JPWO2013187098A1 - Optical transmission system, station side optical termination device, and communication line switching method - Google Patents

Abstract

An optical transmission system comprising an ONU that can be shifted to a power saving mode, an OLT, and an optical splitter that is connected to the OLT and a redundant trunk line and is connected to the ONU by a branch line. A state management table, which is information related to the power saving mode, is held, and it is determined whether or not to perform redundant switching of the trunk line based on the state management table.

Description

  The present invention relates to an optical transmission system, a station-side optical terminal device, and a communication line switching method.

  In recent years, an optical network has been introduced in order to cope with the high speed and wide bandwidth of a communication network. In an optical network, one OLT (Optical Line Terminal) and one ONU (Optical Network Unit: subscriber side optical terminator) communicate via an optical transmission line (optical fiber). . In addition, a PON (Passive Optical Network) system, which is one of the optical network systems, has a high-speed access because one OLT forms a PDS (Passive Double Star) network with multiple ONUs via an optical splitter. Services can be provided at low cost. A typical PON standard is EPON (Ethernet (registered trademark) PON) standardized by the Institute of Electrical and Electronic Engineers (IEEE) 802.3.

  As a PON communication method, an upstream optical signal transmitted from the ONU to the OLT and a downstream optical signal transmitted from the OLT to the ONU are multiplexed by WDM (Wavelength Division Multiplexing). The ONU uses TDMA (Time Division Multiple Access) that transmits an upstream optical signal according to the transmission timing permitted by the OLT. In other words, the OLT dynamically assigns transmission timings for the upstream signals of each ONU so that upstream optical signals of a plurality of connected ONUs do not overlap each other. A downstream optical signal transmitted from the OLT toward the ONU uses TDM (Time Division Multiplexing), and is received by all ONUs connected via the optical transmission path. At that time, the ONU refers to the destination information included in the preamble portion of the downstream optical signal, and discards the downstream optical signal that is not addressed to itself.

  As the communication speed increases and the number of connected electronic devices increases, the power consumption of the ONU tends to increase. Since ONUs are installed at subscriber's homes, many ONUs are arranged on the network. Further, the ONU requires a shorter time for the available bandwidth than the OLT and the upper switch group. Therefore, the ONU is left while using wasted power while not performing communication.

  In the following Patent Document 1, in the PON system, the OLT has an ONU downstream sleep management table for managing whether the downstream optical signal processing unit of the ONU is in a sleep (power saving) state, and the upstream optical signal processing unit of the ONU is in a sleep (saving) A method using an ONU upstream sleep management table for managing whether the state is (power) state is disclosed.

  In the following Patent Document 2, a table for managing ONU identification information and a management for managing a return time that is a time when the ONU returns from a sleep (power saving) state in which a part of the upstream and downstream processing units are stopped A method using a table is disclosed (Patent Document 2).

JP 2012-004642 A JP 2011-229094 A

  There is a system having a redundant configuration in which when a failure occurs in a communication line forming a communication network, the communication line is switched to another communication line. Thus, by adopting a redundant configuration of the communication line, it is possible to improve the robustness against communication failure. In a communication network with a redundant configuration of communication lines, when a communication line failure is detected on the current line being used by the communication device, the communication line that has failed is switched from the communication line to the other communication line, and a link is established to establish communication. Resume.

  On the other hand, with the recent increase in demand for high-speed and large-capacity communication as described above, the power consumption of ONUs is increasing and low power operation is required. The ONU in the sleep (power saving) state aims to reduce power consumption by stopping both the transmitter and the receiver used for data communication with the OLT, or by stopping only the transmitter. The ONU in the sleep (power saving) state does not transmit an upstream optical signal to the OLT and does not respond to a control signal from the OLT. Therefore, when the redundant configuration and the ONU power save coexist, the following problems are considered to occur.

  In the PON system in which the redundant configuration of the optical transmission path and the ONU sleep coexist, when the sleep (power saving) state of all ONUs connected to the OLT temporarily overlaps, the ONU issues a control light issued by the OLT. Does not respond to the signal. Therefore, there is a problem that the OLT erroneously detects that a failure has occurred in the optical transmission path and switches the communication line.

  Patent Document 1 discloses a method using a sleep management table in which the OLT manages the sleep (power saving) state of the upper and lower optical signal processing units of the ONU. Although it is possible to reduce the power consumption of the ONU by monitoring the existence and data type of communication data using the status management table, the above-described problem when the redundant configuration of the optical transmission path coexists, that is, the failure No patent document 1 discloses a solution for erroneous detection. Also in Patent Document 2, there is no disclosure at all regarding the above-described problem when a redundant configuration of an optical transmission line coexists, that is, a solution to erroneous detection of a failure.

  In Patent Document 1, in order to reduce power consumption during non-communication of ONUs, the OLT monitors the communication state of each ONU and uses the sleep management table to perform sleep (power saving) control for the ONUs during non-communication. It discloses the technique to do. Using this method, it is possible to reduce power consumption by controlling the ONU to be in a sleep (power saving) state in a time range not corresponding to the redundancy switching condition, but the sleep (power saving) time is limited. Therefore, the ONU frequently repeats state transitions, occupying a band that cannot be ignored on the optical transmission line of the multi-branch PON system, and the power consumption reduction effect of the ONU is limited.

  The present invention has been made in view of the above, and an optical transmission system capable of preventing erroneous detection of a failure in an optical transmission line when the ONU power saving control and the redundant configuration of the optical transmission line coexist. An object of the present invention is to provide a station side optical termination device and a communication line switching method.

  In order to solve the above-described problems and achieve the object, the present invention is made redundant with a subscriber-side optical termination device, a station-side optical termination device, and the station-side optical termination device that can be shifted to a power saving mode. And an optical splitter connected to each of the subscriber-side optical terminators and each of the branch lines, wherein the station-side optical terminator is a saving of the subscriber-side optical terminator. Power saving information, which is information related to the power mode, is managed, and redundancy switching of the trunk line is controlled based on the power saving information.

  The optical transmission system, the station-side optical termination device, and the communication line switching method according to the present invention prevent erroneous detection of a failure in an optical transmission line when the power saving control of the ONU and the redundant configuration of the optical transmission line coexist. There is an effect that can be.

FIG. 1 is a diagram showing a configuration example of an optical access network including a PON system according to the present invention. FIG. 2 is a diagram illustrating a configuration example of the PON system. FIG. 3 is a diagram illustrating a configuration example of the OLT unit. FIG. 4 is a diagram illustrating a configuration example of the ONU. FIG. 5 is a diagram illustrating a communication operation sequence example of discovery processing. FIG. 6 is a diagram illustrating an example of a sequence when a failure occurs in the active trunk optical fiber. FIG. 7 is a diagram illustrating an example of a trunk optical fiber switching sequence when a failure occurs in the active trunk optical fiber. FIG. 8 is a diagram illustrating an example of a communication operation sequence in a case where a normal operation is hindered by the conventional communication path switching method. FIG. 9 is a flowchart illustrating an example of basic control of the OLT. FIG. 10 is a flowchart illustrating an example of OLT power saving control. FIG. 11 is a diagram illustrating an example of the state management table. FIG. 12 is a flowchart illustrating an example of a communication path switching procedure. FIG. 13 is a diagram showing an example of a sequence when the communication path switching method in the OLT according to the present invention is implemented. FIG. 14 is a diagram illustrating an example of a sequence when power saving control is performed in the OLT. FIG. 15A is a diagram illustrating an example of a power saving control procedure in the ONU. FIG. 15-2 is a diagram illustrating an example of a power saving control procedure in the ONU. FIG. 16 is a diagram illustrating a configuration example in which branch lines have multiple stages. FIG. 17 is a diagram illustrating a configuration example of the PON system according to the second embodiment. FIG. 18 is a diagram illustrating a configuration example of a state management table according to the second embodiment. FIG. 19 is a diagram illustrating an example of the power saving control method according to the second embodiment.

  Embodiments of an optical transmission system, a station-side optical terminal device, and a communication line switching method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration example of an optical access network including a PON system (optical transmission system) according to the present invention. The PON system of the present embodiment includes an OLT (station side optical terminal device) 1 and ONUs (subscriber side optical terminal devices) 2-1 to 2-N (N is an integer of 1 or more). The OLT 1 is connected to the upper network 4. The ONU 2-1 is connected to the user terminal 5-1, and the ONU 2-N is connected to the user terminal 5-2.

  The OLT 1 is connected to the ONU 2-1 to ONU 2-N via the optical splitter 3, and the OLT 1 and the optical splitter 3 are connected to each other via a trunk optical fiber 7, and between the optical splitter 3 and the ONU 2-1 to ONU 2-N. Are connected by branch optical fibers 6-1 to 6-N, respectively. The number of ONUs connected to the OLT 1 is not limited.

  Since the OLT 1 and the ONUs 2-1 to ONU2-N communicate using optical signals multiplexed by WDM, the upstream optical signal and the downstream optical signal do not collide. On the other hand, since the plurality of ONUs 2-1 to ONU2-N communicate at the same wavelength, the OLT 1 transmits the optical transmission times (upstream transmission times) of the ONUs 2-1 to ONU2-N so that the optical transmission times do not overlap. Is controlling.

  FIG. 2 is a diagram illustrating a configuration example of the PON system according to the present embodiment. As shown in FIG. 2, the OLT 1 of the present embodiment has a redundant configuration, and includes an OLT unit 1-1, an OLT unit 1-2, and a control unit 9 that controls the entire OLT 1. Each of the OLT unit 1-1 and the OLT unit 1-2 has a function as an OLT alone, and either one is used for operation. Here, it is assumed that the OLT unit 1-1 is the active system (wOLT1-1) and the OLT unit 1-2 is the standby system (sOLT1-2). The OLT unit 1-1 and the OLT unit 1-2 are each connected to an L2SW (Layer 2 Switch) 8, and are connected to the upper network 4 via the L2SW 8. The trunk optical fiber 7 is composed of a working trunk optical fiber 7-1 and a standby trunk optical fiber 7-2, and the working trunk optical fiber 7-1 is connected to the wOLT 1-1, and the spare trunk optical fiber. 7-2 is connected to sOLT1-2. In FIG. 2, the number of ONUs is four, but the number of ONUs is not limited to this.

  The optical splitter 3 is a passive optical element. In downstream communication, the downstream optical signal transmitted from the OLT 1 via the active trunk optical fiber 7-1 or the standby trunk optical fiber 7-2 is transmitted to itself. The number of ONUs 2 to be connected (four in the example in FIG. 2) is divided, and the divided optical signals are output to branch optical fibers 6-1 to 6-4, respectively. In the upstream communication, the optical splitter 3 converts the upstream optical signal transmitted from the branch optical fibers 6-1 to 6-4 into the active trunk optical fiber 7-1 and the standby trunk optical fiber 7-2. Output to.

  The OLT 1 has a function capable of setting and controlling communication paths with the ONUs 2-1 to 2-4. The ONUs 2-1 to 2-4 are communication devices that transmit and receive optical signals under the control of the OLT 1, and have a power saving (sleep) mode function to be described later.

  FIG. 3 is a diagram illustrating a configuration example of the OLT unit 1-1 (wOLT1-1). The OLT unit 1-2 (sOLT1-2) has the same configuration as the OLT unit 1-1. As shown in FIGS. 2 and 3, the OLT unit 1-1 includes a PON control unit 10 that performs processing on the OLT side based on the PON protocol, a physical layer processing unit (PHY) 11, an upstream optical signal, and downstream light. Received from a WDM coupler (WDM) 12 that wavelength-multiplexes signals, a transmission buffer 13 that is a buffer for storing data of downstream optical signals to be transmitted to the ONUs 2-1 to 2-4, and ONUs 2-1 to 2-4 A reception buffer 14 that is a buffer for storing upstream optical signal data, and an optical transceiver 15.

  The optical transmitter / receiver 15 converts an optical signal received from the ONUs 2-1 to 2-4 into an electric signal and outputs the electric signal to the PON control unit 10, and from the PON control unit 10 And an optical transmitter (Tx: Transmitter) 17 that performs a process of converting the input electric signal into an optical signal and transmitting it to the ONUs 2-1 to 2-4. The physical layer processing unit 11 implements a physical interface function such as NNI (Network Node Interface) with the network, and performs a reception unit (Rx) 18 that performs reception processing, and a transmission unit (Tx) 19 that performs transmission processing. Consists of. In the PON system of the present embodiment, the WDM 12 is used because wavelength multiplexing is used. However, the WDM 12 is not indispensable when performing communication at a single wavelength.

  The PON control unit 10 includes a signal processing unit 30, a buffer monitoring unit 31, a sleep control signal processing unit 32, a state management table 33, and a time counter 34.

  FIG. 4 is a diagram illustrating a configuration example of the ONU 2-1. The ONUs 2-2 to 2-4 have the same configuration as the ONU 2-1. As shown in FIGS. 2 and 4, the ONU 2-1 is a PON control unit 20 that performs processing on the ONU side based on the PON protocol, and a transmission that is a buffer for storing upstream optical signal data to be transmitted to the OLT 1. A buffer 23, a reception buffer 24 that is a buffer for storing data of a downstream optical signal received from the OLT 1, a WDM coupler (WDM) 22 that wavelength-multiplexes upstream and downstream optical signals, and a user terminal 5-1. And a physical layer processing unit (PHY) 21 for realizing a physical interface function such as UNI (Unser Network Interface).

  The optical transceiver 25 includes an optical transmitter (Tx) 27 for transmitting an optical signal and an optical receiver (Rx) 26 for receiving an optical signal. The physical layer processing unit (PHY) 21 includes a reception unit (Rx) 28 that performs reception processing and a transmission unit (Tx) 29 that performs transmission processing. Note that the WDM 22 is not essential when communication is performed at a single wavelength without using wavelength multiplexing.

  The PON control unit 20 includes a signal processing unit 35, a buffer monitoring unit 36, a link monitoring unit 37, a state table 38, a sleep control unit 39, and a time counter 40.

  In this embodiment, the OLT 1 has a failure detection function. In the PON control unit 10, the signal processing unit 30 detects a failure when the optical signal does not reach the ONUs 2-1 to 2-4 for a certain time. Send a signal. Fault detection in the PON system is studied by IEEE and ITU-T (International Telecommunication Union Telecommunication Standardization Sector).

For example, IEEE P1904.1 ^™ defines failure detection of MAC LoS (Loss of Signal) and optical LoS. Both the MAC LoS and the optical LoS are detected when a failure of the active trunk optical fiber is detected. When this failure is detected, the OLT switches from the active system to the standby system. MAC LoS is a failure detection that is detected when the OLT does not receive a report (REPORT message) from any ONU within a certain period, and the optical LoS is valid within a certain period at the optical receiver of the OLT. Detected when an optical signal cannot be received.

  In addition, ITU-T G.I. In 987.3, LOBi (Loss of burst for ONUi) and LOS (Loss of Signal) are defined as failure detection. LOBi is detected when the OLT fails to receive a burst (signal transmitted from the ONU) scheduled for each ONU four times in succession. The LOS is detected when the OLT fails to receive the expected uplink transmission frame four times in succession. Since LOBi is detected for each ONU, it indicates an ONU or branch line failure. In the case of an ONU or branch line failure, switching from the active system to the standby system in the OLT is not performed, and for example, the failure is notified to the operation manager. When the LOS is sent out, switching from the active system of the trunk fiber to the standby system is performed as in the case of the optical LoS and MAC LoS described above.

  In the configuration example illustrated in FIG. 2, the PON control unit 10 detects the optical LoS based on the notification from the optical transceiver 15. Specifically, when the optical transceiver 15 has a time counter and the state in which the level of the optical signal detected by the Rx 16 is equal to or less than a threshold value continues for a certain period or longer, the PON control unit 10 is notified, and this notification The signal processing unit 30 may send out the optical LoS, or the optical transceiver 15 notifies the signal processing unit 30 of the reception level of Rx16, and the PON control unit 10 uses the time counter 34 to set the reception level to the threshold value. When the following state continues for a certain period or longer, the optical LoS may be transmitted.

  For the MAC LoS, the PON control unit 10 measures the elapsed time since the last reception of the report from the ONUs 2-1 to 2-4 by the time counter 34, and from which ONU until a certain period elapses. Is also detected when a report (REPORT message) is not received. For LOBi and LOS, the PON control unit 10 holds information on the upstream bandwidth (upstream transmission permission time zone) allocated to the ONUs 2-1 to 2-4 by itself. Detection is based on this information. When these failures are detected, the PON control unit 10 sends a corresponding alarm. The control unit 9 receives this warning.

  When an optical LoS, MAC LoS, or LOS alarm is sent, the control unit 9 of the OLT 1 switches the trunk optical fiber to be used from the active trunk optical fiber 7-1 to the standby trunk optical fiber 7-2. As shown in FIG. 2, the working trunk optical fiber 7-1 is connected to the wOLT 1-1, the standby trunk optical fiber 7-2 is connected to the sOLT 1-2, and the OLT used for the operation is designated as wOLT1-. By switching from 1 to sOLT1-2, the trunk optical fiber is switched. In addition, you may implement switching from wOLT1-1 to sOLT1-2 by not providing the control part 9, but wOLT1-1 notifying sOLT1-2 of an alarm directly.

  Hereinafter, in the present embodiment, out of the fault detection signals, fault detection (optical LoS, MAC LoS, and so on) that requires switching of the trunk optical fiber (that is, switching of the OLT units 1-1 and 1-2 used for operation) is performed. LOS etc.) will be referred to as trunk line fault detection. The trunk line failure detection may be, for example, the above-described optical LoS, MAC LoS, or LOS, or may be a failure detection method other than these as long as it detects a trunk line optical fiber failure.

From the above, when the trunk line fault detection methods such as optical LoS, MAC LoS, and LOS are summarized, a trunk fault is detected when one or more of the following conditions are satisfied.
(1) The optical receiver of the OLT does not receive an optical signal during X [ms] (X is a predetermined constant).
(2) When the OLT does not receive a control signal response (for example, MPCP (Multi-Point Control Protocol) frame) from the ONU for Y [ms] (Y is a predetermined constant).
(3) When ONU does not react continuously Z times to the OLT transmission permission signal (Z is a predetermined constant).

  Hereinafter, functions of the PON control unit 10 of the OLT 1 will be described with reference to FIGS. The PON control unit 10 includes a time counter 34. When the optical signals from the ONUs 2-1 to 2-4 do not reach a certain time (the optical receiver 16 does not receive an optical signal valid for a certain time), Raise the LoS alarm.

  The signal processing unit 30 performs discovery processing for communicating with the detected ONUs 2-1 to 2-4, band allocation processing for allocating communication bands (upstream transmission time zones) of the respective ONUs 2-1 to 2-4, and the like. Do. The signal processing unit 30 transmits the band allocation result to the ONUs 2-1 to 2-4 by a GATE message (band allocation notification). The signal processing unit 30 allocates a band to each ONU 2-1 to 2-4 based on a REPORT message (response signal) including an uplink allocation request transmitted from each ONU 2-1 to 2-4. Further, the signal processing unit 30 detects response signals (MPCP frames) transmitted from the ONUs 2-1 to 2-4, and uses the time counter 34 to respond to the ONUs 2-1 to 2-4 for each response signal (MPCP frame). Signal processing unit 30 raises the MAC LoS alarm when the signal does not reach for a certain time. The MPCP frame is a GATE frame and a REPORT frame that are transmitted and received at regular intervals, and data, sleep permission, and response are transmitted by the data frame.

  The sleep control signal processing unit 32 refers to the state management table 33 that is a table for managing the power saving state of each ONU 2-1 to 2-4, and sleeps (power saving) for each ONU 2-1 to 2-4. ) A mode is selected, and a sleep permission (Sleep_Allow) control signal for transitioning to the sleep mode is transmitted. Further, the sleep control signal processing unit 32 updates the state management table 33 when receiving a sleep permission response (Sleep_Ack) control signal from the ONU. When the sleep control signal processing unit 32 returns the ONUs 2-1 to 2-4 from the sleep (power saving) mode, the sleep control signal processing unit 32 normally performs the ONUs 2-1 to 2-4 in the corresponding sleep (power saving) mode. A control signal for returning to the mode (WakeUp_Allow) is transmitted. The sleep control signal processing unit 32 also updates the state management table 33 when receiving a return permission response (WakeUp_Ack) control signal from the ONUs 2-1 to 2-4. Further, when a power-off notification (R-INH or the like) is received, the state management table 33 may be updated so that the state of the transmission source ONUs 2-1 to 2-4 is set to the sleep mode.

  For example, the processing related to the power-off notification is performed as follows. The power-off detection unit (not shown) of the ONUs 2-1 to 2-4 notifies the PON control unit 20 when it detects its own power-off. When notified of the power-off detection, the PON control unit 20 transmits to the OLT 1 a power-off notification notifying that the power-off has occurred.

  In the present embodiment, when the ONUs 2-1 to 2-4 detect their own power-off, a power-off notification is transmitted to the OLT 1, but the ONUs 2-1 to 2-4 are in a sleep state (power saving state). In some cases, when a power failure occurs, a power failure notification may or may not be transmitted. Whether or not the power-off notification can be transmitted depends on the bandwidth update cycle, the activation time of the transmission / reception function from the power saving state of the ONUs 2-1 to 2-4, and the like.

  An example in which power-off notification during sleep is possible is shown. The OLT 1 transmits a GATE frame for each band update period even when the connected ONUs 2-1 to 2-4 are in the sleep mode. The bandwidth allocated to each ONU 2-1 to 2-4 in the sleep mode is a bandwidth for each ONU 2-1 to 2-4 to transmit a REPORT frame.

  When a power failure occurs in the ONUs 2-1 to 2-4 in the power saving state (during sleep), the PON control unit 20 of the ONUs 2-1 to 2-4 cancels the sleep mode and replaces the part that has been turned off. to start. As an example, the Rx activation time (reception side activation time: time until the portion that has been stopped due to the sleep state among the components that perform reception processing of the ONUs 2-1 to 2-4 becomes operable) Based on the GATE frame received first after the elapse of time, a REPORT frame requesting a band for transmitting a power-off notification is transmitted. The Rx activation time is the Tx activation time (transmission side activation time: of the components that perform transmission processing of the ONUs 2-1 to 2-4, and the portion that has been stopped becomes operable by entering the sleep state. Therefore, the REPORT frame can be transmitted when the Rx activation time has elapsed.

  When the PON control unit 20 of the ONUs 2-1 to 2-4 receives the GATE frame for notifying the band allocation for transmitting the power-off notification, the power-off notification is performed in the band (transmission time period) indicated by the GATE frame. Send. Since the power-off notification is completed between the occurrence of the power-off and the power-off power holding time (the time during which power can be held using a capacitor after the power-off) elapses, the power-off notification during sleep Is possible.

  The buffer monitoring unit 31 monitors the accumulation amount of the transmission buffer 13 and notifies the sleep control signal processing unit 32 of the monitoring result. The sleep control signal processing unit 32 shifts the optical transmitter 27 of the optical transceivers 25 of the ONUs 2-1 to 2-4 to the sleep (power saving) mode, or sleeps both the optical transmitter 27 and the optical receiver 26. Whether to shift to the (power saving) mode is determined based on the information from the buffer monitoring unit 31 and the buffer monitoring unit 36 of the ONUs 2-1 to 2-4 received from the ONUs 2-1 to 2-4. The signal processing unit 30 generates control signals for sleep permission (Sleep_Allow) and return permission (WakeUp_Allow) based on the determination result of the sleep control signal processing unit 32, and transmits the control signal from the optical transmitter 17.

  In both the optical transmitter 27 and the optical receiver 26 in the sleep (power saving) mode, the sleep (power saving) state and the temporary activation state are intermittently repeated. Even in the mode, signals from the OLT 1 can be received at regular intervals.

  When the optical receiver 16 receives a sleep permission response (Sleep_Ack) or a return permission response (WakeUp_Ack) from the ONUs 2-1 to 2-4, the sleep control signal processing unit 32 passes through the signal processing unit 30 to the state management table 33. Update. At the same time, the sleep control signal processing unit 32 monitors the sleep (power saving) time using the time counter 34.

  When the optical receiver 16 receives the upstream optical signal data from the ONUs 2-1 to 2-4, the signal processing unit 30 temporarily stores the received data in the reception buffer 14. The signal processing unit 30 determines the processing timing using the time counter 34, reads the data stored in the reception buffer 14 at the determined timing, and sends it to the L2SW 8 via the receiving unit 18 of the physical layer processing unit 11.

  Next, the function of the ONU 2-1 will be described with reference to FIGS. The ONUs 2-2 to 2-4 are the same as the ONU 2-1. The ONU 2-1 has a function of shifting to a sleep (power saving) mode as a communication state. The sleep (power saving) mode here refers to powering off only the optical transmitter 27 or both the optical transmitter 27 and the optical receiver 26 when there is no data to be transmitted in the upstream direction or the downstream direction. This is a mode for stopping power consumption and reducing power consumption. Here, the OLT 1 requests the ONUs 2-1 to 2-4 to transition to the sleep (power saving) mode, and the ONUs 2-1 to 2-4 transmit a response to the request, and then transition to the sleep mode. The procedure will be described as an example.

  In addition, the procedure of the transition to the sleep mode of the ONUs 2-1 to 2-4 is not limited to this, and the OLT 1 permits the request for the transition from the ONUs 2-1 to 2-4 to the sleep mode. Requesting the OLT 1 to transition to the sleep mode from the OLT 1 to the ONUs 2-1 to 2-4, and the ONUs 2-1 to 2-4 transitioning to the sleep mode without transmitting a response to the request, Various procedures can be applied.

  The buffer monitoring unit 36 monitors the accumulation amount in the transmission buffer 23 and notifies the signal processing unit 35 of the monitoring result. The signal processing unit 35 grasps the upstream transmission time zone assigned to the own device by the GATE frame received from the OLT 1 via the optical receiver 26. Further, the signal processing unit 35 stores the accumulated amount of the transmission buffer 23 by the REPORT message when the transmission data is accumulated in the transmission buffer 23 based on the notification from the buffer monitoring unit 36 and allocates the bandwidth. Request.

  When receiving upstream transmission data from the transmission unit 29 of the physical layer processing unit 21, the signal processing unit 35 temporarily stores the transmission data in the transmission buffer 23. The signal processing unit 35 reads the transmission data from the transmission buffer 23 in the upstream transmission time zone assigned from the OLT 1 and transmits it as an upstream optical signal from the optical transmitter 27.

  In the PON control unit 20 of the ONU 2-1, when the sleep processing response (Sleep_Allow) transmitted from the OLT 1 is received by the signal processing unit 35, the sleep control unit 39 refers to the buffer monitoring unit 36 and performs non-communication (transmission buffer, and If no data is stored in the reception buffer), a sleep permission response (Sleep_Ack) is returned via the signal processing unit 35. The sleep control unit 39 identifies and selects a sleep (power saving) mode, and transitions its own state to the sleep (power saving) mode. Further, the ONU 2-1 has a state table 38 indicating the power saving state of its own device, and updates the state table 38 according to the state transition at that time. Further, even in the sleep mode, the ONU 2-1 transits to the normal state temporarily and periodically in order to respond to the control signal (MPCP frame) from the OLT 1. By temporarily returning to the normal state, a REPORT message can be returned in response to the GATE message transmitted from the OLT 1.

  When the optical receiver 26 receives a sleep permission (Sleep_Allow) from the OLT 1, the sleep control unit 39 passes through the signal processing unit 35 and the optical transmitter 27 and the optical receiver 26 (or the optical transmitter 27) of the optical transmitter / receiver 25. Only) is controlled to transit to the sleep mode in which the sleep state and the temporary activation state are periodically repeated. In addition, the sleep control unit 39 transmits a sleep permission response (Sleep_Ack) from the optical transmitter 27 via the signal processing unit 35 and updates the state table 38. At the same time, the sleep (power saving) time is monitored using the internal time counter 40.

  When the optical receiver 26 receives a return permission response (WakeUp_Ack) from the OLT 1, the sleep control unit 39 passes through the signal processing unit 35 and the optical transmitter 27 and the optical receiver 26 (or optical transmission) of the optical transmitter / receiver 25. (Only the device 27) is shifted from the sleep mode to the normal state, a return permission response (WakeUp_Ack) message is transmitted from the optical transmitter 27 via the signal processing unit 35, and the state table 38 is updated.

  Next, an example of redundant switching from the active trunk optical fiber 7-1 to the standby trunk optical fiber 7-2 in the OLT 1 will be described. Here, the active wOLT 1-1 does not receive an optical signal from any of the connected ONU 2-1 to ONU 2-4 for a certain period (failure monitoring time) as a trunk failure detection signal that is a condition for redundant switching. An example using an optical LoS alarm that is sometimes transmitted will be described.

  FIG. 5 is a diagram illustrating a communication operation sequence example of discovery processing. In order to start communication between the OLT 1 and the ONUs 2-1 to 2-4, the OLT 1 performs a discovery process to set a logical link, and holds the synchronization required for matching the transmission permission timing and the ONU 2 Communication can be performed by setting control function information. When unconnected ONUs 2-1 to 2-4 are newly connected to branch optical fibers, or when ONUs 2-1 to 2-4 are turned off, ONUs 2-1 to 2 are turned on. -4 indicates that an optical line necessary for communication with the OLT 1 is not set. Further, since the control function information of the ONU 2 is not registered in the OLT 1, communication cannot be performed. This state is called an unregistered state. The unregistered ONUs 2-1 to 2-4 perform only reception until they are registered (Registered) in the OLT 1, and are in a standby state until communication is permitted from the OLT 1.

  FIG. 5 shows an example in which the ONU 2-1 is newly connected. The ONU 2-1 receives a GATE message (Discovery Gate) that accepts new registration from the OLT 1 (step S1). The GATE message stores a transmission permission time (start time of the transmission permission time zone) and a transmission amount (information on how many uplink signals can be transmitted from when). However, in the case of a GATE message (Discovery Gate) during the discovery process, there is a possibility that a plurality of ONUs may be discovered at the same time, so each ONU performs transmission after waiting for a random time. When the ONU 2-1 receives the GATE message (Discovery Gate), the ONU 2-1 transitions to a state for performing initial settings (discovery state). When transitioning to this state, the ONU 2-1 synchronizes its own time with the time T1 of the OLT 1 stored in the GATE message (step S2), and the transmission time T2 (the transmission time specified by the GATE message is added to the random time). Wait for a random time (step S3). After this standby, the ONU 2-1 stores and transmits it in a REGISTER_REQ message that stores information necessary for communication with the OLT 1 such as its own identification information (function information held when necessary) (step S4). ).

  The OLT 1 registers the ONU 2-1 as a communication terminal based on the REGISTER_REQ message information, and calculates an RTT (Round Trip Time) with the ONU 2-1 (step S5). When the OLT 1 registers the ONU 2-1, the OLT 1 transmits a control message (REGISTER message) informing the registration to the ONU 2-1 (step S 6). The REGISTER message includes communication link setting information. When this REGISTER message is received, the ONU 2-1 stores the setting information and becomes in a communicable state by performing necessary communication settings on the own apparatus. The ONU 2-1 that has transitioned to the REGISTER message registration state transmits and receives data to and from the OLT 1 using the stored setting information. The setting information may include information regarding the sleep mode.

  When transmission is permitted by the GATE message (step S7), the ONU 2-1 synchronizes its time with the time T3 of the OLT 1 included in the received message (step S8), and waits for a random time (step S7). After S9), a REGISTER_ACK message notifying that the communication setting has been completed is transmitted (step S10). As described above, the discovery process between the OLT 1 and the ONU 2-1 is completed, and the communication between the OLT 1 and the ONU 2-1 becomes possible thereafter (step S11).

  FIG. 6 is a diagram illustrating an example of a sequence when a failure occurs in the active trunk optical fiber 7-1. After completion of the discovery process described with reference to FIG. 5 (step S11), the OLT 1 performs bandwidth allocation to the connected ONU 2-1 for each fixed GATE cycle Ts and notifies the bandwidth allocation result by a GATE message (step S12). , S16, S20). In FIG. 6, it is assumed that only the ONU 2-1 is connected to the OLT 1. The ONU 2-1 synchronizes its own time with the time of the OLT 1 included in the GATE message (steps S13, S17, S21). And it waits until the transmission permission time notified by the GATE message (steps S14 and S18), and transmits the REPORT message after waiting (steps S15 and S19).

  Each time the OLT 1 receives a REPORT message as an optical signal, it starts counting a timer (fault monitoring timer) for measuring the fault monitoring time by using the time counter 34, and resets the count when receiving the next REPORT message. And the start of the next measurement is repeated.

  Here, as shown in FIG. 6, the ONU 2-1 receives the third GATE frame after the completion of the discovery process (step S20), and after performing time synchronization (step S21), the active trunk optical fiber 7- It is assumed that a failure has occurred in 1 (step S22). Then, even if a GATE frame is transmitted from the OLT 1 (step S23), the OLT 1 cannot receive the REPORT message from the ONU 2-1, the failure monitoring timer times out, and an optical LoS alarm is generated (step S24).

  FIG. 7 is a diagram illustrating an example of a trunk optical fiber switching sequence when a failure occurs in the active trunk optical fiber 7-1. In the example of FIG. 7, initially, it is assumed that no failure has occurred in the active trunk optical fiber 7-1 and that the OLT 1 is operating the wOLT 1-1. First, the ONU 2-1 to ONU 2-4 are connected to the OLT 1, and the discovery process for the ONU 2-1 to ONU 2-4 is completed (step S11). The OLT 1 performs bandwidth allocation for each of the connected ONUs 2-1 to 2-4, and notifies the bandwidth allocation result by a GATE message (step S31). Each of the ONUs 2-1 to 2-4 transmits a REPORT message at the transmission permission time notified by the GATE message (step S32).

  As described in the example of FIG. 6, the OLT 1 starts counting of the failure monitoring timer every time an optical signal is received (step S34). When a failure occurs in the active trunk optical fiber 7-1 (step S35), even if the OLT 1 transmits a GATE message, the REPORT message is not returned from all the ONUs 2-1 to 2-4, and the failure monitoring timer is activated. A time-out occurs, and an optical LoS alarm is generated by the PON control unit 10 in the wOLT 1-1 (step S36).

  Upon receiving the optical LoS alarm, the control unit 9 switches the OLT to be operated from wOLT1-1 to sOLT1-2, and changes the route of the main signal with the L2SW8 accordingly. Thereby, the switching process from the active trunk optical fiber 7-1 to the standby trunk optical fiber 7-2 is performed. After the switching time for performing these switching processes (step S37), the sOLT 1-2 transmits a GATE message to each of the connected ONUs 2-1 to 2-4 (step S38). The ONU 2-1 to ONU 2-4 return a REPORT message in response to the received GATE message (step S39). The sOLT 1-2 updates the RTT for any one of the ONUs 2-1 to 2-4 (step S40). In this way, the communication line is maintained again using the standby trunk optical fiber 7-2.

  In the example of FIG. 7, when switching to a communication path connected via the sOLT 1-2, the standby trunk optical fiber 7-2, the optical splitter 3, and the branch optical fibers 6-1 to 6-4, the sOLT1- 2 starts communication based on the setting information of the ONUs 2-1 to 2-4 acquired by the wOLT 1-1 during the discovery process. The setting information may be stored in a common storage unit in the OLT 1 so that both the wOLT 1-1 and the sOLT 1-2 can be referred to. May be transmitted to sOLT1-2. Further, since there is a possibility that the RTT may change due to the switching of the communication path, the PON control unit 10 on the standby sOLT 1-2 side switches the RTT with any ONU among the ONUs 2-1 to 2-4 after the switching. Calculate again. RTTs with other ONUs are updated based on the difference between the recalculated value and the value before recalculation. In this way, by reflecting the setting information acquired by wOLT 1-1 in sOLT 1-2, the discovery process when the communication path is switched from the active system to the standby system can be omitted.

  As described above, the discovery processing, trunk failure detection processing, and communication path switching processing described in FIGS. 5, 6, and 7 are the same as those in the normal PON system. 6 and 7 show an example in which the optical LoS alarm is used as the main line failure detection signal. However, the main line failure detection signal as a switching condition is not limited to this, and the MAC LoS alarm may be used. It may be a LOBi alarm, a LOS alarm, or the like. However, in the case of a LOBi alarm or the like in which an alarm is transmitted for each ONU, the communication path is switched when the LOBi alarm is transmitted for all ONUs.

  Next, problems when both the power saving control and failure detection of the ONUs 2-1 to 2-4 are performed will be described. FIG. 8 is a diagram illustrating an example of a communication operation sequence in a case where a normal operation is hindered by the conventional communication path switching method. There are cases where all the ONUs 2-1 to 2-4 connected to the OLT 1 temporarily shift to a sleep (power saving) mode mainly during a time period when the user does not use a communication service, such as at night. FIG. 8 shows an example in which the OLT 1 operates in accordance with a communication path switching method similar to the conventional one.

  As in the example of FIG. 7, after the discovery process (step S11), the OLT 1 performs bandwidth allocation for each of the connected ONUs 2-1 to 2-4 and notifies the bandwidth allocation result by a GATE message (step S31). . Each of the ONUs 2-1 to 2-4 transmits a REPORT message at the transmission permission time notified by the GATE message (step S32).

  When the OLT 1 determines that there is no transmission / reception data between the ONUs 2-1 to 2-4 and the ONUs 2-1 to 2-4 are to be shifted to the sleep mode, the sleep (power saving state) transition permission (Sleep_Allow) is set to the ONU 2-1. To 2-4 (step S42). Each of the ONUs 2-1 to 2-4 returns a response signal (Sleep_Ack) indicating transition to the sleep mode to Sleep_Allow (step S43), and transitions to the sleep mode.

  In this case, when viewed from the OLT 1 side, the optical signals and control signal responses from all the ONUs 2-1 to 2-4 are temporarily not received. The fault monitoring timer that has started counting upon reception of the last REPORT message (step S41) times out, and an optical LoS alarm is generated (step S44). Then, similarly to FIG. 7, the communication path is switched (step S45).

  As described above, in the conventional communication path switching method, when all the ONUs 2-1 to 2-4 shift to the sleep mode, the active trunk optical fiber 7-1 is used even if no failure occurs in the optical transmission path. It is erroneously determined that a failure has occurred, and the active trunk optical fiber 7-1 is switched to the standby trunk optical fiber 7-2.

  Further, the OLT 1 needs to switch the communication path as described above in the case of a trunk line failure, but does not have to switch the communication path in the case of a branch line failure. If there are a plurality of ONUs 2-1 to 2-4 to be connected, there is no response from only one ONU, or there is no response from all ONUs (no optical signal is received). Can be determined. However, if there is only one ONU 2-1 to 2-4 in a normal state that is not in the sleep mode, and a failure occurs in the ONU or a branch line connected to the ONU, the OLT 1 has all the ONUs 2-1 to 2-4. No optical signal will be received from. In this case, the OLT 1 cannot distinguish between a main line failure and a branch line failure, and the communication line is switched even in the case of a branch line failure that does not need to switch the communication path, resulting in unnecessary communication interruption. There is also a problem.

  Therefore, in the present embodiment, as described below, the OLT 1 manages the state (whether or not it is in the sleep mode) of each ONU 2-1 to 2-4 using the state management table 33, and the ONU 2-1. When all of ˜2-4 are in the sleep mode, a LoS alarm or the like that is a condition for switching the communication path is not transmitted, or the communication path is not switched even if a LoS alarm is issued. Further, if the sleep mode time is controlled so that the number of ONUs 2-1 to 2-4 that are not in the sleep mode is one or more, erroneous detection of a trunk line failure can be prevented. Further, by controlling the time of the sleep mode so that the number of ONUs 2-1 to 2-4 that are not in the sleep mode becomes two or more, it becomes possible to distinguish between a trunk line failure and a branch line failure. In the following, when all of the ONUs 2-1 to 2-4 are in the sleep mode, the number of ONUs 2-1 to 2-4 that are in the sleep mode at the same time as the control for preventing the communication path switching is performed. Although an example in which both of the control to set two or more (or one or more) is performed will be described, only one of them may be performed.

  In order to distinguish between a main line failure and a branch line failure, it is necessary to set the number of ONUs 2-1 to 2-4 in the sleep mode at the same time to two or more. To prevent erroneous detection of a main line failure, The number of ONUs 2-1 to 2-4 that simultaneously enter the sleep mode may be one or more. Therefore, when aiming at preventing erroneous detection of a trunk line failure, it is sufficient to set one or more ONUs 2-1 to 2-4 that simultaneously enter the sleep mode.

  Hereinafter, the operation of the OLT 1 using the state management table 33 will be described in detail. FIG. 9 is a flowchart illustrating an example of the basic control of the OLT 1, and FIG. 10 is a flowchart illustrating an example of the power saving control of the OLT 1.

  As shown in FIG. 9, in the OLT 1, the signal processing unit 30 performs a discovery process as an initial setting (step S51), and when the discovery process is completed, the ONUs 2-1 to 2-4 that have completed the discovery process. Bandwidth allocation is performed for the ONUs 2-1 to 2-4 by a GATE message (Gate Frame) (step S52). Further, when the signal processing unit 30 receives signals from the ONUs 2-1 to 2-4, the signal processing unit 30 performs data processing for the received signal processing (step S53). In addition, the sleep control signal processing unit 32 of the OLT 1 performs power saving control on the ONUs 2-1 to 2-4 (step S54). Further, the PON control unit 10 of the OLT 1 performs fault monitoring such as the above-described optical LoS detection (step S55). Then, steps S52 to S55 are repeated. In addition, the order in step S52-S55 is not limited to this, The order of a process may differ, and two or more of these processes may be implemented simultaneously.

  FIG. 10 shows the details of the bandwidth allocation in step S52 and the power saving control in step S54. After the initial setting (step S61), the OLT 1 performs bandwidth allocation, and the ONU 2-1 to ONU 2-1 through the GATE message. 2-4 is notified (step S62). The OLT 1 receives the REPORT message (Report Frame) from the ONUs 2-1 to 2-4 (step S63), and the transmission buffer amount (accumulated amount of the transmission buffer 23) in the ONUs 2-1 to 2-4 stored in the REPORT message. It is determined whether or not there is (a certain amount or more) (step S64). If there is a transmission buffer amount (Yes in step S64), the process returns to step S62.

  When there is no transmission buffer amount (No in step S64), the OLT 1 refers to the state management table 33 (step S65). FIG. 11 is a diagram illustrating an example of the state management table 33. As shown in FIG. 11, the state management table 33 stores the identification numbers of ONUs 2-1 to 2-4 (here, ONUs 2-i (i = 1, 2, 3, 4) for each of the ONUs 2-1 to 2-4. ) Is set to ONU # i), a state (State) that is information indicating whether the ONUs 2-1 to 2-4 are in a sleep mode or a normal state (active), and for each ONU Alarm (Alarm) that is information indicating whether to mask the alarm, switching trigger, start time (start time of sleep mode when in sleep mode), return time (sleep mode when in sleep mode) (Return time from) is stored. The switching trigger indicates a trigger for switching the communication path when the alarm is not masked, and the monitoring in the example of FIG. 11 means monitoring of the alarm. When the alarm is generated, immediately This means that the switching process is performed.

  Immediately after the discovery process, the connected ONUs 2-1 to 2-4 are all in the normal state, and the alarm is not masked. When the OLT 1 receives Sleep_Ack that is a response indicating that the ONU 2-1 to 2-4 shifts to the sleep mode for each of the ONUs 2-1 to 2-4, the ONUs 2-1 to 2 that have received the Sleep_Ack are received. -4, the state management table 33 is updated to the sleep mode (Sleep), and the start time and return time are updated. Note that the start time and the return time are updated based on this information because the OLT 1 knows the Sleep_Request message for the ONUs 2-1 to 2-4. Further, when the OLT 1 instructs the OLTs 2-1 to 2-4 to return from the sleep mode and receives a response, the state management table 33 is updated to be in the same state as immediately after the discovery process. . Even when a return request to the normal state is transmitted from the ONUs 2-1 to -4 in the sleep mode due to the generation of transmission data, when the return request is received, the state management table 33 is used for the discovery process. Update to the same state as immediately after. FIG. 11 shows an example of the state management table 33, and the items of the state management table 33 are not limited to these. Information on whether or not the ONUs 2-1 to 2-4 are in the sleep mode at least should be included.

  Returning to the description of FIG. The OLT 1 determines whether there are three or more active ONUs 2-1 to 2-4 based on the state management table 33 (step S66), and if not three or more (step S66 No), step Return to S62. When the number of active ONUs 2-1 to 2-4 is two or less, if the ONUs 2-1 to 2-4 determined to have no transmission buffer capacity in step S64 are shifted to the sleep mode, the active ONU 2 -1 to 2-4 will be 1 or less. For this reason, when the number of active ONUs 2-1 to 2-4 is two or less, the ONUs 2-1 to 2-4 having no transmission buffer amount are not shifted to the sleep mode.

  When there are three or more active ONUs 2-1 to 2-4 (step S66 Yes), the OLT 1 performs power saving control for shifting the ONUs 2-1 to 2-4 having no transmission buffer amount to the sleep mode. The start and end times of the sleep mode for the ONU are determined (step S67), and Sleep_Allow is transmitted to the ONU (step S68). Thereafter, it is determined whether or not Sleep_Ack has been received from the ONU (step S69). If received (step S69 Yes), the state management table 33 is updated (step S70), and the process returns to step S62. If Sleep_Ack is not received (No in step S69), the process directly returns to step S62.

  If it is determined that there is no transmission buffer capacity for a plurality of ONUs 2-1 to 2-4 almost simultaneously, not all of the ONUs (pause candidate ONUs) are shifted to the sleep mode, but the sleep candidate ONU and the sleep candidate already have a sleep. Control may be performed such that two or more units are always active by shifting the time of entering the sleep mode between the ONUs 2-1 to 2-4 in the mode.

  In this embodiment, whether or not the sleep mode is set is managed as an ONU state, and control is performed so that all the ONUs do not enter the sleep mode at the same time. In consideration of the start state, it is also possible to manage whether the power saving state or the temporary start state, and control the power saving state so that it does not overlap in all ONUs.

  Next, communication path switching processing in the OLT 1 of the present embodiment will be described in detail. In this embodiment, in order to prevent erroneous detection of a trunk line failure, control is performed that does not perform communication path switching when all ONUs are in the sleep mode. However, there are various variations in this control method. . For example, when all the ONUs are in the sleep mode, there is a method that does not generate a main line fault detection signal such as an optical LoS alarm even if no signal is received from the ONUs 2-1 to 2-4 for the fault monitoring time or longer. is there. In addition, if all ONUs are in sleep mode instead of generating main line fault detection signals such as optical LoS alarms, the fault monitoring timer count is reset periodically (before expiration), etc. There is also a method that does not expire the monitoring timer. Further, there is a method in which the communication path switching process is not performed when all the ONUs are in the sleep mode even when a trunk line failure detection signal such as an optical LoS alarm is generated. Any of these methods and methods other than these may be implemented. However, here, when all the ONUs are in the sleep mode even if a trunk failure detection signal such as an optical LoS alarm is generated. An example of adopting a method for preventing the communication path switching process from being performed will be described. That is, in this embodiment, the control unit 9 does not immediately switch the communication path (redundant switching) even after receiving the optical LoS alarm, but switches the communication path after receiving the Holdover signal instructing the switching. To implement.

  FIG. 12 is a flowchart illustrating an example of a communication path switching procedure according to the present embodiment. The PON control unit 10 of the OLT 1 performs bandwidth allocation and notifies the ONUs 2-1 to 2-4 with a GATE message (step S71). Then, the failure monitoring timer starts counting (step S72). Then, it is determined whether or not a REPORT message has been received as a response to the GATE message (step S73). If received (step S73 Yes), the process returns to step S71, and after transmitting the GATE message, the fault monitoring timer is counted again. Start.

  Here, an example is described in which the failure monitoring timer starts counting when a GATE message is transmitted. The failure time monitoring by the failure monitoring timer only needs to be able to monitor whether or not the response signal that should be received within a predetermined time can be received. Therefore, a signal that requests a response signal as in the example of FIG. ) May be started as a count, or as shown in FIG. 6 and the like, the count may be started when a response signal scheduled to be received within a certain period is received. When counting is started when the response signal is received, step S72 is moved after the REPORT message is received (step S73 Yes), and the process returns to step S71 via step S72.

  When the REPORT message is not received (No at Step S73), the PON control unit 10 determines whether or not the failure monitoring timer count has expired (Step S74), and when it has not expired, the process returns to Step S73 (Step S73). S74 No). Here, an example in which MAC LoS is detected as trunk failure detection will be described. However, in the case of detecting optical LoS, it is determined whether a valid optical signal is received instead of whether a REPORT message is received. It becomes.

  When the count of the fault monitoring timer expires (step S74 Yes), the PON control unit 10 issues an alarm (Report Alarm) indicating that a trunk line fault such as optical LoS has been detected (step S75), and the state management table 33 Is updated (step S76). Specifically, the information is updated in the alarm column of the state management table 33 to information indicating that an alarm has occurred. Then, the PON control unit 10 refers to the state management table 33 (step S77) and determines whether or not one or more ONUs are active (step S78). When one or more ONUs are active (Step S78 Yes), a Holdover signal is transmitted to the control unit 9 (Step S79). In the case of a configuration that does not include the control unit 9, a Holdover signal is transmitted to the PON control unit 10 of the sOLT1-2.

  The control unit 9 that has received the Holdover signal transmits a redundancy switching notification instructing to switch the communication path switching to the standby system to the sOLT 1-2 (step S80). As a result, the OLT 1 performs redundancy switching, and the RTT is recalculated by the sOLT 1-2 (step S81), and the process returns to the step S71.

  If it is determined in step S78 that all the ONUs are not active (No in step S78), it is determined that the ONUs 2-1 to 2-4 in the sleep mode are to be masked with alarms (LOBi, etc.) for each ONU (step S82). The state management table 33 is updated so that the alarms of the mode ONUs 2-1 to 2-4 are set to Mask (step S83), and the process returns to step S71. Masking an alarm for each ONU means, for example, that even if a failure is detected for each ONU, processing corresponding to the detection result is not performed. Note that the process of setting the alarm for each ONU as Mask in the state management table 33 may be performed when each ONU is shifted to the sleep mode.

  In the case of a method for detecting a failure by counting the number of times that an expected received frame has not been received, such as LOBi or LOS, instead of determining whether the failure monitoring time has elapsed by the failure monitoring timer. In addition, the same communication path switching process can be performed by using the determination of whether or not the number of times the expected received frame has not been received has become a certain number.

  In addition, as described with reference to FIG. 11, in this embodiment, since two or more ONUs 2-1 to 2-4 are controlled to be active, a branch line (or ONU) failure is erroneously caused by a trunk line. The possibility of being detected as a failure can be greatly reduced.

  FIG. 13 is a diagram showing an example of a sequence when the communication path switching method in the OLT 1 according to the present invention is implemented. In the example of FIG. 13, an example is shown in which the same control as the conventional control is performed for power saving control without performing control to turn on two or more ONUs 2-1 to 2-4 that are simultaneously active. As in the example of FIG. 8, wOLT 1-1 and ONUs 2-1 to 2-4 of OLT 1 transmit GATE message (step S31), REPORT message transmission (step S32), Sleep_Allow transmission (step S42), and Sleep_Ack transmission (step S43) is performed. Then, when receiving the Sleep_Ack, the PON control unit 10 of the wOLT 1-1 updates the state management table 33 as described above (step S85).

  When receiving the REPORT frame, the PON control unit 10 of the wOLT 1-1 starts counting the failure monitoring timer (step S41). Since all of the ONUs 2-1 to 2-4 have shifted to the sleep mode, the failure monitoring timer expires, An alarm for detecting a trunk line failure is generated (step S44). In the present embodiment, as described with reference to FIG. 12, even if a main line failure detection alarm is generated, the PON control unit 10 of the wOLT 1-1 refers to the state management table 33 and sets all the ONUs 2-1 and 2. Since it is understood that -4 is the sleep mode, redundant switching is not performed. As a result, the GATE frame is transmitted from the wOLT 1-1 to the ONUs 2-1 to 2-4 that have returned from the sleep mode, as before the occurrence of the alarm (step S31a). Thus, in this embodiment, unnecessary redundant switching due to erroneous detection of a trunk line failure can be prevented.

  FIG. 14 is a diagram illustrating an example of a sequence when power saving control is performed in the OLT 1 of the present embodiment. FIG. 14 shows an example in which there is no transmission buffer amount for all of the ONUs 2-1 to 2-4, and all of the ONUs 2-1 to 2-4 can be shifted to the sleep mode. In the case of such an example, in the past, since the ONUs 2-1 to 2-4 are shifted to the sleep mode almost simultaneously, there is a time zone in which all of the ONUs 2-1 to 2-4 are in the sleep mode. In this form, Sleep_Allow transmission (step S42) is performed in which two or more ONUs 2-1 to 2-4 that are simultaneously active. And OLT1 will update the state management table 33, if Sleep_Ack is received (step S43) (step S85). Specifically, in the example of FIG. 14, the ONU 2 that is simultaneously active by shifting the time to shift to the sleep mode by the ONU 2-1 to 2-4 by the round robin method in consideration of the fairness of the power saving effect. −1 to 2-4 are controlled to be two or more. A specific method for determining the start time of the sleep mode of each ONU 2-1 to 2-4, in which two or more ONUs 2-1 to 2-4 are simultaneously active, is not limited to the example of FIG.

  In the example of FIG. 10, when there are three or less active ONUs 2-1 to 2-4, the new ONUs 2-1 to 2-4 are not shifted to the sleep mode. When shifting 1 to 2-4 to the sleep mode, the ONUs 2-1 to 2-4 that are shifting to the sleep mode are temporarily returned to the normal state or the end time of the sleep mode is shifted to control as shown in FIG. May be performed. That is, two or more units are activated by shifting the sleep time as shown in FIG. 14 for the ONUs 2-1 to 2-4 that are already in the sleep mode and the ONUs 2-1 to 2-4 that are newly shifted to the sleep mode. Control may be performed as follows.

  Next, power saving control in the ONUs 2-1 to 2-4 will be described. 15A and 15B are diagrams illustrating an example of the power saving control procedure in the ONUs 2-1 to 2-4. The PON control unit 20 of the ONUs 2-1 to 2-4 first performs an initial setting (discovery) process (step S91). When a frame is received from the OLT 1 (step S92), it is determined whether or not the received frame is a GATE message (Gate Frame) (step S93), and if it is not a GATE message (that is, a data frame (Data Frame)) (No in step S93), the data frame is received (step S94), and the type of data is determined (step S95).

  Then, it is determined whether or not the received frame is Sleep_Allow (Step S96). If it is Sleep_Allow (Yes in Step S96), the PON control unit 20 refers to the transmission buffer amount (accumulated amount of the transmission buffer 23). (Step S97), it is determined whether there is a transmission buffer amount (Step S98). If there is no transmission buffer amount (No in step S98), Sleep_Ack is returned (step S99). Then, the PON control unit 20 starts counting a timer (Sleep_Timer) for measuring the sleep time, which is the duration of one power saving state in the sleep mode (step S100), and the optical transmitter 27 (or optical The transmitter 27 and the optical receiver 26) are shifted to the power saving state (Sleep_Duration) (step S101). The PON control unit 20 determines whether or not the Sleep_Timer count has expired (step S102), and if it has expired (step S102 Yes), the optical transmitter 27 (or the optical transmitter 27 and the optical receiver 26) is temporarily suspended. Transition to the activated state (step S103).

  The PON control unit 20 receives the GATE message (step S104), refers to the transmission buffer amount (step S105), and determines whether there is a transmission buffer amount (step S106). If there is no transmission buffer amount (No in step S106), the transmission buffer amount (in this case, a value indicating that there is no transmission buffer amount) is input to the REPORT message (step S107), and the REPORT message is transmitted (step S108). Return to step S101.

  If it is determined in step S96 that it is not Sleep_Allow (No in step S96), predetermined data processing is performed on the received data (step S109), and the process returns to step S92. If it is determined in step S98 that there is a transmission buffer amount (step S98 Yes), Sleep_Ack (Wakeup) is returned (step S110). Sleep_Ack (Wakeup) is a frame that requests a return to the normal state, unlike the above-described Sleep_Ack that accepts the transition to the sleep mode. Then, a REPORT message and a data frame are transmitted (step S111), and the process returns to step S92.

  If it is a GATE message in step S93 (step S93 Yes), the GATE message is received (step S112), the transmission buffer amount is referred to (step S113), and the transmission buffer amount is input to the REPORT message (step S114). Then, after waiting until the transmission permission time (step S115), a REPORT message is transmitted (step S116), and the process returns to step S92.

  If there is a transmission buffer amount in step S106 (Yes in step S106), the PON control unit 20 returns a Sleep_Ack (Wakeup) (step S117), transmits a REPORT message and a data frame (step S118), and step S92. Return to.

  In the above description, there is one optical splitter and one branch line. However, a configuration in which the optical splitter is set in multiple stages and the branch lines have multiple stages is also conceivable. FIG. 16 is a diagram illustrating a configuration example in which branch lines have multiple stages. The OLT 1, the active trunk optical fiber 7-1, and the standby trunk optical fiber 7-2 are the same as in the example of FIG. 2, but in the example of FIG. 16, the first stage optical splitter 3-1 and the second stage optical fiber 7-1. The optical splitters 3-2 and 3-3 have a two-stage configuration. The optical splitter 3-1 is connected to the active trunk optical fiber 7-1 and the standby trunk optical fiber 7-2, and branch optical fibers 6-1 and 6-2 to the optical splitters 3-2 and 3-3. Are connected to each other. The optical splitter 3-2 is connected to the optical splitter 3-1 by the branch optical fiber 6-1, and is connected to the ONUs 2-1 to 2-4 by the respective branch lines, and the optical splitter 3-3 is connected to the branch optical fiber 6. -2 is connected to the optical splitter 3-1 and is connected to the ONUs 2-5 to 2-8 through the branch lines. Here, branch optical fibers 6-1 and 6-2 which are branch lines in the first stage are defined as branch line # 1, and branch lines connecting optical splitters 3-2 and 3-3 and ONUs 2-1 to 2-8 are defined as branch line # 1. 2.

  In the case of a multi-stage configuration as shown in FIG. 16, when two or more ONUs that are simultaneously active are ONUs connected to the same branch line # 1 (for example, ONU2-1 and ONU2-2 are active) ), It is not possible to distinguish between the failure of branch line # 1 or the failure of the trunk line. Therefore, in such a case, the OLT 1 holds information about which branch line # 1 is connected to each ONU, and at the same time, an ONU that connects an active ONU to a different branch line # 1. It is desirable to control so that For example, as shown in FIG. 16, the ONU 2-1 connected to the branch optical fiber 6-1 and the ONU 2-5 connected to the branch optical fiber 6-2 are activated.

  As described above, in this embodiment, the OLT 1 manages the power saving state of the ONUs 2-1 to 2-4 using the state management table 33, and performs redundancy switching using the state management table 33. Judged whether or not. For this reason, unnecessary redundant switching due to erroneous detection of a trunk line failure can be prevented. Further, by performing power saving control so that the number of ONUs 2-1 to 2-4 that are simultaneously active is set to two or more, it is possible to determine a branch line failure and a trunk line failure.

Embodiment 2. FIG.
FIG. 17 is a diagram showing a configuration example of the second embodiment of the PON system according to the present invention. As shown in FIG. 17, the PON system of the present embodiment has a multi-stage configuration, and the optical splitter 3 connected by the OLT 1 and the trunk fiber 7 includes branch optical fibers 50-1 to 50-4 (first stage). Branch optical fiber). Components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and redundant description is omitted. The branch line optical fibers 50-1, 50-2, 50-3, and 50-4 are connected to branch line splitters 51-1, 51-2, 51-3, and 51-4, respectively. The branch line splitter 51-1 is connected to the ONUs 71-1 to 71-8 via branch line optical fibers 61-1 to 61-8 (second-stage branch line optical fibers). Similarly, the branch line splitters 51-2, 51-3, and 51-4 are connected to the branch line optical fibers 52-2, 52-3, and 52-4, respectively, and the branch line optical fibers 62-1 to 62-8, and 63-. 1 to 63-8 and 64-1 to 64-8, respectively. The configurations of the ONUs 71-1 to 71-8, 72-1 to 72-8, 73-1 to 73-8, and 74-1 to 74-8 are the same as those of the ONU 2-1 described in the first embodiment. In FIG. 17, for simplification of the drawing, the branch optical fibers 62-1 to 62-8, 63-1 to 63-8 connected to the branch optical fibers 50-2 and 50-3, and the ONUs 72-1 to 72-1. Illustrations of 72-8 and 73-1 to 73-8 are omitted. Further, the number of branch splitters and the number of ONUs connected to each branch splitter via the second branch optical fiber are not limited to the example of FIG.

  The OLT 1 is connected to an administrator device (EMS (Element Management System)) 80 and a data center 90. Although FIG. 17 shows an example in which the OLT 1 is connected to both the administrator device 80 and the data center 90, the OLT 1 may be connected to only one of them. It is assumed that at least one of the administrator device 80 and the data center 90 grasps the connection relationship illustrated in FIG. It is assumed that ONU position information such as which splitter each ONU is located under and which splitter stage the ONU is connected to is stored as a database.

  In the present embodiment, in the case of a multi-stage configuration, the OLT 1 acquires ONU position information from the database held by the administrator device 80 or the data center 90, and the PON control unit 10 identifies individual ONUs managed by itself. Based on the information, position information is added to the state management table 33 described in the first embodiment. FIG. 18 is a diagram illustrating a configuration example of the state management table 33 according to the present embodiment. The status information column of FIG. 18 stores the same information as the status management table 33 of the first embodiment, and further stores location information for each ONU in this embodiment. The OLT 1 updates the state information in the state management table 33 in the same procedure as in the first embodiment.

  In the multistage configuration shown in FIG. 17, when the power saving control of the ONU is performed as described in the first embodiment, the failure of the first branch optical fiber (branch optical fibers 50-1 to 50-4) and the trunk line In order to distinguish the failure of the fiber 7, power saving control of the ONU may be performed so that a plurality of ONUs connected to different branch line splitters 51-1 to 51-4 are simultaneously active.

  FIG. 19 is a diagram illustrating an example of the power saving control method according to the present embodiment. In FIG. 19, the sleep mode period is indicated by a dotted line, and the active period is indicated by a solid line. As shown in FIG. 19, two or more ONUs connected to different branch line splitters 51-1 to 51-4 (connected to different branch line splitters 51-1 to 51-4) are activated at the same time. Implement power saving control. If two or more ONUs connected to different branch line splitters 51-1 to 51-4 are activated simultaneously, branch line optical fibers 50-1 to 50-4 (or branch line splitters 51-1 to 51-4). ), The OLT 1 can receive a response from the ONU connected to the branch optical fibers 50-1 to 50-4 in which no failure has occurred. In FIG. 19, for simplification of the drawing, one ONU under each branch splitter is shown one by one, but the same applies when there are two or more ONUs under the branch splitter. It is sufficient that two or more ONUs under the control of 51-1 to 51-4 are simultaneously active.

  The OLT 1 uses the state management table 33 including the position information illustrated in FIG. 18 to perform the power saving control of the ONU as in the first embodiment. The power saving control method is the same as that of the first embodiment except that two or more ONUs connected to different branch line splitters 51-1 to 51-4 are simultaneously activated.

  In the example described above, an example in which the branch line has two stages is shown, but the number of branch lines may be three or more. In the case of three or more stages, control is performed so that two or more ONUs under different optical splitters are active at the same time for the branch splitter connected directly below the branch to be distinguished from the trunk failure.

  Also in the present embodiment, various types of information in the state management table 33 managed by the active OLT are transferred to the standby OLT via the control unit 9, and after the main line switching, the standby OLT stores these information. The power saving control of the ONU is performed using

  In this embodiment, the ONU location information is acquired from the administrator device 80 and the data center 90. However, the service usage status for each ONU is also acquired from the administrator device 80 and the data center 90. It may be.

  As described above, in this embodiment, when the OLT 1 has a multi-stage configuration, the OLT 1 acquires the position information of each ONU from at least one of the administrator device 80 and the data center 90 and stores the position information in the state management table 33. Information is also stored and managed. Based on the state management table 33, the OLT 1 performs power saving control of the ONUs so that two or more ONUs connected to different branch line splitters 51-1 to 51-4 are simultaneously active. For this reason, unnecessary redundant switching due to erroneous detection of a trunk line failure can be prevented.

  As described above, the optical transmission system, the station-side optical terminal device, and the communication line switching method according to the present invention are useful for a PON system with redundant OLT, and are particularly suitable for a PON system that performs power saving control. .

  1 OLT, 1-1 wOLT, 1-2 sOLT, 2-1 to 2-N, 71-1 to 71-8, 74-1 to 74-8 ONU, 3 optical splitter, 4 upper network, 5-1, 5-2 User terminal, 6-1 to 6-N, 50-1 to 50-4, 61-1 to 61-8, 64-1 to 64-8 Branch optical fiber, 7 trunk optical fiber, 7-1 System trunk optical fiber, 7-2 Standby system trunk optical fiber, 8 L2SW, 9 control unit, 10, 20 PON control unit, 11, 21 physical layer processing unit, 12, 22 WDM coupler, 13, 23 transmission buffer, 14, 24 reception buffer, 15, 25 optical transceiver, 16, 26 optical receiver, 17, 27 optical transmitter, 18, 28 reception unit, 19, 29 transmission unit, 30, 35 signal processing unit, 31, 36 buffer monitoring unit , 32 sleep system Control signal processing unit, 33 status management table, 34, 40 time counter, 37 link monitoring unit, 38 status table, 39 sleep control unit, 51-1 to 51-4 branch splitter.

In order to solve the above-described problems and achieve the object, the present invention is made redundant with a subscriber-side optical termination device, a station-side optical termination device, and the station-side optical termination device that can be shifted to a power saving mode. And an optical splitter connected to each of the subscriber-side optical terminators and each of the branch lines, wherein the station-side optical terminator is a saving of the subscriber-side optical terminator. It manages power save information which is information about the power mode, the power saving mode in the power saving controlling the redundancy switching before Symbol mains based on information, the subscriber-side optical termination unit for each of the subscriber-side optical termination unit For each subscriber-side optical termination device so that there is at least one subscriber-side optical termination device that is not in the power-saving mode. Determine the serial start and end times, and performing a determination of whether to implement the redundancy switching of the main line based on a response signal from the subscriber-side optical termination unit not in the power saving mode.

Therefore, in the present embodiment, as described below, the OLT 1 manages the state (whether or not it is in the sleep mode) of each ONU 2-1 to 2-4 using the state management table 33, and the ONU 2-1. When all of ˜2-4 are in the sleep mode, a LoS alarm or the like that is a condition for switching the communication path is not transmitted, or the communication path is not switched even if a LoS alarm is issued. Further, if the sleep mode time is controlled so that the number of ONUs 2-1 to 2-4 that are not in the sleep mode is one or more, erroneous detection of a trunk line failure can be prevented. Further, by controlling the time of the sleep mode so that the number of ONUs 2-1 to 2-4 that are not in the sleep mode becomes two or more, it becomes possible to distinguish between a trunk line failure and a branch line failure. In the following, when all ONU2-1~2-4 is in the sleep mode, a control to make the communication path switching is not performed, the number of ONU2-1~2-4 not sleep mode Although an example in which both of two or more (or one or more) controls are implemented will be described, only one of them may be implemented.

In order to distinguish between mains failure and the branch failure, although the number of ONU2-1~2-4 not sleep mode it needs to be two or more, to prevent erroneous detection of mains failure, the scan The number of ONUs 2-1 to 2-4 that are not in the reap mode may be one or more. Therefore, for the purpose of preventing erroneous detection of mains failure, ONU2-1～2-4 not sleep mode may be set to more than one.

Claims (17)

It is connected to the subscriber-side optical termination device, the station-side optical termination device, and the station-side optical termination device that are made redundant to the power-saving mode. An optical transmission system comprising a connected optical splitter,
The station-side optical terminal device manages power-saving information that is information related to a power-saving mode of the subscriber-side optical terminal device, and controls redundancy switching of the trunk line based on the power-saving information. Optical transmission system. The station side optical terminator is:
The power saving information includes status information indicating whether or not the subscriber side optical termination device is in a power saving mode for each subscriber side optical termination device,
Based on the status information, it is determined whether the subscriber-side optical termination device is in a power saving mode, and redundant switching of the trunk line is performed based on a response signal from the subscriber-side optical termination device that is not in the power saving mode. 2. The optical transmission according to claim 1, wherein it is determined whether or not to execute, and the response signal from the subscriber-side optical terminal device in the power saving mode is not used for determining whether to perform redundancy switching of the trunk line. system. The station side optical terminator is:
When the notification indicating that the subscriber-side optical termination device shifts to the power saving mode is received from the subscriber-side optical termination device, the state information is updated based on the notification,
When the subscriber-side optical termination device receives a notification indicating that the subscriber-side optical termination device returns from the power saving mode to the normal mode, the state information is updated based on the notification. The optical transmission system according to claim 2. The station side optical terminator is:
When a power-off notification is received from the subscriber-side optical termination device, the status information corresponding to the subscriber-side optical termination device that is the transmission source of the power-off notification is updated to a value indicating that it is in a power saving mode. The optical transmission system according to claim 2 or 3,   The station-side optical termination device performs failure detection processing for detecting a failure when the response signal is not received within a predetermined failure detection time for each subscriber-side optical termination device, and the power-saving mode 5. The light according to claim 1, wherein the subscriber-side optical termination device does not detect the failure when the response signal is not received within the predetermined failure detection time. Transmission system.   The station side optical termination device performs trunk failure detection processing for detecting as a trunk failure when the response signal is not received within a predetermined failure detection time from any of the subscriber side optical termination devices. When the subscriber-side optical terminating device is in a power saving mode, the response signal is not detected as the main line failure when not received within the predetermined failure detection time. 5. The optical transmission system according to claim 5.   The station side optical termination device performs trunk failure detection processing for detecting as a trunk failure when the response signal is not received within a predetermined failure detection time from any of the subscriber side optical termination devices. The redundant switching of the trunk line is not performed even if the trunk line failure is detected when the subscriber-side optical terminal device is in a power saving mode. Optical transmission system. The station side optical terminator is:
Controls start and end times of power saving modes in the subscriber side optical termination devices for each of the subscriber side optical termination devices, manages the start and end times as the power saving information, and is not in the power saving mode. The start and end times for each of the subscriber-side optical termination devices are determined so that one or more side-side optical termination devices exist, and based on response signals from the subscriber-side optical termination devices that are not in the power saving mode, The optical transmission system according to claim 1, wherein it is determined whether or not to perform redundancy switching.   9. The optical transmission system according to claim 8, wherein the start and end times for each of the subscriber-side optical termination devices are determined so that there are two or more of the subscriber-side optical termination devices that are not in the power saving mode.   The optical transmission system according to any one of claims 2 to 9, wherein the response signal is a response signal to a band allocation notification. A station-side optical termination device connected via an optical splitter to a subscriber-side optical termination device capable of transitioning to a power saving mode,
The trunk line between the optical splitter is made redundant and connected to the optical splitter by a branch line,
A PON control unit that manages power saving information that is information related to a power saving mode of the subscriber-side optical termination device, and controls redundancy switching of the trunk line based on the power saving information;
A station-side optical termination device comprising: It is connected to the subscriber-side optical termination device, the station-side optical termination device, and the station-side optical termination device that are made redundant to the power-saving mode. A communication line switching method in an optical transmission system comprising an optical splitter to be connected,
The station side optical terminator is
A management step of managing power saving information related to a power saving mode of the subscriber side optical termination device;
A switching step for controlling redundancy switching of the trunk line based on the power saving information;
A communication line switching method comprising: The branch line and the optical splitter are connected in multiple stages,
The station side optical terminator holds position information including information indicating the optical splitter connected to the subscriber side optical terminator for each subscriber side optical terminator, and the position information, the power saving information, 9. The optical transmission system according to claim 8, wherein the start time and the end time for each of the subscriber-side optical terminal devices are determined based on the following.   Based on the position information and the power-saving information, the station-side optical terminal device is in a state where two or more subscriber-side optical terminal devices connected to the different optical splitters in the same stage are not in the power-saving mode. The optical transmission system according to claim 13, wherein the start and end times for each of the subscriber-side optical termination devices are determined.   The optical transmission system according to claim 13 or 14, wherein the station side optical termination device acquires the position information from an administrator device or a data center. The branch line and the optical splitter are connected in multiple stages,
The PON control unit holds position information including information indicating the optical splitter connected to the subscriber-side optical termination device for each subscriber-side optical termination device, and Controlling the start and end times of the power saving mode in the subscriber side optical termination device, managing the start and end times as the power saving information, and based on the position information and the power saving information, the subscriber side light Determining the start and end times for each terminating device, and determining whether to perform redundant switching of the trunk line based on a response signal from the subscriber side optical terminating device that is not in a power saving mode, The station side optical termination device according to claim 11. The branch line and the optical splitter are connected in multiple stages,
The station side optical termination device holds position information including information indicating the optical splitter to which the subscriber side optical termination device is connected for each subscriber side optical termination device, and for each subscriber side optical termination device. Controls start and end times of a power saving mode in the subscriber side optical termination device, manages the start and end times as the power saving information, and based on the location information and the power saving information, the subscriber A power saving control step for determining the start and end times for each side optical termination device;
Further including
13. The communication according to claim 12, wherein in the switching step, it is determined whether or not to perform redundant switching of the trunk line based on a response signal from the subscriber-side optical terminal device that is not in a power saving mode. Line switching method.

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