signal identification information of a requested data signal DT is detected by the transmission instruction signal CMD (Yes in Step St 63 ), the control unit transmits the requested data signal DT to the reception device  91  (Step St 64 ). That is, the control unit sets the switch unit  13  so that the data signal DT is transmitted to the reception device  91  when the transmission device  1  receives the requested data signal DT. 
     On the other hand, when signal identification information of the requested data signal DT is not detected (No in Step St 63 ), the control unit executes the detection processing of a further transmission device  1  that has received a data signal that is identical to the requested data signal DT (Step St 65 ). That is, when the transmission device  1  does not receive the requested data signal DT, the control unit executes the above-described processing with reference to  FIG. 13 or 19 . As described above, the request side transmission device  1  executes the detection processing of a data signal DT. 
     As described above, when a data signal DT is not allowed to be received due to occurrence of a failure, or when a transmission instruction of a data signal DT is received from the reception device  91 , the transmission device  1  according to the embodiment sets a transmission path of the data signal DT autonomously. 
     As described above, as the request side transmission device  1 , the transmission devices  1  of the nodes (3-1) to (3-3) that are adjacent to the reception device  91  are used as examples, but the embodiment is not limited to such examples, and a transmission path may be set by the similar configuration even when the transmission device  1  of a further node is used as the request side transmission device  1 . In this case, in the control units  14  and  14   a  of the request side transmission device  1 , the switch unit  13  is set so that a data signal DT that has been transmitted from the non-request side transmission device  1  is output to the transmission side ODU processing unit  110  of the corresponding route, instead of the transmission side ODU processing unit  120 . 
     As described above, the transmission device  1  according to the embodiment is connected to the mesh network  8  and includes the control unit  14  or  14   a . In the control units  14  and  14   a , a further transmission device  1  that has received a data signal DT that is identical to a data signal DT that has been requested to the transmission device  1  is detected, and the data signal DT is caused to branch to the transmission device  1  from the detected further transmission device  1 . 
     Thus, the transmission device  1  according to the embodiments saves the effort of setting a transmission path that ranges from the server  90  that is a transmission source of the data signal DT to the reception device  91 , and may transmit the data signal DT from the detected further transmission device  1  to the transmission device  1 . Therefore, in the embodiment, the transmission path of broadcast distribution may be rapidly set. 
     In addition, the transmission system according to the embodiment includes the plurality of transmission devices  1  connected to the mesh network  8 . From among the plurality of transmission devices  1 , the request side transmission device  1  detects a further transmission device  1  (non-request side transmission device  1 ) that has received a data signal DT that is identical to a data signal DT that has been requested to the transmission device  1 , and transmits the data signal DT to branch from the detected further transmission device  1  to the transmission device  1 . When the non-request side transmission device  1  is detected by the request side transmission device  1 , the non-request side transmission device  1  transmits the received data signal DT to branch to the request side transmission device  1 . 
     The transmission system according to the embodiment includes the transmission device  1  according to the embodiment, so that an operation effect that is similar to the above-described content is obtained. 
     The transmission method according to the embodiment includes detecting a further transmission device  1  that has received a data signal DT that has been requested to one of the plurality of transmission devices  1  connected to the mesh network  8 , and causing the data signal DT to branch from the detected further transmission device  1  to the one of the plurality of transmission devices. 
     Thus, the transmission method according to the embodiment obtains an operation effect that is similar to the above-described content. 
     The embodiments discussed herein are described above with reference to the examples, but it is obvious that various modifications ca be made by those skilled in the art based on the basic technical idea and teachings and of the present disclosure. 
     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.