Station-side device, optical subscriber-side terminating device, communication system, bandwidth allocation method, frame transmission method, and computer program

Abstract

This station-side device comprises: a cycle division unit that causes a plurality of bandwidth allocation methods to be alternatingly executed within a prescribed cycle; a first bandwidth allocation unit that performs fixed bandwidth allocation for evenly allocating bandwidths to each among one or more optical subscriber line terminating devices connected to the station-side device according to an instruction from the cycle division unit, and that transmits a control signal including a bandwidth allocation result and information indicating that a transmission target frame is a first frame for which the demand for a real-time property is high to the one or more optical subscriber line terminating devices; and a second bandwidth allocation unit that performs dynamic bandwidth allocation for allocating bandwidths according to the demand from each of the one or more optical subscriber line terminating devices connected to the station-side device according to an instruction from the cycle division unit, and that transmits a control signal including a bandwidth allocation result and information indicating that a transmission target frame is a second frame other than the first frame to the one or more optical subscriber line terminating devices.　

Description

Station side device, optical subscriber side terminal device, communication system, bandwidth allocation method, frame transmission method, and computer program

[0001] The present invention relates to a station device, an optical subscriber terminal device, a communication system, a bandwidth allocation method, a frame transmission method, and a computer program.

[0002] Conventionally, a dynamic bandwidth allocation (DBA) algorithm, as shown in Fig. 7, has been used as a method for allocating bandwidth in the upstream direction in a PON (Passive Optical Network) system composed of an OLT (Optical Line Terminal) and one or more ONUs (Optical Network Units) (see, for example, Non-Patent Document 1). Fig. 7 is a diagram showing an example of upstream bandwidth allocation in a conventional PON system. As shown in Fig. 7, when an upstream signal (referred to as a frame in Fig. 6) to be transmitted is generated, each ONU stores the upstream signal in a buffer.

[0003] In the DBA algorithm, the OLT transmits a GATE frame to each ONU to notify the ONU of the transmission timing and transmission data volume of the upstream signal calculated by the DBA algorithm, and each ONU transmits to the OLT a REPORT frame indicating the notified transmission data volume from among the buffered frames and the current buffer volume of the ONU frames, etc. In the DBA algorithm, bandwidth is allocated to each ONU using an arbitrary algorithm according to the information in the REPORT frame.

[0004] As a method of allocating bandwidth other than DBA, the Fixed Bandwidth Allocation (FBA) algorithm has been proposed. The FBA algorithm is a method of allocating bandwidth equally to N ONUs (N is an integer equal to or greater than 1) connected to an OLT without using a REPORT frame.

[0005] On the other hand, when applying a PON system to an industrial network, the issue is how to process IRT (Isochronous Real-time) class frames (hereinafter referred to as "IRT frames"), which require high real-time performance, and frames other than IRT frames (hereinafter referred to as "other frames"). For IRT frames, low jitter is achieved by sending a fixed amount of data within a fixed cycle and repeating that cycle. In one prior study, a scheduler that achieves time determinism and a general DBA algorithm are simultaneously operated, and the final bandwidth allocation is determined by merging the bandwidth allocation information scheduled separately by these algorithms (see, for example, Non-Patent Document 2).

[0006] NTT Access Network Service Systems Laboratories, "GE-PON Technology," NTT Technical Journal, Basic Technology Course, October 2005. K. Christodoulopoulos, S. Bidkar, T. Pfeiffer, R. Bonk, "Deterministically Scheduled PON for Industrial Applications," Optical Fiber Communication Conference (OFC), Tu3F.5, 2023.

[0007] When applying a PON system to an industrial network, if bandwidth allocation is performed using only the DBA algorithm, the time determinism of IRT frames cannot be guaranteed. On the other hand, if bandwidth for IRT frames is allocated using only the FBA algorithm, the network becomes dedicated to IRT frames, and other frames cannot be used on the line, resulting in a problem of reduced bandwidth utilization efficiency. Furthermore, the method shown in Non-Patent Document 2 also has the problem of an increased amount of calculations.

[0008] In view of the above circumstances, an object of the present invention is to provide a technique that can improve bandwidth utilization efficiency while suppressing an increase in the amount of calculation.

[0009] One aspect of the present invention is a line terminal in a communication system comprising one or more optical line terminals and a line terminal accommodating the one or more optical line terminals, the line terminal comprising: a periodic allocation unit that alternately executes a plurality of bandwidth allocation methods within a predetermined period; a first bandwidth allocating unit that, in response to an instruction from the periodic allocation unit, performs a fixed bandwidth allocation that allocates bandwidth equally to each of the one or more optical line terminals connected to the line terminal, and transmits a control signal to the one or more optical line terminals, the control signal including the bandwidth allocation result and information indicating that the frame to be transmitted is a first frame with a high requirement for real-time performance; and a second bandwidth allocating unit that, in response to an instruction from the periodic allocation unit, performs a dynamic bandwidth allocation that allocates bandwidth in accordance with a request from each of the one or more optical line terminals connected to the line terminal, and transmits a control signal to the one or more optical line terminals, the control signal including the bandwidth allocation result and information indicating that the frame to be transmitted is a second frame other than the first frame.

[0010] One aspect of the present invention is an optical subscriber line termination device in a communication system comprising one or more optical subscriber line termination devices and a central office device accommodating the one or more optical subscriber line termination devices, the optical subscriber line termination device comprising: a frame allocation unit that identifies whether a frame input as data to be transmitted is a first frame that has a high requirement for real-time performance or a second frame other than the first frame and allocates the frame; a first frame processing unit that transmits the first frame allocated to the frame allocation unit to the central office device within a predetermined period based on a control signal including a bandwidth allocation result obtained from the central office device and information indicating the frame to be transmitted; and a second frame processing unit that transmits the second frame allocated to the frame allocation unit to the central office device at a timing within the predetermined period that is different from the transmission timing of the first frame based on a control signal including a bandwidth allocation result obtained from the central office device and information indicating the frame to be transmitted.

[0011] One aspect of the present invention is a communication system comprising one or more optical line terminals and a central office device accommodating the one or more optical line terminals, wherein the central office device comprises a periodic allocation unit that alternately executes a plurality of bandwidth allocation methods within a predetermined period, a first bandwidth allocation unit that, in response to an instruction from the periodic allocation unit, performs fixed bandwidth allocation to equally allocate bandwidth to each of the one or more optical line terminals connected to the central office device, and transmits a control signal to the one or more optical line terminals including a bandwidth allocation result and information indicating that the frame to be transmitted is a first frame with a high real-time requirement, and a dynamic bandwidth allocation that, in response to an instruction from the periodic allocation unit, allocates bandwidth according to a request from each of the one or more optical line terminals connected to the central office device, and the bandwidth allocation result and the frame to be transmitted are transmitted in the first frame. and a second bandwidth allocation unit that transmits to the one or more optical subscriber line terminals a control signal including information indicating that the frame is a second frame other than a first frame, wherein the one or more optical subscriber line terminals comprise: a frame allocation unit that identifies whether a frame input as data to be transmitted is the first frame or the second frame and allocates the frame; a first frame processing unit that transmits the first frame allocated to the frame allocation unit to the optical line terminal within a predetermined period based on the control signal received from the optical line terminal; and a second frame processing unit that transmits the second frame allocated to the frame allocation unit to the optical line terminal at a timing within the predetermined period that is different from the transmission timing of the first frame based on the control signal received from the optical line terminal.

[0012] One aspect of the present invention is a bandwidth allocation method performed by an optical line terminal in a communication system including one or more optical subscriber line terminals and an optical line terminal accommodating the one or more optical subscriber line terminals, the method comprising: performing fixed bandwidth allocation, which allocates bandwidth equally to each of the one or more optical subscriber line terminals connected to the optical line terminal, within a predetermined period; transmitting a control signal to the one or more optical subscriber line terminals, the control signal including the bandwidth allocation result of the fixed bandwidth allocation and information indicating that a frame to be transmitted is a first frame having a high real-time requirement; performing dynamic bandwidth allocation, which allocates bandwidth in accordance with a request from each of the one or more optical subscriber line terminals connected to the optical line terminal, at a timing within the predetermined period different from the timing at which the fixed bandwidth allocation is performed; transmitting a control signal to the one or more optical subscriber line terminals, the control signal including the bandwidth allocation result of the dynamic bandwidth allocation and information indicating that the frame to be transmitted is a second frame other than the first frame; and alternately performing the fixed bandwidth allocation and the dynamic bandwidth allocation within the predetermined period.

[0013] One aspect of the present invention is a frame transmission method performed by an optical line terminal in a communication system including one or more optical line terminals and a central office device accommodating the one or more optical line terminals, the frame transmission method identifying whether a frame input as data to be transmitted is a first frame having a high requirement for real-time performance or a second frame other than the first frame, and allocating the frame, transmitting the first frame to the central office device within a predetermined period based on a control signal including a bandwidth allocation result obtained from the central office device and information indicating the frame to be transmitted, and transmitting the second frame to the central office device at a timing within the predetermined period that is different from the transmission timing of the first frame, based on a control signal including a bandwidth allocation result obtained from the central office device and information indicating the frame to be transmitted.

[0014] One aspect of the present invention is a computer program for causing a computer to function as an optical line terminal in a communication system including one or more optical line terminals and an optical line terminal accommodating the one or more optical line terminals, the computer program causing a computer to function as the optical line terminal within a predetermined period to perform fixed bandwidth allocation, which allocates bandwidth equally to each of the one or more optical line terminals connected to the optical line terminal, and to transmit to the one or more optical line terminals a control signal including a bandwidth allocation result from the fixed bandwidth allocation and information indicating that the frame to be transmitted is a first frame with a high requirement for real-time performance, and at a timing within the predetermined period different from the timing at which the fixed bandwidth allocation is performed, to perform dynamic bandwidth allocation, which allocates bandwidth in accordance with a request from each of the one or more optical line terminals connected to the optical line terminal, and to transmit to the one or more optical line terminals a control signal including a bandwidth allocation result from the dynamic bandwidth allocation and information indicating that the frame to be transmitted is a second frame other than the first frame, and the computer program causing the fixed bandwidth allocation and the dynamic bandwidth allocation to be alternately performed within the predetermined period.

[0015] One aspect of the present invention is a computer program for causing a computer to function as an optical subscriber line terminal in a communication system comprising one or more optical subscriber line terminals and a station side terminal accommodating the one or more optical subscriber line terminals, the computer program causing the computer to identify whether a frame input as data to be transmitted is a first frame which has a high requirement for real-time performance or a second frame other than the first frame, and to allocate the frame; causing the computer to transmit the first frame to the station side device within a predetermined period based on a control signal including a bandwidth allocation result obtained from the station side device and information indicating the frame to be transmitted; and causing the computer to transmit the second frame to the station side device at a timing within the predetermined period that is different from the transmission timing of the first frame, based on a control signal including a bandwidth allocation result obtained from the station side device and information indicating the frame to be transmitted.

[0016] According to the present invention, it is possible to improve the bandwidth utilization efficiency while suppressing an increase in the amount of calculation.

[0017] Fig. 1 is a diagram for explaining an overview of processing in a communication system in an embodiment. Fig. 2 is a diagram showing an example of the configuration of a communication system in an embodiment. Fig. 3 is a diagram showing an example of the configuration of a transmission control unit provided in an ONU in an embodiment. Fig. 4 is a diagram showing an example of the configuration of a bandwidth allocation unit provided in an OLT in an embodiment. Fig. 5 is a sequence diagram showing an example of the processing flow of a communication system in an embodiment. Fig. 6 is a diagram showing an example of bandwidth allocation in the upstream direction in a conventional PON system.

[0018] An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining an overview of processing in a communication system in the embodiment. FIG. 1 shows one OLT and three ONUs as an example. As shown in FIG. 1, the OLT in the embodiment allocates bandwidth by alternately repeating, at a predetermined cycle, an FBA algorithm that allocates bandwidth for transferring only IRT frames and a DBA algorithm that allocates bandwidth for transferring other frames. The IRT frame is one aspect of a first frame. The other frames are one aspect of a second frame.

[0019] Specifically, each ONU has a buffer for IRT frames and a buffer for other frames, and stores IRT frames and other frames in the respective buffers. The OLT assigns information indicating whether to transmit an IRT frame or information indicating whether to transmit other frames, as well as the transmission timing and transmission data amount, to a GATE frame and transmits it to each ONU. Based on the GATE frame transmitted from the OLT, each ONU determines whether to transmit an IRT frame or other frames at the transmission timing indicated in the GATE frame. Note that the example shown in Figure 1 is just one example, and the range of the FBA section that accepts IRT frames and the DBA section that accepts other frames within a specified period is variable.

[0020] As in the past, when N ONUs are connected, the OLT divides the bandwidth into N parts and allocates it to each ONU using the FBA algorithm, while in the DBA algorithm, it allocates bandwidth to each ONU using an arbitrary algorithm. This configuration allows IRT frames for each ONU to be allocated fixedly within a predetermined cycle, enabling time-deterministic frame transfer. Other frames can also be transmitted from the ONU to the OLT using surplus bandwidth (bandwidth not used for transmitting IRT frames). As a result, bandwidth utilization efficiency can be improved while suppressing increases in computational complexity. The configuration of each device used to realize the above processing is described in detail below.

[0021] (Details) Fig. 2 is a diagram showing an example of the configuration of a communication system 100 according to an embodiment. The communication system 100 includes one or more ONUs 10-1 to 10-N, an OLT 20, and an optical splitter 30. The one or more ONUs 10 and the OLT 20 are connected via the optical splitter 30. As shown in Fig. 2, the communication system 100 is, for example, a PON system. Note that the communication system 100 may also be configured such that one ONU 10 and the OLT 20 are directly connected (one-to-one).

[0022] The ONU 10 converts an IRT frame or other frame into an optical signal using the allocated bandwidth at the transmission timing allocated by the OLT 20 and transmits it to the OLT 20. The ONU 10 is provided on the electric utility side and is an optical subscriber side termination device that terminates an optical signal.

[0023] The OLT 20 transmits a GATE frame indicating that it will accept frames corresponding to each section in an FBA section, which is a section for accepting transmission of IRT frames, and a DBA section, which is a section for accepting transmission of other frames, to each ONU 10 during a predetermined period. Specifically, the OLT 20 transmits a GATE frame including information indicating that it will accept transmission of IRT frames to each ONU 10 in the FBA section, and transmits a GATE frame including information indicating that it will accept transmission of other frames to each ONU 10 in the DBA section. The OLT 20 is provided on the electric utility side and is a central office device that terminates optical signals.

[0024] The optical splitter 30 connects each ONU 10 to the OLT 20. The optical splitter 30 multiplexes optical signals transmitted from each ONU 10 and outputs the multiplexed optical signals to the OLT 20, and splits optical signals transmitted from the OLT 20 and outputs the split optical signals to each ONU 10.

[0025] Next, the configuration of each of the ONU 10 and the OLT 20 will be described. The ONU 10 includes a physical layer function unit 11 and a transmission control unit 12. The physical layer function unit 11 performs processing related to the transmission and reception of optical signals. The physical layer function unit 11 performs processing such as converting various frames (e.g., REPORT frames, IRT frames, and other frames) into optical signals and converting optical signals transmitted from the OLT 20 into electrical signals.

[0026] The transmission control unit 12 controls the transmission timing of the IRT frame and other frames based on the GATE frame transmitted from the OLT 20. The transmission control unit 12 determines the transmission timing of the IRT frame and other frames based on, for example, the GATE frame, and causes the IRT frame to be transmitted to the OLT 20 via the physical layer function unit 11 at the transmission timing of the IRT frame. The transmission control unit 12 determines the transmission timing of the IRT frame and other frames based on, for example, the GATE frame, and causes the other frames to be transmitted to the OLT 20 via the physical layer function unit 11 at the transmission timing of the other frames.

[0027] The OLT 20 includes a physical layer function unit 21 and a bandwidth allocation unit 22. The physical layer function unit 21 performs processing related to the transmission and reception of optical signals. The physical layer function unit 21 performs processing such as converting a GATE frame output from the bandwidth allocation unit 22 into an optical signal, and converting an optical signal (REPORT frame) transmitted from the ONU 10 into an electrical signal.

[0028] The bandwidth allocating unit 22 allocates bandwidth using the FBA algorithm and the DBA algorithm. The bandwidth allocating unit 22 allocates bandwidth by switching the algorithm used for bandwidth allocation at a predetermined period. The bandwidth allocating unit 22 allocates bandwidth using either the FBA or DBA algorithm based on the REPORT frame transmitted from each ONU 10, and transmits the result of the bandwidth allocation to each ONU 10 in a GATE frame.

[0029] The ONU 10 and the OLT 20 may be implemented as dedicated hardware, or may be implemented as a combination of general-purpose hardware and software, or a combination thereof.

[0030] 3 is a diagram illustrating an example of the configuration of the transmission control unit 12 included in the ONU 10 according to the embodiment. The transmission control unit 12 includes a main signal transmission control unit 121, a frame distribution unit 122, an IRT frame processing unit 123, and an other frame processing unit 124.

[0031] The main signal transmission control unit 121 controls the IRT frame processing unit 123 or the other frame processing unit 124 as to what time and how much data to transmit an IRT frame or other frame based on the GATE frame converted by the physical layer function unit 11. In other words, the main signal transmission control unit 121 controls the transmission timing and transmission data amount of the IRT frame processing unit 123 or the other frame processing unit 124 based on the GATE frame.

[0032] The frame allocation unit 122 identifies whether a frame input as data to be transmitted is an IRT frame or another frame and allocates the frame. For example, if the frame allocation unit 122 identifies an input frame as an IRT frame, it outputs the IRT frame to the IRT frame processing unit 123. For example, if the frame allocation unit 122 identifies an input frame as another frame, it outputs the other frame to the other frame processing unit 124.

[0033] The IRT frame processing unit 123 accumulates IRT frames output from the frame distribution unit 122. The IRT frame processing unit 123 transmits the accumulated IRT frames to the OLT 20 via the physical layer function unit 11 based on the transmission timing and transmission data amount instructed by the main signal transmission control unit 121. In this way, the IRT frame processing unit 123 processes IRT class frames that require high real-time performance.

[0034] The other frame processing unit 124 accumulates other frames output from the frame distribution unit 122. The other frame processing unit 124 transmits the accumulated other frames to the OLT 20 via the physical layer function unit 11 based on the transmission timing and transmission data amount instructed by the main signal transmission control unit 121. In this way, the other frame processing unit 124 processes frames that require less real-time performance than IRT frames.

[0035] 4 is a diagram illustrating an example of the configuration of the bandwidth allocating unit 22 included in the OLT 20 according to the embodiment. The bandwidth allocating unit 22 includes a periodic allocation unit 221, a first bandwidth allocating unit 222, and a second bandwidth allocating unit 223.

[0036] The periodic allocation unit 221 alternately executes a plurality of bandwidth allocation methods within a predetermined period. Specifically, the periodic allocation unit 221 alternately executes a plurality of bandwidth allocation methods by switching the allocation destination of the REPORT frame converted by the physical layer function unit 21 between the first bandwidth allocation unit 222 and the second bandwidth allocation unit 223 within the predetermined period.

[0037] Methods for distributing REPORT frames by the periodic distribution unit 221 include distributing by time, distributing based on the distribution information embedded in the REPORT frame in the ONU 10 to identify whether the REPORT frame is an IRT frame or another frame, and distributing based on the embedded distribution information, and distributing based on the number of times the frame is received.

[0038] (Method of Allocating Based on Time) The period allocating unit 221 allocates a time of a predetermined period to the first band allocating unit 222 as time A, and allocates a time of a predetermined period to the second band allocating unit 223 as time B. Time A + time B is the predetermined period. In this case, when the period allocating unit 221 receives a REPORT frame, it determines whether the time of reception is time A or time B. Here, the reception time may be the time when the REPORT frame is input to the period allocating unit 221, or the time when the REPORT frame is received by the physical layer function unit 21. If the time when the REPORT frame is received is time A, the period allocating unit 221 outputs the REPORT frame to the first band allocating unit 222. On the other hand, if the time when the REPORT frame is received is time B, the period allocating unit 221 outputs the REPORT frame to the second band allocating unit 223.

[0039] (Method of allocating based on allocation information) The periodic allocation unit 221 determines whether an IRT frame or another frame is being transmitted based on the allocation information included in the REPORT frame. If an IRT frame is being transmitted, the periodic allocation unit 221 outputs the REPORT frame to the first band allocation unit 222. On the other hand, if another frame is being transmitted, the periodic allocation unit 221 outputs the REPORT frame to the second band allocation unit 223.

[0040] (Method of Allocating Based on the Number of Receptions) The periodic allocation unit 221 allocates REPORT frames to the first band allocation unit 222 or the second band allocation unit 223 depending on the number of receptions of the REPORT frame. For example, if the number of receptions is set to three, the periodic allocation unit 221 switches the allocation destination of the REPORT frame every time it receives the REPORT frame three times. As a specific example, the periodic allocation unit 221 allocates received REPORT frames to the first band allocation unit 222 until it receives the REPORT frame three times. In other words, the first band allocation unit 222 acquires the REPORT frame three times. Then, after receiving the REPORT frame three times, the periodic allocation unit 221 allocates received REPORT frames to the second band allocation unit 223 until it receives the next three REPORT frames. That is, the second bandwidth allocating unit 223 receives the REPORT frame three times. In this manner, the periodic allocating unit 221 allocates the REPORT frames based on the number of times they are received.

[0041] The first bandwidth allocating unit 222 allocates bandwidth to each ONU 10 using the FBA algorithm based on the REPORT frame output from the periodic allocation unit 221. The FBA algorithm allocates bandwidth equally to each ONU 10, so the first bandwidth allocating unit 222 does not need to use the information included in the REPORT frame. The first bandwidth allocating unit 222 allocates bandwidth to each ONU 10 using the FBA algorithm in response to the input of the REPORT frame output from the periodic allocation unit 221. The first bandwidth allocating unit 222 generates a GATE frame that includes the result of the bandwidth allocation and information indicating that the frame to be transmitted is an IRT frame. The first bandwidth allocating unit 222 outputs the generated GATE frame to the physical layer function unit 21.

[0042] The second bandwidth allocating unit 223 allocates bandwidth to the ONU 10 that is the sender of the REPORT frame using the DBA algorithm, based on the REPORT frame output from the periodic allocation unit 221. The DBA algorithm allocates bandwidth based on the buffer capacity of the ONU 10 included in the REPORT frame. The second bandwidth allocating unit 223 generates a GATE frame that includes the result of the bandwidth allocation and information indicating that the frame to be transmitted is another frame. The second bandwidth allocating unit 223 outputs the generated GATE frame to the physical layer function unit 21.

[0043] 5 and 6 are sequence diagrams showing an example of the processing flow of the communication system 100 in this embodiment. Note that FIGS. 5 and 6 will be explained using two ONUs 10 and an OLT 20 as examples. An IRT frame or other frame is input to ONU 10-1 as data to be transmitted. Here, it is assumed that the IRT frame and other frame are input to ONU 10-1 in order. The frame distribution unit 122-1 buffers the input IRT frame in the IRT frame processing unit 123-1 and buffers the other frame in the other frame processing unit 124-1 (step S101). The transmission control unit 12-1 generates a REPORT frame including the amount of transmission data of the buffered frame. Note that the transmission control unit 12-1 generates a REPORT frame including the amount of transmission data buffered in either the IRT frame processing unit 123-1 or the other frame processing unit 124-1.

[0044] The transmission control unit 12-1 outputs the generated REPORT frame to the physical layer function unit 11-1. The physical layer function unit 11-1 converts the REPORT frame output from the transmission control unit 12-1 into an optical signal and transmits it to the OLT 20 (step S102). The optical signal transmitted from the ONU 10-1 is received by the OLT 20 via the optical splitter 30.

[0045] An IRT frame or other frame is input to ONU 10-2 as data to be transmitted. Here, it is assumed that the IRT frame and other frame are input to ONU 10-2 in order. The frame distribution unit 122-2 buffers the input IRT frame in the IRT frame processing unit 123-2 and buffers the other frame in the other frame processing unit 124-2 (step S103). The transmission control unit 12-2 generates a REPORT frame including the amount of transmission data of the buffered frame. The transmission control unit 12-2 generates a REPORT frame including the amount of transmission data buffered in either the IRT frame processing unit 123-2 or the other frame processing unit 124-2.

[0046] The transmission control unit 12-2 outputs the generated REPORT frame to the physical layer function unit 11-2. The physical layer function unit 11-2 converts the REPORT frame output from the transmission control unit 12-2 into an optical signal and transmits it to the OLT 20 (step S104). The optical signal transmitted from the ONU 10-2 is received by the OLT 20 via the optical splitter 30.

[0047] The physical layer function unit 21 of the OLT 20 receives the optical signals transmitted from the ONUs 10-1 and 10-2 (step S105). The physical layer function unit 21 converts the received optical signals into electrical signals. As a result, the REPORT frames transmitted from the ONUs 10-1 and 10-2 are restored. The physical layer function unit 21 outputs the REPORT frames to the periodic distribution unit 221. The periodic distribution unit 221 distributes the REPORT frames output from the physical layer function unit 21 (step S106). Here, it is assumed that the periodic distribution unit 221 is set to distribute based on time.

[0048] When the periodic allocation unit 221 receives a REPORT frame, it determines whether the time of reception is time A or time B. Here, it is assumed that the time of reception is time A. The periodic allocation unit 221 outputs each received REPORT frame to the first bandwidth allocation unit 222. The first bandwidth allocation unit 222 allocates bandwidth using the FBA algorithm based on each REPORT frame output from the periodic allocation unit 221 (step S107). In the example shown in Figures 5 and 6, since there are two ONUs 10, the first bandwidth allocation unit 222 divides the bandwidth in half and allocates it to ONUs 10-1 and 10-2, respectively.

[0049] The first bandwidth allocating unit 222 generates a GATE frame including the bandwidth allocation result obtained by the FBA algorithm and information indicating that the frame to be transmitted is an IRT frame. The first bandwidth allocating unit 222 outputs the generated GATE frame to the physical layer function unit 21. The physical layer function unit 21 converts the GATE frame output from the first bandwidth allocating unit 222 into an optical signal and transmits it to each ONU 10 (step S108). The optical signal (GATE frame) output from ONU 10 includes information indicating the transmission timing and bandwidth of the IRT frame allocated to ONU 10-1, and information indicating the transmission timing and bandwidth of the IRT frame allocated to ONU 10-2.

[0050] The physical layer function unit 11-1 of the ONU 10-1 receives an optical signal transmitted from the OLT 20. The physical layer function unit 11-1 converts the received optical signal into a GATE frame, which is an electrical signal, and outputs it to the main signal transmission control unit 121-1. The main signal transmission control unit 121-1 references the GATE frame output from the physical layer function unit 11-1 and controls the transmission timing in the IRT frame processing unit 123-1. The main signal transmission control unit 121-1 notifies the IRT frame processing unit 123-1 of information on the transmission timing of the IRT frame included in the GATE frame and information on the allocated bandwidth. In accordance with the transmission timing notified by the main signal transmission control unit 121-1, the IRT frame processing unit 123-1 transmits, from the buffered IRT frames, an IRT frame corresponding to the allocated bandwidth to the OLT 20 via the physical layer function unit 21-1 (step S109). As a result, the OLT 20 processes the IRT frame transmitted from the ONU 10-1.

[0051] The physical layer function unit 11-2 of the ONU 10-2 receives an optical signal transmitted from the OLT 20. The physical layer function unit 11-2 converts the received optical signal into a GATE frame, which is an electrical signal, and outputs it to the main signal transmission control unit 121-2. The main signal transmission control unit 121-2 references the GATE frame output from the physical layer function unit 11-2 and controls the transmission timing in the IRT frame processing unit 123-2. The main signal transmission control unit 121-2 notifies the IRT frame processing unit 123-2 of information on the transmission timing of the IRT frame included in the GATE frame and information on the allocated bandwidth. In accordance with the transmission timing notified by the main signal transmission control unit 121-2, the IRT frame processing unit 123-2 transmits, from the buffered IRT frames, an IRT frame corresponding to the allocated bandwidth to the OLT 20 via the physical layer function unit 21-2 (step S110). As a result, the OLT 20 processes the IRT frame transmitted from the ONU 10-2.

[0052] Thereafter, the transmission control unit 12-1 of the ONU 10-1 generates a REPORT frame including the amount of transmission data of the buffered frame. Here, the transmission control unit 12-1 generates a REPORT frame including the amount of transmission data buffered in the other frame processing unit 124-1. The transmission control unit 12-1 outputs the generated REPORT frame to the physical layer function unit 11-1. The physical layer function unit 11-1 converts the REPORT frame output from the transmission control unit 12-1 into an optical signal and transmits it to the OLT 20 (step S111). The optical signal transmitted from the ONU 10-1 is received by the OLT 20 via the optical splitter 30.

[0053] The transmission control unit 12-2 of ONU 10-2 generates a REPORT frame including the amount of transmission data of the buffered frame. Here, the transmission control unit 12-1 generates a REPORT frame including the amount of transmission data buffered in the other frame processing unit 124-2. The transmission control unit 12-2 outputs the generated REPORT frame to the physical layer function unit 11-2. The physical layer function unit 11-2 converts the REPORT frame output from the transmission control unit 12-2 into an optical signal and transmits it to the OLT 20 (step S112). The optical signal transmitted from ONU 10-2 is received by the OLT 20 via the optical splitter 30.

[0054] The physical layer function unit 21 of the OLT 20 receives the optical signals transmitted from the ONUs 10-1 and 10-2 (step S113). The physical layer function unit 21 converts the received optical signals into electrical signals. As a result, the REPORT frames transmitted from the ONUs 10-1 and 10-2 are restored. The physical layer function unit 21 outputs the REPORT frames to the periodic distribution unit 221. The periodic distribution unit 221 distributes the REPORT frames output from the physical layer function unit 21 (step S114). Here, it is assumed that the periodic distribution unit 221 is set to distribute based on time.

[0055] When the periodic allocation unit 221 receives a REPORT frame, it determines whether the time of reception is time A or time B. Here, it is assumed that the time of reception is time B. The periodic allocation unit 221 outputs each received REPORT frame to the second bandwidth allocation unit 223. The second bandwidth allocation unit 223 allocates bandwidth using the DBA algorithm based on each REPORT frame output from the periodic allocation unit 221 (step S115). The second bandwidth allocation unit 223 allocates bandwidth to each of ONUs 10-1 and 10-2 based on the amount of transmission data included in each REPORT frame.

[0056] The second bandwidth allocating unit 223 generates a GATE frame including the bandwidth allocation result obtained by the DBA algorithm and information indicating that the frame to be transmitted is another frame. The second bandwidth allocating unit 223 outputs the generated GATE frame to the physical layer function unit 21. The physical layer function unit 21 converts the GATE frame output from the second bandwidth allocating unit 223 into an optical signal and transmits it to each ONU 10 (step S116). The optical signal (GATE frame) output from ONU 10 includes information indicating the transmission timing and bandwidth of the other frame allocated to ONU 10-1, and information indicating the transmission timing and bandwidth of the other frame allocated to ONU 10-2.

[0057] The physical layer function unit 11-1 of the ONU 10-1 receives an optical signal transmitted from the OLT 20. The physical layer function unit 11-1 converts the received optical signal into a GATE frame, which is an electrical signal, and outputs it to the main signal transmission control unit 121-1. The main signal transmission control unit 121-1 references the GATE frame output from the physical layer function unit 11-1 and controls the transmission timing in the other frame processing unit 124-1. The main signal transmission control unit 121-1 notifies the other frame processing unit 124-1 of information on the transmission timing of the other frame included in the GATE frame and information on the assigned bandwidth. In response to the transmission timing notified by the main signal transmission control unit 121-1, the other frame processing unit 124-1 transmits, from the buffered other frames, other frames corresponding to the assigned bandwidth to the OLT 20 via the physical layer function unit 21-1 (step S117). As a result, the OLT 20 processes the other frames transmitted from the ONU 10-1.

[0058] The physical layer function unit 11-2 of the ONU 10-2 receives an optical signal transmitted from the OLT 20. The physical layer function unit 11-2 converts the received optical signal into a GATE frame, which is an electrical signal, and outputs the converted signal to the main signal transmission control unit 121-2. The main signal transmission control unit 121-2 references the GATE frame output from the physical layer function unit 11-2 and controls the transmission timing in the other frame processing unit 124-2. The main signal transmission control unit 121-2 notifies the other frame processing unit 124-2 of information on the transmission timing of the other frame included in the GATE frame and information on the allocated bandwidth. In response to the transmission timing notified by the main signal transmission control unit 121-2, the other frame processing unit 124-2 transmits the buffered other frames corresponding to the allocated bandwidth to the OLT 20 via the physical layer function unit 21-2 (step S118). As a result, the OLT 20 processes the other frames transmitted from the ONU 10-2.

[0059] According to the communication system 100 configured as described above, the OLT 20 comprises a periodic allocation unit 221 that alternately executes a plurality of bandwidth allocation methods within a predetermined period, a first bandwidth allocation unit 222 that performs fixed bandwidth allocation in response to instructions from the periodic allocation unit 221 and transmits to each ONU 10 a GATE frame that includes the bandwidth allocation result and information indicating that the frame to be transmitted is an IRT frame, and a second bandwidth allocation unit 223 that performs dynamic bandwidth allocation in response to instructions from the periodic allocation unit 221 and transmits to each ONU 10 a GATE signal that includes the bandwidth allocation result and information indicating that the frame to be transmitted is another frame. Each ONU 10 comprises a frame distribution unit 122 that identifies whether a frame input as data to be transmitted is an IRT frame or another frame and distributes the frame; an IRT frame processing unit 123 that transmits the IRT frame distributed by the frame distribution unit 122 to the OLT 20 within a predetermined period based on a GATE frame received from the OLT 20; and an other frame processing unit 124 that transmits the other frame distributed by the frame distribution unit 122 to the OLT 20 at a timing within the predetermined period that is different from the transmission timing of the IRT frame based on the GATE frame received from the OLT 20.

[0060] In this way, since the IRT frames in each ONU 10 can be fixedly allocated within a predetermined period, time-determined frame transfer can be realized, and other frames can also be transmitted from the ONU 10 to the OLT 20 using surplus bandwidth (bandwidth not used for transmitting IRT frames).As a result, it is possible to improve the bandwidth utilization efficiency while suppressing an increase in the amount of calculation.

[0061] The ONU 10 identifies whether an input frame is an IRT frame or another frame, and stores the IRT frame and other frames in different buffers in advance. Then, when it is time to transmit the IRT frame, the ONU 10 retrieves the IRT frame from the buffer storing the IRT frame and transmits it to the OLT 20. In this way, since the IRT frame and other frames are stored in different buffers in advance, the IRT frame can be transmitted with priority at the IRT frame transmission timing. This ensures the real-time performance required for IRT frames.

[0062] (Variation) In the example shown in FIG. 1, a configuration is shown in which bandwidth allocation is performed in the order of fixed bandwidth allocation and dynamic bandwidth allocation within a predetermined period, but bandwidth allocation may also be performed in the order of dynamic bandwidth allocation, fixed bandwidth allocation, dynamic bandwidth allocation, ...

[0063] Some of the functional units of the ONU 10 and the OLT 20 in the above-described embodiment may be implemented by a computer. In this case, a program for implementing these functions may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read into a computer system and executed. Note that the term "computer system" here includes hardware such as an OS and peripheral devices.

[0064] Furthermore, "computer-readable recording media" refers to portable media such as flexible disks, optical magnetic disks, ROMs (Read Only Memory), and CD-ROMs, as well as storage devices such as hard disks built into computer systems. Furthermore, "computer-readable recording media" may also include devices that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks like the Internet or communication lines like telephone lines, or devices that store programs for a fixed period of time, such as volatile memory within the computer systems that serve as servers or clients. Furthermore, the programs may be designed to realize some of the aforementioned functions, or may be capable of realizing the aforementioned functions in combination with programs already stored in the computer system, or may be realized using programmable logic devices such as FPGAs (Field Programmable Gate Arrays).

[0065] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0066] The present invention can be applied to a communication system that performs bandwidth allocation.

[0067] 10, 10-1 to 10-N...ONU, 20...OLT, 30...optical splitter, 11, 21...physical layer function unit, 12...transmission control unit, 121...main signal transmission control unit, 122...frame distribution unit, 123...IRT frame processing unit, 124...other frame processing unit, 22...band allocation unit, 221...period distribution unit, 222...first band allocation unit, 223...second band allocation unit

Claims

1. A station side device in a communication system comprising one or more optical subscriber line terminals and a station side device accommodating the one or more optical subscriber line terminals, the station side device comprising: a periodic allocation unit that alternately executes a plurality of bandwidth allocation methods within a predetermined period; a first bandwidth allocation unit that, in response to an instruction from the periodic allocation unit, performs a fixed bandwidth allocation that allocates bandwidth evenly to each of the one or more optical subscriber line terminals connected to the station side device, and transmits to the one or more optical subscriber line terminals a control signal including the bandwidth allocation result and information indicating that the frame to be transmitted is a first frame having a high real-time requirement; and a second bandwidth allocation unit that, in response to an instruction from the periodic allocation unit, performs a dynamic bandwidth allocation that allocates bandwidth in accordance with a request from each of the one or more optical subscriber line terminals connected to the station side device, and transmits to the one or more optical subscriber line terminals a control signal including the bandwidth allocation result and information indicating that the frame to be transmitted is a second frame other than the first frame.

2. An optical subscriber line termination device in a communication system comprising one or more optical subscriber line termination devices and a central office device accommodating the one or more optical subscriber line termination devices, comprising: a frame distribution unit that identifies whether a frame input as data to be transmitted is a first frame having a high requirement for real-time performance or a second frame other than the first frame and distributes the frames; a first frame processing unit that transmits the first frame distributed to the frame distribution unit to the central office device within a specified period based on a control signal including a bandwidth allocation result obtained from the central office device and information indicating the frame to be transmitted; and a second frame processing unit that transmits the second frame distributed to the frame distribution unit to the central office device at a timing different from the transmission timing of the first frame within the specified period based on a control signal including a bandwidth allocation result obtained from the central office device and information indicating the frame to be transmitted.

3. A communications system comprising one or more optical subscriber line terminals and a central office device accommodating the one or more optical subscriber line terminals, wherein the central office device comprises: a periodic allocation unit that alternately executes a plurality of bandwidth allocation methods within a predetermined period; a first bandwidth allocation unit that, in response to an instruction from the periodic allocation unit, performs fixed bandwidth allocation to equally allocate bandwidth to each of the one or more optical subscriber line terminals connected to the central office device, and transmits to the one or more optical subscriber line terminals a control signal including the bandwidth allocation result and information indicating that the frame to be transmitted is a first frame having a high real-time requirement; and a second bandwidth allocation unit that, in response to an instruction from the periodic allocation unit, performs dynamic bandwidth allocation to allocate bandwidth in accordance with a request from each of the one or more optical subscriber line terminals connected to the central office device, and transmits to the one or more optical subscriber line terminals a control signal including the bandwidth allocation result and information indicating that the frame to be transmitted is a second frame other than the first frame; and the one or more optical subscriber line terminals comprise: a frame distribution unit that identifies whether a frame input as data to be transmitted is the first frame or the second frame and distributes the frames; a first frame processing unit that transmits the first frame, distributed to the frame distribution unit, to the station side device within a predetermined period based on the control signal received from the station side device; and a second frame processing unit that transmits the second frame, distributed to the frame distribution unit, to the station side device at a timing within the predetermined period that is different from the transmission timing of the first frame, based on the control signal received from the station side device.

4. The communications system of claim 3, wherein the periodic allocation unit alternates between the fixed bandwidth allocation and the dynamic bandwidth allocation depending on time within a predetermined period, alternates between the fixed bandwidth allocation and the dynamic bandwidth allocation based on information transmitted from the one or more optical subscriber side termination devices, or alternates between the fixed bandwidth allocation and the dynamic bandwidth allocation based on the number of times information transmitted from the one or more optical subscriber side termination devices is received.

5. A bandwidth allocation method performed by an optical line terminal in a communication system comprising one or more optical subscriber line terminals and a central office terminal accommodating the one or more optical subscriber line terminals, comprising: performing a fixed bandwidth allocation that allocates bandwidth equally to each of the one or more optical subscriber line terminals connected to the central office terminal within a predetermined period; transmitting a control signal to the one or more optical subscriber line terminals including a bandwidth allocation result from the fixed bandwidth allocation and information indicating that a frame to be transmitted is a first frame having a high real-time requirement; performing a dynamic bandwidth allocation that allocates bandwidth in response to a request from each of the one or more optical subscriber line terminals connected to the central office terminal at a timing different from a timing at which the fixed bandwidth allocation is performed within the predetermined period; transmitting a control signal to the one or more optical subscriber line terminals including a bandwidth allocation result from the dynamic bandwidth allocation and information indicating that the frame to be transmitted is a second frame other than the first frame; and alternately performing the fixed bandwidth allocation and the dynamic bandwidth allocation within the predetermined period.

6. A frame transmission method performed by an optical line terminal in a communication system comprising one or more optical line terminals and a central office terminal accommodating the one or more optical line terminals, the method comprising: identifying whether a frame input as data to be transmitted is a first frame having a high requirement for real-time performance or a second frame other than the first frame, and distributing the frame; transmitting the first frame to the central office terminal within a predetermined period based on a control signal including a bandwidth allocation result obtained from the central office terminal and information indicating the frame to be transmitted; and transmitting the second frame to the central office terminal at a timing within the predetermined period different from the transmission timing of the first frame, based on a control signal including a bandwidth allocation result obtained from the central office terminal and information indicating the frame to be transmitted.

7. A computer program for causing a computer to function as an optical line terminal in a communications system comprising one or more optical subscriber line terminals and an optical line terminal accommodating the one or more optical subscriber line terminals, the computer program causing a computer to function as the optical line terminal in a communications system comprising the one or more optical subscriber line terminals, the computer program causing a computer to perform fixed bandwidth allocation, which allocates bandwidth equally to each of the one or more optical subscriber line terminals connected to the optical line terminal, within a specified period; causing a computer to transmit a control signal including a bandwidth allocation result from the fixed bandwidth allocation and information indicating that the frame to be transmitted is a first frame having a high real-time requirement, to the one or more optical subscriber line terminals; causing a computer to perform dynamic bandwidth allocation, which allocates bandwidth in response to a request from each of the one or more optical subscriber line terminals connected to the optical line terminal, at a timing different from the timing at which the fixed bandwidth allocation is performed within the specified period; causing a computer to transmit a control signal including a bandwidth allocation result from the dynamic bandwidth allocation and information indicating that the frame to be transmitted is a second frame other than the first frame, to the one or more optical subscriber line terminals; and causing the computer program to alternately perform the fixed bandwidth allocation and the dynamic bandwidth allocation within the specified period.

8. A computer program for causing a computer to function as an optical subscriber line terminal in a communication system comprising one or more optical subscriber line terminals and a station side device accommodating the one or more optical subscriber line terminals, the computer program causing the computer to identify whether a frame input as data to be transmitted is a first frame having a high requirement for real-time performance or a second frame other than the first frame and to allocate the frame; causing the computer to transmit the first frame to the station side device within a specified period based on a control signal including a bandwidth allocation result obtained from the station side device and information indicating the frame to be transmitted; and causing the computer to transmit the second frame to the station side device at a timing within the specified period different from the transmission timing of the first frame based on a control signal including a bandwidth allocation result obtained from the station side device and information indicating the frame to be transmitted.

Images