Method, system and OLT for OLT state switching in a dual-homed PON protection system

Abstract

The object of the present disclosure is to provide a method, a system and an OLT for OLT state switching in a dual-homed PON protection system. The dual-homed PON protection system includes a primary OLT and a standby OLT, and the configuration information of the ONUs has been synchronized on the two OLTs. Among them, in the second specified time window, when the standby OLT fails to detect the communication with the primary OLT and the optical signal from the ONU, the standby OLT switches to the primary state. Therefore, the embodiments of the present disclosure make the PON system more highly maintainable, more robust, more reliable and more resilient, and can also stabilize the service interruption time at 50 milliseconds or even lower.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to the technical field of PON (Passive Optical Network) technology, and in particular, to a technology for OLT (Optical Line Terminal) state switching in a PON system for dual-parenting resilience protection. Background Art

[0002] ITU-T (ITU Telecommunication Standardization Sector) G.984.1 / G.9804.1 / BBF (Broadband Forum) TR352 propose dual-parenting resilience protection to prevent catastrophic failures of OLT devices, their power supplies, and the physical locations where the OLT devices are placed. Dual-parenting resilience protection refers to a system that uses two OLT line devices to achieve PON redundancy protection, where these two OLT line devices are typically provided in two independent devices at physically different locations. This can bring benefits such as reliable components with a resilient system design, thereby protecting high-value customers from service interruptions caused by physical device failures and certain electronic failures. Moreover, this can enable embedded devices to have an availability level of 99.999% or even higher, making them more maintainable and having better service resilience.

[0003] When a fault is detected on the active PON, the embedded software automatically switches the current active PON to the standby PON, enabling PON protection with a service interruption of less than 50 milliseconds. For type B protection, the switchover requires migrating the ONU (Optical Network Unit) to a new OLT port, which may take several seconds. The ranging compensation values are shared between the primary OLT and the standby OLT, enabling a faster ranging convergence speed. When combined with GPON POPUP messages, a faster ONU state migration can be achieved. Summary of the Invention

[0004] The objectives of the embodiments of the present disclosure are to provide a method, a system, and an OLT for OLT state switching in a dual-homed PON protection system.

[0005] According to one aspect of the present disclosure, there is provided a method for OLT state switching in a dual-homed PON protection system. The dual-homed PON protection system includes a primary OLT and a standby OLT, and the configuration information of the ONUs has been synchronized on the two OLTs. The method includes the following steps:

[0006] In a second specified time window, when the standby OLT fails to detect communication with the primary OLT and optical signals from the ONUs, the standby OLT switches to the primary state.

[0007] According to one aspect of the present disclosure, there is also provided a system for OLT state switching in a dual-homed PON protection system. The dual-homed PON system includes a primary OLT and a standby OLT, and the configuration information of the ONUs has been synchronized on the two OLTs.

[0008] The standby OLT is configured to:

[0009] Detect communication with the primary OLT and optical signals from the ONUs according to a second specified time window to determine whether to perform state switching;

[0010] The primary OLT is configured to:

[0011] Detect communication with the standby OLT and communication with the ONUs according to a first specified time window to determine whether to perform state switching.

[0012] According to one aspect of the present disclosure, there is also provided a standby OLT for performing state switching in a dual-homed PON protection system. The dual-homed PON system includes a primary OLT and the standby OLT, and the configuration information of the ONUs has been synchronized on the two OLTs.

[0013] The standby OLT includes a processor and a memory. Computer-executable instructions are stored in the memory. When the computer-executable instructions are executed by the processor, the standby OLT is configured to:

[0014] In a second specified time window, when the standby OLT fails to detect communication with the primary OLT and optical signals from the ONUs, switch to the primary state.

[0015] According to one aspect of the present disclosure, there is also provided a primary OLT for performing state switching in a dual-homed PON protection system. The dual-homed PON system includes the primary OLT and a standby OLT, and the configuration information of the ONUs has been synchronized on the two OLTs.

[0016] Among them, the primary OLT includes a processor and a memory, and computer-executable instructions are stored in the memory. When the computer-executable instructions are executed by the processor, the primary OLT is configured to:

[0017] In a first specified time window, when the primary OLT fails to detect communication with the standby OLT and communication with the ONU, switch to the standby state.

[0018] Embodiments of the present disclosure propose solutions to the split-brain problem of a dual-homed PON protection system. By each distributed OLT node detecting whether a preset state switching condition is met, the current node determines whether to perform a state switch itself, such as the standby OLT switching to the primary state or the primary OLT switching to the standby state. Therefore, embodiments of the present disclosure make the PON system more highly maintainable, more robust, more reliable and resilient, and can also stabilize the service interruption time at 50 milliseconds or even lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Other features, objects, and advantages of the present disclosure will become more apparent by reading the detailed description of the non-limiting embodiments with reference to the following drawings:

[0020] Figure 1 A schematic diagram showing the architecture of an exemplary dual-homed resilient protection PON system according to the present disclosure;

[0021] Figure 2 A flowchart showing an exemplary method for OLT state switching in a dual-homed resilient protection PON system according to the present disclosure.

[0022] Identical or similar reference numerals in the drawings represent identical or similar components. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The following will further describe the specific embodiments of the present disclosure with reference to the drawings.

[0024] Before discussing the exemplary embodiments in more detail, it should be noted that some exemplary embodiments of the present disclosure are described as devices represented by block diagrams and processes or methods represented by flowcharts. Although the flowcharts describe the operation processes of the embodiments of the present disclosure as sequential processes, many of the operations can be implemented in parallel, concurrently, or simultaneously. In addition, the order of the operations can be rearranged. The processes of the embodiments of the present disclosure can be terminated when their operations are completed, but can also include additional steps not shown in the flowcharts. The processes of the embodiments of the present disclosure can correspond to methods, functions, procedures, subroutines, subprograms, etc.

[0025] The methods illustrated by the flowcharts and the apparatuses illustrated by the block diagrams discussed below can be implemented by hardware, software, firmware, middleware, microcode, a hardware description language, or any combination thereof. When implemented in software, firmware, middleware, or microcode, the program code or code segments to perform the necessary tasks can be stored in a machine or a computer-readable medium such as a storage medium. The (one or more) processors can execute the necessary tasks.

[0026] Similarly, it will also be understood that any flowchart, flow diagram, state transition diagram, and the like, representing various processes, can be fully described as program code stored in a computer-readable medium and thus executed by a computing device or a processor, whether or not these computing devices or processors are explicitly shown.

[0027] In this document, the term "storage medium" can represent one or more devices for storing data, including read-only memory (ROM), random access memory (RAM), magnetic RAM, core memory, disk storage media, optical storage media, flash devices, and / or other machine-readable media for storing information. The term "computer-readable medium" can include, but is not limited to, portable or fixed storage devices, optical storage devices, and various other media capable of storing and / or containing instructions and / or data.

[0028] A code segment can represent a procedure, function, subroutine, program, routine, subroutine, module, software package, class, or any combination described by instructions, data structures, or program descriptions. A code segment can be coupled to another code segment or a hardware circuit by passing and / or receiving information, data, arguments, parameters, or stored content. Information, arguments, parameters, data, etc., can be passed, forwarded, or transmitted via any suitable means including storage sharing, information transfer, token passing, network transmission, etc.

[0029] The specific structural and functional details disclosed herein are merely representative and are for the purpose of describing exemplary embodiments of the present disclosure. However, the embodiments of the present disclosure can be specifically implemented in many alternative forms and should not be construed as being limited only to the embodiments set forth herein.

[0030] It should be understood that although terms such as "first", "second", etc. may be used herein to describe various units, these units should not be limited by these terms. These terms are only used to distinguish one unit from another. For example, without departing from the scope of the exemplary embodiments, the first unit can be called the second unit, and similarly the second unit can be called the first unit. The term "and / or" used herein includes any and all combinations of one or more of the listed associated items.

[0031] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the exemplary embodiments. Unless the context clearly dictates otherwise, the singular forms "a", "an" used herein are also intended to include the plural. It should also be understood that the terms "comprises" and / or "comprising" specify the presence of the stated features, integers, steps, operations, units and / or components, and do not preclude the presence or addition of one or more other features, integers, steps, operations, units, components and / or combinations thereof.

[0032] It should also be noted that in some alternative implementations, the functions / actions mentioned may occur in a different order than that indicated in the figures. For example, depending on the functions / actions involved, two successive figures shown may actually be executed substantially simultaneously or sometimes in the reverse order.

[0033] Since the two OLT devices in a dual-homed PON protection system are usually located relatively far apart, the internal communication link and heartbeat connection between the OLT devices are more likely to fail than in a same-frame Type-B protection. When the communication between distributed nodes (i.e., OLT devices) fails due to network connection problems, this situation is called network partition, which may lead to split-brain, that is, both OLT devices switch to the master node when the connection is disconnected. After split-brain occurs, both consider themselves the master node and will create new data (e.g., running state data) on their respective nodes and will not be synchronized to the peer node, so two separate data sets may result and they cannot be simply merged and integrated. In addition, split-brain in a dual-homed PON system may also lead to serious and irreparable errors. If each node considers itself the master OLT and interacts with the ONU, all ONUs will become unstable or even go offline and cannot provide normal services. The occurrence of two master nodes in this dual-homed PON protection system will also cause other OLT node errors and irreparable exceptions.

[0034] Existing "split-brain" prevention mechanisms, such as the "Heartbeat" mechanism and the node majority quorum witness mechanism, obviously require adding additional heartbeat links or third-party arbitration devices, thus increasing the system cost and complexity.

[0035] Combined with the characteristics of PON technology, the embodiments of the present disclosure propose solutions to the split-brain problem of the dual-homed PON protection system. The embodiments of the present disclosure make full use of the redundant protection decision logic in the dual-homed PON system, and combine the PON_LOS / Light-Not-Seen signal status generated by the PON FPGA / hardware and the PeerFail signal status generated by the underlying communication module to specifically solve the intractable split-brain problem in the dual-homed PON system without manual intervention and quickly restore services. Accordingly, the embodiments of the present disclosure avoid the increase in system cost and complexity caused by additional dedicated heartbeat links, node isolation protection, or third-party arbitration nodes such as a quorum arbitration mechanism, and can improve the high availability and service resilience of the PON system.

[0036] Figure 1 FIG. shows a schematic architecture diagram of an exemplary dual-homed resilient protection PON system according to the present disclosure.

[0037] As Figure 1 shown, multiple ONUs 101, such as those respectively labeled ONU1, ONU2... ONUi, are all connected via a splitter 102 to two channel terminations (CTs) located in different OLT racks. Generally, the two OLTs 103 and 104 in the dual-homed PON protection system are geographically far from each other. In traditional PON protection, both PON parts terminate at the same OLT device. Different from traditional PON protection, dual-homed PON protection requires functional coordination of the PON parts in two OLT devices respectively.

[0038] Among them, the protected OLT 103 provides the primary PON, labeled PONLT(0), and communicates with multiple ONUs 101 as the primary OLT to provide services for the ONUs 101. The protection OLT 104 provides a standby PON, labeled PONLT(1), and can receive the upstream data of multiple ONUs 101 through the splitter 102. Therefore, ONU1, ONU2... ONUi are all registered at the primary OLT 103 and the standby OLT 104. When the primary OLT 103 fails, the standby OLT 104 can reproduce the logical state of the primary OLT 103 with minimal delay. In addition, the dual-homed PON system must also support the protection switching of the upstream traffic of the two OLTs 103 and 104. As a distributed system, the dual-homed PON protection system must keep the standby OLT or all standby OLT CTs in standby until a working state switch occurs. Therefore, by switching the standby OLT device to the primary OLT device, the PON system can recover from the failure of the original primary OLT device at any time.

[0039] Taking the dual-homed type BPON protection as an example for illustration. The main functions for implementing resilient protection are located within the OLT. It requires the standby OLT to be in a standby state, so the operating states of the two OLTs must be synchronized. In addition, a data communication channel is needed between the two OLTs to share the service configurations of all ONUs, which is necessary for reconstructing the connections between all UNIs (User Network Interface) and SNIs (Service Node Interface) on the remote OLT (i.e., the standby OLT).

[0040] The active OLT 103 and the standby OLT 104 exchange heartbeat / P2P messages through an internal link. When the heartbeat / P2P message exchange is successful, the active OLT 103 and the standby OLT 104 can easily identify their respective operating states, i.e., whether it is the active OLT or the standby OLT. Therefore, the exchange of heartbeat / P2P messages is considered a very simple and effective method to prevent split-brain. Here, the active OLT 103 and the standby OLT 104 can be respectively configured with a PON protection decision module to determine their respective operating states in the PON system, i.e., the active state or the standby state. Among them, the PON protection decision module in the active OLT 103 is marked as the first PON protection decision module, and the PON protection decision module in the standby OLT 104 is marked as the second PON protection decision module.

[0041] If the communication of the internal link between the primary OLT 103 and the standby OLT 104 is interrupted, a split-brain situation will occur in the dual-homed PON system. Generally, heartbeat / P2P messages are sent to each other between the two OLT devices at a specified interval of several seconds to transmit their respective working states. The communication layer of each OLT receives and identifies the heartbeat / P2P messages. If the current OLT fails to receive the heartbeat / P2P message from the other party within a predetermined time interval, it can be determined that the peer OLT node has failed, shut down, or is unavailable, or its network connection resources are unavailable. Then, the underlying communication layer of the current OLT can notify the PeerFail notification message to the PON protection decision module of this OLT. If an abnormal situation occurs in the primary OLT 103, the primary OLT 103 cannot send control packets (bandwidth map), such as authorized traffic or OMCI (ONU Management Control Interface) messages, to the ONU 101. At this time, the FPGA (field-programmable gate array) of the primary OLT 103 can notify the PON_LOS message to the first PON protection decision module. Subsequently, the first PON protection decision module of the primary OLT 103 can make a judgment and switch the working state of this OLT to the standby state.

[0042] According to an example of the present disclosure, the FPGA of the standby OLT 104 can rely on the existing Light-Not-Seen function to determine the PON_LOS fault on the primary PON and periodically send an optical signal interruption message of "Light-Not-Seen" to the second PON protection decision module of the standby OLT 104. The primary OLT 103 can communicate with the ONU 101 within a specified time window. Therefore, when the primary OLT 103 fails, the standby OLT 104 may not detect the optical signal from the ONU 101 within the specified time window. However, this alone does not trigger the state switch of the standby OLT 104. Since it is impossible to determine on the standby OLT 104 whether it is due to the specified time window or the fiber fault of the standby OLT 104 that the standby OLT 104 fails to detect the optical signal from the ONU 101, according to an example of the present disclosure, the configuration of this time window can be implemented by software. However, the granularity of the duration of the "Light-Not-Seen" state is in milliseconds, rather than 125 μs or the number of upstream frames. Therefore, it is also feasible to incorporate this change into the FPGA. When the second PON protection decision module of the standby OLT 104 receives the PeerFail notification message and the optical signal interruption message of Light-Not-Seen within a given time window, it is determined that the standby OLT 104 is switched from the standby state to the primary state.

[0043] Figure 2 The flowchart shows an exemplary method for OLT state switching in a dual-homed resilient protection PON system according to the present disclosure.

[0044] Refer to Figure 1 and Figure 2 , the dual-homed PON protection system includes a primary OLT 103 and a standby OLT 104. The ONU 101 has been successfully registered on the primary OLT 103, and the relevant data has been synchronized to the standby OLT 104.

[0045] In step S201, according to the second specified time window, the standby OLT 104 detects the communication between it and the primary OLT 103 and the optical signal from the ONU 101 to determine whether to perform a state switch.

[0046] In step S202, according to the first specified time window, the primary OLT 103 detects the communication between it and the standby OLT 104 and the communication between it and the ONU 101 to determine whether to perform a state switch.

[0047] It should be noted that there is no sequential relationship between the above steps S201 and S202. Since both the primary OLT 103 and the standby OLT 104 independently detect whether they meet the status switching conditions, step S201 may occur before step S202 or after step S202.

[0048] Among them, the primary OLT 103 and the standby OLT 104 exchange their operation states with each other at a specified interval time to synchronize the status information. The primary OLT 103 communicates with the ONU 101 to send control messages to the ONU 101, such as authorized traffic or OMCI messages. The standby OLT 104 detects the upstream optical signal of the ONU 101.

[0049] The specified detection time window for determining whether to perform a status switch is in milliseconds, typically 20 milliseconds for example. The second specified time window for the standby OLT 104 and the first specified time window for the primary OLT 103 can be the same, such as both being 20 milliseconds, or different, such as being set according to actual deployment needs. According to an example of the present disclosure, when the standby OLT 104 fails to detect the communication between it and the primary OLT 103 and the optical signal from the ONU 101 within 20 milliseconds, it is determined to switch to the primary state. According to an example of the present disclosure, when the primary OLT 103 fails to detect the communication between it and the standby OLT 104 and the communication with the ONU 101 within 20 milliseconds, it is determined to switch to the standby state.

[0050] Here, various scenarios when the internal communication between the primary OLT 103 and the standby OLT 104 is interrupted in each embodiment of the present disclosure and the corresponding status switches of the primary OLT 103 and the standby OLT 104 will be described with reference to Table 1 below.

[0051]

[0052] Table 1: Scenario description of communication interruption between the primary OLT 103 and the standby OLT 104

[0053] Note: For PeerFail notification messages / PON_LOS notification messages / Light-Not-Seen optical signal interruption messages, "Y" indicates that the PON protection decision module has received the notification / interruption message, and "N" indicates that the PON_LOS notification message or Light-Not-Seen interruption message has not been received. "N" indicates an error situation, such as the PON protection decision module not receiving the notification / interruption message or the notification / interruption message not being generated due to some anomalies. According to an example of the present disclosure, for example, for the Light-Not-Seen optical signal interruption message, "N" means that the Light-Not-Seen optical signal interruption message should have been received, but the message was not generated. "-" indicates that the OLT device is unavailable due to restart / removal. For example, the cut / pull-out action of the standby PON optical fiber only affects the status of the relevant components on the standby OLT, and does not affect the status of the relevant components on the primary OLT. The standby PON must receive the PeerFail notification message and the Light-Not-Seen optical signal interruption message within the second specified time window to meet the condition for switching to the primary state. This second specified time window can be predefined, usually in milliseconds, typically 20 milliseconds for example.

[0054] Scenario 1: Fiber failure event occurs in the primary OLT 103

[0055] Here, the fiber failure event of the primary PON is, for example, that the optical fiber is cut or pulled out. At this time, the communication link between the primary OLT 103 and the standby OLT 104 is interrupted, and the communication between the primary OLT 103 and the ONU 101 is also interrupted. The standby OLT 104 cannot receive the upstream optical signal from the ONU 101.

[0056] 1) If the standby OLT 104 fails to detect the communication with the primary OLT 103 and the optical signal from the ONU 101 within the second specified time window, it should be determined to switch to the primary state.

[0057] For example, within the second specified time window, the underlying communication module of the standby OLT 104 fails to receive the P2P message from the primary OLT 103, thus triggering a PeerFail notification message, and the FPGA of the standby OLT 104 also fails to receive the upstream optical signal from the ONU 101, thus triggering a Light-Not-Seen optical signal interruption message. Accordingly, the second PON protection decision module of the standby OLT 104 can determine to switch the standby OLT 104 to the primary state.

[0058] If, within the first specified time window, the primary OLT 103 fails to detect communication with the standby OLT 104 and communication with the ONU 101, it should be determined to switch to the standby state.

[0059] For example, the optical fiber of the current primary OLT 103 is cut or pulled out. As a result, the underlying communication module of the primary OLT 103 fails to receive the P2P message from the standby OLT 104, triggering a PeerFail notification message. Moreover, the primary OLT 103 is unable to send control OMCI messages, such as authorized traffic or OMCI messages, to the ONU 101. Consequently, the FPGA of the primary OLT 103 also does not receive the optical signal from the ONU 101 within this first specified time window, triggering a PON_LOS notification message to the first PON protection decision module. Based on this, the first PON protection decision module of the primary OLT 103 can determine to switch the primary OLT 103 to the standby state.

[0060] 2) If, within the second specified time window, the standby OLT 104 fails to detect communication with the primary OLT 103 and fails to identify the interruption of the upstream optical signal of the ONU 101, it is determined not to perform a state switch.

[0061] For example, within the second specified time window, the underlying communication module of the standby OLT 104 fails to receive the P2P message from the primary OLT 103, triggering a PeerFail notification message. However, at this time, due to a fiber failure event of the primary OLT 103, the FPGA of the standby OLT 104 also fails to receive the upstream optical signal from the ONU 101, but does not correctly trigger a Light-Not-Seen optical signal interruption message to the second PON protection decision module. Based on this, the second PON protection decision module of the standby OLT 104 makes a decision not to switch.

[0062] If, within the first specified time window, the primary OLT 103 fails to detect communication with the standby OLT 104 and fails to identify the failure of communication with the ONU 101, it is determined not to perform a state switch.

[0063] For example, the optical fiber of the current primary OLT 103 is cut or pulled out. Therefore, within the specified time window, the underlying communication layer of the primary OLT 103 fails to receive the P2P message from the standby OLT 104, triggering a PeerFail notification message. However, since the FPGA of the primary OLT 103 fails to detect that the communication of the PON port has been disconnected, a PON_LOS notification message is not triggered within this first given time window. Based on this, the first PON protection decision module of the primary OLT 103 makes a decision not to switch.

[0064] 3) In the second specified time window, if the standby OLT 104 fails to detect communication with the primary OLT 103 and the optical signal from the ONU 101, it should be determined to switch to the primary state.

[0065] In the first specified time window, if the primary OLT 103 fails to detect communication with the standby OLT 104 and fails to identify the communication failure with the ONU 101, it is determined not to perform a state switch.

[0066] Obviously, at this time, there may seemingly be two primary OLTs in the PON system, resulting in a split-brain situation. However, this is not the actual case.

[0067] In the case where the optical fiber of the primary OLT 103 is disconnected / pulled out, the standby OLT 104 combines the PeerFail notification message and the Light-Not-Seen optical signal interruption message to know the failure of the peer OLT 103 and immediately changes to the primary state. When the optical fiber is pulled out or cut off, even if the PON protection decision module of the initial primary OLT 103 cannot receive the PON_LOS message on the primary OLT 103 and the PON port of the primary OLT 103 will erroneously remain active, due to the disconnection of the main PON optical fiber link, the authorized traffic or OMCI message of the ONU 101 is actually managed by the new primary PON. Once the internal communication link between the two OLTs is restored, the first PON protection decision module and the second PON protection decision module can re-determine the new primary node and secondary node based on this P2P communication, that is, at this time, the OLT 104 that actually provides services to the ONU 101 will be used as the primary node, and the initial primary node 103 will switch to the standby state.

[0068] Here, when the PON optical fiber link of the initial primary OLT 103 is restored from being cut off or pulled out, its FPGA will trigger a Light-Not-Seen optical signal interruption message to the first PON protection decision module. The first PON protection decision module knows that the PON port of the primary OLT 103 cannot send control OMCI packets to the ONU 101, so it can immediately switch the primary OLT 103 from the primary state to the standby state to prevent split-brain. Since the OLT 103 is in the situation of optical fiber disconnection / pullout when it decides not to perform a state switch, it actually cannot communicate with the ONU 101, so its primary state will not cause split-brain and affect the service to the ONU 101.

[0069] 4) In the second specified time window, if the standby OLT 104 fails to detect communication with the primary OLT 103 and fails to identify the interruption of the upstream optical signal of the ONU 101, it is determined not to perform a state switch.

[0070] In the first specified time window, if the primary OLT 103 fails to detect the communication between itself and the standby OLT 104 and the communication between itself and the ONU 101, it should be determined to switch to the standby state.

[0071] At this time, since both OLTs are in the standby state, although the PON protection system will not have a split-brain situation, no OLT provides services to the ONU. The embodiments of the present disclosure do not discuss such a situation.

[0072] Scenario 2: A fiber fault event occurs in the standby OLT 104

[0073] Here, the fiber fault event of the standby PON is, for example, that the optical fiber is cut or pulled out. At this time, the communication link between the primary OLT 103 and the standby OLT 104 is interrupted. The communication between the primary OLT 103 and the ONU 101 is not affected, but the standby OLT 104 cannot receive the upstream optical signal from the ONU 101.

[0074] 1) In the second specified time window, if the standby OLT 104 fails to detect the communication with the primary OLT 103 and the optical signal from the ONU 101, it should be determined to switch to the primary state.

[0075] For example, when the optical fiber of the current standby OLT 104 is cut or pulled out, within the second specified time window, the underlying communication module of the standby OLT 104 fails to receive the P2P message from the primary OLT 103, thereby triggering a PeerFail notification message, and the FPGA of the standby OLT 104 also fails to receive the upstream optical signal from the ONU 101, thereby triggering an optical signal interruption message of Light-Not-Seen. Accordingly, the second PON protection decision module of the standby OLT 104 can determine to switch the standby OLT 104 to the primary state.

[0076] In the first specified time window, if the primary OLT 103 fails to detect the communication with the standby OLT 104 but can detect the communication with the ONU 101, it is determined not to perform a state switch.

[0077] For example, in this first specified time window, if the underlying communication module of the active OLT 103 fails to receive the P2P message of the internal link with the standby OLT 104, it will trigger a PeerFail notification message to the first PON protection decision module. Moreover, the active OLT 103 can send a control OMCI message to the ONU 101, so that the FPGA of the active OLT 103 will not trigger a PON_LOS notification message. Accordingly, the first PON protection decision module of the active OLT 103 will not make a handover decision.

[0078] Obviously, at this time, there may seemingly be two active OLTs in the PON system, resulting in a split-brain situation. However, this is not the actual case.

[0079] In the case where the standby PON optical fiber is disconnected / pulled out, the FPGA of the standby OLT 104 will trigger a "Light-Not-Seen" optical signal interruption message, but this is not sufficient to constitute a handover condition. Instead, it is necessary to trigger a PeerFail notification message and a "Light-Not-Seen" optical signal interruption message within the second specified time window. That is, the connection failure of the internal link between the OLTs and the disconnection / pull-out of the standby PON optical fiber occur almost simultaneously (i.e., within the second specified time window). The occurrence of this situation has only a very small probability. Moreover, even if this situation occurs, once the disconnection / pull-out of the standby PON from the optical fiber is restored, it can resume internal link communication with the OLT 103, and the master node and the slave node can be quickly determined through P2P message exchange, that is, the OLT 104 will quickly switch back to the standby state, thus avoiding the occurrence of a split-brain situation. Since the OLT 104 is in a situation where the optical fiber is disconnected / pulled out when it decides to switch itself to the active state, it is actually unable to communicate with the ONU 101, so its active state will not cause a split-brain situation and affect the service of the ONU101.

[0080] 2) In the second specified time window, if the standby OLT 104 fails to detect the communication with the active OLT 103 and fails to identify the interruption of the upstream optical signal of the ONU 101, it is judged not to perform a state handover.

[0081] For example, within the second specified time window, the FPGA of the standby OLT 104 fails to receive the P2P message from the active OLT 103, thus triggering a PeerFail notification message. However, at this time, due to an optical fiber failure event of the standby OLT 104, the FPGA of the standby OLT 104 also fails to receive the upstream optical signal from the ONU 101, but the FPGA fails to correctly trigger the "Light-Not-Seen" optical signal interruption message. Accordingly, the second PON protection decision module of the standby OLT 104 makes a non-handover decision and remains in the standby state.

[0082] In the first specified time window, if the primary OLT 103 fails to detect communication with the standby OLT 104 but can detect communication with the ONU 101, it is determined that no state switch is to be performed.

[0083] Scenario 3: A node failure event occurs in the primary OLT 103

[0084] Here, a node failure event of the primary OLT 103 is, for example, that the node is restarted or removed. At this time, the communication link between the primary OLT 103 and the standby OLT 104 is interrupted, the communication between the primary OLT 103 and the ONU 101 is also interrupted, and the standby OLT 104 cannot receive the upstream optical signal from the ONU 101.

[0085] 1) In the second specified time window, if the standby OLT 104 fails to detect communication with the primary OLT 103 and the optical signal from the ONU 101, it should be determined to switch to the primary state.

[0086] For example, if the optical fiber of the current standby OLT 104 is cut or pulled out, within the second specified time window, the underlying communication module of the standby OLT 104 fails to receive the P2P message from the primary OLT 103, thus triggering a PeerFail notification message, and the FPGA of the standby OLT 104 also fails to receive the upstream optical signal from the ONU 101, thus triggering a Light-Not-Seen optical signal interruption message. Accordingly, the second PON protection decision module of the standby OLT 104 can determine to switch the standby OLT 104 to the primary state.

[0087] If the primary OLT 103 is restarted or removed, the primary OLT 103 cannot detect communication with the standby OLT 104 and its communication with the ONU 101. Further, if the primary OLT 103 is restarted, communication with the standby OLT 104 is restored after the restart and the state is switched to the standby state. If the primary OLT 103 is removed, it is unavailable.

[0088] 2) In the second specified time window, if the standby OLT 104 fails to detect communication with the primary OLT 103 and fails to identify the interruption of the upstream optical signal of the ONU 101, it is determined that no state switch is to be performed.

[0089] If the primary OLT 103 is restarted or removed, the primary OLT 103 cannot detect the communication with the standby OLT 104 and its communication with the ONU 101. Further, if the primary OLT 103 is restarted, the communication with the standby OLT 104 is restored after the restart and the state is switched to the standby state. If the primary OLT 103 is removed, it becomes unavailable.

[0090] At this time, there will also be a situation where both OLTs are in the standby state, which is not within the scope of discussion of the embodiments of the present disclosure.

[0091] Scenario 4: Node failure event occurs in the standby OLT 104

[0092] Here, the node failure event of the standby OLT 104 is, for example, that the node is restarted or removed. At this time, the communication link between the primary OLT 103 and the standby OLT 104 is interrupted, the communication between the primary OLT 103 and the ONU 101 is not affected, and the standby OLT 104 cannot receive the upstream optical signal from the ONU 101.

[0093] If the standby OLT 104 is restarted or removed, the standby OLT 104 cannot detect the communication with the primary OLT 103 and the optical signal from the ONU 101. Further, if the standby OLT 104 is restarted, the communication with the primary OLT 103 is restored after the restart and the state is switched to the standby state. If the standby OLT 104 is removed, it becomes unavailable.

[0094] In the first specified time window, if the primary OLT 103 fails to detect the communication with the standby OLT 104 but can detect the communication with the ONU 101, it is determined that no state switch is performed.

[0095] For example, in this first specified time window, if the underlying communication module of the primary OLT 103 fails to receive the P2P message of the internal link with the standby OLT 104, it will trigger a PeerFail notification message to the first PON protection decision module. And the primary OLT 103 can send a control OMCI message to the ONU 101, so that the FPGA of the primary OLT 103 does not trigger the PON_LOS notification message. Accordingly, the first PON protection decision module of the primary OLT 103 does not make a switching decision.

[0096] For Scenarios 3 and 4, due to the restart / removal of the primary / standby OLT, the respective PON protection decision modules will decide that the corresponding OLT should enter the standby state or maintain the initial state without knowing the status information of the peer OLT to prevent the split-brain problem. The new primary PON can serve all ONUs.

[0097] It should be noted that the embodiments of the present disclosure can be implemented in software and / or a combination of software and hardware. For example, an application-specific integrated circuit (ASIC), a general-purpose computer, or any other similar hardware device can be used to implement them. In one embodiment, the software programs of the embodiments of the present disclosure can be executed by a processor to implement the steps or functions described above. Similarly, the software programs (including related data structures) of the embodiments of the present disclosure can be stored in a computer-readable recording medium, such as a RAM memory, a magnetic or optical drive, or a floppy disk and similar devices. In addition, some steps or functions of the embodiments of the present disclosure can be implemented using hardware, for example, as a circuit that cooperates with the processor to execute each step or function.

[0098] In addition, at least a part of the embodiments of the present disclosure can be applied as a computer program product, such as computer program instructions. When executed by a computing device, through the operation of the computing device, the methods and / or technical solutions according to the embodiments of the present disclosure can be invoked or provided. The program instructions for invoking / providing the methods of the embodiments of the present disclosure may be stored in a fixed or removable recording medium, and / or transmitted through a data stream in a broadcast or other signal-bearing medium, and / or stored in the working memory of the computing device that runs according to the program instructions.

[0099] For those skilled in the art, it is obvious that the embodiments of the present disclosure are not limited to the details of the above-described exemplary embodiments, and without departing from the spirit or basic characteristics of the embodiments of the present disclosure, the embodiments of the present disclosure can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the embodiments of the present disclosure is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the embodiments of the present disclosure. Any reference signs in the claims should not be construed as limiting the claimed rights. In addition, obviously, the word "comprising" does not exclude other units or steps, and the singular does not exclude the plural. The multiple units or devices stated in the system claims can also be implemented by one unit or device through software or hardware. First, second, etc. are used to denote names and do not denote any particular order.

Claims

1. A method for OLT status switching in a dual-homed PON protection system, wherein, the dual-homed PON protection system includes a primary OLT and a standby OLT, and the configuration information of the ONUs has been synchronized on the two OLTs. Among them, the method includes the following steps: In a second specified time window, when the standby OLT fails to detect communication with the primary OLT and the optical signal from the ONU, the standby OLT switches to the primary state; wherein, the method further includes the following steps: wherein, a fiber failure event occurs in the primary OLT, In a first specified time window, when the primary OLT fails to detect communication with the standby OLT and communication with the ONU, the primary OLT switches to the standby state; or, In the first specified time window, when the primary OLT fails to detect communication with the standby OLT and fails to identify the communication failure with the ONU, the primary OLT does not perform a status switch; When the primary OLT recovers from its fiber failure event, the primary OLT switches to the standby state; wherein, a node failure event occurs in the primary OLT, When the primary OLT recovers from its node failure event, the primary OLT switches to the standby state.

2. The method according to claim 1, wherein, a fiber failure event occurs in the standby OLT, the method further includes the following steps: When the standby OLT recovers from its fiber failure event, the standby OLT switches back to the standby state again.

3. A system for OLT status switching in a dual-homed PON protection system, wherein, the dual-homed PON system includes a primary OLT and a standby OLT, and the configuration information of the ONUs has been synchronized on the two OLTs. Among them, the standby OLT is configured to: Detect communication with the primary OLT and the optical signal from the ONU according to a second specified time window to determine whether to perform a status switch; the primary OLT is configured to: Detect communication with the standby OLT and communication with the ONU according to a first specified time window to determine whether to perform a status switch.

4. The system according to claim 3, wherein, the standby OLT is further configured to: In the second specified time window, when the standby OLT fails to detect communication with the primary OLT and the optical signal from the ONU, switch to the primary state.

5. The system according to claim 4, wherein, a fiber failure event occurs in the standby OLT, the standby OLT is further configured to: When the standby OLT recovers from its fiber failure event, switch back to the standby state again.

6. The system according to claim 3 or 4, wherein, the primary OLT is further configured to: In the first specified time window, when the primary OLT fails to detect communication with the standby OLT and communication with the ONU, switch to the standby state.

7. The system according to claim 3 or 4, wherein, The primary OLT has a fiber failure event, and the primary OLT is further configured to: In the first specified time window, when the primary OLT fails to detect communication with the standby OLT and fails to identify communication failure with the ONU, no state switch is performed; The primary OLT is further configured to: when the primary OLT recovers from its fiber failure event, switch to the standby state.

8. A standby OLT for performing state switching in a dual-homed PON protection system, Wherein, The dual-homed PON system includes a primary OLT and the standby OLT, and the configuration information of the ONU has been synchronized on the two OLTs. Wherein, the standby OLT includes a processor and a memory, and computer-executable instructions are stored in the memory. When the computer-executable instructions are executed by the processor, the standby OLT is configured to: In the second specified time window, when the standby OLT fails to detect communication with the primary OLT and an optical signal from the ONU, switch to the primary state; Wherein, the primary OLT has a fiber failure event, In the first specified time window, when the primary OLT fails to detect communication with the standby OLT and communication with the ONU, the primary OLT switches to the standby state; Or, In the first specified time window, when the primary OLT fails to detect communication with the standby OLT and fails to identify communication failure with the ONU, the primary OLT does not perform a state switch; When the primary OLT recovers from its fiber failure event, the primary OLT switches to the standby state; Wherein, the primary OLT has a node failure event, When the primary OLT recovers from its node failure event, the primary OLT switches to the standby state.

9. The standby OLT according to claim 8, Wherein, The standby OLT has a fiber failure event, The standby OLT is further configured to: When the standby OLT recovers from its fiber failure event, switch back to the standby state again.

10. A primary OLT for performing state switching in a dual-homed PON protection system, Wherein, The dual-homed PON system includes the primary OLT and the standby OLT, and the configuration information of the ONU has been synchronized on the two OLTs. Wherein, the primary OLT includes a processor and a memory, and computer-executable instructions are stored in the memory. When the computer-executable instructions are executed by the processor, the primary OLT is configured to: In the first specified time window, when the primary OLT fails to detect communication with the standby OLT and communication with the ONU, switch to the standby state; Wherein, in the second specified time window, when the standby OLT fails to detect communication with the primary OLT and an optical signal from the ONU, the standby OLT switches to the primary state.

11. The primary OLT according to claim 10, Wherein, The primary OLT has a fiber failure event, and the primary OLT is further configured to: During the first specified time window, when the primary OLT fails to detect communication with the standby OLT and fails to identify communication failure with the ONU, no state switch is performed. When the primary OLT recovers from its optical fiber fault event, it switches to the standby state.

12. The primary OLT according to claim 10, wherein, a node fault event occurs to the primary OLT, the primary OLT is further configured to: when the primary OLT recovers from its node fault event, it switches to the standby state.

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