JP2002196969A - Cache server - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cache server capable of reducing a load of a communication access network. SOLUTION: In this cache server for caching an object down-loaded from a server to a client terminal through an access network of a communication system in a temporary storage region, or caching an object up-loaded from the client terminal to the server in the temporary storage region, it is predicted by using an evaluation function whether the object up-loaded from the client terminal to the server is down-loaded to another client terminal or not. When the possibility of being down-loaded is low based on the prediction result, the object is not cached in the temporary storage region of the cache server but up-loaded to the server, and when the possibility of being down-loaded is high, the object is cached in the temporary storage region of the cache server and simultaneously up-loaded to the server.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cache server that relays information transfer in an information communication access network, and more particularly to a cache server that also takes account of information upload.

[0002]

2. Description of the Related Art Communication services supporting the information-oriented society have been diversifying from those based on a long-time wired telephone network to new service forms. Among them, as a non-PC type Internet connection network, a mobile communication network has been regarded as important both as an infrastructure and as a medium. With the expansion of the use of the Internet as well as the original function as a mobile phone, Features other than the primary ones, such as web access and e-mail, have come to the fore. Mobile phones are less expensive than PCs in terms of equipment and educational expenses. For example, mobile intranets can be built in-house, Hi-Fi music distribution services, game distribution using Java, and so on. In the year,
It is expected that data traffic will dominate and voice traffic will be modest.

[0003] IMT-2000 (International
In the third generation mobile communication system called Mobile Telecommunication 2000), the Ministry of Posts and Telecommunications has issued licenses to several operators.
It aims at realizing high-speed data transmission at 28 to 384 kbps and up to about 61 kbps.

Further, as a second step, MMAC
(Multimedia Mobile Access Communication system;
Multimedia mobile access communication systems) aim at ultra-high-speed, high-quality wireless access networks, and high-speed wireless access technologies of 30 to 100 Mbps are expected.

[0005] In addition, access equipment between homes and offices and exchanges, which was conventionally built around wired facilities, has been changed to FW.
A (fixed wireless station access) or WLL (Wireless Local L
(wireless access networks), such as wireless access networks, is becoming more active, replacing aging metal cables with optical fiber cables, and developing basic telephone networks in developing countries. Maintenance is underway.

[0006] Core services such as telephone service networks and mobile communication networks
Since the network can integrate voice and data and can be constructed at low cost, IP (Internet Protocol) for transmitting packet data from conventional circuit switching
l) Moves to change to nets are emerging.

[0007]

As described above, in order to respond to the expansion of so-called non-telephone communication such as data communication and image communication, and the expansion of multimedia-oriented needs for combining various information expressions, telecommunications carriers must Therefore, it is necessary to further increase the capacity of the core network.

In a mobile communication network, the service area covered by one base station is about 3 to 5 k in a large city.
m, it is said that the radius is about 5 to 10 km in middle cities and suburbs, but recently, especially in urban areas, the radius of the service area is gradually reduced by increasing the number of service areas. There are various reasons for this. One is to avoid traffic congestion due to an increase in the number of users, and in reality the telecommunications carrier is worried about how to handle traffic.

Conventionally, in a mobile communication network or the like, the transmission speed of a "down" channel for transmitting data from a node to a terminal is increased, and the transmission speed of an "up" channel for transmitting request data or the like from a terminal to a node is increased. In many cases, an asymmetric transmission system in which is reduced. In addition to mobile communication, for example, ADSL (Asymmetric Dig)
In the case of ital Subscriber Line (asymmetric digital subscriber line transmission system), the transmission speed of the “downstream” channel is about 10 Mb.
While the transmission speed is as high as ps, the transmission speed of “up” is about 1/10 of that. In addition, CATV (CAble TeleVi
Although a method of using the distribution network of the C.I.S.T.sion as the access network of the communication system is also used, the current mainstream of the cable modem is a high-speed downlink in which data is transmitted from the CATV station to the user. , The uplink direction (uplink) is an asymmetric type with a low speed.

[0010] Such an asymmetric transmission system is based on the Web
The "down" direction, which downloads a large amount of data from a server or the like, was extremely effective in a usage mode mainly using the direction. However, in recent years, there has been an increasing need to utilize the interactive nature of data, and a large amount of data has been frequently uploaded from a user terminal. For this reason, in particular, a high load is being applied to a line in the “up” direction, which was not so much loaded until now.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a cache server capable of reducing a load on a communication access network.

[0012]

In order to achieve the above object, the present invention provides a method for caching an object downloaded from a server to a client terminal in a temporary storage area via an access network of a communication system. A cache server that caches objects uploaded from a terminal to a server in a temporary storage area, and predicts, using an evaluation function, whether an object uploaded from a client terminal to a server is downloaded to another client terminal. If the possibility that the object is downloaded based on the prediction result is low, the object is uploaded to the server without caching in the temporary storage area of the cache server, and if the object is likely to be downloaded, the object is downloaded. Before the object And wherein the uploading to the server along with the cached in the temporary storage area of the cache server.

[0013] The evaluation function is a URI (Uniform Resource) used when the object is uploaded to the server.
If the Identifiers are already cached in the cache server, it is determined that the object is highly likely to be downloaded to the client terminal, and if not, the object is likely to be downloaded to the client terminal. It is characterized in that it is determined to be low.

According to the present invention, not only when downloading, but also when uploading an object to a server,
Content that is likely to be requested by a user is temporarily cached in a cache server serving as a relay point. Therefore, when a user requests cached content, instead of the server responding, the cache server only has to respond to the user, so that upstream traffic can be reduced.

According to the present invention, an object downloaded from a server to a client terminal is cached in a temporary storage area via an access network of a communication system, or an object uploaded from the client terminal to the server is temporarily stored. A cache server for caching in an area, wherein when an object is uploaded from a client terminal to a server, the object is temporarily cached in the temporary storage area, and the state of the cache server, the server, and the network are evaluated. Uploading the object from the cache server to the server during a time period when the value of the evaluation function to be performed is under a predetermined condition, or a time period statistically set as being under the condition. I do.

At this time, more preferably, a flag indicating whether or not the upload of the object to the server has been completed is provided, and the object whose upload has not been completed is deleted from the temporary storage area of the cache server. It is characterized in that it is excluded from candidates.

According to the present invention, instead of immediately uploading data from the cache server to the server, the data can be shifted to a time period in which the load on the network environment is low. Congestion can be reduced. Objects that have not been uploaded to the server are not deleted from the cache server.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 1 is a diagram showing an outline of an access network using a cache server according to the present invention in a mobile communication network. Base stations 1a to 1c for forming an access network in mobile communication are several k
The radius r of a communicable area (service area) 9a covered by one base station, for example, the base station 1a, is about 3 to 5 km. The terminals 2a to 2c owned by the user are provided in the service areas 9a to 9c.
The communication by the wireless transmission method can be performed with the base stations 1a to 1c within the range of. Also, the service area 9a
The shops 51 to 54 belonging to the station square shopping street 5 existing in
Each having a client terminal, the base station 1a
And can communicate with each other.

The base stations 1a to 1c are interconnected with a base control station 10, and this base control station 10 is connected to the terminals 2a to 2c.
c and the base stations 1a to 1c that are closest to each other,
It performs control such as checking and selecting.

The communication lines 11a to 11c collected from each of the base stations 1a to 1c are collected by the base control station 10 and connected to an external network such as the subscribed telephone network 30 or the Internet 20 from the base control station 10. , The terminals 2a to 2c, and the shops 51 to 54 can be communicated.

Each of the base stations 1a to 1c is provided with a cache server 3a to 3b, respectively. The cache servers 3a to 3c have the following functions.

First, the user terminals 2a to 2c are
b) When an object such as digital content is downloaded from the server 25, the object is cached in a temporary storage area in the cache servers 3a to 3c (stored for a certain period of time). Web server 2
5 instead of responding, this cache server 3a-
3c has a function of responding to the user the object cached in the temporary storage area.

Second, it has a function of caching, in a temporary storage area, objects to be uploaded from the user terminals 2a to 2c or client terminals of the shops 51 to 54 to the web server 25. This second function will be described in more detail later.

The objects cached in the cache servers 3a to 3c correspond to the respective base stations 1a to 1c.
Caches objects for which a download request or an upload request has been made to the web server 25 from the user terminals 2a to 2c in the service areas 9a to 9c respectively covered by. That is, as illustrated in FIG. 1, an object for which a download request or an upload request is made from the user terminal 2a in the service area 9a covered by the base station 1a is cached in the cache server 3a. The object requested to be downloaded or uploaded from the user terminal 2b is cached in the cache server 3b.

A large amount of information from all over the world is constantly flowing on the Internet 20, and although the information requested by the users is varied from person to person, information that is closely related to the area is often requested. For example, as shown in FIG. 1, a station shopping street 5 is located near the station 4 in the service area 9a of the base station 1a. Stores 51 to 54 belonging to this station square shopping street 5 are web servers 2
The information provided from the base station 1a has a higher cache ratio than the ratio distributed via the cache servers 3b to 3c installed in the other base stations 1b to 1c.
It is considered that the ratio of distribution via the server 3a tends to be higher. Therefore, by caching each of the cache servers 3a to 3c for an object that is likely to have a relatively large number of requests, traffic upstream from the base stations 1a to 1c can be reduced.

The base stations 1a to 1c, on which the cache servers 3a to 3c are installed, for example, base stations such as mobile phones, are relatively large-scale facilities, partly because they were originally developed as car telephone infrastructure. In recent years, relatively small ones have been created to complement places where radio waves are difficult to reach, such as behind buildings, so that they can be installed on telephone poles, building walls, and underpass ceilings. As described above, when the apparatus is installed in an environment where the conditions are poorer than the facilities in the base station, the operating temperature range of the components used in the cache servers 3a to 3c (for example, the disk drive for the cache storage). Therefore, it is necessary to take measures such as a heater and a heat radiation means.

Subsequently, the user terminals 2a to 2c
When uploading an object such as digital content to the server 25, the cache server 3a to
The operation of 3c will be described in detail.

As exemplified in FIG. 1, for example, the operator that operates the mobile communication network as the access network and the operator of the web server 25 on the Internet 20 are not always the same. . Using the client terminal of the store 54 belonging to the shopping district 5 in the service area 9a of the base station 1a, certain object information (for example,
When uploading information such as shop advertisements) to the web server 25, data is transmitted from the store 54 to the base station 1a, and the base station 1a sends the data to the base control station 10 upstream thereof.
Furthermore, it is uploaded from the base control station 10 to the web server 25 via the Internet 20.

When there is a request for the object from the user terminal 2a, if the information is not cached in the cache server 3a of the base station 1a as in the prior art, the request from the terminal 2a is sent to the base station. 1a via the base control station 10 and the Internet 20
The information sent to the b server 25 and returned from the web server 25 are returned to the Internet 20 and the base control station 2
0 and the terminal 2a via the base station 1a.
That is, one round trip is made between the base station 1a, the base control station 10, the Internet 20, and the web server 25.

Therefore, when uploading an object from the client terminal of the store 54, the base station 1a
The object is cached in the temporary storage area of the cache server 3a provided in the server. Thereby, the base station 1
When access is made from the terminal 2a in the service area 9a of a, the cache server 3a of the base station 1a only has to respond in place of the web server 25, so that traffic upstream from the base station 1a can be reduced. it can.

When the cache server 2a caches an object uploaded from the store 54, if the result of the evaluation function for predicting whether the object is downloaded and cached is lower than a predetermined threshold, the cache server 2a determines whether the object is downloaded and cached. W without caching the object
If the object is passed through to the eb server 25, and if it is higher than the threshold value, the object is cached in the temporary storage area of the cache server 3a, and the object is stored in w
Upload to the web server 25.

As an evaluation function for predicting whether or not to cache an uploaded object, for example,
URI (Uniform Resource Identifier) when the content to be uploaded is published on the web server 25
If s) is already cached in the cache server 25, it is determined as "true", and if not, it is determined as "false". In this case, a temporary copy of the object identified by the URI is created / updated in the cache server 3a. That is, an object that has already been requested by the user is cached. Thereby, when uploading the object to the web server 25, the content likely to be requested by the user can be efficiently cached in the cache server as the relay point.

At this time, the timing at which the object is uploaded from the cache server 3a to the web server 25 may not be the same as the timing at which the store 54 uploads the object. For example, if the web server 25 is operated from the cache server 3a during a time period in which traffic upstream from the base station 1a is relatively small (for example, early morning or late night), traffic upstream from the base station 1a, particularly in the upward direction, Congestion can be dispersed.

Objects that are cached in the cache server 3a and have not been uploaded to the web server 25 yet are stored in the terminal 2c in an area other than the service area 9a of the base station 1a (for example, the service area 9c). A request for the object is sent to the web server 25 from a terminal in another access network (for example, the terminal 35 connected to the subscriber telephone network 30 or the terminal 26 connected to the Internet). In this case, the web server 25 stores the cache of the base station 1a.
What is necessary is just to receive the object from the server 3a and distribute it to the request source. When the object is requested from the terminal 2b in the service area 9b, the object is cached in the cache server 3a by inquiring from the base station 1b to the base station 1a without inquiring to the web server 25. You can get the object that is.

Whether or not the upload to the target web server 25 has been completed so that objects not uploaded to the web server 25 are not automatically deleted from the temporary storage area of the cache server 3a. The incomplete object is excluded from candidates for deletion from the temporary storage area.

The process flow when an object is uploaded from the terminal to the web server as described above is illustrated in the flowchart of FIG. 2 and the time chart of FIG.

First, from the terminal of the store 54,
A request (Open request) for establishing a connection for uploading to the server 25 is issued. At this time, the request from the terminal of the store 54 is transmitted to the cache of the base station 1a.
This is performed via the server 3a (Step 01).

The cache server 3a functions as a proxy server (local proxy server) for the web server 25, temporarily establishes a connection to the web server 25 to which the object is permanently registered, and stores a user ID and a password. It is determined whether the web server 25 requests the authentication information. When the web server 25 is seeking authentication information, the terminal of the store 54 is prompted to input a user ID and a password, and the input data is transmitted to the web server 2.
5 (Step 02).

When the web server 25 authenticates the user ID and the password, the cache server 3a shifts to a state of accepting an object from the terminal of the store 54 (Step 03 to Step 04).

On the other hand, when the web server 25 does not accept the user ID or the password, it returns to the terminal of the store 54 that the temporary registration of the object is rejected (Step 09).

Here, an example in which user authentication is performed using a user ID and a password has been described. However, the present invention is not limited to this. For example, user authentication may be performed using an electronic signature. Further, the connection between the cache server 3a and the web server 25 may be closed when the user authentication is completed.

The cache server 3a, which has transitioned to the state of accepting the upload of the object, receives the subcommand from the terminal of the store 54, interprets and executes it (Step 05). The subcommands accepted here are, in addition to the "post" command for writing an object, the name of the object is changed (for example, "today.mpeg" is changed to "yes"
terday.mpeg "), and a" delete "subcommand for deleting objects that no longer need to be published.

FIG. 4 exemplifies a processing flow of the cache server 3a when the "post" subcommand is accepted.

When the result of the evaluation function for predicting whether or not the object being processed is downloaded is lower than a predetermined threshold, the object is not cached and the Web
The post operation is transferred to the server 25 (Step 21, Step 24).

Conversely, if the value is higher than the predetermined threshold value, the object is cached in the temporary storage area of the cache server 3a, and the attribute of the object is made unerasable (Steps 21 to 23).

When the objects are cached in Step 22, an object having a low hit rate (a frequency requested by the user is low) may be deleted, and an empty area may be secured in the temporary storage area.

Returning to FIGS. 2 and 3, the process of interpreting and executing the subcommand shown in Step 05 is repeated until a "Close" subcommand indicating that a series of maintenance work has been completed is sent from the terminal. (Step06).

When accepting the "Close" subcommand from the terminal of the store 54, the cache server 3a notifies the web server 25 of what kind of change has occurred in an update list (Step 07). ).

Then, the cache server 3a sends the we
The upload of the real object to the server b is executed during a time period during which traffic upstream from the base station 1a is relatively small (a busy season) (Step 08).

During Step 07 to Step 08, the latest object exists in the cache server 3a, but has not been updated in the web server 25. During this time difference t, the terminals 2c and 2 of the user who do not pass through the base station 1a
When the web server 25 makes a request to the web server 25 from Steps 6 and 35 (Step 11), the web server 25 refers to the update list, and if the latest object is stored in the cache server 3a.
, The request data is transferred to the cache server 3a. (Step12). Then, the cache server 3a transmits the cached object to the web server (Step 13), and the web server 25 distributes the cached object to the user (Step 14).

Note that the above definition of the off-peak period is not particularly limited. For example, the following definitions are assumed.

(1) A time period during which traffic upstream from the base station 1a is relatively free is investigated and set in advance.

(2) The amount of traffic upstream from the base station 1a is checked in a fixed cycle, and when the amount of traffic falls below a predetermined threshold, uploading is performed.

(3) When the load on the cache server falls below a predetermined threshold, uploading is performed.

(4) Load of the web server 25 (for example,
A time period in which the processing amount per unit time or the amount of objects that have not been uploaded to the web server 25 in the temporary storage area is relatively free is investigated and set in advance.

(5) The load on the web server 25 is checked in a fixed cycle, and when the load falls below a predetermined threshold, uploading is performed.

The definition of the off-peak period can be arbitrarily determined by the system operator in consideration of the status of the system and the like.

If this function of uploading during the off-peak period is further extended, the Web server 2 shown in Step 08 above can be used.
It is also conceivable that the user does not dare to upload the file to V5. That is, the real content of the object uploaded via the base station 1a is
Until the event of ep12 occurs, the real server (web server 2
Not registered in 5). Therefore, the cache server 3
a functions as a real server, and the web server 25 can also function as a cache server for access from other users 2c, 26, and 35 that do not pass through the base station 1a.

In this way, the cache server 3
a is a proxy server (proxy server) of the web server 25 as seen from the store 54 that is the registrant. The registrant places contents which can be accessed only from the service area 9a other than the service area 9a of the base station 1a in the external web server 25 without being aware of the existence of the cache server 3a, and places the contents in the service area 9a of the base station 1a. Objects are often placed in the right place at the right place, such as placing content that is frequently accessed from the cache server 3a.

In addition, contents which are not registered in the web server 25 and are not accessed from the service area 9a of the base station 1a are in a sibling relationship, and the contents are frequently hit. If there is a cache server 3b, the cache server 3
It is also possible to change the object on b to an attribute that cannot be automatically deleted, and divert the cache server 3b to an apparent real server. In this way, traffic from the access network to a higher network can be reduced.

It is useless to cache an object that has been cached but is rarely accessed from anywhere. Therefore, an object that has not been accessed for a long time with an attribute that cannot be automatically erased is stored in the above-described step.
The upload to the web server 25 shown in 08 may not be performed.

(Embodiment 2) FIG. 5 is a diagram showing an outline of an access network in which a cache server according to the present invention is applied to a CATV distribution network.

As shown in FIG. 5, the topology of the CATV network may be such that signals of the same program (data) are simultaneously delivered in one direction from the head-end center 40 to each home (user) 46a, 46b, 50a. Therefore, unlike a telephone network, it is not necessary to separately lay cables one by one, and the coaxial cable is divided into small parts while being distributed by distributors 61 to 64 on the way. Also,
Since the electric signal is attenuated in the coaxial cable, repeater amplifiers (Bidirectional amplifers) 7 are arranged at regular intervals.
The signal level is compensated by 6 to 80. Also, CATV
The head end 40 of the business operator is provided with a router for connecting to an ISP (Internet service provider) and a head end modem for exchanging data between the user's cable modem.

Such a conventional CATV distribution network is based on LA.
Similar to N (Local Area Network), one transmission medium (coaxial cable or optical fiber cable) is shared by many users, so if many users access the Internet at the same time, the data transmission speed is reduced. There was a problem.

Therefore, as shown in FIG. 5, in this embodiment, cache servers 86 to 90 are installed in the relay amplifiers 76 to 80, respectively. Each of the cache servers 86 to 90 has the same function as the cache server shown in the first embodiment.

That is, by installing the cache servers 86 to 90 for each of the branch lines 46 to 50, users 46a and 46b using the same cache server 86 can
If an attempt is made to access the same content, the content is delivered from the cache server 86, so that the traffic does not occur on the other branch lines 41 to 45, 47 to 50. Further, for example, when the user 46b uploads the content to a web server on the Internet, if the content is cached in the cache server 86 as in the first embodiment, other users connected to the branch line 46 can be used. When the content 46a accesses this content, the cache server 86 may respond. Therefore, it is possible to reduce the amount of traffic in the downlink (downlink) and uplink (uplink) upstream of the cache server.

FIG. 5 shows an example in which the cache servers 86 to 90 are installed in the relay amplifiers 76 to 80. However, the location where the cache servers are installed is not limited to this. You may make it install in 61-64. If a cache server is installed in the distributor 63, users belonging to the branch lines 46 to 47 can use it. If a cache server is installed in the distributor 61, it belongs to all the branch lines 46 to 50 shown in FIG. This is available to the user.

Although the embodiments of the present invention have been described in detail, the present invention is not limited to the embodiments, and various improvements and modifications may be made without departing from the gist of the present invention. .

For example, in this specification, a mobile communication network, C
Although an example in which the present invention is applied to an ATV distribution network has been described, the present invention is not limited to these, and can be similarly applied to other types of access networks.

[0071]

According to the present invention, not only at the time of downloading but also at the time of uploading an object to the server, the content which is likely to be requested by the user is temporarily cached in the cache server as a relay point. I am trying to do it. Therefore, when another user requests the cached content, instead of the server responding, the cache server only has to respond to the user, so that upstream traffic can be reduced. Furthermore, content that is highly likely to be requested by a user can be efficiently cached in a cache server that is a relay point.

Instead of immediately uploading data from the cache server to the server, the data can be shifted to a time period when the load on the network environment is low, and congestion can be alleviated especially for "up" traffic. be able to. Objects that have not been uploaded to the server are not deleted from the cache server.

Therefore, the load on the communication access network can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a network system in which a cache server of the present invention is applied to a mobile communication network.

FIG. 2 is a flowchart illustrating an example of a procedure of a processing operation of the cache server illustrated in FIG. 1;

FIG. 3 is a time chart showing a timing of a processing operation of the cache server shown in FIG. 1;

FIG. 4 is a flowchart showing an example of a processing procedure when a post subcommand is received from a client terminal in the processing procedure shown in FIG. 2;

FIG. 5 is a block diagram showing an embodiment of a network system in which the cache server of the present invention is applied to a CATV distribution network.

[Explanation of symbols]

 1a, 1b, 1c .... Base stations 2a, 2b, 2c .... Terminals 3a, 3b, 3c .... Cash servers 4 .... Stations 5 .... Station shopping streets 51- 54 ... Store 6 .... Rail 9a, 9b, 9c ... Service area 10 .... Base control station 11a, 11b, 11c ... Line 20 ... Internet 25. ... Web server 26 ... Terminal 30 ... Subscribed telephone network 35 ... Terminal 40 ... CATV center (head-end center) 41 ... Trunk line 42-50 ... .. branch lines 46a, 46b, 50a... User terminals 61-64... Distributors 76-80... Relay amplifiers 86-90....

Claims (4)

[Claims] An object downloaded from a server to a client terminal is cached in a temporary storage area via an access network of a communication system, or an object uploaded from a client terminal to a server is cached in a temporary storage area. A cache server that predicts, using an evaluation function, whether an object uploaded from a client terminal to a server is downloaded to another client terminal, and is unlikely to be downloaded based on the prediction result. In such a case, the object is uploaded to the server without being cached in the temporary storage area of the cache server. If the object is likely to be downloaded, the object is cached in the temporary storage area of the cache server. Cache server, wherein the uploading to the server along with. 2. The cache server according to claim 1, wherein the evaluation function is a URI (Uniform Resource Identifier) when the object is uploaded to the server.
If s) is already cached in the cache server, it is determined that the object is likely to be downloaded to the client terminal, and if not cached, the object is likely to be downloaded to the client terminal. A cache server, which is determined to be low. 3. An object downloaded from the server to the client terminal is cached in a temporary storage area via the access network of the communication system, or an object uploaded from the client terminal to the server is cached in the temporary storage area. A cache server, wherein when an object is uploaded from a client terminal to a server, the object is temporarily cached in the temporary storage area, and an evaluation function for evaluating the state of the cache server, the server, and the network is provided. A cache server that uploads the object from the cache server to the server during a time period when the value is under a predetermined condition or a time period that is statistically set as being under the condition. . 4. The cache server according to claim 3, wherein a flag indicating whether or not the upload of the object to the server has been completed is provided, and the object whose upload has not been completed is temporarily stored in the cache server. A cache server that is excluded from candidates for deletion from a storage area.