JP2000115282A - Data re-transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a data re-transmission system where reduction in a data transfer efficiency due to frequent occurrence of data re-transmission is prevented in the case of re-transmitting data. SOLUTION: After transmission of a maximum outstanding information frame number '5' to a terminal 10 from a data transmission control means 6 of a host computer system 1, when data are re-transmitted to the terminal 10, a data re-transmission monitor means 3 informs a statistic information storage means 4 of re-transmission information of data transmitted from the host computer system 1 to the terminal 10, a transmission data quantity discrimination means 5 allows a maximum transmission available data number revision means 7 to change the information into a maximum outstanding information frame number '1' based on a data quantity of the statistic information storage means 4 and allows the maximum transmission available data number revision means 7 to gradually increase the maximum outstanding information frame number '1' to be restored to the number '5', after the completion of the data re-transmission.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication system supporting a data retransmission function, which temporarily changes the maximum number of transmittable data of its own station when data retransmission occurs, thereby reducing the number of data transmitted without acknowledgment. Data retransmission system that prevents retransmissions from occurring frequently and detects that data retransmission no longer occurs, gradually increases the maximum number of data that can be transmitted, and eventually increases to the original value About.

[0002]

2. Description of the Related Art A data transmission method employing a high-level data link (hereinafter referred to as HDLC) procedure as a data link control procedure is disclosed in, for example, Japanese Patent Application Laid-Open No. 07-1230.
No. 81 discloses that information frames are continuously transmitted from one station to the other station without transmission confirmation up to the maximum number of standing information frames in order to improve data transmission efficiency according to transmission quality. Conversely, the other station transmits to one station.

[0003] One station or the other station receives an information frame transmitted by the other station, and determines the number of received information frames and the number of received information frames.
The number of erroneous frames with errors is counted, and the transmission error rate is calculated from the number of received frames and the number of erroneous frames at regular time intervals. It is disclosed that the maximum number of standing information frames is updated based on the transmission error rate, and the updated maximum number of standing information frames is used.

Further, among window control systems for data transmission control in packet communication, a window control system in which a window size is changed during communication is also known. This window control method allows, in packet communication, when a data packet is transmitted from a transmission side, a data packet up to the maximum window size number is postponed without waiting for reception of an acknowledgment packet transmitted from a reception side. .

Various such window control systems have been developed so far.
Japanese Patent Application Laid-Open No. 4-20755 discloses that a transmission-side window size is determined based on an average reception interval on a communication side of a delivery confirmation packet transmitted from a reception side as a response to a transmitted packet and the number of retransmission request packets received on the transmission side. It is disclosed therein to change the window size.

As is apparent from the above description, transmission of an outstanding information frame with the maximum number of standing information frames according to the HDLC procedure as an upper limit, or transmission in a window control method for data transmission control in packet communication, is also possible. They are trying to improve efficiency or network utilization efficiency.

Here, when transmitting the standing information frame up to the maximum number of standing information frames according to the former HDLC procedure, when the data of the transmitted standing information frame is lost, the transmission is performed from the receiving side. A data retransmission control method is known in which a data retransmission is requested to a data transmission side, and the data is retransmitted in response to the request. FIG. 4 is a time chart for explaining HDLC sequence control by a conventional data retransmission control method supporting a data retransmission function. This figure 4
A conventional data retransmission control method will be described with reference to FIG.

In FIG. 4, data is transmitted between the host computer system 1 and the terminal 10 through the communication line 8. In the normal response mode, the terminal 10 receives a P-bit ON command frame from the host computer 1. Only when the permission is obtained, an ON response frame of the F bit is transmitted to the host computer 10. In the normal response mode, when the terminal 10 requests data retransmission by losing the data transmitted from the host computer system 1, the communication line 8 is transmitted from the terminal 10 to the host computer system 1.
In step S 1, an RR (receivable) OF frame is transmitted to the host computer 1.

When this frame is received by the host computer system 1, the host computer system 1 starts retransmission of data. At this time, the host computer system 1 is set to continuously transmit up to the maximum number of standing information frames = 5. Shows the case. Therefore, the first retransmission of data means that five retransmissions 1 are continuously transmitted. When these five retransmission 1 data are retransmitted,
In step S2, the RR0 frame is transmitted again from the terminal 10 to the host computer system 1 through the communication line 8,
In step S3, the RR0P frame is transmitted from the host computer system 1 to the terminal 10 via the communication line 8.

As a result, the terminal 10 can now use the RR1F
Is transmitted to the host computer system 1, the data of "retransmission 2" is sequentially transmitted up to the standing information frame "4" in the same manner as the transmission of the data of "retransmission 1". Hereinafter, similarly, the data of “retransmission 3” is transmitted from the host computer system 1 to the terminal 10 again.

[0011]

However, in a conventional data retransmission control method in a communication system supporting such a data retransmission function, when data is retransmitted, a communication line 8 is transmitted from the host computer system 1 to the terminal 10. If there is data to be transmitted via the, the maximum number of transmittable data is transmitted unconditionally. That is, when the maximum number of standing information frames = 5 and there is data to be retransmitted within the range of “5”, in the example of FIG.
"Retransmission 1" is "5", "Retransmission 2" is "4", "Retransmission 3" is "2", and so on, while there is retransmission data, unconditionally transmitted from the host computer system 1 to the terminal 10. are doing.

Therefore, while there is retransmission data, in the above example, five transmission signals of "retransmission 1" data,
Data of "retransmission 1" are transmitted, and then three data of "retransmission 3" are transmitted. In other words,
When data retransmission occurs, data is retransmitted without transmission confirmation, and there is a problem that data transmission efficiency is reduced.

A first invention of the present invention has been made to solve the above-mentioned conventional problem, and has been modified to temporarily reduce the maximum number of standing information frames of a host computer system when data retransmission occurs. Accordingly, it is an object of the present invention to provide a data retransmission control method capable of reducing the number of data to be transmitted without confirming the maximum transmittable data number and preventing a decrease in data transfer efficiency due to frequent data retransmission.

According to a second aspect of the present invention, when a data retransmission occurs, the window size is set to a predetermined window size smaller than the window size initially set, data is retransmitted, and the data is first set after the retransmission is completed. By gradually increasing the number of window sizes obtained, it is possible to reduce the number of data items that can be transmitted without confirming the maximum number of transmittable data items, and to provide a data retransmission control method capable of preventing a reduction in data transfer efficiency due to frequent data retransmission. The purpose is to:

[0015]

To achieve the above object, a data retransmission control method according to a first aspect of the present invention is a data retransmission control method for transmitting data after receiving an standing information frame by a high-level data link control procedure through a communication line. A terminal that transfers the receivable final bit when retransmission is required,
After receiving the receivable final bit transmitted from the terminal, after determining the data retransmission amount at the start of data retransmission to the terminal, and changing the maximum number of standing information frames to a predetermined maximum number of standing information frames, A host computer system having communication control means for gradually increasing the number of standing information frames so as to return to the initially determined maximum number of standing information frames when the data retransmission is completed.

According to the data retransmission control method according to the first aspect of the present invention, the terminal needs to retransmit data from the host computer system to the received signal of the standing information frame according to the high-level data link control procedure via the communication line. When this occurs, the terminal sends a receivable final bit to the host computer system. When the host computer system receives this final bit, the host computer system starts retransmitting data to the terminal. At the start of retransmission of this data, the communication control means of the host computer system determines the amount of retransmission and sets the maximum number of outstanding information frames to a value smaller than the maximum number of outstanding information frames which was determined first. The number of frames is temporarily changed, and data is retransmitted. When the retransmission of data is completed with the changed maximum number of standing information frames, the initially determined maximum number of standing information frames is gradually increased so as to reach the initially determined maximum number of standing information frames.

Therefore, in the first invention of the present invention,
When data retransmission occurs, the maximum number of data that can be transmitted is temporarily changed to reduce the number of data to be transmitted without acknowledgment, so that retransmissions can be prevented from occurring frequently and the data transfer efficiency can be prevented from lowering.

According to a second aspect of the present invention, there is provided a data retransmission control system for transmitting a reject packet through a communication line, receiving the reject packet transmitted from the terminal, and retransmitting data to the terminal. After the start of the data reproduction, the data is changed from a predetermined maximum Windows size number at the start of reproduction of the data to a maximum Windows size number reduced to a predetermined value smaller than the predetermined maximum window size number. And a host computer system having communication control means for gradually increasing the number of window sizes to return.

According to the data retransmission control method of the second invention according to the present invention, since the terminal needs to retransmit data from the host computer system, the data is transmitted from the terminal through the communication line. When the host computer system receives a rejected packet according to the 25 recommendation procedure, the host computer system starts retransmission of data to the terminal, and the communication control means of the host computer system first sets the window size according to the data retransmission amount. The maximum window size is changed to a smaller maximum window size. Data is retransmitted from the host computer system to the terminal with the changed maximum window size. When the data transfer state is improved and the need for retransmission is eliminated, the communication control means returns to the initially set maximum window size. , Gradually increase the window size.

Therefore, in the second invention according to the present invention, the data is retransmitted by setting a predetermined maximum window size smaller than the maximum window size initially set when data retransmission occurs, and the first retransmission is performed after the retransmission is completed. By gradually increasing the number of window sizes set in
The maximum number of data that can be transmitted can be reduced without confirming the delivery, and the data transfer efficiency can be prevented from lowering due to frequent data retransmission.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a data retransmission control system according to the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of the first embodiment according to the present invention. In FIG. 1, the host computer system 1 can transmit data and retransmit data through a communication line 8. The terminal 10 includes a communication control unit 9 of a conventional specification which has been used conventionally.

Further, the host computer system 1 includes a communication control means 2. Hereinafter, the configuration of the communication control means 2 will be described. This communication control means 2 has a data retransmission monitoring means 3. The data retransmission monitoring means 3 monitors the state of retransmission of data from the host computer system 1 to the terminal 10 through the type communication line 8, outputs the monitoring information to the statistical information storage means 4, and sends the monitoring information to the data transmission control means 5. Also outputs monitoring information of the data retransmission status.

The statistical information storage unit 4 stores monitoring information of the data retransmission state input from the data retransmission monitoring unit 3. The storage amount of the monitoring information in the retransmission state of the data stored in the statistical information storage unit 4 is determined by the transmission data amount determination unit 5. According to the storage amount of the monitoring information of the retransmission state of the data stored in the statistical information storage unit 4 determined by the transmission data amount determination unit 5, the maximum transmittable data number changing unit 7 transmits the information from the host computer system 1 to the terminal. When data retransmission to be transmitted to the host computer 10 occurs, the maximum transmittable data number of the host computer system 1 is temporarily changed.

The data transmission control means 5 receives the data retransmission status monitoring information from the data retransmission monitoring means 3 and controls the data transmission from the host computer system 1 to the terminal 10 through the communication line 8. It is.

Next, the operation of the first embodiment configured as described above will be described with reference to the sequence explanation diagram for controlling the HLDC of FIG. 2 in the case of the HDLC procedure. The host computer system 1 and the terminal 10 of the partner station are connected via the communication line 8 as the communication control means 2 as an HDLC.
A case where communication is performed according to a procedure (High-level Data Link Control: ISO4335 standard) will be described. Here, it is assumed that the data link is already established.

The maximum number of outstanding information frames (hereinafter referred to as I-frames), which is the maximum number of transmittable data of HDLC, is "5" in both the host computer system 1 and the terminal 10, and is transmitted to the host computer system 1. Description will be made on the assumption that there are "10" pieces of transmission data to be transmitted. More specifically, there are five “retransmission 1” data and five “retransmission 2” data, for a total of ten data. The outstanding I frame is transmitted to the terminal 10 through the communication line 8 by the data transmission control means 6 of the communication control means 2 in the host computer system 1.

It is assumed that the terminal 10 receiving the outstanding I frame has lost the data transmitted from the host computer system 1 due to the deterioration of the data transfer state. As a result, the terminal 10 needs to retransmit data, and the terminal 10 transmits the RR0 frame to the host computer system 1 through the communication line 8 in step S11. When receiving the RR0 frame, the host computer system 1 transmits an RROP frame to the terminal 10 from the host computer system 1 through the communication line 8 in step S12.

In response to the RR0P frame, the terminal 10 transmits an RR0F response frame to the host computer system 1 in step S13. The host computer system 1 that has received the RR0F response frame
Transmits the data of “retransmission 1” (the frame of I0, 0) to the terminal 10 via the communication line 8 in step S14. Hereinafter, up to the fifth data of “retransmission 1” (“I1,0”, “I2,
0, I3,0, I4,0) to the terminal 10 via the communication line 8.

In the host computer system 1, when the "retransmission 1" of data occurs as described above, the data retransmission monitoring means 3 of the communication control means 2 notifies the statistical information storage means 4 of the data retransmission information and simultaneously transmits the data. The control unit 6 is also notified. Of these, the statistical information storage means 4 stores the data retransmission information every time the data retransmission information is input, and the transmission data amount determination means 5 stores the data retransmission information in the statistical information storage means 4 at regular intervals. In view of the information on the data transmission amount of "retransmission 1", if "retransmission 1" has occurred, the transmission data amount determination means 5 controls the maximum transmittable data number changing means 7 to determine the maximum transmission possible. The maximum number of outstanding I frames is changed from “5” to “1” by the data number changing means 7.

Next, the terminal 10 and the host computer system 1
When the data retransmission monitoring unit 3 determines that the data transfer state between the host computer system 1 and the terminal 10 will not be retransmitted due to the improved data transfer state, the data retransmission monitoring unit 3 And the data transmission control means 6 at the same time. After the retransmission of the data no longer occurs, the terminal 10 returns to step S2
0, when the data transmitted from the host computer system 1 is lost and the data needs to be retransmitted, the RR0 frame is transmitted from the terminal 10 through the communication line 8 in step S19 in the same manner as in steps S11 to S13. Is transmitted from the host computer system 1 to the terminal 10 via the communication line 8 in step S20, and an RR0F response frame is transmitted from the terminal 10 via the communication line 8 in step S21.

At this time, since the maximum number of outstanding I frames has already been changed from "5" to "1", the number of outstanding I frames that can be transmitted without acknowledgment is recognized as "1" and controlled. . Therefore, in step S22, one piece of data, “Resend 2” data of the I0,0 frame is transmitted from the host computer system 1 through the communication line 8. The terminal 10 uses this I
When the data of the “0,0” frame “retransmission 2” is received, the RR 1 response frame is transmitted to the host computer system 1 via the communication line 8 in step S 23.

At this point, the maximum number of outstanding I frames is still "1", and the host computer system 1 transmits the data of "Retransmission 2" of the I1,0 frame to the terminal 10 through the communication line 8 in step S24. One (one outstanding I frame) is transmitted. The terminal 10, upon receiving the single “retransmission 2” data, transmits the RR2 frame to the host computer system 1 via the communication line 8 in step S25.

At this time, since data retransmission from the host computer system 1 to the terminal 10 has been stopped, the data retransmission monitoring means 3 detects a state in which the data is not retransmitted, and accumulates the detection result in statistical information. Output to the means 4 and the data transmission control means 6. Therefore, the data transmission amount is not stored in the statistical information storage unit 4, and this state is determined by the transmission data amount determination unit 5, and the transmission data amount determination unit 5 uses the maximum transmittable data number changing unit 7 to determine the maximum. The number of outstanding I-frames is increased from “1” to “2”. Hereinafter, in the same manner as when one piece of “retransmission 2” data is transmitted in the case of the maximum number of outstanding I-frames “1”, This time, because the maximum number of outstanding I-frames is “2”,
"Retransmission 2" data is transmitted two by two.

Hereinafter, the number of maximum outstanding I frames is gradually increased in the same manner, and finally the original value
(Here, the maximum number of outstanding I frames determined first is “5”).

As described above, in the first embodiment, when data retransmission occurs, the maximum transmittable data number of the host computer system 1 is temporarily reduced to a number smaller than the initially set maximum outstanding I frame number. Since the number of data to be transmitted without transmission confirmation is reduced by making the change, it is possible to prevent repetition of retransmission and improve data transmission efficiency. Further, when it is detected that retransmission of data is no longer occurring, the maximum number of outstanding I frames is gradually increased to return to the original maximum number of outstanding I frames, so that a normal communication state can be ensured. it can.

Next, a second embodiment according to the present invention will be described with reference to FIGS. In the first embodiment, the case has been described in which the communication control means 2 that performs communication control between the host computer system 1 and the terminal 10 performs communication using the HDLC procedure, but the same applies to data retransmission in other communication procedures. Can be implemented. In the second embodiment, the host computer system 1 and the terminal 1 will be described with reference to FIG.
X.25 procedure (communication control means 2 between I.T.
X.25) will be described.

Here, it is assumed that the packet connection has already been established. The window size, which is the maximum number of transmittable data of X.25, is set to “5” between the host computer system 1 and the terminal 10, and the host computer system 1 has ten pieces of transmission data to be transmitted to the terminal 10. Shall be. That is, five “retransmission 1” and “retransmission 2”
Are 5 in total. Also, in the X.25 procedure,
The packet retransmission function is optional, but it is assumed that agreement has been reached on the use of this function.

In FIG. 3, a packet with the maximum window size "5" initially set is transmitted from the data transmission control means 6 of the communication control means 2 to the terminal 10 via the communication line 8. In this state, the host computer system 1 that has received the REJ0 packet from the terminal 10 via the communication line 8 in step S31 restarts data retransmission in step S32, and transmits the “retransmission 1” packet from the host computer system 1 to the communication line 8 To the terminal 10 via Five “retransmission 1” packets are sequentially transmitted to the terminal 10 from step S33 to step S36. At this time, in the host computer system 1, the data retransmission monitoring unit 3 changes the transmission state of the “retransmission 1” packet. Each time the host computer system 1 transmits a “retransmission 1” packet, the data retransmission monitoring unit 3 notifies the data retransmission information to the statistical information storage unit 4 and also transmits the data to the data transmission unit 6. Notice.

The statistical information storage means 4 inputs and stores the data retransmission information. The transmission data amount determining means 5 determines the data retransmission information amount stored in the statistical information storage means 4 and controls the maximum transmittable data number changing means 7. At this point, the host computer system 1 has already received the REJ packet transmitted from the terminal 10 in step S31, and the data retransmission 1 has occurred, so the transmission data amount determination means 5 changes the maximum transmittable data number. By controlling the means 7, the maximum transmittable data number changing means 7 changes the window size from "5" to "1".

Next, as described above, five “retransmissions 1” are transmitted from the host computer system 1 to the terminal 10 via the communication line 8.
After the transmission, the data transfer state between the host computer system 1 and the terminal 10 is improved and retransmission does not occur. In the host computer system 1, the data retransmission monitoring means 3 detects the stop of the retransmission, Notify the statistical information storage means 4. At this time, since the window size has already been changed from "5" to "1", the data transmission control means 6 recognizes and controls the number of data packets that can be transmitted without acknowledgment as "1".

After the transmission of the five "retransmissions 1" is completed, the transmission data amount determination means 5 detects from the statistical information storage means 4 that data retransmission has stopped. In a state where the data retransmission does not occur, if the data transfer state between the host computer system 1 and the terminal 10 deteriorates again, the terminal 10 needs to retransmit the data. Sends a REJ0 packet to the host computer system 1 from
The host computer system 1 that has received it receives a message at step S3.
At step 8, one “retransmission 2” is transmitted to the terminal 10 via the communication line 8.

In this case, since the window size has already been changed from "5" to "1", as described above, data transmission control means 6 sets the number of data packets that can be transmitted without acknowledgment to "1". Therefore, the host computer system 1 recognizes this one “retransmission 2”
(The packet of DT0,0). In this state, if the terminal 10 further determines that there is a need to retransmit the data, the RR1
Packet of the host computer system 1 via the communication line 8
Send to The host computer 1 that has received the RR1 packet re-transmits one “retransmission 2” (D
(T1, 0 packet) is transmitted to the terminal 10 via the communication line 8.

As described above, the data transmission control means 6
Recognizes that the number of data packets that can be transmitted without acknowledgment is "1", and after the transfer of this one "retransmission 2" data, the transmission data amount determination means 5 performs the data retransmission. Each time it is detected that no occurrence has occurred, the data retransmission information from the data retransmission monitoring means 3 is not input to the statistical information storage means 4, and the statistical information storage means 4
The storage result of the data retransmission information of the transmission data amount determination means 5
Is determined. Based on the transmission data amount discrimination result by the transmission data amount discriminating means 5, the transmission data amount discriminating means 5 uses the maximum transmittable data number changing means 7 to gradually change the window size from "1" to "2", "3",. And gradually increases to the value of the originally set maximum window size (here, “5”).

As described above, in the second embodiment, X.25
According to the procedure, when data retransmission occurs, the window size, which is the maximum transmittable data number of the host computer system 1, is temporarily reduced to a number smaller than the initially set window size number, and the data to be transmitted without transmission confirmation is changed. Since the number is reduced, frequent retransmissions can be prevented as in the case of the first embodiment, and the data transmission efficiency can be increased. Further, when it is detected that the retransmission of the data will not occur, the number of the maximum window sizes is gradually increased to return to the original number of the maximum window sizes, so that a normal communication state can be secured.

[0045]

As described above, according to the first aspect of the present invention, when data retransmission occurs, the maximum transmittable data number of the host computer system 1 is reduced to a number smaller than the initially set maximum outstanding I frame number. Since the number is temporarily reduced and the number of data to be transmitted without transmission confirmation is reduced, frequent retransmissions can be prevented, and data transmission efficiency can be increased. in addition,
When it is detected that the retransmission of data is no longer occurring, the maximum number of outstanding I frames is gradually increased to return to the original maximum number of outstanding I frames, so that a normal communication state can be ensured.

According to the second aspect of the present invention, X.
According to the 25 procedures, when data retransmission occurs, the window size, which is the maximum transmittable data number of the host computer system 1, is changed to be temporarily reduced to a number smaller than the initially set window size number, and transmitted without transmission confirmation. Since the number of data is reduced, frequent retransmissions can be prevented, and data transmission efficiency can be increased. Further, when it is detected that the retransmission of data is no longer occurring, the number of maximum window sizes is gradually increased to return to the original number of maximum window sizes, so that a normal communication state can be ensured.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of a data retransmission control method according to the present invention.

FIG. 2 is an explanatory diagram of an HDLC sequence applied to the first embodiment of the data retransmission control method according to the present invention.

FIG. 3 is an explanatory diagram of an X.25 sequence applied to the second embodiment of the data retransmission control method according to the present invention.

FIG. 4 is an explanatory diagram of an HDLC sequence applied to a conventional data retransmission control method.

[Explanation of symbols]

1 ... host computer system, 2 ... communication control means, 3
... data retransmission monitoring means, 4 ... statistical information storage means, 5
... Transmission data amount discriminating means 6 Data transmission control means 7 Maximum transmittable data number changing means 8 Communication line.

Claims (6)

[Claims] 1. A terminal for transferring a receivable final bit when data retransmission is required after receiving an outstanding information frame by a high-level data link control procedure through a communication line, and receiving the receivable final bit transmitted from the terminal. Later, when the data retransmission to the terminal is started, the amount of data retransmission is determined and the maximum number of standing information frames is changed to a predetermined maximum number of standing information frames. A host computer system having communication control means for gradually increasing the number of standing information frames so as to return to the number of standing information frames. 2. The communication control means includes: data transmission control means for transmitting a maximum standing information frame initially set from the host computer system to the terminal; and retransmission data transmitted from the host computer system to the terminal. Data retransmission monitoring means for monitoring status to obtain data retransmission information, statistical information storage means for accumulating data every time data retransmission information is obtained by the data retransmission monitoring means, and data retransmission stored in the statistical information storage means Transmission data discriminating means for discriminating the amount of information, wherein the transmission data discriminating means is controlled by the transmission data discriminating means when the amount of data retransmission information is detected, and is based on the initially set maximum number of standing information frames. Update to the smaller maximum number of standing information frames, and When the data discriminating means no longer detects the data retransmission information, the maximum number of standing information frames is gradually increased so as to return from the updated maximum number of standing information frames to the initially set maximum number of standing information frames. 2. The data retransmission control device according to claim 1, further comprising a maximum number of transmittable data. 3. The data retransmission control device according to claim 2, wherein the transmission data determination unit determines the amount of the retransmission data information stored in the statistical information storage unit at regular time intervals. 4. A terminal for transmitting a re-get packet through a communication line, receiving the re-get packet transmitted from the terminal, starting retransmission of data to the terminal, and being predetermined when reproduction of the data is started. After changing from the maximum number of windows sizes to the maximum number of windows sizes reduced to a predetermined value smaller than that, when the data retransmission is completed, there is provided communication control means for gradually increasing the number of window sizes so as to return to the predetermined maximum number of window sizes. A data retransmission control method, comprising: a host computer system; 5. The data transmission control means for transmitting a packet having the maximum window size set first to the terminal from the host computer system, and the communication control means being transmitted from the host computer system to the terminal. Data retransmission monitoring means for monitoring retransmission data status to obtain data retransmission information, statistical information storage means for accumulating data every time data retransmission information is obtained by the data retransmission monitoring means, and data stored in the statistical information storage means Transmission data discriminating means for discriminating the amount of data retransmission information, wherein the transmission data discrimination means is controlled by the transmission data discrimination means when the amount of data retransmission information is detected, and is based on the initially set maximum window size number. The data is updated to a smaller maximum window size number, and the transmission data discriminating means updates the data retransmission information. And the maximum transmittable data number changing means for gradually increasing the maximum window size number so as to return from the updated maximum window size number to the initially set maximum window size number when no more is detected. The data retransmission control device according to claim 4. 6. The data retransmission control device according to claim 5, wherein the transmission data determination unit determines the amount of the retransmission data information stored in the statistical information storage unit at regular time intervals.