Patent Publication Number: US-2005144220-A1

Title: Communication system, server device used in communication system, communication device, and program for executing communication method of the communication device

Description:
TECHNICAL FIELD  
      The present invention relates to a communication system and the like including mobile terminals.  
     BACKGROUND ART  
      Mobile IP (Internet Protocol) is known as the first communication technology in a conventional communication system including mobile terminals. This technology will be described by using the communication system of  FIG. 11 .  
      The communication system of  FIG. 11  includes fixed terminal  1101 , mobile terminal  1102 , and server device  1103 .  
      In this communication system, suppose a phone call is made from fixed terminal  1101  to mobile terminal  1102  by using IP address.  
      When mobile terminal  1102  moves to a space that a different network is used, fixed terminal  1101  is usually unable to communicate because it has no information of IP address of mobile terminal  1102 . However, server device  1103  has a function of getting the information of IP address even when mobile terminal  1102  moves to the space that the different network is used.  
      Accordingly, fixed terminal  1101  transmits a communication packet to server device  1103  via path  1111  and path  1112  in  FIG. 11  to communicate with mobile terminal  1102 .  
      Next, the communication packet is transmitted from server device  1103  to mobile terminal  1102  via path  1113  and path  1114  in  FIG. 11 .  
      Further, mobile terminal  1102  directly transmits a communication packet to fixed terminal  1101  via path, 1115  and path  1116  in  FIG. 11 .  
      In  FIG. 11 , the function of controlling the paths in server device  1103  is called a home agent the function of controlling the paths in mobile terminal  1102  is called a foreign agent. Also, an exclusive line is usually employed for the network between path  1115  and path  1116  in  FIG. 11 .  
      Next, the second communication technology in a communication system including mobile terminals will be described in the following.  
      A communication system using this communication technology is shown in  FIG. 12 .  
      The communication system of  FIG. 12  includes fixed terminal  1201 , mobile terminal  1202 , and server device  1203 . In this communication system, suppose a phone call is made from fixed terminal  1201  to mobile terminal  1202  by using IP address.  
      When mobile terminal  1202  moves to a space on a different network, fixed terminal  1201  is usually unable to communicate because it has no information of IP address of mobile terminal  1202 . However, server device  1203  has a function of getting the information of IP address even when mobile terminal  1202  moves to a space of different network.  
      Fixed terminal  1201  transmits a communication packet to server device  1203  via path  1211  and path  1212  in  FIG. 12  communicate with mobile terminal  1202 .  
      Next, the communication packet is transmitted from server device  1203  to mobile terminal  1202  via path  1213  and path  1214  in  FIG. 12 .  
      Next, mobile terminal  1202  transmits a communication packet to server device  1203  via path  1215  and path  1216  in  FIG. 12 . Further, server device  1203  transmits the communication packet to fixed terminal  1201  via path  1217  and path  1218  in  FIG. 12 . In the second conventional technology, server device  1202  maintains the IP address of fixed terminal  1201  and mobile terminal  1202 .  
      Next, the third communication technology in a communication system including mobile terminals will be described. The third communication technology is a technology for communication between a mobile terminal and a mobile terminal.  
      A communication system using this communication technology is shown in  FIG. 13 .  
      This communication system includes first mobile terminal  1301 , second mobile terminal  1302 , first server device  1303 , and second server device  1304 .  
      In this communication system, suppose a phone call is made from first mobile terminal  1301  to second mobile terminal  1302  by using IP address.  
      The communication packet transmitted from first mobile terminal  1301  is transmitted to first server device  1303  via path  1311  and path  1312  in  FIG. 13 .  
      Next, the communication packet is transmitted from first server device  1303  to second server device  1304  via path  1313  and path  1314  in  FIG. 13 . Next, the communication packet is transmitted from second server device  1304  to second mobile terminal  1302  via path  1315  and path  1316  in  FIG. 13 .  
      Thus, the communication packet is transmitted from first mobile terminal  1301  to second mobile terminal  1302 .  
      In communication packet transmission from second mobile terminal  1302  to first mobile terminal  1301 , the communication packet follows the paths in the opposite direction to the above.  
      In the third conventional technology, first server device  1303  serves to control the IP address of second mobile terminal  1302 , and second server device  1304  serves to control the IP address of first mobile terminal  1301 .  
      First server device  1303  and second server device  1304  may be one unit (server device).  
      In such a case as described above, a copy of communication packet is generated in the server device, causing the server load to be increased.  
      Thus, in a communication system based on the conventional technology, the server device accesses the network every communication made by each terminal. Accordingly, the communication traffic between server device and network will become massive, and it may cause congestion.  
     SUMMARY OF THE INVENTION  
      The communication system of the present invention includes a first communication device, a second communication device for communicating with the first communication device, and a server device which accesses the first communication device.  
      In the server device, the communication information memory stores unique information that is information for identifying the second communication device and communication destination information that is information for establishing communication with the second communication device.  
      In the first communication device, the first server device identification information memory stores server device identification information that is information for accessing the server device. The input receiver receives the input of unique information. When the input receiver receives the input of unique information, the first communication destination information acquisition unit accesses the server device identified by the server device identification information and obtains the communication destination information corresponding to the unique information from the server device. The first communication unit uses the communication destination information to communicate with the second communication device without using the server device.  
      In the communication device of the present invention, the server device identification information memory stores server device identification information that is information for accessing the server device. The input receiver receives the input of unique information. The communication destination information acquisition unit accesses the server device identified by server device identification information when the input receiver receives the input of unique information, and obtains communication destination information corresponding to the unique information from the server device. The communication unit uses the communication destination information to communicate with another communication device without using the server device.  
      In the server device of the present invention, the communication unit communicates with the communication device. The communication information memory stores unique information that is information for identifying the communication device and communication destination information that is information for communicating with the communication device. Further, the server device transmits communication destination information corresponding to the unique information of the second communication device received from the first communication device to the first communication device.  
      In a program readable for a computer, by which the computer executes the communication method of a communication device in a communication system including a server device, the communication method comprises the following steps. 
          a) Receiving communication destination information that is information for establishing communication with another communication device.     b) Communicating with another communication device by using communication destination information without using the server device.     c) Receiving the input of unique information that is information for identifying another communication device.        

      Here, in step a), communication destination information corresponding to the unique information is acquired from the server device.  
      Also, information for establishing communication with the communication device itself is transmitted to the server device. Here, in step a), information for communicating with the communication device itself is acquired as communication destination information.  
      According to the communication system, communication device, server device, and program as described above, it is possible to provide a communication system that may reduce the volume of communication between server device and Internet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a structural diagram of a communication system in the preferred embodiment 1.  
       FIG. 2  is a flow chart for describing the operation of the first communication device in the preferred embodiment 1.  
       FIG. 3  shows a table of communication information management in the preferred embodiment 1.  
       FIG. 4  is a structural diagram of a communication system in the preferred embodiment 2.  
       FIG. 5  is a flow chart for describing the operation of the second communication device transmitting communication destination information to the server device in the preferred embodiment 2.  
       FIG. 6  is a flow chart for describing the operation of the server device receiving and registering communication destination information in the preferred embodiment 2.  
       FIG. 7  shows a table of communication information management in the preferred embodiment 2.  
       FIG. 8  is a structural diagram of a communication system in the preferred embodiment 3.  
       FIG. 9  is a flow chart for describing the operation of the first communication device in the preferred embodiment 3.  
       FIG. 10  is a flow chart for describing the operation of the second communication device in the preferred embodiment 3.  
       FIG. 11  shows the configuration of a communication system in the conventional technology.  
       FIG. 12  shows the configuration of a communication system in the conventional technology.  
       FIG. 13  shows the configuration of a communication system in the conventional technology.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The preferred embodiments of the present invention will be described in detail in the following with reference to the drawings. In the preferred embodiments, a component element and a step in flow charts using the same reference numeral or sign perform the same function. Therefore, the description of component elements and steps already described is sometimes omitted.  
     Preferred Embodiment 1  
       FIG. 1  is a structural diagram of a communication system related to this preferred embodiment. The communication system includes first communication device  101 , second communication device  102 , and server device  103 . In this communication system, first communication device  101  makes a call to second communication device  102 . To make a call is to trigger for starting communication and to execute pre-processing for communication.  
      First communication device  101  includes first server device identification information memory  10101 , input receiver  10102 , first communication destination information memory  10103 , and first communication unit  10104 .  
      First server device identification information memory  10101  stores server device identification information that is information for accessing to server device  103 . The server device identification information may be any information used to gain access to server device  103 , for example, an IP address of server device  103  or electronic mail address for information to be received by server device  103 . Here, the IP address may be any one of IP address of IP Ver4, IP address of IP Ver6 and the like.  
      First server device identification information memory  10101  can be realized by non-volatile recording medium or volatile recording medium.  
      Input receiver  10102  receives the input of unique information of second communication device  102 . The unique information is, for example, a telephone number. Also, the unique information may be an electronic mail address, name or nickname of communication destination and the like. Receiving the input of unique information is executed by various methods such as receiving the input of unique information made by ten-key and receiving the input made by menu selection.  
      Input receiver  10102  may be realized by a keyboard and its driver software or a mouse and its driver software and menu processing software.  
      When input receiver  10102  receives the input of unique information, first communication destination information acquisition unit  10103  accesses to server device  103  identified by server device identification information and obtains communication identification information to be matched with the unique information, that is, the information forming a pair with the unique information from server device  103 . Any algorithm may be used for obtaining communication destination information from server device  103 .  
      First communication destination information acquisition unit  10103  may take communication destination information out of server device  103  by retrieving the information of server device  103 .  
      First communication destination information acquisition unit  10103  may instruct server device  103  to transmit the communication identification information matched with the unique information and to receive the communication destination information transmitted from server device  103  according to the instruction.  
      First communication identification information acquisition unit  10103  is usually realized by software, but it may be realized by hardware such as an exclusive line.  
      First communication unit  10104  communicates with second communication device  102  by using communication destination information obtained by first communication destination information acquisition unit  10103  without communicating via server device  103 .  
      Second communication device  102  includes second communication unit  10201 .  
      Second communication unit  10201  establishes communicates with first communication device  101  without communicating via the server device.  
      First communication unit  10104  and second communication unit  10201  can be realized by a both-directional wireless or cable communication device.  
      Server device  103  includes communication information memory  10301 .  
      Also, server device  103  includes a communication unit and a control unit being not shown. The communication unit communicates with the communication device (the second communication device in this preferred embodiment). The control unit controls the server device.  
      Communication information memory  10301  stores unique information that is information for identifying second communication device  102  and communication information having communication destination information that is information for communicating with second communication device  102 . Communication information is, for example, an IP address. Also, an IP address may be any one of IP address of IP Ver4, IP address of IP Ver6 and the like.  
      Communication information storage  10301  can be realized by non-volatile recording medium or volatile recording medium.  
      The operation of this communication system will be described in the following.  
      First, the operation of first communication device  101  is described by using the flow chart of  FIG. 2 .  
      (Step S 201 ) It is judged whether input receiver  10102  has received the input of unique information of second communication device  102 . In case it has received the input of unique information, it goes to step S 202 , and if it has not received the input of unique information, then step S 201  is repeated.  
      (Step S 202 ) First communication destination information acquisition unit  10103  acquires the first server device identification information stored in first server device identification information memory  10101 .  
      (Step S 203 ) First communication destination information acquisition unit  10103  accesses the sever device identified by the first server identification information acquired in step S 202  and obtains communication destination information according to the unique information received in step S 201 .  
      (Step S 204 ) First communication unit  10104  obtains communication destination information acquired in step S 203 .  
      (Step S 205 ) First communication unit  10104  communicates with second communication device  102 . To establish the communication, a call is established as initial processing, and a process is executed to attain a status that enables communication. After the initial processing is once made, the information is transmitted and received in both directions.  
      (Step S 206 ) First communication unit  10104  judges whether input receiver  10102  or first communication unit  10104  has received a termination signal. In case it has received a termination signal, the step is terminated, and if it has not received a termination signal, then the process returns to step S 205 . If it returns to step S 205  in a state of communication, initial processing will not be executed.  
      In the flow chart of  FIG. 2 , unique information received by input receiver  10102  is the unique information of second communication device  102  in the above description. It is intended to make the description easier in the preferred embodiment.  
      Unique information received by input receiver  10102  may be any information provided that it is the unique information of the counterpart to communicate with.  
      The operation of second communication device  102  is described in the following.  
      Second communication device  102  communicates with first communication device  101 . In detail, it responds to the request for communication from first communication device  101  and opens a call to enter into a state of communication. After entering into a state of communication, second communication device  102  transmits and receives information to and from first communication device  101  in both directions.  
      As for second communication device  102 , in the configuration of  FIG. 1 , shown is only the function of receiving a request for communication from first communication device  101  and communicating with first communication device  101 .  
      However, the configuration of second communication device  102  of  FIG. 1  is a simplified configuration for making easier the description of the preferred embodiment. That is, second communication device  102  usually includes a configuration similar to that of first communication device  101 . Therefore, the communication can be started by designating the counterpart from second communication device  102 .  
      That is, second communication device  102  also may include an input receiver, a server device identification information memory equivalent to the first server device identification information memory, and a communication destination information acquisition unit equivalent to the first communication destination information acquisition unit.  
      The operation of server device  103  is described in the following.  
      Server device  103  gives communication destination information to first communication device  101  according to the request from first communication device  101 . Any algorithm may be employed for giving communication destination information to first communication device  101 . For example, server device  103  receives a communication destination information transmitting command from first communication device  101 . The transmitting command includes unique information. Here, server device  103  retrieves communication destination information to be a pair with the unique information. Further, server device  103  transmits communication destination information to first communication device  101 .  
      The operation of the communication system in this preferred embodiment is specifically described in the following.  
      Here, the first communication device and the second communication device are mobile portable telephones.  
      The server device stores communication information shown in  FIG. 3 .  FIG. 3  is a table of communication information management.  
      In  FIG. 3 , unique information is a telephone number, and communication destination information is an IP address of IP Ver6.  
      Also, assume that unique information of the second communication device is “010-2222-3333.” That is, the second communication device is IP telephone using Internet.  
      The second communication device moves, and the communication destination information of the second communication device changes according to the movement. Assume that the communication destination information changed in accordance with the movement of the second communication device is “1080::8:800:200C:417A.” Here, “1080::8:800:200C:417A.” is a representation using the abbreviation of IP address of IP Ver6.  
      Also, an example of algorithm for providing the server device with communication destination information changed in accordance with the movement of the second communication device will be described in the preferred embodiment 2. Here, any algorithm is preferable for providing the server device with communication destination information changed in accordance with the movement of the second communication device.  
      In such a case, the user of the first communication device inputs the telephone number “1010-2222-3333” to the first communication device to speak with the user of the second communication device.  
      Next, the first communication device receives the input of telephone number “010-2222-3333”, and obtains server device identification information for identifying the server device from the first server device identification information memory. Here, the first server device identification information memory stores an IP address “24FE:1:503::4” (abbreviated expression in IP Ver6) assigned to the server device.  
      Next, the first communication device obtains an IP address “24FE:1:503::4” from the first server device identification information memory.  
      Subsequently, the first communication device transmits a sending command for transmitting communication destination information to the server device identified by an IP address “24FE:1:503::4”. The sending command includes the telephone number “010-2222-3333.” 
      Next, the server device receives the sending command.  
      Subsequently, the server device fetches telephone number “010-2222-3333” included in the sending command.  
      Next, the server device fetches communication destination information to be matched with the telephone number “010-2222-3333.” That is, the server device obtains communication destination information “1080::8:800:200C:417A” to be matched with the telephone number “010-2222-3333” from the table of communication information management of  FIG. 3 .  
      Next, the server device transmits communication destination information “1080::8:800:200C:417A” to the first communication device.  
      Subsequently, the first communication device receives communication destination information “1080::800:200C:417A.” 
      Next, the first communication device makes a call to the second communication device identified by communication destination information “1080::8:800:200C:417A.” 
      The second communication device receives a request for communication from the first communication device, then a call is established between both communication devices, and the bidirectional communication is started between both communication devices.  
      Thus, bidirectional communication, that is, a talk by telephone is established until a communication ending signal is input from either the user of the first communication device or the user of the second communication device.  
      As described above, according to the present preferred embodiment, in communication with a mobile communication device, it enables the bidirectional communication and prevents the traffic of network from becoming too much expanded.  
      Specifically, it is possible to greatly reduce the number of communications and the amount of communication data between the server that manages the communication destination information of mobile communication device and Internet, thereby preventing the increase of traffic.  
      In the present preferred embodiment, communication destination information has been described by using an IP address of IP Ver6 as an example, but the communication destination information used may be any information for establishing communication with a communication device such as an IP address of IP Ver4. The same holds true in other preferred embodiments.  
      Also, in the present preferred embodiment, the unique information has been described by using a telephone number as an example, but the unique information may be information such as the nickname of the user of the communication device. The same holds true in other preferred embodiments.  
      Also, in the present preferred embodiment, any algorithm is preferable for the first communication device to obtain communication destination information. The same holds true in other preferred embodiments.  
      Further, regarding the operation of the first communication device, the second communication device and the server device described in the present preferred embodiment, the operation may be realized with use of software.  
      By putting the software on a server for example, it may be used to distribute the software by software download. Further, it may be performed to distribute the software recorded in a recording medium such as CD-ROM. The same holds true in all the preferred embodiments.  
     Preferred Embodiment 2  
       FIG. 4  is a structural diagram of a communication system in this preferred embodiment. The communication system includes first communication device  101 , second communication device  402 , and server device  403 . In this communication system, a call is made from first communication device  101  to second communication device  402 .  
      Second communication device  402  includes second communication unit  1020 , second communication destination information acquisition unit  40201 , second server device identification information memory  40202 , and communication destination information transmitter  40203 .  
      Second communication destination information acquisition unit  40201  acquires communication destination information that is information for establishing communication with second communication device  402 .  
      Any method is preferable for second communication destination information acquisition unit  40201  to obtain communication destination information.  
      Second communication destination information acquisition unit  40201  receives, for example, communication destination information from an external device of a wireless communication base station. The way of realizing second communication destination information acquisition unit  40201  varies with the method of acquiring communication destination information. Second communication destination information acquisition unit  40201  is, for example, realized by a wireless communication device.  
      Second server device identification information memory  40202  stores server device identification information that is information for accessing to server device  403 . Any server device identification information is preferable, if the information is for accessing to server device  403 . Server device identification information is, for example, the IP address of server device  403  or an electronic mail address for delivering the information to server device  403 . Also, the IP address may be any address such as an IP address of IP Ver4 or an IP address of IP Ver6.  
      Second server device identification information memory  40202  can be realized by non-volatile recording medium or volatile recording medium.  
      Communication destination information transmitter  40203  transmits communication destination information acquired by second communication destination information acquisition unit  40201  to server device  403  identified by server device identification information. Communication destination information transmitter  40203  can be usually realized by a wireless communication device.  
      Here, second communication unit  10201  usually has a function of receiving communication destination information from a wireless communication base station.  
      In second communication device  402 , it is preferable to realize second communication unit  10201 , second communication destination information acquisition unit  40201 , and communication destination information transmitter  40203  with physically one wireless communication device.  
      Second communication device  402  has been described above, but as described in the preferred embodiment 1, first communication device  101  may be configured in the same structure as second communication device  402 . Accordingly, first communication device  101  may have the same functions as those of second communication device  402 . Here, first communication destination acquisition unit  10103  and second communication destination acquisition unit  40202  acquire communication destination information that is information for communicating with the communication device itself, and also acquire communication destination information of the communication counterpart from server device  403 .  
      Also, second communication device  402 , as described in the preferred embodiment 1, may include an input receiver.  
      Server device  403  includes communication information memory  10301 , communication destination information receiver  40301 , and communication destination updating unit  40302 . That is, communication destination information receiver  40301  and communication destination information updating unit  40302  are added to the configuration of the preferred embodiment 1.  
      Communication destination information receiver  40301  receives communication destination information from second communication device  402 . Communication destination information receiver  40301  can be realized by a wireless or cable communication device.  
      Communication destination information updating unit  40302  registers the communication destination information received by communication destination information receiver  40301  as updated communication destination information of communication information memory  10301 . Here, to register means, for example, overwriting the received communication destination with respect to communication destination information stored in communication information memory  10301 . Communication destination information updating unit  40302  can be usually realized by software, but it may be realized by using hardware such as an exclusive circuit.  
      The operation of the communication system will be described in the following.  
      First, the operation of second communication device  402  for transmitting communication destination information to server device  403  is described by using the flow chart of  FIG. 5 .  
      (Step S 501 ) It is judged whether second communication destination information acquisition unit  40201  has acquired the communication destination information of second communication device  402  itself. In case it has acquired the communication destination information, it goes to step S 502 , and if it has not acquired the communication destination information, then step S 501  is repeated.  
      (Step S 502 ) Communication destination information transmitter  40203  takes out server device identification information from second server device identification information memory  40202 .  
      (Step S 503 ) Communication destination information transmitter  40203  transmits communication destination information obtained in step S 501  to the server device identified by server device identification information fetched in step S 502 .  
      In the flow chart of  FIG. 5 , with communication destination obtained, the communication destination is always transmitted to the server device.  
      Also, the second communication device judges whether the communication destination information of the second communication device itself is changed, and only when changed, the second communication device may transmit the communication destination information to the server device. In that case, second communication device  402  is configured as described in the following.  
      Further, there is provided a change detector not shown which detects the change of communication destination information that is information for communicating with second communication device  402 . Communication destination information transmitter  40203  transmits communication destination information to server device  403  when the change detector detects the change of communication destination information.  
      Also, in the flow chart of  FIG. 5 , nothing is mentioned about a case that communication destination information is obtained, but communication destination information may be acquired periodically. Also, only when communication destination information is changed due to a movement of the second communication device, communication destination information may be acquired by transmitting communication destination information from a base station or the like to the second communication device.  
      Further, communication destination information transmitter  40203  usually transmits unique information of second communication device  402  together with communication destination information to server device  403 . Server device  403  rewrites the communication information that corresponds, that is, matches with the unique information.  
      Next, the operation of server device  403  for receiving and registering communication destination information will be described by using the flow chart of  FIG. 6 .  
      (Step S 601 ) It is judged whether communication destination information receiver  40301  has received communication destination information. In case it has received communication destination information, it goes to step S 602 , and if it has not received communication destination information, then step S 601  is repeated.  
      (Step S 602 ) Communication destination information updating unit  40302  retrieves the portion of registering the communication destination information received in step S 601 . The registering portion exists in communication information memory  10301 . Here, retrieving the registering portion means, for example, executing the following processing.  
      Communication destination information receiver  40301  receives, for example, the communication destination information and the unique information of second communication device  402  in the form of a pair. Further, communication destination information updating unit  40302  obtains communication information including communication destination information, by using the received unique information as a key.  
      (Step S 603 ) Communication destination information updating unit  40302  registers the communication destination information received in step S 601  in the registering portion retrieved in step S 602 .  
      The operation of the communication system in the present preferred embodiment will be specifically described in the following.  
      Here, the first communication device and the second communication device are mobile portable telephones.  
      The server device stores communication information shown in  FIG. 3 . Also, assume that unique information of the second communication device is “010-2222-3333.” That is, the second communication device is an IP telephone using Internet.  
      Here, the second communication device moves, and the communication destination information of the second communication device changes according to the movement. Assume that the communication destination information of the second communication device changed in accordance with the movement of the second communication device is “1080::5:2A11:11DE:555C.” 
      The second communication device receives, for example, an IP address “1080::5:2A11:11DE:555C” assigned to the second communication device from a wireless communication base station of the destination. Then, the second communication device transmits the received IP address “1080::5:2A11:11DE:555C” to the server device. In transmission, the second communication device also transmits its unique information “010-2222-3333” to the server device.  
      The server device receives the IP address “1080::5:2A11:11DE:555C” and the unique information “010-2222-3333” from the second communication device. Subsequently, the server device changes communication destination information corresponding to the unique information “010-2222-3333” of the table (communication information management table) for the management of communication information of  FIG. 3  into “1080::5:2A11:11DE:555C.” As a result, the communication information management table becomes as shown in  FIG. 7 .  
      The second communication device may transmit communication destination information to the server device when the change of the communication destination information is detected by the change detector. Also, the second communication device may always transmit communication destination information to the server device when it acquires communication destination information.  
      Also, the server device may always register the communication destination information received from the second communication device. Also, the server device compares the communication destination information stored in the communication information memory with the communication destination information, and there is a difference between the two, to the server device may register the communication destination information received.  
      As described above, according to the present preferred embodiment, in communication with a mobile communication device, it is possible to make bidirectional communication in both directions and to prevent the traffic of network from becoming too much expanded. In addition, the server device receives communication destination information from the second communication device which are moving, and the server device is always able to maintain the communication destination information of the place at which the second communication device moves. Accordingly, wherever the second communication device moves, the first communication device is able to properly establish communication with the second communication device.  
     Preferred Embodiment 3  
       FIG. 8  is a structural diagram of a communication system in this preferred embodiment.  
      The communication system includes first communication device  801 , second communication device  802 , and server device  403 . In this communication system, a call is made from first communication device  801  to second communication device  802 .  
      Server device  403  is configured in the same structure as in the preferred embodiment 2.  
      First communication device  801  includes first server device identification information memory  10101 , input receiver  10102 , first communication destination information acquisition unit  10103 , first communication unit  80103 , communication destination information receiver  80101 , and communication controller  80102 .  
      Communication destination information receiver  80101  receives communication destination information from second communication device  802  during the communication with second communication device  802 . Communication destination information receiver  80101  is usually realized by a wireless communication device.  
      Communication controller  80102  instructs first communication unit  10104  to change over the destination to the destination shown by the received communication destination information when communication destination information receiver  80101  receives new communication destination information. Communication controller  80102  can be usually realized by software, but it may be realized by hardware (an exclusive circuit).  
      First communication unit  80103  establishes communication with second communication device  802 . Also, when new communication destination information is received from communication controller  80102  during the communication, the communication is made by changing it over to the destination shown by the new communication destination information. First communication unit  80103  can be usually realized by wireless communication device. First communication unit  80103  includes software or the like for communicating by changing it over to the destination shown by the new communication destination information.  
      Second communication device  802  includes second communication unit  10201 , second communication destination information acquisition unit  40201 , second server device identification information memory  40202 , change detector  80201 , and communication destination information transmitter  80202 .  
      Change detector  80201  detects that the change of the communication destination information of second communication device  802  itself. Any method for detecting the change may be employed. Change detector  80201  receives communication destination information from a base station for wireless communication, for example, only when the communication destination information of second communication device  802  itself is changed. Also, change detector  80201  receives communication destination information from a wireless communication base station for example periodically or at all times, and compares the last communication destination information being stored with the communication destination information received, and if both do not coincide with each other, it is judged that the communication destination information is changed.  
      Change detector  80201  is usually realized by software, but it may be realized by hardware.  
      Here, second communication unit  10201  usually has a function of receiving communication destination information from a wireless communication base station.  
      Communication destination information transmitter  80202  transmits communication destination information acquired by second communication destination information acquisition unit  40201  to first communication device  801  when the change of communication destination information is detected by change detector  80201  during communication with first communication device  801 .  
      Also, communication destination information transmitter  80202  transmits the communication destination information acquired by second communication destination information acquisition unit  40201  to server device  403  as well, when change detector  80201  detects the change of communication destination information. Since second communication device  802  and first communication device  801  are communicating with each other, communication destination information transmitter  80202  is able to transmit the new communication destination information to first communication device  801 .  
      Also, the server device identification information of server device  403  is obtained from second server device identification information memory  40202 .  
      Communication destination information  80202  is usually realized by a wireless communication device.  
      The operation of the communication system will be described in the following.  
      First, the operation of first communication device  801  is described by using the flow chart of  FIG. 9 .  
      Here, first communication device  801  obtains communication destination information of second communication device  802  from second communication device  802  during communication with second communication device  802 . Thus, the communication is continued between first communication device  801  and second communication device  802 .  
      The operation of first communication device  801  for starting communication with second communication device  802  is preformed in the same manner as the operation described by using the flow chart of  FIG. 2 , and the description is omitted.  
      (Step S 901 ) Communication destination information receiver  80101  judges whether it has received communication destination information from second communication device  802  during the communication with second communication device  802 . In case it has received communication destination information, it goes to step S 902 , and if it has not received communication destination information, then step S 901  is repeated.  
      (Step S 902 ) Communication controller  80102  instructs first communication unit  10104  to change over the destination to the destination shown by the communication destination information received.  
      (Step S 903 ) First communication unit  80103 , during communication with second communication device  802 , changes over the communication destination information of second communication device  802  to new communication destination information in order to continue the communication with second communication device  802 .  
      Such processing is usually executed according to the following procedure.  
      First communication unit  80103  finishes calling to second communication device  802  shown by the previous communication destination information, and makes a call to second communication device  802  shown by the new communication destination information to resume the communication with second communication device  802 . That is, first communication unit  80103  immediately resumes the communication after once finishing communication. Because the processing speed is very fast, the users of first communication device  801  and second communication device  802  will feel like that the communication is made continuously.  
      Next, the operation of second communication device  802  will be described by using the flow chart of  FIG. 10 .  
      Here, second communication device  802  transmits communication destination information to first communication device  801  during communication with first communication device  801 . Thus, the communication is continued between first communication device  801  and second communication device  802 .  
      (Step S 1001 ) Second communication destination information acquisition unit  40201  acquires communication destination information of second communication device  802  itself. Any method is preferable for second communication destination information acquisition unit  40201  to obtain communication destination information. For example, second communication destination information acquisition unit  40201  periodically receives communication destination information from a wireless communication base station located in the neighborhood.  
      (Step S 1002 ) Change detector  80201  compares the latest communication destination information with communication destination information received in step S 1001 , and judges whether the communication destination information of second communication device  802  is changed.  
      In case the communication destination information is changed, the process goes to step S 1003 , and if the communication destination information is not changed, then it returns to step S 1001 .  
      Here, second communication device  802  always stores the latest communication destination information (current communication destination information). That is, second communication device  802  records the new communication destination information as the current communication destination information when the communication destination information is changed.  
      (Step S 1003 ) Communication destination information transmitter  80202  transmits the communication destination information acquired in step S 1001  to first communication device  801 . Second communication device  802  is able to transmit the communication destination information because second communication device  802  are communicating with first communication device  801 .  
      (Step S 1004 ) Communication destination information transmitter  80202  obtains server device identification information from second server device identification information memory  40202 .  
      (Step S 1005 ) Communication destination information transmitter  80202  transmits the communication destination information obtained in step S 1001  to server device  403  identified by the server device identification information obtained in step S 1004 .  
      After that, the process returns to step S 1001 .  
      In the flow chart of  FIG. 10 , when second communication device  802  has received a termination signal, the operation is terminated because of interruption.  
      Also, in the flow chart of  FIG. 10 , change detector  80201  detects the change of communication destination information.  
      Also, communication destination information may be processed in the following way.  
      Only when the communication destination information of second communication device  802  changes, second communication device  802  obtains communication destination information from the outside. In that case, second communication device  802  may transmit communication destination information to first communication device  801  and server device  403  without making any judgment.  
      Further, in the flow chart of  FIG. 10 , when first communication device  801  and second communication device  802  are communicating with each other, second communication device  802  transmits new communication destination information to server device  403 . Also, after the termination of communication, second communication device  802  may transmit new communication destination information to server device  403 .  
      First communication device  801  and second communication device  802  have been described above.  
      As described in the preferred embodiments 1 and 2, first communication device  801  and second communication device  802  may have the same configuration.  
      Accordingly, first communication device  801  may further include a communication destination information transmitter equivalent to communication destination information transmitter  80202  and a change detector equivalent to change detector  80201 .  
      Also, second communication device  802  may further include an input receiver equivalent to input receiver  10102 , a communication destination information receiver equivalent to communication destination information receiver  80101 , and a communication controller equivalent to communication controller  80102 .  
      The operation of the communication system in the present preferred embodiment will be specifically described in the following.  
      Here, the first communication device and the second communication device are mobile portable telephones.  
      The server device stores communication information shown in  FIG. 3 .  
      Assume that the unique information of the second communication device is “010-2222-3333.” That is, the second communication device operates as an IP telephone using Internet.  
      Here, assume that the first communication device and the second communication device are communicating with each other, and that the second communication device moves. The communication destination information of the second communication device changes in accordance with the movement of the second communication device. Suppose that the communication destination information of the second communication device changed in accordance with the movement is “1080::5:2A11:11DE:555C.” The second communication device for example receives IP address “1080::5:2A11:11DE:555C” assigned to the second communication device from a wireless communication base station of the area to which the second communication device has moved. Subsequently, the second communication device transmits the received IP address “1080::5:2A11:11DE:555C” to the first communication device with which it is communicating. Also, the second communication device transmits the received IP address “1080::5:2A11:11DE:555C” to the server device as well.  
      The first communication device receives a new IP address of the second communication device, and changes over the destination to the new IP address “1080::5:2A11:11DE:555C” to continue the communication.  
      Also, the server device changes the communication information management table to the one shown in  FIG. 7  as described in the preferred embodiment 2.  
      As described above, according to the present preferred embodiment, in communication with a mobile communication device, it is possible to establish communicate in both directions. Also, it is possible to prevent the traffic of network from becoming too much expanded. Further, even when communication destination is changed due to the movement of the communication device, a state of stable communication can be continuously obtained.  
     Industrial Applicability  
      According to the present invention, the amount of communication traffic between server device and Internet can be reduced, and it is possible to provide a communication system being free from problems such as congestion.