Station side optical line terminating device and information processing method

Abstract

A station-side optical line terminating device in a passive optical network according to one embodiment comprises: a communication control unit that transmits a DiscoveryGate during a ranging window and performs P2MP discovery that establishes a link with an unlinked optical line terminating device; an error detection unit that determines whether to detect a bit error in communication after the ranging window; and a ranging window control unit that changes the configuration of the next ranging window when it is determined that a bit error has been detected.

Description

Optical line terminal and information processing method

[0001] The present invention relates to an optical line terminal and an information processing method.

[0002] In general, an optical subscriber network called a passive optical network (PON) is configured such that an ONU (Optical Network Unit) is provided for each of a large number of subscribers as a subscriber-side optical line terminal, and these ONUs are connected to an OLT (Optical Line Terminal) as a central office-side optical line terminal located in a corresponding regional equipment center, and then connected to a higher-level network from the OLT.

[0003] For example, in a PON, it is necessary to reserve a time slot (ranging window) during which data cannot be transmitted, exclusively for processing when a link is established (see, for example, Non-Patent Document 1).

[0004] "Technical Basics Course: GE-PON Technology," NTT Technical Journal, pp. 91-94, September 2005

[0005] Generally, the link establishment distance and the ranging window are proportional to each other, so extending the link establishment distance reduces data transfer efficiency. Therefore, when establishing a long-distance link, there is a problem of reduced transmission efficiency.

[0006] The present invention has been made in light of the above circumstances, and its object is to propose a technique that can establish a long-distance link while maintaining transmission efficiency.

[0007] In order to solve the above problem, one embodiment of the present invention provides a station-side optical line terminal in a passive optical network, which includes a communication control unit that transmits a Discovery Gate during a ranging window and performs P2MP discovery to establish a link with an unlinked optical line terminal, an error detection unit that determines whether a bit error is detected in communication after the ranging window, and a ranging window control unit that changes the setting of the next ranging window when it is determined that the bit error has been detected.

[0008] According to one aspect of the present invention, a technique is provided that can establish a long-distance link while maintaining transmission efficiency.

[0009] Fig. 1 is a diagram illustrating a schematic diagram of a communication system according to an embodiment of the present invention. Fig. 2 is a block diagram illustrating an example of the hardware and software configurations of an OLT and an ONU according to an embodiment of the present invention. Fig. 3 is a flowchart illustrating an example of the processing operation of an OLT, which is an information processing device according to an embodiment of the present invention. Fig. 4 is a diagram illustrating the operations of steps ST101 to ST103 as a sequence diagram.

[0010] Hereinafter, the optical line terminal and the information processing method will be described in detail with reference to the drawings. In the following embodiments, parts with the same numbers perform the same operations, and redundant description will be omitted. For example, when there are multiple identical or similar elements, a common symbol may be used to describe each element without distinguishing between them, or a subnumber may be used in addition to the common symbol to describe each element with distinction between them.

[0011] [Embodiment] (Configuration) Fig. 1 is a diagram that schematically illustrates a communication system according to an embodiment of the present invention. The communication system 100 illustrated in Fig. 1 includes a passive optical network (PON) 3 and an upper network 4. The upper network 4 may include, for example, the Internet. Herein, the terms "system" and "network" may be used interchangeably.

[0012] The PON 3 is a point-to-multipoint optical access network. The PON 3 includes an optical line terminal (OLT) 1 as a central office-side optical line terminal and an optical network unit (ONU) 2 as a subscriber-side optical line terminal. For example, the OLT 1 ​​is located in the facilities of a service provider such as a telecommunications carrier, and the ONU 2 is located in the facilities of a subscriber (e.g., a home or office building).

[0013] The OLT 1 ​​is connected to a plurality of ONUs 2 via optical fiber cables in an optical distribution network (ODN) and an optical splitter 31, which is a passive element. An optical signal transmitted by the OLT 1 ​​is split by the optical splitter 31 and reaches each ONU 2. The optical splitter 31 is further configured to combine optical signals transmitted from each ONU 2 and transmit the combined optical signals to the OLT 1.

[0014] The OLT 1 ​​is connected to an upper network 4 via an optical fiber cable. The OLT 1 ​​relays communications between a plurality of ONUs 2 and the upper network 4. Specifically, the OLT 1 ​​transfers data from a plurality of ONUs 2 to the upper network 4. The OLT 1 ​​also transfers data from the upper network 4 to the ONUs 2.

[0015] In one embodiment, optical communication is used for communication between the OLT 1 ​​and the upper network 4. In another embodiment, electrical communication may be used for communication between the OLT 1 ​​and the upper network 4.

[0016] Each of the multiple ONUs 2 is connected to a user network. The user network includes user terminals such as personal computers (PCs) and smartphones. The ONUs 2 relay communications between the user network and the OLT 1. Specifically, the ONUs 2 transfer data from the OLT 1 ​​to the user network. The ONUs 2 also transfer data from the user network to the OLT 1.

[0017] For example, when ONU 2 is connected to PON 3, OLT 1 ​​performs P2MP discovery. For example, P2MP discovery automatically finds the ONU 2 and assigns a logical link ID (LLID) that identifies the ONU 2 to the ONU 2, automatically establishing a communication link. P2MP discovery is performed during a ranging window. Note that the ranging window is a time slot during which P2MP discovery is performed and is a period during which linked ONU 2 cannot transmit data.

[0018] In P2MP discovery, when establishing a link between the OLT 1 ​​and an unlinked ONU 2, the OLT 1 ​​measures the distance based on the transmission and reception time of a control signal. If the distance between the OLT 1 ​​and the unlinked ONU 2 exceeds a predetermined distance, the transmission and reception of the control signal may not be completed within the ranging window. In such a case, during the user data communication time after the ranging window, the control signal transmitted by the unlinked ONU 2 collides with the user data transmitted by the linked ONU 2. Therefore, in one embodiment, the OLT 1 ​​changes the setting of the ranging window if there is an unlinked ONU 2 whose control signal collides with other user data. Details of the setting of the ranging window will be described later.

[0019] 2 is a block diagram showing an example of the hardware and software configurations of the OLT 1 ​​and the ONU 2 according to an embodiment of the present invention. First, the details of the hardware and software configurations of the OLT 1 ​​will be described.

[0020] 2, the OLT 1 ​​includes a control unit 11, a program storage unit 12, a data storage unit 13, a subscriber-side communication interface 14, and a higher-level communication interface 15. The OLT 1 ​​is made up of one or more computers.

[0021] The control unit 11 controls the OLT 1. The control unit 11 includes a hardware processor such as a central processing unit (CPU).

[0022] The program storage unit 12 is configured by combining, for example, a nonvolatile memory such as a solid-state drive (SSD) as a storage medium that can be written to and read from at any time, and a nonvolatile memory such as a read-only memory (ROM), and stores middleware such as an operating system (OS), as well as application programs required to execute various control processes according to an embodiment. Hereinafter, the OS and each application program will be collectively referred to as the program.

[0023] The data storage unit 13 may be, for example, a combination of a nonvolatile memory such as an SSD that can be written to and read from at any time, and a volatile memory such as a RAM (Random Access Memory), as a storage medium.

[0024] The subscriber-side communication interface 14 is an interface for communicating with the ONUs 2. For example, the subscriber-side communication interface 14 has multiple processes for communicating with multiple ONUs 2. Under the control of the control unit 11, the subscriber-side communication interface 14 sets up communication sessions with the multiple ONUs 2 and transmits and receives various information to and from the ONUs 2.

[0025] The upper communication interface 15 is an interface for communicating with the upper network 4. For example, the upper communication interface 15 transmits and receives various information to and from server devices and terminal devices connected to the upper network 4 in accordance with a communication protocol defined in the upper network 4, such as TCP / IP.

[0026] The control unit 11 includes, as processing functions necessary for executing various processes according to an embodiment of the present invention, a communication control unit 111, an error detection unit 112, and a ranging window control unit 113. The processes performed by the communication control unit 111, the error detection unit 112, and the ranging window control unit 113 are all realized by causing the CPU to execute programs stored in the program storage unit 12.

[0027] The communication control unit 111 is a control unit that controls communication with the ONU 2. For example, the communication control unit 111 performs a P2MP discovery operation. The communication control unit 111 reads information stored in a ranging window information storage unit 131, which will be described later. Then, the communication control unit 111 performs P2MP discovery within the read ranging window. Here, P2MP discovery includes transmitting a Discovery Gate that notifies transmission timing to at least unregistered (unlinked) ONU 2.

[0028] The error detection unit 112 is a detection unit that detects reception errors. For example, the error detection unit 112 determines whether or not a bit error is detected during the user data communication time after the ranging window. If a bit error is detected, the error detection unit 112 determines that a reception error has been detected. On the other hand, if no bit error is detected, the error detection unit 112 determines that a reception error has not been detected.

[0029] The ranging window control unit 113 is a control unit that controls the setting of the ranging window. For example, the ranging window control unit 113 controls the ranging window of a predetermined length to be expanded or shifted.

[0030] To realize one embodiment of the present invention, data storage unit 13 includes ranging window information storage unit 131. Ranging window information storage unit 131 is used to store information such as the length of the ranging window. Typically, the length of the ranging window is a predetermined length. However, when ranging window control unit 113 adjusts the length of the ranging window, ranging window information storage unit 131 stores the adjusted length of the ranging window.

[0031] Next, the hardware and software configurations of the ONU 2 will be described in detail.

[0032] 2, the ONU 2 includes a control unit 21, a program storage unit 22, a data storage unit 23, and a station-side communication interface 24. The ONU 2 is made up of one or more computers.

[0033] The control unit 21 controls the ONU 2. The control unit 21 includes a hardware processor such as a central processing unit (CPU).

[0034] The program storage unit 22 is configured by combining, for example, a nonvolatile memory such as an SSD as a storage medium that can be written to and read from at any time, and a nonvolatile memory such as a ROM, and stores middleware such as an OS as well as application programs required to execute various control processes according to an embodiment. Hereinafter, the OS and each application program will be collectively referred to as a program.

[0035] The data storage unit 23 may be, for example, a combination of a nonvolatile memory such as an SSD that can be written to and read from as needed, and a volatile memory such as a RAM, as a storage medium.

[0036] The station-side communication interface 24 is an interface for communicating with the OLT 1. For example, under the control of the control unit 21, the station-side communication interface 24 sets up a communication session with the OLT 1 ​​and transmits and receives various information to and from the OLT 1.

[0037] Although not shown in FIG. 2, the ONU 2 may also be provided with a user terminal side communication interface that is capable of transmitting and receiving various types of information to and from a user terminal connected via a user network.

[0038] The control unit 21 includes a communication control unit 211 as a processing function required for executing various processes according to an embodiment of the present invention. The processes by the communication control unit 211 are realized by causing the CPU to execute the programs stored in the program storage unit 22.

[0039] The communication control unit 211 is a control unit that controls communication with the OLT 1. For example, the communication control unit 211 receives a Discovery Gate transmitted from the OLT 1, and generates a Register Request in response to the reception. Then, the communication control unit 211 transmits the generated Request Request to the OLT 1. The communication control unit 211 may also perform control so that user data is transmitted to the OLT 1 ​​during user data communication time.

[0040] In order to realize one embodiment of the present invention, the data storage unit 23 includes an acquired information storage unit 231. The acquired information storage unit 231 is used to store information acquired through various communications with the OLT 1.

[0041] 3 is a flowchart showing an example of the processing operation of the OLT 1, which is an information processing device according to one embodiment of the present invention. For example, the control unit 11 of the OLT 1 ​​reads and executes a program stored in the program storage unit 12, thereby realizing the operation of this sequence. This flowchart is started when the power supply of the OLT 1 ​​is turned on or by an instruction from an administrator who manages the OLT 1.

[0042] In step ST101, the communication control unit 111 performs a P2MP discovery operation. For example, the communication control unit 111 reads information stored in the ranging window information storage unit 131. Then, within the read ranging window, the communication control unit 111 transmits a Discovery Gate to the unregistered (unlinked) ONU 2 to notify it of the transmission timing. Furthermore, upon receiving the Discovery Gate, the communication control unit 211 of the unlinked ONU 2 generates a Register Request requesting registration. Then, the communication control unit 211 transmits the generated Register Request to the OLT 1.

[0043] For example, if there is no unlinked ONU 2, a Discovery Gate will not be received. Therefore, P2MP discovery includes transmitting a Discovery Gate at least during the ranging window. Note that P2MP discovery may include a Register transmitted by the communication control unit 111 of the OLT 1 ​​to notify the unlinked ONU 2 of registration (including, for example, an LLID), a GATE transmitted by the communication control unit 111 to notify the transmission band and transmission timing, and a Register ACK transmitted by the communication control unit 211 of the unlinked ONU 2 as a reception response to the Register.

[0044] In step ST102, the error detection unit 112 determines whether a reception error has been detected. If there is an unlinked ONU 2 that is farther away than the predetermined distance, the communication control unit 111 does not receive a Register Request during the ranging window. For example, the communication control unit 111 receives a Register Request within the user data communication time after the ranging window. In this case, the user data transmitted by the linked ONU 2 collides with the Register Request. In such a case, the error detection unit 112 detects a bit error. That is, the error detection unit 112 determines whether a bit error has been detected in the communication after the ranging window (user data communication time). If a bit error has been detected, the error detection unit 112 outputs a signal indicating that a bit error has been detected to the ranging window control unit 113. Then, the process proceeds to step ST103. On the other hand, if it is determined that a bit error has not been detected, the error detection unit 112 outputs a signal indicating that a bit error has not been detected to the ranging window control unit 113. Then, the process proceeds to step ST105.

[0045] In step ST103, the ranging window control unit 113 sets the ranging window to be expanded. The ranging window control unit 113 changes the setting of the next ranging window. For example, the ranging window control unit 113 expands the next ranging window. Alternatively, the ranging window control unit 113 may shift the ranging window. For example, the ranging window control unit 113 calculates the round trip time (RTT) from the time from the transmission of the Discovery Gate to the reception of the Register Request in which a bit error was detected, and measures the distance to the unlinked ONU 2. The ranging window control unit 113 then expands or shifts the ranging window to include the period in which the bit error was detected. This makes it possible to receive a Register Request transmitted from an unlinked ONU 2 that is farther than a predetermined distance within the ranging window. The ranging window control unit 113 stores information about the set (i.e., expanded or shifted) ranging window in the ranging window information storage unit 131. Then, the process returns to step ST101.

[0046] The ranging window in P2MP discovery performed after returning to step ST101 is a ranging window that is expanded from a predetermined length (original length) or a ranging window that is shifted to a predetermined length. Note that when the ranging window is shifted, the transmission of the Discovery Gate does not have to be within the ranging window.

[0047] 4 is a sequence diagram showing the operations of steps ST101 to ST103. In the example of FIG. 4, it is assumed that there are linked ONU 201, unlinked ONU 202, and unlinked ONU 203. It is assumed that unlinked ONU 202 is within a predetermined distance from OLT 1, and unlinked ONU 203 is farther away from OLT 1 ​​than the predetermined distance.

[0048] As shown in Figure 4, the communication control unit 111 transmits a Discovery Gate to the unlinked ONU 202 and the unlinked ONU 203. The Register Request transmitted by the unlinked ONU 202, which is within a predetermined distance from the OLT 1, is received within the ranging window. On the other hand, the Register Request transmitted by the unlinked ONU 203, which is farther away from the OLT 1 ​​than the predetermined distance, is received during the user data communication time after the ranging window. As a result, the Register Request collides with the user data transmitted from the linked ONU 201.

[0049] Therefore, if a collision occurs, that is, if a bit error is detected, the ranging window control unit 113 expands or shifts the next ranging window. This allows the communication control unit 111 to receive the Register Request sent by the unlinked ONU 203 within the expanded or shifted ranging window. As a result, the user data sent by the linked ONU 201 and the RegisterRegister do not collide.

[0050] In step ST104, the communication control unit 111 determines whether or not a Register Request has been received. The communication control unit 111 determines whether or not a Register Request has been received when P2MP discovery is performed. If it is determined that a Register Request has been received, an unlinked ONU 2 exists, and the process returns to step ST101. On the other hand, if it is determined that a Register Request has not been received, that is, if an unlinked ONU 2 does not exist, the communication control unit 111 outputs a signal indicating that a Register Request has not been received to the ranging window control unit 113. Then, the process proceeds to step ST105.

[0051] In step ST105, ranging window control unit 113 sets the ranging window to its original length, i.e., a ranging window of a predetermined length. If ranging window control unit 113 does not receive a Register Request, it controls the ranging window to return to its original length. For example, ranging window control unit 113 sets the length of the ranging window stored in ranging window information storage unit 131 to the predetermined length. Then, the processing returns to step ST101.

[0052] By returning the ranging window to its original length, the ranging window is expanded or shifted only when establishing a link with an ONU 2 that is farther away from the OLT 1 ​​than a predetermined distance, and after the link is established, the ranging window is returned to its original length, thereby lengthening the user data communication time, thereby improving the transmission efficiency in the PON 3.

[0053] This flowchart ends when the power supply to the OLT 1 ​​is turned off or when an instruction is given by the administrator of the OLT 1.

[0054] (Effects of the embodiment) According to one embodiment, if an error is detected in communication after the ranging window, the OLT 1 ​​changes the setting of the next ranging window. That is, the ranging window control unit 113 controls to expand or shift the ranging window. Furthermore, if no bit error is detected and no Register Request is received from the unlinked ONU 2, the ranging window control unit 113 controls to return the ranging window to its original length. Through these controls, the OLT 1 ​​can establish a link with the unlinked ONU 2 over a long distance while maintaining transmission efficiency.

[0055] [Other Embodiments] Note that the present invention is not limited to the above-described embodiment. For example, ranging window control unit 113 may expand and further shift the ranging window. Furthermore, if a Register Request is not received when the ranging window has a predetermined length, ranging window control unit 113 may control the ranging window to be reduced.

[0056] The flow of each process described above is not limited to the procedures described, and the order of some steps may be changed, or some steps may be performed simultaneously in parallel. Furthermore, the series of processes described above do not need to be performed consecutively, and each step may be performed at any timing.

[0057] Furthermore, the techniques described in the above embodiments can be stored as a program (software means) that can be executed by a computer on a storage medium such as a magnetic disk (e.g., a floppy disk, a hard disk, etc.), an optical disk (e.g., a CD-ROM, a DVD, an MO, etc.), or a semiconductor memory (e.g., a ROM, a RAM, a flash memory, etc.), and can also be distributed by transmitting it via a communication medium. The program stored on the medium also includes a configuration program that configures the software means (including not only execution programs but also tables and data structures) that the computer executes. The computer that realizes this device loads the program stored on the storage medium and, in some cases, configures the software means using the configuration program, and executes the above-mentioned processing by controlling the operation of this software means. Note that the term "storage medium" as used herein is not limited to storage media for distribution, but also includes storage media such as magnetic disks and semiconductor memories installed inside the computer or in devices connected via a network.

[0058] In short, this invention is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the spirit of the invention. Furthermore, the embodiments may be implemented in combination as appropriate as possible, and in such cases, the combined effects can be obtained. Furthermore, the above-described embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining the disclosed multiple constituent elements.

[0059] REFERENCE SIGNS LIST 100...communication system 1...OLT 11...controller 111...communication controller 112...error detector 113...ranging window controller 12...program memory 13...data memory 131...ranging window information memory 14...subscriber-side communication interface 15...higher-level communication interface 2...ONU 21...controller 211...communication controller 22...program memory 23...data memory 231...acquired information memory 24...station-side communication interface 3...optical receiving network 31...optical splitter 4...higher-level network

Claims

1. A station-side optical line terminal in a passive optical network, comprising: a communication control unit that transmits a DiscoveryGate during a ranging window and performs P2MP discovery to establish a link with an unlinked optical line terminal; an error detection unit that determines whether a bit error is detected in communication after the ranging window; and a ranging window control unit that changes the setting of the next ranging window when it determines that the bit error has been detected.

2. The optical line terminal according to claim 1, wherein the ranging window control unit controls the next ranging window to be expanded or shifted.

3. The optical line terminal of claim 1, wherein the error detection unit determines that the bit error has been detected by receiving a Register Request from the unlinked optical line terminal in response to the transmission of the Discovery Gate after the ranging window, and when it determines that the bit error has not been detected and does not receive the Register Request, the ranging window control unit sets the next ranging window to a ranging window of a predetermined length.

4. An information processing method executed by a processor of a central office optical line terminal in a passive optical network, comprising: transmitting a DiscoveryGate during a ranging window and performing P2MP discovery to establish a link with an unlinked optical line terminal; determining whether a bit error is detected in communication after the ranging window; and changing the settings of the next ranging window if it is determined that the bit error is detected.

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