JP2008092346A - Transmitter and receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transmitter and receiver, wherein reduction in load relating to processing of a re-transmission request is attained and there is an effect that a loss packet can be surely recovered. <P>SOLUTION: The transmitter 20 comprises: a packet output unit 21 for outputting a packet of video or audio data; a packet buffer 22 for storing the packet outputted by the packet output unit 21; a re-transmission request accepting unit 23 for accepting a re-transmission request from a receiving apparatus 30; a block constitution unit 24 which constitutes a block for generating a re-transmission response packet in place of a re-transmission requested packet; an encoding unit 25 which generates a check symbol relating to the constituted block in accordance with a predetermined encoding method; and a re-transmission response packet output unit 26 for outputting the re-transmission response packet. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transmission device that packetizes and transmits data such as video and audio, and a reception device that receives a packet from the transmission device.

  Conventionally, a Real-time Transport Protocol (RTP) has been standardized as a method for streaming transmission of data such as video and audio using IP (Internet Protocol) packets (for example, see Non-Patent Document 1). ). By setting a class D address as a destination address of a packet configured based on this RTP, one-to-many communication using a multicast group address becomes possible. That is, only the transmitting device transmits a single packet, and a plurality of receiving devices that have requested reception can receive the same packet.

  When using RTP, there is UDP (User Datagram Protocol) as a transport protocol in an IP network. As a technique for realizing communication with reliability in RTP / UDP, ARQ (Automatic Repeat reQuest) or error correction code technology is used. The FEC (Forward Error Correction) used is known.

  First, in data transmission using ARQ, when a receiving apparatus detects a loss of a packet, the receiving apparatus requests the transmitting apparatus to retransmit the packet and receives it again to recover the loss of the packet. Can do.

  Next, regarding FEC, RFC 2733 has been standardized as a method of performing error correction on a packet based on inspection information by XOR (eXclusive OR) (see, for example, Non-Patent Document 2). By extending RFC 2733, general error correction code for generating multi-bit check information, for example, check information by Reed-Solomon code is added as redundant data to transmission data with a predetermined redundancy and lost during transmission. The received packet can be recovered by the inspection information at the receiving side device.

  On the other hand, a technique called hybrid ARQ in which ARQ and FEC are combined is also known. In response to a retransmission request by ARQ, a packet storing a check symbol generated in advance by FEC is transmitted as a response packet. In order to transmit a packet storing check symbols, even when different packets are lost in a plurality of receiving apparatuses, by transmitting the same packet in a one-to-many manner, packets lost in a plurality of receiving apparatuses (hereinafter referred to as “loss packets”). Can be recovered.

  As described above, in general, even when a communication path in which reliability is not ensured is used, transmission of a packet with ensured reliability can be realized by making a retransmission request. However, when data such as video and audio is distributed to a large number of receiving devices by multicast communication, it is expected that packet retransmission requests will be generated from a plurality of receiving devices. In addition, the packets requested for retransmission by each receiving apparatus may be different from each other, and the load corresponding to the retransmission request increases as the number of receiving apparatuses increases. Therefore, when the number of receiving apparatuses is extremely large, there is a problem that it is difficult to apply reliability ensuring by a retransmission request to distribution using multicast communication.

  As an object for solving this problem, for example, those disclosed in Patent Documents 1 and 2 are known.

  First, the technique disclosed in Patent Document 1 includes an error correction unit that performs error correction processing for restoring a lost packet when a packet loss is detected, and a retransmission request for the lost packet to the packet transmission device. A retransmission request transmission unit for transmitting, and a retransmission request control unit for controlling the transmission timing of the retransmission request to the packet transmission device by the retransmission request transmission unit according to whether or not the error correction unit can restore the lost packet within a predetermined time; The retransmission request control unit controls the retransmission request transmission timing when packet loss occurs, so that it is possible to reproduce video, audio, etc. with an optimal delay time while suppressing unnecessary retransmission request transmission. It has become.

  Next, what is disclosed in Patent Document 2 is an encoding unit that encodes redundant data for error correction from original data related to transmission, and data storage for retransmission that stores a part of the encoded redundant data as data for retransmission. A data packet transmission unit that transmits part or all of the original data and redundant data, and a retransmission request reception unit that receives a retransmission request from a transmission destination, and performs encoding by FEC each time a retransmission request is made. Then, by generating those check packets from the untransmitted check packets, it is possible to increase the number of different redundant packets and improve the communication quality.

RFC3550 "RTP: A Transport Protocol for Real-Time Applications" RFC 2733 "An RTP Payload Format for Generic Forward Error Correction" JP 2005-159433 A JP 2004-349891 A

  However, the conventional ones shown in Patent Documents 1 and 2 have the following first to third problems.

  First, in Patent Document 1, there are a plurality of receiving apparatuses that control the transmission timing of a retransmission request, and when the transmitting apparatus transmits a packet including data such as video and audio to these receiving apparatuses, it is generated from each receiving apparatus. It does not describe how the transmission apparatus copes with the retransmission request. Therefore, the technique disclosed in Patent Document 1 has a first problem that a load corresponding to a retransmission request increases in a transmission apparatus as the number of reception apparatuses increases.

  On the other hand, since the configuration shown in Patent Document 2 is configured to generate the inspection packet in units of blocks, if the packet requested for retransmission exists in a plurality of blocks, the packet requested for retransmission It is necessary to encode each check packet of all the blocks to which the block belongs by FEC and generate a check packet for each block, and then transmit the generated check packet as a response packet for a retransmission request. Therefore, the technique disclosed in Patent Document 2 has a second problem that the load on the transmission apparatus increases because the number of packets for responding to a retransmission request is larger than the number of packets requested for retransmission. is doing.

  Further, in the configuration disclosed in Patent Document 2, the number of recoverable packets in the block is determined based on the number of inspection packets generated in advance in units of blocks. When retransmission of a larger number of packets than the number is requested, there is a third problem in that a lost packet cannot be recovered by a receiving device only by transmitting a previously generated inspection packet.

  The present invention has been made to solve the conventional problems, and provides a transmission device and a reception device that can reduce a load related to retransmission request processing and can reliably recover a lost packet. For the purpose.

  A transmitting apparatus of the present invention is a transmitting apparatus connected to at least one receiving apparatus and receiving retransmission request information for requesting retransmission of a lost packet from the receiving apparatus, packet transmitting means for transmitting a packet; A retransmission request information receiving means for receiving the retransmission request information, and a check symbol for generating a check symbol by a predetermined error correction code based on information included in the packet transmitted by the packet transmission means and the packet related to the retransmission request information It has a configuration comprising generation means and retransmission response packet transmission means for transmitting a packet including the check symbol as a retransmission response packet instead of the packet related to the retransmission request information.

  With this configuration, the transmission apparatus of the present invention transmits a retransmission response packet that can be commonly used in the receiving apparatus that has requested retransmission, instead of the packet related to retransmission request information. There is no need to individually transmit a packet related to retransmission request information to the receiving apparatus that has made the request. Therefore, the transmitting apparatus of the present invention can solve the first problem that the load corresponding to the retransmission request increases in the transmitting apparatus as the number of receiving apparatuses increases. That is, the transmission apparatus of the present invention can reduce the load related to the retransmission request processing regardless of the number of reception apparatuses, and can reliably recover lost packets in the reception apparatus.

  The transmission apparatus according to the present invention has a configuration in which the retransmission response packet includes information indicating a packet to be encoded when the check symbol generation unit generates the check symbol.

  With this configuration, the transmission apparatus of the present invention can reliably recover lost packets in the reception apparatus.

  Furthermore, the transmission apparatus of the present invention has a configuration including retransmission request information aggregating means for aggregating the received retransmission request information when the retransmission request information receiving means receives the retransmission request information from a plurality of receiving apparatuses. is doing.

  With this configuration, the transmission apparatus of the present invention can identify the packet to be encoded when the check symbol generation unit generates the check symbol by the retransmission request information aggregation unit collecting the retransmission request information. .

  Furthermore, the transmission apparatus of the present invention includes a packet determination unit that determines a packet to be encoded when the check symbol generation unit generates the check symbol based on the aggregated retransmission request information. Have.

  With this configuration, in the transmission apparatus of the present invention, the packet determination unit determines a packet to be encoded when the check symbol generation unit generates a check symbol based on the aggregated retransmission request information. In the case where the packet requested for retransmission exists in a plurality of blocks like the above, it is not necessary to transmit all the inspection packets of the block. Therefore, the transmission apparatus of the present invention solves the second conventional problem that the load on the transmission apparatus increases because the number of packets for responding to a retransmission request is larger than the number of packets requested for retransmission. Can do.

  Furthermore, the transmission apparatus of the present invention has a configuration including check symbol number determining means for determining the number of symbols of the check symbols based on the aggregated retransmission request information.

  With this configuration, since the check symbol number determining means determines the number of check symbol symbols based on the aggregated retransmission request information, the transmitting apparatus according to the present invention is necessary and sufficient for the receiving apparatus to recover the lost packet. Can be generated without waste and transmitted as a retransmission response packet. Therefore, the transmission apparatus of the present invention can solve the third problem that the lost packet cannot be recovered by the reception apparatus only by transmitting the inspection packet generated in advance.

  The receiving apparatus according to the present invention is a receiving apparatus that receives the packet from the transmitting apparatus according to any one of claims 1 to 5, wherein the retransmission request information is detected when the lost packet is detected. The retransmission request information transmitting means for transmitting the retransmission response packet receiving means for receiving the retransmission response packet.

  With this configuration, since the retransmission response packet receiving unit receives the retransmission response packet, the receiving apparatus of the present invention can reliably recover the lost packet based on the received retransmission response packet.

  The present invention can provide a transmission device and a reception device that have the effect of reducing the load related to the processing of a retransmission request and also capable of reliably recovering a lost packet.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. An example in which the transmission device and the reception device of the present invention are applied to a packet transmission system that packetizes data such as video and audio and transmits the data by multicast communication will be described.

  First, the configuration of the packet transmission system according to the present embodiment will be described.

  As shown in FIG. 1, the packet transmission system 10 according to the present exemplary embodiment includes a transmission device 20 that packetizes and transmits input video and audio data using a predetermined protocol, and a packet transmitted from the transmission device 20. Is received. In FIG. 1, only one receiving device 30 is shown, but in the following description, it is assumed that one or more receiving devices 30 are connected to the transmitting device 20. The transmission device 20 and the reception device 30 include, for example, a CPU (Central Processing Unit), a ROM (Read-Only Memory), a RAM (Random-Access Memory), and the like, and are operated by a predetermined program.

  First, the configuration of the transmission device 20 will be described. The transmission device 20 includes a packet output unit 21 that outputs a packet including data such as video and audio, a packet buffer 22 that stores a packet output from the packet output unit 21, and a retransmission request reception that receives a retransmission request from the reception device 30. Unit 23, a block configuration unit 24 that configures a block for generating a retransmission response packet in place of the packet requested to be retransmitted, and an encoding unit 25 that generates a check symbol related to the configured block by a predetermined encoding scheme, A retransmission response packet output unit 26 for outputting a retransmission response packet.

  Data such as video and audio input to the packet output unit 21 is a transport stream compressed by, for example, MPEG (Moving Picture Experts Group) -2. For example, the packet output unit 21 converts input data such as video and audio into an IP packet according to RFC2250 and outputs the packet to the receiving device 30 based on RTP. Here, the packet output unit 21 corresponds to the packet transmission means in the present invention. RFC2250 indicates the RFC standard “RTP Payload Format for MPEG1 / MPEG2 Video”.

  The packet buffer 22 stores a packet output from the packet output unit 21 for a predetermined time (for example, 4 seconds), and performs a first-in first-out buffering operation for discarding the stored packet after a predetermined time elapses.

  The retransmission request reception unit 23 receives retransmission request information for requesting retransmission of the packet within a predetermined retransmission request reception time (for example, 4 seconds) after the packet output unit 21 outputs the packet. To receive from. The retransmission request information includes, for example, sequence number information added to the packet at the time of transmission, and can specify a packet related to the retransmission request (hereinafter referred to as “retransmission request packet”).

  In addition, when receiving retransmission request information from a plurality of receiving devices 30, the retransmission request receiving unit 23 aggregates received retransmission request information every time the number of retransmission request packets reaches a predetermined number (for example, 16). It has become. As a result, the retransmission request receiving unit 23 can acquire the sequence number information of all the retransmission request packets requested from the plurality of receiving devices 30 and the information on the number of retransmission request packets for each receiving device 30. The retransmission request receiving unit 23 outputs the acquired sequence number information of the retransmission request packet and maximum value information on the number of retransmission request packets for each receiving device 30 to the block configuration unit 24. The retransmission request accepting unit 23 corresponds to the retransmission request information receiving unit and the retransmission request information aggregating unit in the present invention.

  Based on the sequence number information and the maximum value information of the retransmission request packet received from the retransmission request accepting unit 23, the block configuration unit 24 configures a block for generating a retransmission response packet for responding to the retransmission request. Yes. Here, the block refers to a set of packets including data such as video and audio. In this specification, a plurality of packets to be encoded when the encoding unit 25 described later generates a check symbol. Applicable.

  Further, the block configuration unit 24 notifies the packet buffer 22 of packet sequence number information necessary for the configuration of the block, and causes the encoding unit 25 to output the packet. Also, the block configuration unit 24 notifies the encoding unit 25 of the number of packets to be encoded and the number of check symbols to be generated. Note that the block configuration unit 24 corresponds to the packet determination unit and the check symbol number determination unit in the present invention.

  The encoding unit 25 generates a check symbol by encoding the block formed by the block configuration unit 24 using, for example, Reed-Solomon code. Specifically, the encoding unit 25, for a packet related to the block input from the packet buffer 22, based on the number of packets and the number of check symbols notified from the block configuration unit 24, for example, check symbols by Reed-Solomon code Is supposed to generate. In addition, the encoding unit 25 outputs the generated check symbol to the retransmission response packet output unit 26. The encoding unit 25 corresponds to the check symbol generation means in the present invention.

  The retransmission response packet output unit 26 configures a retransmission response packet including the check symbol generated by the encoding unit 25 and the sequence number information of the packet used to generate the check symbol, and receives the retransmission request. The data is output to the device 30. The retransmission response packet output unit 26 corresponds to the retransmission response packet transmission unit in the present invention.

  Next, the configuration of the receiving device 30 will be described. The receiving device 30 includes a packet receiving unit 31 that receives a packet, a lost packet detecting unit 32 that detects a lost packet, and retransmission request information transmission that transmits retransmission request information for requesting retransmission of a packet corresponding to the lost packet. A decoding unit 34 for decoding the received packet, and a video / audio reproduction unit 35 for reproducing data such as video and audio.

  The packet receiving unit 31 receives a packet transmitted from the transmission device 20 and outputs the packet to the decoding unit 34. Further, the packet receiving unit 31 is configured to receive a retransmission response packet transmitted by the transmitting device 20 after the retransmission request information transmitting unit 33 transmits the retransmission request information. The packet receiving unit 31 corresponds to the retransmission response packet receiving unit in the present invention.

  The lost packet detector 32 detects a lost packet based on, for example, sequence number information. Further, when detecting the lost packet, the lost packet detecting unit 32 outputs information for identifying a packet corresponding to the lost packet, for example, sequence number information to the retransmission request information transmitting unit 33 as lost packet information. ing.

  The retransmission request information transmission unit 33 acquires the lost packet information from the lost packet detection unit 32, generates retransmission request information for requesting retransmission of the packet based on the lost packet information, and sets the generated retransmission request information as a predetermined value. The packet is transmitted in accordance with the above protocol and transmitted to the transmission device 20. The retransmission request information transmission unit 33 corresponds to the retransmission request information transmission unit in the present invention.

  The decoding unit 34 includes a reception buffer (not shown) that temporarily stores the received packet, decodes the packet received by the packet reception unit 31, and outputs the decoded packet to the video / audio reproduction unit 35.

  Further, when the packet receiving unit 31 receives the retransmission response packet, the decoding unit 34 recovers the lost packet based on the check symbol included in the retransmission response packet.

  The video / audio reproduction unit 35 includes, for example, a video processing circuit, an audio processing circuit, a liquid crystal display, a speaker, and the like, and reproduces video and audio.

  Next, the operation of the packet transmission system 10 in the present embodiment will be described.

  First, data such as video and audio input to the transmission device 20 is converted into an IP packet by the packet output unit 21 according to, for example, RFC2250 and output to the reception device 30 based on RTP. Here, since the packet output by the packet output unit 21 may be necessary when a retransmission request is made, it is stored in the packet buffer 22 for a predetermined time after being output to the receiving device 30.

  The packet transmitted to the receiving device 30 is received by the packet receiving unit 31.

  Next, the packet received by the packet receiver 31 is detected by the lost packet detector 32 based on, for example, a sequence number. If there is a lost packet, the loss including the sequence number information of the packet is detected. The packet information is output to the retransmission request information transmission unit 33.

  Subsequently, the retransmission request information transmission unit 33 generates retransmission request information for requesting retransmission of the packet based on the input lost packet information, and packetizes and transmits the retransmission request information based on a predetermined protocol. Transmit to device 20.

  The retransmission request information transmitted to the transmission device 20 is received by the retransmission request reception unit 23 within the retransmission request reception time. When the total number of retransmission request packets received by the retransmission request reception unit 23 reaches 16, or when the retransmission request reception time has elapsed, the retransmission request packets are aggregated by the retransmission request reception unit 23, As a result, the sequence number information and maximum value information of the retransmission request packet acquired are output to the block configuration unit 24.

  Specifically, retransmission request accepting unit 23 obtains the union of sequence numbers of retransmission request packets for all receiving apparatuses 30 that have made retransmission requests. For example, when the receiving device 30 includes four receiving devices 30a to 30d and the transmitting device 20 transmits a packet having a sequence number (SN) of 1 to 10, for example, the receiving device 30a includes SN1 and SN2, Assuming that the receiving device 30b requests retransmission of the packets SN2 and SN4, the receiving device 30c requests SN5, 7 and 9, respectively, and the receiving device 30d does not request retransmission, the following processing is performed.

  If the union of A and B is expressed as “A∪B”, the retransmission request accepting unit 23 receives the request (SN1, 2) from the receiving device 30a and the request (SN2, 4) ∪ received from the receiving device 30b. Requests (SN5, 7, 9) from the device 30c are obtained. As a result, the retransmission request receiving unit 23 outputs information indicating the sequence numbers (SN 1, 2, 4, 5, 7, 9) obtained by collecting the retransmission request packets to the block configuration unit 24.

Also, the retransmission request accepting unit 23 sets P ₁ , P ₂ ..., P _k , where P ₁ , P _{2 ,.} The maximum value P _max is output to the block configuration unit 24. That is, the maximum value P _{max of the} number of packets output to the block configuration unit 24 is expressed by Expression (1).

P _max = max (P ₁ , P ₂ ..., P _k ) (1)

For example, when the receivers 30a to 30d are configured as described above, the receiver 30a has two (pieces) packets (P ₁ = 2), and the receiver 30b has two (pieces) packets (P ₂ = 2). ), Since the receiving apparatus 30c requests retransmission of 3 (pieces) packets (P ₃ = 3) and the receiving apparatus 30d requests retransmission of 0 (pieces) packets (P ₄ = 0), (2, 2, 3) , 0) is output to the block configuration unit 24 as the maximum value P _max of the number of packets requested to be retransmitted.

  The retransmission request receiving unit 23 repeats the above-described operation when the number of packets requested for retransmission reaches 16, or every time the retransmission request reception time elapses.

  Subsequently, the block configuration unit 24 determines how many check symbols are generated by the Reed-Solomon code based on the sequence number information and maximum value information of the retransmission request packet. Also, in order to identify a packet to be subjected to Reed-Solomon encoding, the encoding unit 25 determines which sequence number of a packet to generate a check symbol. In the Reed-Solomon code, generating NK check symbols from K data symbols is generally expressed as encoding by RS (N, K). In the present embodiment, since data symbols are extracted from different packets and encoded, generating NK check symbols from K data symbols means that NK check symbols are generated from K packets. This means that NN check symbols are generated and NK check packets storing them are generated. Here, in the present embodiment, N is a fixed value and N = 64 will be specifically described below.

The block configuration unit 24 first determines the number of check symbols (N−K) according to the equation (2) or (3) according to the maximum value P _{max of the} number of packets requested to be retransmitted.

N−K = P _max +2 (P _max ≦ 8) (2)

N−K = P _max +4 (9 ≦ P _max ≦ 16) (3)

  Here, the value of K with respect to N = 64 determined by the block configuration unit 24 using the formula (2) or (3) indicates the number of packets to be encoded by the Reed-Solomon code.

  Next, the block configuration unit 24 determines which sequence number of the packet is to be encoded as follows.

The set of aggregated sequence numbers of retransmission request packets is C, the number of C elements (that is, the number of aggregated sequence numbers) is c = | C |, and the smallest of C elements (that is, the number of retransmission request packets). When the smallest sequence number is expressed as SN _min , the block configuration unit 24 determines the sequence numbers of the K packets to be encoded so as to satisfy the following conditions (1) and (2).
Condition (1): Packet condition in which elements of set C are sequence numbers (2): Starting from sequence number SN _min , (Kc) packets not included in C in ascending order of sequence numbers

  The block configuration unit 24 determines a total of K packets to satisfy the conditions (1) and (2), notifies the determined sequence number to the packet buffer 22, and the packet configuration unit 24 determines the packet buffer 22. The packet having the sequence number is output to the encoding unit 25. At the same time, the block configuration unit 24 notifies the encoding unit 25 of the values of N and K.

  In the above condition (2), a block may be configured by preparing a necessary number of dummy packets having a data portion of “0”, for example, without using the actually transmitted packet.

  Subsequently, the encoding unit 25 generates NK check symbols for constituting a retransmission response packet from the K packets output from the packet buffer 22. Specifically, as illustrated in FIG. 2, the encoding unit 25 sequentially reads out one byte at a time from the UDP payload of K packets, and uses the RS (N, K) code to read N− K 1-byte check symbols are generated. The encoding unit 25 repeats this operation for the size of the UDP payload of the packet, and outputs the generated check symbol to the retransmission response packet output unit 26. Note that the encoding of the Reed-Solomon code is a well-known technique and will not be described.

  Next, the retransmission response packet output unit 26 outputs the retransmission response packet storing the check symbol generated by the encoding unit 25 to the receiving device 30 that has requested retransmission.

  Here, the retransmission response packet will be described.

  In order for the receiving device 30 to recover the lost packet using the retransmission response packet in which the check symbol is stored, it is necessary to clearly indicate from which packet the check symbol included in the retransmission response packet is generated. There is. Therefore, the sequence numbers of the K packets used for encoding are indicated by the following two sets of parameters, stored in a retransmission response packet, and transmitted to the receiving device 30.

baseSN: The sequence number that is the youngest in the packet to be encoded when the encoding unit 25 generates a check symbol (same value as SN _min ).

  flag: A bit string composed of 0 and 1. For example, if the i-th bit of the flag is 1, it indicates that the i-th packet from baseSN is used for the encoding unit 25 encoding. On the other hand, if the bit is 0, it indicates that the packet corresponding to the bit is not used for encoding by the encoding unit 25.

  Hereinafter, an example of baseSN and flag when N = 64 will be described.

The sequence numbers of the packets requested to be retransmitted from the plurality of receiving apparatuses 30 are “9, 10, 11, 12, 13, 31, 32, 33, 34, 54, 55, 56, 77, 78, 79, 80”. When the maximum value P _{max of the} number of packets requested to be retransmitted is P _max = 6, N−K = 8 from Equation (2), and N = 64, so K = 56 is obtained. Therefore, 56 packets of sequence numbers 9 to 60 and 77 to 80 are encoded by the encoding unit 25. Therefore, baseSN = 9 and flag = “1111 1111 1111 1111 1111 1111 1111 1111 1111 1111 1111 1111 1111 0000 0000 0000 0000 1111”.

  The encoding unit 25 outputs the check symbol generated as described above and the values of baseSN and flag to the retransmission response packet output unit 26.

Incidentally, the sequence number assigned to the packet is ^{2 16} ways in RFC3550. Therefore, the sequence number of the 2 ¹⁶ −1 next packet is “0”. Since sequence numbers are used in such a manner, they are omitted in the above description. However, when expressing the size or flag of a sequence number, not a simple size comparison of numbers, but a size comparison that also considers circulation is used. Configure to do.

  Next, the retransmission response packet output unit 26 generates a retransmission response packet including the generated check symbol and each value of baseSN and flag, and transmits the retransmission response packet to the receiving apparatus 30 that has requested retransmission by multicast communication.

  Subsequently, in the receiving device 30 that has made the retransmission request, the packet receiving unit 31 receives the retransmission response packet and outputs the received retransmission response packet to the decoding unit 34. Next, the decoding unit 34 recovers the lost packet based on the check symbol included in the retransmission response packet, and decodes the packet, thereby reproducing the video and audio data included in the packet. To the unit 35. Then, the video / audio reproduction unit 35 reproduces data such as video and audio.

  As described above, according to the transmission device 20 in the present embodiment, the transmission device 20 outputs a packet output unit 21 that outputs a packet of data such as video and audio, and a packet that stores a packet output from the packet output unit 21. A buffer 22, a retransmission request reception unit 23 that receives a retransmission request from the receiving device 30, a block configuration unit 24 that configures a block for generating a retransmission response packet in place of the packet requested for retransmission, and a related block Since it is configured to include a coding unit 25 that generates a check symbol by a predetermined coding method and a retransmission response packet output unit 26 that outputs a retransmission response packet, it is commonly used in the receiving apparatus 30 that has made a retransmission request. A possible retransmission response packet can be transmitted instead of the packet related to the retransmission request information.

  Therefore, transmitting apparatus 20 in the present embodiment can reduce the load related to retransmission request processing, and can reliably recover lost packets in receiving apparatus 30. That is, the transmission device 20 in the present embodiment can be preferably applied to one-to-many communication regardless of the number of reception devices 30.

  Moreover, according to the transmission apparatus 20 in the present embodiment, the retransmission response packet includes the base SN and flag information as information indicating a packet to be encoded when the encoding unit 25 generates a check symbol. Therefore, the loss packet can be reliably recovered in the receiving device 30.

  Further, according to transmitting apparatus 20 in the present embodiment, retransmission request accepting unit 23 is configured to aggregate received retransmission request information when receiving retransmission request information from a plurality of receiving apparatuses 30. When the unit 25 generates a check symbol, it is possible to specify a packet to be encoded.

  Further, according to the transmission device 20 in the present embodiment, the block configuration unit 24 is configured to determine a packet that is a test symbol generation target based on the retransmission request information aggregated by the retransmission request reception unit 23. Unlike conventional ones, when a packet requested for retransmission exists in a plurality of blocks, it is not necessary to transmit all the inspection packets of the block. Therefore, transmitting apparatus 20 in the present embodiment can reduce the load related to retransmission request processing.

  Moreover, according to the transmission apparatus 20 in the present embodiment, the block configuration unit 24 is configured to determine the number of check symbols based on the retransmission request information aggregated by the retransmission request reception unit 23. However, it is possible to generate a sufficient packet necessary for recovering the lost packet without waste and transmit it as a retransmission response packet.

  In addition, according to receiving apparatus 30 in the present embodiment, a configuration including retransmission request information transmitting means for transmitting retransmission request information when a lost packet is detected, and retransmission response packet receiving means for receiving a retransmission response packet Therefore, the lost packet can be reliably recovered based on the received retransmission response packet.

  In the above-described embodiment, the transmission apparatus 20 and the reception apparatus 30 according to the present invention have been described with reference to an example in which the transmission apparatus 20 and the reception apparatus 30 are applied to the packet transmission system 10 that packetizes data such as video and audio and transmits the data by multicast communication. However, the present invention is not limited to this, and the same effect can be obtained if the present invention is applied to one that packetizes predetermined data and performs one-to-many communication.

  In the above-described embodiment, the configuration in which the encoding unit 25 generates the check symbol using the Reed-Solomon code has been described as an example. However, the present invention is not limited to this, and other blocks are used. The same effect can be obtained by using a code, for example, a BCH code.

  As described above, the transmission device and the reception device according to the present invention have the effects of reducing the load related to the retransmission request processing and reliably recovering lost packets, such as video and audio. It is useful as a transmitting device that packetizes and transmits the data of the data and a receiving device that receives packets from the transmitting device.

The block diagram which shows the structural example of the packet transmission system in one embodiment of this invention The figure which shows the operation | movement which the encoding part of the packet transmission system in one embodiment of this invention produces | generates a check symbol.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Packet transmission system 20 Transmission apparatus 21 Packet output part (packet transmission means)
22 Packet buffer 23 Retransmission request acceptance unit (Retransmission request information receiving means, retransmission request information aggregating means)
24 Block component (packet determination means, number of check symbol determination means)
25 Coding section (check symbol generating means)
26 Retransmission response packet output unit (retransmission response packet transmission means)
30 receiver 31 packet receiver (retransmission response packet receiving means)
32 Loss packet detection unit 33 Retransmission request information transmission unit (Retransmission request information transmission means)
34 Decoding unit 35 Video / audio playback unit

Claims (6)

A transmitting apparatus connected to at least one receiving apparatus and receiving retransmission request information for requesting retransmission of a lost packet from the receiving apparatus;
A packet transmitting means for transmitting a packet; a retransmission request information receiving means for receiving the retransmission request information; and a predetermined error correction based on information contained in the packet transmitted by the packet transmitting means and the packet related to the retransmission request information A test symbol generating means for generating a check symbol by a code, and a retransmission response packet transmitting means for transmitting a packet including the check symbol as a retransmission response packet instead of the packet related to the retransmission request information. Transmitter device. The transmission apparatus according to claim 1, wherein the retransmission response packet includes information indicating a packet to be encoded when the check symbol generation unit generates the check symbol. 3. The retransmission request information aggregating unit that aggregates the received retransmission request information when the retransmission request information receiving unit receives the retransmission request information from a plurality of receiving apparatuses. The transmitting device according to 1. The packet determination unit according to claim 3, further comprising a packet determination unit that determines a packet to be encoded when the check symbol generation unit generates the check symbol based on the aggregated retransmission request information. Transmitter device. 5. The transmission apparatus according to claim 3, further comprising check symbol number determining means for determining the number of check symbols based on the aggregated retransmission request information. A reception device that requests retransmission of a lost packet to the transmission device according to any one of claims 1 to 5,
A receiving apparatus comprising: retransmission request information transmitting means for transmitting the retransmission request information when detecting the lost packet; and retransmission response packet receiving means for receiving the retransmission response packet.

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