WO2003105420A1 - Data communication method and data transmission apparatus - Google Patents

Abstract

The sequence numbers of packets stored in a transmission buffer (5) are applied to a retransmit-around number management part (3). The retransmit-around number, which is decremented each time the transmission period starts, is added to each sequence number. When it is determined that this retransmit-around number is equal to or less than a predetermined value, a transmission data management part (4) discards the packet, which corresponds to the thus determined sequence number, from the transmission buffer (5). When the average of the retransmit-around numbers of the packets stored in the transmission buffer (5) is equal to or less than a reference value, it is determined that a abnormal state of communication has occurred.

Description

 Specification

 Data communication method and data transmission device

 The present invention relates to a data communication method and a data transmission device in a communication system using a transmission path in which an error such as wireless communication or power line communication occurs, and in particular, to a data communication method and a data transmission method in a communication system that performs data transfer in real time. Data transmission device. Background art

 In recent years, with the development of communication technology, the complexity of wiring when building a LAN (Local Area Network) has been reduced, and the communication connection between an AV source such as a tuner placed at a distance and an AV playback device such as a display has been improved. For this purpose, a wireless communication system is used. It has also been proposed to use a power line communication system using existing power lines as one of the means for Internet connection.

 However, in a wireless communication system, the longer the transmission distance, the more susceptible to multi-pulse fading. In a power line communication system, the effect of noise from home electric appliances used in the home is reduced. Susceptible. For this reason, the signal is degraded in the transmission process of each of the wireless communication system and the power line communication system.

 Therefore, as a method of compensating for errors occurring in such a transmission process, an error correction code is added for each packet unit or for each of a plurality of block units obtained by dividing one bucket into a plurality. In some cases, the receiving side makes a retransmission request based on the request. When a retransmission request is made by the receiving side in this way, data erroneously received by the receiving side is retransmitted by the transmitting side in accordance with the retransmission request from the receiving side. In a communication method in which such a retransmission operation is performed, a setting is made such that data transmission is performed from a specific transmission device to a reception device in a predetermined period, and a communication band for each communication device is secured.

FIG. 11 is a block diagram showing a data transmission device used in a conventional wireless communication system. 2 shows the internal configuration of the unit 201. In the data transmitting apparatus 201 shown in FIG. 11, when a packet is input from the outside, the sequence number is added by the sequence number adding section 13, and then the time stamp adding section 14 is used to receive the packet. The information about the playback time to be played back by the is added and temporarily stored in the transmission buffer 16.

 Also, the retransmission request analysis unit 18 analyzes the reception status of the reception side from the ACK signal from the reception side received by the reception unit 17 via the antenna 21 and transmits information on the packet to be retransmitted to the transmission data. Inform management unit 15 When the transmission period set for the data transmission device 201 starts, the transmission data management unit 15 transmits the data to be transmitted from the retransmission packet held in the transmission buffer 16 and the new packet. Search for the packet.

 When the sequence number of the packet to be transmitted is stored in the transmission data management unit 15, the packet is transmitted from the transmission buffer 16 in the order of the stored sequence number by a predetermined packet amount until the transmission period ends. read out. The packet read from the transmission buffer 16 has the error correction code added by the error correction code addition unit 20 for each bucket or each of a plurality of blocks, and is transmitted from the transmission unit 19 via the antenna 21. Is performed.

 In such a data transmitting apparatus 201, among the packets stored in the transmission buffer 16, packets that have passed the reproduction time on the receiving side cannot be reproduced on the receiving side. Discarded from transmission buffer 16. This discard control operation operates according to the flowchart of FIG.

When the power is turned on, the discard control operation according to the flowchart of FIG. 12 is started. First, the reproduction time of the packet stored in the transmission buffer 16 and having the earliest reproduction time on the receiving side is determined. Confirm (S101). By comparing the confirmed playback time with the current time, it is determined whether or not the bucket whose playback time has been confirmed is played back after being received by the receiving side (S). 1 0 2). Then, when it is determined that the reproduction on the receiving side is sufficient (Yes), the processing operation of S101 is performed again. On the other hand, if it is determined that the reproduction is not in time for the reproduction on the receiving side (No), the packet whose reproduction time has been confirmed is discarded from the transmission buffer 16 (S103), and S101 Move to Further, the data transmission device performs a transmission operation in a preset transmission period according to the flowchart of FIG. Check the start time of the transmission period using a timer (not shown) in the transmission data management unit 15, or receive a signal indicating transmission permission from the outside at the reception unit 17 and allow the retransmission request analysis unit 18 to permit transmission. When the transmission data management unit 15 confirms the start time of the transmission period by recognizing the transmission period, the transmission period is started and the transmission operation is started (S111).

 Then, the ACK signal from the receiving side received by the receiving unit 17 is analyzed by the retransmission request analysis unit 18, and the retransmission bucket confirmed and the new bucket to be newly transmitted are transmitted to the transmission data management unit. 15 is searched (S1 1 2). Based on the search result, the retransmission bucket to be transmitted and the sequence number of the new bucket stored in the transmission buffer 16 are stored in the transmission data management unit 15 (S113). Based on the sequence number stored in the transmission data management unit 15, the transmission data management unit 15 determines whether the retransmission packet to be transmitted and the new packet exist in the transmission buffer 16 or not. (S114).

 At this time, if it is determined that there is no packet to be transmitted (No), all the processing ends. When it is determined that there is a bucket to be transmitted (Yes), the transmission data management unit 15 confirms the current time, and the remaining transmission period is sufficient to transmit the bucket to be transmitted. It is determined whether or not (S1 15). At this time, if it is determined that transmission is not possible (No), all processing is terminated, while if it is determined that transmission is sufficient (Yes), the packet to be transmitted is transmitted. Later (S116), the process proceeds to S114. Then, the processing of 3114 to 3116 is repeated until there is no more packet to be transmitted or the transmission period is not enough time for transmission.

As described above, in real-time transmission of video and audio, unlike normal data transmission, even if an error occurs during the transmission process, the playback time on the reception side is fixed, so the reception side There is no point in resending beyond the playback time of. Therefore, it is necessary for the transmitting side or the receiving side to constantly manage the time so as to discard packets that are no longer in time for the playback time and to monitor whether the time is in time for the playback time. In addition, in order to use the finite transmission bandwidth effectively, In communications that require a certain amount of data to be transmitted in a certain period of time, the bandwidth that can be used for retransmission is limited. Therefore, when the number of communication errors increases, the error recovery capability by retransmission reaches its limit, and there is a problem that data to be continuously processed such as video and audio is interrupted during processing on the receiving side. To solve this problem, as in the data transmission device shown in Fig. 11, the time stamp given to the packet is compared with the current time, so that the packet can be received at a time that can be reproduced on the receiving side. Let the user determine whether the packet is a packet or not.

 Also, Japanese Patent Application Laid-Open No. 2000-216816 discloses a method of comparing a packet time stamp with the current time and stopping retransmission control if the delay is equal to or greater than a specified value. I have. However, in any of the above methods, a complicated time comparison must be performed to control the discard of buckets from the transmission buffer by checking the playback time on the receiving side, and the circuit scale is large. It will be connected. Also, with reference to Japanese Patent Application Laid-Open No. 2000-212816, if the delay of an arbitrary packet increases, the retransmission control stops, and the state of an error occurring in the transmission process is reduced. It is difficult to know exactly. Disclosure of the invention

 In view of such a problem, the present invention does not have a complicated circuit configuration when transmitting continuously processed data such as a video signal and an audio signal using a communication transmission line having an error. Another object of the present invention is to provide a data communication method and a data transmission device capable of discarding a bucket that has become too late for the reproduction time on the receiving side.

In order to achieve the above object, a data communication method according to the present invention comprises: a data transmission device having a buffer for storing data for each first data unit; and a data reception device for receiving data transmitted by the data transmission device. A data communication method in which the data transmitting device confirms data requested by the data receiving device to retransmit, wherein the data transmitting device checks the data stored in the buffer in the data transmitting device. On the other hand, for each second data unit, the data receiving apparatus is provided with the number of retransmissions, which is information indicating whether retransmission is possible or not. Changing the number of retransmissions assigned to each of the data stored in the buffer, and discarding the data for each of the first data units for the number of retransmissions exceeding a predetermined value from the buffer. Features.

 According to such a data communication method, in the data transmitting apparatus, a trigger is generated at a predetermined timing, and the number of retransmissions of the data stored in the buffer is subtracted or added by one, and the number of retransmissions is calculated. It is checked whether the specified value has been reached. In this way, by monitoring the number of retransmissions of each data in the first data unit, it is possible to easily confirm that the data cannot be reproduced by the data receiving device. Therefore, it is possible to simplify the process of discarding a packet that has been confirmed to be unreproducible from the buffer.

 Further, a data communication method according to the present invention includes a data transmission device having a buffer for storing data for each first data unit, and a data reception device for receiving data transmitted by the data transmission device. A data communication method in which the data transmitting device confirms data requested to be retransmitted by the data receiving device, wherein the data transmitting device includes:

2 For each data unit, the data receiving apparatus is provided with the number of retransmissions, which is information indicating whether or not retransmission is possible, and at predetermined timing, the data allocated to the data stored in the buffer is given. When the number of retransmissions is changed, and when the number of retransmissions for each of the first data units stored in the buffer exceeds a reference value, it is confirmed that a communication error has occurred and the amount of data to be transmitted. It is characterized by the following.

 In this way, by monitoring the number of times data can be retransmitted, it can be easily confirmed that the data cannot be reproduced by the data receiving device. Also, when the number of retransmissions exceeds the reference value, it is confirmed that a retransmission request from the data receiving apparatus is made a plurality of times. Therefore, the data transmission device can easily confirm the state of the communication path with the data reception device by comparing the average value of the number of retransmissions of the data in the buffer with the reference value.

Further, the data communication method of the present invention comprises: a data transmitting device having a buffer for storing data for each first data unit; and a data receiving device for receiving data transmitted by the data transmitting device. In a data communication system configured with a data receiving device, the data receiving device confirms data requested to be retransmitted by the data transmitting device, wherein the data transmitting device stores the data in the buffer. For each second data unit, data is given a number of retransmissions, which is information indicating whether retransmission is possible to the data receiving apparatus. Data stored in the buffer is given at predetermined timings Changing the number of retransmissions assigned to each of the data transmission devices, when the number of retransmissions for each of the first data units transmitted during the transmission period assigned to the data transmission device exceeds a reference value, It is characterized by confirming that the communication is abnormal and reducing the amount of data to be transmitted.

 As described above, by monitoring the number of times data can be retransmitted, it can be easily confirmed that the data cannot be reproduced by the data receiving device. Also, when the number of retransmissions exceeds the reference value, it is confirmed that a retransmission request from the data receiving apparatus is made a plurality of times. Therefore, the data transmission device can easily confirm the state of the communication path with the data reception device by comparing the average value of the number of retransmissions of the data transmitted to the data reception device with the reference value.

 Further, a data communication method according to the present invention includes a data transmission device having a buffer for storing data for each first data unit, and a data reception device for receiving data transmitted by the data transmission device. A data communication method in which the data receiving device confirms data requested to be retransmitted by the data transmitting device, wherein the data transmitting device includes: For each unit, the data receiving apparatus is provided with the number of retransmissions, which is information indicating whether or not retransmission is possible, and at predetermined timing, the retransmission possible allocated to the data stored in the buffer is given. The number of times is changed, and the data for each of the first data units corresponding to the retransmittable number of times exceeding a prescribed value is discarded from the buffer. Both can and the amount of data discarded from the buffer exceeds the reference value, to verify that a communication error, characterized in that reducing the amount of data to be transmitted.

As described above, by monitoring the number of times data can be retransmitted, it can be easily confirmed that the data cannot be reproduced by the data receiving device. Also, this resendable number of times When the amount of data discarded exceeds the specified value and exceeds the reference value, it is confirmed that retransmission requests from the data receiving device are made multiple times. Therefore, the data transmitting apparatus can easily determine the state of the communication path with the data receiving apparatus by comparing the amount of data discarded during a predetermined period, such as the generation cycle of the timing for subtracting the number of retransmissions, with the reference value. You can check.

 Also, the data communication device of the present invention includes a buffer for storing data for each first data unit, a transmitting unit for transmitting the data stored in the buffer, and a data receiving device for receiving the data. A receiving unit that receives a reception acknowledgment signal notifying a reception state; and confirming a reception state of the data reception device based on the reception acknowledgment signal received by the reception unit. A retransmission request analysis unit for recognizing, and for the data stored in the buffer, for each second data unit, a retransmission possible number serving as information indicating whether retransmission is possible to the data receiving apparatus. And a transmission data management unit for discarding data in the buffer and controlling input / output of the data, wherein the retransmission possible number management unit checks the value of the retransmission possible number. The control unit changes the number of retransmissions assigned to each of the data stored in the buffer at each predetermined timing, and the transmission data management unit changes the number of retransmissions that exceeds a predetermined value. The data for each of the first data units is confirmed and discarded from the buffer.

Also, the data communication device of the present invention includes a buffer for storing data for each first data unit, a transmitting unit for transmitting the data stored in the buffer, and a data for receiving the data. A receiving unit that receives a reception acknowledgment signal for notifying a reception state of the reception device; and a reception status of the data reception device based on the reception acknowledgment signal received by the reception unit. A retransmission request analysis unit for recognizing data to be transmitted, and a retransmission capability serving as information indicating whether retransmission can be performed to the data receiving apparatus for each second data unit with respect to data stored in the buffer. A number of retransmissions, a retransmission possible number management unit for confirming the value of the retransmittable number, and a retransmission possible number for each of the first data units stored in the buffer. And a transmission data management unit for confirming whether a communication error, in the allowable number of retransmissions management unit, at predetermined timing, stored in the buffer The number of retransmissions assigned to each of the data to be transmitted is changed by the transmission data management unit, and the number of retransmissions for each of the first data units stored in the buffer is set to a reference value. When the number exceeds the limit, it is confirmed that the communication is abnormal, and the amount of data to be transmitted is reduced.

 Also, the data communication device of the present invention includes a buffer for storing data for each first data unit, a transmitting unit for transmitting the data stored in the buffer, and a data receiving device for receiving the data. A receiving unit that receives a reception acknowledgment signal for notifying the reception status of the data reception device; and a reception status of the data reception device based on the reception acknowledgment signal received by the reception unit. A retransmission request analysis unit for recognizing the number of retransmissions, which is information indicating whether retransmission is possible to the data receiving apparatus for each second data unit for data stored in the buffer. A retransmission count management unit for checking the value of the retransmission count, and a data transmission unit for each of the first data units transmitted during a transmission period allocated to the data transmission device. A transmission data management unit that checks whether or not the communication is abnormal based on the number of retransmissions that can be performed.The transmission data management unit stores the data in the buffer at predetermined times at the retransmission possible number management unit. The retransmittable number of times assigned to each of the data is changed, and the transmission data management unit applies the data to each of the first data units transmitted during the transmission period assigned to the data transmission device. When the number of retransmissions exceeds a reference value, it is confirmed that a communication error has occurred and the amount of data to be transmitted is reduced.

Also, the data communication device of the present invention includes a buffer for storing data for each first data unit, a transmitting unit for transmitting the data stored in the buffer, and a receiving unit for receiving the data. A receiving unit for receiving a reception confirmation signal for notifying a state; and confirming a reception state of the data reception device based on the reception confirmation signal received by the reception unit, and recognizing data requested by the data reception device for retransmission. A retransmission request analysis unit for performing the retransmission request count, which is information indicating whether retransmission is possible to the data receiving apparatus for each second data unit, for the data stored in the buffer. Both, a resend count control unit for checking the value of the resend count, a function of discarding data in the buffer and input / output control, and And a transmission data management unit that checks whether or not the communication is in an abnormal state based on the data amount, wherein the retransmission possible number management unit allocates each of the data stored in the buffer at each predetermined timing. The transmission data management unit checks the data for each of the first data units for the number of retransmissions that exceeds a predetermined value, and discards the data from the buffer. When the amount of data discarded from the buffer exceeds the reference value, it is confirmed that a communication error has occurred and the amount of data to be transmitted is reduced. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is a block diagram illustrating an internal configuration of a data transmission device in the communication system according to the first embodiment;

 FIG. 2 is a flowchart showing the bucket discard control operation of the data transmitting apparatus of FIG. 1,

 FIG. 3 is a flowchart showing a transmission control operation of the data transmission device of FIG. 1,

 FIGS. 4A and 4B are diagrams showing the format of a packet transmitted from the data transmitting apparatus,

 FIG. 5 is a block diagram showing an internal configuration of a data transmission device in the communication system of the second embodiment,

 FIG. 6 is a flowchart showing the transmission control operation of the data transmission device of FIG. FIG. 7 is a block diagram showing an internal configuration of a data transmission device in the communication system according to the third embodiment.

 FIG. 8 is a flowchart showing a transmission control operation of the data transmission device of FIG. 7,

 FIG. 9 is a block diagram showing another example of the internal configuration of the data transmission device in the communication system according to the third embodiment;

 FIG. 10 is a block diagram showing another example of the internal configuration of the data transmission device in the communication system according to the third embodiment;

FIG. 11 is a block diagram showing the internal configuration of a data transmission device in a conventional communication system. It is a lock diagram,

 FIG. 12 is a flowchart showing a bucket discarding control operation of the conventional data transmitting apparatus.

 FIG. 13 is a flowchart showing a transmission control operation of the conventional data transmission device. BEST MODE FOR CARRYING OUT THE INVENTION

<First embodiment>

 Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an internal configuration of a data transmission device used in the communication system of the present embodiment. In the present embodiment, a device in which data is externally input to a data transmission device will be described as an example. However, the data transmission device includes a recording medium for storing data to be transmitted and is recorded on a recording medium such as a hard disk or an optical disk. It may be a data transmission device that transmits data.

 The data transmitting apparatus 101 shown in FIG. 1 includes a sequence number adding section 1 for adding input data to each packet with a sequence number, and a time for adding a time stamp serving as a reproduction time to each packet. A stamp addition unit 2, a retransmission possible number management unit 3 that manages the number of retransmissions possible for each packet, a transmission data management unit 4 that manages transmission data, and a bucket to which a sequence number and a time stamp are added A transmission buffer 5 for temporarily storing data, a reception unit 6 for receiving a signal indicating the reception state of the reception side, a retransmission request analysis unit 7 for confirming a packet requested to be retransmitted by the reception side, and a packet. A transmitting unit 8 for transmitting a packet to the receiving side, an error correcting code adding unit 9 for adding an error correcting code to a packet read from the transmitting buffer 5, and an antenna 10 for transmitting and receiving data. It is.

When data to be transmitted is input to the data transmitting device 101 for each packet, the sequence number adding unit 1 adds a sequence number that is incremented for each packet for each input packet. . The packet to which the sequence number is added is given to the time stamp adding unit 2, and a time stamp serving as information on the reproduction time on the receiving side is added. This sequence number and timestamp The packet to which is added is temporarily stored in the transmission buffer 5.

The retransmission allowable number management unit 3 is given the sequence number added to the packet by the sequence number addition unit 1. Then, after the transmission period set for the data transmitting apparatus 101 is started, information on the reproduction time on the receiving side for the packet of the sequence number given first is confirmed. The difference between the confirmed playback time and the time input to the data transmission device 101 is divided by the period of the transmission period set for the data transmission device 101, so that the Information on the number of retransmissions is set, and is stored in the retransmission number management unit 3. Then, each time a packet is input to the data transmitting apparatus 101 and the sequence number added to the bucket is given to the retransmittable number management unit 3, the held retransmittable number is added. In the receiving unit 6, a reception confirmation signal such as an ACK signal indicating the reception status of the transmitted packet on the reception side or a transmission period start signal transmitted from a control station or the like indicating the start of a set transmission period. Is received via the antenna 10. In this embodiment, it is assumed that the data transmitting apparatus 101 recognizes the start of the set transmission period by receiving the transmission period start signal, but the period of the set transmission period is set in advance. The start of the transmission period may be recognized each time the period of the transmission period is detected by a timer or the like provided from a control station or the like.

 As described above, when the reception unit 6 receives the transmission period start signal and confirms the start of the transmission period, the remaining retransmission possible number value of each sequence number recorded in the retransmittable number management unit 3 is incremented by one. Decrement by. Then, when the number of retransmittable times added to each sequence number is decremented, retransmittable number management section 3 confirms a sequence number in which the value of the retransmittable number has become equal to or less than a specified value.

The transmission data management unit 4 is notified of the sequence number for which the value of the number of retransmissions becomes equal to or less than the specified value, and the transmission data management unit 4 transmits the packet corresponding to the sequence number notified from the retransmission possible number management unit 3. Discard the packet from transmit buffer 5. The retransmittable number management unit 3 deletes the sequence number of the packet discarded from the transmission buffer 5 from the record. Note that the above-mentioned specified value is a reference value for determining whether or not to prohibit the transmission of the packet on the transmitting side. In the present embodiment, the specified value is set to 0. Shall be.

 The retransmission count management unit 3 monitors the remaining retransmission count added to each held sequence number, and stores it in the transmission buffer 5 when confirming that the transmission period has started. The average value of the number of resend times of the packet is calculated. Then, the transmission data management section 4 determines whether or not the transmission is abnormal, based on whether or not the average value of the number of retransmissions is equal to or less than the reference value. At this time, if the average value of the obtained number of retransmissions is equal to or less than the reference value, it is determined that the transmission is abnormal.

 In addition, the retransmission request analysis unit 7 notifies the transmission data management unit 4 of information on the packet to be retransmitted by analyzing the reception status on the receiving side from the reception confirmation signal received by the reception unit 6. At this time, the retransmission request analysis unit 7 confirms the bucket normally received on the receiving side from the reception confirmation signal, and notifies the transmission data management unit 4 of the sequence number. When the transmission data management unit 4 is notified of the sequence number indicating the packet normally received on the receiving side, the packet of the notified sequence number is discarded from the transmission buffer 5. Thereafter, when the start of the transmission period is confirmed and the transmission period starts, the transmission data management unit 4 determines whether or not the transmission is abnormal, and holds the transmission buffer 5 in the transmission buffer 5 according to the determination. The packet to be transmitted is searched from the retransmitted packet and the new packet.

 Then, after confirming the sequence number of the retrieved packet, the packet is stored in the transmission data management unit 4 and transmitted from the transmission buffer 5 to the error correction code adding unit 9 while controlling so as not to exceed the set transmission period. The output of the packet to be transmitted is controlled. The packet output from the transmission buffer 5 is provided to an error correction code adding unit 9 and added with an error correction code as described later, and then transmitted by the transmission unit 8 to the receiving side via the antenna 10. .

At this time, an error correction code is added to the data transmitted from the transmission unit 8 as shown in FIGS. 4A and 4B. FIGS. 4A and 4B are diagrams showing the format of each packet in the data transmitted in real time from the transmission unit 8. FIG. The packet shown in FIG. 4A is composed of a header 51 containing information such as configuration conditions in the packet, a sequence number 52 and a time stamp 53 added to the packet. The packet is composed of data 54 such as video signals and audio signals included in the packet, and an error correction code 55, and has a configuration in which an error correction code is added for each packet. One packet may be provided with one correction code as in the format shown in FIG. 4A, but as shown in FIG. 4B, the header 15 1 and the sequence number 5 2 and time stamp 53 and data 54 are divided into a plurality of blocks B1 to Bn, and error correction codes b1 to bη are added to each block B1 to Bn. I do not care.

 The bucket discard control operation in the data transmitting apparatus 101 having such a configuration will be described with reference to the flowchart in FIG. When the receiving unit 6 receives the transmission period start signal and confirms the start of the transmission period, the transmission period starts, and the start of the transmission period is notified to the retransmission possible number management unit 3 to start the packet discard control operation. (S 1). Then, the retransmittable number management unit 3 decrements the value of the remaining retransmittable number added to the held sequence number of each packet by one (S 2), and stores it in the transmission buffer 5. When the sequence number corresponding to the oldest packet in the packet is confirmed by the retransmittable number management unit 3, it is determined whether the value of the remaining retransmittable number added to the sequence number is equal to or less than a specified value. (S3). At this time, if it is determined that the value is not less than the specified value (No), the packet discard control operation is terminated.

 If it is determined in S3 that the number is less than the specified value (Y es), the sequence number to which the number of retransmissions that is less than the specified value is added is notified to the transmission data management unit 4, and the transmission data The packet corresponding to the sequence number notified by the management unit 4 is discarded from the transmission buffer 5 (S4). Then, the sequence number of the next oldest packet among the packets stored in the transmission buffer 5 is confirmed (S5), and the process proceeds to S3.

In this way, by repeating the operations of S3 to S5, the sequence numbers of the buckets in which the number of retransmissions becomes equal to or less than the specified value are retransmitted in order from the packet stored in the transmission buffer 5 in the oldest. After being checked by the possible number management unit 3, the transmission data management unit 4 controls discarding from the transmission buffer 5. And, the re- When a sequence number with a large number of transmittable times is confirmed by the retransmittable number management unit 3,

Then, the packet discard control operation ends.

 Next, the transmission control operation in the data transmitting apparatus 101 will be described with reference to the flowchart in FIG. When the receiving unit 6 receives the transmission period start signal and confirms the start of the transmission period, the transmission period starts and the transmission control operation starts (

S 1 1). Then, the average value of the remaining number of retransmittable times added to each sequence number held in the retransmittable number management unit 3 is calculated, and the average value of the remaining number of retransmittable times is equal to or less than the reference value in the transmission data management unit 4. It is determined whether or not the transmission is abnormal by confirming whether or not the transmission is abnormal (S12).

 At this time, if it is determined that the average value of the number of retransmissions that can be retransmitted is larger than the reference value and the transmission is not in an abnormal state (No), the retransmission request analysis unit 7 performs a normal retransmission control by the transmission data management unit 4. The retransmitted packet confirmed in and the new packet to be newly transmitted are searched (S13). In S12, when the average value of the number of retransmissions is less than the reference value and it is determined that the transmission is abnormal (Yes), the retransmission control operation is stopped (S14), and the transmission data management is performed. In part 4, a new bucket to be newly transmitted is searched (S15).

 In S13 and S15, when the retransmission packet to be transmitted or the new packet to be transmitted is confirmed in the transmission data management unit 4, the sequence number of the confirmed packet to be transmitted is transmitted. Stored in 4 (S16). Then, based on the sequence number stored in the transmission data management section 4, it is determined whether or not there is a bucket to be transmitted (S17). At this time, if there is no bucket to be transmitted (No), it is assumed that all the buckets to be transmitted have been transmitted, and the transmission control process ends.

In S17, when it is confirmed that there is a packet to be transmitted (Yes), it is determined whether or not a period long enough to transmit the packet to be transmitted remains. (S18). At this time, when it is determined that a sufficient transmission period does not remain (No), the transmission control process is terminated assuming that the set transmission period has almost ended. When it is determined that a sufficient transmission period remains (Yes), the packet to be transmitted is read out from the transmission buffer 5 and then an error correction code adding unit 9 adds an error correction code to the transmission unit 8. More transmission (S 19). When the bucket is transmitted in S19, the process proceeds to S17, where the sequence number next to the transmitted data is confirmed, and whether or not there is a packet to be transmitted is confirmed. In this way, by repeating the operations of S17 to S19, the sequence numbers of the packets to be transmitted stored in the transmission data management unit 4 are sequentially checked, and there is no packet to be transmitted. Or, when the transmission period is not sufficient and almost complete, the transmission operation control ends.

 Even if a communication system using such a data transmission device does not have a complicated circuit configuration for comparing with time whether or not a packet to be transmitted is in time for the reproduction time on the receiving side, the remaining It can be checked simply by managing the number of retransmissions. The bucket can be discarded by managing the remaining number of resends, so even if the communication path condition deteriorates and the resend capability becomes limited, the resend operation is stopped and the bucket is greatly sent. By discarding from the buffer, quick error recovery can be performed.

 In this embodiment, a new bucket to be newly transmitted is searched for in S15 of the transmission control operation in FIG. 3, but the specified value of the remaining number of retransmissions to be discarded is newly set to a large value. Then, after discarding from the transmission buffer 5 those packets whose remaining number of retransmissions is less than or equal to the newly set specified value from the retransmission packet and the new packet, the remaining number of retransmissions becomes the maximum. Such a retransmission bucket and a new bucket may be searched.

<Second embodiment>

 Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a block diagram showing an internal configuration of a data transmission device used in the communication system of the present embodiment. In the data transmitting apparatus shown in FIG. 5, parts used for the same purpose as the data transmitting apparatus shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. Further, in the present embodiment, similarly to the first embodiment, the data transmission device of FIG. 5 performs the discard control operation of the packet in the transmission buffer 5 according to the flowchart of FIG. Data having a configuration as shown in FIGS. 4A and 4B is transmitted from the transmission unit 8 via the antenna 10.

The data transmission device 102 in FIG. 5 is provided in the data transmission device 101 in FIG. In addition to the blocks described above, a priority adding unit 11 for adding a transmission priority to a packet to which a sequence number is added is provided. The transmission priority is set, for example, according to the type of data included in a packet such as text data, video data, or audio data, or whether the data in the packet is synchronous or asynchronous. And shall be given by a numerical value. Also, the higher the numerical value given as this priority, the higher the priority.

 The sequence number is added to the packet input to the data transmitting apparatus 102 having such a configuration by the sequence number adding unit 1 as in the data transmitting apparatus 101 of FIG. Then, the packet to which the sequence number is added is given to the priority adding section 11 and the priority is added. Then, the time stamp is added in the time stamp adding section 2 and stored in the transmission buffer 5. .

 In addition, the transmission data management unit 4 determines whether or not the transmission is abnormal, and, in accordance with this determination, considers the priority from the retransmission bucket held in the transmission buffer 5 and the new bucket. Search for packets to send. Then, the sequence number of the retrieved bucket is stored in the transmission data management unit 4, and the output control of the bucket is performed on the transmission buffer 5 while managing the transmission sequence so as not to exceed the transmission period.

 The operation of the other blocks in the data transmission device 102 is the same as the operation of the data transmission device 101 in the first embodiment, and a detailed description thereof will be omitted.

 The transmission control operation in the data transmission device 102 having such a configuration will be described with reference to the flowchart in FIG. In the flowchart of FIG. 6, steps that perform the same operations as in the flowchart of FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted. When the receiving unit 6 receives the transmission period start signal and confirms the start of the transmission period, and starts the transmission control operation (S11), it is determined whether or not the transmission is abnormal according to the average value of the number of remaining retransmissions. Is determined (S12).

At this time, if it is determined that the transmission is not abnormal (No), a retransmission bucket to be transmitted and a new bucket are searched (S13). When it is determined in S12 that the transmission is abnormal (Yes), the priority added to each of the retransmission packet and the new packet is checked, and the packet whose priority is equal to or more than the specified value is determined. As a bucket to send (S21). As described above, after searching for packets to be transmitted in S13 and S21, the sequence proceeds to S16 and stores the sequence number of the packet to be transmitted. The packet is transmitted by repeating the operations of S17 to S19 until the transmission time has expired or the transmission period has almost ended.

 Even if the communication path condition deteriorates due to the communication system using such a data transmission device and the retransmission capability becomes the limit, priority is given to the transmission with higher priority, so that, for example, AV data When transmitting, it is possible to prevent frequent interruptions of video and audio.

 In this embodiment, in S21 of the transmission control operation shown in FIG. 6, a search is made for a packet having a high priority from the retransmission packet and the new packet. Similar to the embodiment, after stopping the retransmission control as in S14 in the flowchart of FIG. 3, control is performed in S21 to search for a high-priority packet from among the new packets. It does not matter.

<Third embodiment>

 Hereinafter, a third embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a block diagram showing the internal configuration of the data transmission device used in the communication system of the present embodiment. Note that, in the data transmission device of FIG. 7, parts used for the same purpose as in the data transmission device of FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. Also, in the present embodiment, as in the first embodiment, the data transmission device of FIG. 7 performs the discard control operation of the packet in the transmission buffer 5 according to the flowchart of FIG. The data having the configuration as shown in FIG. 4B is transmitted from the transmission unit 8 via the antenna 10.

The data transmission device 103 of FIG. 7 adjusts the amount of packets input to the data transmission device 103 in addition to the blocks provided in the data transmission device 101 of FIG. This is a configuration in which a bucket amount adjustment unit 12 is provided. In the bucket amount adjusting unit 12, for example, when the data supplied to the data transmitting device 101 is AV data, and when the communication path condition is good, high-definition HDTV AV data is transmitted. Thus, all buckets input from the outside are output to the subsequent block. In addition, when the communication path condition deteriorates, the bit-rate is higher than the standard HDTV AV data. The packet amount adjustment unit 12 thins out packets input from the outside and outputs the data to the subsequent block so that AV data for SDTV with low data rate is transmitted.

 Also, in the case of information such as text data used for the system other than video and audio that is not necessary for reproduction on the receiving side in an MPEG-2 system or the like, the packet amount adjustment unit 12 In this case, the amount of input packets may be adjusted by thinning out packets containing data that is not necessary for reproduction.

 The packet input to the data transmitting apparatus 103 having such a configuration is adjusted by the packet amount adjusting unit 12 to a packet amount according to the communication path state, and is provided to the sequence number adding unit 1. The packet given to the sequence number adding unit 1 is stored in the transmission buffer 5 after the sequence number and the time stamp are added in order similarly to the data transmitting apparatus 101 of FIG.

 Further, the transmission data management unit 4 determines whether or not the transmission is in an abnormal state, and determines whether or not to adjust the amount of the inputted bucket by the bucket amount adjustment unit 12 according to the determination. . When searching for data to be transmitted from the retransmission packet held in the transmission buffer 5 and the new packet, the packet amount reduced by the thinning rate in the packet amount adjustment unit 12 is used. Search for a packet. Therefore, for example, when the thinning rate is 1/2, when the sequence number stored in the transmission data management unit 4 during a normal transmission operation is a continuous number from 1 to 100, the packet amount When the thinning operation is performed by the adjustment unit 12, the sequence numbers stored in the transmission data management unit 4 are 1 to 50.

 The operation of the other blocks in the data transmission device 103 is the same as the operation of the data transmission device 101 in the first embodiment, and a detailed description thereof will be omitted.

The transmission control operation in the data transmission device 103 having such a configuration will be described with reference to the flowchart in FIG. In the flowchart of FIG. 8, steps that perform the same operations as those in the flowchart of FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted. When the receiving unit 6 receives the transmission period start signal and confirms the start of the transmission period, and starts the transmission control operation (S11), it is determined whether or not the transmission is abnormal according to the average value of the number of remaining retransmissions. Is determined (S12). At this time, if it is determined that the transmission is not abnormal (No), a retransmission packet to be transmitted and a new packet are searched (S13). If it is determined in S12 that the transmission is abnormal (Yes), the packets are thinned out in the packet amount adjustment unit 12 so that the packet amount given to the sequence addition unit 1 is reduced. Adjusted (S31). Further, at this time, the thinning rate in the packet amount adjustment unit 12 is given to the transmission data management unit 4.

 After the packet amount is adjusted, the transmission data management unit 4 sets the amount of packets to be transmitted based on the given thinning rate, and transmits a retransmission packet and a new packet according to the amount of packets. Is searched (S32). In this way, after searching for packets to be transmitted in S13 and S32, the sequence proceeds to S16 to store the sequence number of the packet to be transmitted. The packet is transmitted by repeating the operations of S17 to S19 until the transmission period is almost completed.

 Even in the case where the communication channel state deteriorates due to the communication system using such a data transmission device and the retransmission capability becomes limited, the packet amount adjustment unit 12 controls the data transmission device 103 By reducing the amount of data to be processed in, for example, when transmitting AV data, it is possible to prevent frequent interruption of video and audio.

 Note that, in this embodiment, as in the first embodiment, after stopping the retransmission control as in S14 in the flowchart of FIG. 3, transmission is performed from only the new bucket in S32. It may be controlled to search for the packet to be used.

 Further, in the present embodiment, as shown in FIG. 7, the packet adjusting unit 12 is provided before the sequence number adding unit 1, but as in the data transmitting device 104 of FIG. The packet adjusting unit 12 may be provided between the time stamp adding unit 2 and the transmission buffer 5. By doing so, it is possible to search for a packet to be transmitted without giving the thinning rate in the bucket adjustment unit 12 to the transmission data management unit 4.

Therefore, for example, when the thinning rate is 1/2, the sequence number stored in the transmission data management unit 4 when performing a normal transmission operation is a sequence of 1, 2, 3, ..., 100 When the number is a number, when the packet amount adjusting unit 12 performs the thinning operation, the packet amount adjusting unit 12 sets the sequence number 2, 4, 6, 6,... Are stored in the transmission buffer 5 after being decimated, the sequence numbers stored in the transmission data management unit 4 are 1, 3, 5,...

 In addition to the data transmitting device 104 of FIG. 9, like the data transmitting device 105 of FIG. 10, the data transmitting device is provided between the time stamp adding unit 2 and the bucket amount adjusting unit 12. The priority adding unit 11 may be provided. This priority adding section 11 is the same as that provided in the data transmitting apparatus 102 of the second embodiment (FIG. 5). By doing so, when performing the thinning operation in the packet amount adjusting unit 12, based on the priority added by the priority adding unit 11, the bucket with a priority lower than the predetermined value is thinned out. Output to transmission buffer 5.

 In each of the above embodiments, each time the retransmission possible number management unit 3 confirms the start of the set transmission period, the remaining number added to each sequence number stored in the retransmission possible number management unit 3 is checked. Although the value of the number of possible retransmissions is decremented, the value of the number of remaining retransmissions is decremented when a certain time has elapsed since the last transmission operation end time because buckets are transmitted periodically. It does not matter. At this time, either the lapse of a fixed time after the end of transmission or the confirmation of the start of the transmission period may be used as a trigger to decrement the value of the number of remaining retransmissions. Irrespective of this, the remaining number of retransmissions may be decremented when a certain time has elapsed after the end of transmission.

 That is, in the flowchart of FIG. 2 showing the bucket discarding control operation of each of the above-described embodiments, the operation of decrementing the remaining number of retransmissions allowed in S2 is that a certain period of time has elapsed after the end of transmission, or the start of the transmission period. It may be performed by confirming any of the above, or by confirming the elapse of a certain period of time after the end of transmission, regardless of whether the transmission period has been confirmed or not.

Further, in each of the above-described embodiments, whether or not an abnormal state is determined by using the average value of the number of retransmissions of the packet stored in the transmission buffer 5, but the number of retransmissions of the actually transmitted packet is determined. The average value may be used to determine an abnormal state. At this time, first, after receiving from the reception confirmation signal received by the reception unit 6 after transmission from the transmission unit 8, The correct reception is confirmed by the retransmission request analyzer 7. When the number of retransmissions possible for each bucket confirmed to be correctly received is confirmed by the retransmission number management unit 3, the average value is obtained and notified to the transmission data management unit 4. If the calculated average value is less than the reference value, it is determined that the transmission is abnormal.In addition, the number of packets discarded from the transmission buffer 5 due to the number of retransmissions becoming less than the specified value causes transmission error. The state may be determined. At this time, the retransmission request analysis unit 7 counts the number of serial numbers notified to the transmission data management unit 4 when the value of the number of retransmissions becomes equal to or less than the specified value. Then, the number of counted serial numbers is given to the transmission data management unit 4, and when the number of serial numbers exceeds the reference value (that is, the amount of discarded packets exceeds the reference value). ), It is determined that the transmission is abnormal. The packet amount of the discarded packet for determining the abnormal transmission state may be the packet amount of the packet discarded at the start of the transmission period, or may be the packet amount counted at the predetermined period. I do not care.

 That is, in the flowcharts of FIGS. 3, 6, and 8 showing the transmission control operation of each of the above-described embodiments, when it is determined at s12 whether or not the transmission is abnormal, the transmission is actually performed. Judgment may be made based on the average value of the number of retransmittable packets that have been performed, or the number of packets discarded because the number of retransmittable times from the transmission buffer has fallen below the specified value.

 Also, in the data transmitting apparatus, the average value of the number of retransmissions that can be confirmed to be in the transmission abnormal state when operating in the normal state or the reference value for the discarded packet amount is used as the first reference value, The average value of the number of resends or the reference value for the amount of discarded packets, which confirms that the communication path has been improved when operating in the abnormal transmission state, is used as the second reference value. The reference values may be different. At this time, the relationship between the first and second reference values with respect to the average value of the number of retransmissions is set as the second reference value> the first reference value, and the first and second reference values with respect to the amount of discarded packets. The relationship is: 1st reference value> 2nd reference value.

Further, in each of the above-described embodiments, an error detection code addition unit that adds an error detection code may be used instead of the error correction code addition unit 9. At this time, each data of the packet Is added with an error detection code. Also, as an example of a packet configuration, a sequence number follows one header as in the bucket in FIG. 4A or FIG. 4B. The sequence number may be included. Also, the time stamp may not be included in the bucket, and the time stamp may be used only for management in the data transmission device.

 Further, as the reception confirmation signal, an ACK signal indicating a packet correctly received on the receiving side, a NACK signal indicating a packet not received on the receiving side, or the like may be used. Further, although the description has been given based on an example of use for a wireless communication system using an antenna, the present invention may be used for a wired communication system such as a power line communication system using a power line or a communication system using a cable line. 'Further, in each of the above-described embodiments, the number of retransmittable times of each packet is set by dividing the difference between the reproduction time and the time input to the data transmission device by the set transmission period. However, the type of data of each packet may be determined, and the number of retransmissions determined in advance by the data transmitting apparatus may be set for each type. In other words, if the number of retransmissions allowed for a packet based on AV data is predetermined as Nx and the number of retransmissions available for a packet based on text data is predetermined as Ny, If the bucket input to the device is AV data, set the number of retransmissions as NX, and if the bucket input to the data transmission device is text data, set the number of retransmissions as Ny.

In each of the above embodiments, when the transmission period start signal is received and the start of the transmission period is confirmed, the number of retransmissions given to the packet is decremented, and the value becomes equal to or less than the specified value. When the transmission period start signal is received and the start of the transmission period is confirmed, the number of retransmissions given to the packet is incremented and the value is set to the specified value. In this case, the packet may be discarded. Further, at this time, when judging from the average value of the number of retransmissions possible for the packet stored in the buffer, when the average value of the number of retransmissions exceeds the reference value, it is determined that the transmission is abnormal. Is done. When judging from the average value of the number of resend times of transmitted packets, It is determined that the transmission is abnormal when the average of the number of possible times exceeds the reference value.

Industrial applicability

 ADVANTAGE OF THE INVENTION According to the present invention, by monitoring the number of retransmissions given for each bucket of data, it is possible to discard the bucket that is not in time for the reproduction time in the data receiving device and check the communication abnormal state. . Therefore, unlike the conventional case, the comparison between the reproduction time and the current time is not always performed by the data transmission device, and the bucket is easily discarded and the abnormal communication state is confirmed only by the number of retransmissions possible. The circuit configuration in can be simplified. In addition, in the data transmitting apparatus, when a communication abnormal state is detected, quick error recovery can be achieved by stopping retransmission control.

 'In addition, the data transmission device is provided with a priority addition unit to add a priority to each packet of data, and according to the added priority, when a communication error condition is detected, the priority is increased from the highest priority. Can be sent. By doing so, for example, at the time of AV data communication, a data receiving device that receives data can perform reproduction such that interruption of data is felt as little as possible. Also, the data transmission device may be provided with a packet amount adjusting unit to start control to reduce the amount of data given to the buffer when a transmission error occurs, thereby reducing the packet amount of data to be transmitted. it can. At this time, data other than the minimum data required for reproduction is thinned out by the packet amount adjustment unit, so that the data receiving device that receives data can perform reproduction that makes the data interruption as small as possible. it can.

Claims

The scope of the claims 1. In a data communication system including a data transmission device having a buffer for storing data for each first data unit, and a data reception device receiving data transmitted by the data transmission device. A data communication method in which the data transmitting device confirms data requested by the data receiving device for retransmission,  In the data transmission device,  For the data stored in the buffer, for each second data unit, the data receiving apparatus is provided with a retransmission count, which is information indicating whether retransmission is possible, to the buffer at every predetermined timing. Changing the number of resends assigned to each of the stored data,  A data communication method comprising: discarding, from the buffer, data for each of the first data units for the number of retransmissions that exceeds a predetermined specified value. 2. The number of retransmissions given when the data is stored in a buffer is calculated by dividing a difference between a time when the data is input and a reproduction time of the data by a predetermined period. 2. The data communication method according to claim 1, wherein: 3. A transmission period for transmitting the data is periodically given to the data transmission device, and the predetermined period is an integral multiple of a period in which the transmission period is given. 3. The data communication method according to claim 2. 4. The data communication method according to claim 2, wherein the predetermined timing is when the predetermined period has elapsed. 5. The data communication method according to claim 2, wherein the predetermined timing is when a transmission period given to the data transmission device starts. 6. The predetermined timing is determined when the predetermined period elapses or the data transmission device is affected. 3. The data communication method according to claim 2, wherein one of the start of the obtained transmission period is confirmed. 7. The data communication method according to claim 1, wherein the number of retransmissions given when the data is stored in a buffer is set according to an attribute of the data. 8. At each of the predetermined timings, subtract the number of retransmissions assigned to each of the data stored in the buffer,  The data according to any one of claims 1 to 7, wherein the data for each of the first data units for the number of retransmissions that has become equal to or less than the predetermined specified value is discarded from the buffer. Communication method. 9. At each of the predetermined timings, add the number of resends assigned to each of the data stored in the buffer,  The data according to any one of claims 1 to 7, wherein the data for each of the first data units for the number of retransmissions that has become equal to or greater than the predetermined specified value is discarded from the buffer. Communication method. 10. A data communication system comprising: a data transmission device having a buffer for storing data for each first data unit; and a data reception device for receiving data transmitted by the data transmission device, wherein the data reception device A data communication method in which the data transmission device confirms data requested to be retransmitted,  In the data transmission device,  For the data stored in the buffer, for each second data unit, the data receiving device is provided with a retransmission count, which is information indicating whether retransmission is possible. Changing the number of resends assigned to each of the stored data, For each data of the first data unit stored in the buffer, A data communication method, characterized in that when the number of retransmissions exceeds a reference value, it is confirmed that a communication error has occurred, and the amount of data to be transmitted is reduced. 11. The data communication method according to claim 10, wherein the data for each of the first data units for the retransmittable number of times exceeding a predetermined specified value is discarded from the buffer. 1 2. At each of the predetermined timings, subtract the number of retransmissions assigned to each of the data stored in the buffer,  When the retransmittable number of times for each of the data in the first data unit stored in the buffer falls below a reference value, it is confirmed that a communication error has occurred, and the amount of data to be transmitted is reduced. The data communication method according to claim 10, wherein 13. The data communication method according to claim 12, wherein the data for each of the first data units for the number of retransmissions that has become equal to or less than a predetermined value is discarded from the buffer. 14. At each of the predetermined timings, add the number of retransmissions assigned to each of the data stored in the buffer,  When the number of retransmissions for each of the first data units stored in the buffer exceeds a reference value, it is confirmed that a communication error has occurred and the amount of data to be transmitted is reduced. The data communication method according to claim 10. 15. The data communication method according to claim 14, wherein the data for each of the first data units for the retransmittable number of times equal to or greater than a predetermined specified value is discarded from the buffer. 16. A data communication system comprising: a data transmitting device having a buffer for storing data for each first data unit; and a data receiving device receiving data transmitted by the data transmitting device, wherein the data receiving device A data communication method in which the data transmission device confirms data requested to be retransmitted,  In the data transmission device,  For the data stored in the buffer, for each second data unit, the data receiving device is provided with a retransmission count, which is information indicating whether retransmission is possible. Changing the number of resends assigned to each of the stored data,  When the retransmittable number of times for each of the first data units transmitted during the transmission period assigned to the data transmission device exceeds a reference value, it is confirmed that the communication is in an abnormal state, and the data to be transmitted is transmitted. A data communication method characterized by reducing the amount. 17. The data communication method according to claim 16, wherein the data for each of the first data units for the number of retransmissions that exceeds a predetermined specified value is discarded from the buffer. 18. For each of the predetermined timings, subtract the number of retransmissions assigned to each of the data stored in the buffer,  When the number of retransmissions for each of the first data units transmitted during the transmission period falls below a reference value, it is confirmed that a communication error has occurred, and the amount of data to be transmitted is reduced. The data communication method according to claim 16, wherein 19. The data communication method according to claim 18, wherein the data for each of the first data units corresponding to the retransmittable number of times equal to or less than a predetermined specified value is discarded from the buffer. 20. At each of the predetermined timings, add the number of retransmissions assigned to each of the data stored in the buffer,  When the retransmittable number of times for each of the data of each of the first data units transmitted during the transmission period exceeds a reference value, it is confirmed that a communication error has occurred, and the amount of data to be transmitted is reduced. The data communication method according to claim 16, wherein 21. The data communication method according to claim 20, wherein the data for each of the first data units for the retransmittable number of times equal to or greater than a predetermined specified value is discarded from the buffer. 22. A data communication system comprising: a data transmission device having a buffer for storing data for each first data unit; and a data reception device for receiving data transmitted by the data transmission device, wherein the data reception device A data communication method in which the data transmission device confirms data requested to be retransmitted,  In the data transmission device,  For the data stored in the buffer, for each second data unit, the data receiving device is provided with a retransmission count, which is information indicating whether retransmission is possible. Changing the number of resends assigned to each of the stored data,  Data for each of the first data units for the number of retransmissions that exceeds a prescribed value is discarded from the buffer,  When the amount of data discarded from the buffer exceeds a reference value, it is confirmed that there is a communication error or state, and the amount of data to be transmitted is reduced. 23. At each of the predetermined timings, subtract the number of retransmissions assigned to each of the data stored in the buffer, The first data unit for the number of retransmissions that has become less than the predetermined value 23. The data communication method according to claim 22, wherein each data is discarded from said buffer. 24. At each of the predetermined timings, add the number of retransmissions assigned to each of the data stored in the buffer,  33. The data communication method according to claim 22, wherein the data for each of the first data units for the retransmittable number of times equal to or greater than the predetermined specified value is discarded from the buffer. 25. calculating the number of retransmissions given when the data is stored in the buffer by dividing a difference between a time when the data is input and a reproduction time of the data by a predetermined period. The data communication method according to claim 10 or claim 11 or claim 16 or claim 17 or claim 22 which is a feature. 26. A transmission period for transmitting the data is periodically given to the data transmission device, and the predetermined period is a period that is an integral multiple of a period in which the transmission period is given. 26. The data communication method according to claim 25, wherein 27. The data communication method according to claim 25, wherein the predetermined timing is when the predetermined period has elapsed. 28. The data communication method according to claim 25, wherein the predetermined timing is when a transmission period given to the data transmission device has started. 29. The method according to claim 25, wherein the predetermined timing is a timing when either the lapse of the predetermined period or the start of a transmission period given to the data transmission device is confirmed. Data communication method. 30. The claim 10 or claim 11 or claim wherein the number of retransmissions given when the data is stored in the buffer is set according to the attribute of the data. The data communication method according to claim 16 or claim 17 or claim 22. 31. In the data transmission device, when it is confirmed that the communication is in the abnormal state, retransmission control of data requested to be retransmitted from the data reception device is stopped, and data to be newly transmitted to the data reception device. The data communication method according to claim 10 or claim 11 or claim 16 or claim 17 or claim 22. 32. In the data transmitting apparatus, when it is confirmed that the communication is in the abnormal state, after the predetermined specified value is changed to increase the amount of data to be discarded from the buffer and discard the data. The data requested to be retransmitted from the data receiving device and the data newly transmitted to the data receiving device are read from the buffer and transmitted. The data communication method according to claim 16 or claim 17 or claim 22. 33. The data transmitting apparatus further includes a priority adding unit that adds a priority to each data of the first data unit in accordance with an attribute of the data.  When it is confirmed that the communication is in an abnormal state, among the data requested to be retransmitted from the data receiving device and the data newly transmitted to the data receiving device, the data having a higher priority is read out from the buffer and transmitted. The data communication method according to claim 10, wherein the claim 10 or claim 11 or claim 16 or claim 17 or claim 22 is performed. 34. In the data transmitting apparatus, a data amount adjusting unit that adjusts an amount of data given to the buffer is provided. When it is confirmed that the communication is abnormal, the data amount adjustment unit Claim 10 or Claim 11 or Claim 16 or Claim 17 or Claim 17 wherein the data input to the data transmitting apparatus is thinned to reduce the amount of data given to the buffer. A data communication method according to range 22. 35. The data transmitting apparatus, further comprising: a priority adding unit that adds a priority to each data of the first data unit according to an attribute thereof,  When it is confirmed that the communication is abnormal, the data amount adjustment unit reduces the data amount given to the buffer by thinning out the low priority data among the data input to the data transmission device. A data communication method according to claim 34, wherein the data communication method is characterized in that: 3 6. A buffer for storing data for each first data unit,  A transmission unit for transmitting the data stored in the buffer,  A receiving unit that receives a reception acknowledgment signal that notifies a reception state of the data receiving device that receives the data,  A retransmission request analysis unit that confirms a reception state of the data reception device based on the reception confirmation signal received by the reception unit, and recognizes data that the data reception device requests retransmission;  For the data stored in the buffer, for each second data unit, the data receiving apparatus is provided with a retransmittable number of times as information indicating whether retransmission is possible, and a value of the retransmittable number is given. A resend count management unit for checking  A transmission data management unit that performs discarding of data in the buffer and input / output control,  The retransmittable number management unit changes the retransmittable number assigned to each of the data stored in the buffer at a predetermined timing, A data transmission device, wherein the transmission data management unit confirms data for each of the first data units for the number of retransmissions that exceeds a prescribed value and discards the data from the buffer. 3 7. A buffer for storing data for each first data unit,  A transmission unit for transmitting the data stored in the buffer;  A receiving unit that receives a reception acknowledgment signal that notifies a reception state of the data receiving device that receives the data,  A retransmission request analysis unit that confirms a reception state of the data reception device based on the reception confirmation signal received by the reception unit, and recognizes data that the data reception device requests retransmission;  For the data stored in the buffer, for each second data unit, the data receiving apparatus is provided with a retransmittable number of times as information indicating whether retransmission is possible, and a value of the retransmittable number is given. A resend count management unit for checking  A transmission data management unit for confirming whether or not there is a communication abnormal state based on the number of retransmissions possible for each data of the first data unit stored in the buffer,  To  The retransmittable number management unit changes the retransmittable number assigned to each of the data stored in the buffer at a predetermined timing,  When the number of retransmissions for each of the first data units stored in the buffer exceeds a reference value, the transmission data management unit confirms that a communication error has occurred, and confirms the amount of data to be transmitted. A data transmission device characterized in that the data transmission is reduced. 38. The transmission data management unit checks data for each of the first data units corresponding to the retransmittable number of times exceeding a predetermined specified value, and discards the data from the buffer. A data transmission device according to claim 1. 3 9. A buffer for storing data for each first data unit,  A transmission unit for transmitting the data stored in the buffer, A receiving unit that receives a reception acknowledgment signal that notifies a reception state of the data receiving device that receives the data, A retransmission request analysis unit that confirms a reception state of the data reception device based on the reception confirmation signal received by the reception unit, and recognizes data that the data reception device requests retransmission;  For the data stored in the buffer, for each second data unit, the data receiving apparatus is provided with a retransmittable number of times as information indicating whether retransmission is possible, and a value of the retransmittable number is given. A resend count management unit for checking  A transmission data management unit for confirming whether or not there is a communication abnormal state based on the number of retransmissions possible for each of the first data units transmitted during a transmission period allocated to the data transmission device;  With  The retransmittable number management unit changes the retransmittable number assigned to each of the data stored in the buffer at a predetermined timing,  The transmission data management unit is in a communication abnormal state when the number of retransmissions for each of the first data units transmitted during the transmission period allocated to the data transmission device exceeds a reference value. A data transmission device characterized in that the data transmission amount is reduced and the amount of data to be transmitted is reduced. 40. The transmission data management unit according to claim 39, wherein the data for each of the first data units corresponding to the number of retransmissions exceeding a prescribed value is confirmed and discarded from the buffer. A data transmission device according to claim 1. 4 1. A buffer for storing data for each first data unit,  A transmission unit that transmits the data stored in the buffer;  A receiving unit that receives a reception acknowledgment signal that notifies a reception state of the data receiving device that receives the data,  A retransmission request analysis unit that confirms a reception state of the data reception device based on the reception confirmation signal received by the reception unit, and recognizes data that the data reception device requests retransmission; For the data stored in the buffer, for each second data unit, the data A retransmission possible number management unit that provides the receiving apparatus with a retransmission possible number serving as information indicating whether or not retransmission is possible, and checks a value of the retransmission possible number;  A transmission data management unit that performs discarding and input / output control of data in the buffer, and confirms whether or not there is a communication abnormal state based on the amount of data discarded from the buffer;  With  The retransmittable number management unit changes the retransmittable number assigned to each of the data stored in the buffer at a predetermined timing,  The transmission data management unit confirms data for each of the first data units for the number of retransmissions that exceeds a predetermined specified value, discards the data from the buffer, and reduces the amount of data discarded from the buffer. A data transmission device characterized in that when the value exceeds a reference value, it is confirmed that a communication error has occurred and the amount of data to be transmitted is reduced. 4 2. A sequence number adding unit for adding a sequence number to the data for each first data unit;  A reproduction time adding unit that adds a reproduction time to be reproduced by the data receiving device to the data for each of the first data units;  With  37. The buffer according to claim 36, wherein the data of the first data unit to which the sequence number and the reproduction time are added by the sequence number addition unit and the reproduction time addition unit are stored in the buffer. A data transmission device, which is a data transmission device. 4 3. A priority adding unit that adds a priority to each data of the first data unit according to its attribute, The data to which the priority is added by the priority adding unit is stored in the buffer, and when it is confirmed by the transmission data management unit that the communication is abnormal, a retransmission request is issued from the data receiving device. Data and newly received data The data transmission device according to any one of claims 37 to 41, wherein, among data to be transmitted to the device, high-priority data is read from the buffer and transmitted from the transmission unit. 4 4. a sequence number adding unit that adds a sequence number to the data for each of the first data units;  A reproduction time adding unit that adds a reproduction time to be reproduced by the data receiving device to the data for each of the first data units;  With  3. The buffer according to claim 3, wherein the data of the first data unit to which the sequence number and the reproduction time are added by the sequence number addition unit and the reproduction time addition unit are stored in the buffer. A data transmission device, which is the data transmission device according to claim 1. 45. A priority adding section for adding a priority to each data of the first data unit according to its attribute,  The data to which the priority is added by the priority adding unit is stored in the buffer, and when it is confirmed by the transmission data management unit that the communication is abnormal, a retransmission request is issued from the data receiving device. 47. The data transmission method according to claim 44, wherein, of the data and the data to be newly transmitted to the data reception device, data having a high priority is read from the buffer and transmitted from the transmission unit. Communication device. 46. A data amount adjusting unit that adjusts an amount of data to be provided in the buffer, and when the transmission data management unit confirms that the communication is abnormal, the data amount adjusting unit includes: The data amount input to the buffer is thinned out to reduce the data amount given to the buffer. 2. The data transmission device according to any one of 1. 47. A priority adding section for adding a priority to each data of the first data unit according to its attribute,  47. The data transmission device according to claim 46, wherein the data to which the priority is added by the priority adding unit is stored in the buffer. 48. A sequence number adding unit that adds a sequence number to the data for each of the first data units.  A reproduction time adding unit that adds a reproduction time to be reproduced by the data receiving device to the data for each of the first data units;  A data amount adjustment unit that adjusts the amount of data to be provided in the buffer;  With  For the data output from the data amount adjustment unit, the sequence number addition unit and the reproduction time addition unit respectively add the sequence number and the reproduction time, and then store the data in the buffer.  When the transmission data management unit confirms that the communication is in the abnormal state, the data amount adjustment unit may reduce the amount of data to be provided to the buffer by thinning out the amount of data input to the data transmission device. The data transmission device according to any one of claims 37 to 41. 49. A priority adding unit that adds a priority to each data of the first data unit according to its attribute,  49. The data transmitting apparatus according to claim 48, wherein the data to which the priority is added by the priority adding unit is stored in the buffer. 50. A data amount adjusting unit for adjusting the amount of data to be provided in the buffer, wherein the sequence number adding unit and the reproduction time adding unit respectively add the sequence number and the reproduction time to the data. The data amount is adjusted by the data amount adjustment unit and stored in the buffer, When the transmission data management unit confirms that the communication is abnormal. The data transmission device according to claim 44, wherein the data amount adjustment unit thins out the data amount given to the sequence number adding unit and reduces the data amount given to the buffer. 5 1. A priority adding unit for adding a priority to each data of the first data unit according to its attribute,  When the transmission data management unit confirms that the communication is abnormal, the data amount adjustment unit thins out the low-priority data and reduces the amount of data to be provided to the buffer. Item 50. The data transmission device according to Item 50.