JP2008252626A - Digital broadcasting data distribution system and method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compensate packet defects in IP multicasting. <P>SOLUTION: The digital broadcasting data distribution system distributes digital broadcasting data to a plurality of receivers from a distribution server. The distribution server is provided with an error detection symbol inserting means which inserts an error detection symbol for detecting a transmission error of each distribution packet, a discontinuous error of a distribution packet, or both the erros into digital broadcasting data; a multicast means for multicasting digital broadcasting data into which error detection symbol is inserted to a plurality of receivers; and a unicast means for unicasting a distribution packet requested for retransmission to the receiver. Each receiver is provided with an error detection means for detecting the transmission error of each distribution packet, the discontinuous error, or both the erros using error detection symbol; and a retransmission demanding means for demanding the retransmission of the distribution packet where errors which are detected are delected to the distribution server. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a digital broadcast data distribution system and method for distributing digital broadcast data.

  With the advancement of infrastructure based on the NGN (Next Generation Network) concept, digital broadcast redistribution services using IP (Internet Protocol) multicast are expected in the future.

  However, in the IP multicast, the bandwidth guarantee technique of the distribution stream by QoS (Quality of Service) is used, but since it is a one-to-many distribution form, it is impossible to prevent the reception packet from being lost on the receiving side.

If a packet is missed on the receiving side, the stream to be reproduced will be lost, causing a phenomenon unpleasant to the viewer such as block noise in the video.
JP 2006-303965 A

  In order to prevent the loss of service, the implementation of services by IP unicast is not realistic because the connection between the server and the client becomes one-to-one and the load on the network line becomes enormous.

  In the present invention, in a redistribution system such as digital broadcasting using IP multicast, the continuity of stored data is ensured by implementing a method that compensates for missing streams caused by spillage, particularly when a recording operation of a distribution service is performed. The purpose is to do.

  According to the present invention, there is provided a digital broadcast distribution system for distributing digital broadcast data from a distribution server to a plurality of receiving devices, wherein the distribution server includes a transmission error of each distribution packet, a discontinuity error of the distribution packet, or the Error detection symbol insertion means for inserting error detection symbols for detecting both into digital broadcast data, multicast means for multicasting the digital broadcast data with the error detection symbols inserted to a plurality of receiving devices, and certain reception Unicast means for unicasting a delivery packet requested to be retransmitted from a device to each receiving device, and each receiving device uses the error detection symbol to transmit a transmission error of each delivery packet and a delivery packet error. Error detection means for detecting continuous errors or both, and errors detected Digital broadcast data distribution system, characterized by comprising: a retransmission request means for retransmission of the distribution packet requests the distribution server has are provided.

  In the above digital broadcast data distribution system, when the error detecting unit detects an error, the receiving device includes a first system time clock corresponding to a packet immediately before the packet in which the error has occurred and a packet after error recovery. A system time clock detecting means for detecting a second system time clock corresponding to the first time stamp corresponding to the packet immediately before the packet in which the error has occurred when the error detecting means detects an error, System time clock detection means for detecting a second time stamp corresponding to the packet after recovery, the retransmission request means, as error location identification information for identifying an error location in the distribution server, A first system time clock, the second system time clock And the first time stamp and the second time stamp are transmitted to the distribution server, and the distribution server includes the first system time clock, the second system time clock, and the first time. There may be further provided means for using the stamp and the second time stamp as error location identification information, reading out the packet at the error location, and unicasting the packet to the receiving apparatus that issued the retransmission request.

  In the digital broadcast data distribution system, the distribution server unicasts the packet at the error location to a receiving apparatus that has issued a retransmission request, and simultaneously receives the first system time clock received from the receiving apparatus. The system further comprises error location identification information return means for returning the second system time clock, the first time stamp, and the second time stamp to the receiving device as they are, and the receiving device includes a packet of the error location. At the same time, using the received first system time clock, the second system time clock, the first time stamp, and the second time stamp as error location identification information, the received error location packet is You may make it insert in the packet sequence received normally.

  In the digital broadcast data distribution system, the receiving apparatus further includes error location specifying information generating means for generating error location specifying information for specifying each error location in the receiving device, and the retransmission requesting means includes the retransmission request means, The error location specifying information is also transmitted to the distribution server, and the distribution server transmits the error location packet at the same time, and the received error location specifying information is also returned to the receiving device as it is. There may be further provided packet insertion means for inserting the packet at a location specified by the error location specifying information.

  In the digital broadcast data distribution system, the receiving device further includes a serial number counting unit that counts a serial number of a packet that has been normally received from the start of reception, and the retransmission request unit includes a packet that has just been received. The serial number is also transmitted to the distribution server, and the distribution server transmits the received packet at the same time, and returns the received serial number as it is to the receiving device. The receiving device receives the serial numbers returned in ascending order. A packet insertion means for inserting a packet retransmitted at an error occurrence location specified by the serial number; and a serial number correction means for increasing the serial number of the subsequent packets by the number of inserted packets. It may be.

  In addition, according to the present invention, there is provided a digital broadcast data distribution system in which a distribution server distributes digital broadcast data divided into a series of packets to a receiving device, and the distribution server includes a packet included in the series of packets. On the other hand, an error detection code generated for detecting a packet error added to the packet immediately before the packet is used as an initial value, and data to be transmitted by the packet is converted into a bit string according to a predetermined arithmetic expression. An error detection code adding means for generating the error detection code by application and adding the error detection code; and a transmission means for transmitting a series of packets to which the error detection code has been added to a network; The packet included in the series of packets received from the network is assigned to the packet immediately before the packet. The error detection code is calculated by applying the error detection code as an initial value and applying the data excluding the error detection code out of the data transmitted by the packet as a bit string to the predetermined arithmetic expression. An error packet determination unit that determines whether the error detection code added to the packet matches the error detection code and determines that the packet is an error packet when the two do not match, and the error packet determination unit There is provided a digital broadcast data distribution system comprising: retransmission request means for requesting the distribution server to retransmit a packet determined to be a packet.

  According to the present invention, in order to detect the continuity of the packet by the error detection symbol for detecting the transmission error of each delivery packet, the discontinuity error of the delivery packet, or both, the dropped packet is detected, Can be requested to resend.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  In the present invention, as shown in FIG. 1, when a defect occurs in a multicast TS packet, the defect is complemented by unicast.

  Referring to FIG. 2, in addition to the receiving path 101 of the IP multicast distribution service, when a stream error is detected, only the TS packet that cannot be normally received is requested from the server arranged at the distribution source (103). A path 105 for obtaining the original data to be accumulated is provided.

  Thereby, it is possible to complement the damaged / missed TS packet by the distribution service by the IP multicast 101.

  Also, since only TS packets that could not be acquired normally are redistributed, the network load can be reduced while ensuring the same quality as IP unicast.

  At the time of transmission of TS packet data, the digital broadcast redistribution server 107 side generates a CRC value of the target TS packet by using a CRC (Cyclic Redundancy Check) value of the immediately preceding TS packet as an initial value of CRC calculation.

  As a result, the receiving side can detect errors / deletions in the TS packet sequence by monitoring / coefficient CRC values.

  The location of the damaged or missing TS packet on the receiver side is identified by the CRC value added to the stream, the time stamp data added outside the TS packet, and the PCR (Program Clock in the stream inside the receiver). STC (System Time Clock) value reproduced by Reference) is used.

  As a result, only the time stamp value and CRC value that are generally required at the time of distribution need only be added to the packet, and there is no need to add new information and increase the amount of distribution data.

[Sender configuration]
Referring to FIG. 2, description will be given by taking as an example a system in which the redistribution server 107 receives the tuner 109 digital broadcast 111 and redistributes the data stored in the storage unit 113 (101).

  The tuner 109 is a tuner for receiving the terrestrial digital broadcast 111 and the BS / CS digital broadcast. When the reception frequency is set, the tuner 109 outputs a transport stream (hereinafter referred to as “TS”).

  Referring to FIG. 3, the demultiplexer 115 extracts a TS packet having a specific packet ID (hereinafter referred to as “PID”) from the TS. Specifically, the demultiplexer 115 extracts a TS packet including a PCR (Program Clock Reference) and acquires a PCR value.

  The clock recovery unit 117 internally holds an STC (System Time Clock: a counter generated as a system clock and counted up at 27 MHz), compares the STC value at the time of PCR acquisition with the PCR value, and performs STC The oscillation frequency of the system clock is controlled so that the value follows the PCR value.

  The clock recovery unit 117 also holds a 32-bit counter that counts up at 27 MHz for assigning a time stamp value, and outputs the count value to the multiplexer as a time stamp value.

  The first multiplexer 119 time-division multiplexes the TS and the time stamp. For this purpose, a TS buffer is required before the first multiplexer 119, which is not shown in the figure.

  The CRC generation control 121 calculates a CRC value from the TS packet data, the time stamp value, and the CRC value of the previous TS packet.

  The calculation of the CRC value is performed in units of one TS packet, and the calculation result is output to the multiplexer 123 and the register 125 when the CRC value for one TS packet can be calculated.

  The CRC value is calculated from the time stamp value of the target TS packet, and when calculating the CRC value, the CRC value calculated from the immediately preceding TS packet in the register 125 is used as the initial value.

  If the accuracy of error detection can be lowered, the time stamp need not be included.

  The register 125 updates and stores the CRC value of the TS packet (including the time stamp) generated by the CRC generation control unit 121 for each TS packet.

  The second multiplexer superimposes the CRC value from the CRC generation control unit 121 on the TS packet output from the first multiplexer and the count value of the 32-bit counter generated in the clock recovery 117.

  The accumulation control unit 127 accumulates the TS packet, the time stamp value, and the CRC value superimposed by the first multiplexer 119 and the second multiplexer 123 in the accumulation unit 113.

  The broadcast service server 129 distributes the digital broadcast stream stored in the storage unit 113 by IP multicast and provides a TV viewing service.

  The TS packet supplement server 131 responds to the supplement data request from the client, and based on the service_id, Start time stamp, End time stamp, Start STC, and End STC sent from the client when the supplement data is requested. TS packets necessary for complementation are specified and sent to the client side.

  The service_id is information transmitted by being added to the stream in digital broadcasting, and is used for specifying a broadcast program. In the present embodiment, service_id is used to specify a stream stored in the storage device. In the case of a service that targets content transmitted at the time of recording, the server side can specify the target stream as a stream that is currently distributed, so that it is not necessary to specify the stream by service_id.

  When a complement request is received, the TS packet complement server 131 searches the inside for all the streams stored in the storage unit 113 and identifies a stream having the requested service_id.

  When the stream can be specified, the start position of the TS packet that needs to be complemented is specified by Start STC.

  The approximate position can be specified by the STC value because the time range that can be expressed by the time stamp value of 27 MHz and 32 bits is about 160 seconds, and the accuracy is less than that.

  When the approximate position is specified, the start time stamp is used to identify a TS packet having a time stamp that matches the Start time stamp in the stream, and the next TS packet of the TS packet is the first TS for complementation. Identify the packet.

  Since the Start time stamp value sent from the client is a normal value as a result of the CRC check, the complement target is from the next TS packet.

  As for the end of the supplementary TS packet, the approximate position is specified by End STC and the exact position is specified by End time stamp in the same manner as Start.

  However, the end is the TS packet immediately before the End time stamp.

  When the head and end complementary TS packets can be specified, the TS packet complement server 131 continuously unicasts from the head to the end as a TS to be complemented to the client.

  When sending the supplementary TS packet, the service_id, the Start STC, the End STC, the Start time stamp, and the End time stamp sent at the time of the request from the client are returned together with the TS data to the client as it is.

  Next, the structure of transmission data will be described.

  Referring to FIG. 4, in addition to detecting whether there is a data error in the packet by generating the CRC value of the current TS packet by using the CRC value of the previous TS packet as an initial value, the TS value It is possible to detect whether the packet sequence is continuous.

  With regard to the CRC, commonly used ones such as CRC-8, CRC-12, CRC-16, CRC-32 and CRC-CCITT may be used.

  In addition, although the accuracy of detecting a data error is lowered, a checksum or the like may be used instead of the CRC.

  The CRC generation unit 121 regards the transmission data as a bit string, adds a remainder value divided by a certain generation polynomial to the transmission data, and transmits the transmission data. The reception side performs the same calculation, and adds the CRC value (transmission data). To determine whether the result is the same.

  When the checksum is used, the data strings are sequentially added and the added value is added. At this time, carry is ignored. The receiving side also performs the same processing and compares it with the added value that has been added.

  Normally, the CRC value is calculated by a program as shown in FIG. 5, but in this embodiment, the CRC value is calculated by a program as shown in FIG. As is apparent from comparing the two, conventionally, the initial value of the CRC value is zero, but in this embodiment, the initial value of the CRC value is the CRC value of the immediately preceding packet.

  On the receiving side, the CRC value of the immediately preceding TS packet that can be received is similarly treated as the initial value of the remainder calculation, and it is evaluated whether the TS packet is sent continuously with the immediately preceding TS packet.

  Since the CRC value is inherently added to the division by the generator polynomial, it does not take an extreme value even if it is treated as an initial value, and no carry that causes inconsistency in the operation occurs.

  Next, the configuration on the receiving side will be described.

  In the present embodiment, the receiving side will be described by taking as an example a system that can receive IP multicast broadcast and perform live viewing and stored content viewing.

  Referring to FIG. 7, the communication control unit 201 performs network-related protocol control and server communication control in order to receive a digital broadcast distribution service based on IP multicast.

  The distribution service TS received by the IP multicast is sent to the error detection unit 203.

  Also, when an abnormality is detected in the stream by error detection, the communication control unit 201 acquires information for specifying the abnormal part from the error detection, and sends it to the TS packet complement server 131 as a complement request.

  When complement data is transmitted from the server 131 side in response to the complement request, the communication control unit 201 outputs a complement TS packet, a service_id, a Start timestamp, an End timestamp, a Start STC, and an End STC to the file complement controller 205. .

  When a complement request is sent to the TS packet complement server 131, the service_id of the currently received stream is also sent to the server 131.

  The currently received service_id is information necessary for the reception start procedure, and is already known at the time of this control.

  However, if the service is intended to complement the currently serviced content, the server knows the stream being sent, so it is unnecessary to send service_id.

  Whether the error detection unit 203 performs the same calculation on the received TS packet as the CRC value calculation performed when the TS distributed by the broadcast service server 129 is generated, and is the same as the added CRC value? The TS packet is checked by determining whether or not.

  When calculating the CRC value, since the CRC value of the immediately preceding TS packet is used as the initial value on the server side, this error detection is calculated in the same way.

  Referring to FIG. 8, within the error detection unit 203, a register 301 for storing the immediately preceding CRC value and a start time for sequentially storing the time stamps of TS packets that have been successfully acquired without detecting an error. A stamp register 303; an end time stamp register 305 that stores a time stamp value of a TS packet that can be normally acquired first after an error is detected; and a start STC that stores an STC value when an abnormality is detected during CRC check. The register 307 and an End STC register 309 for sequentially storing STC values at the time when a normal value is obtained at the time of CRC check are held, and when a normal TS packet is detected for the first time after error detection, the communication control unit 201 For service_id, Start timestamp, End The time stamp, the Start STC, the End STC, and the acquired packet count are output, and the communication control unit 201 is requested to issue a request for a complementary TS packet to the TS packet complementary server 131.

  Returning to FIG. 7, the time reproduction unit 207 measures the processing timing of the TS stream necessary for the stream to normally maintain the buffer state based on the time stamp given to the distributed TS packet. The TS packet output time for the subsequent block is reproduced. Internally, a 27 MHz, 32-bit counter sequentially counts with a clock, and when the value of this counter exceeds the time stamp value, the target TS packet is output to the subsequent stage.

  The clock recovery unit 208 reproduces the clock used by the receiving device based on the received signal.

  The STC unit 209 reproduces the STC used by the receiving device based on the PCR that has received the STC.

  The file complement control unit 205 reads the stream accumulated in the accumulation unit 210, and simultaneously obtains the complement TS packet acquired from the TS packet complement server 131, the service_id, the Start time stamp, the End time stamp, the Start STC, and End. Based on the STC and the acquired packet count, a complement position is specified, and TS packets that could not be normally received are complemented.

  The storage unit 210 stores the stream data from the TS demultiplexer 211.

  The video decoder, audio decoder, and data broadcast browser 213 reproduce video, audio, and data based on the input TS and output them to the monitor 215 and the speaker 217.

  FIG. 9 shows a program for CRC check performed by the error detection unit 203. In crc_check (), crc_code () is called, a CRC value calculated from the packet data is obtained, compared with the CRC value added to the packet, and the validity of the packet is determined based on whether or not they match.

  In the above embodiment, the service_id, the Start time stamp corresponding to the TS packet immediately before the error, the End time stamp corresponding to the TS packet after the error, the Start STC corresponding to the TS packet immediately before the error, and the TS packet after the error The end STC to be received is obtained at the receiving side, and the TS packet complementing server 131 is requested to retransmit the error TS packet identified by them, and the TS packet complementing server 131 receives the service_id, the start time stamp, the end time stamp, the start STC, the end By returning the STC to the receiving apparatus as it is, the file complementing control unit 205 of the receiving apparatus can insert the retransmitted TS packet at the correct position.

  Instead, the receiver assigns a serial number to the error, and the receiver sends it to the TS packet supplement server 131 together with the service_id, the Start timestamp, the End timestamp, the Start STC, and the End STC. Returns the serial number together with the complementary TS packet to the receiving device, and the file complement control unit 205 of the receiving device matches the serial number, so that the retransmitted packet can be inserted at the correct position.

  In addition, the receiving apparatus assigns a serial number to the TS packet that has been successfully received, and the receiving apparatus transmits it to the TS packet complementing server 131 together with the service_id, the Start time stamp, the End time stamp, the Start STC, and the End STC. The packet complementing server 131 returns the serial number together with the complementary TS packet to the receiving device, and the file complementing control unit 205 of the receiving device matches the serial number, so that the retransmitted packet can be inserted at the correct position. However, since the serial number of the TS packet that can be normally received is offset when complementation is normally performed, it is necessary to correct the offset for the serial number together with the insertion. In addition, in the IP network, a complementary TS packet corresponding to an error that occurred later may reach the receiving device earlier than a complementary packet corresponding to an error that occurred earlier. It is necessary to complete the packets after arranging them in the order of error occurrence.

  Both the distribution server and the receiving device can be configured by hardware, software, or a combination thereof.

  FIG. 10 shows an example when a transmission error occurs in one TS packet.

  An error of one packet can be detected by CRC check of the packet.

  When a transmission error occurs in one TS packet, the time stamp corresponding to the packet immediately before the error, the time stamp corresponding to the packet after the error, the value of the system time clock corresponding to the packet immediately before the error, The system time value corresponding to the packet is acquired, and these are transmitted to the TS packet complementing server 131 together with Service_id.

  The TS packet complementing server 131 identifies the packet based on the information sent and unicasts it to the receiving device. At the same time, the time stamp corresponding to the packet immediately before the error sent, the time stamp corresponding to the packet after the error, the value of the system time clock corresponding to the packet immediately before the error, the system time corresponding to the packet after the error And Service_id are transmitted to the receiving apparatus.

  The receiving apparatus inserts the unicast TS packet at the correct position based on the additional information.

  FIG. 11 shows an example when transmission errors occur in a plurality of TS packets.

  When a transmission error occurs in a plurality of packets, the CRC check results in an error from the first error packet to the next packet after the last error packet.

  When a transmission error occurs in a plurality of TS packets, the time stamp corresponding to the packet immediately before the error, the time stamp corresponding to the next packet packet after the error, the value of the system time clock corresponding to the packet immediately before the error, The system time value corresponding to the packet next to the packet after the error is acquired, and these are transmitted to the TS packet complement server 131 together with Service_id.

  The TS packet complementing server 131 identifies the packet based on the information sent and unicasts it to the receiving device. At the same time, the time stamp corresponding to the packet immediately before the error sent, the time stamp corresponding to the packet after the error, the value of the system time clock corresponding to the packet immediately before the error, the system time corresponding to the packet after the error And Service_id are transmitted to the receiving apparatus.

  The receiving apparatus inserts the unicast TS packet at the correct position based on the additional information.

It is a figure which shows that a missing packet is complemented by embodiment of this invention. It is a block diagram which shows the structure of the digital broadcast data delivery system by embodiment of this invention. It is a block diagram which shows the structure of the delivery server by embodiment of this invention. It is a format figure which shows the structure of the transmission packet by embodiment of this invention. It is a figure which shows the program for calculating the CRC value by a prior art example. It is a figure which shows the program for calculating the CRC value by embodiment of this invention. It is a block diagram which shows the structure of the receiver by embodiment of this invention. It is a block diagram which shows the structure of the error detection part 203 shown in FIG. It is a figure which shows the program of the error detection by embodiment of this invention. It is a conceptual diagram which shows Example 1 of this invention. It is a conceptual diagram which shows Example 2 of this invention.

Explanation of symbols

107 Redistribution Server 109 Tuner 113 Storage Unit 115 Demultiplexer 117 Clock Recovery Unit 119 First Multiplexer 121 CRC Generation Control Unit 123 Second Multiplexer 125 Register 127 Storage Control Unit 129 Broadcast Service Server 131 TS Packet Supplementary Server 201 Communication Control Unit 203 Error detection unit 205 File complement control unit 207 Time reproduction unit 208 Clock recovery unit 209 STC generation unit 210 Storage unit 211 TS demultiplexer 213 Video decoder / audio decoder / data broadcast browser 215 monitor 217 speaker

Claims (11)

A digital broadcast data distribution system for distributing digital broadcast data from a distribution server to a plurality of receiving devices,
The distribution server
Error detection symbol insertion means for inserting an error detection symbol for detecting a transmission error of each distribution packet, a discontinuity error of the distribution packet, or both into the digital broadcast data;
Multicast means for multicasting the digital broadcast data in which the error detection symbol is inserted to a plurality of receiving devices;
Unicast means for unicasting a delivery packet requested to be retransmitted from a certain receiving device to the receiving device;
With
Each receiving device
Using the error detection symbol, error detection means for detecting a transmission error of each distribution packet, a discontinuity error of the distribution packet, or both;
Retransmission request means for requesting the distribution server to retransmit the distribution packet in which an error is detected;
A digital broadcast data distribution system comprising: The digital broadcast data distribution system according to claim 1,
The receiving device is:
When the error detecting means detects an error, a system time for detecting a first system time clock corresponding to the packet immediately before the packet in which the error has occurred and a second system time clock corresponding to the packet after the error is recovered Clock detection means;
System time clock detection for detecting a first time stamp corresponding to a packet immediately before a packet in which an error has occurred and a second time stamp corresponding to a packet after error recovery when the error detecting means detects an error Means,
Further comprising
The retransmission request means includes the first system time clock, the second system time clock, the first time stamp, and the second time as error location identification information for identifying an error location in the distribution server. Sending a time stamp to the delivery server;
The distribution server uses the first system time clock, the second system time clock, the first time stamp, and the second time stamp as error location identification information, and uses the error location packet as a packet. A digital broadcast data distribution system further comprising means for reading and unicasting the packet to a receiving apparatus that has issued a retransmission request. The digital broadcast data distribution system according to claim 2,
The distribution server unicasts the packet at the error location to a receiving apparatus that has issued a retransmission request, and simultaneously receives the first system time clock, the second system time clock received from the receiving apparatus, An error location identification information return means for returning the first time stamp and the second time stamp to the receiving device as they are;
The receiving device uses the first system time clock, the second system time clock, the first time stamp, and the second time stamp received simultaneously with the packet at the error location as error location identification information. A digital broadcast data distribution system, wherein the received error packet is inserted into a normally received packet sequence. The digital broadcast data distribution system according to claim 1 or 2,
The receiving device is:
An error location specifying information generating means for generating error location specifying information for specifying each error location in the receiving device;
The retransmission request means also transmits the error location specifying information to the distribution server,
At the same time as sending the packet of the error location, the distribution server returns the received error location specifying information as it is to the receiving device,
The digital broadcast data distribution system, wherein the receiving device further includes a packet insertion unit that inserts a packet at an error location into a location specified by error location specifying information. The digital broadcast data distribution system according to claim 1 or 2,
The receiving device is:
A serial number counting means for counting the serial numbers of packets that have been successfully received from the start of reception;
The retransmission request means also transmits a serial number of a packet immediately before an error occurs to the distribution server,
At the same time as sending the packet at the error location, the distribution server returns the received serial number as it is to the receiving device,
The receiving device is:
A packet insertion means for inserting a packet retransmitted at an error occurrence location specified by the serial number in ascending order of the returned serial number;
Serial number correction means for increasing the serial number of subsequent packets by the number of inserted packets;
A digital broadcast data distribution system further comprising: A digital broadcast distribution method for distributing digital broadcast data from a distribution server to a plurality of receiving devices,
An error detection symbol insertion step in which the distribution server inserts into the digital broadcast data an error detection symbol for detecting a transmission error of each distribution packet, a discontinuity error of the distribution packet, or both;
A multicast step in which the distribution server multicasts the digital broadcast data in which the error detection symbol is inserted to a plurality of receiving devices;
An error detection step in which a receiving device detects a transmission error of each distribution packet, a discontinuity error of the distribution packet, or both using the error detection symbol;
Each of the receiving devices requests a retransmission request to the distribution server to retransmit the distribution packet in which an error is detected;
A unicast step in which the distribution server unicasts a distribution packet requested to be retransmitted from the certain receiving device to the receiving device;
A digital broadcast data distribution method comprising: A distribution server in a digital broadcast distribution system for distributing digital broadcast data from a distribution server to a plurality of receiving devices,
Error detection symbol insertion means for inserting an error detection symbol for detecting a transmission error of each distribution packet, a discontinuity error of the distribution packet, or both into the digital broadcast data;
Multicast means for multicasting the digital broadcast data in which the error detection symbol is inserted to a plurality of receiving devices;
Unicast means for unicasting a delivery packet requested to be retransmitted from a certain receiving device to the receiving device;
A distribution server comprising: A receiving device in a digital broadcast distribution system for distributing digital broadcast data from a distribution server to a plurality of receiving devices,
Error detection means for detecting a transmission error of each distribution packet, a discontinuity error of the distribution packet, or both using an error detection symbol for detecting a transmission error of each distribution packet, a discontinuity error of the distribution packet, or both When,
Retransmission request means for requesting the distribution server to retransmit the distribution packet in which an error is detected;
When the error detecting means detects an error, a system time for detecting a first system time clock corresponding to the packet immediately before the packet in which the error has occurred and a second system time clock corresponding to the packet after the error is recovered Clock detection means;
System time clock detection for detecting a first time stamp corresponding to a packet immediately before a packet in which an error has occurred and a second time stamp corresponding to a packet after error recovery when the error detecting means detects an error Means,
With
The retransmission request means includes the first system time clock, the second system time clock, the first time stamp, and the second time as error location identification information for identifying an error location in the distribution server. A receiving apparatus that transmits a time stamp to the distribution server.   The program for functioning a computer as a delivery server of Claim 7.   A program for causing a computer to function as the receiving device according to claim 8. A digital broadcast data distribution system in which a distribution server distributes digital broadcast data divided into a series of packets to a receiving device,
The distribution server
The packet included in the series of packets should be transmitted by the packet with the error detection code generated to detect the packet error added to the packet immediately before the packet as an initial value. Applying the data as a bit string to a predetermined arithmetic expression to generate the error detection code and adding the error detection code to the packet;
Transmission means for transmitting a series of packets to which the error detection code is added to a network,
The receiving device is:
For packets included in the series of packets received from the network, data excluding the error detection code from data transmitted by the packet with the error detection code given to the packet immediately before the packet as an initial value Is applied to the predetermined arithmetic expression as a bit string, the error detection code is calculated, and it is determined whether the calculated error detection code matches the error detection code added to the packet. Error packet determination means for determining the packet as an error packet when not,
Retransmission request means for requesting the distribution server to retransmit a packet determined to be an error packet by the error packet determination means;
A digital broadcast data distribution system comprising:

Images