JP2013017129A - Optical communication system, optical communication device, and communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure correct data transmission from a downstream device to an upstream device if an erroneous optical emission signal is generated at the downstream device because of sleep control.SOLUTION: In an optical communication system including an upstream device and at least first and second downstream devices which communicate with the upstream device with optical signals, the upstream device comprises: a processing unit for transmitting a transmission grant message to each downstream device; a sleep control unit for transmitting a sleep instruction message and a sleep cancellation message to the second downstream device; and an error detection unit for detecting an erroneous section of data received from the first downstream device. If an erroneous section is detected after the sleep control unit transmits a sleep instruction message or a sleep cancellation message, the processing unit of the upstream device transmits a retransmission grant message for controlling the first downstream device to retransmit at least data corresponding to the erroneous section.

Description

  The present invention relates to an optical communication system, a communication device, and a communication method.

  Introduction of an optical network or an optical communication system has been attempted in order to cope with high speed and wide bandwidth of a communication network. In a passive optical network system (Passive Optical Network: hereinafter referred to as PON), one optical transmission line termination device (hereinafter referred to as OLT) includes a plurality of optical fibers and a plurality of optical splitters that branch the optical fiber through an optical splitter. A star type point-to-multipoint optical network is formed with an optical network unit (hereinafter referred to as ONU). As typical PON standards, EPON (Ethernet (registered trademark) PON) standardized by IEEE 802.3, ITU-T G. There is GPON (Gigabit Capable PON) standardized in 984.

  In PON, an upstream frame (packet) transmitted from the ONU (lower apparatus) to the OLT (upper apparatus) and a downstream frame (packet) transmitted from the OLT to the ONU are wavelength division multiplexed (Wave Division Multiplexing). : Hereinafter referred to as WDM). For the downstream frame, the same data is transmitted from the OLT to all ONUs connected by optical fibers. The ONU that has received the data refers to the destination information included in the signal, discards frames other than that addressed to itself, and transfers only the data addressed to itself to the user side. On the other hand, the uplink frame performs communication multiplexed by time division multiplexing (hereinafter referred to as TDMA) in which the ONU outputs data at a specified time in accordance with transmission permission from the OLT.

  In addition, regarding the improvement of the communication speed of PON, a system that handles a low-speed signal such as 64 kbit / s, a BPON (Broadband PON) that transmits / receives a fixed-length ATM cell at a maximum of about 600 Mbit /, and a variable-length frame of Ethernet at a maximum of about 1 Gbit. The introduction of EPON that transmits / receives at a rate of G / sec or GPON that handles higher-speed signals of about 2.4 Gbit / sec is underway. Further, in the future, it is required to realize a high-speed PON capable of handling signals of 10 Gbit / second to 40 Gbit / second.

  As the communication speed of the PON increases, the power consumption of the relay device on the transmission path tends to increase. A large number of ONUs as relay devices are installed on the network because they are installed at the subscriber's home. On the other hand, the ONU requires less bandwidth than the OLT or the upper switch group. Therefore, the ONU is left while using wasted power even when not communicating.

  From this situation, a request for power saving of the ONU is increased, and a system and a protocol for performing sleep control as power saving control for the ONU have been proposed (for example, see Non-Patent Document 1).

Kuroda, “Examination of next-generation PON power saving by sleep mode”, Proceedings of the IEICE General Conference, IEICE 2010_Communications (2), March 2010, p. 292

  However, in the sleep control, when the ONU returns from the sleep state (sleep mode), or when the ONU shifts to the sleep state, the power supply to the optical signal transmission circuit is started or stopped. There is a possibility that a signal (hereinafter referred to as an erroneous light emission signal) is generated. Specifically, when an ONU that is in a sleep state is activated by OLT, there is a transient period in which power supply to the optical signal transmission unit of the ONU starts. When an ONU in a normal state shifts to a sleep state by OLT, there is a transient period in which power supply to the optical signal transmission unit of the ONU is stopped. During these transient periods, the state of the optical signal transmission unit becomes unstable due to steep voltage fluctuations, and erroneous light emission may occur. As a result, an erroneous light emission signal interferes with an upstream signal of another ONU that is not subject to sleep control, and in this upstream signal, a frame loss in which a frame (packet) is not accurately transmitted from the ONU (lower device) to the OLT (higher device). There is a risk of generating (packet loss).

  Therefore, the risk of generating a frame loss increases with the introduction of sleep control, and this risk is further increased by a request for shortening the time required for activation from the sleep state. However, at present, there is no risk of the erroneous light emission signal interfering with an upstream signal of another ONU that is not subject to sleep control due to sleep control, and a countermeasure for frame loss is not disclosed.

  An object of the present invention is to ensure accurate data transmission from a lower level device to a higher level device when an erroneous light emission signal is generated from the lower level device by sleep control executed by the higher level device.

  A typical example of the present invention is as follows. That is, an optical communication system including a host device that communicates with a host network and at least first and second slave devices that communicate with the host device using optical signals, wherein the host device is the first slave device. A processing unit that transmits a transmission permission notification for setting a time for transmitting data to the higher-level device to each of the device and the second lower-level device; and the second lower-level device transmits data to the higher-level device. A sleep setting notification for shifting to a sleep state for stopping transmission and a sleep release notification for returning from the sleep state to the second lower-level device and the first lower-level device An error detection unit that detects an error interval in which an error has occurred in the data, and the error after the sleep control unit transmits a sleep setting notification or a sleep release notification When an interval is detected, the processing unit of the higher-level device transmits a retransmission permission notification for causing the first lower-level device to retransmit data corresponding to at least the error interval, and The subordinate apparatus is an optical communication system characterized by retransmitting at least data corresponding to the error section in response to the retransmission permission notification.

  According to the embodiment of the present invention, when a lower-level device shifts to the sleep state or returns from the sleep state, an unintended erroneous light emission occurs from this lower-level device, and data transmitted from another lower-level device to the higher-level device is erroneous. Even if this occurs, accurate data transmission from the lower apparatus to the upper apparatus can be ensured by retransmitting at least the data in the erroneous section.

It is a block diagram which shows the structure of the optical access network containing PON. It is a block diagram which shows the structure of OLT as a high-order apparatus. It is a block diagram which shows the structure of ONU as a low-order apparatus. It is a sequence diagram which shows the normal operation | movement of PON. It is a flowchart which shows the return operation | movement from a sleep state. It is a flowchart which shows the transfer operation | movement to a sleep state. It is a sequence diagram which shows an example of operation | movement of PON when ONU returns from a sleep state. It is a sequence diagram which shows an example of operation | movement of PON when ONU transfers to a sleep state. 3 is a flowchart illustrating retransmission control according to the first embodiment. (A) It is a time chart which illustrates the normal optical output signal from ONU. (B) It is a time chart which illustrates the erroneous light emission signal from ONU. (C) It is a time chart which illustrates the optical input signal to OLT. (A) It is a figure which shows the flame | frame stored in the transmission buffer part for resending before the resending request | requirement. (B) It is a figure which shows the flame | frame retransmitted from ONU to OLT. It is a sequence diagram which shows an example of the operation | movement of PON when a frame is retransmitted. It is a schematic diagram of the MAC frame which concerns on 2nd embodiment. It is a figure which shows the 8B / 10B code conversion table which concerns on 3rd embodiment. It is a figure which shows the flame | frame stored in the transmission buffer part for resending in 3rd embodiment.

  FIG. 1 is a block diagram showing a configuration of an optical access network according to each embodiment described later. The optical access network 1 is connected to a public communication network, which is a higher-level communication network, via a PON (passive optical network system) 10, for example, and transmits and receives data. For example, the public communication network is PSTN / Internet 20 (hereinafter may be referred to as an upper network). The PON 10 as an optical communication system includes an optical splitter 120, a trunk optical fiber 130, a branch optical fiber 140, an OLT 100 (optical transmission line termination device), and a plurality of ONUs 110 (optical line termination devices). The ONU 110 communicates by connecting to a subscriber terminal (telephone (TEL) 180, PC 190, etc.). The OLT 100 and each ONU 110 transmit and receive optical signals to and from each other via the trunk optical fiber 130, the optical splitter 120, and the branch optical fiber 140. Thereby, communication between the higher level network 20 and the subscriber terminals or communication between the subscriber terminals is performed. The ONU 110 is an example of a lower apparatus (or lower optical communication apparatus) that performs optical communication with the OLT 100 as an upper apparatus (or upper optical communication apparatus), and is not limited thereto.

  A plurality of (n, for example, 32, etc.) ONUs 110 can be connected to the OLT 100 via a single trunk optical fiber 130, an optical splitter 120, and a branch optical fiber 140. FIG. 1 shows five ONUs 110 (n = 5) as an example, and the fiber lengths from the OLT 100 to each ONU 110 are different. In FIG. 1, the fiber length from the OLT 100 to the ONU 110-1 is 1 km, the fiber length from the OLT 100 to the ONU 110-2 is 10 km, the fiber length from the OLT 100 to the ONU 110-3 is 20 km, and the fiber length from the OLT 100 to the ONU 110-4 is The fiber length from OLT100 to ONU110-n is 15 km. In FIG. 1, the parenthesis (xxKm) under each ONU 110 indicates the fiber length between the OLT and the ONU.

  For the downstream frame 150, the same data is transmitted from the OLT 100 to all ONUs connected by optical fibers. The ONU 110 that has received the data refers to the destination information included in the signal, discards frames other than the frame addressed to itself, and transfers only the data addressed to itself to the terminal side. On the other hand, for the upstream frames 160 and 170, the ONU 110 performs communication multiplexed by time division multiplexing (hereinafter referred to as TDMA) in which data is output at the time specified by the transmission permission notification from the OLT 100. .

  In each embodiment, when a description common to all of the ONUs 110-1, 110-2,..., 110-n is given, these are collectively referred to as ONUs 110. The same applies to the branch optical fiber 140, the upstream frame 170, the telephone 180, and the PC 190.

  FIG. 2 is a block diagram showing a configuration of the OLT 100 according to each embodiment.

  The OLT 100 includes an electrical transmission / reception unit (first interface unit) 200, an electrical / optical conversion unit (second interface unit) 210, an access control unit 220, a control unit 230, and a reception buffer unit (first reception buffer unit). 270, a retransmission reception buffer unit (second reception buffer unit) 271, and a reception power detection unit 290. The electric side transmitting / receiving unit 200 communicates with the relay device on the upper network 20 side by an electric signal. The electrical / optical converter 210 communicates with the ONU using optical signals. The access control unit 220 controls data communication in the normal state (non-sleep state) and sleep state of the ONU. The control unit 230 controls each unit in the OLT 100. The reception buffer unit 270 and the retransmission reception buffer unit 271 temporarily store the upstream frame (or data) transmitted from the ONU. The reception power detection unit 290 detects the reception power of the upstream optical signal for each ONU. The control unit 230 controls each unit according to the detection value of the reception power for each ONU.

  The electrical transmission / reception unit 200 and the electrical / optical conversion unit 210 are configured by an electric circuit, and the reception buffer unit 270 and the retransmission reception buffer unit 271 are configured by a memory such as a DRAM or a memory area. For example, the access control unit 220 may include an arithmetic processing circuit such as an FPGA or an ASIC, or a microcomputer provided with a CPU (Central Processing Unit) and a memory. The reception power detection unit 290 includes an optical sensor such as a photodiode.

  The control unit 230 includes a sleep control unit 240, a grant processing unit 250, an error detection unit 260, and a buffer control unit 280. The sleep control unit 240 executes sleep control. Here, the sleep control includes shifting the ONU from the normal state (normal mode) to the sleep state (sleep mode) and returning the ONU from the sleep state to the normal state. The grant processing unit 250 functions as a dynamic bandwidth allocating unit, sets a transmission permission time for each ONU, and sends a transmission permission notification (transmission permission signal) that gives permission to each ONU to transmit. The error detection unit 260 detects an error (bit error or the like) in the upstream frame (data) sent from the ONU. The buffer control unit 280 controls the reception buffer unit 270 and the retransmission reception buffer unit 271. Each unit (or the entire control unit 230) of the sleep control unit 240, the grant processing unit 250, the error detection unit 260, and the buffer control unit 280 is an arithmetic processing circuit such as an FPGA or an ASIC, or a CPU (central processing unit). You may comprise from the microcomputer provided with memory.

  When the upstream frame is received by the electrical / optical converter 210, the access controller 220 passes the MAC address of the upstream frame and the identification information of the transmission source ONU assigned to the preamble part of the upstream frame. The information is stored in association with the information, and the uplink frame is transmitted via the electrical transmission / reception unit 200. When the downlink frame is received by the electrical transmission / reception unit 200, the access control unit 220 refers to the MAC address of the downlink frame, and transmits the ONU identification information of the transmission destination to the preamble unit of the downlink frame from the route information held in advance. To be transmitted from the electrical / optical conversion unit 210. The access control unit 220 holds such a switching function.

  FIG. 3 is a block diagram showing a configuration of the ONU 110 according to each embodiment.

  The ONU 110 includes an electrical / optical conversion unit 300, an access control unit 310, a queue buffer unit 320, a queue buffer management unit 330, an electrical transmission / reception unit 340, a control unit 350, and a power source 390. The electrical / optical conversion unit 300 communicates with the OLT 100 by an optical signal. In addition, the electrical / optical conversion unit 300 may include a switch 300a that enables or disables (on or off) power supply from the power source 390. The access control unit 310 controls data communication in a normal state (non-sleep state) and a sleep state of the ONU 110. The queue buffer unit 320 stores frames and traffic data. The queue buffer management unit 330 manages the state of the queue buffer unit 320. The electric side transmitting / receiving unit 340 communicates with a subscriber's terminal or the like by an electric signal. The control unit 350 controls each unit and functional block in the ONU 110. The power source 390 supplies power into the ONU 110.

  The electrical / optical conversion unit 300 and the electrical side transmission / reception unit 340 are configured by an electric circuit, and the queue buffer unit 320 is configured by a memory such as a DRAM or a memory area. For example, the access control unit 310 and the queue buffer management unit 330 may be configured by an arithmetic processing circuit such as an FPGA or an ASIC, or a microcomputer including a CPU (Central Processing Unit) and a memory.

  The control unit 350 includes a sleep control unit 360, a retransmission transmission buffer unit 370, and a grant processing unit 380. For example, the sleep control unit 360 and the grant processing unit 380 (or all of them) may be configured by an arithmetic processing circuit such as an FPGA or an ASIC, or a microcomputer provided with a CPU (Central Processing Unit). The retransmission transmission buffer unit 370 includes a memory such as a DRAM or a memory area.

  The retransmission transmission buffer unit 370 temporarily accumulates and stores uplink frames (or data) to be retransmitted before requesting retransmission. Specifically, the retransmission transmission buffer unit 370 accumulates an upstream frame corresponding to a transmission permission time ST and a transmission available time L (described later) included in the transmission permission notification 400 sent from the OLT 100 before the retransmission request. . Corresponding to the transmission permission time ST and the transmittable time L included in the transmission permission notification 1030 (also referred to as a retransmission permission notification) from the uplink frame (data) temporarily stored in the retransmission transmission buffer unit 370 at the time of the retransmission request The part to be selected is selected and transmitted to the OLT 100.

  The grant processing unit 380 sets a transmission time slot and allocates a band corresponding to the transmission permission time ST and the transmission available time L included in the transmission permission notification from the OLT 100. The grant processing unit 380 allocates a band to the frame (data) of the queue buffer unit 320 at normal times, and allocates a band to the frame (data) of the retransmission transmission buffer unit 370 at the time of retransmission request. The sleep control unit 360 analyzes a sleep control signal (instruction signal related to sleep control) sent from the OLT 100, a stop process for shifting the ONU 110 from the normal state to the sleep state, and an activation for returning the ONU 110 from the sleep state to the normal state Process.

  Here, the sleep state of the ONU 110 means that power supply from the power source 390 to the electrical / optical conversion unit 300 is stopped, communication between the OLT 100 and the electrical / optical conversion unit 300 is interrupted, and the access control unit 310 is In this state, only the function of accumulating the upstream frame received by the electrical transmission / reception unit 340 in the queue buffer unit 320 is continued and the other functions are stopped. In the sleep control, the sleep control unit 360 monitors whether the return time to the normal state or the transition time to the sleep state instructed from the sleep control unit 240 of the OLT 100 has been reached.

  When the transition time for shifting to the sleep state is reached, the sleep control unit 360 turns off the switch 300a of the electrical / optical conversion unit 300 and stops the electrical / optical conversion unit 300 from the power source 390 in order to suspend the electrical / optical conversion unit 300. The supply of power to the conversion unit 300 is stopped. When the return time for returning to the normal state is reached, the sleep control unit 360 turns on the switch 300a of the electrical / optical conversion unit 300 to activate the electrical / optical conversion unit 300, and the electrical / optical conversion from the power source 390 is performed. Power is supplied to the conversion unit 300.

  FIG. 4 is a sequence diagram showing a normal operation of the PON 10. FIG. 4 illustrates the relationship between the DBA operation (dynamic bandwidth allocation) and the DBA cycle of the grant processing unit 250, and the grant operation and the grant cycle based on the result of each DBA.

  For example, the OLT 100 transmits a transmission permission notification 400 including a grant instruction (transmission timing instruction) to each of the ONUs 110-1 to 110-3 at every grant period of 125 μs. This transmission permission notification 400 includes a transmission permission time ST and a transmission available time L. Instead, the transmission permission notification 400 may include a transmission start time Start and an end time End.

  Also included is information (report request) for requesting a report of the amount of data waiting for transmission accumulated in the transmission queue (queue buffer unit 320) provided in each ONU. Each ONU 110-1 to 3 transmits data accumulated in the transmission queue in a period (time slot) defined by the transmission start time Start (= ST) and the end time End (= ST + L). At the same time, each ONU 110-1 to 3 reports the amount of data waiting for transmission to the OLT 100 using the queue length (corresponding to the amount of data waiting for transmission) included in the upstream notification 410 (for example, JP2010-81278A). reference).

  FIG. 5 is a flowchart illustrating a routine for returning from the sleep state to the normal state.

  In step S500, the OLT 100 transmits a sleep release notification to the ONU 110 in order to return the sleep state to the normal state. In step S510, the ONU 110 receives the sleep release notification transmitted from the OLT 100. In step S520, the ONU 110 that has received the sleep cancellation notification starts activation. In step S530, after all functions are recovered and startup is completed, the ONU 110 transmits a startup completion notification to the OLT 100 in step S540. In step S550, the OLT 100 confirms the return of the ONU 110 from the sleep state by receiving the activation completion notification transmitted from the ONU 110.

  FIG. 6 is a flowchart illustrating a routine for a transition operation from the normal state to the sleep state.

  In step S600, the OLT 100 transmits a sleep setting notification (sleep permission notification) to the ONU 110 that is to be shifted to the sleep state. In step S610, the ONU 110 receives the sleep setting notification transmitted from the OLT 100. In step S620, the ONU 110 that has received the sleep setting notification starts shifting to the sleep state. In step S630, the ONU 110 enters a sleep state, continues only the function of accumulating frames in the queue buffer unit 320, stops other functions, and completes the transition to the sleep state. In step S640, the OLT 100 confirms the transition of the ONU 110 to the sleep state by confirming the interruption of the optical line with the ONU 110.

  FIG. 7 is a sequence diagram illustrating an example of the operation of the PON 10 when the ONU returns from the sleep state. In this case, erroneous light emission may occur in the ONU that returns from the sleep state.

  The OLT 100 sends a sleep release notification 700 to the ONU 110-2 (ONU # 2) that is to return from the sleep state at the same timing as the transmission permission notification 400 including the grant instruction. The ONU 110-2 that has received the sleep cancellation notification starts activation from the sleep state. If the ONU 110-2 becomes unstable during the start-up period 720 (for example, 5 milliseconds) of the ONU 110 and an unintentional erroneous light emission occurs, an upstream notification 710 of another ONU (ONU 110-1 or ONU 110-3) and an erroneous light emission There is a possibility that a frame loss (packet loss) in which the uplink frame cannot be accurately transmitted to the OLT 100 due to interference with the signal may occur.

  FIG. 8 is a sequence diagram showing an example of the operation of the PON 10 when the ONU shifts to the sleep state. In this case, erroneous light emission may occur in the ONU that shifts to the sleep state.

  The OLT 100 sends a sleep setting notification 800 to the ONU 110-2 (ONU # 2) that is going to shift to the sleep state at the same timing as the transmission permission notification 400 including the grant instruction. The ONU 110-2 that has received the sleep setting notification starts shifting to the sleep state. When the ONU 110 becomes unstable during the sleep transition period 820 (for example, 5 milliseconds) of the ONU 110 and an unintended erroneous light emission occurs, an upstream notification 810 and an erroneous light emission signal of another ONU (ONU 110-1 or ONU 110-3) Cause an uplink frame loss.

  Even when an erroneous light emission signal is generated in the ONU 110 in this way, three embodiments will be described with respect to control for compensating for a frame loss in an upstream signal from another ONU 110. In each embodiment, the OLT 100 uses a transmission permission notification including a grant instruction to compensate for frame loss, and uses data corresponding to a section (location) where an error is detected or a frame (packet) including the section. Retransmit to ONU 110.

[First embodiment]
FIG. 9 is a flowchart illustrating a retransmission control routine executed by the control unit 230 of the OLT 100 in the first embodiment.

  In step S910, the control unit 230 of the OLT 100 transmits a transmission permission notification 400 including a grant instruction to each ONU 110, and transmits a sleep release notification 700 or a sleep setting notification 800 to a specific ONU 110 (here, ONU # 2). Furthermore, the control unit 230 sends a storage command to the ONU 110 other than the specific ONU 110 (here, ONU # 2) so that a frame (packet) to be transmitted to the OLT 100 is stored in the retransmission transmission buffer unit 370. In the configuration in which the retransmission transmission buffer unit 370 always stores frames (packets) to be transmitted to the OLT 100, the OLT 100 does not need to send this storage instruction.

  In step S920, when the control unit 230 receives data from the ONU, the received data from the ONU has an error section (a section or period in which a data error occurs) using the error detection unit 260. Judge. If there is no error section in the data received from the ONU 110, the routine proceeds to step S950. If there is an error interval in the data received from the ONU 110, the routine proceeds to step S930. In the first embodiment, the error detection unit 260 of the control unit 230 monitors the optical output of the optical signal transmitted from the ONU 110 in communication via the reception power detection unit 290. In step S920, when the average light output fluctuates by a predetermined rate or more, the error detection unit 260 determines that there is an error (error) in the data due to the erroneous light emission of the ONU 110, and a data error occurs. The detected section or period is detected as an error section. Here, the predetermined ratio is several tens of percent.

  In step S930, the control unit 230 of the OLT 100 uses the grant processing unit 250 to store the data stored in the retransmission transmission buffer unit 370 with respect to the grant processing unit 380 of the ONU 110 that transmitted the erroneous frame. A retransmission request (retransmission request signal) is transmitted so as to retransmit a part (at least the part corresponding to the error interval). The ONU 110 that has transmitted a frame with an error may be determined from the source address in the frame. Here, retransmission is performed on a frame (packet) basis so that a frame (packet) in which an error has occurred is retransmitted. One or a plurality of frames (packets) selected so as to include a portion corresponding to the error section among the frames (packets) stored in the retransmission transmission buffer unit 370 are retransmitted. In step S <b> 940, the control unit 230 uses the buffer control unit 280 to store the data transmitted from the ONU 110 that has received the retransmission request in the retransmission reception buffer unit 271. In step S950, normal DBA operation is resumed. Thereafter, the routine ends.

  FIGS. 10A to 10C are time charts illustrating levels (sizes) of light input / output of the ONU 110 and the OLT 100 at the time of erroneous light emission. As shown in FIG. 10A, if the optical output level 900 of the ONU 110 (for example, ONU # 1) is constant, the average optical output 910 is also constant. When the OLT 100 returns the ONU 110 (for example, ONU # 2) from the sleep state or shifts to the sleep state, the ONU 110 (for example, ONU # 2) is in a certain light emission period as shown in FIG. In addition, an erroneous light emission signal 930 is generated. Then, as shown in FIG. 10C, the erroneous light emission signal 930 interferes with the optical signal 920 of the ONU 110 (for example, ONU # 1) in communication, and the optical input level 940 of the OLT 100 increases.

  In step S920, the error detection unit 260 detects, via the reception power detection unit 290, that the average optical input 950 fluctuates by a predetermined ratio or more (for example, 30%) compared to the normal state, and the ONU 110 that is performing communication is detected. It is determined that there is an error section in the data (for example, ONU # 1). Further, the error detection unit 260 identifies an error section corresponding to the erroneous light emission period and notifies the grant processing unit 250 of the error interval. In step S930, the grant processing unit 250 makes a retransmission request to the ONU 110 (for example, ONU # 1) in communication. As a result, even if an unintended erroneous light emission occurs while a certain ONU 110 shifts to the sleep state or starts from the sleep state, the frame loss can be compensated for the upstream signal from the other ONU 110.

  FIG. 11A shows a frame (data) stored in the retransmission transmission buffer unit 370 before the retransmission request. When the sleep cancellation / setting notification is transmitted to the ONU 110 with the OLT 100, the other ONUs 110 store a frame to be transmitted to the OLT 100 in the retransmission transmission buffer unit 370 in preparation for a retransmission request from the OLT 100. Frames (packets) assigned to the transmission permission time ST and the transmission available time L of the transmission permission notification 400 sent from the OLT 100 before the retransmission request are stored in the retransmission transmission buffer unit 370. As an example, in the transmission permission notification 400 to ONU # 1, the transmission permission time ST is set to 1000, and the transmittable time L is set to 500.

  In the hatched area of FIG. 11A, there is an erroneous light emission 930 from error ONU # 2 during 100 times from time t = 1100 to time t = 1200 corresponding to two frames, indicating that an error has occurred. Show. For example, the error section (corresponding to the erroneous light emission period in FIG. 10C) is from time t = 1120 to time t = 1180. The error detection unit 260 of the OLT 100 detects an error section of data due to erroneous light emission by the ONU # 2 and notifies the grant processing unit 250 of the error. In this case, the buffer control unit 280 of the OLT 100 stores only data with no error (frames other than the hatched portion) in the reception buffer unit 270.

  FIG. 11B shows a frame (data) retransmitted from the ONU 110 to the OLT 100 in response to the transmission permission notification 1030 (retransmission permission notification) from the OLT 100. At the time of transmission of the transmission permission notification 1030 immediately after detection of the erroneous light emission of ONU # 2 (at the time of grant issuance), the grant processing unit 250, together with the transmission permission notification 1030 including the transmission permission time ST and the transmittable time L, A retransmission request is transmitted to # 1. The transmission permission time ST and the transmission available time L are set so that one or a plurality of frames including data corresponding to the error interval are retransmitted. Here, in the transmission permission notification 1030, the transmission permission time ST is 1100, and the transmittable time L is 100.

  Upon receiving the retransmission request, the grant processing unit 380 of the ONU 110 associates the transmission permission notification 1030 with the frame (packet) stored in the retransmission transmission buffer unit 370, allocates a band, and performs retransmission. Specifically, as shown in FIG. 11B, the grant processing unit 380 can transmit the transmission permission time ST included in the transmission permission notification 1030 from the frame (data) stored in the retransmission transmission buffer unit 370. A part corresponding to the time L is selected and transmitted to the OLT 100.

  The OLT 100 receives the retransmitted frame (packet) and stores it in the retransmission reception buffer unit 271. Further, the buffer control unit 280 of the OLT 100 combines the frame (packet) stored in the reception buffer unit 270 before the retransmission request with the frame (packet) retransmitted and stored in the reception buffer unit 271 for retransmission, The data is sent to the electric side transceiver 200. When the reception buffer unit 270 also stores a frame in which an error has occurred, the buffer control unit 280 deletes the frame in which an error has occurred and stores the frame stored in the reception buffer unit 270 before the retransmission request. The frames stored in the retransmission reception buffer unit 271 may be combined.

  FIG. 12 shows a sequence diagram when a frame is retransmitted. FIG. 12 illustrates a case where the ONU is activated from the sleep state as an example.

  The OLT 100 sends a sleep release notification 700 to the ONU 110 (in this case, ONU # 2) trying to return from the sleep state at the same timing as the transmission permission notification 400 including the grant instruction. The other ONUs 110 (in this case, ONU # 1 and ONU # 3) in the normal state transmit according to the grant instruction, and the ONU # 2 that has received the sleep release notification 700 starts to start from the sleep state.

  During the ONU # 2 startup period 720 (for example, 5 milliseconds), the ONU # 2 state becomes unstable and an unintended erroneous light emission signal 930 is generated, for example, interfering with the ONU # 1 frame. The OLT 100 that has received the signal of each ONU 110 detects the average optical output of each ONU by the reception power detection unit 290 and transmits it to the error detection unit 260. When the error detection unit 260 does not detect an error, the signals from the ONU # 1 and the ONU # 3 are transmitted to the electrical side transmission / reception unit 200 via the access unit 220 and the reception buffer unit 270 as they are.

  When the average optical input 950 of the OLT 100 fluctuates as shown in FIG. 10C, and an error is detected in the ONU # 1 frame in the range from the time t = 1100 to the time t = 1200 in FIG. The frame (packet) of ONU # 1 is stored in the reception buffer unit 270 via the access unit 220 except for this range. In the grant instruction immediately after that, bandwidth allocation is not performed for the ONUs 110 (ONU # 2 and ONU # 3) other than ONU # 1, and a transmission permission notification (ST: 1100, L: 100) and a retransmission request are sent to ONU # 1. ONU # 1 retransmits in response to a request from the OLT 100. The OLT 100 that has received the retransmitted frame (packet) stores it in the retransmission reception buffer unit 271 and combines the frame (packet) stored in the reception buffer unit 270 with the retransmitted frame (packet). The data is sent to the electric side transceiver 200. Thereafter, the OLT 100 resumes normal DBA operation.

-Effect-
According to the first embodiment, the grant processing unit 250 of the OLT 100 (that is, the host device) includes the first ONU 110 (first subordinate device: for example ONU # 1) and the second ONU 110 (second subordinate device: for example ONU). A transmission permission notification for setting a time for transmitting data to the OLT 100 is transmitted to each of # 2). The sleep control unit 240 of the OLT 100 provides a sleep setting notification for shifting to a sleep state in which the second ONU 110 (for example, ONU # 2) stops transmitting data to the OLT 100 and a sleep release notification for returning from the sleep state. Transmit to the second ONU 110. The error detection unit 260 of the OLT 100 detects an error section where an error has occurred in the data received from the first ONU 110. The grant processing unit 250 of the OLT 100 causes the first ONU 110 to transmit data corresponding to at least the error interval again when an error interval is detected after the sleep control unit 240 transmits the sleep setting notification or the sleep release notification. For this purpose, a retransmission permission notification (transmission permission notification 1030) is transmitted. In response to the retransmission permission notification, the first ONU 110 transmits again data corresponding to at least the error section.

  Accordingly, when the second ONU 110 shifts to the sleep state or starts up from the sleep state under the control of the OLT 100, even if an unintentional erroneous light emission occurs from the second ONU 110, the other first ONU 110 is at least in error. By retransmitting data corresponding to a certain section, data loss such as frame loss can be compensated. Therefore, accurate data transmission from the ONU 110 that is not the target of sleep transition / sleep release to the OLT 100 can be ensured.

  The first ONU 110 includes a retransmission transmission buffer unit 370 that temporarily accumulates transmission data that has already been transmitted to the OLT 100, and a control unit 350 that controls the retransmission transmission buffer unit. In response to the retransmission permission notification, the control unit 350 of the first ONU 110 selects at least data corresponding to the error section from the transmission data stored in the retransmission transmission buffer unit 370 and transmits the data again. Thereby, the data corresponding to the error section can be transmitted again easily.

  The OLT 100 includes a reception buffer 270 (first reception buffer) that stores data received from the first ONU 110 before transmission of a retransmission permission notification, and a retransmission reception that stores data transmitted again from the first ONU 110. A buffer unit 271 (second reception buffer unit). The OLT 100 combines the data stored in the first reception buffer 270 and the data stored in the second reception buffer 271 and sends them to the upper network. Thereby, the data from which the error has been removed can be sent to the upper network.

  The error detection unit 260 detects an error section by monitoring the level of the data signal received from the first ONU 110. Thereby, an error can be easily detected using the existing reception power detection unit 290.

  The grant processing unit 250 of the OLT 100 transmits a retransmission permission notification for causing the first ONU 110 to retransmit a frame corresponding to the frame in which the error interval is detected, and the first ONU 110 transmits a retransmission permission notification. In response, the corresponding frame may be transmitted again. Thereby, data can be transmitted again in units of erroneous frames (packets), which is convenient.

[Second Embodiment]
The second embodiment is different from the first embodiment regarding the error detection processing of the OLT 100 and the retransmission processing of the ONU 110. Other configurations are common to the first embodiment and the second embodiment.

  FIG. 13 shows an outline of a MAC frame used in the IEEE 802.3 standard. The error detection unit 260 of the OLT 100 detects an error using an FCS (frame check sequence) in the frame.

  According to the IEEE 802.3 standard, the result of the checksum calculation for the range from the destination address to the user data is stored in the FCS 1200. The frame received by the OLT 100 is sent to the error detection unit 260 via the access control unit 220. Then, the error detection unit 260 compares the result of recalculating the checksum with the checksum described in the FCS 1200, and detects an error in the frame when they are different. When sending the sleep cancellation / setting notification to the ONU 110 with the OLT 100, other ONUs 110 store frames (packets) to be transmitted in the retransmission transmission buffer unit 370 in preparation for a retransmission request from the OLT 100. . The ONU 110 that has transmitted the frame in which the error is detected retransmits the frame corresponding to the frame in which the error is detected among the frames stored in the retransmission transmission buffer unit 370 to the OLT 100 in response to the retransmission request. In the transmission permission notification 1030 (retransmission permission notification), the transmission permission time ST and the transmission available time L are set so that a frame corresponding to a frame in which an error is detected is retransmitted.

  According to the second embodiment, the error detection unit detects an error section using frame check sequence information in data received from the first ONU. Thereby, an error can be easily detected in units of frames, and a frame corresponding to the frame in which the error is detected can be retransmitted.

[Third embodiment]
The third embodiment is different from the first embodiment regarding the error detection processing of the OLT 100 and the retransmission processing of the ONU 110. Other configurations are common to the first embodiment and the third embodiment.

  The ONU 110 performs 8B / 10B encoding, which is a transmission encoding method, on data to be transmitted using an 8B / 10B encoding circuit (not shown) and transmits the data to the OLT 100. Note that 8B / 10B encoding is adopted in the encoding scheme of the IEEE 802.3 standard. The error detection unit 260 of the OLT 100 detects an error using the running disparity RD of 8B / 10B encoding, and if there is an error in the frame of the ONU 110 in communication, the ONU 110 considers that the ONU 110 is emitting light erroneously. . Then, the control unit 230 of the OLT 100 sends a retransmission request for retransmitting data in a predetermined range that includes the error location (or error section) wider than the error location (or error interval) to the ONU 110 in communication. The predetermined range is several bytes before and after the error location (or error section). Note that data does not have to be sent in units of frames.

  FIG. 14 shows a part of the 8B / 10B code conversion table. In 8B / 10B encoding, 8-bit original data 1300 is divided into 3 bits / 5 bits, and 1 bit is added to each of them. According to the complete table of FIG. Is converted to The 8B / 10B encoding circuit outputs RD +/− according to the number of 1/0 of the data immediately before encoding at the time of conversion.

  For example, when the 8-bit original data 1300 is 00h, the 8B / 10B encoding circuit of the ONU 110 has a bit of Current RD- (1310) in FIG. 14 if the number of “0” is large in the data immediately before encoding. A pattern is selected and output. If there is more data immediately before encoding “1”, a bit pattern of Current RD + (1320) is selected and output. Thereby, the error detection unit 260 of the OLT 100 has an error in the data transmitted to the OLT 100 if the selection of the actual bit pattern does not match the running disparity RD +/− estimated from the immediately preceding data. Can be detected.

  The OLT 100 sends the data sent from the ONU 110 to the error detection unit 260 via the access control unit 220. The error detection unit 260 of the OLT 100 includes an 8B / 10B conversion table and detects a bit error. However, with this method, it cannot be guaranteed that all bit errors will be detected, and as an example, the 5 bytes before and after the erroneous part or section are set as the retransmission request range of the OLT 100.

  FIG. 15 shows frames (data) stored in the retransmission transmission buffer unit 370 before the retransmission request. When the sleep cancellation / setting notification is transmitted to the ONU 110 with the OLT 100, the other ONUs 110 store a frame to be transmitted to the OLT 100 in the retransmission transmission buffer unit 370 in preparation for a retransmission request from the OLT 100. Frames assigned to the transmission permission time ST and the transmission available time L of the transmission permission notification 400 sent from the OLT 100 before the retransmission request are stored in the retransmission transmission buffer unit 370. As an example, in FIG. 15, in the transmission permission notification 400 to ONU # 1, the transmission permission time ST is set to 1000, and the transmittable time L is set to 500.

  The hatched area in FIG. 15 indicates that there was a false light emission 930 from ONU # 2. The error detection unit 260 of the OLT 100 detects a location where ONU # 2 has a data error due to erroneous light emission, and notifies the grant processing unit 250 of the location. As described above, since the running disparity RD is not guaranteed to detect errors in all frames, as an example, the grant processing unit 250 transmits the 5 bytes before and after the location or section where the error occurred, Set to data range 1420.

  At the time of transmission of the transmission permission notification 1030 immediately after the ONU # 2 erroneous light emission is detected (at the time of grant issuance), the grant processing unit 250 transmits the transmission permission time ST and the transmission available time L corresponding to the data range 1420 of the retransmission request. And make a retransmission request to ONU # 1. Here, in the transmission permission notification 1030 (retransmission permission notification), the transmission permission time ST is 1100, and the transmittable time L is 100.

  According to the third embodiment, the error detection unit detects the error interval using a running disparity of 8B / 10B encoding. Thereby, an error in data can be easily detected.

  The present invention is not limited to each embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

10 PON (Optical Communication System)
100 OLT (host device)
110 ONU (subordinate device)
120 Splitter 130, 140 Optical fiber 150 Downstream signal 160, 170 Upstream signal 180, 190 Terminal 230 OLT control unit 240 OLT sleep control unit 250 OLT grant processing unit 260 Error detection unit 270 Reception buffer unit 271 Retransmission reception buffer unit 300 Electric / Optical Conversion Unit 300a Switch 320 Queue Buffer Unit 350 ONU Control Unit 370 Retransmission Transmission Buffer Unit 380 ONU Grant Processing Unit 390 Power Supply

Claims (9)

An optical communication system including a host device that communicates with a host network, and at least first and second slave devices that communicate with the host device using optical signals,
The host device is
A processing unit that transmits a transmission permission notification for setting a time for transmitting data to the higher-level device for each of the first lower-level device and the second lower-level device;
Sleep that transmits to the second lower-level device a sleep setting notification that shifts to a sleep state that stops the second lower-level device from transmitting data to the higher-level device, and a sleep release notification that returns from the sleep state A control unit;
An error detection unit for detecting an error section in which an error has occurred in the data received from the first lower-level device,
When the error interval is detected after the sleep control unit transmits a sleep setting notification or a sleep release notification, the processing unit of the higher-level device corresponds to at least the error interval to the first lower-level device. Send a resend permission notice to send the data again,
In response to the retransmission permission notification, the first subordinate apparatus retransmits data corresponding to at least the error section again. The first subordinate device is
A retransmission transmission buffer unit for temporarily storing transmission data already transmitted to the host device;
A control unit for controlling the retransmission transmission buffer unit,
In response to the retransmission permission notification, the control unit of the first lower-level device selects at least data corresponding to the error interval from transmission data accumulated in the retransmission transmission buffer unit, 2. The optical communication system according to claim 1, wherein transmission is performed again. The host device is
A first reception buffer for storing data received from the first lower-level device before transmission of the retransmission permission notification;
A second reception buffer for storing data retransmitted from the first lower-level device,
3. The optical communication according to claim 2, wherein the upper apparatus combines the data stored in the first reception buffer and the data stored in the second reception buffer and sends the combined data to the upper network. system.   The optical communication system according to claim 1, wherein the error detection unit detects the error section by monitoring a level of a data signal received from the first subordinate apparatus.   The optical communication system according to claim 1, wherein the error detection unit detects the error section using frame check sequence information in data received from the first lower-level device.   The optical communication system according to claim 1, wherein the error detection unit detects the error interval using a running disparity of 8B / 10B encoding. The processing unit of the higher-level device transmits the retransmission permission notification for causing the first lower-level device to retransmit a frame corresponding to the frame in which the error interval is detected,
2. The optical communication system according to claim 1, wherein the first subordinate apparatus retransmits the corresponding frame in response to the retransmission permission notification. In an optical communication system, an optical communication device that communicates with at least first and second subordinate devices using optical signals,
A processing unit for transmitting a transmission permission notification for setting a time for transmitting data to the optical communication device, for each of the first lower device and the second lower device;
The second subordinate device transmits a sleep setting notification for shifting to a sleep state that stops transmitting data to the optical communication device, and a sleep release notification for returning from the sleep state to the second subordinate device. A sleep control unit;
An error detection unit for detecting an error section in which an error has occurred in the data received from the first lower-level device,
When the error section is detected after the sleep control section transmits a sleep setting notification or a sleep release notification, the processing section transmits again data corresponding to at least the error section to the first lower device. An optical communication apparatus characterized by transmitting a retransmission permission notice for causing A communication method executed in an optical communication system including a host device that communicates with a host network, and at least first and second slave devices that communicate with the host device using optical signals,
The upper device transmits a transmission permission notification for setting a time for transmitting data to the upper device to each of the first lower device and the second lower device;
The host device sends a sleep setting notification for shifting to a sleep state in which the second lower device stops transmitting data to the host device, and a sleep release notification for returning from the sleep state to the second lower device. Transmitting to the device;
The host device detects an error section in which an error has occurred in data received from the first lower device after the sleep setting notification or sleep release notification is transmitted;
A step of transmitting a retransmission permission notification for causing the first lower-level device to retransmit at least data corresponding to the error interval when the higher-level device detects the error interval;
The first subordinate apparatus, in response to the retransmission permission notification, retransmits data corresponding to at least the error section; and
A communication method comprising:

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