Communication system, control device, and communication control method

Abstract

In this communication system comprising a first terminal station device, a second terminal station device, at least one termination device, and a control device, the control device comprises: a switching control unit that, when all of the termination devices accommodated in the first terminal station device are in a state of not performing communication, switches the accommodation destination of all of the termination devices accommodated in the first terminal station device from the first terminal station device to the second terminal station device; and an activation state control unit that, when all of the termination devices accommodated in the first terminal station device are in a state of not performing communication, switches the activation state of the first terminal station device to a sleep state.

Description

Communication system, control device, and communication control method

[0001] The present invention relates to a communication system, a control device, and a communication control method.

[0002] In a PON (Passive Optical Network) system, an OLT (Optical Line Terminal) and an ONU (Optical Network Unit) communicate with each other in a one-to-many relationship. The OLT manages the transmission timing of all upstream signals to prevent collisions between the upstream signals transmitted from each ONU it accommodates. Therefore, an ONU cannot transmit an upstream signal unless it receives a transmission instruction from the OLT.

[0003] JP 2011-071951 A

[0004] It is possible to put an ONU into sleep mode to reduce power consumption when the user is not communicating. However, it is difficult to put an OLT into sleep mode because it manages the timing of upstream signal transmissions from the ONU. If the OLT goes into sleep mode, the ONUs it accommodates will not be able to transmit upstream signals, and users will not be able to communicate at the times they need.

[0005] Furthermore, even if all ONUs accommodated in the OLT are not communicating (for example, in a sleep state or powered off state), it is still difficult to put the OLT into a sleep state. This is because the OLT does not know when the ONUs will wake up again, so it must constantly monitor the ONUs for wake-up. As such, in the past, it was difficult to put the OLT into a sleep state, which resulted in unnecessary power consumption.

[0006] In view of the above circumstances, an object of the present invention is to provide a communication system, a control device, and a communication control method that can reduce the power consumption of an OLT.

[0007] One aspect of the present invention is a communication system having a first terminal device, a second terminal device, at least one termination device, and a control device, wherein the control device is equipped with a switching control unit that switches the accommodation of all of the termination devices accommodated in the first terminal device from the first terminal device to the second terminal device when all of the termination devices accommodated in the first terminal device are not communicating, and an activation state control unit that switches the activation state of the first terminal device to a sleep state when all of the termination devices accommodated in the first terminal device are not communicating.

[0008] Another aspect of the present invention is a control device that includes a switching control unit that, when all of the terminating devices accommodated in a first terminal device are not communicating, switches the accommodation of all of the terminating devices accommodated in the first terminal device from the first terminal device to a second terminal device, and an activation state control unit that, when all of the terminating devices accommodated in the first terminal device are not communicating, switches the activation state of the first terminal device to a sleep state.

[0009] Another aspect of the present invention is a computer-based communication control method, which includes a switching control step of switching the accommodation of all the terminating devices accommodated in a first terminal device from the first terminal device to a second terminal device when all the terminating devices accommodated in the first terminal device are not communicating, and an activation state control step of switching the activation state of the first terminal device to a sleep state when all the terminating devices accommodated in the first terminal device are not communicating.

[0010] The present invention makes it possible to reduce the power consumption of the OLT.

[0011] 1 is an overall configuration diagram of a communication system 1 according to an embodiment of the present invention. FIG. 2 is a diagram illustrating one state of the communication system 1 according to an embodiment of the present invention. FIG. 3 is a block diagram illustrating the functional configuration of an OLT 10 of the communication system 1 according to an embodiment of the present invention. FIG. 4 is a block diagram illustrating the functional configuration of an ONU 20 of the communication system 1 according to an embodiment of the present invention. FIG. 5 is a block diagram illustrating the functional configuration of a control device 40 of the communication system 1 according to an embodiment of the present invention. FIG. 6 is a diagram for explaining the maximum number of ONUs 20 accommodated by the OLT 10. FIG. 7 is a flowchart illustrating the operation of the control device 40 according to an embodiment of the present invention. FIG. 8 is a sequence diagram illustrating the flow of processing when accommodation is switched to the switching destination OLT 10 by the communication system 1 according to an embodiment of the present invention. FIG. 9 is a sequence diagram illustrating the flow of processing when accommodation is switched back to the switching source OLT 10 by the communication system 1 according to an embodiment of the present invention.

[0012] Hereinafter, a communication system, a control device, and a communication control method according to the present invention will be described in detail with reference to the drawings.

[0013] [Overall Configuration of Communication System] Fig. 1 is a diagram showing the overall configuration of a communication system 1 according to one embodiment of the present invention. As shown in Fig. 1, the communication system 1 includes OLTs 10-1 to 10-3, ONUs 20-1 to 20-2n, an optical switch 30, splitters 35-1 to 35-6, and a control device 40. In the following description, n is an integer equal to or greater than 2.

[0014] In the following description, when it is not necessary to distinguish between the OLTs 10-1 to 10-3, they will simply be referred to as "OLT 10." In the following description, when it is not necessary to distinguish between the ONUs 20-1 to 20-2n, they will simply be referred to as "ONU 20." In the following description, when it is not necessary to distinguish between the splitters 35-1 to 35-6, they will simply be referred to as "splitter 35."

[0015] The OLT 10-1 is a terminal device that accommodates the ONUs 20-1 to 20-n. The OLT 10-1 receives optical signals transmitted from a higher-level device (not shown) and transmits the received optical signals to the ONUs 20-1 to 20-n. The OLT 10-1 also receives optical signals transmitted from the ONUs 20-1 to 20-n and transmits the received optical signals to the higher-level device (not shown).

[0016] The OLT 10-2 is a terminal device that accommodates the ONUs 20-(n+1) to 20-2n. The OLT 10-2 receives optical signals transmitted from a higher-level device (not shown) and transmits the received optical signals to the ONUs 20-(n+1) to 20-2n. The OLT 10-2 also receives optical signals transmitted from the ONUs 20-(n+1) to 20-2n and transmits the received optical signals to the higher-level device (not shown).

[0017] The OLT 10-3 is a terminal device that does not accommodate the ONU 20. Therefore, even if the OLT 10-3 receives an optical signal transmitted from a higher-level device (not shown), the OLT 10-3 does not transmit the received optical signal to the ONU 20.

[0018] The configuration of the communication system 1 shown in FIG. 1 is merely an example. In this embodiment, the number of OLTs 10 is three, but the number of OLTs 10 may be any number greater than or equal to two. In this embodiment, the number of ONUs 20 accommodated by OLT 10-1 and OLT 10-2 is n, but the number of ONUs 20 may be any number. In addition, the number of ONUs 20 accommodated by ONU 10-1 may be different from the number of ONUs 20 accommodated by ONU 10-2. In this embodiment, the OLT 10-3 does not accommodate any ONUs 20, but it may accommodate them.

[0019] 1, the OLT 10-1 is connected to the splitter 35-1 via an optical transmission line 51-1, the OLT 10-2 is connected to the splitter 35-2 via an optical transmission line 51-2, and the OLT 10-3 is connected to the splitter 35-3 via an optical transmission line 51-3.

[0020] Each OLT 10 is communicatively connected to the control device 40 via a communication line 61. Each OLT 10 and the control device 40 transmit and receive control signals to and from each other via the communication line 61. For example, the OLT 10 switches the startup state of the OLT 10 to an active state or a sleep state in accordance with a control signal transmitted from the control device 40.

[0021] ONU 20-1 to ONU 20-n are terminal devices of the optical communication network accommodated in OLT 10-1. ONU 20-1 to ONU 20-n receive optical signals transmitted from OLT 10-1, convert the received optical signals into digital signals, and transmit the converted digital signals to user terminals (not shown). ONU 20-1 to ONU 20-n also receive digital signals transmitted from user terminals (not shown), convert the received digital signals into optical signals, and transmit the converted optical signals to OLT 10-1.

[0022] ONU 20-(n+1) to ONU 20-2n are terminal devices of the optical communication network accommodated in OLT 10-2. ONU 20-(n+1) to ONU 20-2n receive optical signals transmitted from OLT 10-2, convert the received optical signals into digital signals, and transmit the converted digital signals to user terminals (not shown). ONU 20-(n+1) to ONU 20-2n also receive digital signals transmitted from user terminals (not shown), convert the received digital signals into optical signals, and transmit the converted optical signals to OLT 10-2.

[0023] ONU 20-1 to ONU 20-n are connected to the splitter 35-4 via optical transmission paths 54-1 to 54-n, respectively. ONU 20-(n+1) to ONU 20-2n are connected to the splitter 35-5 via optical transmission paths 54-(n+1) to 54-2n, respectively.

[0024] The optical switch 30 switches the transmission path of an optical signal between the OLT 10 and the ONU 20. As shown in Fig. 1 , the optical switch 30 in this embodiment is a 3:9 optical switch that has three communication ports on the lower side (ONU 20 side) of the optical communication network and nine communication ports on the upper side (OLT 10 side).

[0025] The number of communication ports provided in the optical switch 30 is not limited to this. The optical switch 30 only needs to have communication ports at least equal to or greater than the number of OLTs 10 on the downstream side of the optical communication network, and at least equal to or greater than "the number of ports on the downstream side x the number of OLTs 10" on the upstream side of the optical communication network. This allows the optical switch 30 to arbitrarily connect each of the routes to the OLTs 10-1 to 10-3 and each of the routes to the splitters 35-4 to 35-6.

[0026] Splitters 35-1 to 35-3 are 1:3 splitters. As shown in FIG. 1, splitter 35-1 branches optical transmission path 51-1 connected to OLT 10-1 into optical transmission paths 52-1 to 52-3 that respectively connect to three communication ports of optical switch 30. Splitter 35-2 branches optical transmission path 51-2 connected to OLT 10-2 into optical transmission paths 52-4 to 52-6 that respectively connect to three communication ports of optical switch 30. Splitter 35-3 branches optical transmission path 51-3 connected to OLT 10-3 into optical transmission paths 52-7 to 52-9 that respectively connect to three communication ports of optical switch 30.

[0027] Splitters 35-4 to 35-6 are 1:n splitters. As shown in FIG. 1, splitter 35-4 branches optical transmission path 53-1, which is connected to one of the communication ports of optical switch 30, into optical transmission paths 54-1 to 54-n, which are connected to ONUs 20-1 to 20-n, respectively. Splitter 35-5 branches optical transmission path 53-2, which is connected to one of the communication ports of optical switch 30, into optical transmission paths 54-(n+1) to 54-2n, which are connected to ONUs 20-(n+1) to 20-2n, respectively. Splitter 35-6 branches optical transmission path 53-3, which is connected to one of the communication ports of optical switch 30, into optical transmission paths 54-(2n+1) to 54-3n, which are not connected to ONU 20.

[0028] The control device 40 is communicatively connected to each of the OLTs 10 via a communication line 61. The control device 40 is also communicatively connected to the optical switch 30 via a communication line 62. The control device 40 controls the switching of each of the OLTs 10 between an active state and a sleep state by transmitting a control signal to each of the OLTs 10. The control device 40 also controls the switching of the signal path by the optical switch 30 by transmitting a control signal to the optical switch 30.

[0029] [OLT Startup State Control] Hereinafter, the startup state control of the OLT for reducing power consumption in the communication system 1 of this embodiment will be described.

[0030] Each OLT 10 stores ONU information. The ONU information here refers to information about the ONUs 20 accommodated in the OLT 10. For example, the ONU information is authentication data such as a MAC (Media Access Control) address. The control device 40 collects ONU information from each OLT 10 that is in an activated state.

[0031] The control device 40 determines that an OLT 10 that does not store ONU information is an OLT that does not accommodate an ONU 20. For example, the control device 40 transmits a control signal to each OLT 10 requesting the provision of ONU information, and attempts to collect the ONU information. The control device 40 determines that an OLT 10 that does not store ONU information (i.e., an OLT 10 that was unable to collect ONU information) is an OLT that does not accommodate an ONU 20. The control device 40 transmits a control signal to switch the OLT 10 that is determined not to accommodate an ONU 20 to a sleep state. The OLT 10 that receives the control signal switches itself to a sleep state.

[0032] In the communication system 1 illustrated in FIG. 1, the OLT 10-3 is an OLT that does not accommodate an ONU 20. Therefore, ONU information is not transmitted from the OLT 10-3 to the control device 40, and the control device 40 transmits a control signal to the OLT 10-3 to switch it to a sleep state. Upon receiving the control signal, the OLT 10-3 switches itself to a sleep state. In this way, the OLT 10-3 enters a sleep state, thereby achieving low power consumption. Note that the switching to the sleep state may be performed in units of communication packages of the OLT 10, or in units of communication ports of the OLT 10.

[0033] Furthermore, based on the collected ONU information, the control device 40 identifies an OLT 10 in which all of the ONUs 20 it accommodates are in a "state that does not require communication." Here, a state that does not require communication is, for example, a sleep state or a power-off state. The control device 40 transmits a control signal to switch the OLT 10 in which it has identified that all of the ONUs 20 it accommodates are in a state that does not require communication to the sleep state. The OLT 10 that receives this control signal switches itself to the sleep state.

[0034] FIG. 2 is a diagram illustrating one state of a communication system 1 according to an embodiment of the present invention. In the communication system 1 illustrated in FIG. 2, ONUs 20-(n+1) through 20-2n are all in a sleep state or powered off. That is, in the communication system 1 illustrated in FIG. 2, the OLT 10-2 is an OLT that accommodates only ONUs 20 that do not require communication. Therefore, the control device 40 transmits a control signal to the OLT 10-2 to switch it to a sleep state. Upon receiving this control signal, the OLT 10-2 switches itself to a sleep state. In this way, by having the OLT 10-2 enter a sleep state, power consumption is reduced.

[0035] Furthermore, the control device 40 controls the accommodation switching so that the ONUs 20 (ONU 20-(n+1) to ONU 20-2n in FIG. 2) accommodated by the OLT 10 (OLT 10-2 in FIG. 2) that has been switched to the sleep state are accommodated by another OLT 10 (OLT 10-1 in FIG. 2) that is not in the sleep state. Specifically, the control device 40 transfers the ONU information (authentication data) stored in the OLT 10-2 that has been switched to the sleep state to the OLT 10-1 that is the destination of the accommodation switching.

[0036] 2, the control device 40 controls the accommodation switching so that ONUs 20-(n+1) to ONUs 20-2n accommodated by the OLT 10-2 that has been switched to the sleep mode are accommodated by another OLT 10-1 that is not in the sleep mode.The control device 40 then transfers the ONU information (authentication data) stored in the OLT 10-2 that has been switched to the sleep mode to the OLT 10-1 that is the destination of the accommodation switching.The ONU information transferred here is ONU information related to ONUs 20-(n+1) to ONUs 20-2n.

[0037] Then, the control device 40 controls the optical switch 30 to perform a path changeover so that all of the ONUs 20 accommodated in the OLT 10 that has been switched to the sleep state are accommodated in another OLT 10. Hereinafter, the OLT 10 that accommodated the ONUs 20 before the path changeover will be referred to as the "source OLT 10," and the OLT 10 that accommodates the ONUs 20 after the path changeover will be referred to as the "destination OLT 10." Furthermore, the ONUs 20 whose accommodation will be changed will be referred to as the "target ONUs 20."

[0038] 2, the control device 40 controls the optical switch 30 to perform path switching so that ONU 20-(n+1) to ONU 20-2n, which were accommodated in OLT 10-2, are now accommodated in OLT 10-1. Specifically, as shown in FIG. 2, the control device 40 performs path switching to switch the optical transmission path to be connected to the optical transmission path 53-2 from the optical transmission path 52-5 to the optical transmission path 52-2.

[0039] The control device 40 controls so that a logical link is established between the switching destination OLT 10 and the switching target ONU 20. Then, the OLT 10 monitors only the activation of the switching target ONU 20, for example, using MPCP (Multi Point Control Protocol). That is, in the case of FIG. 2, the control device 40 controls so that a logical link is established between the OLT 10-1 and ONU 20-(n+1) to ONU 20-2n. Then, the OLT 10-1 monitors only the activation of ONU 20-(n+1) to ONU 20-2n using MPCP.

[0040] At this time, the OLT 10-1 does not allow the ONUs 20-(n+1) to 20-2n to execute functions other than MPCP. By eliminating the need for functions other than MPCP, the OLT 10 can monitor the activation of a number of ONUs 20 that exceeds the maximum number that can be accommodated.

[0041] The ONUs 20 to be switched are only those ONUs 20 that are in a state where communication is not required. Therefore, the OLT 10 to be switched to does not need to perform various setting and monitoring functions for the ONUs 20 to be switched to. The various setting and monitoring functions referred to here include, for example, monitoring of device failures in the ONUs 20, monitoring of temperature abnormalities, monitoring of the UNI status, setting using extended OAM (Operation Administration and Maintenance), and management of the PON multicast table. Therefore, when designing a communication system, it is not necessary to take these resources into consideration for the OLT 10, and there is no need to improve the performance of the OLT 10 device.

[0042] In this way, the OLT 10 from which the switching originates goes into sleep mode, and the OLT 10 to which the switching is made performs various setting and monitoring functions for the ONU 20 that it originally accommodated, and only performs startup monitoring for the ONU 20 to be switched.

[0043] When the switching destination OLT 10 detects by MPCP that the switching target ONU 20 has started up, it notifies the control device 40. When the control device 40 receives notification from the switching destination OLT 10 that the switching target ONU 20 has started up, it sends a control signal to the switching source OLT 10 to put the switching source OLT 10 back into a starting state. The switching source OLT 10, now in a starting state, uses the ONU information stored in its own device to perform various setting and monitoring functions.

[0044] 2, when OLT 10-1 detects by MPCP that any of ONU 20-(n+1) to ONU 20-2n has started up (i.e., it is no longer in sleep mode or power-off mode), it notifies control device 40. When control device 40 receives notification that any of ONU 20-(n+1) to ONU 20-2n has started up, it sends a control signal to OLT 10-2 to put OLT 10-2 back into a started-up state. OLT 10-2, now in a started-up state, uses the ONU information stored in its own device to perform various setting and monitoring functions.

[0045] Note that the ONU 20 cannot transmit an upstream signal without a transmission instruction from the OLT 10. Therefore, the OLT 10 must continue to grant the right to transmit an upstream signal transmission request to the OLT 10 to the ONU 20 to be switched, even if the ONU 20 is in a state where communication is not required. This allows the OLT 10 to detect that the ONU 20 has entered a startup state again, and the ONU 20 can resume transmitting an upstream signal to the OLT 10.

[0046] [OLT Configuration] The following describes the functional configuration of the OLT 10. Fig. 3 is a block diagram showing the functional configuration of the OLT 10 of the communication system 1 according to an embodiment of the present invention. As shown in Fig. 3, the OLT 10 includes a control unit 100, a signal transmission / reception unit 101, an ONU status management unit 102, an ONU information holding unit 103, and a power supply unit 104.

[0047] The control unit 100 controls the execution of various functions of the OLT 10. The control unit 100 and an ONU status management unit 102 (described later) are configured using a processor such as a CPU (Central Processing Unit). For example, the control unit 100 controls a signal transmission / reception unit 101 (described later) to transmit and receive optical signals to and from the ONUs 20 and a higher-level device (not shown). Also, for example, the control unit 100 controls the ONU status management unit 102 to execute various settings and monitoring functions for the ONUs 20 accommodated therein.

[0048] Furthermore, for example, the control unit 100 further accommodates the ONU 20 to be switched based on a control signal transmitted from the control device 40. At this time, the control unit 100 controls the ONU status management unit 102 to execute only startup monitoring by MPCP for the ONU 20 to be switched. Furthermore, for example, the control unit 100 controls the ONU status management unit 102 to store ONU information related to the ONU 20 to be switched, transmitted from the control device 40, in the ONU information holding unit 103 described below.

[0049] Furthermore, for example, when the ONU status management unit 102 detects the startup of the ONU 20 to be switched, the control unit 100 notifies the control device 40. Furthermore, for example, when the control unit 100 receives a control signal from the control device 40 instructing it to switch to a sleep state, the control unit 100 controls the power supply unit 104 (described later) to switch its own device from a running state to a sleep state. Furthermore, for example, when the control unit 100 receives a control signal from the control device 40 instructing it to switch to a running state, the control unit 100 controls the power supply unit 104 to switch its own device from a sleep state to a running state.

[0050] The signal transmitting / receiving unit 101 transmits and receives optical signals to and from the ONU 20 and a higher-level device (not shown). The signal transmitting / receiving unit 101 is a communication interface for communicating with the ONU 20 and a higher-level device (not shown).

[0051] The ONU status management unit 102 executes various settings and monitoring functions for the ONUs 20 accommodated in the ONU status management unit 102 itself. Furthermore, the ONU status management unit 102 executes only startup monitoring using MPCP for the ONUs 20 to be switched that have taken over from the original OLT 10. Furthermore, the ONU status management unit 102 stores the ONU information related to the ONUs 20 to be switched, output from the control unit 100, in the ONU information holding unit 103. When the ONU status management unit 102 detects the startup of the ONUs 20 to be switched using MPCP, it outputs information indicating the detection to the control unit 100.

[0052] The ONU information holding unit 103 stores ONU information (e.g., authentication data such as MAC addresses) related to the ONUs 20 accommodated in the device itself. The ONU information holding unit 103 also stores information related to various settings and monitoring related to the ONUs 20 accommodated in the device itself. The ONU information holding unit 103 stores ONU information (e.g., authentication data such as MAC addresses) related to the ONUs 20 to be switched that have been taken over from the switching source OLT 10.

[0053] The ONU information holding unit 103 is configured to include, for example, a semiconductor memory such as RAM (Random Access Memory) and EEPROM (Electrically Erasable Programmable Read-Only Memory), a flash memory such as SSD (Solid State Drive), a magnetic disk such as HDD (Hard Disk Drive), an optical disk, or other storage medium, or any combination of these storage media.

[0054] The power supply unit 104 switches the power supply state of the device itself under the control of the control unit 100. For example, the power supply unit 104 switches the device itself between an active state, a sleep state, and a power-off state.

[0055] [ONU Configuration] The following describes the functional configuration of the ONU 20. Fig. 4 is a block diagram showing the functional configuration of the ONU 20 of the communication system 1 according to an embodiment of the present invention. As shown in Fig. 4, the ONU 20 includes a control unit 200, a signal transmission / reception unit 201, and a power supply unit 202.

[0056] The control unit 200 controls the execution of various functions of the ONU 20. The control unit 200 is configured using, for example, a processor such as a CPU. For example, the control unit 200 controls a signal transmission / reception unit 201 (described later) to transmit and receive optical signals to and from the OLT 10. Furthermore, for example, the control unit 200 controls an opto-electrical conversion unit (not shown) to convert optical signals to and from electrical signals. Furthermore, for example, the control unit 200 controls a communication unit (not shown) to transmit and receive electrical signals to and from a user terminal.

[0057] Furthermore, for example, when the control unit 200 receives a signal from the OLT 10 instructing it to switch to a sleep state, it controls the power supply unit 202, which will be described later, to switch its own device from an active state to a sleep state. Furthermore, for example, when the control unit 200 receives a signal from the OLT 10 instructing it to switch to a active state, it controls the power supply unit 202 to switch its own device from a sleep state to a active state.

[0058] The signal transmitting / receiving unit 201 transmits and receives optical signals to and from the OLT 10. The signal transmitting / receiving unit 201 is a communication interface for communicating with the OLT 10.

[0059] The power supply unit 202 switches the power supply state of the device itself under the control of the control unit 200. For example, the power supply unit 202 switches the device itself between an active state, a sleep state, and a power-off state.

[0060] [Configuration of the control device] The functional configuration of the control device 40 will be described below. Fig. 5 is a block diagram showing the functional configuration of the control device 40 of the communication system 1 in one embodiment of the present invention. As shown in Fig. 5, the control device 40 is configured to include an OLT startup state control unit 401 and a path switching control unit 402. The OLT startup state control unit 401 and the path switching control unit 402 are configured using a processor such as a CPU, for example.

[0061] The OLT startup state control unit 401 is connected to each OLT 10 for communication via the communication line 61. The OLT startup state control unit 401 controls accommodation switching so that the ONU 20 to be switched, which is accommodated in the switching source OLT 10, is accommodated in the switching destination OLT 10. Specifically, the control device 40 transfers the ONU information (authentication data) stored in the OLT 10-2 that has been switched to the sleep state to the OLT 10-1, which is the accommodation switching destination.

[0062] The OLT startup state control unit 401 controls switching between the startup state and the sleep state of each OLT 10 by transmitting a control signal to each OLT 10. The OLT startup state control unit 401 collects ONU information from each OLT 10 that is in the startup state. The OLT startup state control unit 401 determines that an OLT 10 that does not store ONU information is an OLT that does not accommodate an ONU 20.

[0063] For example, the OLT startup state control unit 401 attempts to collect ONU information by transmitting a control signal requesting the provision of ONU information to each OLT 10. The OLT startup state control unit 401 determines that an OLT 10 that does not store ONU information (an OLT 10 that was unable to collect ONU information) is an OLT that does not accommodate an ONU 20. The OLT startup state control unit 401 transmits a control signal to switch the OLT 10 that is determined not to accommodate an ONU 20 to a sleep state.

[0064] The OLT startup state control unit 401 identifies an OLT 10 in which all of the accommodated ONUs 20 are in a state in which communication is not required (for example, a sleep state or a power-off state) based on the collected ONU information. The OLT startup state control unit 401 transmits a control signal to switch the OLT 10 to a sleep state when it is identified that all of the accommodated ONUs 20 are in a state in which communication is not required.

[0065] When the OLT startup state control unit 401 receives notification from the destination OLT 10 that the ONU 20 to be switched has started up, it transmits a control signal to the source OLT 10 to put the source OLT 10 back into the startup state.

[0066] The path switching control unit 402 is communicatively connected to the optical switch 30 via the communication line 62. The path switching control unit 402 controls the switching of signal paths by the optical switch 30 by sending a control signal to the optical switch 30. The path switching control unit 402 controls the optical switch 30 to perform path switching so that all ONUs 20 accommodated in the OLT 10 that has been switched to the sleep state are accommodated in another OLT 10. The path switching control unit 402 controls to establish a logical link between the switching destination OLT 10 and the switching target ONU 20.

[0067] [Maximum Number of ONUs] The following describes the maximum number of ONUs 20 that can be accommodated by the OLT 10. FIG.

[0068] In the structure of a communication network, devices are concentrated in higher hierarchical layers. Therefore, if the amount of traffic expected for upstream signals is too large for the upper-level device to handle, the upper-level device will apply back pressure to temporarily stop the transmission of upstream signals from the lower-level device.

[0069] In system design, it is necessary to design the OLT 10 assuming a case where all the accommodated ONUs 20 are in an activated state. Therefore, if the maximum number of ONUs 20 that the OLT 10 can accommodate is simply increased, it becomes necessary to increase the buffer memory of the OLT 10 or the buffer memory of the ONUs 20.

[0070] Generally, as shown in Fig. 6, if the maximum number of ONUs 20 accommodated in the OLT 10 increases, the upstream traffic will increase, but since there is a limit to the transfer speed on the upper device side, the OLT 10 will need a larger buffer memory (the portion marked "buffer memory (large)" of the OLT 10 on the left center of Fig. 6). Alternatively, as shown in Fig. 6, if the maximum number of ONUs 20 accommodated in the OLT 10 increases, the allocated bandwidth will become narrower, and the ONUs 20 will need a larger buffer memory until they transmit the upstream traffic (the portion marked "buffer memory (large)" of the ONU 20 on the right center of Fig. 6).

[0071] On the other hand, in the present invention, the "maximum number of ONUs 20 accommodated < the number of logical links" is set, but ONUs 20 that exceed the maximum number are ONUs 20 to be switched, and therefore do not require communication. Therefore, for these ONUs 20 that exceed the maximum number, there is no need to consider the continuity of the optical signal, which is the main signal, and only the control signal needs to be managed. As a result, in the present invention, since the impact of an increase in the number of accommodated units on the buffer memory of the OLT 10 or ONUs 20 is small, it is possible to monitor the sleep state and power-off state of ONUs 20 that exceed the maximum number (i.e., ONUs 20 to be switched).

[0072] [Operation of Control Device] An example of the operation of the control device 40 in this embodiment will be described below. Fig. 7 is a flowchart showing the operation of the control device 40 in one embodiment of the present invention. The operation of the control device 40 shown in the flowchart of Fig. 7 is started, for example, when the communication system 1 is started.

[0073] When the communication system 1 is started, the control device 40 starts each OLT 10 (step S01). The control device 40 causes each started OLT 10 to accommodate the ONUs 20 and perform various settings based on the ONU information (authentication data) stored in each OLT 10 (step S02).

[0074] The control device 40 collects ONU information from each OLT 10 and checks whether there has been a change in the accommodation or status of the ONU 20 (step S03). If there has been no change in the accommodation or status of the ONU 20 (step S03: No), the communication system 1 continues operation as is (remains in step S03).

[0075] If there is a change in the accommodation or status of the ONUs 20 (step S03, Yes), the control device 40 checks whether or not it has been able to collect ONU information (authentication data) for each ONU 20 (step S04). If the control device 40 has not been able to collect ONU information (authentication data) (step S04, No), the control device 40 sends a control signal to each OLT 10 to switch it to a sleep state (step S05). Then, the communication system 1 continues operation as is (return to step S03).

[0076] For each OLT 10 from which ONU information (authentication data) has been collected (Yes in step S04), the control device 40 checks whether all of the ONUs 20 accommodated therein are in a state in which communication is not required (for example, a sleep state or a power-off state) (step S06). For the OLT 10 in which at least one ONU 20 accommodated therein is in a state in which communication is not required (i.e., an ONU 20 that is active) (No in step S06), the communication system 1 continues operation as is (return to step S03).

[0077] For the OLT 10 in which all the ONUs 20 accommodated therein are in a state in which communication is unnecessary (step S06: Yes), the control device 40 checks (step S07) whether there is another OLT 10 that can switch the accommodation of the ONUs 20. If there is no other OLT 10 that can switch the accommodation of the ONUs 20 (step S07: No), the communication system 1 continues operation as is (return to step S03).

[0078] If there is another OLT 10 that can switch the accommodation of the ONU 20 (step S07: Yes), the control device 40 acquires the ONU information stored in the source OLT 10 and copies it to the destination OLT 10. Furthermore, the control device 40 controls the optical switch 30 to switch the signal path of the optical signal so that the accommodation of the ONU 20 to be switched is switched from the source OLT 10 to the destination OLT 10 (step S08).

[0079] The control device 40 checks whether the switching target ONUs 20, which are in a state where communication is not required, have started up based on whether or not there has been a notification from the switching target OLT 10 (step S09). If none of the switching target ONUs 20 have started up (i.e., if there has been no notification from the switching target OLT 10) (step S09: No), the communication system 1 continues operation as is (return to step S03).

[0080] If there is at least one activated ONU 20 to be switched (i.e., if a notification has been received from the destination OLT 10) (step S09, Yes), the control device 40 sends a control signal to the source OLT 10 to start it. Furthermore, the control device 40 controls the optical switch 30 to switch the signal path of the optical signal so that the accommodation of the ONU 20 to be switched is switched back from the destination OLT 10 to the source OLT 10 (step S10). The communication system 1 then continues operation as is (return to step S03).

[0081] [Processing at the time of accommodation switching to the switching destination OLT by the communication system] Hereinafter, an example of processing at the time of accommodation switching to the switching destination OLT 10 by the communication system 1 in this embodiment will be described. Fig. 8 is a sequence diagram showing the flow of processing at the time of accommodation switching to the switching destination OLT 10 by the communication system 1 in one embodiment of the present invention.

[0082] First, communication is taking place between the switching source OLT 10 and the ONU 20 (step S101). When the ONU 20 goes into sleep mode, it notifies the switching source OLT 10 that it will go into sleep mode (step S102). Then, the ONU 20 switches itself into sleep mode. Alternatively, the ONU 20 is switched to a power-off state by, for example, a user (step S103).

[0083] The switching source OLT 10 receives the notification sent from the ONU 20. The switching source OLT 10 checks whether there are any ONUs 20 that require communication among the ONUs 20 accommodated therein. Here, as an example, it is assumed that there are no ONUs 20 that require communication (step S104). The switching source OLT 10 notifies the control device 40 that there are no ONUs 20 that require communication (step S105). As described above, the control device 40 may be configured to attempt to collect ONU information from each OLT 10, identify the OLTs 10 for which it was unable to collect ONU information, and thereby recognize the OLTs 10 that do not have any ONUs 20 that require communication.

[0084] The control device 40 receives the notification sent from the switching source OLT 10. The control device 40 makes an inquiry to another OLT 10 that is in an active state, and checks whether the switching target ONU 20 accommodated in the switching source OLT 10 can be accommodated (step S106). Note that, as an example, it is assumed here that another OLT 10 exists that can accommodate the switching target ONU 20.

[0085] The destination OLT 10, which is another OLT 10 capable of accommodating the ONU 20 to be switched, transmits a response signal (OK response) indicating that it can accommodate the ONU 20 to the control device 40 (step S107). The control device 40 receives the response signal transmitted from the destination OLT 10. The control device 40 acquires ONU information from the source OLT 10 and transmits it to the destination OLT 10 (step S108). The destination OLT 10 receives the ONU information transmitted from the control device 40. The destination OLT 10 stores (copies) the received ONU information in its own device. The destination OLT 10 transmits a response signal indicating that the copying of the ONU information has been completed to the control device 40 (step S109).

[0086] The control device 40 transmits a pre-switching instruction indicating that the accommodation of the switching target ONU 20 will be switched to the switching source ONU 10 (step S110). The switching source ONU 10 receives the pre-switching instruction transmitted from the control device 40.

[0087] The following steps S111 to S113 are executed only when the ONU 20 is in a sleep state. In other words, when the ONU 20 is in a power-off state, the following steps S111 to S113 are not executed.

[0088] The switching source OLT 10 transmits a start-up instruction to the switching target ONU 20 to temporarily return it from a sleep state to an active state (step S111). The switching target ONU 20 receives the start-up instruction transmitted from the switching source OLT 10. Upon receiving the start-up instruction, the switching target ONU 20 switches its own device from a sleep state to an active state (step S112). Upon switching to the active state, the switching target ONU 20 transmits a start-up report indicating that start-up has been completed to the switching source OLT 10 (step S113).

[0089] The switching source OLT 10 receives the startup report transmitted from the switching target ONU 20. The switching source OLT 10 transmits a response signal (preparation OK response) indicating that the switching target ONU 20 has started up and that advance preparation for accommodation switching has been completed to the control device 40 (step S114). The control device 40 receives the response signal transmitted from the switching source OLT 10. Upon receiving the response signal, the control device 40 transmits a control signal (path switching instruction) to the optical switch 30 instructing switching of the signal path for accommodation switching (step S115).

[0090] The optical switch 30 receives the control signal (path switching instruction) transmitted from the control device 40. Upon receiving the control signal, the optical switch 30 switches the signal path so as to switch the accommodation of the ONU 20 to be switched from the source OLT 10 to the destination OLT 10. Upon completing the switching of the signal path, the optical switch 30 transmits a response signal (path switching completion response) indicating the completion to the control device 40 (step S116).

[0091] The following steps S117 to S120 are executed only when the ONU 20 is in a sleep state. In other words, when the ONU 20 is in a power-off state, the following steps S117 to S120 are not executed.

[0092] When the switching of the signal path is completed, a logical link is established between the switching destination OLT 10 and the switching target ONU 20 (step S117). When the logical link is established, the switching destination OLT 10 transmits a notification (logical link establishment report) indicating that the logical link has been established to the control device 40 (step S118). In addition, the switching destination OLT 10 transmits a control signal (sleep instruction) indicating an instruction to put the switching target ONU 20 into a sleep state again to the switching target ONU 20 (step S119).

[0093] The switching target ONU 20 receives the sleep instruction transmitted from the switching destination OLT 10. Upon receiving the sleep instruction, the switching target ONU 20 switches its own device from the active state to the sleep state again (step S120).

[0094] Furthermore, the control device 40 transmits a control signal (sleep instruction) indicating an instruction to place the switching source OLT 10 in a sleep state to the switching source OLT 10 (step S121). The switching source OLT 10 receives the sleep instruction transmitted from the control device 40. Upon receiving the sleep instruction, the switching source OLT 10 switches its own device from an active state to a sleep state (step S121).

[0095] [Processing when re-accommodating to the switching source OLT by the communication system] Hereinafter, an example of processing when re-accommodating to the switching source OLT 10 by the communication system 1 in this embodiment will be described. Figure 9 is a sequence diagram showing the flow of processing when re-accommodating to the switching source OLT 10 by the communication system 1 in one embodiment of the present invention.

[0096] First, it is assumed that the accommodation destination is switched to the switching destination OLT 10, and at least one of the switching target ONUs 20 that are in a state where communication is not required (sleep state or power-off state) is started up (step S201). When the switching target ONU 20 switches to an active state, it notifies the switching destination OLT 10 that it has started up (step S202).

[0097] The switching destination OLT 10 receives the notification indicating the startup transmitted from the switching target ONU 20. Upon receiving the notification, the switching destination OLT 10 further transmits a notification indicating the startup of the switching target ONU 20 (ONU startup notification) to the control device 40 (step S203).

[0098] The control device 40 receives the notification transmitted from the switching destination OLT 10. Upon receiving the ONU startup notification, the control device 40 transmits a control signal (startup instruction) to the startup source OLT 10, restarting the startup source OLT 10 (step S204). Furthermore, upon receiving the ONU startup notification, the control device 40 transmits a control signal (path switching instruction) to the optical switch 30, causing the signal path to be switched so that the OLT accommodating the ONU 20 to be switched is switched back from the switching destination OLT 10 to the switching source OLT 10 (step S205).

[0099] The optical switch 30 receives a control signal (path switching instruction) transmitted from the control device 40. Upon receiving the control signal (path switching instruction), the optical switch 30 switches the signal path so that the OLT accommodating the ONU 20 to be switched is switched from the destination OLT 10 to the source OLT 10. Upon completing the switching of the signal path, the optical switch 30 transmits a response signal (path switching completion response) indicating the completion to the control device 40 (step S206).

[0100] Furthermore, when the switching source OLT 10 switches from the sleep state to the active state, it transmits a notification (activation completion notification) indicating that the switch to the active state has been completed to the control device 40 (step S207). The control device 40 receives the notification (activation completion notification) transmitted from the switching source OLT 10. When the switching source OLT 10 enters the active state again and the path switching is completed, communication is resumed between the switching source OLT 10 and the ONU 20 (step S208).

[0101] In the embodiment described above, when at least one of the switching target ONUs 20 whose accommodation has been switched to the switching target OLT 10 starts up again, the accommodation of the switching target ONU 20 is immediately returned from the switching target OLT 10 to the switching source OLT 10. However, the present invention is not limited to this configuration, and for example, a predetermined threshold may be set in advance for the number of ONUs 20 accommodated in the switching target OLT 10, and the accommodation of the switching target ONU 20 may be returned from the switching target OLT 10 to the switching source OLT 10 only when the number of ONUs 20 accommodated in the switching target OLT 10 exceeds the threshold.

[0102] In other words, if there is still room for the ONU 20 in the destination OLT 10, rather than immediately returning the accommodation of the ONU 20 to be switched back to the original OLT 10, the destination OLT 10 may remain connected to the ONU 20 to be switched and send and receive optical signals until there is no room for accommodation.

[0103] As described above, the communication system 1 according to one embodiment of the present invention switches the OLT 10 to a sleep state when the OLT 10 does not accommodate an ONU 20. Furthermore, when all of the ONUs 20 accommodated by the OLT 10 are in a state where communication is not required (a sleep state or a power-off state), the communication system 1 switches the accommodation of the ONU 20 (the ONU 20 to be switched) to another active OLT 10 (the OLT 10 to be switched to). The communication system 1 then switches the source OLT 10 to a sleep state.

[0104] With this configuration, the communication system 1 according to an embodiment of the present invention can switch the unused OLT 10 to a sleep state while satisfying the requirement that communication is possible when the user uses the OLT 10. This allows the communication system 1 to reduce the power consumption of the OLT 10.

[0105] As described above, in the communication system 1 according to one embodiment of the present invention, the ONU 20 to be switched, whose accommodation has been switched, is an ONU that does not require communication (sleep state or power-off state). Therefore, the OLT 10 to be switched establishes a logical link with the ONU 20 to be switched, and only monitors the startup of the ONU 20 to be switched, and does not perform any other functions. This allows the communication system 1 to suppress an increase in the consumption of resources by the OLT 10.

[0106] By having such a configuration, the communication system 1 in one embodiment of the present invention can allow the OLT 10 (the OLT 10 to be switched to) to accommodate additional ONUs 20 to be switched to without improving the performance of the OLT 10 equipment or reducing the maximum number of ONUs 20 that can be accommodated.

[0107] According to the above-described embodiment, the communication system includes a first terminal device, a second terminal device, at least one terminating device, and a control device. For example, the communication system is the communication system 1 in the embodiment, the first terminal device is the OLT 10 as the switching source in the embodiment, the second terminal device is the OLT 10 as the switching destination in the embodiment, the terminating device is the ONU 20 in the embodiment, and the control device is the control device 40 in the embodiment.

[0108] The control device includes a switching control unit and an activation state control unit. For example, the switching control unit is the path switching control unit 402 in the embodiment, and the state control unit is the OLT activation state control unit 401 in the embodiment. When all the terminating devices accommodated in the first terminal device are not communicating, the switching control unit switches the accommodation of all the terminating devices accommodated in the first terminal device from the first terminal device to the second terminal device. When all the terminating devices accommodated in the first terminal device are not communicating, the activation state control unit switches the activation state of the first terminal device to a sleep state.

[0109] In the above communication system, the activation state control unit may switch the activation state of the first terminal device to a sleep state when the first terminal device does not accommodate a terminating device.

[0110] In the above communication system, the second terminal device may include a monitoring unit. For example, the monitoring unit is the control unit 100 in the embodiment. The monitoring unit may monitor the activation of the terminating device whose accommodation has been switched to the second terminal device. The activation status control unit may start the first terminal device when the monitoring unit detects the activation of the terminating device. The switching control unit may switch the accommodation of the terminating device from the second terminal device to the first terminal device again when the activation is detected.

[0111] In the above communication system, a logical link may be established between the second terminal device and the terminating device.

[0112] In the above communication system, the monitoring unit may monitor the activation of the terminating device using a multipoint control protocol (MPCP).

[0113] In the above communication system, the second terminal device may include a monitoring unit. For example, the monitoring unit is the control unit 100 in the embodiment. The monitoring unit may monitor the activation of a terminating device whose accommodation has been switched to the second terminal device. When the monitoring unit detects activation of a terminating device, the activation status control unit may activate the first terminal device if the number of terminating devices accommodated in the second terminal device exceeds a predetermined threshold. When the activation is detected, the switching control unit may switch the accommodation of the terminating device from the second terminal device back to the first terminal device if the number of terminating devices accommodated in the second terminal device exceeds a predetermined threshold.

[0114] According to the above-described embodiment, the control device includes a switching control unit and a startup state control unit. For example, the switching control unit is the path switching control unit 402 in the embodiment, and the state control unit is the OLT startup state control unit 401 in the embodiment.

[0115] The switching control unit switches the accommodation of all the terminating devices accommodated in the first terminal device from the first terminal device to the second terminal device when all the terminating devices accommodated in the first terminal device are not communicating. For example, the first terminal device is the OLT 10 as the switching source in the embodiment, the second terminal device is the OLT 10 as the switching destination in the embodiment, the terminating devices are the ONUs 20 in the embodiment, and the control device is the control device 40 in the embodiment. The startup state control unit switches the startup state of the first terminal device to a sleep state when all the terminating devices accommodated in the first terminal device are not communicating.

[0116] Some or all of the components of the devices included in the communication system 1 in the above-described embodiment may be implemented by a computer. In this case, a program for implementing the functions may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Note that the term "computer system" as used herein includes hardware such as an OS and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording medium" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs via networks such as the Internet or telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within the computer system serving as the server or client. The program may be designed to implement some of the functions described above, or may be capable of implementing the functions in combination with a program already stored in the computer system, or may be implemented using a programmable logic device such as an FPGA (Field Programmable Gate Array).

[0117] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0118] REFERENCE SIGNS LIST 1 Communication system 30 Optical switch 35 Splitter 40 Control device 51 to 54 Optical transmission path 61, 62 Communication line 100 Control unit 101 Signal transmitting / receiving unit 102 ONU status management unit 103 ONU information holding unit 104 Power supply unit 200 Control unit 201 Signal transmitting / receiving unit 202 Power supply unit 401 OLT startup status control unit 402 Path switching control unit

Claims

1. A communication system having a first terminal device, a second terminal device, at least one terminating device, and a control device, wherein the control device comprises: a switching control unit that switches the accommodation of all of the terminating devices accommodated in the first terminal device from the first terminal device to the second terminal device when all of the terminating devices accommodated in the first terminal device are not communicating; and an activation state control unit that switches the activation state of the first terminal device to a sleep state when all of the terminating devices accommodated in the first terminal device are not communicating.

2. The communication system according to claim 1, wherein said activation state control section switches the activation state of said first terminal device to a sleep state when said first terminal device does not accommodate said terminating device.

3. The communication system described in claim 1, wherein the second terminal device comprises a monitoring unit that monitors the activation of the terminating device whose accommodation has been switched to the second terminal device, the activation status control unit activates the first terminal device when the monitoring unit detects the activation of the terminating device, and the switching control unit switches the accommodation of the terminating device from the second terminal device back to the first terminal device when the activation is detected.

4. The communication system according to claim 3, wherein the second terminal device and the terminating device establish a logical link.

5. The communication system according to claim 3, wherein said monitoring unit monitors said activation of said terminating device using a multipoint control protocol.

6. The communication system of claim 1, wherein the second terminal device comprises a monitoring unit that monitors the activation of the terminating device whose accommodation has been switched to the second terminal device, and the activation status control unit, when the monitoring unit detects the activation of the terminating device, activates the first terminal device if the number of terminating devices accommodated in the second terminal device exceeds a predetermined threshold, and the switching control unit, when the activation is detected, switches the accommodation of the terminating device from the second terminal device back to the first terminal device if the number of terminating devices accommodated in the second terminal device exceeds a predetermined threshold.

7. A control device comprising: a switching control unit that switches the accommodation of all terminating devices accommodated in a first terminal device from the first terminal device to a second terminal device when all terminating devices accommodated in the first terminal device are not communicating; and an activation state control unit that switches the activation state of the first terminal device to a sleep state when all terminating devices accommodated in the first terminal device are not communicating.

8. A communication control method by a computer, comprising: a switching control step of switching the accommodation of all terminating devices accommodated in a first terminal device from the first terminal device to a second terminal device when all terminating devices accommodated in the first terminal device are not communicating; and an activation state control step of switching the activation state of the first terminal device to a sleep state when all terminating devices accommodated in the first terminal device are not communicating.

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