Patent Publication Number: US-2023156382-A1

Title: Communication system

Description:
TECHNICAL FIELD 
     The present invention relates to a communication system technology. 
     BACKGROUND ART 
     In a service for providing optical access, economical servicing is realized by using a passive optical network (PON) in which a terminal office apparatus and a plurality of terminal apparatuses are connected (refer to NPL 1, for example). The PON is a point-to-multipoint network in which a central office provides services to a large number of subscribers. For example, in the PON, a downstream optical signal from a central office is branched by an optical coupler connected to one trunk line fiber, and is distributed to a plurality of subscribers. In the PON, an ONU (Optical Network Unit) on a downstream side and an OLT (Optical Line Terminal) on a host side are used. 
     Citation List 
     Non Patent Literature 
     [NPL 1] “Technology Basic Course GE-OPON Technology”, [online], NTT GIJUTU Journal, 2005.8 pp.71-74, [Retrieved on Feb. 28, 2020], Internet “https://www.ntt.co.jp/journal/0508/files/jn200508071.pdf” 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     However, there is a problem in that, in a known PON, it is difficult to maintain communication when a problem such as a facility failure occurs. 
     The present invention has been made in view of the problem described above, and an object of the present invention is to provide a technique for improving the likelihood of maintaining communication even in a case where a problem occurs in the PON. 
     Means for Solving the Problem 
     One aspect of the present invention is a communication system for a passive optical network that includes; an OLT (Optical Line Terminal): a first splitter configured to output an optical signal that is output from the OLT, to optical communication channels from a first port and a second port; a plurality of second splitters that are connected between the first port and second port of the first splitter using optical communication channels; and ONUs (Optical Network Units) that are connected to the respective second splitters using optical communication channels. 
     Effects of the Invention 
     According to the present invention, even if a problem occurs in the PON, the likelihood of maintaining communication can be increased. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram illustrating an exemplary system configuration of a communication system  100  of the present invention. 
         FIG.  2    is a diagram illustrating an exemplary configuration of an OLT  20  and a first splitter  21 . 
         FIG.  3    is a diagram illustrating an exemplary configuration of a second splitter  30  and an ONU  40 . 
         FIG.  4    is a diagram illustrating a specific example of operations of the communication system  100  at a time of normal communication. 
         FIG.  5    is a diagram illustrating a specific example of operations of the communication system  100  at a time of troubled communication. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present invention will be described in detail with reference to the drawings. 
       FIG.  1    is a diagram illustrating an exemplary system configuration of a communication system  100  of the present invention. The communication system  100  includes a host apparatus  10 , an OLT  20 , a first splitter  21 , a plurality of second splitters  30 , a plurality of ONUs  40 , subordinate apparatuses  50  and user apparatuses  60 . The host apparatus  10  is connected to a host network of the communication system  100 . The first splitter  21  and the plurality of second splitters  30  are connected to a communication channel (hereinafter, referred to as a “trunk communication channel”) that is formed in a ring shape. In  FIG.  1   , three second splitters  30  and three ONUs  40  are illustrated, but the number “three” is merely a specific example. That is, the number of the second splitters  30  and the ONUs  40  need only be two or more. 
     The OLT  20  is installed so as to be able to communicate with the host apparatus  10 . The OLT  20  functions as an OLT in the PON. The first splitter  21  receives an input of an optical signal from the OLT  20 , and outputs the optical signal to the trunk communication channel through a plurality of paths. The first splitter  21  receives inputs of optical signals from the trunk communication channel through the plurality of paths, puts together the optical signals, and outputs the resultant signal to the OLT  20 . The second splitters  30  each receive an input of an optical signal, and output the optical signal to a plurality of paths. The second splitters  30  are each configured using an optical splitter with two inputs and two outputs, for example. 
     The ONUs  40  are communicably connected to respective subordinate apparatuses  50 . Each subordinate apparatus  50  is communicably connected to one or more user apparatuses  60 . In the following, each apparatus will be described in detail. Note that, for the sake of description, the host apparatus  10 , the subordinate apparatuses  50 , and the user apparatuses  60  will be described prior to the description of the OLT  20 , the first splitter  21 , the second splitters  30 , and the ONUs  40 . 
     The host apparatus  10  is communicably connected to a plurality of subordinate apparatuses  50  via the OLT  20 , the first splitter  21 , the second splitters  30  and the ONUs  40 . The host apparatus  10  is an apparatus that realizes a predetermined function by performing communication with the plurality of subordinate apparatuses  50 . The host apparatus  10  is a base band unit (BBU) in a mobile network, for example. The host apparatus  10  may also be a communication device that constitutes a relay network, for example. 
     Each subordinate apparatus  50  is an apparatus that realizes a predetermined function by performing communication with the host apparatus  10 . The subordinate apparatus  50  is an apparatus that is installed at a position closer to a user side than the host apparatus  10  is. For example, when the host apparatus  10  is a BBU, the subordinate apparatus  50  is a remote radio head (RRH) in a mobile network. In this case, the communication channel between the subordinate apparatus  50  and the corresponding user apparatus  60  is an access section of the mobile network. On the other hand, when the host apparatus  10  is a communication device that constitutes a relay network, the subordinate apparatus  50  may also be an apparatus such as a set-top box. In this case, the communication channel between the subordinate apparatus  50  and the corresponding user apparatus  60  may also be a network such as a home network. The subordinate apparatus  50  houses one or more user apparatuses  60 , for example. Note that the configuration may also be such that the user apparatus  60  is connected to an ONU  40  without the subordinate apparatus  50  mediating communication. 
     Each user apparatus  60  is an apparatus that is communicably connected to other apparatuses as a result of being connected to a subordinate apparatus  50  via a communication channel. The user apparatus  60  is an information processing apparatus such as a smartphone, a tablet, or a personal computer, for example. The user apparatus  60  may also be a sensor in IoT (Internet of Things), for example. The user apparatus  60  may also be an apparatus for business use such as an ATM (Automatic Teller Machine), a vending machine, or a POS (Point Of Sale) terminal, for example. 
     Next, the OLT  20  and the first splitter  21  will be described.  FIG.  2    is a diagram illustrating an exemplary configuration of the OLT  20  and the first splitter  21 . The OLT  20  includes an optical interface  201  and a signal processing unit  202 . The OLT  20  is an apparatus that provides an OLT function in a known PON. 
     The optical interface  201  outputs an optical signal generated by the signal processing unit  202  to the first splitter  21 . The optical interface  201  transmits the optical signal to the ONUs  40  via the first splitter  21  and the second splitters  30 . On the optical signal transmitted by the optical interface  201 , optical signals addressed to a plurality of ONUs  40  may also be superimposed. 
     The optical interface  201  receives an optical signal from the first splitter  21 , and outputs the received optical signal to the signal processing unit  202 . The optical interface  201  receives an optical signal from an ONU  40  via a second splitter  30  and the first splitter  21 . On the optical signal received by the optical interface  201 , optical signals transmitted from a plurality of ONUs  40  may also be superimposed. 
     The signal processing unit  202  functions as a known OLT. In the following, an example of processing to be performed by such a signal processing unit  202  will be described. The signal processing unit  202  converts an electric signal transmitted from the host apparatus  10  to a subordinate apparatus  50  to an optical signal, and outputs the optical signal to the optical interface  201 . The signal processing unit  202  may also superimpose (multiplex) optical signals addressed to a plurality of subordinate apparatuses  50 . The signal processing unit  202  converts an optical signal received by the optical interface  201  to an electric signal, and outputs the electric signal to the host apparatus  10 , which is the destination. 
     The first splitter  21  is constituted by using an optical signal splitter. The first splitter  21  includes at least three ports ( 211 ,  212 , and  213 ). The first splitter  21  distributes and outputs an optical signal input from the OLT  20  via the port  211  to a plurality of ports (ports  212  and port  213 ) connected to the trunk communication channel. The ratio of distribution of the optical signal between the port  212  and the port  213  may be an equal ratio (50:50), or may also be an unequal ratio (i.e., 40:60). The first splitter  21  puts together a plurality of optical signals that are input from the trunk communication channel via the ports  212  and  213 , and outputs the resultant signal to the port  211  connected to the OLT  20 . 
       FIG.  3    is a diagram illustrating an exemplary configuration of each second splitter  30  and ONU  40 . The second splitter  30  is constituted by using an optical signal second splitter with two inputs and two outputs. The second splitter  30  distributes and outputs an optical signal input from the trunk communication channel to a downstream apparatus and the ONU  40  connected to the second splitter  30 . The ratio of distribution, here, may be an equal ratio (50:50), or may also be an unequal ratio (i.e., 40:60). 
     The downstream apparatus is an apparatus, out of two apparatuses connected to one second splitter  30  via the trunk communication channel, that is different from the apparatus that outputs an optical signal to be input to the one second splitter  30 . For example, in  FIG.  1   , when a second splitter  30 - 1  is taken as a reference, in the case where an optical signal input from the first splitter  21  is to be distributed, the downstream apparatus is a second splitter  30 - 2 . For example, in  FIG.  1   , when the second splitter  30 - 2  is taken as a reference, in the case where an optical signal input from the second splitter  30 - 1  is to be distributed, the downstream apparatus is a second splitter  30 - 3 . For example, in  FIG.  1   , when the second splitter  30 - 2  is taken as a reference, in the case where an optical signal input from the second splitter  30 - 3  is to be distributed, the downstream apparatus is the second splitter  30 - 1 . 
     Also, each second splitter  30  outputs an optical signal to be output to the ONU  40  connected to the second splitter  30 , to the ONU  40  through a communication channel that differs depending on the port to which the optical signal has been input. For example, the second splitter  30  outputs an optical signal input through an upper left port in  FIG.  3    to an upper right port and a lower right port. Therefore, when the second splitter  30 - 1  in  FIG.  1    is described as an example, an optical signal input from the first splitter  21  is output to a path  91 - 2  and the second splitter  30 - 2 . The optical signal output to the path  91 - 2  is input to an ONU  40 - 1 . Also, the second splitter  30  outputs an optical signal input through an upper right port in  FIG.  3    to an upper left port and a lower left port, for example. Therefore, when the second splitter  30 - 1  in  FIG.  1    is described as an example, an optical signal input from the second splitter  30 - 2  is output to a path  91 - 1  and the first splitter  21 . The optical signal output to the path  91 - 1  is input to the ONU  40 - 1 . Note that the path  91 - 1  and the path  91 - 2  are connected to different optical meters. For example, the path  91 - 1  is connected to a first optical meter  41 , and the path  91 - 2  is connected to a second optical meter  42 . 
     Each ONU  40  includes a first optical meter  41 , a second optical meter  42 , an optical switch  43 , a control unit  44 , a signal processing unit  45 , and a communication unit  46 . The first optical meter  41  receives an optical signal output from the connected second splitter  30 . The first optical meter  41  outputs information indicating the light intensity of the received optical signal to the control unit  44 . The first optical meter  41  outputs the received optical signal to the optical switch  43 . The second optical meter  42  receives an optical signal output from the second splitter  30 . The second optical meter  42  outputs information indicating the light intensity of the received optical signal to the control unit  44 . The second optical meter  42  outputs the received optical signal to the optical switch  43 . 
     The optical switch  43  outputs one of the optical signal output from the first optical meter  41  and the optical signal output from the second optical meter  42  to the signal processing unit  45 , in accordance with the control of the control unit  44 . The optical switch  43  outputs the optical signal output from the signal processing unit  45  to the second splitter  30  via one of the first optical meter  41  and the second optical meter  42 , in accordance with the control of the control unit  44 . 
     The control unit  44  receives light intensity information from each of the first optical meter  41  and the second optical meter  42 , and selects one of them in accordance with a predetermined criteria. The control unit  44  controls the optical switch  43  such that the selected optical signal is output to the signal processing unit  45 . The predetermined criteria for selection is higher reliability, for example. The level of reliability may be determined based on the light intensity of the optical signal. For example, the control unit  44  may select an optical signal with higher light intensity. 
     A portion or the entirety of the operations of the control unit  44  may be realized using hardware including an electronic circuit in which an LSI (Large Scale Integration circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), an FPGA (Field Programmable Gate Array), or the like is used. 
     The signal processing unit  45  functions as an ONU in a known PON. In the following, an example of the processing of this signal processing unit  45  will be described. The signal processing unit  45  converts an optical signal indicating a signal transmitted from the host apparatus  10  to the connected subordinate apparatus  50 , to an electric signal, and outputs the electric signal to the communication unit  46 . Here, if optical signals addressed to a plurality of subordinate apparatuses  50  are superimposed (multiplexed), the signal processing unit  45  takes out an optical signal addressed to the subordinate apparatus  50  connected to the ONU  40  of the signal processing unit  45 , and converts the taken out optical signal to an electric signal. The signal processing unit  45  converts an electric signal received by the communication unit  46  to an optical signal, and outputs the optical signal to the optical switch  43 . 
     The communication unit  46  is a communication interface for communication with the subordinate apparatus  50 . 
       FIG.  4    is a diagram illustrating a specific example of operations of the communication system  100  at a time of normal communication. The arrows shown in  FIG.  4    indicate the flow of a downstream signal (signal flowing from the host apparatus  10  to a subordinate apparatus  50 ). As shown in  FIG.  4   , in the communication system  100 , as a result of arranging the first splitter  21  between the OLT  20  and the trunk communication channel, the downstream signal can be transmitted through both of a clockwise path and a counterclockwise path. 
     In the example in  FIG.  4   , a problem does not occur in the communication system  100 , in particular. Therefore, the downstream signals obtained by branching made by the first splitter  21  reach the first splitter  21  through all of the second splitters  30 . As a result, an optical signal transmitted through the trunk communication channel in a clockwise direction, and an optical signal transmitted through the trunk communication channel in a counterclockwise direction reach each of the ONUs  40 . Each ONU  40  selects one of the optical signals in accordance with a predetermined criteria (e.g., higher light intensity), and uses the selected optical signal for processing. 
       FIG.  5    is a diagram illustrating a specific example of operations of the communication system  100  at a time of troubled communication. In  FIG.  5   , the communication channel shown by a broken line, out of the two communication channels extending from a second splitter  30  to the connected ONUs  40 , indicates a communication channel through which the optical signal (downstream signal) transmitted from the OLT  20  does not pass. The communication channels shown by solid lines with arrows indicate communication channels through which the optical signal (downstream signal) transmitted from the OLT  20  passes. 
     In the example in  FIG.  5   , a problem occurs in a communication channel between the second splitter  30 - 2  and the second splitter  30 - 3 . Therefore, a downstream signal output from the second splitter  30 - 2  does not reach the second splitter  30 - 3 . Similarly, a downstream signal output from the second splitter  30 - 3  does not reach the second splitter  30 - 2 . 
     The second splitter  30 - 2  cannot receive an optical signal transmitted in the clockwise direction due to the occurrence of a problem, but can receive an optical signal transmitted in the counterclockwise direction. An ONU  40 - 2  receives the optical signal transmitted in the counterclockwise direction via the second splitter  30 - 2 . 
     The second splitter  30 - 3  cannot receive an optical signal transmitted in the counterclockwise direction due to the occurrence of the problem, but can receive an optical signal transmitted in the clockwise direction. An ONU  40 - 3  receives the optical signal transmitted in the clockwise direction via the second splitter  30 - 3 . 
     As a result of the operations described above, all of the ONUs (ONU  40 - 1 , ONU  40 - 2 , and ONU  40 - 3 ) can receive the downstream signal from the OLT  20  and can maintain communication, regardless of the occurrence of a problem. 
     The flow of a downstream signal has been described. An upstream signal is transmitted to the OLT  20  from each ONU  40  as a result of a signal flowing through solid line paths in the drawings described above in a direction opposite to the arrow direction. Also, in  FIGS.  4  and  5   , the arrows between the second splitters  30  and the connected ONUs  40  each indicate single direction, and these arrows indicate the flow direction of a downstream signal. In the case of an upstream signal, the signal is transmitted using the paths selected by the optical switches  43 . 
     In the communication system  100  configured as described above, an optical signal output from the OLT  20  is distributed to a plurality of paths by the first splitter  21 , and transmits through the trunk communication channel. For example, the downstream signal is transmitted through two paths, namely a clockwise path and a counterclockwise path. As a result, even if a problem occurs in a communication channel or the like, the likelihood that the ONUs  40  can each receive an optical signal from one of the paths increases. Therefore, even if a problem occurs in the PON, the likelihood of being able to maintain communication can be increased. 
     Although an embodiment of the present invention have been described with reference to the drawings, the specific configuration is not limited to the embodiment, and designs or the like that do not depart from the gist of the invention are intended to be within the scope of the invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to a system for performing communication using the PON.  
     
       
         
           
               
               
               
             
               
                 Reference Signs List 
               
             
            
               
                 
                   100 
                 
                 Communication system 
               
               
                 
                   10 
                 
                 Host apparatus 
               
               
                 
                   20 
                 
                 OLT 
               
               
                 
                   21 
                 
                 First splitter 
               
               
                 
                   30 
                 
                 Second splitter 
               
               
                 
                   40 
                 
                 ONU 
               
               
                 
                   50 
                 
                 Subordinate apparatus 
               
               
                 
                   60 
                 
                 User apparatus 
               
               
                 
                   201 
                 
                 Optical interface 
               
               
                 
                   202 
                 
                 Signal processing unit 
               
               
                   211  to  213 
 
                 Port 
               
               
                 
                   41 
                 
                 First optical meter 
               
               
                 
                   42 
                 
                 Second optical meter 
               
               
                 
                   43 
                 
                 Optical switch 
               
               
                 
                   44 
                 
                 Control unit 
               
               
                 
                   45 
                 
                 Signal processing unit 
               
               
                 
                   46 
                 
                 Communication unit