hereinafter , embodiments of the invention will be described with reference to the drawings . fig1 shows a conceptual diagram depicting a client / server system according to an embodiment of the invention . as shown in fig1 , a client / server system 100 is configured in which a plurality of client apparatuses 1 such as digital video recorders and tv sets is connected to a server 2 and a plurality of download servers 3 over a network 101 such as the internet . for example , the client apparatus 1 and the server 2 communicate with each other through polling communications or p2p ( peer to peer ), and a file in which control information for access to the download server 3 is described ( hereinafter , this file is referred to as a “ file b ”) is distributed from the server 2 to the client apparatus 2 . in addition , a file downloaded from the download server 3 to the client apparatus 2 ( a moving image file such as a movie and an update file to the client apparatus 1 ) is a file a . fig2 shows a block diagram depicting the configurations of the client apparatus 1 , the server 2 and the download server 3 . as shown in fig2 , the client apparatus 1 has a ui ( user interface ) application part 4 , an update script part 5 , an update agent part 6 , an interface part 7 and a client apparatus common library part 8 . to the update agent part 6 , the ui application part 4 makes a request to acquire a file b , an instruction to start a process of a request to acquire a file a and an instruction to finish the process of the request to acquire the file a as it is triggered by a user input manipulation of information from an input part , not shown . for example , in the case in which the file a downloaded from the download server 3 by the client apparatus 1 is an update file , the update script part 5 updates software of the client apparatus 1 based on the update file . the update agent part 6 accepts requests and processed results relating to downloads and updates from the ui application part 4 , the interface part 7 , and the update script part 5 , and controls the update process for the client apparatus 1 . ( 1 ) the update agent part 6 and the interface part 7 are started when the power source of the client apparatus 1 is tuned on . ( 2 ) a manual update instruction is accepted from the ui application part 4 to inform the interface part 7 . ( 3 ) the interface part 7 communicates with the server 2 and the download server 3 to download an update file . ( 4 ) the result of the update file download process is received from the interface part 7 , and an instruction is made to start an upgrade mode for the client apparatus 1 . ( 5 ) the result of the update process is received from the update script part 5 to inform the ui application part 4 , the client apparatus common library part 8 of the result . ( 6 ) in the case in which it is necessary to stop downloading because of the constraints of the client apparatus 1 , the interface part 7 is informed of that . the interface part 7 communicates with the server 2 and with the download server 3 , and downloads a necessary update file ( file a ) from the download server 3 . more specifically , the interface part 7 communicates with the server 2 at regular time intervals by background processing for confirming the existence of update files . in the case in which it is found that the latest update file exists , the interface part 7 informs the update agent part 6 of that . in the case in which the latest update file exists and a certain condition is satisfied , the interface part 7 makes access to the download server 3 to acquire the update file ( file a ) and downloads it . the client apparatus common library part 8 provides a common function in the client apparatus 1 . more specifically , the client apparatus common library part 8 answers the current time instant managed in the client apparatus 1 and the current software version of the client apparatus 1 , and further has a network diagnostic function . in addition , the update script part 5 and the update agent part 6 performs the processes above in the case in which the file a is an update file . however , for example , in the case in which a file a to be downloaded from the download server 3 by the client apparatus 1 is a large sized file such as moving images , the update agent part 6 and the update script part 5 become a content manager and a moving image title management function . the server 2 has a web server 9 that communicates with the client apparatus 1 over the network 101 . in addition , for example , the uri of the external interface of the server 2 is embedded in advance when the client apparatus 1 is shipped . the download server 3 also has a web server 10 that communicates with the client apparatus 1 over the network 101 . in addition , for example , the uri of the download server 3 is given as a “ download destination url ” to the client apparatus 1 from the server 2 . fig3 and 4 show a diagram depicting an exemplary file b sent to the client apparatus 1 by the server 2 . in addition , the file shown in fig3 is a file in the case in which the client apparatus 1 is a digital video recorder ( dvr ), and the file shown in fig4 is a file in the case in which the client apparatus 1 is a television set ( tv set ). as shown in fig3 and 4 , the file b has items of information , including “ a model id and update number ”, “ a file distribution parameter ”, “ a download content ( dl content )”, “ a download valid period start date and time ( dl valid period from )”, “ a download valid period end date and time ( dl valid period to )”, “ a download distribution parameter ( dl distribution parameter )” and “ a download destination url ( dl destination url )”. “ the model id ” is a unique id to the client apparatus 1 , which is information such as “ pony_digital video recorder 1001 ”. “ the update number ” is information indicating the number of updates of the file b , for example , which is “ 0001 ” when not updated . the update number is incremented by ‘ 1 ’ when one of the following items is changed , the download valid period start date and time , the download valid period end date and time and the download distribution parameter shown in fig3 . “ the file distribution parameter ” is a parameter that distributes dates and times for every client apparatus 1 on which the client apparatus 1 automatically makes access to the download server 3 . for example , “ 0 . 5 day ” means that the client apparatus 1 automatically makes access to the download server 3 at a predetermined time interval based on a random number generated in 0 to 12 hours ( 12 h × 60 min .× 60 sec . ), for instance . “ the download content ” is information about the title of a content to be downloaded . “ the download valid period start date and time ” is information about the date and time to start a period in which the client apparatus 1 is permitted to download a file a from the download server 3 . “ the download valid period end date and time ” is information about the date and time to end a period in which the client apparatus 1 is permitted to download a file a from the download server 3 . the client apparatus 1 is permitted to download a file a during the period from the download valid period start date and time to the download valid period end date and time . “ the download distribution parameter ” is a parameter that changes information about the date and time to start the period in which the client apparatus 1 is permitted to download a file a from the download server 3 and alters forced waiting time . for example , the parameter is “ 7 days ”, “ 5 days ” and “ 1 day ”. for instance , in the case of “ 7 days ”, the client apparatus 1 is not permitted to download a file a from the download server 3 until seven days , the forced waiting time , have elapsed . “ the download destination url ” is information about the url of the download server 3 providing the file a . next , the operation of an automatic process when the client apparatus 1 downloads the file a from the download server 3 will be described . fig5 shows a flow chart depicting the operation of this automatic process . after purchase , the client apparatus 1 makes a request to the server 2 to acquire a device specified id ( client id ) on the first setup ( s 1 ). more specifically , the client apparatus 1 informs the server 2 of a model id unique to every model recorded on the client apparatus 1 when shipped . based on the model id , the server 2 determines whether the model corresponding to the model id is the model for services . if it is the model for services , the server 2 issues a client id , and informs the client apparatus 1 of the issued client id ( s 2 ). the client apparatus 1 stores the client id informed by the server 2 in the client apparatus common library part 8 . at the time of starting the client apparatus 1 next time and later , the process steps after s 3 are performed . for example , the case will be described in which the client apparatus 1 downloads a file b from the server 2 . first , the client apparatus 1 makes a request to the server 2 to acquire a file b ( s 3 ). more specifically , the client apparatus 1 informs the server 2 of the client id for acquiring the file b . subsequently , based on the client id , the server 2 extracts information corresponding to the client id , for example , information about the file b shown in fig3 from data stored in the server 2 to generate the file b , and distributes the file b to the client apparatus 1 ( s 4 ). the client apparatus 1 stores the file b in the client apparatus common library part 8 . subsequently , the client apparatus 1 analyzes the file b ( s 5 ). for example , based on “ the file distribution parameter ” described in the file b shown in fig3 , the client apparatus 1 calculates “ the next scheduled time to execute the request to automatically acquire the file b ”. for example , the client apparatus 1 acquires the value “ 0 . 5 day ” that is the file distribution parameter shown in fig3 as an example , generates a random number in the time from 0 to 0 . 5 ( 12 h × 60 min .× 60 sec . ), and adds the generated random number to the current time instant for “ the next scheduled time to execute the request to automatically acquire the file b ”. thus , the client apparatus 1 will not have overlapping access timing with the other client apparatuses 1 . in addition , based on “ the download distribution parameter ” shown in fig3 , the client apparatus 1 calculates “ the next scheduled time to execute the automatic download process ”. for example , when “ an update file ver . 1 ” is downloaded in “ the download contents ” shown in fig3 , based on the value “ 7 days ” that is “ the download distribution parameter ” corresponding thereto , the client apparatus 1 generates a random number in the time from 0 to 7 days × 24 h × 60 min .× 60 sec ., forms the generated random number into units of “ seconds ”, and adds the value to “ 4 / 1 / 2006 12 : 00 ” that is “ the download valid period start date and time ” for “ the next scheduled time to execute the automatic download process ”. in addition , in calculating “ the next scheduled time to execute the automatic download process ”, such a scheme may be possible in which a random number is generated in the time between “ the download valid period start date and time ” and “ the download valid period end date and time ”, for example , and based on the generated random number , “ the next scheduled time to execute the automatic download process ” is calculated . subsequently , the client apparatus 1 determines whether the current time instant is “ the scheduled time to execute the request to automatically acquire the file b ” ( s 7 ). if it is “ the scheduled time to execute the request to automatically acquire the file b ”, the client apparatus 1 returns to step 3 , and performs making a request to acquire the file b already described . if it is not “ the scheduled time to execute the request to automatically acquire the file b ”, the client apparatus 1 determines whether it is “ the scheduled time to execute the automatic download process ” ( s 8 ). if it is neither “ the scheduled time to execute the request to automatically acquire the file b ” nor “ the scheduled time to execute the automatic download process ”, the client apparatus 1 waits ( s 6 ). if it is “ the scheduled time to execute the automatic download process ” in s 8 , the client apparatus 1 downloads the file a from the download server 3 ( s 9 ). in other words , the client apparatus 1 makes a request to the download server 3 to download the file a , and the download server 3 distributes the file a to the client apparatus 1 ( s 10 ) here , for example , in the case in which the file b is updated during the waiting time ( s 6 ), based on new information about the file b , “ the scheduled time to execute the request to automatically acquire the file b ” and “ the scheduled time to execute the automatic download process ” are again recalculated ( updated ). fig6 shows a time chart depicting the recalculation ( update ) of “ the scheduled time to execute the request to automatically acquire the file b ” and “ the scheduled time to execute the automatic download process ”. as shown in fig6 , the client apparatus 1 executes “ the process of the request to automatically acquire the file b ” ( s 31 ). the server 2 informs the client apparatus 1 of a file b whose “ update number ” shown in fig3 is ‘ 1 ’ ( s 41 ). based on the file b , the client apparatus 1 calculates “ the next scheduled time to execute the request to automatically acquire the file b ” to be “ 6 / 1 / 2007 10 : 00 ”, and “ the scheduled time to execute the automatic download process ” to be “ 6 / 5 / 2007 0 : 00 ” ( s 51 ). as the result , the client apparatus 1 waits until the current time instant reaches “ 6 / 1 / 2007 10 : 00 ” ( s 61 ). if the client apparatus 1 determines that it reaches this time instant , the client apparatus 1 executes “ the process of the request to automatically acquire the file b ” ( s 32 ). since “ the scheduled time to execute the automatic download process ” is “ 6 / 5 / 2007 0 : 00 ” but “ the scheduled time to execute the request to automatically acquire the file b ” is “ 6 / 1 / 2007 10 : 00 ”, the download process is not executed . in the case in which “ the update number ” is not changed , the server 2 again informs the client apparatus 1 of a file b whose update number ″ is ‘ 1 ’ ( s 42 ) based on the file b , the client apparatus 1 calculates “ the next scheduled time to execute the request to automatically acquire the file b ” to be “ jun . 6 / 2 / 2007 11 : 00 ”, and “ the scheduled time to execute the automatic download process ” to be “ 6 / 5 / 2007 0 : 00 ” ( s 52 ). in the case in which “ the update number ” is not changed , only “ the scheduled time to execute the request to automatically acquire the file b ” is again calculated , and “ the scheduled time to execute the automatic download process ” is not again calculated . as the result , the client apparatus 1 waits until the current time instant reaches “ 6 / 2 / 2007 11 : 00 ” ( s 62 ), and if the client apparatus 1 determines that it reaches this time instant , the client apparatus 1 executes “ the process of the request to automatically acquire the file b ” ( s 33 ). since “ the scheduled time to execute the automatic download process ” is “ 6 / 5 / 2007 0 : 00 ” but “ the scheduled time to execute the request to automatically acquire the file b ” is “ 6 / 2 / 2007 11 : 00 ”, the download process is not executed . in the case in which the update number is changed , the server 2 informs the client apparatus 1 of a file b whose update number is ‘ 2 ’ ( s 43 ). based on the file b whose update number is ‘ 2 ’, the client apparatus 1 calculates “ the next scheduled time to execute the request to automatically acquire the file b ” to be “ 6 / 3 / 2007 9 : 00 ”, and “ the scheduled time to execute the automatic download process ” to be “ 6 / 3 / 2007 10 : 00 ” ( s 53 ). in the case in which the update number is changed , “ the scheduled time to execute the request to automatically acquire the file b ” and “ the scheduled time to execute the automatic download process ” are again calculated . as the result , the client apparatus 1 waits until the current time instant reaches “ 6 / 3 / 2007 9 : 00 ” ( s 63 ), and if the client apparatus 1 determines that it reaches this time instant , the client apparatus 1 automatically makes a request to acquire the file b ( s 34 ). since “ the scheduled time to execute the automatic download process ” is “ 6 / 3 / 2007 10 : 00 ” but the scheduled time to execute the request to automatically acquire the file b ″ is “ 6 / 3 / 2007 9 : 00 ”, the download process is not executed . in the case in which the update number is not changed , the server 2 informs the client apparatus 1 of a file b whose update number is ‘ 2 ’ ( s 44 ). based on the file b whose update number is ‘ 2 ’, the client apparatus 1 calculates “ the next scheduled time to execute the request to automatically acquire the file b ” to be “ 6 / 4 / 2007 13 : 00 ”, and “ the scheduled time to execute the automatic download process ” to be “ 6 / 3 / 2007 10 : 00 ” ( s 54 ). in the case in which the update number is not changed , only “ the scheduled time to execute the request to automatically acquire the file b ” is again calculated , and “ the scheduled time to execute the automatic download process ” is not again calculated . as the result , the client apparatus 1 waits until the current time instant reaches “ 6 / 3 / 2007 10 : 00 ” ( s 64 ), and if the client apparatus 1 determines that it reaches this time instant , the client apparatus 1 automatically downloads the file b ( s 91 ). fig7 shows a flowchart depicting the operation of manual processing in downloading a file . in addition , steps s 1 and s 2 are the same as those described above , omitting the descriptions . here , fig8 to 11 show an exemplary screen displayed on the client apparatus 1 in manually downloading the file a . first , as shown in fig8 , a screen is displayed to determine whether to acquire a file b . the client apparatus 1 determines whether a user clicks a run button of the screen shown in fig8 or clicks a cancel button . if the user clicks the run button , the client apparatus 1 makes a request to the server 2 to acquire the file b ( s 3 ). for example , the client apparatus 1 informs the server 2 of the client id , and acquires the file b . if the user clicks the cancel button , the client apparatus 1 closes the screen shown in fig8 . based on the client id , the server 2 extracts information corresponding to the client id in data stored in the server 2 , generates the file b shown in fig3 , for example , and distributes the file b to the client apparatus 1 ( s 4 ). subsequently , the client apparatus 1 analyzes the file b ( s 5 ). in other words , the client apparatus 1 analyzes control information when making access to the download server 3 . more specifically , as described above , based on the file distribution parameter shown in fig3 , the client apparatus 1 calculates the next scheduled time to execute the request to automatically acquire the file b . subsequently , the client apparatus 1 determines whether the download is executable ( s 6 ). in other words , in the case of manual processing , the client apparatus 1 ignores the download distribution parameter shown in fig3 . for example , in the case in which the client apparatus 1 downloads “ an update file ver . 1 ” in “ the download contents ” shown in fig3 , the client apparatus 1 determines whether the current time instant ( the scheduled time to execute the request to automatically acquire the file b ) is between “ 4 / 1 / 2007 12 : 00 ” that is the download valid period start date and time and “ 3 / 31 / 2007 23 : 59 ” that is the download valid period end date and time . for example , during this analysis , the client apparatus 1 displays a screen shown in fig9 . if the current time instant is between them , the client apparatus 1 displays a screen shown in fig1 , whereas if the current time instant is not between them , the client apparatus 1 displays a screen , not shown , showing that a file for download is not found ( download is not permitted ). the client apparatus 1 determines whether the user clicks a “ yes ” button for updating software or clicks a “ no ” button on the screen shown in fig1 . if the user clicks “ yes ”, a screen shown in fig1 is displayed , showing that the file is now being downloaded , whereas the user clicks “ no ”, the screen shown in fig1 is deleted . in s 6 , if the client apparatus 1 determines that it is difficult to download the file , for example , the client apparatus 1 makes “ the request to acquire the file b ” as described above , and calculates ( updates ) “ the next scheduled time to execute the automatic download process ”. as discussed above , according to the embodiment , when the client apparatus 1 makes a request to the server 2 to acquire a file a , the client apparatus is informed of a file b including information about access control to the download server 3 in which the file a is placed , based on information about “ the download valid period start date and time ”, “ the download valid period end date and time ” and “ the download distribution parameter ” contained in the file b , the time instant to permit the client apparatus 1 to download the file a from the download server 3 can be controlled ( distributed ). therefore , the traffic peaks can be suppressed in every download server 3 . accordingly , since it is unnecessary to allocate resources such as servers to manage extreme traffic peaks , system construction initial costs and service costs can be curtailed . in addition , the information about “ the download distribution parameter ” contained in the file b is set to every download destination url , whereby access distribution and integration are feasible as the performance of the individual servers is used at the maximum . moreover , “ the download valid period start date and time ” and “ the download valid period end date and time ” contained in the file b are informed to the client apparatus 1 , and then the client apparatus 1 is not permitted to make access to the download server 3 other than this period , whereby the maintenance of the download server 3 can be performed for convenience on the service provider side . in addition , in the case in which acquiring the file b is failed , or the acquired file b does not contain “ the file distribution parameter ” or “ the download distribution parameter ”, “ the next scheduled time to execute the request to automatically acquire the file b ” may be calculated based on the default value embedded in the client apparatus 1 in advance when shipped , or by computing the default value based on partial information about the client apparatus 1 ( a mac address , a substrate id , an ip address and so on ). in addition , “ the download valid period start date and time ” and “ the download valid period end date and time ” contained in the file b are informed to the client apparatus 1 , and as soon as it reaches a given time instant in this period , the client apparatus 1 is permitted to automatically make access to the server to download a file , whereby a user can download files anytime , day and night , and weekdays and holidays . from a broad view , a larger number of the client apparatuses 1 are permitted to download files more quickly than the client apparatus 1 is triggered by a user manipulation to download a file . fig1 shows a timing chart illustrative of the operation of a client / server system according to another embodiment of the invention . as shown in fig1 , a server 2 according to the embodiment has an optimizing function that optimizes the descriptions of the file b depending on the access conditions to the server 2 or to the download server 3 by the client apparatus 1 . in addition , of cause , the optimizing function may be provided in other apparatuses other than the server 2 . the optimizing function of the server 2 makes a request to the server 2 itself to acquire server resource information , and acquires server resource information . for example , the term server resource information includes information such as the access log , server resources ( a cpu usage rate and a memory usage rate ), and network band usage rate of the server 2 . thus , the optimizing function of the server 2 acquires information such as the access log , server resources ( the cpu usage rate and the memory usage rate ), and network band usage rate of the server 2 ( s 11 ). based on these items of information , the optimizing function of the server 2 updates “ the value of the file distribution parameter ” ( s 12 ). examples thereof are shown below . 1 . when the cpu usage rate exceeds 80 %, the value of the file distribution parameter is set to 1 . 25 times . 2 . when the cpu usage rate exceeds 90 %, the value of the file distribution parameter is set to 1 . 5 times . 3 . when the network band usage rate exceeds 75 %, the value of the file distribution parameter is set to 2 . 0 times . subsequently , the optimizing function of the server 2 makes a request to the download server 3 to acquire server resource information , and then acquires server resource information . for example , the term server resource information includes information such as the access log , server resources ( a cpu usage rate and a memory usage rate ), and network band usage rate of the download server 3 . thus , the optimizing function of the server 2 acquires information such as the access log , server resources ( the cpu usage rate and the memory usage rate ), and network band usage rate of the download server 3 ( s 13 ). based on these items of information , the optimizing function of the server 2 updates “ the value of the download distribution parameter ” ( s 14 ). examples thereof are shown below . 1 . when the cpu usage rate exceeds 80 %, the value of the file distribution parameter is set to 1 . 25 times . 2 . when the cpu usage rate exceeds 90 %, the value of the file distribution parameter is set to 1 . 5 times . 3 . when the network band usage rate exceeds 75 %, the value of the file distribution parameter is set to 2 . 0 times . as discussed above , according to the embodiment , since such a function is provided that can automatically optimize the value of the file distribution parameter of the file b based on the resource information of the server 2 and the download server 3 , the distribution of loads to the download server 3 and other servers can be effectively implemented . in addition , the embodiment of the invention is not restricted to the embodiments described above , which can be variously modified within the technical concepts according to the embodiment of the invention . it should be understood by those skilled in the art that various modifications , combinations , sub - combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof .