Abstract:
A technique for easily realizing data communication without limiting the application layer protocol during data communication while maintaining the proxy function. A mobile communication terminal ( 2 ) includes a control protocol processing section ( 203 ) which transmits an address request to a proxy device ( 5 ) to acquire global address information using the HTTP that is preset so as to be used by the mobile communication terminal ( 2 ) and the proxy device ( 5 ), a TCP/UDP data transmitter/receiver section ( 205 ) which establishes a connection with the proxy device ( 5 ), and an application section ( 201 ) which transmits data via a communication path between the proxy device ( 5 ) and a server device ( 6 ) using the global address information as the transmitter address. The control protocol processing section ( 203 ) transmits information relating to the connection destination of the server device ( 6 ) to the proxy device ( 5 ) using the HTTP, and requests a connection between the proxy device ( 5 ) and the server device ( 6 ) using a predetermined transport layer protocol.

Description:
TECHNICAL FIELD 
     The present invention relates to a data communication terminal, a proxy device, a data communication system, and a data communication method. 
     BACKGROUND ART 
     In data communication using the Internet, etc., when an internal network, such as a specific carrier&#39;s data communication network or a corporate intranet, is connected to the Internet, in order to ensure high-speed access and the safety of communication, a proxy server is conventionally used. For such a proxy server, an HTTP (Hypertext Transfer Protocol) proxy, an FTP (File Transfer Protocol) proxy, etc., where an application layer protocol usable between a terminal and its communication destination is limited are widely used. 
     On the other hand, a data communication device is known that implements data communication using a plurality of application layer protocols (see the following Patent Document 1). The data communication device has the function of allowing, when receiving a SIP (Session Initiation Protocol) message from a client that includes protocol information, the client to perform data communication by a corresponding protocol. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Document 1: Japanese Patent Application Laid-Open No. 2007-201688 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in the above-described conventional proxy device, there is a tendency that an application layer protocol usable by a terminal is limited, and accepting a plurality of application layer protocols requires replacement of the proxy device or an extensive addition of functions. Meanwhile, it is also considered that data communication is directly performed between a terminal and its communication destination without passing through the proxy device. However, since the proxy device also has the function of translation between a private address and a global address, inconveniences such as global address exhaustion may occur and a problem of deterioration in the safety of communication also occurs. 
     The present invention is made in view of such problems, and an object of the present invention is therefore to provide a data communication terminal, a proxy device, a data communication system, and a data communication method which are capable of easily implementing data communication where an application layer protocol used upon data communication is not limited, while a proxy function is maintained. 
     Solution to Problem 
     To solve the above-described problems, a data communication terminal of the present invention performs data communication with a communication destination device through a proxy device in a data communication network, using a predetermined transport layer protocol, and comprises: address getting means for transmitting an address request to the proxy device using an application layer protocol, to get global address information which is used when establishing a connection with the communication destination device by the predetermined transport layer protocol, the application layer protocol being set to be usable in advance between the proxy device and the data communication terminal; connection establishing means for establishing a connection with the proxy device by the predetermined transport layer protocol; connection requesting means for transmitting connection destination information of the communication destination device to the proxy device using the application layer protocol, to request for a connection by the predetermined transport layer protocol between the proxy device and the communication destination device; and data communication means for transmitting data over a communication channel connected by the connection establishing means and the connection requesting means, via a communication channel established by the connection establishing means, using the global address information as a source address in data of an application layer. 
     Alternatively, a proxy device of the present invention is set up in a data communication network and relays data communication between a data communication terminal and a communication destination device using a predetermined transport layer protocol, and comprises: address assigning means for receiving an address request using an application layer protocol from the data communication terminal, and assigning global address information to the data communication terminal and transmitting the global address information to the data communication terminal, the application layer protocol being set to be usable in advance between the data communication terminal and the proxy device and the global address information being used when establishing a connection with the communication destination device by the predetermined transport layer protocol; connection establishing means for receiving connection destination information of the communication destination device from the data communication terminal using the application layer protocol, and establishing a connection with the communication destination device by the predetermined transport layer protocol; and data transferring means for setting the global address information as a source and thereafter transferring data received from the data communication terminal on the predetermined transport layer protocol to the communication destination device, using a communication channel connected by the connection establishing means. 
     In addition, a data communication system of the present invention comprises the above-described data communication terminal and proxy device. 
     In addition, a data communication method of the present invention performs data communication from a data communication terminal to a communication destination device via a proxy device in a data communication network, using a predetermined transport layer protocol, and comprises: an address getting step of transmitting, by the data communication terminal, an address request to the proxy device using an application layer protocol, to get from the proxy device global address information which is used when establishing a connection with the communication destination device by the predetermined transport layer protocol, the application layer protocol being set to be usable in advance between the proxy device and the data communication terminal; a first connection establishing step of establishing, by the data communication terminal, a connection with the proxy device by the predetermined transport layer protocol; a second connection establishing step of receiving, by the proxy device, connection destination information of the communication destination device from the data communication terminal and establishing a connection with the communication destination device by the predetermined transport layer protocol; a data communication step of transmitting, by the data communication terminal, data over a communication channel connected in the first connection establishing step, via the proxy device using the global address information as a source address in data of an application layer; and a data transferring step of setting, by the proxy device, the global address information as a source and thereafter transferring the data received from the data communication terminal in the data communication step to the communication destination device, using a communication channel connected in the second connection establishing step. 
     According to such a data communication terminal, a proxy device, a data communication system, and a data communication method, the data communication terminal obtains global address information which is used when establishing a connection with an external network, from the proxy device using an application layer protocol made usable in advance such as HTTP, and the data communication terminal is connected to the proxy device by a predetermined transport layer protocol such as TCP (Transmission Control Protocol) or UDP (User Datagram Protocol). Note that the “proxy device” as referred to here is a device having a role in terminating, when transferring data between the data communication terminal and its communication destination, a transport layer with the data communication terminal and its communication destination. Then, the data communication terminal passes connection information of a communication destination device to the proxy device using the application layer protocol, and the proxy device and the communication destination device are connected by a predetermined transport layer protocol. Data transmitted from the data communication terminal to the proxy device is transmitted to the communication destination device via the proxy device such that the global address information assigned to the data communication terminal is set as a source. Thereby, even if an application layer protocol made usable in advance in a data communication network is limited, data transfer using any application layer protocol is easily implemented via the proxy device. Namely, unlike NAT (Network Address Translation) technology that performs transparent transfer of packets by simply translating an IP address and a port number into preset ones, since an application program on the data communication terminal side can obtain global address information which is assigned to the terminal in a network outside the proxy device, any application program can perform data communication on a predetermined transport layer protocol. Furthermore, since the existing proxy function is also maintained, global addresses can be conserved and the safety of communication can also be maintained. 
     Advantageous Effects of Invention 
     According to the present invention, data communication can be easily implemented where an application layer protocol used upon data communication is not limited, while a proxy function is maintained. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration diagram of a data communication system according to a first embodiment of the present invention. 
         FIG. 2  is a hardware configuration diagram of a mobile communication terminal in  FIG. 1 . 
         FIG. 3  is a hardware configuration diagram of a proxy device in  FIG. 1 . 
         FIG. 4  is a functional block diagram showing functional configurations of the mobile communication terminal and the proxy device in  FIG. 1 . 
         FIG. 5  is a diagram showing a data configuration of a port management table in  FIG. 4 . 
         FIG. 6  is a diagram showing a schematic configuration of data at the transport layer protocol level which is transferred by a TCP/UDP data relaying section in  FIG. 4 . 
         FIG. 7  is a sequence diagram showing the operation of the data communication system in  FIG. 1 . 
         FIG. 8  is a diagram showing an image of communication channels which are connected in the data communication system according to the operation in  FIG. 7 . 
         FIG. 9  is a diagram showing protocol stacks in the data communication system in  FIG. 1 . 
         FIG. 10  is a schematic configuration diagram of a data communication system according to a second embodiment of the present invention. 
         FIG. 11  is a functional block diagram showing functional configurations of a mobile communication terminal and a proxy device in  FIG. 10 . 
         FIG. 12  is a diagram showing a data configuration of a matching address management table in  FIG. 11 . 
         FIG. 13  is a sequence diagram showing the operation of the data communication system in  FIG. 10 . 
         FIG. 14  is a diagram showing an image of communication channels which are connected in the data communication system according to the operation in  FIG. 13 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Preferred embodiments of a data communication terminal, a proxy device, a data communication system, and a data communication method by the present invention will be described in detail below with the drawings. Note that in description of the drawings the same elements are denoted by the same reference numerals and overlapping description is omitted. 
     [First Embodiment] 
       FIG. 1  is a schematic configuration diagram of a data communication system  1  according to a first embodiment of the present invention. As shown in  FIG. 1 , the data communication system  1  according to the present embodiment is configured to include a mobile communication terminal (data communication terminal)  2  used by a user who attempts to transmit and receive data; an exchange  4  and a proxy device  5  which are provided in a mobile communication network NW 1 ; and server devices (communication destination devices)  6  which are connected to an Internet network NW 2  and managed by content providers, etc. The data communication system  1  is a communication system that implements data communication between the mobile communication terminal  2  and the server devices  6  in a data communication network including the mobile communication network NW 1  and the Internet network NW 2 . 
     The mobile communication terminal  2  included in the data communication system  1  is connected to the proxy device  5  in the mobile communication network NW 1  via a radio base station  3  and the exchange  4  at a transport layer protocol level, using wireless communication. Here, when the mobile communication terminal  2  communicates with the proxy device  5  at the transport layer protocol level, the mobile communication terminal  2  uses a local IP address and port number which are assigned in advance. 
     The proxy device  5  is allowed to be simultaneously connected to the mobile communication network NW 1  and the Internet network NW 2  at the transport layer protocol level, and relays data transmitted from the mobile communication terminal  2 , to a server device  6  via the Internet network NW 2  and relays data received from the server device  6  via the Internet network NW 2  to the mobile communication terminal  2 . Namely, the proxy device  5  terminates the connection with the mobile communication terminal  2  and the connection with the server device  6  at the transport layer protocol level. The proxy device  5  has a proxy function for ensuring the safety of data communication and preventing a shortage of global IP addresses. When the proxy device  5  communicates with the mobile communication terminal  2  on the side of the mobile communication network NW 1 , they mutually use private IP addresses and port numbers. When the proxy device  5  communicates with the server devices  6  on the side of the Internet network NW 2 , they mutually use global IP addresses and port numbers. Note that the proxy device  5  is set in advance such that, when the proxy device  5  directly transmits and receives control signals to/from the mobile communication terminal  2 , only a specific application layer protocol such as HTTP is usable. 
       FIG. 2  is a hardware configuration diagram of the mobile communication terminal  2 . The mobile communication terminal  2  is physically configured as a terminal device that includes, as shown in the figure, a CPU  21 ; a RAM  22  and a ROM  23  which are main storage units; an auxiliary storage unit  25  such as a hard disk device; an input unit  26  which is an input device, such as input keys; an output unit  27  such as a display; a wireless communication module  24  including a wireless transceiver, etc.; and the like. The wireless communication module  24  is a module that performs wireless communication using a mobile communication system, and implements a data communication function with any terminal device and server device in cooperation with the CPU  21 , the RAM  22 , the ROM  23 , etc. Each of the functions of the mobile communication terminal  2  which will be described later is implemented by loading predetermined software onto hardware such as the CPU  21  and the RAM  22  to allow the wireless communication module  24 , the input unit  26 , and the output unit  27  to operate under control of the CPU  21 , and to perform reading and writing of data in the RAM  22  and the auxiliary storage unit  25 . 
       FIG. 3  is a hardware configuration diagram of the proxy device  5 . The proxy device  5  is physically configured as a server device that includes, as shown in the figure, a CPU  51 ; a RAM  52  and a ROM  53  which are main storage units; an auxiliary storage unit  55  such as a hard disk device; an input unit  56  which is an input device, such as input keys; an output unit  57  such as a display; a communication module  54  including a network card, etc.; and the like. The communication module  54  is a module that performs data communication with the mobile communication network NW 1  and the Internet network NW 2 , and implements a data communication function with any terminal device and server device in cooperation with the CPU  51 , the RAM  52 , the ROM  53 , etc. Each of the functions of the proxy device  5  which will be described later is implemented by loading predetermined software onto hardware such as the CPU  51  and the RAM  52  to allow the wireless communication module  54 , the input unit  56 , and the output unit  57  to operate under control of the CPU  51 , and to perform reading and writing of data in the RAM  52  and the auxiliary storage unit  55 . 
     The functional configurations of the mobile communication terminal  2  and the proxy device  5  will be described in detail below. 
     As shown in  FIG. 4 , the mobile communication terminal  2  includes an application section (data communication means)  201 , a communication interface section  202 , a control protocol processing section (address getting means and connection requesting means)  203 , a port/connection managing section  204 , and a TCP/UDP data transmitting and receiving section (connection establishing means)  205 . 
     The application section  201  transmits and receives data to/from the server devices  6  and other mobile communication terminals, using an application layer protocol such as HTTP, FTP, or SIP. The application section  201  corresponds, for example, to a Web browser or an IP phone application program. Furthermore, the application section  201  can also request for a connection with a server device  6  by a predetermined transport layer protocol such as TCP/IP or UDP/IP, in response to a request from a user. In that case, the application section  201  performs transmission and reception of data via the proxy device  5  over a TCP/IP or UDP/IP communication channel that connects the mobile communication terminal  2  to the server device  6 , using, as a source address, a global IP address and port number which are assigned by the proxy device  5  and using any application layer protocol. 
     The communication interface section  202  is a portion that performs an interface function between the application section  201  and the TCP/UDP data transmitting and receiving section  205 . Specifically, the communication interface section  202  adds a data header used in the transport layer protocol to data at the application layer protocol level transmitted from the application section  201  and passes the resulting data to the TCP/UDP data transmitting and receiving section  205 , and extracts data at the application layer protocol level from data at the transport layer protocol level received by the TCP/UDP data transmitting and receiving section  205  and passes the extracted data to the application section  201 . 
     The control protocol processing section  203  transmits and receives various control signals to/from the proxy device  5 , using HTTP which is an application layer protocol made usable in advance with respect to the proxy device  5 , when the application section  201  requests for a connection by a predetermined transport layer protocol such as TCP/IP or UDP/IP. Specifically, the control protocol processing section  203  transmits an address request signal using HTTP to the proxy device  5 , gets a global IP address and port number (global address information) which are assigned by the proxy device  5  in response to the address request signal, and a connection ID and registers the gotten global IP address, port number, and connection ID in the port/connection managing section  204  and passes over the gotten global IP address, port number, and connection ID to the application section  201 . The global IP address and port number are an address used when establishing a TCP/IP or UDP/IP connection with the server device  6 , and are managed by the proxy device  5  in advance. 
     In addition, after the control protocol processing section  203  gets the global IP address and port number, the control protocol processing section  203  transmits, using HTTP, a connection request signal requesting for a TCP/IP or UDP/IP connection with the server device  6 , to the proxy device  5 . At this time, the control protocol processing section  203  transmits, using HTTP, a global IP address and port number (connection destination information) of the server device  6  which is a communication destination of the application section  201 , to the proxy device  5 . The connection destination information of the server device  6  is stored in the port/connection managing section  204  by the user inputting or selecting the information in advance. 
     The TCP/UDP data transmitting and receiving section  205  is a portion that terminates data communication at the TCP/IP or UDP/IP transport layer protocol level, with the proxy device  5 . The TCP/UDP data transmitting and receiving section  205  also performs the process of establishing a connection for a TCP/IP or UDP/IP communication session with the proxy device  5 , after the control protocol processing section  203  gets a global IP address and port number from the proxy device  5 . At this time, the TCP/UDP data transmitting and receiving section  205  uses a private IP address and port number assigned in advance between the proxy device  5  and the mobile communication terminal  2 . Furthermore, when data communication by the application section  201  is completed, the TCP/UDP data transmitting and receiving section  205  releases the communication session with the proxy device  5 . 
     The proxy device  5  includes a TCP/UDP data transmitting and receiving section (connection establishing means)  501 , a port/connection managing section (address assigning means)  502 , a control protocol processing section  503 , a TCP/UDP data relaying section (data transferring means)  504 , a billing packet count processing section  505 , and a port management table (routing information storage means)  506 . 
     The TCP/UDP data transmitting and receiving section  501  terminates data communication at the TCP/IP or UDP/IP transport layer protocol level, with both the mobile communication terminal  2  and the server device  6 . In addition, when the TCP/UDP data transmitting and receiving section  501  receives a connection request signal including connection destination information of the server device  6  from the mobile communication terminal  2 , the TCP/UDP data transmitting and receiving section  501  establishes a connection for a TCP/IP or UDP/IP communication session with the server device  6 . At this time, the TCP/UDP data transmitting and receiving section  501  uses, for communication with the mobile communication terminal  2 , a private IP address and port number which are assigned in advance, and uses, for communication with the server device  6 , a global IP address and port number which are assigned to the mobile communication terminal  2  by the port/connection managing section  502 . Furthermore, when a communication session is released by the mobile communication terminal  2 , the TCP/UDP data transmitting and receiving section  205  releases the communication session with the server device  6 . 
     The port/connection managing section  502  assigns a global IP address and port number to the mobile communication terminal  2  when receiving an address request signal requesting for global address information from the mobile communication terminal  2 , and returns the assigned global IP address and port number to the mobile communication terminal  2  via the control protocol processing section  503 . At this time, the port/connection managing section  502  allocates a connection ID for managing the assigned global IP address and port number in an association manner, and returns the connection ID to the mobile communication terminal  2  and stores the global IP address and port number and the connection ID in the port management table  506  in an association manner. 
       FIG. 5  shows routing table information stored in the port management table  506  in the above-described manner. As shown in the figure, the local (private) IP address “10.XXX.XX.1” and the local (private) port number “1100” which correspond to a connection destination communication port on the side of the mobile communication terminal  2 , the used protocol “TCP”, the assigned global IP address “15.XXX.XX.1”, and the assigned port number “2004” are stored to be associated with the connection ID “25”. By this routing table information, a communication session at the transport layer level between the mobile communication terminal  2  and the server device  6  is managed. The “own node port on the mobile device side” in the routing table information indicates a port number corresponding to a communication port of the proxy device  5  that is connected to the mobile communication terminal  2 , the “own node port on the server side” indicates a port number corresponding to a communication port that is connected to the server device  6 , and the “connection destination IP address” and the “connection destination port” indicate connection destination information of the server device  6  notified from the mobile communication terminal  2 . 
     Referring back to  FIG. 4 , the control protocol processing section  503  transmits and receives various control signals by HTTP to/from the mobile communication terminal  2  via the TCP/UDP data transmitting and receiving section  501 . Specifically, when an address request signal is received from the mobile communication terminal  2 , the control protocol processing section  503  notifies the port/connection managing section  502  of the address request signal, and returns a response signal including a global IP address, a port number, and a connection ID which are assigned by the port/connection managing section  502  in response to the address request signal, to the mobile communication terminal  2 . In addition, when the control protocol processing section  503  receives a connection request signal including connection destination information of the server device  6  from the mobile communication terminal  2 , the control protocol processing section  503  notifies the TCP/UDP data transmitting and receiving section  501  of the connection request signal. When, in response to the connection request signal, a communication session with the server device  6  is established by the TCP/UDP data transmitting and receiving section  501 , the control protocol processing section  503  returns a response signal to the mobile communication terminal  2 . 
     The TCP/UDP data relaying section  504  relays data to be transmitted and received between the mobile communication terminal  2  and the server device  6 , at the transport layer protocol level after a TCP/IP communication session or a UDP/IP communication session with the server device  6  is established by the TCP/UDP data transmitting and receiving section  501 . Specifically, the TCP/UDP data relaying section  504  sets a source address in a TCP header or a UDP header of data received from the mobile communication terminal  2  by replacing the source address with the global address information which is assigned to the mobile communication terminal  2 , and transfers the data to the server device  6  using a communication channel that connects the proxy device  5  to the server device  6 . 
       FIG. 6  shows schematic configurations of data at the transport layer protocol level which is transferred by the TCP/UDP data relaying section  504 . As shown in the figure, the TCP/UDP data relaying section  504  receives data whose destination IP and destination port are set to a local IP address and a local port number of the proxy device  5 , from a communication port to which a source IP and a source port on the side of the mobile communication terminal  2  are assigned ( FIG. 6(   a )). Then, the TCP/UDP data relaying section  504  extracts, by referring to the routing table information stored in the port management table  506 , a record of the routing table information that matches a source IP and a source port in a header of the received data. The TCP/UDP data relaying section  504  then reads a connection destination IP address and a connection destination port (see  FIG. 5)  in the extracted record and embeds the connection destination IP address and the connection destination port in the destination IP and the destination port in the data received from the mobile communication terminal  2 . The TCP/UDP data relaying section  504  further replaces the source IP and the source port in the data in which the connection destination IP address and the connection destination port are embedded, with a global IP address and a global port number which are assigned to the mobile communication terminal  2  ( FIG. 6(   b )). Then, the TCP/UDP data relaying section  504  outputs the data whose header portion is thus transformed, to a communication port that is connected on the side of the server device  6  as one for data communication of the mobile communication terminal  2 , via the TCP/UDP data transmitting and receiving section  501  and thereby transfers the data to the server device  6 . 
     Likewise, when the TCP/UDP data relaying section  504  receives data destined for a global IP address and a global port number which are assigned to the mobile communication terminal  2  from the server device  6 , the TCP/UDP data relaying section  504  transforms a header portion of the data and transfers the data through a local communication port on the side of the mobile communication terminal  2 . 
     Referring back to  FIG. 4 , the billing packet count processing section  505  monitors control signals transmitted and received from/by the control protocol processing section  503  and data relayed by the TCP/UDP data relaying section  504 , to count the amount of such data and performs an adding-up process and a charging data generation process for billing targeted for the mobile communication terminal  2 . 
     The server device  6  is configured to include application sections  601   a  and  601   b  and a TCP/UDP data transmitting and receiving section  602 . The application sections  601   a  and  601   b  are a Web server program, a data processing program, etc., and transmit and receive data to/from the mobile communication terminal  2 , using an application layer protocol. The TCP/UDP data transmitting and receiving section  602  is a portion that terminates data communication at the TCP/IP or UDP/IP transport layer protocol level, with the proxy device  5 . 
     Next, with reference to  FIGS. 7 and 8 , the operation of the data communication system  1  will be described, together with which a data communication method performed by the data communication system  1  will be described in detail.  FIG. 7  is a sequence diagram showing the operation of the data communication system  1  and  FIG. 8  is a diagram showing an image of communication channels which are connected in the data communication system  1  according to the operation in  FIG. 7 . 
     First, when the application section  201  of the mobile communication terminal  2  requests for a TCP/IP or UDP/IP connection with the server device  6 , the port/connection managing section  204  reserves a local communication port P 21  of the mobile communication terminal  2  for a connection with the proxy device  5  (step S 01 ). Then, the control protocol processing section  203  transmits an address request to the proxy device  5  via a communication channel L 11  where HTTP is set to be usable in advance between the mobile communication terminal  2  and the proxy device  5  (step S 02 ). 
     In response to this, the port/connection managing section  502  of the proxy device  5  assigns a global IP address, port number and a connection ID for the mobile communication terminal  2  and adds a record to the routing table information in the port management table  506 . At the same time, a global communication port P 51  for a connection with a server device  6  having the assigned global IP address and port number is reserved (step S 03 ). When the global communication port P 51  is reserved, the control protocol processing section  503  transmits a response signal to the mobile communication terminal  2  (step S 04 ). 
     Thereafter, the TCP/UDP data transmitting and receiving section  205  of the mobile communication terminal  2  establishes a communication channel L 12  by TCP/IP communication or UDP/IP communication, between the local communication port P 21  and a local communication port P 52  which is set in advance in the proxy device  5  (step S 05 ). Here, in the case of UDP/IP communication, the logical communication channel L 12 , i.e., a virtual path, is established. Furthermore, the control protocol processing section  203  transmits to the proxy device  5  a connection request signal including connection destination information of the server device  6 , using HTTP (step S 06 ). 
     In response to this, the TCP/UDP data transmitting and receiving section  501  of the proxy device  5  establishes a communication channel L 21  by TCP/IP communication or UDP/IP communication, between the global communication port P 51  and a global communication port P 61  of the server device  6  for a connection with the proxy device  5  (step S 07 ). Likewise, in the case of UDP/IP communication, the communication channel L 12  is a logical communication channel. When the communication channel L 21  is established, the TCP/UDP data transmitting and receiving section  501  of the proxy device  5  returns a response signal to the mobile communication terminal  2  (step S 08 ). 
     Thereafter, the TCP/UDP data relaying section  504  of the proxy device  5  relays data transmitted and received between the application section  201  of the mobile communication terminal  2  and the application sections  601   a  and  601   b  of the server device  6 , while referring to the routing table information (step S 09 ). Furthermore, when the application section  201  of the mobile communication terminal  2  requests to terminate the data communication, the communication channels L 12  and L 21  are released and a corresponding record is deleted from the routing table information in the proxy device  5  (step S 10 ). 
     According to the above-described data communication system  1  and data communication method using the data communication system  1 , the mobile communication terminal  2  gets global address information from the proxy device  5  using HTTP which is an application layer protocol made usable in advance, and the mobile communication terminal  2  and the proxy device  5  are connected by a predetermined transport layer protocol such as TCP or UDP. Then, the mobile communication terminal  2  passes connection destination information of the server device  6  to the proxy device  5  using HTTP, and the proxy device  5  and the server device  6  are connected by a predetermined transport layer protocol ( FIG. 9 ). Data transmitted from the mobile communication terminal  2  to the proxy device  5  is transmitted to the server device  6  via the proxy device  5  such that the global address information assigned to the mobile communication terminal  2  is set as a source. 
     By this, even if an application layer protocol made usable in advance in a data communication network is limited, data transfer using any application layer protocol is easily implemented via the proxy device  5 . Namely, unlike simple NAT technology, since an application program on the side of the mobile communication terminal  2  can obtain global address information which is assigned to the mobile communication terminal  2  in a network outside the proxy device  5 , any application program can perform data communication on a predetermined transport layer protocol. For example, even if the protocol is one (SIP, etc.) that operates such that an IP address is embedded in data of an application layer, by obtaining and embedding this global IP address, the protocol can operate normally. 
     Furthermore, since the existing proxy function is also maintained and data is exchanged through the proxy function, the safety of data communication in the terminal can be maintained. In addition, while data communication on any application layer protocol using TCP or UDP is enabled, global IP addresses assigned to the mobile communication terminal  2  can be conserved. 
     [Second Embodiment] 
       FIG. 10  is a schematic configuration diagram of a data communication system  101  according to a second embodiment of the present invention. As shown in the figure, in the data communication system  101  according to the present embodiment, separately from a mobile communication terminal  2 , a mobile communication terminal  2 A serving as a connection partner of the mobile communication terminal  2  in data communication is provided to be connectable to a mobile communication network NW 3 , and a radio base station  3 A, an exchange  4 A, and a proxy device  5 A are provided in the mobile communication network NW 3 . Furthermore, a matching server device  6 A for address information exchange which is managed by a content provider, etc., is connected to an Internet network NW 2 . 
     The mobile communication terminal  2 A has the same functions as the mobile communication terminal  2 , and is allowed to be connected to the proxy device  5 A via the radio base station  3 A and the exchange  4 A at the transport layer protocol level. The proxy device  5 A has the same functions as a proxy device  5 , and is allowed to be simultaneously connected to the mobile communication network NW 3  and the Internet network NW 2  at the transport layer protocol level. 
       FIG. 11  is a block diagram showing a functional configuration of the data communication system  101 . The functional configurations of the mobile communication terminal  2  and the proxy device  5  are the same as those in the first embodiment. 
     As shown in the figure, the matching server device  6 A includes a TCP/UDP data transmitting and receiving section  603 , a data processing section  604 , a matching information processing section  605 , and a matching address management table  606 . The TCP/UDP data transmitting and receiving section  603  is a portion that terminates data communication at the transport layer protocol level, with the proxy devices  5  and  5 A. The data processing section  604  extracts data at the application layer protocol level from data transmitted from the proxy devices  5  and  5 A via the TCP/UDP data transmitting and receiving section  603 , and outputs data at the application layer protocol level to be transmitted to the proxy devices  5  and  5 A, to the TCP/UDP data transmitting and receiving section  603  and thereby transmits the data to the proxy devices  5  and  5 A. 
     The matching information processing section  605  transmits and receives global address information such as global IP addresses and port numbers which are assigned to the mobile communication terminals  2  and  2 A, using an application layer protocol, such as HTTP, which is made usable in advance between the mobile communication terminals  2  and  2 A and the matching server device  6 A. Specifically, while the matching information processing section  605  stores in the matching address management table  606  pieces of global address information which are received from the mobile communication terminals  2  and  2 A via the TCP/UDP data transmitting and receiving section  603  and the data processing section  604 , the matching information processing section  605  transmits pieces of each other&#39;s global address information which have a match in terms of a communication partner and which are read from the matching address management table  606 , to the mobile communication terminals  2  and  2 A via the data processing section  604  and the TCP/UDP data transmitting and receiving section  603 .  FIG. 12  shows data configuration of global address information stored in the matching address management table  606  in the above-described manner. As shown in the figure, the IP address “15.XXX.XX.1” and the port number “2004” which are global address information received from the mobile communication terminal  2  are stored to be associated with the ID “1” which identifies the mobile communication terminal  2  and the ID “2” which identifies the connection partner of the mobile communication terminal  2 . 
     With reference to  FIGS. 13 and 14 , the operation of the data communication system  101  will be described below.  FIG. 13  is a sequence diagram showing the operation of the data communication system  101  and  FIG. 14  is a diagram showing an image of communication channels which are connected in the data communication system  1  according to the operation in  FIG. 13 . 
     First, when TCP/IP or UDP/IP data communication with the mobile communication terminal  2 A starts, the mobile communication terminal  2  which functions as a client gets a global IP address and a global port number from the proxy device  5  by performing the same operations as those at steps S 01  to S 04  described with reference to FIG.  7  (steps S 21  to S 24 ). In parallel with this, the mobile communication terminal  2 A which functions as a server when connected to the mobile communication terminal  2  gets a global IP address and a global port number from the proxy device  5 A (steps S 25  to S 28 ). 
     Thereafter, the global IP address and the global port number which are gotten by the mobile communication terminal  2  are transmitted to the matching server device  6 A from the mobile communication terminal  2  via an HTTP communication channel L 13  which is established in advance between the mobile communication terminal  2  and the matching server device  6 A, and are registered in the matching address management table  606 . At the same time, the mobile communication terminal  2  receives the global IP address and global port number of the mobile communication terminal  2 A which is a communication destination device from the matching server device  6 A (step S 29 ). On the other hand, the global IP address and the global port number which are gotten by the mobile communication terminal  2 A are transmitted to the matching server device  6 A from the mobile communication terminal  2 A via an HTTP communication channel L 16  which is established in advance between the mobile communication terminal  2 A and the matching server device  6 A, and are registered in the matching address management table  606 . At the same time, the mobile communication terminal  2 A receives the global IP address and global port number of the mobile communication terminal  2  which is a communication destination device from the matching server device  6 A (step S 30 ). 
     Then, the mobile communication terminal  2 A transmits a TCP/IP or UDP/IP communication session establishment wait request signal to the proxy device  5 A (step S 31 ). The establishment wait request signal includes the global address information of the mobile communication terminal  2 . The proxy device  5 A having received the signal transitions to a state of waiting for the establishment of a communication session with the mobile communication terminal  2  (step S 32 ). 
     Thereafter, the mobile communication terminal  2  establishes a communication channel L 12  by TCP/IP communication or UDP/IP communication, between a local communication port P 21  and a local communication port P 52  of the proxy device  5  (step S 33 ). Note that in the case of UDP/IP communication the communication channel L 12  is a logical communication channel. Furthermore, the mobile communication terminal  2  transmits a connection request signal including the global address information of the mobile communication terminal  2 A to the proxy device  5 , using HTTP (step S 34 ). 
     In response to this, the proxy device  5  establishes a communication channel L 22  by TCP/IP communication or UDP/IP communication, between a global communication port P 51  and a global communication port P 53  of the proxy device  5 A corresponding to the global address information (step S 35 ). When the communication channel L 22  is established, the proxy device  5  returns a response signal to the mobile communication terminal  2  (step S 36 ), and at the same time, a communication channel L 15  by TCP/IP communication or UDP/IP communication is established between a local communication port P 54  of the proxy device  5 A and a local communication port P 22  of the mobile communication terminal  2 A (step S 37 ). Likewise, in the case of UDP/IP communication, the communication channels L 22  and L 15  are logical communication channels. 
     Thereafter, data to be transmitted and received between the mobile communication terminal  2  and the mobile communication terminal  2 A is relayed by the proxy device  5  and the proxy device  5 A (step S 38 ). Furthermore, when either the mobile communication terminal  2  or the mobile communication terminal  2 A requests to terminate the data communication, the communication channels L 12 , L 22 , and L 15  are released and corresponding records are deleted from the routing table information in the proxy devices  5  and  5 A (step S 39 ). 
     According to the above-described data communication system  101  and data communication method, a connection can be established at the level of a predetermined transport layer protocol via a plurality of proxy devices. In addition, the mobile communication terminals  2  and  2 A can easily establish a connection with their communication destinations using any application layer protocol. Specifically, even if addresses assigned to the mobile communication terminals  2  and  2 A are, for example, local IP addresses, since the application layer can obtain global IP addresses from the proxy devices  5  and  5 A, as with when global IP addresses are assigned to the mobile communication terminals  2  and  2 A in advance, any application layer protocol can be used. Furthermore, by the proxy devices  5  and  5 A working in cooperation with each other, even when an IP address of an end node is changed and when trouble occurs in a proxy device, an end-to-end communication session can be easily maintained. 
     It is preferred that the above-described data communication terminal further include address exchanging means for transmitting global address information gotten by the data address getting means to the data communication network and receiving global address information of a communication destination device, and the connection requesting means transmit the global address information of the communication destination device received by the address exchanging means to the proxy device. 
     By adopting such a configuration, the data communication terminal can easily establish a connection with its communication destination, using any application layer protocol. Specifically, even if an address assigned to the data communication terminal is, for example, a local IP address, since the application layer can obtain a global IP address from the proxy device, as with when a global IP address is assigned to the data communication terminal in advance, any application layer protocol can be used. 
     It is preferred that the above-described proxy device further include routing information storage means for storing a piece of information on a first communication port which is a connection destination on the data communication terminal side and a piece of information on a second communication port connected to a communication destination device by a predetermined transport layer protocol such that the pieces of information are associated with connection destination information of the communication destination device, and the data transferring means output data received from the first communication port to the second communication port by referring to the routing information storage means, and thereby transmit the data to the communication destination device. 
     In this case, by the proxy device transmitting data while referring to the routing information storage means, data sent out from the first communication port on the data communication terminal side is turned out to be relayed to the second communication port and thus the data can be reliably transmitted to the communication destination device. 
     INDUSTRIAL APPLICABILITY 
     Applications of the present invention include data communication terminals, proxy devices, data communication systems, and data communication methods, and the present invention allows to easily implement data communication where an application layer protocol used upon data communication is not limited, while a proxy function is maintained. 
     REFERENCE SIGNS LIST 
       1  and  101 : DATA COMMUNICATION SYSTEM,  2  and  2 A: MOBILE COMMUNICATION TERMINAL,  5  and  5 A: PROXY DEVICE,  6 : SERVER DEVICE (COMMUNICATION DESTINATION DEVICE),  6 A: MATCHING SERVER DEVICE,  201 : APPLICATION SECTION (DATA COMMUNICATION MEANS),  203 : CONTROL PROTOCOL PROCESSING SECTION (ADDRESS GETTING MEANS, CONNECTION REQUESTING MEANS, and ADDRESS EXCHANGING MEANS),  205 : TCP/UDP DATA TRANSMITTING AND RECEIVING SECTION (CONNECTION ESTABLISHING MEANS),  501 : TCP/UDP DATA TRANSMITTING AND RECEIVING SECTION (CONNECTION ESTABLISHING MEANS),  502 : PORT/CONNECTION MANAGING SECTION (ADDRESS ASSIGNING MEANS),  504 : TCP/UDP DATA RELAYING SECTION (DATA TRANSFERRING MEANS),  506 : PORT MANAGEMENT TABLE (ROUTING INFORMATION STORAGE MEANS), NW 1  and NW 3 : MOBILE COMMUNICATION NETWORK (DATA COMMUNICATION NETWORK), and NW 2 : INTERNET NETWORK (DATA COMMUNICATION NETWORK).