JP2001053783A - Data distribution system, and machine readable recording medium recorded with program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain efficient data distribution by subjecting retransmission data to a broadcast communication in a block unit. SOLUTION: A distribution origin system 1 divides a distribution object file into plural blocks, adds a block number each block, and distributes them to plural distributed party systems 2-1 to 2-N by way of a communication satellite 3 by means of the broadcast communication. Also, the system receives a response which includes a received maximum block number transmitted through a ground line network 4 from each of the distributed party systems 2-1 to 2-N and manages the distribution condition of each distributed party system. When data retransmission is necessitated, a minimum block number that needs retransmission is decided from the distribution condition for every distributed party system, blocks on and after the decided block number are added with the block number one by one, and is retransmitted to plural distributed party systems through the communication satellite 3 by means of the broadcast communication. Also, the distribution destination system which repeats reception fault is eliminated from a distribution object.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a data distribution system for distributing data by broadcast communication using satellite communication.

[0002]

2. Description of the Related Art When data is distributed by satellite communication from a single distribution source system to terminals and computers scattered in remote places as distribution destination systems, generally, data is transmitted to the satellite communication system for efficient use of satellite communication. Data is distributed by broadcast communication. In addition, since the destination system often does not have a satellite communication transmission facility due to cost considerations, a ground line is used for response communication from the destination system to the source system. An example of such a data distribution system is described in Japanese Patent Application Laid-Open No. 10-336089 (hereinafter, referred to as Document 1).

[0003] In the data distribution system described in Document 1,
The data is broadcast from the distribution source system to a plurality of distribution destination systems by satellite communication, and each of the distribution destination systems requests retransmission to the distribution source system via the ground line when the data cannot be normally received. The distribution source system broadcasts all data from the beginning by satellite communication to all distribution destination systems for which retransmission has been requested.

[0004] On the other hand, Japanese Patent No. 2525669 (hereinafter referred to as Document 2) discloses that a distribution source system divides distribution data into blocks and broadcasts each block to a plurality of distribution destination systems. At the end of the broadcast, an acknowledgment request message is sent for each destination system, and upon receiving this message, the destination system checks whether there was any omission of reception, and if so, retransmits it with the block number specified. A data distribution system is described in which an acknowledgment message including a request is returned to a distribution source system, and the distribution source system transmits only a block requested to be retransmitted to the distribution destination system.

[0005]

In the prior art described in Document 1, all data is retransmitted even to a distribution destination system that cannot receive only a part of the data. Therefore, when the size of the distribution target data is large, Retransmission takes time, making it difficult to use satellite communications efficiently. On the other hand, in the prior art described in Document 2, since retransmission is performed in block units, there is no useless retransmission of data when viewed in units of distribution destination systems that request retransmission. However, since data is retransmitted individually to each destination system, if there are multiple destination systems that require the same block to be retransmitted, it is necessary to retransmit the same block at different times. In other words, the unnecessary data is retransmitted.

As described above, in the prior art, batch transmission of all data is adopted when retransmission data is broadcast, and individual transmission is adopted when retransmission data is transmitted in block units. Therefore, there has been a problem that useless data retransmission occurs.

An object of the present invention is to enable efficient data distribution by broadcasting retransmission data in block units.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention divides data to be distributed into a plurality of blocks, adds a block number to each block, and transmits the data to a plurality of distribution destination systems by satellite communication. A data distribution system that distributes data by broadcast, and receives a response containing the maximum received block number transmitted from a distribution destination system via a terrestrial network and determines the distribution status of each distribution destination system. When data retransmission is required by the system, the minimum block number that requires retransmission is determined based on the distribution status of each distribution destination system, and blocks after the determined block number are assigned block numbers one by one. , And distributes to a plurality of distribution destination systems by broadcast communication by satellite communication.

More specifically, in a data distribution system that distributes data from a distribution source system to a plurality of distribution destination systems by broadcast communication using satellite communication, the distribution source system divides distribution target data into predetermined sizes. Satellite communication transmitting means for adding the number to the block of the designated block number and broadcasting the data to a plurality of data distribution destination systems by satellite communication, and a terrestrial network. Distribution status management means for managing the distribution status of each data distribution destination system based on a response including the maximum received block number sent from each data distribution destination system via The data to be distributed is specified in block units by designating the number to the satellite communication transmitting means one by one in order from the block of Controlling the distribution is started, and it is determined whether retransmission is necessary based on the distribution status of each data distribution destination system managed by the distribution status management means. If retransmission is necessary, the satellite communication transmission is performed. The block number specified for the means is reduced to the minimum block number that requires retransmission, and thereafter, the data to be distributed is distributed in block units by sequentially specifying the block number one by one from the block to the satellite communication transmitting means. Each distribution destination system receives a block broadcast by satellite communication, and the block number added to the block is the next block number following the maximum block number already received by its own system. Satellite communication receiving means for storing the block in the storage device and updating the received maximum block number, And a communication control means for transmitting no response to the delivery source system via the terrestrial network.

As described above, in the data distribution system of the present invention, since the distribution status including the maximum received block number for each distribution destination system is managed by the distribution source system, data retransmission is required. At this time, it is possible to judge which block number should be retransmitted at least, and it is possible to prevent useless retransmission as in the related art described in Document 1 in which all data to be distributed is retransmitted. When data retransmission is required, blocks subsequent to the minimum block number requiring retransmission are sequentially added with block numbers one block at a time, and distributed to a plurality of distribution destination systems by broadcast using satellite communication. Therefore, it is possible to prevent useless retransmission as in the related art described in Reference 2 in which blocks are retransmitted individually for each distribution destination system.

[0011] When a response including the maximum received block number is transmitted from the distribution destination system to the distribution source system, the response message increases when a response is received every time one block is received, and the load on both the distribution destination and the distribution source increases. , It is desirable to perform this process each time a plurality of blocks having consecutive block numbers are received. However, when a block larger than the number next to the maximum received block number is received, that is, when a missing reception block is detected, it is desired to respond each time.

[0012] Since it takes a certain amount of time for a response including the maximum received block number to be returned from each distribution destination system regarding blocks broadcast by the distribution source system, if all blocks are continuously transmitted without interruption, If any of the distribution destination systems has a missing reception block, the return amount increases. Therefore, preferably, when the difference between the block number of the previously transmitted block and the minimum value of the maximum received block number exceeds a predetermined value, the control unit of the distribution source system temporarily stops the subsequent block transmission by the satellite communication transmitting unit. It stops and restarts block transmission when the difference falls below a predetermined value.

[0013] When a receiving block is frequently dropped in a certain distribution destination system, retransmission for retransmission frequently occurs, and the completion of data distribution to another normal distribution destination system is greatly delayed. Therefore, preferably, the control unit of the distribution source system excludes the distribution destination system having a large block reception failure from the target of the block retransmission. As a specific method of excluding from the target of block retransmission, the distribution status management means of the distribution source system determines the distribution status of each data distribution destination system as the number of successful transmission blocks in addition to the maximum received block number. And the number of unsuccessfully transmitted blocks, and the control means of the delivery source system determines, when retransmission is necessary, the transfer failure rate and untransmitted data determined from the number of successfully transmitted blocks and the number of failed transmission blocks of each data distribution destination system. The number of blocks necessary for transmission is predicted from the number of blocks and, when the ratio of the predicted number of blocks to the total number of blocks exceeds a predetermined value, the distribution destination system having the smallest received maximum block number is retransmitted. It is possible to adopt a method of excluding from the target.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, a data distribution system according to an embodiment of the present invention includes a distribution source system 1 that distributes data, and a plurality of distribution destinations that receive data distributed from the distribution source system 1. System 2-1 to 2-
N and the distribution destination system 2-1 to 2
-N, and a terrestrial network 4 used to transmit a response from the destination systems 2-1 to 2-N to the distribution source system 1. Have been.

The distribution source system 1 includes an input / output means 11 for controlling input / output between an input / output device (not shown) operated by a system administrator and the distribution source system 1, a storage device 12 for holding distribution target files, A satellite communication transmitting means 13 for transmitting a distribution target file by broadcast to the distribution source systems 2-1 to 2-N via the communication satellite 3;
Terrestrial communication receiving means 14 for receiving various responses transmitted from the communication network 1 to 2-N via the terrestrial network 4, distribution status management means 15 for managing the distribution status of each destination system,
Communication control means 16 for controlling main control of distribution source system 1
And retransmission control means 17.

Each of the distribution destination systems 2-1 to 2-N
Is a satellite communication receiving means 21 for receiving a distribution target file distributed from the distribution source system 1 via the communication satellite 3,
A storage device 23 for storing the received distribution target file;
It includes a terrestrial communication transmitting means 22 for transmitting various responses to the distribution source system 1 via the terrestrial network 4, and a communication control means 24 for controlling the main control of the own system.

Hereinafter, the functions of each unit in the distribution source system 1 and the distribution destination systems 2-1 to 2-N will be described in detail together with the overall operation.

(1) Distribution Process of Distribution Source System 1 FIG. 2 is a flowchart showing a flow of distribution process in the distribution source system 1. When the administrator of the distribution source system 1 wants to distribute a file to any of the distribution destination systems 2-1 to 2-N, the name of the distribution target file stored in an external storage device (not shown) (for example, ABC) ) Is input to the input / output unit 11 from an input device such as a keyboard (not shown).
1 reads the distribution target file having the designated file name (ABC) from the external storage device and stores it in the storage device 12 (step 1). Next, when the administrator inputs a destination to distribute the distribution target file from the input device and instructs distribution, the input / output unit 11 creates a distribution request and inputs the request to the communication control unit 16 (step S2). In the distribution request, a distribution destination and a distribution target file name are specified. Here, as the distribution destination, for example, each of the distribution destination systems 2-1 to 2-N
Can be used. A plurality of distribution destinations can be specified. Here, the identifiers of the distribution destination systems 2-1 to 2-N are M1
To MN, and three of M1, M2, and M3 are designated.

Upon receiving a distribution request specifying the distribution destinations (M1, M2, M3) and the file name (ABC) from the input / output unit 11, the communication control unit 16 accesses the distribution target file in the storage device 12. Then, by obtaining the file size and dividing the file size by a block size L predetermined by the system, the number of blocks into which the distribution target file is divided, that is, the total number of blocks is calculated (step S1). S3). Here, X is the total number of blocks. Thereafter, an initial generation process of various management information is performed in the distribution source system 1 as follows (step S4).

First, the communication control means 16 holds information on distribution destinations M1, M2, M3 corresponding to file names (ABC). Next, the communication control means 16 controls the retransmission control means 1.
7, a transmission start notification specifying the distribution destination (M1, M2, M3), the file name (ABC), and the total number of blocks X is issued. Upon receiving the transmission start notification, the retransmission control unit 17 generates transmission management information 171 having a file name (ABC), the total number of blocks X, and the previous transmission block number 0 as shown in FIG. For the situation management means 15,
The transmission status notification specifying the distribution destination, the file name (ABC), and the block number 0 is performed for all the distribution destinations M1, M2, and M3. That is, the distribution destination (M1), the file name (AB
C), transmission status notification for distribution destination M1 specifying block number 0, distribution destination (M2), file name (ABC), transmission status notification for distribution destination M2 specifying block number 0, distribution destination (M3) , File name (ABC), block number 0
Are transmitted to the distribution status management means 15 in order.

Each time one transmission status notification with the block number set to 0 is received, the distribution status management means 15 generates one distribution status management information for the destination. The distribution status management information to be generated includes items such as a distribution destination, a file name, a distribution status, a distribution destination status, a transmission success block number, and a transmission failure block number. Therefore, the distribution destinations M1, M2, M
In the present example where three transmission status notifications for three are received, three distribution status management information 151, 152, and 153 shown in FIG. 3 are generated.

Here, the distribution status is an item in which a block number indicating how many blocks of the distribution target file have been confirmed to be received at the distribution destination is set.
At the time of initial generation, a block number 0 is set as shown in FIG. In addition, the distribution destination status is “transmitting”, “NG”,
An item in which any one of “NG decision” and “end” is set, and “transmitting” is set in an initial state in which transmission of the file to the distribution destination is started. When the distribution of the file is completed, “End” is set. In addition, if transmission is not successful for some reason during file transmission, “NG” is set. If distribution of the file to the distribution destination is abandoned, “NG” is set.
"OK" is set. Further, the number of successfully transmitted blocks and the number of failed transmission blocks are items for setting the total number of blocks successfully transmitted and the total number of blocks failed in transmission when the file is transmitted to the distribution destination. Is set.

The management information 171, 151 to 1 as described above
When the initial generation of 53 is completed, the distribution source system 1
Step S5 and subsequent steps are executed.

First, the communication control means 16 inquires of the retransmission control means 17 about a block number by designating a file name (ABC) (step S5).

Upon receiving an inquiry about the block number, the retransmission control unit 17 receives the distribution status management information 151 to 15 for each distribution destination system managed by the distribution status management unit 15.
3 and the transmission management information 171 held by the communication control means 161,
A block number inquiry response is returned to the
6). The response from the retransmission control unit 17 includes an inquiry response specifying a block number to be transmitted next, an inquiry response with the response set to "final data" in order to perform transmission end processing, and a pause in transmission. And an inquiry response instructing to end the process. The inquiry answer has a block number item. In the inquiry answer specifying the block number to be transmitted next, the block number itself is set in the block number item. In the inquiry response designating the final data, the suspension of the transmission, and the end of the processing, “final data”, “pause”, and “end” are set in the item of the block number.

The details of the inquiry / response determination processing executed by the retransmission control means 17 will be described later. However, under an ideal situation where there is no reception failure such as a missing reception block in the distribution destination system, the communication control means 16 sends the block number Every time there is an inquiry, an inquiry response specifying block number 1, an inquiry response specifying block number 2, ...,
As in the case of an inquiry response specifying the block number X, the process is to sequentially answer block numbers starting from 1 up to the total number of blocks X, then to the final data inquiry response, and finally to the processing end inquiry response. However, if there is a delay in the response from the distribution destination system, a response to stop may be issued, and data must be retransmitted because a reception failure such as a missing reception block has occurred in the distribution destination system. In this case, the specified block number is rewound to a past number requiring data retransmission.

The communication control means 16 having received the block number inquiry response from the retransmission control means 17 executes the following control according to the content of the response.

Next, when an inquiry response specifying a block number to be transmitted is received (YES in step S7)
S), the distribution destination (M1,
M2, M3), file name (ABC), block number P
Is issued (step S9). here,
The block number P specified by the transmission instruction is the block number specified by the retransmission control unit 17 in the inquiry response.

The satellite communication transmitting means 13 includes the communication control means 1
When the above transmission instruction is received from 6, the storage device 12 is accessed to read the distribution target file having the file name (ABC) by the block size in order from the beginning, and read out the block corresponding to the block number P. Then, transmission data is created by adding the distribution source (M0), the distribution destinations (M1, M2, M3), the file name (ABC), and the block number P added to the read block data. , Via the communication satellite 3, the distribution destination systems 2-1 to 2-1
Broadcast to 2-N. Here, as the value M0 of the item of the distribution source in the transmission data, an identifier that uniquely identifies the distribution source system 1 can be used.

When an inquiry response specifying a temporary stop is received (YES in step S8), the communication control means 16 waits for a predetermined time predetermined by the system (step S10), and then proceeds to step S5.
Then, the retransmission control unit 17 is again inquired about the block number.

When the inquiry response specifying the final data is received (YES in step S11), the communication control means 16 sends the distribution destination (M1, M2, M3), A transmission end instruction specifying the name (ABC) and the total number of blocks X is issued (step S1).
2). When receiving the transmission end instruction, the satellite communication transmitting means 13 receives the transmission destination (M1, M2) designated by the transmission end instruction.
2, M3), file name (ABC), total number of blocks X
Then, transmission data to which a distribution source (M0) and a block number ("transmission end") are added is created, and the transmission data is broadcasted to the distribution destination systems 2-1 to 2-N via the communication satellite 3.

When an inquiry response to the end of the process is received (NO in step S11), the communication control means 16 ends the distribution control process for the file.

(2) Data reception at each distribution destination system
Response Processing FIG. 4 is a flowchart showing the flow of data reception and response processing in each distribution destination system. Satellite communication receiving means 21
Receives the data broadcast from the distribution source system 1 via the communication satellite 3, extracts the distribution destinations (M1, M2, M3) included in the received data (step S21), and It is determined whether or not the own system is included (step S22). If the own system is not included in the distribution destination, the received data is discarded and the process is terminated.

If the distribution destination includes the own system, the satellite communication receiving means 21 determines the distribution source (M0),
The file name (ABC) is extracted, and it is determined whether reception management information having the same delivery source and file name already exists (step S23), does not exist yet (NO in step S23), and If block number 1 is specified (YES in step S24), it is determined that the first system has received the first block of the file for the first time, and reception management information is initially generated (step S25).
In this initial generation, as shown in FIG. 5, reception management information 211 having a distribution source, a file name, and a previous reception block number as items is generated, and the distribution source is M0 and the file name is A.
BC and 0 are respectively set to the last reception block number.
Next, the satellite communication receiving means 21 stores the block data in the received data as the first block data of the file name ABC in the storage device 23 (step S26), and stores the current received block number in the reception management information 211 in this time. The received block number is set to “1” (step S2
7). Thereafter, a reception response process to the distribution source system 1 is performed in the distribution destination system (step S2).
8).

If there is no corresponding reception management information (NO in step S23), but a block number other than 1 is specified in the reception data (NO in step S24), the own system It is determined that a reception failure has occurred due to a missing reception block. At this time, a reception NG response process to the distribution source system 1 is performed in the distribution destination system (step S32).

If the corresponding reception management information exists (YES in step S23), and the value of the block number in the received data is other than the value indicating "end of transmission", that is, the block number itself (step S29). NO), it is determined whether or not the block number (referred to as P) matches the number next to the previous reception block number in the reception management information 211 (step S30). If they match, it is determined that consecutive blocks are received in order, and the block data in the received data is stored in the storage device 23 as the P-th block data of the file name ABC (step S26),
The block number P received this time is set as the previous reception block number of the reception management information 211 (step S27). Thereafter, a reception response process to the distribution source system 1 is performed in the distribution destination system (step S28).

On the other hand, the block number P is the reception management information 21
If it does not match the number following the previous received block number (NO in step S30), it is determined whether the block number P is greater than the number next to the previous received block number (step S31). When the block number P is not larger than the number following the previous reception block number (step S31)
NO), the received data is determined to have been broadcast for retransmission to another distribution destination system, the received data is discarded, and the process ends. However, if the block number P is larger than the number next to the previous reception block number (YES in step S31), it is determined that the own system has caused a reception failure due to a missing reception block. At this time, a reception NG response process to the distribution source system 1 is performed in the distribution destination system (step S32).

If the corresponding reception management information exists (YES in step S23) and the value of the block number in the reception data is a value indicating "end of transmission" (step S23).
It is determined whether the total block number (X) included in the reception data matches the previous reception block number of the reception management information 211 (step S33). If they do not match (NO in step S33), it is determined that the own system has caused a reception failure due to a missing reception block.
At this time, a reception NG response process to the distribution source system 1 is performed in the distribution destination system (step S3).
2). On the other hand, if they match (YES in step S33)
S), a reception end response process to the distribution source system 1 is performed in the distribution destination system (step S34).

In the reception response process of step S28, the following process is executed. First, the satellite communication receiving means 21
Sends to the communication control means 24 a reception notification specifying the distribution source (M0), the file name (ABC), and the block number (P) included in the reception data. When the communication control unit 24 receives the reception notification of the block number 1, the communication control unit 24 has the distribution source (M0), the file name (ABC), and the number of times of reception notification 1 specified in the reception notification as shown in FIG. When such reception notification management information 241 is generated and a reception notification with a block number other than 1 is received, the reception notification management information 241 having the distribution source (M0) and file name (ABC) specified in the reception notification is received. The number of reception notifications is incremented by one. Then, the number of reception notifications is set to a value (D) predetermined by the system.
If not, the process ends. Conversely, if the value D has been reached, the distribution source (M0) specified in this reception notification,
A reception response notification including the file name (ABC) and the block number (P) is sent to the terrestrial communication transmitting means 22, and the number of reception notifications of the reception notification management information 241 is initialized to zero. The terrestrial communication transmitting means 22 transmits the distribution destination (M
0), and transmits a reception response via the terrestrial network 4 to the other party. The reception response includes items of a response source, a file name, and a block number. The response source includes an identifier of the own system, and the file name and the block number include a file name (ABC) specified by the reception response instruction. , Block number (P) are set. Here, D is adjusted in advance based on the difference between the communication speed of the satellite link and the communication rate of the terrestrial link.

In the reception NG response process in step S32,
The following processing is executed. First, the satellite communication receiving means 21 designates the distribution source (M0) and the file name (ABC) included in the reception data, and the previous reception block number in the reception management information 211 having the distribution source and the file name that match the distribution source (M0). Communication control means 2
Put in 4. Upon receiving the received data omission notification, the communication control unit 24 specifies the distribution source (M0), the file name (ABC), and the previous reception block number designated by this notification as the distribution source, the file name, and the block number, respectively. The reception NG response instruction is issued to the ground communication transmission means 22. Upon receiving the reception NG response instruction, the terrestrial communication transmission means 22 transmits the reception NG response via the terrestrial network 4 to the distribution destination (M0) specified by the instruction. This reception NG
The response includes items such as a response source, a file name, and a block number. The response source includes an identifier of the own system, a file name, a block number, a file name (ABC) specified by a reception NG response instruction, A block number (previous reception block number) is set.

In the reception end response process in step S34,
The following processing is executed. First, the satellite communication receiving means 21 sends an end notification specifying the distribution source (M0), the file name (ABC), and the total number of blocks (X) included in the received data to the communication control means 24, and the distribution source (M0 ) And the file name (ABC) are discarded. Upon receiving the end notification, the communication control unit 24 determines the distribution source (M0) and the file name (AB
C) and issues a reception end response instruction designating the total number of blocks (X) as a distribution source, a file name, and a block number to the terrestrial communication transmitting means 22, and receives the distribution source (M0) and the file name (ABC). The notification management information 241 is discarded. Upon receiving the reception end response instruction, the terrestrial communication transmission means 22 transmits a reception end response via the terrestrial network 4 to the distribution destination (M0) specified by the instruction.
The reception end response includes items of a response source, a file name, and a block number. The response source includes the identifier of the own system, and the file name and the block number specify the file name (in the reception end response instruction). ABC) and a block number (total number of blocks X).

As described above, each distribution destination system 2-1 to 2-
When the blocks are normally received from N, a reception response indicating which block number has been received is sent every time D blocks are received, and the received data is missing. At that point, a reception NG response indicating which block number has been received is sent immediately. When receiving data indicating the end of transmission, if the own system has completed receiving all blocks, a reception end response indicating that fact is sent, and if the received data is missing, to which block number A reception NG response indicating whether the reception has been received is sent.

(3) Processing of the response received from the distribution destination system by the distribution source system FIG.
9 is a flowchart showing a flow of processing of the distribution source system 1 when a response is received via the server. Ground communication receiving means 14
Receives any response from any of the distribution destination systems via the terrestrial network 4 and transmits the contents to the communication control unit 16.
(Step S41). Specifically, when a reception response is received, a response reception notification including a response source, a file name, and a block number included in the response is issued, and the reception N
When a G response is received, a response source included in the response,
An NG response reception notification including a file name and a block number is issued. When a reception end response is received, an end response reception notification including a response source, a file name, and a block number included in the response is issued.

The communication control means 16 includes the terrestrial communication receiving means 1
When the above notification is received from No. 4, the content is notified to the retransmission control means 17 (step S42). Specifically, when a response reception notification is received, the response source included in the response,
A transmission status notification including the file name and block number as a distribution destination, a file name, and a block number is issued. When an NG response reception notification is received, a response source, a file name, and a block number included in the response are transmitted to the distribution destination. , A transmission status NG notification including the file name and the block number, and a response source included in the response when the termination response reception notification is received,
A transmission end notification including the file name and the block number (total number of blocks) as the distribution destination, the file name, and the block number (total number of blocks) is issued.

Upon receiving the above notification from the communication control unit 16, the retransmission control unit 17 updates the distribution status in the distribution status management information 151 to 153 corresponding to the notified destination and file from the distribution status management unit 15. The number of newly transmitted blocks and the number of failed transmission blocks are calculated from the acquired block number indicated by the distribution status, the type of notification, and the notified block number (step S4).
3).

More specifically, when the transmission status notification and the transmission end notification are received, if the block number included in the notification is a and the block number indicated by the obtained distribution status is b, a-b is newly transmitted. It is assumed that the number of successful blocks is 0, and the number of newly failed transmission blocks is 0.

When a transmission status NG notification is received, a is a block number included in the notification, and c is a block number indicated by the obtained distribution status. The number of newly failed transmission blocks is a constant determined in advance by the system. Here, the constant may be determined in advance based on the frequency of occurrence of a reception failure or the like. For example, in a situation in which a reception failure occurs only during transmission of at most one block, considering that a transmission status NG notification is generated at the time of receiving each block after the block following the one block in which data reception was lost, The constant may be 1, for example. Of course, a value such as 2, 3 may be used.

When the retransmission control means 17 calculates the new number of successful transmission / failure blocks as described above, the retransmission control section 17 receives the transmission status notification, the transmission status NG notification,
Information on the calculated number of transmission success / failure blocks is added to the transmission end notification, and the information is transferred to the distribution status management unit 15 (step S44).

The distribution status management means 15 is provided by the retransmission control means 1
7, the transmission status notification, the transmission status NG notification, and the transmission end notification are received from the transmission status management information 151 to 153 corresponding to the distribution destination and the file name of the notification. Is set (step S45). The distribution destination status is updated according to the content of the notification (step S46). In other words, the transmission destination N indicates “transmitting” in the case of the transmission status notification and the transmission status N
“NG” is set for the G notification, and “end” is set for the transmission end notification. Further, the number of new transmission success blocks specified in the notification is added to the number of transmission success blocks in the distribution status management information, and the number of new transmission failure blocks specified in the notification is determined as transmission failure in the distribution status management information. It is added to the number of blocks (step S47).

In this way, the distribution destination systems 2-1 to 2-1
2-N, based on the response including the maximum received block number transmitted via the terrestrial network 4,
The distribution status management means 15 of the distribution status management information 151 to 153 for each distribution destination system initially generated as shown in FIG.
Will be updated as appropriate. Therefore, by referring to the distribution status management information 151 to 153, it is possible to immediately determine which distribution destination system requires data retransmission, the minimum block number requiring retransmission, and the like.

Next, the retransmission control means 17 is controlled by the communication control means 1
The processing executed when there is an inquiry about the block number from No. 6 will be described with reference to the flowcharts of FIGS.

The retransmission control means 17 stores the file name (AB
When you receive an inquiry for the block number specifying C),
The process shown in FIG. 7 is started (step 200). First,
The distribution status management information 151 to 153 of the file is acquired from the distribution status management means 15 (step 201), and it is checked whether or not all the distribution destination states are completed or NG is determined (step 202). If the state of all the distribution destinations is completed or NG is determined, the distribution processing of the file can be completed. Therefore, a response to the end is returned to the communication control means 16 (step 220), and the processing is completed (step 22)
1).

If the status of all the destinations is not completed or NG is not determined (NO in step 202), it is checked whether or not there is a destination whose destination is NG (step 203). Proceed to. The processing of FIG. 8 will be described later. On the other hand, if the block number does not exist, the smallest block number (which is Ne
) And its delivery destination (this is He) is checked (step 204), and the difference between the previous transmission block number in the transmission management information 171 and the Ne block number is determined by a threshold Tn predetermined in the system. Is checked, or whether the previous transmission block number is equal to the total block number X + 1 (step 205).

If the difference between the previous transmission block number and the Ne block number does not exceed the threshold Tn predetermined in the system, and if the previous transmission block number is not equal to the total block number X + 1, N in step 205
O) If there is delay delivery destination information to be described later, it is deleted and the number of delays is set to 0 (step 20).
6) It is checked whether or not the previous transmission block number is equal to the total block number X (step 207). If not, the previous transmission block number is incremented by one, and the inquiry response in which the number is set is sent to the communication control means 16. Return (Step 2
08), the current process ends (step 221). If the previous transmission block number is equal to the total block number X (YES in step 207), the answer has been completed up to the last block number.
A response to the inquiry about the final data is returned to the communication control means 16 (step 208), and the current processing is terminated (step 221).

If the difference between the previous transmission block number and the Ne block number exceeds the threshold value Tn, or if the previous transmission block number is equal to the total block number X + 1 (YES in step 205), the delayed delivery destination information It is checked whether or not this is information relating to the same distribution destination as the He, and whether the number of delays has exceeded a threshold predetermined by the system (step 210). If the delayed delivery destination information is not held, or if it is held, it is not the same as He, or if the number of delays does not exceed the threshold (NO in step 210), He is used as the delayed delivery destination information.
Is held by incrementing the number of delays (the initial value of which is 0) by one, and a response to the inquiry about suspension is returned to the communication control means 16 (step 211), and the current processing is terminated (step 221). On the other hand, if the result of the determination in step 210 is YE
In the case of S, that is, if there is a delivery destination that does not return a reception response even though it has been waiting for a reception response by issuing a temporary inquiry response for a predetermined number of times, the block number receiving the reception response is The number of transmission failure blocks in the distribution status management information corresponding to the smallest distribution destination is incremented by + Tn, and the process proceeds to the processing in FIG. 8 (step 212).

In the processing shown in FIG. 8, first, the transfer failure rate is calculated based on the number of transmission success / transmission failure blocks for all the distribution destinations except the NG determined distribution destination (the calculated transmission failure rate is set to Re). ) (Step S213). For example, the number of successful transmission blocks of the distribution destinations M1, M2, and M3 is s1, s
Assuming that 2, s3 and the number of transmission failure blocks are f1, f2, and f3, the transfer failure rate can be obtained by the following equation, for example. Transfer failure rate = (f1 + f2 + f3) / (s1 + s2 + s3 + f1 + f2 + f3) (1) Further, in addition to the number of transmission success / transmission failure blocks, a transfer failure rate may be obtained by taking into account a correction coefficient predetermined in the system.

Next, the number of untransmitted blocks is calculated from the total number of blocks X and the previously transmitted block number (the calculated number of untransmitted blocks is set to Nl) (step 214).

Next, the number of blocks expected to be retransmitted is calculated based on Re and Nl (this calculated number of blocks is referred to as Nr) (step 215). For this calculation, for example, the following equation can be used. Nr = Nl × (1 + Re) (2) In addition to Re and Nl, the number of blocks expected to be retransmitted may be calculated in consideration of a correction coefficient predetermined by the system.

Next, it is checked whether or not the ratio of Nr to the total number of blocks X has exceeded a predetermined value predetermined by the system (step 216). If not, if the distribution destination state is NG, this is checked. "Transmitting" (step 21)
7) Except for the NG-confirmed distribution destination, an inquiry response in which the smallest block number for which the reception response was received is set to a number obtained by adding +1 to the communication control means 16 is returned (step 21).
8), end the current processing (step 221).

On the other hand, if the ratio of Nr to the total number of blocks X exceeds a predetermined value predetermined by the system (YES in step 216), NG determination is made for the distribution destination having the smallest block number for which the reception response has been received. A notification is made (step 219). The information 151 to 153 managed by the distribution status management means 15 by the NG confirmation notification.
Of the distribution destinations, the distribution destination state of the distribution destination having the smallest block number that has received the reception response is set to NG determined. In addition, the communication control unit 16 excludes the distribution destination that has received the NG confirmation notification from the distribution destination of the file ABC. Thereafter, the retransmission control unit 17 returns to Step 201 and continues the processing.

Next, the operation of this embodiment will be described with a specific example.

Now, the distribution target file (file name AB
C), the total number of blocks is “150”, the distribution destination is the distribution destination system 2-1, 2-2, 2-3, and the threshold Tn in step 205 in FIG. 7 is “10”. Further, each of the distribution destination systems 2-1 to 2-3 returns a reception response every time five blocks are received.

The management information 171 and 15 as shown in FIG.
When the communication control unit 16 of the distribution source system 1 sends a block number inquiry to the retransmission control unit 17 after the initial generation of 1 to 153, the retransmission control unit 17 acquires the distribution status management information 151 to 153. (Step 201),
The status of all destinations is not completed or not confirmed (step 2
02), since there is no distribution destination whose distribution state is NG (NO in step 203), the process proceeds to step 204, where Ne = 0, He = M1 to M3, and the previous transmission block number (= 0) −Ne (= 0) <Tn (= 10) and the previous transmission block number (= 0) <total number of blocks (=
150) +1 (NO in step 205), previous transmission block number (= 0) ≠ total number of blocks (= 150) (NO in step 207), so that the previous transmission block number (=
0) is incremented by 1, and an inquiry response in which the block number "1" is set is returned to the communication control means 16 (step 20).
8). Accordingly, under the instruction of the communication control unit 16, the satellite communication transmitting unit 13 transmits the first block of the distribution target file ABC via the communication satellite 3 to the distribution destination systems 2-1 to 2-
Broadcast to 3

Each of the delivery destination systems 2-1 to 2-3 generates the management information 211 and 241 as shown in FIG. 5 when the block of the block number "0" is received, and stores the management information 211 and 241 in the delivery target file ABC. One block is stored in the storage device 23.

Thereafter, the retransmission control means 17 responds to the block number inquiry from the communication control means 16 by the block number "2", the block number "3", the block number "4",
The block number “5” is sequentially answered, and the distribution target file ABC is transmitted from the satellite communication transmitting unit 13 accordingly.
, The third block, the fourth block, and the fifth block are sequentially broadcast. Each destination system 2-
In 1-2, each time these blocks are received, they are stored in the storage device 23. When the fifth block is received,
Under the control of the communication control unit 24, a reception response specifying the block number “5” is returned from the terrestrial communication transmission unit 22 to the distribution source system 1, and is managed by the distribution status management unit 15 of the distribution source system 1. Delivery status management information 151 to 15
3 is updated to the block number “5”.

In the case where the distribution is performed without any trouble, as shown in the sequence diagram of FIG. 9, every time the distribution source system 1 transmits five blocks, one reception from the distribution destination system is performed. A response is returned.

The last transmission block number in the transmission management information 171 is “91”, and the distribution destination systems 2-1 and 2-
2, 2-3 distribution status management information 151, 152, 153
Distribution status of the block numbers "85", "87",
"90", the distribution destination status is "NG", "NG",
Consider the situation of "sending". That is, the distribution destination system 2-1 fails to receive the block with the block number “86” due to a satellite communication failure or the like, and the distribution destination system 2-
It is assumed that 2 failed to receive the block with the block number “88”.

Under such circumstances, the retransmission control means 17
Receives a block number inquiry from the communication control means 16, it is detected in step 203 in FIG. 7 that an NG distribution destination exists, and the processing in FIG. 8 is executed. First, at step 213, the transfer failure rate Re is calculated, then at step 214, the number Nl of untransmitted blocks is calculated,
Next, in step 215, the number of blocks Nr expected to be retransmitted is calculated. If the ratio of Nr to the total number of blocks (= 150) does not exceed a certain value (NO in step 216), distribution destination system 2-
The NGs of the distribution destination statuses 1 and 2-2 are deleted, and an inquiry in which the smallest block number (= 85) for which the reception response has been received is set to the block number “86” obtained by adding +1 to the communication control means 16. As a result, the block number “8”
Block 6 "is retransmitted by broadcast. At this time,
The previous transmission block number in the transmission management information 171 is “8
6 ".

When the retransmission control unit 17 receives a block number inquiry from the communication control unit 16 after transmitting the block with the block number "86", the distribution destination state is NG because there is no distribution destination (NO in step 203). Proceeding to step 209 via steps 204 to 207, an inquiry response in which the block number "87" is set is returned, and the block having the block number "87" is broadcast. Thereafter, the block numbers “88”, “89”, “9”
.., "91",...

In the distribution destination system 2-1, the blocks subsequent to the block number “86” are sequentially received and stored in the storage device 23.
To be stored. In the distribution destination system 2-2, the block numbers “86” and “87” are ignored, but the blocks subsequent to the block number “88” are sequentially received and stored in the storage device 23. Further, the distribution destination system 2-3 ignores the blocks up to the already received block number, but sequentially receives and stores the blocks with the subsequent block numbers in the storage device 23. In this way, even if there are a plurality of distribution destination systems that need to be retransmitted, the blocks can be retransmitted without waste by the broadcast transmission.

On the other hand, for example, when the reception of the NG response from the distribution destination system 2-1 is repeated, the distribution destination system 2-1
Since the number of failed transmission blocks increases, the number of blocks Nr expected to be required for retransmission also increases.
As a result, when the ratio of Nr to the total number of blocks exceeds a certain value, the distribution destination state of the distribution destination system 2-1 having the smallest block number for which the reception response has been received is “NG”.
"Confirmed" (step 219), and thereafter, distribution is continued only for the distribution destination systems 2-2, 2-3.

As described above, only the necessary retransmission after the block for which reception failed is performed without retransmitting all blocks to the distribution destination where a temporary satellite communication failure or the like has occurred. When a delivery destination that repeatedly fails is included, the delivery destination is excluded from retransmission targets, thereby preventing a decrease in transfer speed due to repeated retransmission.

The above is the operation in the case where the NG response is repeatedly received. Under the condition that even the NG response is not transmitted, the operation is as follows. For example, if retransmission is started from the block number “86” to the distribution destination system 2-1 and neither a reception response nor an NG response is returned from the distribution destination system 2-1, the previous transmission block number is “96”. ”, The previous transmission block number (= 96) −Ne (= 85) in step 205 of FIG.
> Tn (= 10), the delayed delivery destination information of the delivery destination system 2-1 is held, the number of delays becomes “1”, and the inquiry response of the suspension is sent from the retransmission control unit 17 to the communication control unit 16. The communication control unit 16 issues a block number inquiry again after waiting for a predetermined time (step 211). If the distribution destination system 2-1 has not yet returned a response, the above-described processing is repeated, and when the number of delays exceeds the threshold, the processing in FIG. 8 is started. Accordingly, if the ratio of the number of blocks Nr predicted to require retransmission to the total number of blocks exceeds a certain value, the delivery destination system 2-1 is determined to be NG,
Excluded from retransmission.

Now, after the last block of the distribution target file ABC is broadcast from the distribution source system 1 and a block number inquiry is issued from the communication control means 16 to the retransmission control means 17, the step shown in FIG. In 209, the previous transmission block number is incremented by 1 to become "151", and a response to the inquiry about the final data is returned. As a result, from the distribution source system 1 to the distribution destination system,
Transmission data in which “transmission end” is set in the block number is distributed. The distribution destination system that has received the transmission data returns a reception end response if blocks for the total number of blocks have been received (step S34 in FIG. 4), and returns a reception NG response if reception is missing. (Step S32).

The distribution destination status in the distribution status management information corresponding to the distribution destination system for which the reception end response has been returned is "end".
Is set to Further, the delivery destination systems excluded from the delivery destinations are "NG confirmed" as described above. Therefore, when subsequently receiving the block number inquiry from the communication control means 16, the retransmission control means 17 determines YES in step 202 of FIG. 7 and returns an end inquiry response, and the communication control means 16 returns the distribution target file AB.
The control for C is ended. If the reception end response from each distribution destination system is delayed and a block number inquiry is received from the communication control unit 16 before the distribution destination status becomes “end”, the retransmission control unit 17 performs step 205
, The previous transmission block number (= 151) = total number of blocks (= 150) +1 is detected, the delayed delivery destination information and the number of delays are held, and a response to the temporary stop inquiry is returned to the communication control means 16. . And usually,
The delayed reception end response is sent from the distribution destination system before the number of delays exceeds the threshold value, and the distribution destination state becomes “end”.

As a response to the transmission data in which the “final data” is set, the reception NG
When a response is returned, the destination state of the destination system becomes "NG". Therefore, at the time of the next block number inquiry, the retransmission control unit 17 proceeds from step 203 to the processing in FIG. And Nr with respect to the total number of blocks
If the ratio does not exceed a certain value, the NG is erased (step 217), and an inquiry response in which the block number + 1 notified by the received NG response is set is returned,
Retransmit the block. Thereafter, when there is a block number inquiry again, if the previous transmission block number is equal to the total number of blocks (YES in step 207), the retransmission control unit 17 returns a final data inquiry response again (step 209) and must not be equal. In this case, an inquiry response with the next block number set is returned.

FIG. 10 is a block diagram showing a configuration example of another embodiment of the present invention. In FIG. 10, H1 corresponds to FIG.
Computer constituting the distribution source system 1 shown in FIG.
1 to TN are distribution destination systems 2-1 to 2-N shown in FIG.
Is a machine-readable recording medium such as a CD-ROM, a magnetic disk, and a semiconductor memory, and stores a distribution source program and a distribution destination program. The distribution source program recorded on the recording medium M is read by the computer H1 when the computer H1 is started, and by controlling the operation of the computer H1, the distribution program is input to the input / output unit 11 shown in FIG. , Storage device 12, satellite communication transmitting means 1
3. The terrestrial communication receiving means 14, the distribution status managing means 15, the communication controlling means 16 and the retransmission controlling means 17 are realized. The distribution destination program recorded on the recording medium M is stored in the computer T1 when the computers T1 to TN are started up.
1 to TN and read by computers T1 to TN
By controlling the operations of the computers T1 to TN
Above, the satellite communication receiving means 21, the terrestrial communication transmitting means 22, the storage device 23, and the communication control means 24 shown in FIG. 1 are realized.

The embodiments of the present invention have been described above.
The present invention is not limited to the above embodiments, and various other additions and changes are possible. For example, when the communication control unit 24 in each distribution destination system monitors the time until the next reception notification is received from the satellite communication reception unit 21 and the reception notification cannot be received even after exceeding a certain fixed time, It may be determined that a failure has occurred in the distribution source system 1 or the like, and the receiving process of the file being received may be terminated.

[0080]

According to the present invention as described above, the following effects can be obtained.

Broadcasting of retransmission data in units of blocks enables efficient data distribution.

Since each distribution destination system returns a response to the distribution source system every time a plurality of blocks are received during normal reception, the load on the distribution destination system and the distribution source system can be reduced. When the destination system detects a missing reception block, a response is returned each time, so that data can be retransmitted immediately.

When the difference between the block number of the previously transmitted block and the minimum value of the maximum received block number exceeds a predetermined value, the distribution source system temporarily stops the subsequent block transmission by the satellite communication transmitting means, By restarting the block transmission when the difference becomes equal to or less than the predetermined value, it is possible to reduce the amount of retrace of data retransmission when a reception block is missing in any of the distribution destination systems.

The distribution source system excludes a distribution destination system having a large number of block reception failures from the target of block retransmission, so that other normal distribution due to a specific distribution destination system in which a reception failure frequently occurs can be performed. It is possible to prevent the adverse effect of delaying the completion of data distribution to the destination system.

[Brief description of the drawings]

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

FIG. 2 is a flowchart illustrating a flow of a distribution process in a distribution source system.

FIG. 3 is a diagram illustrating an example of management information held by a distribution source system.

FIG. 4 is a flowchart showing a flow of data reception and response processing in the distribution destination system.

FIG. 5 is a diagram illustrating an example of management information held by a distribution destination system.

FIG. 6 is a flowchart showing a flow of processing of the distribution source system when receiving a response from the distribution destination system via the terrestrial network.

FIG. 7 is a flowchart illustrating a part of a processing example executed when the retransmission control unit receives a block number inquiry from the communication control unit;

FIG. 8 is a flowchart showing the remaining part of the processing example executed when the retransmission control unit receives a block number inquiry from the communication control unit.

FIG. 9 is a transmission / reception sequence diagram between a distribution source system and a distribution destination system.

FIG. 10 is a block diagram showing a configuration example of another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Distribution source system 11 ... Input / output means 12 ... Storage device 13 ... Satellite communication transmission means 14 ... Terrestrial communication reception means 15 ... Distribution status management means 16 ... Communication control means 17 ... Retransmission control means 2-1-2-N ... Distribution destination system 21: satellite communication receiving means 22: terrestrial communication transmitting means 23: storage device 24: communication control means 3: communication satellite 4: terrestrial network

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04L 12/18 F term (Reference) 5K030 HA05 HA08 HC01 JL02 KA04 LA01 LA04 LA20 LD02 LE12 LE14 LE16 5K067 BB02 CC14 DD25 DD51 EE07 EE10 EE16 KK15 5K072 AA18 BB02 BB22 BB25 CC03 CC05 DD01 DD15 DD20 EE05 EE06 FF23 GG11 GG14

Claims (7)

[Claims] 1. A data distribution system for dividing distribution target data into a plurality of blocks, adding a block number to each block, and distributing the data to a plurality of distribution destination systems by satellite communication by broadcast communication. When a response including the maximum received block number transmitted through the terrestrial network is received and the distribution status of each distribution destination system is managed by the distribution source system, when data retransmission is required, The minimum block number that requires retransmission is determined from the distribution status of each distribution destination system, and blocks subsequent to the determined block number are added with block numbers one block at a time and broadcast to a plurality of distribution destination systems by satellite communication. A data distribution system to distribute with. 2. A data distribution system for distributing data from a distribution source system to a plurality of distribution destination systems by broadcast communication using satellite communication, wherein the distribution source system is generated when data to be distributed is divided by a predetermined size. Satellite communication transmitting means for adding the number to the block of the designated block number and broadcasting the data to a plurality of data distribution destination systems by satellite communication, and A distribution status management means for managing the distribution status of each data distribution destination system based on a response including the maximum received block number sent from the data distribution destination system; and A system for distributing data to be distributed in units of blocks by designating the number one block at a time to the satellite communication transmitting means. Is started, and whether or not retransmission is necessary is determined based on the distribution status of each data distribution destination system managed by the distribution status management unit, and if retransmission is necessary, the retransmission is designated to the satellite communication transmission unit. The number of blocks to be distributed is reduced to the minimum block number that requires retransmission, and thereafter, the control is performed to distribute the data to be distributed in block units by designating the numbers one block at a time from the block to the satellite communication transmitting means. Each distribution destination system receives a block broadcast by satellite communication, and the block number added to the block is the next number of the maximum block number already received by the own system. If so, the satellite communication receiving means for storing the block in the storage device and updating the received maximum block number, and a response including the received maximum block number as a base. Communication control means for transmitting the data to the distribution source system via the upper network. 3. The transmission of a response including the maximum received block number from the distribution destination system to the distribution source system is performed every time a predetermined number of blocks having continuous block numbers are received and every time a missing reception block is detected. 3. The data distribution system according to claim 2, wherein the data distribution system performs the operation. 4. The control means of the distribution source system, if the difference between the block number of the previously transmitted block and the minimum value of the maximum received block number exceeds a predetermined value, performs the subsequent block transmission by the satellite communication transmitting means. 4. The data distribution system according to claim 3, wherein the data transmission system pauses and restarts block transmission when the difference becomes equal to or less than a predetermined value. 5. The data distribution system according to claim 3, wherein the control unit of the distribution source system excludes a distribution destination system having a large block reception failure from a target of block retransmission. 6. The distribution status management means of the distribution source system,
As the distribution status of each data distribution destination system, in addition to the maximum received block number, the number of successful transmission blocks and the number of transmission failure blocks are managed, and the control means of the distribution source system, when retransmission is necessary, The number of blocks required for transmission is predicted from the transfer failure rate and the number of untransmitted blocks determined from the number of successful transmission blocks and the number of failed transmission blocks of each data distribution destination system, and the ratio of the predicted number of blocks to the total number of blocks 4. The data distribution system according to claim 3, wherein when the value exceeds a predetermined value, the distribution destination system having the smallest received maximum block number is excluded from the target of block retransmission. 7. A computer constituting the distribution source system in a data distribution system for distributing data from a distribution source system to a plurality of distribution destination systems by broadcast using satellite communication, divides distribution target data into predetermined sizes. Of a plurality of blocks generated at the same time, the number is added to the block of the designated block number and the satellite communication transmitting means for broadcasting to a plurality of data distribution destination systems by satellite communication, via a terrestrial network Distribution status management means for managing the distribution status of each data distribution destination system based on the response including the maximum received block number sent from each data distribution destination system, and the first block constituting the distribution target data The data to be distributed is blocked by designating the number to the satellite communication transmitting means one block at a time from Start the control of distribution on a per-network basis, determine whether retransmission is necessary based on the distribution status of each data distribution destination system managed by the distribution status management means, and if retransmission is necessary, The block number designated to the satellite communication transmitting means is reduced to the minimum block number requiring retransmission, and thereafter, the distribution target data is blocked by designating the number to the satellite communication transmitting means one block at a time starting from that block. Control means for continuing the control of distributing in units of: a computer constituting the distribution destination system receives a block broadcast by satellite communication, and a block number added to the block is used by the own system. If it is the next number after the received maximum block number, the corresponding block is stored in the storage device and the satellite that updates the received maximum block number is updated. The receive unit, a machine-readable recording medium recording a program for causing a communication control unit functions as, to be transmitted to the delivery source system via the terrestrial network a response containing Received maximum block number.