JP4228296B2 - Variable length packet storage apparatus and method - Google Patents

Description

  The present invention relates to a variable-length packet storage apparatus and method, and more particularly to the use of a buffering shared memory that temporarily stores variable-length data packets in a relay device or a packet switch of the Internet or a LAN (Local Area Network) network. The present invention relates to a variable-length packet storage apparatus and method for improving efficiency.

  In recent years, with the widespread use of the Internet, high-speed packet relay processing and improvement of relay quality in the network are required. The packet switch, packet relay device, etc. temporarily store the received packet in a buffering shared memory (RAM, etc.), determine the destination based on the destination address in the header of the packet, and store each stored packet Sequentially read from the buffering shared memory and transmit.

  In such a packet accumulating device, when accumulating received packets in the buffering shared memory, the received packets are divided into fixed lengths and stored. The buffering shared memory is also divided into fixed-length buffer areas, and received packets are stored in the fixed-length buffer areas. At this time, it is not necessary to store one received packet in a continuous fixed-length buffer area, but sequentially use and store discontinuous unused (empty) buffer areas.

  Even if the packets are stored sequentially in the buffering shared memory in the order of arrival of the received packets, the order of packets read from the buffering shared memory is not necessarily the order of arrival of the received packets. ) Buffer areas are scattered discontinuously and sparsely. Therefore, the buffering shared memory can be used efficiently by linking and using discontinuous unused (empty) buffer areas. This buffering shared memory storage method is generally known as a memory management method using a linked list.

  A conventional management method for storing data in a buffering shared memory will be described with reference to FIG. FIG. 9 shows an example in which a received packet is stored by dividing a buffering shared memory of size S bytes into buffer areas of a fixed length of m bytes. In the figure, since the packet length of the packet A is one byte larger than the buffer size m bytes, the storage area of the packet A uses two buffer areas 9-1 and 9-2. In this case, the buffer area 9-2 stores only 1 byte of data, and the remaining area becomes an unused area. In such a state, the usage efficiency is about 50%.

  In the figure, the hatched buffer area of the shared memory indicates that the packet data is stored and in use, and the blank buffer area indicates that it is unused (empty). Incidentally, if the packet length is slightly smaller than the buffer size m as in the packet B of FIG. 9, or the packet length is {buffer size m × j (j is an arbitrary integer greater than or equal to 2) −1 byte}. For example, the usage efficiency of the buffering shared memory is close to 100%.

  However, if the fixed-size buffer size m is reduced, the usage efficiency approaches as much as 100%. However, as the buffer size m is reduced, pointers for managing the connection of buffer areas for storing packets (buffer areas to be connected) The number of the first address in the shared memory) increases, the memory for storing the pointer requires a large capacity, leading to an increase in hardware scale.

  As a method for improving the use efficiency of the buffering shared memory, several fixed-size buffer areas of different sizes are prepared, and when the packet is received, the packet length is measured (during the measurement period) One packet is held in a temporary storage memory other than the buffering shared memory), and a fixed-length buffer area that minimizes a wasteful unused area is selected and stored according to the packet length, thereby solving the above-described problem. The technology is described in Patent Documents 1 and 2 below.

The following Patent Document 1 relates to a packet memory monitoring device that guarantees continuity of a memory space when storing a variable-length packet and at the same time prevents waste of the memory space. The present invention relates to a packet storage type data exchange processing device that uses a plurality of temporary storage areas composed of areas of different sizes and a reference flag based on a terminal identification number to effectively use the storage area.
JP 2002-185505 A JP 2001-77851 A

  However, in the above-described conventional technique, it is necessary to determine the buffer size in advance by assuming the length of the received packet and delimit the buffering shared memory to the size. However, it is impossible to accurately estimate the size of a large number of packets flowing through the network, and if the packet size is not correctly estimated, packets larger than the expected size cannot be received, or the estimated size However, when only a very small packet is received, a lot of unused areas are generated in the buffer area, which causes a problem that the use efficiency of the shared memory is lowered.

  In addition, jumbo packets (around 9 Kbytes) are frequently generated in packets flowing through recent networks, and in order to keep these jumbo packets in temporary storage memory for size measurement, it is essential to increase the hardware scale. It becomes. Also, when using a transmission interface in which multiple ports are mixed (for example, SPI4P2: System Packet Interface Level 4, Phase 2, etc.), temporary storage memory is required for the number of mixed ports, which further increases the hardware scale. End up. As described above, there is a problem that the buffering shared memory is not efficiently used for a received packet having a packet length different from that assumed in advance.

  The present invention can use the buffering shared memory efficiently without being influenced by the size of the packet flowing through the network, and the number of pointers for managing the blockage of the buffer area for storing the packet and its connection An object of the present invention is to provide a variable-length packet accumulating apparatus and method capable of suppressing the increase of the packet.

  The variable length packet accumulating device of the present invention is different from (1) a reception packet length monitoring means for calculating reception frequency statistical data for the length of an input variable length reception packet and a size for storing a variable length reception packet. The length of the variable-length received packet obtained from the received packet length monitoring means by comparing the configuration ratio of the buffering shared memory composed of a plurality of types of buffer areas and the plurality of types of buffer areas having different sizes in the buffering shared memory. And a means for changing based on the statistical data of the reception frequency for.

  (2) The received packet length monitoring means determines whether the length of the input variable-length received packet is equal to or greater than a predetermined threshold and distributes the variable-length received packet into one of two types, large and small. A large-sized variable-length received packet distributed by the distributing means is stored in a large-sized buffer area, and a small-sized variable-length received packet is stored in a small-sized buffer area.

  (3) The buffer area is composed of a large buffer area and a small buffer area obtained by dividing the large buffer area into a plurality of parts, and the start address of each large buffer area is a unit. And a buffer size management memory for storing a sub-address flag indicating the free state of each small-sized buffer area for each unit of the large-sized buffer area.

  The variable length packet storage method of the present invention includes (4) a reception packet length monitoring step for calculating reception frequency statistical data for the length of an input variable length reception packet, and a plurality of types of buffer areas having different sizes. For the buffered shared memory for storing received packets configured in the above, the composition ratios of a plurality of types of buffer areas having different sizes are received for the length of the variable-length received packet obtained from the received packet length monitoring means. A step of changing based on the statistical data of the frequency, and a step of selecting the buffer area that is the least unused area according to the length of the input variable-length received packet and storing the variable-length received packet. It is a waste.

  (5) The received packet length monitoring step includes a step of determining whether or not the length of the input variable-length received packet is equal to or greater than a predetermined threshold and allocating the variable-length received packet to one of two types, large and small. Including a step of storing a large variable-length received packet distributed in the distribution step in a large buffer area and storing a small variable-length received packet in a small buffer area.

  According to the present invention, when a variable-length packet is divided and stored in a buffering shared memory composed of a plurality of types of fixed-length buffer areas of different sizes, the reception frequency related to the size of the packet length is calculated when the packet is received. Depends on the length of the packet flowing through the network by changing the composition ratio of multiple types of buffer areas of different sizes in the buffering shared memory based on the statistical data of the reception frequency related to the size of the packet length In addition, the buffering shared memory can be used efficiently, and the performance of the variable-length packet storage device can be improved.

  In addition, by determining the size of the received packet length and allocating the received packet to one of two sizes depending on the determination result, a large buffer area is provided for storing large sized received packets by the distribution. This makes it easy to control the use of a small buffer area for storing small received packets, and makes it possible to efficiently use a buffering shared memory.

  The buffer area is composed of a large buffer area and a buffer area of a small size obtained by dividing the large buffer area into a plurality of pieces, and only the head address of the large buffer area is a free pointer. By managing sub-address flags indicating the free state of each small-sized buffer area for each unit of the large-sized buffer area, An increase in the number of pointers for managing concatenation can be suppressed, and an increase in hardware scale can be prevented.

  FIG. 1 shows a configuration of a buffer management unit in a packet storage apparatus according to the present invention. The buffer management unit is provided with a received packet length monitoring unit 1-1. The received packet length monitoring unit 1-1 observes the length of the received packet, and uses this observation result to dynamically (operate the operation). (Continued) This changes the configuration of the buffer area of the buffering shared memory.

  Changing the configuration of the buffer area means that the buffering shared memory is composed of buffer areas of two sizes of m bytes and n bytes (m> n), and the number of buffer areas of m bytes and the buffer area of n bytes It is to change the ratio with the number of. The packet length monitoring unit 1-1 collects statistical data on the length of the received packet. The statistical data is collected by setting a certain threshold value and counting the number of received packets having a packet length equal to or greater than the threshold and the number of received packets having a packet length equal to or less than the threshold using two counters.

  Based on the count values of the two counters, a ratio between the number of received packets having a packet length equal to or greater than the threshold and the number of received packets having a packet length equal to or less than the threshold is calculated, and the ratio is used as the reception status notification information. -2 is notified, and the buffer size distribution unit 1-2 recognizes the state of the length of the received packet at regular intervals.

  When the buffer size distribution unit 1-2 receives a pointer (used pointer) of a used buffer area (used pointer) from the pointer management unit 1-6, the buffer area of the used pointer is used next. Is determined based on the ratio of the number of received packets with respect to the above-mentioned received packet length, and the empty pointer management unit 1-4 is instructed about the size to be used next for the buffer area of the used pointer. To do.

  That is, when the used buffer area is reused, the buffer size distribution unit 1-2 determines which one of two types of buffer sizes, m bytes or n bytes, is used, and the empty pointer management unit 1-4 The pointer of the used buffer area whose size is determined is registered in the empty pointer queue for each of the two types of buffer sizes to create a linked list of empty pointers. The empty pointer memory 1-5 is a memory for storing a pointer in an empty buffer area, and is managed by an empty pointer queue for each of two types of buffer sizes in the empty pointer management unit 1-4.

  When writing the input received packet to the buffering shared memory, the size of the buffer area to be used is matched with the length of the received packet, and the empty pointer management unit 1-4 sets the empty pointer of the buffer area of that size to the empty pointer memory 1-. 5 and transfers the empty pointer to the buffering shared memory via the pointer management unit 1-6, and the buffering shared memory writes the received packet using the empty pointer as a write address.

  FIG. 2 shows a configuration example of the empty pointer management unit of the present invention. The empty pointer manager 1-4 includes an empty pointer queue (# 0) 1-41 for a large buffer area and an empty pointer queue (# 1) 1-42 for a small size buffer area. (# 0) 1-41 stores the empty head pointer TOP and tail pointer END of the large size buffer area, and the empty pointer queue (# 1) 1-42 stores the empty head pointer TOP and tail pointer of the small size buffer area. Store END.

  The free pointer queue (# 0) 1-41 for the large size buffer area and the free pointer queue (# 1) 1-42 for the small size buffer area each have a free space for the large size buffer area. Each free pointer for the pointer and the small size buffer area is sequentially concatenated in the free pointer memory 1-5 (the next free pointer is stored at each address of the free pointer memory) to be used for the large size buffer area and the small size buffer area. Organize each free pointer queue.

  When the empty pointer management unit 1-4 is notified of the empty pointer and its size instruction from the buffer size distribution unit 1-2, the empty pointer management unit 1-4 uses the empty pointer for the large size buffer area or the small size buffer area according to the size instruction. It is registered in the end pointer END of the empty pointer queue for one of the buffer areas. As will be described later, a free pointer queue is organized using pointers in units of large size buffer areas instead of pointers in units of small size buffer areas as free pointers for small size buffer areas.

  FIG. 3 and FIG. 4 show a configuration change example of the buffering shared memory according to the present invention. FIG. 3 shows an example in which the buffering shared memory is configured with the same amount of the small size (n size) buffer area and the large size (m size) buffer area as the initial values. Thereafter, when the reception ratio notification informs the reception ratio of the large and small reception packets, the configuration of the buffering shared memory is changed according to the reception ratio as shown in the example of FIG.

In the configuration change of the buffering shared memory, the number of memories in the small size buffer area is set to {(m / n) × reception ratio × S}, and the rest is set to the small size buffer area. Here, m is the size of the large buffer area, n is the size of the small buffer area, the reception ratio is the ratio of the number of received packets of size m or less to the total number of received packets, and S is the entire buffering shared memory Is the size of
FIG. 5 shows the configuration of the buffer size management memory of the present invention. Only a pointer with a large buffer size (m bytes) is used as a pointer for managing the buffer area, and each empty pointer of two types of buffer sizes is also managed with a pointer in units of a large buffer size (m bytes). Management of a buffer area having a small buffer size (n bytes) is performed by defining a sub-address in a buffer area having a large buffer size (m bytes). That is, the buffer area is managed by attaching a pointer in units of m bytes. Therefore, the number of pointers to be managed is the total buffering shared memory capacity S bytes ÷ m bytes.

  The number of subaddresses (k + 1) is determined by the ratio of the large buffer size (m bytes) to the small buffer size (n bytes). That is, it is determined so that n × (k + 1) = m. Each subaddress is uniquely determined by adding a counter value from 0 to k to the value of the pointer.

  Each area of this sub-address is used as a storage buffer area for short received packets that are equal to or smaller than a threshold value, and one large size buffer area indicated by one pointer is used as a continuous (k + 1) small size buffer area. The buffer management memory 1-3 is provided with a flag storage area that indicates a free blockage of the subaddress in units of subaddresses. This sub-address flag is a bit corresponding to the division number of m bytes (m ÷ n = k + 1).

  The sub-address flag is set to “all 1” for the buffer area defined and used for the m-byte size, and “all 0” for the buffer area defined and used for the n-byte size. After the received packet stored in the buffering shared memory is read from the buffering shared memory for transmission and output, the pointer of the buffer area in which the packet is stored is an empty pointer (used pointer). Is registered in the empty pointer memory 1-5, but at that time, the subaddress flag that has been used for each subaddress is set to the empty state "1" bit by bit, and all the subaddresses in one large size buffer area are set. When the flag is set to the empty state “all 1”, the pointer of the buffer area is set as an empty pointer. In this way, the used pointer can be used as an empty pointer in either the large size buffer or the small size buffer when the used pointer is used next time.

  The pointer registered in the empty pointer queue of the small size buffer is stored when a packet is stored in a part of the subaddress of the buffer area of the pointer and the part of the subaddress is unused (empty state). Are connected to the empty pointer queue, and when the packet is stored in all the sub-addresses of the buffer area of the pointer, it is removed from the empty pointer queue as being in use (blocked). When the received packet is stored in the small buffer area, the subaddress flag in the buffer area of the empty pointer is referred to, and the received packet is stored in order from the first subaddress indicating the empty state (“1”). Then, the flag of the sub address that has been stored is set to the in-use state (“0”).

  FIG. 6 shows an example of allocation of a small size (n bytes) buffer area in the buffering shared memory. In the figure, the shaded area indicates a small size (n byte) buffer area, and the small size (n byte) buffer area is allocated to an arbitrary area in the buffering shared memory in units of m bytes. Can do.

  In this way, by implementing a sub-address flag in units of sub-addresses and using the sub-address flag to identify the empty state of a small-sized buffer area, pointer management is not necessary in units of sub-addresses, and pointer management is performed in units of large buffer sizes. Therefore, the empty pointer management memory can be small in size and can prevent an increase in hardware scale, and if it is a packet of n bytes or less, (m / n) packets are m-sized buffers. Packets that can be stored in the area and are not larger than m size can be efficiently stored in the buffering shared memory.

  FIG. 7 shows a configuration example of a packet switch according to the present invention. The packet switch multiplexes a receiving unit (# 0, # 1) 7-1 that implements a packet receiving port, a packet from a plurality of receiving ports into one output port, and a temporary storage memory. (MUX) receive buffer 7-2, buffering shared memory 7-5 for storing received packets, buffer management unit 7-3 for managing buffering shared memory 7-5, and header information of received packets. A routing processing unit 7-4 that performs destination determination and traffic control based on the packet, a separation unit 7-6 that separates packets read from the buffering shared memory 7-5 into output ports, and a separation (DMUX) unit 7- 6 includes a transmission unit 7-7 that performs processing for converting a packet output from the transmission port 6 into a transmission port format.

  When storing the received packet in the buffering shared memory 7-5, the size of the buffer area to be used is used according to the received packet length. In FIG. 7, after a packet is received by the receiving unit 7-1, a certain amount of received packet is stored in a temporary storage memory mounted in a multiplexing (MUX) receiving buffer unit 7-2. Thereafter, the buffer management unit 7-3 is notified of the storage completion information (data write completion flag) and the received packet length information.

  The buffer management unit 7-3 determines the buffer size used when writing the received packet based on the notification information. Here, the temporary storage memory is made the same size as the large size of the buffer area of the buffering shared memory 7-5, and when a packet larger than the temporary storage memory size is received, the accumulation completion information (data write completion flag) is valid. Thus, the received packet is controlled to be written into a large buffer area.

  The packet length of the received packet is measured by the receiving unit 7-1, and the received packet length is transferred to the buffer managing unit 7-3. A reception packet is stored for each reception port in a temporary storage memory mounted in the multiplexing (MUX) reception unit 7-2. When the temporary storage memory is full of received packets or when storage of one received packet is completed, the data write completion flag is validated.

  The data write completion flag can be a 2-bit flag that includes information on whether or not the received packet length is greater than the threshold. This information is used to determine which buffer area of two types of sizes managed in the buffer management unit 7-3 is used. The configuration of the buffer management unit 7-3 is the same as that shown in FIG.

  The buffer management unit 7-3 obtains information on the received packet length and the data write completion flag from the receiving unit 7-1 and the multiplexing (MUX) receiving buffer 7-2, and performs the following processing procedure to obtain the buffering shared memory 7 Manage -5. FIG. 8 shows the flow of the processing procedure. When the packet is received, the buffer management unit 7-3 compares the received packet length with the set threshold value (8-1). Each time this magnitude comparison result is output, the reception number counter M / N in the packet length monitoring unit 1-1 is counted up (8-2). That is, if the comparison result is large, the reception number counter M is counted up. If the comparison result is small, the reception number counter N is counted up.

  The timer in the packet length monitoring unit 1-1 compares and calculates the count number of the reception number counter M / N within a certain time (8-3), and calculates the reception ratio. The calculation result of the reception ratio is transferred to the buffer size distribution unit 1-2 as reception state notification information. The reception status notification information indicates the ratio of the number of received large-size packets and small-size packets at the set threshold in the size comparison in step 8-1.

  When receiving the reception status notification information, the buffer size distribution unit 1-2 holds the ratio of the received number until the next update (8-4), and uses the received number ratio (empty pointer). ) Is used next time, it is determined whether to use a large or small size (8-7). When the used pointer (empty pointer) is received from the pointer management unit 1-6 (8-5), it is checked whether all the sub-address flags in the buffer size management memory 1-3 are “1” (8-6). When all the sub-address flags are “1”, the next use size of the used pointer (empty pointer) is determined (8-7).

  As a method for determining the size in step 8-7, a configuration in which the ratio of the number of receptions obtained in step 8-4 and the ratio of the number of allocations for each size of used pointers (empty pointers) are matched. It can be. Also, the past composition ratio of large and small buffer areas is stored, the difference between the composition ratio of the buffer area and the ratio of the number of large and small packet lengths received is calculated, and the difference is used in the direction of decreasing the difference. It is also possible to adopt a configuration for determining the size of the pointer (empty pointer).

  After the buffer size distribution unit 1-2 determines the next size of the empty pointer, the empty pointer is transferred to the empty pointer management unit 1-4 together with an empty pointer size instruction. The empty pointer management unit 1-4 queues an empty pointer in the empty pointer queue # 0 or # 1 for each different buffer size based on the empty pointer size instruction and the empty pointer information (8-8). Create a linked list of

  The number of empty buffer areas queued in empty pointer queues # 0 and # 1 for different buffer sizes is determined by the determination process in step 8-7, and as shown in FIG. The composition ratio of the buffer areas having different sizes is changed. The composition ratio of the buffer size of the buffering shared memory can be adaptively changed as needed according to the situation of the packet length of the received packet, and the use efficiency of the buffering shared memory can be improved.

  Hereinafter, improvement of the use efficiency of the buffering shared memory according to the present invention will be described with specific numerical examples. Here, as an example, the size of the buffering shared memory is 1 Mbytes, the sizes of the two fixed-length buffer areas are 512 bytes and 64 bytes, respectively, and the buffering shared memory in the initial state has a buffer area of 512 bytes of 1000 bytes. It is assumed that there are 8000 buffer areas of 64 bytes and 64 bytes.

  In the reception packet length monitoring unit 1-1, a reception number counter A for counting the number of received packets having a packet length of 512 bytes or more and a reception number counter B for counting the number of received packets having a packet length of less than 512 bytes are provided. The ratio of the amount of received packets received within a predetermined time is monitored, and the buffer size distribution unit 1-2 uses the used pointer as a 512-byte buffer area based on the ratio, or 64 bytes. Determine whether to use as a size buffer area. Thus, the following effects can be obtained by properly using the buffer size based on the statistical data of the length of the received packet.

In the conventional type, if the buffering shared memory configuration is all 512-byte buffer area, the fixed-length buffer area is 2000, and if it is all 64-byte buffer area, the fixed-length buffer area is 16000. When buffering shared memory is configured in the buffer area,
・ When a 64-byte packet is received, the usage efficiency is 64/512 = 12.5%
・ When a 65-byte packet is received, the usage efficiency is 65/512 = 12.7%
・ When 512-byte packet is received, usage efficiency is 512/512 = 100%
・ When a 513-byte packet is received, the usage efficiency is (513/512) × 2 = 50%
It becomes.

On the other hand, when a buffering shared memory is configured with a buffer area of all 64 bytes,
・ When a 64-byte packet is received, the usage efficiency is 64/64 = 100%
・ When a 65-byte packet is received, the usage efficiency is (65/64) × 2 = 50%
・ When a 512-byte packet is received, the usage efficiency is (512/64) × 8 = 100%
・ When a 513-byte packet is received, the usage efficiency is (513/64) × 9 = 89%
It becomes.

  As is clear from the above numerical example, the use efficiency is better when the buffering shared memory is configured with a buffer size of 64 bytes than 512 bytes. However, the number of buffer areas (pointers) to be managed is 8 times the size of 64 bytes compared to the size of 512 bytes. If only the size of 64 bytes is used, the hardware scale of the pointer management unit increases.

  Thus, by dividing the buffering shared memory into two large and small buffer areas as in the present invention, the advantages and disadvantages of the two large and small buffer areas can be compensated. By changing the ratio of the two types of buffer areas according to the received packet length statistical data, the buffer area can be efficiently used even when received packets of various packet lengths are input together. It is possible to configure a buffering shared memory that is frequently used and minimizes an increase in hardware scale.

It is a figure which shows the structure of the buffer management part in the packet storage apparatus by this invention. It is a figure which shows the structural example of the empty pointer management part of this invention. It is a figure which shows the example of a structure change of the buffering shared memory by this invention. It is a figure which shows the example of a structure change of the buffering shared memory by this invention. It is a figure which shows the structure of the buffer size management memory of this invention. It is a figure which shows the example of allocation of the small size (n byte) buffer area | region in a buffering shared memory. It is a figure which shows the structural example of the packet switch by this invention. It is a figure which shows the process sequence of management of the buffering shared memory by this invention. It is explanatory drawing of the management system of the accumulation | storage to the conventional buffering shared memory.

Explanation of symbols

1-1 Received packet length monitoring unit 1-2 Buffer size distribution unit 1-3 Buffer management memory 1-4 Empty pointer management unit 1-5 Empty pointer memory 1-6 Pointer management unit

Claims (5)

Received packet length monitoring means for calculating reception frequency statistical data on the length of the input variable-length received packet;
A buffering shared memory composed of multiple types of buffer areas of different sizes for storing variable-length received packets;
Means for changing the composition ratio of a plurality of types of buffer areas having different sizes in the buffering shared memory based on reception frequency statistical data on the length of the variable-length reception packet obtained from the reception packet length monitoring means; A variable-length packet storage device comprising: The received packet length monitoring means includes means for determining whether the length of the input variable-length received packet is equal to or greater than a predetermined threshold and allocating the variable-length received packet to one of two types, large and small,
2. A configuration in which a large variable-length received packet distributed by the distributing unit is stored in a large buffer area, and a small variable-length received packet is stored in a small buffer area. A variable-length packet storage device according to claim 1. The buffer area is composed of a large-sized buffer area and a small-sized buffer area obtained by dividing the large-sized buffer area into a plurality of pieces, and only the head address of the large-sized buffer area is used as an empty pointer. Free pointer memory to manage,
The variable-length packet storage according to claim 1 or 2, further comprising: a buffer size management memory for storing a subaddress flag indicating a free state of each small size buffer area for each unit of the large size buffer area. apparatus. A reception packet length monitoring step for calculating reception frequency statistical data on the length of the input variable-length reception packet;
A variable length obtained from the received packet length monitoring means, with respect to a buffering shared memory for storing received packets configured with a plurality of types of buffer areas of different sizes, the composition ratio of the plurality of types of buffer areas of different sizes. Changing the received frequency based on the received packet length statistics,
And selecting a buffer area that is the least unused area according to the length of the input variable-length received packet and storing the variable-length received packet. The received packet length monitoring step includes a step of determining whether or not the length of the input variable-length received packet is equal to or greater than a predetermined threshold and allocating the variable-length received packet to one of two types, large and small,
5. The method according to claim 4, further comprising the steps of: storing a large variable-length received packet distributed in the distribution step in a large buffer area; and storing a small variable-length received packet in a small buffer area. The variable length packet storage method described in 1.

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