Patent Publication Number: US-2016241332-A1

Title: Reception device, transmission device, optical transmission device, optical transmission system, and monitoring method

Description:
TECHNICAL FIELD 
     The present disclosure relates to a reception device, a transmission device, an optical transmission device, an optical transmission system and a monitoring method. 
     BACKGROUND ART 
     Optical transmission systems for transmission of large volumes of data in a short time are put into practical use in recent years. In this type of optical transmission system, in addition to modulation using optical intensity alone, the signal is modulated using properties such as phase information. Thus signal processing devices are required such as complex optical modulation-demodulation circuits and electrical circuits operating at high speed. However, such signal processing devices are expensive in optical transmission systems for signal transmission at speeds in excess of 100 Gbit/s, and implementation itself of such a signal processing device is difficult. 
     Thus in a core network requiring high speed communication, often data is partitioned into multiple lanes, and subcarriers, polarized waves, and the like for transmission of the partitioned data are multiplexed. When data is partitioned into multiple lanes, the speed of operation of the signal processing device processing the partitioned data can be restricted (for example, see Non-Patent Literature 1). 
     For example, in an optical transponder for transmitting a signal at 0.100 Gbit/s, data in an optical channel transport unit (OTU) format determined according to Non-Patent Literature 1 is allocated among multiple lanes and is transmitted, Moreover, this optical transponder receives a signal through multiple channels, that is, lanes, and reproduces the original signal by executing alignment and deskewing between channels. A function for transmission of data of multiple lanes is implemented in the optical transponder by such processing, and the optical transponder can realize high speed data transmission. 
     CITATION LIST 
     Patent Literature 
     Non-Patent Literature 1: ITU-T Recommendation G.709 
     SUMMARY OF INVENTION 
     Technical Problem 
     In addition to a payload, data formatted for an OTU includes monitoring-control data for monitoring the condition of the communication path and for control of communication based on the results of such monitoring. When data formatted for the OTU is partitioned into multiple lanes, the monitoring-control data also becomes partitioned. As a result, even if a communication obstacle occurs in only one of the multiple lanes, the monitoring-control data transmitted through the multiple lanes becomes incomplete, and monitoring and the like of the condition of the communication path becomes difficult. However, an ability to monitor and the like the condition of the communication path even when this type of difficulty occurs is desired. Thus there is potential for improvement of resistance to obstacles in optical communication performed through multiple lanes. 
     In consideration of the aforementioned circumstances, an object of the present disclosure is to improve resistance to obstacles of optical communication performed through multiple lanes. 
     Solution to Problem 
     In order to achieve the aforementioned object, a reception device of the present disclosure includes: a receiving part to receive a plurality of lane signals transmitted through a plurality of lanes from a transmission device partitioning an OTU frame into the plurality of the lane signals; an extracting part, for each lane of the plurality of lanes, to extract data included in an overhead of the OTU frame from a respective lane signal of the plurality of lane signals received by the receiving part; and an outputting part to output, as information indicating a communication condition of the lane transmitting the lane signal from which the data is extracted by the extracting part, information relating to the data extracted by the extracting part. 
     Advantageous Effects of Invention 
     According to the present disclosure, a reception device outputs information indicating a communication condition of each lane of a plurality of lanes. Thus even when an obstacle to communication occurs in any of the plurality of lanes, monitoring of the communication condition of each lane becomes possible. Therefore resistance to obstacles to optical communication through the plurality of lanes can be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing configuration of an optical transmission system; 
         FIG. 2  is a diagram showing configuration of an OTU frame; 
         FIG. 3  is a diagram for explanation of signals when a communication obstacle occurs in a lane; 
         FIG. 4  is a diagram for explanation of a multi-frame number included in a lane signal; 
         FIG. 5  is a diagram showing an optical communication network using an undersea cable; and 
         FIG. 6  is a diagram showing a media converter system. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present disclosure are explained below while referring to figures. 
       FIG. 1  shows configuration of an optical transmission system  100  according to an embodiment of the present disclosure. The optical transmission system  100  has an optical transmission device  10  and an opposite device  50  that are mutually interconnected through an optical communication line. The optical communication line, for example, is an optical fiber forming a core network. Moreover, the optical communication line of the present embodiment includes lanes L 1  and L 2 , which correspond to respective multiplexed subcarriers. Each of lanes L 1  and L 2  transmits a lane signal, that is, an optical signal. The lane signal, for example, is an OTL 4.2 (Optical channel Transport Lane 4.2) signal. 
     The optical transmission device  10  has a reception device  20  for receiving the lane signal from the opposite device  50  and has a transmission device  30  for transmitting the lane signal to the opposite device  50 . The optical transmission device  10  has the reception device  20  and the transmission device  30 , and thus communicates bi-directionally with the opposite device  50 . 
     The reception device  20  generates a client signal from the lane signal received from the opposite device  50 , and transmits to a client. The client signal, for example, is a 100 GbE digital signal. Moreover, the client, for example, is an OLT (Optical Line Terminal) operated by a radio station or a telecommunication carrier. The reception device  20  includes a receiving unit  21  for receiving the lane signal, a terminal processing device  22  for executing terminal processing of the OTU frame carried by the lane signals, and an OTN-LSI  23  for generating the client signal from the OTU signal carrying the OTU frame. 
     The receiving receives the respective lane signals transmitted using the lanes L 1  and L 2 . The receiving unit  21  has DSP-LSIs (Digital Signal Processing-Large Scale Integration)  21   a  and  21   b  for performing digital signal processing of the respective lane signals of the lanes L 1  and L 2 . The receiving unit  21  forwards the received lane signals to the terminal processing device  22 . 
     The terminal processing device  22  reproduces a single OTU signal from the two lane signals obtained by the opposite device  50  partitioning the single OTU signal. That is to say, the terminal processing device  22  reproduces the OTU frame from the two lane signals carried by subcarriers. 
     The terminal processing device  22  has: SFI-RXs (SerDes Framer Interface Receivers)  221   a  and  221   b  for receiving lane signals formatted for optical communication, an extracting unit  222  for extracting data from the lane signals, an outputting part  223  for outputting information indicating communication conditions of the lanes L 1  and L 2 , a deskewing part  224  for eliminating skew, and an SFI-TX (transmitter)  225  for sending the OTU signal formatted for optical communication. 
     The extracting unit  222 , through the SFI-RXs  221   a  and  221   b,  receives the lane signals received by the receiving unit  21  from each of the lanes L 1  and L 2 . Moreover, from each of the received lane signals, the extracting unit  222  extracts data included in the GCC (General Communication Channel) region of the overhead of the OTU frame. 
     Configuration of the OTU frame is indicated in  FIG. 2 . As indicated in  FIG. 2 , the OTU frame includes an overhead, a payload, and a forward error correction (FEC) parity region, the overhead being appended to the payload, the payload being a region for storing user data, and the FEC parity region being for correction of bit errors that occur during transmission. 
     Moreover, GCC regions and RES (Reserve) regions, as indicated by the double-framed regions in  FIG. 2 , are included in the overhead and can be freely used by a user. Specifically, GCC regions in  FIG. 2  are indicated as “GCC0”, “GCC1” and “GCC2”. Five RES regions are indicated as “RES” in  FIG. 2 . The GCC regions and RES regions are normally used in a management plane for transmission of information such as OAM (Operation Administration and Maintenance) information. Furthermore, although data of the GCC regions is extracted in the present embodiment, rather than the GCC regions, data can be extracted from the RES regions. 
     As indicated in the previously discussed  FIG. 1 , the extracting unit  222  has frame aligning parts  222   a  and  222   b  for alignment of the OTU frame, and has GCC extracting parts  222   c  and  222   d  for extraction of data of the GCC regions form the lane signals. 
     The frame aligning parts  222   a  and  222   b  use the frame alignment pattern (FAS, Frame Alignment Signal) included in the lane signal, and align the lane signals transmitted through the lanes L 1  and L 2 , respectively. More specifically, based on the multi-frame number (MFRS, Multi-Frame Alignment Signal), each of the frame aligning parts  222   a  and  222   b  identifies the overhead of the OTU frame. Thereafter, each of the frame aligning parts  222   a  and  222   b  aligns the OTU frame by separate alignments of the lane signals. The frame aligning parts  222   a  and  222   b  send sequentially to the outputting part  223  the multi-frame number of the identified overhead, and send the aligned lane signals to the GCC extracting parts  222   c  and  222   d,  respectively. 
     The GCC extracting parts  222   c  and  222   d  are implemented, for example, as functions of an LSI. The GCC extracting part  222   c  sequentially extracts data of the GCC regions from the lane signal transmitted through the lane L 1  and outputs the extracted data to the outputting part  223 . The GCC extracting part  222   d  sequentially extracts data of the GCC regions from the lane signal transmitted through the lane L 2  and outputs the extracted data to the outputting part  223 . Moreover, the GCC extracting parts  222   c  and  222   d  transmit the lane signals to the deskewing part  224 , 
     The outputting part  223  is implemented, for example, as a function of an LSI, The outputting part  223  acquires the multi-frame numbers sent from each of the frame aligning parts  222   a  and  222   b  and the data sent from each of the of the GCC extracting parts  222   c  and  222   d,  and performs aggregating for each of the lanes, For example, the outputting part  223  performs aggregation to form a single datum extracted most frequently by the GCC extracting part  222   c  by aggregating data outputted sequentially from the GCC extracting part  222   c.  Thereafter, the outputting part  223  outputs to the writing part  32  of the transmission device  30  this single datum as information indicating that the communication condition of the lane L 1  is normal. 
     When at least a fixed fraction of the multi-frame numbers sent from the frame aligning part  222   a  is missing, or when frequency of output of data from the GCC extracting part  222   c  is less than or equal to a fixed value, the outputting part  223  can output to the writing part  32  information indicating that the communication condition of the lane L 1  is abnormal. 
     Also, for the data outputted from the frame aligning part  222   b  and the GCC extracting part  222   d,  the outputting part  223  outputs to the writing part  32  information indicating the communication condition of the lane L 2 . 
     A normal communication condition for the respective lane L 1  or L 2  means that the baud rate is greater than or equal to a fixed rate and the bit error rate is less than or equal to a fixed value. Moreover, abnormal communication conditions for the respective lane L 1  or L 2 , in addition to a conditions in which communication is disrupted, include conditions in which the baud rate is extremely low, and conditions in which the bit error rate is extremely high. For example, when degradation only occurs in the semiconductor laser used for generating the optical signal of the lane L 2 , or When wavelength error of the optical signal for only the same semiconductor laser becomes large due to unsuitable control of the temperature, then an abnormal communication condition is considered to occur only for lane L 2 . 
     The deskewing part  224  reproduces a single OTU signal from the two lane signals and then sends the reproduced signal to the OTN-LSI  23  through the SFI-TX  225 . 
     The OTN-LSI  23  has a GCC extracting part  23   a.  The GCC extracting part  23   a,  in the same manner as the GCC extracting parts  222   c  and  222   d,  extracts data included in the GCC region of the overhead of the OTU frame. However, the GCC extracting part  23   a  extracts data from the reproduced OTU signal rather than from the lane signal. 
     The transmission device  30  generates two lane signals from the client signal and sends the generated lane signals through the lanes L 1  and L 2  to the opposite device  50 . The transmission device  30  has a generating part  31  for generating the OTU frame from the client signal, a writing part  32  for writing data to the overhead of the OTU frame, a partitioning part  33  for partitioning the OTU frame into the two lane signals, and a transmitting part  34  for transmitting the lane signals to the opposite device  50 . 
     Based on information outputted from the outputting part  223 , the writing part  32  writes data for determination of the communication conditions of the lanes L 1  and L 2  to the GCC region of the overhead of the OTU frame generated by the generating part  31 . Furthermore, the writing part  32  according to the present embodiment in principle writes data fixing all bit values at zero. 
     The partitioning part  33  partitions the OTU frame, to which data is written by the writing part  32 , into a plurality of lane signals. The partitioning part  33 , for example, performs partitioning by round robin for each block of 16 bytes forming the OTU frame, as specified in ITU-T Recommendation G.709. However, in order to partition the OTU frame into the two lane signals, the partitioning part  33  according to the present embodiment allocates the OTU frame-forming 16 byte blocks alternatingly between the lane L 1  and the lane L 2 . The odd multi-frame numbers are allocated to one of the lane L 1  and L 2 , and the even multi-frame numbers are allocated to the other lane. 
     The transmitting part  34  sends each of the lane signals partitioned by the partitioning part  33  to the opposite device  50  through the respective lane L 1  or L 2 . 
     The opposite device  50  is a communication device that has a configuration similar to that of the optical transmission device  10 . That is to say, the opposite device  50  has a receiver configured in a manner similar to that of the reception device  20  and has a transmitter configured in a manner similar to that of the transmission device  30 . 
     The receiver of the opposite device  50  receives the lane signals transmitted from the transmission device  30  through the lanes L 1  and L 2 . Moreover, the receiver of the opposite device  50  extracts from the lane signals the data written by the writing part  32 . In the present embodiment, due to the writing of fixed data by the writing part  32 , the receiver of the opposite device  50  extracts the same data for any of lanes L 1  and L 2 . However, the ting part  32  can also write data such that the data extracted by the receiver of the opposite device  50  is individualized for each of the lanes L 1  and L 2 . 
     The transmitter of the opposite device  50  transmits the lane signals to the reception device  20  through the lanes L 1  and L 2 . Moreover, the data written to the overhead of the OTU frame by the transmitter of the opposite device  50  becomes extracted by the extracting unit  222 . 
     Next,  FIGS. 3 and 4  are used to explain an example of operation of an optical transmission system  100  when there is a change, from a normal communication condition for both of the lanes L 1  and L 2 , to an abnormal communication condition for only the lane L 2 . 
       FIG. 3 , indicating an OTU signal  60  and lane signals  71  and  72 , is a schematic example of a case in which a communication obstacle occurs in the lane L 2 . 
     As indicated in  FIG. 3 , the OTU signal  60  carries OTU frames  61 ,  62 ,  63 ,  64  and the like. The OTU frames  61 ,  62 ,  63  and  64  include respective GCC regions  61   g ,  62   g,    63   g  and  64   g.  Furthermore, the OTU signal  60 , for example, is an OTU4 signal having a baud rate of approximately 100 Gbit/s. 
     When the OTU frames  61  to  64  are partitioned by round robin, the OTU frame  61  is divided into the data  61   a  and  61   b,  the OTU frame  62  is divided into the data  62   a  and  62   b,  the OTU frame  63  is divided into the data  63   a  and  63   b,  and the OTU frame  64  is divided into the data  64   a  and  64   b.    
     Thereafter when the OTU signal  60  is sent through the two lanes L 1  and L 2 , the lane signal  71 , which includes data such as data  61   a,    62   a,    63   a  and  64   a,  is transmitted through the lane L 1 ; and the lane signal  72 , which includes data such as data  61   b ,  62   b ,  63   b  and  64   b,  is transmitted through the lane L 2 . By this configuration, each of the lane signals  71  and  72  is transmitted under conditions in which the symbol rate is more controlled than for the OTU signal  60 . 
     Then when a transmission fault occurs in lane L 2 , the lane signal  72  is lost. In a state in which the lane signal  72  is disrupted, the reception device  20  receives only the lane signal  71 . Then when the reception device  20  attempts to combine the lane signals  71  and  72  into a single OTU signal  60 , although the data  61   a,    62   a,    63   a  and  64   a  are reproduced normally, the data  61   b,    62   b,    63   b  and  64   b  are not reproduced normally, that is, are abnormal. 
     Thus even though the reception device  20  attempts reproduction of the OTU signal  60 , due to loss of the lane signal  72 , alignment of the OTU frames  61  to  64  is not possible. Thus the reception device  20  is unable to reproduce the OTU frames  61 - 64 . That is to say, even though no fault occurs in the lane L 1 , the OM signal  60  is disrupted due to loss of the lane signal  72 . 
       FIG. 4  shows the multi-frame numbers included in the lane signals and the multi-frame numbers acquired by the outputting part  223 , comparing the case in which the communication condition is normal for both lanes L 1  and L 2 , versus the case in which a communication obstacle occurs in the lane L 2 . Furthermore, the multi-frame number group  81  indicates the case in which the communication condition is normal for both lanes L 1  and L 2 , and the multi-frame number group  82  indicates the case in which the communication obstacle occurs in the lane L 2 . 
     Moreover, the multi-frame numbers in  FIG. 4  are indicated by the numbers shown following “MF”. That is to say, “MF0” indicates that the multi-frame number is 0, and “MF1” indicates that the multi-frame number is 1. The even multi-frame numbers are included in the lane signal transmitted through the lane L 1 . Moreover, the odd multi-frame numbers are included in the lane signal transmitted through the lane L 2 . 
     As shown in  FIG. 4 , when the communication condition is normal for both lanes L 1  and L 2 , all the multi-frame numbers, that is, 0, 1, 2 and the like, are present together without omission. Thus the GCC extracting part  23   a  of the OTN-LSI  23  can extract data from the reproduced OTU frame. Moreover, the outputting part  223  outputs information indicating that the communication condition is normal for both lanes L 1  and L 2 . 
     On the other hand, when the communication condition of the lane L 2  becomes abnormal, the odd multi-frame numbers become missing. In this case, the OTU frame is not reproduced, and thus the GCC extracting part  23   a  is unable to extract data. However, the outputting part  223  is able to acquire the even multi-frame numbers included in the lane signal that is transmitted through the lane L 1 . Thus the outputting part  223  outputs information indicating that the communication condition of the lane L 1  is normal and information indicating that the communication condition of the lane L 2  is abnormal. 
     When information is outputted by the outputting part  223  indicating that the communication condition of the lane L 2  is abnormal, the writing part  32 , among the data written to the overhead of the OTU frame, stops the writing of data included in the lane signal sent through the lane L 2 . Specifically, when the even-numbered (odd-numbered) blocks among every 16 byte block forming the OTU frame are transmitted through the lane L 2 , the writing part  32 , among the data written to the overhead of the OTU frame, stops the writing of data to the even-numbered (odd-numbered) blocks. Useless transmission of data can be prevented by this means. 
     Moreover, when information is outputted by the outputting part  223  that indicates that the communication condition of the lane L 2  is abnormal, the writing part  32  writes data indicating that the communication condition of the lane L 2  is abnormal. By this means, the writing part  32  notifies the opposite device  50  through the lane L 1  that the communication condition of the lane L 2  is abnormal. 
     Moreover, when the communication condition of the lane L 2  becomes abnormal, the opposite device  50  is considered to notify the reception device  20  that the communication condition of the lane L 2  is abnormal. In this case, the outputting part  223  determines that the communication condition of the lane L 2 , for which notification is received from the opposite device  50 , is abnormal based on the data extracted by the extracting unit  222 . Thereafter, by the output of the specific information, the outputting part  22  stops the writing by the writing part  32  of data that is included in the lane signal transmitted through the lane L 2 . Thus the useless transmission of data can be prevented. 
     In the above-explained manner, the outputting part  223  according to the present embodiment outputs information indicating the communication condition of each of the lanes L 1  and L 2 . By this means, even when a communication obstacle occurs in lane L 1  or L 2 , monitoring becomes possible of the respective communication conditions of the lanes L 1  and L 2 . Thus resistance to obstacles to optical communication through the lanes L 1  and L 2  can be improved. 
     Moreover, the writing part  32  writes the specific data to the overhead of the OTU frame based on the information outputted from the outputting part  223 . Due to the writing part  32  using data included in the lane signal transmitted through one of the lanes L 1  and L 2 , even when a communication obstacle occurs in the other lane of the lanes L 1  and L 2 , communication is possible between the optical transmission device  10  and the opposite device  50  by the use of the control monitoring data. By this means, when at least a single lane conducts signals, a robust in-band control monitoring channel is realized that becomes capable of communication. 
     In a general optical communication network, data for HDLC (High-level Data Link Control) or data formatted according to a user-specified format is often stored in the GCC region. In order to realize a network for communication at a baud rate in excess of 100 Gbit/s, such as at 150 Gbit/s, 200 Gbit/s and 400 Gbit/s, means are used such as partitioning the signal into multiple lanes in the communication path, and arranging multiple line/client cards constituting the communication device. Thus the GCC regions included in the overhead of the OTU frame are also partitioned and then transmitted. The application of the optical transmission system  100  of the present embodiment to this type of general optical communication network is thought o improve resistance to obstacles and to be advantageous. 
     Moreover,  FIG. 5  is a schematic diagram indicating an optical communication network  90  that communicates through an undersea cable. In this optical communication network  90 , the number of FEC errors included in the data received from the transponder  91  is stored in the GCC region (RES region), and the transponder  92  transmits the data including this GCC region to the transponder  91 . That is to say, the GCC region is used for checking the quality of transmission, that is, opposing performance, at the remote location for the channel used for sending the signal of the transponder  91  itself. During on-site adjustment of the transponder  91 , optimization is performed based on a Q value determined from the number of FEC errors. 
     However, when communication in a subcarrier unit of the main signal is lost, the condition of the other subcarriers also becomes unclear, and confirmation itself of quality of the signal transmission channel of the transponder  91  is thought to become difficult. The dashed line arrow in  FIG. 5  indicates a disrupted main signal, that is, lane signal. 
     if the optical transmission system  100  of the present embodiment is used in this optical communication network  90 , even if communication in a subcarrier unit of the main signal is lost, self-confirmation of quality of the transmission channel of the transponder  91  becomes possible. 
       FIG. 6  shows schematically a general media converter system  95 . According to this media converter system  95 , the carrier device is arranged directly in an end user building  96  as a media converter  97 . in this form of service, due to the lack of an out-of-band OAM channel, performance of control and monitoring of the media converter  97  often depends on an in-band channel. According to this type of media converter system  95 , even when the main signal data is disrupted, communication for control and monitoring of the media converter  97  preferably can be continued as much as possible. Furthermore, the dashed line double arrow in  FIG. 6  indicates a disrupted main signal, that is, lane signal. 
     If the optical transmission system  100  according to the present embodiment is used for this media converter system  95 , even when the main signal data is disrupted, control and monitoring of the media converter  97  can be continued as much as possible. 
     Although embodiments of the present disclosure are explained above, the present disclosure is not limited to the aforementioned embodiments. 
     For example, the number of lanes is not limited to 2, and there may be 3 or more lanes. Moreover, although the lanes L 1  and L 2  in the aforementioned embodiments correspond to sub-carriers, these lanes can correspond to polarized waves or multi-valued phases of an Ich and Qch. 
     The foregoing describes some example embodiments for explanatory purposes. Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined only by the included claims, along with the full range of equivalents to which such claims are entitled. 
     INDUSTRIAL APPLICABILITY 
     The reception device, transmission device, optical transmission device, optical transmission system and monitoring method of the present disclosure are suitable for highly fault-resistant optical communication. 
     REFERENCE SIGNS LIST 
       100  Optical transmission system 
       10  Optical transmission device 
       20  Reception device 
       21  Receiving unit 
       21   a,    21   b  DSP-LSI 
       22  Terminal processing device 
       221   a ,  221   b  SFI-RX 
       222  Extracting 
       222   a,    222   b  Frame aligning part 
       222   c,    222   d  GCC extracting part 
       223  Outputting part 
       224  Deskewing part 
       225  SFI-TX 
       23  OTN-LSI 
       23   a  GCC extracting part 
       30  Transmission device 
       31  Generating part 
       32  Writing part 
       33  Partitioning part 
       34  Transmitting part 
       50  Opposite device 
       60  OTU signal 
       61 ,  62 ,  63 ,  64  OTU frame 
       61   a,    61   b,    62   a,    62   b,    63   a,    63   b,    64   a,    64   b  Data 
       61   g,    62   g,    63   g,    64   g  GCC region 
       71 ,  72  Lane signal 
       81 ,  82  Multi-frame number group 
       90  Optical communication network 
       91 ,  92  Transponder 
       95  Media converter system 
       96  End user building 
       97  Media converter 
     L 1 , L 2  Lane