JP2013175836A - Optical terminal apparatus and optical communication system, and dynamic band allocation apparatus and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an OLT (optical terminal apparatus) in a PON system, capable of increasing accuracy of a predicted and allocated upward signal allocation band.SOLUTION: The OLT includes: receiving means for receiving a transmission request amount transmitted from each ONU for each allocation period; for each ONU, dynamic band allocation means for determining allocation band permitted for an upward signal for each allocation period; and transmission means for transmitting the determined allocation band to the corresponding optical ONU for each allocation period. At least for a portion of ONU, the dynamic band allocation means determines as the allocation band a value obtained by adding to a fixed band a value that is obtained by subtracting the total value of the allocation band in a predetermined period at the most recent past, from a transmission request amount received in an allocation period at the present time.

Description

  The present invention relates to an optical terminal device, an optical communication system, a dynamic band allocation device, and a program. For example, an EPON (Ethernet (registered trademark) PON (Passive Optical Network) system (see Non-Patent Document 1 and Non-Patent Document 2). ).

  The PON system is an optical network in which an OLT (Optical Line Terminal) and a plurality of ONUs (Optical Network Unit) are connected via an optical transmission line such as an optical fiber or an optical splitter. is there.

  Among EPON systems in which OLT and ONU communicate using Ethernet (registered trademark) frames, a GE-PON (Gigabit Ethernet PON) system with a transmission speed of 1 Gbps, or a 10 G-EPON with a transmission speed increased to 10 Gbps. There are systems.

  In many PON systems such as the GE-PON system, upstream communication from the ONU to the OLT is performed by time division multiple access. By controlling the transmission timing of each ONU by the OLT, a plurality of ONUs can perform time division communication with the OLT.

  In many PON systems in which uplink communication is performed by time division multiple access, in order to efficiently use the uplink bandwidth, the dynamic allocation of the uplink bandwidth to each ONU according to the communication status is performed. Bandwidth allocation is important.

  The dynamic bandwidth allocation method in the conventional EPON system is as follows.

  As shown in FIG. 6, the ONU 2-i that intends to transmit data makes a transmission data band permission request to the OLT 1 by a report frame, and the OLT 1 determines the allocated band by a predetermined dynamic band allocation method. The ONU 2-i is given permission for a transmission data band having a transmission start time, a data transfer time, etc. by the gate frame, and the ONU 2-i transmits data to the OLT 1 in accordance with an instruction from the OLT 1. It should be noted that the OLT 1 reviews the bandwidth allocation, that is, the grant allocation cycle (grant allocation cycle) so that an upstream bandwidth request and response to the ONU farthest from the OLT 1 can be appropriately executed. Hereinafter, it is simply referred to as an allocation cycle or a cycle).

  Here, the plurality of ONUs accommodated in the OLT 1 do not necessarily have the same distance from the OLT 1. In a situation where the distance difference between an ONU close to the OLT 1 (short-distance ONU) and a distant ONU (long-distance ONU) is large, it has the following problems. The allocation cycle is determined according to the distance between the long distance ONU2-j and the OLT1. In other words, among the ONUs accommodated in the OLT 1, an allocation period is required that can appropriately execute an upstream bandwidth request by sending and receiving a gate frame and a report frame and a reply to the ONU located at the farthest distance. Further, since data transmission from the ONU is performed based on the transmission start time and data transfer time given by the gate frame for each allocation period, there is a problem that the uplink data transmission delay increases as the allocation period increases. .

  In order to solve such a problem, in Patent Document 1, even in a PON system in which a long-distance ONU and a short-distance ONU are mixed, the grant allocation period is shortened and transmission from the ONU to the OLT is performed so that the delay time can be shortened. A method of allocating an uplink bandwidth predicted based on a change in request amount or an actual transmission amount is proposed.

Specifically, it is as follows. If the transmission request amount based on the report received in the previous allocation cycle is R0, and the transmission request amount based on the report received in the current allocation cycle is R, the temporal change amount of the transmission request amount is DR = R−R0. When the absolute value of the time change amount DR is larger than the absolute value of a predetermined threshold (A or B), the operator sets the predicted allocation amount G determined in the current allocation cycle in advance from the allocation amount G0 of the previous cycle. It is assumed that the changed bandwidth (DG _A or DG _B ) is changed, and in other cases, the predicted allocation amount G determined in the current allocation cycle is made the same as the allocation amount G0 of the previous cycle. This allocation method is expressed as follows.

G = G0 + DG _A (DR> A (A> 0))
G = G0−DG _B (DR <B (B <0))
G = G0 (B ≦ DR ≦ A)

JP2011-234242A

IEEE802.3ah IEEE802.3av

  However, the method described in Patent Document 1 has a problem that the use efficiency of the band is reduced when the predicted allocation amount based on the change in the transmission request amount is significantly different from the band that can be actually allocated.

FIG. 7 is an explanatory diagram of this problem. An upstream input bandwidth corresponding to the amount of data input to the ONU is notified to the OLT as a transmission request amount R. Since the transmission request amount has greatly increased from the allocation cycle T1 to T2, the OLT increases the predicted allocation amount of the allocation cycle T3 by the change bandwidth DG _A from the predicted allocation amount of the allocation cycle T2. However, in this case, a large band DR is insufficient from the upstream input band. Since the transmission request amounts in the allocation periods T2 and T3 are large but equal, the OLT makes the predicted allocation amount in the allocation period T4 the same as the predicted allocation amount in the allocation period T3. It continues to be the same as the predicted allocation amount of the previous allocation cycle (continue to cycle T9 in FIG. 7), and the state where the predicted allocation amount is insufficient by the DR from the necessary bandwidth continues.

  Therefore, there is a demand for an optical terminal device, an optical communication system, a dynamic band allocation device, and a program that can increase the accuracy of the allocated bandwidth that is predicted and allocated.

  According to a first aspect of the present invention, in an optical terminal device accommodating a plurality of optical line terminators, (1) a transmission request amount receiving means for receiving a transmission request quantity transmitted by each optical line terminator for each allocation period And (2) a dynamic band that determines, for each allocation period, an allocation band that is permitted for an uplink signal from the optical line termination apparatus to the optical terminal apparatus for each optical line termination apparatus that has transmitted the transmission request amount. Allocating means; and (3) allocating band transmitting means for transmitting the determined allocated band to the corresponding optical line terminating device for each allocating period. (2) The dynamic band allocating means is at least partially The optical line terminating device is characterized in that the allocated bandwidth is determined based on a value obtained by subtracting a total value of allocated bandwidths in a predetermined period in the past from the transmission request amount received in the current allocated cycle. To do.

  According to a second aspect of the present invention, there is provided an optical communication system having a plurality of optical line termination devices and an optical terminal device that accommodates the optical line termination devices. A station apparatus is applied.

  According to a third aspect of the present invention, in the dynamic bandwidth allocating device mounted on the optical terminal device, which determines an allocated bandwidth allowed for an upstream signal from the optical network unit to the optical terminal device, (1) an allocation period A transmission request amount acquisition means for taking in the transmission request amount transmitted by the optical line termination device for each time, and (2) the optical line termination device that transmits the transmission request amount for each allocation period. And (3) an allocation band output unit that outputs the determined allocation band for each allocation period, and (3) 2) The dynamic bandwidth allocating unit determines an allocated bandwidth based on a value obtained by subtracting a total value of allocated bandwidths in a predetermined past period from a transmission request amount received in the current allocation cycle. And

  According to a fourth aspect of the present invention, a dynamic bandwidth allocation for determining an allocation bandwidth allowed for an upstream signal from an optical line termination device to an optical terminal device for an optical line termination device that transmits a transmission request amount for each allocation period. A program comprising: (1) a transmission request amount acquisition unit that takes in a transmission request amount transmitted by the optical line termination device for each allocation cycle; and (2) a current allocation cycle for each allocation cycle. A dynamic bandwidth allocating means for determining an allocated bandwidth based on a value obtained by subtracting a total value of allocated bandwidths for a predetermined period in the past in the received transmission request amount; and (3) an allocation determined for each allocation cycle. It is characterized by functioning as allocated bandwidth output means for outputting a bandwidth.

  According to the optical terminal device, the optical communication system, the dynamic band allocation apparatus, and the program of the present invention, it is possible to increase the accuracy of the allocation band of the uplink signal to be predicted and allocated.

It is a block diagram which shows the structure of the PON system of embodiment. It is a block diagram which shows the internal structure of OLT of embodiment. It is a block diagram which shows the internal structure of ONU of embodiment. It is a flowchart which shows the dynamic band allocation operation | movement which OLT of embodiment performs. It is explanatory drawing of the change of an allocation band by the dynamic band allocation operation | movement with respect to long distance ONU which OLT of embodiment performs, and the change of a transmission request amount. It is explanatory drawing which shows the mode of transmission / reception of the gate frame and report frame performed for dynamic bandwidth allocation. 10 is an explanatory diagram of a problem of the dynamic bandwidth allocation method described in Patent Literature 1. FIG.

(A) Main Embodiment Hereinafter, an embodiment of an optical terminal device, an optical communication system, a dynamic band allocation device, and a program according to the present invention will be described with reference to the drawings. The optical communication system of the embodiment is a PON system.

(A-1) Configuration of Embodiment As shown in FIG. 1, the PON system 10 according to the embodiment includes an OLT 11, a plurality of ONUs 12-1 to 12 -N, and an optical splitter 13. The OLT 11 and the optical splitter 13 are connected via an optical fiber 14 common to all the ONUs 12-1 to 12-N, and the optical splitter 13 and each of the ONUs 12-1, ..., 12-N are connected. Are connected via individual optical fibers 15-1, ..., 15-N.

  In this embodiment, the OLT 11 classifies the ONUs 12-1 to 12-N into a short-distance ONU and a long-distance ONU. Here, the long distance ONU refers to an ONU whose distance from the OLT 11 is a distance in which a gate frame and a report frame cannot be exchanged within the same allocation period, and the short distance ONU refers to a distance from the OLT 11. The ONU is located at a distance that allows transmission and reception of the gate frame and the report frame within the same allocation period. For example, the OLT 11 measures the round-trip propagation time (RTT; Round Trip Time) with the ONU 12-n (n = 1 to N), compares the RTT with the classification threshold, and the ONT whose RTT is equal to or less than the classification threshold. Is a short distance ONU, and an ONU having an RTT greater than the classification threshold is a long distance ONU. In the example of FIG. 1, ONUs 12-1 and 12-N are long-distance ONUs, and ONUs 12-2 and 12-3 are short-distance ONUs.

  FIG. 2 is a block diagram illustrating an internal configuration of the OLT 11 according to the embodiment.

  In FIG. 2, the OLT 11 includes a downlink upper interface unit 20, a downlink buffer memory 21, a multiplexing unit 22, and a light emitting element 23 with respect to the downlink signal. Further, the OLT 11 includes a light receiving element 25, a separation unit 26, an upstream upper interface unit 27, an upstream bandwidth request extraction unit 28, and a dynamic upstream bandwidth allocation unit 29 with respect to upstream signals. Further, the OLT 11 includes a wavelength multiplexing / separating unit 24 at the interface with the optical fiber 14.

  The downstream upper interface unit 20 receives and processes a downstream signal from a host device (not shown), and provides the downstream buffer memory 21 with the downstream signal from the host device.

  The downlink buffer memory 21 buffers the downlink signal from the downlink higher-level interface unit 20, reads the downlink signal according to an instruction from the multiplexing unit 22, and gives the downlink signal to the multiplexing unit 22.

  The multiplexing unit 22 multiplexes the downlink signal read from the downlink buffer memory 21 and the gate frame given from the dynamic uplink band allocation unit 29 and gives the multiplexed signal to the light emitting element 23.

  The light emitting element 23 is, for example, a laser diode, and converts the signal (electric signal) given from the multiplexing unit 22 into an optical signal having a downstream wavelength and gives it to the wavelength demultiplexing unit 24.

  The wavelength demultiplexing unit 24 sends the optical signal emitted from the light emitting element 23 to the optical fiber 14 and gives the upstream optical signal coming from the optical fiber 14 to the light receiving element 25.

  The light receiving element 25 is, for example, a photodiode, and converts the upstream optical signal from the wavelength demultiplexing unit 24 into an electrical signal (upstream signal, report frame, etc.).

  The separation unit 26 extracts a report frame from the upstream signal from the light receiving element 25, notifies the upstream bandwidth request extraction unit 28 of the report frame, and supplies the other frames to the upstream host interface unit 27.

  The upstream upper interface unit 27 transmits the frame from the separation unit 26 to a host device (not shown).

  The upstream bandwidth request extraction unit 28 extracts an upstream bandwidth request (transmission request amount) included in the report frame for each ONU and gives it to the dynamic upstream bandwidth allocation unit 29.

  The dynamic uplink bandwidth allocation unit 29 allocates an uplink bandwidth to each ONU based on an upstream bandwidth request for each ONU. The dynamic uplink bandwidth allocation unit 29 gives a gate frame including allocation information to the multiplexing unit 22. The dynamic band allocation method by the dynamic uplink band allocation unit 29 will be clarified in the description of the operation section described later.

  The upstream bandwidth request extraction unit 28 and the dynamic upstream bandwidth allocation unit 29 may be configured by a CPU and a program executed by the CPU. Further, the upstream bandwidth request extraction unit 28 and the dynamic upstream bandwidth allocation unit 29 may be configured and sold as one chip or one device.

  FIG. 3 is a block diagram illustrating an internal configuration of the ONU 12-n according to the embodiment.

  In FIG. 3, the ONU 12-n includes an interface unit 40, an upstream signal processing unit 41, a light emitting element 42, a wavelength demultiplexing unit 43, a light receiving element 44, a downstream signal processing unit 45, and an upstream band control unit 46. And.

  The interface unit 40 interfaces with a terminal (not shown) under its control, and has built-in uplink and downlink buffer memories to receive and buffer uplink data from the terminal and buffer downlink data to the terminal. Or something to ring. The interface unit 40 is configured such that the data amount (transmission request amount) buffered in the upstream buffer memory is extracted by the upstream bandwidth control unit 46.

  The upstream signal processing unit 41 forms an upstream signal from the upstream data of the interface unit 40, and transmits the upstream signal (upstream signal according to the allocated bandwidth) of the data amount designated from the timing designated by the bandwidth control unit 46 as a light emitting element. 42 is output. Further, the upstream signal processing unit 41 forms a transmission signal of a report frame including the requested transmission amount given from the band control unit 46, and outputs it to the light emitting element 42 at a predetermined timing.

  The light emitting element 42 is, for example, a laser diode, and converts the signal (electric signal) supplied from the upstream signal processing unit 41 into an optical signal having an upstream wavelength and supplies the optical signal to the wavelength demultiplexing unit 43.

  The wavelength demultiplexing unit 43 sends the optical signal emitted from the light emitting element 42 to the optical fiber 15-n and gives the downstream optical signal coming from the optical fiber 15-n to the light receiving element 44.

  The light receiving element 44 is formed of, for example, a photodiode, and converts a downstream optical signal from the wavelength demultiplexing unit 43 into an electrical signal (downstream signal, gate frame, or the like).

  The downlink signal processing unit 45 gives downlink data related to the downlink signal to the interface unit 40 and gives a gate frame to the uplink band control unit 46.

  The upstream bandwidth control unit 46 obtains information on the permitted upstream bandwidth from the gate frame, controls the transmission timing and transmission amount of the upstream signal, and also stores the amount of data buffered in the upstream buffer memory ( Control such as transmitting a report frame based on (transmission request amount).

(A-2) Operation of Embodiment Next, a dynamic bandwidth allocation operation executed by the OLT 11 that is a characteristic operation in the PON system 10 of the embodiment will be described.

  FIG. 4 is a flowchart illustrating a dynamic band allocation operation executed by the OLT 11 (the dynamic uplink band allocation unit 29) according to the embodiment. FIG. 4 shows a dynamic band allocation operation for one long-distance ONU, and the same operation as that of FIG. 4 is executed for another long-distance ONU. It should be noted that other existing dynamic bandwidth allocation operations may be applied to the short-distance ONU, or the dynamic bandwidth allocation operation shown in FIG. 4 may be applied. FIG. 4 shows the operation of the OLT 11 in a certain allocation cycle, and the operation shown in FIG. 4 is repeated for each allocation cycle.

  When the OLT 11 starts the process shown in FIG. 4 for a certain long-distance ONU (hereinafter referred to as reference numeral 12-L) in a new allocation cycle, first, the OLT 11 sets the fixed band Gfix set in advance this time. Is temporarily set to a bandwidth (hereinafter referred to as a current allocated bandwidth) Gnow assigned to the period (step ST1). The value of the fixed band Gfix may be changed according to the service to be applied. For example, different values may be set for the voice communication service, the video communication service, and the data communication service. For example, the service type may be specified and set by negotiation at the start of communication. The value of the fixed bandwidth Gfix secures a minimum allocated bandwidth, but may be 0 if the system allows it.

  Next, the OLT 11 compares the bandwidth requested for transmission (transmission request amount) Rnow in the received report frame with the total Glast_sum of the bandwidth allocated in the past predetermined period (step ST2). When the received transmission request amount Rnow is equal to or greater than the most recently allocated total Glast_sum, the OLT 11 adds a value Rnow-Glast_sum obtained by subtracting the most recently allocated total Glast_sum from the received transmission request amount Rnow to the current allocated bandwidth Gnow. To a new current allocated bandwidth Gnow (step ST3). On the other hand, when the most recently allocated total Glast_sum is larger than the received transmission request amount Rnow, the current allocated bandwidth Gnow (= fixed bandwidth Gfix) is left as it is.

  The meaning of the above processing will be described. As shown in FIG. 5 to be described later, in the case of the long-distance ONU 12-L, even if the current allocation band Gnow is determined according to the received transmission request amount Rnow and transmitted to the long-distance ONU 12-L, the current allocation band Gnow is long. It takes a long time to reach the distance ONU 12-L, and the long distance ONU 12-L transmits the next report frame before the current allocated bandwidth Gnow reaches the long distance ONU 12-L. As described above, the current allocation band Gnow is reflected in the transmission request amount notified in the next report frame transmitted by the long-distance ONU 12-L before the current allocation band Gnow reaches the long-distance ONU 12-L. It has not been. That is, the received transmission request amount Rnow does not reflect the bandwidth allocated in the previous predetermined cycle immediately before reaching the long-distance ONU 12-L, so the total bandwidth allocated in the past previous predetermined cycle (the most recent allocation) (Sum total) Glast_sum becomes larger than the actual transmission request amount Rnow, and the bandwidth is allocated more than necessary. For this purpose, the received transmission request amount Rnow is compared with the most recently allocated total Glast_sum, and the current allocated bandwidth Gnow is appropriately updated according to the comparison result.

  Further, the current allocation band Gnow must be equal to or less than the maximum value Gmax of the uplink transmission permission amount, and the OLT 11 allows the uplink transmission permission when the current allocation band Gnow exceeds the maximum value Gmax of the uplink transmission permission amount. The maximum value Gmax of the amount is updated to a new current allocated bandwidth Gnow (step ST4). Considering the processing of steps ST1 and ST3 described above, the current allocated bandwidth Gnow is equal to or larger than the fixed bandwidth Gfix, and considering step ST4, the current allocated bandwidth Gnow is the maximum uplink transmission permission amount Gmax. Therefore, Gfix ≦ Gnow ≦ Gmax is established when step ST4 is completed.

  For example, the maximum value Gmax of the uplink transmission permission amount may be dynamically determined according to the number of ONUs transmitting uplink signals at that time. For example, the uplink signal is transmitted at that time. It may be dynamically determined according to the ratio of the total value of transmission request amounts (Rnow) from all ONUs currently being transmitted and the transmission request amount Rnow from the target ONU. As the determination method, an existing determination method can be applied. Further, a fixed value may be applied as the maximum uplink transmission permission value Gmax.

  When the current allocation bandwidth Gnow is determined as described above, the OLT 11 holds the bandwidth allocated in the past predetermined period and the current allocation bandwidth Gnow allocated this time (step ST5). Here, the previous predetermined cycle (that is, the number of cycles) in the past is changed depending on the distance (in other words, RTT) between the long distance ONU 12-L and the OLT 11 which are the current target, for example. That is, the number of cycles is increased for a long-distance ONU having a long distance, and the number of cycles is decreased for a long-distance ONU having a short distance. It should be noted that any long-distance ONU 12-L may apply a fixed value as a predetermined period (number of periods) immediately before the past in a system installed at the same distance from the OLT 11 or the like.

  Thereafter, the OLT 11 adds the previous predetermined period and the band allocated this time, and calculates the most recently allocated total Glast_sum used in the next period (step ST6).

  Finally, the bandwidth Gnow to be allocated this time is set as a gate frame and transmitted to the ONU 12-L (step ST7), and a series of bandwidth allocation processing in the current cycle is completed.

  Next, an example of a change in the allocated bandwidth Gnow and a change in the transmission request amount Rnow due to the processing shown in FIG. 4 will be described with reference to FIG. The long distance ONU 12-L shown in FIG. 5 transmits an uplink signal reflecting the allocated band after two allocation periods.

  First, when the OLT 11 receives the first report frame R1 after the long-distance ONU 12-L is connected, the OLT 11 is fixed in advance in this allocation cycle T101 as shown in the equation (1-2). The bandwidth G1 is added to the transmission request amount Rnow (= R1 = ΔG1) requested in the report frame, and the bandwidth G1 is assigned to the ONU 12-L. Since the most recently allocated total Glast_sum at this timing is 0, the band allocation as described above is performed by performing the processing of FIG. Here, the symbols G1 to G5 represent gate frames, and also represent assigned bands included in the gate frames. Reference numerals R1 to R5 represent a report frame and also represent a transmission request amount included in the report frame. Symbols ΔG1 to ΔG4 described in the following mathematical expressions represent the difference Rnow-Glast_sum in the calculation of step ST3 in FIG.

ΔG1 = R1 (1-1)
G1 = Gfix + ΔG1 (1-2)
At the timing of the next allocation cycle T102, transmission of data is not started because the band G1 allocated in the previous allocation cycle T101 has not reached the long-distance ONU 12-L, and an attempt is made to transmit only one cycle. Since the data amount increases in the long distance ONU 12-L, it is assumed that the transmission request amount R2 is equal to or greater than the most recently assigned total Glast_sum = G1. Therefore, when receiving the report frame with the transmission request amount R2, as shown in the equation (2-2), the OLT 11 has already subtracted the bandwidth G1 allocated in the previous cycle T101 from the transmission request amount R2 to obtain the band ΔG2. Is assigned to the fixed band value Gfix to determine the allocated band G2.

ΔG2 = R2-G1 (2-1)
G2 = Gfix + ΔG2 (2-2)
Furthermore, at the timing of the next allocation cycle T103, transmission of data starts because the bandwidth G1 allocated in the previous allocation cycle T101 and the bandwidth G2 allocated in the previous allocation cycle T102 have not reached the long-distance ONU 12-L. In addition, since the amount of data to be transmitted by one cycle is increased in the long-distance ONU 12-L from the transmission request amount R2 of the previous cycle, the transmission request amount R3 is the total allocated last Glast_sum = G1 + G2. Suppose that it is above. Therefore, when the report frame with the transmission request amount R3 is received, the OLT 11 uses the transmission request amount R3 for the band G1 + G2 that has already been allocated in the previous cycle T101 and the previous cycle T102 as shown in the equation (3-2). The allocated band G3 is obtained by using the band ΔG3 subtracted from the fixed band value Gfix as an addition.

ΔG3 = R3- (G2 + G1) (3-1)
G3 = Gfix + ΔG3 (3-2)
On the other hand, when sending the report frame R4 that reaches the OLT 11 at the timing of the next allocation cycle T104, the long-distance ONU 12-L already knows the band G1 allocated to the long-distance ONU 12-L in the allocation cycle T101, and the report The transmission request amount R4 in the frame R4 reflects that the band G1 has already been allocated. Therefore, in the allocation cycle T104, it is not necessary to consider the bandwidth G1 allocated in the allocation cycle T101 three cycles before. Assume that the transmission request amount R4 in the report frame received in the current cycle T104 is equal to or greater than the allocated total Glast_sum = G2 + G3 in the last two cycles. Therefore, as shown in the equation (4-2), the OLT 11 uses the band ΔG4 obtained by subtracting the band G2 + G3 allocated in the latest two periods T101 and T102 from the transmission request amount R4 as an addition from the fixed band value Gfix. The allocated bandwidth G4 is obtained.

ΔG4 = R4− (G3 + G2) (4-1)
G4 = Gfix + ΔG4 (4-2)
Similarly, in each allocation cycle, the total bandwidth allocated in the two most recent cycles is subtracted from the transmission request amount received in the allocation cycle, and the bandwidth is added to the fixed bandwidth value in the allocation cycle. The allocated bandwidth is determined.

  In the above, the case of the long-distance ONU that considers the total of the bandwidth allocated in the two most recent cycles has been described, but the number of cycles that consider the total of the most recently allocated bandwidth is not limited to two, It is determined according to the distance (in other words, RTT) between the long distance ONU and the OLT.

(A-3) Effect of Embodiment According to the above embodiment, prediction is made based on the transmission request amount transmitted from the long-distance ONU in a state in which the bandwidth information allocated in the past allocation cycle does not reach the long-distance ONU. In determining the allocated bandwidth, the allocated bandwidth is determined in consideration of the total allocated bandwidth for the most recent allocation cycle that is not reflected in the transmission request amount. Band accuracy can be increased. That is, the shortage of allocated bandwidth can be suppressed and unnecessary bandwidth allocation is eliminated, so that an efficient upstream bandwidth can be allocated.

(B) Other Embodiments In the above embodiment, a PON system in which long-distance ONUs and short-distance ONUs are mixed has been described. However, the present invention is also applied to a PON system that does not discriminate ONUs according to distance. can do. The dynamic band allocation operation shown in FIG. 4 may be applied to all ONUs.

  In the above embodiment, the PON system that performs bandwidth allocation so as to adjust the upstream bandwidth from all ONUs has been described, but the form of the PON system is not limited to this. For example, when the group is divided into a group of ONUs that transmit uplink signals to the OLT at the first wavelength and a group of ONUs that transmit uplink signals to the OLT at the second wavelength, dynamic allocation is performed for each group. It is sufficient to execute the operation.

  The expression format of the information on the allocated bandwidth from the OLT to the ONU is arbitrary. For example, it may be a combination of the transmission start time and the data amount, or simply the data amount. Further, the data amount is not limited to a general quantitative expression such as the number of bytes, and may be expressed by the number of time slots.

  DESCRIPTION OF SYMBOLS 10 ... PON system, 11 ... OLT, 12-1-12-N ... ONU, 31 ... Up-band request extraction part, 32 ... Dynamic up-band allocation part.

Claims (7)

In an optical terminal device containing a plurality of optical line terminators,
Transmission request amount receiving means for receiving the transmission request amount transmitted by each optical line terminating device for each allocation period;
Dynamic bandwidth allocating means for determining, for each of the optical line termination devices that have transmitted the transmission request amount, for each allocation period, an allocation band permitted for an uplink signal from the optical line termination device to the optical terminal device;
An allocation band transmitting means for transmitting the determined allocation band to the corresponding optical line terminating device for each allocation period;
The dynamic bandwidth allocating means is based on a value obtained by subtracting a total value of allocated bandwidths in a predetermined past period from a transmission request amount received in the current allocation cycle for at least some of the optical line termination devices. And determining the allocated bandwidth.   2. The optical system according to claim 1, wherein the most recent predetermined period for obtaining the total value of the allocated bandwidth is selected according to a distance between the optical line terminating device to be allocated and the optical terminal device. Terminal equipment.   The dynamic band allocating unit determines a value obtained by adding a fixed band to a value obtained by subtracting a total value of allocated bands in a predetermined period in the past from a transmission request amount received in the current allocated period. The optical terminal device according to claim 1, wherein the optical terminal device is an optical terminal device.   4. The optical terminal apparatus according to claim 3, wherein the fixed band can be set according to a type of service. In an optical communication system having a plurality of optical line terminators and an optical terminal device containing the optical line terminators,
An optical communication system, wherein the optical terminal device according to claim 1 is applied as the optical terminal device. In the dynamic bandwidth allocating device mounted on the optical terminal device, which determines the allocated bandwidth allowed for the upstream signal from the optical line terminal device to the optical terminal device,
Transmission request amount acquisition means for capturing the transmission request amount transmitted by the optical line termination device for each allocation period;
Dynamic bandwidth allocating means for determining an allocated bandwidth allowed for an uplink signal from the optical line terminating device to the optical terminal device for the optical line terminating device that has transmitted the transmission request amount for each allocation period;
Allocation bandwidth output means for outputting the determined allocation bandwidth for each allocation cycle;
The dynamic band allocating means determines an allocated band based on a value obtained by subtracting a total value of allocated bands in the most recent predetermined period from a transmission request amount received in the present allocated period. Dynamic bandwidth allocation device. A dynamic bandwidth allocation program for determining an allocation bandwidth allowed for an upstream signal from an optical line termination device to an optical terminal device for an optical line termination device that has transmitted a transmission request amount for each allocation cycle,
Computer
Transmission request amount acquisition means for capturing the transmission request amount transmitted by the optical line termination device for each allocation period;
Dynamic bandwidth allocating means for determining an allocated bandwidth based on a value obtained by subtracting a total value of allocated bandwidths in a predetermined cycle in the past from the transmission request amount received in the current allocation cycle for each allocation cycle;
A dynamic bandwidth allocation program which functions as an allocated bandwidth output means for outputting a determined allocated bandwidth for each allocation cycle.

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