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`EP 2 597 869 A1
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`Description
`
`Technical Field
`
`[0001] The present invention relates to a content dis-
`tribution service in which a server distributes content to
`
`the client in response to arequestfrom a client for playing
`the content.
`
`Background Art
`
`[0002] Therehas been conventionally and widely used
`techniques for providing content, such as moving imag-
`es, via communication networks. Examples of the tech-
`niques encompassa video on demand (VOD)service in
`which a requestis transmitted from a client which plays
`content and, in response to the request, the content is
`distributed to the client from a server which managesthe
`content. In the content distribution services such as the
`
`VOD, content is provided to clients by means of a stream-
`ing method, a download method, or a progressive down-
`load method.
`
`[0003] The following Patent Literature 1 discloses an
`example where a contentdistribution service is provided
`by meansof the progressive download method. The Pat-
`ent Literature 1 discloses a content distribution service
`
`system in which a request for contentis transmitted to a
`server from a client with use of HTTP and the client plays
`the content in response to the request.
`
`Citation List
`
`Patent Literature
`
`[0004]
`
`Patent Literature 1: Japanese Patent Application
`Publication, Tokukai, No. 2005-110244 A(Publica-
`tion Date: April 21, 2005)
`
`Summaryof Invention
`
`Technical Problem
`
`[0005] Whatever method (the streaming method, the
`download method, or the progressive download method)
`is used, it is necessary to continuously transfer a great
`amount of data to a client from a server in a case where
`a contentdistribution service is provided, specifically,dif-
`ferent kinds of content are distributed to a plurality of
`clients. When the numberof clients increases and a load
`of a network, which is used to transmit the data from the
`server, and a load of the server exceedtheir limits, the
`data transfer is, for example, delayed. This decreases
`quality of the content distribution service.
`[0006] The present invention has been made in view
`of the aforementioned problem, and an object of the
`present invention is to achieve (A) a content distributing
`
`device, (B) a content playing device, (C) a content dis-
`tributing system, (D) a method for controlling the content
`distributing device, (E) a controlling program, and (F) a
`recording medium, each of which, reduces, in a content
`distributing system in which contentis distributed to a
`client from a server, reduces an increase in load of the
`server and a network andfor data transmission from the
`server.
`
`Solution to Problem
`
`In order to achieve aforementioned object, a
`[0007]
`content distributing device for transmitting, in response
`to a request, a content to a source which is a sender of
`the request, in accordance with the present invention,
`includes: determining means for determining whether the
`source is (A) a relaying device for receiving the content
`thus requested and possessing and transferring the con-
`tent to a content playing device or (B) the content playing
`device for playing the content thus requested; content
`transmitting means for transmitting, in response to the
`request, the content thus requested to the relaying device
`in a case where the determining means determines that
`the source is a relaying device; content-storage-location
`information generating means for generating content-
`storage-location information by associating (A) the con-
`tent transmitted by the content transmitting means with
`(B) an address of the relaying device, which is a cesti-
`nation to which the content is to be transmitted, or an
`address of the content playing device, to which the con-
`tent is to be transferred from the relaying device; and
`content-acquiring-location instructing means for trans-
`mitting, in response to the request, an instruction to the
`content playing device which is the source in a case
`wherethe determining means determinesthat the source
`is a content playing device, which instruction is to acquire
`the content from (i) a relaying device indicated by an ad-
`dress that the content-storage-location information as-
`sociates with the content thus requested or(ii) a content
`playing device indicated by an addressthat the content-
`storage-location information associates with the content
`thus requested.
`[0008]
`In order to achieve aforementioned object, a
`method for controlling content distributing device for
`transmitting,
`in response to a request, a content to a
`source which is a sender of the request, the method in
`accordance with the present invention includes: a deter-
`mining step of determining whether the sourceis (A) a
`relaying device for receiving the content thus requested
`and possessing and transferring the content to a content
`playing device or (B) the content playing device for play-
`ing the content thus requested; a content transmitting
`step of transmitting, in response to the request, the con-
`tent thus requested to the relaying device in a case where
`itis determined that, in the determining step, the source
`is a relaying device; a content-storage-location informa-
`tion generating step of generating content-storage-loca-
`tion information by associating (A) the content transmit-
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`Ex. 1072 - Page 443
`Ex. 1072 - Page 443
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`Code200, UABv. BrightData Ltd.
`Code200's Exhibit 1072
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`Code200, UAB v. BrightData Ltd.
`Code200's Exhibit 1072
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`EP 2 597 869 A1
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`ted in the content transmitting step with (B) an address
`of the relaying device, which is a destination to which the
`content is to be transmitted, or an address of the content
`playing device, to which the content is to be transferred
`from the relaying device; and a content-acquiring-loca-
`tion instructing step of transmitting, in response to the
`request, an instruction to the content playing device
`whichis the source in a case whereit is determined that,
`in the content-storage-location information generating
`step, the sourceis the content playing device, which in-
`struction is to acquire the content from (i) a relaying de-
`vice indicated by an address associated, in the content-
`storage-location information, with the content thus re-
`quested or (ii) a content playing device indicated by an
`address associated, in the content-storage-location in-
`formation, with the content thus requested.
`[0009] According to the arrangement, upon receipt of
`the request from the relaying device, the content trans-
`mitting means transmits the content thus requested to
`the relaying device which is the source, and the con-
`tent-storage-location information generating means gen-
`erates the content-storage-location information by asso-
`ciating (A) the content transmitted from the content trans-
`mitting means with (B) the addressofthe relaying device,
`whichis the destination of the content, or the address of
`the content playing device, to which the content is trans-
`ferred from the relaying device. Further, upon receipt of
`the request from the content playing device, the content-
`acquiring-location instructing means transmits,
`to the
`content playing device whichis the source, the instruction
`to acquire the content from (1) the relaying device indi-
`cated by an address associated, in the content-storage-
`location information, with the content thus requested or
`(II) the content playing device indicated by an address
`associated, in the content-storage-location information,
`with the content thus requested. Here, the relaying device
`and the content playing device possess the content thus
`acquired, and the content-storage-location information
`is information indicating which relaying device or content
`playing device possesses a content.
`[0010] That is, the content distributing device associ-
`ates (A) a content which has been transmitted before
`with (B) a relaying device or a content playing device
`which possessesthe content, and, upon receipt of a re-
`quest from a certain content playing device, the content
`distributing device does not directly transmit the content
`to the content playing device which is the source, but
`transmits,
`to the content playing device which is the
`source, an instruction to acquire the content from a re-
`laying device or a content playing device which possess-
`es the content thus requested. The content playing de-
`vice, which is the source, acquires the content thus re-
`quested from a designated relaying device or a desig-
`nated content playing device. Therefore, if the designat-
`ed relaying device or the designated content playing de-
`vice possesses the content,
`it is possible to complete
`transmission and reception of the content with use of only
`(A) the content playing device which is the source and
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`(B) the designated relaying device or the designated con-
`tent playing device. That is, the content playing device,
`which is the source, can acquire content, without carrying
`out a process for transmitting the content.
`[0011] This makesit possible to reduce (A) a load ofa
`network, which is used to transmit data from the content
`distributing device, and (B) a load of the content distrib-
`uting device. Among processescarried out by the content
`distributing device, the relaying device, and the content
`playing device, a process for transmitting and receiving
`the content is a process which applies the heaviest load,
`and the process applies the heaviestload of the network
`among the contentdistributing device, the relaying de-
`vice, and the content playing device. However, even if,
`for example, the number of content playing devices is
`increased and the number of requeststo the contentdis-
`tributing devices is therefore increased, it is possible to
`reduce (A) an increase in load of the network whichis
`used to transmit data from the content distributing device
`and (B) an increase in load of the content distributing
`device. Therefore, a large number of content playing de-
`vices can acquire contents, without increasing through-
`put of the content distributing device or capacity of the
`network.
`
`Advantageous Effects of Invention
`
`[0012] As described above, a content distributing de-
`vice for transmitting, in response to a request, a content
`to a source which is a sender of the request, in accord-
`ance with the present invention, includes: determining
`means for determining whether the sourceis (A) a relay-
`ing device for receiving the content thus requested and
`possessing and transferring the content to acontent play-
`ing device or (B) the content playing device for playing
`the content thus requested; content transmitting means
`for transmitting, in response to the request, the content
`thus requested to the relaying device in a case where
`the determining means determines that the source is a
`relaying device; content-storage-location information
`generating means for generating content-storage-loca-
`tion information by associating (A) the content transmit-
`ted by the content transmitting means with (B) an address
`of the relaying device, which is a destination to which the
`content is to be transmitted, or an address of the content
`playing device, to which the content is to be transferred
`from the relaying device; and content-acquiring-location
`instructing means for transmitting, in response to the re-
`quest, an instruction to the content playing device which
`is the source in a case where the determining means
`determines that the source is a content playing device,
`whichinstruction is to acquire the content from (i) a re-
`laying device indicated by an address that the content-
`storage-location information associates with the content
`thus requested or(ii) a content playing device indicated
`by an addressthat the content-storage-location informa-
`tion associates with the content thus requested.
`[0013] Amethod for controlling contentdistributing de-
`
`Ex. 1072 - Page 444
`Ex. 1072 - Page 444
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`Code200, UABv. BrightData Ltd.
`Code200's Exhibit 1072
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`Code200, UAB v. BrightData Ltd.
`Code200's Exhibit 1072
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`vice for transmitting, in response to a request, a content
`to a source which is a senderof the request, the method
`in accordance with the present invention includes: a de-
`termining step of determining whether the source is (A)
`arelaying device for receiving the content thus requested
`and possessing and transferring the content to a content
`playing device or (B) the content playing device for play-
`ing the content thus requested; a content transmitting
`step of transmitting, in response to the request, the con-
`tent thus requested to the relaying device in a case where
`it is determined that, in the determining step, the source
`is a relaying device; a content-storage-location informa-
`tion generating step of generating content-storage-loca-
`tion information by associating (A) the content transmit-
`ted in the content transmitting step with (B) an address
`of the relaying device, whichis a destination to which the
`contentis to be transmitted, or an address of the content
`playing device, to which the content is to be transferred
`from the relaying device; and a content-acquiring-loca-
`tion instructing step of transmitting, in response to the
`request, an instruction to the content playing device
`whichis the source in a case whereit is determined that,
`in the content-storage-location information generating
`step, the source is the content playing device, which in-
`struction is to acquire the content from (i) a relaying de-
`vice indicated by an address associated, in the content-
`storage-location information, with the content thus re-
`quested or (ii) a content playing device indicated by an
`address associated, in the content-storage-location in-
`formation, with the content thus requested.
`[0014] This makes it possible to reduce (A) a load of
`the network, which is used to transmit data from the con-
`tent distributing device and (B) a load of the content dis-
`tributing device.
`[0015] Additional objects, features, and strengths of
`the presentinvention will be made clear by the description
`below. Further, the advantages of the present invention
`will be evident from the following explanation in reference
`to the drawings.
`
`Brief Description of Drawings
`
`[0016]
`
`Fig. 1
`1 of the
`is a view illustrating Embodiment
`Fig.
`1
`present invention, and illustrates a schematic con-
`figuration of a content distributing system in accord-
`ance with Embodiment 1 and main configurations of
`devices constituting the content distributing system.
`Fig. 2
`Fig. 2 is a view showing an exemplary transmission
`log stored in a transmission log storage section in-
`cluded in the content distributing system.
`Fig. 3
`Fig. 3 is a view illustrating exemplary content-stor-
`age-location information stored in a content-stor-
`age-location information storage section included in
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`the content distributing system.
`Fig. 4
`Fig. 4 is a flowchart showing an exemplary process
`whichis carried out by a serverconstituting the con-
`tent distributing system.
`Fig. 5
`Fig. 5 is a flowchart showing an exemplary process
`which is carried out by a proxy constituting the con-
`tent distributing system.
`Fig. 6
`Fig. 6 is a flowchart showing an exemplary process
`whichis carried out by a client constituting the con-
`tent distributing system.
`Fig. 7
`Fig. 7 is a viewillustrating an exemplary operation
`sequenceof a content distributing system in Exam-
`ple of Embodiment 1.
`Fig. 8
`Fig. 8 is a viewillustrating exemplary HTTP messag-
`es which are transmitted/received as a request or a
`response.(a), (c), and (d) of Fig. 8 show HTTP mes-
`sages of respective requestsillustrated in Fig. 7, and
`(b), (e), and (f) of Fig. 8 show HTTP messages of
`respective responsesillustrated in Fig. 7.
`Fig. 9
`Fig. 9 is a viewillustrating exemplary HTTP messag-
`es which are transmitted/received as a request ora
`response.(a), (c), and (d) of Fig. 9 show HTTP mes-
`sages of respective requestsillustrated in Fig. 7, and
`(b), (e), and (f) of Fig. 9 show HTTP messages of
`respective responsesillustrated in Fig. 7.
`Fig. 10
`Fig. 10 is a viewillustrating exemplary HTTP mes-
`sages which are transmitted/received as a request
`or aresponse. (a), (c), and (d) of Fig. 10 show HTTP
`messagesof respective requests illustrated in Fig.
`7, and (b), (e), and (f) of Fig. 10 show HTTP mes-
`sages of respective responsesillustrated in Fig. 7.
`Fig. 11
`Fig. 11 is a view illustrating Embodiment 2 of the
`present invention, and illustrates a schematic con-
`figuration of a content distributing system in accord-
`ance with Embodiment 2 and main configurations of
`devices constituting the content distributing system.
`Fig. 12
`Fig. 12 is a view showing an exemplary transmission
`log stored in a transmission log storage section in-
`cludedin the content distributing system.
`Fig. 13
`Fig. 13 is a viewillustrating exemplary content-stor-
`age-location information stored in a content-stor-
`age-location information storage section included in
`the content distributing system.
`Fig. 14
`Fig. 14 is a flowchart showing an exemplary process
`which is carried out by a server constituting the con-
`tent distributing system.
`Fig. 15
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`Ex. 1072 - Page 445
`Ex. 1072 - Page 445
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`Code200, UABv. BrightData Ltd.
`Code200's Exhibit 1072
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`Code200, UAB v. BrightData Ltd.
`Code200's Exhibit 1072
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`

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`Fig. 15is a flowchart showing an exemplary process
`which is carried out by a client which serves as a
`content playing device and constitutes the content
`distributing system.
`Fig. 16
`Fig. 16 is a flowchart showing an exemplary process
`which is carried out by a client which serves as a
`relaying device and constitutes the content distrib-
`uting system.
`Fig. 17
`Fig. 17 is a view illustrating an exemplary operation
`sequence of a content distributing system in Exam-
`ple of Embodiment2.
`Fig. 18
`Fig. 18 is a viewillustrating example HTTP messag-
`es which are transmitted/received as a request or a
`response. (a), (c), and (d) of Fig. 18 show HTTP mes-
`sages of respective requests illustrated in Fig. 17,
`and (b), (e), and (f) of Fig. 18 show HTTP messages
`of respective responsesillustrated in Fig. 17.
`Fig. 19
`Fig. 19 is a view illustrating example HTTP messag-
`es which are transmitted/received as a request or a
`response. (a), (c), and (d) of Fig. 19 show HTTP mes-
`sages of respective requests illustrated in Fig. 17,
`and (b), (e), and (f) of Fig. 19 show HTTP messages
`of respective responsesillustrated in Fig. 17.
`Fig. 20
`Fig. 20 is a view illustrating Embodiment 3 of the
`present invention, and illustrates a schematic con-
`figuration of a content distributing system in accord-
`ance with Embodiment 3 and main configurations of
`devices constituting the content distributing system.
`Fig. 21
`Fig. 21 is a format of content dealt by the content
`distributing system.
`Fig. 22
`Fig. 22 is a flowchart showing an exemplary process
`whichis carried out by a server constituting the con-
`tent distributing system.
`Fig. 23
`Fig. 23 is a flowchart showing an exemplary process
`which is carried out by a client which serves as a
`content playing device and constitutes the content
`distributing system.
`Fig. 24
`Fig. 24 is a view illustrating an exemplary operation
`sequence of a content distributing system in Exam-
`ple of Embodiment3.
`Fig. 25
`Fig. 25 is a view showing an exemplarytransmission
`log stored in a transmission log storage section in-
`cluded in the content distributing system.
`Fig. 26
`Fig. 26 is a view illustrating exemplary content-stor-
`age-location information stored in a content-stor-
`age-location information storage section includedin
`the content distributing system.
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`Fig. 27
`Fig. 27 is a view illustrating exemplary HTTP mes-
`sages which are transmitted/received as a request
`or aresponse. (a), (c), and (d) of Fig. 27 show HTTP
`messages of respective requests illustrated in Fig.
`24, and (b), (e), and (f) of Fig. 27 show HTTP mes-
`sages of respective responsesillustrated in Fig. 24.
`Fig. 28
`Fig. 28 is a view illustrating exemplary HTTP mes-
`sages which are transmitted/received as a request
`or a response. (a) and (b) of Fig. 28 show HTTP
`messages of respective requests illustrated in Fig.
`24, and (c) and (d) of Fig. 28 show HTTP messages
`of respective responsesillustrated in Fig. 24.
`Fig. 29
`Fig. 29 is a view illustrating Embodiment 4 of the
`present invention, and illustrates a schematic con-
`figuration of a content distributing system in accord-
`ance with Embodiment4 and main configurations of
`devices constituting the content distributing system.
`Fig. 30
`Fig. 30 is a viewillustrating exemplary content-stor-
`age-location information stored in a content-stor-
`age-location information storage section included in
`the content distributing system.
`Fig. 31
`Fig. 31 is a flowchart showing an exemplary process
`whichis carried out by a serverconstituting the con-
`tent distributing system.
`Fig. 32
`Fig. 32 is a flowchart showing an exemplary process
`which is carried out by a client which serves as a
`content playing device and constitutes the content
`distributing system.
`Fig. 33
`Fig. 33 is a view illustrating an exemplary operation
`sequence of a contentdistributing system in Exam-
`ple of Embodiment 4.
`Fig. 34
`Fig. 34 is a viewillustrating an exemplary HTTP mes-
`sage which is transmitted and received as a re-
`sponse.
`Fig. 35
`Fig. 35 is a view illustrating exemplary MPD data
`which is meta data of content dealt by a content dis-
`tributing system in accordance with Embodiment 5
`of the presentinvention.
`Fig. 36
`Fig. 36 is a view illustrating exemplary MPD data
`whichis dealt by the content distributing system.
`Fig. 37
`Fig. 37 is a view illustrating an exemplary external
`resource which is dealt by the content distributing
`system.
`Fig. 38
`Fig. 38 is a viewillustrating exemplary MPD data and
`an example external resource which are dealt by the
`content distributing system.
`
`Ex. 1072 - Page 446
`Ex. 1072 - Page 446
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`Code200, UABv. BrightData Ltd.
`Code200's Exhibit 1072
`
`Code200, UAB v. BrightData Ltd.
`Code200's Exhibit 1072
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`

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`Fig. 39
`Fig. 39 is a flowchart showing an exemplary process
`whichis carried out by a server constituting the con-
`tent distributing system.
`Fig. 40
`Fig. 40 is a flowchart showing an exemplary process
`which is carried out by a client which serves as a
`content playing device and constitutes the content
`distributing system.
`Fig. 41
`Fig. 41 is a viewillustrating an exemplary operation
`sequence of a content distributing system in Exam-
`ple of Embodiment5.
`
`Description of Embodiments
`
`<Embodiment 1>
`
`[0017] The description will discuss Embodiment 1 of
`the present invention with reference to Fig. 1 to Fig. 10.
`First, an outline of a content distributing system 1 of Em-
`bodiment 1 will be described with reference to Fig. 1.
`
`[Cutline of content distributing system 1]
`
`illustrates a schematic configuration of
`1
`Fig.
`[0018]
`the content distributing system 1 in accordance with Em-
`bodiment 1 and main configurations of devices constitut-
`ing the content distributing system 1. Asillustrated in Fig.
`1, the content distributing system 1
`includes a server
`(contentdistributing device) 2, proxies (relaying devices,
`content acquiring devices) 3a and 3b, and clients (con-
`tent playing devices, content acquiring devices) 4a and
`4b. The content distributing system 1 also includes: a
`content storage section 5 connected to the server 2; and
`cache storage sections 6a and 6b connectedto the re-
`spective proxies 3a and 3b.
`[0019] Asillustrated in Fig. 1, the server 2, the proxies
`3a and 3b, and the client 4a and 4b are connected to one
`another via a network 7. Note that the network 7 is not
`
`particularly limited, provided that the aforementioned de-
`vices can be communicated with one another. Accord-
`ingly, the network 7 may be a wired communication net-
`work or a wireless communication network.
`
`[0020] Note that, in the following description, the prox-
`ies 3a and 3b will be called generally as a proxy 3; the
`cache storage sections 6a and 6b, a cache storage sec-
`tion 6; and the client 4a and 4b, a client 4.
`[0021]
`Further, the present invention is not limited to
`the exampleillustrated in Fig. 1,
`in which the content
`distributing system 1 includes two proxies 3 and twocli-
`ents 4. The content distributing system 1 may include
`one proxyor three or more proxies, and may include three
`or more clients 4. Thatis, the content distributing system
`1 only needsto include at least one proxy 3 and a plurality
`of clients 4.
`
`In Embodiment 1, a content distributed by the
`[0022]
`server 2 is assumed to be a video content for a VOD
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`service, and a format of the content is assumed to be a
`MP4file format. Further, a transfer protocol on the net-
`work 7 in the content distributing system 1
`is assumed
`to use the HTTP, whichis widely used as a general file
`transferring protocol. Note that,
`in Embodiment 1, the
`content distributed by the server 2 and the transfer pro-
`tocol on the network7 in the content distributing system
`1 are not limited to this configuration.
`
`[Server 2]
`
`[0023] The server 2 is a content distributing device
`which receives a request message (request) to request
`to transmit a content from the proxy 3 and the client 4
`(content acquiring device) and transmits a response
`message (response) inresponseto the request message
`thus received. As described above, the server 2 is con-
`nected to the content storage section 5 which stores con-
`tents such as moving images, and managesthe contents
`stored in the content storage section 5. Note that the
`content storage section 5 may be provided inside the
`server 2.
`
`[0024] Note that the server 2 may simultaneously dis-
`tribute the same content to an unspecified number of
`devices, may distribute a content to a single device, or
`may simultaneously distribute the same content to a pre-
`determined number of devices.
`
`Asillustrated in Fig. 1, the server 2 includes: a
`[0025]
`server controlling section 14 for collectively controlling
`operations of the server 2; a server communication sec-
`tion 11 which is provided so that the server 2 can com-
`municate to an external device; a transmission log stor-
`age section 12 in which a response transmitted by the
`server 2 is stored; and a content-storage-location infor-
`mation storage section 13 for storing content-storage-
`location information (details will be described below). The
`server controlling section 14 includes: a response exe-
`cuting section (determining means, content transmitting
`means, content-acquiring-location instructing means,
`transmission record creating means) 15; a relaying de-
`vice specifying section (content-acquiring-location in-
`structing means, distance calculating means) 16; anda
`content-storagelocation information generating section
`(content-storage-location
`information
`generating
`means) 17.
`[0026] The response executing section 15 receives,
`via the server communication section 11, arequest mes-
`sage to request to transmit a content, and then the re-
`sponse executing section 15 transmits, to a device (proxy
`3 or client 4) which is the senderof the request message,
`aresponse message inresponseto the request message
`thus received.
`
`Specifically, the response executing section 15
`[0027]
`is ready to receive the request message to request to
`transmit the content, and, upon receiving, via the server
`communication section 11, the request message to re-
`quest to transmit the content, the response executing
`section 15 checks a header of the request message in
`
`Ex. 1072 - Page 447
`Ex. 1072 - Page 447
`
`Code200, UABv. BrightData Ltd.
`Code200's Exhibit 1072
`
`Code200, UAB v. BrightData Ltd.
`Code200's Exhibit 1072
`
`

`

`11
`
`EP 2 597 869 A1
`
`12
`
`order to determine whether or not the request message
`data of the content held by the proxy 3 is latest, the re-
`sponse executing section 15 transmits, to the proxy3, in
`thus received is transmitted via the proxy 3. For example,
`response to the request message transmitted from the
`it may be so configured that in a case of receiving a re-
`quest message which includes a "Via" header, the re-
`proxy 3, aresponse messagethat the data of the content
`held by the proxy 3 is latest. The response executing
`sponse executing section 15 determinesthat the request
`message thus received has been transmitted by the
`section 15 transmits, to the proxy 3, for example, "304
`NOT modified" serving as the response message that
`proxy 3 in response to a request message of the client
`
`4, whereas, in a case of receiving a request message the data of the content held by the proxy3is latest.
`which does not include the "Via" header, the response
`[0032]
`Further, the response executing section 15 cre-
`executing section 15 may determine that the request
`ates a transmission log (response transmission record)
`message thus received has been transmitted directly
`based on the response message thus sent, and causes
`from the client 4.
`the transmission log storage section 12 to store the trans-
`mission log thus created. The transmission log created
`by the response executing section 15 will be described
`later in detail.
`[0033] As for the content to be transmitted from the
`response executing section 15 to the proxy 3, for exam-
`ple, "Cache-Control: must-revalidate" or "Cache-Control:
`proxy-revalidate" may be added to a headerof the con-
`tent. Accordingly, when the proxy 3 which receives the
`content uses,i.e., transmits the content held by the cache
`storage section 6 in response to another request, it is
`possible to confirm the server 2 before the transmission
`of the content from the proxy 3, as to whether or not the
`content is the latest version.
`[0034]
`In response to an instruction of the response
`executing section 15, the relaying device specifying sec-
`tion 16 specifies which proxy 3 (possibly) possesses the
`content that the client 4 requests.
`[0035]
`Specifically, the relaying device specifying sec-
`tion 16 reads out content-storage-location information
`from the content-storage-location information storage
`section 13 in responseto the instruction of the response
`executing section 15. With reference to the content-stor-
`age-location information thus read out, the relaying de-
`vice specifying section 16 specifies, as address informa-
`tion of a device from which the content is acquired, the
`addressinformation (e.g., URI) of the proxy 3 associated
`with the content that the client 4 requests. The relaying
`device specifying section 16 transmits the address infor-
`mation thus specified to the response executing section
`15.
`Inacase where the content-storage-location in-
`[0036]
`formation for the content that the client 4 requests is not
`stored in the content-storage-location information stor-
`age section 13, the relaying device specifying section 16
`may specify, as address information of a device from
`which the content is acquired, predetermined (default)
`address information of the content that the client 4 re-
`quests. Alternatively, in a case where the content-stor-
`age-location information storage section 13 does not
`store the content-storage-location information for the
`content that the client 4 requests, the relaying device
`specifying section 16 mayselect, at random, from proxies
`3 connected to the server 2 via the network 7, address
`information of a device from which the content is ac-
`quired.
`[0037]
`
`45
`
`50
`
`55
`
`Inacase where the content-storage-location in-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`[0028] Uponreceipt of the request message to request
`the content directly from the client 4, the response exe-
`cuting section 15 transmits, to the relaying device spec-
`ifying section 16, an instruction to specify addressinfor-
`mation (e.g., URI of proxy 3 etc.) of the proxy 3 which
`(possibly) possesses the content that the client 4 re-
`quests. Then,
`the response executing section 15 re-
`ceives, from the relaying device specifying section 16,
`the address information of the proxy 3 which possesses
`the content that the client 4 requests. After that, in re-
`sponse to the request message from the client 4, the
`response executing section 15 transmits, to the client 4,
`aninstruction (i.¢e., a response message) to acquire such
`a requested content based on the address information
`specified by the relaying device specifying section 16.
`For example, by giving, to "Location field", with use of a
`"305 USE Proxy" serving as the response message, the
`address information specified by the relaying device
`specifying section 16, the response executing section 15
`transmits, to the client 4, an instruction to transmit, to the
`proxy 3 which (possibly) possesses the contentthat the
`client 4 requests, the request message of the content.
`[0029] When receiving, from the proxy 3, the request
`message to request the content, the response executing
`section 15 determines whetheror not the