Station-side equipment, optical communication system, program, and search method

Abstract

To more accurately identify an abnormally light emitting ONU.SOLUTION: An OLT 110 comprises: an optical transmitting / receiving section 111 which transmits / receives an optical signal to / from a plurality of ONUs 130 in a time division manner; an abnormal light emission detection section 112 for monitoring an optical signal received by the optical transmitting / receiving section 111 and detecting a state where the optical signals are being received as long as or longer than a predetermined period as abnormal light emission in which an optical signal from one or more ONUs 130 included in the plurality of ONUs 130 cannot be received more; and an optical communication control section 114 by which one ONU 130 is selected as a target PNU 130 successively from among the plurality of ONUs 130 excluding the one or more ONUs 130, it is inspected whether or not the abnormal light emission is cancelled by stopping the transmission of the optical signal from the target ONU 130 via the optical transmitting / receiving section 111 and, in a case where the abnormal light emission is cancelled, the target ONU 130 is identified as an abnormally light emitting ONU 130.SELECTED DRAWING: Figure 1

Description

Technical Field

[0005]

[0001] The present disclosure relates to a local device and an optical communication system , program and and a search method.

Background Art

[0002] As a method for providing a user with an optical access service such as FTTH (Fiber To The Home), there is a PON (Passive Optical Network) method. In a PON system, which is a system using this PON method, a plurality of ONUs (Optical Network Units), which are subscriber-side devices, are connected to an OLT (Optical Line Terminal), which is a local device. In the PON system, by using an optical fiber as a transmission path, it is possible to provide a high-speed access service at a low cost. Currently, ONUs have become widespread in each household.

[0003] In the PON system, the OLT and a plurality of ONUs are connected by an optical fiber. In order to correctly reproduce a signal at the OLT, it is necessary to manage the optical transmission timing of the ONUs so that the plurality of ONUs do not emit light simultaneously. For this reason, the OLT instructs the target ONU of the emission timing, and the ONU is controlled to emit light only at the instructed time.

[0004] And Patent Document 1 discloses an OLT that can identify an ONU that is always emitting light. In Patent Document 1, when all ONUs other than one ONU become unregistered within a predetermined time, the OLT identifies that one ONU is an ONU that is always emitting light.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] With conventional technology, if an irregular abnormal light emission occurs, for example, when the abnormal light emission temporarily resolves, and the system is searching for an ONU at the time the abnormal light emission resolves, it may mistakenly identify a normal ONU as being in an abnormal state, potentially leading to the shutdown of several normal ONUs.

[0007] Therefore, one or more aspects of this disclosure aim to enable more accurate identification of an ONU that emits abnormal light. [Means for solving the problem]

[0008] A central office-side device according to one aspect of this disclosure is an optical transceiver that transmits and receives optical signals in time division with multiple subscriber-side devices. In the club An abnormal light emission detection unit monitors the received optical signal and detects a state in which the optical signal has been received for a predetermined period of time or longer as an abnormal light emission in which an optical signal cannot be received from one or more subscriber-side devices included in the plurality of subscriber-side devices, and the plurality of subscriber-side devices excluding the one or more subscriber-side devices Included By selecting one subscriber-side device as the target subscriber-side device and stopping the transmission of optical signals from the said target subscriber-side device, 、 When the abnormal light emission is resolved, the target subscriber-side device but , the abnormal light emission described above is being performed and It is characterized by comprising a specified optical communication control unit.

[0009] An optical communication system relating to one aspect of this disclosure is: The above Station-side equipment and, The plurality of subscriber-side devices, It is characterized by being equipped with.

[0010] A search method according to one aspect of this disclosure receives optical signals in time division with multiple subscriber-side devices, monitors the received optical signals, detects a state in which optical signals have been received for a predetermined period of time or longer as an abnormal emission in which optical signals can no longer be received from one or more subscriber-side devices included in the multiple subscriber-side devices, and detects the multiple subscriber-side devices excluding the one or more subscriber-side devices Included By selecting one subscriber-side device as the target subscriber-side device and stopping the transmission of optical signals from the said target subscriber-side device, 、 When the abnormal light emission is resolved, the target subscriber-side device but , the abnormal light emission described above is being performed and It is characterized by its ability to specify. [Effects of the Invention]

[0011] According to one or more aspects of this disclosure, an ONU exhibiting abnormal light emission can be identified more accurately. [Brief explanation of the drawing]

[0012] [Figure 1] This is a block diagram schematically showing the configuration of the PON system according to Embodiments 1 and 2. [Figure 2] This is a schematic diagram showing a first example of link status management information in Embodiment 1. [Figure 3] (A) and (B) are block diagrams showing hardware configuration examples. [Figure 4] This flowchart shows the operation of the OLT when searching for an ONU that is emitting abnormal light in Embodiment 1. [Figure 5] This is a schematic diagram showing a second example of link status management information in Embodiment 1. [Figure 6] This is a schematic diagram showing a third example of link status management information in Embodiment 1. [Figure 7] This is a schematic diagram showing a fourth example of link status management information in Embodiment 1. [Figure 8] This is a schematic diagram showing a fifth example of link status management information in Embodiment 1. [Figure 9] It is a schematic diagram showing a sixth example of link state management information in Embodiment 1. [Figure 10] It is a schematic diagram showing a seventh example of link state management information in Embodiment 1. [Figure 11] It is a first schematic diagram for explaining an overview of operations in the PON system in Embodiment 1. [Figure 12] It is a second schematic diagram for explaining an overview of operations in the PON system in Embodiment 1. [Figure 13] It is a third schematic diagram for explaining an overview of operations in the PON system in Embodiment 1. [Figure 14] It is a schematic diagram showing a first example of link state management information in Embodiment 2. [Figure 15] In Embodiment 2, it is a first flowchart showing operations when the OLT searches for an ONU that is emitting light abnormally. [Figure 16] In Embodiment 2, it is a second flowchart showing operations when the OLT searches for an ONU that is emitting light abnormally. [Figure 17] In Embodiment 2, it is a third flowchart showing operations when the OLT searches for an ONU that is emitting light abnormally. [Figure 18] It is a schematic diagram showing a second example of link state management information in Embodiment 2. [Figure 19] It is a schematic diagram showing a third example of link state management information in Embodiment 2. [Figure 20] It is a schematic diagram showing a fourth example of link state management information in Embodiment 2. [Figure 21] It is a schematic diagram showing a fifth example of link state management information in Embodiment 2. [Figure 22] It is a schematic diagram showing a sixth example of link state management information in Embodiment 2. [Figure 23] It is a schematic diagram showing a seventh example of link state management information in Embodiment 2. [Figure 24]This is a schematic diagram showing an eighth example of link status management information in Embodiment 2. [Modes for carrying out the invention]

[0013] Embodiment 1. Figure 1 is a block diagram schematically showing the configuration of the PON system 100 as an optical communication system according to Embodiment 1. The PON system 100 comprises an OLT 110, which is a terminal device on the central office side, and multiple ONUs 130. In the PON system 100, the OLT 110 and the multiple ONUs 130 are connected via optical fiber 101 and optical splitter 102.

[0014] Each of the multiple ONU130s is assigned an ID (IDentification) as ONU identification information to distinguish each of the multiple ONU130s. Here, we assume that positive integers are assigned sequentially starting from "1". In the following explanation, an ONU130 with ID=i may be referred to as ONU#i. For example, an ONU130 with ID=1 may be referred to as ONU#1. As shown in Figure 1, i is a positive integer satisfying 1 ≤ i ≤ n (where n is a positive integer greater than or equal to 2).

[0015] The OLT110 comprises an optical transceiver unit 111, an abnormal light emission detection unit 112, a link state storage unit 113, an optical communication control unit 114, and a communication unit 118.

[0016] The optical transceiver unit 111 transmits and receives optical signals in time division with multiple ONUs 130. For example, the optical transceiver 111 receives an upstream signal from the ONU 130 and provides that signal to the PON control unit 117. The optical transceiver 111 also transmits a downstream signal to the ONU 130. The optical transceiver 111 has a WDM (Wavelength Division Multiplexing) function that combines the upstream signal and the downstream signal.

[0017] The abnormal light emission detection unit 112 monitors the optical signals received by the optical transceiver unit 111 and detects a state in which an optical signal has been received for a predetermined period of time or longer as an abnormal light emission in which an optical signal cannot be received from one or more ONUs 130 included in the multiple ONUs 130. For example, the abnormal light emission detection unit 112 monitors the upstream signal from the ONU 130 received by the optical transceiver unit 111, and if the light emission state continues for a predetermined period, it detects abnormal light emission from the ONU 130 and sends an abnormal light emission notification to the link status management unit 115 to notify it of the abnormal light emission from the ONU 130. Note that if the link between the OLT 110 and each ONU 130 is normal, each ONU 130 will not maintain a light emission state for longer than a predetermined period. Therefore, if the light emission state exceeds the predetermined period, it is possible to detect that one of the multiple ONU 130s is emitting abnormal light. When the light emission state for the predetermined period is resolved, the abnormal light emission detection unit 112 sends an abnormal light emission release notification to the link status management unit 115 to notify it that the abnormal light emission from the ONU 130 has been released.

[0018] The link state storage unit 113 stores link state management information for managing the link state of the ONU 130. Figure 2 is a schematic diagram showing an example of link status management information in Embodiment 1. As shown in Figure 2, the link status management table 113a, which is an example of link status management information, is a table-format data comprising an ID column 113b, an ONU status column 113c, an abnormal light emission detection status column 113d, and a classification column 113e.

[0019] ID column 113b stores the ID assigned to ONU130. The ONU status column 113c stores the ONU status, which is the state of the ONU 130. The ONU status is "Register" when linked to the OLT 110, "Deregister" when not linked to the OLT 110, and "Power off" when the ONU 130 is powered off.

[0020] The abnormal light emission detection status column 113d stores the abnormal light emission detection status, indicating whether or not abnormal light emission has been detected in the ONU 130 connected to the OLT 110. If no abnormal light emission has been detected in any of the ONU 130s connected to the OLT 110, it will be "Normal," which means a normal light emission state. If abnormal light emission has been detected in any of the ONU 130s connected to the OLT 110, it will be "Abnormal," which means an abnormal light emission state.

[0021] Classification column 113e stores the classification of the inspection status of the light emission state of the ONU 130 in the OLT 110. For example, if no abnormal light emission is detected in the ONU130 connected to the OLT110, in other words, if "Normal" is stored in the abnormal light emission detection status column 113d, then the classification column 113e will store "normal" if the ONU status column 113c is "Register", and the same value as the ONU status column 113c will be stored if the ONU status column 113c is anything other than "Register". On the other hand, if abnormal light emission is detected in the ONU130 connected to the OLT110, in other words, if "Abnormal" is stored in the abnormal light emission detection status column 113d, then the classification column 113e will store "damaged" if the corresponding ONU130 is deregistered when abnormal light emission is detected, indicating that it is not subject to inspection; "in test" if the corresponding ONU130 is being inspected; "tested" if the inspection of the corresponding ONU130 is completed and it is determined that there is no abnormal light emission, indicating that the inspection is complete; and "suspected" if there is a possibility that the corresponding ONU130 is emitting abnormal light.

[0022] Returning to Figure 1, the optical communication control unit 114 controls communication at the OLT 110. For example, when the optical communication control unit 114 detects abnormal light emission that prevents it from receiving optical signals from one or more ONUs 130 included in the multiple ONUs 130, it sequentially selects one ONU 130 from the remaining ONUs 130 as the target ONU 130, and checks whether the abnormal light emission is resolved by stopping the transmission of optical signals from the target ONU 130 via the optical transceiver unit 111. If the abnormal light emission is resolved, the unit identifies the currently selected target ONU 130 as the causative ONU 130 that is causing the abnormal light emission. The optical communication control unit 114 includes a link status management unit 115, an abnormal light emission management unit 116, and a PON control unit 117.

[0023] The link status management unit 115 manages the link status of each ONU 130 and the abnormal light emission status of each ONU 130 using the link status management information stored in the link status storage unit 113. The link status management unit 115 receives notifications of changes in the link status of each ONU 130 and requests from the PON control unit 117, updates or verifies the link status of each ONU 130 in the link status management information, and notifies the PON control unit 117 of the details. Furthermore, the link status management unit 115 receives an abnormal light emission notification or an abnormal light emission cancellation notification from the abnormal light emission detection unit 112, and updates the abnormal light emission detection status in the link status management information in order to manage the abnormal light emission detection status of the ONU 130.

[0024] Furthermore, the link status management unit 115 manages the classification of the light emission inspection status in the link status management information based on the abnormal light emission notification or abnormal light emission release notification from the abnormal light emission detection unit 112 and the link status of each ONU 130. Based on the link status of each ONU 130 and the classification of the light emission inspection status, the link status management unit 115 notifies the abnormal light emission management unit 116 of the ID of the ONU 130 to be subjected to ONU optical shutdown or ONU optical shutdown release, and the flag for ONU optical shutdown or ONU optical shutdown release.

[0025] The abnormal light emission management unit 116, based on the ID notified by the link status management unit 115 and the flags for ONU optical shutdown or ONU optical shutdown release, provides the PON control unit 117 with an ONU optical shutdown notification to notify the ONU 130 corresponding to that ID to perform an optical shutdown, or an ONU optical shutdown release notification to notify the ONU 130 corresponding to that ID to release the optical shutdown.

[0026] The PON control unit 117 controls the overall processing in the OLT 110. For example, the PON control unit 117 performs PON interface control. Specifically, when the PON control unit 117 receives an ONU optical shutdown notification or an ONU optical shutdown release notification from the abnormal light emission management unit 116, it forwards the ONU optical shutdown notification or ONU optical shutdown release notification to the ONU 130 via the optical transceiver unit 111.

[0027] Furthermore, the PON control unit 117 transmits the alarm information sent from the ONU 130 to the external monitoring system 150 via the communication unit 118, and also provides that information to the link status management unit 115.

[0028] Furthermore, the PON control unit 117 receives setting or request notifications regarding PON termination between the OLT 110 and each ONU 130 from the external monitoring system 150 via the communication unit 118. The PON control unit 117 receives information regarding the link status of the ONU 130 from the external monitoring system 150 via the communication unit 118, provides this information to the link status management unit 115, receives a response from the link status management unit 115, and sends it to the external monitoring system 150 via the communication unit 118.

[0029] The communications unit 118 communicates with the external monitoring system 150.

[0030] Some or all of the abnormal light emission detection unit 112 and optical communication control unit 114 described above can be configured, for example, as shown in Figure 3(A), with a memory 10 and a processor 11 such as a CPU (Central Processing Unit) that executes the program stored in the memory 10. Such a program may be provided via a network or recorded on a recording medium. That is, such a program may be provided, for example, as a program product.

[0031] Furthermore, some or all of the abnormal light emission detection unit 112 and the optical communication control unit 114 can be composed of processing circuits 12 such as a single circuit, a composite circuit, a program-operated processor, a program-operated parallel processor, an ASIC (Application Specific Integrated Circuit), or an FPGA (Field Programmable Gate Array), as shown in Figure 3(B). As described above, the optical communication control unit 114 can be realized by a processing circuit network.

[0032] The optical transceiver unit 111 can be realized by connecting the optical fiber 101 and using an optical communication interface for performing optical communication. Furthermore, the communication unit 118 can be implemented using a communication interface such as a NIC (Network Interface Card) that communicates using wired or wireless connections. The link state storage unit 113 can be implemented using volatile memory or non-volatile memory.

[0033] Returning to Figure 1, the ONU 130 comprises an optical transceiver unit 131, a PON control unit 132, and an optical output control unit 133. Figure 1 shows the internal configuration only for the top-most ONU130, but the other ONU130s are configured similarly.

[0034] The optical transceiver 131 receives the signal transmitted from the optical transceiver 111 of the OLT 110 and travels through the optical fiber 101 and the optical splitter 102. The optical transceiver 131 then provides this signal to the PON control unit 132. Furthermore, the optical transceiver 131 transmits the signal provided by the PON control unit 132 to the OLT 110. Furthermore, the optical transceiver 131 stops or resumes the emission of transmitted light based on a notification to stop or to resume the transmission of transmitted light instructed by the optical output control unit 133.

[0035] The PON control unit 132 controls the processing performed by the ONU 130. For example, the PON control unit 132 performs PON interface control. Specifically, the PON control unit 132 performs PON termination processing on the ONU 130 side for signals transmitted from the OLT 110 via the optical transceiver unit 111. Furthermore, the PON control unit 132 notifies the OLT 110 of alarm information from the ONU 130 and the current status of the ONU 130 via the optical transceiver unit 131. Furthermore, the PON control unit 132 forwards the downstream signal received from the optical transceiver unit 131 to an external terminal (not shown). In addition, the PON control unit 132 provides the optical output control unit 133 with an ONU optical shutdown notification or an ONU optical shutdown release notification transmitted from the OLT 110.

[0036] Based on an ONU optical shutdown notification or an ONU optical shutdown release notification provided by the PON control unit 132, the optical transceiver unit 133 instructs the optical transceiver unit 131 to stop or resume transmitting light emitted by the optical transceiver unit 131.

[0037] Some or all of the PON control unit 132 and optical output control unit 133 described above can be configured, for example, with a memory 10 and a processor 11 such as a CPU that executes the program stored in the memory 10, as shown in Figure 3(A). Such a program may be provided via a network or by being recorded on a recording medium. That is, such a program may be provided, for example, as a program product.

[0038] Furthermore, part or all of the PON control unit 132 and the optical output control unit 133 can also be composed of a processing circuit 12 such as a single circuit, a composite circuit, a program-operated processor, a program-operated parallel processor, an ASIC, or an FPGA, as shown in Figure 3(B). As described above, the PON control unit 132 and the optical output control unit 133 can be implemented by a processing circuit network.

[0039] The optical transceiver unit 131 can be realized by connecting the optical fiber 101 and using an optical communication interface for performing optical communication.

[0040] Next, we will explain how the OLT110 manages the link status of the ONU130. Figure 4 is a flowchart showing the operation of OLT110 when it searches for ONU130 which is emitting abnormal light. Furthermore, if the ONU130 that is emitting abnormal light is not connected to the OLT110, the abnormal light emission detection status column 113d will contain "Normal," as shown in the link status management table 113a in Figure 2.

[0041] First, the abnormal light emission detection unit 112 monitors the uplink signal from the ONU 130 received by the optical transceiver unit 111 to determine whether or not abnormal light emission is detected (S10). Here, the abnormal light emission detection unit 112 detects abnormal light emission if the light emission state continues for a predetermined period of time. If abnormal light emission is detected (Yes in S10), the abnormal light emission detection unit 112 notifies the link status management unit 115 of the abnormal light emission from the ONU 130, and the process proceeds to step S11.

[0042] When the link status management unit 115 receives an abnormal light emission notification, it updates the abnormal light emission detection status in the link status management information stored in the link status storage unit 113 to indicate an abnormal light emission status, and confirms the ONU status and classification (S11). For example, as shown in the link status management table 113a#1 shown in Figure 5, the link status management unit 115 updates the abnormal light emission detection status column 113d to "Abnormal" to indicate an abnormal light emission status, and confirms the values ​​of the ONU status column 113c and the classification column 113e.

[0043] The link status management unit 115 then checks the ONU status and classification of the link status management information stored in the link status storage unit 113 to determine whether or not there are any ONUs 130 that have entered a deregistered state when abnormal light emission is detected (S12). When abnormal light emission is detected, the light emission state of a certain ONU 130 continues for a predetermined period, making it impossible to receive the optical signal of the ONU 130 that is supposed to transmit an optical signal during that period. For this reason, as shown in the link status management table 113a#2 shown in Figure 6, there are ONUs 130 in which "normal" is stored in the classification column 113e and "Deregister" is stored in the ONU status column 113c. In the example shown in Figure 6, ONU#2 and ONU#3 are ONUs 130 that have entered a deregistered state. If there are any ONUs 130 that have entered a deregistered state (Yes in S12), the process proceeds to step S13; if there are no ONUs 130 that have entered a deregistered state (No in S12), the process proceeds to step S14.

[0044] In step S13, the link status management unit 115 updates the inspection status classification of the ONU 130 that has entered a deregistered state when abnormal light emission is detected to exclude it from the target. For example, if ONU#2 and ONU#3 enter a deregistered state as shown in Figure 6, the link status management unit 115 updates the value of the classification column 113e for ONU#2 and ONU#3 to "damaged", as shown in the link status management table 113a#3 shown in Figure 7. Then the process proceeds to step S14.

[0045] In step S14, the link status management unit 115 identifies one ONU 130 from among the ONUs 130 whose inspection status is classified as normal, and notifies the abnormal light emission management unit 116 of its ID and an optical shutdown flag so that the identified ONU 130 should be optically shut down. Here, the link status management unit 115 identifies one ONU 130 in order from the lowest ID. The identified ONU 130 is also called the target ONU 130. Upon receiving notification of the ID and the optical shutdown flag, the abnormal light emission management unit 116 generates an ONU optical shutdown notification informing the ONU 130 corresponding to that ID to perform an optical shutdown, and provides the ONU optical shutdown notification to the PON control unit 117. When the PON control unit 117 receives the ONU optical shutdown notification from the abnormal light emission management unit 116, it forwards the ONU optical shutdown notification to the corresponding ONU 130 via the optical transceiver unit 111.

[0046] Upon receiving an ONU optical shutdown notification, the PON control unit 132 of the ONU 130 transmits the notification to the optical output control unit 133. The optical output control unit 133 then instructs the optical transceiver unit 131 to stop emitting transmitted light and to send an optical shutdown notification response to the OLT 110. Upon receiving such a response, the OLT 110 sends the response to the link status management unit 115 via the PON control unit 117. The link status management unit 115 updates the inspection status classification of the ONU 130 that sent the response during the inspection (S15). For example, as shown in Figure 8, when a response is received from ONU#1, the value of the classification column 113e corresponding to ONU#1 in the link status management table 113a#4 is updated to "in test". Note that if there is an ONU 130 in the "in test" state, the link status management unit 115 does not send an optical shutdown notification to another ONU 130.

[0047] Next, the abnormal light emission detection unit 112 monitors the uplink signal from the ONU 130 received by the optical transceiver unit 111 to determine whether the abnormal light emission will be resolved after the ONU optical shutdown is performed (S16). Here, the abnormal light emission detection unit 112 monitors the uplink signal from the ONU 130 for a certain period of time, and if the light emission state is resolved within that period, it detects that the abnormal light emission has been resolved. If the abnormal light emission is resolved (Yes in S16), the abnormal light emission detection unit 112 sends an abnormal light emission release notification from the ONU 130 to the link status management unit 115, and the process proceeds to step S17. If the abnormal light emission is not resolved (No in S16), the process proceeds to step S18.

[0048] In step S17, since the abnormal light emission is resolved by shutting down the optical signal of the target ONU 130, the link status management unit 115 identifies the target ONU 130 as the cause ONU 130 that is causing the abnormal light emission. For example, if ONU#1 is the target ONU 130, the value in the classification column 113e of ONU#1 is updated to "suspected," as shown in link status management table 113a#5 in Figure 9. In this case, the ONU status of ONU 130, which was in the unregistered state, returns to the registered state. Therefore, for example, if ONU#2 and ONU#3 were in the unregistered state, as shown in Figure 8, the value in the ONU status column 113c corresponding to ONU#2 and ONU#3 is updated to "Register," and the value in the classification column 113e corresponding to ONU#2 and ONU#3 is updated to "normal." Furthermore, the value in the abnormal light emission detection status column 113d is updated to "Normal."

[0049] On the other hand, in step S18, even if the optical signal of the target ONU 130 is shut down, the abnormal light emission is not resolved, so the target ONU 130 is not the causative ONU 130. For this reason, the link status management unit 115 notifies the abnormal light emission management unit 116 of the ID of the target ONU 130 and the optical shutdown release flag (S18). Upon receiving the ID and the optical shutdown release flag, the abnormal light emission management unit 116 generates an ONU optical shutdown release notification that notifies the ONU 130 corresponding to that ID to release the optical shutdown, and provides the ONU optical shutdown release notification to the PON control unit 117. When the PON control unit 117 receives the ONU optical shutdown release notification from the abnormal light emission management unit 116, it forwards the ONU optical shutdown release notification to the corresponding ONU 130 via the optical transceiver unit 111.

[0050] Upon receiving the ONU optical shutdown release notification, the PON control unit 132 of the ONU 130 transmits the notification to the optical output control unit 133. The optical output control unit 133 then instructs the optical transceiver unit 131 to resume emitting the transmission light and to send a response to the optical shutdown release notification to the OLT 110. Upon receiving such a response, the OLT 110 sends the response to the link status management unit 115 via the PON control unit 117. The link status management unit 115 updates the inspection status classification of the target ONU 130 to "tested" (S19). For example, if a response is received from ONU#1, the value in the classification column 113e of ONU#1 is updated to "tested," as shown in the link status management table 113a#6 in Figure 10. Furthermore, by releasing the transmission light emission stop, the link between the target ONU 130 and the OLT 110 is restored, the PON control unit 117 notifies the link status management unit 115 of the ONU link up status, and the ONU status of the target ONU 130 is updated to the registered status. For example, if the target ONU 130 is ONU#1, as shown in Figure 10, the value of the ONU status column 113c for ONU#1 in the link status management table 113a#6 is updated to "Register".

[0051] Next, the link status management unit 115 refers to the link status management information stored in the link status storage unit 113 to determine whether or not there are still ONU 130s remaining that are classified as registered (S20). If there are still ONU130s with a normal classification (Yes in S20), the process returns to step S14, and the link status management unit 115 identifies one of the ONU130s with a normal classification as the target ONU. For example, in the link status management table 113a#6 shown in Figure 10, among the ONU130s whose classification column 113e is "normal", ONU#3, which has the lowest number, is identified as the next target ONU. On the other hand, if there are no ONU130s remaining in the normal classification state (No in S20), the process proceeds to step S21.

[0052] In step S21, the link status management unit 115 determines that there are no ONUs 130 in an abnormal light emission state among the ONUs 130 that are currently linked up, since all ONUs 130 are classified as being in a state other than normal. Therefore, the link status management unit 115 notifies the external monitoring system 150 via the PON control unit 117 that the ONU emitting abnormal light emission is unidentified. This terminates the search for the ONU 130 in an abnormal light emission state.

[0053] The operation described in the flowchart above will be explained in detail using Figures 11 to 13. Figures 11 to 13 are schematic diagrams illustrating the overview of the operation of the PON system 100 in Embodiment 1. In Figures 11 to 13, it is assumed that four ONU130 units are connected to one OLT110 unit.

[0054] Figure 11 shows an overview of the normal operation of each ONU130. Upstream frames 1 to 4, input to each ONU 130 from lower-level terminals (not shown), are transmitted to the OLT 110 at their respective time-division controlled intervals. Under normal circumstances, frames received by OLT110 are transmitted using time-division multiplexing, so there are no collisions, and the ONU status of each ONU130 in OLT110 will be "Register," indicating the registered state.

[0055] Figure 12 shows an overview of the operation when ONU#1 experiences a failure and an abnormal uplink signal is generated intermittently. When ONU#1 intermittently enters an abnormal light emission state, the signals received by OLT110 will be the collision signal of frame 1 transmitted from ONU#1, frame 2 transmitted from ONU#2, and frame 3 transmitted from ONU#3, as well as frame 4 transmitted from ONU#4. In this case, OLT110 will be unable to accurately receive frame 2 and frame 3. Therefore, OLT110 will set the ONU status of ONU#1 and ONU#4 to "Register," and the ONU status of ONU#2 and ONU#3 to "Deregister."

[0056] Figure 13 shows an overview of the operation when detecting abnormally emitting light from ONU#1. When OLT110 detects abnormal light emission from ONU130, it sequentially issues optical shutdown commands to ONU130, which is in the normal "Register" state. In this case, issuing an optical shutdown command to ONU#1 eliminates frame 1, which was in conflict with frames 2 and 3, allowing OLT110 to receive frames 2 and 3. As a result, ONU#2 and ONU#3 return to the registered "Register" state. Therefore, OLT110 can identify ONU#1 as the faulty ONU130.

[0057] As described above, according to Embodiment 1, without providing special detection circuits in the OLT 110 and ONU 130, it is possible to automatically search for and identify the ONU 130 that is emitting light intermittently during link-up. Therefore, the operator can take action without having to do so manually.

[0058] Embodiment 2. Embodiment 1 describes a configuration for automatically searching for devices that are emitting abnormal light intermittently. Embodiment 2 describes a configuration that prevents a normal device from being mistakenly identified as a device emitting abnormal light when the system is searching for a normal device at a time when the intermittent abnormal light emission has temporarily subsided.

[0059] As shown in Figure 1, the PON system 200 according to Embodiment 2 comprises an OLT 210 which is a terminal device on the central office side, and a plurality of ONUs 130. The ONU 130 in the PON system 200 according to Embodiment 2 is the same as the ONU 130 in the PON system 100 according to Embodiment 1.

[0060] The OLT210 comprises an optical transceiver unit 111, an abnormal light emission detection unit 112, a link state storage unit 213, an optical communication control unit 214, and a communication unit 118. The optical transmitting / receiving unit 111, abnormal light emission detection unit 112, and communication unit 118 of the OLT210 in Embodiment 2 are the same as those of the optical transmitting / receiving unit 111, abnormal light emission detection unit 112, and communication unit 118 of the OLT110 in Embodiment 1.

[0061] The optical communication control unit 214 controls communication in the OLT 210. The optical communication control unit 214 in Embodiment 2 performs processing almost the same as the optical communication control unit 114 in Embodiment 1. However, in Embodiment 2, the optical communication control unit 214 counts the number of times the abnormal light emission has been resolved by stopping the transmission of optical signals from the target ONU 130, and identifies the target ONU 130 whose count exceeds a predetermined threshold as the ONU 130 causing the abnormal light emission.

[0062] The link state storage unit 213 stores link state management information for managing the link state of the ONU 130. Figure 14 is a schematic diagram showing an example of link status management information in Embodiment 2. As shown in Figure 14, the link status management table 213a, an example of link status management information, is a table-format data comprising an ID column 113b, an ONU status column 113c, an abnormal light emission detection status column 113d, a classification column 113e, and an inspection count column 213f. The ID column 113b, ONU status column 113c, abnormal light emission detection status column 113d, and classification column 113e of the link status management table 213a in Embodiment 2 are the same as the ID column 113b, ONU status column 113c, abnormal light emission detection status column 113d, and classification column 113e of the link status management table 113a in Embodiment 1.

[0063] The test count column 213f stores the number of tests performed on the ONU130. This section stores the number of times the ONU130 has been optically shut down and checked to see if it is emitting abnormal light.

[0064] The optical communication control unit 214 includes a link status management unit 215, an abnormal light emission management unit 116, and a PON control unit 117. The abnormal light emission management unit 116 and PON control unit 117 of the optical communication control unit 214 in Embodiment 2 are the same as the abnormal light emission management unit 116 and PON control unit 117 of the optical communication control unit 114 in Embodiment 1.

[0065] The link status management unit 215 manages the link status of each ONU 130 and the abnormal light emission status of each ONU 130 using the link status management information stored in the link status storage unit 213. The link status management unit 215 in Embodiment 2 performs processing almost the same as the link status management unit 115 in Embodiment 1, but when searching for an ONU 130 that is exhibiting abnormal light emission, if it is determined multiple times that there is a suspicion of abnormal light emission, it identifies that ONU 130 as the ONU 130 that is exhibiting abnormal light emission.

[0066] Next, we will explain how the OLT210 manages the link status of the ONU130. Figures 15 to 17 are flowcharts showing the operation of the OLT210 when it searches for the ONU130 that is emitting abnormal light. Furthermore, if no ONU130 exhibiting abnormal light emission is connected to the OLT210, the abnormal light emission detection status column 113d will contain "Normal," and the inspection count column 213f will contain "0" for all ONU130s, as shown in the link status management table 213a in Figure 14. Furthermore, among the processes in the flowcharts shown in Figures 15 to 17, processes that are the same as those in the flowchart shown in Figure 4 of Embodiment 1 are denoted by the same reference numerals as those shown in Figure 4.

[0067] The processes from steps S10 to S13 in the flowchart shown in Figure 15 are the same as those in the flowchart shown in Figure 4. However, in Figure 15, after the process in step S13, the process proceeds to step S30.

[0068] In step S30, the link status management unit 215 identifies one ONU 130 from among the ONU 130 whose inspection status is classified as normal, and notifies the abnormal light emission management unit 116 of its ID and the optical shutdown flag to optically shut down the identified ONU 130. Here, the link status management unit 215 identifies one ONU 130 in order from the lowest ID. The identified ONU 130 is also called the target ONU 130. Upon receiving notification of the ID and the optical shutdown flag, the abnormal light emission management unit 116 generates an ONU optical shutdown notification informing the ONU 130 corresponding to that ID to perform an optical shutdown, and provides the ONU optical shutdown notification to the PON control unit 117. When the PON control unit 117 receives the ONU optical shutdown notification from the abnormal light emission management unit 116, it forwards the ONU optical shutdown notification to the corresponding ONU 130 via the optical transceiver unit 111. Furthermore, the link status management unit 215 increments the inspection count of the target ONU by 1 in the link status management information stored in the link status storage unit 213. For example, if the target ONU is ONU#1 and it is the first inspection, the value of the inspection count column 213f corresponding to ONU#1 is updated to "1", as shown in the link status management table 213a#1 shown in Figure 18. Then the process proceeds to step S15.

[0069] The processes in steps S15 and S16 shown in Figure 15 are the same as those in steps S15 and S16 shown in Figure 4. However, in Figure 15, if the abnormal light emission is resolved in step S16 (Yes in S16), the abnormal light emission detection unit 112 notifies the link status management unit 215 of the release of the abnormal light emission from the ONU 130, and the process proceeds to step S31. If the abnormal light emission is not resolved in step S16 (No in S16), the process proceeds to step S18 in Figure 16. For example, in step S14, the link status management information is the link status management table 213a#1 shown in Figure 18, and in the case of the first inspection, steps S15 and S16 shown in Figure 15 are performed, so the link status management information becomes the link status management table 213a#2 shown in Figure 19.

[0070] In step S31, since the abnormal light emission is resolved by shutting down the optical signal of the target ONU 130, the link status management unit 215 determines that the target ONU 130 is suspected to be the ONU 130 that is emitting abnormal light, and identifies it as the ONU 130 suspected of emitting abnormal light. For example, if ONU#1 is the target ONU and the link status management information when the determination in step S16 is made is the link status management table 213a#2 shown in Figure 19, then the value of the classification column 113e for ONU#1 is updated to "suspected", as shown in the link status management table 213a#3 shown in Figure 20. In this case, the ONU status of ONU 130, which was in the unregistered state, returns to the registered state. For example, if ONU#2 and ONU#3 were in the unregistered state, the value of the ONU status column 113c corresponding to ONU#2 and ONU#3 is updated to "Register", and the value of the classification column 113e corresponding to ONU#2 and ONU#3 is updated to "normal". Furthermore, the value of the abnormal light emission detection status column 113d is updated to "Normal".

[0071] The link status management unit 215 then determines whether the number of inspections M of the target ONU 130 is greater than a predetermined threshold L (S32). Here, the threshold L is an integer greater than or equal to 1. If the number of inspections M is greater than the threshold L (Yes in S32), the process proceeds to step S33; if the number of inspections M is less than or equal to the threshold L (No in S32), the process proceeds to step S34 in Figure 17.

[0072] In step S33, the abnormal light emission is resolved by shutting down the optical signal of the target ONU 130, and the number of inspections has exceeded the threshold. Therefore, the link status management unit 215 identifies the target ONU 130 at that time as the causative ONU 130 that is causing the abnormal light emission.

[0073] Furthermore, the processes in steps S18 to S21 of the flowchart shown in Figure 16 are the same as the processes in steps S18 to S21 of Figure 4.

[0074] In step S34 of Figure 17, the link status management unit 215 releases the optical shutdown for the ONU 130 suspected of abnormal light emission, changes its classification to "under inspection," and increments its inspection count by 1. For example, the link status management unit 215 notifies the abnormal light emission management unit 116 of the ID of the ONU 130 suspected of abnormal light emission and the optical shutdown flag, instructing it to perform an optical shutdown. Upon receiving the ID and optical shutdown flag, the abnormal light emission management unit 116 generates an ONU optical shutdown notification informing the ONU 130 corresponding to that ID to perform an optical shutdown, and provides this ONU optical shutdown notification to the PON control unit 117. Upon receiving the ONU optical shutdown notification from the abnormal light emission management unit 116, the PON control unit 117 forwards the ONU optical shutdown notification to the corresponding ONU 130 via the optical transceiver unit 111. Furthermore, the link status management unit 215 sets the value of the ONU status column 113c of the suspected abnormal light emission ONU 130 to the registered status "Register" in the link status management information stored in the link status storage unit 213, and increments the value of the inspection count column 213f of the suspected abnormal light emission ONU 130 by 1. For example, if the link status management information before the processing in step S34 is the link status management table 213a#3 shown in Figure 20, then the value in the ONU status column 113c of ONU#1 is updated to "Register", the value in the classification column 113e of ONU#1 is updated to "in test", and the value in the inspection count column 213f of ONU#1 is updated to "2", as shown in the link status management table 213a#4 shown in Figure 21.

[0075] Next, the abnormal light emission detection unit 112 monitors the upstream signal from the ONU 130 received by the optical transceiver unit 111 to determine whether or not abnormal light emission is detected (S35). Here, the abnormal light emission detection unit 112 monitors the upstream signal from the ONU 130 for a certain period of time and detects whether or not the light emission state continues for a predetermined period of time. If abnormal light emission is detected (Yes in S35), the process proceeds to step S36; if abnormal light emission is not detected (No in S35), the process proceeds to step S39.

[0076] In step S36, the link status management unit 215 receives an abnormal light emission notification from the abnormal light emission detection unit 112 and updates the link status management information stored in the link status storage unit 213 from the abnormal light emission detection state to the abnormal light emission state. For example, if the link status management information before the processing in step S36 is as shown in link status management table 213a#4 in Figure 21, the link status management unit 215 updates the value of the abnormal light emission detection status column 113d to "Abnormal", which indicates an abnormal light emission state, as shown in link status management table 213a#5 in Figure 22.

[0077] The link status management unit 115 then checks the ONU status and classification of the link status management information to determine whether or not there are any ONUs 130 that have entered a deregistered state when abnormal light emission is detected (S37). When abnormal light emission is detected, the light emission state of a certain ONU 130 continues for a predetermined period, making it impossible to receive the optical signal of the ONU 130 that is supposed to transmit an optical signal during that period. For this reason, for example, as shown in the link status management table 213a#5 shown in Figure 22, there are ONUs 130 in which "normal" is stored in the classification column 113e and "Deregister" is stored in the ONU status column 113c. In the example shown in Figure 22, ONU#2 and ONU#3 are ONUs 130 that have entered a deregistered state. If there are any ONUs 130 that have entered a deregistered state (Yes in S37), the process proceeds to step S38; if there are no ONUs 130 that have entered a deregistered state (No in S37), the process proceeds to step S39.

[0078] In step S38, the link status management unit 215 updates the inspection status classification of the ONU 130 that has entered a deregistered state when abnormal light emission is detected to exclude it from the target. For example, if ONU#2 and ONU#3 enter a deregistered state as shown in Figure 22, the link status management unit 215 updates the value of the classification column 113e for ONU#2 and ONU#3 to "damaged", as shown in link status management table 213a#6 in Figure 23. Then the process proceeds to step S39.

[0079] In step S39, the link status management unit 215 notifies the abnormal light emission management unit 116 of the ID of the target ONU 130 and the optical shutdown flag, instructing it to perform an optical shutdown. Upon receiving the ID and the optical shutdown flag, the abnormal light emission management unit 116 generates an ONU optical shutdown notification informing the ONU 130 corresponding to that ID to perform an optical shutdown, and provides this ONU optical shutdown notification to the PON control unit 117. Upon receiving the ONU optical shutdown notification from the abnormal light emission management unit 116, the PON control unit 117 forwards the ONU optical shutdown notification to the corresponding ONU 130 via the optical transceiver unit 111.

[0080] Upon receiving the ONU optical shutdown notification, the PON control unit 132 of the ONU 130 transmits the notification to the optical output control unit 133. The optical output control unit 133 then instructs the optical transceiver unit 131 to stop emitting the transmitted light and to send a response of the optical shutdown notification to the OLT 110. The process then returns to step S16 in Figure 15.

[0081] On the other hand, in step S40, even if the optical signal of the target ONU 130 is released from shutdown, no abnormal light emission is detected, so the target ONU 130 is not the cause ONU 130. For this reason, the link status management unit 215 updates the inspection status classification of the target ONU 130 to "tested" in the link status management information stored in the link status storage unit 213. For example, if the link status management information before processing in step S40 is as shown in link status management table 213a#4 in Figure 21, the link status management unit 215 updates the value of the classification column 113e of ONU#1 to "tested", as shown in link status management table 213a#7 in Figure 24. Then, the process returns to step S20 in Figure 16.

[0082] As described above, according to Embodiment 2, when a normal ONU 130 is being inspected at the time when the irregular abnormal light emission temporarily disappears, it is possible to avoid cases where a normal ONU 130 is mistakenly identified as an ONU 130 exhibiting abnormal light emission by performing multiple inspections on that ONU 130.

[0083] In Embodiments 1 and 2, when searching for an ONU 130 that is emitting abnormal light, optical shutdown is performed on each unit individually. However, Embodiment 1 is not limited to this example. For example, multiple units may be optically shut down at once to reduce the number of searches required to find a single ONU 130 that is emitting abnormal light. Specifically, by performing optical shutdown on multiple ONU 130s and resolving the abnormal light emission, the number of searches can be reduced by performing optical shutdown on each of those multiple ONU 130s one by one. [Explanation of Symbols]

[0084] 100,200 PON system, 110,210 OLT, 111 Optical transceiver unit, 112 Abnormal light emission detection unit, 113,213 Link state storage unit, 114,214 Optical communication control unit, 115,215 Link state management unit, 116 Abnormal light emission management unit, 117 PON control unit, 118 Communication unit, 130 ONU, 131 Optical transceiver unit, 132 PON control unit, 133 Optical output control unit.

Claims

1. An abnormal light emission detection unit monitors the optical signals received by an optical transceiver unit that transmits and receives optical signals in time division with multiple subscriber-side devices, and detects a state in which optical signals have been received for a predetermined period of time or longer as an abnormal light emission in which optical signals cannot be received from one or more subscriber-side devices included in the multiple subscriber-side devices. The optical communication control unit selects one subscriber-side device among the multiple subscriber-side devices excluding the one or more subscriber-side devices mentioned above as the target subscriber-side device, and stops the transmission of optical signals from the target subscriber-side device, thereby identifying the target subscriber-side device as the one that caused the abnormal light emission when the abnormal light emission is resolved. A station-side device characterized by the following.

2. An abnormal light emission detection unit monitors the optical signals received by an optical transceiver unit that transmits and receives optical signals in time division with multiple subscriber-side devices, and detects a state in which optical signals have been received for a predetermined period of time or longer as an abnormal light emission in which optical signals cannot be received from one or more subscriber-side devices included in the multiple subscriber-side devices. The optical communication control unit performs an inspection to determine whether the abnormal light emission is resolved by selecting one subscriber-side device among the plurality of subscriber-side devices, excluding the one or more subscriber-side devices mentioned above, as the target subscriber-side device, and stopping the transmission of optical signals from the target subscriber-side device. When the optical communication control unit determines that the abnormal light emission has been resolved, the abnormal light emission detection unit and the optical communication control unit repeat the inspection on the target subscriber-side device, count the number of times the inspection has been performed, and when the number of times exceeds a predetermined threshold, they determine that the target subscriber-side device is emitting the abnormal light emission. A station-side device characterized by the following.

3. The optical communication control unit selects, in order from the plurality of subscriber-side devices excluding the one or more subscriber-side devices, one subscriber-side device as the target subscriber-side device. The station-side device according to claim 1 or 2, characterized by the above.

4. The optical communication control unit stops the transmission of optical signals to two or more subscriber-side devices included in the plurality of subscriber-side devices, excluding the one or more subscriber-side devices, and when the abnormal light emission is resolved, it sequentially selects one of the two or more subscriber-side devices as the target subscriber-side device. The station-side device according to claim 1 or 2, characterized by the above.

5. The system comprises a central office-side device according to any one of claims 1 to 4, and the plurality of subscriber-side devices. An optical communication system characterized by [this feature].

6. A program that causes a processor to function as a station-side device according to any one of claims 1 to 4.

7. Multiple subscriber-side devices receive optical signals in time division multiplexing. The system monitors the received optical signals and detects a state in which optical signals have been received for a predetermined period of time or longer as an abnormal emission in which optical signals cannot be received from one or more subscriber-side devices included in the plurality of subscriber-side devices. Select one subscriber-side device among the multiple subscriber-side devices excluding the one or more subscriber-side devices mentioned above as the target subscriber-side device, and stop the transmission of optical signals from the target subscriber-side device. If the abnormal light emission is resolved by doing so, the target subscriber-side device is identified as the one causing the abnormal light emission. A search method characterized by the following.

8. Multiple subscriber-side devices receive optical signals in time division multiplexing. The system monitors the received optical signals and detects a state in which optical signals have been received for a predetermined period of time or longer as an abnormal emission in which optical signals cannot be received from one or more subscriber-side devices included in the plurality of subscriber-side devices. An inspection is performed to determine whether the abnormal light emission is resolved by selecting one subscriber-side device from the plurality of subscriber-side devices, excluding the one or more subscriber-side devices mentioned above, as the target subscriber-side device, and stopping the transmission of optical signals from the selected target subscriber-side device. If it is determined that the abnormal light emission has been resolved, the inspection is repeated on the target subscriber-side device, and the number of times the inspection has been performed is counted. If the number of times exceeds a predetermined threshold, it is determined that the target subscriber-side device is exhibiting the abnormal light emission. A search method characterized by the following.

9. The search method according to claim 7 or 8 involves stopping the transmission of optical signals for two or more subscriber-side devices included in the plurality of subscriber-side devices, excluding the one or more subscriber-side devices, and, when the abnormal light emission is resolved, selecting one subscriber-side device from the two or more subscriber-side devices in order as the target subscriber-side device. A search method characterized by the following.

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