JP2002101074A - Data distribution system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a data distribution system, suitable for transmitting information generated in one location to plural portions scattered over a wide region, in a short time without errors, by using a satellite line. SOLUTION: This system is constituted of center equipment 10 and distributed server equipment 20a, 20b. The center equipment repeats simultaneous transmission regarding identical data asynchronously with the receiving of receiving finish information which is returned from the dispersed server equipment 20a, 20b concerning the data transmitted simultaneously. The distributed server equipment 20a, 20b receives data which are transmitted repeatedly, and returns the receiving finish information to the center equipment 10, only when completion of data, free of transmission errors is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a data distribution system for distributing data from a center device to a plurality of terminal devices via a satellite line, and more particularly to a technology for synchronizing information held by the center device and the terminal devices.

[0002]

2. Description of the Related Art Information generated in one place can be obtained in a short time.
In addition, a satellite line is one of suitable means as a transmission medium for transmitting to a plurality of locations scattered in a wide area. For example, information requiring urgency such as weather information, earthquake information, disaster occurrence information, etc. is sent from a center device installed at an information source such as the Japan Meteorological Agency to a plurality of terminal devices scattered nationwide periodically or For irregular distribution, it is convenient to use a satellite line.

However, in transmitting character information and control information, data transmitted from the center device must be reliably transmitted to the terminal device without error. Data reception confirmation (confirmation that data has been received securely) because transmission errors are more likely to occur, transmission delays are longer, and transmission bandwidth and transmission output are more restricted than in It is difficult to adopt a protocol.

For example, when TCP, which is widely used as a LAN protocol, is adopted as a communication protocol between ground stations connected by a satellite line, a reception confirmation packet is always returned from the reception side to the transmission side. Therefore, a transmission delay of one round trip or more occurs every time data is transmitted, and the throughput is significantly reduced. On the other hand, a method has been proposed in which an apparatus that returns a pseudo acknowledgment is inserted in an input unit to a satellite line of a ground station to make it appear as if the other apparatus is connected immediately. According to this method, although the throughput is ensured, there is a problem that the status of the transmission error actually occurring in the satellite link is not reflected on the transmitting side.

[0005] Japanese Patent Application Laid-Open No. 10-215246 discloses a data distribution apparatus for realizing efficient data transmission by using a satellite line and a terrestrial line together and using a predetermined transmission pattern. Is disclosed,
In such a device, there is a restriction that a ground line and its connection means are always required.

[0006]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above-mentioned problems, and uses only a satellite line as a transmission path to transmit information generated in one place in a short time. It is another object of the present invention to provide a data distribution system suitable for transmitting data to a plurality of locations scattered in a wide area without error.

[0007]

In order to achieve the above object, a data distribution system according to the present invention is a data distribution system in which a center device distributes data to a plurality of terminal devices via a satellite line, The center device broadcasts the data to be distributed to the terminal device through the satellite line, and waits for a reply about the reception confirmation from the terminal device with respect to the broadcast data. A broadcast repetition control unit that repeats the broadcast by the broadcast unit, wherein the terminal device receives the broadcast data, and completes the transmission without error by the reception by the reception unit. Reception completion determining means for determining whether or not data has been obtained;
Only when complete data without transmission errors can be obtained, a message to that effect is returned to the center device via the satellite line, and when complete data without transmission errors cannot be obtained. Is characterized by comprising a reception repetition control means for repeating reception of the same data by the reception means.

For example, the center device repeats the broadcast of the same data asynchronously with the reception of the reception completion notification returned from each terminal device to the broadcast data, and each terminal device repeatedly transmits the data. Only when the received data is received and complete data without transmission errors can be obtained, a reception completion notification is returned to the center device.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a data distribution system 100 according to the present invention. This data distribution system 100 is a distribution system for weather information and disaster occurrence information (disaster situation distribution map),
A center device 10 which is a source of these information, a plurality of terminal devices 31 to 33 connected to the center device 10 by a LAN 30, and a plurality of terminal devices connected to the center device 10 via a bidirectional satellite line by a communication satellite 50. It is composed of a distributed server device 20 and a plurality of terminal devices 41 to 43 connected to each distributed server device 20 via a LAN 40.

The data distribution system 100 distributes weather information that periodically occurs in the center device 10 and disaster occurrence information that occurs irregularly to a plurality of distributed server devices 20 in a short time. By doing
The information placed in the center device 10 browsed by the terminal devices 31 to 33 and the information placed in the distributed server device 20 browsed by the terminal devices 41 to 43 are synchronized (the content is kept within the shortest possible time lag). Maintain the same).

The center device 10 is a data distribution server for weather information and disaster occurrence information, and
A computer functioning as a WWW server on the N30; a transmission unit 11, a transmission data storage unit 12, and a reception unit 13
And a reception status confirmation unit 14 and the like. The transmission data accumulation unit 12 is a source of information in the data distribution system 100. When acquiring weather information and disaster information from an information provider such as the Meteorological Agency via a dedicated line or the like, an ID (data ID) for identifying the information. And a communication device for storing and storing the information together with the information. The weather information is received and stored, for example, every 15 minutes, and the disaster occurrence information is received at each occurrence. Accumulate. When new information is acquired, the fact (data ID) is notified to the transmission unit 11 and the reception status confirmation unit 1
Notify 4.

When the transmitting unit 11 receives a notification from the transmission data storage unit 12 that new weather information or disaster occurrence information has occurred, the transmission unit 11 reads the corresponding information from the transmission data storage unit 12, and stores the information, the data ID, and the like. The error detection code added to each block data of a fixed length (for example, 2 Kbytes) is sent to a plurality of distributed server devices 20 installed throughout Japan by using the downstream channel of the satellite link by the communication satellite 50. A transmission control circuit, a modulator, an amplifier, etc., which repeats broadcasting.

In this embodiment, the repetition cycle and timing of the broadcast are values determined from the transmission band of the downlink channel and the total amount of data to be transmitted. Are not synchronized. This is to complete data distribution in as short a time as possible. The transmitting unit 11 receives a notification from the reception status confirming unit 14 that the transmission may be terminated, or informs the transmission data storage unit 12 that new weather information has been generated. Until the notification is received, on the other hand, as for the disaster occurrence information, the same data I
The broadcast of the information on D is repeated. As described above, the difference in the transmission end condition between the weather information and the disaster occurrence information is based on the nature of the information (whether the immediately preceding information becomes obsolete due to the occurrence of new information). Because.

The receiving unit 13 receives data (notification of completion of reception of weather information and the like) returned from each distributed server device 20 using the upstream channel of the satellite link by the communication satellite 50, and receives the data. ID (number specifying the distributed server device 20 that sent back) and data ID included in
And a demodulator or the like for extracting the information and transmitting it to the reception status confirmation unit 14.

The reception status confirmation unit 14 transmits the data based on the data ID notified from the transmission data storage unit 12 and the device ID and the data ID of the distributed server device 20 related to the completion of the reception notified from the reception unit 13. The reception status is managed for each type of data and for each distributed server device, and the number of distributed server devices that have completed reception is reduced to 90% of the total number (all the number of distributed servers managed in advance as receivable servers). Monitors whether or not the data has been reached, and if so, sends the transmission data (repeated broadcast)
Is transmitted to the transmitting unit 11 together with the data ID. The reason why the reception completion notification from all the distribution server devices 20 is not waited is that the reception completion notification cannot be returned due to a failure or the like.
This is because it is considered that there may be 0 devices.

FIG. 2 shows a group of tables (reception status tables) for managing the reception status of each distributed server device 20, that is, storage data held and updated inside the reception status confirmation unit 14. Here, it is determined whether each distributed server device (device ID = 1, 2, 3, 4,...) Has completed reception of three different types of transmission data 1 to 3 (data ID = 1 to 3). Three reception status tables in which reception statuses (flags) indicating the above are recorded are shown.

The reception status confirmation unit 14 notifies the transmission data storage unit 12 that new information has been generated (data ID).
Is received, a single reception status table (recorded as “reception incomplete” for all distributed server devices) for managing the transmission data of the data ID is created and received from the reception unit 13. When the device ID and the data ID of the completed distributed server device are received, the corresponding part is rewritten to “reception completed”.

The distribution server device 20 is a central device 10
Is a computer that serves as a terminal for receiving weather information and disaster occurrence information distributed from the Internet and also functions as a WWW server on the LAN 40.
It includes a reception data storage unit 23, a data restoration unit 24, and the like. The receiving unit 21 receives the data broadcast from the center device 10 using the downlink channel of the satellite link by the communication satellite 50, and converts the information (weather information or disaster occurrence information) and the data ID included therein. The data is extracted and sent to the received data storage unit 23, and the error detection code included in the received data is used to check whether transmission errors have occurred in all block data constituting the received data. If it does not occur, a demodulator, an error detector, or the like that notifies the transmitting unit 22 of that fact.

The receiving unit 21 manages each data ID using a flag or the like so that the same (data ID)
Is the same), it is detected that no transmission error has occurred in all block data, or
Until the data restoration unit 24 receives a notification that the data restoration is completed, the reception of the data associated with the data ID is repeated.

When receiving the data such as weather information and the data ID transmitted from the receiving unit 21, the received data storage unit 23 receives the data ID regardless of whether a transmission error is detected in the received data. The data restoring unit 24 is a disk device or the like for storing and storing information, and when new data is accumulated, the data restoring unit 24 notifies the data restoring unit 24 of the fact (data ID). When a notification that new data has been stored is received from the reception data storage unit 23, all stored data having the same data ID as the data ID of the data is read from the reception data storage unit 23, and each block data at the same location is read out. By applying the principle of majority vote to the data and reconstructing the data, an attempt is made to restore the data to the data estimated to be correct.

FIG. 3 is a diagram showing how data is restored by the data restoring unit 24. Here, data consisting of 11 block data accumulated by three times of repeated reception (FIG. 3A) -(C)) and data (FIG. 3 (d)) restored from the three received data.
In the figure, each cell corresponds to one block data, and the symbol written on each cell indicates the same content. That is, the block data in which the same symbol is described indicates that the contents are completely the same.

The data restoring unit 24 outputs the largest number (two or more in this figure) of the same contents of block data for each block data (three squares located at the same digit in this figure) at the same location. Identify (apply the principle of majority voting)
By reconstructing using the block data, an attempt is made to restore the entire data. For example, in the second block data shown in the figure, the contents “B” and “X” exist, but the content “B” is adopted according to the principle of majority rule. When one block data can be adopted for all the block data in accordance with the principle of majority decision in this way, the data reconstructing unit 24 converts the data reconstructed from the group of the adopted block data. The received data is stored in the received data storage unit 23 as correct received data, and the transmission unit 22 and the reception unit 21 are notified that the restoration of the data of the data ID is completed (data ID).

The transmitting unit 22 receives a notification from the receiving unit 21 that complete data without transmission errors has been received (data ID), or that the data has been restored from the data restoring unit 24 (data ID). If you receive a notification,
The completion of the reception is indicated by its data ID and its own device I
Along with D, a reply is sent to the center device 10 using the upstream channel of the satellite link by the communication satellite 50.

The terminal devices 31 to 33 and 41 to 43 are placed in the transmission data storage unit 12 of the center device 10 and the reception data storage unit 23 of the distributed server device 20 by way of a WWW browser via the LANs 30 and 40, respectively. Computer that provides a function of browsing the latest weather information and disaster occurrence information. Next, the operation of the data distribution system 100 configured as described above will be described.

FIG. 4 shows a communication sequence of the data distribution system 100 when focusing on one data. In this figure, one center device 10 is shown for convenience.
2 shows communication exchanges between the two distributed server devices 20 (20a, 20b). In this figure, when transmission data (data n) such as new weather information is generated, the center device 10 continuously repeats the broadcast of the data n. Immediately after completing the four transmissions, the transmission termination condition is satisfied (here, the number of distributed server devices that have completed the reception of data n has reached 90% of the total, or new weather information has been transmitted. Therefore, the transmission of the data n has been completed.

On the other hand, the distributed server device 20a stores data n
In the first reception for, no transmission error was detected, so that the reception was completed (device ID and data I
D (including D). Also,
The distributed server device 20b detects a transmission error in at least one block data in any of the three receptions of the data n, but restores the data as shown in FIG. 3 when the third reception is completed. That reception has been completed (including device ID and data ID).
To the center device 10.

In practice, if it becomes necessary to distribute other data (such as disaster occurrence information that occurs asynchronously) by the time the distribution of one data by the above exchange is completed, the center device 10 Is that the two or more types of data are temporally overlapped as a distribution process (a series of processes from the start of repetition of broadcasting to the end), and each transmission is performed in a time-division manner. The distribution of these two or more types of data is advanced in parallel in time.

FIG. 5 is a flowchart showing the operation procedure of the center device 10 when focusing on one data. The transmitting unit 11 that has received notification from the transmission data storage unit 12 that new weather information or disaster occurrence information has occurred.
Reads out the information from the transmission data storage unit 12, generates and incorporates an error detection code in block units, and broadcasts the error detection code to the plurality of distributed server devices 20 using the downlink channel of the satellite line together with the data ID. Is repeated (step S70).

The receiving unit 13 collects (receives) the reception completion notification returned from each distributed server device 20 (step S71), and passes it to the reception status confirmation unit 14, thereby receiving the reception status table shown in FIG. Is updated (step S7).
2). As a result, when the number of distributed server devices 20 that have completed reception reaches 90% of the total (Yes in step S73), the reception status confirmation unit 14 may end the repeated broadcast of the data. Is transmitted to the transmission unit 11, and the transmission unit 11 terminates transmission of the data (step S75).

On the other hand, even if there is no notification from the reception status confirmation unit 14 (No in step S73), if a notification that new information has occurred is received from the transmission data storage unit 12, the transmission The unit 11 determines whether the data has become stale (step S74). As a result, if it is determined that the data is obsolete (Yes in step S74), for example, a notification that the transmitted data is weather information and that the latest weather information instead of the content is newly generated If the data has been received, the transmission of the data is terminated (step S75), and repeated broadcasting of new weather information is started (steps S70 to S70).
S75).

On the other hand, when it is determined that new information (disaster occurrence information or the like) has occurred but the data has not become stale (No in step S74), the termination condition for the data (steps S73 and S74) Until one of the conditions is satisfied, the broadcast of the data is repeated and the same monitoring is continued (steps S71 to S74).
In addition, for newly generated information, a new repetitive broadcast is started independently and in parallel with the data (steps S70 to S75).

In this way, as for the weather information, until 90% or more of the distributed server devices 20 of the total number have completed the reception or new weather information to replace the weather information is generated, As for the occurrence information, data distribution is repeatedly repeated until 90% or more of the distributed server devices 20 of the total number have completed the reception. FIG.
Server device 20 when focusing on two pieces of data
6 is a flowchart showing the operation procedure of FIG.

Receiving unit 2 that has received the transmitted data
1 (step S80), the data is sent to the reception status confirmation unit 14 to be accumulated and stored for each data ID (step S81), and it is checked whether a transmission error has occurred for each block data. (Step S
82). As a result, if no transmission error has occurred for all block data (Y in step S82)
es), the receiving unit 21 notifies the transmitting unit 22 of the fact, and ends the subsequent reception of the data (even if the same data is transmitted thereafter, the reception process is not performed). Then, the transmitting unit 22 that has received the notification returns a message to the effect that reception of the data has been completed to the center device 10 together with the data ID and the device ID.

On the other hand, when a transmission error is detected for at least one block data (step S8).
2), the data restoring unit 24, which has been notified from the received data storage unit 23 that new data has been stored, reads out from the received data storage unit 23 all data having the same data ID as the data. By applying the principle of majority rule to each block data, an attempt is made to restore data having contents estimated to be correct (step S83).

As a result, when the entire data can be restored by the principle of majority decision for all block data (Yes in step S83), the data restoring unit 24 notifies the receiving unit 21 and the transmitting unit 22, the receiving unit 21 receiving the notification terminates the subsequent reception of the data, and the transmission unit 22 returns to the center device 10 that the reception of the data is completed.

If a transmission error is detected in the received data (No in step S82) and complete data is not restored by using the received data (step S8)
(No in 3), the receiving unit 21 repeats the reception of the data (step S80). In this way, until data without transmission errors is received or until all block data is determined deterministically by the principle of majority (1
The reception of that data is repeated until the entire data is restored).

As described above, the present data distribution system 10
0, the same data is transmitted from the center device 10 to the distributed server device 20 until a certain transmission end condition is satisfied.
Will be broadcast repeatedly. Then, the repetition period and the broadcast timing are performed asynchronously with the reception completion notification returned from each distributed server device 20. As a result, the data identity between the center device 10 and each distributed server device 20 is maintained in a shorter time than before.

In addition, in response to the broadcast from the center device 10, only the notification that the reception has been completed is sent to the distributed server device 20.
Is returned to the center device 10. Therefore, compared to the conventional protocol that returns "reception complete" or "reception incomplete" every time data is transmitted, communication traffic on the upstream channel of the satellite line is reduced, and processing time associated with reception confirmation is reduced. Be transformed into

As described above, since the data placed in the center device 10 and the data placed in each distributed server device 20 are kept synchronized and synchronized within a small time lag, For example, the terminal devices 41 to 43 are connected to the distributed server device 2 connected to the LAN 40 without accessing the data of the center device 10 installed remotely.
By simply accessing 0, the same data can be referred to, and the total amount of data passing through the satellite line is reduced.

Although the data distribution system according to the present invention has been described based on the embodiment, it goes without saying that the present invention is not limited to this embodiment. For example, in the present embodiment, as one of the transmission termination conditions, a certain percentage (90%) of all the distributed server devices 20
Although it is adopted that this device completes reception, an end condition based on the maximum number of times of broadcasting, the maximum time, or the like may be used instead or in addition to this.

In the data distribution system 100,
Only the notification of “reception completed” is returned from the distributed server device 20 to the center device 10, but instead, only the notification of “reception not completed” may be returned. This also allows traffic on the satellite link to be suppressed and the center device 10 to know (estimate) that data has been transmitted to each distributed server device 20.

In the data distribution system 100,
A data ID is assigned to each piece of information such as weather information, and the information is used as a unit for repeated transmission. However, if one piece of information is composed of a plurality of files, a data ID is assigned to each file. Alternatively, a file may be used as a unit for repeated transmission. The data restoration unit 24 of the distributed server device 20 restores data by applying the principle of majority decision.
Alternatively, when block data without a transmission error is received at least once for each block data, the entire data is restored by reconstructing using only the block data without a transmission error. Is also good.

[0043]

As is apparent from the above description, the data distribution system according to the present invention is a data distribution system in which a center device distributes data to a plurality of terminal devices via a satellite line. Means for broadcasting the data to be distributed to the terminal device via the satellite line, and the same means for the same data without waiting for a reply regarding the reception confirmation of the broadcast data from the terminal device. A broadcast repetition control unit for repeating the broadcast by the broadcast unit, wherein the terminal device obtains complete data without transmission errors by receiving the broadcast data and receiving the broadcast data by the reception unit. Reception completion judgment means for judging whether or not transmission was completed, and only when complete data without transmission errors could be obtained,
This is returned to the center device via the satellite line, and if complete data without a transmission error cannot be obtained, reception repetition for repeating reception of the same data by the reception means is repeated. Control means.

As a result, since the broadcast by the center device is repeated asynchronously with the response from the terminal device regarding the reception confirmation, the data distribution is completed in a shorter time as compared with the conventional method of waiting for the certainty of reception at each transmission. Is done. In addition, since replies related to reception confirmation are limited to only notification that reception has been completed, traffic on the upstream side of the satellite line is suppressed, processing associated with reception confirmation is reduced, and data distribution throughput is reduced. Be improved.

Here, the data is composed of a plurality of block data, and the reception completion judging means is configured to accumulate and store the repeatedly received data and a storage unit for storing the same based on the plurality of stored data. For each block of data, identify the block data that is presumed to be correct,
A data restoration unit that attempts to restore one piece of data without transmission errors by reconstructing with the identified block data, and completes data without transmission errors when the restoration by the data restoration unit is completed. A determination unit that determines that the information has been acquired may be provided.

For example, the data restoring unit specifies one block data that is estimated to be correct by applying the principle of majority decision regarding the identity of contents to each block data at the same location, and When one block data is specified by the data restoring unit for all the block data, it may be determined that complete data without a transmission error has been obtained.

As a result, even if a transmission error occurs in all of the repeatedly received data, the data is restored to the data estimated to be correct in block units. Is completed. The broadcast repetition control unit includes a counting unit that counts the number of terminal devices that have returned a notification that complete data has been acquired, and the broadcast control unit includes a counter that counts the number when the number reaches a predetermined constant value. And a termination control unit for terminating the broadcasting by the reporting means.

As a result, it is possible to avoid a problem caused by returning only the notification of the completion of reception, for example, a problem caused by the presence of a terminal device which cannot reply to that effect due to a failure or the like. Is done. The broadcast repetition control means includes a detection unit that detects that new data has occurred in place of data that has already been repeatedly broadcast, and a broadcast unit that detects that new data has been generated. And a termination control unit for terminating the broadcast by the broadcast means for the data repeating the above.

As a result, it is possible to avoid useless transmission caused by repeatedly transmitting stale data. As described above, according to the present invention, data generated or changed in the center device is distributed to each terminal device in a short time, and data synchronization is maintained. For example, data generated in one WWW site Can be made to follow the change of other mirror sites, and the practical effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a data distribution system according to the present invention.

FIG. 2 is a diagram showing a reception status table for managing the reception status of each distributed server device.

FIG. 3 is a diagram illustrating a state of data restoration by a data restoration unit of the distributed server device.

FIG. 4 is a communication sequence diagram of the data distribution system when focusing on one data.

FIG. 5 is a flowchart showing an operation procedure of the center device when focusing on one data.

FIG. 6 is a flowchart illustrating an operation procedure of the distributed server device when focusing on one piece of data.

[Explanation of symbols]

 Reference Signs List 10 center device 11 transmission unit 12 transmission data storage unit 13 reception unit 14 reception status confirmation unit 20, 20a, 20b distributed server device 21 reception unit 22 transmission unit 23 reception data storage unit 24 data restoration unit 30, 40 LAN 31 to 33, 41 to 43 terminal device 50 communication satellite 100 data distribution system

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 7/20 630 H04L 11/00 310B

Claims (5)

[Claims] 1. A data distribution system in which a center device distributes data to a plurality of terminal devices via a satellite line, wherein the center device transmits data to be distributed to the terminal device over the satellite line. Broadcast means for broadcasting, and a broadcast repetition control means for repeating the broadcast by the broadcast means for the same data without waiting for a reply about the reception confirmation from the terminal device for the broadcast data, A receiving unit that receives the broadcast data; a reception completion determining unit that determines whether or not complete data without a transmission error has been acquired by the reception by the receiving unit; Only when complete data without any errors can be obtained, this is returned to the center device via the satellite line, and complete data without transmission errors is returned. If it has not been possible to obtain the data, set data distribution system characterized in that it comprises a receiving repetitive control means for causing repeated reception by said receiving means for the same data. 2. The method according to claim 1, wherein the data includes a plurality of block data, the reception completion determining unit stores and stores the repeatedly received data, and a storage unit for storing the same data based on the plurality of stored data. A data restoring unit that attempts to restore one piece of data without a transmission error by identifying block data that is estimated to be correct for each block of data, and reconstructing the block data with the identified block data; The data distribution system according to claim 1, further comprising: a determination unit configured to determine that complete data without a transmission error has been obtained when the restoration by the unit is completed. 3. The data restoration unit specifies one block data that is estimated to be correct by applying the principle of majority rule regarding the identity of contents to each block data at the same location. 3. The data according to claim 2, wherein when one block data is specified by the data restoring unit for all the block data, it is determined that complete data without a transmission error has been obtained. Delivery system. 4. The broadcast repetition control means includes: a counting unit that counts the number of terminal devices that have returned a notification that complete data has been obtained; and a counter that counts the number to a predetermined constant value. 4. The data distribution system according to claim 3, further comprising: a termination control unit that terminates the broadcast by the broadcast unit when the broadcast reaches. 5. The broadcast repetition control means, comprising: a detection unit that detects that new data has occurred in place of data that has already been repeatedly broadcast; and a detection unit that detects that the new data has been generated. 4. The data distribution system according to claim 3, further comprising an end control unit for ending the broadcasting by the broadcasting means for the data which has been repeatedly broadcast.