Abstract:
An object of the present invention is to provide a communication apparatus and a data distribution system which are fast in the response speed of data distribution and require less space and less electric power. The present invention provides a communication apparatus which is provided with a broadband transmission module for reproduction by which a constant amount of data is transmitted from an initial data transmission server in a broad band immediately after a client instructs to distribute the data and then, subsequent data is transmitted from a subsequent data transmission server in a normal band, a load balancing module (a module for dispersing a distribution request from a client among plural servers accumulating the same file) and a file dispersion access module (a module for sorting a distribution request from a client into a server storing the file corresponding to the distribution request), and which includes a server arraying module for directly arraying plural servers without using a disk array to integrate resources of the servers into one. Further, the present invention provides a VOD distribution system including the communication apparatus and the plural servers.

Description:
CLAIM OF PRIORITY 
     The present application claims priority from Japanese patent application JP2008-313876 filed on Dec. 10, 2009, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a technique in which, by using a communication apparatus which is connected to a network, which receives packets transferred through the network to perform different processes in accordance with communication states between a client and a server that transmit and receive packets, and which changes data accumulated within the apparatus, and generates and transmits a new packet to the outside, plural servers are arrayed (coupled as one server), simultaneous transmission of large-volume data to plural users is realized by a system which requires less space and less electric power, and data reproduction in a high-speed response is realized by broadband transmission at the time of reproduction. 
     The progress of integration of broadcasting and communications increases the needs of large volume of video distribution services, improving a sensory speed, and reduction in server installation cost and power consumption in a data center. A VOD high-speed distribution apparatus and a VOD distribution system for satisfying these needs are required. 
     As shown in  FIG. 28 , a conventional video distribution system is a system  2800  which includes a disk array  2801 , servers  2802 , and a load balancer  2803 . 
     The disk array  2801  is an apparatus obtained by logically integrating plural hard disks into one. Reading and writing are performed using disk access dedicated lines  2805  such as fiber channels or iSCSI. 
     The servers  2802  are connected to normal communication lines  2806  and the disk access dedicated lines  2805 . When receiving a video data distribution request from a client  2804  through the communication line  2806 , video data is read from the disk array  2801  through the disk access dedicated line  2805 , and the read data is transmitted to the client  2804  through the communication line  2806 . 
     The load balancer  2803  disperses, among plural servers  2802 - i  (i=1 to n), the video data distribution request received from the client  2804  through a communication line  2807 . 
     As shown in  FIG. 27 , each piece of video reproducing software  2705  of a client  2702  includes a reproducing unit which generates a video and a reception buffer which temporarily accumulates video data. 
     When the video reproducing software  2705  instructs to reproduce data, a video data distribution request is transmitted from the client  2702  to a server  2701 . When the server  2701  receives the video data distribution request from the client  2702 , distribution of video data  2703  is started. The video data  2703  is temporarily accumulated in the reception buffer of the video reproducing software  2705  of the client  2702 . If the amount of video data accumulated in the reception buffer exceeds a threshold value for starting reproduction, the reproducing unit of the video reproducing software  2705  reads the video data from the reception buffer, and reproducing of the video is started. 
     After the video reproducing software  2705  instructs to reproduce data, the server transmits the video data corresponding to the threshold value for starting reproduction in a broad band, and shortens time for the amount of video data accumulated in the reception buffer to exceed the threshold value for starting reproduction, so that the response speed (time from an instruction of reproduction to starting of reproduction) of video reproduction can be shortened. It is possible to realize video reproduction with a high sensory speed. 
     In the case where the server transmits the video data in a broad band after the instruction of reproduction, the server needs to be provided with a throughput performance  2603  for high-speed reproduction in addition to a throughput performance  2604  for normal distribution, as shown in  FIG. 26 . 
     BRIEF SUMMARY OF THE INVENTION 
     Two problems involved in the data distribution system obtained by combining the disk array, the servers and the load balancer such as the above-described video data distribution system will be described below. 
     The first problem will be described first. 
     In the system using the disk array and the servers, an arithmetic circuit substrate for arraying the hard disks, and interfaces such as fiber channels or iSCSI are mounted in the disk array. Interfaces to be connected to the disk array are mounted in the servers as well. The elements mounted in the disk array cause a problem that power consumption and a system-occupied space are increased. 
     Next, the second problem will be described using  FIG. 25  and  FIG. 26 . 
     In the case where a server  2601  transmits the video data in a broad band after the instruction of reproduction, the server  2601  needs to be provided with the throughput performance  2603  for high-speed reproduction in addition to the throughput performance  2604  for normal distribution. The throughput performance  2603  for high-speed reproduction is used when data corresponding to the threshold value for starting reproduction is transmitted. 
     In a data distribution system used for conventional video distribution, a load balancer  2500  transmits a data distribution request received from a client to each server on the basis of only the load of each server which changes every second. Accordingly, it is impossible to preliminarily recognize what server distributes data, and as a result, each of servers  2504 ,  2505 , and  2506  transmits data corresponding to the threshold value for starting reproduction in a broad band after the instruction of reproduction. Thus, the throughput performance for high-speed reproduction in addition to the throughput performance for normal distribution is needed in each server. If it is assumed that an average transmission band at the time of broadband transmission is bh (Mbps), a transmission band at the time of normal distribution is bl (Mbps), the number of server lines is m (lines), the number of clients is n (pieces), a frequency of changing an instruction of reproduction and a reproduced section per one client is r (the number of times/second), and a threshold value for starting reproduction (represented by multiplying a transmission band at the time of normal distribution by t seconds) of the reception buffer of the data reproducing software is bl/8·t (Mbyte), a total value Bh of the throughput performances for high-speed reproduction necessary for the lines of each server is obtained as follows. 
     In each line of the servers, bl/8·t (Mbyte) of data corresponding to the threshold value for starting reproduction is transmitted at a frequency of n/m·r (the number of times/second). Thus, an average throughput performance of bl/8·t·8·n/m·r (Mbps) for high-speed reproduction is required. Further, transmission of data corresponding to the threshold value for starting reproduction requires a broad band. Accordingly, a throughput performance for high-speed reproduction corresponding to the average transmission band bh (Mbps) at the time of broadband transmission is additionally required. 
     On the basis of the above, a throughput performance Bh′ for high-speed reproduction necessary for each line of the servers and the total value Bh (Mbps) of the throughput performances for high-speed reproduction necessary for the all lines are represented by formulae  2401  and  2402  of  FIG. 24 , respectively. 
     Further, if it is assumed that the total value of the throughput performances of the all lines of the servers is B (Mbps), the total value Bh of the throughput performances for high-speed reproduction necessary for the all lines corresponds to a difference between the total value B of the throughput performances of the all lines and a total value n·bl of transmission bands at the time of normal distribution. (formula  2403 ) 
     By using the formulae  2402  and  2403 , the average transmission band bh (Mbps) at the time of broadband transmission is represented by a formula  2404 . 
     Thus, the response time (transmission time when data corresponding to the threshold value for starting reproduction is transmitted in a broad band) T (seconds) of reproduction is represented by a formula  2405 . Accordingly, in the conventional data distribution system where each of the servers  2504 ,  2505 , and  2506  transmits data corresponding to the threshold value for starting reproduction after the instruction of reproduction, the larger the number m of server lines becomes, the longer the response time T of reproduction becomes. 
     As described above, the data distribution system obtained by combining the disk array, the servers, and the load balancer involves two problems, namely, power consumption and a system-occupied space become large, and the larger the number of server lines becomes, the longer the response time of reproduction becomes. 
     Next, a problem involved in the load balancer used in data distribution such as the video distribution will be described below. 
     The load balancer  2500  used for the data distribution system such as the conventional video distribution transmits a data distribution request received from a client to each server on the basis of only the load of each server. Accordingly, in the data distribution system using the disk array and the servers, it is necessary to control an access to the requested file in the disk array, and an arithmetic circuit substrate for arraying the hard disks or interfaces such as fiber channels or iSCSI need to be mounted. Further, it is necessary for even the servers to be provided with interfaces to be connected to the disk array. That is, the data distribution request is transmitted by the load balancer  2500  to each server on the basis of only the load of the server, which leads to the necessity of the elements mounted in the disk array, resulting in increase of power consumption and a system-occupied space of the data distribution system. 
     Further, as described above, the load balancer  2500  used for the data distribution system such as the conventional video distribution system transmits the data distribution request received from the client to each server on the basis of only the load of each server which changes every second. Accordingly, it is impossible to preliminarily recognize what server distributes data, and as a result, each of the servers  2504 ,  2505 , and  2506  transmits data corresponding to the threshold value for starting reproduction in a broad band after the instruction of reproduction as shown in  FIG. 25 . Thus, if the conventional load balancer  2500  is used for the data distribution system, the throughput performance for high-speed reproduction in addition to the throughput performance for normal distribution is needed in each server. 
     If it is assumed that an average transmission band at the time of broadband transmission is bh (Mbps), a transmission band at the time of normal distribution is bl (Mbps), the number of server lines is m (lines), the number of clients is n (pieces), a frequency of changing an instruction of reproduction and a reproduced section per one client is r (the number of times/second), and a threshold value for starting reproduction (represented by multiplying a transmission band at the time of normal distribution by t seconds) of the reception buffer of the data reproducing software is bl/8·t (Mbyte), then a total value Bh of the throughput performances for high-speed reproduction necessary for each line of the servers is obtained as follows. 
     In each line of the servers, bl/8·t (Mbyte) of data corresponding to the threshold value for starting reproduction is transmitted at a frequency of n/m·r (the number of times/second). Thus, an average throughput performance of bl/8·t·8·n/m·r (Mbps) for high-speed reproduction is required. Further, transmission of data corresponding to the threshold value for starting reproduction requires a broad band. Accordingly, a throughput performance for high-speed reproduction corresponding to the average transmission band bh (Mbps) at the time of broadband transmission is additionally required. 
     On the basis of the above, a throughput performance Bh′ for high-speed reproduction necessary for each line of the servers and the total value Bh (Mbps) of the throughput performances for high-speed reproduction necessary for the all lines are represented by formulae  2401  and  2402  of  FIG. 24 , respectively. 
     Further, if it is assumed that the total value of the throughput performances of the all lines of the servers is B (Mbps), the total value Bh of the throughput performances for high-speed reproduction necessary for the all lines corresponds to a difference between the total value B of the throughput performances of the all lines and a total value n·bl of transmission bands at the time of normal distribution. (formula  2403 ) 
     By using the formulae  2402  and  2403 , the average transmission band bh (Mbps) at the time of broadband transmission is represented by a formula  2404 . 
     Thus, the response time (transmission time when data corresponding to the threshold value for starting reproduction is transmitted in a broad band) T (seconds) of reproduction is represented by a formula  2405 . Accordingly, if the conventional load balancer is used for the data distribution system such as the video distribution system, the throughput performance for high-speed reproduction in addition to the throughput performance for normal distribution is needed in each server, and the larger the number m of server lines becomes, the longer the response time T of reproduction becomes. 
     According to an aspect of the present invention, there is provided a network system including a first server and a second server which transmit data to a data destination apparatus, and a communication apparatus which is connected to the data destination apparatus, the first server and the second server through communication lines, wherein the communication apparatus includes: a first reception unit which receives a first file access request for requesting transmission of data in files contained in the first server and the second server from the data destination apparatus; a file access request processing unit which generates, on the basis of the first file access request, a second file access request for requesting the first server to transmit part of data in the files and a third file access request for requesting the second server to transmit data subsequent to the part of data in the files; and a first transmission unit which transmits the second file access request to the first server, and transmits the third file access request to the second server after the first server completes the transmission of the part of data on the basis of the second file access request, the first server includes: a second reception unit which receives the second file access request transmitted by the communication apparatus; and a second transmission unit which transmits the part of data in the files on the basis of the second file access request, and the second server includes: a third reception unit which receives the third file access request; and a third transmission unit which transmits the data subsequent to the part of data in the files on the basis of the third file access request. 
     Further, according to another aspect of the present invention, there is provided a network system including a first server and a second server which transmit data to a data destination apparatus, and a communication apparatus which is connected to the data destination apparatus, the first server and the second server through communication lines, wherein the communication apparatus includes: a first reception unit which receives a first file access request for requesting transmission of data in files contained in the first server and the second server from the data destination apparatus; a file access request processing unit which generates, on the basis of the first file access request, a second file access request for requesting the first server to transmit part of data in the files and a third file access request for requesting the second server to transmit data subsequent to the part of data in the files; and a first transmission unit which transmits the second file access request to the first server, and transmits the third file access request to the second server when a specified time passes after transmission of the second file access request, the first server includes: a second reception unit which receives the second file access request transmitted by the communication apparatus; and a second transmission unit which transmits the part of data in the files on the basis of the second file access request, and the second server includes: a third reception unit which receives the third file access request; and a third transmission unit which transmits the data subsequent to the part of data in the files on the basis of the third file access request. 
     On the other hand, according to still another aspect of the present invention, there is provided a communication apparatus connected, through communication lines, to a data destination apparatus, and a first server and a second server which transmit data to the data destination apparatus, the communication apparatus including: a first reception unit which receives a first file access request for requesting transmission of data in files contained in the first server and the second server from the data destination apparatus; a file access request processing unit which generates, on the basis of the first file access request, a second file access request for requesting the first server to transmit part of data in the files and a third file access request for requesting the second server to transmit data subsequent to the part of data in the files; and a first transmission unit which transmits the second file access request to the first server, and transmits the third file access request to the second server after the first server completes the transmission of the part of data on the basis of the second file access request. 
     Further, according to still another aspect of the present invention, there is provided a communication apparatus connected, through communication lines, to a data destination apparatus, and a first server and a second server which transmit data to the data destination apparatus, the communication apparatus including: a first reception unit which receives a first file access request for requesting transmission of data in files contained in the first server and the second server from the data destination apparatus; a file access request processing unit which generates, on the basis of the first file access request, a second file access request for requesting the first server to transmit part of data in the files and a third file access request for requesting the second server to transmit data subsequent to the part of data in the files; and a first transmission unit which transmits the second file access request to the first server, and transmits the third file access request to the second server when a specified time passes after transmission of the second file access request. 
     In the network system disclosed in this application of the present invention, effects obtained from representative aspects will be briefly described. Without using a disk array, plural servers are directly arrayed by a load balancing module (a module for dispersing a distribution request from a client among plural servers which accumulate the same file) and a file dispersion access module (a module for sorting a distribution request from a client into a server storing the file corresponding the distribution request). Accordingly, elements (an arithmetic circuit substrate for arraying the hard disks and interfaces such as fiber channels or iSCSI) to be mounted in the disk array used in the conventional method are not necessary. Thus, it is possible to provide a data distribution apparatus and a data distribution system in which power consumption and an occupied space used by unnecessary elements are reduced and a performance per 1 W·IU is improved. 
     Further, irrespective of the number m of server lines, the response speed of reproduction becomes constant, and thus, it is possible to provide a data distribution apparatus and a data distribution system in which the response time of reproduction becomes fast by m times as compared to the conventional ones. 
     It should be noted that if it is assumed that an average transmission band at the time of broadband transmission is bh (Mbps), a transmission band at the time of normal distribution is bl (Mbps), the number of server lines is m (lines), the number of clients is n (pieces), a frequency of changing an instruction of reproduction and a reproduced section per one client is r (the number of times/second), and a threshold value for starting reproduction (represented by multiplying a transmission band at the time of normal distribution by t seconds) of the reception buffer of the data reproducing software is bl/8·t (Mbyte), then a total value Bh of the throughput performances for high-speed reproduction necessary for the lines of the dedicated servers is obtained as follows. 
     In each line of the servers, bl/8·t (Mbyte) of data corresponding to the threshold value for starting reproduction is transmitted at a frequency of n·r (the number of times/second). Thus, an average throughput performance of bl/8·t·8·n·r (Mbps) for high-speed reproduction is required. Further, transmission of data corresponding to the threshold value for starting reproduction requires a broad band. Accordingly, a throughput performance for high-speed reproduction corresponding to the average transmission band bh (Mbps) at the time of broadband transmission is additionally required. 
     On the basis of the above, the total value Bh (Mbps) of the throughput performances for high-speed reproduction necessary for the lines of the dedicated servers is represented by a formula  2301  of  FIG. 23 . 
     Further, if it is assumed that the total value of the throughput performances of the all lines of the servers is B (Mbps), the total value Bh of the throughput performances for high-speed reproduction necessary for the all lines corresponds to a difference between the total value B of the throughput performances of the all lines and a total value n·bl of transmission bands at the time of normal distribution. (formula  2302 ) 
     By using the formulae  2301  and  2302 , the average transmission band bh (Mbps) at the time of broadband transmission is represented by a formula  2303 . 
     Thus, the response time (transmission time when data corresponding to the threshold value for starting reproduction is transmitted in a broad band) T (seconds) of reproduction is represented by a formula  2304 . The response time T of reproduction is constant irrespective of the number m of server lines. 
     In the communication apparatus disclosed in this application of the present invention, effects obtained from representative aspects will be briefly described. 
     In the communication apparatus disclosed in the application, plural servers can be directly arrayed by a load balancing module (a module for dispersing a distribution request from a client among plural servers which accumulate the same file) and a file dispersion access module (a module for sorting a distribution request from a client into a server storing the file corresponding the distribution request). Accordingly, elements (an arithmetic circuit substrate for arraying the hard disks and interfaces such as fiber channels or iSCSI) to be mounted in the disk array used in the conventional method are not necessary in the data distribution apparatus and the data distribution system. Thus, by using the communication apparatus disclosed in this application in the data distribution apparatus and the data distribution system, it is possible to reduce power consumption and an occupied space used by unnecessary elements of the data distribution apparatus and the data distribution system and to improve a performance per 1 W·IU. 
     Further, by using the communication apparatus disclosed in the application, the response speed of reproduction becomes constant irrespective of the number m of server lines, and thus, it is possible to provide a data distribution apparatus and a data distribution system in which the response time of reproduction becomes fast by m times as compared to the conventional ones. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are explanation diagrams of a data distribution system according to an embodiment of the present invention; 
         FIG. 2  is a configuration block diagram of a communication apparatus according to the embodiment of the present invention; 
         FIG. 3  is a format diagram of a TCP/IP connection table mounted in the communication apparatus according to the embodiment of the present invention; 
         FIG. 4  is a flowchart for showing an address generating method of accessing the TCP/IP connection table mounted in the communication apparatus according to the embodiment of the present invention; 
         FIG. 5  is a flowchart for showing a method of accessing the TCP/IP connection table mounted in the communication apparatus according to the embodiment of the present invention; 
         FIG. 6  is an explanation diagram of the data distribution system including an initial data transmission server and a subsequent data transmission server according to the embodiment of the present invention; 
         FIG. 7  is an explanation diagram for showing a searching method of a conflict of a hash value in the TCP/IP connection table according to the embodiment of the present invention; 
         FIG. 8  is an explanation diagram for showing an aging method in the TCP/IP connection table according to the embodiment of the present invention; 
         FIG. 9  is an explanation diagram for showing a TCP state transition according to the embodiment of the present invention; 
         FIG. 10  is an explanation diagram of packets transmitted and received among the communication apparatus, clients, and servers according to the embodiment of the present invention; 
         FIG. 11  is an explanation diagram of packet headers transmitted and received among the communication apparatus, clients, and servers according to the embodiment of the present invention; 
         FIG. 12  is an explanation diagram of an example of a selecting method of an IP address of the server according to the embodiment of the present invention; 
         FIG. 13  is an explanation diagram of an example of a file accumulating method of the server according to the embodiment of the present invention; 
         FIG. 14  is an explanation diagram of an example of a selecting method of an IP address of the server according to the embodiment of the present invention; 
         FIG. 15  is an explanation diagram of an example of a file accumulating method of the server according to the embodiment of the present invention; 
         FIG. 16  is an explanation diagram of an example of a selecting method of an IP address of the server according to the embodiment of the present invention; 
         FIG. 17  is an explanation diagram of an example of a selecting method of an IP address of the server according to the embodiment of the present invention; 
         FIG. 18  is an explanation diagram of an example of a file accumulating method of the server according to the embodiment of the present invention; 
         FIG. 19  is an explanation diagram of an extended example of the data distribution system according to the embodiment of the present invention; 
         FIG. 20  is an explanation diagram of transmission bands of the server according to the embodiment of the present invention; 
         FIG. 21  is an explanation diagram of an extended example of the communication apparatus according to the embodiment of the present invention; 
         FIG. 22  is an explanation diagram of an extended example of the data distribution system according to the embodiment of the present invention; 
         FIG. 23  shows explanation formulae for a response time of reproduction in a conventional video data distribution system; 
         FIG. 24  shows explanation formulae for a response time of reproduction in the data distribution system according to the embodiment of the present invention; 
         FIG. 25  is an explanation diagram of an example of a conventional data distribution system; 
         FIG. 26  is an explanation diagram of data transmission bands of a data distribution server; 
         FIG. 27  is an explanation diagram of data transmission bands of a data distribution server and data reproducing software mounted in a client; 
         FIG. 28  is an explanation diagram of an example of the conventional data distribution system; 
         FIG. 29  is a format diagram of packet data according to the embodiment of the present invention; and 
         FIG. 30  is a sequence diagram for a case of using a UDP according to the embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following embodiment, an explanation will be made in plural divided sections or embodiments if needed as a matter of convenience. However, the sections or embodiments have a relation with each other unless otherwise specified, and one is for a modified example, a detailed explanation or a complementary explanation of a part or all of the other. In addition, if the number (including value, amount, range and the like) of constitutional elements is referred to in the following embodiment, the embodiment is not limited to a specified number and any number larger or smaller than the specified number may be used unless otherwise specified and unless the embodiment is apparently limited to the specified number in principle. 
     Further, it is obvious that the constituent elements (including element steps and the like) are not necessarily essential in the following embodiment unless otherwise specified and unless they are considered to be apparently essential in principle. Likewise, if the shapes and positional relations of constituent elements are referred to, constituent elements substantially approximate or similar to the shapes and the like are included unless otherwise specified and unless the shapes and positional relations are considered to be incorrect in principle. This is also applied to the value and the range. 
     Hereinafter, an embodiment of the present invention will be described in detail on the basis of the drawings. It should be noted that the same constituent elements are given the same reference numerals in principle throughout the all drawings for explaining the embodiment, and the explanations thereof will not be repeated. 
     Embodiment 
     Hereinafter, an embodiment of the present invention will be described using the drawings. 
       FIG. 1  is a configuration block diagram of an information processing system  101  according to the embodiment. It is assumed that the information processing system  101  is used as a VOD distribution system and a Web distribution system with advertisement. 
     In the case where the information processing system is used as the VOD distribution system, two types, i.e., an initial data transmission server  602 - 1  and a subsequent data transmission server  602 - 2 , are prepared, as shown in, for example,  FIG. 6 . When data is distributed to clients A to C ( 603 - 1  to  603 - 3 ), data corresponding to a threshold value for starting reproduction of a reception buffer is transmitted from the initial data transmission server  602 - 1  in a broad band immediately after each piece of data reproducing software of the clients A to C ( 603 - 1  to  603 - 3 ) instructs to reproduce data. Thereafter, the subsequent data is transmitted from the subsequent data transmission server  602 - 2  in a normal distribution band. 
     The information processing system  101  includes a communication apparatus  100  and servers  102 - i  (i=1 to 4). The communication apparatus  100  is connected to the servers  102  through communication lines  105 - i  (i=1 to 4). Further, the communication apparatus  100  is connected to clients  103 - i  (i=1 to 4) through lines  104  of a network  106 . 
     As shown in  FIG. 1B , each server  102  is an apparatus configured in such a manner that a processor  108 , a memory  107 , a large-capacity storing unit  109 , and a network interface  110  including a transmission unit  111  and a reception unit  112  are connected to each other. 
       FIG. 2  shows a configuration of the communication apparatus  100 . 
     The communication apparatus  100  includes transmission/reception units  240 , a switching unit  201 , and a module implementation unit  200  in which a server arraying module and a broadband transmission module for reproduction are implemented. 
     The switching unit  201  receives packet data through the transmission/reception unit  240 - i  from one of communication lines  202 - i  (i=1 to 8), or from the module implementation unit  200 , and transmits the packet data to a different communication line  202  through the transmission/reception unit  240 - i , or transmits the packet data to the module implementation unit  200 . 
       FIG. 29  shows an example of a format of packet data transmitted and received within the communication apparatus  100 . 
     The packet data includes an InLine  2900 , an OutLine  2901 , a Type  2902 , a Vlan  2903 , an SMAC  2904 , a DMAC  2905 , a Proto  2906 , an SIP  2907 , a DIP  2908 , an SPort  2909 , a DPort  2910 , a TCP Flag  2911 , a PSEQ  2912 , a PACK  2913 , an OtherHeader  2914 , a various-commands  2915 , and a Payload  2916 . Further, the SIP  2907 , DIP  2908 , SPort  2909 , and DPort  2910  are collectively represented as a packet header (P.H.)  2917  in the embodiment. The P.H.  2917  shows the characteristics of the packet data. 
     Here, the InLine  2900  stores an input line number that is an identification number of a line through which the packet is input. The OutLine  2901  stores an output line number that is an identification number of a line through which the packet is output. The Type  2902  stores an identification number for identifying a protocol of a network layer. The Vlan  2903  stores a number for identifying a VLAN. The SMAC  2904  stores a source MAC address that is a source address of a data link layer. The DMAC  2905  stores a destination MAC address that is a destination address. The Proto  2906  stores an identification number for identifying a protocol of a transport layer such as a UDP (User Datagram Protocol). The SIP  2907  stores a source address, namely, a source IP address that is an address of a terminal on the transmission side. The DIP  2908  stores a destination address, namely, a destination IP address that is an address of a terminal on the reception side. The SPort  2909  stores a source port of a TCP. The DPort  2910  stores a destination port of a TCP. The TCP Flag  2911  stores a TCP flag number. The PSEQ  2912  stores a transmission sequence number (SEQ number). The PACK  2913  stores a reception sequence number (ACK number). The OtherHeader  2914  stores other IP/TCP header data. The various-commands  2915  stores a command of an application layer. The Payload  2916  stores data other than the packet header and the various-commands. 
     The module implementation unit  200  ( FIG. 2 ) includes an input/output controlling unit  205 , an ARP/IP/TCP processing unit  204 , a TCP/HTTP processing unit  203 , a TCP/IP connection table  207 , and a file access request temporarily-recording table  206 . 
       FIG. 3  shows an example of a format of the TCP/IP connection table. 
     Each of entries  320 - i  (i=1 to n) includes a C-IP  301 , a D-IP  302 , a C-PORT  303 , a D-PORT  304 , a C-SEQ  305 , a DC-SEQ  306 , a C-ID  307 , a TIME  308 , a STATE  309 , an S-IP  310 , a C-IP  311 , an S-PORT  312 , a D-PORT  313 , an S-SEQ  314 , a DS-SEQ  315 , an S-ID  316 , a NEXT  317 , a POINTER  318 , and a packet header temporarily-storing area  319 . 
     The C-IP  301  records an IP address of a client. The D-IP  302  records a unique IP address released to the network  106  by the communication apparatus  100 . The C-PORT  303  records a TCP port number of a client. The D-PORT  304  records a TCP port number released to the network  106  by the communication apparatus  100 . The C-SEQ  305  records a TCP sequence number of a host on the client side. The DC-SEQ  306  records a TCP sequence number of the communication apparatus  100  for a host on the client side. The C-ID  307  records an ID number of an IP packet transmitted to a host on the client side by the communication apparatus  100 . The TIME  308  records the latest time when the packet is received. The STATE  309  records a state of TCP connection. The S-IP  310  records an IP address of a server. The C-IP  311  records an IP address of a client. The S-PORT  312  records a TCP port number of a server. The D-PORT  313  records a TCP port number released to the network  106  by the communication apparatus  100 . The S-SEQ  314  records a TCP sequence number of a host on the server side. The DS-SEQ  315  records a TCP sequence number of the communication apparatus  100  for a host on the server side. The S-ID  316  records an ID number of an IP packet transmitted to a host on the server side by the communication apparatus  100 . The NEXT  317  records presence or absence of a conflict of a hash value calculated when an address is generated. The POINTER  318  records a pointer to the file access request temporarily-recording table. 
     The input/output controlling unit  205  ( FIG. 2 ) receives a packet  231  from the switching unit  201 , and transmits a packet  230  to the ARP/IP/TCP processing unit  204 . Further, the input/output controlling unit  205  receives packets  227  to  229  transmitted from the ARP/IP/TCP processing unit  204 , and outputs a packet  232  to the switching unit  201 . 
     The ARP/IP/TCP processing unit  204  ( FIG. 2 ) includes a filter unit  215 , an ARP processing unit  214 , and a TCP/IP connection managing unit  213 . When receiving the packet  230  from the input/output controlling unit  205 , the filter unit  215  ( FIG. 2 ) determines whether or not the packet is the processing target. The communication apparatus  100  releases its unique IP address and MAC address to the network  106  on the client side. In the case where the packet  230  is an ARP REQUEST packet used for inquiring the unique MAC address, a packet  226  is transmitted to the ARP processing unit  214 . In addition, in the case where the packet  230  is to be transmitted to the unique IP address and has a specific number (for example, 80 or the like) that is preliminarily set by the destination port number DPort  2910 , a packet  225  is transmitted to the TCP/IP connection managing unit  213 . 
     Upon receiving the ARP REQUEST packet  226 , the ARP processing unit  214  ( FIG. 2 ) generates and outputs an ARP REPLY packet  228  in which the unique MAC address is described. 
     When receiving the TCP/IP packet  225  to be transmitted to the unique IP address and TCP port number, the TCP/IP connection managing unit ( FIG. 2 ) accesses the TCP/IP connection table  207 , and reads and initializes an entry  320  corresponding to the packet header P.H.  2917  ( 224 ). Further, the TCP/IP connection managing unit receives a new TCP state  218  and new packet data  219  from the TCP/HTTP processing unit, writes a new TCP state  224  into the TCP/IP connection table  207  ( 224 ), and outputs the new packet data  219  to the input/output controlling unit  205  ( 227 ). 
       FIG. 4  shows an example of an address generating method when accessing the TCP/IP connection table  207 . 
     In the first place, an XOR operation is performed using four field values (the source IP address SIP  2907 , destination IP address DIP  2908 , source TCP port number  2909 , and destination TCP port number  2910 ) described in the packet header P.H.  2917  shown in  FIG. 29  (Step  401 ). Next, it is determined whether or not the packet is one from the server (Step  402 ). If the packet is one from the server, an XOR operation using the source IP address SIP  2907  descried in the packet header P.H.  2917  and the IP address released by the apparatus (Step  405 ). 
     Finally, a bit shift operation (Step  403 ) and addition of a table beginning address (Step  404 ) are performed so as to generate a table address value. 
       FIG. 5  shows an example of an algorithm accessible to the TCP/IP connection table  207 . 
     In the first place, an address is generated by the method shown in  FIG. 4  (Step  502 ), and an entry is read from the TCP/IP connection table (Step  504 ) to determine whether or not the TCP Flag  2911  of the packet header is SYN (Step  505 ). If the TCP Flag  2911  is SYN in Step  505  (Step  517 ), it is determined whether or not any one of the followings is satisfied: the STATE  309  described in the entry is 0; the packet header P.H.  2917  corresponds to the C-IP  301 , D-IP  302 , C-PORT  303 , and D-PORT  304  described in the entry; and the packet header P.H.  2917  corresponds to the S-IP  310 , C-IP  311 , S-PORT  312 , and D-PORT  313  described in the entry (Step  506 ). If it is determined that one of them is satisfied in Step  506  (Step  519 ), the entry read in Step  504  is initialized (Step  511 ), the update time TIME  308  described in the entry is updated to the current time (Step  512 ), and various processes are performed for the packet (Step  515 ). If it is determined that none of them is satisfied in Step  506  (Step  520 ), 1 indicating a conflict of the hash value is written into the NEXT  317  of the entry read in Step  504  (Step  508 ). After the address value is incremented (Step  509 ), the flow returns to Step  504  to read the entry again using the address value incremented. If the TCP Flag  2911  is not SYN in Step  505  (Step  518 ), it is determined whether or not any one of the followings is satisfied: the packet header P.H.  2917  corresponds to the C-IP  301 , D-IP  302 , C-PORT  303 , and D-PORT  304  described in the entry; and the packet header P.H.  2917  corresponds to S-IP  310 , C-IP  311 , S-PORT  312 , and D-PORT  313  described in the entry (Step  507 ). If it is determined that any one of them is satisfied in Step  507  (Step  522 ), the update time TIME  308  of the entry read in Step  504  is updated to the current time (Step  512 ), and various processes are performed for the packet (Step  515 ). If it is determined that none of them is satisfied in Step  507  (Step  521 ), it is determined whether or not the NEXT of the entry read in Step  504  is 1 (Step  510 ). If it is determined that the NEXT is 1 in Step  510  (Step  523 ), the address value is incremented (Step  509 ), and then, the flow returns to Step  504  to read the entry again using the address value incremented. If it is determined that the NEXT is not 1 in Step  510  (Step  524 ), the packet is discarded and the flow is completed (Step  516 ). 
     By using the method for accessing the TCP/IP connection table  207  described using  FIG. 4  and  FIG. 5 , an access method shown in, for example,  FIG. 7  can be realized. 
     In  FIG. 7 , the address value generated using  FIG. 4  is generated every four entries ( 701 - 1  to  701 - 6 ). When NEXT=0, the entry is initialized for use. When NEXT=1, entries are continuously read while shifting back to the previous entries one by one until the entry with NEXT=0 is found. The above method enables the use of all entries of the table, and it is possible to promptly search for the target entry even in a sate where the usage rate of entries of the table is high (about 90%). 
     As shown in  FIG. 2 , the TCP/HTTP processing unit  203  includes a restructuring unit  212 , a state transition determination unit  211 , an HTTP processing unit  210 , a packet generating unit  209 , and a TCP state updating unit  208 . 
       FIG. 8  shows a method of deleting (aging) old entries. A table  800 - 1  shows a state before deleting (aging), and a table  800 - 2  shows a state after deleting (aging). 
     When the NEXT  317  described in the entry is 0, no conflict of the hash value is present, and the update time TIME  308  is much older than the current time, all the values of 0 described in the entry are cleared for deleting the entry. Further, when the NEXT  317  of the previous entry is 1, 1 is changed to 0. 
     The restructuring unit  212  ( FIG. 2 ) receives a TCP state  220  updated by the TCP/IP connection managing unit, and restructures a circuit configuration of the TCP/HTTP processing unit on the basis of the TCP state  220 . This is used for a case in which a dynamic restructuring processor or the like is used. 
     The state transition determination unit  211  ( FIG. 2 ) determines the state transition of the TCP on the basis of a TCP state  221  updated by the TCP/IP connection managing unit and packet data  222  transmitted from the TCP/IP connection managing unit. The determined state transition of the TCP is transmitted to the TCP state updating unit  208 , the packet generating unit  209 , and the HTTP processing unit  210  ( 216 ). 
     The TCP state updating unit  208  ( FIG. 2 ) generates a new TCP state on the basis of a determination result  216  of the state transition of the TCP, and outputs the same to the TCP/IP connection managing unit  213  ( 218 ). 
       FIG. 9  is a diagram for showing how the TCP state is transited by the state transition determination unit  211  and the TCP state updating unit  208 .  FIG. 9  shows a transition in the case of being used as the VOD distribution system in  FIG. 6 . 
     The initial state of the TCP state STATE  309  is a Close [value 0x00000000]  901  representing that the TCP connection has not been established. Upon receiving a packet in which the TCP Flag  2911  is SYN from the client in the state Close  901  ( 917 ), the state is transited to a state Half Open [value 0x00000001]  902  representing that the TCP connection is about to be established. Upon receiving a packet in which the TCP Flag  2911  is ACK and the PACK  2913  corresponds to the DC-SEQ  306  of the TCP/IP connection table  207  from the client in the state Half Open  902  ( 918 ), the state is transited to a state Open [value 0x00000100]  903  representing that the TCP connection has been established. Upon receiving a packet in which a GET or POST command of an HTTP protocol is described from the client in the state Open  903  ( 919 ), the state is transited to a state Burst Request [value 0x00000200]  904  representing that the TCP connection with the initial data transmission server has been started. Upon receiving a packet in which the TCP Flag  2911  is SYN-ACK and the PACK  2913  corresponds to the DS-SEQ  315  of the TCP/IP connection table  207  from the server in the state Burst Request  904  ( 920 ), the state is transited to a state Burst Half Open [value 0x00000800]  905  representing that the TCP connection with the initial data transmission server is about to be established. Upon receiving a packet in which the TCP Flag  2911  is ACK and the PACK  2913  does not correspond to the DS-SEQ  315  of the TCP/IP connection table  207  from the server in the state Burst Half Open  905  ( 926 ), the state is transited to the state Burst Half Open [value 0x00000800]  905  again. Upon receiving a packet in which the TCP Flag  2911  is ACK and the PACK  2913  corresponds to the DS-SEQ  315  of the TCP/IP connection table  207  from the server in the state Burst Half Open  905  ( 921 ), the state is transited to a state Burst Open [value 0x00010000]  906  representing that the TCP connection with the initial data transmission server has been established ( 921 ). Upon receiving a packet in which the TCP Flag  2911  is RST/PSH/URG/ACK from the server or the client in the state Burst Open  906  ( 927 ), the state is transited to the state Burst Open [value 0x00010000]  906  again ( 927 ). Upon receiving a packet in which the TCP Flag  2911  is FIN from the server in the state Burst Open  906  ( 922 ), the state becomes a state Burst Close Wait [value 0x00000002]  908  representing that the TCP connection with the initial data transmission server is about to end via a state Burst Open (FIN) [value 0x80010000]  907  representing that the FIN has been received. Upon receiving a packet in which the TCP Flag  2911  is ACK and the PACK  2913  corresponds to the DS-SEQ  315  of the TCP/IP connection table  207  from the server in the state Burst Close Wait  908  ( 923 ), the state is transited to a state Static Request [value 0x00000400]  909  representing that the TCP connection with the subsequent data transmission server has been started. Upon receiving a packet in which the TCP Flag  2911  is SYN-ACK and the PACK  2913  corresponds to the DS-SEQ  315  of the TCP/IP connection table  207  from the server in the state Static Request  909  ( 924 ), the state is transited to a state Static Half Open [value 0x00001000]  910  representing that the TCP connection with the subsequent data transmission server is about to be established. Upon receiving a packet in which the TCP Flag  2911  is ACK and the PACK  2913  does not correspond to the DS-SEQ  315  of the TCP/IP connection table  207  from the server in the state Static Half Open  910  ( 928 ), the state is transited to the state Static Half Open  910  again. Upon receiving a packet in which the TCP Flag  2911  is ACK and the PACK  2913  corresponds to the DS-SEQ  315  of the TCP/IP connection table  207  from the server in the state Static Half Open  910  ( 925 ), the state is transited to a state Static Open [value 0x00020000]  911  representing that the TCP connection with the subsequent data transmission server has been established ( 925 ). Upon receiving a packet in which the TCP Flag  2911  is RST/PSH/URG/ACK from the server or the client in the state Static Open  911  ( 929 ), the state is transited to the state Static Open  911  again ( 929 ). Upon receiving a packet in which the TCP Flag  2911  is FIN-ACK and the PACK  2913  corresponds to the DC-SEQ  306  of the TCP/IP connection table  207  from the client in a state after the state Half Open ( 931 ), the state becomes a state Close Wait [value 0x0000000C]  914  representing that the termination of the TCP connection has been started via a state FIN Recv. [value 0x8------- (- is an arbitrary value)]  913  representing that the FIN has been received. Upon receiving a packet in which the TCP Flag  2911  is FIN-ACK and the PACK  2913  corresponds to the DS-SEQ  315  of the TCP/IP connection table  207  in a state after the state Burst Request ( 930 ), the state becomes a state Close Wait [value 0x0000000C]  914  representing that the termination of the TCP connection has been started via a FIN Recv. [value 0x8------- (- is an arbitrary value)]  912  representing that the FIN has been received. Upon receiving a packet in which the TCP Flag  2911  is FIN-ACK/ACK and the PACK  2913  corresponds to the DS-SEQ  315  of the TCP/IP connection table  207  from the server in the state Close Wait  914  ( 933 ), the state is transited to a state Client Close Wait [value 0x00000004]  915  representing that the TCP connection is about to end. Upon receiving a packet in which the TCP Flag  2911  is FIN-ACK/ACK and the PACK  2913  corresponds to the DC-SEQ  306  of the TCP/IP connection table  207  from the client in the state Close Wait  914  ( 932 ), the state is transited to a state Server Close Wait [value 0x00000008]  916  representing that the TCP connection is about to end. Upon receiving a packet in which the TCP Flag  2911  is FIN-ACK/ACK and the PACK  2913  corresponds to the DC-SEQ  306  of the TCP/IP connection table  207  from the client in the state Client Close Wait  915  ( 935 ), the state is transited to the state Close  901 . Upon receiving a packet in which the TCP Flag  2911  is FIN-ACK/ACK and the PACK  2913  corresponds to the DS-SEQ  315  of the TCP/IP connection table  207  in the state Server Close Wait  916  ( 934 ), the state is transited to the Close  901 . 
     As described above, the TCP state is transited in the state transition determination unit  211  and the TCP state updating unit  208 . The TCP connection is established between the dedicated server and the apparatus  100  by the state transition after the instruction of reproduction from the client, and data corresponding to a threshold value for starting reproduction of the reception buffer is transmitted from the dedicated server in a broad band. Thereafter, the TCP connection is switched between the normal server and the apparatus  100 , and the subsequent data can be transmitted from the normal server in a normal distribution band. Accordingly, it is not necessary for each server to be provided with a throughput performance for high-speed reproduction. 
     On the basis of the packet data  222  received from the TCP/IP connection managing unit  213  and the determination result  216  of the state transition of the TCP, the HTTP processing unit  210  ( FIG. 2 ) analyzes an HTTP command described in the packet, or records an HTTP command into the file access request temporarily-recording table ( 223 ), or reads an HTTP command from the file access request temporarily-recording table ( 223 ). The analysis result and the read file access request are output to the packet generating unit  209  ( 217 ). 
     On the basis of the analysis result and the file access request output from the HTTP processing unit  210  and the determination result  216  of the state transition output from the state transition determination unit  211 , the packet generating unit  209  ( FIG. 2 ) generates a new packet to be output to the TCP/IP connection managing unit  213  ( 219 ). Further, the header portion of the generated packet is output to the TCP state updating unit  208  ( 233 ). 
       FIG. 10  is a diagram showing the types of packets transmitted and received among the communication apparatus  100 , a server  602 , and a client  603  by the HTTP processing unit  210  and the packet generating unit  209 .  FIG. 10  shows a case in the VOD distribution system of  FIG. 6 . 
     The client  603  transmits a packet  1004  in which the TCP Flag  2911  is SYN, the PSEQ  2912  is A, and the PACK  2913  is 0 to the communication apparatus  100 . Upon receiving the packet  1004 , the communication apparatus  100  changes the TCP state STATE, the C-SEQ  305 , and the DC-SEQ  306  of the TCP/IP connection table  207  into the Half Open, A+1, and B (random value)+1, respectively, and returns a packet  1005  in which the TCP Flag  2911  is SYN-ACK, the PSEQ  2912  is B, and the PACK  2913  is A+1 to the client  603 . Upon receiving the packet  1005 , the client  603  transmits a packet  1006  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is A+1, and the PACK  2913  is B+1 to the communication apparatus  100 . Upon receiving the packet  1006 , the communication apparatus  100  changes the TCP state STATE of the TCP/IP connection table  207  into the Open. Accordingly, the TCP connection is established between the client  603  and the communication apparatus  100 . 
     After transmitting the packet  1006 , the client  603  transmits a packet  1007  in which the TCP Flag  2911  is PSH-ACK, the PSEQ  2912  is A+1, the PACK  2913  is B+1, and GET is described as a command of an HTTP protocol to the communication apparatus  100 . Upon receiving the packet  1007 , the communication apparatus  100  changes the TCP state STATE, the C-SEQ  305 , the S-SEQ  314 , and the DS-SEQ  315  of the TCP/IP connection table  207  into the Burst Request, A+1+G (the payload length of the packet  1007 ), 0, and C (random value)+1, respectively, and transmits a packet  1008  in which the TCP Flag  2911  is SYN, the PSEQ  2912  is C, and the PACK  2913  is 0 to the initial data transmission server  602 - 1 . Further, the payload data included in the packet  1007  is recorded into the file access request temporarily-recording table  206 , and the recorded beginning address is written into the POINTER  318  of the TCP/IP connection table  207 . Upon receiving the packet  1008 , the initial data transmission server  602 - 1  transmits a packet  1009  in which the TCP Flag  2911  is SYN-ACK, the PSEQ  2912  is D (random value), and the PACK  2913  is C+1. Upon receiving the packet  1009 , the communication apparatus  100  changes the TCP state STATE, the S-SEQ  314 , and the DS-SEQ  315  of the TCP/IP connection table  207  into the Burst Half Open, D+1, and C+1+G (the payload length of the packet  1007 ), respectively, and transmits a packet  1010  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is C+1, and the PACK  2913  is D+1 to the initial data transmission server  602 - 1 . Accordingly, the TOP connection is established between the communication apparatus  100  and the initial data transmission server  602 . 
     After transmitting the packet  1010 , the communication apparatus  100  transmits, to the initial data transmission server  602 - 1 , a packet  1011  in which the TCP Flag  2911  is PSH-ACK, the PSEQ  2912  is C+1, and the PACK  2913  is D+1 while data (the payload data included in the packet  1007 ) read from the file access request temporarily-recording table  206  using the POINTER  318  of the TCP/IP connection table  207  as the beginning address is used as the payload. If the initial data transmission server  602 - 1  cannot correctly receive the packet  1011 , the initial data transmission server  602 - 1  transmits a packet  1012  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is D+1, and the PACK  2913  is C+1. Upon receiving the packet  1012 , the communication apparatus  100  transmits a packet  1013  which is the same as the packet  1011  to the initial data transmission server  602 - 1 . If the initial data transmission server  602 - 1  correctly receives the packet  1011  or the packet  1013 , the initial data transmission server  602 - 1  transmits a packet  1014  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is D+1, and the PACK  2913  is C+1+G (the payload lengths of the packets  1007 ,  1011  and  1013 ). Upon receiving the packet  1014 , the communication apparatus  100  changes the TCP state STATE of the TCP/IP connection table  207  into the Burst Open, and transmits a packet  1015  in which the PSEQ  2912  and the PACK  2913  were changed into B+1 and A+1+G, respectively, to the client  603 . Accordingly, the initial data transmission server  602  is ready for broadband transmission of data towards the client  603 . 
     After transmitting the packet  1014 , the initial data transmission server  602 - 1  starts to transmit data corresponding to a threshold value for starting reproduction of the reception buffer. The initial data transmission server  602 - 1  transmits a packet  1016  in which data (length L) is included as the payload, the TCP Flag  2911  is ACK, the PSEQ  2912  is D+1, and the PACK  2913  is C+1+G. Upon receiving the packet  1016 , the communication apparatus  100  changes the S-SEQ  314  and the DC-SEQ  306  of the TCP/IP connection table  207  into D+1+L and B+1L, respectively, and transmits a packet  1017  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is B+1, and the PACK  2913  is A+1+G to the client  603 . Upon receiving the packet  1017 , the client  603  transmits a packet  1019  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is A+1+G, and the PACK  2913  is B+1+L to the communication apparatus  100 . Upon receiving the packet  1019 , the communication apparatus  100  transmits a packet  1018  in which the PSEQ  2912  and the PACK  2913  were changed into C+1+G and D+1+L, respectively, to the initial data transmission server  602 - 1 . Thereafter, the data corresponding to the threshold value for starting reproduction of the reception buffer is continuously transmitted from the initial data transmission server  602 - 1  to the client  603 . Finally, the initial data transmission server  602 - 1  transmits a packet  1020  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is D+1+(n−1)L, and the PACK  2913  is C+1+G to the communication apparatus  100 . Upon receiving the packet  1020 , the communication apparatus  100  changes the S-SEQ  314  and the DC-SEQ  306  of the TCP/IP connection table  207  into D+1+nL and B+1+nL, respectively, and transmits a packet  1021  in which the PSEQ  2912  and the PACK  2913  were changed into B+1+(n−1)L and A+1+G, respectively, to the client  603 . Upon receiving the packet  1021 , the client  603  transmits a packet  1023  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is A+1+G, and the PACK  2913  is B+1+nL to the communication apparatus  100 . Upon receiving the packet  1023 , the communication apparatus  100  transmits a packet  1022  in which the PSEQ  2912  and the PACK  2913  were changed into C+1+G and D+1+nL, respectively, to the initial data transmission server  602 - 1 . Accordingly, transmission of data corresponding to the threshold value for starting reproduction of the reception buffer is completed. 
     Upon receiving the packet  1022 , the initial data transmission server  602 - 1  transmits a packet  1024  in which the TCP Flag  2911  is FIN-ACK, the PSEQ  2912  is D+1+nL, and the PACK  2913  is C+1+G to the communication apparatus  100  for a request of disconnecting the TCP connection. Upon receiving the packet  1024 , the communication apparatus  100  changes the S-SEQ  314  and the DS-SEQ  315  into D+2+nL and C+2+G, respectively, while changing the TCP state STATE of the TCP/IP connection table  207  into the Burst Close Wait via the Burst FIN Receive, and transmits a packet  1025  in which the TCP Flag  2911  is FIN-ACK, the PSEQ  2912  is C+1+G, and the PACK  2913  is D+2+nL to the initial data transmission server  602 - 1 . Upon receiving the packet  1025 , the initial data transmission server  602 - 1  transmits a packet  1026  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is D+2+nL, and the PACK  2913  is C+2+G to the communication apparatus  100 . Accordingly, the TCP connection between the communication apparatus  100  and the initial data transmission server  602 - 1  is disconnected. 
     Upon receiving the packet  1026 , the communication apparatus  100  changes the TCP state STATE, the S-SEQ  314  and the DS-SEQ  315  of the TCP/IP connection table  207  into the Static Request, 0 and E (random value)+1, respectively, and transmits a packet  1027  in which the TCP Flag  2911  is SYN, the PSEQ  2912  is E, and the PACK  2913  is 0 to the subsequent data transmission server  602 - 2  for establishment of the TCP connection with the subsequent data transmission server  602 - 2 . Upon receiving the packet  1027 , the subsequent data transmission server  602 - 2  transmits a packet  1028  in which the TCP Flag  2911  is SYN-ACK, the PSEQ  2912  is F (random value), and the PACK  2913  is E+1. Upon receiving the packet  1028 , the communication apparatus  100  changes the TCP state STATE, the S-SEQ  314 , and the DS-SEQ  315  of the TCP/IP connection table  207  into the Static Half Open, F+1, and E+1+G (the payload length of the packet  1007 ), respectively, and transmits a packet  1029  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is E+1, and the PACK  2913  is F+1 to the subsequent data transmission server  602 - 2 . Accordingly, the TCP connection between the communication apparatus  100  and the subsequent data transmission server  602 - 2  is established. 
     After transmitting the packet  1029 , the communication apparatus  100  transmits, to the subsequent data transmission server  602 - 2 , a packet  1030  in which the TCP Flag  2911  is PSH-ACK, the PSEQ  2912  is E+1, the PACK  2913  is F+1 while data (the payload data included in the packet  1007 ) read from the file access request temporarily-recording table  206  using the POINTER  318  of the TCP/IP connection table  207  as the beginning address is used as the payload. If the subsequent data transmission server  602 - 2  cannot correctly receive the packet  1030 , the subsequent data transmission server  602 - 2  transmits a packet  1031  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is F+1, and the PACK  2913  is E+1. Upon receiving the packet  1031 , the communication apparatus  100  transmits a packet  1032  which is the same as the packet  1030  to the subsequent data transmission server  602 - 2 . If the subsequent data transmission server  602 - 2  correctly receives the packet  1030  or the packet  1032 , the subsequent data transmission server  602 - 2  transmits a packet  1033  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is F+1, and the PACK  2913  is E+1+G. Upon receiving the packet  1033 , the communication apparatus  100  changes the TCP state STATE of the TCP/IP connection table  207  into the Static Open, and transmits a packet  1034  in which the PSEQ  2912  and the PACK  2913  were changed into B+1+nL and A+1+G, respectively, to the client  603 . Accordingly, the subsequent data transmission server  602 - 2  is ready for data transmission in a normal distribution band towards the client  603 . 
     After transmitting the packet  1033 , the subsequent data transmission server  602 - 2  starts to transmit data subsequent to the data transmitted by the initial data transmission server  602 - 1 . The subsequent data transmission server  602 - 2  transmits a packet  1035  in which data (length L) is included as the payload, the TCP Flag  2911  is ACK, the PSEQ  2912  is F+1, and the PACK  2913  is E+1+G. Upon receiving the packet  1035 , the communication apparatus  100  changes the S-SEQ  314  and the DC-SEQ  306  of the TCP/IP connection table  207  into F+1+L and B+1+(n+1)L, respectively, and transmits a packet  1036  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is B+1+nL, and the PACK  2913  is A+1+G to the client  603 . Upon receiving the packet  1036 , the client  603  transmits a packet  1038  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is A+1+G, and the PACK  2913  is B+1+(n+1)L to the communication apparatus  100 . Upon receiving the packet  1038 , the communication apparatus  100  transmits a packet  1037  in which the PSEQ  2912  and the PACK  2913  were changed into E+1+G and F+1+L, respectively, to the subsequent data transmission server  602 - 2 . Thereafter, data is continuously transmitted from the subsequent data transmission server  602 - 2  to the client  603 . Finally, the subsequent data transmission server  602 - 2  transmits a packet  1039  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is F+1+(m−1)L, and the PACK  2913  is E+1+G to the communication apparatus  100 . Upon receiving the packet  1039 , the communication apparatus  100  changes the S-SEQ  314  and the DC-SEQ  306  of the TCP/IP connection table  207  into F+1+mL and B+1+(m+n)L, respectively, and transmits a packet  1040  in which the PSEQ  2912  and the PACK  2913  were changed into B+1+(m+n−1)L and A+1+G, respectively, to the client  603 . Upon receiving the packet  1040 , the client  603  transmits a packet  1041  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is A+1+G, and the PACK  2913  is B+1+(m+n)L to the communication apparatus  100 . Upon receiving the packet  1041 , the communication apparatus  100  transmits a packet  1042  in which the PSEQ  2912  and the PACK  2913  were changed into E+1+G and F+1+mL, respectively, to the subsequent data transmission server  602 - 2 . Accordingly, transmission of data is completed. 
     Finally, the client  603  transmits a packet  1043  in which the TCP Flag  2911  is FIN-ACK, the PSEQ  2912  is A+1+G, and the PACK  2913  is B+1+(m+n)L to the communication apparatus  100 . The communication apparatus  100  changes the DS-SEQ  315 , the DC-SEQ  306 , and the C-SEQ  305  of the TCP/IP connection table  207  into E+2+G, B+2+(m+n)L, A+2+G, respectively, transmits a packet  1044  in which the TCP Flag  2911  is FIN-ACK, the PSEQ  2912  is B+1+(m+n)L, and the PACK  2913  is A+2+G to the client  603 , and transmits a packet  1045  in which the TCP Flag  2911  is FIN-ACK, the PSEQ  2912  is E+1+G, and the PACK  2913  is F+1+mL to the subsequent data transmission server  602 - 2 . Upon receiving the packet  1044 , the client  603  transmits a packet  1046  in which the TCP Flag  2911  is ACK, the PSEQ  2912  is A+2+G, and the PACK  2913  is B+2+(m+n)L to the communication apparatus  100 . Upon receiving the packet  1045 , the subsequent data transmission server  602 - 2  transmits a packet  1047  in which the TCP Flag  2911  is FIN-ACK, the PSEQ  2912  is F+1+mL, and the PACK  2913  is E+2+G to the communication apparatus  100 . Upon receiving the packet  1047 , the communication apparatus  100  changes the S-SEQ  314  of the TCP/IP connection table  207  into F+2+mL, and transmits a packet  1048  in which the PSEQ  2912  and the PACK  2913  were changed into E+2+G and F+2+mL, respectively, to the subsequent data transmission server  602 - 2 . Accordingly, the TCP connection between the client  603  and the communication apparatus  100  and the TCP connection between the communication apparatus  100  and the subsequent data transmission server  602 - 2  are terminated. 
     As described above, the packets are transmitted and received among the communication apparatus  100 , the server  602 , and the client  603  by the HTTP processing unit  210  and the packet generating unit  209 . 
     There is realized a broadband transmission module for reproduction with a device by which through transmission and reception of the packets, data corresponding to a threshold value for starting reproduction of the reception buffer is transmitted from the dedicated server in a broad band immediately after the data reproducing software instructs to reproduce the data, and then, the subsequent data is transmitted from the normal server in a normal distribution band. 
       FIG. 11  shows a source MAC address, a source IP address, a destination MAC address, and a destination IP address of each packet transmitted and received among the communication apparatus  100 , the server  602 , and the client  603 . 
     Between the client  603  and the communication apparatus  100 , communications are performed using a MAC address c and an IP address C of the client  603 , and a MAC address p and an IP address P released by the communication apparatus  100  to the client side. The MAC address and the IP address of each packet transmitted and received between the client  603  and the communication apparatus  100  are shown as a packet  1101  and a packet  1104 . 
     Between the server  602  and the communication apparatus  100 , communications are performed using the MAC address c and the IP address C of the client  603 , and a MAC address s and an IP address S of the server  602 . The MAC address and the IP address of each packet transmitted and received between the server  602  and the communication apparatus  100  are shown as a packet  1102  and a packet  1103 . 
     It should be noted that since it is assumed that the communication apparatus  100  is used in a system where plural servers  602  are present as shown in  FIG. 1 , the packet generating unit  209  is provided with a device for selecting one of the MAC addresses s and the IP addresses S of plural servers  602 . 
       FIG. 12  shows a first example of the device for selecting one of the IP addresses of plural servers  602 . The MAC address is selected by the similar device. 
     The packet generating unit  209  includes a memory  1203  in which an IP address of the initial data transmission server is recorded. When the communication apparatus  100  receives the packet (the packet  1007  of  FIG. 10 ) including a command for requesting a file and transmits the SYN packet (the packet  1008  of  FIG. 10 ) to the initial data transmission server, first letters (8 bits)  1201  of a requested file name are input to the memory  1203  as an input address, and output data is selected as an IP address  1204  of the initial data transmission server. 
     Further, the packet generating unit  209  includes a memory  1207  in which an IP address of the subsequent data transmission server is recorded. When the communication apparatus  100  receives the packet (for example, the packet  1026  of  FIG. 10 ) for terminating the TCP connection with the initial data transmission server and transmits the SYN packet (the packet  1027  of  FIG. 10 ) to the subsequent data transmission server, first letters (8 bits)  1205  of a requested file name recorded in the file access request temporarily-recording table  206  are input to the memory  1207  as an input address, and output data is selected as an IP address  1208  of the subsequent data transmission server. 
       FIG. 13  shows a method of accumulating files in the servers when the IP address and the MAC address of the server are selected using the device shown in  FIG. 12 . 
     In an initial data transmission server  1300 , a file with file name first letters A to M is accumulated, and in an initial data transmission server  1301 , a file with file name first letters N to Z is accumulated. 
     In a subsequent data transmission server  1302 , a file with file name first letters A to D is accumulated. In a subsequent data transmission server  1303 , a file with file name first letters E to I is accumulated. In a subsequent data transmission server  1304 , a file with file name first letters J to N is accumulated. In a subsequent data transmission server  1305 , a file with file name first letters O to R is accumulated. In a subsequent data transmission server  1306 , a file with file name first letters S to V is accumulated. In a subsequent data transmission server  1307 , a file with file name first letters W to Z is accumulated. 
     Although the first letters (8 bits)  1201  of the requested file name are used as an input address in the explanation related to  FIG. 12  and  FIG. 13 , other letters of the requested file name or a letter string representing a directory path of the requested file can be used as an input address to the memory  1203 . 
       FIG. 14  shows a second example of the device for selecting one of the IP addresses of plural servers  602 . The MAC address is selected by the similar device. 
     The packet generating unit  209  includes a hash value generating circuit  1402  and a memory  1403  in which an IP address of the initial data transmission server is recorded. When the communication apparatus  100  receives the packet (the packet  1007  of  FIG. 10 ) including a command for requesting a file and transmits the SYN packet (the packet  1008  of  FIG. 10 ) to the initial data transmission server, information  1401  representing a requested file name, a directory path, or a letter string representing a part thereof is input to the hash value generating circuit  1402 . Further, a hash value output from the hash value generating circuit  1402  is input to the memory  1403 , and output data is selected as an IP address  1404  of the initial data transmission server. 
     Further, the packet generating unit  209  includes a hash value generating circuit  1406  and a memory  1407  in which an IP address of the subsequent data transmission server is recorded. When the communication apparatus  100  receives the packet (for example, the packet  1026  of  FIG. 10 ) for terminating the TCP connection with the initial data transmission server and transmits the SYN packet (the packet  1027  of  FIG. 10 ) to the subsequent data transmission server, information  1405  representing a requested file name, a directory path, or a letter string representing a part thereof is input to the hash value generating circuit  1406 . Further, a hash value output from the hash value generating circuit  1406  is input to the memory  1407 , and output data is selected as an IP address  1408  of the subsequent data transmission server. 
       FIG. 15  shows a method of accumulating files in the servers when the IP address and the MAC address of the server are selected using the device shown in  FIG. 14 . 
     In an initial data transmission server  1500 , a file with a hash value 0 or 1 is accumulated using the device shown in  FIG. 14 , and in an initial data transmission server  1501 , a file with a hash value 2 or 3 is accumulated using the device shown in  FIG. 14 . 
     In a subsequent data transmission server  1502 , a file with a hash value 0 is accumulated using the device shown in  FIG. 14 . In a subsequent data transmission server  1503 , a file with a hash value 1 is accumulated using the device shown in  FIG. 14 . In a subsequent data transmission server  1504 , a file with a hash value 2 is accumulated using the device shown in  FIG. 14 . In a subsequent data transmission server  1505 , a file with a hash value 3 is accumulated using the device shown in  FIG. 14 . 
       FIG. 16  shows a third example of the device for selecting one of the IP addresses of plural servers  602 . The MAC address is selected by the similar device. 
     The packet generating unit  209  includes a memory  1603  in which an IP address of the initial data transmission server is recorded. When the communication apparatus  100  receives the packet (the packet  1007  of  FIG. 10 ) including a command for requesting a file and transmits the SYN packet (the packet  1008  of  FIG. 10 ) to the initial data transmission server, lower 8 bits  1601  of a client IP address are input to the memory  1603  as an input address, and output data is selected as an IP address  1604  of the initial data transmission server. 
     Further, the packet generating unit  209  includes a memory  1607  in which an IP address of the subsequent data transmission server is recorded. When the communication apparatus  100  receives the packet (for example, the packet  1026  of  FIG. 10 ) for terminating the TCP connection with the initial data transmission server and transmits the SYN packet (the packet  1027  of  FIG. 10 ) to the subsequent data transmission server, lower 8 bits  1605  of a client IP address are input to the memory  1607  as an input address, and output data is selected as an IP address  1608  of the subsequent data transmission server. 
     It should be noted that even if the client IP address is used, a selection device for IP addresses similar to that explained in relation to  FIG. 14  and  FIG. 15  can be realized. The client IP address or a part thereof is input into the hash value generating circuit  1402 , a hash value output from the hash value generating circuit is input into the memory  1403  in which an IP address of the initial data transmission server is recorded, and output data is selected as an IP address of the initial data transmission server. Further, the client IP address, or a part thereof is input into the hash value generating circuit  1402 , a hash value output from the hash value generating circuit is input into the memory  1407  in which an IP address of the subsequent data transmission server is recorded, and output data is selected as an IP address of the subsequent data transmission server. 
       FIG. 17  shows a fourth example of the device for selecting one of the IP addresses of plural servers  602 . The MAC address is selected by the similar device. 
     The packet generating unit  209  includes a server load table  1701  containing n entries each of which records an IP address of an initial data transmission server and the number of TCP connections with the server, and a heap circuit  1702  which repeatedly performs an operation in which the numbers of TCP connections of adjacent entries are compared to each other to extract the entry with the smaller number and extracts the entry with the smallest number of the TCP connections. When receiving the packet (the packet  1007  of  FIG. 10 ) including a command for requesting a file and transmitting the SYN packet (the packet  1008  of  FIG. 10 ) to the initial data transmission server, the entry with the smallest number of TCP connections is extracted from the heap circuit  1702 , and the IP address described in the entry is selected as an IP address of the initial data transmission server. After extraction, the number of TCP connections described in the entry is incremented and the heap circuit is updated ( 1703 ). 
     Further, the packet generating unit  209  includes a server load table  1704  containing n entries each of which records an IP address of a subsequent data transmission server and the number of TCP connections with the server, and a heap circuit  1705  which repeatedly performs an operation in which the numbers of TCP connections of adjacent entries are compared to each other to extract the entry with the smaller number and extracts the entry with the smallest number of the TCP connections. When receiving the packet (the packet  1026  of  FIG. 10 ) including a command for requesting a file and transmitting the SYN packet (the packet  1027  of  FIG. 10 ) to the initial data transmission server, the entry with the smallest number of TCP connections is extracted from the heap circuit  1705 , and the IP address described in the entry is selected as an IP address of the subsequent data transmission server. After extraction, the number of TCP connections described in the entry is incremented and the heap circuit is updated ( 1706 ). 
       FIG. 18  shows a method of accumulating files in the servers when the IP address and the MAC address of the server are selected using the device shown in  FIG. 16  or  FIG. 17 . 
     All servers of initial data transmission servers  1800 - 1  and  1800 - 2  and subsequent data transmission server  1800 - 3  and  1800 - 4  accumulate the same file. 
     As a fifth example of the device for selecting one of the IP addresses of plural servers  602 , a server to be accessed may be selected in accordance with the content of a command. This method is used together with a system including an initial data transmission server  1902  and a fast-forward data transmission server  1903  as shown in, for example,  FIG. 19 . 
     When the communication apparatus  100  receives the packet (the packet  1007  of  FIG. 10 ) including a command for requesting a file and transmits the SYN packet (the packet  1008  of  FIG. 10 ) to the initial data transmission server, the IP address of the initial data transmission server  1902  is selected when the content of the command is a normal file access request, and the IP address of the fast-forward data transmission server  1903  is selected when the content of the command is a digest data request. 
     By using the server selecting methods shown in  FIG. 12  and  FIG. 14  and the file accumulating methods shown in  FIG. 13  and  FIG. 15 , a file dispersion access module (a module for sorting a distribution request from a client into a server storing the file corresponding to the distribution request) can be realized. Further, by using the server selecting methods shown in  FIG. 16  and  FIG. 17  and the file accumulating method shown in  FIG. 18 , a load balancing module (a module for dispersing a distribution request from a client among plural servers accumulating the same file) can be realized. 
     Accordingly, it is possible to provide a communication apparatus which is provided with a server arraying module including the load balancing module (a module for dispersing a distribution request from a client among plural servers accumulating the same file) and the file dispersion access module (a module for sorting a distribution request from a client into a server storing the file corresponding to the distribution request) and which includes a device for integrating resources (CPUs, I/Os, and storages) of servers into one, and a VOD distribution system including the communication apparatus and plural servers. 
       FIG. 20  shows an example of an extended system in which a transmission band for one connection is set for each server. Transmission bands for each one connection of servers  2000 ,  2001 ,  2002 , and  2003  are set to Bn (n=1 to 4). Usage of the system enables changing of the transmission band in accordance with file types. 
       FIG. 21  shows an example of an extended system in which a buffer amount assigned is changed or preferential transfer is controlled on the transmission apparatus side in accordance with the type of a server connected to communication apparatus. A communication apparatus  2101  includes a buffer amount preferentially-assigning module for preferentially accumulating a packet transmitted by the initial data transmission server into a buffer and a preferential transfer module for preferentially transferring a packet transmitted by the initial data transmission server. Usage of the system improves the quality of communications immediately after a file access request. 
       FIG. 22  shows an extended system in which a UDP is used instead of a TCP. When receiving a file access request from a client, a communication apparatus  2201  transmits the file access request to an initial data transmission server  2202 , and transmits the file access request to a subsequent data transmission server  2203  after waiting for a specified time (time specified using a value obtained by dividing the data size corresponding a threshold value for starting reproduction of the reception buffer by the normal communication band of the subsequent data transmission server). Upon receiving a request  2218 , an initial data transmission server  2202  distributes data corresponding to the reception buffer. When receiving a request  2219 , a subsequent data transmission server  2203  distributes subsequent data. Usage of the system enables data distribution using a UDP. 
       FIG. 30  shows a sequence diagram using a UDP. 
     Until data transmission is started, the communication connection is established using a TCP (the packets  1004  to  1015 ). When the communication connection with the initial data transmission server is established, initial data is transmitted from the initial data transmission server using a UDP (the packets  3016  to  3023 ). When the transmission of the initial data is completed, the communication connection with the initial data transmission server is disconnected using a TOP, and the communication connection with the subsequent data transmission server is newly established (the packets  1024  to  1034 ). When the communication connection with the subsequent data transmission server is established, subsequent data is transmitted from the subsequent data transmission server using a UDP (the packets  3035  to  3042 ). When the transmission of the subsequent data is completed, the communication connection with the subsequent data transmission server is disconnected using a TCP (the packets  1043  to  1048 ).