JP4952256B2 - Communication control device and communication control program - Google Patents

Description

  The present invention relates to a communication control device that controls communication between a client device and a server device, and a communication control program that is executed in the communication control device, and more particularly compared to communication from a client device that performs wireless communication to a server device. The present invention relates to a communication control device and a communication control program in a system in which communication from a server device to a client device frequently occurs.

  Conventionally, TCP (Transmission Control Protocol), which is widely used when connecting to communication networks such as the Internet, is a mechanism for improving communication reliability. If not reached, retransmission control using a retransmission timer is performed. That is, on the data transmission side, when a packet is transmitted, a retransmission timer is started, and if an acknowledgment (ACK: Acknowledgment) from the reception side is not returned by the time-out, it is considered that packet loss has occurred, Resending the same packet.

FIG. 1 is a diagram illustrating an example of a data transmission pattern using a retransmission timer.
In FIG. 1, since the client device 11 cannot receive the ACK from the server device 12 when the data N transmitted to the server device 12 is lost for some reason, the retransmission timer started after the data N is transmitted. The data N is transmitted again after the time until (timeout time).

  This timeout time is called a retransmission timeout time (RTO: Retransmission Timeout), and a measured value (MRTT: Measured) of a round trip time (RTT: Round Trip Time) from when a data packet is transmitted to when an ACK is received on the data transmission side. RTT).

  In the initial state, the TCP control unit controlling TCP as described above, when the first MRTT is obtained, uses this to perform the smoothed RTT (SRTT: Smoothed RTT) and the average deviation (RTTVAR: RTT Variation). The RTO is calculated and further determined based on the SRTT and RTTVAR (for example, see Non-Patent Document 1).

Specifically, as described in Non-Patent Document 1, G is the granularity (resolution) of the clock used by the system for RTT measurement, and is calculated by the following Equation 1.
(Formula 1)
SRTT = MRTT
RTTVAR = MRTT / 2
RTO = SRTT + max (G, K x RTTVAR)
Where K = 4
("=" In the expression means assigning the value on the right side to the variable on the left side)

Then, when the second and subsequent MRTTs are obtained, SRTT, RTTVAR, and RTO are calculated by the following Equation 2.
(Formula 2)
RTTVAR = (1-β) × RTTVAR + β × | SRTT−MRTT |
SRTT = (1−α) × SRTT + α × MRTT
Where α = 1/8, β = 1/4
RTO = SRTT + max (G, K x RTTVAR)
("=" In the expression means assigning the value on the right side to the variable on the left side)

  As is clear from Equation 1 above, in a system using a wireless communication network that originally has a large transmission delay and the amount of delay often varies, the RTO value tends to be large. According to the results actually measured by the inventor of the present invention, in a system using a packet communication network of a cellular phone in recent years, the RTO value is about 0.5 seconds to several seconds, although there is a difference depending on the network situation.

  As described above, the conventional TCP calculates a larger RTO value in a system using a wireless communication network. This corresponds to an increase in the waiting time until retransmission when a data packet disappears.

  As a technique for avoiding such a problem, an algorithm has been proposed in which packet loss is detected by receiving duplicate ACKs and retransmission is performed without waiting for a timeout (see, for example, Non-Patent Document 2). ).

For example, the “Fast Retransmit” algorithm described in Non-Patent Document 2 is often implemented in recent TCPs.
FIG. 2 is a diagram illustrating an example of a data transmission pattern in the “Fast Retransmit” algorithm.

  This “Fast Retransmit” algorithm is used in the situation where a plurality of data packets are transmitted continuously, and when a certain data packet is lost, the transmitting side cannot reach the data packet transmitted continuously thereafter. By receiving duplicate ACKs obtained as a trigger successively several times, packet loss is detected, and the packets are retransmitted without waiting for timeout.

  For example, in the example illustrated in FIG. 2, data N, data N + 1, data N + 2, data N + 3, data N + 4,... Are sequentially transmitted from the data communication device 21 to the data communication device 22. Then, the data communication device 22 that has received the first data N returns “ACK N + 1” to the data communication device 21 that the next data N + 1 should be received.

  However, if the data N + 1 is lost for some reason, the data communication device 22 that has received the next data N + 2 does not receive the data N + 1 and returns “ACK N + 1” to the data communication device 21 again. Further, the data communication device 22 returns “ACK N + 1” to the data communication device 21 because it has not received the data N + 1 even if the next data N + 3 is received. When this process is repeated, that is, when “ACK N + 1” is received three times by the data communication device 21, for example, the data communication device 21 detects that the data N + 1 is lost.

Further, in the TCP control unit of the server device that performs communication according to TCP, spurious retransmission (useless retransmission) is detected, the number of detected spurious retransmissions and the amount of data, and the measured acknowledgment response waiting time RTT, Based on the above, a technique for calculating (optimizing) a retransmission timer value that reduces the occurrence of spurious retransmissions is disclosed (see, for example, Patent Document 1).
V.Paxson, M.Allman “Computing TCP's Retransmission Timer” RFC2988, November 2000, http://www.ietf.org/rfc/rfc2988.txt M. Allman, V. Paxson, W. Stevens “TCP Congestion Control” RFC2581, April 1999, http://www.ietf.org/rfc/rfc2581.txt Japanese Patent Laid-Open No. 2005-5906

Here, consider a client-server communication system, which is a general communication form using a wireless communication network.
FIG. 3 is a diagram illustrating a configuration example of a client-server communication system using a wireless communication network, and FIG. 4 is a diagram illustrating an example of data exchange in the client-server communication system.

  As shown in FIG. 3, for example, a client device 31 such as a mobile terminal performs wireless communication with a server device 32 via a base station 33 and the Internet 34. In the communication mode of such a client-server communication system, as shown in FIG. 4, the amount of data in the direction from the client device 31 to the server device 32 is small, and the direction in the direction from the server device 32 to the client device 31 is small. There is a tendency that the amount of data is large.

  For example, considering the case of browsing information on a Web server device on the Internet with a mobile terminal such as a mobile phone, the mobile terminal transmits an acquisition request (command) such as text data or image data in response to a user operation. On the other hand, the Web server device transmits data (response) such as requested image to the mobile terminal. That is, in such a communication form, the data size of the command is very small compared to the data size of the response.

  In such a client-server type communication system, as shown in FIG. 1, since there is little data to be transmitted in the transmission direction from the client device 11, the packet is received by continuous reception of duplicate ACKs such as the “Fast Retransmit” algorithm. The effect of the algorithm for detecting disappearance cannot be expected. For this reason, packet retransmission is triggered by the timeout of the retransmission timer. Furthermore, as described above, in a system using a wireless communication network, the RTO value is large, that is, the waiting time until retransmission is long. This has the problem that the user who operates the client device 11 feels that the operation response is very bad.

  Therefore, the present invention has been made in view of the above problems, and is a communication control for controlling a client device capable of wireless communication with a server device using a transport protocol and having an asymmetrical reception amount compared to a transmission amount. An object of the present invention is to provide a communication control device capable of improving data retransmission processing due to data packet loss and improving a response in a client device, and a communication control program executed in the communication control device And

The present invention employs the following configuration in order to solve the above problems.
That is, according to one aspect of the present invention, the communication control apparatus of the present invention is capable of wireless communication with the first communication apparatus using the transport protocol, and the second reception amount is asymmetrically larger than the transmission amount. A communication control device that controls a communication device, wherein a retransmission time calculation unit that calculates a retransmission time until the communication data to be transmitted to the first communication device is retransmitted, and the first communication device Communication data round-trip time measuring means for measuring communication data round-trip time in which communication data reciprocates, and comparison between retransmission time calculated by the retransmission time calculating means and communication data round-trip time measured by the communication data round-trip time measuring means Comparing the retransmission time with the communication data round-trip time by the comparison means, and the communication data round-trip time as the retransmission time. If Ri becomes large value, and excludes excluding means from the calculation processing of the retransmission time according to the retransmission time calculating means the communication data round-trip time it becomes larger than the retransmission time, and transmits to the first communication device Based on a determination unit that determines whether or not the size of communication data can be stored in one packet of the transport protocol, and based on the determination result determined by the determination unit, the communication data round-trip time by the exclusion unit is excluded And an on / off means for turning on or off the processing .

Also, according to one aspect of the present invention, a communication control program of the present invention, the second reception amount is asymmetrically larger than that of the first communication device and is transmitted amount capable of wireless communication using a transport protocol A retransmission time calculating means for calculating a retransmission time until the communication data to be transmitted to the first communication device is retransmitted by the computer of the communication control device that controls the communication device, and the first communication device. Communication data round-trip time measuring means for measuring communication data round-trip time in which communication data reciprocates, and comparing the retransmission time calculated by the retransmission time calculating means with the communication data round-trip time measured by the communication data round-trip time measuring means As a result of comparing the retransmission time with the communication data round-trip time by the comparison means and the comparison means, the communication data round-trip time is If Muyori becomes large value, excluding excluding means from the calculation processing of a retransmission time of the communication data round-trip time becomes larger than the retransmission time according to the retransmission time calculating means, for transmitting to the first communication device A determination unit that determines whether or not the size of communication data can be stored in one packet of the transport protocol, and a process of excluding the communication data round-trip time by the exclusion unit based on a determination result determined by the determination unit It is a communication control program for functioning as an on / off means for turning on or off .

  According to the present invention, when a data packet loss error occurs, it is possible to promptly perform data retransmission processing and improve the response in the client device.

  The present invention is a client-server type communication system that uses a wireless communication network as described with reference to FIG. 3, and as described with reference to FIG. 4, from the client device 31 to the server device 32. The present invention is applicable to a system in which the amount of direction data is small and the amount of direction data from the server device 32 to the client device 31 is large.

  That is, as shown in FIG. 3, a client device 31 such as a mobile terminal communicates with a server device 32 connected to the Internet 34 via a base station 33. Wireless communication is performed between the client device 31 and the base station 33, and the probability of data loss and the transmission delay change from moment to moment.

  Normally, error compensation is performed between the client device 31 and the base station 33 by performing retransmission in units of frames. For this reason, when a frame is retransmitted, the transmission delay increases accordingly. When a plurality of client devices 31 are connected to the same base station 33 at the same time, the base station 33 performs data transmission schedule control, and the client device 31 stores data according to the control of the base station 33. There is a case where transmission is waited for. Furthermore, the above-mentioned retransmission in units of frames sets an upper limit on the number of retransmissions and the time required for retransmission, and does not compensate for data loss 100%.

Due to these factors, fluctuations in transmission delay time and loss of data packets frequently occur in communication between the client device 31 and the server device 32.
FIG. 5 is a diagram illustrating an outline of a hardware configuration of the client device 31.

  In FIG. 5, a client device 31 includes a CPU (Central Processing Unit) 312, an input device 313 for inputting various data and signals, a display device 314 for displaying images and other information, In addition to a program for executing processing executed in the client device 31, a ROM (Read Only Memory) 315 and a RAM (Random Access Memory) 316 that store control programs for controlling and executing the functions of the client device 31, an image And other information are input by an external storage device 317 for storing information, a wireless LAN (Local Area Network), a communication I / F (Interface) 318 for connecting to a network such as a cellular phone network, and an input device 313 Auxiliary storage device 319 for temporarily storing input events is connected to bus 311 Is, CPU 312 is controlling these units.

FIG. 6 is a functional block diagram illustrating a TCP control unit implemented in the client device 31.
In FIG. 6, a TCP control unit 60 includes a data transmission pattern determination unit 61, a delay spike determination unit 62, an RTO calculation unit 63, a retransmission control unit 64, and other not shown that are not directly related to the present invention. It is realized as a protocol stack.

Next, the flow of processing executed by each unit of the TCP control unit 60 will be described with reference to FIGS.
FIG. 7 is a flowchart showing a flow of processing executed by the data transmission pattern determination unit 61.

  First, in step S71, the data transmission pattern determination unit 61 acquires transmission data (SD: Sending Data) passed from an upper layer, and in step S72, the size of the transmission data SD is the maximum size that can be stored in one TCP packet. It is determined whether it is larger than (MSS: Maximum Segment Size).

  If it is determined that the size of the transmission data SD is not larger than the MSS (is less than or equal to the MSS size) (step S72: N), the EN flag (Enable flag) is set in step S73, while the transmission data If it is determined that the SD size is larger than the MSS (step S72: Y), the EN flag is cleared in step S74. The EN flag is referred to by the delay spike determination unit 62 and the retransmission control unit 64 as described later.

  As a result, in the general client-server communication system shown in FIGS. 3 and 4, the EN flag is set only when small data is transmitted, such as command transmission of the client device 31, and Delay is set. The functions of the spike determination unit 62 and the retransmission control unit 64 are validated.

FIG. 8 is a flowchart showing a flow of processing executed by the delay spike determination unit 62.
The flowchart shown in FIG. 8 includes steps S81 to S89. However, the processing executed by the delay spike determination unit 62 can omit steps S84 and S88.

First, the case where step S84 and step S88 are omitted will be described.
First, the Delay Spike determination unit 62 performs RTT measurement (measurement of round trip time from transmission of a data packet to reception of ACK) in step S81, and obtains the measurement value MRTT.

  In step S82, it is determined whether or not there is an RTO (retransmission timeout period) calculated in the past. If there is no RTO calculated in the initial state (step S82: N), the process proceeds to step S89, and nothing is done. The MRTT acquired in step S81 is handed over to the RTO calculator 63.

  On the other hand, if it is determined that there is RTO (step S82: Y), it is determined in step S83 whether or not the aforementioned EN flag is set, and if it is determined that the EN flag is not set ( In step S83: N), the process proceeds to step S89, and the MRTT acquired in step S81 is passed to the RTO calculation unit 63 without doing anything.

  On the other hand, if it is determined that the EN flag is set, that is, not in the initial state and the EN flag is set (step S83: Y), the MRTT acquired in step S81 is obtained in step S85. Is greater than the current RTO.

  If it is determined that the MRTT is larger than the RTO at that time (step S85: Y), the MRTT is not passed to the RTO calculation unit 63, the Skip flag is set in step S86, and the MRTT is set in step S87. Discard. If the MRTT exceeds the RTO, it is assumed that the MRTT has suddenly become a large value (Delay Spike) due to the above-described link level frame retransmission and schedule control by the base station 33, and the RTO calculation is performed later. Does not apply. By doing so, the MRTT regarded as the Delay Spike is excluded from the RTO calculation process, and it can be avoided that the calculated value of the RTO becomes larger than necessary.

  On the other hand, if it is determined that the MRTT is not larger than the RTO at that time (step S85: N), the process proceeds to step S89, and the MRTT acquired in step S81 is passed to the RTO calculator 63.

Next, the case where step S84 and step S88 are not omitted will be described.
If it is determined in step S83 that the EN flag is set, that is, not the initial state and the EN flag is set (step S83: Y), the skip flag is set in step S84. If it is determined that the Skip flag is set (step S84: Y), the skip flag clears the set in step S88.

  Thus, by providing the Skip flag, the MRTT is not discarded even if the state where the MRTT exceeds the RTO continues. Thereby, for example, when the client device 31 moves to another area of the base station 33 and the RTT changes rapidly and the state continues thereafter, the MRTT is passed to the RTO calculation unit 63. Thus, the RTO calculator 63 can calculate an appropriate RTO.

FIG. 9 is a flowchart showing a flow of processing executed by the RTO calculation unit 63.
First, in step S91, the RTO calculation unit 63 acquires the MRTT passed from the delay spike determination unit 62, and in step S92, determines whether there is an RTO calculated in the past in the initial state.

  When it is determined that there is no RTO (step S92: N), in step S93, the value of RTO is calculated using the above-described equation 1, and when it is determined that there is RTO (step S92: Y). In step S94, the value of RTO is calculated using the above-described equation 2.

In step S95, the values of SRTT, RTTVAR, and RTO are updated.
FIG. 10 is a flowchart showing a flow of processing executed by the retransmission control unit 64.

  First, the retransmission control unit 64 transmits data in step S101, clears a back-off counter (BOC) in step S102, and sets RTO as a timeout value in step S103.

Then, in step S104, driving of the timer is started with data transmission in step S101, and in step S105, it is determined whether or not an ACK has been received.
If it is determined that ACK has been received (step S105: Y), the timer is terminated in step S106. If it is determined that ACK has not been received (step S105: N), whether time-out has occurred in step S107. Judge whether or not. If it is determined that the time-out has not occurred (step S107: N), that is, if the ACK has not been received before the RTO has elapsed (time-out), the same data is retransmitted and the timer is started again to receive the ACK. wait.

  Here, the TCP control unit 60 has a function called exponential backoff, and when a timeout occurs, the timeout time is doubled when the next timer starts. That is, the retransmission control unit 64 has a function of delaying the backoff timing by γ times. For example, when γ = 1, the data is retransmitted without performing the timer back-off at the first time-out, and when the time-out occurs again (the second time), the timer is back-off and the data is re-transmitted. Do. Similarly, if a timeout occurs after the third time, back-off is performed. Here, γ is an adjustment parameter, which is adjusted according to the characteristics of the communication network. By doing this, it is possible to avoid the problem that the timeout time becomes extremely long when communication data is frequently lost. Note that the above-described processing for delaying backoff γ times is performed only when the EN flag is set.

  That is, if it is determined that a timeout has occurred (step S107: Y), data is retransmitted in step S108, and BOC is incremented in step S109. In step S110, it is determined whether or not the BOC is larger than γ. If it is determined that the BOC is larger (step S110: Y), RTO × 2 ^ (BOC−γ) is set as the timeout value in step S111. On the other hand, when it is determined that it is not large (step S110: N), RTO is set as the timeout value in step S112.

  As described above, the TCP control unit 60 according to the present invention uses the wireless communication network by excluding the MRTT regarded as the delay spike from the RTO calculation process so that the RTO value does not become too large. Even in a client-server communication system, a quick data retransmission is performed when communication data such as a data packet is lost.

  Further, the back-off that doubles the timeout value when delay occurs due to timeout is delayed to avoid the problem that the timeout time becomes extremely long when data packets or the like are frequently lost.

  Further, the data transmission pattern is monitored so that the above function is effective only when the size of data to be transmitted at a time is small. Thereby, for example, when a command is transmitted to the server device 32 by performing some operation on the client device 31, for example, the data size of the command is usually small, and therefore communication with priority given to response is performed. Can do. For example, when transferring (uploading) a data file to the server device 32, the above function is disabled, and communication according to conventional TCP control giving priority to throughput and communication network utilization efficiency is performed.

  On the other hand, preventing the RTO value from becoming too large and delaying the exponential backoff of the retransmission timer an arbitrary number of times increases the probability of retransmission that may not be necessary in the first place. It may be possible to put a burden on However, as described above, the function is enabled only when small-size data is transmitted, so that a large burden is not imposed on the communication network.

  As described above, according to the present invention, the RTT measurement value that suddenly becomes a large value is excluded from the RTO calculation process, so that the problem that the RTO becomes too large can be avoided, and when a packet loss error occurs. Data retransmission processing can be performed promptly.

  In addition, since the exponential backoff of the retransmission timer is delayed an arbitrary number of times, it is possible to avoid the problem that the waiting time until retransmission becomes extremely long when packet loss occurs continuously.

  In addition, the size of transmission data in each request from an upper layer is monitored, and the above function is enabled only when the size can be stored in one TCP packet. The increase in the burden on the communication network due to the shortening of the time can be kept small.

  Furthermore, the present invention is intended to realize rapid retransmission in a situation where the amount of data to be transmitted at one time is small and the algorithm for detecting packet loss due to continuous reception of duplicate ACKs is ineffective. -Only the transmission side of the client device 31 in the server type communication system may be mounted, and the server device 32 does not need to be changed at all.

  The data transmission pattern determination unit 61 of the above-described embodiment monitors the data size to be transmitted at a time, and enables the subsequent function only when the size can be stored in one TCP packet. This may be explicitly controlled by the upper layer. Specifically, the control function is added to an API (Application Program Interface) between the TCP control unit 60 and an application program that is an upper layer, and the application program calls the function to control. It can be so.

  As described above, the embodiments of the present invention have been described with reference to the drawings. However, the above-described embodiments of the present invention are not limited to hardware, a DSP (Digital Signal Processor) board or a CPU as a function of the client device 31. It can be realized by firmware or software on the board.

  Further, the client device 31 to which the present invention is applied is not limited to the above-described embodiment as long as the function is executed, and even a single device or a system composed of a plurality of devices can be used. Needless to say, the integrated device may be a system in which processing is performed via a network such as a LAN or a WAN.

  It can also be realized by a system including a CPU, a ROM or RAM memory connected to a bus, an input device, an output device, an external recording device, a medium driving device, and a network connection device. That is, a ROM or RAM memory, an external recording device, or a portable recording medium that records a software program for realizing the system of the above-described embodiment is supplied to the client device 31, and the computer of the client device 31 executes the program. Needless to say, this can also be achieved by reading and executing.

  In this case, the program itself read from the portable recording medium or the like realizes the novel function of the present invention, and the portable recording medium or the like on which the program is recorded constitutes the present invention.

  Examples of portable recording media for supplying the program include flexible disks, hard disks, optical disks, magneto-optical disks, CD-ROMs, CD-Rs, DVD-ROMs, DVD-RAMs, magnetic tapes, and nonvolatile memory cards. Various recording media recorded via a network connection device (in other words, a communication line) such as a ROM card, electronic mail or personal computer communication can be used.

  The computer (information processing apparatus) executes the program read out on the memory, thereby realizing the functions of the above-described embodiment, and an OS running on the computer based on the instructions of the program. Performs part or all of the actual processing, and the functions of the above-described embodiments are also realized by the processing.

  Furthermore, a program read from a portable recording medium or a program (data) provided by a program (data) provider is stored in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. After being written, the CPU of the function expansion board or function expansion unit performs part or all of the actual processing based on the instructions of the program, and the functions of the above-described embodiments are also realized by the processing. obtain.

  That is, the present invention is not limited to the embodiment described above, and can take various configurations or shapes without departing from the gist of the present invention.

It is a figure which shows the example of the data transmission pattern using a retransmission timer. It is a figure which shows the example of the data transmission pattern in a "Fast Retransmit" algorithm. 1 is a diagram illustrating a configuration example of a client-server communication system using a wireless communication network. It is a figure which shows the example of the exchange of data in a client-server type communication system. 2 is a diagram illustrating an outline of a hardware configuration of a client device 31. FIG. 3 is a functional block diagram illustrating a TCP control unit implemented in a client device 31. FIG. It is a flowchart which shows the flow of the process which the data transmission pattern determination part 61 performs. It is a flowchart which shows the flow of the process which the Delay Spike determination part 62 performs. It is a flowchart which shows the flow of the process which the RTO calculation part 63 performs. It is a flowchart which shows the flow of the process which the resending control part 64 performs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Client apparatus 12 Server apparatus 21 Data communication apparatus 22 Data communication apparatus 31 Client apparatus 32 Server apparatus 33 Base station 34 Internet 60 TCP control part 61 Data transmission pattern determination part 62 Delay Spike determination part 63 RTO calculation part 64 Retransmission control part 311 Bus 312 CPU
313 Input device 314 Display device 315 ROM
316 RAM
317 External storage device 318 Communication I / F
319 Auxiliary storage device 321 Bus 322 CPU
323 Input device 324 Display device 325 ROM
326 RAM
327 External storage device 328 Communication I / F
329 Auxiliary storage device

Claims (5)

A communication control device that controls a second communication device that can wirelessly communicate with a first communication device using a transport protocol and has an asymmetrically large reception amount compared to a transmission amount,
Retransmission time calculation means for calculating a retransmission time until retransmission of communication data to be transmitted to the first communication device;
Communication data round-trip time measuring means for measuring communication data round-trip time in which the communication data goes back and forth with the first communication device;
Comparing means for comparing the retransmission time calculated by the retransmission time calculating means with the communication data round-trip time measured by the communication data round-trip time measuring means;
As a result of comparing the retransmission time and the communication data round-trip time by the comparison means, when the communication data round-trip time becomes larger than the retransmission time, the communication data round-trip time becomes larger than the retransmission time. Excluding means from the retransmission time calculation processing by the retransmission time calculating means,
Determining means for determining whether the size of communication data to be transmitted to the first communication device can be stored in one packet of the transport protocol;
On / off means for turning on or off the process of excluding the communication data round-trip time by the excluding means based on the determination result determined by the determining means;
A communication control apparatus comprising: further,
Retransmission detection means for detecting retransmission of the communication data due to timeout;
When retransmission of the communication data is detected by the retransmission detection means, backoff control means for delaying exponential backoff of the retransmission timer an arbitrary number of times;
Equipped with a,
The on / off means includes
Based on the determination result determined by the determination means, turn on or off the process of delaying the exponential backoff by the backoff control means,
The communication control apparatus according to claim 1.   The backoff control means skips the exponential backoff calculation by a set number of times and delays the increase of the retransmission time when increasing the retransmission time by an exponential backoff calculation for increasing the retransmission time by a power of 2. Item 3. The communication control device according to Item 2. The transport protocol, the communication control device according to any one of claims 1 to 3, characterized in that a TCP (Transmission Control Protocol). A computer of a communication control device that controls a second communication device that can wirelessly communicate with a first communication device using a transport protocol and has a reception amount asymmetrically larger than a transmission amount,
Retransmission time calculation means for calculating a retransmission time until retransmission of communication data to be transmitted to the first communication device;
A communication data round-trip time measuring means for measuring a communication data round-trip time in which the communication data makes a round trip with the first communication device;
Comparing means for comparing the retransmission time calculated by the retransmission time calculating means with the communication data round-trip time measured by the communication data round-trip time measuring means;
As a result of comparing the retransmission time and the communication data round-trip time by the comparison means, when the communication data round-trip time becomes larger than the retransmission time, the communication data round-trip time becomes larger than the retransmission time. Excluding means for excluding from retransmission time calculation processing by the retransmission time calculating means,
Determining means for determining whether the size of communication data to be transmitted to the first communication device can be stored in one packet of the transport protocol;
An on / off means for turning on or off the process of excluding the communication data round-trip time by the excluding means based on the determination result determined by the determining means;
Communication control program to function as