Station-side optical line termination device, method, and system

Abstract

One aspect of a station-side optical line termination device according to the present invention is used for an optical access network connected to a subscriber-side optical line termination device via at least, between an optical splitter and an optical switch, the optical splitter. The station-side optical line termination device includes a first optical subscriber line termination board, a second optical subscriber line termination board, and a control unit. The first optical subscriber line termination board is used at normal times and is connected to the optical splitter. The second optical subscriber line termination board is used as an alternative to the first optical subscriber line termination board and is connected to the optical switch. Upon detection of an abnormality of the first optical subscriber line termination board, the control unit determines whether or not switching is necessary on the basis of communication information related to the first optical subscriber line termination board and, only when the switching is necessary, controls the optical switch so as to connect the second optical subscriber line termination board to the optical splitter.

Description

Optical line terminal, method and system

[0001] One aspect of the present invention relates to an optical line terminal, a method, and a system.

[0002] As one type of optical access network, a passive optical network (PON) is known in which an optical line terminal (OLT) as a station-side optical line terminal and one or more optical network units (ONUs) as subscriber-side optical line terminals are connected via optical fibers and optical splitters.

[0003] 8 is a block diagram showing an example of a system using a PON. This system includes an OLT 10, an optical switch 20, an optical splitter 21, and an ONU 30. The OLT 10 includes an OSU 11, a redundant OSU 12, a switch 13, a switching status DB 14, and a control unit 15. Here, the OSU 11 is an optical subscriber unit (OSU) on the central office side. The redundant OSU 12 is a redundant OSU used as a substitute for the OSU 11. The switch 13 is, for example, a Layer 2 switch, and is connected to a network (not shown).

[0004] In this type of OLT 10, when the OSU 11 is operating normally, the OSU 11 connected to the switch 13 communicates with the ONU 30 via the optical fiber 40 and the optical splitter 21.

[0005] On the other hand, the OLT 10 may have a PON protection automatic switching (hereinafter referred to as automatic switching) function to continue communication services even when an abnormality occurs in the OSU 11. In this case, the control unit 15 of the OLT 10 performs automatic switching when a fault alarm from the OSU 11 is triggered. That is, when an abnormality occurs in the OSU 11, the OSU 11 issues a fault alarm indicating the abnormality. As shown in FIG. 9 , when the control unit 15 detects a fault alarm from the OSU 11 (step ST100), it controls the optical switch 20 to switch from the OSU 11 to the redundant OSU 12 (step ST200). At this time, the control unit 15, for example, connects the OLT-side port P0 and the ONU-side port P1 of the optical switch 20, changes the setting of the switch 13, shuts down the OSU 11 (from an emitting state to an emitting stop state), and starts up the redundant OSU 12 (from an emitting stop state to an emitting start state).

[0006] Thereafter, the control unit 15 updates the switching result in the switching status DB 14 (step ST300). As a result, in the OLT 10, the redundant OSU 12 connected to the switch 13 communicates with the ONU 30 via the optical fiber 40, the optical switch 20, and the optical splitter 21.

[0007] JP 2011-071951 A

[0008] The OLT 10 described above does not pose any particular problems, but according to the inventor's investigation, there are cases where communication continues between the OSU 11 and the ONU 30 even when an abnormality occurs in the OSU 11. In this case, the OLT 10 may cause communication interruptions or delays due to automatic switching of the OSU 11 during ongoing communication.

[0009] The present invention has been made in consideration of the above circumstances, and provides a technology that can prevent communication interruptions and delays that occur due to automatic switching of optical subscriber line termination panels when an abnormality occurs in the optical subscriber line termination panel.

[0010] In order to solve the above problems, one aspect of an optical line terminal according to the present invention is an optical line terminal in an optical access network. The optical access network is a network in which an optical line terminal is connected to a subscriber-side optical line terminal via at least the optical splitter of an optical splitter and an optical switch. Here, the optical line terminal includes a first optical line terminal, a second optical line terminal, and a control unit. The first optical line terminal is used normally and is connected to the optical splitter. The second optical line terminal is used as a substitute for the first optical line terminal and is connected to the optical switch. When the control unit detects an abnormality in the first optical line terminal, it determines whether switching is necessary based on communication information related to the first optical line terminal, and controls the optical switch to connect the second optical line terminal to the optical splitter only if switching is necessary.

[0011] According to one aspect of the present invention, when an abnormality in the first optical line termination board is detected, the necessity of switching is determined based on communication information related to the first optical line termination board, and the optical switch is controlled only if switching is necessary. Therefore, it is possible to prevent communication interruptions and delays due to automatic switching of the optical line termination board when an abnormality occurs in the optical line termination board.

[0012] That is, according to one aspect of the present invention, when an abnormality occurs in the optical line termination board, it is possible to prevent communication interruptions and delays that occur due to automatic switching of the optical line termination board.

[0013] FIG. 1 is a block diagram showing an example of the configuration of a system including an optical line terminal according to a first embodiment of the present invention. FIG. 2 is a flowchart for explaining an example of operation in the first embodiment. FIG. 3 is a schematic diagram for explaining an example of operation in the first embodiment. FIG. 4 is a flowchart for explaining operation as a first specific example of the first embodiment. FIG. 5 is a flowchart for explaining operation as a second specific example of the first embodiment. FIG. 6 is a flowchart for explaining operation as a third specific example of the first embodiment. FIG. 7 is a schematic diagram for explaining an example of the hardware configuration of an optical line terminal according to a second embodiment of the present invention. FIG. 8 is a block diagram showing an example of a general system using a PON. FIG. 9 is a flowchart for explaining an example of automatic switching operation in the event of an abnormality in an OSU in the system of FIG. 8.

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, "OLT" may be read as "OLT device" or "office side optical line terminal." "OSU" may be read as "OSU device," "optical subscriber line termination board," "PKG," or "PKG device." "ONU" may be read as "ONU device" or "subscriber side optical line terminal." In other words, terms with the same meaning may be read interchangeably as appropriate. OLT is an abbreviation for optical line terminal. OSU is an abbreviation for optical subscriber unit. PKG is an abbreviation for package. ONU is an abbreviation for optical network unit.

[0015] First Embodiment Fig. 1 is a block diagram showing an example of the configuration of a system including an optical line terminal (OLT) according to a first embodiment of the present invention. This system uses a passive optical network (PON) and includes an OLT 1, an optical switch 20, an optical splitter 21, and ONUs 30. The PON is a point-to-multipoint optical access network in which an OSU 11 included in a single OLT 1 ​​and one or more ONUs 30 are connected via optical fiber 40 and the optical splitter 21. In addition, the optical access network includes an optical switch 20 to provide redundancy for the OSU 11, allowing a redundant OSU 12 to be used in place of the OSU 11. In other words, in the optical access network shown in Fig. 1, the OLT 1 ​​is connected to the ONUs 30 via the optical splitter 21 and at least the optical splitter 21 of the optical switch 20.

[0016] Here, the OLT 1 ​​is a communication node that performs switching between an optical access network and a communication network (not shown), and is installed in the facilities of a service provider such as a telecommunications carrier. The OLT 1 ​​includes an OSU 11, a redundant OSU 12, a switch 13, a switching status DB 14, a control unit 16, and a communication information monitor unit 17. The OLT 1 ​​is an example of a central office optical line termination device.

[0017] The OSU 11 is a first optical subscriber line termination board used under normal conditions and connected to the optical splitter 21. The OSU 11 is controlled to start up and shut down by the control unit 16, and is activated when started up and deactivated when shut down. The OSU may be called a normal system OSU or a regular system OSU. The OLT 1 ​​may accommodate not only one OSU 11, but also multiple OSUs. In this case, for example, a second communication path (not shown) from the switch 13 to the second OSU, optical fiber, optical splitter, optical fiber, and second ONU is formed in parallel to the first communication path shown in FIG. 1 . The optical splitter in the second communication path is connected to port P2 of the optical switch 20 by an optical fiber. Similarly, additional communication paths are formed in parallel for the third and subsequent OSUs. The OSU 11 is an example of a first optical subscriber line termination board.

[0018] The redundant OSU 12 is used as a substitute for the OSU 11 under the control of the control unit 16, and is a second optical subscriber line termination board connected to the optical switch 20. The startup / shutdown of the OSU 11 is controlled by the control unit 16, and the OSU 11 starts up when started up and stops use when shut down. The "redundant OSU" may also be called a "redundant system OSU" or a "standby system OSU." The redundant OSU 12 is an example of a second optical subscriber line termination board.

[0019] The switch 13 is, for example, a layer 2 switch, and is controlled by the control unit 16 to connect a communication network (not shown) to the OSU 11 or the redundant OSU 12 .

[0020] The switching status DB 14 is read / written by the control unit 16 and stores whether the switching status is the OSU 11 or the redundant OSU. For example, the switching status DB 14 stores the use / non-use status of the OSU 11, the use / non-use status of the redundant OSU 12, the connection status of the switch 13, and the connection status of the optical switch 20.

[0021] The control unit 16 controls the operation of the OLT 1 ​​via each unit. For example, the control unit 16 has a switchover determination function and a switchover function from the OSU 11 to the redundant OSU 12 to continue communication services even when the OSU 11 malfunctions. For example, the control unit 16 determines whether switchover is necessary when a fault alarm for the OSU 11 is triggered, and if switchover is necessary, executes switchover. Specifically, for example, when the control unit 16 detects an abnormality in the OSU 11, it determines whether switchover is necessary based on communication information related to the OSU 11, and controls the optical switch 20 to connect the redundant OSU 12 to the optical splitter 21 only if switchover is necessary. For example, if switchover is necessary, the control unit 16 performs switchover by connecting the OLT-side port P0 and the ONU-side port P1 of the optical switch 20, changing the settings of the switch 13, shutting down the OSU 11, and starting up the redundant OSU 12. The control unit 16 also updates the switchover result in the switchover status DB 14. The control unit 16 may further determine whether a retry is necessary, and if a retry is necessary, may again determine whether switching is necessary based on newly acquired communication information. Here, communication information may be, for example, total communication volume, communication volume by class, communication volume by service used, or communication volume by destination, as appropriate. However, the communication information is not limited to this, and may be any communication information that is referenced in the determination logic for whether switching is necessary. Furthermore, whether switching is necessary may be referred to as "whether switching is necessary," "whether immediate switching is necessary," or "whether immediate automatic switching is necessary."

[0022] The communication information monitor 17 monitors the communication information of the OSU 11 and, in response to a request from the control unit 16, sends the latest communication information of the OSU 11 to the control unit 16. After switching to the redundant OSU 12, the communication information monitor 17 may monitor the communication information of the redundant OSU 12 and, in response to a request from the control unit 16, send the latest communication information of the redundant OSU 12 to the control unit 16.

[0023] The optical switch 20 has one OLT-side port P0 and at least one ONU-side port P1, ..., and the connection or disconnection between the OLT-side port P0 and the ONU-side ports P1, ... is controlled by the control unit 16. The OLT-side port P0 is connected to the redundant OSU 12. The ONU-side port P1 is connected to the optical splitter 21. Note that in FIG. 1, the ONU-side ports P1, ... are four ONU-side ports P1 to P4, but this is not limitative, and any N number of ONU-side ports P1, ... greater than or equal to one can be used as appropriate.

[0024] The optical splitter 21 may be called a 1:2 splitter, and has one port on the ONU 30 side and two ports on the OLT 1 ​​side. The one port on the ONU 30 side is connected to one ONU 30. Furthermore, one of the two ports on the OLT 1 ​​side is connected to the OSU 11, and the other is connected to the ONU-side port P1 of the optical switch 20.

[0025] The ONU 30 is placed in a subscriber's facility (e.g., a home or office building) and is connected to a user network (not shown). The user network includes one or more user terminals, such as personal computers (PCs) or smartphones. The multiple user terminals may be used individually by different users or by the same user. The ONU 30 relays communications between the user network and the OLT 1. Specifically, the ONU 30 transfers data from the OLT 1 ​​to the user network. The ONU 30 also transfers data from the user network to the OLT 1. The ONU 30 can communicate with the communication network via the OLT 1, but cannot communicate with other ONUs.

[0026] Next, the operation of a system equipped with the OLT configured as described above will be explained using the flowchart in Fig. 2 and the schematic diagrams in Fig. 3 to Fig. 6. Note that the operations of steps ST110 to ST140 enclosed by dashed lines in Fig. 2 are significantly different from the operations of steps ST100 to ST300 shown in Fig. 9.

[0027] First, in the OLT 1, when the OSU 11 is operating normally, the OSU 11 connected to the switch 13 communicates with the ONU 30 via the optical fiber 40 and the optical splitter 21. In addition, the communication information monitor 17 in the OLT monitors the communication information of the OSU 11.

[0028] In step ST100, if an abnormality occurs in the OSU 11, the OSU 11 issues a fault alarm indicating the abnormality. The control unit 15 detects the fault alarm of the OSU 11 as shown in Figures 2 and 3. In this example, it is assumed that, among various fault alarms, a fault alarm indicating an abnormality that allows continued communication is detected, rather than a fault that involves communication interruption. An example of an abnormality that allows continued communication is degradation of the OSU 11 detected by a decrease in optical signal strength.

[0029] In step ST110, upon detecting the fault alarm, the control unit 16 requests the communication information monitor unit 17 to send communication information of the OSU 11. In response to the request from the control unit 16, the communication information monitor unit 17 sends the latest communication information of the OSU 11 to the control unit 16. As a result, the control unit 16 obtains communication information from the OSU 11 via the communication information monitor unit 17.

[0030] After step ST110, the control unit 16 executes step ST120, which determines whether or not switching from the OSU 11 to the redundant OSU 12 is necessary. Step ST120 includes steps ST121 to ST123. Specifically, the control unit 16 sets the acquired communication information as a parameter (step ST121). The control unit 16 also compares the parameter with a preset reference value (step ST122). Based on the comparison result, the control unit 16 also sets an immediate switching necessity value "Y" or "N" indicating whether or not switching is necessary, and a retry necessity value "Y" or "N" indicating whether or not a retry is necessary (step ST123). The immediate switching necessity value "Y" indicates that immediate switching is necessary, and the immediate switching necessity value "N" indicates that immediate switching is not necessary. Similarly, the retry necessity value "Y" indicates that a retry is necessary, and the retry necessity value "N" indicates that a retry is not necessary. After step ST123, step ST120 ends.

[0031] After step ST120, in step ST130, the control unit 16 determines whether switching is necessary based on the set value of whether immediate switching is necessary, and proceeds to step ST200 only if switching is necessary. On the other hand, if the result of the determination in step ST130 is that switching is not necessary, the control unit 16 proceeds to step ST140.

[0032] In step ST140, the control unit 16 determines whether a retry is necessary based on the set contents, and proceeds to step ST150 only if a retry is necessary. On the other hand, if the result of the determination in step ST140 is that a retry is not necessary, the operation related to switching is terminated.

[0033] In step ST150, the control unit 16 waits for a predetermined waiting time, and returns to step ST110 after the waiting time has elapsed. In step ST110, the control unit 16 requests the communication information monitor unit 17 to send new communication information from the OSU 11. In response to the request from the control unit 16, the communication information monitor unit 17 sends the latest communication information from the OSU 11 to the control unit 16. As a result, the control unit 16 acquires new communication information from the OSU 11 via the communication information monitor unit 17. After step ST110, the control unit 16 executes step ST120 and subsequent operations to again determine whether switching is necessary based on the newly acquired communication information. Note that the waiting time is the retry interval when a retry is necessary, and can be determined in advance taking into account the allowable time until service recovery, the system load required for acquiring communication information, and determining whether switching is necessary.

[0034] On the other hand, after step ST130, in step ST200, the control unit 16 connects the OLT side port P0 and the ONU side port P1 of the optical switch 20, changes the setting of the switch 13, shuts down the OSU 11 (stops light emission from the light-emitting state), and starts up the redundant OSU 12 (starts light emission from the light-emitting stopped state), thereby performing the switchover.

[0035] Thereafter, in step ST300, the control unit 16 updates the switching result in the switching status DB 14. As a result, in the OLT 1, the redundant OSU 12 connected to the switch 13 communicates with the ONU 30 via the optical fiber 40, the optical switch 20, and the optical splitter 21.

[0036] Next, three specific examples of steps ST110 and ST120 among the above steps ST100 to ST300 will be described using the flowcharts of Figures 4 to 6. In the following description of the specific examples, the corresponding step numbers ST121, ST122, and ST123 will be assigned lowercase letters a, b, and c to identify the three specific examples, and sub-numbers -1, -2, and -3 to indicate the divided steps.

[0037] (First Specific Example: FIG. 4) The first specific example is an implementation example based on the following switching policies (a1) to (a2).

[0038] (a1) Immediate switching is performed only when the total communication volume of the OSU 11 showing an abnormality is 0 [Mbps].

[0039] (a2) If the total communication volume is greater than 0 [Mbps], immediate switching is not performed, and after waiting for 10 seconds, the same operation is repeated from the acquisition of the total communication volume.

[0040] Based on these switching policies (a1) to (a2), the OLT 1 ​​operates as shown in FIG.

[0041] That is, after step ST100, in step ST110a, upon detecting a fault alarm of the OSU 11, the control unit 16 requests the communication information monitor unit 17 to send the total communication volume as communication information of the OSU 11. In response to the request from the control unit 16, the communication information monitor unit 17 sends the latest total communication volume of the OSU 11 to the control unit 16. As a result, the control unit 16 obtains the total communication volume of the OSU 11 as communication information via the communication information monitor unit 17.

[0042] After step ST110a, the control unit 16 executes step ST120a to determine whether or not it is necessary to switch from the OSU 11 to the redundant OSU 12. Step ST120a includes steps ST121a to ST123a-2.

[0043] That is, the control unit 16 sets the acquired total communication volume as a parameter (step ST121a).

[0044] The control unit 16 also compares the total communication volume with a preset reference value of 0 Mbps to determine whether the total communication volume exceeds 0 Mbps (step ST122a). If the result of this determination is that the total communication volume exceeds 0 Mbps, the control unit 16 assigns (sets) a value "N" indicating whether immediate switching is necessary and a value "Y" indicating whether a retry is necessary to each parameter (step ST123a-1). After step ST123a-1, step ST120a ends, and the process proceeds to step ST130.

[0045] On the other hand, if the result of the determination in step ST122a is No, the control unit 16 assigns (sets) the value "Y" indicating whether immediate switching is necessary and the value "N" indicating whether a retry is necessary to each parameter (step ST123a-2).

[0046] After step ST123a-2, step ST120a ends and the process proceeds to step ST130.

[0047] Thereafter, the processing from step ST130 onwards is executed in the same manner as in Fig. 2. However, since there is no combination of the value "N" for whether immediate switching is necessary and the value "N" for whether a retry is necessary, the determination of whether a retry is necessary in step ST140 can be omitted. That is, if immediate switching is not necessary in step ST130 (ST130: N), step ST140 may be skipped and the process may proceed to step ST150. Furthermore, if the communication information is the total communication volume, a time of, for example, about 10 seconds is used as the wait time in step ST150.

[0048] (Second Specific Example: FIG. 5) The second specific example is an implementation example based on the following switching policies (b1) to (b4).

[0049] (b1) Class A / B communications are important services, so immediate switching is not performed if the class-specific communication volume is greater than 0 [Mbps].

[0050] (b2) Class C communication is a semi-essential service, so immediate switching is not performed if the class-specific communication volume is greater than 5 Mbps. This is because class C communication is often used for long periods of time.

[0051] (b3) If neither (b1) nor (b2) above applies, execute immediate switching. Note that, because Class D communication is best effort, it is not determined whether immediate switching is necessary.

[0052] (b4) If immediate switching is not required and the wait time is 0, the operation is terminated. If (b4) does not apply, the operation is repeated from obtaining the communication volume after waiting for the wait time.

[0053] Based on these switching policies (b1) to (b4), the OLT 1 ​​operates as shown in FIG.

[0054] That is, after step ST100, in step ST110b, the control unit 16, upon detecting a fault alarm for the OSU 11, requests the communication information monitor unit 17 to send the communication volume for each class A / B / C / D as communication information of the OSU 11. In response to the request from the control unit 16, the communication information monitor unit 17 sends the latest communication volume for each class A / B / C / D of the OSU 11 to the control unit 16. As a result, the control unit 16 obtains the communication volume for each class A / B / C / D of the OSU 11 as communication information via the communication information monitor unit 17.

[0055] After step ST110b, the control unit 16 executes step ST120b to determine whether or not it is necessary to switch from the OSU 11 to the redundant OSU 12. Step ST120b includes steps ST121b to ST123b-3.

[0056] That is, the control unit 16 sets the acquired communication volume for each of classes A / B / C / D as a parameter (step ST121b).

[0057] If the set communication volume is a Class A communication volume, the control unit 16 compares the set communication volume with a preset reference value of 0 Mbps to determine whether the total communication volume exceeds 0 Mbps (step ST122b-1). If the total communication volume exceeds 0 Mbps, the control unit 16 assigns (sets) the value "N" indicating whether immediate switching is required and the value "N" indicating whether a retry is required to each parameter (step ST123b-1).

[0058] If the result of the determination in step ST122b-1 is negative, and if the set communication volume is a Class B communication volume, the control unit 16 compares the communication volume with a preset reference value of 0 Mbps to determine whether the total communication volume exceeds 0 Mbps (step ST122b-2). If the result of this determination is that the total communication volume exceeds 0 Mbps, the control unit 16 assigns (sets) a value "N" indicating whether immediate switching is necessary and a value "Y" indicating whether a retry is necessary to each parameter (step ST123b-2).

[0059] If the result of the determination in step ST122b-2 is negative, and if the set communication volume is a communication volume of class C, the control unit 16 compares the communication volume with a preset reference value of 5 Mbps to determine whether the total communication volume exceeds 5 Mbps (step ST122b-3). If the result of this determination is that the total communication volume exceeds 5 Mbps, the control unit 16 proceeds to step ST123b-2, and, as described above, assigns (sets) the value "N" indicating whether immediate switching is necessary and the value "Y" indicating whether a retry is necessary to each parameter.

[0060] If the result of the determination in step ST122b-3 is negative, the control unit 16 assigns (sets) a value "Y" indicating whether immediate switching is necessary and a value "N" indicating whether a retry is necessary to each parameter (step ST123b-3). Note that step ST123b-3 is performed when the communication volume of class A / B is 0 [Mbps] or less, when the communication volume of class C is 5 [Mbps] or less, when communication is class D, etc.

[0061] After step ST123b-1, ST123b-2, or ST123b-3, step ST120b ends and the process proceeds to step ST130.

[0062] Thereafter, the processes from step ST130 onwards are executed in the same manner as in Fig. 2. When the communication information indicates a communication volume of class C, the wait time in step ST150 is set to, for example, about 5 seconds.

[0063] (Third Specific Example: FIG. 6) The third specific example is an implementation example based on the following switching policies (c1) to (c2).

[0064] (c1) If the traffic volume of communication originating or destined for the address of a specific company game server (game server address) is greater than 0 [Mbps], immediate switching is not performed, and after waiting for a waiting time, the operation is repeated from obtaining the traffic volume.

[0065] (c2) If the traffic volume of communication originating or destined for the game server address is 0 [Mbps], immediate switching is performed.

[0066] Based on these switching policies (c1) to (c2), the OLT 1 ​​operates as shown in FIG.

[0067] That is, after step ST100, in step ST110c, upon detecting a fault alarm for OSU 11, control unit 16 requests communication information monitor unit 17 to send the total communication volume of communications whose source or destination is a game server address as communication information for OSU 11. In response to the request from control unit 16, communication information monitor unit 17 sends the latest total communication volume of the game server address in OSU 11 to control unit 16. As a result, control unit 16 obtains the total communication volume of the game server address as communication information via communication information monitor unit 17.

[0068] After step ST110c, the control unit 16 executes step ST120c to determine whether or not it is necessary to switch from the OSU 11 to the redundant OSU 12. Step ST120c includes steps ST121c to ST123c-2.

[0069] That is, the control unit 16 sets the acquired total communication volume as a parameter (X) (step ST121c).

[0070] The control unit 16 also compares the total communication volume (X) with a preset reference value of 0 Mbps to determine whether the total communication volume (X) exceeds 0 Mbps (step ST122c). If the result of this determination is that the total communication volume (X) exceeds 0 Mbps, the control unit 16 assigns (sets) a value "N" indicating whether immediate switching is necessary and a value "Y" indicating whether a retry is necessary to each parameter (step ST123c-1). After step ST123c-1, step ST120c ends, and the process proceeds to step ST130.

[0071] On the other hand, if the result of the determination in step ST122c is No, the control unit 16 assigns (sets) the value "Y" indicating whether immediate switching is necessary and the value "N" indicating whether a retry is necessary to each parameter (step ST123a-2).

[0072] After step ST123a-2, step ST120c ends and the process proceeds to step ST130.

[0073] Thereafter, the processing from step ST130 onwards is executed in the same manner as in Fig. 2. However, since there is no combination of the value "N" for whether immediate switching is necessary and the value "N" for whether a retry is necessary, the determination of whether a retry is necessary in step ST140 can be omitted. In other words, if immediate switching is not necessary in step ST130 (ST130: N), step ST140 may be skipped and the process may proceed to step ST150. Furthermore, if the communication information is the total communication volume of the game server address, a time of, for example, about 60 seconds is used as the wait time in step ST150.

[0074] As described above, according to the first embodiment, the OLT 1 ​​is used in an optical access network in which the OLT 1 ​​is connected to the ONUs 30 via at least the optical splitter 21 of the optical splitter 21 and the optical switch 20. The OLT 1 ​​includes the OSU 11, the redundant OSU 12, and the control unit 16. The OSU 11 is used under normal conditions and is connected to the optical splitter 21. The redundant OSU 12 is used as a substitute for the OSU 11 and is connected to the optical switch 20. When the control unit 16 detects an abnormality in the OSU 11, it determines whether or not switching is necessary based on communication information related to the OSU 11, and controls the optical switch 20 to connect the redundant OSU 12 to the optical splitter 21 only if switching is necessary. In this way, when an abnormality in the OSU 11 is detected, instead of immediately and automatically switching, it determines whether or not switching is necessary based on communication information related to the OSU 11, and switches only if switching is necessary. Therefore, when an abnormality occurs in the OSU 11, communication interruptions and delays due to automatic switching of the OSU 11 can be prevented.

[0075] Furthermore, according to the first embodiment, the control unit 16 further determines whether a retry is necessary, and if a retry is necessary, determines again whether switching is necessary based on newly acquired communication information. As a result, even if the first determination indicates that switching is not necessary, if the second or subsequent determination indicates that switching is necessary due to changes in the latest communication information in the OSU 11, switching can be performed. Therefore, in addition to the effects described above, if a retry is necessary even if switching is not necessary, by performing a determination again, switching can be performed in accordance with changes in the communication information in the OSU 11.

[0076] 7 is a schematic diagram for explaining an example of the hardware configuration of an optical line terminal (OLT) according to a second embodiment, in which the same parts as those in FIG. 1 are assigned the same reference numerals and detailed explanations thereof are omitted, and the following mainly describes the differences. The peripheral configuration of the OLT 1 ​​is indicated by dashed lines.

[0077] 7, the OLT 1 ​​includes, as hardware components, a first communication IF 101, a second communication IF 102, a control IF 103, a memory 104, and a processing circuit 105. The OSU 11 and redundant OSU 12 shown in FIG. 1 are implemented by the first communication IF 101. The switch 13 shown in FIG. 1 is implemented by the second communication IF 102. The switching status DB 14 shown in FIG. 1 is implemented by the memory 104. The control unit 16 and communication information monitor unit 17 shown in FIG. 1 are implemented by the processing circuit 105.

[0078] The first communication IF 101 is an interface (IF) for communicating with the ONU 30. The first communication IF 101 includes an optical-electrical (O / E) converter that converts an optical signal into an electrical signal, and an electrical-optical (E / O) converter that converts an electrical signal into an optical signal.

[0079] The second communication IF 102 is an interface for communicating with an external device such as the game server 60 via the network 50. The second communication IF 102 includes, for example, a layer 2 switch. Note that the second communication IF 102 may further include, for example, a higher-level network IF between the network 50 and the layer 2 switch.

[0080] The control IF 103 is an interface for controlling the optical switch 20 from the processing circuit 101 .

[0081] The memory 104 is, for example, a combination of a nonvolatile memory such as an SSD that can be written to and read from at any time and a volatile memory such as a RAM (Random Access Memory) as a storage medium. The memory 104 stores programs for realizing the functions of the OLT 1 ​​and data such as data in the switching status DB.

[0082] The processing circuit 105 may be a dedicated circuit such as an ASIC or an FPGA (field programmable gate array). Alternatively, the processing circuit 105 may include a general-purpose circuit instead of or in addition to the dedicated circuit. For example, a central processing unit (CPU) may be used as the general-purpose circuit. When the program in the memory 104 is read and executed by the general-purpose circuit, it causes the general-purpose circuit to perform at least a portion of the operations of the control unit 16 and the communication information monitor unit 17 shown in FIG. 1 .

[0083] The program may be provided to the OLT 1 ​​in a state where it is stored in a non-transitory computer-readable storage medium. In this case, the OLT 1 ​​is equipped with a drive that reads data from the storage medium and acquires the program from the storage medium. Examples of storage media include magnetic disks, optical disks (CD-ROM, CD-R, DVD-ROM, DVD-R, etc.), magneto-optical disks (MO, etc.), and semiconductor memories. The program may also be distributed over a network. Specifically, the program may be stored on a server on the network, and the OLT 1 ​​may download the program from the server.

[0084] According to the second embodiment described above, even if the OLT 1 ​​is implemented by hardware components, it is possible to implement the first embodiment in the same manner and obtain the same effects.

[0085] <Other Embodiments> The functional configuration of the OLT 1, its processing procedures, processing contents, etc. can be modified in various ways without departing from the gist of the present invention.

[0086] For example, the number of OSUs 11 is not limited to one, and any number of OSUs 11 may be accommodated in the OLT 1. In this case, for example, a second communication path (not shown) from the switch 13 to the second OSU, optical fiber, optical splitter, optical fiber, and second ONU is formed in parallel to the first communication path shown in Fig. 1. Also, an optical fiber connects the optical splitter in the second communication path to port P2 of the optical switch 20. Similarly, additional communication paths are formed in parallel for the third and subsequent OSUs.

[0087] Furthermore, for example, in an optical access network, an optical splitter may be inserted between the optical splitter 21 and the ONU 30, and the inserted optical splitter may be connected to another ONU. In other words, an optical fiber may be branched between the optical splitter 21 and the ONU 30 to another ONU.

[0088] Furthermore, for example, the optical splitter 21 is a 1:2 splitter having one port on the ONU 30 side and two ports on the OLT 1 ​​side, but is not limited to this. For example, the optical splitter 21 may be a 2:2 splitter having two ports on the ONU 30 side and two ports on the OLT 1 ​​side.

[0089] Although the embodiments of the present invention have been described in detail above, the above description is merely an example of the present invention in every respect. It goes without saying that various improvements and modifications can be made without departing from the scope of the present invention. In other words, when implementing the present invention, specific configurations according to the embodiments may be appropriately adopted.

[0090] In short, this invention is not limited to the above-described embodiments, and in the implementation stage, the components can be modified and embodied without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined.

[0091] REFERENCE SIGNS LIST 1 OLT 11 OSU 12 Redundant OSU 13 Switch 14 Switching status DB 16 Control unit 17 Communication information monitor unit 20 Optical switch 21 Optical splitter 30 ONU 40 Optical fiber 50 Network 60 Game server

Claims

1. An optical line terminal on an optical access network in which an optical line terminal on an optical line terminal on an optical line terminal on a central office side is connected to an optical line terminal on a subscriber side via at least the optical splitter of an optical splitter and an optical switch, comprising: a first optical line terminal board that is used in normal operation and connected to the optical splitter; a second optical line terminal board that is used as a substitute for the first optical line terminal board and connected to the optical switch; and a control unit that, when an abnormality in the first optical line terminal board is detected, determines whether or not switching is necessary based on communication information related to the first optical line terminal board, and controls the optical switch to connect the second optical line terminal to the optical splitter only if switching is necessary.

2. The optical line terminal device according to claim 1, wherein the control unit further determines whether a retry is necessary, and if a retry is necessary, determines again whether the switching is necessary based on the newly acquired communication information.

3. A method executed by an optical line terminal in an optical access network in which an optical line terminal is connected to a subscriber-side optical line terminal via at least the optical splitter of an optical splitter and an optical switch, the optical line terminal comprising: a first optical line terminal board that is used in normal times and connected to the optical splitter; and a second optical line terminal board that is used as a substitute for the first optical line terminal board and connected to the optical switch, the method comprising: detecting an abnormality in the first optical line terminal board; determining, upon detecting the abnormality, whether or not switching is necessary based on communication information related to the first optical line terminal board; and controlling the optical switch to connect the second optical line terminal to the optical splitter only if, as a result of the determination, switching is necessary.

4. A system in which a central office optical line terminal is connected to a subscriber office optical line terminal via at least the optical splitter of an optical splitter and an optical switch, the central office optical line terminal comprising: a first optical line terminal board that is used under normal conditions and connected to the optical splitter; a second optical line terminal board that is used as a substitute for the first optical line terminal board and connected to the optical switch; and a control unit that, when an abnormality in the first optical line terminal board is detected, determines whether switching is necessary based on communication information related to the first optical line terminal board, and controls the optical switch to connect the second optical line terminal board to the optical splitter only if switching is necessary.

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