Patent Publication Number: US-2023133100-A1

Title: Communication system and onu system

Description:
TECHNICAL FIELD 
     The present invention relates to a communication system technology and an ONU 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 p.71 to 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 system including a first OLT (Optical Line Terminal), a second OLT, and an OLT control apparatus that controls the first OLT and the second OLT; a plurality of splitters that are connected between the first OLT and the second OLT using optical communication channels; and ONU systems that are connected to the respective splitters using optical communication channels, and each include a first session establishing unit that establishes a session with the first OLT, a second session establishing unit that establishes a session with the second OLT, and a signal processing unit that executes signal processing of an ONU (Optical Network Unit) based on an optical signal output from the first session establishing unit or the second session establishing unit. 
     One aspect of the present invention is an ONU system that includes: a first session establishing unit that is connected to an OLT system including a first OLT (Optical Line Terminal), a second OLT, and an OLT control apparatus that controls the first OLT and the second OLT, via a splitter using optical communication channels, and is configured to establish a session with the first OLT; a second session establishing unit that is connected to the OLT system via the splitter using optical communication channels, and is configured to establish a session with the second OLT; and a signal processing unit configured to execute signal processing of an ONU (Optical Network Unit) based on an optical signal output from the first session establishing unit or the second session establishing unit. 
     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 system  20 . 
         FIG.  3    is a diagram illustrating a first exemplary configuration of a splitter  30  and an ONU system  40 . 
         FIG.  4    is a diagram illustrating a second exemplary configuration of the splitter  30  and the ONU system  40 . 
         FIG.  5    is a diagram illustrating a specific example of operations of the communication system  100  at a time of normal communication. 
         FIG.  6    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 system  20 , a plurality of splitters  30 , a plurality of ONU systems  40 , subordinate apparatuses  50 , and user apparatuses  60 . The host apparatus  10  is connected to a host network of the communication system  100 . In  FIG.  1   , three splitters  30  and three ONU systems  40  are illustrated, but the number “three” is merely a specific example. That is, the number of the splitters  30  and the ONU systems  40  need only be two or more. 
     The OLT system  20  is installed so as to be able to communicate with the host apparatus  10 . The OLT system  20  functions as an OLT in the PON. The splitters  30  each receive an input of an optical signal, and output the optical signal to a plurality of paths. The splitters  30  are each configured using an optical splitter with two inputs and two outputs, for example. 
     The ONU systems  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 system  20 , the splitters  30 , and the ONU systems  40 . 
     The host apparatus  10  is communicably connected to a plurality of subordinate apparatuses  50  via the OLT system  20 , the splitters  30  and the ONU systems  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 system  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 system  20  will be described.  FIG.  2    is a diagram illustrating an exemplary configuration of the OLT system  20 . The OLT system  20  includes a first OLT  21 , a second OLT  22 , and an OLT control apparatus  23 . The first OLT  21  and the second OLT  22  are each an apparatus that provides an OLT function in a known PON. That is, the OLT system  20  includes at least two apparatuses that provide an OLT function. The first OLT  21  and the second OLT  22  may be configured as independent apparatuses that have separate casings, or may be configured as a board or a chip. In any cases, the first OLT  21  and the second OLT  22  may also be configured as software. The basic configurations of the first OLT  21  and the second OLT  22  are the same, therefore in the following, the first OLT  21  will be described as a representative apparatus. 
     The first OLT  21  includes an optical interface  211  and a signal processing unit  212 . The optical interface  211  outputs an optical signal generated by the signal processing unit  212  to a communication channel. The optical interface  211  transmits an optical signal to the ONU systems  40  via the splitters  30 . Optical signals addressed to a plurality of ONU systems  40  may be superimposed on the optical signal transmitted from the optical interface  211 . Also, the optical interface  211  receives an optical signal from the communication channel, and outputs the received optical signal to the signal processing unit  212 . The optical interface  211  receives optical signals from the ONU systems  40  via the splitters  30 . Optical signals transmitted from a plurality of ONU systems  40  may be superimposed on the optical signal received by the optical interface  211 . 
     The signal processing unit  212  functions as a known OLT. In the following, an example of processing to be performed by this signal processing unit  212  will be described. The signal processing unit  212  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  211 . The signal processing unit  212  may also superimpose (multiplex) optical signals addressed to a plurality of subordinate apparatuses  50 . The signal processing unit  212  converts an optical signal received by the optical interface  211  to an electric signal, and outputs the electric signal to the host apparatus  10 , which is the destination, via the OLT control apparatus  23 . 
     The optical interface  211  and the signal processing unit  212  in the first OLT  21  respectively correspond to an optical interface  221  and a signal processing unit  222  in the second OLT  22 . 
     The OLT control apparatus  23  includes a signal distributing unit  231  and a signal concentrating unit  232 . The signal distributing unit  231  outputs downstream signals (signals transmitted to ONU systems  40 ) output from the host apparatus  10  to both of the first OLT  21  and second OLT  22 . The signal concentrating unit  232  outputs upstream signals (signals received from ONU systems  40 ) that are output from both of the first OLT  21  and second OLT  22  to the host apparatus  10 . 
       FIG.  3    is a diagram illustrating a first exemplary configuration of each splitter  30  and ONU system  40 . The splitter  30  is constituted by using an optical signal splitter with two inputs and two outputs. The splitter  30  distributes and outputs an optical signal input from a communication channel (hereinafter, referred to as a “trunk communication channel”) that connects the OLT system  20  and the splitters  30 , and is formed in a ring shape, to a downstream apparatus and the ONU system  40  connected to the 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 splitter  30  via the trunk communication channel, that is different from the apparatus that outputs an optical signal to be input to the one splitter  30 . For example, in  FIG.  1   , when a splitter  30 - 1  is taken as a reference, in the case where an optical signal input from the OLT system  20  is to be distributed, the downstream apparatus is a splitter  30 - 2 . For example, in  FIG.  1   , when the splitter  30 - 2  is taken as a reference, in the case where an optical signal input from the splitter  30 - 1  is to be distributed, the downstream apparatus is a splitter  30 - 3 . For example, in  FIG.  1   , when the splitter  30 - 2  is taken as a reference, in the case where an optical signal input from the splitter  30 - 3  is to be distributed, the downstream apparatus is the splitter  30 - 1 . 
     Also, each splitter  30  outputs an optical signal to be output to the ONU system  40  connected to the splitter  30 , to the ONU system  40  through a communication channel that differs depending on the port to which the optical signal has been input. For example, the 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 splitter  30 - 1  in  FIG.  1    is described as an example, an optical signal input from the first OLT  21  is output to a path  91 - 2  and the splitter  30 - 2 . The optical signal output to the path  91 - 2  is input to an ONU system  40 - 1 . Also, the 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 splitter  30 - 1  in  FIG.  1    is described as an example, an optical signal input from the splitter  30 - 2  is output to a path  91 - 1  and the first OLT  21 . The optical signal output to the path  91 - 1  is input to the ONU system  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 system  40  includes a first optical meter  41 , a second optical meter  42 , a first session establishing unit  43 , a second session establishing unit  44 , an optical switch  45 , a control unit  46 , a signal processing unit  47 , and a communication unit  48 . The first optical meter  41  receives an optical signal output from the connected splitter  30 . The first optical meter  41  outputs information indicating the light intensity of the received optical signal to the control unit  46 . The first optical meter  41  outputs the received optical signal to the first session establishing unit  43 . The second optical meter  42  receives an optical signal output from the splitter  30 . The second optical meter  42  outputs information indicating the light intensity of the received optical signal to the control unit  46 . The second optical meter  42  outputs the received optical signal to the second session establishing unit  44 . 
     The first session establishing unit  43  establishes a session with the OLT system  20 . Specifically, the first session establishing unit  43  establishes a session with the first OLT  21  of the OLT system  20 . The first session establishing unit  43  may include a PHY (physical interface) and MAC (Medium Access Control), for example. The first session establishing unit  43  outputs an optical signal received from the first OLT  21  to the optical switch  45 . 
     The second session establishing unit  44  establishes a session with the OLT system  20 . Specifically, the second session establishing unit  44  establishes a session with the second OLT  22  of the OLT system  20 . The second session establishing unit  44  may include a PHY (physical interface) and MAC (Medium Access Control), for example. The second session establishing unit  44  outputs an optical signal received from the second OLT  22  to the optical switch  45 . 
     The optical switch  45  outputs one of the optical signal output from the first session establishing unit  43  and the optical signal output from the second session establishing unit  44  to the signal processing unit  47 , in accordance with the control of the control unit  46 . The optical switch  45  outputs the optical signal output from the signal processing unit  47  to the splitter  30  via one of the first session establishing unit  43  and the second session establishing unit  44 , in accordance with the control of the control unit  46 . 
     The control unit  46  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 criterion. The control unit  46  controls the optical switch  45  such that the selected optical signal is output to the signal processing unit  47 . The predetermined criterion 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  46  may select an optical signal with higher light intensity. 
     The control unit  46  determines the OLT to which the ONU system  40  thereof belongs. The control unit  46  may determine the OLT (first OLT  21  or second OLT  22 ) to which the ONU system  40  thereof belongs, according to the selected optical meter (first optical meter  41  or second optical meter  42 ), for example. For example, when the first optical meter  41  is selected, it may be determined that the ONU system  40  belongs to the first OLT  21 . If the received optical signal includes transmission source information (information indicating the transmission source OLT), the control unit  46  may also determine the OLT to which the ONU system  40  thereof belongs based on the transmission source information. The control unit  46  notifies the OLT system  20  of information indicating the OLT to which the ONU system  40  thereof belongs. A portion or the entirety of the operations of the control unit  46  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  47  functions as an ONU in a known PON. In the following, an example of the processing of this signal processing unit  47  will be described. The signal processing unit  47  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  48 . Here, if optical signals addressed to a plurality of subordinate apparatuses  50  are superimposed (multiplexed), the signal processing unit  47  takes out an optical signal addressed to the subordinate apparatus  50  connected to the ONU system  40  of the signal processing unit  47 , and converts the taken out optical signal to an electric signal. The signal processing unit  47  converts an electric signal received by the communication unit  48  to an optical signal, and outputs the optical signal to the optical switch  45 . 
     The communication unit  48  is a communication interface for communication with the subordinate apparatus  50 . 
       FIG.  4    is a diagram illustrating a second exemplary configuration of each splitter  30  and ONU system  40 . In the following, the second exemplary configuration will be described focusing on the differences from the first exemplary configuration. The configuration of the splitter  30  is the same between the first exemplary configuration and the second exemplary configuration. Note that the path  91 - 1  and the path  91 - 2  are connected to different session establishing units, instead of the optical meters. For example, the path  91 - 1  is connected to the first session establishing unit  43 , and the path  91 - 2  is connected to the second session establishing unit  44 . 
     Each ONU system  40  includes a first session establishing unit  43 , a second session establishing unit  44 , an optical switch  45 , a control unit  46 , a signal processing unit  47 , and a communication unit  48 . Among these constituent elements, the configurations of the optical switch  45 , the signal processing unit  47 , and the communication unit  48  are similar to those of the first exemplary configuration. 
     The first session establishing unit  43  receives an optical signal output from the connected splitter  30 . The first session establishing unit  43  establishes a session with the OLT system  20 . Specifically, the first session establishing unit  43  establishes a session with the first OLT  21  of the OLT system  20 . The first session establishing unit  43  may include a PHY and MAC, for example. The first session establishing unit  43  outputs the optical signal received from the first OLT  21  to the optical switch  45 . 
     The first session establishing unit  43  acquires delay information regarding communication with the first OLT  21 , which is a communication partner apparatus, based on the optical signal received from the connected splitter  30 . The delay information is information indicating the length of delay that is occurring in the communication. The delay information may be acquired by an MPCP (Multi-Point Control Protocol) function in MAC, for example. The first session establishing unit  43  outputs the acquired delay information to the control unit  46 . 
     The second session establishing unit  44  receives an optical signal output from the connected splitter  30 . The second session establishing unit  44  establishes a session with the OLT system  20 . Specifically, the second session establishing unit  44  establishes a session with the second OLT  22  of the OLT system  20 . The second session establishing unit  44  may include a PHY and MAC, for example. The second session establishing unit  44  outputs the optical signal received from the second OLT  22  to the optical switch  45 . 
     The second session establishing unit  44  acquires delay information regarding communication with the second OLT  22 , which is a communication partner apparatus, based on the optical signal received from the connected splitter  30 . The second session establishing unit  44  outputs the acquired delay information to the control unit  46 . 
     The control unit  46  receives delay information from each of the first session establishing unit  43  and the second session establishing unit  44 , and selects one of the optical signals, in accordance with a predetermined criterion. The control unit  46  controls the optical switch  45  such that the selected optical signal is output to the signal processing unit  47 . The predetermined criterion for selection is higher reliability, for example. The level of reliability may be determined based on the length of delay time. For example, the control unit  46  may select an optical signal with shorter delay time. 
     The control unit  46  determines the OLT to which the ONU system  40  thereof belongs. The control unit  46  may determine the OLT (first OLT  21  or second OLT  22 ) to which the ONU system  40  thereof belongs, according to the selected session establishing unit, for example. For example, when the first session establishing unit  43  is selected, it may be determined that the ONU system  40  belongs to the first OLT  21 . If the received optical signal includes transmission source information (information indicating the transmission source OLT), the control unit  46  may also determine the OLT to which the ONU system  40  thereof belongs based on the transmission source information. The control unit  46  notifies the OLT system  20  of information indicating the OLT to which the ONU system  40  thereof belongs. A portion or the entirety of the operations of the control unit  46  may be realized using hardware including an electronic circuit in which an LSI, an ASIC, a PLD, an FPGA, or the like is used. 
       FIG.  5    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.  5    indicate the flow of a downstream signal (signal flowing from the host apparatus  10  to a subordinate apparatus  50 ). As shown in  FIG.  5   , in the communication system  100 , a downstream signal is transmitted from both of the first OLT  21  and the second OLT  22 . Therefore, the downstream signal can be transmitted through both of a clockwise path and a counterclockwise path. For example, the downstream signal transmitted from the first OLT  21  is transmitted through the clockwise path, and the downstream signal transmitted from the second OLT  22  is transmitted through the counterclockwise path. 
     In the example in  FIG.  4   , a problem does not occur in the communication system  100 , in particular. Therefore, the downstream signal transmitted from the first OLT  21  and the downstream signal transmitted from the second OLT  22  are both transmitted through all of the 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 ONU systems  40 . Each ONU system  40  selects one of the optical signals in accordance with a predetermined criteria (light intensity or delay information), and uses the selected optical signal for processing. 
       FIG.  6    is a diagram illustrating a specific example of operations of the communication system  100  at a time of troubled communication. In  FIG.  6   , the communication channel shown by a broken line, out of the two communication channels extending from a splitter  30  to the connected ONU systems  40 , indicates a communication channel through which the optical signal (downstream signal) transmitted from the OLT system  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 system  20  passes. 
     In the example in  FIG.  6   , a problem occurs in a communication channel between the splitter  30 - 2  and the splitter  30 - 3 . Therefore, a downstream signal output from the splitter  30 - 2  does not reach the splitter  30 - 3 . Similarly, a downstream signal output from the splitter  30 - 3  does not reach the splitter  30 - 2 . 
     The splitter  30 - 2  cannot receive an optical signal (downstream signal of first OLT  21 ) transmitted in the clockwise direction due to the occurrence of a problem, but can receive an optical signal (downstream signal of second OLT  22 ) transmitted in the counterclockwise direction. An ONU system  40 - 2  receives the optical signal transmitted in the counterclockwise direction via the splitter  30 - 2 . 
     The splitter  30 - 3  cannot receive an optical signal (downstream signal of second OLT  22 ) transmitted in the counterclockwise direction due to the occurrence of the problem, but can receive an optical signal (downstream signal of first OLT  21 ) transmitted in the clockwise direction. An ONU system  40 - 3  receives the optical signal transmitted in the clockwise direction via the splitter  30 - 3 . 
     If the belonging OLT (first OLT  21  or second OLT  22 ) before the occurrence of a problem is the same as the OLT with which communication is possible after the occurrence of the problem, each ONU system  40  continues the communication, as is. If the belonging OLT (first OLT  21  or second OLT  22 ) before the occurrence of a problem differs from the OLT with which communication is possible after the occurrence of the problem, each ONU system  40  performs switching of the optical switch  45  in accordance with the control of the control unit  46 . Note that a session has been established, in advance, with the OLT with which communication is performed after switching, by the session establishing unit (first session establishing unit  43  or second session establishing unit  44 ). Therefore, the time required for switching can be kept short. 
     As a result of the operations described above, all of the ONU systems (ONU system  40 - 1 , ONU system  40 - 2 , and ONU system  40 - 3 ) can receive the downstream signal from the OLT system  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 system  20  from each ONU system  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.  5  and  6   , the arrows between the splitters  30  and the connected ONU systems  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  45 . 
     In the communication system  100  configured as described above, the OLT system  20  is provided with a plurality of (e.g., two) OLT functions. Even if a problem occurs in a communication channel or the like, the likelihood that the ONU systems  40  can each receive an optical signal from one of the OLTs increases. Therefore, even if a problem occurs in the PON, the likelihood of being able to maintain communication can be increased. 
     Modifications 
     In the OLT system  20 , the OLT control apparatus may also be configured as a functional unit in one of or both of the first OLT  21  and the second OLT  22 . 
     In each ONU system  40 , the first optical meter  41 , the second optical meter  42 , the first session establishing unit  43 , the second session establishing unit  44 , the optical switch  45 , the control unit  46 , the signal processing unit  47 , and the communication unit  48  may be housed in one casing and configured as one apparatus, or housed in a plurality of casings and configured as separate apparatuses. 
     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 system 
           21  First OLT 
           22  Second OLT 
           23  OLT control apparatus 
           30  Splitter 
           40  ONU system 
           50  Subordinate apparatus 
           60  User apparatus 
           211  Optical interface 
           212  Signal processing unit 
           221  Optical interface 
           222  Signal processing unit 
           231  Signal distributing unit 
           232  Signal concentrating unit 
           41  First optical meter 
           42  Second optical meter 
           43  First session establishing unit 
           44  Second session establishing unit 
           45  Optical switch 
           46  Control unit 
           47  Signal processing unit 
           48  Communication unit