JP2012049711A - Station side termination device and optical communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an OLT for PON protection and an optical communication system with PON protection capable of switching a communication path in a short time when a communication path failure occurs.SOLUTION: An optical communication system includes a plurality of optical transceivers for PON and a control circuit section capable of controlling all ONUs, connected to the optical transceivers for the PON, based on an administration table storing the information on the ONU grasped through a signal for a registration process or a propagation time measurement and a maintenance survey signal for each of the ONUs. An OLT performs failure recovery by switching a communication path within a predetermined period of time while the control circuit maintains the information stored in the administration table, when a failure of the optical transceiver for PON is detected.

Description

  The present invention relates to a PON system using a redundancy technology and having a protection function.

  As broadband spreads, network communication plays an increasingly important role, and it is required to provide a stable service. In the current access network, a station-side terminal device (OLT: Optical Network Unit) including a plurality of optical subscriber service units (OSUs), a subscriber-side terminal device (ONU: Optical Network Unit), a fiber, PON (Passive Optical Network) composed of optical splitters is widespread. Specifically, a PON is a system in which one OSU and a plurality of (for example, 32) ONUs are connected to an optical splitter via a fiber, and a fiber between the OSU and the OSU-optical splitter is shared by the plurality of ONUs. Thus, the service can be provided at a low cost. However, if a service disconnection occurs due to a fiber disconnection in the shared portion or an OSU failure, there is a possibility that the influence may affect a large number of users. Therefore, in order to supply services stably, it is important to make OSUs and paths redundant in preparation for device failures and fiber breaks.

  Making part or all of the devices constituting the PON redundant is called PON protection, and various methods have been proposed depending on the redundant part and the redundant method. However, in general, PON protection involves an additional cost of redundant equipment at a redundant portion, so that there is a problem that the cost per user is higher than the case where protection is not performed. In many proposed PON protection systems, the added redundant equipment is not used at all when the system is normal, and is used only after a failure of the current equipment at the redundant location. There was also.

  For example, a method called type B described in Non-Patent Document 1 is a redundant fiber between the OSU and the OSU-splitter. FIG. 1 shows the configuration of the type B system where the maximum number of ONUs accommodated per OSU is 32. In FIG. 1, the backup OSU that is the added redundant device does not perform data transmission when the active OSU that is the current device is normal, and performs data transmission only after the failure of the active OSU. In addition, since 32 users bear the cost of two OSUs (active OSU, backup OSU), the OSU cost per user is larger than the case where 32 users who bear no protection bear one OSU. Will double.

  The method called 1: N described in Non-Patent Document 2 is an OSU redundant configuration in which one backup OSU is added to N active OSUs, and all users under N OSUs ( The additional cost of one backup OSU can be shared at a maximum of 32 × N). Therefore, as the value of N is increased and the system is constructed, the cost for the additional OSU per user can be reduced. However, since the 1: N system does not perform data transmission when the backup OSU is normal as in the type B system, the utilization efficiency of the redundant equipment is low.

  In response to such a problem, the inventors have made it possible to provide redundancy for an OSU that has a particularly large impact at the time of failure, and at the same time, as a PON protection method that does not require a redundant OSU that does not transmit data during normal operation, the inventors have established N: M protection ( N <M) is proposed (see, for example, Patent Document 1). Here, N represents the number of OSUs required to accommodate all ONUs when protection is not performed, and M represents the total number of OSUs used in this method. 32 OSUs can be accommodated per OSU. For example, when N: M protection is constructed using 96 ONUs in total, the number of OSUs required to accommodate 96 ONUs without protection is 3 Since (N = 3), it is constructed using four or more OSUs from N <M.

  As a specific example, FIG. 2 shows a configuration when N = 3 and M = 4. In this configuration, the splitter has a two-stage configuration of a four-branch splitter and an eight-branch splitter, and a changeover switch is installed between both splitters so as to straddle four PONs. The change-over switch connects the fiber from the branch side of each 4-branch splitter (referred to as the first branch fiber) and the fiber from the junction side of each 8-branch splitter (as the branch line), and the connection between them is free. Can be rearranged. The controller is connected to each OSU and each changeover switch, and periodically communicates with each OSU, and detects a failure and gives a changeover instruction to the changeover switch. By initially constructing one branch of each first branch fiber in an unconnected state, each OSU has 24 ONUs under its normal condition. Under normal conditions, each OSU can accommodate up to 32 ONUs but only 24, so compared to the case where 32 OSUs are accommodated, the bandwidth for each ONU is 4/3 times higher. Become. In other words, this system has an advantage that extra traffic for one added OSU can be used in a normal state because one extra OSU is added to the number of ONUs that can be accommodated by three OSUs.

  As an explanation of the protection function in the system of FIG. 2, FIG. 3 shows the switching operation when the OSU 4 fails. When the OSU 4 fails, the controller detects a failure of the OSU 4 triggered by, for example, not receiving a signal from the OSU 4 for a certain period of time. Then, the controller instructs the changeover switch to switch the connection destination of the three branch lines connected to the OSU 4 to the unconnected portion of the first branch fiber connected to each of the different normal OSUs (OSU 1, 2, 3). Put out. When the changeover switch switches the connection destination first branch fiber of the corresponding branch line according to the instruction, OSUs 1, 2, and 3 each newly incorporate 8 ONUs under their own control, and each accommodates a total of 32 ONUs. Become. By such switching operation, the ONU accommodated in the OSU 4 at the normal time can continue communication under the control of another normal OSU even after the OSU 4 failure.

  As described above, when N: M protection is normal, all the OSUs are in an operating state, and the ONU can use extra traffic of (MN) OSUs corresponding to the surplus when normal. Compared to a system in which a plurality of ONUs are accommodated at maximum in one OSU as in the case of 1 as in normal, there is an advantage that the bandwidth obtained per normal ONU becomes larger. When an OSU failure occurs, another normal OSU can bring the ONU under the failed OSU into its own via the changeover switch, thereby providing a protection function.

Japanese Patent Application 2010-000606

ITU-T G. 983.1 SERIES G: Transmission Systems and Media, Digital Systems and Networks, Appendix IV. 3.1 K. Tanaka and Y.M. Horizon, “1: N OLT Redundant Protection Architecture in Ethernet (registered trademark) PON System,” OFC / NFOEC, pp. 1-6, 2008. IEEE 802.3ah CSMA / CD Access Method and Physical Layer SpecificationsAmendment: Media Access Control Parameters, Physical Layers, and Management Parameters for Subscriber Access Networks, 64.2.1,1, 64.3.3, 64.3.4. 1

  Before the ONU in the PON starts data communication, the ONU registration by the OSU and the signal propagation time between the OSU and each ONU must be measured, and a link must be established between the OSU and the ONU. For example, in the GE-PON (Gigabit Ethernet (registered trademark) PON) system described in Non-Patent Document 3, registration and signaling are performed by exchanging MPCP frames with the OSU based on the specifications of MPCP (Multi Point Control Protocol). A propagation time measurement is performed and an MPCP link is established with the OSU. Therefore, these processes are first required in GE-PON. After the MPCP link is established, the ONU establishes the OAM link and exchanges authentication / encryption key through the exchange of OAM (Operation, Administration and Maintenance) frames, which are maintenance monitoring signals, with the OSU. Data communication can be started only after all of the above is completed.

  Here, similarly in the N: M protection configuration, each OSU establishes an MPCP link, establishes an OAM link, authenticates, and exchanges an encryption key with the ONU under its control. In the OSU-ONU relationship in which the MPCP link establishment or the like is completed, if the OSU fails, all the MPCP links between the failed OSU and the subordinate ONUs are disconnected. When each OSU in N: M protection is normal, it does not exchange MPCP frames and OAM frames with ONUs other than its own, and does not know any information about ONUs other than its own, so it is in a state where it does not understand Subordinate ONUs cannot resume communication unless the MPCP link is established with the switching destination OSU after the path is switched by the changeover switch. The time (switching time) until the data communication is resumed after disconnecting the MPCP link and re-establishing the MPCP link with the switching destination OSU after the failure of the OSU is the ONU under the failed OSU. Since communication is interrupted and frame loss occurs, it is desirable that the switching time is as short as possible. As a guide, a switching time of 50 ms or less is desired as high-speed switching.

  Here, Non-Patent Document 3 stipulates that if an MPCP frame is not received for 1 s or longer between an OSU and a registered ONU under its control, the registration of that ONU is deleted. From this rule, even if the OSU fails, the MPCP link of the ONU under the failed OSU is maintained for at least 1 s. However, since switching with ONU MPCP link disconnection requires about 1 s only by detecting MPCP link disconnection, it is difficult to realize a switching time of 50 ms. In other words, there is a problem that high-speed switching is difficult for N: M protection in which an MPU link disconnection of the ONU occurs during OSU switching due to an OSU failure.

  In order to solve this problem, an object of the present invention is to provide an OLT for PON protection capable of switching a communication path in a short time when a communication path failure occurs, and an optical communication system for PON protection. To do.

  In order to achieve the above object, the OLT according to the present invention accommodates a plurality of PON lines and enables collective management of all ONUs. The above problem is solved by applying this OLT to N: M protection.

Specifically, the OLT according to the present invention is:
A plurality of ONU groups including one or more ONUs are connected via a changeover switch, and a plurality of optical transceivers transmit and receive optical signals to and from the ONUs;
A service node interface (SNI) connected to an external access network;
Connected to the optical transceiver,
A transmission path for transmitting a signal between the optical transceiver and the SNI;
The registration processing signal for the ONU registration processing or the propagation time measurement signal for propagation time measurement is used to establish a link with the ONU and determine the ONU uplink bandwidth allocation amount. A discovery DBA processing unit for acquiring ONU information related to the ONU link;
OAM / authentication / encryption that establishes, authenticates, and exchanges encryption keys with the ONU using the maintenance monitoring signal with the ONU, and acquires ONU information related to the link of the ONU The processing unit,
The ONU information acquired by the discovery DBA processing unit and the OAM / authentication /
A management table for storing ONU information acquired by the encryption processing unit and updated as needed;
A switching control unit that determines which optical transceiver to connect to the ONU group based on the ONU information stored in the management table and issues a path switching instruction to the switch;
A control circuit having
Is provided.

  The OLT according to the present invention was grasped through a signal for registration processing or propagation time measurement and a maintenance monitoring signal for each ONU for a plurality of PON optical transceivers and all ONUs connected to the PON optical transceiver. A control circuit unit capable of controlling all the ONUs based on a management table storing information related to the ONUs. When a failure of the optical transceiver for PON is detected, the OLT performs failure recovery by switching the communication path within a predetermined time while maintaining the information stored in the management table.

  Therefore, the present invention can provide an OLT for PON protection capable of switching a communication path in a short time when a communication path failure occurs.

The control circuit of the OLT according to the present invention includes:
Failure information that the optical transceiver outputs when its own failure occurs, the discovery D
Failure information output when a BA processing unit recognizes an abnormality in the section from the optical transceiver to the ONU by transmitting and receiving the registration processing signal or the propagation time measurement signal, and the OAM / authentication / encryption The processor detects the fault location based on the fault information output when it recognizes an abnormality in the section from the optical transceiver to the ONU by sending and receiving the maintenance monitoring signal, and the detected fault location is switched. It further has a failure detection unit to notify the control unit,
The switching control unit
Based on the failure information notified from the failure detection unit and the ONU information stored in the management table, the ONU information stored in the management table is maintained when it is determined that a failure recovery by path switching is possible A route switching instruction is issued to the changeover switch in a state.

  Since the failure detection unit manages the failure information, the communication path can be switched in a short time.

  In addition, the OLT according to the present invention further includes a spare control circuit having the same configuration as the control circuit, and the spare control circuit is connected to the optical transceiver, and the transmission path is connected when the control circuit is normal. The control circuit shuts off the transmission path and issues a control circuit switching instruction to open the transmission path to the backup control circuit when a failure occurs in the control circuit.

  Since the control circuit is made redundant, the communication path can be switched even if the control circuit fails.

  The switching control unit of the control circuit of the OLT according to the present invention is configured so that the switching control unit of all the spare control circuits updates the ONU information to be updated every time the management table updates the ONU information. The switching control unit of the backup control circuit updates the management table of the backup control circuit according to the ONU information to be updated notified from the switching control unit of the control circuit, and the control When the control circuit switching instruction notified from the switching control unit of the circuit is received, communication with the ONU is started based on the ONU information stored in the management table of the spare control circuit. To do.

  Even if the control circuit fails, the spare control circuit takes over the latest management table, so the MPCP link of the ONU is not cut off by switching the control circuit, and therefore the MPCP link between the spare control circuit and the ONU. Therefore, it is not necessary to reconnect such as, so that high-speed switching can be realized.

  The OLT according to the present invention includes a plurality of the control circuits, and each of the control circuits is normally connected to one or more different optical transceivers of the optical transceivers. When a failure occurs in the circuit, all the optical transceivers connected to the circuit are reconnected to one other control circuit or a plurality of other control circuits in a batch or distributed, The control circuit is instructed to start communication with the ONU via the optical transceiver, and the control circuit that has received the control circuit switching instruction retransmits the control circuit in addition to the previously connected optical transceiver. It communicates with the ONU through the connected optical transceiver.

  Since the control circuit is redundant, the communication path can be switched even if the control circuit fails. Furthermore, the utilization efficiency of the control circuit can be increased.

  Each time the control circuit of the OLT according to the present invention updates the ONU information of the management table, the control circuit notifies the switching control unit of the other control circuit of the ONU information updated by the switching control unit. When the ONU information is notified from the switching control unit of the other control circuit, the switching control unit updates the management table according to the ONU information and the notified ONU information, When a control circuit switching instruction is received, communication with the ONU is started based on the ONU information stored in the management table.

  Even if one control circuit fails, the other control circuit can take over the latest management table. Therefore, the MPCP link of the ONU is not cut off by switching the control circuit. Therefore, between the spare control circuit and the ONU, Since it is not necessary to reconnect the MPCP link or the like, high-speed switching can be realized.

  The optical communication system according to the present invention includes an OLT having M (M is an integer of 2 or more) optical transceivers and a control circuit, and a branching ratio of 1: X (X is an integer of 2 or more). Each of the M splitters connected to one of the optical transceivers on the junction side and X first branch fibers on the branch side, and K (K is 2 or more and (M−1) × X or less) (Integer) branch fibers, branching ratio is 1: Y (Y is an integer of 2 or more), and for each branch fiber, the merge side is connected to one of the branch fibers, and the branch side is Y second branch K second splitters connected to the fiber, Z ONUs (Z is a natural number equal to or less than K × Y) connected to any of the K × Y second branch fibers, the branch fiber, and the The first branch fiber is connected 1: 1, and the OLT A path switching instruction from the serial control circuit and a selector switch that allows changing the connection between the first branch fiber and the branch fibers.

  The optical communication system according to the present invention is N: M protection. The optical communication system according to the present invention can be switched while maintaining the ONU's MPCP link or the like according to an instruction from the control circuit, so that the time required for detecting the MPCP link disconnection and the time required for reconnecting the MPCP link is not required. Fast switching is possible.

  The optical communication system according to the present invention is an OLT having M (M is an integer of 2 or more) optical transceivers and a control circuit capable of accommodating a maximum of α (α is an integer of 1 or more) ONUs per unit. And K (K is an integer of 1 or more and (M-1) or less) branch fibers and a branching ratio of 1: X (X is an integer of 2 or more), and the merge side is connected to one of the branch fibers. The branch side is connected to A (A is an integer not less than 1 and not more than X) branch fibers K (K is an integer not less than 1 and not more than (M−1)) first splitters, An integer number of ONUs connected to each of the first splitters, the total number of which is not less than K and not more than K and not more than (K × α), M transceiver-side ports connecting the respective optical transceivers, and Has K branch ports to connect branch fibers And a switch for connecting the transceiver side port to any branch line side port or not connecting to the branch side port in response to a path switching instruction from the control circuit of the OLT.

  The optical communication system according to the present invention has 1: N protection. The optical communication system according to the present invention can be switched while maintaining the ONU's MPCP link or the like according to an instruction from the control circuit, so that the time required for detecting the MPCP link disconnection and the time required for reconnecting the MPCP link is not required. Fast switching is possible.

  The optical communication system according to the present invention includes an OLT having M (M is an integer of 2 or more) optical transceivers and a control circuit, and a branching ratio of 1: X (X is an integer of 2 or more). Each of the M splitters connected to one of the optical transceivers on the junction side and X first branch fibers on the branch side, and K (K is 2 or more and (M−1) × X or less) (Integer) branch fibers, L spare branch fibers arranged in parallel with L (L is an integer of 1 to K) of the branch fibers, and a branching ratio of 1: Y (Y is An integer greater than or equal to 2), the junction side is connected to one of the branch fibers, and the branch side is connected to Y second branch fibers (K−L) second splitters, and the branch ratio is 2: Y ( Y is an integer of 2 or more), and the merge side is one of the branch fibers and Connected to the auxiliary branch fiber in parallel with the branch fiber, the branch side is connected to one of L third splitters connected to Y second branch fibers, and K × Y second branch fibers. Z (Z is a natural number equal to or less than K × Y) ONUs and the branch fiber and the first branch fiber are connected at a 1: 1 ratio, or the branch fiber and the backup branch fiber are in parallel. One of the first branch fiber and the first branch fiber are connected in a 1: 1 ratio, and the branch fiber and the first branch fiber are connected in response to a path switching instruction from the control circuit of the OLT, or the branch fiber or the spare branch line. A change-over switch that can change a connection between the fiber and the first branch fiber.

  The branch fiber is also redundant, and the communication path can be maintained even when the branch line is disconnected.

  An optical communication system according to the present invention includes an MLT (M is an integer of 2 or more) optical transceivers and a control circuit capable of accommodating a maximum of α (α is an integer of 1 or more) ONUs per unit, K (K is an integer greater than or equal to 1 and less than or equal to (M−1)) branch fibers and L spares arranged in parallel with L (L is an integer greater than or equal to 1 and less than or equal to K) of the branch fibers. Branch fiber, branching ratio is 1: X (X is an integer of 2 or more), the merge side is connected to one of the branch fibers, and the branch side is A (A is an integer of 1 or more and X or less) (K−L) first splitters connected to each other, the branching ratio is 2: X, the joining side is connected to one of the branching fibers and the auxiliary branching fiber parallel to the branching fiber, and the branching side is A L second splitters connected to the two branch fibers and the front Connected to each of the optical transceivers with an integer number of ONUs of α or less and a total number of K or more and (K × α) or less connected to each of the first splitter or the second splitter via the branching fiber. M (transceiver side) ports and (K + L) branch side ports connecting the branch fiber or the backup branch fiber, and the transceiver side port is arbitrarily set by a path switching instruction from the control circuit of the OLT. A changeover switch connected to the branch line side port or not connected to the branch line side port.

  The branch fiber is also redundant, and the communication path can be maintained even when the branch line is disconnected.

  The OLT of the optical communication system according to the present invention is the OLT according to the present invention.

  The present invention can provide an OLT for PON protection and an optical communication system for PON protection that can switch communication paths in a short time when a communication path failure occurs.

It is a block diagram explaining the conventional optical communication system. It is a block diagram explaining the conventional optical communication system. It is a block diagram explaining the conventional optical communication system. 1 is a block diagram illustrating an optical communication system according to the present invention. It is a block diagram explaining OLT concerning the present invention. It is an example of the management table of OLT which concerns on this invention. 1 is a block diagram illustrating an optical communication system according to the present invention. It is an example of the management table of OLT which concerns on this invention. 1 is a block diagram illustrating an optical communication system according to the present invention. It is a block diagram explaining OLT concerning the present invention. 1 is a block diagram illustrating an optical communication system according to the present invention. It is a block diagram explaining OLT concerning the present invention. 1 is a block diagram illustrating an optical communication system according to the present invention. 1 is a block diagram illustrating an optical communication system according to the present invention. 1 is a block diagram illustrating an optical communication system according to the present invention. 1 is a block diagram illustrating an optical communication system according to the present invention.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components. Moreover, when it demonstrates without attaching | subjecting a branch number to a code | symbol, it is description common to all the branch numbers of the code | symbol. In the drawings, only representative parts are denoted by reference numerals.

(Embodiment 1)
FIG. 4 is a block diagram illustrating the optical communication system 301 of the present embodiment. The optical communication system 301 includes an OLT 11 having M (M is an integer of 2 or more) optical transceivers 41 and a control circuit 43, and a branching ratio of 1: X (X is an integer of 2 or more). Furthermore, M first splitters 12 whose junction side is connected to one of the optical transceivers 41 and whose branch side is connected to X first branch fibers 13, and K (K is 2 or more and (M−1) × X or less). The branching ratio is 1: Y (Y is an integer of 2 or more), and for each branching fiber 14, the merge side is connected to one of the branching fibers 14, and the branching side is Y K number of second splitters 15 connected to the bifurcated fiber 18, Z ONUs 16 (Z is a natural number equal to or less than K × Y) connected to any of the K × Y second branch fibers 18, and branch lines A fiber 14 and a first branch fiber 13; 1: Connect with 1, comprises a, a selector switch 17, can change the connection to the branch fibers 14 and the first branch fiber 13 the path switching instruction from the control circuit 43 of the OLT 11.

  The optical communication system 301 is N: M protection when N = 3 and M = 4. The difference in configuration between FIG. 2 and FIG. 4 is that the optical communication system 301 uses an optical transceiver redundancy configuration in which four optical transceivers 41 (transceivers # 1 to # 4) are used instead of the four OSUs in FIG. And a control circuit 43 having a function capable of collectively controlling all ONUs under a plurality of PON lines corresponding to the extension of the control function for ONUs under its own control by the OSU. The optical transceiver is an optical transceiver for PON, but is simply described as “optical transceiver” in the following description. Each optical transceiver 41 can accommodate a maximum of 32 ONUs 16 per unit, and each optical transceiver 41 accommodates 24 ONUs 16 via the changeover switch 17 at the time of initial construction.

FIG. 5 is a diagram illustrating a specific configuration of the OLT 11. The OLT 11 is connected to a plurality of ONU groups including one or more ONUs 16 via the changeover switch 17 and connected to a plurality of optical transceivers 41 for transmitting / receiving optical signals to / from the ONUs 16 and an external access network (not shown). A service node interface (SNI) 44 and a control circuit 43 connected to the optical transceiver 41. Here, the ONU group indicates all ONUs connected to each branch line fiber 14. For example, in the case of FIG. 4, the first ONU group is all ONUs connected to the branch line fiber 14-1.
The control circuit 43 uses the transmission path 51 for transmitting a signal between the optical transceiver 41 and the SNI 44 and the registration processing signal for the registration processing of the ONU 16 or the propagation time measurement signal for measurement of the propagation time. The ONU 16 is established by using a maintenance monitoring signal between the discovery DBA processing unit 52 that acquires ONU information related to the link of the ONU 16 and the ONU 16. The OAM / authentication / encryption processing unit 53 for acquiring ONU information related to the link of the ONU 16, and the ONU information and OAM acquired by the discovery DBA processing unit 52. A management table 54 that stores ONU information acquired by the authentication / encryption processing unit 53 and updates it as needed. Has a on the basis of the ONU information, either of the optical transceiver 41 and a switching control unit 55 determines whether to connect the ONU group issues a path switching instruction to the changeover switch 17 for storing the management table 54, a.

The control circuit 43 detects failure information output by the optical transceiver 41 when a failure occurs, and an abnormality in a section from the optical transceiver 41 to the ONU 16 when the discovery DBA processing unit 52 transmits or receives the registration processing signal or the propagation time measurement signal. Information output when the OAM / authentication / encryption processing unit 53 recognizes an abnormality in the section from the optical transceiver 41 to the ONU 16 by transmitting / receiving the maintenance monitoring signal. A failure detection unit 56 is further provided for detecting a failure location based on the above and for notifying the switching control unit 55 of the detected failure location.
When the switching control unit 55 determines that the failure can be recovered by path switching based on the failure information notified from the failure detection unit 56 and the ONU information stored in the management table 54, the management table 54 A route switching instruction is issued to the change-over switch 17 in a state where the ONU information stored by is maintained.

  The OLT 11 according to the present embodiment includes four optical transceivers 41, one concentrator and a frame separator, a discovery DBA (Dynamic Bandwidth Allocation) processor 52, an OAM / authentication / encryption processor 53, and the like. , A failure detection unit 56, a switching control unit 55, and a management table 54. The operation of each block will be described below. The transmission path 51 includes a concentrator and a frame separator.

  Each of the four optical transceivers 41 is connected to a PON line, receives an optical upstream signal from the ONU 16, converts it into an electrical signal, outputs it to the concentrator, and outputs from the upper L2SW (Layer 2 Switch). The electrical downstream signal is received by the SNI 44 and converted into an optical signal, which is then output to the PON line. Further, when a failure occurs in each optical transceiver 41, the failure information is output to the failure detection unit 56.

  The concentrator unit connects each optical transceiver 41, receives the upstream frame from each optical transceiver 41, sequentially outputs the received upstream frame to the frame separation unit, receives the downstream frame from the frame separation unit, and receives it. The downstream frames are copied to prepare a total of four, and output one by one to the four optical transceivers 41. Here, each ONU 16 also receives a downlink frame other than its own, but the ONU 16 receives only the downlink frame addressed to itself and discards the downlink frame not addressed to itself.

  The frame separation unit receives the upstream frame from the concentrator, and among the received upstream frames, the MPCP frame is sent to the discovery DBA processing unit 52, the OAM frame is sent to the OAM / authentication / encryption processing unit 53, and the upstream data is sent to the SNI 44. And a downstream frame from the SNI 44, a downstream MPCP frame from the discovery DBA processing unit 52, and a downstream OAM frame from the OAM / authentication / encryption processing unit 53, respectively. Output to the concentrator.

  The discovery DBA processing unit 52 performs transmission / reception of MPCP frames and uplink bandwidth allocation of each ONU 16 in accordance with the MPCP rules with the frame separation unit. Specifically, if the frame received from the frame separation unit is a report frame, the uplink bandwidth allocation amount to the ONU 16 is determined based on the content, and the Gate frame describing the determined allocation amount and transmission permission time is frame-separated. Output to the section. Further, the discovery DBA processing unit 52 informs the switching control unit 55 of each ONU information (registration state, RTT (Round Trip Time), allocated bandwidth amount, etc.) obtained through the exchange of MPCP frames and DBA, When MPCP frames from a plurality of ONUs 16 are not received for a certain period of time, failure information indicating that a signal from the corresponding ONU group does not rise is output to the failure detection unit 56.

  The OAM / authentication / encryption processing unit 53 exchanges OAM frames with the frame separation unit. For example, the encryption key exchange with each ONU 16 is described in the OAM frame output from each ONU 16 and the OAM / authentication / encryption processing unit 53, and the encryption key exchange is performed via the frame separation unit. Further, the OAM / authentication / encryption processing unit 53 notifies each switching unit of information (authentication state, encryption key, etc.) of each ONU 16 obtained through the exchange of the OAM frame, and a failure is detected by the OAM frame. If detected, the detected failure information is output to the failure detection unit 56.

  The failure detection unit 56 receives failure information from the optical transceiver 41, the discovery DBA processing unit 52, and the OAM / authentication / encryption processing unit 53, detects the failure location based on the received failure information, and detects the failure location. Informs the switching control unit 55 that a failure has occurred.

  The switching control unit 55 includes each ONU information (registration status, RTT, allocated bandwidth amount, etc.) from the discovery DBA processing unit 52 and each ONU information (authentication status, encryption key, etc.) from the OAM / authentication / encryption processing unit 53. And updates the corresponding part of the management table 54 managed by itself according to the received ONU information, and always grasps the information described in the management table 54. In addition, the switching control unit 55 receives the failure information from the failure detection unit 56, determines whether the failure can be recovered by switching the route based on the received failure information, and if it is determined that it is possible, The switch 17 is instructed to switch to a path that can recover from a failure, and the item in the management table 54 that is changed by switching is updated.

  Since the switching control unit 55 knows in advance the branching ratio of the first splitter 12, the management table 54 can know how many unconnected fibers are in each first splitter 12, and receive this information and reception. The route information that can recover from the failure is determined by checking the failure information. For example, in the system of FIG. 4, the switching control unit 55 grasps that the branching ratio of the first splitter 12 is four branches at the time of initial setting, and uses the management table 54 to connect the branch line to the optical transceiver 41-1. Fibers (14-1, 14-2, 14-3), branch fibers (14-4, 14-5, 14-6) for the optical transceiver 41-2, and branch fibers (14-4, 14-5, 14-6) for the optical transceiver 41-3. 14-7, 14-8, 14-9) know that the branch fibers (14-10, 14-11, 14-12) are connected to the optical transceiver 41-4. It can be understood that one splitter 12 has one unconnected fiber.

In this system, the switching determination algorithm of the switching control unit 55 when the optical transceiver 41-4 fails can be considered as follows.
1. The switching control unit 55 recognizes that it is necessary to switch the three branch lines of the branch line fibers (14-10, 14-11, 14-12) connected to the optical transceiver 41-4 based on the received failure information.
2. Each of the first splitters 12 connected to the optical transceivers (41-1, 41-2, 41-3) has one unconnected fiber. Therefore, the switching control unit 55 connects the branch fiber 14-11 to the unconnected fiber of the first splitter 12 to which the optical transceiver 41-1 is connected, as shown in FIG. It is determined that the failure can be recovered by switching the unconnected fiber of the first splitter 12 to the unconnected fiber of the first splitter 12 to which the optical transceiver 41-3 is connected.
3. The change control unit 55 issues a change instruction to the changeover switch 17 so as to make such a change.

  The management table 54 includes not only information that the OSU grasps in the current PON system, such as the registration status, LLID (Logical Link ID), and RTT of all ONUs, but also correspondence between branch fiber numbers, optical transceiver numbers, and ONUs, etc. Information regarding all ONUs in the system, including information grasped by each OSU in N: M protection, is listed and updated by the switching control unit 55 as needed. FIG. 6 is an example of the management table 54 of the control circuit 43 in the optical communication system 301.

  In the optical communication system of FIG. 2, each OSU exchanges MPCP frames and allocates upstream bandwidth to 24 ONUs under its control. On the other hand, in the optical communication system 301, the OLT 11 having the functional blocks as described above is applied to N: M protection, and the control circuit 43 directly exchanges MPCP frames and assigns upstream bandwidth to all 96 ONUs 16. It can be performed.

  Therefore, in the optical communication system 301, even if a failure occurs in the optical transceiver 41, the MPCP link and authentication / encryption key information established by the control circuit 43 with the ONU 16 under the failed optical transceiver are stored on the management table 54. Since it remains without disappearing, the information can be used as it is after switching to the normal optical transceiver 41. Therefore, the control circuit 43 does not have to re-establish the MPCP link and re-authenticate / re-exchange the encryption key with the ONU 16 under the faulty optical transceiver after the path is switched.

FIG. 7 is a diagram illustrating a switching procedure when the optical transceiver 41-4 fails in the optical communication system 301.
1. The optical transceiver 41-4 recognizes its own failure (for example, a decrease in output power) and outputs failure information to the failure detection unit 56.
2. The failure detection unit 56 notifies the switching control unit 55 that the optical transceiver 41-4 has failed.
3. Upon receiving the notification, the switching control unit 55 sets the connection destinations of the three branch fibers (14-10, 14-11, 14-12) connected to the optical transceiver 41-4 to separate optical transceivers (41-1, 41-2, 41-3), it is determined that communication interruption can be avoided. Here, the connection destination of the branch fiber 14-10 is connected to the optical transceiver 41-1, and the connection destination of the branch fiber 14-11 is changed to the optical destination. The connection destination of the branch fiber 14-12 is switched to the optical transceiver 41-3 to the transceiver 41-2, and the switching instruction is transmitted to the changeover switch 17.
4). Upon receiving the switching instruction from the switching control unit 55, the selector switch 17 switches the route according to the switching instruction.
5. With this path switching, the ONU 16 (73 to 80th unit) is connected to the optical transceiver 41-1, the ONU 16 (81 to 88th unit) is connected to the optical transceiver 41-2, and the ONU 16 (89th to 96th unit). ) Changes to the optical transceiver 41-3. Then, the switching control unit 55 updates the items in the management table 54 that are changed by this path switching.

  FIG. 8 shows the management table 54 updated by the above switching procedure. The difference between FIG. 8 and FIG. 6 is only the optical transceiver number of the ONU 16 (73rd to 96th units). Although the connection destination optical transceiver number of the ONU 16 (73rd to 96th units) under the fault optical transceiver 41-4 is changed by the path switching, the branch fiber number and LLID associated with the initial registration change by the path switching. There is nothing. In addition, for example, in Non-Patent Document 3, there is a rule that causes an error when the measured value of RTT is different from the previous measured value by 8 time quantum or more with respect to synchronization between OSU and ONU (link break). In order to prevent this from happening, the system is constructed by paying attention to the length of the optical fiber so that the difference between the measured RTT values before and after switching is 8 time quantum or less. For example, in FIG. 7, if the distances between the optical transceivers 41 and the changeover switch 17 are substantially the same, the path length before and after the switching is almost the same for the ONU 16 under the faulty optical transceiver even if the switching due to the optical transceiver failure occurs. Since it does not change, the RTT is almost unchanged. Therefore, it is possible to prevent the link breakage according to the provisions of Non-Patent Document 3.

  As described above, in the optical communication system 301, the operation after switching the optical transceiver only changes the item of the optical transceiver number in the management table 54. Since the MPCP link and the OAM link are established and the authentication / encryption key exchange is performed between the control circuit 43 and the ONU 16, items related to the MPCP link and the like in the management table 54 do not change even when switching occurs due to an optical transceiver failure. Therefore, the optical communication system 301 can switch the connection destination optical transceiver without disconnecting the MPCP link of the ONU 16 under the faulty optical transceiver.

  In the optical communication system of FIG. 2, MPCP links and OAM links are established and authentication / encryption key exchange is performed between the OSU and the ONU. Therefore, when switching due to an OSU failure occurs, the MPCP link of the ONU under the failed OSU is disconnected. Accordingly, reconnection of the MPCP link and OAM link and re-authentication / re-encryption of the encryption key are required with the connection destination OSU. On the other hand, as described above, the optical communication system 301 can be switched while maintaining the MPCP link or the like of the ONU, so that the time required for detecting the MPCP link disconnection and the time required for reconnecting the MPCP link are not required, Fast switching is possible.

(Embodiment 2)
FIG. 9 is a diagram illustrating a configuration of the optical communication system 302 in which the reliability of the optical communication system 301 in FIG. 4 is further improved. In the optical communication system 301, since one control circuit 43 manages all the ONUs 16, if the control circuit 43 fails, the MPCP link, OAM link, authentication, and encryption key exchange information of all the ONUs 16 disappear and communication is interrupted. End up. Therefore, the OLT 11 ′ of the optical communication system 302 has a redundant control circuit in preparation for a failure of the control circuit 43.

  FIG. 10 is a block diagram showing the configuration of the control circuit 43 and the spare control circuit 43-b. The OLT 11 ′ of the optical communication system 302 further includes a spare control circuit 43-b having the same configuration as the control circuit 43. The spare control circuit 43-b is connected to the optical transceiver 41, and the control circuit 43 is normal. In this case, the transmission path 51-b is cut off, and the control circuit 43 cuts off the transmission path 51 and causes the backup control circuit 43-b to open the transmission path 51-b when a failure occurs in itself. A circuit switching instruction is issued.

  The switching control unit 55 of the control circuit 43 notifies the ONU information to be updated to the switching control units 55-b of all the standby control circuits 43-b every time the management table 54 updates the ONU information at the normal time. The switching control unit 55-b of the backup control circuit 43-b updates the management table 54-b of the backup control circuit 43-b in accordance with the updated ONU information notified from the switching control unit 55 of the control circuit 43. When the control circuit switching instruction notified from the switching control unit 55 of the control circuit 43 is received, communication with the ONU 16 is started based on the ONU information stored in the management table 54-b of the backup control circuit 43-b. .

  As a spare for the control circuit 43 (active control circuit) that operates normally, a spare control circuit 43-b is added to the OLT 11 ′ and connected to the optical transceiver 41 and the changeover switch 17 respectively. Also connect. In the configuration of FIG. 9, it is desirable that the control circuit switching from the control circuit 43 to the standby control circuit 43-b accompanying the failure of the control circuit 43 can be performed at high speed. Therefore, it is necessary to switch the control circuit without disconnecting the MPCP link of the ONU 16 or the like. If the control circuit is switched while the spare control circuit 43-b knows the latest ONU information of the control circuit 54 held by the control circuit 43 immediately before the control circuit switch, the spare control circuit 43-b Since the latest management table including items related to the MPCP link and the like is switched over, the MPCP link and the like of the ONU 16 is not disconnected by switching the control circuit. Therefore, the spare control circuit 43-b does not need to reconnect the MPCP link or the like with the ONU 16, so that high-speed switching can be realized.

  In the control circuit 43 and the backup control circuit 43-b, the operations of the blocks other than the switching control unit (55, 55-b) are the same as the corresponding blocks of the control circuit 43 of the first embodiment. Whenever the management table 54 of the control circuit 43 is updated, the switching control unit 55 of the control circuit 43 notifies the update information to the switching control unit 55-b of the backup control circuit 43-b.

  The switching control unit 55-b receives the ONU information to be updated from the switching control unit 55, and updates the management table 54-b of the backup control circuit 43-b according to the content. As a result, when the control circuit 43 is normal, the management table 54-b can maintain exactly the same contents as the latest management table 54.

  The upstream signal transmitted from each optical transceiver 41 may reach both the concentrator of the control circuit 43 and the concentrator of the standby control circuit 43-b. In this case, when the same uplink data transmitted from the optical transceiver 41 is output to both the SNI line of the control circuit 43 and the SNI line of the backup control circuit 43-b when the control circuit 43 is normal, the upper L2SW side However, in order to avoid signal collision, it is necessary to output only one of the received two data to the core network. Therefore, in the optical communication system 302, the concentrator of the standby control circuit 43-b does not receive the upstream signal from each optical transceiver 41 or receives it but does not output it to the frame separator. The same applies to the downlink signal from the SNI line. In the optical communication system 302, the concentrator of the standby control circuit 43-b does not receive the downlink signal or receives it but does not output it to the optical transceiver 41. .

  Here, as an example, a switching procedure when the switching control unit 55 fails is shown below. In order for the standby control circuit 43-b to detect a failure of the control circuit 43 and perform high-speed switching of 50 ms or less, the switching control unit 55 is switched to the switching control unit 55-b at intervals of 50 ms or less even during normal operation. It is necessary to make notifications. The notification content is the update content when the management table is updated, or the content that there is no change when there is no substantial change in the management table for 50 ms. The spare control circuit 43-b considers that the control circuit 43 is out of order when neither the update notification (update contents) nor the notification of no change is received within 50 ms.

1. The switching control unit 55-b is triggered by the fact that neither the update notification (update contents) of the management table 54 information nor the notification of no change is received from the switching control unit 55 for a certain time (50 ms or less). Is detected.
2. The switching control unit 55-b instructs the concentrating unit of the backup control circuit 43-b to start transmission / reception of the uplink / downlink signal.
3. In response to an instruction from the switching control unit 55-b, the concentrator of the standby control circuit 43-b receives the uplink / downlink signal, outputs the received uplink signal, creates a copy of the received downlink signal, and all of them. Output to the optical transceiver 41 is started.

  Through the above procedure, the concentrator of the spare control circuit 43-b starts to conduct, and the control circuit switching is completed. Since the same information is written in the management table 54-b and the management table 54 at the time of switching, the spare control circuit 43-b takes over all information related to all ONUs possessed by the control circuit 43 and then controls the control circuit 43-b. It will be switched from. That is, since the switching is performed while maintaining the MPCP link of the ONU 16 and the like, there is no disconnection of the MPCP link of the ONU 16 due to the switching of the control circuit, and the work of reestablishing the link is not necessary.

  As described above, the optical communication system 302 can realize high-speed switching not only in the case of a failure of the optical transceiver 41 but also in the case of a failure of the control circuit 43, and by adding the spare control circuit 43-b, the optical communication system of FIG. Higher reliability than 301 can be ensured.

  Note that the switching control unit 55-b does not receive a signal from the switching control unit 55 for a certain period of time as a detection trigger for an abnormality in the control circuit 43 in the procedure 1 described above, but the control circuit 43 detects its own failure. Then, the failure may be notified to the switching control unit 55-b via the switching control unit 55. In this case, the procedure after the switching control unit 55-b receives the failure notification is the same as the procedures 2 and 3 described above.

(Embodiment 3)
FIG. 11 is a block diagram of an optical communication system 303 having a configuration in which another control circuit 43-2 is added instead of the backup control circuit 43-b in the optical communication system 302 of FIG. Since the standby control circuit 43-b of the optical communication system 302 is not used at all when the control circuit 43 is normal, the utilization efficiency is low. Therefore, the concept of N: M protection is also applied to the control circuit 43 in the optical communication system 303.

  FIG. 12 is a block diagram illustrating the configuration of the control circuit 43-1 and the control circuit 43-2. The OLT 11 ″ of the optical communication system 303 includes a plurality of control circuits 43, and each control circuit 43 is connected to one or more different optical transceivers 41 among the optical transceivers 41 in a normal state. When a failure occurs in the control circuit 43, all the connected optical transceivers 41 are reconnected to one other control circuit 43 or another plurality of control circuits 43 in a batch or distributed manner. The control circuit 43 is instructed to start communication with the ONU 16 via the optical transceiver 41, and the control circuit 43 that has received the control circuit switching instruction adds to the optical transceiver 41 that has been connected. The communication with the ONU 16 is also made via the reconnected optical transceiver 41.

  Each time the management table 54 updates its own ONU information, each control circuit 43 notifies the ONU information updated by the switching control unit 55 to the switching control unit 55 of the other control circuit 43, and the other control circuit 43. When the ONU information is notified from the switching control unit 55, the switching control unit 55 updates the management table 54 according to its own ONU information and the notified ONU information, and receives the control circuit switching instruction. Communication with the ONU 16 is started based on the ONU information stored in the table 54.

  In the two control circuits (43-1, 43-2), the corresponding concentrators (concentrator 1, concentrator 2) each have four optical transceivers (41-1, 41-2, 41-3, 41-). Connect 4). When normal, each control circuit 43 communicates with the ONUs 16 under the two optical transceivers 41. That is, the control circuit 43-1 communicates with 48 ONUs (1st to 48th units) under the optical transceivers (41-1, 41-2). The control circuit 43-1 is a spare for the control circuit 43-2 when viewed from the ONU 16 under the optical transceiver (41-3, 41-4). When the control circuit 43-2 is normal, the optical transceiver (41-3, 41-4) It does not communicate with 48 ONUs (49th to 96th) under its control. On the other hand, the control circuit 43-2 communicates with 48 ONU units (49th to 96th units) under the optical transceiver (41-3, 41-4) at the normal time. The control circuit 43-2 is a spare for the control circuit 43-1, as viewed from the ONU 16 under the optical transceiver (41-1, 41-2). When the control circuit 43-1 is normal, the optical transceiver (41-1, 41-2) It does not communicate with 48 ONUs (1st to 48th units) under its control.

  Similarly to the optical communication system 302 of FIG. 9, the two control circuits 43 are connected to each other, and each control circuit 43 receives the ONU information of the management table 54 of the partner control circuit 43 from time to time. The latest ONU information described in the management table 54 is also stored for the ONU 16.

  A block that operates differently from the control circuit 43 in the optical communication system 301 in FIG. 4 and the control circuit 43 in the optical communication system 302 in FIG. 9 will be described below using FIG.

  The switching control unit 55-1 of the control circuit 43-1 and the switching control unit 55-2 of the control circuit 43-2 each update their own control circuit management tables (54-1, 54-2) when they are normal. The updated ONU information is notified to the switching control unit of the other control circuit. Each switching control unit (55-1, 55-2) receives the update information from the other switching control unit and updates the corresponding item for the other ONU in the management table of the own control circuit according to the update information. . As a result, when normal, the management table 54-1 and the management table 54-2 store exactly the same contents.

  For example, when the control circuit 43-2 fails, the switching control unit 55-1 of the normal control circuit 43-1 detects the failure of the control circuit 43-2. As a detection method, for example, the switching control unit 55-2 may detect an abnormality in the control circuit 43-2 and notify the switching control unit 55-1. Upon receiving the notification, the switching control unit 55-1 instructs the concentrating unit of the control circuit 43-1 to start communication with the ONUs 16 (49th to 96th units) under the control circuit 43-2. Upon receiving the instruction, the concentrator of the control circuit 43-1 also starts communication with the ONUs 16 (49th to 96th units) and communicates with all the ONUs 16.

  Similar to the optical communication system 302 in FIG. 9, the optical communication system 303 can be switched while maintaining the MPCP link of the ONU 16 and the like, so that not only the optical transceiver switching but also the control circuit switching can be performed at high speed. Switching is possible. Further, since the optical communication system 303 does not have a control circuit that is not normally used, the control circuit is more reliable than the standby control circuit 43-b of the optical communication system 302 while ensuring the same level of reliability as the optical communication system 302. The utilization efficiency of 43 can be increased.

(Embodiment 4)
FIG. 13 is a block diagram of an optical communication system 304 in which all (or part of) the branch fiber 14 of the optical communication system 301 of FIG. 4 is redundant. In the optical communication system 301, when the branch line fiber 14 is disconnected, the communication with the ONU 16 under the branch line fiber is disconnected. The optical communication system 304 is configured to be able to cope with such branch fiber breaks.

  The optical communication system 304 includes an MLT (M is an integer of 2 or more) optical transceivers 41 and a control circuit 43, and a branching ratio of 1: X (X is an integer of 2 or more). Furthermore, M first splitters 12 whose junction side is connected to one of the optical transceivers 41 and whose branch side is connected to X first branch fibers 13, and K (K is 2 or more and (M−1) × X or less). ) Branch fibers 14, L spare branch fibers 34 arranged in parallel with L (L is an integer of 1 to K) of the branch fibers 14, and the branching ratio is 1: Y. (Y is an integer greater than or equal to 2), the merging side is connected to one of the branch fibers 14, and the branching side is connected to Y second branching fibers 18 (K-L) second splitters 15, and the branching ratio Is 2: Y (Y is an integer of 2 or more) Is connected to one of the branch fibers 14 and a spare branch fiber 34 parallel to the branch fiber 14, and the L third splitters 15 ′ connected to the Y second branch fibers 18 on the branch side, and K × Y The Z ONUs 16 connected to any one of the second branch fibers 18 (Z is a natural number equal to or less than K × Y), the branch fiber 14 and the first branch fiber 13 are connected in a 1: 1 ratio, or the branch fiber 14 Are connected in parallel with the first branch fiber 13, and the branch fiber 14 and the first branch fiber 13 are connected by a path switching instruction from the control circuit 43 of the OLT 11. Or a changeover switch 17 that can change the connection between the branch fiber 14 or the spare branch fiber 34 and the first branch fiber 13.

  At the place where the branch fiber 14 is made redundant, the 2: 8 splitter of the third splitter 15 ′ is used instead of the 1: 8 splitter of the second splitter 15, and between the third splitter 15 ′ and the changeover switch 17 is in a normal state. The branch fiber 14 to be used and the spare branch fiber 34 to be used when the branch fiber 14 is disconnected are connected to each other. However, the changeover switch 17 is not connected to the auxiliary branch fiber 34 and the first branch fiber 13 at the time of initial construction. In FIG. 13, all the third splitters 15 'are shown.

Here, as an example, the switching procedure when the branch fiber 14-1 is cut is shown below.
1. The discovery DBA processing unit 52 of the control circuit 43 notifies the failure detection unit 56 that no MPCP frame is received from the ONU 16 (1st to 8th units) for a certain time (50 ms or less).
2. Upon receiving the notification, the failure detection unit 56 detects the disconnection of the branch fiber 14-1 and notifies the switching control unit 55 to that effect.
3. In response to the notification, the switching control unit 55 determines that the communication disconnection can be avoided by switching the branch fiber 14-1 to the standby branch fiber 34-1, and issues a switching instruction to switch to the switch 17.
4). In response to the switching instruction from the switching control unit 55, the selector switch 17 switches the route according to the instruction.

  With the above procedure, the optical communication system 304 can avoid the communication disconnection even if the branch fiber 14 is disconnected, and can be switched while maintaining the MPCP link of the ONU 16 as in the optical communication system 301 of FIG. Therefore, high-speed switching can be realized even when the branch fiber is disconnected.

  Note that the redundancy of all or part of the branch fiber 14 can be applied not only to the optical communication system 301 in FIG. 4 but also to the optical communication system 302 in FIG. 9 and the optical communication system 303 in FIG. The configuration and the branch fiber breakage detection method applied to these are the same as those of the optical communication system 304.

(Embodiment 5)
FIG. 14 is a block diagram illustrating an optical communication system 305 having a configuration in which the OLT 11 of the optical communication system 301 of FIG. 4 is applied to 1: N protection. The optical communication system 305 includes an OLT 11 having M (M is an integer of 2 or more) optical transceivers 41 and a control circuit 43 that can accommodate a maximum of α (α is an integer of 1 or more) ONUs 16 per unit, and K (K is an integer greater than or equal to 1 and less than or equal to (M−1)) the branch fiber 14 and the branching ratio is 1: X (X is an integer greater than or equal to 2), and the merging side is connected to one of the branch fibers 14. On the branch side, there are K (K is an integer not less than 1 and not more than (M−1)) first splitters 12 connected to A (A is an integer not less than 1 and not more than X) branch fibers 38, and branch fibers 38. Through which the number of ONUs 16 connected to one first splitter 12 is less than or equal to K and the total number is equal to or greater than K and equal to or less than (K × α), and M transceiver-side ports and branch lines connecting each optical transceiver 41 K pieces connecting the fibers 14 And a changeover switch 17 that has a branch line side port and connects the transceiver side port to an arbitrary branch side port in response to a path switching instruction from the control circuit 43 of the OLT 11 or disconnects the transceiver side port from the branch line side port.

  The changeover switch 17 is installed so as to straddle three PONs between the OLT 11 and the first splitter 12 (1: 4 splitter), and the three optical transceivers 41 and the three splitters from the three first splitters 12 are arranged. The connection with the branch fiber 14 can be changed. The optical communication system 305 has a two-stage splitter configuration in which the branch fiber 38 from each first splitter 12 is connected to a second splitter (1: 8 splitter). In the first to fourth embodiments, it has been described that the OLT 11 capable of managing all ONUs 16 in a batch is applied to N: M protection, so that high-speed switching is possible. However, the present OLT 11 is applied to 1: N protection. Even in this case, the switching procedure similar to that of the first embodiment can be applied, so that high-speed switching is possible. For example, the switching procedure when the optical transceiver 41-3 fails will be described below.

1. The optical transceiver 41-3 recognizes its own failure (for example, a decrease in output power) and outputs failure information to the failure detection unit in the control circuit 43.
2. The failure detection unit 56 notifies the switching control unit 55 that the optical transceiver 41-3 has failed.
3. Upon receiving the notification, the switching control unit 55 determines that the communication disconnection can be avoided by switching the connection destination of the branch fiber 14-3 connected to the optical transceiver 41-3 to the optical transceiver 41-4 that is a spare optical transceiver. Then, the switch 17 is informed of a switching instruction for switching.
4). In response to the switching instruction from the switching control unit 55, the selector switch 17 switches the route according to the instruction.

  With this switching, the connection destination of the ONU 16 (65th to 96th) is changed from the optical transceiver 41-3 to the optical transceiver 41-4, and the switching control unit 55 updates the items changed by this switching in the management table 54. .

  Since the items related to the MPCP link and the like in the management table 54 for the ONU 16 (65th to 96th unit) do not change, the optical transceiver of the connection destination can be connected without disconnecting the MPCP link or the like of the ONU 16 (65th to 96th unit). 41 can be switched. Therefore, high-speed switching is also possible in this embodiment.

  Similarly to the conventional 1: N protection PON in which the spare OSU is not used when the working OSU is normal, the spare optical transceiver is not used when the working optical transceiver is normal in the optical communication system 305. The cost is lower, and the optical communication system 305 is more advantageous as the redundant equipment cost.

  Note that there is no problem even if the splitter of the optical communication system 305 is not a two-stage configuration but a one-stage configuration. FIG. 15 is a block diagram illustrating an optical communication system 306 having a single-stage splitter configuration. In the optical communication system 306, a fourth splitter 45 (1:32 splitter) is used instead of the first splitter 12 and the second splitter 15 of FIG.

(Embodiment 6)
FIG. 16 is a block diagram of an optical communication system 307 having a configuration in which all (or part of) the branch fiber 14 of the optical communication system 306 of FIG. 15 is redundant. The optical communication system 307 includes an OLT 11 having M (M is an integer of 2 or more) optical transceivers 41 and a control circuit 43 capable of accommodating a maximum of α (α is an integer of 1 or more) ONUs 16 per unit, and K (K is an integer greater than or equal to 1 and less than or equal to (M−1)) L branch spare fibers 14 and L spares arranged in parallel with L (L is an integer greater than or equal to 1 and less than K) of the branch fiber 14 The branch fiber 34 has a branching ratio of 1: X (X is an integer of 2 or more), the merge side is connected to one of the branch fibers 14, and the branch side is A (A is an integer of 1 to X). (K−L) fourth splitters 45 connected to the bifurcated fiber 18, a branching ratio of 2: X, and the merge side includes one of the branch fibers 14 and a spare branch fiber 34 parallel to the branch fiber 14. Connected, branch fiber with 1 branch fiber on branch side 1 8 or less and a total number of K or more connected to one of the fourth splitter 45 or the fifth splitter 45 ′ via the L number of fifth splitters 45 ′ connected to 8 and the second branch fiber 18. K × α) or less ONUs 16, M transceiver-side ports for connecting the respective optical transceivers 41 and (K + L) branch-side ports for connecting the branch fiber 14 or the backup branch fiber 34, and the OLT 11 The switch 17 connects the transceiver side port to an arbitrary branch line port in response to a path switching instruction from the control circuit 43, or disconnects the transceiver side port from the branch line port.

  The optical communication system 307 uses a fifth splitter 45 ′ (2:32 splitter) instead of the fourth splitter 45 of the optical communication system 306, and the branch fiber 14 and the spare branch line on the two branch sides of each fifth splitter 45 ′. The fiber 34 is connected. At the time of initial construction, the changeover switch 17 keeps the standby branch fiber 34 not connected to any optical transceiver 41. In the optical communication system 307, for example, the switching procedure when the branch fiber 14-1 is disconnected is as follows.

1. The discovery DBA processing unit 52 of the control circuit 43 notifies the failure detection unit 56 that the MPCP frame from the ONU 16 (first to thirty-second units) is not received for a certain time (50 ms or less).
2. The failure detection unit 56 detects the disconnection of the branch fiber 14-1 based on the notification and the failure information received from the optical transceiver 41-1, and notifies the switching control unit 55 accordingly.
3. In response to the notification, the switching control unit 55 determines that the communication disconnection can be avoided by switching the branch fiber 14-1 to the standby branch fiber 34-1, and issues a switching instruction to switch to the switch 17.
4). In response to the switching instruction from the switching control unit 55, the selector switch 17 switches the route according to the instruction.

  With the above procedure, the optical communication system 307 can avoid the communication disconnection even if the branch fiber 14 is disconnected, and can be switched while maintaining the MPCP link of the ONU 16 as in the optical communication system 301 of FIG. Therefore, high-speed switching can be realized even when the branch fiber is disconnected.

  The configuration in which the OLT 11 of the optical communication system 301 in FIG. 4 is applied to 1: N protection is not limited to FIGS. 14 and 15, but a configuration in which branch fibers are redundant as shown in FIG. 16 or a configuration corresponding to FIGS. 9 and 11. Is also possible. Their configuration and the switching procedure in the configuration are the same as the contents described in each of the above embodiments.

11, 11 ′, 11 ″: OLT (station side terminal equipment)
12: 1st splitter (1: X splitter)
13: 1st branch fiber 14, 14-1, 14-2, ..., 14-K: Branch fiber 15: 2nd splitter (1: Y splitter)
15 ': Third splitter (2: Y splitter)
16: ONU (subscriber-side terminal equipment)
17: changeover switch 18: second branch fibers 34, 34-1, 34-2,..., 34-K: spare branch fiber 38: branch fiber 41: optical transceivers 43, 43-1, 43-2: control Circuit 43-b: Preliminary control circuit 44: SNI
45: Fourth splitter (1:32 splitter)
45 ': Fifth splitter (2:32 splitter)
51: Transmission path 52: Discovery DBA processing unit 53: OAM / authentication / encryption processing unit 54: Management table 55: Switching control unit 56: Failure detection units 301 to 307: Optical communication system

Claims (11)

A plurality of ONU groups including one or more subscriber-side terminal units (ONUs) (Optical Network Units) connected via a changeover switch, and a plurality of optical transceivers for transmitting and receiving optical signals to and from the ONUs;
A service node interface (SNI) connected to an external access network;
Connected to the optical transceiver,
A transmission path for transmitting a signal between the optical transceiver and the SNI;
The registration processing signal for the ONU registration processing or the propagation time measurement signal for propagation time measurement is used to establish a link with the ONU and determine the ONU uplink bandwidth allocation amount. A discovery DBA (Dynamic Bandwidth Allocation) processing unit for acquiring ONU information related to the link of the ONU;
Using the maintenance monitoring signal with the ONU, link establishment with the ONU, authentication, and encryption key exchange are performed, and OAM (Operation, Administration) that acquires ONU information related to the link of the ONU. and Mai
maintenance) / authentication / encryption processing unit,
The ONU information acquired by the discovery DBA processing unit and the OAM / authentication /
A management table for storing ONU information acquired by the encryption processing unit and updated as needed;
A switching control unit that determines which optical transceiver to connect to the ONU group based on the ONU information stored in the management table and issues a path switching instruction to the switch;
A control circuit having
A station side terminal device (OLT: Optical Line Terminal). The control circuit includes:
Failure information that the optical transceiver outputs when its own failure occurs, the discovery D
Failure information output when a BA processing unit recognizes an abnormality in the section from the optical transceiver to the ONU by transmitting and receiving the registration processing signal or the propagation time measurement signal, and the OAM / authentication / encryption The processor detects the fault location based on the fault information output when it recognizes an abnormality in the section from the optical transceiver to the ONU by sending and receiving the maintenance monitoring signal, and the detected fault location is switched. It further has a failure detection unit to notify the control unit,
The switching control unit
Based on the failure information notified from the failure detection unit and the ONU information stored in the management table, the ONU information stored in the management table is maintained when it is determined that a failure recovery by path switching is possible 2. The OLT according to claim 1, wherein a route switching instruction is issued to the changeover switch in a state. Further comprising a spare control circuit having the same configuration as the control circuit,
The preliminary control circuit includes:
When connected to the optical transceiver and the control circuit is normal, the transmission path is interrupted,
The control circuit includes:
3. The OLT according to claim 1, wherein when a failure occurs in the OLT, the control circuit switching instruction for cutting off the transmission path and opening the transmission path to the backup control circuit is issued. 4. The switching control unit of the control circuit includes:
When normal, each time the management table updates the ONU information, the ONU information to be updated is notified to the switching control units of all the spare control circuits,
The switching control unit of the spare control circuit is
In accordance with the ONU information to be updated notified from the switching control unit of the control circuit, update the management table of the spare control circuit,
When the control circuit switching instruction notified from the switching control unit of the control circuit is received, communication with the ONU is started based on the ONU information stored in the management table of the backup control circuit. The OLT according to claim 3. A plurality of the control circuits,
Each of the control circuits is normally connected to one or more different optical transceivers of the optical transceivers,
Each of the control circuits re-distributes all of the optical transceivers connected to the other control circuit or a plurality of other control circuits in a batch or distributed manner when a failure occurs. Connect the control circuit to issue a control circuit switching instruction to start communication with the ONU via the optical transceiver,
The control circuit that has received the control circuit switching instruction communicates with the ONU via the reconnected optical transceiver in addition to the previously connected optical transceiver. 2. OLT according to 2. Each of the control circuits
Each time the management table updates its own ONU information, it notifies the ONU information updated by the switching control unit to the switching control unit of the other control circuit,
When the ONU information is notified from the switching control unit of the other control circuit, the switching control unit updates the management table according to the ONU information and the notified ONU information,
The OLT according to claim 5, wherein when the control circuit switching instruction is received, communication with the ONU is started based on the ONU information stored in the management table. An OLT having M (M is an integer of 2 or more) optical transceivers and a control circuit;
The branching ratio is 1: X (X is an integer equal to or greater than 2), and for each of the optical transceivers, the merging side is connected to one of the optical transceivers, and the branching side is connected to X first branch fibers. One splitter,
K (K is an integer of 2 or more and (M−1) × X or less) branch fibers;
The branching ratio is 1: Y (Y is an integer of 2 or more), and for each branch fiber, the merging side is connected to one of the branch fibers, and the branching side is connected to Y second branch fibers. Two splitters,
Z (Z is a natural number equal to or less than K × Y) ONUs connected to any one of the K × Y second branch fibers;
A changeover switch that connects the branch fiber and the first branch fiber in a 1: 1 ratio and that can change a connection between the branch fiber and the first branch fiber in response to a path switching instruction from the control circuit of the OLT; ,
An optical communication system comprising: OLT having M (M is an integer of 2 or more) optical transceivers and control circuits capable of accommodating a maximum of α (α is an integer of 1 or more) ONUs per unit;
K branch fibers (K is an integer not less than 1 and not more than (M−1)),
The branching ratio is 1: X (X is an integer of 2 or more), the merge side is connected to one of the branch fibers, and the branch side is connected to A (A is an integer of 1 to X) branch fibers. (K is an integer greater than or equal to 1 and less than or equal to (M−1)) first splitters;
An integer number of ONUs that are less than or equal to α connected to each of the first splitters via the branch fiber, and the total number is K or more and (K × α) or less;
M transceiver side ports for connecting the optical transceivers and K branch side ports for connecting the branch fibers, and the transceiver side ports can be arbitrarily set by a path switching instruction from the control circuit of the OLT. A changeover switch connected to the branch line side port or unconnected to the branch line side port,
An optical communication system comprising: An OLT having M (M is an integer of 2 or more) optical transceivers and a control circuit;
The branching ratio is 1: X (X is an integer equal to or greater than 2), and for each of the optical transceivers, the merging side is connected to one of the optical transceivers, and the branching side is connected to X first branch fibers. One splitter,
K (K is an integer of 2 or more and (M−1) × X or less) branch fibers;
L spare branch fibers arranged in parallel with L (L is an integer of 1 to K) of the branch fibers;
The branching ratio is 1: Y (Y is an integer of 2 or more), the merging side is connected to one of the branch fibers, and the branching side is connected to Y second branching fibers (KL) second splitters. When,
The branching ratio is 2: Y (Y is an integer greater than or equal to 2), the merging side is connected to one of the branching fibers and the auxiliary branching fiber parallel to the branching fiber, and the branching side is connected to Y second branching fibers. L third splitters to be connected;
Z (Z is a natural number equal to or less than K × Y) ONUs connected to any one of the K × Y second branch fibers;
The branch fiber and the first branch fiber are connected at a ratio of 1: 1, or when the branch fiber and the backup branch fiber are arranged in parallel, the first branch fiber is connected at a ratio of 1: 1, A changeover switch that can change the connection between the branch fiber and the first branch fiber or the connection between the branch fiber or the spare branch fiber and the first branch fiber by a path switching instruction from the control circuit of the OLT. When,
An optical communication system comprising: OLT having M (M is an integer of 2 or more) optical transceivers and control circuits capable of accommodating a maximum of α (α is an integer of 1 or more) ONUs per unit;
K branch fibers (K is an integer not less than 1 and not more than (M−1)),
L spare branch fibers arranged in parallel with L (L is an integer of 1 to K) of the branch fibers;
The branching ratio is 1: X (X is an integer of 2 or more), the merge side is connected to one of the branch fibers, and the branch side is connected to A (A is an integer of 1 to X) branch fibers ( KL) first splitters;
L second splitters having a branching ratio of 2: X, a merging side connected to one of the branch fibers and the spare branch fiber parallel to the branch fibers, and a branch side connected to A branch fibers;
An integer number of ONUs of α or less and a total number of K or more and (K × α) or less connected to each of the first splitter or the second splitter via the branch fiber;
M transceiver side ports connecting each of the optical transceivers and (K + L) branch side ports connecting the branch fiber or the backup branch fiber, and a path switching instruction from the control circuit of the OLT A changeover switch for connecting the transceiver side port to any branch line side port or unconnected to the branch line side port;
An optical communication system comprising:   The optical communication system according to any one of claims 7 to 10, wherein the OLT is the OLT according to any one of claims 1 to 6.

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