JP2019191812A - Content download system, content download method, and content download computer program - Google Patents

Abstract

To provide a content download system, method, and computer program capable of starting download without delay and speeding up download of a content file without downloading data unnecessary for a user.SOLUTION: A system 1 includes a content acquisition unit 9A, a speed measurement unit 9B, a speed comparison unit 9C, and a server switching instruction unit 9D. The content acquisition unit 9A downloads a main body file MF from CDN1 and a key file KF from CDN2 in response to a switching command. The speed comparison unit 9C compares a download speed of the key file KF measured by the speed measurement unit 9B with a reference speed. When the server switching instruction unit 9D determines that the download speed of the key file KF is faster than the reference speed, the server switching is performed so that the main body file MF is downloaded from the CDN2 when another content file is downloaded next.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a content download system, a content download method, and a content download computer program for selecting a server suitable for downloading a content file and downloading the content file.

  Distribution of content files such as electronic magazines, electronic newspapers, electronic books, and content files containing moving images is actively performed through the network. In order to respond to content file download requests (large-scale access) from a large number of users, content distributors can store content files having the same content in advance in a plurality of servers or server groups (hereinafter, simply referred to as “servers”). In order to distribute the access by the user to a plurality of servers and server groups.

  Distribution of contents by the server group includes distribution using a so-called CDN (Content Delivery Network). CDN is a cloud service that holds a copy (cache) of content files in a large number of server groups. When using a CDN, if there is a content download request from the user and no content file exists in the cache server, the cache server obtains the content file from the origin server and is defined. During this period, a cache that is a copy of the content file is maintained. When there is a request for downloading the same content from another user, the origin server and / or the cache server can respond to the download request, thereby enabling large-scale access distribution. The CDN is disclosed in, for example, JP-T-2004-507128 (Patent Document 1), JP-T-2006-502465 (Patent Document 2), and the like.

Conventionally, when a plurality of servers are used together for downloading a content file, the following two methods are adopted:
(i) Load balancing model In this model, multiple servers are registered in DNS (Domain Name System) in the same domain, and access is automatically distributed on the DNS side to use multiple servers. Is. In this model, the convenience of some users is lost when some servers fail or performance is low. In addition, DNS failures can cause complete interruption:
(ii) Backup model This model automatically switches access to a backup server when a failure occurs in the default server.

  These conventional methods are mainly aimed at improving fault tolerance, and have a problem in performance (mainly download speed). Therefore, another system has been developed as disclosed in Japanese Patent Application Laid-Open No. 2014-96103 (Patent Document 3) so that a server that is optimal for each user, that is, a server having a high download speed can be used. .

  In the system described in Patent Document 3, measurement data is prepared in advance for each of a plurality of servers, and before the download of the content file is started, the measurement data is downloaded from each of the servers and the download speed is increased. Measure and compare measurement results. Then, the content file is downloaded from the server having the fastest download speed.

Special table 2004-507128 gazette JP-T-2006-502465 JP 2014-96103 A

  However, the measurement data itself downloaded by the system described in Patent Document 3 is unnecessary for the user. That is, the conventional system has a problem that a plurality of data unnecessary for the user needs to be downloaded in order to measure the download speed. In addition, since the download of the content file is not started until the measurement result of the download speed and the comparison result are obtained, there is a problem that a delay occurs before the start of downloading the content file.

  An object of the present invention is to provide a content download system, a content download method, and a content download computer program that can start downloading without delay without downloading data unnecessary for the user and speed up the download of the content file. Is to provide.

  The content download system of the present invention selects a server suitable for downloading a content file from a plurality of servers storing the same content file, and downloads the content file. In addition, the content file is intended to be composed of a partial file constituting the content file and a remaining file having a larger data amount than the partial file.

  The content download system includes a content acquisition unit, a speed measurement unit, a speed comparison unit, and a server switching instruction unit. In response to the switching command, the content acquisition unit downloads the remaining file from one server included in the plurality of servers, and downloads some files from the other one server included in the plurality of servers. The speed measurement unit measures the download speed of some files. The speed comparison unit compares the download speed of the partial file measured by the speed measurement unit with the reference speed. When the server switching instruction unit determines that the download speed of the partial file is faster than the reference speed as a result of the comparison by the speed comparison unit, the remaining file of the other content file is downloaded the next time the other content file is downloaded. Is output from the other server so as to instruct the content acquisition unit to switch the download destination server.

  In this way, the content download system of the present invention separates the download destination of the partial file and the remaining file, and downloads the content file next when the download speed of the partial file exceeds the reference speed. At this time, by switching the download destination so that the remaining file is downloaded from the server that is the download destination of the partial file, the content file can be downloaded using a server having a high download speed. Although the content file is not downloaded from the server having the fastest download speed among many servers, the content file can be downloaded using a server having a relatively fast download speed. The partial file is a part of data that the user desires to download, and does not cause the user to download useless data. Also, since downloading of some files and remaining files has started, the start of downloading is not delayed.

  The “download speed” is an actually measured value (value expressed in Mbps or MB / s) divided by the time required to download the data amount of the content file.

  The switching command preferably includes command content for instructing the content acquisition unit to switch the download destination server so that a part of other content files is downloaded from a server other than the other one server. . In this way, it is possible to measure and compare download speeds when downloading other content files.

  The method for determining the reference speed is arbitrary. For example, a preset threshold value may be used. Also, the download speed measured by the speed measurement unit when a part of other content files is downloaded from one server in the previous download may be used. In this way, for example, when downloading a content file for the first time, the download speed of one server is measured, and then when downloading another content file, the reference speed (download speed of one server), The download speed of one other server can be compared, and the download speed of one server and another server can be compared. The download speed of a server that downloads some files and the download speed of the remaining files It becomes possible to compare the download speed.

  The speed comparison unit may store the download speed as the reference speed when it is determined that the download speed of the partial file is faster than the reference speed. In this way, the next download speed can be compared based on the download speed of the server determined to be fast.

  The content of the content file is arbitrary, but may be, for example, an electronic publication such as an electronic magazine, an electronic newspaper, an electronic book, or a moving image. In the case of electronic publications, many electronic publications include thumbnail images obtained by reducing the images of each page in order to increase the visibility of the contents of each page. Therefore, this thumbnail image can be a partial file and the rest can be a remaining file. In general, since a thumbnail image is about several MB, the file size is suitable for measuring the download speed of the server.

  The present invention can also be understood (or expressed) as a content download method. In a content download method for downloading a content file by selecting a server suitable for downloading the content file from a plurality of servers storing the same content file using a computer, the content file constitutes the content file. It consists of a partial file and a remaining file with a larger amount of data than the partial file. In response to the switching command, the remaining file is downloaded from one server included in a plurality of servers, and the partial file Download from another server included in a plurality of servers, a speed measurement step for measuring the download speed of some files, a download speed for some files measured in the speed measurement step, a reference speed, Compare the speed As a result of the comparison in the comparison step and the speed comparison step, if the download speed of a part of the files is faster than the reference speed, the remaining file of the other content file is transferred to another one when the other content file is downloaded next. The computer executes a server switching instruction step for outputting a switching instruction for instructing switching of a download destination server so as to download from the server.

  The present invention can also be understood (or expressed) as a content download computer program. In a content download computer program that is installed and executed on a computer in order to select a server suitable for downloading a content file from a plurality of servers storing the same content file and to download the content file, the content file Consists of a partial file that constitutes a content file and a remaining file that has a larger amount of data than the partial file. In response to the switching command, the remaining file is downloaded from one server included in a plurality of servers. And a content acquisition unit that downloads a partial file from another server included in a plurality of servers, a speed measurement unit that measures the download speed of the partial file, and a partial file measured by the speed measurement unit Download If the download speed of some files is determined to be faster than the reference speed as a result of the comparison by the speed comparison section and the speed comparison section comparing the speed and the reference speed, the next time you download another content file A server switching instruction unit that outputs a switching command for instructing the content acquisition unit to switch the download destination server so as to download the remaining file of the other content file from another one server is realized in the computer. It is configured. Of course, this program may be recorded on a computer-readable recording medium.

It is a block diagram which shows the structure of embodiment of the content download system of this invention. It is an example of the algorithm of the computer program for a content download when an optimization setting is OFF. It is an example of an algorithm of a content download computer program when the optimization setting is on. It is a matrix table | surface which shows CDN of the download destination of the key file KF and main body file MF at the time of the first download. It is the matrix table which shows the key file KF at the time of the download before the CDN switching after the second time and the CDN of the download destination of the main body file MF. 10 is a matrix table showing a download destination CDN of a key file KF and a main body file MF at the time of download after the first CDN switching. It is a matrix table | surface which shows CDN of the download destination of the key file KF and main body file MF at the time of the download after the 2nd CDN switch.

  Hereinafter, an embodiment of a content download system of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of a content download system according to the present invention. FIGS. 2 and 3 show a case where the content download system according to the present invention is realized using a computer. It is a flowchart which shows an example of the algorithm of the program to be used.

<Content download system>
As shown in FIG. 1, the main part of the content download system 1 according to the present embodiment is configured in a terminal device 3 that executes a computer program for content download. The terminal device 3 may be a mobile terminal such as a smartphone, a tablet PC, or a notebook PC, or may be a stationary PC or the like. The terminal device 3 is configured to be able to communicate with the origin server 5 via the communication line NW. In the present embodiment, the origin server 5 uses three CDNs (Content Delivery Network) (CDN1, CDN2, CDN3) to respond to content download requests from a large number of users. Each CDN is composed of a server group composed of a plurality of servers. However, since each CDN can be regarded as one server when viewed macroscopically, in this specification, each CDN is represented as CDN1. , CDN2 and CDN3. In the CDN, access priorities are set in advance in the order of CDN1, CDN2, and CDN3. Also, for convenience of explanation, it is assumed that each of CDN1, CDN2, and CDN3 already holds a cache of content files having the same contents.

  The content file to be downloaded by the content download system 1 of the present embodiment is an electronic publication such as an electronic magazine, an electronic newspaper, and an electronic book. Further, the electronic publication targeted by this embodiment is not composed of a single file, but is composed of a plurality of file groups. In the present specification, among the file groups constituting the electronic publication, the file group of thumbnail images of each page is defined as a key file KF (partial file), and other file groups excluding the key file KF are the main body files. MF (remainder file) is defined. Depending on the contents of the electronic publication, the key file KF is about several MB, and the main body file MF is about several tens to several hundreds MB.

  The origin server 5 is a management server that stores the original file of the content file. The origin server 5 can turn on / off the optimization setting. Normally, the optimization setting is on, and the optimization setting can be turned off at the judgment of the administrator of the origin server 5 when a failure occurs in a plurality of CDNs.

  In this specification, “optimization” means that the main body file MF, which is a remaining file with a large amount of data, can be downloaded from a server with a high download speed in accordance with the user's environment. More specifically, download processing is performed based on the flowchart shown in FIG.

  The terminal device 3 is installed with a content / downloading computer program, and includes an input unit 7 operated by a user, a control unit 9, a communication unit 11, a data storage unit 13, and a display screen 15. ing.

  The input unit 7 may correspond to the type of the terminal device 3. For example, in the case of a smartphone, if the display screen 15 is a touch panel type liquid crystal screen, the display screen 15 also serves as the input unit 7.

  The control unit 9 includes a content acquisition unit 9A, a speed measurement unit 9B, a speed comparison unit 9C, a server switching instruction unit 9D, and a display screen control unit 9E.

  The content acquisition unit 9A accesses the origin server 5 via the communication unit 11, and confirms the optimization setting state and the location of the content file. The content acquisition unit 9A performs a content file download process according to the optimization setting state (details will be described later).

  The speed measurement unit 9B, the speed comparison unit 9C, and the server switching instruction unit 9D function when the optimization setting of the origin server 5 is on. The speed measurement unit 9B measures the download speed of the key file KF when the optimization setting is on. The speed comparison unit 9C compares the download speed of the key file KF measured by the speed measurement unit 9B with the reference speed. If the server switching instruction section 9D determines that the download speed of the key file KF is faster than the reference speed as a result of the comparison by the speed comparison section 9C, the main body of the content file is next downloaded when another content file is downloaded. It instructs the switching content acquisition unit 9A of the download destination CDN to download the file MF from another CDN. The display screen control unit 9E outputs an image display signal, and an image is displayed on the display screen 15.

  The data storage unit 13 stores the downloaded content file and a reference speed (evaluation data) that is a comparison target of the speed comparison unit 9C.

<Download process>
When the user selects a content file (electronic publication) to be downloaded using the input unit 7 and requests download, the content acquisition unit 9A accesses the origin server 5 via the communication unit 11 and the optimization setting state The download process is performed as follows.

[When optimization setting is off]
When the optimization setting of the origin server 5 is off, downloading is performed according to the flowchart of FIG. FIG. 2 is an example of the algorithm of the content download computer program when the optimization setting is off.

  In this case, the content download system 1 performs the same operation as the conventional backup model. The content acquisition unit 9A accesses the CDN set with a high priority and starts downloading (step ST1). In the present embodiment, since “CDN1” is set as the default CDN, downloading from CDN1 is started. If the download is successful in step ST2, the user obtains the desired electronic publication and the process ends. If the download fails in step ST2 due to an error in the accessed CDN or the like, the download is attempted for a predetermined number of retries (step ST3). If the upper limit of the number of retries is exceeded, it is confirmed whether the terminal device 3 is not connected to the communication line NW and is in an offline state (step ST4). If it is offline, an error is displayed on the display screen 15. I do. If the download fails even though it is not offline, the download destination CDN is switched (step ST5), and the download is attempted again.

[When optimization setting is on]
When the optimization setting of the origin server 5 is on, downloading is performed according to the flowchart of FIG. FIG. 3 is an example of the algorithm of the content download computer program when the optimization setting is ON.

  FIGS. 4 to 7 are matrix tables showing the transition of the download destination CDN of the key file KF and the main body file MF when the optimization setting is on. The matrix table indicates a file group in which the row is CDN (repeated twice) and the column is downloaded. For example, if “O” is added at the position where CDN “1” and “main body” intersect, CDN1 Indicates that the main body file MF is to be downloaded. FIG. 4 is a matrix table at the time of the first download, FIG. 5 is a matrix table at the time of the second and subsequent downloads before CDN switching, and FIG. 6 is a matrix table at the time of download after the first CDN switching. FIG. 7 is a matrix table at the time of download after the second CDN switching.

  When the optimization setting is on, the content acquisition unit 9A performs the download process separately for the key file KF and the main body file MF.

(First download: Fig. 4)
The evaluation data (reference speed) is empty at the time of the first download, and the content acquisition unit 9A determines the CDN for downloading the key file KF and the main body file MF as follows:
Key file KF: Step ST10 → Step ST12 → Step ST13 → CDN-Level
Main file MF: Step ST10 → Step ST11 → CDN-Level.

  Since “CDN1” is set as the default CDN in CDN-Level, both the key file KF and the main body file MF are downloaded from CDN1 when downloaded for the first time, as shown in FIG. For the key file KF, the speed measuring unit 9B measures the download speed at the time of downloading (step ST15).

  If the download is successful (step ST16), the process ends for the main body file MF, but for the key file KF, the download speed measured by the speed measuring unit 9B is recorded as evaluation data (reference speed) (step ST17 → step). ST18 → step ST19).

  In addition, since the process of step ST23-step ST25 is a backup model like the process of step ST3-step ST5 of FIG. 2, description is abbreviate | omitted.

(From the second time, before downloading before switching CDN: Fig. 5)
At the time of the second download (when downloading a content file different from the first time), the content acquisition unit 9A determines the CDN for downloading the key file KF and the main body file MF as follows:
Key file KF: Step ST10 → Step ST12 → Step ST14 → CDN-Level + 1
Main file MF: Step ST10 → Step ST11 → CDN-Level.

  Since “CDN1” is set in CDN-Level, at the time of the second download, as shown in FIG. 5, the key file KF is downloaded from CDN2, and the main body file MF is downloaded from CDN1. For the key file KF, the speed measuring unit 9B measures the download speed at the time of downloading (step ST15).

  If the download is successful (step ST16), the process ends for the main body file MF. For the key file KF, the speed comparison unit 9C compares the download speed measured by the speed measurement unit 9B with the evaluation data (reference speed) (step ST17 → step ST18 → step ST20). Thereby, the download speed of CDN1 and the download speed of CDN2 can be compared. As a result of the comparison, if the download speed measured by the speed measuring unit 9B is slower, the process ends, and the next download is performed with the combination of CDNs shown in FIG.

  As a result of the comparison, if the download speed measured by the speed measurement unit 9B is faster, the speed comparison unit 9C updates the evaluation data (reference speed) (stores the download speed of CDN2) (step ST21). Then, the server switching instruction unit 9D outputs a switching command so as to switch the download destination CDN of the key file KF and the main body file MF in preparation for the next download (step ST22). That is, CDN-Level is switched from “CDN1” to “CDN2”.

(When downloading after the first CDN switch: Fig. 6)
When another content file is downloaded after the CDN of the download destination is switched by the switching command, the content acquisition unit 9A determines the CDN for downloading the key file KF and the main body file MF as follows:
Key file KF: Step ST10 → Step ST12 → Step ST14 → CDN-Level + 1
Main file MF: Step ST10 → Step ST11 → CDN-Level.

  Since “CDN2” is set in the CDN-Level, at the time of this download, as shown in FIG. 6, the key file KF is downloaded from CDN3, and the main body file MF is downloaded from CDN2. For the key file KF, the speed measuring unit 9B measures the download speed at the time of downloading (step ST15).

  If the download is successful (step ST16), the process ends for the main body file MF. For the key file KF, the speed comparison unit 9C compares the download speed measured by the speed measurement unit 9B with the evaluation data (reference speed) (step ST17 → step ST18 → step ST20). Thereby, the download speed of CDN2 and the download speed of CDN3 can be compared. As a result of the comparison, if the download speed measured by the speed measuring unit 9B is slower, the process ends, and the next download is performed with the combination of CDNs shown in FIG.

  As a result of the comparison, if the download speed measured by the speed measuring unit 9B is faster, the speed comparing unit 9C updates the evaluation data (reference speed) (stores the download speed of CDN3) (step ST21). Then, the server switching instruction unit 9D outputs a switching command so as to switch the download destination CDN of the key file KF and the main body file MF in preparation for the next download (step ST22). That is, the CDN-Level setting is switched from “CDN2” to “CDN3”.

(When downloading after the second CDN switch: Fig. 7)
When another content file is downloaded after the CDN of the download destination is switched by the switching command, the content acquisition unit 9A determines the CDN for downloading the key file KF and the main body file MF as follows:
Key file KF: Step ST10 → Step ST12 → Step ST14 → CDN-Level + 1
Main file MF: Step ST10 → Step ST11 → CDN-Level.

  Since “CDN3” is set in CDN-Level, at the time of this download, as shown in FIG. 7, the key file KF is downloaded from CDN1, and the main body file MF is downloaded from CDN3. For the key file KF, the speed measuring unit 9B measures the download speed at the time of downloading (step ST15).

  If the download is successful (step ST16), the process ends for the main body file MF. For the key file KF, the speed comparison unit 9C compares the download speed measured by the speed measurement unit 9B with the evaluation data (reference speed) (step ST17 → step ST18 → step ST20). Thereby, the download speed of CDN3 and the download speed of CDN1 can be compared. As a result of the comparison, if the download speed measured by the speed measuring unit 9B is slower, the processing is terminated, and the next download is performed with the combination of CDNs shown in FIG.

  As a result of the comparison, if the download speed measured by the speed measuring unit 9B is faster, the speed comparing unit 9C updates the evaluation data (reference speed) (stores the download speed of CDN1) (step ST21). Then, the server switching instruction unit 9D outputs a switching command so as to switch the download destination CDN of the key file KF and the main body file MF in preparation for the next download (step ST22). That is, the setting of CDN-Level is switched from “CDN3” to “CDN1”.

  Thereafter, the flowchart of FIG. 3 is repeated for each download.

  Initialize the reference speed and / or CDN-Level settings (ie, set the reference speed to “empty” and / or CDN-Level to “CDN1”) at any time (eg, once every few days). You may do it. If the reference speed is initialized, the downloaded key file KF is a small file that is not suitable for the measurement of the download speed, so if the download speed faster than normal is recorded as the reference speed, again, The reference speed can be recorded again. Also, if the CDN-Level setting is initialized, the optimization can be executed again from the CDN that originally has the fastest download speed.

  The above-described embodiment has been described as an example, and the present invention is not limited to this embodiment without departing from the gist thereof. For example, in the above embodiment, the reference speed (evaluation data) is empty at the time of the initial download, but an ideal download speed may be recorded as the reference speed in advance. In such a case, the content file download process is performed in the state shown in FIG. 5 from the first download.

  In the above embodiment, the download destination server is three CDNs, but the number of servers is not limited to this, and the number of servers may be two or four or more. In that case, the matrix tables shown in FIGS. 4 to 7 may be increased or decreased in rows to match the number.

  Of course, the download destination server may be a server other than the CDN, such as a mirror server in which a content file having the same contents is recorded.

  In the above embodiment, the thumbnail image of the electronic publication, which is a content file, is the key file KF, but other files may of course be the key file KF.

  Furthermore, the content file is not limited to an electronic publication, and may be another content file such as a moving image. In the case of a moving image, for example, a part of the moving image may be a partial file and the other may be a remaining file.

  According to the present invention, a content download system, a content download method, and a content download computer capable of starting download without delay and speeding up download of a content file without downloading unnecessary data. A program can be provided.

DESCRIPTION OF SYMBOLS 1 Content download system 3 Terminal device 5 Origin server 7 Input part 9 Control part 9A Content acquisition part 9B Speed measurement part 9C Speed comparison part 9D Server switching instruction part 9E Display screen control part 11 Communication part 13 Data storage part 15 Display screen KF Key file MF Main unit file CDN1,2,3 CDN

Claims (7)

A content download system for selecting the server suitable for downloading the content file from a plurality of servers storing the same content file, and downloading the content file,
The content file is composed of a partial file constituting the content file and a remaining file having a larger data amount than the partial file.
A content acquisition unit that downloads the remaining file from one server included in the plurality of servers and downloads the partial file from another server included in the plurality of servers in response to a switching command; ,
A speed measuring unit that measures the download speed of the partial file;
A speed comparison unit that compares the download speed of the partial file measured by the speed measurement unit with a reference speed;
As a result of comparison by the speed comparison unit, when it is determined that the download speed of the partial file is faster than the reference speed, the remaining file of the other content file is downloaded when the other content file is downloaded next. A content download system, comprising: a server switching instruction unit that outputs the switching command that instructs the content acquisition unit to switch a download destination server so as to download from another one server.   In the switching command output by the server switching instruction unit, the content acquisition unit is switched to a download destination server so that a part of the other content file is downloaded from a server other than the one other server. The content download system according to claim 1, wherein the instruction content to be instructed is included.   The content download / downloading content according to claim 1, wherein the reference speed is a download speed measured by the speed measurement unit when a part of another content file is downloaded from the one server in the previous download. system.   The content download system according to claim 1, wherein the speed comparison unit stores the download speed as the reference speed when the download speed of the partial file is determined to be faster than the reference speed. The content file is an electronic publication;
The content download system according to claim 1, wherein the partial file is a thumbnail image of each page of the electronic publication. A content download method for selecting the server suitable for downloading the content file from a plurality of servers storing the same content file using a computer, and downloading the content file,
The content file is composed of a partial file constituting the content file and a remaining file having a larger data amount than the partial file.
Downloading the remaining file from one server included in the plurality of servers and downloading the partial file from another server included in the plurality of servers in response to a switching command;
A speed measurement step for measuring a download speed of the partial file;
A speed comparison step of comparing the download speed of the partial file measured in the speed measurement step with a reference speed;
If the download speed of the partial file is faster than the reference speed as a result of the comparison in the speed comparison step, the remaining file of the other content file is replaced with the other one when the other content file is downloaded next. A content download method, wherein the computer executes a server switching instruction step for outputting the switching instruction for instructing switching of a download destination server so as to download from one server. A content download computer program that is installed in a computer and executed to select the server suitable for downloading the content file from a plurality of servers storing the same content file and to download the content file There,
The content file is composed of a partial file constituting the content file and a remaining file having a larger data amount than the partial file.
A content acquisition unit that downloads the remaining file from one server included in the plurality of servers and downloads the partial file from another server included in the plurality of servers in response to a switching command; ,
A speed measuring unit that measures the download speed of the partial file;
A speed comparison unit that compares the download speed of the partial file measured by the speed measurement unit with a reference speed;
As a result of comparison by the speed comparison unit, when it is determined that the download speed of the partial file is faster than the reference speed, the remaining file of the other content file is downloaded when the other content file is downloaded next. Content configured to realize in the computer a server switching instruction unit that outputs the switching command to instruct the content acquisition unit to switch a download destination server so as to be downloaded from another one server Download computer program.

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