JP4120929B2 - Packet transfer device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a packet output device, and is suitable for application to an access point of a wireless LAN system, for example.
[0002]
[Prior art]
Conventionally, in a wireless local area network (LAN) system such as IEEE (Institute of Electrical and Electronics Engineers) 802.11, a transmitted data packet is surely transmitted due to a collision between packets or a change in a radio wave propagation environment. There is no guarantee of reaching first. For this reason, in a wireless LAN system, after transmitting a data packet, it waits for a data receipt signal (referred to as ACK) sent back from the transmission destination, and retransmits the data packet when the ACK cannot be received within a predetermined time. Thus, the arrival rate of the data packet is improved (for example, Patent Document 1).
[0003]
This retransmission operation is called retry. In the wireless LAN system, when ACK cannot be received, the retry is repeated until the preset maximum number of retries (for example, 10 times) is reached.
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 11-252114
[Problems to be solved by the invention]
As described above, in the conventional wireless LAN system, when the ACK cannot be received, the retry is repeated up to the maximum number of retries. Since the next data packet cannot be transmitted while a retry is being performed, if a retry occurs with a large number of data packets being input, the output (transmission) cannot catch up with the input to the transmission buffer, and the The number of packets waiting for transmission (queue length) increases. The increase in the queue length causes a delay in the transmission buffer to increase, resulting in a decrease in transmission efficiency and a buffer overflow.
[0006]
In order to avoid such a buffer overflow, it is conceivable to increase the buffer size of the transmission buffer. However, this increases the queue length and further increases the delay in the transmission buffer.
[0007]
It is also possible to reduce the maximum number of retries in order to reduce the delay in the transmission buffer due to retries, but this increases the number of data packets that cannot be delivered even after retrying up to the maximum number of retries, resulting in a packet transmission error rate. As a result, the transmission efficiency is reduced.
[0008]
The present invention has been made in consideration of the above points, and an object of the present invention is to propose a packet transfer apparatus that can transfer a packet efficiently with a simple configuration and a minimum delay.
[0009]
[Means for Solving the Problems]
In order to solve such a problem, in the packet transfer apparatus of the present invention , a buffer for accumulating packets input from the outside, a packet transmission means for sequentially reading out the packets accumulated in the buffer and transmitting them to the destination, and reception of the packets a packet reception signal receiving means for receiving a packet reception signal returned from the destination in accordance with, obtains the accumulated amount of packets stored in the buffer from the buffer, when the amount of accumulation is less than the first set value The accumulated amount is determined to be at a low level, the maximum number of retransmissions is fixed to a predetermined number, and the accumulated amount is greater than or equal to the first set value and less than the second set value greater than the first set value. In this case, the maximum number of retransmissions is adaptively decreased according to the increase in the accumulated amount, and when the accumulated amount is equal to or greater than the second set value, it is determined that the accumulated amount is changing at a high level and the maximum re-transmission is performed. A retransmission count control means for setting the count to 0, when it can not receive the packet reception signal to the transmitted packet, so providing a packet retransmission control means for retransmitting a packet to a maximum of the maximum number of retransmissions to control the packet transmission unit I made it.
Further, in the present invention, in a retransmission control method for a packet transfer apparatus that sequentially reads out externally input packets stored in a buffer and transmits the packets to a transmission destination, the stored amount of packets stored in the buffer is acquired from the buffer. When the accumulated amount acquisition step and the accumulated amount are less than the first set value, it is determined that the accumulated amount is changing at a low level, the maximum number of retransmissions is fixed to a predetermined number, and the accumulated amount is the first set value. As described above, when the value is less than the second set value larger than the first set value, the maximum number of retransmissions is adaptively decreased according to the increase in the accumulated amount, and when the accumulated amount is equal to or greater than the second set value Retransmission count control step that determines that the amount is changing at a high level and sets the maximum number of retransmissions to 0, and a packet reception signal that is returned from the transmission destination in response to reception of the transmitted packet cannot be received It can, and be provided with a packet retransmission step of retransmitting the packets maximum number of retransmissions as an upper limit.
Furthermore, in the retransmission control program of the present invention, for the packet transfer device that sequentially reads the externally input packets stored in the buffer and transmits them to the transmission destination, the stored amount of packets stored in the buffer is acquired from the buffer. When the accumulated amount is less than the first set value, it is determined that the accumulated amount is changing at a low level, the maximum number of retransmissions is fixed to a predetermined number, and the accumulated amount is set to the first setting. More than the value and less than the second set value greater than the first set value, the maximum number of retransmissions is adaptively decreased according to the increase in the accumulated amount, and when the accumulated amount is greater than or equal to the second set value, Retransmission count control step for determining that the accumulated amount is changing at a high level and setting the maximum retransmission count to 0, and receiving a packet reception signal returned from the transmission destination in response to reception of the transmitted packet No time, was provided a packet retransmission step of retransmitting the packets maximum number of retransmissions as an upper limit.
[0010]
As a result, when the accumulated amount is less than the first set value that is changing at a low level, sufficient error correction is performed by fixing the maximum number of retransmissions to a predetermined number and retransmitting the packet up to the predetermined number of times. Can be stored by setting the maximum number of retransmissions to 0 so that the packet is not retransmitted when the accumulated amount is greater than or equal to a second set value that is larger than the first set value that is moving at a high level. The increase in the amount can be prevented, transmission delay and buffer overflow can be avoided, and when the accumulation amount is not less than the first setting value and less than the second setting value, the maximum number of retransmissions can be increased according to the increase in the accumulation amount. By adaptively decreasing and determining the maximum number of retransmissions that balances error correction with avoidance of transmission delay and buffer overflow, error correction is performed and transmission delay and buffer overflow are determined. It is possible to forward packets in good condition of balance to avoid flow.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described in detail below with reference to the drawings.
[0012]
(1) First Embodiment (1-1) Overall Configuration of Wireless LAN System In FIG. 1, reference numeral 1 denotes a wireless LAN system according to a first embodiment of the present invention as a whole, and access as a packet transfer apparatus It is composed of point 2 and a plurality of wireless communication terminals 3. The access point 2 and the wireless communication terminal 3 perform wireless communication with each other, for example, in the 2.4 [GHz] band.
[0013]
In practice, the wireless communication terminal 3 is a PC card type wireless LAN card, and is inserted into a PC card slot of a corresponding notebook type personal computer (hereinafter referred to as a notebook personal computer) 4. On the other hand, the access point 2 is connected to an external network 5 such as the Internet or an intranet.
[0014]
In the wireless LAN system 1, data communication can be performed between each notebook computer 4 and an information processing apparatus such as a personal computer connected to the external network 5 via the access point 2 and the wireless communication terminal 3. Has been made.
[0015]
(1-2) Configuration of Access Point Next, the configuration of the access point 2 will be described with reference to FIG.
[0016]
As shown in FIG. 2, in the access point 2, a RAM (Random Access Memory) 12, a ROM (Read Only Memory) 13, a network interface 14, and a buffer memory 15 are connected to a CPU (Central Processing Unit) 10 via a bus 11. The transmitter / receiver 16 is connected. The CPU 10 reads out a communication control program stored in the ROM 13 and executes it on the RAM 12 so as to comprehensively control each unit of the access point 2.
[0017]
The transmission / reception unit 16 receives and demodulates an upstream transmission signal transmitted from the wireless communication terminal 3 via the antenna 17, generates a packet of reception data, and sequentially inputs the packet to the reception buffer 15 </ b> B of the buffer memory 15. The network interface 14 sequentially reads packets of received data from the reception buffer 15B and supplies them to the external network 5.
[0018]
Further, the network interface 14 sequentially inputs transmission data packets supplied from the external network 5 to the wireless communication terminal 3 to the transmission buffer 15 </ b> A of the buffer memory 15. The transmission / reception unit 16 serving as a packet transmission unit sequentially reads packets of transmission data from the transmission buffer 15 </ b> A and transmits the packets to the wireless communication terminal 3 via the antenna 17.
[0019]
At this time, the CPU 10 as a packet retransmission control unit controls the transmission / reception unit 16 according to a retry control process described later, and an ACK as a packet reception signal returned from the wireless communication terminal 3 as a packet transmission destination is used as the packet reception signal reception unit. When the transmission / reception unit 16 cannot receive within a predetermined time, the retry is repeated up to the maximum number of retries as the maximum number of retransmissions.
[0020]
Further, at this time, the CPU 10 as the retransmission number control means monitors the queue length in the transmission buffer 15A, and appropriately sets the queue length by increasing / decreasing the maximum number of retries according to the change of the queue length as the accumulated amount of packets. It is designed to avoid transmission delays and buffer overflows.
[0021]
(1-3) Access Point Retry Control Processing Next, the above-described retry control processing of the access point 2 will be described in detail with reference to the flowchart shown in FIG.
[0022]
The CPU 10 of the access point 2 enters from the start step of the retry control processing procedure RT1 shown in FIG. 3 according to the communication control program and proceeds to step SP1. In step SP1, the CPU 10 acquires the queue length Lq, which is the number of packets waiting for transmission in the transmission buffer 15A, from the buffer memory 15, and proceeds to the next step SP2.
[0023]
In step SP2, the CPU 10 determines whether or not the acquired queue length Lq is 1 packet or more. In step SP2, when the queue length Lq is less than 1 packet (that is, 0 packet, there is no packet waiting for transmission in the transmission buffer 15A), the CPU 10 returns to step SP1 and the transmission packet is input to the transmission buffer 15A. I wait.
[0024]
On the other hand, when the queue length Lq is 1 packet or more (the state where there is a transmission waiting packet in the transmission buffer 15A), the CPU 10 moves to step SP3 and based on the acquired queue length Lq, the maximum retry is performed using the following equation. The number of times Rmax is determined.
[0025]
Rmax = 10 (1 ≦ Lq <10)
Rmax = 20−Lq (10 ≦ Lq <20)
Rmax = 0 (20 ≦ Lq) (1)
[0026]
That is, when the queue length Lq is 1 to 10, the maximum number of retries is 10, and thereafter, whenever the queue length Lq is increased by 1, the maximum number of retries is decreased by 1 and when the queue length Lq is 20 or more, the maximum number of retries is increased. The number of times is 0 (no retry is performed).
[0027]
In step SP4, the CPU 10 controls the buffer memory 15, extracts one packet from the transmission queue in the transmission buffer 15A and inputs it to the transmission / reception unit 16, and proceeds to the next step SP5. In step SP5, the CPU 10 sets a retry number Rn, which is a counter value of a retry number counter (not shown), to 0, and proceeds to step SP6.
[0028]
In step SP6, the CPU 10 controls the transmission / reception unit 16, transmits the packet via the antenna 17, and proceeds to step SP7. In step SP7, the CPU 10 waits for an ACK returned from the transmission destination for the transmitted packet for a predetermined waiting time.
[0029]
If ACK is received within the waiting time in step SP7, the CPU 10 ends the process for the current packet, returns to step SP1, and starts the process for the next packet. On the other hand, if the ACK cannot be received within the waiting time in step SP7, the CPU 10 moves to step SP8.
[0030]
In step SP8, the CPU 10 compares the current number of retries Rn with the maximum number of retries Rmax.
[0031]
In step SP8, when the number of retries Rn is less than the maximum number of retries Rmax, the CPU 10 moves to step SP9, adds “1” to the number of retries Rn, moves to step SP6, and retransmits the packet (retry).
[0032]
On the other hand, if the retry count Rn is not less than the maximum retry count Rmax in step SP8 (actually Rn = Rmax), the CPU 10 discards the current packet without retrying any more and returns to step SP1. Start processing for the next packet. The CPU 10 of the access point 2 always executes the processing procedure described above.
[0033]
(1-4) Operation and Effect In the above configuration, the CPU 10 of the access point 2 acquires the queue length Lq from the transmission buffer 15A of the buffer memory 15, determines the maximum number of retries Rmax based on the queue length Lq, and packet Perform the retry process.
[0034]
Then, the CPU 10 sequentially refers to the queue length Lq, decreases the maximum retry count Rmax as the queue length Lq increases, and increases the maximum retry count Rmax as the transmission queue length Lq decreases.
[0035]
For example, when the data rate of transmission data is high and retries occur at a constant rate, the queue length Lq of the transmission buffer 15A gradually increases. In this case, the CPU 10 prevents the queue length Lq from increasing by decreasing the maximum number of retries in accordance with the increase in the queue length Lq, and keeps the queue length Lq appropriate to avoid transmission delay and buffer overflow. Here, if the maximum number of retries is reduced, non-delivery of packets due to retry failure will increase. However, in wireless LAN systems, non-delivery packets will be retransmitted by the upper layer protocol, so the entire system will cover non-delivery of packets. can do.
[0036]
When the data rate of the transmission data is low, the queue length Lq of the transmission buffer 15A changes at a small level. In this case, the CPU 10 increases the maximum number of retries according to the small queue length Lq, and performs sufficient error correction by retry.
[0037]
According to the above configuration, by increasing or decreasing the maximum number of retries according to the queue length of the transmission buffer 15A, when the data rate is high and the queue length is long, the maximum number of retries is decreased to increase the queue length. In addition to preventing this, when the data rate is low and the queue length is short, the maximum number of retries can be increased to perform sufficient error correction, and packets can be transferred efficiently with minimal delay.
[0038]
(2) Second Embodiment In the first embodiment described above, the maximum number of retries is sequentially increased or decreased according to the queue length of the transmission buffer 15A at the time of packet transmission. Not limited to this, an average value of queue lengths within a certain period may be obtained, and the maximum number of retries may be increased or decreased according to the average value. In this case, the change in the maximum number of retries becomes moderate, and a stable retry operation is possible.
[0039]
As an average queue length calculation method, the average value in real time (for example, the average queue length for 5 seconds) may be calculated accurately. However, the effective queue length is simply calculated using the following formula, If the maximum number of retries is increased or decreased according to the effective queue length, the retry operation can be stabilized with a small amount of calculation processing.
[0040]
Ln = 1 / 2.Lq + 1 / 2.Ln-1 (L0 = 0) (2)
[0041]
That is, the effective queue length at the n-th packet output is Ln, and the average value of the current queue length Lq and the effective queue length Ln-1 at the previous packet output is the effective queue length Ln at the current packet output. . This effective queue length Ln corresponds to a weighted average of the queue length at the previous packet output and the queue length at the current packet output.
[0042]
The retry control process of the second embodiment using the effective queue length Ln will be described in detail with reference to the flowchart shown in FIG. Since the overall configuration of the wireless LAN system 1 and the configuration of the access point 2 are the same as those in the first embodiment described above, description thereof is omitted.
[0043]
That is, the CPU 10 of the access point 2 enters from the start step of the retry control processing procedure RT2 shown in FIG. 4 according to the communication control program and proceeds to step SP11. In step SP11, the CPU 10 sets the effective queue length Ln to 0, and proceeds to the next step SP12.
[0044]
In step SP12, the CPU 10 acquires the queue length Lq of the transmission buffer 15A from the buffer memory 15, and proceeds to the next step SP13.
[0045]
In step SP13, the CPU 10 determines whether or not the acquired queue length Lq is 1 packet or more. In step SP2, when the queue length Lq is less than 1 packet and there is no transmission waiting packet, the CPU 10 returns to step SP11 and waits for the transmission packet to be input to the transmission buffer 15A.
[0046]
On the other hand, when the output queue length Lq is 1 packet or more and there is a packet waiting to be transmitted, the CPU 10 moves to step SP14, and based on the acquired queue length Lq, the effective queue length Ln using the above-described equation (2). Is calculated. Furthermore, in step SP15, the CPU 10 determines the maximum retry count Rmax using the following equation based on the calculated effective queue length Ln.
[0047]
Rmax = 10 (1≤Ln <10)
Rmax = 20-Ln (10≤Ln <20)
Rmax = 0 (20 ≦ Ln) (3)
[0048]
In step SP16, the CPU 10 controls the buffer memory 15, extracts one packet from the transmission queue in the transmission buffer 15A, inputs it to the transmission / reception unit 16, and proceeds to the next step SP17. In step SP17, the CPU 10 sets the retry count Rn to 0, and proceeds to step SP18.
[0049]
In step SP18, the CPU 10 controls the transmitting / receiving unit 16, transmits the packet via the antenna 17, and proceeds to step SP19. In step SP19, the CPU 10 waits for an ACK returned from the transmission destination for the transmitted packet for a predetermined waiting time.
[0050]
If the ACK is received within the waiting time in step SP19, the CPU 10 ends the process for the current packet, returns to step SP11, and starts the process for the next packet. On the other hand, if the ACK cannot be received within the waiting time in step SP19, the CPU 10 proceeds to step SP20.
[0051]
In step SP20, the CPU 10 compares the current retry count Rn with the maximum retry count Rmax. If the retry count Rn is less than the maximum retry count Rmax, the CPU 10 proceeds to step SP21 and adds “1” to the retry count Rn. Then, the process proceeds to step SP18 to retransmit the packet (retry).
[0052]
On the other hand, if the retry number Rn is not less than the maximum retry number Rmax in step SP20, the CPU 10 discards the current packet without retrying and returns to step SP11 to start processing for the next packet. The CPU 10 of the access point 2 continues to execute the above processing procedure.
[0053]
According to the above configuration, the retry operation can be stabilized by simple processing by obtaining the effective queue length from the queue length of the transmission buffer 15A and increasing or decreasing the maximum number of retries according to the effective queue length.
[0054]
(3) Other Embodiments In the above-described embodiments, the number of retries is increased or decreased according to the queue length or effective queue length of the transmission buffer 15A. The queue length may be acquired individually for each transmission destination, and the number of retries may be increased or decreased for each transmission destination according to the queue length for each transmission destination or the effective queue length for each transmission destination. As a result, even when the radio wave propagation environment differs greatly from destination to destination, packets can be transferred more efficiently by individually controlling the number of retries according to each radio wave propagation environment.
[0055]
Furthermore, in the above-described embodiment, the case where the present invention is applied to the retry count control at the access point of the wireless LAN system as the packet transfer device has been described. However, the present invention is not limited to this, and wireless communication of the wireless LAN system is performed. The present invention can be applied to retry count control in various packet transfer apparatuses such as terminals, bridges and routers of wired LAN systems.
[0056]
Further, in the above-described embodiment, the CPU 10 of the access point 2 executes the retry control process according to the communication control program stored in the memory of the ROM 13, but the present invention is not limited to this, and the communication control described above is performed. The retry control process described above may be executed by installing a program storage medium in which the program is stored.
[0057]
In this case, as a program storage medium for installing the above-described communication control program, not only a package medium such as a CD-ROM (Compact Disk-Read Only Memory) or a DVD (Digital Versatile Disk) but also a program is temporarily stored. Alternatively, it may be realized by a permanently stored semiconductor memory, magnetic disk, or the like. Further, as means for storing the programs in these program storage media, wired and wireless communication media such as a local area network, the Internet, and digital satellite broadcasting may be used.
[0058]
【The invention's effect】
As described above, according to the present invention, when the accumulated amount is less than the first set value that is changing at a low level, the maximum number of retransmissions is fixed to a predetermined number and the packet is always retransmitted up to the predetermined number. makes it possible to perform adequate error correction, when more than a first set value larger than the second set value accumulated amount has remained at a high level, retransmitting a packet by setting the maximum number of retransmissions 0 By preventing the accumulation amount from increasing, transmission delay and buffer overflow can be avoided, and when the accumulation amount is greater than or equal to the first setting value and less than the second setting value, the accumulation amount increases. The maximum number of retransmissions is adaptively reduced according to the error, and error correction is performed and transmission delay is determined by determining the maximum number of retransmissions that balances error correction with avoidance of transmission delay and buffer overflow. Packet can be transferred in good condition of balance to avoid buffer overflow, thus the packet transfer device that can transfer efficiently packets with minimal delay can be realized packet transfer method and a packet transfer program.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an overall configuration of a wireless LAN system according to a first embodiment;
FIG. 2 is a block diagram showing a circuit configuration of an access point.
FIG. 3 is a flowchart illustrating a retry control processing procedure according to the first embodiment;
FIG. 4 is a flowchart illustrating a retry control processing procedure according to the second embodiment;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Wireless LAN system, 2 ... Access point, 3 ... Wireless communication terminal, 10 ... CPU10, 11 ... Bus, 12 ... RAM, 13 ... ROM, 14 ... Network interface, 15 ... Buffer, 16 ... Transceiver, 17 ... Antenna.

Claims (7)

A buffer for accumulating packets input from the outside;
Packet transmission means for sequentially reading out the packets stored in the buffer and transmitting them to a transmission destination;
A packet reception signal receiving means for receiving a packet reception signal returned from the destination in response to reception of the packet;
The accumulated amount of the packet accumulated in the buffer is acquired from the buffer , and when the accumulated amount is less than the first set value, it is determined that the accumulated amount is changing at a low level and the maximum number of retransmissions Is fixed at a predetermined number, and the accumulated amount is greater than or equal to the first set value and less than a second set value that is greater than the first set value and the maximum number of retransmissions according to an increase in the accumulated amount A retransmission number control means for determining that the accumulated amount is changing at a high level and setting the maximum number of retransmissions to 0 when the accumulated amount is equal to or greater than the second set value. ,
A packet retransmission control means for controlling the packet transmission means to retransmit the packet up to the maximum number of retransmissions when the packet reception signal for the packet transmitted by the packet transmission means cannot be received;
A packet transfer apparatus comprising: The retransmission number control means calculates a time average accumulation amount as an average value of the accumulation amount within a predetermined time, and when the time average accumulation amount is less than a first set value, the time average accumulation amount is low. The maximum number of retransmissions is fixed to a predetermined number because it is determined that the transition has occurred, and the time average accumulation amount is greater than or equal to the first set value and less than a second set value that is greater than the first set value. The maximum number of retransmissions is adaptively decreased according to the increase in the time average accumulation amount, and when the time average accumulation amount is equal to or greater than the second set value, the time average accumulation amount changes at a high level. The packet transfer apparatus according to claim 1, wherein the maximum number of retransmissions is set to 0 based on the determination that the number of retransmissions is zero . The retransmission number control means calculates an average accumulated amount as an average value of the accumulated amount at the previous packet output and the accumulated amount at the current packet output , and the average accumulated amount is less than the first set value. The maximum accumulated number of times is fixed to a predetermined number because it is determined that the average accumulated amount is changing at a low level, and the average accumulated amount is greater than or equal to the first set value and greater than the first set value. When the average accumulated amount is less than the second set value, the maximum number of retransmissions is adaptively decreased according to the increase in the average accumulated amount, and when the average accumulated amount is equal to or greater than the second set value, the average accumulated amount is high. 2. The packet transfer apparatus according to claim 1, wherein the maximum number of retransmissions is set to 0 by judging that the level is changing . The retransmission count control means calculates the average accumulated amount by performing predetermined weighting on the accumulated amount at the previous packet output and the accumulated amount at the current packet output, respectively. 4. The packet transfer device according to 3. The buffer stores the packet for each destination,
The retransmission count control means, the accumulation amount of the packet per the destination acquired from each of the above buffer, in accordance with the accumulated amount for each said destination, corresponding to the maximum number of retransmissions for the transmission destination, respectively The packet transfer device according to claim 1, wherein the packet transfer device is controlled. In the retransmission control method of the packet transfer apparatus that sequentially reads out the externally input packets stored in the buffer and transmits them to the transmission destination.
An accumulation amount obtaining step of obtaining the accumulated amount of the packet accumulated in the buffer from the buffer;
When the accumulated amount is less than the first set value, it is determined that the accumulated amount is changing at a low level, the maximum number of retransmissions is fixed to a predetermined number, and the accumulated amount is equal to or greater than the first set value. And when the value is less than the second set value greater than the first set value, the maximum number of retransmissions is adaptively decreased according to the increase in the accumulated amount, and the accumulated amount is greater than or equal to the second set value. A retransmission count control step for determining that the accumulated amount is changing at a high level and setting the maximum retransmission count to 0 ;
A packet retransmission step for retransmitting the packet up to the maximum number of retransmissions when the packet reception signal returned from the transmission destination cannot be received in response to reception of the transmitted packet. Retransmission control method. For a packet transfer device that sequentially reads packets input from the outside stored in the buffer and sends them to the destination,
An accumulation amount obtaining step of obtaining the accumulated amount of the packet accumulated in the buffer from the buffer;
When the accumulated amount is less than the first set value, it is determined that the accumulated amount is changing at a low level, the maximum number of retransmissions is fixed to a predetermined number, and the accumulated amount is equal to or greater than the first set value. And when the value is less than the second set value greater than the first set value, the maximum number of retransmissions is adaptively decreased according to the increase in the accumulated amount, and the accumulated amount is greater than or equal to the second set value. A retransmission count control step for determining that the accumulated amount is changing at a high level and setting the maximum retransmission count to 0 ;
A retransmission control program for executing a packet retransmission step for retransmitting the packet with the maximum number of retransmissions as an upper limit when a packet reception signal returned from the transmission destination cannot be received in response to reception of the transmitted packet.

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