Video-on-demand system of reduced storage capacity which can provide noninterrupted broadcast to a plurality of users

Claims

What is claimed is:

1. A video-on-demand system, comprising:

an image data storage device, including a plurality of recording media for storing a plurality of programs, for storing image data for the programs divided into a plurality of blocks which are distributed among all of the recording media;

an image data management device, including image data management tables in which management information for the image data is stored, for consulting the image data management tables and transmitting management information separately for each block, when there is a request from outside the device for information about one of the programs, wherein the image data management tables comprise a title table for corresponding a title of each of the programs with starting block identification information for each of the programs, a block table for corresponding block identification information for each of the blocks with starting frame identification information for each of the blocks, and a frame table for corresponding frame identification information for each frame with position information showing at which position on which recording medium out of the recording media each of the frames is stored; and

an image data transmission device for requesting to the image data management device for management information related to a block which is to be transmitted in a transmission of a program requested by a user, for receiving the management information from the image data management device, for retrieving image block data separately for each block from the recording media and for transmitting the image block data to the user.

2. The video-on-demand system of claim 1, wherein a number of the recording media disposed in the image data storage device is equal to or above a number of the blocks of image data in one program.

3. The video-on-demand system of claim 2, wherein

the image data transmission device includes:

request means for receiving a request for a televising of one of the programs from the user, and requesting to the image data management device a transmission of storage position information which shows at which position on which recording medium each separate block in the program is stored;

image data retrieval/transmission means for receiving the transmission of the storage position information for each separate block of the program from the image data management device, for retrieving the image block data for each separate block from the position designated by the storage position information on the recording medium designated by the storage position information, and transmitting the image block data to the user;

request continuation means for requesting to the image data management device, when the image data retrieval/transmission means has finished retrieving the image block data for one block, a transmission of storage position information of image block data for a next block following after the block for which retrieving is finished; and

image data retrieval/transmission continuation means for receiving the transmission of the storage position information of the image block data for the next block from image data management device, for retrieving the image block data for the next block from a position designated by the storage position information on a recording medium designated by the storage position information, and transmitting the image block data to the user, and

wherein the image data management device includes:

first request processing means for receiving a transmission request for the storage position information for the image block data for each separate block from the request means, for consulting the image data management tables and for transmitting the storage position information as to in which position on which recording medium the image block data is stored to the image data retrieval/transmission means; and

second request processing means for receiving a transmission request for the storage position information for the image block data from the request continuation means, for consulting the image data management tables and transmitting the storage position information for the image block data to the image data retrieval/transmission continuation means.

4. The video-on-demand system of claim 3, wherein

the request means includes:

a title information request unit for receiving an indication of a program name from the user and for requesting title information for the program name from the first request processing means;

a first block identification information request unit for receiving the title information, for consulting the title information and for requesting the starting first block identification information from the first request processing means;

a first frame table request unit for receiving the starting block identification information, for consulting the starting block identification information and requesting a frame table column specified in the starting block identification information from the first request processing means;

a first frame table storage unit for storing the frame table column;

a second block identification information request unit for consulting, once one of the image data retrieval transmission means and the image data retrieval transmission continuation means has completed retrieving the image block data of one block, the block identification information of a completed block and requesting new block identification information for the next block from the second request processing means;

a second frame table request unit for receiving the new block identification information, for consulting the new block identification information and requesting a new frame table column from the second request processing means; and

a second frame table storage unit for storing the new frame table column,

wherein the first request processing means includes:

a title information transmission unit for receiving a request from the title information request unit, for consulting the title table, and transmitting the title information corresponding to the program to the first block identification information request unit;

a first block identification information transmission unit for receiving a request from the first block identification information request unit, for consulting the block table and for transmitting the starting block identification information to the first frame table request unit; and

a first frame table transmission unit for receiving a request from the first frame table request unit, for consulting the frame table and for transmitting to the first frame table memory unit the frame table column for an indicated starting block, and

wherein the second request processing means includes:

a second block identification information transmission unit for receiving a request from the second block identification information request unit, for consulting the block table and for transmitting the block identification information for the next block to the second frame table request unit; and

a second frame table transmission unit for receiving a request from the second frame table request unit, for consulting the frame table and for transmitting to the second frame table memory unit the new frame table column for the next block.

5. The video-on-demand system of claim 4, wherein

the image data management device further includes:

number of users storage means for storing a number of users who are simultaneously viewing blocks having a same block number in any of the programs;

image data transmission possibility judgement means for judging whether the number of users for a starting block recorded in the number of users storage means is within a range for which uninterrupted transmission of the image data is possible; and

block identification information transmission cancellation indication means for giving an indication to the first block identification information transmission unit to cancel transmission of the starting block identification information, when the image data transmission possibility judgement means judges that the transmission is not possible.

6. The video-on-demand system of claim 5, wherein the number of users storage means updates the number of users viewing a block, when the block identification information of the block is transmitted by one of the first block identification information transmission unit and the second block identification information transmission unit, and when one of the image data retrieval/transmission means and the image data retrieval/transmission continuation means has finished retrieving the image block data for one block.

7. The video-on-demand system of claim 6, wherein

the image data transmission possibility judgement means includes:

number of users retrieval means for retrieving the number of users for each block from the number of users storage means;

maximum number of transmissions calculator for calculating a maximum number of transmissions which is a value given by dividing an average retrieval rate for the image data from the image data storage device by the image data retrieval/transmission means by a transfer rate for a transfer of the image data to the user and subtracting a constant; and

a possibility judgement unit for judging that the transmission is not possible when the number of users of the starting block, retrieved by the number of users retrieval means, is equal to or above the maximum number of transmissions calculated by the maximum number of transmissions calculator.

8. The video-on-demand system of claim 7, wherein

the image data management device further includes:

schedule storage means for storing programs being viewed in terms of each separate block unit for each user; and

copy indication means for giving an indication, when the number of user viewing a given block retrieved by the number of users retrieval unit becomes equal to the maximum number of transmissions calculated by the maximum number of transmissions calculator, and, in the schedule storage means, a program for a block which is one of a block preceding and following the given block coincides with one of the programs for the given block, to the image data storage device to copy image block data for the given block in the coinciding program,

wherein the image data storage device includes reserve image data storage means, comprising a reserve recording medium separate from the recording media, for copying image data onto the reserve recording medium at the indication from the copy indication means.

9. The video-on-demand system of claim 8, wherein

the image data management device further includes:

image data management table writing means for writing new block identification information and a new frame table column corresponding to the image data copied by the reserve image data storage means into the block table and the frame table in the image data management tables; and

number of users addition storage means, which provides a storage column corresponding to a new block in the reserve image data storage means to the number of users storage means aside from storage columns for storing the number of users, for adding and storing the number of users viewing a block in a corresponding storage column.

10. The video-on-demand system of claim 9, wherein after the reserve image data storage means has notified the image data management device that it has finished copying the image block data onto the reserve recording medium, then when there has been a request for a frame table column corresponding to the image block data, from one of the first frame table request unit and the second frame table request unit, then one of the first frame table transmission unit and the second frame table transmission unit transmits the frame table column newly written in by the image data management table writing means.

11. The video-on-demand system of claim 10, wherein the reserve recording medium in the reserve image data storage means is constructed of an optical magnetic disc.

12. The video-on-demand system of claim 10, wherein the reserve recording medium in the reserve image data storage means is constructed of phase change rewritable optical disc.

13. The video-on-demand system of claim 4, wherein

the image data management device further includes:

number of users storage means for storing a number of users who are simultaneously viewing blocks having a same block number in any of the programs;

image data transmission possibility judgement means for judging whether the number of users for a given block number recorded in the number of users storage means is within a range for which uninterrupted transmission of the image data is possible; and

block identification information transmission cancellation indication means for giving an indication to one of the first block identification information transmission unit and the second block identification information transmission unit to cancel transmission of the block identification information of a block having the given block number, when the image data transmission possibility judgement means judges that the transmission is not possible.

14. The video-on-demand system of claim 13, wherein

the image data transmission possibility judgement means includes:

number of users retrieval means for retrieving the number of users for each block from the number of users storage means;

maximum number of transmissions calculator for calculating a maximum number of transmissions which is a value given by dividing an average retrieval rate for the image data from the image data storage device by the image data retrieval/transmission means by a transfer rate for a transfer of the image data to the user; and

a possibility judgement unit for judging that transmission is not possible when the number of users retrieved by the number of users retrieval means is not below the maximum number of transmissions calculated by the maximum number of transmissions calculator.

15. The video-on-demand system of claim 1, wherein

the image data management device includes:

number of users storage means for storing a number of users who are simultaneously viewing blocks having a same block number in any of the programs;

image data transmission possibility judgement means for judging whether the number of users for a starting block recorded in the number of users storage means is within a range for which uninterrupted transmission of the image data is possible; and

necessary information transmission cancellation means for cancelling a transmission of necessary information for the starting block when the image data transmission possibility judgement means has judged that the transmission is not possible.

16. A method for supplying programs in a video-on-demand system, comprising:

an image data storage step for storing image data for a plurality of programs divided into a plurality of blocks which are distributed among a plurality of recording media;

an image data management step for storing image data management tables including a title table for corresponding a title of each of the programs with starting block identification information for each of the programs, a block table for corresponding block identification information for each of the blocks with starting frame identification information for each of the blocks, and a frame table for corresponding frame identification information for each frame with position information showing at which position on which recording medium out of the recording media each of the frames is stored, and for consulting the image data management tables and transmitting management information separately for each block, when there is a request for information about one of the programs; and

an image data transmission step for requesting that management information related to a block which is to be transmitted in a transmission of a program requested by a user be transmitted by the image data management step, for receiving the management information transmitted by the image data management step, for retrieving image block data separately for each block from the recording media and for transmitting the image block data to the user.

17. The method of claim 16 wherein, in the image data storage step, each program is divided so that a number of blocks of image data in one program is not greater than a number of recording media.

18. The method of claim 17, wherein the image; data transmission step includes:

a request step for receiving a request for a televising of one of the programs from the user, and requesting from the stored image data management tables for a transmission of storage position information which shows at which position on which recording medium each separate block in the program is stored;

an image data retrieval/transmission step for receiving the transmission of the storage position information for each separate block of the program from the image data management tables, for retrieving the image block data for each separate block from the position designated by the storage position information on the recording medium designated by the storage position information, and transmitting the image block data to the user;

a request continuation step for requesting to the image data management tables, when the image data retrieval/transmission step has finished retrieving the image block data for one block, for a transmission of storage position information of image block data for a next block following after the block for which retrieving is finished; and

an image data retrieval/transmission continuation step for receiving the transmission of the storage position information of the image block data for the next block from the image data management tables, for retrieving the image block data for the next block from a position designated by the storage position information on a recording medium designated by the storage position information, and transmitting the image block data to the user,

wherein the image data management step further includes:

a first request processing step for receiving a transmission request for the storage position information for the image block data for each separate block from the request step, for consulting the image data management tables and for transmitting the storage position information as to in which position on which recording medium the image block data is stored to the image data retrieval/transmission step; and

a second request processing step for receiving a transmission request for the storage position information for the image block data from the request continuation step, for consulting the image data management tables and transmitting the storage position information for the image block data to the image data retrieval/transmission continuation step.

19. The method of claim 18, wherein the request step includes:

a title information request step for receiving an indication of a program name from the user and for requesting title information for the program name from the first request processing step;

a first block identification information request step for receiving the title information, for consulting the title information and for requesting the starting first block identification information from the first request processing step;

a first frame table request step for receiving the starting block identification information, for consulting the starting block identification information and requesting a frame table column specified in the starting block identification information from the first request processing step;

a first frame table storage step for storing the frame table column;

a second block identification information request step for consulting, once one of the image data retrieval transmission step and the image data retrieval transmission continuation step has completed retrieving the image block data of one block, the block identification information of a completed block and requesting new block identification information for the next block from the second request processing step;

a second frame table request step for receiving the new block identification information, for consulting the new block identification information and requesting a new frame table column from the second request processing step; and

a second frame table storage step for storing the new frame, table column,

wherein the first request processing step includes:

a title information transmission step for receiving a request from the title information request step, for consulting the title table, and transmitting the title information corresponding to the program to the first block identification information request step;

a first block identification information transmission step for receiving a request from the first block identification information request step, for consulting the block table and for transmitting the starting block identification information to the first frame table request step; and

a first frame table transmission step for receiving a request from the first frame table request step, for consulting the frame table and for transmitting to the first frame table memory step the frame table column for an indicated starting block, and

wherein the second request processing step includes:

a second block identification information transmission step for receiving a request from the second block identification information request step, for consulting the block table and for transmitting the block identification information for the next block to the second frame table request step; and

a second frame table transmission step for receiving a request from the second frame table request step, for consulting the frame table and for transmitting to the second frame table memory step the new frame table column for the next block.

20. The method of claim 19, wherein the image data management step further includes:

a number of users storage step for storing a number of users who are simultaneously viewing blocks having a same block number in any of the programs;

an image data transmission possibility judgment step for judging whether the number of users for a starting block recorded in the number of users storage step is within a range for which uninterrupted transmission of the image data is possible; and

a block identification information transmission cancellation indication step for giving an indication to the first block identification information transmission step to cancel transmission of the starting block identification information, when the image data transmission possibility judgment step judges that the transmission is not possible.

21. The method of claim 20, wherein the number of users storage step updates the number of users viewing a block, when the block identification information of the block is transmitted by one of the first block identification information transmission step and the second block identification information transmission step, and when one of the image data retrieval/transmission step and the image data retrieval/transmission continuation step has finished retrieving the image block data for one block.

22. The method of claim 21, wherein the image data transmission possibility judgment step includes:

a number of users retrieval step for retrieving the number of users for each block from the number of users storage step;

a maximum number of transmissions calculation step for calculating a maximum number of transmissions which is a value given by dividing an average retrieval rate for the image data from the image data storage step by the image data retrieval/transmission step by a transfer rate for a transfer of the image data to the user and subtracting a constant; and

a possibility judgment step for judging that the transmission is not possible when the number of users of the starting block, retrieved by the number of users retrieval step, is equal to or above the maximum number of transmissions calculated by the maximum number of transmissions calculation step.

23. The method of claim 22, wherein the image data management step further includes:

a schedule storage step for storing programs being viewed in terms of each separate block unit for each user; and

a copy indication step for giving an indication, when the number of users viewing a given block retrieved by the number of users retrieval step becomes equal to the maximum number of transmissions calculated by the maximum number of transmissions calculation step and, in the schedule storage step, a program for a block which is one of a block preceding and following the given block coincides with one of the programs for the given block, to the image data storage step to copy image block data for the given block in the coinciding program,

wherein the image data storage step includes a reserve image data storage step, for copying image data onto a reserve recording medium separate from the recording media, at the indication from the copy indication step.

24. The method of claim 23, wherein the image data management step further includes:

an image data management table writing step for writing new block identification information and a new frame table column corresponding to the image data copied by the reserve image data storage step into the block table and the frame table in the image data management tables; and

a number of users addition storage step, which provides a storage column corresponding to a new block in the reserve image data storage step to the number of users storage step aside from storage columns for storing the number of users, for adding and storing the number of users viewing a block in a correspond storage column.

25. The method of claim 24, wherein after the reserve image data storage step has notified the image data management step that it has finished copying the image block data onto the reserve recording medium, then when there has been a request for a frame table column corresponding to the image block data, from one of the first frame table request step and the second frame table request step, then one of the first frame table transmission step and the second frame table transmission step transmits the frame table column newly written in by the image data management table writing step.

26. The method of claim 19, wherein the image data management step further includes:

a number of users storage step for storing a number of users who are simultaneously viewing blocks having a same block number in any of the programs;

an image data transmission possibility judgment step for judging whether the number of users for a given block number recorded in the number of users storage step is within a range for which uninterrupted transmission of the image data is possible; and

block identification information transmission cancellation indication step for giving an indication to one of the first block identification information transmission step and the second block identification information transmission step to cancel transmission of the block identification information of a block having the given block number, when the image data transmission possibility judgment step judges that the transmission is not possible.

27. The video-on-demand system of claim 26, wherein the image data transmission possibility judgment step includes:

a number of users retrieval step for retrieving the number of users for each block from the number of users storage step;

a maximum number of transmissions calculation step for calculating a maximum number of transmissions which is a value given by dividing an average retrieval rate for the image data from the image data storage step by the image data retrieval/transmission step by a transfer rate for a transfer of the image data to the user; and

a possibility judgment step for judging that transmission is not possible when the number of users retrieved by the number of users retrieval step is not below the maximum number of transmissions calculated by the maximum number of transmissions calculation step.

28. The video-on-demand system of claim 16, wherein the image data management step includes:

a number of users storage step for storing a number of users who are simultaneously viewing blocks having a same block number in any of the programs;

image data transmission possibility judgment step for judging whether the number of users for a starting block recorded in the number of users storage step is within a range for which uninterrupted transmission of the image data is possible; and

a necessary information transmission cancellation step for cancelling a transmission of necessary information for the starting block when the image data transmission possibility judgment step has judged that the transmission is not possible.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a video-on-demand system for the supply of audio-visual programs via a cable network in accordance with user requests from a number of users and the method for the management of image data used therein.

2. Description of the Related Art

Recent years have witnessed the spread of CATV systems in a number of countries, with the principle format for the supply of programs being a pay-by-view system wherein the user can watch programs, such as movies or whatever, which are broadcast at a scheduled time. There have also been advances in the possibilities for two-way communication between the user and the cable network which broadcasts the program, so that there have been experiments using systems wherein the user can manipulate the program broadcast on a cable network using the same functions (rewind, fast forward, slow motion) which would be available if he/she were watching the program reproduced by a VCR. However, such techniques are still at a developmental stage, so that the functions present for VCRs have not yet been realized for CATV systems, and for the time being, an improved system for gathering information about users' desired viewing and a control method for such a system are necessary.

The following is an explanation of a video-on-demand system constructed according to present techniques, and the image data control method used therein, with reference to the drawings.

FIG. 1 shows a construction of a video-on-demand system according to the prior art. This video-on-demand system includes an image data transmission unit 111 for transmitting image data to the user, an image data storage unit 112 for storing the image data, usually composed of magnetic discs 113, and an image data management unit 114 for managing the storage information for the image data storage unit 112 and the information about the users, and is connected via a cable network 116 to the users' terminals 115.

FIGS. 2A and 2B show the image management tables for managing the image data in the image data management unit 114 in the video-on-demand system constructed according to the prior art, which was shown in FIG. 1.

These image management tables are comprised of a title table 121 and a frame table 122. The title table 121 stores all of the titles of the programs stored in the image data storage unit 112 together with the first address of the frame information for each title in the frame table 122.

The programs (image data) in the image data storage unit 112 are managed in a format divided into areas of a fixed length.

The frame table 122 stores for every frame the storage position (address) in the image data storage unit 112 of the first address of the image data (frames) divided into areas of fixed length. For example, the program indicated by the title information 123 for title A (program A) in the title table 121 is divided into A1, A2, A3, A4, . . . A7200 as shown in the frame information 124 for program A in the frame table 122.

On receiving a request of the title of the program which a user wishes to view from the terminal 115, the image data transmission unit 111 requests the appropriate title information in the title table 121 from the image data management unit 114. Having obtained the necessary title information, the image data transmission unit 111 requests from the image data management unit 114 the frame information corresponding to the title of the program, for example, frame information 124 for program A, out of the frame table 122, by reading the first address for the frame information 124. Having obtained the necessary frame information 124 out of the frame table 122, the image data transmission unit 11 stores this frame information 124, and accesses the address corresponding to the title of the program in the image data storage unit 112, thereby requesting the image data. Having obtained the image data, it then transmits the image data via the cable network 116 to the user's terminal 115.

The following is an explanation of the operation of the video-on-demand system constructed as described above.

FIG. 3 is a drawing showing the transmission process for the image data for the video-on-demand system of the prior art shown in FIG. 1, including the interaction with the user. The areas enclosed by broken lines show the operations performed by the image data transmission unit 111, the image data storage unit 112, the image data management unit 114, and the user's terminal 115, respectively.

The user accesses the image data transmission unit 111 using the terminal 115 via the cable network 116, and requests the program to be viewed, for example, program A (step 1302). The image data transmission unit 111 then requests the title information 123 for program A in the title table 121 from the image data management unit 114 (S1304). The image data management unit 114 then transmits the program A title information 123 in the title table 121 to the image data transmission unit 111 (S1306), when the program requested by the user is A. The image data transmission unit 111 obtains this program A title information 123 and accesses the address in given in the program A title information 123 from the image data management unit 114, before requesting the frame information 124 which corresponds to program A in the frame table 122 (S1308). The image data management unit 114 then transmits the requested frame information 124 (S1310). The image data transmission unit 111 obtains this frame information 124 from the image data management unit 114, and stores this frame information 124 (S1312). The image data transmission unit 111 then successively accesses the addresses on the magnetic disc 113 in the image data storage unit 112 given in frames A1 through A7200 in said frame information 124 (S1314). The image data storage unit 112 then transmits the accessed image data (S1316). In this way, the image data transmission unit 111 obtains the necessary image data from the image data storage unit 112 (S1318). The image data transmission unit 111 then transmits the obtained image data to the user's terminal 115 (S1320). The transmitted image data is then televised using the terminal 115 (S1322). The user watches the televised image, and may make use of the same operations (rewind, play, fast forward) as with a VCR (S1324). The image data transmission unit 111 then judges whether such a VCR operation has been made (S1326) and, if there has been such an operation, receives the operation, returns to step S1314, and has the image televised according to the wishes of the user (S1314-S1322). If there has not been a VCR operation, then the image data transmission unit 111 checks whether the final frame has already been transmitted (S1328), repeating the process in steps S1314-S1326 when the program has not finished, and moving on to step S1330 when it has. Having transmitted all of the image data, the image data transmission unit 111 then executes a post-completion process (S1330), for example, a fee-charging process.

For video-on-demand systems under the prior art, there have been no problems so long as programs are sent to the users at a fixed speed, but, when using such program supplying techniques, if there are a number of users watching the same program at the same time, all watching the same part of the program repeatedly by rewinding and fast forwarding, then there is the possibility that the system will be unable to send the image data to the user uninterruptedly. The same problems may occur if there are a number of titles stored on the same recording medium.

The situation described below can be thought of as a typical example. When magnetic discs 113 are installed in the image data storage unit 112, then if the average retrieval rate is 2 MBytes/second and the necessary transfer rate for transmitting image data to 1 user is set at 256 KBytes/second, then this means that a total of around 8 users can view images from one magnetic disc 113. If 10 magnetic discs 113 are arranged in parallel, then, if the load is shared effectively, a total of 8.times.10=80 users can be served. Therefore, if the requesting of a title by the users is performed at a predetermined fixed interval, then the video-on-demand system can commence the transmission of the image data. However, if after a given time, all 80 users make use of operations such as fast forward or rewind which all concern the images stored on 1 disc out of the magnetic discs 113, then, since the image data storage unit 112 can only transfer the data for 8 users, there will be a breakdown in the transmission of image data to the users' terminals 115, and the normal transmission of image data will no longer be possible.

Also, since it is necessary for the image data transmission unit 111 to store all of the frame information for the programs requested by the users, then it is necessary to equip the image data transmission unit 111 with a large storage capacity.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a video-on-demand system with an image data transmission unit of reduced storage capacity.

It is another object of the present invention to provide a video-on-demand system and a method for the management of image data which can televise programs without interruptions, even when a number of users all request the televising of a same part of a same program.

The first object stated above can be achieved by a video-on-demand system, comprising: an image data storage device, including a plurality of recording media for storing a plurality of programs, for storing image data for the programs divided into a plurality of blocks which are distributed among all of the recording media; an image data management device, including image data management tables in which management information for the image data is stored, for consulting the image data management tables and transmitting necessary information separately for each block, when there is a request from outside the device for information about one of the programs, wherein the image data management tables comprise a title table to a title of each of the programs with starting block identification in, formation for each of the programs, a block table corresponding block identification information for each of the blocks with starting frame identification information for each of the blocks, and a frame table corresponding frame identification information for each frame with position information showing at which position on which recording medium out of the recording media each of the frames is stored; and an image data transmission device for requesting to the image data management device for the necessary information for a transmission of a program requested by a user, for receiving the necessary information from the image data management device, for retrieving image block data separately for each block from the recording media and for transmitting the image block data to the user.

By means of the construction described above, it becomes possible to have the image data for a number of programs handled in sections.

Also, the number of the recording media disposed in the image data storage device lay be equal to or above a number of the blocks of image data in one program.

Also, the image data transmission device may include: a request unit for receiving a request for a televising of one of the programs from the user, and requesting to the image data management device a transmission of storage position information which shows at which position on which recording medium each separate block in the program is stored; an image data retrieval/transmission unit for receiving the transmission of the storage position information for each separate block of the program from the image data management device, for retrieving the image block data for each separate block from the position designated by the storage position information on the recording medium designated by the storage position information, and transmitting the image block data to the user; a request continuation unit for requesting to the image data management device, when the image data retrieval/transmission unit has finished retrieving the image block data for one block, a transmission of storage position information of image block data for a next block following after the block for which retrieving is finished; and an image data retrieval/transmission continuation unit for receiving the transmission of the storage position information of the image block data for the next block from image data management device, for retrieving the image block data for the next block from a position designated by the storage position information on a recording medium designated by the storage position information, and transmitting the image block data to the user, wherein the image data management device may include: a first request processing unit for receiving a tr