JP5376855B2 - Data transmission apparatus and data transmission method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To raise a probability of data restoration when performing burst transmission for the unit of a frame, while using FEC, on moving image or audio data packets. <P>SOLUTION: While considering the situation of packet missing that may occur actually on a network with a high probability, a transmission order of data packets that become the base of generating an FEC packet for controlling the transmission order of data packets is devised. Thus, even in FEC employing a parity code, high durability can be provided against burst missing of a packet caused by network congestion or the like, thereby increasing a data recoverable probability when packet missing occurs. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a data transmission apparatus and a data transmission method, and more particularly to a technique suitable for use in transmitting a packet including data generated by error correction coding via a wired or wireless network.

  In recent years, with the development of communication systems, viewing of moving image data through a communication line such as the Internet is generally performed. However, moving image data requires a relatively large data communication band.

  When communicating moving image data such as live video, real-time performance is particularly required. For this reason, when moving image data is transmitted over a long period of time, a format called RTP (A Transport Protocol for Real-Time Applications) is common.

  RTP is a protocol for transferring data such as voice and moving images in real time, and is defined as RFC1889 and RFC1890 by IETF. RTP is an upper protocol of UDP (User Datagram Protocol). In communication processing, instead of securing resources and compensating for communication errors, the communication speed can be expected from a relatively simple mechanism.

  However, as described above, since RTP does not compensate for communication errors, there is a concern that when a packet loss occurs in the communication path, the transferred voice or moving image is disturbed. Therefore, there is a technique for retransmitting a packet lost due to a communication error (this is referred to as retransmission control) when transferring voice or moving image data using RTP. It is also known to avoid communication errors by a technique called FEC (Forward Error Correction).

  FEC is a technique for recovering packet loss that occurs during data transfer by using an error correction code technique. On the transmission side, redundant data necessary for data restoration processing on the reception side is generated from the transmission data by error correction coding, and is added to the transmission data and transmitted.

  On the other hand, on the receiving side, when an error in the received data and a missing packet are detected, the packet in error can be restored using the received normal data and redundant data. Both FEC and packet retransmission control are techniques for recovering packet errors in the communication path, but FEC adds redundant data generated from transmission data, so the amount of data to be transmitted increases. There is a demerit to do. However, as compared with the case where retransmission control is used, there is no time loss associated with retransmission, and therefore, it is used for the purpose of particularly reducing transmission delay.

  As types of FEC, there are block coding in which an information bit string is divided into blocks and coding is performed for each block, and convolutional coding in which the coding of each block still depends on the block. Among them, well-known coding methods include parity (XOR) code, BCH code, and Reed-Solomon code, which belong to block coding.

  When FEC is used when transferring media data such as moving image data, a parity code is often used at present, but recently, a Reed-Solomon code is also used. In both of these encoding methods, in general, the processing load is lighter in the parity encoding, and the Reed-Solomon code is more efficient in the compression rate of redundant data. The Reed-Solomon code is also superior against packet burst loss.

  That is, except for the processing load, the Reed-Solomon code is generally superior to the parity code, but there are cases where the Reed-Solomon code cannot be adopted due to restrictions on the processing capability of the transmission / reception device.

  With a parity code, if a packet storing redundant data generated from several data packets (hereinafter referred to as an FEC packet) is lost, the original data packet cannot be restored. In order to solve such problems, a method has been proposed in which, when a packet is transmitted in bursts, FEC packet loss is reduced by transmitting the FEC packet before the data packet (for example, Patent Documents). 1).

JP 2005-136546 A

  However, the method for determining the transmission order of FEC packets in the above-described conventional technique does not always give a good result depending on the transmission order of data packets transmitted thereafter.

For example, even if the loss of FEC packets can be avoided, if a large number of originally required data packets are lost, redundant FEC packets are received preferentially, so the number of important data packets received It may become less. In such a case, there arises a problem that the number of packets that cannot be restored increases as a result.
The present invention has been made in view of the above-described problems, and an object of the present invention is to increase the probability that data can be restored when packet loss occurs.

A data transmission apparatus according to the present invention is a data transmission apparatus that transmits data via a network, the packet generation means generating a plurality of data packets storing the data to be transmitted, and the data generated by the packet generation means A group dividing means for dividing the packet into a plurality of groups; and an error correction packet storing error correction data for repairing a missing packet that was not transmitted due to an error during network transmission of the data packet. divided group - error correction packet generating means for generating for each flop, for each of the groups, and the packet selecting means for the error correction packets to select the data packets within the missing number of packets that can be repaired, the packet Transmission control means for controlling the transmission order, and Shin control means, the transmission order of data packets selected by the packet selecting means, and controls so that after the last group of the plurality of groups.

The data transmission method of the present invention is a data transmission method for transmitting data via a network, the packet generation step generating a plurality of data packets storing the data to be transmitted, and the data generated in the packet generation step A group dividing step of dividing the packet into a plurality of groups, and an error correction packet storing error correction data for repairing a missing packet that has not been transmitted due to an error during network transmission of the data packet. divided group - an error correction packet generation step of generating per-flop, for each of the groups, the packet selecting step of error correction packets to select the data packet within the number of missing packets that can be repaired, the packet A transmission control step for controlling the transmission order, Serial transmission control step, the transmission order of data packets selected in the packet selecting step, and controlling such that after the last group of the plurality of groups.

A computer program of the present invention is a program for causing a computer to execute a data transmission method for transmitting data via a network, the packet generation step for generating a plurality of data packets storing the data to be transmitted, and the packet generation step An error correction packet storing error correction data for repairing a missing packet that was not transmitted due to an error during network transmission of the data packet; guru divided in the group division process - an error correction packet generation step of generating per-flop, for each of the groups, the packet selecting step the error correction packets to select the data packets within the missing number of packets that can be repaired And the packet And a transmission control step of controlling the transmission sequence, the transmission control step, the transmission order of data packets selected in the packet selecting step is controlled to be later than the last group of the plurality of groups Each process of the data transmission method is executed by a computer.

According to the present invention, an error in which data packets storing data to be transmitted are divided into a plurality of groups, and error correction data is stored to repair missing packets that were not transmitted due to errors in network transmission of the data packets. A correction packet is generated for each of the divided groups, and for each group, a data packet within the number of missing packets that can be repaired by the error correction packet is selected, and the selected data packet The transmission order is made after the last group of the plurality of groups. As a result, the amount of data that can be restored by the error correction code can be improved, and the inconvenience of reducing the number of received data packets can be avoided while avoiding missing error correction packets .

(First embodiment)
FIG. 1 is a block diagram illustrating a basic configuration example of a moving image data transmission apparatus according to an embodiment of the present invention.
As illustrated in FIG. 1, the moving image data transmission apparatus 100 includes a control unit 10, a moving image / audio input unit 101, an encoding unit 102, an RTP packet generation unit 103, an FEC packet generation unit 104, and a packet transmission buffer 105. doing. In addition, a scheduling unit 106 and a packet transmission unit 107 are included. The operation of each unit of the moving image data transmission apparatus 100 is controlled by the control unit 10.

  The encoding unit 102 compresses the data amount by encoding the moving image and audio data input from the moving image / audio input unit 101 by, for example, the MPEG-4 system. The method of compressing moving image data is not limited to MPEG-4, but MPEG-2 and H.264. An encoding method such as H.264 may be used.

  The RTP packet generation unit 103 divides the data encoded by the encoding unit 102 into a size suitable for communication, and generates a plurality of RTP data packets by adding a header necessary for communication as an RTP protocol. To do.

  The FEC packet generation unit 104 generates an FEC packet according to a predetermined redundancy from the RTP packet generated by the RTP packet generation unit 103. The generated RTP packet and FEC packet are temporarily stored in the packet transmission buffer 105.

  The RTP packet and FEC packet temporarily stored in the packet transmission buffer 105 are controlled by the control unit 10 according to the transmission order and transmission time determined by the scheduling unit 106 and transmitted from the packet transmission unit 107 to the transmission path 108. The Here, the transmission path 108 is a transmission path represented by various networks, and in this embodiment, is a network that transmits packetized moving image and audio data.

  By the way, there are various causes of packet loss that occurs when data communication is performed via a network such as the Internet. One of the typical causes is congestion of the network bandwidth.

  Due to the congestion of the network bandwidth, if there are too many packets that try to pass within a relatively short period of time in communication devices such as hubs and routers that make up the network, there will be insufficient buffers to process the packets. Packet loss occurs.

  In addition, moving image data and audio data are generally composed of a plurality of frames per second. Therefore, when communication is performed by packetizing these pieces of data, it is common to generate packets in units of frames constituting each and transmit them in units of frames.

  In such a transmission method, the state of packet loss when network congestion occurs will be described with reference to FIG. In FIG. 2, each square (□) represents one packet and represents a state in which transmission is performed in units of frames.

  At this time, when the network is congested, among the packets constituting each frame in FIG. 2, the packet located at the rear end of each frame indicated by hatching tends to be lost. Then, next, the determination method of the transmission order of the RTP packet and FEC packet performed in the scheduling part 106 is demonstrated.

  Prior to the description, first, when data packets to be transmitted within a certain time period are divided into groups A to D as shown in FIG. 3, FECs generated from groups of data packets A to D by parity codes are used. The packets are denoted by a to d as shown in FIG.

  In the parity code, when the FEC packet is generated in this way, even if any one data packet is lost from each group among the data packets in the groups A to D, the lost data packet is restored. It becomes possible. This is because the lost data packet can be restored by the other data packet and the FEC packet.

  Therefore, in the present embodiment, a case is considered in which the data packets A to D and the FEC packets a to d shown in FIG. 3 are burst-transmitted within a predetermined time. For example, the method for determining the transmission order of the packets in FIG. 4 for transmitting in the transmission order shown in FIG. 4 is as follows. First, an arbitrary packet is selected from each group of data packets A to D (reference numeral 401), and the transmission order of the selected packet is arranged last.

  As described above, the data packet arranged last in the transmission order is likely to be lost when the network is congested. Even if all the data packets selected by the code 401 are lost, the data can be restored by the error correction code. However, if more packets are lost, the restoration is impossible.

  Therefore, considering the importance of the remaining data packets and FEC packets excluding the packet 401, the FEC packets cannot be used for decoding moving image or audio data as they are. For this reason, in this embodiment, it can be judged that the importance is lower than other data packets. Therefore, as indicated by reference numeral 402 in FIG. 4, the FEC packets a to d are arranged immediately before the data packet having the reference numeral 401 in the transmission order.

  Further, the remaining data packets other than the arbitrarily selected data packet may be transmitted in an arbitrary transmission order when there is no difference in importance between the packets. However, if the transmission order of the remaining data packets is randomly arranged as indicated by reference numeral 403 shown in FIG. 4, a burst error can be avoided even when a missing packet reaches this part of the data packet. As a result, there is a high possibility that the quality of the decoded moving image or sound is improved.

  It should be noted that the actual packet loss often differs depending on the cause of the packet loss, that is, the missing pattern. In the case of FIG. 4 describing the transmission order determination method in the present embodiment, an effective transmission order determination method is shown when packet loss mainly occurs due to network congestion. However, for example, when packets in an arbitrary transmission order are often lost due to some disturbance other than network congestion, the transmission order shown in FIG. 5 or FIG. 6 may be used.

  As in FIG. 4, FIG. 5 selects any one packet from each group that generated the FEC packet and places it at the end of the transmission order (reference numeral 501). The other data packets and FEC packets are The transmission order is collectively determined at random (reference numeral 502).

  In FIG. 6 as well, the part of selecting one arbitrary packet from each group that generated the FEC packet and placing it at the end of the transmission order (reference numeral 601) is the same as the method of FIGS. . However, for the remaining packets indicated by reference numerals 602 and 603, the FEC packet may be arranged at the head of the transmission order, contrary to the method of FIG.

  Regardless of the method, the transmission order determination method according to the present embodiment restores a packet using an error correction code by arranging a packet that can be restored even if it is lost at a position that is most likely to be lost in the transmission order. Probability can be improved.

  In this embodiment, the parity correction code has been described as an example of the error correction code method. However, the transmission order determination method of the present invention can be applied even when a similar error correction code is used. Needless to say.

The schematic processing of the data transmission method of the present embodiment described above will be described with reference to the flowchart of FIG.
First, in step S71, group division is performed to divide a data packet to be burst transmitted within a certain time into a plurality of groups.

  Next, proceeding to step S72, an FEC packet is generated from each group of data packets generated at step S71. As described above, the FEC packet generated here is an error correction packet storing error correction data for repairing an error that occurs during network transmission of the data packet generated in step S71 via the network. In the present embodiment, error correction packet generation is performed for each grouped data packet.

  Next, proceeding to step S73, packet selection is performed in which a data packet is arbitrarily selected from each group of the plurality of data packets divided in step S71 to generate one packet. Next, proceeding to step S74, the packets are arranged so that the selected packets are in a predetermined transmission order.

  In this embodiment, the packets selected in step S73 are arranged so that the transmission order is last. Further, the FEC packet is arranged immediately before the data to be transmitted last. Next, the process proceeds to step S75, where it is determined whether there is an unallocated data packet. As a result of the determination, if there is an unallocated data packet, the process returns to step S74 to continue the data packet allocation process. On the other hand, if there is no unallocated data packet as a result of the determination in step S75, the process is terminated.

  Note that various orders can be considered as the order of transmitting the remaining data packets other than the arbitrarily selected data packet. For example, the transmission order of error correction packets may be controlled to be random.

  Further, the error correction packet may be transmitted first, and the remaining data packets other than the arbitrarily selected data packet may be transmitted in the middle. Furthermore, the transmission order of data packets to be transmitted in the middle of the transmission order may be determined at random.

(Another embodiment according to the present invention)
Each means constituting the data transmitting apparatus according to the embodiment of the present invention described above can be realized by operating a program stored in a RAM or ROM of a computer. This program and a computer-readable recording medium recording the program are included in the present invention.

  In addition, the present invention can be implemented as a system, apparatus, method, program, storage medium, or the like, and can be applied to a system composed of a plurality of devices. Moreover, you may apply to the apparatus which consists of one apparatus.

  In the present invention, a software program (in the embodiment, a program corresponding to the flowchart shown in FIG. 7) for executing each step in the above-described data transmission method is directly or remotely supplied to the system or apparatus. In addition, this includes a case where the system or the computer of the apparatus is also achieved by reading and executing the supplied program code.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, and the like.

  Various recording media can be used as a recording medium for supplying the program. For example, floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD- R).

  As another program supply method, a browser on a client computer is used to connect to an Internet home page. The computer program itself of the present invention or a compressed file including an automatic installation function can be downloaded from the homepage by downloading it to a recording medium such as a hard disk.

  It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. Let me. It is also possible to execute the encrypted program by using the key information and install the program on a computer.

  In addition to the functions of the above-described embodiments being realized by the computer executing the read program, the OS running on the computer performs part or all of the actual processing. Also, the functions of the above-described embodiments can be realized.

  Further, the program read from the recording medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, the CPU of the function expansion board or function expansion unit performs part or all of the actual processing based on the instructions of the program, and the functions of the above-described embodiments are realized by the processing.

1 is a block diagram illustrating a basic configuration of a moving image data transmission device according to an embodiment of the present invention. It is a figure which shows the mode of the typical packet loss at the time of network congestion. It is a figure which shows embodiment of this invention and shows a mode that a FEC packet is produced | generated by the error correction code | cord | chord from several groups of data packets. It is a figure which shows embodiment of this invention and shows the determination method of a packet transmission order. FIG. 5 is a diagram illustrating a packet transmission order determination method different from that in FIG. 4 according to the embodiment of this invention. FIG. 6 is a diagram illustrating an embodiment of the present invention and a packet transmission order determination method different from those in FIGS. 4 and 5. It is a flowchart which shows embodiment of this invention and demonstrates the schematic procedure of the data transmission method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Control part 100 Moving image data transmitter 101 Moving image / voice input part 102 Encoding part 103 RTP packet generation part 104 FEC packet generation part 105 Packet transmission buffer 106 Scheduling part 107 Packet transmission part 108 Transmission path

Claims (10)

A data transmission device that transmits data via a network,
Packet generating means for generating a plurality of data packets storing the data to be transmitted;
Group dividing means for dividing the data packet generated by the packet generating means into a plurality of groups;
The error correction packets containing error correction data for repairing the missing packets that were not transmitted due to an error during the network transmission of data packets, divided by the group dividing means Group - error correction packets generated for each flop Generating means;
For each group, packet selection means for selecting data packets within the number of missing packets that the error correction packet can repair ,
Transmission control means for controlling the transmission order of the packets,
The transmission control unit controls the transmission order of the data packets selected by the packet selection unit to be after the last group of the plurality of groups . The transmission control means controls the transmission order so that the error correction packet generated by the error correction packet generation means is transmitted immediately before the data packet selected by the packet selection means. The data transmission apparatus according to 1. It said transmission control means, out of the generated data packet by the packet generator, the transmission order of the remaining data packets other than the selected data packet by the packet selecting means randomly among the remaining data packets The data transmission apparatus according to claim 2, wherein the transmission order is controlled so that The transmission control means includes a remaining data packet other than the data packet selected by the packet selection means among the data packets generated by the packet generation means, and an error correction packet generated by the error correction packet generation means. The data transmission apparatus according to claim 1, wherein the transmission order is controlled so that the transmission order is random. The transmission control unit controls the transmission order so that the error correction packet is transmitted first, and the remaining data packets other than the data packet selected by the packet selection unit are transmitted in the middle. The data transmission device according to claim 1.   6. The data transmission apparatus according to claim 5, wherein the transmission control means randomly determines the transmission order of data packets to be transmitted in the middle of the transmission order.   The data transmission apparatus according to claim 1, wherein the error correction packet generation unit uses a parity code and an error correction code similar to the parity code. A data transmission method for transmitting data via a network,
A packet generation step of generating a plurality of data packets storing the data to be transmitted;
A group dividing step of dividing the data packet generated in the packet generating step into a plurality of groups;
The error correction packets containing error correction data for repairing the missing packets that were not transmitted due to an error during the network transmission of data packets, divided in the group division process Group - error correction packets generated for each flop Generation process;
For each group, a packet selection step for selecting data packets within the number of missing packets that can be repaired by the error correction packet ;
A transmission control step for controlling the transmission order of the packets,
The transmission control step controls the transmission order of the data packets selected in the packet selection step to be after the last group of the plurality of groups . A program for causing a computer to execute a data transmission method for transmitting data via a network,
A packet generation step of generating a plurality of data packets storing the data to be transmitted;
A group dividing step of dividing the data packet generated in the packet generating step into a plurality of groups;
The error correction packets containing error correction data for repairing the missing packets that were not transmitted due to an error during the network transmission of data packets, divided in the group division process Group - error correction packets generated for each flop Generation process;
For each group, a packet selection step for selecting data packets within the number of missing packets that can be repaired by the error correction packet ;
A transmission control step for controlling the transmission order of the packets,
The transmission control step causes the computer to execute each process of the data transmission method for controlling the transmission order of the data packets selected in the packet selection step to be after the last group of the plurality of groups. A featured computer program.   A computer-readable storage medium storing the computer program according to claim 9.

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