Abstract:
A transmission apparatus includes: a first input-output unit; a second input-output unit; a third input-output unit located in a first direction that is a transmission direction from the first input output unit and the second input-output unit; and a switch coupled to the first input-output unit, the second input-output unit, and the third input-output unit, wherein the first input-output unit requests the third input-output unit via the switch to notify in a second direction opposite to the first direction of a defect upon detecting the defect, wherein the third input-output unit transmits defect information indicating the defect to one of the first input-output unit and the second input-output unit via the switch in response to a requesting from the first input-output unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2014-121781, filed on Jun. 12, 2014, the entire contents of which are incorporated herein by reference. 
       FIELD 
       [0002]    The embodiments discussed herein are related to a transmission apparatus and a transmission method. 
       BACKGROUND 
       [0003]    The optical transport network (OTN), standardized by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T), is used in long distance large capacity network. 
         [0004]    An optical transport unit (OTU) signal as a main signal of OTN has a nest structure of layer. In the nest structure, an OTUk layer is arranged on the outermost side, followed by an ODUk-tandem connection monitoring (TCM) layer, and an ODUk-path monitoring (PM) as described in ITU-T G.709. In a channelized structure, the outermost layer is followed by an ODUj-TCM layer and ODUj-PM layer. 
         [0005]    A redundancy structure is incorporated in OTN in case of a defect in an apparatus or a transmission path (a disconnection of an optical fiber). The incorporation of redundancy is standardized as subnetwork connection (SNC) protection in Standard ITU-T G. 873.1 (July 2011). 
         [0006]      FIG. 5  and  FIG. 6  illustrate OTN.  FIG. 5  is  FIG. 11-3  in ITU-T G.798.1 (January 2013). A functional model is illustrated in the left -hand portion of  FIG. 5 , and an implementation model is illustrated in the right-hand portion of  FIG. 5 .  FIG. 6  is  FIG. 11-4  in ITU-T G.798.1 (January 2013). A functional model is illustrated in the left -hand portion of  FIG. 6 , and an implementation model is illustrated in the right-hand portion of  FIG. 6 . 
         [0007]    In the SNC protection, HO ODUk SNC/S in  FIG. 5  and HO ODUk SNC/I in  FIG. 6  are configured so that a lower layer having the redundancy structure is switched if a defect is detected in the termination of the higher layer of the nest structure. 
         [0008]    Related technique is disclosed in ITU-T G.798 (January 2013) Appendix II. 
       SUMMARY 
       [0009]    According to an aspect of the embodiments, a transmission apparatus includes: a first input-output unit; a second input-output unit; a third input-output unit located in a first direction that is a transmission direction from the first input output unit and the second input-output unit; and a switch coupled to the first input-output unit, the second input-output unit, and the third input-output unit, wherein the first input-output unit requests the third input-output unit via the switch to notify in a second direction opposite to the first direction of a defect upon detecting the defect, wherein the third input-output unit transmits defect information indicating the defect to one of the first input-output unit and the second input-output unit via the switch in response to a requesting from the first input-output unit. 
         [0010]    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. 
         [0011]    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 
         [0012]      FIG. 1  illustrates an example of a transmission apparatus; 
           [0013]      FIG. 2  illustrates an example of a transmission apparatus; 
           [0014]      FIG. 3  illustrates an example of an operation of a transmission apparatus; 
           [0015]      FIG. 4  illustrates an example of an OTN frame; 
           [0016]      FIG. 5  illustrates an example of an OTN; 
           [0017]      FIG. 6  illustrates an example of an OTN; 
           [0018]      FIG. 7  illustrates an example of BDI transmission during an occurrence of a defect; 
           [0019]      FIG. 8  illustrates an example of an input-output port unit; and 
           [0020]      FIG. 9  illustrates an example of a transmission apparatus. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0021]    A transmission apparatus of the OTN includes a plurality of input-output port unit configured to be connected to another apparatus to transmit and receive an OTN signal (optical signal) (hereinafter also referred to as an input-output unit), and a switch unit configured to perform a cross-connection process or a redundancy process (protection process) on the OTN signal. In the transmission apparatus, the input-output units and the switch unit are coupled via physical wire on a back board (back wired board (BWB)), for example, an electronic signal. 
         [0022]    The OTN includes a process referred to as an alarm transfer. If a defect is detected in a transmission path at a given layer, an alarm indication signal (AIS) and a bit interleaved parity (BIP) are transmitted in the alarm transfer using overhead information to an input-output unit in a forward direction at that layer. A backward defect indication (BDI)/backward error indication (BEI) are transmitted using overhead information to an input-output unit in a backward direction. 
         [0023]    Referring to the left-hand portion of  FIG. 6 , an optical channel transport unit (OTUk) is terminated at triangles on the bottom side of the left-hand portion with respect to a line coming from a lower layer. At the termination, SNC protections are switched at an optical channel data unit (ODUk) level in response to network defect information serving as a trigger. An ODUk-tandem connection monitoring (TCM) layer is terminated at the ODUkT triangle. If a network defect causing TCM-BDI is detected at this termination, ODUk TCM-BDI is transmitted in the backward direction. An ODUk-path monitoring (PM) layer is terminated, and if a network defect causing ODUk-BDI is detected at this termination, ODUk-BDI is transmitted in the backward direction. An ODUj TCM layer is terminated at an ODUjT triangle, and if a network defect causing ODUj TCM-BDI is detected at this termination, ODUj TCM-BDI is transmitted in the backward direction. A remaining ODUj signal is cross-connected by a switch unit in an oval shape at the top of the left-hand portion. 
         [0024]    For example, the implementation model is illustrated in the right-hand side of  FIG. 6 . The ODUk SNC protection and the ODUj cross-connect function are performed by the switch unit. All the layers of OTUk, ODUk-TCM, ODUk-PM, and ODUj-TCM are terminated at input-output units at both sides of the redundancy structure (ACT (act, actually-used) side, STBY (standby, backup) side). 
         [0025]    Since the ODUk-TCM, ODUk-PM, and ODUj-TCM layers are functionally (logically) selected by the SNC protection as illustrated in the left-hand side of  FIG. 6 , only the act side is present. In the implementation apparatus, the act side and the standby side are present as illustrated in the right-hand side of  FIG. 6 . For this reason, the ODUk-TCM, ODUk-PM, and ODUj-TCM layers are terminated at the act side and the standby side, and the BDI alarm transfer is performed at each of the terminations. 
         [0026]    BDI based on the network defect causes at one of the ODUk-TCM, ODUk-PM, and ODUj-TCM layers in the forward direction of the act side is transmitted (transferred) in the backward direction of both the act side and the standby side. In the implementation model, however, the transfer may be performed in the backward direction on each of the act side and the standby side. For this reason, a case in which the AIS alarm is output in the forward direction in unidirectional line protection and the BDI alarm is not output in the backward direction, and an inconsistency case which is opposite to the case may occur. 
         [0027]      FIG. 7  illustrates an example of BDI transmission during an occurrence of a defect. Referring to  FIG. 7 , letters “A” and “D” represent transponders that convert from  1 GE (giga bit Ethernet (registered trademark)) to OTU 0  or conversely convert from OTU 0  to  1 GE. Letters “B” and “C” represent cross-connect apparatuses that connect SNC/I segments (OTU 2 ). Referring to  FIG. 7 , in case C 1 , an ODU-AIS alarm is output in the forward direction from the apparatus C to the apparatus D, but BDI-ODU 1 T is not output in the backward direction from the transponder B to the transponder A, in response to the occurrence of a cutoff (network defect) in the SNC/I segment (OTU 2 ). Conversely, in case C 2 , the ODU 1 -AIS is not output in the forward direction, but BDI-ODU 1 T is output in the backward direction, in response to the occurrence of a cutoff (network defect) in the SNC/I segment (OTU 2 ). 
         [0028]    To reduce the inconsistency cases C 1  and case C 2 , the two input-output units are coupled via physical wires to exchange BDI/BEI (hereinafter BEI is occasionally omitted) information. 
         [0029]      FIG. 8  illustrates an example of input-output port units. Two input-output port units at the top portion and the bottom portion are physically coupled as illustrated in  FIG. 8 .  FIG. 9  illustrates an example of a transmission apparatus. 
         [0030]    As illustrated in  FIG. 8 , two adjacent input-output units having protection are coupled via physical wires (BDI/BEI cross-coupling to mate card). As illustrated in  FIG. 9 , for example, a transmission apparatus  200  includes input-output units  210 A,  210 B and  210 C coupled to each other via back boards  230 , and a switch unit  220 . Path terminations  211  of the two adjacent input-output units  210 A and  210 B are coupled to each other via a physical wire  231 . The two adjacent input-output units  210 A and  210 B exchange the BDI/BEI information detected at the ODUk-TCM, ODUk-PM, and ODUj-TCM layers via the physical wire  231 . 
         [0031]    A new physical wire is arranged between any input-output units arranged on the back board in order to exchange the BDI/BEI information between the input-output units. For example, if line protection is performed in any combination of input-output units other than the two adjacent input-output units, a physical wire is arranged to couple those input-output units. For this reason, exchanging the BDI/BEI information between any input-output units to share the BDI/BEI information may be difficult. A back board having no pre-arranged physical wire to couple input-output units is replaced with a back board having a new physical wire, and such a replacement operation may be time consuming. 
         [0032]    Elements having the same or similar functions in the present embodiment are designated with the same reference numerals and the discussion thereof may be omitted or reduced. 
         [0033]      FIG. 1  illustrates a transmission apparatus. Referring to  FIG. 1 , the transmission apparatus  1  may be a shelf-type apparatus that includes a back board  30  having a plurality of slots that receive input-output units  10 , and a switch unit  20 . The input-output units  10  and the switch unit  20  loaded onto the back board  30  are coupled to each other via a cable (physical wires) on the back board  30 . 
         [0034]    The input-output unit  10  may be an interface unit having a plurality of ports. Each port is coupled to a transmission line, such as an optical fiber cable or Ethernet (registered trademark) cable, included in a network. The input-output unit  10  transmits and receives a signal via the transmission path coupled to each port. In view of a defect in apparatuses and the transmission path, for example, a cutoff of the optical fiber, the input-output unit  10  may include an act unit that is normally used and a standby unit that is switchably used during the defect. 
         [0035]    The switch unit  20  performs a cross-connect process to sort signals received by each of the ports of the input-output unit  10  to each of the ports serving as destinations of the signals, respectively. If a defect takes place in the act input-output unit  10 , the switch unit  20  performs a protection process to switch to the standby input-output unit  10 . 
         [0036]    In the shelf-type transmission apparatus  1 , the input-output unit  10  or the switch unit  20  loaded in the slots of the back board  30  is reconfigured according to desired performance and function so that a configuration appropriate for intended service may be flexibly set up. 
         [0037]      FIG. 2  illustrates an example of a transmission apparatus. In  FIG. 2 , a functional configuration of the transmission apparatus  1  is illustrated. In  FIG. 2 , regarding a transmission direction of a network via transmission paths  2 A,  2 B, and  2 C, the right direction is set to the forward direction with respect to the transmission direction. The left direction is set to the backward direction with respect to the transmission direction. 
         [0038]    As illustrated in  FIG. 2 , the switch unit  20  is coupled to input-output units  10 A,  10 B, and  10 C and a higher layer apparatus  40  via the back boards  30 . The higher layer apparatus  40  may be a micro control unit (MCU), and controls the cross-connect process and the protection process of the switch unit  20 . 
         [0039]    The input-output units  10 A,  10 B, and  10 C are respectively coupled to transmission paths  2 A,  2 B, and  2 C. The redundancy structure may be employed in which one of the input-output units  10 A and  10 B is set to the act unit and the other of the input-output units  10 A and  10 B is set to the standby unit. For example, the input-output unit  10 A may be set to the act unit and the input-output unit  10 B may be set to the standby unit. The input-output unit  10 C is a unit placed in the forward direction of the paths routed through the input-output units  10 A and  10 B. 
         [0040]    Each of the input-output units  10 A and  10 B includes an alarm transfer unit  11  that transfers an alarm when a defect is detected in one of the paths  2 A and  2 B. The alarm transfer unit  11  may include a hardware circuit or a processor that executes a software program. 
         [0041]    The alarm transfer unit  11  includes a BDI alarm determination unit  110 , a request transmission unit  111 , and a BDI transmission unit  112 . The BDI alarm determination unit  110  detects an alarm (alert) causing the BDI transmission in response to a signal input via the transmission path. The BDI alarm determination unit  110  outputs detection results to the request transmission unit  111 . 
         [0042]    If an alarm causing the BDI transmission is detected, the request transmission unit  111  notifies, to the input-output unit  10 C in the forward direction, a BDI transmission request I 1  requesting the BDI transmission responsive to the detected alarm, using the switch unit  20 . For example, the request transmission unit  111  may make a notification with including the BDI transmission request I 1  in an overhead of the OTU signal as a main signal that is transmitted via the switch unit  20 . 
         [0043]    The BDI transmission request I 1  may be notified using a reserve region reserved for expansion use in the overhead of the OTU signal. The BDI transmission request I 1  may be notified using a BDI/BEI region of each layer in the forward direction of the overhead of the OTU signal. BDI/BEI in the forward direction is terminated at the input-output unit  10 A on the input side. Therefore, there is no regulation standard concerning the BDI/BEI region in the forward direction at each layer of the overhead of the OTU signal in a way from the input-output unit  10 A to the input-output unit  10 C via the switch unit  20 . For this reason, the BDI transmission request I 1  may be notified using the BDI/BEI region. 
         [0044]    If a defect is detected in the transmission path  2 A, the alarm transfer unit  11  in the input-output unit  10 A, by using the BDI alarm determination unit  110  and the request transmission unit  111 , requests the input-output unit  10 C, via the switch unit  20 , to transmit BDI for notifying of the defect in the backward direction. The BDI transmission unit  112  transmits BDI in the backward direction of the transmission direction in response to BDI information I 2  that the input-output unit  10 C has transmitted via the switch unit  20 . 
         [0045]    The input-output unit  10 C includes an alarm transfer unit  12 . In response to the BDI transmission request I 1  from the input-output unit  10 A, the alarm transfer unit  12  performs a transfer process to transfer the BDI information I 2  to the input-output units  10 A and  10 B. The alarm transfer unit  12  may include a hardware circuit or a processor that executes a software program. 
         [0046]    The alarm transfer unit  12  includes a BDI request reception unit  120  and a BDI information transmission unit  121 . The BDI request reception unit  120  receives the BDI transmission request I 1  in the OTU signal that the input-output unit  10 A has transmitted via the switch unit  20 . The BDI request reception unit  120  notifies the BDI information transmission unit  121  of the received BDI transmission request I 1 , and terminates the transmission of the BDI transmission request I 1  in the forward direction. 
         [0047]    In response to the notification of the BDI transmission request I 1 , the BDI information transmission unit  121  transmits the BDI information I 2  in the backward direction to transmit BDI. For example, the BDI information transmission unit  121  includes the BDI information I 2  in the overhead of the OTU signal that is a main signal to be transmitted via the switch unit  20 , and then transmits the OTU signal. A bridge  22  in the switch unit  20  transmits the OTU signal to the input-output units  10 A and  10 B, each having a redundancy structure. 
         [0048]    In the same way as the BDI transmission request I 1 , the BDI information I 2  may be notified using a reserve region reserved to be used for expansion use in the overhead of the OTU signal. The BDI information I 2  may be notified using the BDI/BEI region of each layer in the backward direction of the overhead of the OTU signal. 
         [0049]    The switch unit  20  includes a selector  21  and bridge  22 . The selector  21 , controlled by the higher layer apparatus  40 , selects between a signal from the input-output unit  10 A as an act system and a signal from the input-output unit  10 B as a backup system, and then transmits the selected signal to the input-output unit  10 C. For example, if a defect occurs in the act system, the selector  21  selects the signal from the input-output unit  10 B as the backup system and then transmits the selected signal to the input-output unit  10 C. The bridge  22 , controlled by the higher layer apparatus  40 , transmits a signal from the input-output unit  10 C to the input-output units  10 A and  10 B, each having the redundancy structure. 
         [0050]      FIG. 3  illustrates an example of an operation of a transmission apparatus. The transmission apparatus illustrated in  FIG. 1  and  FIG. 2  may operate as illustrated in  FIG. 3 . In the input-output unit  10 A at the input side as illustrated in  FIG. 3 , the BDI alarm determination unit  110  checks an alarm of the cause of the BDI transmission based on a signal input via the transmission path  2 A, and performs a transmission determination of the BDI alarm (S 1 ). If an alarm is triggered, the request transmission unit  111  includes the BDI transmission request I 1  requesting the BDI transmission responsive to the alarm into the overhead of the OTU signal and notifies the input-output unit  10 C in the forward direction (output side) of the OTU signal (S 2 ). 
         [0051]      FIG. 4  illustrates an example of an OTN frame. As illustrated in  FIG. 4 , the BDI transmission request I 1  may be included in a BDI/BEI region R 1  of the ODUk overhead terminated at the input-output unit  10 A and the BDI transmission request I 1  may be notified in S 2 . In this way, the BDI transmission request I 1  is notified after being included in the OTU signal that is transmitted via the switch unit  20 . The BDI transmission request I 1  may thus be notified without modifying the configuration of the transmission apparatus. 
         [0052]    The BDI request reception unit  120  in the input-output unit  10 C at the output side receives the BDI transmission request I 1  (S 3 ). The BDI information transmission unit  121  verifies the reception of the BDI transmission request I 1  and then performs a transmission determination of the BDI information I 2  (S 4 ). If the BDI transmission request I 1  has been received from the input-output unit  10 A, the BDI information transmission unit  121  includes the BDI information I 2  in the overhead of the OTU signal and then transmits the OTU signal to the input-output units  10 A and  10 B in the backward direction (input side) (S 5 ). 
         [0053]    Referring to  FIG. 4 , the BDI information I 2  may be included in the BDI/BEI region R 1  of the ODUk overhead and then the OTU signal may be transmitted in S 5 . In this way, the BDI information I 2  is included in the OTU signal that is to be transmitted via the switch unit  20 . Therefore, the BDI transmission request I 1  may be transmitted without modifying the configuration of the transmission apparatus. 
         [0054]    In each of the input-output units  10 A and  10 B at the input side, the BDI transmission unit  112  receives the BDI information I 2  (S 6 ). If the BDI information I 2  has been received, the BDI transmission unit  112  transmits BDI in the backward direction of the transmission direction (to the transmission paths  2 A and  2 B of the input-output units  10 A and  10 B). 
         [0055]    Upon detecting a defect in the transmission path  2 A, the input-output unit  10 A in the transmission apparatus  1  notifies the input-output unit  10 C of the BDI transmission request I 1  via the switch unit  20 . In response to the notification of the BDI transmission request I 1  from the input-output unit  10 A, the input-output unit  10 C transmits to the input-output units  10 A and  10 B the BDI information I 2  responsive to the defect in the input-output unit  10 A via the switch unit  20 . The input-output unit  10 A and the input-output unit  10 C thus easily share the BDI/BEI information without arranging a new physical wire on the switch unit  20 . 
         [0056]    If a new physical wire is arranged on the switch unit  20  to share the BDI/BEI information, power consumption may increase because of an increase of the new physical wire. 5 bits per path may be used in BDI/BEI. Seven layers of 6 TCM+PM are used per ODU. 80 TS (tributary slots) are used in ODU 0  in OTU 4  (100 G). If the frame period of ODU 0  is 1.168 μs, for example, transmission speed is 5 bits×7 layers×80 TS/1.168 μs=2.4 Gbps so that the transmission speed becomes fast. 
         [0057]    The alarm transfer is performed in the backward direction of ODUx PM, TCM at the termination, but the transmission speed is different at ODUx. Arbitration may be performed if physical wires are used for connection. For example, if no physical wires are used, the BDI/BEI information may be easily shared. 
         [0058]    The input-output unit  10 A may be an act system, and the input-output unit  10 B may be a standby system. Alternatively, the input-output unit  10 B may be an act system, and the input-output unit  10 A may be a standby system. In such a case, the request transmission unit  111  in the input-output unit  10 B transmits the BDI transmission request Il to the input-output unit  10 C. 
         [0059]    The BDI information transmission unit  121  may transmit the BDI information I 2  to only the input-output unit  10 B as the standby system. Since the input-output unit  10 A itself as the act system detects a defect, the BDI/BEI information is shared and then BDI is transmitted without receiving the BDI information I 2  from the input-output unit  10 C. 
         [0060]    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.