JP2004343734A - Optical subscriber line terminal station device and frame scheduling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical subscriber line terminal station device in which a control frame can be transmitted to an optical subscriber line terminating apparatus before a scheduled time, and the delay of a user data frame can be suppressed to a minimum. <P>SOLUTION: When a scheduled transmission time contained in a leading descriptor which is queued in a control frame queue 21 is over a present time of a timer 18, a queue management part 32 transmits the descriptor of the control frame queued in the control frame queue 21 to a descriptor transmitting part 33. A transmitting part 16 reads a frame corresponding to the descriptor outputted from the descriptor transmission part 33 from a buffer memory 15 and transmits it to the optical subscriber line terminating apparatus. Therefore, the control frame can be transmitted to the optical subscriber line terminating apparatus before the scheduled time, and the delay of the user data frame can be suppressed to a minimum. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a PON (Passive Optical Network) which is a medium sharing type communication in which a plurality of home-side devices share a medium and transmit data, and in particular, an EPON (EPON (Transmission Optical Network)) which transmits data in the form of an Ethernet frame. The present invention relates to an OLT (optical subscriber line terminal) and a frame scheduling method for efficiently performing downlink frame scheduling in Ethernet (R) PON.

  2. Description of the Related Art In recent years, the Internet has become widespread, and users can access various types of information on sites operated around the world and obtain the information. Accordingly, demands for broadband access such as ADSL (Asymmetric Digital Subscriber Line) and FTTH (Fiber To The Home) are rapidly increasing.

  FIG. 7 is a block diagram showing a schematic configuration of a conventional PON system. This PON system is mainly transmitted from an OLT 101 installed in a telephone office or the like, a plurality of ONUs (optical subscriber line termination devices) 102-1 to 102-n installed in each house, and transmitted from the OLT 101. The splitter 105 splits the optical signal and sends it to the ONUs 102-1 to 102-n, converges the optical signal sent from the ONUs 102-1 to 102-n, and sends it to the OLT 101; And a user terminal 111 connected to each. The first ONU 102-1 to the n-th ONU 102-n have the same configuration.

  The OLT 101 sends out downlink information frames received via the upper network 109 to the ONUs 102-1 to 102-n via the transmission path 104 and the splitter 105. The OLT 101 also determines the transmission start time of the data stored in the buffers 103-1 to 103-n in the ONUs 102-1 to 102-n based on the report 107 transmitted from the ONUs 102-1 to 102-n. The transmission permission amount is calculated, and the grant 106 into which the instruction signal is inserted is transmitted to the ONUs 102-1 to 102-n via the transmission path 104 and the splitter 105.

  For example, when the ONU 102-1 receives the upstream information frame 108 from the user terminal 111 via the lower network 110, the ONU 102-1 temporarily stores the upstream information frame 108 in the buffer 103-1. When receiving the grant 106 from the OLT 101, the ONU 102-1 notifies the OLT 101 of the amount of data in the buffer 103-1 by the report 107 at the time designated by the grant 106. Note that the uplink information frame 108 arrives in variable length packet units.

  When receiving the grant 106 in which the instruction signal is inserted from the OLT 101, the ONU 102-1 sends the data in the buffer 103-1 to the OLT 101 together with the report 107 based on the instruction signal.

  FIG. 8 is a sequence diagram for explaining the operation procedure of the conventional PON system. Although this sequence diagram is for the operations of the OLT 101 and the ONUs 102-1, the same applies to the operations of the other ONUs 102-2 to 102-n.

  At the operation time start time T0, the OLT 101 has already calculated the RTT (Round Trip Time) for the ONUs 102-1 to 102-n. At time Ta1, the OLT 101 transmits the grant 121 including the report transmission start time Tb2 to the ONU 102-1 in order to notify the transmission request amount. The report transmission start time Tb2 is calculated so as not to collide with a report transmitted from another ONU.

  When receiving the grant 121 for itself, the ONU 102-1 calculates the transmission request amount by referring to the amount of data stored in the buffer 103-1. The ONU 102-1 transmits the report transmission start time Tb2 included in the grant 121 to the OLT 101. The report 122 including the transmission request amount is transmitted.

  When receiving the report 122, the OLT 101 calculates a value that is equal to or smaller than the fixed or variable maximum transmission permission amount and can transmit as much data of the amount of data in the buffer included in the report 122 as possible. Insert into 123. When the transmission request amount included in the report 122 is zero, the bandwidth is not allocated because the operation result by the OLT 101 is zero, but the OLT 101 needs to transmit the report to the ONU 102-1. Grant 123 is always sent out.

  The transmission start time Tb4 included in the grant 123 is calculated by using the calculated scheduled reception time of the previous ONU data, the transmission permission amount of the previous ONU, the RTT for the current ONU, and the guard time as a fixed time, using a data and report. Is calculated so as not to conflict with data or reports from other ONUs. The OLT 101 calculates the time Ta3 at which the grant 123 including the transmission permission amount and the transmission start time Tb4 is transmitted so that the grant 123 reaches the ONU 102-1 by the transmission start time Tb4.

  When receiving the grant 123 for itself, the ONU 102-1 sends the data 124 corresponding to the transmission permission amount to the OLT 101 at the transmission start time Tb4 included in the grant 123 together with the report including the next transmission request amount. This report is transmitted immediately before or immediately after the data. However, when the report is transmitted immediately before the data, the value reported to the OLT 101 as the transmission request amount depends on the data amount accumulated in the buffer 103-1 and the data 124 Is the difference from the data amount.

  When receiving the data and the report 124, the OLT 101 sends the data to the upper network 109, and performs the same processing as the report 122 on the report. The processing described above is performed independently for all ONUs 102-1 to 102-n, and the processing from time Ta3 to time Ta4 is repeated until the operation time ends.

  As a prior art related thereto, "IPACT: A Dynamic Protocol for an Ethernet (R) PON" (Glen Kramer et al., Pp74-80, IEEE Commun, Feb. 2002.) (hereinafter, referred to as a first prior art). ) And "A Dynamic Bandwidth Allocation Algorithm Suitable for GE-PON" (Yoshihara et al., IEICE Technical Report, NS2002-17, pp1-4, 2002.04) (hereinafter referred to as a second prior art).

  The first prior art relates to a dynamic allocation method in an EPON FTTH service, in which a distributed type in which the OLT sends a report to each ONU independently and each time the OLT issues a grant to the corresponding ONU. It relates to an allocation method.

Further, the second prior art relates to a centralized allocation method, in which an ONU specifies a buffer amount up to a maximum data size that can be allocated per grant cycle and a buffer amount equal to or smaller than a specified upper limit from the head of the buffer. Are sent as a report. The OLT reduces the allocation loss by permitting a buffer amount equal to or less than the upper limit in order from the top ONU and giving the unallocated bandwidth as a grant only to the last ONU in the grant cycle.
"IPACT: A Dynamic Protocol for an Ethernet (R) PON" (Glen Kramer et al., Pp74-80, IEEE Commun, Feb. 2002.) "A Dynamic Bandwidth Allocation Algorithm Suitable for GE-PON" (Yoshihara et al., IEICE Technical Report, NS2002-17, pp1-4,2002.04)

  In the above-described conventional PON system, when a grant (downlink control frame) generated in the OLT 101 and a downlink user data frame compete with each other, some scheduling is required. For example, when scheduling is performed by the round robin method, the transmission of the control frame is delayed by the transmission of the user data frame, the control frame does not reach the ONUs 102-1 to 102-n by the scheduled time and the OLT 101 -1 to 102-n may not be controlled.

  Further, when scheduling is used such that the control frame is always given a high priority, the control frame is transmitted with priority even when it is not necessary to transmit the control frame immediately. In other words, if the control frame arrives by a certain time, its purpose can be sufficiently achieved, and it does not make any sense if the control frame arrives at the ONU early. Therefore, there is a problem that the user data frame is meaninglessly waited, the real-time property of the user data frame is impaired, and the service is deteriorated.

  Furthermore, the above-mentioned first prior art and second prior art do not specifically disclose the scheduling of the downlink control frame and the downlink user data frame, and thus cannot solve the above-mentioned problem.

  The present invention has been made to solve the above problems, and an object of the present invention is to transmit a control frame to an ONU by a scheduled time and to minimize a delay of a user data frame. It is an object of the present invention to provide a possible optical network unit and a frame scheduling method.

  According to an aspect of the present invention, the optical line terminal includes a generation unit for generating a control frame to be transmitted to the optical network unit in response to the control frame received from the optical network unit. Means, a storage means for storing the user data frame received from the upper network and the control frame generated by the generation means, and comparing the scheduled transmission time and the current time of the control frame stored by the storage means. Scheduling means for scheduling the user data frame and the control frame stored in the storage means, and the user data frame and the control frame stored in the storage means according to the scheduling result by the scheduling means. Transmitting means for transmitting to the device.

  Preferably, the scheduling means includes a control frame queue for queuing a descriptor corresponding to the control frame stored in the storage means, and a user for queuing the descriptor corresponding to the user data frame stored in the storage means. A data queue, comparison means for comparing the current time with the scheduled transmission time included in the first descriptor queued in the control frame queue, and a control frame queue and a user data queue according to the comparison result by the comparison means. And a descriptor output unit for selectively outputting the descriptor queued in the storage unit, wherein the transmission unit reads a frame corresponding to the descriptor output by the descriptor output unit from the storage unit, and sends the read frame to the optical network unit. Send out

  More preferably, when the scheduled transmission time included in the first descriptor queued in the control frame queue exceeds the current time, the descriptor output means includes a descriptor of the control frame queued in the control frame queue. To the transmitting means, and if the scheduled transmission time included in the first descriptor queued in the control frame queue does not exceed the current time, the descriptor of the user data frame queued in the user data queue is deleted. Send it to the sending means.

  More preferably, the scheduling means further includes a high-priority queue for queuing a descriptor of an emergency frame to be transmitted to the optical network unit, and the descriptor output means includes a step of determining whether a descriptor is present in the high-priority queue. Sends the descriptor of the emergency frame stored in the storage unit to the transmission unit preferentially.

  Preferably, the scheduling means includes a control frame queue for queuing a descriptor corresponding to the control frame stored in the storage means, and a user for queuing the descriptor corresponding to the user data frame stored in the storage means. Comparison means for comparing the current time with the data queue, the scheduled transmission time calculated from the time information contained in the control frame corresponding to the first descriptor queued in the control frame queue and stored in the storage means, and And a descriptor output unit for selectively outputting the descriptors queued in the control frame queue and the user data queue according to the comparison result by the comparison unit, and the transmission unit is output by the descriptor output unit. To the descriptor It reads the frame response from the storage means and sent to the optical network unit.

  More preferably, the descriptor output means, if the scheduled transmission time calculated from the time information included in the control frame corresponding to the first descriptor queued in the control frame queue exceeds the current time, the control frame The descriptor of the control frame queued in the queue is sent to the transmitting means, and the scheduled transmission time calculated from the time information included in the control frame corresponding to the first descriptor queued in the control frame queue indicates the current time. If not exceeded, the descriptor of the user data frame queued in the user data queue is sent to the transmitting means.

  Preferably, the scheduling means includes a table means for storing a descriptor corresponding to the control frame stored in the storage means for each optical network unit, and a descriptor corresponding to the user data frame stored in the storage means. A user data queue for queuing, a comparing unit for comparing a scheduled transmission time and a current time included in the descriptor stored in the table unit with a predetermined period, and a table unit according to a comparison result by the comparing unit. And a descriptor output unit for selectively outputting a descriptor stored in the user data queue and a descriptor queued in the user data queue, wherein the transmission unit outputs a frame corresponding to the descriptor output by the descriptor output unit from the storage unit. Readout, optical subscriber line And it sends to the end device.

  More preferably, if the earliest time among the scheduled transmission times included in the descriptor stored in the table means exceeds the current time, the descriptor output means may output the descriptor of the control frame stored in the table means. To the transmitting means, and if the earliest time among the scheduled transmission times included in the descriptor stored in the table means does not exceed the current time, the descriptor of the user data frame queued in the user data queue To the transmitting means.

  Preferably, the scheduling means includes a table means for storing a descriptor corresponding to the control frame stored in the storage means for each optical network unit, and a descriptor corresponding to the user data frame stored in the storage means. A user data queue for queuing is compared with a scheduled time and a current time at a predetermined cycle, which is calculated from time information included in a control frame corresponding to the descriptor stored in the table means and stored in the storage means. Transmitting means for selectively outputting a descriptor stored in a table means and a descriptor queued in a user data queue in accordance with a result of comparison by the comparing means. Is output by the descriptor output means. It sends a frame corresponding to the descriptor from the storage means reads, to the optical network unit.

  More preferably, the descriptor output means is provided when the earliest time among the scheduled transmission times calculated from the time information included in the control frame corresponding to the descriptor stored in the table means exceeds the current time. Sends the descriptor of the control frame queued in the control frame queue to the transmitting means, and the earliest time among the scheduled transmission times calculated from the time information included in the control frame corresponding to the descriptor stored in the table means If the current time does not exceed the current time, the descriptor of the user data frame queued in the user data queue is transmitted to the transmitting means.

  According to another aspect of the present invention, there is provided a frame scheduling method for an optical line terminal which transmits a control frame and a user data frame to an optical network unit, comprising: Generating and storing a control frame to be transmitted to the optical network unit in response to the control frame obtained, receiving and storing a user data frame from an upper network, and a scheduled transmission time of the stored control frame. Scheduling the stored user data frame and control frame by comparing the stored user data frame and control frame, and transmitting the stored user data frame and control frame to the optical network unit according to the scheduling result. Steps.

  According to an aspect of the present invention, the scheduling unit compares the scheduled transmission time of the control frame stored by the storage unit with the current time, and schedules the user data frame and the control frame stored in the storage unit. Therefore, the control frame can be sent to the optical network unit by the scheduled time, and the delay of the user data frame can be minimized.

  Further, the descriptor output means selectively outputs the descriptors queued in the control frame queue and the user data queue according to the comparison result by the comparison means. It is possible to transmit to the optical network unit.

  Further, it is possible to easily determine the transmission timing of the control frame and the user data frame.

  In addition, urgent notices such as a notice of a system abnormality can be immediately sent to the optical network unit.

  Further, since the comparing means compares the estimated transmission time calculated from the time information included in the control frame corresponding to the first descriptor queued in the control frame queue stored in the storage means with the current time, There is no need to queue the scheduled transmission time in the control frame queue, and the capacity of the control frame queue can be reduced.

  Further, since the comparing means compares the scheduled time and the current time included in the descriptor stored in the table means with a predetermined cycle, the generating means does not care about the order in which the control frames are actually transmitted to the transmission path. It is possible to perform a control frame generation process at the same time.

  In addition, the comparison unit compares the current transmission time and the scheduled transmission time calculated from the time information included in the control frame corresponding to the descriptor stored in the table unit stored in the storage unit with the predetermined time. The means can perform the control frame generation processing without regard to the order in which the control frames are actually transmitted to the transmission path, and it is not necessary to queue the scheduled transmission time in the control frame queue. The capacity can be reduced.

(First Embodiment)
FIG. 1 is a block diagram showing a schematic configuration of the OLT according to the first embodiment of the present invention. The OLT includes a receiving unit 11 that receives a frame by converting an optical signal from an ONU into an electric signal, a transmitting unit 12 that sends a data frame received from the receiving unit 11 to an upper network, and a receiving unit 11 that receives a data frame from the receiving unit 11. A control frame processing unit 13 that generates a grant frame based on the received report frame and controls its transmission, a user data receiving unit 14 that receives a user data frame from an upper network, and a user data receiving unit 14 that receives the grant frame A buffer memory 15 for storing user data frames and control frames generated by the control frame processing unit 13; a transmission unit 16 for transmitting frames stored in the buffer memory 15 to the ONU; and user data stored in the buffer memory 15 Scheduling of frames and control frames A scheduler 17 for the ring, and a timer 18. Note that the buffer memory 15 may be any one that can store data, such as a register, a flip-flop circuit, and a latch circuit.

  Further, the scheduler 17 includes a control frame queue 21 for queuing the descriptor of the control frame, a user data queue 22 for queuing the descriptor of the user data frame, and a descriptor of the control frame queued in the control frame queue 21. And a selector 23 for selectively outputting a descriptor of the user data frame queued in the user data queue 22.

  Further, the selector 23 includes a comparator unit 31 that compares the scheduled transmission time of the first control frame queued in the control frame queue 21 with the current time of the timer 18, and the control frame according to the comparison result by the comparator unit 31. A queue management unit 32 that manages a descriptor of a control frame queued in the queue 21 and a descriptor of a user data frame stored in the user data queue 22, and transmits the descriptor output from the queue management unit 32 to the transmission unit 16. And a descriptor transmitting unit 33 that performs the processing.

  The receiving unit 11 receives the optical signal from the ONU, converts it into an electric signal, and reads a header portion of the received frame to determine whether the received frame is a data frame or a control frame such as a report frame. If the received frame is a data frame, the receiving unit 11 transfers the data frame to the transmitting unit 12. If the received frame is a control frame, the receiving unit 11 transfers the control frame to the control frame processing unit 13.

  When receiving the data frame from the receiving unit 11, the transmitting unit 12 sends the data frame to the upper network.

  The control frame processing unit 13 has a band allocation calculation function and a downlink control frame creation function. Upon receiving the report frame from the receiving unit 11, the control frame processing unit 13 creates a grant frame (control frame) and transfers it to the buffer memory 15, and creates a descriptor corresponding to the control frame to create a control frame queue 21 Transfer to This descriptor includes the frame length of the control frame, information indicating where the control frame is stored in the buffer memory 15, the scheduled transmission time of the control frame (GATEtx), and the like.

  Grant_start indicates the start time of the grant notified by the control frame, Proc indicates the processing time required from when the ONU receives the control frame to actually start transmitting the frame, RTT indicates the propagation delay time between the OLT and the ONU, and Assuming that the time required for transmitting a user data frame having a frame length is Tx1500, the scheduled transmission time GATEtx is as follows.

GATEtx = Grant_start-Proc-RTT-Tx1500 (1)
Equation (1) indicates that the control frame must arrive at the ONU at the time of (Grant_start-Proc).

  The user data receiving unit 14 receives a user data frame from the upper network, transfers the user data frame to the buffer memory 15, creates a descriptor corresponding to the user data frame, and transfers the descriptor to the user data queue 22. The descriptor stores the frame length of the user data frame, information indicating where the user data frame is stored in the buffer memory 15, and the like.

  The buffer memory 15 accumulates control frames and user data frames transferred from the control frame processing unit 13 and the user data receiving unit 14. Then, the transmission unit 16 refers to the descriptor transmitted from the descriptor transmission unit 33, reads a control frame or a user data frame corresponding to the descriptor from the buffer memory 15, and transmits the read control frame or user data frame to the ONU.

  The control frame queue 21 is configured by a FIFO (First In First Out), and queues the descriptor of the control frame output from the control frame processing unit 13. The user data queue 22 is constituted by a FIFO, and queues a descriptor of a user data frame output from the user data receiving unit 14. The user data queue 22 is assumed to be a queue equivalent to IEEE (the Institute of Electrical and Electronics Engineers, Inc.) 802.1, and may be plural or one.

  The comparator unit 31 compares the scheduled transmission time of the first control frame queued in the control frame queue 21 with the current time of the timer 18, and outputs the comparison result to the queue management unit 32.

  When the control frame queue 21 is empty and the user data queue 22 is not empty, the queue management unit 32 reads the descriptor of the first user data frame from the user data queue 22 and sends the descriptor to the descriptor transmission unit 33.

  When the control frame queue 21 is not empty and the user data queue 22 is empty, the queue management unit 32 refers to the result of comparison by the comparator unit 31 and determines that the scheduled transmission time of the first descriptor of the control frame queue 21 is It is determined whether the time has passed. If the scheduled transmission time of the head descriptor exceeds the current time, the head descriptor is sent to the descriptor transmission unit 33. If the scheduled transmission time of the head descriptor does not exceed the current time, the head descriptor is not transmitted.

  When both the control frame queue 21 and the user data queue 22 are not empty, the queue management unit 32 refers to the comparison result by the comparator unit 31 and sets the scheduled transmission time of the head descriptor of the control frame queue 21 to the current time. Determine if it is exceeded. If the scheduled transmission time of the head descriptor exceeds the current time, the head descriptor is sent to the descriptor transmission unit 33. If the scheduled transmission time of the first descriptor does not exceed the current time, a descriptor for one frame is read from the user data queue 22 and the descriptor is transmitted to the descriptor transmission unit 33.

  The queue management unit 32 repeats the above-described processing each time a descriptor corresponding to one frame is transmitted to the descriptor transmission unit 33. When there are a plurality of user data queues 22, when it is determined that the user data queue is to be transmitted, any one of the plurality of user data queues 22 is selected, and a descriptor is selected from the selected user data queue 22. What is necessary is just to read and send it to the descriptor transmission unit 33.

  As described above, according to the OLT according to the present embodiment, the queue management unit 32 determines whether or not the scheduled transmission time of the control frame exceeds the current time by using the descriptor of one of the control frame and the user data frame. Is selected, the control frame can be sent to the ONU by the scheduled time, and the delay of the user data frame can be minimized to prevent the service from deteriorating.

  Further, since the scheduler 17 performs scheduling of control frames and user data frames, when the control frame processing unit 13 is realized by a microprocessor, the processor can concentrate on only control frame generation, thereby improving processing performance. Becomes possible. For example, when the microprocessor also performs scheduling, in order to generate a control frame and transmit the control frame at a certain time, it is conceivable to set that time in a timer and perform another process until the time comes. . However, at that time, the microprocessor must perform control frame transmission processing, and must temporarily suspend the processing that has been performed. If the interrupted process requires real-time processing, the overhead may impair the real-time processing. By separately providing the scheduler 17, all of these problems can be solved.

  In the case of a synchronous system in which the ONU timer operates in synchronization with a frame received from the OLT, there is no deviation of the timer between the ONU and the OLT. However, in the case of an asynchronous system in which the ONU timer operates independently of the OLT, a timer shift occurs between the ONU and the OLT. That is, in an asynchronous system, the ONU starts a timer when a grant frame arrives and waits until the scheduled transmission time of the control frame or performs another process. If the time until is long, the time lag due to the difference in the accuracy of the timer becomes large. Therefore, the ONU may not be able to transmit at the transmission time of the ONU assumed by the OLT. In order to avoid this, the OLT must allocate a surplus bandwidth to the ONU, and the surplus bandwidth is required according to the number of ONUs, leading to a decrease in upstream bandwidth efficiency.

  In this embodiment, since the control frame is not transmitted until the OLT reaches the scheduled transmission time, the time from when the ONU starts the timer to when the ONU transmits the control frame is shortened, and the shift of the timer is reduced. As a result, it is possible to reduce the above-mentioned surplus bandwidth allocation as much as possible.

(Second embodiment)
The OLT according to the second embodiment of the present invention is different from the OLT according to the first embodiment shown in FIG. 1 only in that a high priority queue 24 is added. Therefore, detailed description of the same configurations and functions will not be repeated.

  FIG. 2 is a diagram showing only a queue portion of the OLT according to the second embodiment of the present invention. In addition to the control frame queue 21 and the user data queue 22, a high priority queue 24 is provided. The control frame processing unit 13 stores in the buffer memory 15 a frame that the user wants to transmit to the ONU immediately, for example, a frame for notifying that an abnormality has occurred, and queues the descriptor of the frame in the high-priority queue 24.

  The queue management unit 32 first determines whether the high-priority queue 24 is empty. If the high-priority queue 24 is not empty, the descriptor is read from the high-priority queue 24 and sent to the descriptor transmission unit 33. When the high-priority queue 24 is empty, the queue management unit 32 sends the descriptor of the control frame or the user data frame to the descriptor transmission unit 33 according to the procedure described in the first embodiment.

  As described above, according to the OLT according to the present embodiment, the queue management unit 32 preferentially selects the descriptor stored in the high-priority queue 24. Can be immediately sent to the ONU.

(Third embodiment)
FIG. 3 is a block diagram showing a schematic configuration of the OLT according to the third embodiment of the present invention. The OLT according to the present embodiment is different from the schematic configuration of the OLT according to the first embodiment shown in FIG. 1 in that the function of the control frame processing unit 13a is different and the function of the control frame queue 21a in the scheduler 17a is different. The only difference is that the function of the queue management unit 32a in the selector 23a is different and that the control information storage unit 34 is added in the selector 23a. Therefore, detailed description of the same configurations and functions will not be repeated.

  The control frame processing unit 13a has a band allocation calculation function and a downlink control frame creation function. When receiving the report frame from the receiving unit 11, the control frame processing unit 13a creates a gate frame (control frame) and transfers it to the buffer memory 15, and creates a descriptor corresponding to the control frame to create a control frame queue 21a. Transfer to The descriptor includes data part information such as information indicating where the control frame is stored in the buffer memory 15, but does not include the scheduled transmission time (GATEtx) of the control frame. In addition, the control frame processing unit 13a queues the descriptor (data part information) corresponding to the control frame in the control frame queue 21a in the descending order of the scheduled transmission time calculated using the equation (1).

  The control information storage unit 34 stores, for each ONU, parameters such as a processing time Proc, a propagation delay time RTT, and a time Tx1500 required for transmitting a user data frame having a maximum frame length used in the calculation of the equation (1). .

  The queue management unit 32a refers to the head descriptor of the control frame queue 21a, reads the grant start time (Grant # 1 Start time) in the control frame (gate frame) stored in the buffer memory 15, and stores the control information. The transmission scheduled time GATEtx shown in Expression (1) is calculated with reference to the parameters stored in the unit 34.

  The comparator section 31 compares the scheduled transmission time calculated by the queue management section 32a with the current time of the timer 18, and outputs the comparison result to the queue management section 32a. The queue management unit 32a performs the same processing as the processing described in the first embodiment with reference to the comparison result by the comparator unit 31.

  FIG. 4 is a diagram showing a configuration of a gate frame defined in IEEE802.3. The gate frame includes a destination address (Destination Address) of the gate frame, a source address (Source Address), information (Length / Type) such as a frame length, data frame / control frame identification information, and a gate frame / report. Identification information such as a frame (Opcode), a time stamp (Timestamp) used for time adjustment in the ONU, information indicating the number of grants (Number of Grants / Flags), and start of the first grant Time (Grant # 1 Start time) and grant amount (Grant # 1 Length), second grant start time (Grant # 2 Start time) and grant amount (Grant # 2 Length), and third grant start The time (Grant # 3 Start time) and the grant amount (Grant # 3 Length), the start time of the fourth grant (Grant # 4 Start time) and the grant amount (Grant # 4 Length), and the ON-side laser ON Later synchronization Including the time (Sync Time) for taking, padding data (Pad / Reserved), and FCS (Frame Check Sequence). It is assumed that the gate frame has a fixed length of 64 bytes, and the first to fourth grants are arranged in order of earliest start time.

  The queue management unit 32a calculates the scheduled transmission time GATEtx with reference to the start time (Grant # 1 Start time) of the first grant shown in FIG.

  As described above, according to the OLT in the present embodiment, the queue management unit 32a calculates the scheduled transmission time GATEtx by referring to the grant start time included in the gate frame stored in the buffer memory 15. Therefore, it is not necessary to queue the scheduled transmission time in the control frame queue 21a, and the capacity of the control frame queue 21a can be reduced.

  Further, since the process of reflecting the scheduled transmission time on the descriptor by the control frame processing unit 13a can be reduced, the control frame processing unit 13a can concentrate on the GATE creation process (Grant start, Grant length).

(Fourth embodiment)
FIG. 5 is a block diagram showing a schematic configuration of the OLT according to the fourth embodiment of the present invention. The OLT according to the present embodiment is different from the schematic configuration of the OLT according to the first embodiment shown in FIG. 1 in that the function of the control frame processing unit 13b is different. The only difference is that it is replaced by the transmission table 25 and the function of the queue management unit 32b in the selector 23b is different. Therefore, detailed description of the same configurations and functions will not be repeated.

  The control frame transmission table 25 stores the descriptor of the control frame output from the control frame processing unit 13b, and has an area in which the descriptor of the control frame corresponding to each ONU is stored. This descriptor includes information indicating where the control frame is stored in the buffer memory 15, a scheduled transmission time of the control frame (GATEtx), and the like.

  The control frame processing unit 13b has a band allocation calculation function and a downlink control frame creation function. When receiving the report frame from the receiving unit 11, the control frame processing unit 13b creates a gate frame as shown in FIG. 4 and transfers it to the buffer memory 15, and creates a descriptor corresponding to the gate frame to create a control frame. It is stored in an area of the transmission table 25 corresponding to the ONU.

  The queue management unit 32b searches for the scheduled transmission time of each ONU stored in the control frame transmission table 25 at a predetermined cycle, extracts the earliest scheduled transmission time, and outputs it to the comparator unit 31.

  The comparator unit 31 compares the scheduled transmission time output from the queue management unit 32b with the current time of the timer 18, and outputs the comparison result to the queue management unit 32b. The queue management unit 32b performs the same process as the process described in the first embodiment with reference to the comparison result by the comparator unit 31. The processing target of the queue management unit 32b is a descriptor corresponding to the scheduled transmission time output to the comparator unit 31.

  As described above, according to the OLT according to the present embodiment, the queue management unit 32b searches the scheduled transmission time of each ONU stored in the control frame transmission table 25 at a predetermined cycle, and determines the scheduled transmission time with the earliest time. Since the time is extracted and output to the comparator unit 23b, the control frame processing unit 13b can perform the control frame generation processing without regard to the order in which the control frame is actually transmitted to the transmission path. became.

  For example, the control frame processing unit 13b needs to transmit a control frame to a transmission path earlier for an ONU with a large RTT than for an ONU with a small RTT. It is not necessary to always match the order of generating frames with the order of transmission on the transmission path.

  In addition, even when a control frame to be transmitted immediately is generated, the control frame processing unit 13b can perform the control simply by storing the descriptor in the control frame transmission table 25, and the high-priority control described in the second embodiment can be performed. It is no longer necessary to provide the degree queue 24.

(Fifth embodiment)
FIG. 6 is a block diagram illustrating a schematic configuration of the OLT according to the fifth embodiment of the present invention. The OLT according to the present embodiment is different from the schematic configuration of the OLT according to the fourth embodiment shown in FIG. 5 in that the function of the control frame processing unit 13c is different and the function of the queue management unit 32c in the selector 23c is different. The only difference is that the control information storage unit 34 is added to the selector 23c. Therefore, detailed description of the same configurations and functions will not be repeated.

  The control frame processing unit 13c has a band allocation calculation function and a downlink control frame creation function. Upon receiving the report frame from the receiving unit 11, the control frame processing unit 13c creates a gate frame (control frame) and transfers it to the buffer memory 15, and creates a descriptor corresponding to the gate frame to create a control frame transmission table. It is stored in an area corresponding to 25 ONUs. The descriptor includes data part information such as information indicating where the control frame is stored in the buffer memory 15, but does not include the scheduled transmission time (GATEtx) of the control frame.

  The control information storage unit 34 stores, for each ONU, parameters such as a processing time Proc, a propagation delay time RTT, and a time Tx1500 required for transmitting a user data frame having a maximum frame length, which are used in the calculation of Expression (1). .

  The queue management unit 32c refers to the descriptor of each ONU stored in the control frame transmission table 25 at a predetermined cycle and refers to the start time of the grant (gate frame) in the control frame (gate frame) of each ONU stored in the buffer memory 15. Grant # 1 Start time) is read out, and the scheduled transmission time GATEtx shown in Expression (1) is calculated with reference to the parameters stored in the control information storage unit 34. Then, the scheduled transmission time with the earliest time is output to the comparator unit 31.

  The comparator unit 31 compares the scheduled transmission time calculated by the queue management unit 32c with the current time of the timer 18, and outputs the comparison result to the queue management unit 32c. The queue management unit 32c performs the same processing as the processing described in the first embodiment with reference to the comparison result by the comparator unit 31. The processing target of the queue management unit 32c is a descriptor corresponding to the scheduled transmission time output to the comparator unit 31.

  As described above, according to the OLT in the present embodiment, the queue management unit 32c calculates the scheduled transmission time GATEtx with reference to the grant start time included in the gate frame stored in the buffer memory 15. Therefore, in addition to the effects described in the fourth embodiment, the capacity of the control frame transmission table 25 can be reduced.

  In addition, the control frame processing unit 13c can reduce the scheduled transmission time calculation process and the process of reflecting the calculated scheduled transmission time on the descriptor, so that the control frame processing unit 13c performs the GATE creation process (Grant start, Grant length). Can concentrate on

  The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

FIG. 2 is a block diagram illustrating a schematic configuration of an OLT according to the first embodiment of the present invention. FIG. 14 is a diagram illustrating only a queue part of an OLT according to the second embodiment of this invention. It is a block diagram showing a schematic structure of OLT in a 3rd embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration of a gate frame defined in IEEE802.3. It is a block diagram showing a schematic structure of OLT in a 4th embodiment of the present invention. It is a block diagram showing a schematic structure of OLT in a 5th embodiment of the present invention. It is a block diagram showing a schematic structure of a conventional PON system. FIG. 10 is a sequence diagram for explaining an operation procedure of a conventional PON system.

Explanation of reference numerals

  Reference Signs List 11 receiving unit, 12, 16 transmitting unit, 13, 13a, 13b, 13c control frame processing unit, 14 user data receiving unit, 15 buffer memory, 17, 17a, 17b, 17c scheduler, 18 timer, 21, 21a control frame queue , 22 user data queue, 23, 23a, 23b, 23c selector, 24 high priority queue, 25 control frame transmission table, 31 comparator section, 32, 32a, 32b, 32c queue management section, 33 descriptor transmission section, 34 control information Storage unit, 101 OLT, 102-1 to n ONUs, 103-1 to 103-n buffers, 104 transmission lines, 105 splitters, 106 grants, 107 reports, 108 upstream information frames, 109 upper networks, 110 lower networks, 111 user terminal.

Claims (11)

Generating means for generating a control frame to be transmitted to the optical network unit in response to a control frame received from the optical network unit;
Storage means for storing a user data frame received from an upper network and a control frame generated by the generation means;
Scheduling means for comparing the scheduled transmission time of the control frame stored by the storage means and the current time, and scheduling the user data frame and the control frame stored in the storage means;
Transmitting means for transmitting a user data frame and a control frame stored in the storage means to the optical line terminal according to a scheduling result by the scheduling means. The scheduling means, a control frame queue for queuing a descriptor corresponding to the control frame stored in the storage means,
A user data queue for queuing a descriptor corresponding to the user data frame stored in the storage means,
Comparison means for comparing the current time with the scheduled transmission time included in the first descriptor queued in the control frame queue,
Descriptor output means for selectively outputting descriptors queued in the control frame queue and the user data queue according to a comparison result by the comparison means,
2. The optical line terminal according to claim 1, wherein said transmitting means reads out a frame corresponding to the descriptor output by said descriptor output means from said storage means and sends it to said optical network unit. The descriptor output unit, when the scheduled transmission time included in the first descriptor queued in the control frame queue exceeds the current time, the descriptor of the control frame queued in the control frame queue. Sending to the transmitting means,
If the scheduled transmission time included in the first descriptor queued in the control frame queue does not exceed the current time, the descriptor of the user data frame queued in the user data queue is sent to the transmission unit. 3. The optical line terminal according to claim 2, wherein: The scheduling means further includes a high-priority queue for queuing a descriptor of an emergency frame to be transmitted to the optical network unit,
4. The optical subscription according to claim 2, wherein the descriptor output unit sends the descriptor of the urgent frame stored in the storage unit to the transmission unit preferentially when there is a descriptor in the high priority queue. Line terminal equipment. The scheduling means, a control frame queue for queuing a descriptor corresponding to the control frame stored in the storage means,
A user data queue for queuing a descriptor corresponding to the user data frame stored in the storage means,
Comparison means for comparing the current transmission time with the scheduled transmission time calculated from the time information included in the control frame corresponding to the first descriptor queued in the control frame queue, stored in the storage means,
Descriptor output means for selectively outputting descriptors queued in the control frame queue and the user data queue according to a comparison result by the comparison means,
2. The optical line terminal according to claim 1, wherein said transmitting means reads out a frame corresponding to the descriptor output by said descriptor output means from said storage means and sends it to said optical network unit. The descriptor output means, if the scheduled transmission time calculated from the time information included in the control frame corresponding to the first descriptor queued in the control frame queue exceeds the current time, the control frame queue Sending the descriptor of the control frame queued to the transmitting means,
If the scheduled transmission time calculated from the time information included in the control frame corresponding to the first descriptor queued in the control frame queue does not exceed the current time, it is queued in the user data queue. 6. The optical line terminal according to claim 5, wherein a descriptor of a user data frame is transmitted to said transmitting means. Table means for storing a descriptor corresponding to the control frame stored in the storage means for each optical network unit,
A user data queue for queuing a descriptor corresponding to the user data frame stored in the storage means,
A comparing unit for comparing the scheduled transmission time and the current time included in the descriptor stored in the table unit with a predetermined period,
Descriptor output means for selectively outputting descriptors stored in the table means and descriptors queued in the user data queue, according to a comparison result by the comparison means,
2. The optical line terminal according to claim 1, wherein said transmitting means reads out a frame corresponding to the descriptor output by said descriptor output means from said storage means and sends it to said optical network unit. The descriptor output means, when the earliest time among the scheduled transmission times included in the descriptor stored in the table means exceeds the current time, outputs the descriptor of the control frame stored in the table means. Sending to the transmitting means,
If the earliest time among the scheduled transmission times included in the descriptor stored in the table means does not exceed the current time, the descriptor of the user data frame queued in the user data queue is sent to the transmission means. The optical line terminal according to claim 7, which transmits the signal. Table means for storing a descriptor corresponding to the control frame stored in the storage means for each optical network unit,
A user data queue for queuing a descriptor corresponding to the user data frame stored in the storage means,
Comparison means for comparing the scheduled time and the current time calculated from the time information included in the control frame corresponding to the descriptor stored in the table means at a predetermined cycle, stored in the storage means,
Descriptor output means for selectively outputting descriptors stored in the table means and descriptors queued in a user data queue, according to a comparison result by the comparison means,
2. The optical line terminal according to claim 1, wherein said transmitting means reads out a frame corresponding to the descriptor output by said descriptor output means from said storage means and sends it to said optical network unit. The descriptor output means, if the earliest time among the scheduled transmission times calculated from the time information included in the control frame corresponding to the descriptor stored in the table means exceeds the current time, the control frame Sending a descriptor of the control frame queued in the queue to the transmitting means,
If the earliest time among the scheduled transmission times calculated from the time information included in the control frame corresponding to the descriptor stored in the table means does not exceed the current time, the data is queued in the user data queue. 10. The optical line terminal according to claim 9, wherein a descriptor of a user data frame is transmitted to said transmitting means. A frame scheduling method for an optical line terminal transmitting a control frame and a user data frame to an optical network unit, comprising:
Generating and storing a control frame to be transmitted to the optical network unit according to the control frame received from the optical network unit;
Receiving and storing the user data frame from the upper network;
Comparing the scheduled transmission time and the current time of the stored control frame, and scheduling the stored user data frame and control frame;
Sending the stored user data frame and control frame to the optical network unit according to the scheduling result.

Images