JP4328794B2 - COMMUNICATION SYSTEM, COMMUNICATION DEVICE, AND TRANSMISSION CONTROL METHOD - Google Patents

Description

  The present invention relates to a communication system including a communication device that transmits data to a counterpart device via a communication network, a communication device in the communication system, and a transmission control method in the communication device.

  TCP (Transmission Control Protocol) is widely used as a transport layer protocol of the OSI reference model. In communication performed in accordance with TCP, when a packet loss occurs, an operation of retransmitting the missing data packet and reducing the subsequent data transmission amount is performed.

  In general, packet loss is caused by the fact that the network is in a congested state or the number of data packets that exceed the processing capability of the receiving side. On the transmission side, an operation called congestion control is performed in order to cope with network congestion.

  Specifically, the data transmission amount that can be transmitted within the time required for the transmission side to send a round-trip time, that is, from the time when the data is transmitted until the confirmation response to the data is received, is determined based on the congestion window size. Congestion control is realized by appropriately updating the congestion window size. The congestion window can be increased from 1 kbyte to the value set by the maximum window size.

  Internet access services and data access services such as browser phones provided in mobile packet communication systems employ W-TCP (RFC3481), which optimizes TCP for mobile communications, as a transport layer protocol.

  In recent years, broadbandization of wireless communication networks has progressed, and the same bandwidth as wired communication networks can be used. However, wireless communication networks are known to be inferior to wired communication networks in terms of transmission delay and packet loss rate. Yes.

  W-TCP performs efficient transmission in a broadband wireless communication network in which a large transmission delay and packet loss occur, so (1) window size expansion, (2) initial window size expansion, and (3) SACK (Selective Acknowledgment) effective And (4) an MTU (Maximum Transmission Unit) expansion optimization profile is defined.

  In general, a value obtained by multiplying the bandwidth of the communication network and the transmission delay is called a bandwidth delay product. If the maximum window size is not larger than the bandwidth delay product, the bandwidth of the communication network cannot be used effectively. For this reason, the above (1) window size expansion is determined in consideration of the maximum bandwidth of the wireless communication network and the amount of transmission delay.

 In TCP, when the maximum throughput is to be obtained by using the bandwidth of the transmission path, a maximum window size larger than the bandwidth delay product must be set. The congestion window of W-TCP is set to 4 kbytes when (2) the initial window size is expanded at the start of data transmission, increases every time an acknowledgment is received, and expands to the upper limit value of the window size.

On the other hand, in order to avoid packet loss in a wired communication network, a method has been proposed in which a communication device on the transmission side monitors whether the network is congested using a round-trip time with the communication device on the reception side. (For example, see Non-Patent Document 1 and Patent Document 1).
R. Braden, “Requirements for Internet Hosts--Communication Layers”, IETF RFC 1122, October 1989 Japanese Patent No. 3044658

  However, the characteristics of the transmission path (wireless link) of the wireless communication network change every moment due to the movement of the client terminal, and the bandwidth and transmission delay always change. Therefore, even if the value of the maximum window size is set as the upper limit of the assumed bandwidth delay product, an event that the actual bandwidth delay product is much smaller than the maximum window size occurs.

  Data transmitted exceeding the bandwidth delay product is mainly stored in a queuing buffer on the radio control device or router. When data overflows and is lost from the queuing buffer, the congestion window is reduced by the TCP congestion control operation, and a state where excessive data is accumulated in the queuing buffer is avoided.

  When the queuing buffer is set to be larger than the maximum window size, no packet loss occurs, and various adverse effects occur due to the state where data is stored in the queuing buffer.

  First, by filling up the radio control device, the router, and the queuing buffer, there is a problem that a large amount of memory resources are consumed in each device and the number of accommodated subscribers per device is reduced.

  Second, in the state where data is stored in the queuing buffer, there is a problem that it takes a long time for an acknowledgment response to the data transmitted by the server device to arrive. Along with this problem, it is conceivable that the TCP retransmission timeout timer becomes longer following the transmission delay, and the retransmission operation when a packet loss occurs is delayed.

  In view of the above problems, the present invention can control the amount of newly transmitted data while accurately estimating the state of the communication network, specifically the amount of data stored in the queuing buffer. It is an object to provide a communication system, a communication apparatus, and a transmission control method.

  In order to achieve the above object, a first feature of the present invention is that a first communication device (client terminal 100) and the first communication device via a wireless communication network (wireless communication network 1, wired communication network 2). A communication system including a second communication device (server device 400) that transmits data to the first communication device, wherein the first communication device sends an acknowledgment indicating the reception result of the data transmitted by the second communication device. An acknowledgment transmission unit (TCP processing unit 104) for transmitting to the second communication device, wherein the second communication device transmits the data to the first communication device, and then sends the confirmation response from the first communication device. A round-trip time measuring unit (round-trip time measuring unit 406) that measures a time until reception as a round-trip time, and a reception amount for determining a reception amount of data normally received by the first communication device based on the confirmation response Judgment unit Amount determination unit 407), and a transmission amount control unit (throughput calculation unit 408, history management unit 409) that controls the transmission amount of data to be newly transmitted to the first communication device based on the round trip time and the reception amount. And a threshold value determination unit 410 and a congestion control activation unit 411).

  According to such a configuration, the second communication device controls the transmission amount of data to be newly transmitted to the first communication device based on the round trip time (RTT) and the reception amount in the first communication device. That is, transmission amount control is performed in consideration of the bandwidth and transmission delay of the communication network. As a result, the second communication device controls the transmission amount of data newly transmitted to the first communication device while accurately estimating the state of the communication network, specifically, the amount of data stored in the queuing buffer. can do.

  In the communication system according to the first aspect of the present invention, the transmission amount control unit calculates a reception amount per unit time as a throughput from the round trip time and the reception amount (throughput calculation unit 408). And a reduction processing unit (threshold determination unit 410, congestion control activation unit 411) that reduces the transmission amount based on the throughput.

  According to such a configuration, the amount of data transmission (congestion window) can be obtained without calculating the congestion control of TCP due to packet loss by calculating the reception amount per unit time as the throughput and reducing the transmission amount based on the throughput. ) Can be reduced.

  The communication system according to the first aspect of the present invention further includes a history management unit (history management unit 409) that manages the throughput history, wherein the reduction processing unit refers to the history, and the throughput is predetermined. It is preferable to reduce the transmission amount when the threshold value is exceeded.

  According to such a configuration, when the throughput falls below a predetermined threshold (for example, the maximum value of throughput existing in the history), specifically, when the throughput decreases, the data transmission amount (congestion window) is reduced. By reducing, the data transmission amount can be appropriately reduced.

  A second feature of the present invention is a communication device (server device 400) that transmits data to a partner device (client terminal 100) via a wireless communication network (wireless communication network 1, wired communication network 2). After receiving the confirmation response indicating the reception result of the data at the counterpart device from the counterpart device (TCP processing unit 404), and transmitting the data to the counterpart device, A round-trip time measuring unit (round-trip time measuring unit 406) that measures a time until the reception unit receives the confirmation response as a round-trip time, and reception of data normally received by the counterpart device based on the confirmation response A reception amount determination unit (reception amount determination unit 407) that determines the amount, and a transmission amount control unit that controls the transmission amount of data to be newly transmitted to the counterpart device based on the round trip time and the reception amount ( Thru Tsu DOO calculator 408, the history management unit 409, threshold decision unit 410, and summarized in that and a congestion control activation unit 411).

  In the communication device according to the second aspect of the present invention, the transmission amount control unit calculates a reception amount per unit time as a throughput from the round trip time and the reception amount (throughput calculation unit 408). And a reduction processing unit (threshold determination unit 410, congestion control activation unit 411) that reduces the transmission amount based on the throughput.

  The communication apparatus according to the second aspect of the present invention further includes a history management unit (history management unit 409) that manages the history of the throughput, the reduction processing unit refers to the history, and the throughput is predetermined. It is preferable to reduce the transmission amount when the threshold value is exceeded.

  A third feature of the present invention is a transmission control method in a communication device that transmits data to a partner device via a communication network, wherein the confirmation response indicating the reception result of the data in the partner device is A step of receiving from the counterpart device, a step of measuring a time from when the data is transmitted to the counterpart device until the reception of the confirmation response as a round trip time, and the destination based on the confirmation response. Determining a reception amount of data normally received by the device, and controlling a transmission amount of data newly transmitted to the counterpart device based on the round-trip time and the reception amount. The gist.

  In the transmission control method according to the third aspect of the present invention, the controlling step includes calculating the received amount per unit time as a throughput from the round trip time and the received amount, and based on the throughput. And reducing the transmission amount.

  The transmission control method according to the third aspect of the present invention further includes a step of managing the history of the throughput, and in the step of reducing, referring to the history, and when the throughput falls below a predetermined threshold, It is preferable to reduce the transmission amount.

  According to the present invention, a communication system capable of controlling the amount of newly transmitted data while accurately estimating the state of the communication network, specifically, the amount of data stored in the queuing buffer, and communication An apparatus and a transmission control method can be provided.

  Next, an embodiment of the present invention will be described with reference to the drawings. In the description of the drawings in the following embodiments, the same or similar parts are denoted by the same or similar reference numerals.

(Configuration example of communication system)
First, a configuration example of a communication system according to the present embodiment will be described. FIG. 1 is a diagram illustrating a configuration example of a communication system according to the present embodiment. FIG. 2 is a diagram showing a protocol stack of the communication system according to the present embodiment.

  The communication system shown in FIG. 1 includes a client terminal 100, a wireless control device 200, a wireless communication network 1, a POI (Point Of Interface) 300, a wired communication network 2, and a server device 400.

  The wireless communication network 1 takes the form of a WAN or LAN to which a wireless LAN is connected, or an exchange network for a mobile phone system. The wired communication network 2 takes the form of a LAN or the Internet.

  The client terminal 100 takes the form of a mobile phone terminal or a notebook PC having a wireless communication function. In the present embodiment, the client terminal 100 downloads content from the server device 400 via the wireless control device 200, the wireless communication network 1, the POI 300, and the wired communication network 2.

  Radio control apparatus 200 takes the form of a wireless LAN access point (AP) or a base station apparatus of a mobile phone system. The wireless control device 200 communicates with the client terminal 100 via a wireless link and functions as a wireless interface between the client terminal 100 and the wireless communication network 1.

  The POI 300 takes the form of a router device, for example. The POI 300 connects the wireless communication network 1 and the wired communication network 2 to each other.

  Server device 400 takes the form of a PC or a workstation. The server device 400 distributes content to the client terminal 100 via the wired communication network 2, the POI 300, the wireless communication network 1, and the wireless control device 200.

  As shown in FIG. 2, the client terminal 100 and the server device 400 communicate according to TCP located in the transport layer of the OSI reference model. In TCP, communication waiting for a confirmation response for each data transmission, that is, confirmation communication is performed.

  The server apparatus 400 transmits a plurality of data packets to the client terminal 100 in the order of the sequence numbers included in each data packet. In the confirmation response number included in the confirmation response transmitted from the client terminal 100, the value of the sequence number of the data packet to be received next by the client terminal 100 is stored.

(Configuration example of client terminal)
Next, a configuration example of the client terminal 100 will be described. FIG. 3 is a functional block diagram illustrating a configuration example of the client terminal 100.

  The client terminal 100 includes a wireless interface 101, an IP (Internet Protocol) processing unit 102, an application processing unit 103, and a TCP processing unit 104.

  The wireless interface 101 functions as an interface with the wireless communication network 1. Specifically, the wireless interface 101 includes an antenna, a high frequency (RF) processing unit, a baseband (BB) processing unit, and the like.

  The IP processing unit 102 provides an identification function of the client terminal 100 in the wireless communication network 1 and the wired communication network 2 by an address notified from the wireless communication network 1 or a unique address set by the user in the client terminal 100.

  The application processing unit 103 executes an application used by a user, such as a Web browser, an FTP (File Transfer Protocol) client, and a mail client.

The TCP processing unit 104 can perform highly reliable communication by retransmission control and congestion control.
(Configuration example of server device)
Next, a configuration example of the server device 400 will be described. FIG. 4 is a functional block diagram illustrating a configuration example of the server device 400.

  The server device 400 includes a network interface 401, an IP processing unit 402, an application processing unit 403, a TCP processing unit 404, and a congestion control unit 405.

  The network interface 401 takes the form of, for example, an Ethernet (registered trademark) interface. The network interface 401 functions as an interface with the wired communication network 2.

  The IP processing unit 402 is assigned a unique IP address in the wired communication network 2 and provides an identification function of the server device 400.

  The application processing unit 403 provides an application used by the user, such as a Web server, an FTP server, or a mail server.

  The TCP processing unit 404 can perform highly reliable communication by retransmission control and congestion control. Here, retransmission control by the TCP processing unit 404 will be briefly described. The TCP processing unit 404 detects a packet loss and retransmits the missing data packet. Specifically, a packet loss is detected depending on whether an acknowledgment indicating that the data has been received is transmitted from the client terminal 100 within a predetermined time (retransmission timeout period) after transmitting the TCP data. Alternatively, the TCP processing unit 404 detects a packet loss depending on whether or not a duplicate confirmation response packet has been transmitted from the client terminal 100 a predetermined number of times (for example, three times).

  The congestion control unit 405 performs congestion control in cooperation with the TCP processing unit 404. The congestion control unit 405 includes a round trip time measurement unit 406, a reception amount determination unit 407, a throughput calculation unit 408, a history management unit 409, a threshold determination unit 410, and a congestion control activation unit 411.

  The round trip time measuring unit 406 measures the elapsed time from the start of TCP data transmission to the confirmation response, that is, the round trip time (RTT).

  The reception amount determination unit 407 determines the reception amount of data normally received by the client terminal 100 based on the confirmation response.

The throughput calculation unit 408 calculates the data transmission throughput based on the values notified from the round trip time measurement unit 406 and the reception amount determination unit 407. Here, when the round trip time measured by the round trip time measuring unit 406 is “RTT” and the received amount of data normally received by the client terminal 100 is “RD”, the throughput “TP” is
TP = RD / RTT (1)
Is calculated by

  The history management unit 409 manages the history of throughput calculated by the throughput calculation unit 408.

  The threshold determination unit 410 refers to the throughput history and detects that the throughput has fallen below a certain value. For example, the threshold determination unit 410 compares the throughput calculated by the throughput calculation unit 408 with the maximum value of the throughput existing in the history, and detects that the throughput is below the maximum value.

  The congestion control activation unit 411 instructs the TCP processing unit 404 to activate congestion control based on the result of the threshold determination by the threshold determination unit 410.

(Throughput calculation sequence)
Next, a throughput calculation sequence by the server device 400 will be described. FIG. 5 is a sequence diagram showing a throughput calculation sequence by the server apparatus 400.

  In step S <b> 1, the server apparatus 400 transmits data (SEQ: x) to the client terminal 100. “X” is a sequence number and indicates the relative position of the transmission packet in bytes.

  In step S <b> 2, the client terminal 100 transmits an acknowledgment (ACK: x + y) to the server device 400. “X + y” is an acknowledgment number, which means that a packet up to sequence number x is normally received and further y-byte data transmission is requested.

  Here, the data reception amount of the client terminal 100 is equal to the data transmission amount (x bytes) transmitted in step S1 because the data transmission in step S1 was normally performed by the confirmation response in step S2. It is determined that

  The round trip time measuring unit 406 measures the round trip time at the timings of step S1 and step S2. The throughput calculation unit 408 calculates the throughput from the above equation (1). The calculated throughput is stored in the history management unit 409.

  Next, in step S <b> 3, the server apparatus 400 transmits data (SEQ: x + y) to the client terminal 100. “X + y” is a sequence number. The amount of data transmitted in step S3 is x + y−x = y bytes from the sequence numbers in steps S1 and S3.

  In step S <b> 4, the client terminal 100 transmits an acknowledgment (ACK: x + y + z) to the server device 400. “X + y + z” is an acknowledgment number, which means that the packet up to the sequence number x + y is normally received and further requests for data transmission of z bytes.

  Here, the data reception amount of the client terminal 100 is the data transmission amount (y bytes) transmitted in step S3 because the data transmission in step S3 was normally performed by the confirmation response in step S4. It is determined that

  The round trip time measuring unit 406 measures the round trip time at the timings of step S3 and step S4. The throughput calculation unit 408 calculates the throughput from the above equation (1). The calculated throughput is stored in the history management unit 409.

(Connection establishment sequence)
Next, a connection establishment sequence between the client terminal 100 and the server device 400 will be described. FIG. 6 is a sequence diagram showing a connection establishment sequence between the client terminal 100 and the server device 400.

  In step S <b> 10, the client terminal 100 transmits a connection request (SYN) packet to the server device 400. The SYN packet is also used to synchronize the sequence number and the acknowledgment number in the client terminal 100 and the server device 400.

  In step S20, the server apparatus 400 transmits a connection request / connection response signal (TCP SYN + ACK) to the client terminal 100.

  In step S <b> 30, the client terminal 100 transmits a connection response (TCP ACK) to the server device 400.

  In this way, the client terminal 100 and the server apparatus 400 transmit a SYN packet to each other and transmit an acknowledgment response using an ACK packet. As a result, three packets are transmitted or received. Such a procedure is called “3-way handshake”.

(Data transmission sequence)
Next, a data transmission sequence from the server apparatus 400 to the client terminal 100 will be described. FIG. 7 is a sequence diagram showing a data transmission sequence from the server apparatus 400 to the client terminal 100.

  In step S <b> 40, the server apparatus 400 transmits TCP data for one packet to the client terminal 100.

  In step S50, the client terminal 100 transmits to the server apparatus 400 a confirmation response indicating that the TCP data transmitted in step S40 has been successfully received.

  In step S <b> 60, when the server apparatus 400 receives the confirmation response from the client terminal 100, the server apparatus 400 doubles the data transmission amount and transmits TCP data for two packets to the client terminal 100.

  Thereafter, the server apparatus 400 increases the data transmission amount exponentially until the maximum window size is reached. Such control is called “slow start control”.

(Congestion control sequence)
Next, an example of a congestion control sequence by the server device 400 will be described. FIG. 8 is a sequence diagram illustrating an example of a congestion control sequence by the server device 400.

  In step S <b> 100, the server apparatus 400 transmits 4 packets of TCP data to the client terminal 100.

  In step S <b> 110, the client terminal 100 transmits a confirmation response to the server device 400. At this time, if the threshold determination unit 410 of the congestion control unit 405 of the server device 400 refers to the history of throughput of the history management unit 409 and satisfies a predetermined condition, the congestion control activation unit 411 To start congestion control. As a result, the server apparatus 400 reduces the next data transmission amount.

  In step S <b> 120, the server apparatus 400 transmits TCP data for one packet to the client terminal 100, for example. In the subsequent communication, the above-described slow start control is executed.

  In this way, when the congestion control is activated, the server apparatus 400 reduces the data transmission amount.

(Action / Effect)
As described above in detail, according to the present embodiment, the server apparatus 400 transmits the data to be newly transmitted to the client terminal 100 based on the round trip time (RTT) and the data reception amount at the client terminal 100. Control the amount (congestion window). That is, data transmission amount control (congestion control) is performed in consideration of the bandwidth and transmission delay of the wireless communication network 1 and the wired communication network 2. As a result, the server device 400 estimates the state of the wireless communication network 1 and the wired communication network 2, specifically, the amount of data stored in the queuing buffer with high accuracy, and newly transmits data to the client terminal 100. The amount of data transmission can be controlled.

  Further, according to the present embodiment, the server apparatus 400 calculates the data reception amount per unit time as the throughput, and reduces the data transmission amount based on the throughput. Therefore, the amount of data transmission can be reduced without relying on TCP congestion control due to packet loss.

  Furthermore, according to the present embodiment, the server device 400 reduces the data transmission amount by decreasing the data transmission amount when the throughput falls below the maximum value of the throughput existing in the history, that is, when the throughput is reduced. It can be reduced appropriately.

(Other embodiments)
As mentioned above, although this invention was described by embodiment, it should not be understood that the description and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the above-described embodiment, an example in which the data transmission amount is reduced when the throughput falls below the maximum value of the throughput existing in the history has been described. However, the data transmission amount may be reduced when the throughput falls below a predetermined threshold value set in advance. Alternatively, the data transmission amount may be reduced when the throughput falls below the previous (immediately preceding) throughput value existing in the history or the average value of the throughput existing in the history.

  As described above, the present invention naturally includes various embodiments that are not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

It is a figure which shows the structural example of the communication system which concerns on embodiment of this invention. It is a figure which shows the protocol stack of the communication system which concerns on embodiment of this invention. It is a functional block diagram which shows the structural example of the client terminal which concerns on embodiment of this invention. It is a functional block diagram which shows the structural example of the server apparatus which concerns on embodiment of this invention. It is a sequence diagram which shows the throughput calculation sequence by the server apparatus which concerns on embodiment of this invention. It is a sequence diagram which shows the connection establishment sequence between the client terminal and server apparatus which concern on embodiment of this invention. It is a sequence diagram which shows the data transmission sequence from the server apparatus which concerns on embodiment of this invention to a client terminal. It is a sequence diagram which shows the congestion control sequence by the server apparatus which concerns on embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Client terminal, 101 ... Wireless interface, 102 ... IP processing part, 103 ... Application processing part, 104 ... TCP processing part, 200 ... Wireless control apparatus, 300 ... POI, 400 ... Server apparatus, 401 ... Network interface, 402 ... IP processing unit 403 Application processing unit 404 TCP processing unit 405 Congestion control unit 406 Round trip time measurement unit 407 Reception amount determination unit 408 Throughput calculation unit 409 History management unit 410 Threshold determination unit, 411 ... congestion control start unit

Claims (3)

A communication system comprising: a first communication device; and a second communication device that transmits data to the first communication device via a wireless communication network having a wireless control device that is an access point or a base station device ,
The first communication device includes a confirmation response transmission unit that transmits a confirmation response indicating a reception result of data transmitted by the second communication device to the second communication device,
The second communication device is
A round trip time measuring unit that measures a time from when the data is transmitted to the first communication device to when the confirmation response is received from the first communication device as a round trip time;
A reception amount determination unit that determines a reception amount of data normally received by the first communication device based on the confirmation response;
Based on the round trip time and the received amount, the transmission amount of data to be newly transmitted to the first communication device is controlled , and the transmission amount is received every time the confirmation response is received until the transmission amount reaches a certain amount. The transmission amount control unit to increase
With
The transmission amount control unit
From the round trip time and the received amount, a throughput calculating unit that calculates a throughput that is the received amount per unit time for each reception of the confirmation response;
Among the throughputs calculated for each reception of the confirmation response by the throughput calculation unit, at least a previously calculated value is stored as a history, and a history management unit that manages the history,
A threshold value determination unit that determines whether or not the throughput newly calculated by the throughput calculation unit is lower than the threshold value, using the maximum value existing in the history as a threshold value;
A communication system comprising: a reduction processing unit that reduces the transmission amount to a predetermined amount when it is determined that the throughput newly calculated by the throughput calculation unit is below the threshold value . A communication device that transmits data to a partner device via a wireless communication network having a wireless control device that is an access point or a base station device ,
An acknowledgment receiving unit that receives an acknowledgment indicating the reception result of the data at the counterpart device from the counterpart device;
A round trip time measuring unit that measures a time from when the data is transmitted to the counterpart device until the receiving unit receives the confirmation response as a round trip time;
Based on the confirmation response, a reception amount determination unit that determines a reception amount of data normally received by the counterpart device;
Based on the round trip time and the received amount, the transmission amount of data to be newly transmitted to the counterpart device is controlled , and the transmission amount is set every time the confirmation response is received until the transmission amount reaches a certain amount. A transmission amount control unit for increasing ,
The transmission amount control unit
From the round trip time and the received amount, a throughput calculating unit that calculates a throughput that is the received amount per unit time for each reception of the confirmation response;
Among the throughputs calculated for each reception of the confirmation response by the throughput calculation unit, at least a previously calculated value is stored as a history, and a history management unit that manages the history,
A threshold value determination unit that determines whether or not the throughput newly calculated by the throughput calculation unit is lower than the threshold value, using the maximum value existing in the history as a threshold value;
A reduction processing unit that reduces the transmission amount to a predetermined amount when it is determined that the throughput newly calculated by the throughput calculation unit is below the threshold;
A communication device comprising: A transmission control method in a communication device that transmits data to a counterpart device via a wireless communication network having a wireless control device that is an access point or a base station device ,
Receiving a confirmation response indicating the reception result of the data at the counterpart device from the counterpart device;
Measuring the time from sending the data to the counterpart device until receiving the confirmation response as a round trip time;
Determining a reception amount of data normally received by the counterpart device based on the confirmation response;
Based on the round trip time and the received amount, the transmission amount of data to be newly transmitted to the counterpart device is controlled , and the transmission amount is set every time the confirmation response is received until the transmission amount reaches a certain amount. A transmission amount control step for increasing ,
The transmission amount control step includes:
Calculating the throughput, which is the received amount per unit time, for each reception of the confirmation response from the round-trip time and the received amount;
Storing at least the previously calculated value as a history of the throughput calculated for each reception of the confirmation response, and managing the history;
Determining whether the newly calculated throughput falls below the threshold, with the maximum value existing in the history as a threshold;
Reducing the amount of transmission to a predetermined amount when it is determined that the newly calculated throughput is below the threshold;
Including transmission control method.

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