Abstract:
Terminal management information concerning a plurality of communication terminals of a user is managed. When a call addressed to the user is initiated, one or more terminals that can accept the call is identified by referring to an ability needed for a communication involved in the call and the terminal management information concerning the plurality of communication terminals managed by the step (a). Information involved in the call into items of information to be sent to the above one or more terminals identified by the step (b) and combining items of information from the above one or more terminals identified by the step (b) is separated into information to be sent to one of the plurality of communication terminals that initiates the call. A virtual terminal is formed by the above one or more terminals identified by the step (b) and communicates with the above one of the plurality of communication terminals.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a virtual terminal configuring method and device, and more particularly to a virtual terminal configuring method and device in which a virtual terminal is formed by combining a plurality of terminals. 
   2. Description of the Related Art 
     FIG. 1  is a diagram of a conventional videophone communication system. A videophone terminal  10  owned by user A and a videophone terminal  12  owned by user B are mutually connected via a network  14  such as an ISDN (Integrated Services Digital Network). Video information and voice information are transferred between the videophone terminals  10  and  12  via the network  14 . The videophone terminals  10  and  12  communicate with each other by using a video and voice compression coding rule and protocol for ISDN. 
   Conventionally, videophone communications can take place only when both the users A and B have the videophone terminals using the same video and voice compression coding rule and protocol. 
   Nowadays, users have various kinds of communication terminals such as cellular phones, PDA (Personal Digital Assistants), and personal computers. When the users wish to use a new communication service such as videophone communications, the users are required to prepare a new terminal such as a videophone terminal. 
   SUMMARY OF THE INVENTION 
   It is a general object of the present invention to overcome the above disadvantage. 
   A more specific object of the present invention is to provide a virtual terminal configuring method and device in which a plurality of terminals are arranged so as to form a virtual terminal capable of handing various types of communications. 
   The above objects of the present invention are achieved by a method comprising the steps of: (a) managing terminal management information concerning a plurality of communication terminals of a user; (b) identifying, when a call addressed to the above user is initiated, one or more terminals that can accept the call by referring to an ability needed for a communication involved in the call and the terminal management information concerning the plurality of communication terminals managed by the step (a); and (c) separating information involved in the call into items of information to be sent to the above one or more terminals identified by the step (b) and combining items of information from the above one or more terminals identified by step (b) into information to be sent to one of the plurality of communication terminals that initiates the call. A virtual terminal is formed by the above one or more terminals identified by the step (b) and communicates with the above one of the plurality of communication terminals. 
   The above objects of the present invention are also achieved by a virtual terminal configuring device comprising: a first part managing terminal management information concerning a plurality of communication terminals of a user; a second part identifying, when a call addressed to the user is initiated, one or more terminals that can accept the call by referring to an ability needed for a communication involved in the call and the terminal management information concerning the plurality of communication terminals managed by said first part; and a third part separating information involved in the call into items of information to be sent to the above one or more terminals identified by the second part and combining items of information from the above one or more terminals identified by the second part into information to be sent to one of the plurality of communication terminals that initiates the call. A virtual terminal being formed by the above one or more terminals identified by the second part and communicates with the above one of the plurality of communication terminals. 
   The above objects of the present invention are also achieved by a device comprising: a plurality of communication terminals of users; and a virtual terminal configuring device to which the plurality of communication terminals are coupled. The virtual terminal configuring device comprises: a first part managing terminal management information concerning the plurality of communication terminals; a second part identifying, when a call addressed to a first one of the users is initiated, one or more terminals of the first one of the users that can accept the call by referring to an ability needed for a communication involved in the call and the terminal management information concerning the communication terminals; and a third part separating information involved in the call into items of information to be sent to the above one or more terminals identified by the second part and combining items of information from the above one or more terminals identified by the second part into information to be sent to one of the communication terminals of a second one of the users that initiates the call. A virtual terminal is formed by the above one or more terminals identified by the second part so that the virtual terminal of the first one of the users and the above one of the communication terminals of the second user can communicate with each other. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a diagram of a conventional videophone communication system; 
       FIG. 2  is a block diagram of a communication system including a virtual terminal configuring device according to a first embodiment of the present invention; 
       FIG. 3  is a block diagram of a communication system including a virtual terminal configuring device according to a second embodiment of the present invention; 
       FIG. 4  is a block diagram of a communication system including a virtual terminal configuring device according to a third embodiment of the present invention; 
       FIG. 5  is a block diagram of a communication system including a virtual terminal configuring device according to a fourth embodiment of the present invention; 
       FIG. 6  is a diagram of a network structure of a communication system including the virtual terminal configuring system of the present invention; 
       FIG. 7  is a diagram showing how a device management function unit acknowledges kinds of information handled by communication terminals; 
       FIG. 8  is a diagram showing how the device management function unit integrates communication terminals coupled to a network. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2  is a block diagram of a communication system of a virtual terminal configuring device according to a first embodiment of the present invention. 
   Referring to  FIG. 2 , user A is allowed to use communication terminals  20   1  through  20   N , which are connected to a virtual terminal configuring device  22 . The virtual terminal configuring device  22  is connected, via a network  25 , to a communication terminal  26  allowed to be used by user B. The communication terminals  20   1  through  20   N  are capable of inputting and outputting various kinds of information, such as voices, images, characters and numeral values. The communication terminal  26  is capable of integrally inputting and outputting the various kinds of information as those handled by the communication terminals  20   1  through  20   N . 
   The virtual terminal configuring device  22  is primarily made up of a virtual terminal function unit  23  and a device management function unit  24 . The virtual terminal function  23  has communication protocol units  27   1  through  27   N , to which the communication terminals  20   1  through  20   N  are connected, respectively. Thus, two-way communications can take place between the communication terminals  20   1  through  20   N  and the communication protocol units  27   1  through  27   N , respectively. The communication terminal  26  is connected, via the network  25 , to a communication protocol unit  34  provided in the virtual terminal function unit  23 . The communication protocol unit  34  has a communication protocol of the communication terminal  26 , and communicates therewith in two ways. 
   The communication protocol units  27   1  through  27   N  are respectively connected to information coding scheme converting units  28   1  through  28   N , which respectively implement the mutual conversions between the information coding scheme of the communication protocol unit  34  and the information coding schemes of the communication protocol units  27   1  through  27   N . For example, in a virtual terminal communication, if the communication protocol unit  34  employs MPEG1 as an information coding scheme for moving pictures and one of the communication protocol units  27   1  through  27   N , for example, the communication protocol unit  27   1  employs MPEG4 as an information coding scheme for moving pictures, the information coding scheme converting unit  28   1  performs the mutual conversion between MPEG1 and MPEG4. When the information coding scheme includes information produced by data compression, the information coding scheme converting unit performs associated data decompression and data compression at the time of converting the information coding scheme. That is, data decompression and data compression are part of the work along with the conversion of the information coding scheme. 
   The information coding scheme converting units  28   1  through  28   N  have a filtering function. The filtering function is used in case where there is a large difference between the bit rate of channels of the network  25  to which the communication protocol unit  34  is connected and the bit rate of channels of a network to which the communication protocol units  27   1  through  27   N  are connected. In the above case, the filtering function extracts information assigned comparatively high priority from the entire information. With the filtering function, it is possible to reduce the amount of information handled by an information coding scheme used in a comparatively high bit rate to the amount of information handled by another information coding scheme used in a comparatively low bit rate. 
   The items of information respectively output by the information coding scheme converting units  28   1  through  28   N  are supplied to an information combining unit  30 . Then, the information combining unit  30  combines the items of information which are supplied from the information coding scheme converting units  28   1  through  28   N  and are processed by the same information coding scheme. The combined or multiplexed information thus obtained is supplied to the communication protocol unit  34 , which sends the synthesized information from the information combining unit  30  to the communication terminal  26 . 
   The communication protocol  34  supplies information received from the communication terminal  26  to an information separating unit  32 . The information separating unit  32  separates the multiplexed information into the respective kinds of information such as voices, images, characters and numeral values. The kinds of information are supplied to the corresponding information coding scheme converting units  28   1  through  28   N . Then, the converting units  28   1  through  28   N  convert the information of the information coding scheme employed in the communication protocol unit  34  into the respective information coding schemes of the communication protocol units  27   1  through  27   N , and supply the items of the converted information thereto. 
   The device management function unit  24  of the virtual terminal configuring device  22  includes a terminal management unit  36 . The terminal management unit  36  is informed, by the communication protocol units  27   1  through  27   N  and  34  of the virtual terminal function unit  23 , of a variety of management information on the communication terminals  20   1  through  20   N , such as the kinds of information handled thereby, functions, human interface abilities, communication abilities and communication status (indicating whether a requested communication should be allowed) of the communication terminals  20   1  through  20   N . Then, in accordance with the kinds of information that are input to and output from the communication terminals  20   1  through  20   N , the terminal management unit  36  supplies control signals to the communication protocol units  27   1  through  27   N  and  34 , the information coding scheme converting units  28   1  through  28   N , the information combining unit  30  and the information separating unit  32  in order to control the operations thereof. 
   When the communication terminal  26  of user B initiates a call addressed to any of the communication terminals  20   1  through  20   N  of user A, the device management function unit  24  checks the abilities of communication terminals of user A which are available for communications at that time by referring to the human interface and communication abilities needed by the communication terminal  26 . Then, the device management function unit  24  identifies communication terminals which can accept the call made by the communication terminal  26 . The selected communication terminal among the communication terminals  20   1  through  20   N  of user A is virtually integrated into a single communication terminal (virtual terminal) by the virtual terminal function unit  23 . Thus, a communication can take place between the virtual terminal thus constructed and the communication terminal  26  of user B. 
     FIG. 3  is a block diagram of a communication system of a virtual terminal configuring device according to a second embodiment of the present invention. 
   Referring to  FIG. 3 , a cellular phone  40  and a PDA  41  that can be used by user A are connected to a virtual terminal configuring device  42 . The virtual terminal configuring device  42  is connected, via a network  45 , to a videophone communication terminal  46  that can be used by user B. 
   The virtual terminal configuring device  42  is primarily made up of a virtual terminal function unit  43  and a device management function unit  44 . The cellular phone  40  and the PDA  41  are respectively connected to communication protocol units  47   1  and  47   2  in the virtual terminal function unit  43 . Thus, two-way communications can take place between the cellular phone  40  and the communication protocol unit  47   1  and between the PDA  41  and the communication protocol unit  47   2 . The videophone communication terminal  46  is connected, via the network  45 , to a communication protocol unit  54  provided in the virtual terminal function unit  43 . The videophone communication terminal  46  and the communication protocol unit  54  communicate with each other in two ways. 
   The communication protocol units  47   1  and  47   2  are respectively connected to the information coding scheme converting units  48   1  and  48   2 . The information coding scheme converting unit  48   1  converts voice information of the information coding scheme employed in the cellular phone supplied by the communication protocol unit  47   1 , into voice information of the information coding scheme employed in the videophone. The converted voice information thus obtained is supplied to an information combining unit  50 . The information coding scheme converting unit  48   2  converts video information of the information coding scheme for the PDA supplied by the communication protocol unit  47   2  into video information of the information coding scheme for the videophone. The converted video information thus obtained is supplied to the information combining unit  50 . For example, when information supplied from the PDA  41  forms a still picture, it is converted into video information describing animation by the information coding scheme converting unit  48   2 . The information coding scheme converting units  48   1  and  48   2  are respectively equipped with the filtering functions. 
   The information combining unit  50  combines the voice and video information of the information coding scheme for the videophone respectively supplied from the information coding scheme converting units  48   1  and  48   2  into integrated videophone information conforming to the videophone. The integrated videophone information is then sent to the communication protocol unit  54 , which sends the received videophone information to the videophone communication terminal  46  via the network  45 . 
   The communication protocol unit  54  supplies videophone information received from the videophone communication terminal  46  to an information separating unit  52 . Then, the information separating unit  52  separates the received videophone information into voice information and video information, which are respectively supplied to the information coding scheme converting units  48   1  and  48   2 . Then, the unit  48   1  converts the voice information conforming to the videophone into voice information conforming to the cellular phone. The voice information thus converted is then supplied to the communication protocol unit  47   1 . Similarly, the unit  48   2  converts the video information conforming to the videophone into video information conforming to the cellular phone. The video information thus converted is then supplied to the communication protocol unit  47   2 . 
   The device management function unit  42  of the virtual terminal configuring device  42  includes a terminal management unit  56 . The terminal management unit  56  is informed, by the communication protocol units  47   1    47   2  and  54  of the virtual terminal function unit  43 , of a variety of management information on the cellular phone  40 , the PDA  41  and the videophone communication terminal  46 , such as the kinds of information handled thereby, functions, human interface abilities, communication abilities and communication status of the cellular phone  40 , the PDA  41  and the videophone communication terminal  46 . Then, in accordance with the kinds of information that are input to and output from the cellular phone  40 , the PDA  41  and the videophone communication terminal  46 , the terminal management unit  56  supplies control signals to the communication protocol units  47   1 ,  47   2  and  54 , the information coding scheme converting units  48   1  and  48   2 , the information combining unit  50  and the information separating unit  52  in order to control the operations thereof. 
   When the videophone communication terminal  46  of user B makes a call addressed to either the cellular phone  40  or the PDA  41  of user A, the device management function unit  44  checks the abilities of communication terminals of user A which are available for communications at that time by referring to the human interface and communication abilities needed by the videophone communication terminal  46 . Then, the device management unit  44  identifies the cellular phone  40  or the PDA  41  which can accept the call made by the videophone communication terminal  46 . The selected terminal of user A is virtually integrated into a single communication terminal (virtual terminal) by the virtual terminal function unit  43 . Thus, a communication can take place between the virtual terminal and the videophone communication terminal  46  of user B. 
     FIG. 4  is a block diagram of a communication system of a virtual terminal configuring device according to a third embodiment of the present invention. Any part shown in  FIG. 2  that is the same as a part shown in  FIG. 4  is denoted by the same reference numeral in both figures. A virtual terminal configuring device  37  is substituted for the communication terminal  26  and is connected to the network  25 . The virtual terminal configuring device  37  has the same configuration and operation as those of the virtual terminal configuring device  22 . Communication terminals  38   1  through  38   M  that can be used by user B are connected to the virtual terminal configuring device  37 . 
   With the above configuration, the communication terminals  20   1  through  20   N  that can be used by user A are virtually integrated into a single communication terminal (virtual terminal) by means of the virtual terminal configuring device  22 , and the communication terminals  38   1  through  38   M  that can be used by user B are virtually integrated into a single communication terminal (virtual terminal) by means of the virtual terminal configuring device  37 . Thus, a communication can take place between the virtual terminal devices of users A and B. 
     FIG. 5  is a block diagram of a communication system of a virtual terminal configuring device according to a fourth embodiment of the present invention. Communication terminals  60   1  through  60   N  that can be used by user A are connected to a virtual terminal configuring device  62 , which is connected, via the network  25 , to communication terminals  66   1  through  66   M  that can be used by user B. The communications terminals  60   1  through  60   N  and  66   1  through  66   M  are capable of inputting and outputting various kinds of information such as voices, images, characters and numeral values. 
   The virtual terminal configuring device  62  is primarily made up of a virtual terminal function unit  63  and a device management function unit  64 . The communication terminals  60   1  through  60   N  are respectively connected to associated communication protocol units  67   1  through  67   N  provided in the virtual terminal function unit  63 . Thus, two-way communications take place between the communication terminals  60   1  through  60   N  and the communication protocol units  67   1  through  67   N , respectively. The communication terminals  66   1  through  66   M  are connected to associated communication protocol units  76   1  through  76   M  provided in the virtual terminal function unit  63 . Thus, two-way communications can take place between the communication terminals  66   1  through  66   M  and the communication protocol units  76   1  through  76   M . 
   The communication protocol units  67   1  through  67   N  are connected to information coding scheme converting units  68   1  through  68   N . The units  68   1  through  68   N  convert the items of information that are supplied from the communication protocol units  67   1  through  67   N  and conform to the respective information coding schemes into information of a common information coding scheme. Then, the information of the common information coding scheme is supplied to an information combining unit  70 . Each of the information coding scheme converting units  68   1  through  68   N  has the aforementioned filtering function. 
   The information combining unit  70  combines the items of information of the common coding scheme respectively supplied from the information coding scheme converting units  68   1  through  68   N , and thus produces combined or multiplexed information, which is then supplied to an information separating unit  71 . The information separating unit  71  separates the multiplexed information into the respective kinds of information such as voices, images, characters and numeral values. The respective kinds of information thus obtained are supplied to the corresponding information coding scheme converting units  74   1  through  74   N . Then, the converting units  74   1  through  74   N  convert the information of the common information coding scheme into the respective information coding schemes of the communication protocol units  76   1  through  76   N , and supply the items of the converted information thereto. Each of the information coding scheme converting units  74   1  through  74   M  has the aforementioned filtering function. The communication protocol units  76   1  through  76   M  send the respective kinds of information thus obtained to the corresponding communication terminals  66   1  through  66   M . 
   The communication protocol units  76   1  through  76   M  supply various kinds of information such as voices, images, characters and numeral values received from the communication terminals  66   1  through  66   M  to the information coding scheme converting units  74   1  through  74   N , respectively. The corresponding information coding scheme converting units  74   1  through  74   N  convert the items of information of the respective information coding schemes into information of the common information coding scheme. The information thus obtained is then supplied to an information combining unit  73 . 
   The information combining unit  73  combines the items of the information data of the common information coding scheme respectively supplied from the information coding scheme converting units  74   1  through  74   M , and supplies the combined or multiplexed data to an information separating unit  72 . The information separating unit  72  separates the multiplexed information into the respective kinds of information such as voices, images, characters and numeral values. Then, the respective kinds of information are supplied to the corresponding information coding scheme converting units  68   1  through  68   N . The units  68   1  through  68   N  convert the information of the common information coding scheme supplied from the information separating unit  72  into the items of information of the respective information coding schemes of the communication protocol units  67   1  through  67   N . The items of information thus converted are then supplied to the communication protocol units  76   1  through  76   N , which send the corresponding items of information to the communication terminals  60   1  through  60   N . 
   The device management function unit  64  of the virtual terminal configuring device  62  includes a terminal management unit  78 . The terminal management unit  78  is informed, by the communication protocol units  67   1  through  67   N  and  76   1  through  76   M  a of the virtual terminal function unit  63 , of a variety of management information on the communication terminals  60   1  through  60   N  and  66   1  through  66   M , such as the kinds of information handled thereby, functions, human interface abilities, communication abilities and communication status of the communication terminals  60   1  through  60   N  and  66   1  through  66   M . Then, in accordance with the kinds of information that are input to and output from the communication terminals  60   1  through  60   N  and  66   1  through  66   M , the terminal management unit  78  supplies control signals to the communication protocol units  67   1  through  67   N .  76   1  through  76   M , the information coding scheme converting units  68   1  through  68   N  and  74   1  through  74   M , the information combining units  70  and  73 , and the information separating units  71  and  72  in order to control the operations thereof. 
   Thus, the communication terminals  20   1  through  20   N  that can be used by user A are virtually integrated into a single communication terminal (virtual terminal) by means of the virtual terminal configuring device  62 , and similarly the communication terminals  66   1  through  66   M  that can be used by user B. With the virtual terminal configuring device  62 , the virtual terminals of users A and B can communicate with each other. 
   In the above-mentioned embodiments of the present invention, the virtual terminal configuring device which virtually integrates the communication terminals is installed on the user side and is connected to the network. However, the present invention is not limited to the above formation. 
   The virtual terminal configuring devices  22 ,  42  and  62  can be implemented by the function of software. Similarly, the virtual terminal function units  23 ,  43  and  63  can be implemented by the function of software, and the device management function units  24 ,  44  and  64  can be implemented by the function of software. The virtual terminal function units  23 ,  43  and  63  may be provided as devices separate from (for example, remote from) the device management function units  24 ,  44  and  64 . 
   A description will be given of other embodiments of the present invention. 
     FIG. 6  is a diagram of a network structure of a communication system using the virtual terminal configuring device according to any of the first through fourth embodiments of the present invention. Referring to  FIG. 6 , communication terminals  80   1  through  80   3  are connected to a wire IP network  81 . A communication terminal  80   4  is connected to an IMT-2000 (which is the next generation mobile communications system). A communication terminal  80   5  is connected to a wireless LAN  83 . Communication terminals  80   6  and  80   7  are connected to a fourth-generation mobile communication system  84 . 
   A virtual terminal function device(VTF)  86  and a device management function device (DMF)  88 , which form a virtual terminal configuring device, are connected to the fourth-generation mobile communication system  84 , and are thus connected mutually. Communication terminals  80   8  and  80   9  are connected to the virtual terminal function device  86  by Bruetooth (a radio communication interface). 
   The virtual terminal function device  86  corresponds to one of the aforementioned virtual terminal function units  23 ,  43  and  63  respectively shown in  FIGS. 2 ,  4  and  5 . The device management function device  88  corresponds to one of the aforementioned device management units  24 ,  44  and  64  respectively shown in  FIGS. 2 ,  4  and  5 . 
   Each of the networks  25 ,  45  and  65  shown in  FIGS. 2 through 5  correspond to the whole network shown in  FIG. 6 . The virtual terminal function unit  23  and the device management unit  24  shown in  FIGS. 2 and 4  can be installed in any position in the whole network. Similarly, the virtual terminal function unit  43  and the device management unit  44  shown in  FIG. 3  can be installed in any position in the whole network, and the virtual terminal function unit  63  and the device management unit  64  shown in  FIG. 5  can be installed in any position in the whole network. In the network shown in  FIG. 6 , the virtual terminal function management device  86  and the device management function device  88  are connected to the fourth-generation mobile communication network, as has been described previously. 
   In  FIG. 6 , the virtual terminal function device  86  and the device management function device  88  are installed separate from each other. Alternatively, the device management function device  88  can be incorporated with the virtual terminal function device  86  so that these devices are installed in the same position in the network. 
   The virtual terminal function device  86  and the device management function device  88  can be implemented by the function of software. 
   As shown in  FIG. 7 , the device management function device  88  communicates with the communication terminals  80   1  through  80   9  and thus acknowledges management information on the communication terminals  80   1  through  80   9 , such as the kinds of information handled thereby, functions, human interface abilities, communication abilities and communication status of the communication terminals  80   1  through  80   9 . Alternatively, the device management function device  88  may access the communication terminals  80   1  through  80   N  and collect a variety of management information on the communication terminals  80   1  through  80   9 , such as the kinds of information handled thereby as well as functions, human interface abilities, communication abilities and communication status of the communication terminals  80   1  through  80   9 . 
   The virtual terminal function device  86  acquires a control signal from the device management function device  88  via the fourth-generation mobile communication network  84 . Thus, as shown in  FIG. 8 , the communication terminals  80   1 ,  80   4 ,  80   5 ,  80   8  and  80   9  that can be used by user A are virtually integrated into a single communication terminal (virtualterminal), and can communicate with the communication terminal  80   3  that can be used by user B. 
   Each of the above-mentioned communication terminals has any of an audio input function, an image input function, a character input function, a numeral value input function such as a sensor, an acoustic output function, an image output function, a character output function, a memory function, an information converting function such as speech codec. For example, the communication terminal  80   3  of user B shown in  FIG. 8  is a videophone communication terminal, and the communication terminal  80   1  of user A is a video camera installed at a street corner. The communication terminal  80   4  is a cellular phone, and the communication terminal  80   5  is a large-size display. The communication terminal  80   8  is a PDA, and the communication terminal  80   9  is a hard disk drive. 
   In light of the relationship between the relative positions of the virtual terminal function device  86  and the device management function device  88  is considered, when the virtual terminal function device  86  and the device management function device  88  are arranged in a server, communications therebetween are implemented by the function of software. When the virtual terminal function device  86  and the device management function device  88  are arranged in different servers, communications therebetween take place via one or a plurality of networks linked together. 
   In light of the relationship between the absolute positions of the virtual terminal function device  86  and the device management function device  88 , it is possible to employ the following two arrangements. In the first arrangement, the virtual terminal function device  86  and the device management function device  88  are installed in a terminal that is not owned by any user. In the second arrangement, the virtual terminal function device  86  and the device management function device  88  are installed in a terminal owned by a user. In the first arrangement, the virtual terminal function device  86  and the device management function device  88  are installed in a server connected to a plurality of kinds of networks in which a terminal used as a virtual terminal exists. In the second arrangement, the virtual terminal function device  86  and the device management function device  88  are installed in a terminal that can be connected to a plurality of kinds of networks. The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention. 
   The present application is based on Japanese priority application no. 11-375794 filed on Dec. 28, 1999, the entire contents of which are hereby incorporated by reference.