JP7601727B2 - Buffer allocation device, subscriber line termination device, buffer allocation method and program - Google Patents

Description

The present invention relates to a buffer allocation device, a subscriber line termination device, a buffer allocation method, and a program.

In response to the growing need for faster access services, FTTH (Fiber To The Home) is becoming more widespread worldwide. In Japan, the main FTTH services include GE-PON (Gigabit Ethernet PON), which achieves gigabit-class transmission speeds, and 10G-EPON (10 Gigabit Ethernet PON).

In GE-PON and 10G-EPON, TDMA (Time Division Multiple Access) technology is used for upstream communications from the ONU to the OLT. In addition, one of the functions required for GE-PON and 10G-EPON to operate as a system is the DBA (Dynamic Bandwidth Allocation) function. The DBA function is a bandwidth control function that dynamically allocates bandwidth for upstream communications according to the amount of traffic. The DBA function realizes efficient upstream bandwidth without generating unused bandwidth by appropriately switching the allocated bandwidth according to the status of the upstream traffic flowing to each ONU.

In the DBA function, each ONU communicates to the OLT, via a REPORT frame, the amount of upstream data waiting to be sent that is stored in the upstream transmission buffer. Meanwhile, the OLT uses a GATE frame to instruct each ONU on the upstream data transmission start time and permitted transmission amount so that each ONU can transmit upstream data without time collisions based on the received REPORT frame. Each ONU transmits upstream data based on the permitted transmission amount at the transmission start time instructed by the GATE frame. In this way, the DBA function is realized through communication using GATE and REPORT frames.

"Technical Basics Course [GE-PON Technology] Part 4: Systemization Functions of GE-PON", NTT Technical Journal, pp. 59-61, November 2005

When providing multiple services to one user, for example when quality-guaranteed communications such as VoIP (Voice over Internet Protocol) and video distribution are multiplexed, a priority control function is required to ensure the quality of the services (see Non-Patent Document 1). The priority control function makes it possible to transmit data with higher importance first, and ensures the quality of the high-priority service even if low-priority data (Internet service) and high-priority data (VoIP, video distribution, etc.) are input simultaneously.

In general, an ONU performs priority control for the transmission of upstream data. The ONU requires a large amount of buffer space to control the timing of upstream data transmission. For this reason, the ONU is equipped with an upstream transmission buffer (hereafter referred to as the "built-in buffer") in its internal PON chip to temporarily store upstream data. This built-in buffer also has multiple upstream transmission queues. The PON chip referred to here is an ONU whose main functions have been integrated into an LSI (Large Scale Integration) to reduce costs.

However, even so, there are cases where the built-in buffer mounted on the PON chip does not have enough buffer capacity. In this case, it is necessary to add an external upstream transmission buffer (hereinafter referred to as "external buffer") such as a DDR SDRAM (Double-Data-Rate Synchronous Dynamic Random Access Memory) to create a two-stage buffer configuration. This external buffer is also configured to have multiple upstream transmission queues. Each upstream transmission queue of the built-in buffer and each upstream transmission queue of the external buffer are in one-to-one correspondence. With the two-stage buffer configuration, even if there is no free space in the built-in buffer, buffering is performed in the external buffer, preventing the occurrence of buffer overflows, etc.

However, in the past, there was no clear method for setting a necessary and sufficient buffer capacity for each buffer in such a two-stage buffer. Therefore, in order to prevent a situation in which the entire set buffer capacity cannot be allocated to the built-in buffer (hereinafter referred to as "oversubscription"), it was necessary to set the buffer capacity of the external buffer with a margin. This resulted in an issue of increased equipment costs for the transmission buffer.

The present invention has been made in consideration of the above points, and aims to provide a buffer allocation device, a subscriber line termination device, a buffer allocation method, and a program that can implement equipment for buffering transmission data at lower cost.

One aspect of the present invention is a buffer allocation device that includes an acquisition unit that acquires information indicating a requested buffer amount for each of a plurality of queues, and a setting unit that converts the requested buffer amount for each queue into a first minimum converted buffer amount based on the lowest data storage efficiency that can occur in the first storage unit, assigns a buffer amount calculated based on the first minimum converted buffer amount and the minimum buffer amount required per cycle of a dynamic bandwidth allocation function to the queue with the lowest priority in the first storage unit, assigns the first minimum converted buffer amount to queues other than the queue with the lowest priority in the first storage unit, determines for each queue whether oversubscription may occur based on the total capacity of the first storage unit and the first minimum converted buffer amount for each queue in the first storage unit, and assigns a predetermined buffer amount to the queue in the second storage unit for the queue for which it is determined that oversubscription will occur.

Moreover, one aspect of the present invention is a subscriber line termination device comprising: an acquisition unit that acquires information indicating a requested buffer amount for each of a plurality of upstream transmission queues; and a setting unit that converts the requested buffer amount for each of the upstream transmission queues into a first minimum converted data length based on the lowest data storage efficiency that can occur in an internal buffer, assigns a buffer amount calculated based on the first minimum converted data length and a minimum buffer amount required per cycle of a dynamic bandwidth allocation function to the upstream transmission queue having the lowest priority of the internal buffer, assigns the first minimum converted data length to upstream transmission queues other than the upstream transmission queue having the lowest priority of the internal buffer, determines for each upstream transmission queue whether or not oversubscription may occur based on a total capacity of the internal buffer and the first minimum converted data length for each upstream transmission queue of the internal buffer, and assigns a predetermined buffer amount to the upstream transmission queue of an external buffer for the upstream transmission queue for which it is determined that oversubscription will occur.

In addition, one aspect of the present invention is a buffer allocation method having an acquisition step of acquiring information indicating a requested buffer amount for each of a plurality of queues, and a setting step of converting the requested buffer amount for each queue into a first minimum converted buffer amount based on the lowest data storage efficiency that can occur in the first storage unit, allocating a buffer amount calculated based on the first minimum converted buffer amount and the minimum buffer amount required per cycle of the dynamic bandwidth allocation function to the queue with the lowest priority in the first storage unit, allocating the first minimum converted buffer amount to queues other than the queue with the lowest priority in the first storage unit, determining for each queue whether oversubscription may occur based on the total capacity of the first storage unit and the first minimum converted buffer amount for each queue in the first storage unit, and allocating a predetermined buffer amount to the queue in the second storage unit for the queue for which it is determined that oversubscription may occur.

Another aspect of the present invention is a program for causing a computer to function as the above-mentioned buffer allocation device.

The present invention allows equipment for buffering transmission data to be implemented at lower cost.

1 is an overall configuration diagram of a PON1 according to an embodiment of the present invention. 2 is a block diagram showing a configuration of an ONU 20 according to an embodiment of the present invention. 10A and 10B are diagrams for explaining an upstream transmission buffer setting process by an ONU 20 according to an embodiment of the present invention. 10A and 10B are diagrams for explaining an upstream transmission buffer setting process by an ONU 20 according to an embodiment of the present invention. 10A and 10B are diagrams for explaining an upstream transmission buffer setting process by an ONU 20 according to an embodiment of the present invention. 4 is a flowchart showing an example of an operation of an ONU 20 according to the embodiment of the present invention.

The following describes an embodiment of the present invention with reference to the drawings.

[PON Configuration]
PON (Passive Optical Network) is an optical access system that provides FTTH services at high speed and low cost. PON does not perform optical-electrical conversion, but splits optical signals into multiple signals using an optical splitter, which is a low-cost passive element. As a result, PON can realize an economical network by sharing a single optical fiber among multiple users. The main FTTH services in Japan include, for example, GE-PON, which realizes gigabit-class transmission speeds, and 10G-EPON, which has a bandwidth 10 times that of GE-PON.

The overall configuration of PON1 in this embodiment will be described below. FIG. 1 is an overall configuration diagram of PON1 in this embodiment of the present invention. As shown in FIG. 1, PON1 is configured to include an OLT (Optical Line Terminal) 10, a plurality of ONUs (Optical Network Units) 20 (n units in FIG. 1), an optical fiber 30, and an optical splitter 40.

The OLT 10 is installed, for example, in a telecommunications carrier's office. The ONU 20 is installed, for example, in a user's home (or premises). The optical fiber 30 is laid, for example, between the telecommunications carrier's office and the user's home. The optical splitter 40 branches the optical fiber 30. By installing the optical splitter 40 between the OLT 10 and the ONU 20, which multiplexes and splits optical signals, multiple ONUs 20 are connected to one OLT 10.

The OLT 10 receives optical signals transmitted from the ONUs 20 and forwards them to a higher-level device or a higher-level network (e.g., the Internet). The OLT 10 also receives signals from the higher-level device or the higher-level network and forwards them to each ONU 20. The OLT 10 is responsible for controlling and monitoring the PON section and the ONUs 20.

ONU 20 receives optical signals transmitted from OLT 10 and converts them into electrical signals. ONU 20 then transfers the converted electrical signals to the user's terminal device (e.g., a PC, etc.). ONU 20 also receives electrical signals transmitted from the user's terminal device and converts them into optical signals. ONU 20 then transfers the converted optical signals to OLT 10.

In PON1, TDM (Time Division Multiplexing) technology is used for communication from OLT 10 to ONU 20 (hereinafter referred to as "downstream communication"). TDM is a technology that multiplexes and transmits signals from multiple users so that they do not overlap in time.

In downstream communication, the same signal (hereinafter referred to as the "downstream signal") transmitted from the OLT 10 and split by the optical splitter 40 is forwarded to all ONUs 20 connected to the OLT 10. In other words, data other than data addressed to the ONU 20 itself is also forwarded to each ONU 20. Therefore, each ONU 20 extracts only the data addressed to itself from the forwarded data, and discards the other data (addressed to other ONUs 20).

In addition, in PON1, TDMA technology is used for communication from ONU 20 to OLT 10 (hereinafter referred to as "upstream communication"). In upstream communication, signals from multiple ONUs 20 (hereinafter referred to as "upstream signals") are multiplexed by optical splitter 40. Therefore, if the upstream signals from each ONU 20 are transmitted in a disorderly manner, there is a possibility that collisions will occur on the optical fiber 30. Therefore, TDMA controls the transmission timing of the upstream signals from ONU 20 and the transmission amount of upstream data so that the upstream signals from each ONU 20 are multiplexed without collisions on the optical fiber 30.

The DBA function is one of the functions required for GE-PON and 10G-EPON to operate as a system. The DBA function is a bandwidth control function that dynamically allocates the bandwidth for upstream communication (hereinafter referred to as "upstream bandwidth") according to the amount of traffic. The DBA function can flexibly allocate the upstream bandwidth according to the upstream communication traffic (hereinafter referred to as "upstream traffic") from each ONU 20. The DBA function allocates the upstream bandwidth only to ONUs 20 through which upstream traffic is flowing, so the upstream bandwidth can be used without waste. The DBA function realizes efficient upstream bandwidth without generating unused bandwidth by appropriately switching the allocated bandwidth according to the status of the upstream traffic flowing through each ONU 20.

GE-PON and 10G-EPON use a protocol called MPCP (Multi Point Control Protocol) to control the transmission of upstream signals. The OLT 10 uses a GATE frame to instruct each ONU 20 on the start time of upstream signal transmission and the permitted transmission amount so that each ONU 20 can transmit upstream signals without time collisions.

Meanwhile, each ONU 20 communicates the amount of upstream data waiting to be sent that is stored in the upstream transmission buffer of its own ONU 20 to the OLT 10 by a REPORT frame. The DBA function is realized by using this GATE frame and REPORT frame.

Below is a brief explanation of how the DBA function works. When ONU 20 receives upstream data, it first stores the upstream data in an upstream transmission buffer. ONU 20 writes the amount of stored upstream data in a REPORT frame and transmits the REPORT frame to OLT 10.

From the received REPORT frame, OLT 10 determines the amount of upstream data stored in ONU 20 and waiting to be sent. OLT 10 calculates the upstream bandwidth to be allocated to ONU 20 based on the amount of stored data in that ONU 20 and the bandwidth used by other ONUs 20. Specifically, OLT 10 calculates the transmission start time and permitted transmission amount of the ONU 20's upstream signal. OLT 10 writes the calculated values in a GATE frame and transmits the GATE frame to ONU 20.

ONU 20 transmits the specified amount of data (permitted transmission amount) of upstream data at the specified transmission start time according to the instructions written in the received GATE frame. At this time, ONU 20 may notify OLT 10 again of the amount of upstream data stored in the upstream transmission buffer for the next allocation of upstream bandwidth.

By repeating the above procedure, the OLT 10 can grasp the upstream traffic situation in each ONU 20 and appropriately allocate the upstream bandwidth to each ONU 20 according to the situation.

[ONU Configuration]
The configuration of the ONU 20 in this embodiment will be described below. Fig. 2 is a block diagram showing the configuration of the ONU 20 in this embodiment. As shown in Fig. 2, the ONU 20 includes a TRx 21, a MAC processing unit 22, a PHY 23, and an external buffer 24.

The TRx (Transmitter/Receiver) 21 is an optical transmitter/receiver that transmits and receives optical signals between the device itself and the OLT 10. The TRx 21 converts the digital data (electrical signal) for upstream transmission output from the MAC processing unit 22 into an optical signal (upstream signal) and outputs it to the optical fiber 30, and also receives an optical signal (downstream signal) transmitted from the OLT 10, converts the received optical signal into digital data (electrical signal) and outputs it to the MAC processing unit 22.

The MAC (Media Access Control) processing unit 22 is a functional unit of the data link sublayer that controls the transmission and reception of data. The MAC processing unit 22 is generally configured using a PON chip. The MAC processing unit 22 includes a buffer setting unit 220 and an internal buffer 221. The buffer setting unit 220 sets the buffer amount of the internal buffer 221 and the external buffer 24. In the following description, the internal buffer 221 and the external buffer 24 are sometimes collectively referred to as the "upstream transmission buffer."

The built-in buffer 221 and the external buffer 24 are configured using a storage medium such as a magnetic hard disk device or a semiconductor storage device. The built-in buffer 221 and the external buffer 24 accumulate upstream data received by the PHY 23. The built-in buffer 221 and the external buffer 24 each have multiple upstream transmission queues. In the following description, the upstream transmission queue of the built-in buffer 221 may be referred to as the "built-in queue," and the upstream transmission queue of the external buffer 24 may be referred to as the "external queue."

The PHY (PHYsical sublayer) 23 is a functional part of the physical layer. The PHY 23 is a communication interface that connects the device itself to a lower device (e.g., a user communication terminal, etc.). The PHY 23 acquires an analog signal transmitted from the lower device, converts it to a digital signal, and outputs the converted digital signal to the MAC processing unit 22. The PHY 23 also acquires a digital signal output from the MAC processing unit 22, converts it to an analog signal, and transmits the converted analog signal to the lower device.

[How to set the upstream transmit buffer]
A specific example will now be described of a method for setting an upstream transmission buffer by the ONU 20 in this embodiment. Figures 3 to 5 are diagrams for explaining the upstream transmission buffer setting process by the ONU 20 in this embodiment of the present invention.

Here, it is assumed that the internal buffer 221 and the external buffer 24 of the ONU 20 each have four upstream transmission queues. As shown in FIG. 3, the internal buffer 221 and the external buffer 24 each have four upstream transmission queues, from upstream transmission queue #0 to upstream transmission queue #3. Here, the upstream transmission queue #3 has the highest priority, followed by upstream transmission queue #2 and upstream transmission queue #1, and the upstream data is stored in the upstream transmission queues in this order. Then, the ONU 20 transmits the upstream data stored in transmission queue #3 with the highest priority, and after that queue becomes empty, it transmits the upstream data stored in transmission queue #2, and then similarly transmits the upstream data in the order of transmission queue #1 and transmission queue #0.

Hereinafter, the upstream transmission queue #0 to the upstream transmission queue #3 of the internal buffer 221 will be referred to as the internal queue q#0 to the internal queue q#3, respectively, and the upstream transmission queue #0 to the upstream transmission queue #3 of the external buffer 24 will be referred to as the external queue Q#0 to the external queue Q#3, respectively.

The buffer setting unit 220 stores in the external queue Q#0 the upstream data that does not fall within the buffer capacity allocated to the built-in queue q#0. Similarly, the buffer setting unit 220 stores in the external queue Q#1 the upstream data that does not fall within the buffer capacity allocated to the built-in queue q#1, stores in the external queue Q#2 the upstream data that does not fall within the buffer capacity allocated to the built-in queue q#2, and stores in the external queue Q#3 the upstream data that does not fall within the buffer capacity allocated to the built-in queue q#3. In this way, the built-in queue q#n and the external queue Q#n form corresponding two-stage buffers, and each upstream data is temporarily stored by this pair of upstream transmission queues.

First, the buffer setting unit 220 determines the amount of upstream data buffering to be set in each of the built-in queues q#0 to q#3 (hereinafter simply referred to as the "buffer amount to be set") in accordance with instructions from a predefined device or line maintenance and monitoring function (e.g., an extended OAM (Operation, Administration, and Maintenance) function).

As shown in FIG. 3, the buffer capacity to be set for built-in queue q#0 is 600 [KB], the buffer capacity to be set for built-in queue q#1 is 300 [KB], the buffer capacity to be set for built-in queue q#2 is 200 [KB], and the buffer capacity to be set for built-in queue q#3 is 100 [KB].

The buffer setting unit 220 then converts the determined buffer amounts to be set for each of the built-in queues q#0 to q#3 into buffer amounts equivalent to the data length that provides the lowest storage efficiency in the built-in buffer 221. The data length that provides the lowest storage efficiency is the data length that provides the largest unused buffer space when upstream data is stored in the upstream transmission queue. The buffer setting unit 220 determines the converted buffer amounts as the buffer amounts for upstream data to be secured for each of the built-in queues q#0 to q#3 (hereinafter also simply referred to as "secured buffer amounts").

Here, the minimum storage efficiency of the built-in buffer 221 is assumed to be 1/1.5. Therefore, the buffer capacity reserved for the built-in queue q#0 is 900 [KB] (= 600 x 1.5), the buffer capacity reserved for the built-in queue q#1 is 450 [KB] (= 300 x 1.5), the buffer capacity reserved for the built-in queue q#2 is 300 [KB] (= 200 x 1.5), and the buffer capacity reserved for the built-in queue q#3 is 150 [KB] (= 100 x 1.5).

Next, the buffer setting unit 220 calculates the minimum buffer amount required per cycle of the DBA function. The reason why the minimum buffer amount required per cycle of the DBA function is calculated is due to the constraint on the PON chip that only the built-in buffer 221 can output upstream data per cycle. In other words, the buffer setting unit 220 calculates a buffer amount equivalent to the maximum upstream data transmission permission amount (Data Grant) that can be granted by the OLT 10 per cycle of the DBA function (note that, as above, the buffer setting unit 220 converts into a buffer amount equivalent to the data length that provides the minimum storage efficiency in the built-in buffer 221).

Here, the buffer capacity equivalent to the data length of the maximum upstream data transmission permission amount (Data Grant) that can be granted is assumed to be 525 [KB].

Next, the buffer setting unit 220 allocates a buffer amount so that the built-in queue q#0, which is the lowest priority upstream transmission queue, has the maximum upstream rate. Specifically, the buffer setting unit 220 compares the calculated buffer amount (hereinafter also referred to as "buffer amount A") to be secured in the built-in queue q#0 with the buffer amount (hereinafter also referred to as "buffer amount B") equivalent to the data length that is the minimum storage efficiency in the built-in buffer 221 for the calculated maximum amount of upstream data transmission permission (Data Grant) that can be granted. If the buffer amount A is greater than the buffer amount B, the buffer setting unit 220 sets the built-in queue q#0 to be allocated the buffer amount B. On the other hand, if the buffer amount A is equal to or less than the buffer amount B, the buffer setting unit 220 sets the built-in queue q#0 to be allocated the buffer amount A.

As described above, in this example, buffer amount A is 900 [KB] and buffer amount B is 525 [KB]. Since buffer amount A is greater than buffer amount B, a buffer amount of 525 [KB] (buffer amount B) is allocated to built-in queue q#0, as shown in FIG. 3.

Next, the buffer setting unit 220 calculates the buffer amount to be actually allocated to the external queue Q#0. Specifically, when the buffer amount B is allocated to the built-in queue q#0 as described above, the buffer setting unit 220 allocates to the external queue Q#0 the buffer amount that cannot be fully set by setting the buffer amount for the built-in queue q#0 out of the buffer amount reserved for the built-in queue q#0 (note that the buffer setting unit 220 converts this into a buffer amount equivalent to the data length that provides the minimum storage efficiency in the external buffer 24).

Here, as described above, a buffer capacity of 525 [KB] is allocated to the built-in queue q#0. This buffer capacity of 525 [KB] is the buffer capacity equivalent to the data length that provides the lowest storage efficiency in the built-in buffer 221, so 350 [KB] (= 525 ÷ 1.5) of the 600 [KB] buffer capacity originally desired to be set in the built-in queue q#0 has been allocated to the built-in queue q#0. Therefore, the remaining 250 [KB] (= 600 - 350) of the 600 [KB] buffer capacity originally desired to be set in the built-in queue q#0 needs to be allocated to the external queue Q#0.

Here, the minimum storage efficiency of the external buffer 24 is assumed to be 1/1.2. Therefore, as shown in FIG. 3, a buffer capacity of 300 KB (= 250 x 1.2) is allocated to the external queue Q#0.

The buffer setting unit 220 also allocates the calculated buffer amount to be secured in the built-in queue q#1, the buffer amount to be secured in the built-in queue q#2, and the buffer amount to be secured in the built-in queue q#3 to the built-in queue q#1, the built-in queue q#2, and the built-in queue q#3, respectively.

Here, as shown in FIG. 3, buffer sizes of 450 KB, 300 KB, and 150 KB are allocated to built-in queue q#1, built-in queue q#2, and built-in queue q#3, respectively.

Next, the buffer setting unit 220 determines whether or not oversubscription can occur in each of the built-in queues q#0 to q#3 based on the total capacity of the built-in buffer 221 (built-in queues q#0 to q#3). For example, if the total capacity of the built-in buffer 221 is used up in the built-in queues q#0 to q#2, the buffer amount of the built-in queue q#3 becomes 0 [KB]. In this case, even if upstream data is acquired from the built-in queue q#3, the built-in queue q#3 cannot store the upstream data. As a result, oversubscription occurs in the built-in buffer for the upstream data, and data that cannot be stored is stored in the external buffer. The buffer setting unit 220 determines whether oversubscription can occur in a certain built-in queue based on the buffer amount of other built-in queues.

As shown in FIG. 4, it is assumed here that the total capacity of the built-in buffer 221 (built-in queue q#0 to built-in queue q#3) is 1 MB. As described above, built-in queue q#0, built-in queue q#1, and built-in queue q#2 are assigned buffer capacities of 525 KB, 450 KB, and 300 KB, respectively. Therefore, the total buffer capacity of built-in queue q#0 to built-in queue q#2 is 1,275 KB, which exceeds 1 MB (= 1,024 KB). Therefore, it is determined that oversubscription may occur in built-in queue q#3.

In this way, since the total amount of buffer space allocated to built-in queue q#0, built-in queue q#1, and built-in queue q#2 is 1,275 [KB] (= 525 + 450 + 300) > 1 [MB], it is determined that oversubscription may occur in built-in queue q#3, and since the total amount of buffer space allocated to built-in queue q#0, built-in queue q#1, and built-in queue q#3 is 1,125 [KB] (= 525 + 450 + 150) > 1 [MB], it is determined that oversubscription may occur in built-in queue q#2.

On the other hand, since the total amount of buffer space allocated to built-in queue q#0, built-in queue q#2, and built-in queue q#3 is 975 [KB] (= 525 + 300 + 150) ≦ 1 [MB], it is determined that oversubscription will not occur in built-in queue q#1, and since the total amount of buffer space allocated to built-in queue q#1, built-in queue q#2, and built-in queue q#3 is 900 [KB] (= 450 + 300 + 150) ≦ 1 [MB], it is determined that oversubscription will not occur in built-in queue q#0.

Next, the buffer setting unit 220 allocates a buffer amount to the external queue corresponding to the internal queue determined in the above judgment that oversubscription may occur (note that the buffer setting unit 220 converts this into a buffer amount equivalent to the data length that provides the minimum storage efficiency in the external buffer 24).

Here, as described above, since it is determined that oversubscription may occur in the built-in queue q#2 and the built-in queue q#3, buffer amounts are allocated to the external queues Q#2 and Q#3. As described above, the buffer amount to be initially set for the built-in queue q#2 is 200 [KB], so as shown in FIG. 5, a buffer amount of 240 [KB] (= 200 x 1.2) is allocated to the external queue Q#2, which corresponds to the data length that provides the minimum storage efficiency in the external buffer 24. Also, since the buffer amount to be initially set for the built-in queue q#3 is 100 [KB], as shown in FIG. 5, a buffer amount of 120 [KB] (= 100 x 1.2) is allocated to the external queue Q#3, which corresponds to the data length that provides the minimum storage efficiency in the external buffer 24.

[ONU Operation]
The operation of the ONU 20 in this embodiment during the setting process of the upstream transmission buffer will be described below. Fig. 6 is a flowchart showing an example of the operation of the ONU 20 in this embodiment. Note that here, it is assumed that the built-in buffer 221 and the external buffer 24 each have n (n is an integer equal to or greater than 1) upstream transmission queues.

First, the buffer setting unit 220 determines the buffer amount to be set for each of the built-in queues q#0 to q#n-1 based on the upstream data acquired from the PHY 23 (step S01).

Then, the buffer setting unit 220 converts the buffer amounts to be set for each of the built-in queues q#0 to q#n-1 determined in step S01 into buffer amounts equivalent to the data length that provides the lowest storage efficiency in the built-in buffer 221 (step S02). The buffer setting unit 220 determines the converted buffer amounts as the buffer amounts to be secured for each of the built-in queues q#0 to q#n-1.

Next, the buffer setting unit 220 calculates the minimum amount of buffer required per cycle of the DBA function (step S03).

Next, the buffer setting unit 220 allocates a buffer amount so that the built-in queue q#m (m is an integer satisfying 0≦m≦n-1), which is the lowest priority upstream transmission queue, has the maximum upstream rate. Specifically, the buffer setting unit 220 compares the calculated buffer amount (buffer amount A) to be secured in the built-in queue q#m with the buffer amount (buffer amount B) corresponding to the data length that is the minimum storage efficiency in the built-in buffer 221 for the calculated maximum amount of upstream data transmission permission (Data Grant) that can be granted. If the buffer amount A is greater than the buffer amount B, the buffer setting unit 220 sets the built-in queue q#m to be allocated the buffer amount B. On the other hand, if the buffer amount A is equal to or less than the buffer amount B, the buffer setting unit 220 sets the built-in queue q#m to be allocated the buffer amount A (step S04).

Next, the buffer setting unit 220 determines whether or not a buffer amount needs to be allocated to the external queue Q#m corresponding to the built-in queue q#m, which is the lowest priority upstream transmission queue (step S05). Specifically, the buffer setting unit 220 determines that a buffer amount needs to be allocated to the external queue Q#m when there is a buffer amount that cannot be fully set by setting the buffer amount for the built-in queue q#m in step S04 among the buffer amounts secured in the built-in queue q#m (i.e., when the buffer amount B is allocated to the built-in queue q#m).

If it is determined that a buffer capacity needs to be allocated to the external queue Q#m (step S05: YES), the buffer setting unit 220 allocates to the external queue Q#0 the buffer capacity reserved in the built-in queue q#0 that could not be fully set by setting the buffer capacity for the built-in queue q#0 (step S06).

Next, the buffer setting unit 220 assigns the buffer amount to be secured in the built-in buffer calculated in step S02 to each built-in queue other than the built-in queue q#m, which is the lowest priority upstream transmission queue (step S07).

Next, the buffer setting unit 220 determines whether or not oversubscription may occur in each of the built-in queues q#0 to q#n based on the total capacity of the built-in buffer 221 (step S08).

Next, the buffer setting unit 220 allocates a buffer amount to the external queue corresponding to the internal queue determined in the above judgment that oversubscription may occur (step S09). This completes the operation of the ONU 20 shown in the flowchart of FIG. 6.

As described above, in this embodiment, the ONU 20 converts the buffer amount to be set for each upstream transmission queue into the buffer amount when the built-in buffer 221 provides the lowest capacity. The ONU 20 first preferentially allocates the built-in buffer 221 to the upstream transmission queue with the lowest priority. At this time, if the buffer amount to be set is greater than the minimum buffer amount required per cycle of the DBA function, the ONU 20 allocates the minimum required buffer amount to the built-in buffer 221, and allocates the remaining buffer amount to the external buffer 24.

With such a configuration, the ONU 20 in this embodiment can appropriately set the buffer amount of the two-stage upstream transmission buffer. Specifically, the external buffer 24 stores the upstream data that does not fit in the built-in buffer 221. Then, while allocating a sufficient buffer amount to the upstream transmission queue #0, which is the class assumed to be the best effort class and has the largest buffer requirement, the upstream transmission queues #1 to #3, which are the classes assumed to be the bandwidth guaranteed classes, are secured in the built-in buffer 221 with only the data amount guaranteed per cycle of the DBA function, so that the upstream data can be transmitted efficiently based on priority. The best effort class here is a quality class for providing communication services that prioritize economy and freedom similar to the general Internet. The bandwidth compensation class here is a priority class, for example, a quality class suitable for providing communication services that require real-time performance such as video telephony and video distribution. As a result, according to the ONU 20 in this embodiment, it is possible to use a combination of low-cost, low-capacity buffers, and a configuration that meets the necessary performance of the ONU 20 at a lower cost can be achieved. Therefore, with the ONU 20 in this embodiment, equipment for buffering transmission data can be implemented at lower cost.

As described above, in this embodiment, ONU 20 allocates the remaining buffer capacity to upstream transmission queues other than the upstream transmission queue with the lowest priority. At this time, if there is a possibility of oversubscription, in which the buffer capacity to be set exceeds the capacity of the built-in buffer 221, ONU 20 sets the upstream transmission queue where the oversubscription may occur in the external buffer 24.

By having such a configuration, the ONU 20 in this embodiment can prevent oversubscription and suppress an increase in the amount of buffer required for the external buffer 24.

According to the above-described embodiment, the buffer allocation device includes an acquisition unit and a setting unit.
For example, the buffer allocation device is the ONU 20 or the MAC processing unit 22 in the embodiment, the acquisition unit is a part of the MAC processing unit 22 in the embodiment, and the setting unit is the buffer setting unit 220 in the embodiment. The acquisition unit acquires information indicating the requested buffer amount for each of the multiple queues. For example, the multiple queues are the upstream transmission queue #0 to the upstream transmission queue #n in the embodiment, and the requested buffer amount is the buffer amount of upstream data to be set in each of the built-in queues q#0 to q#n in the embodiment.

The setting unit converts the requested buffer amount for each queue into a first minimum conversion buffer amount based on the lowest data storage efficiency that can occur in the first storage unit. For example, the first storage unit is the built-in buffer 221 in the embodiment, and the first minimum conversion buffer amount is a buffer amount corresponding to a data length that is the lowest storage efficiency in the built-in buffer 221 in the embodiment. The setting unit assigns a buffer amount calculated based on the first minimum conversion buffer amount and the minimum buffer amount required per cycle of the dynamic bandwidth allocation function to the queue with the lowest priority in the first storage unit. For example, the queue with the lowest priority in the first storage unit is the built-in queue q#0 in the embodiment, and the dynamic bandwidth allocation function is the DBA function in the embodiment. The setting unit converts the buffer amount that was not set in the first storage unit into a second minimum conversion buffer amount based on the lowest data storage efficiency that can occur in the second storage unit, and assigns the second minimum conversion buffer amount to the queue with the lowest priority in the second storage unit. For example, the second storage unit is the external buffer 24 in the embodiment, the second minimum converted buffer amount is the buffer amount corresponding to the data length that results in the minimum storage efficiency of the external buffer 24 in the embodiment, and the lowest priority queue of the second storage unit is the external queue Q#0 in the embodiment.

In the above-mentioned buffer allocation device, the setting unit may compare the first minimum conversion buffer amount with a required buffer amount indicating the minimum buffer amount required per one cycle of the dynamic bandwidth allocation function, and if the first minimum conversion buffer amount is greater than the required buffer amount, allocate the required buffer amount to the lowest priority queue of the first storage unit, and if the first minimum conversion buffer amount is equal to or less than the required buffer amount, allocate the first minimum conversion buffer amount to the lowest priority queue of the first storage unit. For example, the required buffer amount is a buffer amount equivalent to a data length equivalent to the maximum upstream data transmission grant amount (Data Grant) that can be granted by the OLT 10 per one cycle of the DBA function in the embodiment.

In the above-mentioned buffer allocation device, the setting unit may allocate the first minimum converted buffer amount to a queue other than the lowest priority queue in the first storage unit, determine for each queue whether oversubscription may occur based on the total capacity of the first storage unit and the first minimum converted buffer amount for each queue in the first storage unit, and allocate a predetermined buffer amount to a queue in the second storage unit for which oversubscription is determined to occur. For example, the queue other than the lowest priority queue in the first storage unit is an internal queue q#n other than the internal queue q#0 in the embodiment.

In the above-mentioned buffer allocation device, the setting unit may determine that oversubscription may occur in a specific queue of the first storage unit when the total amount of buffers allocated to queues other than the specific queue of the first storage unit is greater than the total capacity of the first storage unit.

In addition, in the above-mentioned buffer allocation device, the setting unit may allocate the above-mentioned predetermined buffer amount calculated based on the lowest data storage efficiency that can occur in the second storage unit.

A part or all of the ONU 20 in the above-mentioned embodiment may be realized by a computer. In that case, a program for realizing this function 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 to realize the function. Note that the term "computer system" here includes the OS and hardware of peripheral devices. Furthermore, the term "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, and recording devices such as hard disks built into a computer system. Furthermore, the term "computer-readable recording medium" may include a medium that dynamically holds a program for a short period of time, such as a communication line when a program is transmitted via a network such as the Internet or a communication line such as a telephone line, and a medium that holds a program for a certain period of time, such as a volatile memory inside a computer system that is a server or client in such a case. Furthermore, the above-mentioned program may be a program for realizing a part of the above-mentioned function, or may be a program that can realize the above-mentioned function in combination with a program already recorded in the computer system, or may be a program that is realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

The above describes an embodiment of the present invention in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and includes designs that do not deviate from the gist of the present invention.

1: PON, 10: OLT, 20: ONU, 21: TRx, 22: MAC processing unit, 23: PHY, 24: external buffer, 30: optical fiber, 40: optical splitter, 220: buffer setting unit, 221: built-in buffer

Claims (8)

an acquisition unit that acquires information indicating a requested buffer amount for each of a plurality of queues;
a setting unit that converts the requested buffer amount for each of the queues into a first minimum converted buffer amount based on the lowest data storage efficiency that can occur in the first storage unit, allocates a buffer amount calculated based on the first minimum converted buffer amount and a minimum buffer amount required per cycle of a dynamic bandwidth allocation function to the queue with the lowest priority in the first storage unit, allocates the first minimum converted buffer amount to queues other than the queue with the lowest priority in the first storage unit, determines for each of the queues whether or not oversubscription may occur based on a total capacity of the first storage unit and the first minimum converted buffer amount for each of the queues in the first storage unit, and allocates a predetermined buffer amount to the queue in the second storage unit for the queue for which it is determined that oversubscription will occur;
A buffer allocation apparatus comprising: 2. The buffer allocation device of claim 1, wherein the setting unit determines that the oversubscription may occur in the specific queue of the first storage unit when a total of buffer amounts allocated to queues other than the specific queue of the first storage unit is greater than a total capacity of the first storage unit. 3. The buffer allocation device according to claim 1, wherein the setting unit compares the first minimum converted buffer amount with a required buffer amount indicating a minimum buffer amount required per cycle of the dynamic bandwidth allocation function, and if the first minimum converted buffer amount is greater than the required buffer amount, allocates the required buffer amount to the queue with the lowest priority in the first memory unit, and if the first minimum converted buffer amount is equal to or less than the required buffer amount, allocates the first minimum converted buffer amount to the queue with the lowest priority in the first memory unit. 4. The buffer allocation device according to claim 1, wherein the setting unit converts the buffer amount not set in the first memory unit into a second minimum converted buffer amount based on the lowest data storage efficiency that can occur in the second memory unit, and allocates the second minimum converted buffer amount to the queue with the lowest priority in the second memory unit. The buffer allocation device according to claim 1 , wherein the setting unit allocates the predetermined buffer amount calculated based on a lowest data storage efficiency that can occur in the second storage unit. an acquisition unit that acquires information indicating a requested buffer capacity for each of a plurality of upstream transmission queues;
a setting unit that converts the requested buffer amount for each of the upstream transmission queues into a first minimum converted data length based on the lowest data storage efficiency that can occur in the built-in buffer, allocates a buffer amount calculated based on the first minimum converted data length and a minimum buffer amount required per cycle of a dynamic bandwidth allocation function to the upstream transmission queue with the lowest priority of the built-in buffer, allocates the first minimum converted data length to upstream transmission queues other than the upstream transmission queue with the lowest priority of the built-in buffer, determines for each of the upstream transmission queues whether or not oversubscription may occur based on a total capacity of the built-in buffer and the first minimum converted data length for each of the upstream transmission queues of the built-in buffer, and allocates a predetermined buffer amount to the upstream transmission queue of an external buffer for the upstream transmission queue for which it is determined that oversubscription will occur;
A subscriber line termination device comprising: An acquisition step in which the computer acquires information indicating a required buffer amount for each of a plurality of queues;
a setting step of: a computer converting the requested buffer amount for each of the queues into a first minimum converted buffer amount based on the lowest data storage efficiency that can occur in a first storage unit, allocating a buffer amount calculated based on the first minimum converted buffer amount and a minimum buffer amount required per cycle of a dynamic bandwidth allocation function to the queue with the lowest priority in the first storage unit, allocating the first minimum converted buffer amount to queues other than the queue with the lowest priority in the first storage unit, determining for each of the queues whether or not oversubscription may occur based on a total capacity of the first storage unit and the first minimum converted buffer amount for each of the queues in the first storage unit, and allocating a predetermined buffer amount to the queue in the second storage unit for the queue for which it is determined that oversubscription will occur;
The buffer allocation method has the following structure: A program for causing a computer to function as a buffer allocation device according to any one of claims 1 to 5.

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